Transportation projects which extend across soft ground present unique challenges –impacting projects from a time, cost and risk perspective.

These challenges can be significant, with the potential to impact both the cost and longevity of your project. However if managed effectively these challenges can also reap economic benefits. 

There are a number of considerations to take into account to get your ground improvement strategy right including early planning, staged construction, an early works program and selecting different ground treatment solutions at different sites along the project.

Whole of life considerations

Construction on soft soils typically takes longer and costs more than on a ‘normal’ site.  If you understand the geological profile and plan for the long term, construction program issues and increased costs can be avoided.

A funding strategy that considers how early works affect the life of the project can save money in the long run. By balancing capital cost and long-term maintenance cost, a whole-of-life approach can provide the best value for money solution. 

 Figure 4 Soft soils

Ground treatment options

There are multiple options for ground treatment and what you choose is another key driver of cost and time. The depth and properties of the soft soil, the embankment height and the construction time associated with the ground improvement method will affect the construction time.

Similar factors will affect the cost associated with ground treatment, including the depth and properties of the soft soil as well as availability of local material sources suitable for the ground treatment.

Embankment strategy

When sufficient project lead time is available, an early works strategy could comprise simple and economical solutions such as early construction of the embankment to minimise post-construction settlement and reduce delays and costs.

Embankments founded over soft ground adjacent to structures such as bridges are generally divided into three broad zones: structural, transition and low embankment zones. Embankment zoning is important, as it provides ready identification of where early works or accelerated ground treatment is required. Long stretches of road or railway away from bridge abutments or culverts may have relatively low embankments, and it may not be economically feasible to treat the soft ground in these areas.  Post-construction settlement is less critical in its effect on operational performance for low embankments, and in these circumstances we recommend a whole-of-life low embankment strategy.

How we can help

Coffey can rapidly assess different ground treatment options at multiple sites and assist you with estimates of time, cost and risk so that you can select the appropriate solutions based on critical paths on your construction program.

A low embankment strategy (LES) with a whole-of-life approach that balances capital cost and long term maintenance should be considered.  Coffey can incorporate the LES as one of the options along the project to assist you in developing the most suitable and cost-effective solutions over the design life of the project.

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