Fracturing Mechanism in Soils with Three Dimension Stress State

Hydraulic and pneumatic fracturing has been used to improve the permeability of the soil and rock and has been widely used in geotechnical practices. Although two soil fracturing mechanisms (i.e., tensile failure mechanism and shear failure mechanism) were proposed in literatures, the soil fracturing mechanism is still not yet fully understood. A comprehensive review was conducted on the available approaches existing in the literature to calculate the fracture-initiation pressures around a borehole. And then, two fracture-initiation pressure calculating formulas with three dimension stress state were put forward in this paper, based on tensile failure mechanism and shear failure mechanism, respectively. In addition, the suitability of those two calculating formulas was assessed. The results imply that the possibility of shear failure mechanism is increased with the increasing of the minor principal stress and decreasing of undrained shear strength of soil. A hydraulic fracturing test results in literatures were also verified the suitability of proposed methods.