Practice and Research of Geosynthetic Reinforced Soil Walls in Australia - Reinforced Soil Engineering: Advances in Research and Practice - page 248

varied during construction, any change in design requirements constitutes a
contractual variation (and possible contractual disputes). Hence, studies have
been undertaken in an attempt to develop a model for specifying design
requirements. The design requirements may be prescribed in detail, and this is the
current practice of the SRA of New South Wales; or a broad-based (and brief)
design specification may be used, which is the current practice of the SRA of
Victoria. In the latter case, the specialist GRS contractor will, as part of his tender
bid, provide a more comprehensive set of design methods and criteria. The SRA
of Queensland has adopted a somewhat intermediate approach. The SRA of
Western Australia, until 1997, only allowed steel soil reinforcement, although a
brief draft document on the design requirements of RS walls for a range of
reinforcement systems is currently under consideration. The road authorities of
other states, to the best of the author's knowledge, do not have design
specifications for GRS walls. This somewhat justifies restricting the scope of
reference of this paper to the three eastern states of Australia.
Although the “best” approach in specifying design requirements in a design
and construct contract for GRS walls is still being debated, the ability of GRS
walls to gain market share under such a design and construct contractual system
attests to its cost-effectiveness. Indeed, GRS walls have been adopted in a
number of milestone projects in Australia. It is pertinent to note that GRS walls
are well adapted to a design and construct contract. Because geosynthetic
reinforcements are normally manufactured in rolls, the reinforcement length and
grade are not constrained by the logistics of prefabrication (which is often the
case for metallic reinforcement). It is not uncommon to have GRS wall sections
that utilize different reinforcement grades at different spacing and of different
length, as shown in Fig. 1 for a GRS wall constructed in the state of Queensland.
Geosynthetic reinforcement only has to be cut to the design length during
installation; hence the cost and time impact of any design changes as a result of
deviations from expected site conditions is also smaller.
3 DESIGN
A range of design methods has been used for the design of GRS walls in
Australia. The term “design methods” includes the calculation model(s) for
assessing actions (such as maximum reinforcement tension) and the methodology
for assessing resistance (such as the long-term design strength of geosynthetic
reinforcement). The design methods can be either specified by the SRA or
proposed by the specialist GRS wall contractor as part of the tender. In either
case, the design methods form part of the contractual agreement once the contract
is awarded.