GEOTECHNICAL REPORT –
REV. 01
FOR
THE NEW RAW WATER INTAKE AND WATER TREATMENT PLANT AT AROUCA
FOR
WATER AND SEWERAGE AUTHORITY
FEBRUARY 2017
Trintoplan Consultants Limited P.O. Box 2080, National Mail Centre, Piarco.
Orange Grove Road, Tacarigua TRINIDAD & TOBAGO W.I.
GEOTECHNICAL REPORT
FOR
THE NEW RAW WATER INTAKE AND WATER TREATMENT PLANT AT AROUCA
FOR
WATER AND SEWERAGE AUTHORITY
FEBRUARY 2017
GEOTECHNICAL REPORT FOR THE AROUCA WATER TREATMENT PLANT (WTP) AND INTAKE, AROUCA
(REVISION 01)
TABLE OF CONTENTS
CHAPTER DESCRIPTION PAGE
1.0 INTRODUCTION 1-1
2.0 THE SITE 2-1
2.1 Site Location and Description 2-1
2.2 Proposed Structure 2-1
2.3 Geology 2-1
2.4 Seismology 2-1
3.0 FIELD INVESTIGATION 3-1
3.1 Borehole Investigation 3-1
3.2 Testpit Investigation 3-2
4.0 LABORATORY TESTING 4-1
5.0 DATA PRESENTATION 5-1
6.0 SUBSURFACE CONDITIONS 6-1 6.1 Boreholes 1 to 6 6-1
6.2 Testpits 1 & 2 6-6
7.0 GROUNDWATER CONDITIONS 7-1
8.0 FOUNDATION ANALYSIS AND DESIGN 8-1
8.1 General 8-1
8.2 Seismic Hazard Parameters 8-1
8.3 Foundation Recommendations 8-5
9.0 SLOPE STABILITY ANALYSIS 9-1
9.1 General 9-1
9.2 Slope Stability Assessment 9-1
10.0 RECOMMENDATIONS 10-1
10.1 General 10-1
10.2 Excavation and Backfilling 10-1 10.3 Structural Backfill 10-2
10.4 Lateral Pressures 10-2
11.0 FOUNDATION CONSTRUCTION 11-1
11.1 General 11-1
11.2 Concrete Requirements 11-1
12.0 CLOSURE 12-1
List of Enclosures
GEOTECHNICAL REPORT FOR THE AROUCA WATER TREATMENT PLANT (WTP) AND INTAKE, AROUCA
(REVISION 01)
TABLE OF CONTENTS (CONT’D)
LIST OF ENCLOSURES
Enclosure 1 - Explanation of Terms used in this Report
Enclosure 2 - Site Location Plan
Enclosure 3 - Borehole/Testpit Location Plan
Enclosures 4 – 10 - Record of Borehole Sheets
Enclosures 11 - 12 - Testpit Log Sheets
Enclosures 13 - 19 - Atterberg Limits Results
Enclosures 20 - 27 - Gradation Curves
Enclosure 28 - Unconfined Compression Test Results
Enclosures 29 – 32 - Direct Shear Test Results
Enclosure 33 - Soil Chemistry Test Results
Enclosures 34 - 35 - Modified Proctor Test Results
Enclosures 36 - 39 - California Bearing Ratio Test Results
Enclosure 40 - Cross-Section A-A of the Site
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CHAPTER 1.0
INTRODUCTION
Trintoplan Consultants Limited was retained by the Water and Sewerage Authority (WASA) to carry out a geotechnical investigation to facilitate the foundation designs necessary for a New Raw Water Intake and Water Treatment Plant at a site off Savannah Trace, off Arima Old Road, Arouca. It is understood that the plant is being proposed in order to satisfy the increase in demand within the catchment area as a result of the planned Trestrail Development.
The investigation was carried out in accordance with our proposal dated June 27, 2016.
The objectives of the investigation were to:
• Identify the subsoil conditions at the site and determine the allowable bearing capacities of
the subsoil and,
• Determine the most appropriate foundation design for the proposed structures.
The Terms of Reference (TOR) included the advancement of six (6) boreholes, each to a depth of 15m, and the excavation of two (2) testpits, each to a depth of 3m.
This revised report presents the findings of the geotechnical investigation conducted at the site and provides recommendations for the design of the proposed structures, based upon discussions held in a meeting on February 13, 2017 with the Client representative, Mr. Dale Arneaud. It also includes recommendations regarding geotechnically related construction considerations.
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CHAPTER 2.0
THE SITE
2.1 SITE LOCATION AND DESCRIPTION
The site is located off Savannah Trace North, off Arima Old Road, Arouca.
It is bounded to the north by an earthen drain, west and south by open grassed areas and to the east by the Arouca River.
The topography of the site is varied. The proposed location for the service reservoir is relatively flat; however, the land slopes downward east of this area approximately 1 vertical to 3 horizontal, towards the Arouca River.
The site was covered with medium vegetation and some trees.
2.2 PROPOSED STRUCTURE
It is understood that the Client is desirous of constructing a new Raw Water Intake Station and Water Treatment Plant to treat approximately 1.32 IMGD of raw water.
2.3 GEOLOGY
According to the Geological map of Trinidad and Tobago (Scale 1:100,000), the site is underlain by the Cedros Formation of the Pleistocene epoch.
The Cedros Formation is comprised largely of poorly consolidated yellow, red and brown sands and grey blocky mudstones. The sands are poorly sorted, varying from fine to coarse grained. Interbedded with the sands are lenses of hard, "iron-cemented" sandstone and conglomerate, the latter containing pebbles of white quartz, chert and porcellanite.
2.4 SEISMOLOGY
The most dominant structural geological feature of interest to the study area is the El Pilar fault zone system which runs from east to west across Trinidad just south of the Northern Range. The El Pilar Fault Zone extends for about 700 km in an approximately E - W direction, from the Cariaco Trench to a point about 200 km northeast of Trinidad. It marks the southern boundary of the Araya-Paria peninsulas (eastern Caribbean Mts.) and of the Northern Range of Trinidad. It is characterized along its length by straight valleys, fault wedges, fumaroles, thermal springs, and sulfur deposits. The displacement along the El Pilar fault zone has been the subject of much controversy. Various authors recognize the following types of displacement: (1) southward thrust; (2) normal or graben faulting; (3) right-lateral strike-slip. The El Pilar fault zone probably represents a transform fault between the Caribbean and South America plates, and a hinge fault at its contact with the subduction zone east and south of the Lesser Antilles.
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Figure 2.1 Map of Fault Zones in Trinidad
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CHAPTER 3.0
FIELD INVESTIGATION
The field investigation was carried out during the period November 17, 2016 to December 2, 2016 and consisted of:
• The advancement ofsix (6) boreholes to depths ranging from 4.6m to 15.3m and,
• Excavation of two (2) testpits to depths of 2.7m and 3m.
Although the TOR required the boreholes be advanced to 15m, practical refusal was encountered in all the boreholes, with the exception of Borehole 1. This resulted in boreholes being terminated at shallower depths. Practical refusal is defined as “N” values from the Standard Penetration Test of greater than 100 blows/300mm over a depth of 3m.
A topographical survey map of the site was provided by the Client on January 9, 2017. The locations of the boreholes and testpits were determined by the Client and set out by Trintoplan. Borehole and testpit elevations and coordinates (referenced to Mean Sea Level) are summarized in Table 3.1 below. The Borehole and Testpit Location Plan is included as Enclosure No. 3.
Borehole ID
Location (m)
Depth
Advanced
(m)
Date Advanced
Northing Easting Elevation
B1 1176482.69 683791.46 51.000 15.3 17-Nov-16
B2 1176480.40 683755.36 50.877 4.6 19-Nov-16
B3 1176457.31 683743.09 50.614 9.5 18-Nov-16
B4 1176457.17 683777.53 50.222 10.9 19-Nov-16
B5 1176507.93 683821.76 42.848 9.2 24-Nov-16
B6 1176525.99 683827.43 41.634 9.5 2-Dec-16
TP1 1176448 683726 ---- 2.7 23-Nov-2016
TP2 1176459 683781 ---- 3.0 23-Nov-2016
Table 3.1 Borehole and Testpit Locations
3.1 BOREHOLE INVESTIGATION
Boreholes 1 to 4 were advanced using a CME-55 drill rig, utilizing hollow stem augering techniques. Due to the ground conditions at Boreholes 5 and 6, these were advanced using an Acker tripod mounted portable drill rig utilizing dry sampling and wash boring techniques.
Sampling was carried out at intervals of 0.76 m for the first 4.57 m and then at intervals of 1.5 m until the end of each borehole.
Disturbed samples were obtained using the Standard Penetration Test (SPT), where the number of blows required to drive a split spoon sampler 0.3 m into the soil was recorded. This figure is designated as the ‘N’ value of the soil, and is related to soil strength and relative
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CHAPTER 4.0
LABORATORY TESTING
The soil samples were transported to TCL’s laboratory where, prior to the assignment of laboratory testing, a visual examination of each sample was performed by an engineer. Confirmatory classification testing for index properties such as Atterberg Limits and grain size distribution were performed on representative samples from each borehole. Moisture content tests were carried out on all samples.
Engineering properties tests were performed on the undisturbed Shelby Tube sample as well as bag samples for cohesionless soils. These tests included Pilcon Vane (PV), Unconfined Compression (UC) and Unconsolidated Undrained Direct Shear tests (UUDS) in order to measure the total and effective stress parameters of the soils.
Modified Proctor and California Bearing Ration (CBR) tests were performed on samples retrieved from the testpits.
Representative soil samples were sent to the Environmental Engineering Laboratory of the Department of the Civil and Environmental Engineering of the University of the West Indies (EELDC&EEUWI), where pH value and sulphate content tests were performed in order to determine the potential detrimental effects of the soils on foundations.
Laboratory Tests performed by Trintoplan were carried out in accordance with the relevant American
Society for Testing and Materials (ASTM) Standard Test Methods. The Chemical tests performed by EELDC&EEUWI will be carried out in accordance with the relevant British Standard (BS) Test Methods.
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CHAPTER 5.0
DATA PRESENTATION
Data Presented Enclosure Nos.
Borehole and Testpit Field and Laboratory Test Results
Record of Borehole Log Sheets (Boreholes, BH1 - BH6) 4 - 10
Data includes descriptions of the soil types, sample types and also provide summarized
laboratory test results
Testpit Log Sheets (Testpit Nos. TP1, TP2) 11 - 12
Data includes descriptions of the soil types, sample types and also provide summarized
laboratory test results
Atterberg Limits 13 - 19
Summary of data presented in Borehole and Testpit Logs; Details of tests, that is, Liquid Limit, Plastic Limits and Plasticity Indices are detailed in Enclosures
Grain Size Distribution 20 - 27
Summary of data presented in the "Remarks" column of the Borehole Logs and within the "Tests" column of the Testpit Logs; Due to rounding errors, the percentages may not add to 100. For details of tests i.e. Grain Size Distribution curves see Enclosures
Engineering Properties Tests
Pilcon Vane Tests
See Borehole Logs
Unconfined Compression Test 28
Unconsolidated Undrained Direct Shear Test 29 - 32
Chemical Tests Soil Chemistry 33
Compaction Characteristics
Modified Proctor 34, 35
Soaked California Bearing Ratio 36 - 39
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CHAPTER 6.0
SUBSURFACE CONDITIONS
The soil stratigraphy in the boreholes and testpits comprised primarily of gravel, sand and silt with varying proportions of clay. The detailed soil and ground conditions are shown on the Borehole Logs (Enclosure Nos. 4 to 10) and the Testpit Logs (Enclosure Nos. 11 and 12). A summarized account of the soil conditions encountered across the site is presented below.
6.1 BOREHOLES 1 TO 6
6.1.1 SOIL UNIT 1
The first soil unit was encountered within Borehole 2 only. It occurred from existing ground elevation and extended to a depth of 1.2m. It consisted of medium stiff to very stiff, dark brown and reddish brown Sandy Clayey Silt.
‘N’ values of 4 and 20 were recorded from the SPT.
Natural moisture contents of 19.4% and 18% were recorded.
The results of the Atterberg Limits test, provided in Enclosure No. 13, shows that the sample tested recorded a Liquid Limit of 34, Plastic Limit of 22 and Plasticity Index of 12. The results indicated that the soil sample tested plots within the CL section of the Plasticity Chart, indicating that the fines can be classified as clays of low plasticity.
The grain size distribution curve shown on Enclosure 20 indicates the soils predominantly comprise clay, siltand sand. The analysis recorded a clay content of 20%, silt content of 38%, sand content of 40% and gravel content of 2%.
Engineering Properties
No engineering properties tests were performed on samples obtained within this unit. However, based on correlation with the ‘N’ values, the following total stress parameters are considered to be representative of this unit:
• Bulk Unit weight, γB = 19.0 kN/m3
• Angle of Internal Friction , φ = 0 degrees
• Undrained shear strength, cu = 40 kPa
6.1.2 SOIL UNIT 2
The secondsoil unit was encountered from the ground surface in Boreholes 1 and 4 and extended to depths of 8.1m and 1.2m respectively. This unit was also encountered in Borehole 2 at depths of 1.2m and 4.6m.
It consisted of medium dense to very dense, moderately reddish brown, orange brown and dark brown Silty Clayey Sand with Gravel.
‘N’ values from the SPT ranged from 18 to values in excess of 100. On this basis the soil may be described as being medium dense to very dense.
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Natural moisture contents recorded ranged from 3% to 18%.
The results of the Atterberg Limits test, provided in Enclosure No. 14, show that the samples tested recorded Liquid Limits ranging between 24 and 36 and Plastic Limits ranging between 19 and 25 and Plasticity Indices ranging between 5 and 15. The results indicated that the soil samples tested plot within the CL, CL-ML and ML section of the Plasticity Chart, indicating that the fines can be classified as inorganic clays, silts and sands of low plasticity.
The grain size distribution curves shown on Enclosure 21 indicate the soils predominantly comprise gravels and sands with some silt and traces of clay. The analyses recorded clay contents ranging between 3% and 7%, silt contents ranging between 12% and 29%, sand contents ranging between 38% and 54% and gravel contents ranging between 27% and 44%.
