大帽山小净距隧道群中夹岩累计损伤效应研究

 小净距隧道的爆破施工不可避免地造成围岩累计损伤，岩体力学性能劣化。结合大帽山小净距隧道群的监控量测实践，基于动力损伤变量和围岩内部位移，研究小净距隧道群中夹岩的累计损伤效应。声波波速和围岩内部位移的监测结果表明，新建大帽山隧道的爆破施工已经导致中夹岩产生一定程度的损伤、破坏和滑移，但围岩位移并没有持续变化失稳，岩体仍具有一定的强度；通过对新建隧道和原有隧道损伤范围的比较发现，双侧壁导坑法施工造成围岩的累计损伤范围比全断面法施工大近3倍，并且循环爆破施工造成围岩的累计损伤更显著，所以围岩累计损伤效应是小净距隧道施工过程中必须高度重视的；上断面爆破施工一般使岩体内的裂纹被激活，声波波速显著下降，下断面爆破致中夹岩墙产生类墙体的振动，使岩体变松散滑动，围岩内部位移显著增大；并且围岩的滑动都是爆破时发生的，爆破停止滑动也就停止；在判断围岩的累计损伤程度和范围时，应充分考虑声波波速变化率和位移量，仅通过声波波速变化率可能做出误判；与爆源越近，围岩的损伤度和位移量越大，越远越小，且累计损伤效应呈现明显的非线性特征。

RESEARCH ON ACCUMULATIVE DAMAGE EFFECT OF INTERLAID ROCK IN DAMAOSHAN TUNNEL GROUP WITH SMALL CLEAR DISTANCE

The blasting construction of small clear distance tunnel inevitably causes accumulative damage of surrounding rocks and its mechanical behaviors will be degenerated. Based on dynamic damage variable and internal displacement of surrounding rock，combining with the monitoring results of Damaoshan tunnel，accumulative damage effects of interlaid rock in tunnel groups with small clear distance are studied. Monitoring results of acoustic velocity and internal displacement show that the newly-built blasting construction has caused damage，breakage and slippage of inter-space rock to a certain degree. However，the internal displacement does not cause instability，and surrounding rocks still possess certain strength. By comparing newly-built tunnel with existing tunnel，damage range caused by construction using two side-wall pilot tunnel method is three times more than the range caused by using whole section excavation. Therefore，accumulative damage effect should be brought to high attention during the construction of small clear distance tunnel. Blasting in upper section will lead to activation of the fissures of rock and significant declines of acoustic velocity；and blasting in lower section will lead to vibration of inter-space rock as wall vibration and significant increase of internal displacement，which causes loosing and slippage of rock mass. The slippage will stop till the blasting stops. Both the changing rate of the acoustic velocity and the displacement should be taken fully consideration in the analysis of the accumulative damage range and degree. If only the changing rate of the acoustic velocity is considered，the analytical results will not be correct. The farther the explosion source is，the bigger the damage degree and the displacement of the surrounding rocks are. The accumulative damage effect has distinct nonlinear characteristics.