Rock Mech. Rock Engng. (1995) 28 (2), 93 110 Rock Mechanics and Rock Engineering 9 Springer-Verlag 1995 Printed in Austria Crack Propagation in Sandstone: Combined Experimental and Numerical Approach By E. Schlangen and J. G. M. Van Mier Stevin Laboratory, Delft University of Technology, Delft, The Netherlands Summary A combined experimental and numerical approach is adopted to investigate crack propagation in sandstone. Experiments on two types of sandstones show a simular behaviour as found in tests on concrete specimens. The heterogeneity of the material in combination with the stress situation, as a result of the applied load, governs the direction of crack propagation. Cracks that develop are not continuous, but overlaps exist mainly around the grain particles in the material. A simple lattice model, in which the material is schematized as a network of small beams, is adopted to simulate the experiments. Using the simulations carried out with the lattice model, the control parameter for stable displacement controlled four-point-shear tests was determined. The crack patterns obtained with the model are in good agreement with the experimental observations. However further study is needed to predict the load-displacement response correctly. 1. Introduction The fracture behaviour of sandstones is of great importance to the oil industry. For example oil reserves are found in sedimentary deposits under the North Sea, and hydraulic fracture techniques are employed to stimulate the wells. The explanation of the physical process occurring if cracks develop through the material can enhance the methods of oil recovery. In this study a combined experimental and numerical approach is used to obtain more insight in the complicated crack initiation and propagation problem in sandstone. The main purpose of the investigation are the final crack patterns and the way they develop, but also attention is focused on the load bearing capacity and the correlated deformations. The experimental part of the research consists of different types of tests. Uniaxial tensile tests are performed on single- and double-edge-notched prismatic specimens. Furthermore, beam specimens with one or two notches are loaded in four-point-shear using different boundary conditions as will be explained in the next section. Both types of test are performed using closed-loop hydraulic testing machines, since this is the only way to perform stable fracture tests and to cover the