Retaining walls - Piling Engineering - page 243

the analysis of geotechnical problems. It is written in American National Standards
Institute Standard Fortran and requires any modern desk-top computer. It uses an
incremental tangent stiffness approach and has a variety of other features.

FREW : This is a program in the OASYS suite, developed by Arup, London. A line of
nodal points and 3 stiffness matrices, relating nodal forces to displacements, represents
the wall. The soil may be described by any one of three methods:

1 a subgrade reaction method;

2 stiffness matrices calculated by a Finite Element program; and

3 the Mindlin method, representing the soil as an elastic solid - this method is

restricted to the case of constant stiffness with depth.

The program presents results for earth pressure, shear forces, wall-bending moments,
strut forces and displacements. Full details are given by Pappin et al . (1986).

FLAC : This is a program for the solution of general geomechanical problems based on
a Finite Difference method. The letters of the title stand for Fast Lagrangian Analysis
of Continua and the program has been developed by ITASCA Consulting Group, Inc.,
PO Box 14806, Minneapolis, Minnesota 55414. Amongst other uses, it is capable of
solving a range of earth retention problems, and any type of non-linear soil stress/strain
relationship can be followed. It is suitable for the solution of retaining wall, tunnel-
lining and rock bolting problems. It is claimed that the Finite Difference method is
as flexible as the Finite Element method and requires less computational effort. The
published works of Wilkins (1963), Jaeger and Starfield (1974), Cundall (1976) and
Marti and Cundall (1982), are relevant to this program.

WALLAP : This program is available from Geosolve, London and offers a limit equi-
librium analysis for calculating 'factors of safety', and a Finite Element analysis for
calculating bending moments, displacements, and strut forces. The stability analy-
sis is carried out only for cantilever or singly propped walls. The finite element
analysis is elasto-plastic, with limits defined by active and passive states. Minimum
effective earth pressure can be prescribed as an equivalent fluid density in accor-
dance with certain codes of practice and fluid pressure within tension cracks can be
specified.

PLAXIS : This program is available from Plaxis of Delft. It is a general geotechnical
engineering finite element package which is suitable for modelling retaining walls and
other structures. It allows graphical input of soil layers, structures, construction stages,
loads and boundary conditions. Special beam elements are used to model the bending
in retaining walls, tunnel linings and other slender structures and elasto-plastic spring
elements are used to model ground anchorages and struts. Pre-stressing of anchorages
and struts is permitted and various soil models and pore-water pressure distributions
may be applied.
The output has enhanced graphical features. All displacement and strain graphs
can be visualized. Graphs and tables are available for axial and shear forces and the
moments in structural elements.