软弱围岩隧道掌子面及超前核心土挤出位移特征研究

Research on extrusion displacement of face and advanced core in tunnel with weak surrounding rock

为研究软弱围岩隧道掌子面及超前核心土的挤出位移特征,用Solexperts AG公司生产的GMD滑动测微计对湄渝高速岐山隧道F215构造破碎带区域进行了挤出位移实测,通过有限差分程序进行系列数值试验,着重研究了隧道穿越软弱围岩期间挤出位移的变化特征,并分析了破碎带长度和硬软岩刚度比的影响。结果表明,(1)挤出位移的大小可反映前方围岩质量,挤出位移在超前核心土内的分布可反映前方围岩的节理裂隙发育情况;(2)隧道开挖在掌子面前方造成的扰动范围大致为1.5倍的隧道开挖跨度;(3)隧道接近前方变化地质区域时,挤出位移的增大或减小具有超前性;(4)软岩段长度在一定范围内会影响掌子面进入软岩区后挤出位移的大小和变化趋势;(5)硬岩与软岩间的刚度比越大,挤出位移变化速率越大,且隧道由软岩区向硬岩区掘进时挤出位移的变化时机越早,而由硬岩区向软岩区掘进时的变化时机不受刚度比影响;(6)可将对挤出位移的监测分析作为超前地质预报的补充手段判断掌子面前方围岩情况。

In order to investigate the characteristics of extrusion displacement in the tunnel face and advanced core in tunnel with weak surrounding rock, the extrusion displacement of the soft fault area F215 in the left line of Qishan tunnel in Fujian province is measured with the GMD sliding micrometers produced by Solexperts AG Company. A series of numerical simulations are carried out with finite difference program to study the characteristics of extrusion displacement during the time tunnel passes through the weak rock zone; and the influence of the length of weak rock zone and the stiffness ratio of hard rock to weak rock are analyzed. The results show that: (1) The magnitude of extrusion displacement can reflect the quality of the surrounding rock of the advanced core, while the distribution of extrusion displacement in advanced core can reflect the condition of joint crack ahead of the tunnel face. (2) The range of disturbance in front of the tunnel face caused by excavation are around 1.5 times as long as the excavation span of the tunnel. (3) The extrusion displacement is able to increase or decrease in advance before the tunnel face approaches the area where the surrounding rock is changed. (4) When the tunnel face enters into weak rock zone from hard rock zone, the length of weak rock zone can affect the magnitude and the change trend of extrusion displacement in some extent. (5) The bigger the stiffness ratio of hard rock to weak rock, the faster the rate of extrusion displacement change increases; and the earlier the extrusion change occurs when the tunnel face approaches from hard rock zone to weak rock zone, while there is no difference when the tunnel face approaches from weak rock zone to hard rock zone. (6) The monitoring and analysis of extrusion displacement can be a supplementary method of advance geological forecast to distinguish the condition of surrounding rock ahead of the tunnel face.