Sydney's geology is dominated by Hawkesbury Sandstone, a massive quartz-rich sandstone interbedded with shale lenses. This layered profile creates a highly variable lateral stress regime. The Flat Dilatometer Test (DMT) provides direct measurements of lateral earth pressure coefficient (K0), dilatometer modulus (ED), and horizontal stress index (KD). Unlike SPT or CPT, the DMT captures the in-situ stress state with minimal disturbance. In Sydney, this is critical for designing retaining walls, deep basements, and tunnel linings in the eastern suburbs where sandstone stiffness varies dramatically within meters. We deploy the DMT to complement other in-situ methods, ensuring the design parameters reflect actual ground conditions. The test follows AS 1289.6.5.2 and is executed with a standard 15 cm² blade advanced at 20 mm/s. Before field work, we review borehole logs to select test depths that avoid shale stringers. The team then correlates DMT results with laboratory triaxial data from adjacent cimentaciones-sismicas studies to validate the design profile.
The DMT provides the only direct field measurement of lateral earth pressure in Sydney's sandstone profiles, cutting uncertainty in retaining wall design by up to 40 percent.