Case Study: Temporary Sacrificial Cofferdam, Lalit Hotel

Temporary Sacrificial Cofferdam, Lalit Hotel

Contract No:C1061
Client:J Coffey Construction Ltd
Location:Southwark, London
Value:Approximately £410,000
Summary:Design, Supply and Installation of Sheet Piles and associated temporary propping to form a sacrificial part single/part double storey cofferdam.

Sheet Piling (UK) Ltd were employed by J Coffey Construction Ltd to undertake the ‘Design, Supply & Installation’ of sheet piles and associated temporary steelwork bracing to allow the construction of a new permanent basement as part of the luxury ‘The Lalit London’ hotel development near Tower Bridge.

The Lalit London is the conversion of a 180 year old listed building which once housed the St Olave’s Grammar School into a luxury boutique hotel formed of 70 beautifully designed rooms in close proximity to Tower Bridge.

The nature of the works were complex on this project due to the following restrictions and requirements:-

  • Construction of a double storey basement required in the front court yard of the existing building which was located adjacent to the main A200 A-Road running between Tower Bridge and Greenwich.
  • The basement was required to retain the existing foundation loadings of the existing 4 storey listed building to 2 elevations.
  • Some of the sheet piling works had to be undertaken within restricted headroom access constraints as the basement footprint extended under the main entrance porch.

Working closely with both the Consulting Engineers (URS), Main Contractor and Party Wall Surveyor, Sheet Piling (UK) Ltd proposed a solution involving a single level of bracing for the majority of the basement construction but with two levels of bracing for the double storey basement section.

Due to site restrictions and logistics of the site, the construction sequence for the overall construction of the basement was critical and consequently Sheet Piling (UK) Ltd provided detailed sequence drawings on a ‘stage by stage’ basis.

In total 226No. Arcelor Mittal GU section sheet piles were installed ranging in length from 10m to 14m together with approximately 50Te of temporary steelwork bracing.

Due to the location of the works and ground conditions, the pile line was pre-augered in advance through the River Terrace Gravels prior to installation using a Giken Pile Press c/w high pressure water jetting to assist pile driveability.

The plant used on the scheme consisted of Sheet Piling (UK) Ltd own in-house fleet of Giken UP150 Pile Presses, High Pressure Water Jetting Unit and Sennebogen Telescopic Crawler Cranes.

In the area of restricted access and adjacent to the existing Party Wall foundation, the pre-augering was undertaken using a restricted access augering rig to overcome the issue of limited headroom. The pre-augering was also only undertaken nominally in advance of pile installation so as to satisfy the Party Wall Surveyor that ‘industry best practice’ was being followed to avoid any potential for damage to the existing building.

In order to carry out pile installation in the restricted access area, the sheet piles were installed in 2No. sections and butt welded in-situ prior to installation using a Super Jet Reel for high pressure water jetting which over comes the problem created by the normal steel jetting lance.

The works were successfully completed over a 30 week period between May 2015 and December 2015