Abstract: This study aimed to develop an appropriate similar material for weak surrounding rock mass which can be used in physical model test of tunnel surrounding rock mass stability. The weak surrounding rock mass of class IV has been chosen as reference prototype for our research. Five raw materials, namely, barite powder, gypsum, fine sand, laundry detergent, and water were used to produce the similar material. Direct shear tests, uniaxial compression tests and triaxial compression tests were performed to obtain strength characteristics and physico-mechanical parameters of the material, including cohesive strength c, internal friction angle ? uniaxial compressive strength Rc, elastic modulus E, Poisson ratio ?. Firstly, a large number of the above mentioned tests were carried out to analyze the impact of various proportions of each raw material on strength characteristics and physico-mechanical parameters of the similar material; thus selecting appropriate raw material proportion to simulate the weak surrounding rock mass of class IV. Secondly, strength characteristics and failure behavior of the similar material which had been developed with selected raw material proportion, is further studied by a large numbers of triaxial compression tests under various confining pressures. The results indicate that, either decreasing water content or increasing gypsum content can lead to an obvious increase in Rc, E and c, along with a slight decrease in ?. On the other hand, the mounting of fine sand content resulted in an increase of E and ?, while Rc value decreased. In addition, while gypsum content turned out to be the most important factor affecting the brittle and ductile characteristics of similar material; water content affected the strength of such material significantly. The results also show that the developed material presents brittleness under low confining pressure, and becomes more ductile with the increase of confining pressure. Furthermore, failure data of the material are smaller than that calculated from linear Mohr-Coulomb failure criterion and slightly higher than that of nonlinear Hoek-Brown failure criterion. However, similar material obeys far better the Hoek-Brown criterion. The results of this study will be very useful for future research on tunnel surrounding rock mass stability in physical model tests, as well as in numerical simulations.

Key words: weak surrounding rock mass, similar material, physical model test, failure criterion