KINGSTONS HOUSE ENVISAGED BASEMENT CONSTRUCTION SEQUENCE

Transcription

1 Intended for J Document type Kingstons House Envisaged Basement Construction Sequence Date August, 2015 KINGSTONS HOUSE ENVISAGED BASEMENT CONSTRUCTION SEQUENCE

2 KINGSTONS HOUSE ENVISAGED BASEMENT CONSTRUCTION SEQUENCE Revision 01 Date 14/08/2015 Made by Grace Richardson Checked by Chris Papanastasiou Ref Kingstons House Envisaged Basement Construction Sequence Ramboll 240 Blackfriars Road SE1 8NW T +44 (0)

3 CONTENTS 1. INTRODUCTION 1 2. METHOD OF CONSTRUCTION 1 3. FURTHER CONSIDERATIONS Soil Conditions Network Rail Asset Protection Existing Building Foundations 3 APPENDICES Appendix 1 Sketches Outlining Envisaged Basement Construction Sequence Appendix 2 Outline Risk Assessment

4 1 of 3 1. INTRODUCTION The proposed development is situated on the corner of Station Road and Coombe Road in Kingston upon Thames. The site is not within a conservation area and none of the existing buildings currently on the site are statutory or locally listed. It is proposed to demolish the existing building to make way for a new mixed use development that will include a new purpose built two form early primary school and 25 residential units. This Report summarises a possible construction sequence for the basement construction at Kingstons House. The content of the Report is for the exclusive use of J and should not be used in whole or in part by any third parties without the express permission of Ramboll UK in writing. It should not be relied upon exclusively for decision making purposes and should be read in conjunction with all other relevant reports and drawings submitted as part of the planning application. The following information was provided by the architect to inform this Report: Architecture Initiative, Proposed Plans evels -1 & -2, Drawing No. KH-100 Rev D; Architecture Initiative, Proposed Plans evel 0, Drawing No. KH-101 Rev E; and Architecture Initiative, Proposed Section, Drawing No. KH-202 Rev A. An outline risk assessment highlighting the key design risks at this stage has been included in Appendix B. 2. METHOD OF CONSTRUCTION Reference should be made to the Ramboll sketch numbers sk001 and sk002 in Appendix A for an indicative construction sequence for the proposed basement. A piled wall such as a secant wall is the recommended form of construction for the basement with a reinforced concrete capping beam. This will allow for construction in most soil types and it will also provide a temporary barrier to groundwater during construction if the ground water levels are above formation level. A secant piled wall has vertical load bearing capacity which will allow the superstructure to be constructed directly above the capping beam. A concrete liner wall is likely to be required to meet the waterproofing requirements for a Grade 3 habitable basement. In the temporary condition, props will be required to support the wall until the ground and basement floor slabs have been constructed. In the permanent state the floor slabs will prop the piled wall. 3. FURTHER CONSIDERATIONS 3.1 Soil Conditions The site geology and associated soil design parameters will greatly influence the design of the piled wall in both the temporary and permanent condition. A full site investigation will need to be undertaken including a representative number of boreholes across the site to understand the soil strata and ground water levels. This information can then be used to inform the design and determine the lengths and diameters of piles required as well as the number of props and their locations in the temporary state. Wall and adjacent ground movement predictions can then be made.

5 2 of Network Rail Asset Protection Given the close proximity of the South West Trains railway line to the development, we would recommend early engagement with Network Rail to ensure that their requirements are incorporated into the scheme. The first stage of the formal ageement process with Network Rail is a Form A. This includes a summary of the analysis undertaken to justify the negligible impact on the rail tracks. Following this, if Network Rail do not believe that the works are sufficiently far from their assets, they may require further submission under Forms B & C. Since the proposed scheme is adjacent to the bottom of the slope that the rail lines sit on, the following analyses will likely be required to satisfy the Network Rail requirements regardless of the level of the basement: Slope stability analysis; Ground movement assessment of rails and other key Network Rail assets; Condition surveys before and after construction; and The above may include a requirement for monitoring before construction begins, during construction and for a certain time after construction has finished. The current scheme includes a basement which extends into both the track and slope support zones. Usually, the Network Rail guidelines advise that if a new structure is proposed within a 3:2 slope that starts 2.75m from the edge of the closest rail track or below a notional extension of an embankment then analysis will have to be carried out to demonstrate that the development will not affect the operation of the railway. Figure 1 shows an indicative line of influence from the rail tracks and the slope. New development (Kingstons House) South West Trains railway line ocation of Network Rail fence unknown ~ 2.75m 2 ine of influence of slope 3 ine of influence of rail tracks Figure 1: Indicative line of influence from Network Rail lines During construction the following should also be considered: Tower cranes cannot over-sail Network Rail land. Tower cranes will have to be overdesigned by 25% as will working platforms for mobile plant. Mobile cranes cannot work towards the railway if working within a collapse radius of the Network Rail boundary. Piling rigs must be perpendicular to the railway. A façade glare assessment may be required. Design and Method Statement submissions will be required for any element of temporary or permanent works that has potential to affect the railway.

