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Abstract The mechanical properties of underground tunnel，cavern and pillar in deep high stress area are closely linked to the mechanical properties of rock after failure. Research on residual strength and post-peak mechanical properties of rock mass has very important significance for engineering design. Through cyclic loading and unloading experiments of failure rock mass，variation law of residual strength under different confining pressures(30，20，10，5 and 1 MPa) and different unloading degrees (90%，70%，30%) has been studied. The results show that the relationship between residual strength and cycle number can be fitted with the exponential function，no matter how the initial conditions are. When the confining pressure is relatively lower(≤20 MPa)，at the same confining pressure，the reduction degree of residual strength is the maximum at unloading degree of 70%，followed by unloading degree of 90%. On the other hand，the reduction degree of residual strength is the minimum at unloading degree of 30%. With the same amount of unloading degree，the lower the confining pressure is，the greater the reduction degree of residual strength is；under confining pressure of 1 MPa，the residual strength even may reduce by 73%. As confining pressure is large(＞20 MPa)，because of binding and compressive effect of the confining pressure，cyclic loading and unloading will not result in lower residual strength of rock samples.
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Received: 13 May 2010
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2010, Vol. 29 
