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Abstract:
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Gabion faced re.taining walls are essentially semi rigid structures that
can generally accommodate large lateral and vertical movements without
excessive structural distress. Because of this inherent feature, they offer
technical and economical advantage over the conventional concrete gravity
retaining walls. Although they can be constructed either as gravity type or
reinforced soil type, this work mainly deals with gabion faced reinforced earth
walls as they are more suitable to larger heights.
The main focus of the present investigation was the development of a
viable plane strain two dimensional non linear finite element analysis code
which can predict the stress - strain behaviour of gabion faced retaining walls -
both gravity type and reinforced soil type. The gabion facing, backfill soil,
In - situ soil and foundation soil were modelled using 20 four noded
isoparametric quadrilateral elements. The confinement provided by the gabion
boxes was converted into an induced apparent cohesion as per the membrane
correction theory proposed by Henkel and Gilbert (1952). The mesh
reinforcement was modelled using 20 two noded linear truss elements.
The interactions between the soil and the mesh reinforcement as well as the
facing and backfill were modelled using 20 four noded zero thickness line
interface elements (Desai et al., 1974) by incorporating the nonlinear hyperbolic
formulation for the tangential shear stiffness. The well known hyperbolic
formulation by Ouncan and Chang (1970) was used for modelling the
non - linearity of the soil matrix. The failure of soil matrix, gabion facing and
the interfaces were modelled using Mohr - Coulomb failure criterion.
The construction stages were also modelled.Experimental investigations were conducted on small scale model walls
(both in field as well as in laboratory) to suggest an alternative fill material for the gabion faced retaining walls. The same were also used to validate the finite
element programme developed as a part of the study. The studies were
conducted using different types of gabion fill materials. The variation was
achieved by placing coarse aggregate and quarry dust in different proportions
as layers one above the other or they were mixed together in the required
proportions. The deformation of the wall face was measured and the behaviour
of the walls with the variation of fill materials was analysed. It was seen that
25% of the fill material in gabions can be replaced by a soft material (any locally
available material) without affecting the deformation behaviour to large extents.
In circumstances where deformation can be allowed to some extents, even up to
50% replacement with soft material can be possible.The developed finite element code was validated using experimental test
results and other published results. Encouraged by the close comparison
between the theory and experiments, an extensive and systematic parametric
study was conducted, in order to gain a closer understanding of the behaviour
of the system. Geometric parameters as well as material parameters were
varied to understand their effect on the behaviour of the walls.
The final phase of the study consisted of developing a simplified method
for the design of gabion faced retaining walls. The design was based on the
limit state method considering both the stability and deformation criteria.
The design parameters were selected for the system and converted to
dimensionless parameters. Thus the procedure for fixing the dimensions of the
wall was simplified by eliminating the conventional trial and error procedure.
Handy design charts were developed which would prove as a hands - on - tool
to the design engineers at site. Economic studies were also conducted to prove
the cost effectiveness of the structures with respect to the conventional RCC
gravity walls and cost prediction models and cost breakdown ratios were
proposed.
The studies as a whole are expected to contribute substantially to
understand the actual behaviour of gabion faced retaining wall systems with
particular reference to the lateral deformations. |