Engineering Properties
A UU Direct Shear test was performed on a sample from within this unit. The results of these tests are plotted on the Borehole logs and presented in Table 6.1. Measured bulk unit weights (γB) and dry unit weights (γD) are also presented in Table 6.1.
Sample ID
Depth (m)
Unit
Weight (kN/m3)
Shear Strength (kN/m2)
Internal Friction
Angle, φ (degrees)
γΒ γD
B1/S3 1.7 18.3 16.7 4.1 46.3
Table 6.1
Unconsolidated Undrained Direct Shear Test Result
Soil Chemistry Results
Chemical testing was conducted on a representative sample from this soil unit. The sample was tested for pH and the presence of sulphates in order to establish whether the soil contains any corrosive properties. The results of these tests can be found in Enclosure No. 33, and are summarized in Table 6.2.
Sample ID
Sample
Depth
(m)
pH Value
Sulphate
Content
(%)
B1/S1 1.0 4.8 0.036
Table 6.2 Soil Chemistry Results
6.1.3 SOIL UNIT 3
Soil Unit 3 was encountered within Borehole 1 only. It occurred from a depth of 8.1m and extended to a depth of 12.7m. It consisted of hard, light brown and gray Silty Clay with little sand.
‘N’ values of 65 and 142 were recorded from the SPT.
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Natural moisture contents recorded ranged from 14% to 22%.
The results of the Atterberg Limits test, provided in Enclosure No. 15, shows that the sample tested recorded a Liquid Limit of 51, Plastic Limit of 23 and Plasticity Index of 28. The results indicated that the soil sample tested plots within the CH section of the Plasticity Chart, indicating that the fines can be classified as clays of high plasticity.
The grain size distribution curve shown on Enclosure 22 indicates the soils predominantly comprise clays and silts with little sand. The analysis recorded a clay content of 35%, silt content of 57%, sand content of 9% and gravel content of 0%.
Engineering Properties
PV and UC strength tests were performed on a sample from within this unit. The results of these tests are plotted on the Borehole logs and presented in Table 6.3. The measured bulk unit weight (γB) and dry unit weight (γD) is also presented in Table 6.3.
Sample ID
Depth (m)
Unit Weight (kN/m3)
Shear Strength (kPa)
γΒ γD PV UC
B1/S11 10.9 19.3 16.0 47 140
Table 6.3 Undrained Shear Strength Results
6.1.4 SOIL UNIT 4
Soil Unit 4 was encountered within Boreholes 1 and 4 only. It occurred from depths of 12.7m and 4.2m and extended through to the end Boreholes 1 and 4 at depths of 15.3m and 10.9m respectively. It consisted of very dense, light brown and grayish brown Silty Sand with Gravel, trace clay.
‘N’ values from the SPT ranged from 67 to values in excess of 100.
Natural moisture contents recorded ranged from 3% to 17%.
The results of the Atterberg Limits test, provided in Enclosure No. 16, shows that the sample tested recorded a Liquid Limit of 29, Plastic Limit of 23 and Plasticity Index of 6. The results indicated that the soil sample tested plots within the CL-ML section of the Plasticity Chart, indicating that the fines can be classified as clays and silts of low plasticity.
Grain Size distribution curves, included as Enclosure No. 23, indicates the soils predominantly comprise sands and gravels. The analyses recorded clay and silt contents of 17% and 29%, sand contents of 43% and 45% and gravel contents of 39% and 26%.
Engineering Properties
No engineering properties tests were performed on samples obtained within this unit. However, based on correlation with the ‘N’ values, the following total stress parameters are considered to be representative of this unit:
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• Bulk Unit weight, γB = 18.0 kN/m3
• Angle of Internal Friction , φ = 32 degrees
• Undrained shear strength, cu = 0 kPa
6.1.5 SOIL UNIT
Soil Unit 5 was encountered within Boreholes 3 and 4 only. It occurred from existing ground elevation and extended to a depth of 1.2m in Borehole 3 and from a depth of 1.2m to 4.3m in Borehole 4. It consisted of medium dense to very dense, orange brown and light brown well-graded gravel with sand.
‘N’ values from the SPT ranged from 11 to 149.
Natural moisture contents recorded ranged from 4% to 8%.
Grain Size distribution curves, included as Enclosure No. 24, indicates the soils predominantly comprise sands and gravels. The analyses recorded clay contents of 0.4% and 1.1%, silt contents of 2.1% and 3%, sand contents of 37.9% and 35.8% and gravel contents of 59.7% and 60.1%.
Engineering Properties
No engineering properties tests were performed on samples obtained within this unit. However, based on correlation with the ‘N’ values, the following total stress parameters are considered to be representative of this unit:
• Bulk Unit weight, γB = 16.8 kN/m3
• Angle of Internal Friction , φ = 33 degrees
• Undrained shear strength, cu = 0 kPa
6.1.6 SOIL UNIT 6
Soil Unit 6 was encountered within Boreholes 5 and 6 only. It occurred from existing ground elevation and extended to depths of 1.2m and 0.5m. It consisted of loose, brown sandy silt with little clay.
‘N’ values from the SPT ranged from 5 to 13.
Natural moisture contents of 28% and 29% were recorded.
The results of the Atterberg Limits test, provided in Enclosure No. 17, shows that the sample tested recorded a Liquid Limit of 33, Plastic Limit of 28 and Plasticity Index of 5. The results indicated that the soil sample tested plots within the ML section of the Plasticity Chart, indicating that the fines can be classified as silts of low plasticity.
Grain Size distribution curves, included as Enclosure No. 25, indicates the soils predominantly comprise silts and sands. The analysis recorded a clay content of 13%, silt content of 52%, sand contentsof 34% and a gravel content of 0%.
Engineering Properties
No engineering properties tests were performed on samples obtained within this unit. However, based on correlation with the ‘N’ values, the following total stress parameters are considered to be representative of this unit:
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• Bulk Unit weight, γB = 17 kN/m3
• Angle of Internal Friction , φ = 25 degrees
• Undrained shear strength, cu = 0 kPa
6.1.7 SOIL UNIT 7
Soil Unit 7 was encountered within Boreholes 3, 5 and 6 only. It occurred from depths of 1.2m in Boreholes 3 and 5, and 0.5m in Borehole 6 and extended to the end of each borehole at depths of 9.5m, 9.2m and 9.5m respectively. It consisted of medium dense to very dense, brown silty gravel with sand.
‘N’ values from the SPT ranged from 13 to values in excess of 100.
Natural moisture contents ranging between 2% and 24% were recorded.
The results of the Atterberg Limits test, provided in Enclosure No. 18, show that the samples tested recorded Liquid Limits ranging between 24 and 36 and Plastic Limits ranging between 27 and 31 and Plasticity Indices ranging between 21 and 29. The results indicated that the soil samples tested plot within the CL and ML section of the Plasticity Chart, indicating that the fines can be classified as inorganic clays, silts and sands of low plasticity. Two samples, B6/SA4 and B6/SA8 tested were non-plastic with Liquid Limits of 27 and 28 respectively.
Grain Size distribution curves, included as Enclosure No. 26, indicates the soils predominantly comprise sands and gravels. The analyses recorded clay contents ranging between 1% and 4%, silt contents ranging between 9% and 20%, sand contents ranging between 27% and 39% and gravel contents ranging between 41% and 60%.
Engineering Properties
UU Direct Shear tests were performed on samples from within this unit. The results of these tests are plotted on the Borehole logs and presented in Table 6.4. Measured bulk unit weights (γB) and dry unit weights (γD) are also presented in Table 6.4.
Sample ID
Depth (m)
Unit Weight (kN/m3)
Shear
Strength (kN/m2)
Internal Friction
Angle, φ
(degrees) γΒ
γD
B3/S5 3.2 18.7 17.6 0 40
B5/S4 2.5 22.8 20.3 11.5 33.4
B6/S5 3.3 19.1 17.8 6 39.3
Table 6.4
Unconsolidated Undrained
Direct Shear Test Result
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6.2 TESTPITS 1 & 2
6.2.1 SOIL UNIT 1
A single soil unit was found within Testpits 1 and 2. It occurred from the existing ground surface and extended through to the end of each testpit at depths of 2.74m and 3.05m respectively. It consisted of brown Silty Clayey Gravel with sand.
Natural moisture contents of 8% and 9% were recorded.
The results of the Atterberg Limits test, presented on Enclosure No. 19, performed on the samples within this unit shows that the samples recorded Liquid Limits of 25 and 29, Plastic Limits of 18 and 16 and Plasticity Indices of 7 and 13. The soil samples tested plot within the CL section of the Plasticity Chart, indicating that the fines can be classified as clay of low plasticity.
Grain Size distribution curves, included as Enclosure No. 27, indicates the soils predominantly comprise sands and gravels. The analyses recorded clay contents of 3% and 4%, silt contents of 12% and 13%, sand contents of 32% and 33% and gravel contents of 54% and 51%.
The compaction characteristics included as Enclosure Nos. 34 and 35 of the soil (Maximum Dry Unit Weight and Optimum Moisture Content), as well as the bearing strength (California Bearing Ratio – Enclosure Nos. 36 to 39) of the soil samples tested are presented in Table 6.5 below.
Testpit ID
Depth (m)
Maximum
Dry Unit
Weight (kN/m3)
Optimum
Moisture
Content
(%)
CBR
(%)
TP1 1.4 21.7 5.8 21
TP2 1.5 21.7 6.2 36
Table 6.5 Compaction Characteristics
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CHAPTER 7.0
GROUNDWATER CONDITIONS
Water levels encountered on the site during ground investigation operations are summarised in Table 7.1. The depth to groundwater was measured within the boreholes during drilling and at the end of drilling operations.
Borehole No.
Measured
Groundwater
Level, m
Elevation, m Date
BH 1 11.6 39.4 17-Nov-16
BH 2 None recorded --- 19-Nov-16
BH 3 None recorded --- 18-Nov-16
BH 4 None recorded --- 19-Nov-16
BH 5 2.5 40.3 24-Nov-16
BH 6 4.4 37.2 2-Dec-16
Table 7.1 Depths of Groundwater Table
The groundwater levels are phreatic and are influenced by rainfall. The groundwater levels may also be controlled by the water levels in the river. As such,the variations in the water level readings within Boreholes 5 and 6, which were in close proximity to the river, were likely due to rainfall events (or lack thereof) in the days prior to the advancement of the boreholes.
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CHAPTER 8.0
FOUNDATION DESIGN AND ANALYSIS
8.1 GENERAL
Foundations for structures may be classified based on the means by which the load is transferred to the ground. There can be either shallow foundations or deep foundations. They are designed to ensure that the load transfer does not produce settlements beyond acceptable limits, and are constructed at adequate depths to mobilize sufficient soil resistance for supporting the imposed loads.
Further to a meeting with the Client held on February 13th, 2017, it was understood that the
structures to be constructed at the plant include:
• An Operator Room
• Clarifier Filters
• Chemical Building
• Clearwell Tank and
• An Intake Station
It was also understood that the Clearwell Tank will be a partially buried structure with a proposed foundation depth of 3.825m below existing grade.
For the proposed structures within the Water Treatment Plant only shallow foundations were considered for supporting the structures as competent load bearing strata was encountered at shallow depths (see Borehole Logs included as Enclosure Nos. 4 to 10).
8.2 SEISMIC HAZARD PARAMETERS
The seismic hazard parameters defined in accordance with IBC (2009) and ASCE7-2005 include the spectral ground accelerations at 0.2 seconds and 1.0 seconds and the peak ground acceleration for return period of 2475 years. The design parameters are as included in Table 8.1.
Ground motions for design
Mapped spectral acceleration parameters
Range (g) Range (m/s)
Spectral acceleration at short period (0.2 seconds) Ss
1.461- 1.550 14.332 – 15.206
Spectral acceleration at 1 second period S1
0.371 -0.391 3.640 – 3.836
Spectral acceleration peak ground acceleration (PGA)
0.562 -0.590 5.513 - 5.788
Table 8.1 Spectral Accelerati
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Figure 8.1
Spectral Acceleration Parameters 0.2s, Ss (RP=2475 years)
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Figure 8.2
Spectral Acceleration Parameters 1s, S1 (RP=2475 years)
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Figure 8.3
Spectral Acceleration Parameters PGA (RP=2475 years)
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8.3 FOUNDATION RECOMMENDATIONS
8.3.1 Shallow Foundations
Analyses were carried out to determine the allowable bearing capacities of continuous (strip) footings and pad footings placed at depths of 1.5 m and 3.825 m below existing grade level and using undrained shear strength, c, of 0 kPa and an internal angle of friction of 33.4 degrees. The estimated allowable bearing capacity was determined using Meyerhof’s bearing capacity equation:
qa =
cNcscdc+qNqsqdq +1/2γBNγsγdγ
FS
Where:
qa = Allowable bearing capacity c = Undrained cohesion of soil
q = Effective overburden pressure of soil
γ = Bulk unit weight of soil B = Width of foundation sc, sγ= Shape factors dc,dq,dγ= Depth factors
Nc, Nq and Nγ = Bearing Capacity factors
FS = Factor of Safety
A Factor of Safety of 3 was used in the estimation of allowable bearing capacities.
Settlement estimates were determined using the results of the standard penetration test and calculation methods established by Burland and Burbidge (Tomlinson 2001, 67-69).
Based upon the analyses conducted it was determined that an allowable bearing capacity of 400 kN/m2 can be used for both:
Square pad foundations varying in dimension of 1.0m x 1.0m to 3.0m x 3.0m
and,
Continuous (strip) foundations varying in width from 1.0m to 3.0m.
Allowable bearing pressures will be governed by both safe bearing capacities and allowable settlement. At these allowable bearing capacities, the settlements are estimated to be less than 25mm and would occur during the construction period.
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CHAPTER 9.0
SLOPE STABILITY ANALYSIS
9.1 GENERAL
The site is sloped (1 vertical to 3 horizontal) within the area where Boreholes 5 and 6 were advanced. At the time of the field investigation the sloped surface was covered with tall vegetation and evidence of existing slope failure or soil movement was not observed.
It was observed that the Arouca River which traverses in a north -south direction is situated at the base of the slope. It is unclear how the river behaves during periods of heavy rainfall and essentially how far inland, toward the existing site, the increased water flows may affect the existing slope.
