INTERFERENCE EFFECT ON THE BEHAVIOUR OF FOOTINGS

Abstract

The changes in bearing capacity,) which occur when foundations from groups, has been the subject of a number of experimental investigations which have been carried out with model foundations of various sizes and depths, both in sand and clay. In this study the effec-t of interference on the behaviour of footings which occurs when two parallel flexible strip footings are placed at various distances.from each other has been studied analytically for two types of _soils (i) clay (0 = 0) and (ii) sand (c = 0). The changes in the behaviour of interfering footings have been studied in terms of bearing capacity of soil and tilt of the footing. The estimation of bearing Capacity and tilt have been done from the pressure settlement characteristics of the foundation soil. Pressure - settlemefit relationship' is essentially a function of non-linear stress-strain behaviour of soil. Constitutive laws defining such a behaviour of soil have been used in this investigation to predict the rela-tionships. In case of sand, flexible strip footings have been analysed on Ranipur sand at relative density of 75% only. A rational contact pressure distribution has been assumed. The soil mass below. the footings have been divided into a large number of thin strips and stresses and strains in each strip have been considered as uniform at any vertical section. To obtain settlement at a particular load, the strains have been multiplied ,by thickness of the strip and then numerical integration from surface to a 'depth upto which the strains become negligible has been carried out. (iv) Results obtained from analysis indicate that bearing capacity increases as the spacing decreases upto a certain spacing and then shows a slight decrease in bearing capacity after further reduction in spacing. Results are in reasonable agreement with the experimental results of Agarwal (1970) in case of sand. The results also indicate that the tilt of the footing at failure increases as the spacing decreases upto a cer-tain spacing and then reduces and finally becomes zero at a particular spacing after further reduction in spacing as block action starts taking place at that spacing.