Appendix B Method Statement - Planning Alerts | UK

Job Number: 201105 30th November 2020

Revision Date Comment - 30/11/2020 First issue

ECHRO Project LTD The LINK Unit 37B, 49 Effra Road London, SW2 1BZ T: +44 7592110508 E: [email protected] W: www.echroproject.co.uk

Appendix B Method Statement Site Details 86 St Dionis Road London SW6 4TU

Clients Details Mr Jacob Parker Miss. Olivia Cartwright

Job Number: 202015 – 86 St Dionis Road

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Statement_Rev00.docx

Table of content TABLE OF CONTENT................................................................................................................................................. 1

1.0 BASEMENT FORMATION SUGGESTED METHOD STATEMENT ........................................................................ 2

2.0 SITE PREPARATION & ENABLING WORKS ..................................................................................................... 3

3.0 DEMOLITION AND STRIP OUT ........................................................................................................................ 3

4.0 BASEMENT SEQUENCING ............................................................................................................................... 4

5.0 SUPPORTING EXISTING WALLS ABOVE BASEMENT EXCAVATION ................................................................. 6

6.0 APPROVAL ..................................................................................................................................................... 8

7.0 BASEMENT TEMPORARY WORKS DESIGN LATERAL PROPPING .................................................................... 8

A. APPENDIX A ................................................................................................................................................... 9

SITE PHOTOGRAPHS ..................................................................................................... ERROR! BOOKMARK NOT DEFINED.

B. APPENDIX B .............................................................................................. ERROR! BOOKMARK NOT DEFINED.

GROUNDSURE ENVIRO INSIGHT REPORT ........................................................................... ERROR! BOOKMARK NOT DEFINED.

Figures No table of figures entries found.

Tables No table of figures entries found.




1.0 Basement Formation Suggested Method Statement 1.1 This method statement provides an approach that will allow the basement design to be correctly

considered during construction. The statement also contains proposals for the temporary support to be provided during the works. The Contractor is responsible for the works on site and the final temporary works methodology and design on this site and any adjacent sites.

1.2 This method statement has been written by a Chartered Engineer. The sequencing has been developed using guidance from ASUC (Association of Specialist Underpinning Contractors).

1.3 This method has been produced to allow for improved costings and for inclusion in the Party Wall

Award. Final site conditions need there to be flexibility in the method statement: Should the site staff require alterations to the Method statement this is allowed once an alternative methodology, of the changes is provided, and an Addendum to the Party Wall Award will be required.

1.4 Contact Party Wall Surveyors to inform them of any changes to this method statement.

1.5 On this development, the approach is: construct the underpin segments that will support the

permanent steel work insert the new steelwork remove load from above and place it onto new supporting steelwork cast the remainder of the retaining walls that will form the perimeter of the basement.

1.6 On this project, the cantilever pins are designed to be inherently stable without lateral support to the

top of the wall. However, temporary props will be provided near the head and will provide support until the concrete has gained sufficient strength. The base benefits from propping. This is provided in the final condition by the ground slab. In the temporary condition, the edge of the slab is buttressed against the soil in the middle of the property. Also, the skin friction between the concrete base and the soil provides further resistance. The central soil mass is to be removed in 1/3 portions and cross propping subsequently added as the central soil ass is removed.

1.7 A ground investigation has not been undertaken. A nearby available borehole is showing that the

soil is Weathered Kempton Park Gravel up to 8.6m BGL and London Clay below to the end of borehole at 10m BGL, soil condition firm to stiff. It is expected that at basement formation level to ground condition to be dry Ballast and Sand

1.8 The bearing pressures have been limited to 100kN/m2.

1.9 Ground Water is not expected to be encountered during the work. Retaining wall design allow for

2/3 of the height water against the retaining wall. However, contractor should allow for local dewatering, water from broken local drainage.

1.10 The structural waterproofer (not EP) must comment on the proposed design and ensure that he is

satisfied that the proposals will provide adequate waterproofing.




1.11 Provide engineers with concrete mix, supplier, delivery and placement methods two weeks prior to the first pour. Site mixing of concrete should not be employed apart from in small sections (less than 1m3). The contractor must provide a method on how to achieve site mixing to the correct specification. The contractor must undertake toolbox talks with staff to ensure site quality is maintained.

2.0 Site Preparation & Enabling Works 2.1 The property will not be occupied during the construction period. Applications will be made to

Fulham Council for permission to site a builders hoarding to the front of the property.

