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OPG 16057 CEB Geotechnical Investigations at Fort Victoria of 52

Executive Summary

In January 2016, the Central Electricity Board (CEB) awarded Water Research Co Limited a contract (Ref.

Q18298) to carry out geotechnical investigations at Fort Victoria power station. The investigation aimed to

support the design and construction of a proposed 6,500m3 heavy fuel oil tank (approximate diameter 23m &

height 14m).

The field works comprised of 4No. trial pits and 1No. coreholes with SPT tests. The trial pits were generally

excavated at the maximum explored depth of 2.55m bgl and the corehole was drilled to 20.om bgl. The

identified soil sequence generally consists of approx. 1m of Fill Material, ii) 12.5m of Clay (Completely to Highly

Weathered Basalt), and iii) Moderately to Slightly Weathered Basalts. Although 6m of Fill Material was observed

at only one location, corehole. Groundwater prevailed as from a depth of 3.5m.

Selected samples were collected from the trial pits were couriered to the Gets Laboratory for geotechnical

testing and to Alcontrol for contaminant tests.

Engineering Fill is recommended as the founding stratum for the tank if shallow circular raft foundations are

entertained. It is proposed that the existing Fill Material and natural strata is excavated down to 2.0m and

replaced with Engineering Fill. Bearing capacity and settlements were estimated by considering two scenarios;

i) a double layered profile of medium dense Gravel over firm Clay and ii) a triple layered profile of medium

dense Gravel underlain by loose gravel (Fill Material) and firm Clay. The assessment indicated that the

allowable bearing capacity (factor of safety) estimated is 145kPa with a maximum settlement of 140mm and a

differential; settlement of 10mm at a founding depth of 0.6m bgl. If shallow foundations are implemented, the

tank is expected to sink uniformly. According to Klepikov (1989) the magnitude of settlement (maximum of

140mm) may be considered as acceptable. Settlements may be curtailed by reducing the designed height of the

tank.

The settlements can be mitigated by using piles as foundation solution by transferring the load to the competent

stratum at a depth of 14.0m. This solution shall also increase the bearing capacity.

OPG 16057 CEB Geotechnical Investigations at Fort Victoria

of 52

Contents Executive Summary 3

Introduction 7

Desk study information 8

2.1 Site location and topography 8

2.2 Published geology 8

Field and laboratory works 9

3.1 Geotechnical investigation works 9

3.2 Rotary core drilling 9

3.3 Trial Pits 10

3.4 In Situ Tests 10

3.5 Laboratory testing 13

Results and ground conditions 17

4.1 Identified soil profile 17

4.2 Groundwater 19

4.3 Dynamic Cone Penetration Test Results19

4.4 Plate Load Test Results 20

4.5 Chemical Environment 20

Geotechnical engineering assessment 23

5.1 Identified Soil Profile 23

5.2 Foundation options 25

5.3 Bearing capacity and settlement for Engineering Fill on natural strata (Scenario 1) 25

5.4 Bearing capacity and settlement for Engineering Fill on Fill Material (Scenario 2) 26

5.5 Deep foundations 28

References 30


Figures 31

Appendix A Site Layout 39

Appendix B Photographs of Site Works 40

Appendix C Exploratory Hole Logs 43

Appendix C-1 Corehole Logs 44

Appendix C-2 Photographs of Cores 45

Appendix C-3 Trial Pit Logs 46

Appendix C-4 Photographs of Trial Pits 47

Appendix C-5 Geological Profiles 48

Appendix D In-Situ Testing 49

Appendix D-1 DCP Test results 50

Appendix D-2 Plate Load Test Results 51

Appendix E Geotechnical Laboratory Test Schedules and Results 52

Appendix F Contamination Test Schedules, Standards and Results 53

LIST OF TABLES

Table 3-1 Summary of rotary drilled coreholes ..................................................................................................................... 9

Table 3-2 Summary of Trial Pits .................................................................................................................................................. 10

Table 3-3 Summary of SPT N results .................................................................................................................................... 11

Table 3-4 Location and Depths of DCPT ................................................................................................................................ 11

Table 3-5 Location and Depths of PLT .................................................................................................................................... 12

Table 3-6 Standards for laboratory tests ................................................................................................................................. 13

Table 3-7 Summary of Laboratory Testing Results on clayey material ..................................................................... 15


Table 3-9 Summary of Laboratory Testing Results on Rock Cores ........................................................................... 16

Table 4-1 Summary of strata encountered in metres ......................................................................................................... 17

Table 4-2 Summary of DCPT Results ...................................................................................................................................... 19

Table 4-3 PLT Results Summary ................................................................................................................................................ 20

Table 4-4 Soil Chemical Tests Summary ............................................................................................................................... 21

Table 4-5 Water Chemical Tests Summary ........................................................................................................................... 22

Table 5-1 Cast-in-situ piles indicative characteristics ..................................................................................................... 28

LIST OF FIGURES Figure 2-1 General location of the site .................................................................................................................................... 31

Figure 2-2 Site Location .................................................................................................................................................................. 32

Figure 2-3 Aerial Map of site and location of Trial Pits and Coreholes .................................................................... 33

Figure 2-4 Location of the site on geological map ............................................................................................................. 34

Figure 2-5 Location of the site on Soil Map ........................................................................................................................... 35

Figure 2-6 Standard Penetration Test N Value Variation with Depth – As per Stratum .................................... 36

Figure 2-7 Rock Quality Designation Variation with Depth ........................................................................................... 37

Figure 2-8 A Line Plasticity Chart .............................................................................................................................................. 38


Introduction

On 7th January 2016, the Central Electricity Board (CEB) awarded Water Research Co Limited (Water

Research) a contract (Ref. Q18298) to carry out geotechnical investigations at Fort Victoria power station, in the

district of Port Louis. The geotechnical investigation aimed to support the design and construction of a

proposed 6,500m3 heavy fuel oil tank (approximate diameter 23m & height 14m) and ancillary infrastructures.

Appendix A depicts the proposed layout of the tank and the site.

Water Research’s brief comprised the following items:

Formation of 4No. trial pits

Drilling 1No.rotary coring borehole

Soil and rock sampling. Undisturbed soil samples were 50mm diameter U2 samplers. Rock cores

were 52mm diameter. Disturbed samples included large and small bulks

Compaction, compressibility, strength and chemical laboratory tests

Report on findings and general geotechnical evaluation.

This Report is presented in the following format:

Desk study information for the site, including geological maps and plans

Factual information comprising: description of fieldwork and exploratory hole logs

Geotechnical assessment comprising: profile definition; discussion on geotechnical parameters for

foundation design; recommendations for selection of foundation solutions; general foundation

comments including bearing capacity and settlements.


Desk study information

2.1 Site location and topography

The subject site is situated within the Fort Victoria power station, in the locality of Bain des Dames (Figures 2.1

to 2.3). The site lies on the shoreline of the western coast and is surrounded by residential dwellings. Bain des

Dames public beach adjoins the site to the north west. The site can be accessed from Cassis Road which

branches off the M1 motorway.

The site is an operational power station which comprises of existing tanks and heavy engines. The investigated

area is on a strip of land in the western portion of the power station. The area was being used as a storage spot

with scrap metals and other heavy duty materials. According to the Client there used to be a trench crossing the

site after which it was backfilled.