9.2 SLOPE STABILITY ASSESSMENT
Factors leading to slope instability include:
• Increased unit weight of the soils due to saturation of the soils, i.e. increased moisture
content and increased pore pressures of the soils;
• Added external loads, e.g. buildings
• Steepened slopes either by excavation or erosion
• Vibration and earthquakes
A slope stability analysis was carried out using sections generated from a topographical survey submitted by the Water and Sewerage Authority on January 9, 2017. The section generated is graphically shown on Enclosure 40.
From soil data within Boreholes 5 and 6 it was observed that surficial deposits of loosesandy silts occurred from existing ground level to a maximum depth of 1.2m below grade and is underlain by medium dense to very dense layer of silty gravel deposits.
Based on the cohesionless nature of the subsoils, the most likely failure type which may occur along the existing slopes will be a translational slide. This type of failure is associated with movement largely controlled by surfaces of weakness.Almost all translational slides occur along the line between the substratum, in this case the medium dense to very dense layer of silty gravel depositsand superficial soils i.e. the loosesandy silt. They therefore tend to be shallow and mainly affect thin soil layers.
Analyses were carried out with the slope under varying saturated conditions (unsaturated, 50% saturated and fully saturated) to closely assimilate anticipated soil conditions which will occur annually. Each analysis was performed under normal conditions.
Shear Strength values and the angles of internal friction for each layer was determined by using the results of CU Triaxial tests which were derived from the results of laboratory testing performed on samples. The parameters used in the analyses are summarized in Table 9.1.
9-2
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Geotechnical Investigation for the
Arouca Water Treatment Plant And Intake, Arouca
Material Description
Effective
Shear
Strength
, c’ (kN/m2)
Effective
Angle of
Internal
Friction, (degrees)
Pore Pressure Ratio, ru
Bulk Unit Weight
0%
Saturation
50%
Saturation
100%
Saturation
(kN/m3)
Loose Sandy
Silt
0 25 0 0.24 0.48 17
Medium dense to very dense Silty Gravel
11.5 33.4 0 0.15 0.30 22.5
Table 9.1 Stability Analysis Parameters for Cross-Section
From the analyses performed, factors of safety for the varying conditions were determined.
A factor of safety greater than 1.3 is deemed to be satisfactory in slope stability analyses.
Saturation Conditions Factor of Safety
Unsaturated (0% Saturation) 1.402
50% Saturation 0.997
Fully Saturated (100%
Saturation)
0.593
Table 9.2 Slope Stability Analysis Results
From Table 9.2 it can be seen that the existing slopes are stable for unsaturated conditions only. As the degree of saturation increases, the slope becomes unstable.
Section 9.0 outlines recommendations that should be considered in the finalization of designs for the structures located within this sloped area.
10-1
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Geotechnical Investigation for the
Arouca Water Treatment Plant And Intake, Arouca
CHAPTER 10.0
RECOMMENDATIONS
10.1 GENERAL
Further to a meeting held on February 13, 2017 with the Client representative, Mr. Dale Arneaud, it was understood that there is a consideration by WASA to install an Intake Station structure along the slope. This however may be subject to change once designs are finalised.
In order to arrest the potential slope instability and soil movements which are likely to occur along the slope, it must be ensured that the slope is stabilized and proper drainage infrastructure be constructed at the site.
Based on the site survey, in conjunction with nature of the sub-soils encountered at the site the following remediation measures are recommended for this area of the site:
• Incorporation of proper drainage designs prior to construction to reduce infiltration of
surface water runoff into the affected area,
• Structural solutions, wherein physical structures are used to support the existing
embankment and thus prevent movement.
10.2 EXCAVATION AND BACKFILLING
Prior to excavation or backfilling, the areas to be cut or filled should be stripped to remove vegetation, roots and weak topsoil. These soils should not be re-used in areas that will support structures, pavements and slabs. They could be re-used for general landscaping or other non-structural purposes.
The following methods for excavation should be used to protect personnel, to maintain stable excavation slopes and to protect bottom excavation:
• Side slopes at a maximum gradient of 1.8 horizontal to 1.0 vertical.
• Shoring of excavations where the depth of excavation exceeds 2 m or where
space is not available to achieve the recommended side slopes for depths of excavation less than 2 m.
• Excavated material should not be stockpiled at the edges of excavations as this
could result in slope instability.
Prior to placement of concrete for foundations, the top 300 mm of subgrade at foundation level should be compacted to at least 100% of the maximum dry unit weight determined in accordance with ASTM D 1557 (Modified Proctor).
10-2
6312
Geotechnical Investigation for the
Arouca Water Treatment Plant And Intake, Arouca
10.3 STRUCTURAL BACKFILL
The use of imported fill or excavated material from the site as structural fill should be free from organic matter (leaves, grass, roots, trees, brush, mulch, etc.), topsoil and other such objectionable debris and should have the properties detailed below.
• Gradation (ASTM C 136) Well graded granular material with
100% passing a 75mm sieve, not more than 40% by weight passing a 0.425mm (No. 40% sieve) and not more than 10% by weight passing a 0.075mm (No. 200) sieve.
• Liquid Limit (ASTM D 4318) ≤ 25
• Plasticity Index (ASTM D 4318) ≤ 6
• Soaked California
Bearing Ratio (ASTM D 1883) ≥ 3% for imported fill installed in
embankments to within 300mm of subgrade level ≥15% for imported fill installed within the top 300mm of embankments.
Structural fill material should be placed in lifts not exceeding 200mm (loose) thickness, except for the top 600mm, which should be placed in lifts not exceeding 150mm (loose) thickness. Each lift of material should be compacted to at least 95% of the maximum dry unit weight determined in accordance with ASTM D 1557 (Modified Proctor) before the next layer is placed, except for the top two 150mm thick layers, which should be compacted to 100% of the maximum dry unit weight.
10.4 LATERAL PRESSURES
The lateral pressures that should be considered in the design of retaining walls at the site are:
• Static earth pressure
• Hydrostatic (water) pressure
• Live load or surcharge pressures
• Seismic pressure
10.4.1 Static Earth Pressure
The backfill to the Retaining Wall should be a free draining well-graded granular material meeting and installed in accordance with the specifications given in Section 10.3 (Structural Backfill).
The following parameters should be used in the calculation of earth pressures for the structural backfill material. An active earth pressure (yielding foundation) condition may be assumed.
10-3
6312
Geotechnical Investigation for the
Arouca Water Treatment Plant And Intake, Arouca
• Angle of internal friction, φ‘ 30°
• Cohesion, c’ 0 kPa
• Bulk Unit weight, γB 20 kN/m3
• Active earth pressure coefficient, ka 0.33
The recommended maximum gradient for the surface of the structural backfill material behind the retaining structure (i.e., on the active side) is 3 horizontal to 1 vertical.
As far as practical, removal of ground in front of the retaining wall, e.g., to install services should be avoided, since this reduces the passive resistance and hence the stability of the wall. If this cannot be avoided, then adequate lateral support for the excavation should be provided.
10.4.2 Hydrostatic (Water) Pressure
Walls should be designed to resist the maximum anticipated hydrostatic pressure, which as a minimum, should be taken as the hydrostatic pressure occurring up to the lowest level of weep-holes. Adequate weep-holes and a granular drainage layer (e.g., single size clean 19 mm gravel wrapped in geo-textile filter fabric) should be provided to avoid the buildup of excessive hydrostatic pressures for long-term conditions.
10.4.3 Live Load or Surcharge Pressures
If anticipated, the effects of live loads and/or surcharges within close proximity of the retaining wall should be taken into account in the design of the wall. Design loads established by American Association of State Highway and Transportation Officials (AASHTO) Standards should be used to determine the effective surcharge from traffic loads.
10.4.4 Seismic Pressures
The pseudo static approach developed by Monobe and Okabe may be used to estimate the equivalent static forces for seismic loads. The estimation of seismic design forces should account for wall inertia forces in addition to the equivalent static forces.
10.4.5 Sliding and Overturning
The stability of the wall should be checked for sliding and overturning. The minimum factor of safety against sliding should be 2.0 and the minimum factor of safety against overturning should be 1.5.
For computation of sliding resistance, the angle of internal friction of the foundation soil, φf, should be taken as 33 degrees and 0 kPa should be used for the base cohesion, cf. The base friction angle, δ, should be taken as 0.67φf, i.e., 22 degrees.
11-1
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Geotechnical Investigation for the
Arouca Water Treatment Plant And Intake, Arouca
Enclosure 1 - Explanation of Terms used in this Report
Enclosure 2 - Site Location Plan
Enclosure 3 - Borehole/Testpit Location Plan
Enclosures 4 – 10 - Record of Borehole Sheets
Enclosures 11, 12 - Testpit Log Sheets
Enclosures 13 - 19 - Atterberg Limits Results
Enclosures 20 - 27 - Gradation Curves
Enclosure 28 - Unconfined Compression Test Results
Enclosures 29 – 32 - Direct Shear Test Results
Enclosure 33 - Soil Chemistry Test Results
Enclosures 34, 35 - Modified Proctor Test Results
Enclosures 36 - 39 - California Bearing Ratio Test Results
Enclosure 40 - Cross-section A-A of the Site
ENCLOSURE 1
EXPLANATION OF TERMS USED IN THIS REPORT
N VALUE: THE STANDARD PENETRATION TEST (SPT) N VALUE IS THE NUMBER OF BLOWS REQUIRED TO CAUSE A
STANDARD 51mm O.D. SPLIT BARREL SAMPLER TO PENETRATE 0.3 m INTO UNDISTURBED GROUND IN A
BOREHOLE WHEN DRIVEN BY A HAMMER WITH A MASS OF 63.5kg, FALLING FREELY A DISTANCE OF 0.76m. FOR
PENETRATION OF LESS THAN 0.3m, N VALUES ARE INDICATED AS THE NUMBER OF BLOWS FOR THE PENETRATION ACHIEVED.
SOILS ARE DESCRIBED BY THEIR COMPOSITION AND CONSISTENCY OR DENSENESS
CONSISTENCY: COHESIVE SOILS ARE DESCRIBED ON THE BASIS OF THEIR UNDRAINED SHEAR STRENGTH (Cu ) AND N VALUES AS FOLLOWS:
Cu (kPa) 0-12 12-25 25-50 50-100 100-200 >200
N VALUE 0-2 2-4 4-8 8-15 15-30 >30
VERY SOFT SOFT FIRM STIFF VERY STIFF HARD
DENSENESS: NON COHESIVE SOILS ARE DESCRIBED ON THE BASIS OF THEIR N VALUES AS FOLLOWS
N VALUE 0-5 5-10 10-30 30-50 >50
VERY LOOSE LOOSE COMPACT DENSE VERY DENSE
ROCKS ARE DESCRIBED BY THEIR COMPOSITION AND STRUCTURAL FEATURES AND / OR STRENGTH
RECOVERY: SUM OF ALL RECOVERED ROCK CORE PIECES FROM A CORING RUN EXPRESSED AS A PERCENT OF THE TOTAL
LENGTH OF THE CORING RUN
MODIFIED RECOVERY: SUM OF THOSE INTACT CORE PIECES 100 mm+ IN LENGTH EXPRESSED AS A PERCENT OF THE LENGTH OF THE CORING RUN. THE ROCK QUALITY DESIGNATION (RQD) FOR MODIFIED RECOVERY IS
RQD (%) 0-25 25-50 50-75 75-90 90-100 VERY POOR POOR FAIR GOOD EXCELLENT
JOINTING AND BEDDING
SPACING 50 mm 50-300 mm 0.3m -1m 1m -3m >3m
JOINTING VERY CLOSE CLOSE MOD. CLOSE WIDE VERY WIDE
BEDDING VERY THIN THIN MEDIUM THICK VERY THICK
ABBREVIATIONS AND SYMBOLS
FIELD SAMPLING MECHANICAL PROPERTIES OF SOIL
DO SPLIT SPOON mv kPa-1 COEFFICIENT OF VOLUME CHANGE
TO THINWALL OPEN Cc 1 COMPRESSION INDEX
TP THINWALL PISTON Cs 1 SWELLING INDEX
WS WASH SAMPLE C 1 RATE OF SECONDARY CONSOLIDATION
CS CHUNK SAMPLE cv m
2/s COEFFICIENT OF CONSOLIDATION
BS BLOCK SAMPLE H m DRAINAGE PATH RC ROCK CORE Tv 1 TIME FACTOR
PH ADVANCED HYDRAULICALLY U % DEGREE OF CONSOLIDATION
WH ADVANCED WITH HAMMER Po kPa EFFECTIVE OVERBURDEN PRESSURE
Pc kPa PRECONSOLIDATION PRESSURE
kPa SHEAR STRENGTH
STRESS AND STRAIN c’ kPa EFFECTIVE COHESION INTERCEPT uw kPa PORE WATER PRESSURE cu kPa APPARENT COHESION INTERCEPT ru 1 PORE PRESSURE RATIO u -
o APPARENT ANGLE OF INT. FRICTION
kPa TOTAL NORMAL STRESS R kPa RESIDUAL SHEAR STRENGTH
’ kPa EFFECTIVE NORMAL STRESS st 1 SENSITIVITY
1,2,3 kPa PRINCIPAL STRESSES ’ -o EFFECTIVE ANGLE OF INT. FRICTION
% LINEAR STRAIN
1,2,3 % PRINCIPAL STRAINS
E kPa MODULUS OF LINEAR DEFORMATION
G kPa MODULUS OF SHEAR DEFORMATION
1 COEFFICIENT OF FRICTION
PHYSICAL PROPERTIES OF SOIL
s kg/m3 DENSITY OF SOLID PARTICLES e 1% VOID RATIO
s kN/m3 UNIT WEIGHT OF SOIL n 1% POROSITY Gs 1 SPECIFIC GRAVITY w 1% MOISTURE CONTENT
w kg/m3 DENSITY OF WATER sr % DEGREE OF SATURATION kg/m3 DENSITY OF SOIL LL % LIQUID LIMIT
w kN/m3 UNIT WEIGHT OF WATER PL % PLASTIC LIMIT
d kN/m3 DRY UNIT WEIGHT PI % PLASTICITY INDEX
sat kN/m3 SATURATED UNIT WEIGHT OF SOIL
sat kg/m3 SATURATED DENSITY OF SOIL
' kg/m3 DENSITY OF SUBMERGED SOIL
' kN/m3 UNIT WEIGHT OF SUBMERGED SOIL
Medium dense to very dense, brown and reddish brown, SILTY, CLAYEY SAND with gravel
- - - - - - - - - - - - -
Very dense
Brown and reddish brown Very dense, dark brown and light brown, SILTY SAND with gravel
Very dense
Dark brown and light brown Hard, light brown and grey, SILTY
CLAY, little sand
Hard
Light brown and grey Very dense, light brown, SILTY
SAND with gravel
U.U. Direct Shear (Sa.3)
Cohesion = 4.1 kN/m2
Angle of friction = 46.3 o
1
2
3
4
5
6
7
8
9
10
11
12
19.6
19.8
4
6
35
33
28 0
19
29
57
45
38 9
100/6"
100/6"
100/3"
51.000 Ground Surface
11-17-16 11-17-16
CME 55 DRILL RIG
0.2 N/A
M.S.L
HOLLOW STEM AUGERING
11.6
39.4
BH 1
4
50.00
49.00
48.00
47.00
46.00
45.00
44.00
43.00
42.00
41.00
40.00
39.00
38.00
0
1
2
3
4
5
6
7
8
9
10
11
12
13
1 2
GEOTECHNICAL INVESTIGATION AT THE AROUCA WATER TREATMENT PLANT AND INTAKE - AROUCA
6312
BH 1 ENCLOSURE 4
N 1176482.689, E 683791.464
BULK UNIT WEIGHT
kN/m3
PENETRATION RESISTANCE BLOWS/0.3 m
N-VALUE N CONE PENETRATION
20 40 60 80 100
UNDRAINED SHEAR STRENGTH kN/m2
20 40 60 80 100
WATER CONTENT, PERCENT
Wp W WL
20 40 60 80
REMARKS
AND
GRAIN SIZE
DISTRIBUTION
GR SA SI CL
GROUNDWATER TABLE
m m
TO
DIAMETER OF DRILL BIT
PROJECT
TYPE
SOIL PROFILE
STRAT. PLOT
WELL
INSTALLATION
DESCRIPTION
ELEV. DEPTH
SPLIT SPOON
SHELBY TUBE
DISTURBED BULK
SAMPLE LOST
ROCK CORE
BLOCK SAMPLE
WL - LIQUID LIMIT
Wp - PLASTIC LIMIT
W - MOISTURE CONTENT
- ORGANIC CONTENT
CLAY
SILT
SAND
GRAVEL
METAMORPHIC
TOP SOIL
ORGANIC
NATURAL VANE
REMOULDED VANE
UNCONFINED - NAT'L.
