High in-situ stress evaluation and disaster case analysis for the Sichuan–Xizang railway

The challenges posed by high in-situ stress along the newly constructed Sichuan–Xizang railway are significant, characterized by frequent catastrophic events such as rock bursts and large deformations in soft rocks, which substantially impact tunnel construction for the Sichuan–Xizang railway.

Based on 366 sets of in-situ stress measurement data from the Yalin section of the Sichuan–Xizang railway and 28 documented cases of tunnel catastrophes in the areas along the Sichuan–Xizang railway, this study analyzes the characteristics of in-situ stress along the route, categorizes the catastrophic events, and evaluates the high in-situ stress conditions of the Sichuan–Xizang railway.

In the B218, B219, and B222 stress divisions traversed by the Yalin section of the Sichuan–Xizang railway, the maximum (S_H) and minimum (S_h) horizontal principal stresses increase with depth. Within a burial depth of 1000 m, S_H and S_h range from 30.80–37.50 MPa and 21.40–23.56 MPa, respectively. At a burial depth of 2500 m, S_H and S_h increase to 69.80–90.0 MPa and 48.40–56.56 MPa, respectively. The preferred orientations of S_H are NWW, NW, and NE, consistent with focal mechanism solutions, albeit with some local deviations. The lateral pressure coefficient (k_H/k_h) is generally greater than 1, indicating that the Sichuan–Xizang railway is predominantly influenced by S_H. Stress values in each stress division exhibit the pattern S_H > S_V > S_h, reflecting a strike-slip fault stress state in the deeper regions below 500 m burial depth. The stress accumulation level (μ_m) values for each stress division are concentrated around 0.3, suggesting a low regional stress accumulation level. Among the 28 documented tunnel catastrophe cases (12 involving rock bursts and 16 involving large deformations in soft rocks), the minimum burial depth for tunnels experiencing rock bursts is 700 m, while the minimum burial depth for tunnels experiencing large deformations in soft rocks is 275 m. Six tunnels are rated as under high stresses, and eight tunnels are rated as under extremely high stresses. High in-situ stress serves as the energy source and the fundamental cause of frequent catastrophes.

Through comparing the actual grades of tunnel disasters, the most appropriate criterion for predicting rock burst and large deformations in Sichuan–Xizang railway tunnels is determined after comparison and selection. Therefore, they should be prioritized in the studies for the subsequent construction of Sichuan–Xizang railway tunnels as a reference basis. [Significance] The research findings offer crucial evidence for the analysis of in-situ stress states and the prevention and control of high in-situ stress disasters in the regions along the Sichuan–Xizang railway, and possess significant engineering guiding significance for enhancing the safety of tunnel engineering and construction efficiency.