Slope stability analysis is one of the most important topics in geomechanics. 

Depending on the modeling strategy, these models can vary in complexity from simple to sophisticated. The most basic models use a fluid mass-balance equation, neglecting the soil skeleton’s deformation and the pore fluids’ thermal behavior.

Soil Properties

The properties of the soil mass influence slope stability. Among available methods, numerical modelling is the most widely used approach to study slope stability. For example, soil microorganisms play an important role in stabilizing slopes by increasing the soil’s pore space, thereby improving soil structure and aeration. This promotes root growth and improves soil fertility.

Slope movement, commonly called landslides, can damage infrastructure and cause casualties. This is typically triggered by rainfalls that exceed the soil pore water pressure or by degradation of the ground’s mechanical properties. 

It is, therefore, critical to consider the influence of the inherent variability of soil properties in slope stability analyses. This can be achieved by performing probabilistic analysis using a Monte Carlo simulation model. This approach calculates a reliability index used to conduct preliminary sensitivity analysis.

Geometry

Geometry is the study of shapes and their dimensions, like length or distance, the area occupied by flat bodies, and the volume of solids. Different geometric shapes, like polygons, pentagons, and octagons, have different angles and sides.

The geometry of slopes has a significant influence on the behavior and failure mechanisms of a pitch. For instance, if the hill is a shallow toe-to-deep mechanism, it has more choices in its path and can lead to higher instability. Similarly, if a slope is orientation dependent, it can fail circularly through new or existing discontinuities in intact rock blocks. The interactions between soil, vegetation and atmosphere cause the variation of the piezometric conditions within a slope. This generates water exchanges within the hill and changes the soil porewater pressures with time.

Environmental Conditions

Slope stability is a key concern for civil/geotechnical engineering, and various design and mitigation countermeasures can control slope movements. Slopes are often globally stable if the safety factor computed along any potential sliding surface that runs through the entire pitch (from its head to its toe) is always larger than 1.

Environmental conditions such as groundwater flow and soil pore water pressure influence slope stability. The paper discusses a sensitivity analysis of a slope under climate change, analyzing the effects of water net infiltration, degradation of soil strength parameters, water volume content and changes in pore water pressure on the slope’s safety factor during extreme rainfall. The analysis shows that the safety factor decreases continuously for three days after the onset of the rainfall event.

Hydraulic Conditions

The variability of the hydraulic properties of slope soil is a major factor affecting the infiltration of rainwater and, consequently, the landslide process. The spatial variability of the saturated hydraulic conductivity has the strongest influence on the infiltration process and, thus, on the stability of slopes.

To obtain a more realistic analysis result, it is necessary to consider the effect of the variation of hydraulic parameters on the displacement-time curves. The cyclic shear test of the rock-soil mass unit state determines the final safety factor and the position of the critical sliding surface. The strain-softening and vibration deterioration models are combined to calculate the dynamic shear stress of the necessary sliding surface and evaluate the seismic slope stability.

Time

Slope stability is affected by many factors, many of which can be attributed to natural events. However, humans can also contribute to slope failure by filling slopes, cutting and building structures in the slopes, changing the surface drainage characteristics and groundwater dynamics etc.

Using the dichotomy strength reduction method, engineers determine an upper and lower limit value of the safety factor (Kmax and Kmin) and the shear stress at the critical sliding body within the slope geometry. They then use ideal elastoplastic, strain-softening or vibration deterioration constitutive models to locate the potential necessary slip surface in the analysis.

Slope stability is crucial when designing any project, whether a roadway, railway or building. Engineers calculate the safety factor to ensure a slope is stable before construction begins.