TRIAXIAL QUICK
TORVANE
PILCON VANE
B.H. No.
ENCLOSURE
/
m DRILLING MUD
TRINTOPLAN CONSULTANTS LTD.
SHEET OF
PROJECT No.
RECORD OF BOREHOLE
LOCATION BORING DATE DATUM
SAMPLER HAMMER WEIGHT PENETRATION TEST HAMMER WEIGHT
63.5 kg, DROP 762 mm
BORING EQUIPMENT / METHOD
ELEV. (m) DEPTH (m)
SAMPLE
NUMBER
140.85
23
80
51
52
160
161
65
142
Very dense, light brown, SILTY SAND with gravel
Very dense
Light brown
End of borehole at 15.32m
13
14 20.0
100/3"
100/3"
Continued
11-17-16 11-17-16
CME 55 DRILL RIG
0.2 N/A
M.S.L
HOLLOW STEM AUGERING
11.6
39.4
BH 1
5
37.00
36.00
35.00
34.00
33.00
32.00
31.00
30.00
29.00
28.00
27.00
26.00
25.00
14
15
16
17
18
19
20
21
22
23
24
25
26
2 2
GEOTECHNICAL INVESTIGATION AT THE AROUCA WATER TREATMENT PLANT AND INTAKE - AROUCA
6312
BH 1 ENCLOSURE 5
N 1176482.689, E 683791.464
BULK UNIT WEIGHT
kN/m3
PENETRATION RESISTANCE BLOWS/0.3 m
N-VALUE N CONE PENETRATION
20 40 60 80 100
UNDRAINED SHEAR STRENGTH kN/m2
20 40 60 80 100
WATER CONTENT, PERCENT
Wp W WL
20 40 60 80
REMARKS
AND
GRAIN SIZE
DISTRIBUTION
GR SA SI CL
GROUNDWATER TABLE
m m
TO
DIAMETER OF DRILL BIT
PROJECT
TYPE
SOIL PROFILE
STRAT. PLOT
WELL
INSTALLATION
DESCRIPTION
ELEV. DEPTH
SPLIT SPOON
SHELBY TUBE
DISTURBED BULK
SAMPLE LOST
ROCK CORE
BLOCK SAMPLE
WL - LIQUID LIMIT
Wp - PLASTIC LIMIT
W - MOISTURE CONTENT
- ORGANIC CONTENT
CLAY
SILT
SAND
GRAVEL
METAMORPHIC
TOP SOIL
ORGANIC
NATURAL VANE
REMOULDED VANE
UNCONFINED - NAT'L.
TRIAXIAL QUICK
TORVANE
PILCON VANE
B.H. No.
ENCLOSURE
/
m DRILLING MUD
TRINTOPLAN CONSULTANTS LTD.
SHEET OF
PROJECT No.
RECORD OF BOREHOLE
LOCATION BORING DATE DATUM
SAMPLER HAMMER WEIGHT PENETRATION TEST HAMMER WEIGHT
63.5 kg, DROP 762 mm
BORING EQUIPMENT / METHOD
ELEV. (m) DEPTH (m)
SAMPLE
NUMBER
Medium stiff to very stiff, dark brown and medium reddish brown, SANDY CLAYEY SILT
- - - - - - - - - - - - -
Very stiff
Dark brown and medium reddish brown Dense to very dense, reddish brown, orange brown, dark brown, SILTY CLAYEY SAND with gravel Dense
- - - - - - - - - - - - -
Very dense
Reddish brown, orange brown, dark brown End of borehole at 4.62m
1
2
3
4
5
6
7
19.3
16.7
19
20 6
3
43
36
38
20
40
38
38
100/6"
100/6"
50.877 Ground Surface
11-19-16 11-19-16
CME 55 DRILL RIG
0.2 N/A
M.S.L
HOLLOW STEM AUGERING
BH 2
6
49.88
48.88
47.88
46.88
45.88
44.88
43.88
42.88
41.88
40.88
39.88
38.88
37.88
0
1
2
3
4
5
6
7
8
9
10
11
12
13
1 1
GEOTECHNICAL INVESTIGATION AT THE AROUCA WATER TREATMENT PLANT AND INTAKE - AROUCA
6312
BH 2 ENCLOSURE 6
N 1176480.403, E 683755.364
BULK UNIT WEIGHT
kN/m3
PENETRATION RESISTANCE BLOWS/0.3 m
N-VALUE N CONE PENETRATION
20 40 60 80 100
UNDRAINED SHEAR STRENGTH kN/m2
20 40 60 80 100
WATER CONTENT, PERCENT
Wp W WL
20 40 60 80
REMARKS
AND
GRAIN SIZE
DISTRIBUTION
GR SA SI CL
GROUNDWATER TABLE
m m
TO
DIAMETER OF DRILL BIT
PROJECT
TYPE
SOIL PROFILE
STRAT. PLOT
WELL
INSTALLATION
DESCRIPTION
ELEV. DEPTH
SPLIT SPOON
SHELBY TUBE
DISTURBED BULK
SAMPLE LOST
ROCK CORE
BLOCK SAMPLE
WL - LIQUID LIMIT
Wp - PLASTIC LIMIT
W - MOISTURE CONTENT
- ORGANIC CONTENT
CLAY
SILT
SAND
GRAVEL
METAMORPHIC
TOP SOIL
ORGANIC
NATURAL VANE
REMOULDED VANE
UNCONFINED - NAT'L.
TRIAXIAL QUICK
TORVANE
PILCON VANE
B.H. No.
ENCLOSURE
/
m DRILLING MUD
TRINTOPLAN CONSULTANTS LTD.
SHEET OF
PROJECT No.
RECORD OF BOREHOLE
LOCATION BORING DATE DATUM
SAMPLER HAMMER WEIGHT PENETRATION TEST HAMMER WEIGHT
63.5 kg, DROP 762 mm
BORING EQUIPMENT / METHOD
ELEV. (m) DEPTH (m)
SAMPLE
NUMBER
4
20
42
44
100
Medium dense, dark brown, orange brown, WELL GRADED GRAVEL with sand
Medium dense
Dark brown, orange brown Very dense, red, orange, brown, grey brown, SILTY GRAVEL with
SAND, trace clay
Very dense
Red, orange, brown, grey, brown
End of borehole at 9.45m
U.U. Direct Shear (Sa.5)
Cohesion = 0.0 kN/m2 Angle of friction = 40 o
1
2
3
4
5
6
7
8
9
10
25.7
1
4
60
42
3
16
36
38
100/6"
100/3"
100/5"
100/5"
50.614 Ground Surface
11-18-16 11-18-16
CME 55 DRILL RIG
0.2 N/A
M.S.L
HOLLOW STEM AUGERING
BH 3
7
49.61
48.61
47.61
46.61
45.61
44.61
43.61
42.61
41.61
40.61
39.61
38.61
37.61
0
1
2
3
4
5
6
7
8
9
10
11
12
13
1 1
GEOTECHNICAL INVESTIGATION AT THE AROUCA WATER TREATMENT PLANT AND INTAKE - AROUCA
6312
BH 3 ENCLOSURE 7
N 1176457.311, E 683743.088
BULK UNIT WEIGHT
kN/m3
PENETRATION RESISTANCE BLOWS/0.3 m
N-VALUE N CONE PENETRATION
20 40 60 80 100
UNDRAINED SHEAR STRENGTH kN/m2
20 40 60 80 100
WATER CONTENT, PERCENT
Wp W WL
20 40 60 80
REMARKS
AND
GRAIN SIZE
DISTRIBUTION
GR SA SI CL
GROUNDWATER TABLE
m m
TO
DIAMETER OF DRILL BIT
PROJECT
TYPE
SOIL PROFILE
STRAT. PLOT
WELL
INSTALLATION
DESCRIPTION
ELEV. DEPTH
SPLIT SPOON
SHELBY TUBE
DISTURBED BULK
SAMPLE LOST
ROCK CORE
BLOCK SAMPLE
WL - LIQUID LIMIT
Wp - PLASTIC LIMIT
W - MOISTURE CONTENT
- ORGANIC CONTENT
CLAY
SILT
SAND
GRAVEL
METAMORPHIC
TOP SOIL
ORGANIC
NATURAL VANE
REMOULDED VANE
UNCONFINED - NAT'L.
TRIAXIAL QUICK
TORVANE
PILCON VANE
B.H. No.
ENCLOSURE
/
m DRILLING MUD
TRINTOPLAN CONSULTANTS LTD.
SHEET OF
PROJECT No.
RECORD OF BOREHOLE
LOCATION BORING DATE DATUM
SAMPLER HAMMER WEIGHT PENETRATION TEST HAMMER WEIGHT
63.5 kg, DROP 762 mm
BORING EQUIPMENT / METHOD
ELEV. (m) DEPTH (m)
SAMPLE
NUMBER
14
11
82
88
133
134
Medium dense to very dense, brown and reddish brown, SILTY CLAYEY SAND with gravel
Brown, reddish brown Dense to very dense, orange brown, light brown, WELL GRADED GRAVEL with sand Dense
- - - - - - - - - - - - - -
Very dense
Orange brown, light brown Very dense, light brown, SILTY
SAND with gravel
Very dense
Light brown
End of borehole at 10.9m
1
2
3
4
5
6
7
8
9
10
11
16.8
29
6
0
4
29
60
40
26
12
2
13
53
38
43
45
100/6"
100/6"
100/5"
100/4"
50.222 Ground Surface
11-19-16 11-19-16
CME 55 DRILL RIG
0.2 N/A
M.S.L
HOLLOW STEM AUGERING
BH 4
8
49.22
48.22
47.22
46.22
45.22
44.22
43.22
42.22
41.22
40.22
39.22
38.22
37.22
0
1
2
3
4
5
6
7
8
9
10
11
12
13
1 1
GEOTECHNICAL INVESTIGATION AT THE AROUCA WATER TREATMENT PLANT AND INTAKE - AROUCA
6312
BH 4 ENCLOSURE 8
N 1176457.171, E 683777.533
BULK UNIT WEIGHT
kN/m3
PENETRATION RESISTANCE BLOWS/0.3 m
N-VALUE N CONE PENETRATION
20 40 60 80 100
UNDRAINED SHEAR STRENGTH kN/m2
20 40 60 80 100
WATER CONTENT, PERCENT
Wp W WL
20 40 60 80
REMARKS
AND
GRAIN SIZE
DISTRIBUTION
GR SA SI CL
GROUNDWATER TABLE
m m
TO
DIAMETER OF DRILL BIT
PROJECT
TYPE
SOIL PROFILE
STRAT. PLOT
WELL
INSTALLATION
DESCRIPTION
ELEV. DEPTH
SPLIT SPOON
SHELBY TUBE
DISTURBED BULK
SAMPLE LOST
ROCK CORE
BLOCK SAMPLE
WL - LIQUID LIMIT
Wp - PLASTIC LIMIT
W - MOISTURE CONTENT
- ORGANIC CONTENT
CLAY
SILT
SAND
GRAVEL
METAMORPHIC
TOP SOIL
ORGANIC
NATURAL VANE
REMOULDED VANE
UNCONFINED - NAT'L.
TRIAXIAL QUICK
TORVANE
PILCON VANE
B.H. No.
ENCLOSURE
/
m DRILLING MUD
TRINTOPLAN CONSULTANTS LTD.
SHEET OF
PROJECT No.
RECORD OF BOREHOLE
LOCATION BORING DATE DATUM
SAMPLER HAMMER WEIGHT PENETRATION TEST HAMMER WEIGHT
63.5 kg, DROP 762 mm
BORING EQUIPMENT / METHOD
ELEV. (m) DEPTH (m)
SAMPLE
NUMBER
18
REV. 01
FOR
THE NEW RAW WATER INTAKE AND WATER TREATMENT PLANT AT AROUCA
FOR
WATER AND SEWERAGE AUTHORITY
FEBRUARY 2017
Trintoplan Consultants Limited P.O. Box 2080, National Mail Centre, Piarco.
