CIVIL ENGINEERING NOTES

I see it opportune here, to clarify that when we speak of earth, we are referring not only to the solid particles that compose it, but also to the content of hollow spaces or pores, which can be liquid or gaseous (water or air respectively). The percentage of each of them, in relation to the solid matter, will have an important influence on the mechanical characteristics of the terrain. Having clarified this, we are in a position to understand that the seat of a rigid foundation, on a compressible ground, occurs in two different ways:

a) By lateral sliding: Phenomenon that affects granular soils in particular (sand, gravel, etc.). The particles that form the soil immediately below the foundation, suffer a displacement towards the constants, due to the weight that impinges on it (hence the need to "box" this type of soil).

In this type of seat does not produce a reduction of the volume of the ground, but it moves until occupying both flanks of the foundation. Since this phenomenon occurs in granular soils, the lateral movement will depend on the size of the grains, since this factor determines the slip resistance of these soils. It is a phenomenon that occurs relatively quickly and its effect is more important, the smaller the section of the foundation.

From what has been said it follows that granular soils suffer a rapid seat. In case they are saturated, there will be an immediate expulsion of the water contained therein, which; when the load ceases; is not reabsorbed. Hence, they are considered to be compressible and inelastic lands.

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b) By consolidation:

In sum we can say that a non-granular soil, such as saturated clay, experiences very slow seats, since its poor permeability does not allow the rapid expulsion of water. if the incident load is removed, a slow and gradual reabsorption of the previously expelled water occurs. We therefore determine that in addition to being compressible they are also elastic, since their consistency varies with the water content.

The worst soils from all points of view and especially as regards seats, are mud and the peat, since they have the property to expel the water very quickly before the action of a charge and to reabsorb it with equal speed when that action ceases; in this they differ from the clays, in which the phenomenon is much slower. This is because the expulsion of the water is much slower, the finer the grains that make up the soil, and it is known that the type of soil with the smallest grains is the clay.

  • Adam Floyd