强震区成兰铁路某隧道小净距段大变形特性分析

针对处于"汶川5.12"强震区龙门山断裂带之前山活动断裂及中央活动断裂之间的在建成兰铁路柿子园隧道4号横洞工区隧道小净距D3K87+500~+350段大变形破坏现象,在现场调绘、岩石试验、地应力测试及监控量测数据等资料分析的基础上,从地质构造、围岩条件、地震作用、地应力场、地下水及工程结构形式和施工影响等方面对隧道小净距段的大变形特性进行分析,并探讨其成因机制。主要结论有:(1)小净距段呈现仰拱左右剪切错动、边墙侵陷、拱顶沉降为特征的纵向张裂变形特性;(2)大变形成因机制可归纳为软弱破碎的围岩条件、复杂活跃的地质构造条件、高应力场条件、地形偏压作用、地下水软化作用等客观地质环境因素及小净距隧道结构形式、施工影响及较弱的支护措施等主观因素的综合影响;(3)小净距结构形式的设置位置应综合考虑地层岩性、地质构造、地应力场及地震震裂作用等客观地质环境因素的影响;(4)研究结论对强震区类似工程地质条件下川藏、滇藏铁路破碎围岩隧道的设计和施工具有借鉴意义。

Analysis of Large Deformation Characteristics of a Small Spacing Section Tunnel of Chengdu-Lanzhou Railway in Meizoseismal Area

The D3K87 + 500 ~ + 350 section of small spacing tunnel with obvious large deformation is located between front active fault and central active fault of Longmen mountain fault zone in"Wenchuan5. 12"meizoseimal area and the No.4 adit area of Shiziyuan tunnel,which is under construction as part of the Chengdu-Lanzhou railway. Based on the analysis of the datum of the survey,rock tests,geo-stress test,and monitoring measurements,the large deformation characteristics in perspective of geological structure, surrounding rock, earthquake action, geo-stress field, underground water, engineering structure type,and construction influence,the formation mechanism of large deformation is studied. Main research conclusions are as follows:( 1) the small spacing section are characteristic of longitudinal tension crack deformation,inverted arc shear dislocation,side wall intrusion and arch crown settlement;( 2) the formation mechanism of large deformation can be summarized as the comprehensive effect of the objective geological environment factors such as the soft and broken surrounding rock condition,complex and active geological structure condition, high geo-stress field condition, topographic bias action,groundwater softening action,and the subjective factors such as the small spacing tunnel structure type,left and right tunnel construction mutual influence,and weak support measures;( 3) the setting position of small spacing tunnel structure should comprehensive consider the following objective geological environment factors such as formation lithology,geological structure,geo-stress field,and earthquake shattering action;( 4) the conclusions of this paper can be widely applied in the design and construction of soft and broken surrounding rock tunnels under similar geological conditions of theSichuan-Tibet railway and the Yunnan-Tibet railway in meizoseismal areas.