Experimental investigation on hydraulic fracturing in cement mortar with tensile stress

A novel device is proposed to test hydraulic fracturing in specimen with tensile stress. The device is composed of splitting apparatus and sealing apparatus. The tensile stress in specimen is realized via splitting load. It is confirmed that the sealing apparatus has a less effect on peak splitting load and the Young's modulus of specimen. Some hydraulic fracturing experiments of cement mortar specimens with tensile stress are conducted. Critical water pressure of hydraulic fracturing will decrease with increase of the tensile stress. Hydraulic fracturing mechanism of cement mortar with tensile stress is revealed based on the Biot's theory and fracture process zone. Applied high water pressure on initial crack surface, water pressure in water flow zone, and drag force along initial crack surface and water flow zone have a promotional effect on fracture propagation. The T stress in the test and pore water pressure caused by tensile strain near crack tip will restrain fracture propagation. A critical water pressure model (CWP) is proposed based on general maximum tangential stress criterion, and it is verified that the CWP model is rational and accurate. The T stress and pore water pressure gradient along polar angle direction have an effect on direction of crack initiation.