Geotech. Drill Report -Cathy School and Tower H

8/10/2019 Geotech. Drill Report -Cathy School and Tower H

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NATIONAL SOCIAL SECURITY AND INSURANCE TRUST AND PARTNERS(NASSIT)

SEWA GROUNDS DEVELOPMENT

PHASE 2- GEOTECHNICAL SITE INVESTIGATION CAR PARK ATCATHEDRAL SCHOOL AND NEW SCHOOL AT TOWER HILL, FREETOWN

Drill Report- Cathedral School and Tower Hill sites

Associates Consulting Engineers and Architects10A Thompson Bay, Carlton Carew Road,Off Wilkinson Road, Freetown, Sierra Leone

SEPTEMBER 2014


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TABLE OF CONTENTS

CONTENT PAGE

1.0 Project Introduction and scope of works 4

1.1 Introduction 4

1.2 Scope of works and Reports 7

2.0 Field work 82.1 Location of Boreholes 82.1 Geotechnical Engineering Field work undertaken 12

3.0 Geology of the project site 13

4.0 Subsurface Investigation Borehole drilling 14

4.1 Borehole drilling 15

5.0 Soil Profile and Borehole in-situ test results 19

6.0 Geotechnical Evaluation 206.1 Allowable Bearing Pressure (capacity) 20

6.2 Consolidation and Settlement 22

6.3 Foundation Size and Depth 22

6.4 Ground water and site flooding 22

7.0 Conclusion 23

APPENDIX 1 Borehole logs 24

APPENDIX 2 Rock Quality Designation 33

APPENDIX 3 Dynamic Penetration Test (DPL) 35

APPENDIX 4 Results and Graphs of DCP Tests at Cathedral School 42

APPENDIX 5 Photo Album


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1.0 Project Introduction and scope of works

1.1 Introduction

1.1.1 Clients project motivation

The Client National Social Security and Insurance Trust and Partners (NASSIT) as part of itsinvestment and revenue scheme propose to construct revenue generating shopping centre andMulti Storey car park at Sewa grounds, Garrison street, Freetown. The project will entailrelocation of the Cathedral Primary School to Tower Hill where a new school will beconstructed.

1.1.2 Project location

Figure1.1 and 1.2 are maps showing the location of the Sewa ground shopping centre and New Cathedral primary School.


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Figure 1.1: Sewa Shopping centre project site


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Figure 1.2 New Cathedral Primary School Project site, Tower Hill


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1.1.3 Project description

The project will consist of the following facilities:

Multi Storey Market Stall blocks Sewa Ground site Multi Storey Storage building- Sewa Ground site Multi Storey car parking block Cathedral School site New Multi Storey primary school blocks Tower Hill

The above facilities will require engineering design and Contract documents prior toConstruction. The structures within the facilities will require a comprehensive geotechnicalsite investigation to determine geotechnical parameters for the foundation design.

1.2 Scope of works and Reports

1.2.1 Scope of WorksThe objectives of the geotechnical investigation are:

Determination of general geology and stratigraphy ( Sub soil) at the project site area;

Determination of the geotechnical design parameters necessary to provide reliableand extensive information of subsoil to be able to define, consolidation settlement ,subsoil swelling, overall stability, bearing capacity of foundations, ground watervariation, seepage, ( if applicable)

1.2.2 Geotechnical Report

The Geotechnical report is in two phases.

Phase 1 is the Geotechnical report of the Sewa Grounds and is a report of Geotechnical (Soil)Investigations carried out within the Sewa Grounds project Site.

Phase 2 is the Geotechnical report of two project sites; the Car park at the Cathedral Schoolsite and at the new multi storey primary school blocks at Tower Hill and is a report ofGeotechnical (Soil) Investigations carried out within the two project Sites.

