小净距隧道下穿薄煤层采空区地层开挖稳定性分析

采空区地层离散性大,小净距隧道近接下穿不同倾角薄煤层采空区开挖将引起采空区内腔塌陷。建立小净距隧道近接下穿采空区地层开挖模型,对比分析采空区倾角为0°、15°、25°、40°时先行洞监测面洞周位移和初支内力。结果表明:后行洞初支闭合时,采空区倾角为15°时,拱顶下沉量最大;采空区倾角为40°时,仰拱隆起量和拱腰水平收敛量最大;随着采空区倾角增大,初期支护正(内)弯矩分布和轴力最大位置有向近接采空区侧移动的趋势,偏压越严重;应力集中逐渐由右拱脚向左拱脚移动。最大偏心距出现在拱脚处,采空区倾角为15°时,偏心距最小,初期支护稳定性最好;倾角为40°时,偏心距最大,不利于初期支护稳定。

Analysis of Excavation Stability of Twin Tunnels Under-crossing Thin Mined-out Coal Area

Mined-out area is of high discreteness. The construction of twin tunnels undercrossing thin mined-out coal area with different dip angles may lead to inner cavity collapse,causing bias load. A model of twin tunnels excavated undercrossing mined-out coal area is established to analyze the hole perimeter displacement and the primary support internal force of the monitoring section of the tunnel first excavated when the dip angle of the mined-out coal area is 0°,15°,25° and 40°. The results show that after the primary support of the second tunnel is closed,the vault settlement of the tunnel first excavated is the biggest when the dip angle is about 15°; when the dip angle of the mined-out coal area is 40°,the invert displacement and the arc spring level convergence is the biggest; as the dip angle of the mined-out area increases, the positive bending moment and the maximum axial force position ofthe primary support tend to move to the side close to the mined-out area,and the load bias is more serious; the stress concentration position tends to move from right arch spring to left arch spring. The maximum eccentricity position is at the arch spring. The minimum eccentricity appears when the dip angle of mined-out coal area is 15°and the stability of primary support is at its best. While,the maximum eccentricity shows up when the dip angle of mined-out coal area is 40°,and the stability of primary support is the weakest.