A method of analysis of pile group, treating it as a frame work with piles as beams on elastic foundation rigidly connected by a pile cap, is proposed. The analysis involves the so-called pile constants which are defined as the forces and moments exerted by the pile on the pile cap per unit vertical or lateral displacements or rotations. It is difficult to give an analytical approach to determine the pile constant corresponding to vertical displacement but those due to lateral displacement and rotation are evaluated treating the pile as beam on elastic foundation.
The model studies showed that the pile constants are functions of the type and nature of soil, angle of batter, the displacement and the spacing of piles in group. Empirical relations based on model tests to correlate the pile constants with a few of these parameters are given. The analysis is finally checked by systematic model and field tests and was found to be reliable provided the constants are properly assessed
The problem of analysis of pile groups comprising of vertical and batter piles is very complicated due to the complex behaviour of soil-pile system. The parameters like properties of soil and pile, disposition, inclination and sequence of driving of piles, restraint offered by pile cap etc. govern the behaviour of a pile group. It is almost impossible to get a correct solution to the problem which takes into account all the above factors simultaneously. Analytical and experimental studies of a few of these parameters have been carried out in the fast by Vetter 9, Vandepitte8, Hrennikoff2, Vesic7 etc. The analysis proposed by the last two investigators are quite rational as they take into account the lateral restraint offered by the soil.
The main drawback of Hrennikoff's and Vesic's methods is that they involve certain the so-called pile constants which cannot readily be deternined. Hrenikoff 2 gives a method to estimate the constants which is not accurate. A better approach has been suggested by Vesic7 to evaluate them. He has developed the pile constants by treating the pile as a beam on elastic supports and as summing that the modulus of subgrade reaction varies linearly with depth of granular soil. However, he has not taken into account the variation of modulus of subgrade reaction with batter, disposition in a group and deflection of pile. The model study of Murthy5 has shown that the variation of modulus of subgrade reaction with depth is nonlinear and it defends on the angle of batter. Studies of Kubo and Gill have shown that the soil does not follow the linear law of subgrade reaction. Hence, it is obvious that the pile constants should vary with deflection. No rational method is so far available to take this fact into account.
In order to overcome some of the difficulties of the pile group analysis, the present study of the authors has been carried out with the following objectives in view.
