Measured Stress Characteristics And Route Selection Strategy Of High In-situ Stress Risk Control In Lalin Section Of Sichuan-tibet Railway

With the extension of China’s railway to the western mountainous areas such as the Qinghai-Tibet Plateau,there are more and more deep buried tunnels.High In-situ stress has become a kind of complex geological condition which controls the route selection scheme.To this day,there has been very limited works on tunnels in the Qinghai-Tibet Plateau,which hinders the construction of railway.On the other hand,the most effective way is to cope in the stage of route selection to decrease the risk of high in-situ stress.Unfortunately,the research on quantitative analysis of the procedure of route selection under high in-situ stress is still on its infancy.The Lalin Section of the Sichuan-Tibet Railway is used as a research area.To tackle the complex circumstance of in-situ stress distribution under different depth,the risk-controlled rout selection strategy was proposed by analyzing the characteristic of the associated in-situ stress and better understanding the nature of the typical region of the southern margin of the Qinghai-Tibet Plateau.The main work and conclusion are summarized as follows:(1)Based on the real-world measurements of in-situ stress of Sichuan-Tibet railway with hydrofracture method,by analyzing the direction and structure of in-situ stress,friction coefficients of fault,and the relationship between the in-situ stress and the buried depth,according to the measured data obtained by hydrofracture method,the dominant stress direction in the study area is N5oE.The in-situ stress structure of the study area is mainly reverse fault and strike slip.Moreover the in-situ stress direction and structure of different geological zones in the study area are discussed and the direction of structure of different zones are obtained.The friction coefficient and stress accumulation coefficient of fault in the study area are mostly distributed in 0.2-0.5.Finally,based on the relationship between the stress and the depth of buried in the Lalin section of Sichuan-Tibet Railway,a model for estimating in-situ stress by Heim formula is proposed.(2)The engineering measures of high ground stress commonly used in large deformation of soft rock and Rockburst of hard rock are summarized.According to analyze on the influence of engineering measures on the cost index of tunnel engineering,earthwork and initial support are considered to be the indicators of the influence of high ground stress on the cost of soft rock tunnel.For the cost of hard rock tunnel,the influence of high ground stress is the index of initial support and monitoring.And,the influence of high ground stress on the cost of soft rock tunnel is more than that on the cost of hard rock tunnel.(3)Summarizes the practical cases of high in-situ stress tunnel engineering,and concludes that the route selection method should be used to control the risk of high in-situ stress in tunnels with deeper buried depths.Tunnel engineering can reduce the risk of high ground stress by three kinds of line selection measures: namely,plane avoidance,three-dimensional adjustment and comprehensive adjustment.The route selection process of high geostress risk control is proposed in this paper.Finally,the universality of the risk process is obtained by discussing the depth of the transformation.