The ultimate axial capacity under compressive or tensile load is computed based on the soil layer properties. The software gives the pile capacity at various depths of soil and also breaks it down to its contributing factors viz. shaft friction and base capacity. The pile capacity estimation is based on the sub-soil layer properties and different methods for assessment of shaft friction and base capacity.

In addition to common procedures used in practice, procedures based on API-2011, ‘α method’ (IS-2911), ‘Semple & Rigden (1984) method’, ‘Kolk & Van der Velde (1996) method’ for clay soil and ‘β method’ (API-2011), ‘k-δ–f_lim method’ (API-2000), ‘k-δ -Z_c method’, ‘Meyerhoff SPT method’, ‘N_q-q_lim method’ (API2011,API-2000), ‘N_q-Z_c method’ (IS-2911), ‘N_q-Berezantsev-Z_c method’ for sandy soil are also included along with ability to include user prescribed parameters. A distance of 3D is used for developing full base resistance in strong layers. A safe distance of from pile tip of 3D is adopted to preclude punch through underlying weak layers. For rock layers an approach based on unconfined strength is adopted.

This module has two independent sub modules:

(a) Axial pile deformation analysis

Pile is modelled as an elastic structural member having the cross section of the pile and the elastic properties of the pile material. The soil support providing the shaft friction is modelled by a set of side springs based on t-z curves. The tip resistance provided by the pile base the base is modelled by a spring based on q-z curve.

The software supports both ‘Elastic Bi-linear’ and ‘Non-Linear’ approaches for modelling and any one of them can be selected for analysis.

In the ‘Non-Linear’ approach, for the soil layer, based on the t_max and q_max values calculated , non-linear t-z curves (interface shear stress- vertical pile movement at that point) and q-z curve (bearing stress and toe displacement) are developed based on API-2011 guidelines. In the case of rock layers, using the tmax and qmax values, t-z and q-z relationships are modelled by a bilinear elastic – plastic curve based on the elastic modulus and Poisson ratio of the rock layer.

In the ‘Elastic Bi-linear’ approach, for the soil layer, t-z and q-z relationships are modelled by bilinear elastic – plastic curves based on the elastic modulus, Poisson ratio ,t_max and q_max for the layer.

The axial pile analysis follows a non-linear finite element model using the axial rigidity of the pile and the nonlinear soil support based on the t-z curves and q-z curve. . The analysis uses an Iterative approach to achieve convergence.

The analysis provides displacement of the pile head under a given load on the pile head, variation of axial load along the pile length, and the load carried by the pile base. Different loads applied on the pile head and the corresponding head displacements provide the load displacement curve.

(b) Generation of t-z and q-z curves

Development of a set of t-z curves along the shaft length and q-z curve at the pile base for compressive loading. Multiple t-z curves are generated for each soil layer. The curves can be based on ‘API-2000 RP’, ‘API-2011 RP GEO’ or ‘Elastic Method’ for sand and clay layers. API based methods, also account for reduction in post peak adhesion in clay layers through a factor R.

This module has two independent sub modules.

Commonly used linear models based horizontal subgrade modulus k_h for clay and rock and linearly varying subgrade modulus with depth n_h for soft clay and sand can also be chosen.

(a) Lateral pile deflection analysis.

Analysis of a pile subjected to lateral load and moment is carried out in this module. Finite element based approach is adopted to model the pile and the soil support in which the pile is divided in to a number of elastic beam bending elements. The method allows consideration of inhomogeneous and non-linear modelling of soil support. The lateral soil support for the pile is modelled by the well-known p-y springs.

The following boundary conditions may be given at the pile head.

For pile having free head condition both lateral load and moment can be prescribed at the pile head. With other conditions only lateral load can be prescribed and pile head moment will be determined from the analysis. The method can consider the effect of axial loading due to beam column action in lateral pile analysis. The pile head can project above the ground.

The finite element discretisation not only takes in to account the specified pile make-up but is also optimized for better accuracy by adopting a graded mesh along the pile length. An iterative procedure based on secant modulus approach is used for convergence.

(b) Generation of p-y curves.

In this module p-y curves are generated for the soil layers based on their properties. Multiple p-y curves are generated for each layer. API-2011 RP-Geo can be used for clay and sand layers. For stiff clay the procedure outlined in ‘L. C. Reese and W. R. Cox, (1975) can also be adopted. For ‘weak rock’ Reese(1997) method is available while for ‘hard rock’ Turner(2006) method is available.