Soil & Rock Slope Stability Surveys & Modeling

Soil slopes are typically composed of the superficial soils and deposits that exist stratigraphically above rockhead level (bedrock). These may in turn be subdivided into depositional soils – soils that have been emplaced by depositional processes such as fluvial or colluvial activity, and soils that are derived as a result of in-situ weathering of the underlying bedrock. These are soils in an engineering sense (as they are typically well less than 1 Mpa in compressive strength), but they may still retain the residual macro structural features (such as bedding structure) of the underlying bedrock, and are likely to increase in strength with depth as the weathering profile recedes back to unweathered bedrock. Soil slopes tend to be at a shallower gradient as these soils have achieved a sustainable angle of repose over time, the failure of these slopes then invariably occurs as a result of the disturbance of this soil profile, typically as a result of loading, excavation or saturation, so as to overcome the interparticle cohesion (shear strength) of the soil. The nature of the slope failure is likely to depend both on the depth to rockhead and the presence of groundwater, with rotational type failure more prevalent in deeper soils (depth to rockhead) and slumping or translational type failure more likely in shallower and water-saturated soils.

Rock slopes by comparison are formed from exposed bedrock, either at natural outcrop or exposure, as would be the case in a coastal environment, or exposed through excavation, such as in a quarry setting. The rock slopes tend to be steeper, and may be vertical or sub vertical, with slope failure typically occurring as rockfall. The nature of the slope failure is defined by the quality (strength) of the rock mass and the way in which the discontinuities (joints and fractures) within the rock mass interact with each other and with the slope face. This gives rise to kinematic mechanisms of slope failure such as wedge, toppling or sliding-type failure.