高速公路大跨隧道最小安全净距研究

The minimum safe net distance between large span expressway tunnels

在江南低山丘陵区高速公路隧道建设中,由于地形条件的限制,高速公路分离式大跨隧道的净距不能满足规范要求而设计采用双洞方案时,隧道净距的减小应做出充分的技术论证和比较研究。在明确小净距隧道最小安全净距概念的基础上,提出以围岩位移、主应力以及支护结构主应力随净距的减小是否发生突变,并结合中间岩柱是否出现塑性区综合判定最小安全净距的新方法。采用三维快速拉格朗日程序,考虑实际地形条件,针对破碎的Ⅳ级围岩在设计支护参数、实际施工方法条件下,不同净距高速公路双向6车道大跨隧道的施工过程进行数值模拟。通过对模拟结果的综合分析,比选出复杂地形高速公路大跨隧道的最小安全净距为隧道开挖跨度的0.5倍。研究成果可为低山丘陵区高速公路小净距隧道的净距优化提供理论参考。

During the construction of expressway tunnels in low mountainous areas south of the Yangtze River in China, the net distance between adjacent large span expressway tunnels sometimes cannot meet the requirements of the Code for Design of Road Tunnels （JTG D70-2004） because of the limitation of terrain conditions. However, since the design is twin tunnels, sufficient technical evaluation and comparative study are done to decrease the net distance between adjacent tunnels. The concept of minimum safe net distance between adjacent tunnels is defined, and an integral method of discrimination is put forward to determine the minimum safe clear distance. This method relies on whether there exist sharp changes of the displacement and principal stress of the surrounding rock and the principal stress of the support system, and whether plastic zone appears in the intermediate rock mass. Numerical simulations of the construction process of a six-lane large span expressway tunnel considering different net distances for grade Ⅳ surrounding rock. The minimum safe net distance for adjacent large span expressway tunnels under complex terrains is suggested as one half of the tunnelling span by using integrated analysis.