Case Study: Temporary Sacrificial Sheet Pile Cofferdam, Phipp St, London

Temporary Sacrificial Sheet Pile Cofferdam, Phipp St, London

Contract No:C1166
Client:HG Construction Ltd
Value:Approximately £420,000
Summary:Design, Supply and installation of sheet piles and associated temporary propping to form a sacrificial sheet pile cofferdam to facilitate the construction of the permanent RC basement.

Sheet Piling UK (Ltd) were employed by HG Construction Ltd to undertake the design, supply and installation of sheet piles and associated temporary steelwork bracing to allow a 5.80m excavation depth for the construction of a new permanent basement as part of a new 5 storey development.

The site is bounded by roads to all elevations and is also in close proximity to 3rd Party properties. This involved complex liaisons and discussions with several Party Wall Surveyors and the Local Highway Authority to ultimately achieve the Clients Engineers design requirements. This required a tightening of the specified deflection criteria and on-going monitoring of the existing properties during both installation and excavation works to satisfy all concerned parties.

In total 320No. Arcelor Mittall GU section steel sheet piles were installed ranging in length from 10.0m to 13.0m together with approximately 100Te 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 using a tracked telescopic leader rig complete with auger motor.

Where required pre-augering was only undertaken nominally in advance of sheet pile installation to satisfy the Party Wall Surveyor that “Industry Best Practice” was being followed to mitigate any potential for damage to existing buildings. Throughout the process the existing buildings were continually monitored.

The installation plant used on the scheme consisted of the Giken UP150 silent vibration free sheet pile press c/w water jetting unit and 50Te Service Crane.

Due to the restricted nature of the site the Main Contractor requested that the temporary propping be installed in a sequential and timely manner to enable access into and excavation of the cofferdam.