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1 S OIL C ONSULTANTS LTD Ground Investigation Geotechnical Analysis Environmental Appraisal Tel: Fax: harwich@soilconsultants.co.uk Haven House Albemarle Street Harwich Essex CO12 3HL 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 /OT 29 th July 2009 Head Office: Chiltern House, Earl Howe Road, High Wycombe, Bucks HP15 6QT Directors Registered No: at Stuart Wagstaff BSc(Hons) MSc FGS 35 Belmont Road, Uxbridge John Bartley BSc MSc CGeol FGS Middlesex UB8 1RH Opher Tolkovsky BSc MSc DIC CGeol FGS VAT No: Associate Directors Keith Gibbs BSc MSc FGS Alan Watson BSc(Eng) CEnv CEng MICE Consultants Ken Bangs MSc, Terry Rickeard BSc, MSc

2 /OT Client: Claude Benveniste Preliminary Report on Ground Investigation 13 Aubrey Walk, London W8 7JHD Consulting Engineer: Aventus Design Ltd TABLE OF CONTENTS 1.0 Introduction Site description Exploratory work Ground conditions Topsoil Made ground Superficial clay London Clay Groundwater Outline geotechnical assessment Basement construction Spread foundations Piled foundations 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 Location Plan 29 th July 2009

3 /OT Preliminary Report on Ground Investigation 13 Aubrey Walk, London W8 7JHD Page 1 Client: Claude Benveniste Consulting Engineer: Aventus Design Ltd 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 E N. 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: Index property test [Atterberg] Unconsolidated, undrained triaxial shear strength test Soluble sulphate/ph tests The results of the laboratory testing together with the engineering logs of the borehole are included in the Appendix. 29 th July 2009

4 /OT Preliminary Report on Ground Investigation 13 Aubrey Walk, London W8 7JHD Page 2 Client: Claude Benveniste Consulting Engineer: Aventus Design Ltd 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. 29 th July 2009

5 /OT Preliminary Report on Ground Investigation 13 Aubrey Walk, London W8 7JHD Page 3 Client: Claude Benveniste Consulting Engineer: Aventus Design Ltd 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. 29 th July 2009

6 /OT Client: Claude Benveniste Preliminary Report on Ground Investigation 13 Aubrey Walk, London W8 7JHD Consulting Engineer: Aventus Design Ltd 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 Location Plan 29 th July 2009

7 S OIL C ONSULTANTS L TD Ground Investigation Geotechnical Analysis Environmental Appraisal Tel: Fax: harwich@soilconsultants.co.uk Haven House Albemarle Street Harwich Essex CO12 3HL 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 opendrive 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. Head Office: Chiltern House, Earl Howe Road, High Wycombe, Bucks HP15 6QT Registered No: at 35 Belmont Road, Uxbridge Middlesex UB8 1RH VAT No: 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

8 Contract & location 13 Aubrey Walk, London W8 7JH Borehole No: BH 1 Client: Sheet 1 of 2 1 Engineer: Claude Benveniste Aventus Design Ltd Samples SPT Strata Comments Type Depth[m] [N] depth [m] Report No: Strata Description Legend BH commenced on 15 July 2009 D D TOPSOIL [within raised planting bed] MADE GROUND: grey/brown slightly humic clayey sand with brick fragments Service pit excavated to 1.20m BH/casing dia: 150mm BH cased to 2.00m S D D U 2.00 D 2.45 MADE GROUND: soft dark grey and brown slightly organic clay with brick fragments, occasional gravel and roots Firm, locally soft, brown slightly silty to silty CLAY with occasional gravel. Locally very silty and sandy. Roots observed to about 3m depth 2 D S D Firm becoming stiff brown fissured CLAY with blue/grey gleying, occasional partings of silt/fine sand and scattered selenite crystals 4 U D S D D 7.50 U D S D Stiff becoming very stiff grey fissured CLAY with scattered selenite crystals 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 :- Note that the borehole was located within a raised planting bed - all depths refer to this bed level which lies 0.30m above general Borehole No: ground level [Scale = 1:50] 10 BH 1

