When an underground structure is built a redistribution of the natural initial stresses takes place. Due to this redistribution, the underground structure will be subjected to a certain level of stresses and hence loads that will depend very much on the geomechanical characteristics of the existing ground.
So, in the case of underground structures made in soil the supporting role will be done almost completely by the structure itself, whereas in the case of rock masses it is a combination of rock and structure that will withstand the stress redistribution in the ground.
So, in order to design the underground structure, it will be necessary to take into account the geotechnical characteristics of the ground, the in-situ natural stresses and the construction procedure that will be followed. This is a complex analysis that can be achieved in different ways, depending on the level of approximation needed.
There 3 main ways by which these parameters can be derived: