In order to study on gradual breakage action of red sandstone in different water contents

rock microcosmic loading apparatus is configured with digital microcosmic observation system. And it can carry out several angles real-time whole and local magnifying monitoring to crack of specimen surface with monitor. Moreover monitored images can be recorded and collected automatically with computer. By this system

red sandstone of Hongshanyao Hydraulic Project in water state. The uniaxial compression experiment is carried out. Images of crack engendering and developing are analyzed by digital image technique for discussing the intrinsic relation between crack process and nonlinear deformational responses. In order to obtain quantitative description of crack development

two physical quantities of damage tensor and crack degree are proposed

which can appraise quantitatively gradual breakage properties of red sandstone in water state and furthermore analyze the law of rock crack damage evolution under uniaxial compression.