The site elevations generally vary between 2m and 5m amsl. The site is flat with no salient topographical

feature. Surface water run-off is expected to be channelled towards the ocean.

2.2 Published geology

According to the Carte Geologique au 1:50,000 of Mauritius, the site is underlain by fresh basalt of the

Intermediate volcanic series (Figure 2.4, Ref. 1). The intermediate volcanic series are composed of basaltic

flows overlying basalt agglomerate. The basalts are not very homogeneous in composition but, on the whole,

they are made up of fine grained olivine rocks, grey to black in colour. The very compact types are rather rare,

and are in general porous and often vesicular, the vesicles being sometimes infilled with a powdery bluish

material. They are also slightly fissured and in some places the fissures and cavities are filled with light cream

coloured clay (Ref. 2).

According to the Soil Map of Mauritius (Figure 2.5, Ref. 3) the natural strata on the site area consists of Low

Humic Latosols. These soils occur in the sub-humid and lower rainfall zones from 1,000mm to 2,750mm

annually, in areas with a distinct dry season. They are deep (+100cm) to moderately deep soils (+60cm) with

good internal drainage. They have a weak to moderately strong structured A horizon varying from red to brown

in colour over a red to reddish brown B horizon. The texture of the A horizon is silty clay to clay; kaolinite is the

dominant clay mineral (Ref. 2).


Field and laboratory works

3.1 Geotechnical investigation works

The scope of fieldworks was specified in the Tender Document and was undertaken in general accordance with

BS 5930 (1999) (Ref. 4). The site works were carried out between the 2nd and 23rd February 2016. The location

of the Trial Pits and Corehole are shown in Appendix A; the photographs of the site activities are presented in

Appendix B. The following sections present a general description of the works carried out.

3.2 Rotary core drilling

1No. corehole were drilled by rotary drilling techniques in order to obtain information on the underlying geology,

delimit the ground profile and carry out in situ testing. The corehole was designated as BH 1.

Core recovery drilling was completed using a triple tube core barrel (hole diameter 76mm and core diameter

52mm) followed by NW casing (outside diameter of 88.9mm and inside diameter of 76.2mm). Water was used

as flushing medium. During coring in soft and weak materials, circulation of water was stopped so as to achieve

the maximum recovery. The term “dry coring” is used in such cases.

The coordinates of the exploratory borehole and the explored depth are shown in Table 3.1. The coordinates

reproduced in Table 3-1 below are from Google Earth.

Table 3-1 Summary of rotary drilled coreholes

Corehole No. Depth (m) Easting Northing Elevation (m) Installations

BH 1 20.0 549897.38 7770400.07 3.0m PVC casing

The core samples recovered from the rotary coreholes were photographed, sampled and described according to

BS5930: 1999 (Ref. 4). The geological description of the strata encountered are given on the corehole logs

along with the assessment of Total Core Recovery (TCR), Solid Core Recovery (SCR) and Rock Quality

Designation (RQD), each expressed as a percentage of the individual core runs. Fracture Index (FI)

representing the number of clearly identifiable fractures per meter of intact core pieces is also reported. The

corehole logs and photos are presented in Appendices C-1 and C-2.


3.3 Trial Pits

4No. Trial Pits were excavated using a JCB 4CX mechanical backhoe excavator at the locations and depths shown in Table 3-2. Small and large bulk disturbed samples were taken at regular intervals where possible for

geotechnical, chemical and contamination testing – the list of samples taken are presented in Table 3-2. The

logs and photos of the Trial Pits are presented in Appendices C-3 and C-4, respectively. The coordinates reproduced in Table 3-2 are from Google Earth. Trial Pits TP 1 and 2 were left open for three weeks in order to

observe the potential presence of groundwater. After 3 weeks, black petroleum like based product was

observed at the base and along the walls of trial pit TP 2 on 23rd February 2016.

Table 3-2 Summary of Trial Pits

TP No. Depth

(m)

Samples Intervals

Easting (UTM)

Northing (UTM)

Elevation (m)

TP 1 2.55 0.5 – 1.0;

1.0 – 1.5 549914 7770411 3.0

TP 2 1.90 0.0 – 0.5;

1.0 – 1.5 549909 7770382 3.0

TP 3 1.5 0.3 ; 1.0 549907 7770409 3.0

TP 4 1.1 0.2 ; 0.7 549892 7770385 3.0

3.4 In Situ Tests

3.4.1 Standard Penetration Tests

6No. of Standard penetration tests (SPT) were carried out in cohesive and granular soils in accordance with

BS1377: Part 9 (1990) (Ref. 5). The test consisted of driving a 50mm split spoon by means of a 63.5kg hammer

falling a height of 760mm. The SPT blow count N is the number of blows required to drive the spoon by 300mm

after initially seating the spoon by 150mm. Tests for which the full penetration of 450mm could not be achieved after 50 blows are termed as “Refusals”. Table 3-3 shows a summary of the SPT test results.


Table 3-3 Summary of SPT N results

BH No. Depth (m) Stratum N value Recovery

BH 1

1.50 – 2.00 Fill Material – gravelly

Clay 10 40

3.50 Fill Material – Gravels and

Cobbles R 0

5.50 – 6.00 Fill Material – gravelly

Clay 11 28

7.50 – 7.84 CWB with cobbles

between 7.84m and

8.19m

R 34

9.50 – 10.00 CWB 16 28

13.00 – 13.50 C to HWB 22 32

3.4.2 Dynamic Cone Penetrometer Test

TRRL type (Ref. 6) dynamic probing tests were carried out by Geotechnical Services Ltd (GETS) on the trial pits at depths shown in Table 3-4.

Table 3-4 Location and Depths of DCPT

TP No. DCPT No. Depth (m) Stratum

TP 1 1 Ground level Fill Material – Clay

2 1.0 C to HWB

TP 2 1 Ground level

Fill Material –

Gravel

2 1.00 HWB

Dynamic probing involves driving a 20mm diameter solid cone (60o angles) into the ground using repeated

blows of a hammer with a mass of 8kg, falling a distance of 575mm. Typically, the rate of driving is between 15

to 30 blows per minute. As the cone is driven into the ground, the number of blows for each 100mm penetration

is recorded. The penetration resistance provides a measure from which the California Bearing Ratio (CBR) can

be calculated using the following formula:

Log10 (CBR) = 2.48 – 1.057 log10 (mm/blow)


The details of the tests, the penetration vs blows and CBR results are presented in Appendix D-1. The existing

asphalt and concrete road surfaces at the location of the tests were removed previous to the execution of the

tests.

3.4.3 Plate Load Test

3No. maintained Plate Load tests (PLT) were carried out by Geotechnical Services Ltd (GETS) on trial pits at

depths as shown in Table 3-5.

Table 3-5 Location and Depths of PLT

TP No. PTL No. Depth (m) Stratum

TP 1 PLT 1 Ground

level

Fill Material– very

gravelly sandy Silt

TP 2 PLT 2 Ground

level

Fill Material – silty

Gravel PLT 2 1.00 CWB – Clay

The Plate Load Tests were carried out with a Geotechnical Testing Equipment’s hydraulically jacked system.

