Reservoir – Slope Stability and Temporary Works Assessment

Geotechnical Support for a Reservoir in North England

Ground and Project Consultants Limited (GPCL) were commissioned to undertake an independent temporary works slope stability assessment associated with the installation of sheet piles through an existing reservoir embankment dam.

The dam comprises an earth embankment, understood to incorporate a puddle clay core, which was constructed over 100 years ago.

A potential leakage was identified on the downstream face of the reservoir, necessitating remedial works to restore the dam’s watertight integrity. The proposed solution involved installing sheet piles along the length of the reservoir crest, with GPCL appointed to independently assess the global stability of the temporary works.

As part of the assessment, Ground and Project Consultants undertook a detailed site walkover together with drone-based photogrammetry. The photogrammetric survey was used to generate a high-resolution 3D point cloud terrain model, enabling accurate measurement of embankment slope angles and providing a clear visualisation tool to support discussion and review with the client.

Characterisation of the ground model for analysis was particularly challenging, due to conflicting ground investigation data regarding the composition and internal structure of the embankment. Engineering judgement was therefore required to develop a conservative and representative ground model for the stability assessment.

A global slope stability analysis was undertaken to assess the impact of the proposed temporary works loading, using GEO5 Slope software. The assessment was carried out in accordance with Eurocode 7 (EC7), Design Approach 1, Combinations 1 and 2.

The results of the analysis indicated that the proposed temporary works configuration could lead to potential global instability of the embankment, highlighting to the client the need for further mitigation measures and careful control of construction activities to ensure the ongoing safety of the reservoir during the works.