S OIL C ONSULTANTS LTD

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Head Office: Chiltern House, Earl Howe Road, High Wycombe, Bucks HP15 6QT www.soilconsultants.co.uk

Registered No: 1814762 at 35 Belmont Road, Uxbridge Middlesex UB8 1RH VAT No: 491 8249 15

Directors

Stuart Wagstaff BSc(Hons) MSc FGS John Bartley BSc MSc CGeol FGS Opher Tolkovsky BSc MSc DIC CGeol FGS

Associate Directors Keith Gibbs BSc MSc FGS

Alan Watson BSc(Eng) CEnv CEng MICE Consultants

Ken Bangs MSc, Terry Rickeard BSc , MSc

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Ground Investigation Geotechnical Analysis Environmental Appraisal Tel: 01255 241639 Fax: 0871 528 9424 e-mail: [email protected]

REPORT ON PRELIMINARY GROUND INVESTIGATION PROPOSED REDEVELOPMENT:

13 AUBREY WALK, LONDON W8 7JH

Client: CLAUDE BENVENISTE

13a Aubrey Walk London W8 7JH

Consulting Engineer: AVENTUS DESIGN LTD

Unit 7 Leaches Farm Business Centre Bicester Road, Kingswood

Aylesbury, Buckinghamshire HP18 0RR 4689/JRCB/OT 29th_{July 2009}

Haven House

Albemarle Street

Harwich

Essex CO12 3HL

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4689/JRCB/OT Preliminary Report on Ground Investigation – 13 Aubrey Walk, London W8 7JHD

Client: Claude Benveniste Consulting Engineer: Aventus Design Ltd

29th_{July 2009} TABLE OF CONTENTS 1.0 Introduction ... 1 2.0 Site description ... 1 3.0 Exploratory work... 1 4.0 Ground conditions ... 2 4.1 Topsoil ... 2 4.2 Made ground... 2 4.3 Superficial clay... 2 4.4 London Clay... 2 4.5 Groundwater... 2

5.0 Outline geotechnical assessment ... 2

5.1 Basement construction ... 2

5.2 Spread foundations... 3

5.3 Piled foundations ... 3

5.4 Foundation concrete... 3

APPENDIX

• Cable percussive borehole record

• Standard Penetration Test [SPT] results

• Index property test results

• Triaxial compression test results

• Soluble sulphate analysis

• Site development plans

• Site Plan

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4689/JRCB/OT Preliminary Report on Ground Investigation – 13 Aubrey Walk, London W8 7JHD Page 1 Client: Claude Benveniste Consulting Engineer: Aventus Design Ltd

29th_{July 2009}

1.0 INTRODUCTION

Consideration is being given to the redevelopment of this site, comprising the demolition of the existing building and construction of two new attached houses, each with double basement. As part of the Royal Borough of Kensington & Chelsea planning requirements a preliminary ground investigation has been carried out in order to provide outline information on the ground conditions.

This report describes the investigation undertaken, gives a summary of the ground conditions encountered and then provides preliminary retaining wall and foundations recommendations.

This report has been prepared for the benefit of the client and no reliance can be assumed by others without the written agreement of Soil Consultants Ltd.

2.0 SITE DESCRIPTION

The site is located in a mainly residential area just to the north-east of Holland Park. The overall dimensions are 28m x 9.5m and its centre lies at NGR 524908E 180116N. No 13 is situated on the southern side of Aubrey Walk and is bound to the east and west by residential properties. A 3m high retaining wall forms the southern boundary with the high-lying ground to the south. A tennis club is present beyond the site to the south of the retaining wall, and we understand that underground courts are present approximately 4m from the boundary.

The existing building on the site is of 3-storey brick construction with no basement and measures about 22m x 4.5m. At the front [northern side] of the building a number of raised planting areas are present, containing ornamental shrubs and bushes. Concrete or paved hardstanding is present to the east, south and west of the building.

A 6m high Strawberry tree is present within the western corner of the site together with a number of smaller shrubs. Just outside the north-eastern boundary is an Indian Bean tree of similar height, whilst a number of Sycamore trees are present outside the southern boundary on the high-lying ground. The species of the trees is identified in the Aboricultural Method Statement which was provided by the client. The site features and layout are shown on the Site Plan which is included in the Appendix.