Orange Grove Road, Tacarigua TRINIDAD & TOBAGO W.I.
GEOTECHNICAL REPORT
FOR
THE NEW RAW WATER INTAKE AND WATER TREATMENT PLANT AT AROUCA
FOR
WATER AND SEWERAGE AUTHORITY
FEBRUARY 2017
GEOTECHNICAL REPORT FOR THE AROUCA WATER TREATMENT PLANT (WTP) AND INTAKE, AROUCA
(REVISION 01)
TABLE OF CONTENTS
CHAPTER DESCRIPTION PAGE
1.0 INTRODUCTION 1-1
2.0 THE SITE 2-1
2.1 Site Location and Description 2-1
2.2 Proposed Structure 2-1
2.3 Geology 2-1
2.4 Seismology 2-1
3.0 FIELD INVESTIGATION 3-1
3.1 Borehole Investigation 3-1
3.2 Testpit Investigation 3-2
4.0 LABORATORY TESTING 4-1
5.0 DATA PRESENTATION 5-1
6.0 SUBSURFACE CONDITIONS 6-1 6.1 Boreholes 1 to 6 6-1
6.2 Testpits 1 & 2 6-6
7.0 GROUNDWATER CONDITIONS 7-1
8.0 FOUNDATION ANALYSIS AND DESIGN 8-1
8.1 General 8-1
8.2 Seismic Hazard Parameters 8-1
8.3 Foundation Recommendations 8-5
9.0 SLOPE STABILITY ANALYSIS 9-1
9.1 General 9-1
9.2 Slope Stability Assessment 9-1
10.0 RECOMMENDATIONS 10-1
10.1 General 10-1
10.2 Excavation and Backfilling 10-1 10.3 Structural Backfill 10-2
10.4 Lateral Pressures 10-2
11.0 FOUNDATION CONSTRUCTION 11-1
11.1 General 11-1
11.2 Concrete Requirements 11-1
12.0 CLOSURE 12-1
List of Enclosures
GEOTECHNICAL REPORT FOR THE AROUCA WATER TREATMENT PLANT (WTP) AND INTAKE, AROUCA
(REVISION 01)
TABLE OF CONTENTS (CONT’D)
LIST OF ENCLOSURES
Enclosure 1 - Explanation of Terms used in this Report
Enclosure 2 - Site Location Plan
Enclosure 3 - Borehole/Testpit Location Plan
Enclosures 4 – 10 - Record of Borehole Sheets
Enclosures 11 - 12 - Testpit Log Sheets
Enclosures 13 - 19 - Atterberg Limits Results
Enclosures 20 - 27 - Gradation Curves
Enclosure 28 - Unconfined Compression Test Results
Enclosures 29 – 32 - Direct Shear Test Results
Enclosure 33 - Soil Chemistry Test Results
Enclosures 34 - 35 - Modified Proctor Test Results
Enclosures 36 - 39 - California Bearing Ratio Test Results
Enclosure 40 - Cross-Section A-A of the Site
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CHAPTER 1.0
INTRODUCTION
Trintoplan Consultants Limited was retained by the Water and Sewerage Authority (WASA) to carry out a geotechnical investigation to facilitate the foundation designs necessary for a New Raw Water Intake and Water Treatment Plant at a site off Savannah Trace, off Arima Old Road, Arouca. It is understood that the plant is being proposed in order to satisfy the increase in demand within the catchment area as a result of the planned Trestrail Development.
The investigation was carried out in accordance with our proposal dated June 27, 2016.
The objectives of the investigation were to:
• Identify the subsoil conditions at the site and determine the allowable bearing capacities of
the subsoil and,
• Determine the most appropriate foundation design for the proposed structures.
The Terms of Reference (TOR) included the advancement of six (6) boreholes, each to a depth of 15m, and the excavation of two (2) testpits, each to a depth of 3m.
This revised report presents the findings of the geotechnical investigation conducted at the site and provides recommendations for the design of the proposed structures, based upon discussions held in a meeting on February 13, 2017 with the Client representative, Mr. Dale Arneaud. It also includes recommendations regarding geotechnically related construction considerations.
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CHAPTER 2.0
THE SITE
2.1 SITE LOCATION AND DESCRIPTION
The site is located off Savannah Trace North, off Arima Old Road, Arouca.
It is bounded to the north by an earthen drain, west and south by open grassed areas and to the east by the Arouca River.
The topography of the site is varied. The proposed location for the service reservoir is relatively flat; however, the land slopes downward east of this area approximately 1 vertical to 3 horizontal, towards the Arouca River.
The site was covered with medium vegetation and some trees.
2.2 PROPOSED STRUCTURE
It is understood that the Client is desirous of constructing a new Raw Water Intake Station and Water Treatment Plant to treat approximately 1.32 IMGD of raw water.
2.3 GEOLOGY
According to the Geological map of Trinidad and Tobago (Scale 1:100,000), the site is underlain by the Cedros Formation of the Pleistocene epoch.
The Cedros Formation is comprised largely of poorly consolidated yellow, red and brown sands and grey blocky mudstones. The sands are poorly sorted, varying from fine to coarse grained. Interbedded with the sands are lenses of hard, "iron-cemented" sandstone and conglomerate, the latter containing pebbles of white quartz, chert and porcellanite.
2.4 SEISMOLOGY
The most dominant structural geological feature of interest to the study area is the El Pilar fault zone system which runs from east to west across Trinidad just south of the Northern Range. The El Pilar Fault Zone extends for about 700 km in an approximately E - W direction, from the Cariaco Trench to a point about 200 km northeast of Trinidad. It marks the southern boundary of the Araya-Paria peninsulas (eastern Caribbean Mts.) and of the Northern Range of Trinidad. It is characterized along its length by straight valleys, fault wedges, fumaroles, thermal springs, and sulfur deposits. The displacement along the El Pilar fault zone has been the subject of much controversy. Various authors recognize the following types of displacement: (1) southward thrust; (2) normal or graben faulting; (3) right-lateral strike-slip. The El Pilar fault zone probably represents a transform fault between the Caribbean and South America plates, and a hinge fault at its contact with the subduction zone east and south of the Lesser Antilles.
2-2
Figure 2.1 Map of Fault Zones in Trinidad
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CHAPTER 3.0
FIELD INVESTIGATION
The field investigation was carried out during the period November 17, 2016 to December 2, 2016 and consisted of:
• The advancement ofsix (6) boreholes to depths ranging from 4.6m to 15.3m and,
• Excavation of two (2) testpits to depths of 2.7m and 3m.
Although the TOR required the boreholes be advanced to 15m, practical refusal was encountered in all the boreholes, with the exception of Borehole 1. This resulted in boreholes being terminated at shallower depths. Practical refusal is defined as “N” values from the Standard Penetration Test of greater than 100 blows/300mm over a depth of 3m.
A topographical survey map of the site was provided by the Client on January 9, 2017. The locations of the boreholes and testpits were determined by the Client and set out by Trintoplan. Borehole and testpit elevations and coordinates (referenced to Mean Sea Level) are summarized in Table 3.1 below. The Borehole and Testpit Location Plan is included as Enclosure No. 3.
Borehole ID
Location (m)
Depth
Advanced
(m)
Date Advanced
Northing Easting Elevation
B1 1176482.69 683791.46 51.000 15.3 17-Nov-16
B2 1176480.40 683755.36 50.877 4.6 19-Nov-16
B3 1176457.31 683743.09 50.614 9.5 18-Nov-16
B4 1176457.17 683777.53 50.222 10.9 19-Nov-16
B5 1176507.93 683821.76 42.848 9.2 24-Nov-16
B6 1176525.99 683827.43 41.634 9.5 2-Dec-16
TP1 1176448 683726 ---- 2.7 23-Nov-2016
TP2 1176459 683781 ---- 3.0 23-Nov-2016
Table 3.1 Borehole and Testpit Locations
3.1 BOREHOLE INVESTIGATION
Boreholes 1 to 4 were advanced using a CME-55 drill rig, utilizing hollow stem augering techniques. Due to the ground conditions at Boreholes 5 and 6, these were advanced using an Acker tripod mounted portable drill rig utilizing dry sampling and wash boring techniques.
Sampling was carried out at intervals of 0.76 m for the first 4.57 m and then at intervals of 1.5 m until the end of each borehole.
Disturbed samples were obtained using the Standard Penetration Test (SPT), where the number of blows required to drive a split spoon sampler 0.3 m into the soil was recorded. This figure is designated as the ‘N’ value of the soil, and is related to soil strength and relative
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CHAPTER 4.0
LABORATORY TESTING
The soil samples were transported to TCL’s laboratory where, prior to the assignment of laboratory testing, a visual examination of each sample was performed by an engineer. Confirmatory classification testing for index properties such as Atterberg Limits and grain size distribution were performed on representative samples from each borehole. Moisture content tests were carried out on all samples.
Engineering properties tests were performed on the undisturbed Shelby Tube sample as well as bag samples for cohesionless soils. These tests included Pilcon Vane (PV), Unconfined Compression (UC) and Unconsolidated Undrained Direct Shear tests (UUDS) in order to measure the total and effective stress parameters of the soils.
Modified Proctor and California Bearing Ration (CBR) tests were performed on samples retrieved from the testpits.
Representative soil samples were sent to the Environmental Engineering Laboratory of the Department of the Civil and Environmental Engineering of the University of the West Indies (EELDC&EEUWI), where pH value and sulphate content tests were performed in order to determine the potential detrimental effects of the soils on foundations.
Laboratory Tests performed by Trintoplan were carried out in accordance with the relevant American
Society for Testing and Materials (ASTM) Standard Test Methods. The Chemical tests performed by EELDC&EEUWI will be carried out in accordance with the relevant British Standard (BS) Test Methods.
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CHAPTER 5.0
DATA PRESENTATION
Data Presented Enclosure Nos.
Borehole and Testpit Field and Laboratory Test Results
Record of Borehole Log Sheets (Boreholes, BH1 - BH6) 4 - 10
Data includes descriptions of the soil types, sample types and also provide summarized
laboratory test results
Testpit Log Sheets (Testpit Nos. TP1, TP2) 11 - 12
Data includes descriptions of the soil types, sample types and also provide summarized
laboratory test results
Atterberg Limits 13 - 19
Summary of data presented in Borehole and Testpit Logs; Details of tests, that is, Liquid Limit, Plastic Limits and Plasticity Indices are detailed in Enclosures
Grain Size Distribution 20 - 27
Summary of data presented in the "Remarks" column of the Borehole Logs and within the "Tests" column of the Testpit Logs; Due to rounding errors, the percentages may not add to 100. For details of tests i.e. Grain Size Distribution curves see Enclosures
Engineering Properties Tests
Pilcon Vane Tests
See Borehole Logs
Unconfined Compression Test 28
Unconsolidated Undrained Direct Shear Test 29 - 32
Chemical Tests Soil Chemistry 33
Compaction Characteristics
Modified Proctor 34, 35
Soaked California Bearing Ratio 36 - 39
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CHAPTER 6.0
SUBSURFACE CONDITIONS
The soil stratigraphy in the boreholes and testpits comprised primarily of gravel, sand and silt with varying proportions of clay. The detailed soil and ground conditions are shown on the Borehole Logs (Enclosure Nos. 4 to 10) and the Testpit Logs (Enclosure Nos. 11 and 12). A summarized account of the soil conditions encountered across the site is presented below.
6.1 BOREHOLES 1 TO 6
6.1.1 SOIL UNIT 1
The first soil unit was encountered within Borehole 2 only. It occurred from existing ground elevation and extended to a depth of 1.2m. It consisted of medium stiff to very stiff, dark brown and reddish brown Sandy Clayey Silt.
‘N’ values of 4 and 20 were recorded from the SPT.
Natural moisture contents of 19.4% and 18% were recorded.
The results of the Atterberg Limits test, provided in Enclosure No. 13, shows that the sample tested recorded a Liquid Limit of 34, Plastic Limit of 22 and Plasticity Index of 12. The results indicated that the soil sample tested plots within the CL section of the Plasticity Chart, indicating that the fines can be classified as clays of low plasticity.
The grain size distribution curve shown on Enclosure 20 indicates the soils predominantly comprise clay, siltand sand. The analysis recorded a clay content of 20%, silt content of 38%, sand content of 40% and gravel content of 2%.
Engineering Properties
No engineering properties tests were performed on samples obtained within this unit. However, based on correlation with the ‘N’ values, the following total stress parameters are considered to be representative of this unit:
• Bulk Unit weight, γB = 19.0 kN/m3
• Angle of Internal Friction , φ = 0 degrees
• Undrained shear strength, cu = 40 kPa
6.1.2 SOIL UNIT 2
The secondsoil unit was encountered from the ground surface in Boreholes 1 and 4 and extended to depths of 8.1m and 1.2m respectively. This unit was also encountered in Borehole 2 at depths of 1.2m and 4.6m.
It consisted of medium dense to very dense, moderately reddish brown, orange brown and dark brown Silty Clayey Sand with Gravel.
‘N’ values from the SPT ranged from 18 to values in excess of 100. On this basis the soil may be described as being medium dense to very dense.
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Natural moisture contents recorded ranged from 3% to 18%.
The results of the Atterberg Limits test, provided in Enclosure No. 14, show that the samples tested recorded Liquid Limits ranging between 24 and 36 and Plastic Limits ranging between 19 and 25 and Plasticity Indices ranging between 5 and 15. The results indicated that the soil samples tested plot within the CL, CL-ML and ML section of the Plasticity Chart, indicating that the fines can be classified as inorganic clays, silts and sands of low plasticity.
The grain size distribution curves shown on Enclosure 21 indicate the soils predominantly comprise gravels and sands with some silt and traces of clay. The analyses recorded clay contents ranging between 3% and 7%, silt contents ranging between 12% and 29%, sand contents ranging between 38% and 54% and gravel contents ranging between 27% and 44%.
Engineering Properties
A UU Direct Shear test was performed on a sample from within this unit. The results of these tests are plotted on the Borehole logs and presented in Table 6.1. Measured bulk unit weights (γB) and dry unit weights (γD) are also presented in Table 6.1.
