Geotechnical Site Investigation – Hampstead


REC was commissioned by Webb Yates Engineers to carry out site investigation works to determine the geotechnical parameters for a residential development.

It was proposed to demolish an existing 1950s two storey dwelling, in Hampstead, North London and replace it with a new two storey ‘superstructure’ with a new 3.5m deep basement beneath.

The purpose of the geotechnical investigation was to enable the design of the works to be undertaken. Two 25m deep boreholes were advanced to identify and confirm the underlying strata.

Laboratory analysis and in-situ geotechnical engineering were undertaken to enable the foundation design parameters to be properly determined, suitable for use with Eurocode 7. Suitability of various foundation types were suggested by REC including basement raft, pad or strip footings or bored, driven or mini piles. Suitability for proposed retaining walls and basement construction such as sheet piling and secant piled walls were also suggested. Groundwater and ground gas information was collected to aid design. Classification of strata was determined with regards to disposal of excavated material offsite.

REC carried out mitigation and risk assessment measures for any soil and groundwater contamination encountered during the investigation.

Challenging access considerations in to the rear garden and services and limited space at the front of the property required innovative methodology to advance the locations.

A cable percussive rig was required to reach the necessary depths to obtain all the essential geotechnical data. The only access to the rear garden was via a narrow footpath beside the property. A full cut down modular cable percussive rig technique was used and access was gained by removing a boundary fence panel. The rig was able to be moved manually over a height difference of nearly 1m in to the rear garden.

All precautionary measures were carried out to limit the impact and damage to the well establish garden. A flexible approach by REC enabled works to progress to budget and often ahead of schedule.

REC’s sub-contractor model allowed for the most appropriate drilling technique to be used to gain access without compromising the sampling depths required.