The tests were carried out in accordance with BS1377: Part 9:1990 (Ref.5) using a 305mm diameter plate on a

maintained load basis and following the procedure:

1. Apply seating load to produce deflection between 0.25 mm and 0.51 mm.

2. Record and release load.

3. Apply ½ seating load.

4. Allow dial needles to come to rest.

5. Set dial needles to zero.

6. Apply load above ½ seating load.

7. Allow action of load to continue until rate of deflection of not more than 0.03 mm/min has been

maintained for at least two consecutive minutes.

8. Record load and deflection readings for applied load increment.

9. Apply next loads increments up to maximum or failure, each time repeating (7)

10. For final load increment maintain load until deflection of not more than 0.03 mm/min for at least two

consecutive minutes.

11. Unload in steps and release the load to load at which dial gages were set to zero.


The complete set of results and the load displacement curves are presented in Appendix D-2.

3.5 Laboratory testing

The laboratory schedule was prepared as stipulated in the tender document and shown in Appendix E. The

laboratory testing aimed at determining site parameters concerning the classification, chemical and strength

properties of the strata to enable geotechnical design. The programme of laboratory testing was carried out in

accordance with BS1377 (1990) (Ref. 5) at the Geotechnical Services (GETS), University of Mauritius

Laboratories and Alcontrol (England) for contaminants testing. The test schedules included:

Natural Moisture Content Determinations

Particle Size Distribution (wet sieving and hydrometer)

Atterberg Limits

Bulk and Dry Density Test

Chloride and Sulphate Content Determination

Organic Matter Content Determination

Unconfined Compression Test on rock cores

Contamination Testing: As, Cd, Cr, Cu, Ni, Zn, Pb, Hg, Se, B, hex Chromium, total cyanide, free

cyanide, total sulphate, sulphide, total sulphur, pH, speciated (16), PAHs, Phenols. Thiocyanate, TPH

(Total Petroleum Hydrocarbons)

The soil and rock tests and the relevant standards for performing the tests are presented in Table 3-6. The list

of scheduled and completed laboratory tests is presented in Appendix E.

Table 3-6 Standards for laboratory tests

Test Standard Moisture content BS1377: Part 2.

Liquid Limit (LL) and Plastic Limit (PL) BS 1377: Part 2, Clauses 4.3 and 5.3

Particle size distribution BS 1377: Part 2. Bulk Density Determination BS1377:Part 2 Loss on Ignition BS 1377: Part 3: 1990 clause 4, test 3

Total sulphate content determination test BS 1377: Part 3: 1990, test 5


Test Standard

Water soluble chloride content determination test BS1377: Part 3: 1990, test 7.2

Uniaxial Rock Compressive Strength & Density of rock

ISRM suggested Methods for Rock Characterisation, Testing and Monitoring – Standard Methods for Determining the Uniaxial Compressive Strength and Deformability of Rock Materials - 1979

Contamination Testing Methods and standards are given in Appendix F

A summary of the laboratory test results is presented in Table 3-7 and Table 3-7 below.


Table 3-7 Summary of Laboratory Testing Results on clayey material

TP/BH No.

Depth (m) Stratum Moisture

Content (%) Loss on Ignition

Bulk Unit

Weight (Mg/cm3)

Atterberg Limits PSD (%)

Total Sulphate Content

(%)

Chloride Content (%)

Liquid Limit

LL

Plastic Limit PL

Plasticity Index PI

Gravel Sand Silt Clay

TP 1 0.5 – 1.0 Clay (Fill Material) 21.3 11 62.5 32.3 30.2 - - - - 0.05 0.03

TP 1 1.5 – 2.0 C to HWB 26.1 10 1.56 59.6 33.1 26.4 40 18.7 23.3 18 - -

TP 2 0.0 – 1.0 Gravel (Fill

Material) 11.5

- 1.67 57.2 29.9 27.3 66 11.8 11.7 10.5 0.07 0.07

TP 2 1.0 – 1.5 H to MWB 26.7 -

- 47.6 24.3 23.3 - - -- - - -


Table 3-8 Summary of Laboratory Testing Results on Rock Cores

TP/BH No. Stratum Depth (m) Unconfined Compressive

Strength / MPa (N/mm2)

BH 1 SWB 14.83 – 15.00 53.5

BH 1 SWB 16.28 – 16.53 38.7

BH 1 SWB 16.86 – 17.00 18.3

BH 1 MWB 18.24 – 18.38 3.6


Results and ground conditions

4.1 Identified soil profile

The depth and thickness of the various strata observed in the Trial Pits and Corehole are shown in the logs and are summarised in Table 4-1.

Table 4-1 Summary of strata encountered in metres

TP / BH No.

Strata Topsoil / Fill

Material C to HWB M WB SWB

TP 1 0.00 – 1.15

(gravelly Clay) 1.15 – 2.55

TP 2 0.00 – 0.60

(Gravel) 0.6 – 1.9 (HWB)

TP 3 0.00 – 0.9 (Silty &

Clay) 0.9 – 1.5

TP 4 0.00 – 0.80

(Gravel and Clay) 0.80 – 1.10

BH 1

0.00 – 2.25 (Clay)

2.25 – 6.0 (clayey

Gravel & Cobbles)

6.00 – 10.0 (CWB)

10.0 – 13.5

13.53 – 14.33

17.64 – 20.0 14.33 – 17.64

The following definitions were considered for weathered basalts:

Residual Soil: No recognisable rock texture. Surface layer contains humus and plant roots.

Completely Weathered (CW) basalt: Rock completely decomposed by weathering in place but texture

still recognisable. Can be excavated by hand.

Highly Weathered (HW) basalt: Rock so weakened by weathering that fairly large pieces can be

broken and crumbled in the hands. Sometimes recovered as core in careful rotary drilling.

Moderately Weathered (MW) basalt: Considerable weathered throughout. Possessing some strength

– large pieces cannot be broken by hand, reasonable core recovery. Often limonite stained. Difficult

to rip.

OPG 16057 CEB Report on Site Investigation at Fort Victoria of 52

Slightly Weathered (SW) basalt: Distinctly weathered through much of the rock fabric with slight

limonite staining. Strength approaches that of the fresh rock. Requires explosive for excavation.

Highly permeable open joints.

The following sections summarise the descriptions for each of the encountered strata.

4.1.1 Topsoil and Fill Material

Topsoil was observed from the ground level to a maximum depth of 0.6m bgl. The Topsoil were represented by

compacted Clay, Silt and Gravel.

Fill Material was encountered on all Trial Pits and the Corehole generally as from the surface or below the

Topsoil to an average depth of 1.0m. It is likely that the Fill Material has been placed all over the site. For the

corehole, the depth of the Fill Material was difficult to ascertain and it is presumed to extend to 6.0m bgl. The

spatial distribution of the suspected 6m Fill Material identified at BH 1 could not be defined due to restricted

mobility on site. The trial pits and plate load tests trenches did not provide further evidence of the 6m thick Fill.

It is possible that this thickness of Fill Material is localised or sporadically spread across the northern portion of

the proposed tank outline. Two excavations done in close proximity of the borehole proved Fill Material up to

1.15m depth.

