Soil mechanics

The soil mechanics is a discipline belonging to the Techniques of civil engineering which has as an aim the study of materials made up of particles solid, liquid, and gas which form the loose grounds, and this in preamble with the Calcul of foundations for the construction of building or any other civil engineer work (bridge, road, tunnel, stopping,…). This discipline thus excludes the behavior from the rocks, which are studied within the Rock mechanics . (Also Let us note the existence of the term of Géomatériaux cemented to indicate intermediate materials between the movable grounds and hard stones). This discipline is used more largely in Géotechnique, discipline and profession treating of the interaction ground-structure.

The ground is thus movable and compressible. These Characteristic soil mechanics founds the great principles of and the installation soil mechanics of the foundations of the works.

We are accustomed to perceive the whole of our environment built like a rigid, real unit. We thus observe a contradiction: would our buildings be built on a movable matter? In order to raise this contradiction, it is necessary to make two note:

the concept of rigidity is valid only relative with more flexible structures. It is the report/ratio of the moduli of elasticity of two materials which make it possible to determine whether one can consider, locally, one of both like rigid and the other like rubber band.
If a ground must be considering, in a theoretical way, like common excavations, this aspect of deformability has its limits. The purpose of the techniques of implementation of the foundations will be final to bring the ground to its limit of deformability (consolidation). (Maintains It of a ground under the conditions of the limit of deformability is not guaranteed. The presence of water moving in the ground is source of structural modifications and can represent a risk as for the stability of a ground.)

It is thus necessary to reflect in two times:

a ground will thus be regarded as piece of furniture during the phases of rehandling, and
like incompressible after effort of consolidation.

This optics will enable us to build side by side, at time different, works of different weights, without fearing to endanger stability, nor maintains it esthetics.

Basic concepts

The soil mechanics defines first of all, to build the models which will be useful for him, of the concepts which are clean for him. One thus considers a sample of ground made up of a solid phase , a phase Liquide, and of a gas Phase.

the solid phase is also called solid Matière, or Grains, the abbreviation which relates to it in the mathematical notations is “.
the liquid phase is, as for it, mainly made up of water, with the common direction of the term. Its abbreviation is “W”.
the gas phase is generally made up by the air of the atmosphere. In the first time, the case of natural gas under pressure is not studied. The weight of the air is neglected in calculations.

Together, the phases liquid and gas constitute what it is agreed to call the Vides, in opposition to the solid matter of the grains.

One first of all defines volumes related to the components of a sample:

the volume of the sample untreated is noted Ve .
the volume of the solid matter constituting the grains, also called volume of the grains, is noted Vs .
the volume of liquid , otg is noted VW .
the volume of the vacuums , made up of the sum of the volume of water (liquid phase) and of the volume of air, is noted Vv .

Then the definitions come from the weights of these components:

the weight of the sample untreated , also called weight apparent, and noted Wh . (H for “humid”)
the weight of the grains , or weight of the solid matter, is noted Ws .
the weight of the liquid , equivalent, by general assumption, with the weight of water present in the sample, is noted Ww .
By assumption, also, the weight of the gas phase is regarded as null. There is thus no symbol which is dependant for him.

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