ABSTRACT
Materials of the Silurian and Lower Devonian periods, generally referred to as the Melbourne mudstone, consist of interbedded claystones, siltstones and sandstones in which the siltstones clearly predominate. In engineering works, the mudstone can be encountered in a range of weathered states. When carrying out tests to derive relevant engineering properties, it is important to apply boundary conditions which are appropriate to the likely full-scale performance of the material concerned. The use of the pressuremeter for establishing engineering properties, particularly the shear and Young's modulus, of sands and clays has been recognised for many years. The mudstone in engineering applications is rarely encountered with a strength greater than about 10 MPa. Although there have been very few plane strain fracture toughness determinations made for the Melbourne mudstone, a comparatively greater number have been made on a synthetic soft rock which has a range of engineering properties very close to those recorded for the mudstone.
