川藏铁路雅安至新都桥段地应力特征及工程效应分析

In-situ geostress characteristics and engineering effect in Ya’an—Xinduqiao section of Sichuan—Tibet Railway

拟建的川藏铁路雅安—新都桥段地处川滇藏构造交汇区,地应力场复杂,针对该区现今地应力场的研究有助于川藏铁路的科学建设。基于水压致裂法地应力实测数据,对川藏铁路雅安—新都桥3个区段(雅安—泸定段、泸定—康定段和康定—新都桥段)的地应力特征和分布规律以及其工程效应进行分析。研究结果表明:(1)主应力值随埋深具有较好的线性关系,3个区段的最大水平主应力增加梯度分别为3.9 MPa/(100 m),2.7 MPa/(100 m),3.6 MPa/(100 m),其中雅安—泸定段的增长梯度最大,埋深1 300 m时实测最大水平主应力值大于51 MPa。(2)最大水平主应力方位以NW向为主,这与该区现今构造作用方向一致。受峡谷地形及区内断层的控制和影响,个别测点最大水平主应力方位呈NE向。(3) 3个区段的侧压力系数均大于1,说明该区主要受水平挤压构造为主。而3个区段埋深小于300,350和500 m的段落侧压力系数最大值分别为1.7,2.3和3.0,说明浅埋段的地应力还受到高山峡谷地形的控制及斜坡应力场的叠加影响。(4)从最大水平主应力方向与隧道轴线夹角对围岩稳定的影响来看,川藏铁路雅安—新都桥段的线路布设总体是合理的。仅在跑马山隧道出口端、康定隧道出口端和折多山隧道深埋段(埋深1 000 m左右)存在对围岩稳定不利的情况。(5)隧道Ⅱ,Ⅲ级围岩岩爆以轻微和中等岩爆为主,深埋段(雅泸段埋深超过870 m、泸康段埋深超过1 140 m、康新段埋深超过930 m)的硬岩可能发生强烈岩爆。(6)隧道Ⅳ,Ⅴ级围岩大变形以轻微、中等和强烈大变形为主。雅泸段Ⅳ级围岩埋深超过1 330 m、Ⅴ级围岩埋深超过940 m,泸康段Ⅴ级围岩埋深超过1 410 m和康新段Ⅴ级围岩埋深超过960 m后,可能发生极强大变形。

The Ya’an—Xinduqiao section of the proposed Sichuan—Tibet railway is located in the geological structure intersection area of Sichuan,Yunnan and Tibet with extremely complex geostress. Research on the present geostress field in this area is conducive to the scientific construction of the Sichuan—Tibet railway. Based on the measured data of in-situ geostress by hydraulic fracturing method,the characteristics and distribution of in-situ geostress as well as engineering effects in the three sections including Ya’an—Ludin,Luding—Kangding and Kangding—Xinduqiao sections of Sichuan-Tibet railway are analyzed. The results show that the main stress value has a good linear relationship with the burial depth,and that the maximum horizontal main stress increase gradients of the three sections are respectively 3.2 MPa per 100 m,2.7 MPa per 100 m and 3.6 MPa per 100 m,among which the growth gradient of Ya’an—Luding section is the largest with a measured maximum horizontal main stress more than 51 MPa at 1300 m the burial depth. The orientation of the maximum horizontal principal stress in this area is NW,which is consistent with the current tectonic direction. Under the control and influence of canyon topography and faults in the area,the maximum horizontal principal stress orientation of some individual measuring points is NE. The lateral pressure coefficients of the three sections are all greater than 1,which indicates that the area is mainly affected by horizontal compression structure. The lateral pressure coefficients of the three sections with a buried depth less than 300 m,350 m and 500 m are 1.7,2.3 and 3 respectively,which shows that the in-situ geostress of the shallow buried section is also controlled by the topography of high mountains and valleys and the superimposed influence of slope stress field. According to the influence of the angle between the maximum horizontal principal stress direction and the tunnel axis on the stability of surrounding rock,the route layout of Ya’an—Xinduqiao section of Sichuan—Tibet railway is generally reasonable,although there maybe exist some unfavorable circumstances for surrounding rock stability only at the exit end of Paomashan and Kangding tunnels and the deep buried section of Zheduoshan tunnel(buried depth about 1 000 m). The rock burst of Ⅱ and Ⅲ surrounding rock of tunnels is mainly slight and medium,while the hard rock with a large buried depth(more than 870 m,1 140 m and 930 m in Ya’an—Luding,Luding—Kangding and Kangding—Xinduqiao sections,respectively) may occur strong rockburst. The large deformation of Ⅳ and Ⅴ surrounding rock presents mainly slight,moderate or strong. Strong deformation may occur for Ⅳ surrounding rock with a buried depth more than 1 330 m and Ⅴ surrounding rock with a buried depth more than 940 m in Ya’an—Luding section,V surrounding rock with a buried depth more than 1 410 m in Luding-Kangding section and Ⅴ surrounding rock with a buried depth over 960 m in Kangding—Xinduqiao section.