Effect of low cohesion in sandy soils on seepage-induced failure of circular sheeted excavation pits

Seepage induced failure mechanisms such as base heave and piping pose serious challenges for the stability of excavation pits in sandy soils. Conventional design approaches rely on Terzaghi's failure criterion and assume fully cohesionless behavior, yet field evidence indicates that even trace cohesion arising from fines content, partial saturation or chemical bonding can meaningfully alter seepage response. To address this gap, the present study employs hydraulically and mechanically coupled axisymmetric finite element analyses to quantify the influence of low cohesion on heave behavior of circular sheeted pits. A homogeneous sand layer is modeled with cohesion values ranging from 0 to 5 kPa, internal friction angles between 25 degrees and 35 degrees and a range of dilation angles. Model results are systematically benchmarked against classical theoretical predictions and reveal three distinct failure modes governed by the interaction of cohesion, friction angle and dilation angle. Results demonstrate that the inclusion of even very low cohesion markedly raises the critical hydraulic gradient required to initiate failure and thereby enhances pit stability. This work offers novel insight by highlighting the importance of incorporating slight cohesion and realistic dilation behavior into seepage stability assessments for deep excavations and other key geotechnical structures.