6 3 of Existing Building Foundations The type and location of any existing foundations from the building that currently sits on the site are unknown. A full site survey will be required to understand the implications that this may have on the construction sequence. It should be noted that if there are existing foundations in the location of proposed piles, these will either have to be removed or piled through which have time and cost implications. The contractor should decide the preferred strategy if this is required.

7 1-1 APPENDIX 1 SKETCHES OUTINING ENVISAGED BASEMENT CONSTRUCTION SEQUENCE

8 Temporary propping KINGSTON HOUSE ENVISAGED BASEMENT CONSTRUCTION SEQUENCE STAGE 1 INVESTIGATIONS TO BE CARRIED OUT TO OCATE ANY EXISTING FOUNDATIONS PRIOR TO PIING AND EXCAVATION. IF THERE ARE EXISTING FOUNDATIONS IN THE PIING OCATIONS, CONTRACTOR TO DECIDE IF THE EXISTING FOUNDATIONS SHOUD BE REMOVED PRIOR TO PIING. PIING ASSUMED TO BE CARRIED OUT FROM GROUND EVE CONSTRUCT CAPPING BEAM 1 A A Indicative location of existing building. A full site investigation should be carried out to understand any clashes with the new and existing foundations. Any clashes may affect the speed of construction. Contractor to decide if existing foundations should be dug out or piled through. Indicative piled wall and capping beam over STAGE 2 EXCAVATUE TO JUST BEOW CAPPING BEAM INSTA FYING SHORES/TEMPORARY WORKS EXCAVATE TO BASEMENT FORMATION EVE 2 B B Temporary propping may be in the form of flying shores SECTION A-A SECTION B-B Capping beam constructed before excavation Indicative piled wall General Notes: 1. Sketches are schematic only and not to scale. 2. Sketches show envisaged sequence of construction. 3. Sketches should be read in conjunction with relevant design philosophy reports and architectural information. 4. Final construction sequence to be developed by the contractor. 5. All temporary works shown is indicative only. The contractor will be responsible for the design, erection and maintenance of all of the temporary works. Project Title Kingstons House Project N Sketch N sk001 Title Basement Construction Sequence Scale NTS Eng: Rev: Date: Checked GR 02 14/08/15 CP

9 KINGSTON HOUSE ENVISAGED BASEMENT CONSTRUCTION SEQUENCE STAGE 3 INSTA INTERMEDIATE PROPPING IF REQUIRED EXCAVATION COMPETED 3 STAGE 4 REMAINING FOUNDATIONS CONSTRUCTED WHERE REQUIRED. BASEMENT SAB AND CONCRETE SUBSTRUCTURE, CONSTRUCTED. INER WA INSTAED TO ENSURE WATERTIGHTNESS. PROPS REMOVED ONY ONCE GROUND FOOR SAB HAS REACHED SUFFICIENT STRENGTH. 4 STAGE 5 SUPERSTRUCTURE FRAME CONSTRUCTED 5 Superstructure frame Props dismantled and removed once ground floor slab has reached sufficient strength iner wall for water tightness Additional props may be required Allow for temporary openings in slab for removal of props Substructure frame Given the space constraints, it may be difficult to fit a rig in for the internal foundations. One possibility is to pile these at the Stage 1 from ground level. The piles can then be broken down during excavation. This will mean that temporary heave forces have to be accounted for in the pile design. If the piles are bored rather than CFA then the bores above formation could be filled with gravels rather than concrete and the steel cages hung at final cut off level to avoid breaking down the piles over the entire basement depth. General Notes: 1. Sketches are schematic only and not to scale. 2. Sketches show envisaged sequence of construction. 3. Sketches should be read in conjunction with relevant design philosophy reports and architectural information. 4. Final construction sequence to be developed by the contractor. 5. All temporary works shown is indicative only. The contractor will be responsible for the design, erection and maintenance of all of the temporary works. Project Title Kingstons House Project N Sketch N sk002 Title Basement Construction Sequence Scale NTS Eng: Rev: Date: Checked GR 02 14/08/15 CP

