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To study the strength properties and evolution laws of cracked sandstone samples in re-loading tests,strength and damage evolution properties of intact sandstone samples were first analyzed through the triaxial compression tests carried on TAW-2000 microcomputer control electro-hydraulic servo rock triaxial test system.Damage evolution models were established based on dilatancy properties realizing the real-time and quantitative evaluation of samples damage state in loading process.On this basis,sam-ples with different damage were obtained by pre-peak,peak point,post-peak and residual strength stage unloading tests in the loading process of intact samples.The characteristics of the stress-strain curves and strength evolution laws were studied through the re-loading tests of samples with different damage under different stress states.The experimental results showed that the slope of stress-strain curves,peak strength and residual strength of cracked samples increased linearly with confining pressure and decreased linearly with damage.The equivalent cohesion decreased with damage in the exponential decay curves.The mechanics properties of samples transformed from strain softening to strain hardening with damage.