Development of a Finite Element Software for Computing Stresses and Deformations in Layered Soils

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Addis Ababa University


Stress and deformation are the two most basic parameters that a geotechnical engineer deals with while analyzing or recommending foundations for any type of structure. The two correlated parameters express the reaction a soil medium exhibits upon application of loading. In the design stage, these parameters need to be estimated accurately and be checked that they lie within acceptable limits as stated in design standard codes so that the structure to be built will be able to serve its intended purpose in a safe and serviceable manner. A number of equations have been provided to compute stresses and deformations of foundation soils. These equations provide stress and deformation values as a function of the load being applied, the elastic properties of the soil, and the location of the point where it is required to find out the stress and deformation values. While computation of the unknowns is relatively easy for homogeneous soils, the problem gets more complicated for multiple-layered foundation soils. In cases of such multiple-layered occurrences, very limited equations are available and hence a geotechnical engineer is usually forced to use less accurate approximation techniques such as averaging the characteristics of the various layers into a single value. The finite element technique provides an alternative approach whereby analysis is conducted through numerical methods which give results that are comparable to the closed form solutions. In addition to its accuracy, the finite element technique has an advantage in enabling the analysis of a wide range of problem types because of its more generalized approach. This research is an applied type of research where a finite element software that enables computation of the stress and deformation values for multi-layered soils has been developed. The analysis considers linearly elastic material model for each layer. The software uses linear displacement functions and can analyze the two dimensional problems of plane strain and axisymmetric conditions. The output of the software has been compared against results of closed form solutions where available and also against output of a commercially available software. The comparison has shown that, with proper modeling and data entry, the finite element software can generate an output of very good accuracy. The role of the computer software will be limited to collecting the input parameters in a user friendly interface, solving the large number of simultaneous equations that are generated in the finite element procedure and displaying the output in a number of handy alternatives. For the whole process, the user will be expected to have a thorough knowledge of geotechnical engineering concepts and the steps being followed by the software.



Geotechnical Engineering