汶川8.0级地震前后福堂隧道应力场变化研究

Geostress Field Analysis of Futang Tunnel,before and after Wenchuan Ms8.0 Earthquake

"5·12"汶川地震后,发震断裂上盘的高地应力本应获得一定程度的释放,但位于该地区的福堂隧道仍出现了较强烈岩爆灾害和饼裂岩芯等高应力特征.为研究该特殊高地应力现象,基于实测地应力值和地震前后区域地应力反演分析,获得了该特殊高应力现象的形成原因.结果表明:"特殊高地应力"主要受断裂带逆冲推覆持续作用、浅表生改造、介质差异及其距发震断裂的距离效应等因素影响而综合形成;强震后福堂隧道靠映秀侧洞段应力有较大降幅,而靠汶川侧洞段应力值降幅较小且仍处于高应力状态;隧道K18+850~K21+450段最大地应力介于20~25 MPa之间.特殊的地应力特征使得隧道两端具有完全不同的工程特性,对不同应力值洞段的支护参数选取、施工方法及隧道造价等都具有重要的工程意义.

After an earthquake,such as the ＂5.12 Wenchuan earthquake＂,some of the high stresses in the hanging wall of seismic faults should be released. However,the rock mass surrounding the Futang Tunnel,is still under high stress,even after the earthquake,as evidenced by rockburst and core cracking. To investigate this issue,in-situ stress tests and back analysis of the tunnel＇s regional stress field,before and after the earthquake,were conducted to deduce the formation mechanism of this high stress. Research shows that the high stresses are produced by the integration of the continuous effects of fault thrusts,epigenetic and superficial reformation,medium differences,the effect of distance to the fault,and so on. The stress on the Yingxiu side of the Futang Tunnel decreased significantly after the earthquake,but on the Wenchuan side,there was little decline,and so the stress is still high. The maximum stress in Section K18 ＋ 850-K21 ＋ 450 is between 20-25 MPa. This unique stress distribution means that both sides of the tunnel require different engineering features,andhave important engineering consequences for the design of support parameters,the construction method and the construction cost in different tunnel sections.