The final reports for the two (2) phase investigation will include all the Borehole logs, fielddata, Laboratory test results, Drill and preliminary Geotechnical evaluation. The followinginformation is considered and will be outlined in the final Geotechnical Reports:

i. Details of the geotechnical site investigation, including description of the methodsemployed for the in situ testing and samplingii. The borehole records and description of the soil strataiii. Results on in situ testing during drilling


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iv. Results of Laboratory testsv. Evaluation of field and Laboratory test resultsvi. Assessment of safe bearing pressure (capacity) for Foundation design

1.2.3 The Drill Reports

Drill report Phase 1

The drill report for the Phase 1 investigation for the Sewa ground was completed on the 16 th August 2014 and submitted to the Client.

Drill report Phase 2

The Phase 2 drill report for the project sites; the Car park at the Cathedral School site and atthe new multi storey primary school blocks at Tower Hill, which now follows outline theBorehole logs completed and information available to the Geotechnical Consultant on the19 th September 2014. Similar to the Phase 1 drill report, the phase 2 drill report seeks to

provide information for the Project Architect, Structural and Foundation Engineers to starttheir input into the Project; assessment of the type of foundation and quick assessment of theGeotechnical bearing capacity values to start preliminary design.

The following information is considered and outlined in the drill Report:

i. Details of the geotechnical site investigation, including descriptions of the methodsemployed for the in situ testing and samplingii. The borehole record and description of the soil strataiii. Results of in situ testingiv. Evaluation of field and Laboratory test resultsv . Assessment of safe bearing pressure (capacity) for Foundation design

The appropriate findings of the drill report will be incorporated in the final GeotechnicalReport.

2.0 Field work

2.1 Location of Boreholes

Phase 2

Car Park at Cathedral School

The field work consists of two (2 no. ) total of boreholes at the car park at Cathedralschool. The location of the boreholes, Dynamic Probing Light (DPL) and DynamicCone Penetrometer (DCP) are shown in Figure 2a . The positioning of the boreholeswas carried out on the basis of DGPS and Total Station survey instrument.


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Figure:2a: Location of boreholes - Car. Park at Cathedral school


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Figure:2b: Location of boreholes - New Multi Storey primary school blocks TowerHill


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2.2 Geotechnical Engineering Field work undertaken

Based on the scope of Services (work) supplied by the Client the following field work wasundertaken:

A site reconnaissance survey and walk over assessment.

Drilling of the 4 No. boreholes; 2 No at Cathedral School and 2 No. Tower hill. TheBoreholes at cathedral school were drilled to a minimum depth of 10m and at TowerHill to a depth of 4m in Gabbro rock ; as requested in the Scope of works; and at the

proposed location requested by the Project Engineer.

Standard penetration test performed continuously at 1.0 m intervals during boreholedrilling in soil and collection of undisturbed soil samples to be subsequently used to

perform laboratory soil tests.

All boreholes were logged by an engineer in accordance with BS 5930; Code ofPractice for Site Investigation.

Pocket Penetrometer and Torvane tests on Windowless undisturbed samples.

Dynamic Penetration ( DPL ) tests and Dynamic Cone Penetration ( DCP) Tests.

Representative soil samples from the boreholes have been selected and sent to theLaboratories for soil testing.


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3.0 Geology of the project sites

The Cathedral school and Tower Hill sites lie in the Freetown peninsula. The Freetown

peninsula of Sierra Leone is predominantly the G eological group The Freetown Intrusive(layered basic) complex . This layered complex is a funnel shaped intrusion of Gabbroic rockthe greater part of which lies out to sea. The layered complex forms inland, steep high hillswith a relatively flat coastal plain/shoreline consisting of thick laterite soil overlyingweathered hard pan laterite and Gabbro parent rock.

Within this flat area of shoreline is found at a few locations another geological group: theBullom sediment. The Bullom sediment is a group of nearly horizontal marine and estuarinesediments. Outcrops are rare with layers generally clay overlain by coarse variable sand .

Due to the high rainfall, the hills of the Freetown peninsula are covered with widespreadthick residual laterite and surface boulders overlying the massive gabbroic rocks. TheCathedral School lies next to the Sewa Ground and is located at the foot of the Tower Hill .