Sample ID
Depth (m)
Unit
Weight (kN/m3)
Shear Strength (kN/m2)
Internal Friction
Angle, φ (degrees)
γΒ γD
B1/S3 1.7 18.3 16.7 4.1 46.3
Table 6.1
Unconsolidated Undrained Direct Shear Test Result
Soil Chemistry Results
Chemical testing was conducted on a representative sample from this soil unit. The sample was tested for pH and the presence of sulphates in order to establish whether the soil contains any corrosive properties. The results of these tests can be found in Enclosure No. 33, and are summarized in Table 6.2.
Sample ID
Sample
Depth
(m)
pH Value
Sulphate
Content
(%)
B1/S1 1.0 4.8 0.036
Table 6.2 Soil Chemistry Results
6.1.3 SOIL UNIT 3
Soil Unit 3 was encountered within Borehole 1 only. It occurred from a depth of 8.1m and extended to a depth of 12.7m. It consisted of hard, light brown and gray Silty Clay with little sand.
‘N’ values of 65 and 142 were recorded from the SPT.
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Natural moisture contents recorded ranged from 14% to 22%.
The results of the Atterberg Limits test, provided in Enclosure No. 15, shows that the sample tested recorded a Liquid Limit of 51, Plastic Limit of 23 and Plasticity Index of 28. The results indicated that the soil sample tested plots within the CH section of the Plasticity Chart, indicating that the fines can be classified as clays of high plasticity.
The grain size distribution curve shown on Enclosure 22 indicates the soils predominantly comprise clays and silts with little sand. The analysis recorded a clay content of 35%, silt content of 57%, sand content of 9% and gravel content of 0%.
Engineering Properties
PV and UC strength tests were performed on a sample from within this unit. The results of these tests are plotted on the Borehole logs and presented in Table 6.3. The measured bulk unit weight (γB) and dry unit weight (γD) is also presented in Table 6.3.
Sample ID
Depth (m)
Unit Weight (kN/m3)
Shear Strength (kPa)
γΒ γD PV UC
B1/S11 10.9 19.3 16.0 47 140
Table 6.3 Undrained Shear Strength Results
6.1.4 SOIL UNIT 4
Soil Unit 4 was encountered within Boreholes 1 and 4 only. It occurred from depths of 12.7m and 4.2m and extended through to the end Boreholes 1 and 4 at depths of 15.3m and 10.9m respectively. It consisted of very dense, light brown and grayish brown Silty Sand with Gravel, trace clay.
‘N’ values from the SPT ranged from 67 to values in excess of 100.
Natural moisture contents recorded ranged from 3% to 17%.
The results of the Atterberg Limits test, provided in Enclosure No. 16, shows that the sample tested recorded a Liquid Limit of 29, Plastic Limit of 23 and Plasticity Index of 6. The results indicated that the soil sample tested plots within the CL-ML section of the Plasticity Chart, indicating that the fines can be classified as clays and silts of low plasticity.
Grain Size distribution curves, included as Enclosure No. 23, indicates the soils predominantly comprise sands and gravels. The analyses recorded clay and silt contents of 17% and 29%, sand contents of 43% and 45% and gravel contents of 39% and 26%.
Engineering Properties
No engineering properties tests were performed on samples obtained within this unit. However, based on correlation with the ‘N’ values, the following total stress parameters are considered to be representative of this unit:
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• Bulk Unit weight, γB = 18.0 kN/m3
• Angle of Internal Friction , φ = 32 degrees
• Undrained shear strength, cu = 0 kPa
6.1.5 SOIL UNIT
Soil Unit 5 was encountered within Boreholes 3 and 4 only. It occurred from existing ground elevation and extended to a depth of 1.2m in Borehole 3 and from a depth of 1.2m to 4.3m in Borehole 4. It consisted of medium dense to very dense, orange brown and light brown well-graded gravel with sand.
‘N’ values from the SPT ranged from 11 to 149.
Natural moisture contents recorded ranged from 4% to 8%.
Grain Size distribution curves, included as Enclosure No. 24, indicates the soils predominantly comprise sands and gravels. The analyses recorded clay contents of 0.4% and 1.1%, silt contents of 2.1% and 3%, sand contents of 37.9% and 35.8% and gravel contents of 59.7% and 60.1%.
Engineering Properties
No engineering properties tests were performed on samples obtained within this unit. However, based on correlation with the ‘N’ values, the following total stress parameters are considered to be representative of this unit:
• Bulk Unit weight, γB = 16.8 kN/m3
• Angle of Internal Friction , φ = 33 degrees
• Undrained shear strength, cu = 0 kPa
6.1.6 SOIL UNIT 6
Soil Unit 6 was encountered within Boreholes 5 and 6 only. It occurred from existing ground elevation and extended to depths of 1.2m and 0.5m. It consisted of loose, brown sandy silt with little clay.
‘N’ values from the SPT ranged from 5 to 13.
Natural moisture contents of 28% and 29% were recorded.
The results of the Atterberg Limits test, provided in Enclosure No. 17, shows that the sample tested recorded a Liquid Limit of 33, Plastic Limit of 28 and Plasticity Index of 5. The results indicated that the soil sample tested plots within the ML section of the Plasticity Chart, indicating that the fines can be classified as silts of low plasticity.
Grain Size distribution curves, included as Enclosure No. 25, indicates the soils predominantly comprise silts and sands. The analysis recorded a clay content of 13%, silt content of 52%, sand contentsof 34% and a gravel content of 0%.
Engineering Properties
No engineering properties tests were performed on samples obtained within this unit. However, based on correlation with the ‘N’ values, the following total stress parameters are considered to be representative of this unit:
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• Bulk Unit weight, γB = 17 kN/m3
• Angle of Internal Friction , φ = 25 degrees
• Undrained shear strength, cu = 0 kPa
6.1.7 SOIL UNIT 7
Soil Unit 7 was encountered within Boreholes 3, 5 and 6 only. It occurred from depths of 1.2m in Boreholes 3 and 5, and 0.5m in Borehole 6 and extended to the end of each borehole at depths of 9.5m, 9.2m and 9.5m respectively. It consisted of medium dense to very dense, brown silty gravel with sand.
‘N’ values from the SPT ranged from 13 to values in excess of 100.
Natural moisture contents ranging between 2% and 24% were recorded.
The results of the Atterberg Limits test, provided in Enclosure No. 18, show that the samples tested recorded Liquid Limits ranging between 24 and 36 and Plastic Limits ranging between 27 and 31 and Plasticity Indices ranging between 21 and 29. The results indicated that the soil samples tested plot within the CL and ML section of the Plasticity Chart, indicating that the fines can be classified as inorganic clays, silts and sands of low plasticity. Two samples, B6/SA4 and B6/SA8 tested were non-plastic with Liquid Limits of 27 and 28 respectively.
Grain Size distribution curves, included as Enclosure No. 26, indicates the soils predominantly comprise sands and gravels. The analyses recorded clay contents ranging between 1% and 4%, silt contents ranging between 9% and 20%, sand contents ranging between 27% and 39% and gravel contents ranging between 41% and 60%.
Engineering Properties
UU Direct Shear tests were performed on samples from within this unit. The results of these tests are plotted on the Borehole logs and presented in Table 6.4. Measured bulk unit weights (γB) and dry unit weights (γD) are also presented in Table 6.4.
Sample ID
Depth (m)
Unit Weight (kN/m3)
Shear
Strength (kN/m2)
Internal Friction
Angle, φ
(degrees) γΒ
γD
B3/S5 3.2 18.7 17.6 0 40
B5/S4 2.5 22.8 20.3 11.5 33.4
B6/S5 3.3 19.1 17.8 6 39.3
Table 6.4
Unconsolidated Undrained
Direct Shear Test Result
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6.2 TESTPITS 1 & 2
6.2.1 SOIL UNIT 1
A single soil unit was found within Testpits 1 and 2. It occurred from the existing ground surface and extended through to the end of each testpit at depths of 2.74m and 3.05m respectively. It consisted of brown Silty Clayey Gravel with sand.
Natural moisture contents of 8% and 9% were recorded.
The results of the Atterberg Limits test, presented on Enclosure No. 19, performed on the samples within this unit shows that the samples recorded Liquid Limits of 25 and 29, Plastic Limits of 18 and 16 and Plasticity Indices of 7 and 13. The soil samples tested plot within the CL section of the Plasticity Chart, indicating that the fines can be classified as clay of low plasticity.
Grain Size distribution curves, included as Enclosure No. 27, indicates the soils predominantly comprise sands and gravels. The analyses recorded clay contents of 3% and 4%, silt contents of 12% and 13%, sand contents of 32% and 33% and gravel contents of 54% and 51%.
The compaction characteristics included as Enclosure Nos. 34 and 35 of the soil (Maximum Dry Unit Weight and Optimum Moisture Content), as well as the bearing strength (California Bearing Ratio – Enclosure Nos. 36 to 39) of the soil samples tested are presented in Table 6.5 below.
Testpit ID
Depth (m)
Maximum
Dry Unit
Weight (kN/m3)
Optimum
Moisture
Content
(%)
CBR
(%)
TP1 1.4 21.7 5.8 21
TP2 1.5 21.7 6.2 36
Table 6.5 Compaction Characteristics
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CHAPTER 7.0
GROUNDWATER CONDITIONS
Water levels encountered on the site during ground investigation operations are summarised in Table 7.1. The depth to groundwater was measured within the boreholes during drilling and at the end of drilling operations.
Borehole No.
Measured
Groundwater
Level, m
Elevation, m Date
BH 1 11.6 39.4 17-Nov-16
BH 2 None recorded --- 19-Nov-16
BH 3 None recorded --- 18-Nov-16
BH 4 None recorded --- 19-Nov-16
BH 5 2.5 40.3 24-Nov-16
BH 6 4.4 37.2 2-Dec-16
Table 7.1 Depths of Groundwater Table
The groundwater levels are phreatic and are influenced by rainfall. The groundwater levels may also be controlled by the water levels in the river. As such,the variations in the water level readings within Boreholes 5 and 6, which were in close proximity to the river, were likely due to rainfall events (or lack thereof) in the days prior to the advancement of the boreholes.
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CHAPTER 8.0
FOUNDATION DESIGN AND ANALYSIS
8.1 GENERAL
Foundations for structures may be classified based on the means by which the load is transferred to the ground. There can be either shallow foundations or deep foundations. They are designed to ensure that the load transfer does not produce settlements beyond acceptable limits, and are constructed at adequate depths to mobilize sufficient soil resistance for supporting the imposed loads.
Further to a meeting with the Client held on February 13th, 2017, it was understood that the
structures to be constructed at the plant include:
• An Operator Room
• Clarifier Filters
• Chemical Building
• Clearwell Tank and
• An Intake Station
It was also understood that the Clearwell Tank will be a partially buried structure with a proposed foundation depth of 3.825m below existing grade.
For the proposed structures within the Water Treatment Plant only shallow foundations were considered for supporting the structures as competent load bearing strata was encountered at shallow depths (see Borehole Logs included as Enclosure Nos. 4 to 10).
8.2 SEISMIC HAZARD PARAMETERS
The seismic hazard parameters defined in accordance with IBC (2009) and ASCE7-2005 include the spectral ground accelerations at 0.2 seconds and 1.0 seconds and the peak ground acceleration for return period of 2475 years. The design parameters are as included in Table 8.1.
Ground motions for design
Mapped spectral acceleration parameters
Range (g) Range (m/s)
Spectral acceleration at short period (0.2 seconds) Ss
1.461- 1.550 14.332 – 15.206
Spectral acceleration at 1 second period S1
0.371 -0.391 3.640 – 3.836
Spectral acceleration peak ground acceleration (PGA)
0.562 -0.590 5.513 - 5.788
Table 8.1 Spectral Accelerati
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Figure 8.1
Spectral Acceleration Parameters 0.2s, Ss (RP=2475 years)
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Figure 8.2
Spectral Acceleration Parameters 1s, S1 (RP=2475 years)
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Figure 8.3
Spectral Acceleration Parameters PGA (RP=2475 years)
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8.3 FOUNDATION RECOMMENDATIONS
8.3.1 Shallow Foundations
Analyses were carried out to determine the allowable bearing capacities of continuous (strip) footings and pad footings placed at depths of 1.5 m and 3.825 m below existing grade level and using undrained shear strength, c, of 0 kPa and an internal angle of friction of 33.4 degrees. The estimated allowable bearing capacity was determined using Meyerhof’s bearing capacity equation:
qa =
cNcscdc+qNqsqdq +1/2γBNγsγdγ
FS
Where:
qa = Allowable bearing capacity c = Undrained cohesion of soil
q = Effective overburden pressure of soil
γ = Bulk unit weight of soil B = Width of foundation sc, sγ= Shape factors dc,dq,dγ= Depth factors
Nc, Nq and Nγ = Bearing Capacity factors
FS = Factor of Safety
A Factor of Safety of 3 was used in the estimation of allowable bearing capacities.
Settlement estimates were determined using the results of the standard penetration test and calculation methods established by Burland and Burbidge (Tomlinson 2001, 67-69).
Based upon the analyses conducted it was determined that an allowable bearing capacity of 400 kN/m2 can be used for both:
Square pad foundations varying in dimension of 1.0m x 1.0m to 3.0m x 3.0m
and,
Continuous (strip) foundations varying in width from 1.0m to 3.0m.
Allowable bearing pressures will be governed by both safe bearing capacities and allowable settlement. At these allowable bearing capacities, the settlements are estimated to be less than 25mm and would occur during the construction period.
9-1
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Geotechnical Investigation for the
Arouca Water Treatment Plant And Intake, Arouca
CHAPTER 9.0
SLOPE STABILITY ANALYSIS
9.1 GENERAL
The site is sloped (1 vertical to 3 horizontal) within the area where Boreholes 5 and 6 were advanced. At the time of the field investigation the sloped surface was covered with tall vegetation and evidence of existing slope failure or soil movement was not observed.
It was observed that the Arouca River which traverses in a north -south direction is situated at the base of the slope. It is unclear how the river behaves during periods of heavy rainfall and essentially how far inland, toward the existing site, the increased water flows may affect the existing slope.
