Abstract
Laboratory hydraulic facture experiments are conducted on monolithologic and dilithologic layered rock specimens as a function of interfacial normal stress to determine the relative influence of the interfacial shear strength (due to the frictional effect of the applied normal stress) and the rock properties on either side of the interface on fracture growth across layer interfaces. Parameters which influence the frictional shear strength of an interface such as surface roughness and time of interfacial contact are varied. Layer interfaces are also separated by low shear strength material such as quartz sand and montmorillonite clay. It is found that facture propagation across unbonded layer interfaces always occurs if a critical interfacial normal stress is exceeded. Differences in the mechanical and physical properties on either side of the interface do not prevent fracture growth across an interface. The critical interfacial normal stress needed for fracture growth across an interface decreases with increasing surface roughness of the interface, increasing time of interfacial contact, and/or decreasing tensile strength of bounding layer. Fracture containment at layer interfaces is achieved only when the layers are separated by a thin layer of montmorillonite clay. It is suggested that containment of a hydraulic facture occurs whenever the frictional shear strength of the interface is sufficiently weak relative to the tensile strength of the bounding layer that the fracture more easily becomes an interfacial fracture than extending across the interface into the bounding layer. In addition, photoelastic experiments are conducted on tensile cracks perpendicular to bonded and unbonded interfaces with interfacial normal stress. These experiments are commensurate with the hydraulic fracture experiments and also indicate that fracture growth across an interface is dependent on the relative shear strength of the interface with respect to the fracture-induced shear stress along the interface due to the fracture approaching the interface. It is suggested that facture containment at an interface will also occur whenever the interfacial shear strength is less than the facture-induced shear stress along the interface...
Teufel, Lawrence William (1979). An experimental study of hydraulic fracture propagation in layered rock. Texas A&M University. Texas A&M University. Libraries. Available electronically from
https : / /hdl .handle .net /1969 .1 /DISSERTATIONS -130191.