浅覆大跨度小净距隧道中岩墙及初支力学特性研究

Study of Mechanical Properties of Middle Rock Wall and Preliminary Lining of Shallow Buried Large Span Tunnel with Small Clear Distance

通过建立后掘隧道的三台阶开挖数值分析模型,模拟D/B分别为0.5,0.75,1,1.25,1.5,2情况下,后掘隧道开挖对中岩墙多次扰动所引起的围岩塑性区分布、主应力差、水平位移等力学特性,并分析其对先行隧道初支内力的影响。通过分析中岩墙应力、变形随净距的变化,表明当中岩墙厚度小于0.75B时,中岩墙上部区域塑性区已贯通,塑性区范围急剧扩大,说明后掘隧道对中岩墙的受力变形和先行隧道支护结构受力极为不利。在D/B=0.5的不利情况下,可对中岩墙进行注浆加固处理,模拟结果表明注浆可极大降低初支受力,最大轴力减小了49.1%,最大弯矩减小了29.1%,大大提高了围岩稳定性。

By using the established 3-step excavation numerical analysis model of later tunnel excavation,which can simulate the situations of D/B = 0. 5,0. 75,1,1. 5,1. 25,2,the mechanical behavior of middle rock wall such as plastic zone distribution, principal stress difference, and horizontal displacement of surrounding rock,etc. caused by multiple disturbances and the influence on advance tunnel initial support＇s internal forces after digging another tunnel with different values of D/B（ 0. 5,0. 75,1,1. 25,1. 5 and 2）are simulated. The analysis of stress and deformation of middle rock wall change with different clear distances shows that when the middle rock wall＇s thickness is less than 0. 75 B,the plastic zone expanded rapidly and the plastic zone linked up in the upper part of the middle rock wall,which indicates later excavated tunnel has great adverse influence on the force and deformation of middle rock wall and the advance tunnel support structure＇s force state. Under the unfavorable situation of D/B = 0. 5,grouting can be used to reinforce the middle rock wall,and the simulation result shows that grouting can greatly reduce initial support force and improve stability of surrounding rock. Analysis date shows that grouting can greatly reduce initial support force,the maximum axial force reduced by 49. 1% and the maximum bending moment reduced by 29. 1%,so surrounding rock＇s stability is greatly improved.