Laterite is the result of decomposition or weathering process and is found in profiles varyingfrom fresh rock at depth, through various stage of decomposition, to residual soil at thesurface. The term has been applied to clays, sands and gravels in various combination, androcks of different degree of cementations. The properties of laterites therefore depend on theirweathering history, and thus on several other factors including the parent rock, climate,drainage, topography and site evolution. In addition the laterite may, since its in-situ

formation, have undergone erosion transportation and redeposit ion as a secondary deposit .

In areas where the laterite layers is thin with exposure of the massive Gabbroic rocks;quarries for hard rock aggregate are set up and the Gabbro is commercially mined to producecoarse aggregates for construction.

At the edge coastal plain adjacent to sea is a strip/layer of coarse to fine sandy beachsurrounding the peninsula. This strip of sand is a major Tourist attraction and at Hamiltonalong the peninsula the sand is extracted commercially and used as fine aggregates for civilconstruction. Within the coastal plain adjacent to the sea are flood plains at the confluence ofrivers and streams originating at the internal hills where they meet the sea.

Figure 3 is a Geology Map of Sierra Leone


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Figure 3: The Geology Map of Sierra Leone

4.0 Subsurface Investigation Borehole drilling

Car Park at Cathedral School

The subsurface Investigation site work commenced on 25 th August 2014 and was completedon 27 th August 2014

The sub surface investigation at the Project site comprised of the two (2 No.) boreholesoriginally requested : BH01,BH02. The Borehole location points were located by using aGPS instrument. The location of the boreholes are shown on Figures 2a


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New Multi Storey primary school blocks Tower Hill

The subsurface Investigation site work commenced on 19 th August 2014 and was completedon 20 th August 2014

The sub surface investigation at the Project site comprised of the two (2 No.) boreholesoriginally requested : BH01,BH02. The Borehole location points were located by using aGPS instrument. The location of the boreholes are shown on Figures 2b

4.1 Borehole drilling

The drilling equipment used in the borehole drilling is the same Dando Terrier Model 2002used in the Phase 1 Geotechnical Investigation ; with provision for mounting both hydraulic

powered rotary and percussion drills. The drilling equipment is shown on Photograph No.1 and is owned by 3BMD Associates Consulting Engineers , Sierra Leone. The rig is equippedwith fittings for Soil investigation work including standard penetration test (SPT), Rotarycore drilling, flight hollow stem Auguring.

The percussion hammer is used to simultaneously drive a 113mm external diameter Duplexcasing and a 86mm external diameter windowless sampler (The sampler being within thehollow of the casing) into the ground. The windowless sampler is then removed from thecasing and the sample retained logged. The windowless sampler is replaced with a split spoonsampler for the SPT. The Hammer for the SPT is hydraulic powered; lifted and dropped afixed distance.The SPT test is performed by driving with the Hammer, a split SPT sampling tube throughthe casing into soil at the tip of the casing. The sample is then extracted, the windowlesssampler inserted and the casing advanced. The SPT is described in ASTM D 1586.Equipment particulars are as follows:

Split sampler internal diameter = 38mmLength driven into soil = 450mmBlow counts counted for last 300mm = (N value)

Weight of hammer = 70kg falling a distance 760mm

Where rock is encountered at N value greater than 50; the rotary head assembly is fitted onthe rig and rotary core drilling done using the hydraulic powered rotary head. A T2 101Double tube swivel type core barrel assembly with a Tungsten Carbide core bit or Diamond

bit is used for drilling in Laterite hardpan and Gabbro rock. The barrel has an externaldiameter of 101mm and internal Plastic liners of 84mm internal diameter. Clean water wasused as drilling fluid to ensure the core cuttings were flushed out. The cores were carefullyremoved and logged during drilling in accordance with BS5930 Code of Practice for SiteInvestigation.

.


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Photograph No.1. Borehole Drill Rig- Cathedral School

.The drilling operation carried out at the project Sites follows:

Continuous sampling and standard penetration test were performed during the boreholedrilling. The standard penetration test (SPT) was performed at intervals of 1.0m and theSPT thin wall sampler (38mm in diameter) carefully removed Photograph No.2 ,examined, photographed, logged and waxed to prevent loss of moisture from the samples.Each sample was then wrapped with plastic sheet and secured with 2 sticks tied externally tothe sides to prevent sample disturbance and damage during transportation.


