Analysis of a slip on a long natural slope

Purpose of calculation:
A slip has developed in a long natural slope, determine the FoS along the slip plane using the critical state parameter, and the residual strength parameter. Analysis the stability of the slope using the limit state method.

Calculation Reference
Craig's Soil Mechanics

Calculation Validation
Reproduction of a sample calculation from a published calculation reference.

Calculation Reference

Geotechnics

Craig's Soil Mechanics

The stability analysis of a slope using the limit state method following Craig's Soil Mechanics involves assessing the shear strength of the soil and comparing it to the shear stresses acting on the slope. The analysis is based on the following assumptions:

1. The soil is homogeneous and isotropic.
2. The soil is in a state of critical equilibrium, meaning that the shear strength of the soil is just sufficient to balance the shear stresses acting on the slope.
3. The soil strength is independent of time and deformation.

The analysis can be performed in the following steps:

1. Determine the soil properties, such as the soil type, unit weight, angle of internal friction, and cohesion.
2. Calculate the shear stresses acting on the slope due to the weight of the soil, groundwater pressure, and any external loads or surcharges.
3. Calculate the shear strength of the soil using the Mohr-Coulomb failure criterion, which relates the shear stress and normal stress on a plane of failure to the angle of internal friction and cohesion of the soil.
4. Compare the calculated shear strength of the soil to the calculated shear stresses acting on the slope, using a factor of safety. The factor of safety is the ratio of the shear strength to the shear stress, and it should be greater than 1.0 to ensure the stability of the slope.

The analysis can be further refined by considering other factors, such as the presence of tension cracks, the effect of weathering and erosion, the effect of pore water pressure, and the effect of seismic activity. The analysis can also be performed using computer software or spreadsheet programs, which can provide more accurate and efficient results.

Overall, the stability analysis of a slope using the limit state method following Craig's Soil Mechanics provides a rigorous and systematic approach to assess the safety and stability of a slope, and to design appropriate slope reinforcement and stabilization measures if necessary.