The encountered Fill Material was described as:

Soft to firm dark brown to reddish brown very gravelly high plasticity Clay / Silt with frequent fragments

of glasses and plastics. In the corehole the Clay Fill is limited to the upper 2.25m.

Loose sub-angular medium to coarse Gravel and Cobbles of strong light grey Slightly Weathered

Basalt.

2No. SPT tests were carried out on the clayey fill material and the measured of SPT N-values of 10 and 11

(Figure 4.1). 1No. SPT tests performed on Gravel and Cobbles (fill material) reported refusal.

4.1.2 Clayey Weathered Basalts

Completely and Completely to Highly Weathered Basalts were encountered on all exploratory holes except on

TP2. This strata was intercepted across the site from a depth of 0.80m to 13.5m bgl with an average thickness

of 2.0m. The strata were generally described as firm to stiff reddish brown to dark brown high plasticity Clay.

2No. SPT tests were carried out on the Completely to Highly Weathered Basalts and the measured SPT N-

values were 11 and 16 (Figure 4.1).


4.1.3 Rock Weathered Basalt

Highly Weathered Basalt was retrieved at trial pit TP 2 between 0.6 and 1.9m. This layer was logged as

moderately weak orangish brownish grey with black discolorations at joints highly vesicular with frequent

amygdales. The joints are infilled with yellowish brown medium plasticity Clay.

Moderately Weathered Basalt (MWB) was encountered at BH 1 at alternating depths between 13.53m to 20.0m

bgl. The average thickness of the stratum is 2.0m and was described as weak to moderately strong grey with

black and yellow mottles vesicular with frequent amygdales very closely jointed. RQD values for the MWB

generally varies between 0% and 16 (Figure 4.2). Unconfined Compressive Strength (UCS) test carried out on a

Moderately Weathered core returned a value of 3.6MPa.

Slightly Weathered (SWB) was encountered between 14.33m to 17.64m and was generally described as strong

to moderately grey vesicular closely to medium jointed. RQD values for the MWB generally varies between 34%

and 61 (Figure 4.2). Unconfined Compressive Strength (UCS) test carried out on the strata returned values

varying between 18MPa and 54MPa.

4.2 Groundwater

Groundwater was encountered only at corehole BH 1 at3.5m bgl measured on 23rd February 2016.

4.3 Dynamic Cone Penetration Test Results

A summary of the DCPT results is presented in Table 4-2.

Table 4-2 Summary of DCPT Results

TP No. DCPT No. Depth (m) Stratum CBR

TP 1 1 Ground

level

Fill Material –

Clay 10

2 1.0 C to HWB 20

TP 2 1 Ground

level

Fill Material –

Gravel 34

2 1.00 HWB 21


4.4 Plate Load Test Results

A summary of the Plate Load Test results is presented in Table 4-3. The detailed results are presented in

Appendix D-2.

Table 4-3 PLT Results Summary

TP No. PTL No. Depth (m)

Stratum Maximum Load

(kN) Maximum Bearing

Pressure (kPa) Settlement (mm)

TP 1 PLT 1 Ground

level

Fill Material–

very gravelly

sandy Silt

43 608 1.58

TP 2

PLT 2 Ground

level

Fill Material –

silty Gravel 43 608 7.43

PLT 2 1.00 CWB – Clay 43 608 0.55

4.5 Chemical Environment

The following tests were carried out on soil samples from the trial pits:

Chloride and Sulphate Content Determination

Organic Matter Content Determination

Contamination Testing: As, Cd, Cr, Cu, Ni, Zn, Pb, Hg, Se, B, hex Chromium, total cyanide, free

cyanide, total sulphate, sulphide, total sulphur, pH, speciated (16), PAHs, Phenols. Thiocyanate, TPH

(Total Petroleum Hydrocarbons).

Selected results are summarised in Table 4-4 and Table 4-5; the complete results are provided as Appendix F.

Guidelines for soils for some of the contaminants for residential and commercial or industrial land use as per the

documents from the Environment Agency UK and the Canadian Council of Ministers of the Environment are also presented in Table 4-4 (Refs. 11 and 12).


Table 4-4 Soil Chemical Tests Summary

Parameter Units Limit of

Detection (LOD)

Soil Results Range

Soil guideline value

(residential) mg/kg

Soil guideline value

(commercial) mg/kg

Chloride % <0.01 0.03 – 0.07

Sulphate % <0.01 0.03 – 0.07

Organic Matter % <0.1 10 - 11

Arsenic, As mg/kg <0.6 <6 - 32 32 640

Cadmium, Cd mg/kg <0.02 <0.2 – 2.29 10 230

Chromium, Cr mg/kg <0.9 86.3 - 271 67 87

Copper, Cu mg/kg <1.4 91.1 - 355 63 91

Nickel, Ni mg/kg <0.2 128 - 407 130 1,800

Zinc, Zn mg/kg <1.9 83.5 – 2370 200 360

Lead, Pb mg/kg <0.7 23.9 - 2850 140 600

Mercury, Hg mg/kg <0.14 <1.4 – 1.56 1 50

Selenium, Se mg/kg <1 <10 350 13,000

Boron, B mg/kg <0.7 10.2 – 30.4

Hexavalent Chromium mg/kg <0.6 <0.6 0.4 1.4

Total Cyanide mg/kg <1 <1

Free Cyanide mg/kg <1 <1 0.9 8

Total Sulphate mg/kg <48 104 - 2740

Sulphide mg/kg <15 <15

Total Sulphur % <0.02 <0.02 – 0.161

pH pH units 1 8.61 – 9.26 6 - 8 6 - 8

Speciated (16), PAHs μg/kg <118 <118 - 6750

Phenols (Total detected

monohydric) mg/kg <0.035 <0.035 3.8 3.8

Thiocyanate mg/kg <1 <1

TPH (Total Petroleum

Hydrocarbons) mg/kg <10 <10 – 68.9

Phenols mg/kg <0.01 <0.01 420 3200


Cresols mg/kg <0.01 <0.01

Xylenols mg/kg <0.015 <0.015 2.4 2.4

Table 4-5 Water Chemical Tests Summary

Parameter Units Limit of

Detection (LOD)

Water Results

Arsenic, As µg/L <0.12 0.405

Cadmium, Cd µg/L <0.1 <0.1

Chromium, Cr µg/L <0.22 5.32

Copper, Cu µg/L <0.85 1.4

Nickel, Ni µg/L <0.15 1.93

Zinc, Zn µg/L <0.41 5.15

Lead, Pb µg/L <0.02 0.174

Mercury, Hg µg/L <0.01 <0.01

Selenium, Se µg/L <0.39 0.96

Boron, B µg/L <9.4 250

Hexavalent Chromium mg/L <0.03 <0.03

Total Cyanide mg/L <0.05 <0.05

Free Cyanide mg/L <0.05 <0.05

Sulphate mg/L <2 33.9

Total (16), PAHs μg/L <0.344 0.344

Phenols (Total detected monohydric) mg/L <0.016 <0.016

TPH (Total Petroleum Hydrocarbons) μg/L <100 3020

Phenols mg/L <0.002 <0.002

Cresols mg/L <0.006 0.006


Geotechnical engineering assessment

This Chapter presents geotechnical evaluation and recommendations for the proposed development based on

the interpreted ground conditions. As stated in Section 1.1, the proposed development consists of a 6,500m3

tank with a diameter of 24m for heavy oil storage. A full tank with its combined load is expected to exert of

pressure of 145 kPa. This pressure was estimated by assuming a 14m high tank storing fuel oil with a density of

10kN/m3. The value of the fuel density was provided by the Client.

