Sydney's coastal humidity and cyclic rainfall drive shrink-swell cycles in the Ashfield Shale and Botany Sands, which directly cause differential movement under slab-on-grade foundations. When clay layers beneath a footing lose moisture during a dry summer, the edge of a house can settle twice as fast as the center — we measure that differential using precise survey arrays and settlement plates. Before we mobilize, we cross-check the local groundwater regime with a permeability test to rule out seepage-driven consolidation. The result is a contour map of predicted vertical displacement across the site, not just a single number.
In Sydney's reclaimed wetlands, differential settlement can exceed 50 mm across a single row of footings — enough to shear a brick veneer wall in two years.