Research on the geological route selection of Sichuan-Tibet Railway passing through Eastern Himalayan syntaxis Areas

Abstract

The eastern Himalayan syntaxis (EHS) area is characterized by complex topography due to the strong collision between the Indian and Eurasian Plates, developing deep fractures, active faults, and prominent high in-situ stresses. The designed Sichuan-Tibet railway passes through this area and connects Bome and Nyingchi on the east and west sides of the syntaxis. We encountered the following dilemma on railway route selection due to the large investment scale and the linear distribution of the railway: 1) the investment might skyrocket if the route runs outside the arc-shaped structure of the Namcha Barwa syntaxis in the Northwestern part of the EHS (detour syntaxis scheme); 2) the dynamic geological risk may increase if the route directly runs through the arc-shaped structure and Yarlung Zangbo Suture zone (crossing syntaxis scheme). Combined with a detailed field investigation, we comprehensively analyzed the regional deep structure, Holocene active faults and earthquakes, and regional in-situ stress and crustal deformation. The crustal stability in the Namcha Barwa syntaxis is extremely poor, having an uncontrollable risk. Concurrently, under topographic control, the tunnel’s bury depth of the crossing syntaxis route scheme is extremely deep, and the risk of rockburst, large deformation of soft rock, and water inrush is extremely high, severely affecting the construction period and potentially causing a significant increase in investment due to construction period delay. Therefore, the Sichuan-Tibet railway project is recommended to avoid crossing the Namcha Barwa syntaxis as much as possible and conduct detailed scheme research based on the bias of the detour syntaxis route scheme.