The geotechnical issues discussed are: design soil profile and parameters and discussion on foundation

solutions. Shallow or deep foundations may in principle be adequate to support the proposed development

under assessment. Engineering Fill has to be used for the case of shallow foundation due to the presence of

Fill Material.

5.1 Identified Soil Profile

The profile at the site, in order of vertical sequence, consists of i) 1m of Fill Material, ii) 12.5m of Clay

(Completely to Highly Weathered Basalt), and iii) Moderately to Slightly Weathered Basalts. Geological profiles

across the corehole and Trial Pits are presented in Appendix C-5. Groundwater prevailed as from a depth of

3.5m.

The presumed thickness of the Fill Material encountered in the corehole is 6m. If this thickness of Fill Material is

localised, it is recommended that the fill material is replaced by engineered fill, however for the case for which

the distribution is relatively widespread, the following scenario will be assessed i) i) 6m of Fill Material, ii) 7.5m

of Clay (Completely to Highly Weathered Basalt), and iii) Moderately to Slightly Weathered Basalts.

The following sections describe the geotechnical properties associated with the encountered strata. Fill Material

should be avoided as founding stratum or for engineering purposes as far as possible.

5.1.1 Properties of Fill Material

The clayey silty Gravel was generally described as loose and the following properties can be considered for

analysis:

Soil unit weight of 18kN/m3.

SPT N values for the clayey Gravel varied between 10 and 11 (Figure 4.1).

Assuming SPT N Value of 10, an angle of shearing resistance of 29o can be used for analysis (Ref. 4).

Relative Density 20%-40%


5.1.2 Clayey Weathered Basalts

The clayey weathered basalt layer is composed of firm high plasticity silty Clay. The following properties are

suggested for geotechnical analysis based on the laboratory test results and correlations:

Soil Unit Weight of 15kN/m3.

Average Natural moisture contents of 26%.

Atterberg Limits indicate the stratum to be silt/clay of high plasticity with average Plasticity Index of 30

(Figure 5.1). The variation of the moisture content and the liquid and plastic limits are presented in

Figure 5.2.

The representative SPT blow count (N) is 16 (Figure 4.1). Based on the SPT N correlation to undrained

shear strength (Su) (Ref. 7), Plasticity Index (PI) of 42 and f1 value of 4.5 the estimated Su value

would be 72kPa. Typical values for firm clay material are between 40kPa and 75kPa. An undrained

shear strength (Su) of 65kPa will be adopted for analysis.

mv can be determined using Stroud’s correlation (Ref. 8) mv= 1 / f2N; where f2 can be defined based

on PI as 0.45, and SPT = 16. Thus mv for the material is in the order of 0.13m2/MN corresponding to a

medium compressibility material.

Sulphate Content of the soil is 0.03% and average Chloride Content is 0.04%.

5.1.3 Moderately and Slightly Weathered Basalt

The following properties can be considered representative of the M to SWB basalt rock:

Bulk unit weight of 22kN/m3.

M to SWB rock was described as moderately strong to strong; UCS values corresponding to this

description varies between 12.5MPa and 50MPa.

Unconfined Compression tests on rock cores at depths varying between 14.83m and 18.38m gave

UCS values varying between 3.6MPa and 53.5MPa.

Rock Quality Designation (RQD) values for rock encountered at shallow depths (between 13.55m and

20.0m) vary between 0 and 61 indicating rock of very poor to fair quality rock (Figures 4.2 and 4.3).

5.1.4 Engineering Fill

The following properties for the granular engineering fill to be placed on site are suggested for analysis:

Achieved soil unit weight of 20kN/m3.

For the granular fill (assumed as a dense gravel), a value of SPT N of 30 can be considered.

A conservative an angle of shearing resistance of 32o can be used for design.

Relative Density 40%-60%


5.2 Foundation options

For economic and practical reasons, shallow foundations are the conventional solution for founding structures.

Deep foundations or alternative solutions (e.g. ground improvement) are implemented for low bearing capacity

or high compressibility strata, subjected to loadings that can result on ultimate or serviceability performance

limitations.

The selection of the foundation solution will be controlled by the loads imposed and the response of the ground

profile. The proposed development includes a 14m high heavy fuel tank with a stress magnitude of 145kPa. It is

recommended that the Fill Material is excavated and replaced by Engineering Fill. For the purpose of analysis it

is assumed that the 2m of the on-site materials are to be replaced by Engineering Fill. Therefore the

Engineering Fill may act as founding layer.

The following analyses are focused on evaluating the bearing capacity and related settlements for the proposed

tank at a foundation depth of 0.6m bgl for a 24m circular raft. Two (2No) profile scenarios are analysed to verify

the shallow foundation behaviour. This will provide a reliable indication of the potential bearing capacity and

settlement threshold of the prevailing stratum. The bearing capacities are computed assuming no eccentric or

inclined loading and without considering sloping ground.

A pile foundation solution shall be implemented in the case that the settlement or bearing capacity for shallow

foundation solutions are inadequate. Piles may be founded on the Moderately to Slightly Weathered

encountered generally at 14.5m bgl.

5.3 Bearing capacity and settlement for Engineering Fill on natural strata (Scenario 1)

In this case a layer of 2.0m thick dense granular Engineering Fill is underlain by a 12.5m thick of clayey

weathered basalt (Plate 1).


GL

GW @ 3.5m

12.5m

2.0m

Firm Clay

SPT N 16 ; Su 65kPa

Strong to moderately strong Moderately to Slightly Weathered Basalt

Granular Engineering Fill

SPT N 30 ; Ф 32°

Scenario 1

Plate 1: Engineering Fill over natural strata

Bearing capacity was computed using the two-layered profile (medium dense Gravel underlain by firm Clay)

using solutions from Meyerhof and Hanna (1978) and Hanna and Meyerhof (1980) for the condition of a strong

drained layer overlying a weak undrained layer. For the Engineering Fill, an SPT of 30 for an angle of shearing

resistance of 32º was applied. As for the Firm Clay an SPT of 16 for an undrained shear strength of 65kPa was

adopted. The settlements for both layers were combined and were calculated by using the Burland and

Burbridge (Ref. 5) for the Gravel and for the Clay a compressibility of 0.13m2/MN.

A bearing capacity of 148 kPa was estimated with settlements in the order of 140mm for a factor of safety of

2.8. Skempton and MacDonald (Ref. 4) concluded that for a limiting angle of distortion of 1 in 500, the limiting

maximum differential settlement is about 25mm, the limiting total settlement is 40mm for isolated foundations

and 40-65mm for raft foundations.

5.4 Bearing capacity and settlement for Engineering Fill on Fill Material (Scenario 2)

This scenario is envisaged if the thickness of Fill Material is relatively large as encountered at BH 1, where it

extended to 6m depths, and also if it is widely distributed. It will not be practical to excavate all the Fill Material.