9 Contract & Location Borehole No: Client Sheet 2 of 2 1 Engineer 13 Aubrey Walk, London W8 7JH BH 1 Claude Benveniste Aventus Design Ltd Samples SPT Strata Comments Type Depth[m] [N] depth [m] Report No Strata Description 0 Legend End of shift: 15 July BH depth: 11.00m - casing depth: 2.00m - water depth pm: dry BH continued: 16 July water depth am: dry U D Stiff becoming very stiff grey fissured CLAY with scattered selenite crystals S D D U D x S D D U D S D U Borehole dry D End of borehole at 20m 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] 20 BH 1

10 Contract & location Report No: 13 Aubrey Walk, London W8 7JH IN SITU STANDARD PENETRATION TEST RESULTS Borehole No: Start depth [m] Test Type Blow counts per 75 mm SPT (N) Remarks BH S S S S S S S [SPT Sheet 1 of 1]

11 S OIL C ONSULTANTS L TD Haven House Albemarle Street Harwich Ground investigation Geotechnical analysis Environmental appraisal Essex Tel: Fax: harwich@soilconsultants.co.uk CO12 3HL Contract & location 13 Aubrey Walk, London W8 7JH Report No: LABORATORY TEST CERTIFICATE - Index Properties Sample Depth Moisture Liquid Plastic Plasticity Percent location [m] Sample Description Content Limit Limit Index Passing Remarks [%] [%] [%] [%] [425μm] BH Brown slightly silty CLAY with occasional gravel > Brown fissured CLAY > Grey fissured CLAY > Grey fissured CLAY >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 [Index property Sheet 1 of 1]

12 Contract & location 13 Aubrey Walk, London W8 7JH Report No: TRIAXIAL COMPRESSION TEST RESULTS Key : 38, 102 = dia in mm, U=Undrained, M= Multistage, MC = Moisture Content, QD = Quick Drained Test Borehole No: Depth [m] Test Type Cell Pressure [kn/m 2 ] Comp Strength [kn/m 2 ] Bulk Density [Mg/m 3 ] Moisture Content [%] Cohesion [kn/m 2 ] Angle of Friction [deg] Remarks U U U U U U U Disturbed sample [Triaxial Sheet 1 of 1]

13 S OIL C ONSULTANTS L TD Haven House Albemarle Street Harwich Ground investigation Geotechnical analysis Environmental appraisal Essex Tel: Fax: harwich@soilconsultants.co.uk CO12 3HL Contract & location 13 Aubrey Walk, London W8 7JH Report No: LABORATORY TEST CERTIFICATE - Sulphate Analysis Sample SOIL WATER Depth location Sample Description SO 4 SO 4 ph Remarks [m] [mg/l] [mg/l] BH Brown slightly silty CLAY with occasional gravel Brown fissured CLAY Grey fissured CLAY Grey fissured CLAY 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 [Sulphate Sheet 1 of 1]

14 Contract & location 13 Aubrey Walk, London W8 7JH Report No: Undrained cohesion/spt versus depth Undrained cohesion - triaxial [kpa] Made ground Superficial clay 5 London Clay Depth [m] [Note: SPT plotted using undrained cohesion = 5 x 'N'] SPT 'N' value Undrained cohesion - triaxial SPT 'N' value

15 Contract & location 13 Aubrey Walk, London W8 7JH Report No: Site Development Plans S OIL C ONSULTANTS L TD Ground Investigation Geotechnical Analysis Environmental Appraisal Haven House, Albemarle Street Harwich, Essex, CO12 3HL T: F: E: harwich@soilconsultants.co.uk

16 Contract & location 13 Aubrey Walk, London W8 7JH Report No: Site Plan [Fieldwork: July 2009] Indian Bean tree [6m] [Retained side] BH-1 Retaining wall approximately 3m high AUBREY WALK Raised bed with bushes and ornamental shrubs No 13 [3-storey] TENNIS CLUB Concrete pathway 0 5m Scale = 1:125@A4 Paving Strawberry tree [6m] [Retained side] S OIL C ONSULTANTS L TD Ground Investigation Geotechnical Analysis Environmental Appraisal Haven House, Albemarle Street Harwich, Essex, CO12 3HL T: F: E: harwich@soilconsultants.co.uk

17 Contract & location 13 Aubrey Walk, London W8 7JH Report No: Location Plan SITE LOCATION Scale S OIL C ONSULTANTS L TD Ground Investigation Geotechnical Analysis Environmental Appraisal Haven House, Albemarle Street Harwich, Essex, CO12 3HL T: F: E: harwich@soilconsultants.co.uk