The Soil: Why Shear, and not Tensile or Compressive Strength?

Soil is a complex material composed of various mineral particles, organic matter, water, and air. Its behaviour under different types of stresses can be quite different from that of other engineering materials like concrete or steel. When subjected to tensile or compressive stresses, soil tends to deform and break apart, resulting in failure. However, when subjected to shear stresses, the soil can deform without necessarily failing, and the shear strength can be a better indicator of the soil's resistance to deformation.

One relevant instance where the analysis of soil shear strength is critical is in the design of foundations for buildings or other structures. Foundations must be designed to support the weight of the structure and any loads it may impose on the soil, such as wind or seismic forces. If the soil beneath the foundation is not strong enough, it can settle or shift, leading to damage or even collapse of the structure. The shear strength of the soil is therefore an important parameter in determining the size and type of foundation required for a given structure.

Another example of where shear strength is important is in the design of retaining walls or slopes. Retaining walls are used to hold back soil and prevent erosion or landslides. The stability of a retaining wall depends on the shear strength of the soil behind it. Similarly, slopes can fail when the shear strength of the soil is exceeded, leading to landslides or soil erosion.