中尼铁路交通廊道现今构造应力场及其工程影响

拟建中尼铁路位于印欧板块碰撞推挤的前缘地带,区域深大断裂发育,地震频发,新构造活动强烈,应力状态复杂。基于中尼铁路交通廊道震源机制解及原地应力测量资料,分析中尼铁路沿线区域构造应力场分布特征,进一步讨论现今构造应力场对铁路方案和重要工程设置的潜在影响。研究结果表明,研究区震源深度主压应力优势方向在板块碰撞边界为NEE向,高原内部则表现出明显的非均匀性特征。中国境内日喀则至吉隆段主要处于拉张-剪切应力环境,尼泊尔境内区段处于印欧板块推挤控制的挤压应力环境。在缺少中尼铁路沿线原地应力实测资料的现状下,结合邻区实测数据分析认为,该区地壳浅表层应力结构以逆断型为主,水平最大主压应力优势方向为NE向。基于研究区内主应力方向分布特征将中尼铁路沿线划分为日喀则―萨迦、萨迦―定结、定结―吉隆、聂拉木、吉隆―讷瓦果德和加德满都共6段。根据构造应力场分析结果并基于σ_θmax/R_c理论对铁路隧道工程围岩岩爆可能性进行了讨论,结果表明最大水平主应力方向与隧道轴向夹角较大时对隧道围岩稳定性不利,且隧道埋深越大则围岩岩爆的可能性越大。中尼铁路大多区段轴向与最大水平主应力方向呈大角度相交甚至近垂直,当隧道埋深较大时具有发生岩爆的可能,需重点防护。研究结果可为中尼铁路交通廊道工程勘察选线提供参考。

Tectonic Stress Field and Engineering Influence of China-Nepal Railway Corridor

The proposed China-Nepal railway is located in the India-Asia collisional-compressive front,which is characterized by regional active faulting,frequent earthquakes,strong neotectonic activities,and complex stress fields.Characteristics of the present-day stress field in the railway corridor and its effects on tunnel stabi-lities is analyzed based on the focal mechanism solutions and in-situ stress measurements.The results show that the local principal compressive stress at the seismogenic depths is ENE along the plate boundary,compared with the heterogeneous stress field inside the Plateau.The Chinese(Xigaze to Jilong)section is mainly in tensile-shear stress field,while the Nepali section is in compressive stress field controlled by the India-Asia collision.Given that there is no in-situ measurement in the China-Nepal railway corridor,we analyzed the shallow stress field based on the measured data in the neighboring areas.Stress regime in the shallow crust is generally conducive to reverse faulting,and the maximum horizontal principal stress is predominantly NE.Based on the distribution characteristics of principal stress direction,the China-Nepal Railway comprises six sections,and the possibility of the wallrock burst is discussed,considering both stress field analysis andσθmax/Rc theory.We concluded that a larger angle between the maximum horizontal principal stress direction and the axial direction of the tunnel is detrimental to the wall rock stability:The greater the tunnel depth,the greater the rock burst possibility.Most sections of the China-Nepal railway intersect the maximum horizontal principal stress axis at a large angle or even nearly perpendicular.Rock bursts likely occur when the tunnel is deep,and major protection measures are required.This study provides scientific reference for railway engineering survey and routeselection.