Soil and Rock Slope Analysis

Engineering analysis of natural and CONSTRUCTED slopes.

Natural and engineered slopes are subject to destabilising actions associated with gravity, water pressures, seismic events and surface erosion.  One or more of these destabilising actions can cause sliding, rotational failure, toppling, slope creep and surface erosion, any of which events can constitute failure. 

Slope stability considerations are particularly critical where infrastructure or buildings are located above, on or below the slope and so are potentially impacted by slope movement. Detailed consideration of slope stability is required where proposed developments may increase destabilising forces (applied loads above or on the upper slope) or reduce stabilising forces (toe excavation), the slope profile is to be steepened, changes to ground and surface water are anticipated or vegetation cover may be removed. 

As with most geotechnical engineering work it is first necessary to formulate a reliable ground model, typically requiring completion of a suitable site investigation and determination of relevant parameters such as soil/rock properties, slope geometry, applied loads, seismic design factors, surface and  groundwater conditions, geohazards/risks and project constraints. 

The nature of the soil or rock material forming the slope, and the slope geometry, will dictate the nature of potential slope failure mechanisms and so the appropriate means of analysis and Safety Factors.  Failure of steep slopes in fractured rock are generally governed by the nature, orientation and distribution of discontinuities in the rock mass and so this must be analysed.  Analysis of soil slopes will be governed by the nature of the soil and, in particular, if cohesive (clay) soils or granular (sand or gravel) soils are present.  Groundwater is also a critical factor for slope stability which must be addressed. 

Appropriate selection of analysis parameters, such as undrained shear strength and the friction angle and, if present, a cohesion intercept (c/) of granular soils, is critical to the slope assessment process.  Appropriate consideration of site specific seismic events, changes to groundwater conditions, erosion forces and possible changes to the slope properties over time are also of fundamental importance.

The CMW geotechnical team combine geological and engineering expertise, and significant slope stability experience, to develop relevant ground models, determine critical site specific parameters, complete appropriate engineering analysis of slope stability, assess associated Factors of Safety and identify risk management issues. In many cases the CMW design team extend the geotechnical scope of work to also include the identification, design and specification of optimised slope remediation, stabilisation and protection measures as well as compatible slope monitoring systems. 

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