Therefore, 2.0m thick Engineering Fill over 4.0m of clayey Gravel (Fill Material) has been analysed.


GL

GW @ 3.5m

7.5m

2.0m

Firm Clay

SPT N 16 ; Su 65kPa

Strong to moderately strong Moderately to Slightly Weathered Basalt

Granular Engineering Fill

SPT N 30 ; Ф 32°

Scenario 2

Fill Material

SPT N 10 ; Ф 29°4.0m

Plate 2: Engineering Fill over Fill Material

Bearing capacity was computed using the two-layered profile (medium dense Gravel underlain by loose Gravel

and firm Clay) using solutions from Meyerhof and Hanna (1978) and Hanna and Meyerhof (1980) for the

condition of a strong drained layer overlying a weak drained layer. The geotechnical parameters considered for

the analysis is depicted on Plate 2 above. For the Engineering Fill, an SPT of 30 for an angle of shearing

resistance of 32º was adopted. A for the loose clayey Gravel an SPT of 10 for an angle of shearing of 29º were

computed. An undrained shear strength of 65kPa and a compressibility of 0.13m2/MN was used for the

underlying firm Clay. The settlements for the three upper layers were combined.

A bearing capacity of 149 kPa was estimated with settlements in the order of 130mm for a factor of safety of

2.8.

The above analysis for both scenarios estimated settlements in the order of 140mm and 130mm. According to

Skempton and MacDonald (Ref. 4) these magnitudes of settlement are considered to be excessive (higher than

40 to 65mm for raft foundations). Differential settlement as a result of heterogeneity of the underlying strata

(clay and gravel) amounts to 10mm which is within the acceptable limit of 25mm. However, Klepikov (1989)

suggests that for a large (53.6m diameter; 18.3m high) circular steel tanks the allowable settlement is 180mm

while for a smaller circular tank (9m diameter; 8m high) it is 110mm.


Ground improvement can be performed to improve the existing sub surface ground via mechanical methods.

These methods can include dynamic compaction, stone columns and soil cement columns. This would increase

bearing capacity and reduce settlements.

If shallow foundations solutions are implemented, the tank is expected to sink uniformly due to the uniformly

circular distributed load. The sinking of the tank is due to serviceability load and according to Klepikov (1989)

the magnitudes of settlement (maximum of 140mm) may be considered as acceptable. Settlements may be

curtailed by reducing the designed height of the tank.

The settlements can be mitigated by using piles as foundation solution by transferring the load to the competent

stratum at a depth of 14.0m. Piles will also significantly increase the allowable bearing capacity. Pile foundations

are expected to cost more than shallow foundations.

5.5 Deep foundations

Selection of type of pile depend on stress applied construction constraints and availability in Mauritius; based

on these criteria, driven precast piles may be implemented. Although, if the scrap metals are cleared, there is

no foreseeable constraints on the site which can hamper mobility. Other types of piles may be suggested by the

piling suppliers. Vibration associated with pilling works should be regulated so that the surrounding

infrastructures are not deleteriously impacted.

Precast piles can provide an economical solution especially in deeper soil profiles. The main considerations for

driven pre-cast piles are: i) small sections available could be a limitation if large loads are expected; ii) faster

installation results on reduced time on site (Ref. 7). Other consideration is the considerable noise and vibration

associated with the driving of the precast pile. Inter-bedded hard layers were not observed on the site, in such a

situation, rock shoes may be used to protect the concrete with a hardened steel point. Although the founding

strata is identified previous to pile installation, the final pile length is determined on site, where the piles are

driven to a predetermined displacement “set” corresponding to a specific number of driving hammer blows. The

depth to the bedrock is 14.0m based on observation from corehole BH1.

For precast concrete driven piles, the exact area of contact with rock is not known. The bearing capacity will

depend on the type and nature of the rock and the depth of penetration of the pile into the rock. Estimation of

the allowable bearing capacity of such piles by analytical method cannot be made. Load capacity of these type

of piles should be estimated based on local experience and driving resistance supported by pile load tests. Table 5-1 summarises typical Precast pile characteristics as presented by Byrne et al. (Ref. 7).

Table 5-1 Cast-in-situ piles indicative characteristics

Diameter, mm 250mm 300mm 350mm


Square Square Square

Typical working load,

kN*

800 - 1000 1200 - 1500 1600 - 2000

Max depth, m Unlimited

Minimum pile spacing

c/c, m

750 900 1050

*Note: The typical working loads are related to the structural characteristics of the piles and not to the soil conditions – the

latter is given below. If the rock is strong at its surface, the carrying capacity of the piles is governed by the strength of the pile

as structural element.

5.5.1 Buried Concrete

An Aggressive Chemical Environment for Concrete (ACEC) site classification has been carried out based on

Water Soluble Sulphate content (2:1 water-soil extract) and pH tests on similar marine deposit samples. The

evaluation is carried out following the UK Building Research Establishment (BRE) Special Digest SD1, Concrete

in Aggressive Ground 2005 (Ref. 8). Typical results for Water Soluble Sulphate content (2:1 water-soil extract)

on the clayey weathered basalts vary between 0.05% and 0.07%; Water-soluble Chloride Content varied

between 0.03% and 0.07%.

Based on these results, a Design Sulphate Class DS-1 and ACEC Class AC-1, for mobile groundwater, can be

used for buried concrete structures. Exposure of concrete to potentially brackish (~10 000 mg/l chloride) or

similarly saline groundwater is, however, beyond the scope of this recommendation.

5.5.2 Conclusions

Based on the analyses presented above, the recommended bearing capacity for the 6,500m3 tank is in the

order of 145kPa with maximum settlements of 140mm for a factor of safety of 2.8. If shallow foundations

solutions are implemented, the tank is expected to sink uniformly. The sinking of the tank is due to serviceability

load and according to Klepikov (1989) the magnitudes of settlement (maximum of 140mm) may be considered

as acceptable

The settlements can be neutralised by using piles as foundation solution by transferring the load to the

competent stratum at a depth of 14.0m


References

1. Ile Maurice Carte Geologique et Hydrogeologique (1996), Republique de Maurice.

2. Proag, V. (1995), The geology and water resources of Mauritius, analysis, Mahatma Gandhi Institute.

3. Directorate of overseas surveys (UK) (1962), Soil Map of Mauritius, Public Works and Survey Department,

Port Louis Mauritius.

4. British Standards (1999), BS 5930, Code of practice for site investigations.

5. British Standards (1990), BS 1377, Methods of tests for soils for Civil Engineering purposes.

6. Transport and Road Research Laboratory (1986), Operation instructions for the TRRL dynamic cone

penetrometer, TRRL Information Note. UK.

7. Tomlinson, Foundation Design and Construction, Seventh Edition, Pearson Education Limited, 2001

8. Stroud, M A (1989), The Standard Penetration Test – its application and interpretation, Penetration Testing

in the UK, Thomas Telford

9. Burland, JB and Burbidge, MC (1985), Settlement of foundations on sand and gravel. Proc Instn Civ Engrs,

part 1.

