When forces are applied to soil by natural processes or by mechanical cultivation, it may fracture. This paper shows how methods of elastic-plastic fracture mechanics which, are normally used to characterize the fracture properties of metals, have been used to quantify some of the fracture properties of soils. Experiments have involved the verification and use of an electrical potential method for the measurement of crack length and the development of a method of propagating cracks through very weak materials in a controlled manner. The soils tested ranged from clays in a plastic state, to granular clays stabilized by the addition of ordinary Portland cement. Like tough metals, the soils tested showed a pronounced increase in their intrinsic crack growth resistance (JR), as the cracks grew. This increase ceased after extensive crack propagation, a tendency which is also seen in metals.