As I mentioned in my last blog, where landscaping is concerned cut and fill sites come with their own set of problems.
What usually happens to a cut and fill site? The excavated material is piled irrespective of its natural layers. Top soil and sub soil is either mixed up together or more often the top soil is moved first to the bottom of the fill and the subsoil ends up at the top. This will create drainage problems for the cut as well as for the fill side.
On the cut side, if vegetation is required, the root system will struggle going into a highly compacted and waterlogged soil resulting in high plant mortality.
On the fill side, often the fill has been deposited on an un-ripped existing soil creating an impervious layer. The new soil medium resulting from the excavation will bring the problem of plants having to make roots straight into a soft soil where large air pockets may have developed. Another problem occurs when the newly planted vegetation roots become exposed as the soil settles.
In Australia there are standards that apply to subsoil drainage but none to subsoil itself. In the UK a new standard for subsoil (BS 8601 Specification for subsoil and requirements for use) has been developed by BSI and supported by WRAP (Waste & Resources Action Programme), British Society of Soil Science, the British Landscape Institute as well as several other organisations.
Cut and fill is a regular occurrence for construction in Australia. It is time that councils, architects, builders, engineers and the landscape and horticulture industry work in a concerted manner and work together towards a greater understanding of the problem.
The solution is simple but requires all parties to work cooperatively. The question is, is this too much to ask?
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