2.2 The hoarding is to have an overall height of 2.4m and to be painted white.

2.3 Electrically operated lights are to be fitted to the perimeter of the hoarding together with chevron

highway reflectors so that it is clearly visible during the hours of darkness.

2.4 A metal skip container is to be located within the hoarding structure for temporary storage of waste

material pending its removal and clearance from site.

2.5 Temporary water supply and electrical services are to be provided to the hoarding zone and will be

retained in a safe condition for the duration of the contract period.

2.6 Form temporary access via front elevation for the location of electrical conveyor system.

2.7 Install electrically operated 450mm wide conveyor belt to provide mechanised removal of spoil

from proposed basement zone. Initially the conveyor is to be located at floor level and inclined not exceeding 40o to the appropriate discharge height located directly over a metal waste container / skip.

2.8 Provide proprietary 110 volt power supplier complete with associated cut out fuse and the like to

the conveyor belt.

2.9 Provide flexible dust sheet protection to the discharge point on the proposed conveyor.

2.10 As the work extends to the deeper sections of the basement provide elongated conveyor sections

suitably restrained to provide mechanised spoil removal from the deepening excavation.

3.0 Demolition and Strip Out 3.1 Provide twin layer dust resistant screening at first floor level to reduce the impact of site works on

the unaffected areas of the first floor.




3.2 Isolate existing gas, electrical and water mains which may be running through ground floor structure.

4.0 Basement Sequencing 4.1 Excavate and cast pins No 01 & 02 following the below underpinning sequencing 4.7 to 4.23 and

construct the Anderton Stepoc block walls.

4.2 Proceed with temporary works to support internal walls above according to chapter “5.0 – Supporting existing walls above basement excavation” to allow for internal pad footing installation.

4.3 Install permanent steel works (Beam GB1) to support the Ground Floor walls and floor.

4.4 When possible to install required new steel beam to support walls above, proceed with temporary

works and install the new permanent steel work. 4.5 Excavate, and cast pins 03, 04 and 05 for the Anderton Stepoc block construction.

4.6 Excavate the remaining pins following the below underpinning sequencing 4.7 to 4.23 4.7 Excavate for underpin bases. Individual bases are not to exceed 1.0m in width and no two adjacent

sections are to be excavated simultaneously. Excavation sequence to pin’s following the numbering sequence on the drawing (eg. 1,2,3...).

Excavation for the next numbered sequential sections of underpinning shall not commence until at least 8 hours after drypacking of previous works. Excavation of adjacent pin to not commence until 48 hours after drypacking. 24hours possible due to inclusion of Conbextra 100 cement accelerator to dry pack mix.

4.8 Excavation of pins involves working in confined spaces and the following measures should be

applied: Operatives must wear a harness and there must be a winch above the excavation. An attendant must be present at all times, at ground level, while excavation is

occupied. A rescue plan must be produced prior to the works as well as a task-specific risk

and method statement. Working in the confined space should require a permit to work.

4.9 If the ground is stable, trench sheets can be removed as the wall reinforcement is placed and the

shuttering is constructed.

4.10 Excavate and cast floor slab. At the prescribed level form the toe section to the proposed underpin installing fabric and general reinforcement as specified on Structural Engineers details. Minimum concrete cover to reinforcement to be 50mm near soil and 35mm elsewhere.




The central soil mass is to be removed in 1/3 portions and cross propping

subsequently added as the central soil ass is removed. As excavation proceeds, place Slim Shore props at a maximum of 2.5m c/c across length of the basement. Locate props at a third of the height of the wall.

Continue excavating the next 1/3 and prop then repeat for the final 1/3. Place below-slab drainage, encased in concrete below the slab and cast

monolithically with the slab. Placing drainage on pea shingle below the slab allows greater penetration for water ingress.

Place reinforcement for basement slab. Building Control Officer and Engineer are to be informed five working days before

reinforcement is ready and invited for inspection. Once inspected, pour concrete.

4.11 Provide structure to ground floor and water proofing to retaining walls as required. It is

recommended to leave 3-4 weeks between completion of the basement and installing drained cavity. This period should be used to locate and fill any localised leakage of the basement.

4.12 To the exposed face of the excavation provide temporary propping which is to be propped back directly to the face of the retained unexcavated central soil mound.

4.13 Visually inspect the footings and provide propping to local brickwork. If necessary install sacrificial

Acrow, or pit props, and cast into the retaining wall.