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Photograph No.2. SPT Sampler and soil sample

When the SPT test showed N values greater than 50; Rotary core drilling was used tocontinue the borehole drilling. The tungsten carbide drill bit was attached to the drill rotaryhead with clean water used as drill fluid. The drilling advanced at 1m intervals. The core

barrel assembly is fitted with a 1m length plastic liner of 84mm internal diameter. The core

barrel is lifted from the drill hole and the plastic liner carefully removed. The core isexamined and logged with plastic end caps attached at both ends of the plastic liner to preventmoisture loss.

The logging and description of the samples was in accordance with BS 5930; Code ofPractice for Site Investigation.

Representative borehole samples were selected and sent to the laboratories for testing. The borehole logs showing the underlying soil profile of the site are shown in Appendix 1.


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Photograph No.3: DPL test in progress- Cathedral School

Photograph No.4: DCP test in progress- Cathedral School


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B=least lateral base dimension, D= depth of the pad footing below ground lelevl

K d=1+0.33 1.33,

F= factors for equation,

N

SI FpsF1 0.04 2F2 0.06 3.2F3 0.3 0.3F4 1.2 1.2

Q (a)= allowable bearing pressure for 25mm or 1in settlement , KPa ( KN/m 2) or Ksf.

Reference: Foundation Analysis and Design 5 th Edition by Joseph E Bowles. PublisherMcGraw Hill. Page 263-265.

The largest foundation within the new Car Park is the foundation of the lift shaft and is4.5lm X 4.06m.

Using The formula by Meyerhoff (1965) the allowable bearing capacity (Net) Q (a) below foundation level when B is 4.06m and N is 25

q allowable = 483 KN/m2We recommend an allowable bearing capacity (Net) Q (a) at foundation level 1.0mbelow existing ground level of 300 KN/m2 for the preliminary foundation designof the foundations within the project site.

New Multi Storey primary school blocks Tower Hill

The average RQD value across the site is 40 and from the chart in Figure 4 below theAllowable bearing stress in rock 5 Mpa (500 KN/m2). For preliminary design a value of 3.0Mpa (300 KN/m2) is recommended


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Figure 4 : Allowable bearing stress-(Capacity) for RQD

6.2 Consolidation and Settlement

. An indicative conservative figure of 25mm based on the Meyerhoff can be used in the

preliminary design calculations.

6.3 Foundation Size and Depth

We recommend for the preliminary design work a minimum depth of 1.0m below groundlevel for founding of the bases..

6.4 Ground water and site flooding

Ground water was not encountered during the borehole drilling at both project sites.


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Both the ground surface slope of the Catherdral school and Tower Hill sites are steep andwell drained. No flooding of the sites is envisaged.

7.0 Conclusion

The Drill report presents the borehole log results of the investigation carried out to achievethe objectives stated in the introduction item 1.0. It provides; based on the StandardPenetration Test (SPT) results and Rock Quality Designation (RQD); GeotechnicalEvaluation of the underlying materials encountered within the project sites andrecommendations on design parameters to be used in the preliminary design of the foundation

bases (pads) for the project buildings. For Preliminary design purposes we recommend anallowable bearing pressure of 300 KN/m2 at the Cathedral School Project site and 300KN/m2 at the Tower hill Project site. Simple pad foundations are recommended. Raftfoundation should be considered as alternative foundation structure if the design results infoundation bases which are too close together.

A more detailed report will be presented in the Preliminary and Final reports as moreinformation and test results become available.

We trust the recommendations in the report meets your requirements and will be available torespond to any queries and clarifications raised.


