The program will generate internally the nonlinear response of the soil, in the form of t-z and q-w curves for axial loading, in the form of p-y curves for lateral loading and in the form of t-r curves for torsional loading. A solution requires iteration to accommodate the nonlinear response of each pile in the group model. Program GROUP solves the nonlinear response of each pile under combined loadings and assures compatibility of geometry and equilibrium of forces between the applied external loads and the reactions of each pile head.

The p-y, t-z, q-w and t-r curves may be generated internally, employing recommendations in technical literature, or may be entered manually by the user. The pile-head forces and movements are introduced into equations that yield the behavior of the pile group in a global coordinate system. The program can internally compute the deflection, bending moment, shear, and soil resistance as a function of depth for each pile.

For closely-spaced piles, the pile-soil-pile interaction can be taken into account by introducing reduction factors for the p-y curves used for each single pile. As an option, the user can ask the program to generate internally some suggestions for p-multipliers to automatically reduce the soil resistance. GROUP is able to generate or lets users specify p-y reduction factors for two orthogonal axes.

The program allows the user to select computations of the required unit side friction at the top and bottom of each soil layer along with a unit tip resistance. The program employs commonly-accepted equations to compute internally the estimated unit side friction and unit tip resistance based on the soil properties that are specified by the user for each soil layer.

Users can also input external nonlinear curves of axial load versus settlement for each pile in the group. Those external curves can be obtained by the user based on load tests or using the Ensoft programs APILE and/or SHAFT.

GROUP v8.0 introduces several enhancements: Use of multiple load cases representing concentrated loads at the pile cap and/or distributed lateral load at the piles; Concentrated loads at the pile cap may be defined at any position; Distributed lateral loads at the piles can be defined by local or global axes; Load combinations can be specified by the user and are set by load factors applied at the defined load cases; Maximum and mini-mum envelopes may be computed for both load cases and load combinations; GROUP v8 can provide flexibility and stiffness matrices (in 2D or 3D models) for different levels of loading.