Pell Frischmann
145 Kensington Church St
Construction Method Statement
In support of a planning application for
145 Kensington Church St
Introduction to Statement
Introduction to Pell Frischmann
Evidence of Competence & Resources
The Site & Existing Structure
Geology - Soil Conditions & Foundations
Proposed Plans
Design Principles
Designers Risk Assessment
Sequence of Construction
Impact on surroundings
Slope Stability
Impact on Hydrology
Prepared by
J. P. Chantler
M.A., C.Eng., MICE.
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Introduction to Statement
This Statement has been prepared to identify the relevant issues relating to the design of the
basement for the proposed development and forms a Construction Method Statement as
required by the Local Authority the Royal Borough of Kensington and Chelsea.
The design consultant referred to in this Statement will be the consultant who will be
responsible for the design of the sub-structure.
Introduction to Pell Frischmann
We are one of the UK's leading firms of consulting engineers, with major operations
throughout Europe, the Middle East and Asia. Since our establishment over 82 years ago, we
have grown into a worldwide organisation with more than 1300 staff and an annual turnover
approaching £50 million. In the UK we have 16 regional offices offering multi-disciplinary
engineering consultancy services spanning the whole construction industry.
We specialise in the structural design of buildings for retail, hotel, leisure, commercial,
residential, medical, educational and defence purposes. We also have extensive experience
in unlocking development potential through the regeneration of brownfield sites and air rights
projects. From the refurbishment of historic buildings to new builds, our expertise is in long
spans, deep basements, tall buildings and buildability.
Evidence of competence and resources
Details of Organisation
Name:
Address:
Contact:
Pell Frischmann
Head Office
5, Manchester Square
London, W1U 3PD, United Kingdom
Tel: +44(0) 20 7486 3661
pflondon@pellfrischmann.com
John Chantler
Nature of Organisation
Consulting Engineers
Membership of Professional Bodies
J P Chantler
M.A., C.Eng., M.ICE.
Professional Indemnity
Details available on request
Details of Persons to be employed
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J. P. Chantler on behalf of Pell Frischamann
Familiarity with construction processes
The Directors have extensive experience in the design and construction of historic and new
buildings including underpinning, basement construction, risk appraisal, geotechnical
engineering and hydrology.
Awareness of relevant Health & Safety and Fire Regulations
Within the Company we have documentation relating to these matters which are regularly
updated and circulated among the Directors and members of staff.
Health & Safety Practices
A copy of the Company’s Health & Safety Policy is available upon request.
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Management systems
A Project Director is responsible for the design and resourcing of the project. All work is
undertaken in accordance with our accredited Integrated Management System.
Resources
Chartered Engineers, engineers and Technicians will be resourced as required under the
supervision of the named Director.
Use of technology
We use state of the art design, analysis and BIM 3D software, all working to current
Eurocodes.
Residual risks
Residual risks are clearly stated on the tender and construction drawings.
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THE SITE
The site is situated between Edge Street to the south, Kensington Place to the north and
fronts on to Kensington Church Street to the east. There is a party or boundary wall with the
immediate neighbour to the west. This property is a residential three storey building in brick.
The existing building on the site has a brick facade and it probably has a concrete frame.
PROPOSED DEVELOPMENT
The architectural drawings are presented in appendix 1 showing the plan and section of the
proposed buildings.
A three level basement is planned with ground plus five levels above.
GEOLOGY - SOIL CONDITIONS & FOUNDATIONS
A site specific investigation has been carried out by RPS and is presented as Appendix 1. It
contains a Phase 1 desk study as well as borehole information.
Referring to the British Geological Survey Maps it appears that the site is underlain by Made
Ground, Lynch HIll Gravel and London Clay.
Archive data from the BGS is available to the north, east and south of the site. It is presented
in the calculations appended. Whilst the geology maps indicate that the site should be at the
edge of an island of gravel over clay, Fig 1, the BGS data confirms the expected profile and
indicates that the likely depth to the London Clay is less than 10m.
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Figure 1 Extract of BGS Geology Plan 1:50,000
Due to the presence of the building and services only one borehole was able to be bored.
This revealed:0
1.8m Made Ground
1.8
5.0m Sand & Gravel (Lynch Hill Sand & Gravel)
From the adjacent data a pessimistic assumption of London Clay level (i.e. taking a lower
horizon) is that the London Clay is present at 10m below Ground Level.
SPT tests in the gravel indicate that the upper levels are loose to medium dense (N approx 10)
becoming dense to very dense below about 2m. (This accords with the authors experience of
a major basement excavation on a property in Kensington Palace Gardens and the adjacent
reports which indicate dense to very dense).
The London Clay is stiff at its horizon with a cohesion in excess of 100kPa which is
normal beneath the relatively thick gravel.
The excavation for the basement will cause an unload of approx 200kPa. The pressure
exerted by the building will be approx 110kPa. If the base of the raft is drained the reduction
in effective stress will be approximately 60kPa which is expected to give rise to a long term
heave of 15mm at the centre of the raft or less than 10mm at the perimeter. A no fines layer
beneath the raft will therefore be provided with a sump and pump. The quantities will be small
due to the relative impermeability of the London Clay.
GROUND WATER
The geotechnical investigation showed that the water table was deeper than 5m bgl. From
adjacent records it will be taken at 7mbgl for the SLS design case. For the ULS cases it will
be taken at 1m bgl.
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To guard against seepage into the basement a drained cavity is being provided inside a
secant pile concrete wall.
IMPACT - HEAVE & SETTLEMENT
In order to safeguard the adjacent properties the new basement will be excavated after the
installation of an embedded piled wall with stiff props to minimise ground movement. The
piled wall provides both temporary support during excavation and permanent support. This is
a common engineering solution often used to safely construct deep basements. The piled
foundation will be constructed using a piling rig which uses a rotary drill to excavate the piles
without vibration.
