临近溶腔内压对隧道初支稳定性影响的模型试验

部分未经处理溶腔填充物复杂且受季节性、突发性降雨影响,溶腔内压增大会影响临近隧道结构稳定性,易导致施做后的初支结构失稳.以某三车道公路隧道为依托,开展了隧道开挖后承压溶腔对初支力学行为影响的模型试验.试验中逐级增加溶腔内压,测试了隧道洞周位移、初期支护内力及背后围岩压力的变化特征,研究承压溶腔位置及内压对隧道初支稳定性的影响.试验结果表明:隧道临近溶腔处洞周位移随溶腔内压增大而变大,达到临界内压时突然增大;承压溶腔内压增大显著增大了钢拱架临近溶腔测点处的弯矩,使钢拱架轴力水平整体提升;同时增大了临近溶腔位置处及墙角处初期支护背后围岩压力,造成初支受力不均匀.洞周位移发生突然增大、钢拱架在轴力和弯矩共同作用下达到屈服强度时,初期支护结构失稳.在试验设定的溶腔尺寸及间距下,仰拱处存在溶腔时,内压增大,隧道初期支护最先失稳.

Model Test of the Influence of the Internal Pressure near Karst Cave on Stability of Tunnel Primary Support Stability

As part of the untreated fillings of concealed Karst cave with internal pressure behind tunnel are complex and influenced by the seasonal precipitation and sudden precipitation, the increase of internal pressure can affect the stability of the structures near the tunnel, and may easily lead to the instability of tunnel primary support structure. Scaled model tests based on a 3-lanes highway tunnel were carried out to investigate the stability of tunnel excavation nearby Karst cave with internal pressure. Characteristics of the tunnel convergence, internal force of steel arch, surrounding rock pressure behind primary support and surrounding rock strain were analyzed to study the effect of position and pressure on the stability of the tunnel. The results show that, under the specific cavity size and spacing, tunnel lost stability firstly for Karst cave in the inverted arch. The convergence of the tunnel near the Karst cave increases with the increase of the pressure and changes suddenly when reaching the critical internal pressure, and the primary support loses its stability. The increase of pressure leads to the obvious increase of the bending moment of steel arch, and increases the axial force of steel arch evenly. Finally, the steel arch reaches the yield state, meanwhile, primary support becomes instability. Surrounding rock pressure behind the primary support near Karst cave increases obviously and leads to the uneven stress of primary support with the increase of Karst cave internal pressure.