The application of fracture mechanics to crack propagation in dry soil

The application of fracture mechanics to dry soil has been investigated. Discs moulded from sand and kaolinite pastes, into which artificial tension cracks were introduced, were fractured using the indirect tension technique. The basic linear elastic fracture mechanics (LEFM) approach was found inadequate to describe the observed relation between the imposed flaw size and the failure stress. Fracture mechanics have been extended to dry soil by adding a crack length increment, Delta c, to the imposed Raw size, c, to account for energy dissipation by processes other than the creation of new surfaces. This increment seems to represent the effective size of a 'process zone' ahead of the crack tip in which energy is dissipated by micro-cracking and internal friction. Further experiments done using specimens containing two collinear cracks separated by a variable distance and using samples of different size showed that the two cracks behaved effectively as one for separation distances less than about Delta c. For specimen sizes much bigger than Delta c fracture testing was found to be scale-invariant for geometrically similar specimens.