10. Prakash S., Sharma H. (1990), Pile Foundations in Engineering Practice, John Wiley and Sons Inc.

11. Environment Agency (2009), Technical Note Science Project, Environment Agency UK.

12. Canadian Soil Quality Guidelines for the protection of Environmental and Human Health (2007), Canadian

Soil Quality Guidelines, Table 1, Canadian Council of Ministers of the Environment.


Figures

Figure 2-1 General location of the site

Site

North


Figure 2-2 Site Location

North

Site


Figure 2-3 Aerial Map of site and location of Trial Pits and Coreholes

Site


Figure 2-4 Location of the site on geological map

North

Site


Figure 2-5 Location of the site on Soil Map

Site


Job: OPG 16057 CEB Figure: 4.1Date: March 2016

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

150 10 20 30 40 50

Dept

h (m

)

SPT N Values

BH 1

Figure 2-6 Standard Penetration Test N Value Variation with Depth – As per Stratum


Rock Quality Designation, RQD %

Date: March 2016 Job: OPG 16057 CEB Figure: 4.1

0

2

4

6

8

10

12

14

16

18

200 10 20 30 40 50 60 70 80 90 100

Dep

th (m

)RQD, % BH 1

BH 1

Figure 2-7 Rock Quality Designation Variation with Depth


0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

0 10 20 30 40 50 60 70 80 90 100 110 120

Plas

ticity

Inde

x (%

)

Liquid Limit (%)

A Line Fill Material C to HWB

Low Plasticity High PlasticityIntermediate Plasticity Very High Plasticity Extremely High Plasticity

CL

ME

CE

CV

CH

CI

MI

ML

MH

MV

A-Line Plasticity Chart Figure : 5.1

Figure 2-8 A Line Plasticity Chart


Appendix A Site Layout

OPG 16057 CEB Report on Site Investigation at Fort Victoria Page 40 of 52

Appendix B Photographs of Site Works

Photo B.1


Photo B.2


Photo B.3


Appendix C Exploratory Hole Logs


Appendix C-1 Corehole Logs

Dark brown very gravelly high plasticitysilty CLAY. FILL MATERIAL?

Soft to firm reddish brown gravelly highplasticity silty CLAY. FILL MATERIAL?

Loose sub-angular fine to medium clayeyGRAVEL of very weak reddish brown Highlyto Completely Weathered Basalt with rarecobbles between 2.25 - 2.35m. Clay isbrown high plasticity FILL MATERIAL?

Loose sub angular fine to medium GRAVEL &COBBLES of strong light grey vesicularSlightly Weathered Basalt. FILL MATERIAL?

Loose sub angular fine to medium denseclayey GRAVEL of very weak dark greyishbrown Highly Weathered Basalt. FILLMATERIAL?

Firm dark brown with mottles highplasticity silty CLAY with cobblesbetween 7.84 - 8.19m. COMPLETELYWEATHERED BASALT.

Firm reddish brown with orange & creammottles high plasticity silty CLAY.COMPLETELY WEATHERED BASALT.

Continued next sheet

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

Lege

nd

Sca

le (m

)

Ele

vatio

n/D

epth

Sam

ple

/ In

Situ

N V

alue

Rec

over

y (c

m)

Cor

e R

un

TCR

(%)

SCR

(%)

RQ

D (%

)

FI Cas

ing

Dep

th

Dril

ling

Test

Description of Strata

BOREHOLE No. :

SITE :

Drilling Rig :

Casing Diameter :

Borehole Diameter :

Core Diameter :

National Grid Coordinates

N :

E :

Ground Level :

Start Date :

End Date :

Final Depth :

Water Depth :

Logged by :

Drillers :

Checked by :

Sheet :Project :Contract No :

Legend : Undisturbed Tube Sample (SPT) Solid Cone Dry Coring

Water Drilling(SPT) Split SpoonDisturbed Sample

Refusal at Jacking of U Sampler

(SPT) Refusal

Non Intact

U :

D :

RU :

R :

C :

S :

NI :

DC :

WD :

M : Mazier Sample

ABYSS 75

OPG 16057 CEB

52mm

88mm

76mm

7770400.00

549897.000

Geotechnical Investigation at Fort Victoria

3.000m amsl

Bain des Dames, les Saline

03/02/2016

02/02/2016

20.00m

3.5m on 02/02/2016

BH 1

1 of 2

MP

ZJ

0.60

2.25

3.50

4.00

6.00

8.10

10.00

SPTLS

U2(R)

SPTLS

SPTLS

SPTLS

(0)

(10)

(11)

>50

(16)

33

40

0

28

34

0.50

1.00

1.50

2.00

2.29

2.78

3.50

4.00

4.42

4.765.00

5.50

6.00

7.50

7.84

8.19

9.50

10.00

100

100

100

0

100

100

100

100

100

100100

100

0

100

0

100

100

0

0

0

0

0

0

0

0

0

0

00

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

00

0

0

0

0

0

0

0

NW6.00

DC

- 76

mm

DC

- 52

mm

Firm reddish brown with cream & blackmottles high plasticity silty CLAY.COMPLETELY TO HIGHLY WEATHEREDBASALT.

Weak to moderately weak creamish greywith black mottles at vesicles closeljointed MODERATELY WEATHEREDBASALT. Joints are smooth.

Strong to moderately strong light greyvesicular closely-medium jointed SLIGHTLYWEATHERED BASALT. Joints are planarsmooth sub horizontal in-filled withcream clay.

Moderately weak to moderately strong greywith yellow & black mottles at vesicleswith frequent amygdales very closelyjointed MODERATELY WEATHEREDBASALT. Joints are undulating rough subhorizontal in-filled with reddish brownclay.

End of Borehole at 20.00 m

11.0

12.0

13.0

14.0

15.0

16.0

17.0

18.0

19.0

Lege

nd

Sca

le (m

)

Ele

vatio

n/D

epth

Sam

ple

/ In

Situ

N V

alue

Rec

over

y (c

m)

Cor

e R

un

TCR

(%)

SCR

(%)

RQ

D (%

)

FI Cas

ing

Dep

th

Dril

ling

Test

Description of Strata

BOREHOLE No. :

SITE :

Drilling Rig :

Casing Diameter :

Borehole Diameter :

Core Diameter :

National Grid Coordinates

N :

E :

Ground Level :

Start Date :

End Date :

Final Depth :

Water Depth :

Logged by :

Drillers :

Checked by :


Legend : Undisturbed Tube Sample (SPT) Solid Cone Dry Coring

Water Drilling(SPT) Split SpoonDisturbed Sample

Refusal at Jacking of U Sampler

(SPT) Refusal

Non Intact

U :

D :

RU :

R :

C :

S :

NI :

DC :

WD :

M : Mazier Sample

ABYSS 75

OPG 16057 CEB

52mm

88mm

76mm

7770400.00

549897.000


3.000m amsl


03/02/2016

02/02/2016

20.00m

3.5m on 02/02/2016

BH 1

2 of 2

MP

ZJ

13.55

14.33

17.64

20.00

SPTLS (22) 28

11.60

13.00

13.50

14.00

14.33

16.00

17.64

19.00

20.00

100

100

0

100

100

100

100

100

100

0

0

0

12

23

72

53

29

25

0

0

0

0

0

61

34

16

0

17

9

10

WD

- 52

mm


Appendix C-2 Photographs of Cores

GEOTECHNICAL INVESTIGATION AT PORT LOUIS FORT

VICTORIA

BH1

Page 1 of 4

CLIENT: CENTRAL ELECTRICITY BOARD

CONTRACT No.: OPG 16057 CEB

COREHOLE BH1

Depth: 0.00 –6.00 metres

CLIENT: CENTRAL ELECTRICITY BOARD PROJECT: GEOTECHNICAL INVESTIGATION AT FORT VICTORIA SITE: PORT LOUIS FORT VICTORIA C/HOLE: BH01 DEPTH: 0.00 – 2.00m DATE: 02/02/2016

