上覆薄煤层采空区公路隧道开挖稳定性试验研究

隧道下穿煤层采空区施工将对周围地层产生扰动,影响隧道围岩及初期支护的稳定性.进行了上覆薄煤层采空区隧道开挖的室内相似模型试验,试验中通过测量隧道开挖过程中采空区地层、隧道拱顶的沉降及初期支护内力等参数,对上下台阶法和单侧壁导坑法进行了对比分析.测试结果表明,隧道开挖引起的采空区地层沉降受开挖方法的影响显著,上下台阶法开挖引起的采空区地层沉降高于单侧壁导坑法,沉降槽曲线较陡、沉降范围更宽.两种开挖方法中,围岩压力的最大值均位于右拱脚处,钢拱架最大弯矩出现在拱脚处,最大轴力位于拱腰或拱肩处.其它条件相同时,采用单侧壁导坑法开挖时初期支护背后的围岩压力、钢拱架内力和偏心距等普遍大于上下台阶法开挖.研究表明在隧道下穿倾斜煤层采空区施工时,采用单侧壁导坑法开挖可以显著减小对采空区地层及围岩的扰动,但同时需增强初期支护的刚度,确保围岩及隧道结构的整体稳定性.

Model Test of Excavation Stability for Highway Tunnel Beneath Mined-out Thin Coal Seam

The construction of tunnels beneath mined-out coal seam disturbs the stratum nearby and influences the stability of surrounding rocks and primary support. Similar indoor model tests were carried out to simulate the excavation of tunnels beneath inclined mined-out thin coal seam. Benching method and side heading method were compared on the basis of the measured data such as subsidence of mined-out coal seam, internal force of primary support and so on. The test results indicate that excavation method has a significant effect on the subsidence of mined-out area. Benching method leads to bigger subsidence than the side heading method, which has a deeper and wider subsidence trough. In both methods, the biggest surrounding rock pressure are located in right arch foot, the biggest bending moment in the arch foot and axial force of the steel frame on the haunch or spandrel. Under the same condition, surrounding rocks pressure, internal force and the eccentricity of steel frame measured in side heading method are generally greater than those in benching method. Although side heading method can reduce the disturbance of surrounding rocks, the primary support of the tunnel should be strengthened to ensure the stability of surrounding rocks and the structure.