Effect of Soil Confinement on Ultimate Bearing Capacity of Square Footing Under Eccentric–Inclined Load

 

Vinod Kumar Singh

Asst. Manager, RITES, Madhubani, India
Email: vinubit@gmail.com

Arun Prasad

Lecturer, Department of Civil Engineering, Institute of Technology, Banaras Hindu University, Varanasi, India
Email: prasada@bhu.ac.in

R.K. Agrawal

Professor, Department of Civil Engineering, Institute of Technology, Banaras Hindu University, Varanasi, India

ABSTRACT

This paper presents the results of laboratory model tests on the effect of soil confinement on the behavior of a model footing resting on Ganga sand under eccentric – inclined load. Confining cells with different heights and widths have been used to confine the sand. The ultimate bearing load of a square footing supported on a confined sand bed has been studied. The studied parameters include the cell height, cell width and the depth from base of footing to the top of the confining cell, load eccentricity and load inclination. Initially, the behavior of footing for an unconfined case is studied and then it is compared with that of confined soil. The results are then analyzed to study the effect of each parameter. The ultimate bearing capacity improvement due to the soil confinement is represented using a non-dimensional factor, called the Bearing Capacity Ratio (BCR). The results indicate that the ultimate bearing capacity of square footing can be appreciably increased by soil confinement under axial load as well under eccentric–inclined load. It has been observed that such confinement resists the lateral displacement of soil underneath the footing leading to a significant decrease in the vertical settlement and hence improving the ultimate bearing capacity. For small cell width, the cell–soil footing behaves as one unit (deep foundation), while this pattern of behavior was no longer observed with large cell width. The recommended cell heights, depths, and widths that give the maximum ultimate bearing capacity improvement are presented and discussed.

Keywords: Model tests; Cohesionless soils; Square Footings; Eccentric-Inclined load; Ultimate Bearing Capacity; Soil Confinement.

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