The altered rock is the soft rock which is scarce in the engineering. For a major engineering project in Southwest China

the altered rock is located in the key position of the project. In order to guarantee the project for long-term stability

the mechanical property of the altered rock should be deeply and fully studied. On the basis of systematic conventional triaxial compression test for the saturated altered rock under different porosities

the test results are analyzed and summarized. It has been put forward that there are three types of stress-strain curve before rock destruction and three types of stress-strain curves after rock destruction. The conclusions have been proposed that the altered rock destruction is effected by both confining pressure and porosity. When the confining pressure is 12 MPa

the brittle failure is dominating. Only when the porosity is more than 16 % and the confining pressure is more than 4 MPa

the brittle-ductile fracture diversion state is possibly found. Furthermore

the confining pressure of brittle-ductile fracture state diversion decreases along with the porosity increases; and the critical state stress ratio increases along with the porosity increases.