3.0 EXPLORATORY WORK

The ground investigation comprised a single cable percussive borehole [BH 1] which was taken to a depth of 20m below ground level. The borehole was constructed using a de-mountable rig [due to access restrictions] and commenced within one of the raised planting beds. Sampling and in-situ Standard Penetration Testing [SPT] were carried out at appropriate intervals and on completion of the fieldwork, samples recovered from the borehole were taken to our laboratory in High Wycombe for visual examination and the following geotechnical testing:

¾ Index property test [Atterberg]

¾ Unconsolidated, undrained triaxial shear strength test

¾ Soluble sulphate/pH tests

The results of the laboratory testing together with the engineering logs of the borehole are included in the Appendix.

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29th_{July 2009}

4.0 GROUND CONDITIONS

The geological survey map indicates that the site is underlain by Clay Head deposits which rest upon River Terrace Gravel; the London Clay is then shown to be present. Our preliminary investigation encountered a moderate thickness of made ground overlying natural Clay Head deposits. Gravel was not present and the superficial clay rested directly upon the London Clay, which extended to the full depth of the borehole.

As discussed in Section 3.0 the borehole was located within one of the raised planting beds. All depths in the following discussion therefore refer to the planting bed level, which lies 0.3m above ground level.

4.1 Topsoil

Topsoil was present to 0.30m depth, which corresponds to the height of the raised planting bed.

4.2 Made ground

The made ground initially comprised grey/brown slightly humic clayey sand with brick fragments. At 0.60m depth, soft dark grey and brown slightly organic clay with brick fragments, gravel and roots was present, extending to 1.80m depth.

4.3 Superficial clay

This deposit comprised brown slightly silty clay with occasional gravel and some silty to very silty sandy pockets. This layer, which extended to 4m depth, probably represents naturally re-worked London Clay. Index property tests indicate the clay to be of high shrinkage potential with a measured Plasticity Index of 56%. The clay was generally of a firm consistency with occasional soft zones.

4.4 London Clay

The London Clay was met at a depth of 4m and initially comprised firm becoming stiff brown fissured clay with occasional silt/sand partings and scattered selenite crystals. The weathered brown zone extended to about 9.9m depth whereupon stiff becoming very stiff grey fissured clay was present. The London Clay extended to the full depth of the borehole at 20m.

4.5 Groundwater

The borehole remained dry with no observed groundwater inflows or standing levels. It should be noted that water levels can undergo significant seasonal variation and can rise during wet periods.

5.0 OUTLINE GEOTECHNICAL ASSESSMENT

The proposed redevelopment comprises the construction a new residential block which will incorporate a double basement extending to about 7m depth. The preliminary investigation has revealed that about 2m of made ground is present overlying natural superficial silty sandy clay; the underlying London Clay was met at about 5m depth.

5.1 Basement construction

We understand that at this preliminary stage a concrete bored pile retaining wall is proposed for the new basement. We agree that this type of wall should provide the optimum solution at this site - either Continuous Flight Auger [CFA] piles or conventional augered piles would be suitable for the ground conditions.

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29th_{July 2009}

Due consideration will need to be given to the effect of the basement construction on adjacent properties, the nearest of which lies <4m from the proposed retaining wall. An effective, well-designed temporary lateral support system should be specified to ensure that the wall remains stable during construction and that deflections are kept within reasonable limits. A robust arrangement of internal bracings/props should be sufficient to control the ground movements. In the permanent case the lateral earth pressures will either be supported by the piled retaining wall, or by a reinforced concrete lining wall cast within the line of contiguous piles. In either case horizontal support will be provided by the new ground floor and basement slabs.

We note that two established trees are present [within the western corner of the site and just outside the north-eastern boundary] and we understand that these are to be retained. The investigation has shown that cohesive soils are present and some desiccation of these soils may well have occurred due to tree root action. There will be a risk that in the event of the death of these trees in the future, swelling of the clay could occur as water is re-absorbed and a new moisture content equilibrium is established. Higher than normal pressures on the back of the retaining wall could occur due to this swelling and the wall designer will need to address this risk.

It will be necessary to consider uplift of the slab due to long term soil heave and potential groundwater pressures.

5.2 Spread foundations

Spread foundations would be constructed within the completed the basement excavation, probably at about 7m below ground where the borehole has shown competent London Clay to be present. Allowable bearing pressures of between 150kPa and 200kPa will probably be acceptable for moderate sized foundations but this will depend to some extent of the column configuration and spacing.

