Comprehensive Pile Foundation Analysis (Land, Bridge & Waterfront Structures)

Overview

Piles are used to provide foundation support to wide ranging structures such as buildings, bridges, wharves, jetties and towers. Piles may be broadly classified into several types as shown below.

Pile types
Based on soil displaced	Displacement		Part displacement			Non- displacement
Based on pile material & method of construction	Driven		Driven			Bored
	Precast concrete	Cast-insitu-concrete	Precast concrete	Steel		Cast-insitu-concrete
	Square or rectangular	Circular	Hollow cylindrical	Tubular	H-section	Circular	With enlarged base	CFA

The choice of the pile type is governed by sub-soil strata, ground water conditions, its chemical composition, facility of construction, local experience, available technology and cost.

The loading on piles can be in axial direction (compressive or tensile) and in lateral direction (shear and moment).  The loading may be due to self-weight of structures, live loads, wind and earthquake forces. In water front-structures forces due to ship impact and mooring forces will require consideration. In bridge piles, scour around piers needs to be taken in to account. Abutment piles will also be subject to lateral earth pressure. In many instances axial and lateral forces will act above the ground level requiring consideration of beam column action. In all cases the piles designed should meet the serviceability and safety requirements under all loading conditions.

The pile analysis software is developed keeping in view all the above requirements.

This software offers is a single platform consideration of different pile types, different codes of practice as well as other well-known procedures adopted in practice.

This pile analysis software can be used in several ways towards achieving design requirements:

· Based on sub-soil properties and pile parameters, analyse the pile for different loading scenarios.

· Perform analysis towards optimizing pile length and size.

· Evaluating performance of different types of piles in making a choice.

· It may be used in comparing results of load tests with the results of analysis and in fine tuning pile design parameters.

The ‘Comprehensive Pile Foundation Analysis (Land, Bridge & Waterfront Structures)’ software of GEMS provides advanced and intuitive modules for the all the above analysis. 

There are three modules available

Pile Capacity Estimation	Axial Pile Analysis	Lateral Pile Analysis

The Piles of circular, square, rectangular, circular-hollow and I or H cross sections can be analysed.  Bored piles (Cast-insitu-concrete)  and driven piles (Precast concrete, Cast-insitu-concrete, Steel) can also be analysed. 

Circular	Square	Rectangular	Hollow circular	I or H Section

Soil scour around the piles and pile lengths projecting above the ground can be specified. These provisions are especially useful in analysing piles used in foundations of bridges and waterfront structures. Depth of ground water table in the subsoil can also be considered.

Key Features

· One click computation and analysis for all load cases and modules. · Piles of circular, square, rectangular, circular-tubular & I or H cross sections can be analysed.  · Axial pile capacity estimation · Analysis of the pile foundation under combined lateral and axial loads. · Linear & Non-linear analysis models · Multiple load cases. · Pictorial representation of the pile and soil layers. · Loading diagrams for each load case. · Export of results to Microsoft Word, Excel & PDF · Supported on Windows, Mac and Cloud · Data can be input in either SI units or ‘Commonly used American units’ (kips for force and foot for length)

· Self-weight of pile may be included if required. · Multiple axial, lateral loads and lateral moments can be specified along the length of the pile at various depths (up to 20 including pile head) for each load case. · Distributed lateral load (triangular, uniform, or trapezoidal) can be given. · Static and cyclic loadings can be incorporated for lateral analysis. · Local scour & ground water table considerations. · Facility of prescribing lateral displacement, rotation & rotational spring at the pile head. · Generation of p-y, t-z and Q-z curves based on soil properties. · Handy tool for resolving forces.

Pile Capacity Estimation

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.  Presently the below methods of analysis are available:

Clay	Sand		Rock
	Side Friction	Base capacity
· API-2011 · α method (IS-2911) · Semple & Rigden method · Kolk & Van-der-velde method	· β method (API-2011) · K-δ method (API-2000) · K-δ-Zc method (IS-2911) · Meyeroff SPT method (IS-2911)	· Nq-qlim method (API-2011, API-2000) · Nq - Zc method (IS-2911) · Nq-Berezantev-Zc method · Meyeroff SPT method (IS-2911)	· Approach based on unconfined strength is adopted

A distance of 3D is used for developing full base resistance in strong layers.  A safe distance of 3D from pile tip is adopted to preclude punch through underlying weak layers. For rock layers an approach based on unconfined strength is adopted.

Axially Loaded Pile Analysis

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 following loading may be given and used for the analysis

a) Axial loads at various depths along the length of the pile (up to 20 including load at pile head). 

b) Self-weight of the pile

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

Modelling soil support using t-z and q-z springs

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 ‘Elastic (continuum) 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 settlement of the pile head under a given load on the pile, 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 settlements  provide the load settlement curve.

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 below methods are available for generation of the t-z for each layer and Q-z curves at the pile base.

Soft Clay	Stiff Clay	Sand	Weak Rock	Hard Rock
· API-2011 · API-2000 · Elastic Method	· API-2011 · API-2000 · Elastic Method	· API-2011 · API-2000 · Elastic Method	· Elastic Method	· Elastic Method

API based methods, also account for reduction in post peak adhesion in clay layers through a factor R.

Laterally Loaded Pile Analysis

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.

Modelling soil support using p-y springs

The following loading may be given and used for the analysis

a) Lateral loads, lateral moments and axial loads can be specified along the length of the pile at various depths (up to 20 including pile head) for each load case.  The axial load applied at the pile head will be considered for taking the beam-column effect into account. 

b) Distributed lateral load for a section along the pile length.  Loading can be triangular,  uniform, or trapezoidal.

The following boundary conditions may be given at the pile head  

a) Prescribed lateral displacement

b) Prescribed rotation

c) Prescribed rotational stiffness.

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

The finite element discretization not only takes in to account the specified pile make-up but is also optimized for better accuracy. An iterative procedure based on secant modulus approach is used for convergence.

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.   The below methods are available for generation of p-y curves based on soil type.

Soft Clay	Stiff Clay	Sand	Weak Rock	Hard Rock
· API-2011 · Kh based horizontal subgrade modulus · Nh based horizontal subgrade modulus	· API-2011 · REESE · Kh based horizontal subgrade modulus	· API-2011 · Nh based horizontal subgrade modulus · Hybrid model for liquified sand (Based on friction angle) · Hybrid model for liquified sand (Based on SPT)	· REESE · Kh based horizontal subgrade modulus	· Turner (2006) · Kh based horizontal subgrade modulus