Slope Stability and Retaining Wall Assessment

Geotechnical Support for a Purpose-built student accommodation (PBSA) Development

Ground Projects were appointed to deliver geotechnical design support for a purpose-built student accommodation (PBSA) development, comprising four buildings of eight and nine storeys.

The brownfield redevelopment site is located on a former railway embankment, with Network Rail land forming the northern boundary and an operational railway line located approximately 10 metres from the site boundary. This proximity, combined with restricted site access, presented significant geotechnical and logistical constraints.

Ground Projects’ scope included slope stability assessments of both temporary and permanent works, together with global stability analysis of temporary retaining structures required as part of the enabling works. These works comprised a temporary contiguous piled wall to the rear of the site, a temporary access ramp to the front of the site for piling operations, and temporary L-shaped precast concrete retaining walls constructed to the east and west to support the piling rig and access arrangements.

The on-site ground conditions were challenging, with highly variable Made Ground associated with the historic railway embankment, underlain by tidal flat deposits. Due to limited ground investigation data, Ground Projects undertook a back-analysis of the existing slope to characterise the shear strength properties of the Made Ground.

Using the derived parameters, global stability analyses were completed in accordance with Eurocode 7 Design Approach 1, Combinations 1 and 2, assessing the stability of the temporary retaining walls, access ramp, and contiguous piled wall. The analysis identified potential instability of the precast L-shaped retaining walls.

A range of stabilisation options was reviewed, including enhanced wall foundations and geosynthetic reinforcement. However, these options were constrained by the small 0.2-hectare site and the projects programme.

Following consultation with the client, Ground Projects quickly developed an alternative solution involving the introduction of a stability berm at the front of the retaining walls. The tailored berm design was produced that ensured global stability while remaining compatible with the site’s restricted access and construction constraints.

This approach delivered a robust, cost-effective, and programme-efficient solution, enabling the safe progression of enabling works on a constrained and technically challenging site.