5.3 Piled foundations

Piled foundations could be used to support the structural loads imposed by the new building. If the retaining wall piles are to be used to support axial loads then the necessary allowance for interaction effects should be made. A preliminary strength profile of the London Clay is included in the Appendix using the results of in-situ Standard Penetration Testing and laboratory undrained triaxial testing.

5.4 Foundation concrete

Low levels of soluble sulphates were measured in selected soil samples with near neutral pH values. The results fall into Site Design Class DS-1 of Table C1 [‘greenfield’] given in BRE Special Digest 1 [2005]. We assess the site as having ‘static’ groundwater conditions and recommend that buried concrete is designed in accordance with ACEC Site Class AC-1s.

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4689/JRCB/OT Preliminary Report on Ground Investigation – 13 Aubrey Walk, London W8 7JHD

Client: Claude Benveniste Consulting Engineer: Aventus Design Ltd

29th_{July 2009}

APPENDIX

• Cable percussive borehole record

• Standard Penetration Test [SPT] results

• Index property test results

• Triaxial compression test results

• Soluble sulphate analysis

• Site development plans

• Site Plan

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Head Office: Chiltern House, Earl Howe Road, High Wycombe, Bucks HP15 6QT www.soilconsultants.co.uk

Registered No: 1814762 at 35 Belmont Road, Uxbridge Middlesex UB8 1RH VAT No: 491 8249 15

Directors

Stuart Wagstaff BSc(Hons) MSc FGS John Bartley BSc MSc CGeol FGS Opher Tolkovsky BSc MSc DIC CGeol FGS

Associate Directors Keith Gibbs BSc MSc FGS

Alan Watson BSc(Eng) CEnv CEng MICE Consultants

Ken Bangs MSc, Terry Rickeard BSc , MSc

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Ground Investigation Geotechnical Analysis Environmental Appraisal Tel: 01255 241639 Fax: 0871 528 9424 e-mail: [email protected]

FOREWORD - GUIDANCE NOTES

GENERAL

The Borehole Records are compiled from the driller’s description of the strata encountered, an examination of the samples by our Geotechnical Engineer and the results of in-situ and laboratory tests. Based on this data, the report presents an opinion on the configuration of strata within the site. However, such reasonable assumptions are given for guidance only and no liability can be accepted for changes in conditions not revealed by the boreholes.

BORING METHODS

The Cable Percussion technique of boring is normally employed and allows the ground conditions to be reasonably well established. However, some disturbance of the ground is inevitable, particularly some “softening” of the upper zone of clay immediately beneath a granular soil. The presence of thin layers of different soils within a stratum may not always be detected.

GROUND WATER

The depth at which ground water was struck is entered on the Borehole Records. However, this observation may not indicate the true water level at that period. Due to the speed of boring and the relatively small diameter of the borehole, natural ground water may be present at a depth slightly higher than the water strike. Moreover, ground water levels are subject to variations caused by changes in the local drainage conditions and by seasonal effects. When a moderate inflow of water does take place, boring is suspended for at least 10 minutes to enable a more accurate short-term water level to be achieved. An estimate of the rate of inflow is also given. This is a relative term and serves only as a guide to the probable flow of water into an excavation.

Further observations of the water level made during the progress of the borehole are shown including end of shift and overnight readings and the depth at which water was sealed off by the borehole casing, if applicable.

Whilst drilling through granular soils, it is usually necessary to introduce water into the borehole to permit their extraction. When additional water has been used a remark is made on the Borehole Record and the implications are discussed in the text.

SAMPLES

Undisturbed samples of the predominantly cohesive soils are obtained using a 100mm diameter open-drive sampler. In granular soils, disturbed bulk samples are taken and placed in polythene bags. Small jar samples are taken at frequent intervals in all soils for subsequent visual examination. Where ground water is encountered in sufficient quantity, a sample of the ground water is also taken.

IN-SITU STANDARD PENETRATION TESTS

This test is performed in accordance with the procedure given in B.S.1377:1990. The individual blow count record for each test is given on a separate table. The ‘N’ value is normally the number of blows to achieve a penetration of 0.3m following a seating distance of 0.15m and is quoted at the mid-depth of the test zone. However if a change of stratum occurs within the test zone then a revised ‘N’ value is calculated to assess one layer in particular. In hard strata full penetration may not be obtained. In such cases the suffix + indicates that the result has been extrapolated from the limited penetration achieved. Where ground water has affected the measured values, the resultant ‘N’ values have been placed in brackets since it is unlikely to represent the true in-situ density of the soil.

