Study On Stability Of Flat Coal Layer In Xi Shanping Tunnel

Although the strength and the stability of rock mass are determined by rock strength, they are weakened more by the joints and fabric. Because of the weakened strata, joints and fabric, in many instances, breakage by lowered strength or unsteady along the joints and fabric is the antinational problem in underground space stability research.In the Dissertation, base on the conclusions of measurements and field monitoring, choosing the representative sections from thick single layer with different angle of dip, coal-bearing strata and the backfilling over or under the tunnel, contrastively construe the space convergence, get the different characters about the speed and the cumulative convergence among them. Analyze the affections of surrounding rock deformation stability due to the layer angle and rock strength. Using the 2D-σ software, through the numerical analysis, it get the properties of stress redistribution in surrounding rock at the coal-bearing strata and the backfilling over or under the tunnel, also, the character of stress in shotcrete strata. These offer some references for security and economy in tunnel support design. At last, combining with space convergence of surround rock, numerical analysis conclusion and field support measurements, it gives a security and stability appraisal of flat dip layer in Xi Shanping Tunnel; also, some advices are given about the monitorial work and numerical simulation.The research results show that:1. The angle of dip give more affection on space convergence, the steep dip layer are stable fast than the flat dip layer. 2. In flat dip layer, the seam thickness control the stability of the wall rock, the thick-bedded hard rock is stable than the thin-bedded hard rock. 3. The arch apex subsidence is varied by the relationship between the tunnel and the coal-bearing strata (or the backfilling). As the coal-bearing strata rising from the bottom of tunnel to the top, the arch apex subsidence, at first, rise to its top, then turn to drop a little. 4. According to the numerical analysis conclusion, the stress change quickly at the bedding surface between the hard rock and soft rock so doesthe shotcrete stress. 5. Affected by the backfilling, the tangential stress of shotcrete has a tendency is for pressure stress to be tensile stress; it is dangerous to induce the axial cranny. 6. As the field work in Xi Shanping Tunnel showing, constructing tunnel in flat dip coal-bearing strata, if there is thick-bedded hard rock nearby, the stability of the wall rock is ensured by the control in soft rock supporting reinforce.These results offer some reference to design and construct by NATM in coal strata regions, which enlarge the knowledge of wall rock stability both in theory and practice, too.