# Geomechanics

Geomechanics is the study of the nature of soil and rock found on the earth's surface. The term is derived from the Greek word 'geo' meaning earth, and the word mechanics, a term that refers to the study of the motion of particles.

## Two main branches – Soil and rock mechanics

Geomechanics is divided into two main branches of study – Soil mechanics and rock mechanics. Soil mechanics deals with the study of the behavior of soil in detail. Rock mechanics is mainly concerned with the behavior of rock mass and is utilized in exploring geotechnical aspects like tunneling and earth drilling.

### Soil mechanics

Soil mechanics deals with the study and prediction of the mechanical behavior of soil. This study is applied in civil engineering and the results are especially important during the design and execution of structures like foundations, embankments, underground channels and retaining walls.

The sizes of particles that make up a certain kind of soil decide the nature of soil. This is how the load-bearing capacity and compressibility can be determined, before the engineering works are carried out.

### Rock mechanics

This branch of geomechanics deals with the study of the behavior of rock masses and their interaction with forces around them. The study of rock mechanics is applied in fields like mining, petroleum and certain civil engineering activities such as building hill roads and tunnels and carrying out underground excavations.

## Terms used in geomechanics

• Effective stress of soil

The effective stress of soil is a measure of the soil to withstand shear stress. It is measured as the difference between the total stress and the pore water pressure. The total stress denotes the weight of soil and structures acting directly over the plane along which the measurement is done. This measurement is essential in geotechnical considerations of soil.

• Shear strength

Shear strength of soil refers to the maximum stress that can be applied tangentially on a plane within the mass of soil before the occurrence of sliding on that plane. The shear strength depends on the frictional resistance of the soil particles and the cohesion between particles.

• Bearing capacity

Another term commonly used in civil engineering is the bearing capacity of soil, which is the average contact stress between a foundation and the soil which will result in the shear failure of the soil.

• Rock failure

Rock failure is said to have occurred when a system or mass of rocks can no longer withstand stress and perform its intended function. Rock failure is seen in the form of fractures, distortion in rock shape and the failure in strength.