Haven House

Albemarle Street

Harwich

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Contract & Borehole No: location

Client: Sheet 1 of 2

1

Engineer: Report No:

SPT Strata

Type Depth[m] [N] depth [m]

0 0 D 0.30 0.30 D 0.60 0.60 1 1 S 1.50 3 D 1.50 1.80 D 1.80 2 2 U 2.00 D 2.45 D 3.00 3 3 S 3.80 13 D 3.80 4.00 4 4 U 5.00 5 5 D 5.45 6 6 S 6.80 20 D 6.80 7 7 D 7.50 U 8.00 8 8 D 8.45 9 9 S 9.80 25 D 9.80 9.90 10 10

Constructed by cable percussion techniques Key: U = Undisturbed B = Bulk D = Small disturbed W = Water S = SPT[split spoon sampler] C = SPT[soild cone]

Remarks :- _{Borehole No:}

[Scale = 1:50]

Firm becoming stiff brown fissured CLAY with blue/grey gleying, occasional partings of silt/fine sand and scattered selenite crystals

BH commenced on 15 July 2009 TOPSOIL [within raised planting bed]

BH 1

13 Aubrey Walk, London W8 7JH

Comments Samples Strata Description Legend

Claude Benveniste

Aventus Design Ltd

4689/JRCB

BH/casing dia: 150mm

BH cased to 2.00m Service pit excavated to 1.20m

BH 1

Stiff becoming very stiff grey fissured CLAY with scattered selenite crystals MADE GROUND: soft dark grey and brown slightly organic clay with brick fragments, occasional gravel and roots

MADE GROUND: grey/brown slightly humic clayey sand with brick fragments

Firm, locally soft, brown slightly silty to silty CLAY with occasional gravel. Locally very silty and sandy. Roots observed to about 3m depth

Note that the borehole was located within a raised planting bed - all depths refer to this bed level which lies 0.30m above general ground level 0 1 2 3 4 5 6 7 8 9 10

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Contract Borehole No:

& Location ₀

Client Sheet 2 of 2

1

Engineer Report No

SPT Strata

Type Depth[m] [N] depth [m]

10 10 U 11.00 11 11 D 11.45 12 12 S 12.80 22 D 12.80 13 13 D 13.50 U 14.00 14 14 D 14.45 15 15 S 15.80 29 D 15.80 16 16 D 16.50 U 17.00 17 17 D 17.45 18 18 S 18.80 29 D 18.80 19 19 U 19.00 D 19.95 20.00 20 20

Constructed by cable percussion techniques Key: U = Undisturbed B = Bulk D = Small disturbed W = Water S = SPT[split spoon sampler] C = SPT[soild cone]

Remarks :- _{Borehole No:}

[Scale = 1:50]

Borehole dry

Aventus Design Ltd

4689/JRCB

Claude Benveniste

13 Aubrey Walk, London W8 7JH

BH 1

Legend Strata Description

- casing depth: 2.00m End of shift: 15 July 2009 - BH depth: 11.00m

Samples

Stiff becoming very stiff grey fissured CLAY with scattered selenite crystals

BH continued: 16 July 2009 - water depth am: dry

Comments

- water depth pm: dry

End of borehole at 20m

BH 1

10 11 12 13 14 15 16 17 18 19 20 x

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Borehole No: Start depth

[m] Test Type SPT (N) Remarks

BH1 1.20 S 1 1 1 1 0 1 3 3.50 S 2 2 3 3 4 3 13 6.50 S 2 4 5 4 5 6 20 9.50 S 3 3 6 5 6 8 25 12.50 S 2 4 4 6 6 6 22 15.50 S 3 5 7 8 7 7 29 18.50 S 3 5 7 8 7 7 29

Blow counts per 75 mm

IN SITU STANDARD PENETRATION TEST RESULTS

4689/JRCB

Report No: Contract &

location

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Haven House

Albemarle Street

Harwich

Ground investigation Geotechnical analysis Environmental appraisal

Essex

Tel: 01255 241639 Fax: 0871 528 9424

[email protected]

