A New Approach for Estimating Thickness of Mat Foundations Under Certain Conditions

This paper presents work based on a modern approach that offers the potential for modeling both the whole structure (superstructure and mat) and the subgrade (soil) component quite accurately, to overcome the shortcoming of the separate modeling of each part. In addition, this approach considers the rigidity of superstructure (flexural stiffness of each floor) and rigidity of mat within one 3-D soil structure interaction model. To implement the model, a complete 3-D model was used for the superstructure, the mat foundation and the soil. The soil was modeled as a 3-D solid finite element elastic material connected to the mat foundation. The mat foundation was modeled as a 3-D finite plate element. Both soil and concrete material of mat were taken as an elastic material, by modulus of elasticity and Poisson's ratio. The superstructure was modeled as a multistory building consisting of 2-15 stories with different column spacing varying from 3 to 7 m. STAAD-PRO software was used for the analysis of this model. The numerical results are studied, and summarized in the form of design charts to show the relationship between thickness of mat foundation and each of the following: number of stories, column spacing, subgrade material (type of soil), total settlement, differential settlement and soil pressure. Thickness of mat foundation can be estimated from the developed curves and charts, for various design parameters, including: soil type, maximum allowable settlement, maximum allowable differential settlement, and maximum allowable bearing capacity.