What is soil mechanics and geotechnical engineering?

Soil mechanics is a science of engineering related to soil as a construction material. Soil mechanics is a relatively young science of which the general physical and mechanical principles were stated and understood in the 1930s-1960s. Soil mechanics is the theoretical basis for geotechnical engineering.

Soil mechanics primarily concerns the action of the interior of the soil, i.e. the reaction to external influence described by the laws of mechanics and hydraulics. Traditionally, geotechnical problems are divided into three main areas: Stability problems (the strength of the soil), deformation problems (the stiffness of the soil) and flow problems (the permeability of the soil to liquids and gasses). The soil often acts as a ductile material, which means that ruptures are not visible, but correspond to large displacements.  Only in rare cases, the rupture is visible and even catastrophic in case of landslides which involve large masses of soil.

To obtain a safe and economic foundation of a structure, you need to know the strength, stiffness and flow parameters of the soil. The parameters are measured by tests of representative soil samples from the construction site and by involvement of the science of geology, as the parameters strongly depend on the mode of formation of the soil.

In general, soil tests are much more comprehensive and costly compared to similar tests of human-made materials such as steel and concrete. Consequently, a lot of research has been carried out, and general soil models have been developed based on series of tests on a number of different soil types. The models describe the fundamental interaction between forces and displacement of the soil, i.e. to what extent the soil is deformed when affected by forces. The tests performed in connection with a specific project give information about the absolute values of the parameters, so that the soil model can be used for the project.

Translation based on: Den store Danske - Gyldendals åbne encyklopædi