10 2-2 APPENDIX 2 OUTINE RISK ASSESSMENT

11 RISK ASSESSMENT (PP12.4) job title KINGSTONS HOUSE file ref. Stage / Section of works BASEMENT CONSTRUCTION METHOD Rev 1-04/06/2015 PD/PM approval The list of risks below is not intended as an exhaustive list. Hazards have been identified where they are project specific and as such hazards that a competent contractor would be expected to identify have not been listed. Design item giving rise to risk² Consequence of item giving rise to risk Residual risks - risks that cannot be designed out or those remaining Action to mitigate/reduce risk Action By Status 7 following risk assessment Activity /Element Item Cat¹ Nº P 1 A site specific Ground Investigation has not been undertaken. Delays due to unforeseen ground conditions; cost and programme implications. Impacting on foundation solution. P 2 The groundwater levels on site are unknown at present. Impact of Excessive and/or differential water uplift. potential dewatering/groundwater control measures of adjacent Delays due to unforeseen ground conditions; cost and structures/services. programme implications. Cost and program implications should remedial water retention measures be required. Impacting on foundation solution. Extensive dewatering measures may be required. P 3 South West Train railway lines. The new development is adjacent to the bottom of the sope that the rail lines sit on and also cuts through the expected line of influence of the rail tracks. Delays due to lengthy approval process with Network Rail. Network Rail may believe that the development will affect their assts and therefore ask for changes to the proposal or reject the proposal altogether. The close proximity of the rail tracks will dictate the construction methodology including type and location of piling rig and tower cranes. The close proximity will also affect the permanent design including the façade access and maintenance strategy, and possibly the building geometry. P/C 4 The location of all the existing services in the vicinity of the site is not known. Risk of damaging services beneath/surrounding the site during site investigation and construction works. Health and safety implications of unexpected service strike during excavation. iability through damage. Removal/re-routing of services will have cost and programme implications. P 5 Undiscovered buried obstructions and existing piles Increased costs due to hold up in construction program and increased costs for removing buried obstructions. Carry out a Ground Investigation to confirm the ground conditions Carry out a Ground Investigation to confirm the ground water level. Any excavation that extends below the groundwater level will require dewatering. Basement walls for levels that extend below the groundwater table will have to be formed by interconnecting embedded concrete or steel piles if required. Early engagement with Network Rail is advised to ensure that their requirements are incorporated into the scheme. A detailed immpact assessment should be carried out for both the slope stability and any additional impact on the rail tracks. Design and method statement submissions will be required for any element of temporary o parmanent works that has the potential to affect the railway. Desk study should be carried out to visually identify the locations of any services on or surrounding the site if the building footprint will extend close to service routes. Contractor to carry out survey prior to works to confirm location of services. Programme to ensure that all services at the sites are located, isolated and disconnected at meter where applicable before commencement of any works. Identification of requirements and scope of works issued to the health and safety site manager. ocation of existing piles to be investigated NR may not approve the scheme. Risk of damaging existing services Risk present until works complete. Client/ Engineer/ Contractor Client/ Engineer/ Contractor Client/ Engineer/ Contractor Client/ Engineer/ Contractor Client/ Engineer/ Contractor P 6 Existing public sewers potentially crossing the development site If public sewerage crosses the site then no build zones may be enforced around them or they may need to be diverted. Diversion agreements will need to be in place with Thames Water before any works can be undertaken. CCTV survey undertaken to confirm the exact location of all sewerage crossing the site. Public sewer diversions may be required. Client P 7 Basement waterproofing. Different waterproofing strategies have different build-up requirements, potential impact on basement size and construction. Structural engineer to assist Architect with waterproofing strategy where integral to the basement structure e.g. waterproof concrete admixture. Design Team / Client 1 (C) CDM / (P) Project / (E) Environmental ² Hazard consideration - harm to human health, construction, cost, project developments, breach of legislation/regulations or the natural environment 7 ive/close ramboll uk PP12.4 Designers Risk Assessment Rev 02/10 Risk Assessment for Basement Construction.xlsx Page 1 of 1