The ground: sand, limestone and clay
Most of Perth is on the Swan Coastal Plain, a band of old dunes and limestone between the ocean and the Darling Scarp. Very roughly, from the coast inland:
- Quindalup dunes along the coast: young, pale, lime-rich sands.
- Spearwood dunes: yellow-brown sands over Tamala Limestone. The limestone can be close to the surface and may need ripping or rock breaking.
- Bassendean dunes: grey, leached quartz sands, often in low-lying areas with wetlands and shallow groundwater.
- Toward the foot of the scarp: the clays and loams of the Pinjarra Plain, which behave very differently in the wet.
Clean sand is easy to dig, drains quickly and often makes good fill. In WA, compaction of sand is commonly checked with the Perth sand penetrometer as well as density testing. Check what your specification requires.
Dust: the summer problem
Dry sand moves in the wind. Perth summers bring strong easterlies in the mornings and the south-westerly sea breeze, the Fremantle Doctor, in the afternoons. A cleared site of loose sand can blow onto neighbouring houses and roads within hours.
WA's guidance for dust from land development is A guideline for managing the impacts of dust and associated contaminants from land development sites, contaminated sites remediation and other related activities, and many local governments ask for a dust management plan as a condition of approval. Common controls include:
- Water carts, and enough water to run them through summer
- Staging the clearing so less ground is open at once
- Stabilising exposed areas with hydromulch, polymer or other stabilisers
- Wind fencing on exposed boundaries
- Stopping dusty work in high winds
Groundwater and acid sulfate soils
On much of the plain, especially on the Bassendean sands and around wetlands, the water table is close to the surface, and highest in late winter and spring. That affects the job in three ways.
- Fill levels: many subdivisions import sand fill to lift lots and roads clear of groundwater and flood levels. That means a lot of truck movements, often through residential streets.
- Dewatering: excavations below the water table, for services, basins or footings, may need dewatering. Taking groundwater can need a licence from the Department of Water and Environmental Regulation (DWER).
- Acid sulfate soils: some low-lying areas have soils that produce acid when they're disturbed or exposed to air, for example by excavation or dewatering. On a site mapped as at risk, an investigation and a management plan may be needed before work starts.
Winter rain
Perth has a Mediterranean climate, with most of the year's rain falling between about May and September. Sand drains quickly and can often be worked soon after rain, but clay sites, unsealed haul roads and access tracks turn to bog.
- Plan clay-heavy work and long hauls on unsealed roads for the drier months where you can.
- Allow for wet-weather days in the programme.
- Sheet or stabilise the haul roads that have to work all year.
- Keep sediment out of drains, wetlands and public roads.
Working hours and neighbours
Under WA's Environmental Protection (Noise) Regulations 1997, construction work is generally done between 7am and 7pm on days that aren't Sundays or public holidays, with equipment and work practices that keep the noise down. Work outside those hours is restricted and usually needs a noise management plan, so talk to the local government early if you'll need it.
Trucks are often what the neighbours notice most. Plan the routes, keep sand off public roads with shaker grids, wheel washes or street sweeping, and agree a traffic management plan before the first load.
Check the requirements for your site
This article is a general overview. Requirements change, and they vary between local governments and sites. Check your approvals and their conditions, the current guidelines, and your engineer's and environmental consultant's advice for your job.