## 1 Introduction  
With the improvement in the world economy and the level of science and technology, the need to develop underground space and resources is increasing rapidly. The scale of the construction of transportation and hydropower infrastructure continues to expand, with hydropower diversion tunnels, railway tunnels, and highway tunnels becoming increasingly longer, larger, and deeper [1; 2; 3; 4; 5; 6]. The southwest region, characterized by significant topographical relief, intense tectonic activity, and widespread construction projects, is particularly affected by high tectonic stress due to the squeezing of mountains by plate tectonics [7]. The complex geological environment, varied lithology, and high ground stress conditions prevalent in this region pose significant risks, leading to engineering disasters such as rockbursts, severe compressive deformations, and time-dependent failures of support structures [8; 9; 10; 11; 12; 13; 14]. These challenges severely impact the design, construction, and long-term operation of tunnels in this area [15]. Both domestic and international scholars have extensively studied the deformation and failure characteristics of shallow-buried, small-clearance tunnels. [PERSON] [16] found that the effects of failure of a nearby tunnel on an otherwise stable tunnel in improved soil surround is sensitive to the center-to-center spacing between the two tunnels. [PERSON] [17] explored the effects of blasting during the construction of shallow-buried urban tunnels and found that blasting had the most significant impact on the arch of existing tunnel sections. [PERSON] [18] identified the failure mode of shallow-buried, offset small-clearance tunnels as an inverted conical fracture, emphasizing the critical role of micro-fracture surfaces and tensile fractures in the tunnel surrounding rock. [PERSON] [19] analyzed stress and deformation in small-clearance tunnels in composite strata and concluded that arch deformation and ground settlement are more pronounced in the backward tunnel when the soil-rock interface is located below the arch foot. [PERSON] [20] compared the deformation of double-arch tunnels under asymmetric loads, identifying greater surrounding rock deformation on the shallow-buried side. [PERSON] [21] indicated that asymmetric loading is a primary cause of local excessive deformation and failure in shallow-buried small-clearance tunnels. Other studies have focused on tunnel spacing, deformation monitoring, and model simulations to optimize construction sequencing and prevent failure [22; 23; 24; 25; 26]. In the study of the failure characteristics and mechanisms of deep tunnels and caverns, extensive research has been conducted across various projects. He [27] investigated the characteristics and causes of floor uplift in deep mine roadways through field failure investigations, theoretical analysis, and field testing, revealing the mechanism of asymmetric floor uplift. [PERSON] [28], combining numerical simulations and field investigations, analyzed the instability, deformation, and failure modes of deep roadways. His research focused on the displacement, stress, and plastic expansion processes, elucidating the evolution of damage and failure in the surrounding rock, while also uncovering the temporal and spatial characteristics of surrounding rock deformation and failure. [PERSON] [29] analyzed 70 marble spalling samples from the second phase of the China Jinping Underground Laboratory (CJPL-II), examining their microstructural morphology and failure mechanisms. His findings clarified that the failure characteristics of the samples are primarily indicative of brittle fracture. [PERSON] [30] used numerical simulations to study failure mechanisms in deep-buried hydropower tunnels, emphasizing the influence of bedding angles and principal stress directions. [PERSON] [31] explored the deformation of tunnels in inclined strata, noting significant asymmetry in failure patterns.