Research On Special Issues In Route Selection Of China-nepal Railway Passing River Basin

The China-Nepal Railway starts at Shigatse City,Tibet,and ends at Kathmandu,Nepal.It is the first mountain railway across the Himalayas under the "One Belt,One Road" international cooperation initiative.Affected by tectonic effects,the dynamic effect of the Qinghai-Tibet Plateau through which the China-Nepal Railway passes is very strong,and it is the fastest-uplifting geomorphic unit among the existing and proposed railways in China.According to the existing related research,the plateau uplift is generally related to the formation and evolution of regional topography and geological disasters,and as the plateau continues to uplift,the plateau geological disasters will be shorter cycles,greater intensity,broader impacts.And stronger the coupling of various disasters.Secondly,affected by the Himalayan orogeny and the Indian Ocean monsoon climate,low-latitude and high-altitude oceanic glaciers developed in the China-Nepal railway corridor in China.The glaciers have a strong ability to shape landforms and have a significant impact on railway construction and safe operation.In view of this,this article chooses to study based on the plateau uplifting geomorphic effects and disaster effects,as well as considering the impact of dynamic changes of glaciers on the railway.In response to the special problems in the three river basins of the China-Nepal Railway,the main results are as follows:(1)Based on the analysis of the relationship between the distribution of knickpunktes formed by the plateau uplift and the development of the landform,the Yarlung Zangbo River basin through which the railway passes is between the middle knickpunktes and the upper knickpunktes.The rejuvenation of the main river’s landform has just begun,and the evolution of the landform has a leveling effect and undercutting.Due to the characteristics of equal importance,the tributary has not been completely reached due to the traceability erosion effect,and the leveling effect is still the main cause,which leads to an upward trend in the river bed of the Yarlung Zangbo River secondary basin through which the railway passes.The ChinaNepal Railway runs along tributaries,and debris flows are densely distributed on both sides of the bank.In view of the general correlation between geomorphic development and geological disasters divided by knickpunktes,the principle of high-level railway route selection for rivers with densely-distributed riverbed debris flows is proposed.(2)In view of the uneven development of the terraces in the north and south of the Pengqu watershed,by analyzing the causes of the terrace development,it is concluded that the river terraces will move to the north under the influence of tectonic movement,and it is proposed to make full use of the wide and gentle terraces on the south side of the Pengqu Routing strategy.Secondly,in view of the different formation and movement conditions of debris flow fans and ice-water fans,a method is proposed to divide the range of action of debris flow fans and ice-water fans by slope,and the principle that railways can use roads to pass through ice-water fan geomorphic areas is proposed.(3)The longitudinal slope of the riverbed in some sections of the Geelong Zangbo River that the China-Nepal Railway passes through is far greater than the usual railway slopes.The route must be extended to meet the requirements of the relevant regulations for the railway longitudinal slope.The railway route may be located in an oceanic glacier-covered area,and the glacier is moving in the area of The impact on the railway is difficult to predict,it is a geomorphic unit with no railway construction experience in China.Based on the marine glaciers in the Geelong Zangbo Basin as the research object,the paper establishes a mathematical model of the evolution of the glacier system based on the characteristics of rapid melting and accumulation of marine glaciers,and combines the historical change law of glacier development,using the long-term that railway operations as the deadline to predict the trend of ocean glacier ablation in the Geelong Zangbo Basin.The area where the glacier retreats in the long-term design year of railway operation is defined as the non-core glacier area.It is proposed that the tunnel layout in the non-core glacier area does can do not consider the influences depth of the tunnel buried by the glacier erosion.