Digging in the Perth coastal plain
Bassendean and Spearwood sands; Tamala limestone near the coast. High winter water table; trench walls collapse in dry sand.
Most of metropolitan Perth sits on the Swan Coastal Plain, a strip of old dunes between the Darling Scarp and the Indian Ocean. The ground is sand almost everywhere: grey, leached Bassendean sand across the inner and eastern suburbs, and yellow-brown Spearwood sand over Tamala limestone closer to the coast. Both dig easily and neither holds a vertical face for long.
What the ground does
Dry sand slumps to its angle of repose within minutes, so trenches and soakwell holes must be dug and used in the same session or battered back. Damp sand behaves for a while, which is why autumn and spring are the easy months. Near the coast, limestone caprock turns up a metre down and stops a light machine; a ripper or breaker solves it. In the low-lying wetland chains through Bayswater, Canning Vale, Cockburn and Wanneroo the water table rises to the surface between June and September, and deep work waits for spring.
Typical jobs
Soakwells, retaining wall footings, paving prep, pools, reticulation and side-access landscaping on suburban lots. Access is usually the deciding factor on newer estates, where side paths are often under a metre.
Machines and attachments that suit
A 1 to 1.8 tonne excavator covers almost all of it. The R15 is the plain's all-rounder; the R18 PRO adds the dig depth for pools and deep soakwells; the R10 and R13 PRO get through tight side paths. A wide toothless mud bucket moves sand fastest and a tilt bucket shapes batters and backfills. Pair it with an RS06 skid steer for shifting sand, mulch and paving base.
Timing
April, May, September and October are the best months. Deep trenches in July on the flats are a losing battle. See the winter water table, why trenches collapse in Perth sand and Tamala limestone.