Three-Dimensional Finite Element Numerical Analysis of Closely Spaced Foundations Resting on Clay Soil Supported with a Geocell Mattress Embedded in a Fly Ash Layer

Abstract

This dissertation studied several models supported by a geocell mattress filled with fly ash material as a filling material on top of a clay soil bed. Two square rigid steel plates presenting footings with different spacing between them were subjected to loading. The effect of spacing between footings on the function of the system was investigated by measuring the footings load and settlement. In the past, limited cases were studied for closely spaced footings. The subject of two closely spaced footings on clay soil supported by geocell has not been researched before. Most of the previous research was on sandy soil; however, clay soil is more critical and worth investigating due to its weakness and induced settlement behavior.

In addition, several numerical models were tested, and the results were reported in this dissertation. For verification purposes, a laboratory model with 1B as a clear spacing between footing was tested where B is the footing width. These two square footings were pushed downward with hydraulic jacks. The numerical models were of two square footings with clear spacing between them 0.5B, 1B, 1.5B, 2B. PLAXIS 3D has been used to study these models.

Furthermore, the experimental model matched the predictions given in the PLAXIS 3D model. Utilizing the same material properties and boundary conditions, finite elements analysis was done on additional models. Plotting the load vs settlement curve indicated that there is an improvement in footing performance and bearing capacity by utilizing a geocell system to support the clay soil. The best performance was recorded for the model with spacing between footings is 2.5 B