An Experimental Study on the Effect of Foundation Depth, Size and Shape on Subgrade Reaction of Cohessionless Soil

Wael N. Abd Elsamee

Faculty of Engineering, Sinai University, El Arish, Egypt.

DOI: 10.4236/eng.2013.510095                

Abstract

The modulus of subgrade reaction k_s depends on several factors such as the size and shape of the foundation as well as the embedment depth of the foundation. The present study is an experimental analysis using plate load test to determine the effect of foundation depth, size as well as the shape on the modulus of subgrade reaction (k_s) of cohesionless soils. It was carried out by using nine rigid steel plates with different sizes and shapes (circular, square and retangular). The tests were carried out on cohessionless soil with different relative densities under different applied pressures. The settlement has been measured at the surface of the plate for different depths of footings. The ultimate bearing capacity [q_u] has been determined from the stress-settlement relationships. The allowable bearing capacity (q_a) was determined by dividing the ultimate bearing capacity (q_u) by F.S. = 3.0, after which the corresponding settlement (S_a) has been obtained. However, k_s was calculated based on dividing the allowable bearing capacity (q_a) by the corresponding settlement (S_a). From the present study it is concluded that the subgrade reaction k_s of cohessionless soil increases with increasing foundation depth as well as foundation size. In addition, subgrade reaction k_s of cohessionless soil under rectangular footing is higher than that under square and that under circular one with same equivalent area. An empirical formula is presented to calculate the subgrade reaction k_s of cohessionless soil under square foundation taking into consideration foundation depth. Fair agreement has been obtained between values of k_s from the empirical formula at depth of footing = 0.00 B and Biot (1937) as well as Meyerhof and Baike (1965).

Keywords

Subgrade Reaction; Plate Load Test; Foundation Depth; Size; Shape

Conflicts of Interest

The authors declare no conflicts of interest.

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