Digging in the Perth Hills and Darling Scarp
Laterite gravel, clay, granite outcrops. Rock-hard in summer, sticky in winter; slopes; bushfire risk.
Twenty kilometres east of the city the sand ends at the Darling Scarp, and from Bedfordale through Kalamunda, Mundaring, Gidgegannup and Chittering the ground is laterite gravel over mottled clay over granite. It is the hardest digging in the metropolitan area and the most seasonal.
What the ground does
In summer the gravel and dry clay set like concrete; a 1 tonne machine bounces off and even a 2 tonne machine wants a ripper first. In winter the clay is workable but sticks to everything, balling in the bucket and turning rubber tracks into skis on a slope. Granite appears as boulders and outcrops exactly where footings were planned. The workable windows are April to June and September to October.
Slopes and fire
Most Hills blocks are on a gradient. Track straight up and down, keep the blade downhill when digging and widen adjustable tracks fully. The Hills are the highest bushfire-risk area in the region: the City of Kalamunda, Shire of Mundaring, City of Armadale and City of Swan issue firebreak notices due in November, and the same machine that digs the footings cuts the breaks.
Machines and attachments that suit
Weight matters more here than anywhere. The R22 PRO is the practical minimum for regular Hills work and the R32 PRO, with a cab and zero tail swing, is the contractor's choice. A ripper is the first attachment to buy, a toothed digging bucket the second, and a breaker for granite the third. A grid bucket sorts rock from soil so the fines can be reused.
Read digging the Darling Scarp and plan around the WA earthmoving calendar.