上覆水平煤层采空区衬砌受荷模型试验研究

隧道近接上覆水平采空区地层施工易扩大上覆围岩松动范围,增大松动荷载,为探明隧道衬砌结构受荷特性,采用室内相似模型试验量测了上覆水平煤层采空区地层隧道二次衬砌结构内力(轴力、弯矩),分析了不同边界压力作用下位移、轴力和弯矩的变化情况和特定压力下间距对二次衬砌受力的影响。结果表明:上覆采空区对洞周位移和二衬内力造成了一定影响,采空区底板与隧道间距越小,位移越大,当竖向压力为1000 k Pa时,与无采空区工况相比,0.5D工况最大位移增加93.73%,1.0D工况增加27.90%;弯矩和轴力的增加越明显,当竖向压力为500 k Pa时,与无采空区工况相比,间距0.5D工况最大弯矩增加139.68%,间距1.0D工况最大弯矩增加34.39%,采空区的存在导致轴力分布形态变化较大,间距0.5D工况平均轴力增加78.39%,间距1.0D工况平均轴力增加37.81%;最大偏心距出现在仰拱部位,承载能力相对较低,是隧道主体结构的薄弱环节;二次衬砌仰拱位置最先开裂,煤层采空区对裂缝展开顺序有一定影响。

Model tests on loading characteristics of linings in overlying horizontal coal mined-out area

The tunnel construction adjacent to the overlying mined-out area is easy to expand the rapping range of the overlying rock and to increase the loose load. In order to study the characteristics of lining structures under loads in overlying horizontal thin coal mined-out area, indoor scaled model tests are carried out to measure contact force between tunnel lining and surrounding rock and structural internal force of the secondary lining (axial force and bending moment) in the strata thin seam mined-out area. The variations of displacement, axial force and bending moment under different pressures and the influences of pitch under confining pressure on the earth pressure and internal forces of the secondary lining are analyzed. The results show that the overlying mined-out area has a certain effect on convergence displacement of tunnel. The smaller the distance, the greater the displacement and the more obvious the increase of bending moment and axial force. The internal force of the secondary lining is discretely distributed, the maximum eccentricity distance appears in the invert site and the bearing capacity has a certain degree of reduction, so it is the weak part of the main structure of the tunnel. The first crack appears in the inverted arch of the secondary lining, and the overlying mined-out area has remarkable influence on the order of cracks.