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APPENDIX 1

Borehole logs


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APPENDIX 2

ROCK QUALITY DESIGNATION (RQD)


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ROCK QUALITY DESIGNATION(RQD)-NEW MUTISTOREY PRIMARY SCHOOL BLOCKS -TOWER HILL

BH 01 TCR (%) SCR(%) RQD(%)DEPTH0.20-1.20 72 72 72

1.20-2.20 40 32 32

2.20-3.20 71 42 42

BH020.40-1.40 100 100 861.40-2.40 65 60 60

2.40-3.40 40 0 0

3.40-4.40 68 68 68


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Dynamic Penetration Test Results At Cathedral School

Dynamic Probing Date: 30/08/2014Project: Muti Strorey Parking BlocksLocation: Cathedral School

N u m

b e r

D P L 1

D P L 2

D P L 3

0.10 4 5 80.10 8 7 50.20 8 7 50.30 5 6 40.40 3 7 50.50 5 8 40.60 9 7 50.70 14 8 6

0.80 16 13 70.90 19 14 81.00 20 4 131.10 23 25 131.20 19 29 161.30 30 31 201.40 34 49 251.50 27 48 301.60 32 45 451.70 50 41 461.80 44 361.90 47 322.00 38 362.10 45 432.20 40 492.30 50 492.40 432.50 452.60 492.70 342.80 492.90 403.00 493.10 503.203.303.40


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APPENDIX 4

Results And Graphs of DCP Tests at Cathedral School


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Report Date: 06-Oct-2014 Page 1 of 1

UK DCP V3.1 DCP Layer Strength Analysis ReportProject Name: DCP results

Chainage (km): 1.000 Surface Type: UnpavedDirection: Thickness (mm): 0Location/Offset: Carriageway Base Type:Cone Angle: 60 degrees Thickness (mm):Zero Error (mm): 5 Surface Moisture: UnknownTest Date: 29/08/2014 Moisture adjustment factor: Not adjusted

Layer Boundaries Chart CBR Chart

Layer Properties

N o. Pene trat ion

Rate

(mm/blow)

CBR

(%)

Thickness

(mm)

Depth to

layer bottom

(mm)

Position Strength

Coefficient

SN SNC SNP

1 22.87 11 458 458 Base 0.03 0.54 0.54 0.542 16.67 15 250 708 Sub-Base 0.08 0.80 0.80 0.823 6.38 43 255 963 Sub-Base 0.11 1.07 1.07 0.784 3.96 70 412 1375 Sub-Base 0.11 1.84 1.84 0.69

Pavement StrengthLayer Contribution

Layer SN SNC SNPSurface -- -- --Base 0.54 0.54 0.54Sub-Base 3.71 3.71 2.29Subgrade -- -- --Pavement Strength 4.25 4.25 2.83

CBR Relationship:TRL equation: log

10(CBR) = 2.48 - 1.057 x log

10(Strength)

Report produced by ...................................................................

DCP 1


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Layer Properties

N o. Pene trat ionRate

(mm/blow)

CBR(%)

Thickness(mm)

Depth tolayer bottom

(mm)

Position StrengthCoefficient

SN SNC SNP





10(CBR) = 2.48 - 1.057 x log

10(Strength)


DCP 2


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Layer Properties

N o. Pene trat ion

Rate

(mm/blow)

CBR

(%)

Thickness

(mm)

Depth to

layer bottom

(mm)

Position Strength

Coefficient

SN SNC SNP

1 13.97 19 650 650 Base 0.05 1.22 1.22 1.222 37.93 6 569 1219 Sub-Base 0.05 1.01 1.01 0.843 5.14 53 36 1255 Sub-Base 0.11 0.16 0.16 0.07

4 1.11 270 139 1394 Sub-Base 0.12 0.63 0.63 0.25




10(CBR) = 2.48 - 1.057 x log

10(Strength)


DCP 3


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Layer Properties

N o. Pene trat ion

Rate

(mm/blow)

CBR

(%)

Thickness

(mm)

Depth to

layer bottom

(mm)

Position Strength

Coefficient

SN SNC SNP




CBR Relationship:TRL equation: log 10 (CBR) = 2.48 - 1.057 x log 10 (Strength)


DCP 4


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APPENDIX 5

Photo Album


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Photograph No.8. DCP Equipment

Photograph No.9. Soil Samples at Cathedral School


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Photograph No.12. Dynamic Probing Light (DPL) Equipment


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Photograph No.13. Dynamic Cone Penetrometer(DCP) Equipment

Geotech. Drill Report -Cathy School and Tower H

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