GEA completed a phased investigation on this tight and complex site in Victoria, which is directly adjacent to the London Underground District and Circle Line cut and cover tunnel. Our work comprised an initial desk study and impact assessment, followed by site investigation and ground movement assessment (GMA) for the new mixed-use development providing office and residential accommodation, public amenities, and a new ‘pocket’ park and play area for Westminster City School.

The investigation included a trial pit to confirm the form of the adjoining TFL retaining wall and its relationship to foundations of the existing residential building site and a deep borehole, drilled with a limited access rig, to prove the base of the London Clay, which was expected to extend to a depth of between 45 m and 50 m beneath the site.

We carried out a detailed ground movement analysis to model the effects of the proposed new basement and subsequent foundation on the adjacent tunnels and demonstrated that ground movement can be maintained within acceptable limits.