Abstract：By using the accessory loading equipment corresponding to the CT machine and simulation material，the CT real-time testing of specimens with single crack with and without water in it is conducted to observe the complete process of crack growth. The failure form of the crack including its generation，evolution，development and final failure under complex stress and various underground water conditions is investigated. Different models of crack propagation in geotechnical engineering under the conditions with and without water and hydraulic pressure are constructed，respectively. It is shown that there exist different failure forms of rock mass under three conditions from the CT scanning，but the CT images with compressed microcrack，damage evolution，microcrack growth and macrocrack generation are clear. It is concluded that the influence of underground water conditions on rock engineering must be taken into consideration. At the same time，some scientific hypotheses of the damage evolution equations and stress-strain relationship as well as the failure mechanism of rock mass are also proposed.
