Geotechnical engineering or simply geotechnics is the branch of geological engineering and civil engineering that is responsible for the study of the mechanical, hydraulic and engineering properties of materials from the geological environment, applied to Civil Engineering works. Geotechnical engineers investigate soil and rocks below the surface to determine their engineering properties and design foundations for structures such as buildings, bridges, dams, and hydroelectric power plants. Actions in the road branch such as the stabilization of slopes "Slope (engineering)"), design and construction of tunnels and roads, design and construction of any type of containment structure for the prevention of geological risks, etc.

Therefore, geotechnical engineers, in addition to fully understanding the principles of mechanics and hydraulics, need a clear and adequate command of the fundamental concepts of geology and geophysics. It is especially important to know the conditions under which certain rocks were created or deposited as well as their appropriate classification, their age in millions of years, and the subsequent structural or diagenetic processes (metamorphic processes, substitution, crystallization, folding, faulting, etc.) that they have undergone.

Designs for structures built above ground include shallow foundations (footings and slabs), semi-deep foundations (slabs and caissons), and deep foundations (piles and piles). Dams and dams are structures that can be built of soil or rock and that for their stability and watertightness depend largely on the materials on which they are based or by which they are surrounded. Finally, tunnels are structures built through soil or rock and whose construction method depends largely on the geological characteristics of the terrain that will be affected (types and conditions of lithologies crossed, hydrogeological conditions, tectonic conditions, etc.), which in turn influences the duration of the work and its costs.

Geotechnical engineers also investigate the risk to humans, property and the environment from natural or human-induced phenomena such as landslides, land subsidence, mudflows and rock falls (mass removal processes), as well as measures to mitigate this risk, such as designs of containment structures (anchors and walls), control of infiltration water and runoff in the geological environment. (subdrains, gutters, filters).