Thames Water: St. Edmunds Terrace

 

The project involved the construction of a new build 5 storey residential block plus basement level car parking.

 

 

  • Project Cost £50 million
  • Architect Squire & Partners
  • Images Fluid / Squire & Partners

The site is located adjacent to Primrose Hill Park and the Barrow Hill Reservoir. It is approximately 80m long x 50m wide and slopes steeply away from the north western corner. There is a 10m difference in level from the northwest to the southeast corner of the site. There are 3no. existing buildings on the site that will need to be demolished prior to commencement of the new development. The development is highly constrained by existing Thames Water assets. In addition there is a requirement to maintain two access routes across the site, along the western edge to the reservoir, and along the eastern edge to an abstraction borehole. A series of construction details were developed in conjunction with Thames Water with respect to the agreed Thames Water parameters.

Main issues that had to be resolved with Thames Water Utilities Limited (TWUL):

  1. Abstraction Borehole Crane Access:- 24/7 access to the abstraction borehole needs to be provided for a mobile crane capable of lifting 25 tonnes.
  2. Reservoir Access along western edge of site. An access road capable of carrying 40 tonne lorries has been designed to allow TWUL to access their reservoir site.
  3. Protection of 2 No. 36” (900mm) Diameter Cast Iron Mains:- The reservoir accessway will run over the 2no.36” diameter mains. A method for the protection of the 2no. 900mm diameter mains both during construction of the development and when the accessway is constructed has been agreed. These mains are very brittle and have ruptured several times in the recent past. These mains can only be shut down during emergencies.
  4. 2No.1000mm and 450mm Diameter Ductile Iron Mains:- Proposals currently involve re-grading site levels where possible to suit the proposed development. Our proposed method for the protection of the 2no. 1000mm diameter and 1no. 450mm diameter water mains has been agreed in principle with TWUL.
  5. 15” and 9” Mains Removal:- TWUL have agreed that these could be removed.
  6. 18” Mains Removal: – TWUL have agreed that this main can be removed.
  7. 600mm Diameter Infusion Main Relocation:- Relocation of the 600mm diameter infusion has been agreed with TWUL.
  8. EDF Substation:- It has been established that the only TWUL assets served by the on-site substation is the abstraction borehole. This is served from a switchboard in the block of flats. Therefore the flats should not be demolished until an alternative power supply is in place. A method of achieving this has been agreed with TWUL.
  9. Observation Borehole:- TWUL have agreed that this can be decommissioned.
  10. Security Fencing:- TWUL have noted that no demolition or construction work can commence on site until the existing boundary fence between TWUL retained land and the development land is upgraded.
  11. Proposed Building Overhanging Mains:- This was agreed with TWUL but we had to allow sufficient headroom so that TWUL could access the mains for maintenance in the future if required.
  12. Additional TWUL infrastructure on the Development Site:- Assets include reservoir embankment drainage, monitoring equipment and other mechanical and electrical equipment, but the only significant assets located to date are the power and telemetry connections for the abstraction borehole. Investigations are necessary to determine whether drainage at the toe of the embankment for the reservoir exists. TWUL to investigate and advise Regents Park Estates (GP) Ltd.
  13. London Ring Main and Thames Lee tunnel:- Both are approximately 3 metres in diameter and are approximately 50 metres below the surface of the site and it was established that these would not be affected by the development.

Risks

  • Possibility of rupturing major water mains. Risk of fatalities and severe damage to properties in the area.
  • Loss of water supply for significant population.
  • Damage to boreholes. Risk of contaminating aquifer.
  • Risk of destabilising reservoir embankment.
  • Risk of unauthorised access on TWUL property.

Design Procedures

  • We contacted TWUL at an early stage in the project before any design work had commenced and agreed methods of construction that would be acceptable close to water mains, tunnels and other facilities.
  • We carried out a detailed site investigation and installed monitoring equipment on the site to establish design parameters and also to confirm the location of all buried services and to confirm as-built details.
  • We had meetings with TWUL on a regular basis and their engineer’s also worked closely with us and produced a report on the feasibility of the relocating some of the major apparatus.
  • Based on our drawings, meetings, TWUL investigations and reports the feasibility and cost of the proposed works was established.