Abstract: The design and construction of the diversion tunnel are very difficult in the soft rock strata of the Northern Xinjiang, which is caused by the complexity of geographical, climatic conditions and engineering geology. The large deformation and even collapse hazards of surrounding rock are very easily to be encountered, due to its bad self-stability, strong permeability and water-softening characteristics. Hence, the uniaxial, triaxial compression tests and uniaxial creep tests were conducted to further study the physical and mechanical properties, water-softening characteristics and energy damage evolution mechanism of the Jurassic and Cretaceous argillaceous sandstones of Northern Xinjiang. Compared with the results of these two kinds of soft rocks both with rich clay minerals, the particle size distribution of the Cretaceous argillaceous sandstone was more uniform, but its cementation degree was lower. As a result, the strength, stability and the wave velocities of strata in the Cretaceous argillaceous sandstone were lower than those in Jurassic argillaceous sandstone. Under the condition of low confining pressure, two kinds of rock deformation were mainly circumferential deformation and volume expansion. With the increase of confining pressure, the failure mode changed from volume expansion to volume compression type. High confining pressure loading can cause internal damage of rock structure, resulting in the reduction of compressive strength. When these two kinds of rocks were saturated, the ductility and strain softening characteristics were significantly enhanced. The water-softening characteristic of the Cretaceous argillaceous sandstone was much more obvious. Cretaceous argillaceous sandstone had more significant creep characteristics, and their long-term strengths were both close to their damage stress values in uniaxial compression tests. The energy damage evolution processes of two kinds of argillaceous sandstones both showed the S-shaped evolution law. The energy-hardening characteristic of Jurassic argillaceous sandstone was more significant, but the Cretaceous argillaceous sandstone was earlier to enter energy-hardening and energy-softening stages.

Key words: Jurassic and Cretaceous, argillaceous sandstone, mechanical properties, water softening, damage evolution