CORE RUN: 0.00 – 0.50m 0.50 – 1.00m

1.00 – 1.50m 1.50 – 2.00m


CORE RUN: 2.00 – 2.29m 2.29 – 2.78m

2.78 – 3.50m 3.50 – 4.00m


CORE RUN: 4.00 – 4.42m 4.42 – 4.76m

4.76 – 5.00m 5.00 – 5.50m 5.50 – 6.00m

SPT 3 – Depth: 5.50 – 6.00m Penetration: 000 – 150mm = 3

150 – 225mm = 3 225 – 300mm = 4 300 – 375mm = 2 375 – 450mm = 2 N Value = 11 Recovery = 28cm

SPT 2 – Depth: 3.50m

Recovery = Refusal




VICTORIA

BH1

Page 2 of 4



COREHOLE BH1



CORE RUN: 6.00 – 7.50m 7.50 – 7.84m 7.84 – 8.19m


150 – 225mm = 8 225 – 300mm = 12 300 – 375mm = 51 N Value = 71 Recovery = 34cm


CORE RUN: 8.19 – 9.50m 9.50 – 10.00m


CORE RUN: 10.00 – 11.60m 11.60 – 13.00m




VICTORIA

BH1

Page 3 of 4



COREHOLE BH1



CORE RUN: 13.00 – 13.50m 13.50 – 14.00m




CORE RUN: 14.00 – 14.33m 14.33 – 16.00m


CORE RUN: 16.00 – 17.64m 17.64 – 19.00m


VICTORIA

BH1

Page 4 of 4



COREHOLE BH1


End of Corehole at 20.00 metres


CORE RUN: 19.00 – 20.00m


Appendix C-3 Trial Pit Logs

TRIALPIT No. :

SITE :

Method : National Grid Coordinates

N :

E :

Ground Level :

Start Date :

End Date :

Final Depth :

Water Depth :


Logged by :Checked by :

NotationP : Percolation TestDT : In Situ Density TestPP : Pocket PenetrometerSB : Small BulkLB : Large Bulk

Remarks :

Description of strataInsitu density/Percolation/

Pocket Pen. kPa

Depthof

WaterStrikes

SampleType

Lege

nd

Sca

le (m

)

Ele

vatio

n/D

epth

Mechanically Excavated

TP 0.4m above G.L

OPG 16057 CEB

7770411.00

549914.000


3.000m amsl


04/02/2016

04/02/2016

2.55m

Not Encountered

TP 1

1 of 1

ZJ

1.15

2.55

SBLB

SBLB

Firm to stiff dark brown medium plasticity CLAY with debrissuch as plastic and glass bottles, concrete and roots. FILLMATERIAL.

Firm to stiff reddish brown with orange and cream mottlesgravelly high plasticity CLAY. Gravels are sub rounded tosub angular medium to coarse moderately strong light grey ofModerately Weathered Basalt. COMPLETELY TO HIGHLYWEATHERED BASALT

End of Trialpit at 2.55 m

1.0

2.0

TRIALPIT No. :

SITE :


N :

E :

Ground Level :

Start Date :

End Date :

Final Depth :

Water Depth :




Remarks :


Pocket Pen. kPa

Depthof

WaterStrikes

SampleType

Lege

nd

Sca

le (m

)

Ele

vatio

n/D

epth

Mechnicaly Excavated

Bucket Refusal at 1.9m

OPG 16057 CEB

7770382.00

549909.000


3.000m amsl


04/02/2016

04/02/2016

1.90m

Not Encountered

TP 2

1 of 1

ZJ

0.60

1.90

SBLB

SBLB

Dense sub rounded to sub angular clayey GRAVELS ofmoderately strong grey with black discoloration at jointsvery vesicular of Moderately Weathered Basalts with concretedebris, iron bars and plastic materials. FILL MATERIAL

Moderately weak orangish brownish grey with black, yellowand cream discolorations at joints. Very vesicular with manyamygdales HIGHLY WEATHERED BASALT in filled with yellowishbrown medium plasticity clay.


1.0

2.0

TRIALPIT No. :

SITE :


N :

E :

Ground Level :

Start Date :

End Date :

Final Depth :

Water Depth :




Remarks :


Pocket Pen. kPa

Depthof

WaterStrikes

SampleType

Lege

nd

Sca

le (m

)

Ele

vatio

n/D

epth


OPG 16057 CEB

7770409.00

549907.000


3.000m amsl


23/02/2016

23/02/2016

1.50m

Not Encountered

TP 3

1 of 1

OB

0.30

0.90

1.50

SB

SB

Soft light grey strong brown very gravelly sandy SILTY withfrequent concrete blocks. TOPSOIL.

Soft black very gravelly medium plasticity silty CLAY withvarious fragments of glasses, pipes. FILL MATERIAL.

Firm moist reddish brown high plasticity gravelly siltyCLAY. COMPLETELY WEATHERED BASALT.


1.0

2.0

TRIALPIT No. :

SITE :


N :

E :

Ground Level :

Start Date :

End Date :

Final Depth :

Water Depth :




Remarks :


Pocket Pen. kPa

Depthof

WaterStrikes

SampleType

Lege

nd

Sca

le (m

)

Ele

vatio

n/D

epth


OPG 16057 CEB

7770385.00

549892.000


3.000m amsl


23/02/2016

23/02/2016

1.10m

Not Encountered.

TP 4

1 of 1

OB

0.15

0.80

1.10

SB

SB

Sub angular coarse silty GRAVEL of strong grey Moderately toSlightly Weathered Basalt. TOPSOIL.

Firm dark brown very gravelly silty clay with numerousfragments of glasses. FILL MATERIAL.

Stiff reddish brown with black mottles high plasticity CLAY.COMPLETELY TO HIGHLY WEATHERED BASALT.


1.0

2.0


Appendix C-4 Photographs of Trial Pits


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TP 1 Page 1 of 7



TP 1


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TP 1 Page 5 of 7




VICTORIA

TP 1 Page 6 of 7




VICTORIA

TP 1 Page 7 of 7



Final Depth at 2.55metres


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TP 2 Page 1 of 5



TP 2


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TP 2 Page 2 of 5




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TP 2 Page 3 of 5




VICTORIA

TP 2 Page 4 of 5




VICTORIA

TP 2 Page 5 of 5



Final Depth at 1.90 metres


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TP 3 Page 1 of 2



TP 3


VICTORIA

TP 3 Page 2 of 2





VICTORIA

TP 4 Page 1 of 4



TP 4


VICTORIA

TP 4 Page 2 of 4




VICTORIA

TP 4 Page 3 of 4




VICTORIA

TP 4 Page 4 of 4




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