When developing or subdividing land, you need to understand that the site you purchase must be able to accommodate its intended development (residential dwellings in this instance) relative to the soil type and classification. If the soil classification and/or site conditions are problematic, you will have to remediate the site so it can accommodate its intended development.
Depending on the soil classification and the scope of works required to rectify (to make the new lots “build ready”) this can be a major work and cost exercise, often resulting in large cost blowouts, particularly for unwary novice developers. It is essential therefore that you understand the importance of investigating what is below the ground, and that you have the ability to comprehend the effect this will have on works scope, cost, and ultimately your projects overall viability.
This article will discuss the following standard condition that you will get in almost every conditional subdivision approval from the WAPC, with reference to the conditions a, b and c below:
Standard WAPC site works condition in a decision letter
To emphasise the point, soil classification of a site is where site works costs begin. To determine the soil classification, we need a geotechnical site investigation and report, performed by a geotechnical engineer. The investigation will give us the soil classification, current bearing capacity of the soil, and remediation recommendations for site. This can include removal of fill, import of fill and compaction specifications. Typical soil classifications in Western Australia are:
A – sand and rock* (Remember whilst rock is A class it poses its own problems for excavation of trenches and footings)
S – slightly cohesive (some clay)
M or H – medium and heavy clays
P – problematic, indeterminate bearing capacity, contaminated