9.2 SLOPE STABILITY ASSESSMENT
Factors leading to slope instability include:
• Increased unit weight of the soils due to saturation of the soils, i.e. increased moisture
content and increased pore pressures of the soils;
• Added external loads, e.g. buildings
• Steepened slopes either by excavation or erosion
• Vibration and earthquakes
A slope stability analysis was carried out using sections generated from a topographical survey submitted by the Water and Sewerage Authority on January 9, 2017. The section generated is graphically shown on Enclosure 40.
From soil data within Boreholes 5 and 6 it was observed that surficial deposits of loosesandy silts occurred from existing ground level to a maximum depth of 1.2m below grade and is underlain by medium dense to very dense layer of silty gravel deposits.
Based on the cohesionless nature of the subsoils, the most likely failure type which may occur along the existing slopes will be a translational slide. This type of failure is associated with movement largely controlled by surfaces of weakness.Almost all translational slides occur along the line between the substratum, in this case the medium dense to very dense layer of silty gravel depositsand superficial soils i.e. the loosesandy silt. They therefore tend to be shallow and mainly affect thin soil layers.
Analyses were carried out with the slope under varying saturated conditions (unsaturated, 50% saturated and fully saturated) to closely assimilate anticipated soil conditions which will occur annually. Each analysis was performed under normal conditions.
Shear Strength values and the angles of internal friction for each layer was determined by using the results of CU Triaxial tests which were derived from the results of laboratory testing performed on samples. The parameters used in the analyses are summarized in Table 9.1.
9-2
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Geotechnical Investigation for the
Arouca Water Treatment Plant And Intake, Arouca
Material Description
Effective
Shear
Strength
, c’ (kN/m2)
Effective
Angle of
Internal
Friction, (degrees)
Pore Pressure Ratio, ru
Bulk Unit Weight
0%
Saturation
50%
Saturation
100%
Saturation
(kN/m3)
Loose Sandy
Silt
0 25 0 0.24 0.48 17
Medium dense to very dense Silty Gravel
11.5 33.4 0 0.15 0.30 22.5
Table 9.1 Stability Analysis Parameters for Cross-Section
From the analyses performed, factors of safety for the varying conditions were determined.
A factor of safety greater than 1.3 is deemed to be satisfactory in slope stability analyses.
Saturation Conditions Factor of Safety
Unsaturated (0% Saturation) 1.402
50% Saturation 0.997
Fully Saturated (100%
Saturation)
0.593
Table 9.2 Slope Stability Analysis Results
From Table 9.2 it can be seen that the existing slopes are stable for unsaturated conditions only. As the degree of saturation increases, the slope becomes unstable.
Section 9.0 outlines recommendations that should be considered in the finalization of designs for the structures located within this sloped area.
10-1
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Geotechnical Investigation for the
Arouca Water Treatment Plant And Intake, Arouca
CHAPTER 10.0
RECOMMENDATIONS
10.1 GENERAL
Further to a meeting held on February 13, 2017 with the Client representative, Mr. Dale Arneaud, it was understood that there is a consideration by WASA to install an Intake Station structure along the slope. This however may be subject to change once designs are finalised.
In order to arrest the potential slope instability and soil movements which are likely to occur along the slope, it must be ensured that the slope is stabilized and proper drainage infrastructure be constructed at the site.
Based on the site survey, in conjunction with nature of the sub-soils encountered at the site the following remediation measures are recommended for this area of the site:
• Incorporation of proper drainage designs prior to construction to reduce infiltration of
surface water runoff into the affected area,
• Structural solutions, wherein physical structures are used to support the existing
embankment and thus prevent movement.
10.2 EXCAVATION AND BACKFILLING
Prior to excavation or backfilling, the areas to be cut or filled should be stripped to remove vegetation, roots and weak topsoil. These soils should not be re-used in areas that will support structures, pavements and slabs. They could be re-used for general landscaping or other non-structural purposes.
The following methods for excavation should be used to protect personnel, to maintain stable excavation slopes and to protect bottom excavation:
• Side slopes at a maximum gradient of 1.8 horizontal to 1.0 vertical.
• Shoring of excavations where the depth of excavation exceeds 2 m or where
space is not available to achieve the recommended side slopes for depths of excavation less than 2 m.
• Excavated material should not be stockpiled at the edges of excavations as this
could result in slope instability.
Prior to placement of concrete for foundations, the top 300 mm of subgrade at foundation level should be compacted to at least 100% of the maximum dry unit weight determined in accordance with ASTM D 1557 (Modified Proctor).
10-2
6312
Geotechnical Investigation for the
Arouca Water Treatment Plant And Intake, Arouca
10.3 STRUCTURAL BACKFILL
The use of imported fill or excavated material from the site as structural fill should be free from organic matter (leaves, grass, roots, trees, brush, mulch, etc.), topsoil and other such objectionable debris and should have the properties detailed below.
• Gradation (ASTM C 136) Well graded granular material with
100% passing a 75mm sieve, not more than 40% by weight passing a 0.425mm (No. 40% sieve) and not more than 10% by weight passing a 0.075mm (No. 200) sieve.
• Liquid Limit (ASTM D 4318) ≤ 25
• Plasticity Index (ASTM D 4318) ≤ 6
• Soaked California
Bearing Ratio (ASTM D 1883) ≥ 3% for imported fill installed in
embankments to within 300mm of subgrade level ≥15% for imported fill installed within the top 300mm of embankments.
Structural fill material should be placed in lifts not exceeding 200mm (loose) thickness, except for the top 600mm, which should be placed in lifts not exceeding 150mm (loose) thickness. Each lift of material should be compacted to at least 95% of the maximum dry unit weight determined in accordance with ASTM D 1557 (Modified Proctor) before the next layer is placed, except for the top two 150mm thick layers, which should be compacted to 100% of the maximum dry unit weight.
10.4 LATERAL PRESSURES
The lateral pressures that should be considered in the design of retaining walls at the site are:
• Static earth pressure
• Hydrostatic (water) pressure
• Live load or surcharge pressures
• Seismic pressure
10.4.1 Static Earth Pressure
The backfill to the Retaining Wall should be a free draining well-graded granular material meeting and installed in accordance with the specifications given in Section 10.3 (Structural Backfill).
The following parameters should be used in the calculation of earth pressures for the structural backfill material. An active earth pressure (yielding foundation) condition may be assumed.
10-3
6312
Geotechnical Investigation for the
Arouca Water Treatment Plant And Intake, Arouca
• Angle of internal friction, φ‘ 30°
• Cohesion, c’ 0 kPa
• Bulk Unit weight, γB 20 kN/m3
• Active earth pressure coefficient, ka 0.33
The recommended maximum gradient for the surface of the structural backfill material behind the retaining structure (i.e., on the active side) is 3 horizontal to 1 vertical.
As far as practical, removal of ground in front of the retaining wall, e.g., to install services should be avoided, since this reduces the passive resistance and hence the stability of the wall. If this cannot be avoided, then adequate lateral support for the excavation should be provided.
10.4.2 Hydrostatic (Water) Pressure
Walls should be designed to resist the maximum anticipated hydrostatic pressure, which as a minimum, should be taken as the hydrostatic pressure occurring up to the lowest level of weep-holes. Adequate weep-holes and a granular drainage layer (e.g., single size clean 19 mm gravel wrapped in geo-textile filter fabric) should be provided to avoid the buildup of excessive hydrostatic pressures for long-term conditions.
10.4.3 Live Load or Surcharge Pressures
If anticipated, the effects of live loads and/or surcharges within close proximity of the retaining wall should be taken into account in the design of the wall. Design loads established by American Association of State Highway and Transportation Officials (AASHTO) Standards should be used to determine the effective surcharge from traffic loads.
10.4.4 Seismic Pressures
The pseudo static approach developed by Monobe and Okabe may be used to estimate the equivalent static forces for seismic loads. The estimation of seismic design forces should account for wall inertia forces in addition to the equivalent static forces.
10.4.5 Sliding and Overturning
The stability of the wall should be checked for sliding and overturning. The minimum factor of safety against sliding should be 2.0 and the minimum factor of safety against overturning should be 1.5.
For computation of sliding resistance, the angle of internal friction of the foundation soil, φf, should be taken as 33 degrees and 0 kPa should be used for the base cohesion, cf. The base friction angle, δ, should be taken as 0.67φf, i.e., 22 degrees.
11-1
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Geotechnical Investigation for the
Arouca Water Treatment Plant And Intake, Arouca
Capitulo 12
Cierre
LIST OF ENCLOSURES
Enclosure 1 - Explanation of Terms used in this Report
Enclosure 2 - Site Location Plan
Enclosure 3 - Borehole/Testpit Location Plan
Enclosures 4 – 10 - Record of Borehole Sheets
Enclosures 11, 12 - Testpit Log Sheets
Enclosures 13 - 19 - Atterberg Limits Results
Enclosures 20 - 27 - Gradation Curves
Enclosure 28 - Unconfined Compression Test Results
Enclosures 29 – 32 - Direct Shear Test Results
Enclosure 33 - Soil Chemistry Test Results
Enclosures 34, 35 - Modified Proctor Test Results
Enclosures 36 - 39 - California Bearing Ratio Test Results
Enclosure 40 - Cross-section A-A of the Site
ENCLOSURE 1
EXPLANATION OF TERMS USED IN THIS REPORT
N VALUE: THE STANDARD PENETRATION TEST (SPT) N VALUE IS THE NUMBER OF BLOWS REQUIRED TO CAUSE A
STANDARD 51mm O.D. SPLIT BARREL SAMPLER TO PENETRATE 0.3 m INTO UNDISTURBED GROUND IN A
BOREHOLE WHEN DRIVEN BY A HAMMER WITH A MASS OF 63.5kg, FALLING FREELY A DISTANCE OF 0.76m. FOR
PENETRATION OF LESS THAN 0.3m, N VALUES ARE INDICATED AS THE NUMBER OF BLOWS FOR THE PENETRATION ACHIEVED.
SOILS ARE DESCRIBED BY THEIR COMPOSITION AND CONSISTENCY OR DENSENESS
CONSISTENCY: COHESIVE SOILS ARE DESCRIBED ON THE BASIS OF THEIR UNDRAINED SHEAR STRENGTH (Cu ) AND N VALUES AS FOLLOWS:
Cu (kPa) 0-12 12-25 25-50 50-100 100-200 >200
N VALUE 0-2 2-4 4-8 8-15 15-30 >30
VERY SOFT SOFT FIRM STIFF VERY STIFF HARD
DENSENESS: NON COHESIVE SOILS ARE DESCRIBED ON THE BASIS OF THEIR N VALUES AS FOLLOWS
N VALUE 0-5 5-10 10-30 30-50 >50
VERY LOOSE LOOSE COMPACT DENSE VERY DENSE
ROCKS ARE DESCRIBED BY THEIR COMPOSITION AND STRUCTURAL FEATURES AND / OR STRENGTH
RECOVERY: SUM OF ALL RECOVERED ROCK CORE PIECES FROM A CORING RUN EXPRESSED AS A PERCENT OF THE TOTAL
LENGTH OF THE CORING RUN
MODIFIED RECOVERY: SUM OF THOSE INTACT CORE PIECES 100 mm+ IN LENGTH EXPRESSED AS A PERCENT OF THE LENGTH OF THE CORING RUN. THE ROCK QUALITY DESIGNATION (RQD) FOR MODIFIED RECOVERY IS
RQD (%) 0-25 25-50 50-75 75-90 90-100 VERY POOR POOR FAIR GOOD EXCELLENT
JOINTING AND BEDDING
SPACING 50 mm 50-300 mm 0.3m -1m 1m -3m >3m
JOINTING VERY CLOSE CLOSE MOD. CLOSE WIDE VERY WIDE
BEDDING VERY THIN THIN MEDIUM THICK VERY THICK
ABBREVIATIONS AND SYMBOLS
FIELD SAMPLING MECHANICAL PROPERTIES OF SOIL
DO SPLIT SPOON mv kPa-1 COEFFICIENT OF VOLUME CHANGE
TO THINWALL OPEN Cc 1 COMPRESSION INDEX
TP THINWALL PISTON Cs 1 SWELLING INDEX
WS WASH SAMPLE C 1 RATE OF SECONDARY CONSOLIDATION
CS CHUNK SAMPLE cv m
2/s COEFFICIENT OF CONSOLIDATION
BS BLOCK SAMPLE H m DRAINAGE PATH RC ROCK CORE Tv 1 TIME FACTOR
PH ADVANCED HYDRAULICALLY U % DEGREE OF CONSOLIDATION
WH ADVANCED WITH HAMMER Po kPa EFFECTIVE OVERBURDEN PRESSURE
Pc kPa PRECONSOLIDATION PRESSURE
kPa SHEAR STRENGTH
STRESS AND STRAIN c’ kPa EFFECTIVE COHESION INTERCEPT uw kPa PORE WATER PRESSURE cu kPa APPARENT COHESION INTERCEPT ru 1 PORE PRESSURE RATIO u -
o APPARENT ANGLE OF INT. FRICTION
kPa TOTAL NORMAL STRESS R kPa RESIDUAL SHEAR STRENGTH
’ kPa EFFECTIVE NORMAL STRESS st 1 SENSITIVITY
1,2,3 kPa PRINCIPAL STRESSES ’ -o EFFECTIVE ANGLE OF INT. FRICTION
% LINEAR STRAIN
1,2,3 % PRINCIPAL STRAINS
E kPa MODULUS OF LINEAR DEFORMATION
G kPa MODULUS OF SHEAR DEFORMATION
1 COEFFICIENT OF FRICTION
PHYSICAL PROPERTIES OF SOIL
s kg/m3 DENSITY OF SOLID PARTICLES e 1% VOID RATIO
s kN/m3 UNIT WEIGHT OF SOIL n 1% POROSITY Gs 1 SPECIFIC GRAVITY w 1% MOISTURE CONTENT
w kg/m3 DENSITY OF WATER sr % DEGREE OF SATURATION kg/m3 DENSITY OF SOIL LL % LIQUID LIMIT
w kN/m3 UNIT WEIGHT OF WATER PL % PLASTIC LIMIT
d kN/m3 DRY UNIT WEIGHT PI % PLASTICITY INDEX
sat kN/m3 SATURATED UNIT WEIGHT OF SOIL
sat kg/m3 SATURATED DENSITY OF SOIL
' kg/m3 DENSITY OF SUBMERGED SOIL
' kN/m3 UNIT WEIGHT OF SUBMERGED SOIL
Medium dense to very dense, brown and reddish brown, SILTY, CLAYEY SAND with gravel
- - - - - - - - - - - - -
Very dense
Brown and reddish brown Very dense, dark brown and light brown, SILTY SAND with gravel
Very dense
Dark brown and light brown Hard, light brown and grey, SILTY
CLAY, little sand
Hard
Light brown and grey Very dense, light brown, SILTY
SAND with gravel
U.U. Direct Shear (Sa.3)
Cohesion = 4.1 kN/m2
Angle of friction = 46.3 o
1
2
3
4
5
6
7
8
9
10
11
12
19.6
19.8
4
6
35
33
28 0
19
29
57
45
38 9
100/6"
100/6"
100/3"
51.000 Ground Surface
11-17-16 11-17-16
CME 55 DRILL RIG
0.2 N/A
M.S.L
HOLLOW STEM AUGERING
11.6
39.4
BH 1
4
50.00
49.00
48.00
47.00
46.00
45.00
44.00
43.00
42.00
41.00
40.00
39.00
38.00
0
1
2
3
4
5
6
7
8
9
10
11
12
13
1 2
GEOTECHNICAL INVESTIGATION AT THE AROUCA WATER TREATMENT PLANT AND INTAKE - AROUCA
6312
BH 1 ENCLOSURE 4
N 1176482.689, E 683791.464
BULK UNIT WEIGHT
kN/m3
PENETRATION RESISTANCE BLOWS/0.3 m
N-VALUE N CONE PENETRATION
20 40 60 80 100
UNDRAINED SHEAR STRENGTH kN/m2
20 40 60 80 100
WATER CONTENT, PERCENT
Wp W WL
20 40 60 80
REMARKS
AND
GRAIN SIZE
DISTRIBUTION
GR SA SI CL
GROUNDWATER TABLE
m m
TO
DIAMETER OF DRILL BIT
PROJECT
TYPE
SOIL PROFILE
STRAT. PLOT
WELL
INSTALLATION
DESCRIPTION
ELEV. DEPTH
SPLIT SPOON
SHELBY TUBE
DISTURBED BULK
SAMPLE LOST
ROCK CORE
BLOCK SAMPLE
WL - LIQUID LIMIT
Wp - PLASTIC LIMIT
W - MOISTURE CONTENT
- ORGANIC CONTENT
CLAY
SILT
SAND
GRAVEL
METAMORPHIC
TOP SOIL
ORGANIC
NATURAL VANE
REMOULDED VANE
UNCONFINED - NAT'L.
