A landslip study in tertiary sediments, Northern Tasmania: Fid-Bau Portal

A landslip study in tertiary sediments, Northern Tasmania

Knights, C. J. / Matthews, W. L.

Summary Landslips occur in overconsolidated Tertiary clay sediments in the Tamar Valley, northern Tasmania. The paper describes methods of investigation of these landslips, techniques used and results obtained. Methods used in studying individual landslips include ascertaining stratigraphic controls, soil mechanics, monitoring piezometric pressures, subsurface monitoring, geophysics, groundwater and clay chemistry and clay mineralogy. Stratigraphic control has been established on four deep slips. Shallow slips occur in the weathered surface layer. A small residual cohesion was shown by shear box testing. The clays have high liquid limits and plasticity indices. Slip movements can be anticipated by the monitoring of piezometric pressures. Refraction seismic techniques, when used in combination with other methods of investigation have proved useful in determining the depth of the slip and the depth to which Tertiary sediments are weathered. Of three resistivity methods employed, bore hole resistivity is the most useful. X-ray diffraction shows kaolinite, montmorillonite, quartz, gibbsite and occasionally illite in the landslip materials. Chemical analyses of water from aquifers and exchangeable cation determinations of the landslip material, indicate some physical properties of the clays.