As a first example a concrete floor of an excavation is considered. Such structures are often used as foundations of basements, or as the pavement of the access road of a tunnel. One of the functions of the concrete plate is to give additional weight to the soil, so that it will not float. Care…
In the previous chapter it has been seen that under certain conditions the effective stresses in the soil may be reduced to zero, so that the soil loses its coherence, and a structure may fail. Even a small additional load, if it has to be carried by shear stresses, can lead to a calamity. Many…
Permeability test In the previous chapter Darcyโs law for the flow of a fluid through a porous medium has been formulated, in its simplest form, as This means that the hydraulic conductivity k can be determined if the specific discharge q can be measured in a test in which the gradient dh/ds is known. An…
The hydrostatic distribution of pore pressures is valid when the groundwater is at rest. When the groundwater is flowing through the soil the pressure distribution will not be hydrostatic, because then the equations of equilibrium (6.1) are no longer complete. The flow of groundwater through the pore space is accompanied by a friction force between…
Hydrostatics As already mentioned in earlier chapters, the stress distribution in groundwater at rest follows the rules of hydrostatics. More precise it can be stated that in the absence of flow the stresses in the fluid in a porous medium must satisfy the equations of equilibrium in the form Here it has been assumed that…
Vertical stresses In many places on earth the soil consists of practically horizontal layers. If such a soil does not carry a local surface load, and if the groundwater is at rest, the vertical stresses can be determined directly from a consideration of vertical equilibrium. The procedure is illustrated in this chapter. A simple case…
On an element of soil normal stresses as well as shear stresses may act. The simplest case, however, is the case of an isotropic normal stress, see Figure 4.4. It is assumed that the magnitude of this stress, acting in all directions, is ฯ. In the interior of the soil, for instance at a cross…
Stresses As in other materials, stresses may act in soils as a result of an external load and the volumetric weight of the material itself. Soils, however, have a number of properties that distinguish it from other materials. Firstly, a special property is that soils can only transfer compressive normal stresses, and no tensile stresses….
For the description of the density and the volumetric weight of a soil, the densities of the various components are needed. The density of a substance is the mass per unit volume of that substance. For water this is denoted by ฯw, and its value is about 1000 kg/m3 . Small deviations from this value…
Porosity Soils usually consist of particles, water and air. In order to describe a soil various parameters are used to describe the distribution of these three components, and their relative contribution to the volume of a soil. These are also useful to determine other parameters, such as the weight of the soil. They are defined…