水下浅埋暗挖小净距隧道安全贯通的力学行为与施工措施

Mechanical behavior and construction measures of transfixing safely to underwater tunnels with small clear spacing by shallow mining method

长沙市浏阳河公路隧道是一座水下浅埋暗挖小净距隧道,从河两岸对头施工,四洞在河底两两先后贯通时,不仅要考虑四洞施工的相互影响,还要考虑水渗流的影响,施工风险高。结合数值模拟与现场实测,首先比较了4种贯通方案以选择最优方案,然后研究了关键部位在贯通过程中的力学性状并提出了相应的施工措施,最后分析了贯通效果与贯通后的延续影响。结果表明:应采用两贯通处纵向间隔23 m、先后单向施工到贯通处的贯通方案;贯通处岩柱的最大压应力出现在岩柱底部,贯通处岩柱呈现顶窄底宽的楔形状态有利于岩柱受力;在贯通时,不用施作临时支护,应快速将隧道上台阶贯通处岩柱从上至下一次性全挖掉后施作初衬;应关注河床沉降的变化;隧道贯通力学行为对于围岩应力场与渗流场的影响具有时间效应;隧道安全贯通而且贯通的效果较好。所得结论可为类似高风险水下隧道的安全贯通提供参考。

The Liuyanghe highway tunnel in Changsha City is a underwater tunnels with small clear spacing by shallow mining method, the excavation faces approached each other respectively from both sides of the river, when two pairs of holes are transfixed successively under the river, the effects of construction interaction of four caves and wa- ter seepage should be considered, and the construction risk is high. By numerical simulation and field measurement, firstly, the 4 transfixion programs were compared to choose the best scheme, then, the mechanical character- istics of key positions in the process of transfixion were studied and the effective construction measures were put for- ward, finally, the transfixion effect and the continued influence after transfixion were analyzed. The results show：the transfixion project should be adopted that the longitudinal separation of two transfixion positions is 23m and the single-track eaves are constructed one after another to the transfixion position; the maximum compressive stress of the transfixion rock pillar appears at its bottom, it would be beneficial to bear the load that the shape of the transfixion rock pillar is wedge of narrow top and wide bottom; when the two eaves are transfixed, it is not necessary to construct the temporary support, the transfixion rock pillar of the upper bench should be cleared rapidly and completely from top to bottom, then the initial lining was constructed ; the variation of the riverbed settlement should be noticed; the influence of the mechanical behaviors of transfixing on the stress field and seepage field of the surrounding rock has time effect; finally, the tunnels are transfixed safely, and the transfixion effect is praiseworthy. The conclusions might offer reference for transfixing safely the similar high-risk underwater tunnels.