Institute of Criminology & Faculty of English, Cambridge University

Contract Details.

Client: May Gurney
Project Start date: August 2002
Project Completion: Early 2004
Overall project value: over £25m

Background.
The redevelopment of the University of Cambridge Sidgwick site involved the construction of two multi-storey structures for the faculty of English and the Institute of Criminology. Both included basements up to 5m deep. The surrounding buildings continued to be used for teaching students and building works were very congested and constrained by existing structures.

Ground Conditions.
The ground conditions comprised Made Ground and superficial Head Deposits overlying River Terrace Gravels and Gault Clay. There was also a high ground water table. There were further complications on the Institute of Criminology site, where a buried channel within the Gault clay infilled with mixed sands and clays was identified beneath part of the proposed structure.

Raison Foster Associates Brief.
To design the hard-soft secant pile walls for basement support, prepare setting out drawings and produce pile schedules for both buildings.

Hard-soft secant pile walls were designed to provide support in both temporary and permanent conditions and to achieve a seal against the ingress of groundwater into the basement excavations during construction works. The walls were also designed to support structural loads from the multi-storey structures. Propping was provided at capping beam level to restrict wall movement and reduce piling costs.

At the Institute of Criminology, the basement wall was constructed approximately 1m from the face of a 4 storey lift tower. The design allowed for the surcharge load from this tower and concern over potential tilting of the tower led to a strict deflection limit of less than10mm in this area. The wall was propped at two levels and movements carefully monitored during pile construction and basement excavation.

Over 400 hard piles, with an equivalent number of soft piles, were installed by our client May Gurney during August and September 2002 and the basement excavation was completed in early 2003.

Both buildings were completed during 2004.