TRIAXIAL QUICK
TORVANE
PILCON VANE
B.H. No.
ENCLOSURE
/
m DRILLING MUD
TRINTOPLAN CONSULTANTS LTD.
SHEET OF
PROJECT No.
RECORD OF BOREHOLE
LOCATION BORING DATE DATUM
SAMPLER HAMMER WEIGHT PENETRATION TEST HAMMER WEIGHT
63.5 kg, DROP 762 mm
BORING EQUIPMENT / METHOD
ELEV. (m) DEPTH (m)
SAMPLE
NUMBER
140.85
23
80
51
52
160
161
65
142
Very dense, light brown, SILTY SAND with gravel
Very dense
Light brown
End of borehole at 15.32m
13
14 20.0
100/3"
100/3"
Continued
11-17-16 11-17-16
CME 55 DRILL RIG
0.2 N/A
M.S.L
HOLLOW STEM AUGERING
11.6
39.4
BH 1
5
37.00
36.00
35.00
34.00
33.00
32.00
31.00
30.00
29.00
28.00
27.00
26.00
25.00
14
15
16
17
18
19
20
21
22
23
24
25
26
2 2
GEOTECHNICAL INVESTIGATION AT THE AROUCA WATER TREATMENT PLANT AND INTAKE - AROUCA
6312
BH 1 ENCLOSURE 5
N 1176482.689, E 683791.464
BULK UNIT WEIGHT
kN/m3
PENETRATION RESISTANCE BLOWS/0.3 m
N-VALUE N CONE PENETRATION
20 40 60 80 100
UNDRAINED SHEAR STRENGTH kN/m2
20 40 60 80 100
WATER CONTENT, PERCENT
Wp W WL
20 40 60 80
REMARKS
AND
GRAIN SIZE
DISTRIBUTION
GR SA SI CL
GROUNDWATER TABLE
m m
TO
DIAMETER OF DRILL BIT
PROJECT
TYPE
SOIL PROFILE
STRAT. PLOT
WELL
INSTALLATION
DESCRIPTION
ELEV. DEPTH
SPLIT SPOON
SHELBY TUBE
DISTURBED BULK
SAMPLE LOST
ROCK CORE
BLOCK SAMPLE
WL - LIQUID LIMIT
Wp - PLASTIC LIMIT
W - MOISTURE CONTENT
- ORGANIC CONTENT
CLAY
SILT
SAND
GRAVEL
METAMORPHIC
TOP SOIL
ORGANIC
NATURAL VANE
REMOULDED VANE
UNCONFINED - NAT'L.
TRIAXIAL QUICK
TORVANE
PILCON VANE
B.H. No.
ENCLOSURE
/
m DRILLING MUD
TRINTOPLAN CONSULTANTS LTD.
SHEET OF
PROJECT No.
RECORD OF BOREHOLE
LOCATION BORING DATE DATUM
SAMPLER HAMMER WEIGHT PENETRATION TEST HAMMER WEIGHT
63.5 kg, DROP 762 mm
BORING EQUIPMENT / METHOD
ELEV. (m) DEPTH (m)
SAMPLE
NUMBER
Medium stiff to very stiff, dark brown and medium reddish brown, SANDY CLAYEY SILT
- - - - - - - - - - - - -
Very stiff
Dark brown and medium reddish brown Dense to very dense, reddish brown, orange brown, dark brown, SILTY CLAYEY SAND with gravel Dense
- - - - - - - - - - - - -
Very dense
Reddish brown, orange brown, dark brown End of borehole at 4.62m
1
2
3
4
5
6
7
19.3
16.7
19
20 6
3
43
36
38
20
40
38
38
100/6"
100/6"
50.877 Ground Surface
11-19-16 11-19-16
CME 55 DRILL RIG
0.2 N/A
M.S.L
HOLLOW STEM AUGERING
BH 2
6
49.88
48.88
47.88
46.88
45.88
44.88
43.88
42.88
41.88
40.88
39.88
38.88
37.88
0
1
2
3
4
5
6
7
8
9
10
11
12
13
1 1
GEOTECHNICAL INVESTIGATION AT THE AROUCA WATER TREATMENT PLANT AND INTAKE - AROUCA
6312
BH 2 ENCLOSURE 6
N 1176480.403, E 683755.364
BULK UNIT WEIGHT
kN/m3
PENETRATION RESISTANCE BLOWS/0.3 m
N-VALUE N CONE PENETRATION
20 40 60 80 100
UNDRAINED SHEAR STRENGTH kN/m2
20 40 60 80 100
WATER CONTENT, PERCENT
Wp W WL
20 40 60 80
REMARKS
AND
GRAIN SIZE
DISTRIBUTION
GR SA SI CL
GROUNDWATER TABLE
m m
TO
DIAMETER OF DRILL BIT
PROJECT
TYPE
SOIL PROFILE
STRAT. PLOT
WELL
INSTALLATION
DESCRIPTION
ELEV. DEPTH
SPLIT SPOON
SHELBY TUBE
DISTURBED BULK
SAMPLE LOST
ROCK CORE
BLOCK SAMPLE
WL - LIQUID LIMIT
Wp - PLASTIC LIMIT
W - MOISTURE CONTENT
- ORGANIC CONTENT
CLAY
SILT
SAND
GRAVEL
METAMORPHIC
TOP SOIL
ORGANIC
NATURAL VANE
REMOULDED VANE
UNCONFINED - NAT'L.
TRIAXIAL QUICK
TORVANE
PILCON VANE
B.H. No.
ENCLOSURE
/
m DRILLING MUD
TRINTOPLAN CONSULTANTS LTD.
SHEET OF
PROJECT No.
RECORD OF BOREHOLE
LOCATION BORING DATE DATUM
SAMPLER HAMMER WEIGHT PENETRATION TEST HAMMER WEIGHT
63.5 kg, DROP 762 mm
BORING EQUIPMENT / METHOD
ELEV. (m) DEPTH (m)
SAMPLE
NUMBER
4
20
42
44
100
Medium dense, dark brown, orange brown, WELL GRADED GRAVEL with sand
Medium dense
Dark brown, orange brown Very dense, red, orange, brown, grey brown, SILTY GRAVEL with
SAND, trace clay
Very dense
Red, orange, brown, grey, brown
End of borehole at 9.45m
U.U. Direct Shear (Sa.5)
Cohesion = 0.0 kN/m2 Angle of friction = 40 o
1
2
3
4
5
6
7
8
9
10
25.7
1
4
60
42
3
16
36
38
100/6"
100/3"
100/5"
100/5"
50.614 Ground Surface
11-18-16 11-18-16
CME 55 DRILL RIG
0.2 N/A
M.S.L
HOLLOW STEM AUGERING
BH 3
7
49.61
48.61
47.61
46.61
45.61
44.61
43.61
42.61
41.61
40.61
39.61
38.61
37.61
0
1
2
3
4
5
6
7
8
9
10
11
12
13
1 1
GEOTECHNICAL INVESTIGATION AT THE AROUCA WATER TREATMENT PLANT AND INTAKE - AROUCA
6312
BH 3 ENCLOSURE 7
N 1176457.311, E 683743.088
BULK UNIT WEIGHT
kN/m3
PENETRATION RESISTANCE BLOWS/0.3 m
N-VALUE N CONE PENETRATION
20 40 60 80 100
UNDRAINED SHEAR STRENGTH kN/m2
20 40 60 80 100
WATER CONTENT, PERCENT
Wp W WL
20 40 60 80
REMARKS
AND
GRAIN SIZE
DISTRIBUTION
GR SA SI CL
GROUNDWATER TABLE
m m
TO
DIAMETER OF DRILL BIT
PROJECT
TYPE
SOIL PROFILE
STRAT. PLOT
WELL
INSTALLATION
DESCRIPTION
ELEV. DEPTH
SPLIT SPOON
SHELBY TUBE
DISTURBED BULK
SAMPLE LOST
ROCK CORE
BLOCK SAMPLE
WL - LIQUID LIMIT
Wp - PLASTIC LIMIT
W - MOISTURE CONTENT
- ORGANIC CONTENT
CLAY
SILT
SAND
GRAVEL
METAMORPHIC
TOP SOIL
ORGANIC
NATURAL VANE
REMOULDED VANE
UNCONFINED - NAT'L.
TRIAXIAL QUICK
TORVANE
PILCON VANE
B.H. No.
ENCLOSURE
/
m DRILLING MUD
TRINTOPLAN CONSULTANTS LTD.
SHEET OF
PROJECT No.
RECORD OF BOREHOLE
LOCATION BORING DATE DATUM
SAMPLER HAMMER WEIGHT PENETRATION TEST HAMMER WEIGHT
63.5 kg, DROP 762 mm
BORING EQUIPMENT / METHOD
ELEV. (m) DEPTH (m)
SAMPLE
NUMBER
14
11
82
88
133
134
Medium dense to very dense, brown and reddish brown, SILTY CLAYEY SAND with gravel
Brown, reddish brown Dense to very dense, orange brown, light brown, WELL GRADED GRAVEL with sand Dense
- - - - - - - - - - - - - -
Very dense
Orange brown, light brown Very dense, light brown, SILTY
SAND with gravel
Very dense
Light brown
End of borehole at 10.9m
1
2
3
4
5
6
7
8
9
10
11
16.8
29
6
0
4
29
60
40
26
12
2
13
53
38
43
45
100/6"
100/6"
100/5"
100/4"
50.222 Ground Surface
11-19-16 11-19-16
CME 55 DRILL RIG
0.2 N/A
M.S.L
HOLLOW STEM AUGERING
BH 4
8
49.22
48.22
47.22
46.22
45.22
44.22
43.22
42.22
41.22
40.22
39.22
38.22
37.22
0
1
2
3
4
5
6
7
8
9
10
11
12
13
1 1
GEOTECHNICAL INVESTIGATION AT THE AROUCA WATER TREATMENT PLANT AND INTAKE - AROUCA
6312
BH 4 ENCLOSURE 8
N 1176457.171, E 683777.533
BULK UNIT WEIGHT
kN/m3
PENETRATION RESISTANCE BLOWS/0.3 m
N-VALUE N CONE PENETRATION
20 40 60 80 100
UNDRAINED SHEAR STRENGTH kN/m2
20 40 60 80 100
WATER CONTENT, PERCENT
Wp W WL
20 40 60 80
REMARKS
AND
GRAIN SIZE
DISTRIBUTION
GR SA SI CL
GROUNDWATER TABLE
m m
TO
DIAMETER OF DRILL BIT
PROJECT
TYPE
SOIL PROFILE
STRAT. PLOT
WELL
INSTALLATION
DESCRIPTION
ELEV. DEPTH
SPLIT SPOON
SHELBY TUBE
DISTURBED BULK
SAMPLE LOST
ROCK CORE
BLOCK SAMPLE
WL - LIQUID LIMIT
Wp - PLASTIC LIMIT
W - MOISTURE CONTENT
- ORGANIC CONTENT
CLAY
SILT
SAND
GRAVEL
METAMORPHIC
TOP SOIL
ORGANIC
NATURAL VANE
REMOULDED VANE
UNCONFINED - NAT'L.
TRIAXIAL QUICK
TORVANE
PILCON VANE
B.H. No.
ENCLOSURE
/
m DRILLING MUD
TRINTOPLAN CONSULTANTS LTD.
SHEET OF
PROJECT No.
RECORD OF BOREHOLE
LOCATION BORING DATE DATUM
SAMPLER HAMMER WEIGHT PENETRATION TEST HAMMER WEIGHT
63.5 kg, DROP 762 mm
BORING EQUIPMENT / METHOD
ELEV. (m) DEPTH (m)
SAMPLE
NUMBER
18
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