| The underground rock is equilibrium state before the tunnel is excavated. Once the tunnel has been excavated, the stress will be redistributed for keeping the balance state. In the course of redistributing, if the intensity of rocks is insuff, the surrounding rocks will lose balance and the tunnel will be destroyed, so it is necessary to take support measures to the soft and weak surrounding rock. The types of supporting are accord to the distinctness of rocks, the size of tunnel section, the service life and groud stress. Some traditional supports in our country have been commonly used, such as wooden supports, all sorts of metal bracket supports and stone or concrete lining supports. The comprehensive supports based on bolt and anchor has becoming a new kind supports that can apply to various rock conditions.The determination of mechanical parameters of rock mass is a basic work of tunnel-supporting project. It is a reliable guarantee to direct design, construction and numerical simulation. Based on test and research of mechanical properties of soft rock, the mechanics and category of soft rocks, damage mechanism of soft tunnel and supporting difficulty of Dafang Mine are determined. Advantages of RMR on the tunnel rock mass quality evaluation- GTMR(General Tunnel Mass Rating) method is proposed, which is applied to estimate the mechanical parameters of rock mass in Defang Mine tunnel. The factors of affecting the rock mass mechanical properties Such as intact rock strength, groundwater condition, rock quality index, the depth of tunnel, earthquake intensity and shape of tunnel are all taken into account by the GTMR system. The continuous modification of the intact rock strength and the rock quality index are put forward, and then the error caused by the subjective judgement is decreased. The tunnel excavating softening factor and anchoring strengthen factor are introduced to Hoek-Brown strength criterion. Using the formula of the above two factors, the mechanical parameters of rock are obtained after excavating and anchoring. It is applied to bolting-grouting support in the tunnel of soft rock in DaFang Mine.Nowadays, as the popular reinforcement form in the soft rocks support, the merits of the bolting-grouting support is construct rapidly, good reinforcement effect and lower cost. The paper is based on the "nested model of computational mechanics of bolt grouting support" in soft tunnel, by using the mechanical model and the elastic-plastic theory. When the elastic-plastic analysis is completed, the expressions stress and displacement in diferent zones, and the relative expressions among radius of plastic zones and bolting-grouting zones and initial supporting forces can be attained. According to the results of theoretic analysis, the mechanism of bolt grouting support is analysised and the quantitative support design of soft rock tunnel is proposed. According to catastrophe theory, the effective bearing cycle and the catastrophic theory model of instability in the area of bolt grouting support of circular tunnel, we find the minimum thickness computing formula of the effective bearing cycle in bolting-grouting support body and the computing formula of the length and the row spacing of grouting bolt.In this paper, take the tunnel reinforcement of DaFang Mine in hunan as the example. Utililizing the mechanical model, the calculation formulas of the stress-strain and the catastrophe model of bolting-grouting loop, theoretic analysis study of representative tunnel reinforcement is completed, and numerical calculation by FLAC-3D analysis software of finite element is also completed. Form the results after reinforcement, the tunnel is stable and then the reliability and practicability of theory is proved by comparing and analysing two results.
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