| Sichuan-Tibet railway is of great strategic significance as a major passage into Tibet,and its construction is faced with unprecedented difficulties and challenges.The Sichuan-Tibet railway needs to pass through the Hengduan mountain area of China’s largest north-south tectonic belt with strong fault tectonic activity.At the same time,due to the influence of the north-south structural belt of Hengduan mountains,the karst rocks in the Jinsha river basin are distributed in the north-south direction,with a large exposed area.Therefore,the railway will certainly pass through the karst area.The tunnel water inrush and other karst geological disasters in karst areas have a great impact on the safety of engineering construction.In addition,the severe climatic and topographic conditions in this area make it extremely difficult to study karst.There is a lack of systematic regional karst studies,and the understanding of karst development characteristics and laws is far less than other karst areas in southwest China.Therefore,the study of karst in this region can provide a scientific basis for the selection of routes for the Sichuan-Tibet railway to cross the Jinsha river basin and other alpine and canyon karst areas from the perspective of karst,and at the same time has important scientific significance for enriching the world’s karst achievements.Based on the proposed Sichuan-Tibet railway crossing Jinsha river section area on the basis of existing information,through the field reconnaissance,the in-situ tracking survey methods,such as find out can lava distribution area,in combination with high-resolution remote sensing image,using the mathematical statistics method to karst development pattern in the area of statistics,induction and summarizes the law of karst development,according to the characteristics of the karst development pattern in the area,starting from the karst development control elements,analyze the effect of various factors on the karst development to summarize the main control factors,karst zone partition piece of paper on the basis of this general area of each block tunnel engineering construction suitability.Gained the following understanding:(1)the study area of this area is about 14000km2,of which the carbonate outcrop area is 3658km2,accounting for 26% of the study area.It is mainly distributed in the east bank of Jinsha river and the northwest of the study area.(2)the surface karst morphology in the region is dominated by karst depressions.A total of 349 depressions were extracted,with a total area of about 118km2.The depressions in the region are widely distributed.The distribution of depressions in the region is controlled by lithology and structure,and the shapes are mainly irregular and polygonal.The distribution elevation is mainly concentrated in the elevation range of 4100-4900 m,mostly in the high elevation.(3)Karst springs are widely distributed in the area.The discharge of the 64 springs in the survey is about 4224L/s,among which carboniferous(C)and Devonian(D)are relatively water-rich aquifers,and the discharge of the exposed springs is more than 100L/s,accounting for 80% of the total discharge of the springs in the region.Meanwhile,the maximum discharge of the exposed springs in Devonian(D)is up to 500L/s.The Triassic system(T)and Permian system(P)have weak water abundance,especially the Permian system(P).Combined with the statistical results of different strata of surface karst morphology,it can be seen that the carboniferous and Devonian karst have the strongest development intensity,followed by Silurian,and Permian and Triassic are relatively weak.(4)karst phenomena in the area are mainly distributed in high elevation,and karst spring points are mainly exposed in medium and low elevation,higher than the drainage datum level.Therefore,the development of alpine and canyon karst in the area has a typical three-stage feature,that is,karst depressions are widely distributed in the peak,and deep and large dissolution fractures are mostly in the rock mass.In the middle part,the karst fissures and small pores are mainly distributed in the shallow surface,and the karst at the bottom is not well developed and the rock mass is relatively complete.Therefore,the karst springs in the survey are mostly exposed in the lower part of the slope or near the bottom of the valley rather than in the low-lying areas at the bottom of the valley.(5)Karst development in the study area is mainly controlled by stratum lithology,geological structure,topography and geomorphology and external environment temperature.Meet the basic conditions of karst development,but the study area is located in the southeast margin of Qinghai-Tibet Plateau,the climate change in the area is great,the Qinghai-Tibet Plateau uplift zone before sharply,warm,moist climate conducive to karst development,along with the sharp long Qinghai-Tibet Plateau and the quaternary glacial impact for many times,area sharply lower temperature,low temperature all the year round on the one hand,the dissolution rate slowing down,on the other hand the vegetation and less carbon dioxide in the air,prompted the karst development ability become weak,only in shallow place developed or less developed,so the outside temperature directly or indirectly affect be caused in alpine valleys present three-step development characteristics of main control factors of karst.(6)When the Sichuan-Tibet railway is proposed to cross the research area,most of the railway projects are tunnel projects.The karst geological disaster most likely to occur when the tunnel crosses the research area is water inrush disaster.At the same time,the karst in the area has typical three-stage development characteristics.According to the classification of engineering construction suitability in geological hazards and the karst development characteristics in the above-mentioned areas,the suitability of tunnel engineering construction of Sichuan-Tibet Railway crossing the karst zone in the study area can be divided into three levels: unsuitable,basically suitable and suitable,and partition of each block adaptive tunnel construction was reviewed. |
