CampbellReith was commissioned to carry out a geotechnical slope stability assessment for a number of operational ball clay pits located in South Devon and Dorset on behalf of Imerys. The objective was to evaluate the current and future stability of pit slopes and to inform any necessary remedial strategies as extraction progresses.
CampbellReith’s geotechnical team began by reviewing historical record information for each site to build a thorough understanding of the site history, geological makeup, and likely hydrogeological regime. This review informed the scoping of an intrusive ground investigation designed to gather additional information on ground conditions and to obtain high quality samples to refine the ground model and to provide characteristic geotechnical parameters for slope stability analysis.
The investigations included a combination of rotary cored boreholes, machine excavated trial pits, and hand excavated block samples as well as the installation of vibrating wire piezometers and data loggers to allow continuous measurement of the pore pressure within the slopes of the pit. Laboratory testing included a combination of shear box and consolidated drained triaxial testing, the results of which were assessed alongside data from previous phases of investigation into the ball clays to allow the selection of characteristic parameters which considered the non-linear nature of the failure envelope with varying confining pressure.
The resulting geotechnical data was input into specialist finite element software to establish the existing groundwater regime and to predict changes in the piezometric surfaces as further extraction was undertaken within the proposed pit extensions. These outputs were then fed into the slope stability models, which were completed using limit equilibrium methods to determine the critical factor of safety for the existing slopes, the proposed slopes and the final end-of-life slopes following remediation of the pits.
The outputs of the slope stability analysis were reported to the client, advising on the factor of safety of the existing and proposed slopes and identifying localised areas where remedial measures are required to maintain slope stability. The analysis provided the client with a clear understanding of slope performance under current and future extraction conditions, enabling proactive remediation and operational planning.
