考虑分部开挖的超大跨度公路隧道围岩压力计算方法研究

A surrounding rock pressure calculation method for super-large-span highway tunnels considering sequential excavation

为了提出一种新的超大跨度公路隧道围岩压力计算方法,基于邻近隧道施工力学理论,研究分部开挖各导洞围岩压力之间的影响关系,分析分部开挖法各导洞相互影响机制。通过选取3个地区5座典型单洞四车道公路隧道18个测试断面,采用现场测试的方法,获得III,IV,V级围岩上下台阶法施工和上台阶CD法施工的围岩压力测试数据,发现后导洞围岩压力受先导洞开挖影响而普遍较大的规律,提出采用导洞影响系数η定量化分析先导洞开挖对后导洞围岩压力的影响程度,进而修正隧规公式中的围岩压力增减率,提出考虑分部开挖法施工的超大跨度公路隧道围岩压力计算方法。结果表明:(1)邻近隧道周边应力的弹性解析结果表明平行(左右)隧道对周边应力影响比较显著,重叠(上下)隧道对周边应力影响较小,应重点考虑左右平行导洞开挖对围岩压力的相互影响;(2)导洞影响系数η整体以大于1为主,IV级围岩η平均值为1.12,V级围岩为1.28;(3)基于隧规提出修正后的围岩压力增减率i’=0.017(S-1);(4)与隧规相比,采用本文提出的围岩压力计算方法,IV级、V级围岩压力分别减少14.6%和2.4%,更接近实测值。

To propose a new surrounding rock pressure calculation method for super-large-span highway tunnels,based on the construction mechanics theory of adjacent tunnels,this paper studied the influence between the surrounding rock pressures of each pilot tunnel excavated in sequence,and analyzed the interaction mechanism of each pilot tunnel excavated in sequence. By selecting 5 typical highway tunnels with four lanes in a single hole at three different regions,the monitoring data of surrounding rock pressure of 18 cross-sections of grade III,IV and V rock mass constructed by upper-lower bench method and upper-bench CD method were obtained,and it was found that the surrounding rock pressure of the rear pilot tunnel was generally affected by the excavation of the first pilot tunnel,and the pilot tunnel influence coefficient η was proposed to quantitatively analyze the influence of the first pilot tunnel excavation on the surrounding rock pressure of the rear pilot tunnel. Then,the variation rate of the surrounding rock pressure in the current tunnel code was modified,and finally a calculation method of the surrounding rock pressure of the super-large-span tunnel considering the sequential excavation was proposed. The results show that:(1) The parallel(left and right) tunnels have a significant impact on the peripheral stress,while the overlapping(upper and lower) tunnels have limited impact on the peripheral stress. The combined impact of the left and right parallel pilot tunnel excavation on the surrounding rock pressure should be considered;(2) The influence coefficient η of the pilot tunnel is mainly greater than 1,and the average values of Grade IV and V surrounding rock are 1.12 and 1.28 respectively;(3) Based on the current tunnel standard,the revised variation rate of the surrounding rock pressure was proposed,which is i’= 0.017(S-1);(4) Compared with the calculation method of the surrounding rock pressure in the current tunnel standard,the Grade-IV and Grade-V surrounding rock pressures calculated by the proposed method in this paper are reduced by 14.6% and 2.4%respectively,which are closer to the measured values.