4.14 In circumstances where the excavated face of the vertical pin section is deemed unstable provide

temporary propping back to central soil mound.

4.15 Clear underside of existing footing.

4.16 Place reinforcement for retaining wall stem. Drive H16 Bars U-bars into soil along centre line of

stem to act as shear ties to adjacent wall underpin.

4.17 Site supervisor to inspect and sign off work before proceeding next stage.

Engineers to check reinforcement prior to cast

4.18 Place shuttering and pour concrete for retaining wall. Stop a minimum of 75mm from the underside

of existing footing. It is essential that pokers/vibrators are used, hitting shutters is not considered adequate.

4.19 24 hours after pouring the concrete pin, the gap shall be filled using a dry-pack mortar. Ram in dry-pack between the top of the retaining wall and existing masonry.




4.20 Commence dry packing to top of vertical pin sections a minimum of 48 hours after concreting. Dry packing shall not exceed 75mm thick and shall only be placed after the underside of the existing foundation has been cleaned and regularised.

4.21 The central spoil mound is to be retained during excavation to provide suitable resistance against

lateral movement in underpin wall sections.

4.22 Following completion of all underpin bays excavate remainder of central soil mound whilst

introducing temporary lateral propping to concrete wall sections.

underpin bases and vertical sections are to be connected via steel reinforcement

starter bars casted into the adjacent concrete underpin at 300mm centres. 4.23 Concrete Testing :

For first 3 pins take 4 cubes and test at 7 days, then 14 days and inform engineer of results. Test last cube at 28 days. If cube test results are low then action into concrete specification and placement method must be considered.

If results are good from first three pins, then from the 4th pin onwards, take 2 cubes of concrete and store for testing from every third pin. Test one at 28 days, if result is low, test second cube. Provide results to client and design team on request or if values are below those required.

A record of pin poured dates must be kept on site. The location of where cubes were taken and their reference number must be

recorded.

5.0 Supporting existing walls above basement excavation 5.1 Where steel beams need to be installed directly under load-bearing walls, temporary works will be

required to enable this installation. Support comprises the temporary installation of steel needle beams at high level, supported on vertical props. This will enable safe removal of brickwork below and installation of the new beams and columns.

The condition of the brickwork must be inspected to determinate the centres of needles. Needles must be spaced at maximum 1000mm centres.

5.2 Props are to be placed on sleepers on firm ground or, if necessary, temporary footings will be cast.

5.3 Once the props are fully tightened, the brickwork will be broken out carefully by hand. All necessary

platforms and crash decks will be provided during this operation.

5.4 Decking and support platforms to enable handling of steel beams and columns will be provided as

required.




5.5 Once full structural bearing is provided via beams and columns down to the new basement floor level, the temporary works will be redundant and can be safely removed.

5.6 Any voids between the top of the permanent steel beams and the underside of the existing walls will

be packed out as necessary. Voids will be drypacked with a 1:3 (cement: sharp sand) drypack layer, between the top of the steel and underside of brickwork above.

5.7 Any voids in the brickwork left after removal of needle beams can at this point be repaired by

bricking up and/or drypacking, to ensure continuity of the structural fabric.




6.0 Approval 6.1 Building Control Officer/Approved Inspector to inspect pin bases and reinforcement prior to casting

concrete.

6.2 Contractor to keep list of dates of pins inspected and cast.

6.3 One month after the work is completed, the contractor is to contact Adjoining Party Wall Surveyor

to attend site and complete final condition survey and to sign off works.

7.0 Basement Temporary Works Design Lateral Propping 7.1 This calculation has been provided for the trench sheet and prop design of standard underpins in

the temporary condition. There are gaps left between the sheeting and as such no water pressure will occur. Any water present will flow through the gaps between the sheeting and will be required to be pumped out.

7.2 Trench sheets should be placed at regular centres to deal with the ground. It is expected that the soil between the trench sheeting will arch. Looser soil will require tighter centres. It is typical for underpins to be placed at 1000c/c in this condition the highest load on a trench sheet is when 3 No.s trench sheets are used. It is for this design that these calculations have been provided.

7.3 Soil and ground conditions are variable. Typically one finds that, in the temporary condition, clays

are more stable and the Cu (cohesive) values in clay reduce the risk of collapse. It is this cohesive nature that allows clays to be cut into a vertical slope. For these calculations, weak sand and gravels have been assumed.




A. Appendix B1 Temporary works design

Documents

Appendix B Method Statement - Planning Alerts | UK