Relation between directional characteristics of resistivity changes and principal stress

Study on the relation between directional characteristics of resistivity changes and principal stress plays an important role in rock resistivity experiments and seismology. Using symmetrical four-electrode method, multi-position, multi-space and multi-direction resistivity arrays were arranged on 10 samples of granite, tuffaceous gritrock (with inclusion of gravel) and aplite granite, which have surface sizes of 4 cm×8 cm, 6 cm×12 cm, 8 cm×16 cm, 4.6 cm×10 cm, respectively, and 1 synthetic model of 100 cm×100 cm. The experiments were carried out with uniaxial, planar elastic constraint, low confining pressure and true triaxial compressions. In the uniaxial and low confining pressure tests, 4 of the 7 rock samples were loaded to rupture with macro-fractures, the other 3 were only loaded to the abnormal stage when resistivity began to decrease obviously. 3 of the 10 rock samples are samples of original resistivity anisotropy. According to the loading process from beginning to end, the resistivity data obtained from all of the 11 samples in the multi-position, multi-space and multi-direction resistivity arrays were divided into 4 rupture stress sections, namely, about 30%, about 50% and about 80% rupture stress sections and 100% rupture stress section. Thereby, the relation between directional characteristics of resistivity changes and principal stress corresponding to the 4 rupture stress sections is studied. However, the results show no confirmative relation between the two.