Basement Impact and Ground Movement Assessment for a Deep Residential Basement in London

Basement Impact Assessment for a Deep Basement Excavation in Central London

Ground and Project Consultants Limited (GPCL) were appointed to assess the geotechnical impacts of a proposed residential development in London, comprising five terraced properties, each including a three-level basement extending to approximately 10.5 m below ground level.

The scheme involved the installation of a 450 mm diameter secant piled wall along the east, west, and south boundaries of the site. An existing garden wall to the west required underpinning as part of the works, while an existing secant piled retaining wall was present along the northern boundary, shared with an adjacent property.

The constrained urban setting and proximity to neighbouring structures required careful assessment of potential ground movements associated with the proposed excavation.

Following a review of the ground conditions, GPCL’s role was to evaluate the impact of constructing the secant piled wall and excavating the basement to a depth of approximately 11 metres below ground level.

A detailed programme of analysis was undertaken, including Finite Element Modelling (FEM) using a two-dimensional numerical model and OASYS XDISP.

The analyses were used to predict potential ground movements and assess their impact on surrounding properties. Building damage was evaluated in accordance with the Burland et al. (1977) damage category criteria and the methodology outlined in CIRIA C760.

The findings indicated that the predicted movements associated with the basement construction were within acceptable limits for the surrounding structures.

As part of the assessment, movement trigger levels were established for use during construction, and practical guidance was provided on construction methodology to help control and monitor ground movements throughout the works.

GPCL’s involvement provided the project team with a clear understanding of the geotechnical risks and ensured that the proposed development could proceed with appropriate controls in place to protect neighbouring properties.