SETTLEMENT OF FOUNDATIONS ON COHESIONLESS SOILS STRIP FOOTINGS

Abstract

Bearing capacity, the settlements and the tilt are the main criteria for design of shallow foundations. Very few inves-tigators have paid attention to the problem of pedicting pressure settlement characteristics resting on cohesionless soil. The study presents a mathematical model conforming to the constitutive laws of soils alongwith some simplifying assumptions for estimating settlements of strip footings resting on cohesion-less soils. Various nondimensional parameters have been defined in the study,and'thecomputations ofdisplacement coefficients for average settlement of strip footings on cohesionless soils for different pressures and stress factors for the stresses with in the soil mass under the footing have been carried out with the help of computor using Finite Element technique. The displacement coefficients for a load factor and stress factors are functions of only two parameters of soils namely, the angle of internal friction 0 and a constant, n, of hyperbolic stress-strain rela-tionship. The other soil parameters, on which the settlements of strip footings on cohesionless soils depend, are Ki and K2. All these four factors are function of only the physical properties which can be determined by triaxial tests. The study has been carried out for Ranipur sand of two different relative densities viz. 84$ and 46$ for twelve load factors in each case. Nondimensional charts of stress-factors with in the soil mass at vertical sections through the centre line of footing and a horizontal distance equal to 1/8, 3/8 and 1/2 times the width of footing from 4..is centre line have been V . given. Nondimensional charts of Load factor - displacement coeffi-cient charts have also been drawn. The pressure-settlement curves for 5 cm wide strip foot-ing on Ranipur sand of relative densities 84A and 46% have been obtained using the above technique and compared with the experi-mental results of model tests and a close agreement is found between the two. The study has also revealed that the actual stresses in the soil mass under a footing up a depth equal to about 2-3 times the width of the footing deviates significantly from those calcu-lated by considering the soil mass to be homogeneous. However, the effect of nonhomogenity of soil mass at deeper depth is not appreciable.