Numerical simulation and analysis of collapsible soils

Collapsible soils are problematic porous media that, when moistened, suffer volumetric shrinkage deformations that can lead to slope instability, foundation collapse and, consequently, to structure failure. One way to analyze these soils is through laboratory tests, using oedometers or special triaxial equipment to measure stress, humidity and suction. In the literature, there are several published works considering the collapse potential of a collapsible soil in the laboratory and field. However, the necessary equipment is difficult to assemble and the tests in general are quite complicated to carry out. In addition, the results can also be difficult to interpret taking into consideration a total stress-based approach, as opposed to conventional effective stress-based soil mechanics. An alternative is the use of numerical analysis to model the behavior of unsaturated solos. This project proposes the implementation of a programmable routine code and a numerical computational constitutive model for collapsible soils, which is focused on effective stresses for unsaturated soils for the analysis of collapse potential.

The collapse of soils and foundations is a well-known phenomenon in geotechnics, occurring in some unsaturated soils whose metastable structure admits an abrupt deformation of the soil when it is moistened, even without a significant increase in the acting stresses. These soils are abundant in many parts of the world, particularly in regions located in arid zones with prolonged periods of drought with alternating rainfall. Collapsible soils have been detected in Europe, South Africa, Asia, North and South America. In Peru, some studies have also been carried out on the soils of Pisco, La Joya, Lambayeque and recently in Ventanilla, among many other places on the arid coast and also in the jungle. In most cases, collapse problems occurred in soils that had characteristics in common, such as a relatively high void ratio (or low density) and a low degree of saturation. Some studies carried out in the laboratory and in the field indicate that soil compaction can decrease the susceptibility to collapse of a soil. On the other hand, this susceptibility can be increased when the degree of soil saturation before wetting is very low. In any case, the results obtained are always analyzed through two stress variables traditionally used in unsaturated soils: net stress and suction. The problem is that the use of these variables does not allow a proper interpretation of results, particularly in the transition between unsaturated and saturated conditions. This difficulty has led to different interpretations without any consensus for the analysis of the potential for soil collapse.