The design predicts wall movements of less than 25mm. The effect of the unload will be to
cause minor ground movement remote from the site with the piled wall tending to restrict
vertical movement on the party wall. Settlements and movements of the adjacent property
are therefore predicted to be of the order of up to 15mm.
Active monitoring will be carried out to ensure that the performance of the wall and propping
system is known. This will allow the contractor to amend his approach should the trends be
indicating that the movements may become unacceptable.
The orders of movement are not considered to be of significant impact on buried services and
utilities.
The LUL tracks are in a cutting some 19m to the west of the development. This is considered
sufficiently distant not to be affected. There will be a need to enter into discussions with the
LUL outside parties engineers to ensure that they are in agreement with this.
INSTABILITY
Since the ground surface is relatively level in this area there will be no implications for
slope stability. Satisfying the requirements for safe basement construction will cover
this.
FURTHER INVESTIGATIONS
It is recommended that, post demolition, further boreholes are drilled to confirm the
stratigraphy laterally and to provide detailed geotechnical parameters for final foundation
design. to investigate the geotechnical properties of the soil.
It will also be necessary to excavate some trial holes adjacent to the neighbouring property to
determine its foundations type and depth. Given the age of the building it is probable that it is
supported on traditional strip foundations.
Please see Appendix 7 for Design Principles & Criteria and Design Risk Assessments, and
Appendix 8 for a typical Sequence of Construction.
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The secant pile wall should be at least 225mm from the existing foundations. (See Appendix
6)
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APPENDIX 1
ARCHITECTURAL DRAWINGS
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APPENDIX 2
RPS SITE INVESTIGATION REPORT
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APPENDIX 3
LUL INFORMATION
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APPENDIX 3
BASEMENT DESIGN CALCULATION
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APPENDIX 5
MAP SHOWING LOST RIVERS OF LONDON
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The Site
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APPENDIX 6
SKETCH A12741-VAA-SK01
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APPENDIX 7
DESIGN PRINCIPLES AND CRITERIA
DESIGNERS RISK ASSESSMENT
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Design principles
Basement box structure
Inside the piled wall will be a drained cavity to provide a class 2/3 habitable environment. If
contiguous bored piles are preferred, it will be necessary to apply a concrete lining wall to
ensure sufficiently water resistant construction.
The secant pile wall will support the full surcharge from the foundations of the adjoining
buildings to ensure only negligible damage to the superstructure of the building.
The wall and floor slab system will prop the secant pile wall.
Concrete
Concrete should specified by the design consultant in accordance with the engineering
design requirements. Concrete grades should be clearly specified on the construction
drawings.
Foundation
The lowest concrete slab will form a raft foundation with the structural capacity to support the
floor, wall and superstructure loads.
Superstructure
The superstructure will be designed and constructed using a cast in-situ reinforced concrete
floor supported on concrete columns and\or blockwork walls.
Design criteria
All to current Eurocodes and UK National Annex.
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Designers risk assessment
Hazards & risks which cannot be designed out
Potential Hazards
Falls from Height
Rating
Action Required
Works being carried
out - provide hand rails
and access scaffolding
to all openings.
Residual Riskt
Medium
High
Falling Debris
High
Works carried out
beside public
pavements. Provide
hoardings, toe boards,
netting and protection
fans.
Lowh
Materials Storage
Medium
Existing roofs and
floors are not to be
used for storage of
materials without
reference to the
Engineer or for
supporting access
scaffolding.
Low
Lifting of Steelwork
High
Steel sections to be
lifted using mechanical
means where unable
to be manually lifted.
Medium
Erection of Steelwork
High
Contractor responsible
for providing method
statement for erection
procedure, including
any temporary
bracing.
Medium
Lifting of Timber
High
Timber rafters and
joists to be lifted using
mechanical means
where unable to be
manually lifted.
Medium
Fixing of Timber
Medium
Timbers to be fixed in
accordance with good
building practice.
Low
Use of Cutting
Equipment – Flame or
Disc.
High
Fire risk - use suitable
protective methods –
remove inflammable
materials.
Medium
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Painting
Low
Touch up steelwork
with primer – take
precautions against
vapour inhalation, eye
and skin contact and
fire. Wear protective
clothing.
Take precaution
against collapse of
excavation and
hazards of persons
falling in.
Low
Excavation
High
Precast Concrete units
High
Lift into position using
mechanical
assistance.
Storage at ground
level in a safe manner.
Medium
Insitu Concrete
Construction
Medium
Low
Formwork/Falsework
Medium
Take precautions to
prevent skin/eye
contact. Protect public
and site staff from
falling objects and
spillage. Ensure
adequate care when
fixing reinforcement.
Design temporary
works
in a manner that
makes allowances for
all loadings, including
accidental loads.
Ensure adequate
vertical and diagonal
bracing. Supports
not to be removed until
period specified.
Medium
Medium
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APPENDIX 8
SEQUENCE OF BASEMENT CONSTRUCTION
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
Construct temporary guide wall
Construct secant bored piles to create an embedded perimeter wall.
Trim piles, remove guide wall and construct pile capping beam.
Excavate to first prop level and install horizontal shoring.
Excavate to second temporary prop level and install second prop
Excavate to third temporary prop level and install third prop
Complete excavation and instal no fines layer and in/under raft drainage.
Place rebar and place concrete for raft by pump.
Commence columns and walls upwards, each slab forming a permenant prop to the
wall, removing the temporary props as they become redundant.
Cast ground floor slab.
Provide cavity floor and block walls to basement box.
Complete superstructure.
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