CO12 3HL

LABORATORY TEST CERTIFICATE - Index Properties

Sample Depth Moisture Liquid Plastic Plasticity Percent

location [m] Sample Description Content Limit Limit Index Passing Remarks

[%] [%] [%] [%] [425μm]

BH1 1.80 Brown slightly silty CLAY with occasional gravel 33 82 26 56 >95 5.00 Brown fissured CLAY 27 73 26 47 >95 11.00 Grey fissured CLAY 27 85 25 60 >95 19.50 Grey fissured CLAY 28 82 29 53 >95

Tests carried out to the following standards:

- moisture content BS 1377:Part 2 [1990] - Clause 3.2 [value in brackets = calculated matrix moisture content for comparison with LL and PL] - plasticity [LL & PL] BS 1377:Part 2 [1990] - Clauses 4.4, 5.2, 5.3, 5.4 is carried out on fine grained soil matrix

- percent passing 425 micron sieve is by estimation, by hand* or by wet sieving** Sample examined by: JRCB [Engineer]

Results checked by: JRCB [Engineer] Certificate date:29th July 2009

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Report No:

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Report No:

TRIAXIAL COMPRESSION TEST RESULTS

Borehole No: Depth

[m] Test Type Cell Pressure [kN/m2_] Comp Strength [kN/m2_] Bulk Density [Mg/m3_] Moisture Content [%] Cohesion [kN/m2_] Angle of Friction [deg]

1

2.00

102U

80

153

2.01

27

76

0

1

5.00

102U

100

121

2.02

24

61

0

1

8.00

102U

160

236

2.02

27

118

0

1

11.00

102U

220

290

2.03

27

145

0

1

14.00

102U

280

322

2.04

26

161

0

2

17.00

102U

340

261

2.02

27

130

0

2

19.50

102U

390

139

1.96

28

70

0

Key : 38, 102 = dia in mm, U=Undrained, M= Multistage, MC = Moisture Content, QD = Quick Drained Test

4689/JRCB

Contract &

location

13 Aubrey Walk, London W8 7JH

Remarks

Disturbed sample

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Haven House

Albemarle Street

Harwich

Ground investigation Geotechnical analysis Environmental appraisal

Essex

Tel: 01255 241639 Fax: 0871 528 9424

[email protected]

CO12 3HL

Sample SOIL WATER

location Sample Description SO4 SO4 pH Remarks

[mg/l] [mg/l]

BH1 1.80 Brown slightly silty CLAY with occasional gravel 37 7.3

5.00 Brown fissured CLAY 49 7.0

11.00 Grey fissured CLAY 478 6.8

19.50 Grey fissured CLAY 453 6.6

Tests carried out to the following standards:

- soil and water sulphate analysis - BS 1377:Part 3 [1990] - Clause 5 - determination of pH value - BS 1377:Part 3 [1990] - Clause 9 Sample examined by: JRCB [Engineer]

Results checked by: JRCB [Engineer] Certificate date : 29th July 2009

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Report No:

LABORATORY TEST CERTIFICATE - Sulphate Analysis

4689/JRCB

Depth [m]

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Contract & location

Report

No: _4689/JRCB

Undrained cohesion/SPT versus depth

0 5 10 15 20 0 50 100 150 200 SPT 'N' value Dept h [ m ] 0 10 20 30 40

Undrained cohesion - triaxial [kPa]

Undrained cohesion - triaxial SPT 'N' value

Made ground

London Clay Superficial clay

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Site Development Plans

Report No:

4689/JRCB

Contract & location

Haven House, Albemarle Street Harwich, Essex, CO12 3HL T: 01255 241639 F: 0871 528 9424 E: [email protected]

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[Retained side] No 13 [3-storey] Strawberry tree [6m] Concrete pathway Retaining wall approximately 3m high BH-1

AUBREY WALK Paving Indian Bean tree [6m]

Raised bed with bushes and ornamental shrubs [Retained side]

Site Plan

Report No:

4689/JRCB

Contract & location

Haven House, Albemarle Street Harwich, Essex, CO12 3HL T: 01255 241639 F: 0871 528 9424 E: [email protected]

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Location Plan

Report No:

4689/JRCB

Contract & location

Haven House, Albemarle Street Harwich, Essex, CO12 3HL T: 01255 241639 F: 0871 528 9424 E: [email protected]

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SITE LOCATION

524500 180000 Scale 1:5,000@A4 525000 180500 ~