method statement for construction of...
TRANSCRIPT
Method Statement for Construction
of Basement
Holly Cottage
Ketton Road
Upper Hambleton
Oakham
LE15 8TH
PCC Document Management
Job Number: 9500
Date of Issue: Nov 2016
Author: Peter Cole
This report has been prepared by PCC Consultants Ltd with all the reasonable skill, care and diligence within
the terms of the Contract with the client, incorporating our General Terms and Conditions
Contents
Contents ............................................................................................................. 1
1INTRODUCTION .............................................................................................. 1
1.1Instructions ......................................................................................................................... 1
1.2Basis of Report ................................................................................................................... 1
2DESIGN PARAMETERS .................................................................................... 2
2.1Geology and Ground Conditions ............................................................................... 2
2.2Layout of Basement ......................................................................................................... 2
2.3Construction Methods .................................................................................................... 3
2.4Conclusion ........................................................................................................................... 4
3APPENDICES .................................................................................................... 5
3.1APPENDIX 1 – Key Plans & Typical Section ............................................................ 5
3.2APPENDIX 2 – Trial Hole Logs – Mary’s Cottage Gable Wall ........................... 9
1 INTRODUCTION
1.1 Instructions
PCC Consultants have been instructed by Grange Developments Ltd. In
connection with the planning application for the construction of a new
dwelling known as Holly Cottage, Ketton Road, Upper Hambleton,
Oakham, LE15 8TH.
This report provides a method statement for the safe construction of a
basement adjacent to a listed building known as Mary’s Cottage located
to the West of Holly cottage, and Gwithian located to the East.
1.2 Basis of Report
This report has been prepared from architectural drawings supplied by
Origin Design Studios and a trial hole investigation undertaken by
subcontractors employed by Grange Developments Ltd.
A proposed sequential process for the construction of the basement is
included in the appendix of this report. We have considered within this
report options for the safe construction of the basement and our proposal
is based upon the considerations of safety, practicality and cost.
2 DESIGN PARAMETERS
2.1 Geology and Ground Conditions
The site of Holly Cottage is located at grid reference SK 90287 07561. The
geology of the location obtained from the British Geological Society maps
indicate that the site is underlain by solid geology comprising the
Northampton sand formation comprising sandstone, siltstone and
mudstone. Trial hole excavations on the site have confirmed a layer of
fragmented ironstone overlying stiff blue clay.
The geology of the site dictates the form that any temporary works and
construction method should take.
2.2 Layout of Basement
Architectural drawings indicate that the basement is set back from the
front elevation of the proposed dwelling. This layout ensures that the
basement will not be constructed immediately adjacent to the sensitive
listed building on the West boundary and sufficiently far from the
property on the eastern boundary (3.5 m) such that no special provisions
are required for the eastern side of the basement (the Part Wall (etc) Act
1996, 6 metre rule does not apply as the basement excavation and
retaining structure will not extend below a line drawn at 45 degrees from
the near face of the existing adjacent foundation). Therefore to the north,
south and east, no specific precautions need to be taken for the
construction of the basement retaining structures except as required to
comply with normal site safety standards such as setting an appropriate
angle for excavation, provision of adequate working space, and
appropriate guarding at the top of the excavation.
The south west corner of the basement is located at a distance of 2.25
metres from the rear left hand corner (north east corner) of Mary’s
Cottage and accordingly it will be necessary to take appropriate steps to
ensure that the construction of this corner of the basement (and the
whole of the west wall of the basement as this runs parallel to the newly
constructed boundary wall) is carried out in a safe manner.
1.1 Construction Methods
There are three methods of construction that have been considered for
the formation of the west retaining structure. These are;
1. The use of sheet piling. Sheet piles can be installed using low
vibration driving methods. The use of sheet piling can produce a
quick and effective temporary or permanent retaining structure. In
this instance the presence of siltstone/ironstone will not allow the
installation of the piling without extensive excavation and
backfilling first. Any rock obstructions will cause deflection of the
piles and may lead to substantial vibration or disturbance. Sheet
piling is not considered viable.
2. Contiguous bored piling. The comments made above regarding
the presence of siltstone/ironstone apply similarly to bored piles.
3. Progressive excavation and mass concrete filling. With
foundations excavated below the level of the base slab and set to
one side of the retaining structure, excavation of 2.5 to 3m long
foundations will allow for the safe installation of a temporary
retaining structure. Each section will be formed with a “Toggle”
joint to ensure adequate key between adjacent sections to ensure
stability and continuity of the permanent works. The use of a long
reach digger will allow for the progressive installation of a
“diaphragm” wall. This would include returns at the front and rear
of the basement, which would be installed first as noted upon the
attached sketches in Appendix 3.0 of this method statement.
Excavation behind the diaphragm wall will be undertaken only
when a waling beam is in place, and use can be made of a capping
beam in the zone of the foundations to provide this waling beam.
During the process of excavation and particularly when
constructing those legs adjacent to Mary’s Cottage, use should be
made of trench boxes to ensure that the sides of excavations are
properly restrained.
The basement floor will be constructed sequentially in co-
ordination with the excavation of the basement void. The
basement slab will be part of the foundation construction and
provides the support to the load bearing inner skin and internal
walls.
1.2 Site Drainage
Trial hole logs indicate the presence of ground water particularly at the
interface between the ironstone and the clay. This has been highlighted
by Stephen Johnson, the consulting engineer who has been appointed by
the owner of Mary’s Cottage. The basement excavation will necessitate
the process of dewatering, and taking into account the need to maintain
stability of excavations, well point de-watering would be prudent. Well
point dewatering should be installed as soon as possible to a depth of
approximately 4.0m below ground level and for a period that will ensure
that water is not a factor during the excavation of the diaphragm
construction.
2.3 Conclusion
Sectional construction of a mass concrete diaphragm construction will
provide a safe temporary retaining structure permitting the formation of
the basement. The construction will ensure that there is no disturbance to
the adjacent listed building.
The proposed mass concrete reinforced diaphragm wall will provide a
permanent stability and support to the adjacent foundations of Mary’s
Cottage.
P J Cole BSc CEng FIStructE MICE
PCC Consultants Ltd., Chartered Structural Engineers
Signed:
28 November 2016
Amended 11 January 2017
3 APPENDICES
3.1 APPENDIX 1 – Key Plans & Typical Section
Key Plan
Proposed Permanent Mass Concrete Sectional Diaphram Wall Plan
Proposed Section to Permanent Mass Concrete Sectional Diaphram Wall Plan
3.2 APPENDIX 2 – Trial Hole Logs – Mary’s Cottage Gable Wall