In situ Shear Strength Tester for Coal

摘要

The objective of this research was to develop a device for rapid in situ measurement of rock shearing strength and to compare the shearing strength results with those obtained by other test methods. The rock borehole shear test (RBST) operates by expansion of two opposed steel plates against rock in the periphery of a 76-mm (3-in) diameter borehole, followed by axial movement of the plates. Small teeth on the contact plates cause shearing to occur with the rock itself. Several tests are conducted at different applied expansion pressures to generate a failure envelope of shearing strength versus applied normal stress. The envelope is plotted while the test is conducted, and a complete envelope may be generated by four tests in about 45 min. The slope of the envelope is the angle of internal friction, and the extrapolated shearing strength at zero normal stress is the cohesion.