Abstract:It is one of the main tasks of laboratory test to determine the strength parameters. However there are some difficulties to calculate the cohesion and internal friction angle. The specimens are less,or their divergence is so great that the strength of specimen in higher confining pressure is lower. Based on the servo-control testing machine,a method is suggested in this paper to determine the Coulomb curves of sandstone and marble with only one specimen. Marble specimen has a clear yield platform when it is compressed in high confining pressure. A series of strengths can be obtained by stepping up the confining pressure in the yield platform,which is regressed for the Coulomb curves. A sandstone specimen is broken under uniaxial pressure with higher confining pressure,and then the confining pressure is reduced to keep axial deformation constant. The axial bearing capacity of the broken specimen decreases with reduction of the confining pressure,and the linear relation of them is nearly the same with the relation of the peak strength and confining pressure.