**Study of Unsaturated Soils by Coupled Numerical Analyses of Water Flow-Slope Stability**

Norma Patricia López-Acosta and José Alfredo Mendoza-Promotor

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/63903

#### **Abstract**

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DOI: 10.1016/j.agwat.2006.06.013

162 Groundwater - Contaminant and Resource Management

The geotechnical engineering, among the problems related to water flow, is specifically interested in soil and water that it contains, and also on the movement of water through their pores, in addition to the laws governing this phenomenon. A very important subject is to quantify the retention and filtration of water within the soil structure; however, the emphasis should be not only on how much water flows through the soil but also on the state of pore water pressures because this pressure, either positive or negative, has a direct influence on the stress state and changes in volume of soil. Several publications address the issue of water flow in saturated state; however, only some of them consider the flow under unsaturated conditions. In this chapter, the main emphasis is focused on the study of water flow in unsaturated soils.

Initially, the basic concepts and the main equations applicable to the study of water flow in unsaturated media are defined. Then, fitting and estimation models of soil hydraulic functions (soil-water characteristic curve and hydraulic conductivity function) necessa‐ ry to solve this type of problems are discussed. The importance of considering calcula‐ tions in the unsaturated zone of the flow region is demonstrated by the analysis of a tailings dam. It is explained how to perform two-dimensional (2D) and three-dimensional (3D) numerical analysis of water flow by finite element method (FEM) under steady and transient-state conditions, whose results are evaluated and coupled to study the stability of the structure assuming the *phi-b* linear model for unsaturated soils. Special attention to the analysis of the variations obtained in 2D and 3D models constructed with extrusions and rough topography of the site is given. Finally, important recommendations for engineering practice according to the results obtained are issued.

Some concluding remarks and recommendations of the analyses presented in this chapter are as follows:

**•** The mathematical models for estimating soil-water characteristic curve and hydraulic conductivity function are an important tool when laboratory test results

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are not available because of the high costs of these tests or the requirements of specialized equipment and personnel to perform them.


**Keywords:** water flow, unsaturated soils, numerical analysis, coupled water flowslope stability analysis, soil-water characteristic curve, hydraulic conductivity func‐ tion
