Abstract: The rock is highly fractured with low strength and poor self-stability in the diversion tunnel of water transferring project from Hongyan River to Shitou River. Due to the large deformation of the soft rock tunnel, a series of special problems such as TBM jamming occurs during tunnel construction. This paper is aimed to analyze the effects of sample composition and clay mineral content on the disintegration through X-ray diffraction and the disintegration test. In addition, the deformation and failure characteristics and creep properties of rock mass under different stress conditions are studied through a series of uniaxial compression tests, triaxial compression tests and the triaxial creep tests, respectively. The test results show that the surrounding rock is softened, because the clay minerals (33.49%) like montmorillonite and illite of the rock are sensitive to water. The sample has a large plastic compression deformation, and its stress-strain curve presents a strain-hardening type but no obvious peak intensity. The large deformation mechanism of the soft rock tunnel is analyzed, and a new support technology for installing polyurethane buffer layer between surrounding rock and lining is proposed based on the experimental studies and on-site monitoring data. The rationality of the proposed support technology is also verified through the numerical calculation. The results show that the polyurethane buffer layer can absorb the deformation pressure of the surrounding rock, and avoid the dislocation of segment caused by stress concentration, which can greatly reduce the failure zone of the lining. Research results of this study provide significant references for the tunnel design and construction as well as long-term stability analysis.

Key words: broken soft rock, mechanical properties, large deformation, creep test, support technology