Prediction of bearing capacity of fine grained soils from field Dynamic Cone Penetration reading

Case of clayey soil from Asella, Ethiopia

Abstract

Bearing capacity is one of the important parameters that needs to be considered for design and construction of foundations of civil engineering structures. The conventional method of estimating this parameter is commonly using Terzaghi’s equation, which requires the shear strength parameter of soil. Shear strength test is expensive and time consuming, hence conventional method of estimating bearing capacity is uneconomical especially for small scale projects. Dynamic cone penetrometer (DCP) is one of the simple in situ test methods widely used in site investigation for estimating the strength and density of soils. This work is, therefore, aimed at predicting bearing capacity of shallow foundations from field in situ DCP reading for fine grained soils of Asella town, Ethiopia.. The soil index properties and tri-axial tests to determine the shear strength parameters were performed on soil samples extracted from different pits. On the same pits, DCP test have been performed in the field to record D-value (mm/blow). Then regression analysis have been performed to determine relationship of allowable bearing capacity (q_all) with D-value and index properties. Regression analyses results showed that q_all have strong relation with D-value having coefficient of determination (R²=0.89) than index properties. The footing dimension have no effect on the predicted bearing capacity of foundation. The comparison between the developed equation and the actual q_all obtained from Terzagi’s bearing capacity equation shows average variations of 11.7%, suggesting the validity of the developed equation.