# Mechanisms of Tunnel Rockburst Development Under Complex Geostress Conditions in Plateau Regions
## 1 Introduction  
The Qinghai-Xizang Plateau, known as the \"Rof of the World,\" is regarded as the \"Third Pole\" of the Earth. In recent years, with the gradual implementation of major national strategies such as the Western Development Program, the Belt and Road Initiative, and the New Western Land-Sea Corridor, numerous large-scale transportation and hydropower infrastructure projects have been constructed across the plateau and its surrounding regions. Notable examples include the under-construction Sichuan-Xizang Railway, as well as the planned Xinjiang-Xizang Railway and Yunnan-Xizang Railway, which are of significantimportance for safeguarding national defense, promoting social progress, and driving regional economic development [1; 2]. Due to the crisscrossing mountain ranges on the plateau, major transportation corridors are predominantly composed of tunnels. For example, in the Ya'an-Linzhi section of the CZ Railway, tunnels account for up to 82.6% of the total length [3], making the successful construction of tunnels crucial for establishing transportation corridors across the plateau. However, under the combined influence of internal and external geological forces [4; 5], the terrain, landforms, and lithology in the plateau region are extremely complex, with deep and long tunnels facing prominent high geostress challenges. Against this backdrop, rockburst disasters frequently occur in hard rock tunnels on the plateau. For instance, in the 12 km long Bayu Tunnel of the Lalin Railway, rockbursts have been recorded along as much as 94% of its length, severely affecting construction progress and worker safety [6; 7; 8]. Understanding the mechanisms underlying rockburst disasters is essential for their effective prevention and mitigation [9]. Due to their sudden, violent, and complex nature [10; 11], the mechanisms of rockbursts have long been regarded as a global challenge in the field of rock mechanics and engineering [9]. Among the numerous factors contributing to rockburst occurrence, high geostress has been widely recognized as a necessary condition for their development [12; 13]. In terms of the influence mechanisms of geostress on rockbursts, both domestic and international scholars--such as [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], and [PERSON] et al. [14; 15; 16; 17; 18; 19]--have conducted extensive and fruitful studies. Through field investigations, laboratory experiments, and numerical simulations, they have analyzed how geostress controls rockburst risks and characteristics. These studies have provided valuable references for understanding rockburst mechanisms, as well as for their prediction and risk assessment. In addition, previous studies have attempted to investigate the evolution of rockburst behavior under varying in-situ stress conditions through numerical simulation. For example, [PERSON] et al. [20] established a deep-buried cavern model using FLAC3D to analyze the influence of different stress orientations and lateral pressure coefficients on the spatial distribution and intensity of rockbursts, providing a quantitative simulation framework for studying rockburst characteristics in complex stress environments. However, the geostress environment of plateau tunnels is significantly more complex than that in other regions. Controlled by the collision of tectonic plates, the plateau experiences intense tectonic activity, resulting in large-magnitude horizontal tectonic stresses with highly variable directions. The combined effects of surrounding rock self-weight stress and tectonic stress create an exceptionally complex high geostress field [21; 22], characterized by strong horizontal tectonic stress, geostress magnitudes greatly influenced by terrain, and principal stress directions that are highly variable [19]. These factors lead to rockbursts in plateau tunnels exhibiting unique characteristics distinct from conventional cases.