Settlement cracking
Introduction
Consolidation of a soil is a process of volume reduction of fine cohesive "Soil (engineering)" soils (plastic clays and silts), caused by the action of stresses (loads) on its mass and which occurs over a generally long time. They produce settlements, that is, vertical collapses, in constructions that can break if they occur with great amplitude. An important part of the consolidation process is linked to the expulsion of fluids present in the soil, associated with a reduction in pore pressure and the subsequent increase in effective stresses, which produce a reduction in the volume of the soil layers.[1].
Description
When observing the deposits of very soft material located at the bottom of a body of water, for example a lake, it is noted that the soil reduces its volume as time passes and the loads on the soil increase, this is called a consolidation process.
It frequently happens that during the consolidation process the relative position of the solid particles on the same horizontal plane remains essentially the same. Thus, the movement of soil particles can occur only in the vertical direction, a process called one-dimensional consolidation.
Soil consolidation is a slow process, it can last months or even years. It is an asymptotic process, that is, at the beginning it is faster, and it becomes increasingly slower, until the ground reaches a new equilibrium situation in which it no longer moves.
Failure to take this possible ground movement into account when designing a structure on it can lead to catastrophic consequences such as tilting, cracking and even collapse. In many cases it is necessary to pre-consolidate the soil before proceeding with the construction of an important work, such as, for example, a building or a road. Pre-consolidation is done on the land with a weight similar to or greater than that which it must support once the work is built. For this, an amount of earth with the equivalent weight of the work is deposited in the interested area.
Consolidation analysis
Spring analogy
The consolidation process is usually explained with the idealized model of a system composed of a spring, a cylinder with a hole and filled with water. In this system, the spring represents the compressibility or the structure of the soil, and water is the fluid found in the voids between the pores. The model was proposed by Terzaghi as a modification of a model originally suggested by Lord Kelvin for other purposes.[2].