# Study of the Failure Mechanism of Soft Rock Mining Roadways Based on Limit Analysis Theory
## 1 Introduction  
This study focuses on the complex engineering geological conditions of soft rock roadways. It is very important to maintain the stability and smoothness of soft rock mining roadways for the safe operation of mines [1, 2]. Therefore, it is of great significance to study the failure mechanism of soft rock mining roadways. Many scholars in China have carried out in-depth research on the deformation and failure mechanisms and control technology of roadway-adjacent rock. [PERSON] et al. [3, 4] stated that the deformation and failure of roadways are related to many factors, which can be summarized into geological factors and external factors. The physical and mechanical properties of weakly cemented strata are the most basic factors affecting the stability of rock surrounding a roadway [5, 6]. Due to the different mineral compositions and structures of rock masses, the physical and mechanical properties of different rocks are very different [7]. Especially for expansive soft rock roadways [8], a high expansion stress will be generated during the water absorption process of hydrophilic minerals, which is unfavorable for the stability of roadway-adjacent rock. [PERSON] et al. [9] believed that the deformation of soft rock roadways is mainly due to the low strength of the roadway-adjacent rock and the high composition of argillaceous minerals, which leads to a mismatch between the surrounding rock and the supporting body under the action of groundwater. The influence of groundwater on the surrounding rock in the failurezone is mainly manifested in two aspects: one is the formation of hydrostatic pressure, and the other is the generation of hydrodynamic pressure. Under the condition of high ground stress, the rock mass is broken and joints and cracks develop. Under the action of groundwater, the groundwater flows along the cracks to the rock surrounding the roadway, which reduces the strength of the rock mass. With a change in hydrodynamic pressure, the deformation of the roadway is accelerated, which leads to the phenomena of roof fall and rib spalling in the surrounding rock and finally makes the roadway unstable. An increase in pore water pressure in rock can reduce the effective normal stress of rock, thus reducing the shear strength of the rock mass [10; 11]. [PERSON], [PERSON] et al. [12; 13] believed that a high ground stress is the main reason for the deformation and failure of surrounding rock in deep soft rock roadways. Deep rock masses feature complex stress fields, mainly including the interaction of self-weight stress and tectonic stress generated by the overlying strata. With increasing excavation depths, the self-weight stress generated by the overlying strata also increases, and the stress in the rock surrounding the roadway is larger. Damage to the roadway support always begins at the weakest point. In most cases, the tectonic stress is larger than the self-weight stress and is highly variable. The tectonic stress is also very different in time and space, and its existence directly determines the stability of the roadway. Rheology is an important aspect of soft rock [14; 15], and the deformation of roadways occurs over time. Soft rock is a kind of material with an obviously weak rheology. The rheological properties of such rocks mainly include creep and shrinkage. The soft rock mass not only has a fast rheological speed and large deformation but also obviously shows three stages of creep deformation. There is no obvious elastic stage in the stress-strain curve of a soft rock mass, and only a plastic rheological stage is observed. The control theory of roadway-adjacent rock has achieved fruitful results, and the forms of support have also undergone major changes. The concept of support has changed from passive to active. The support of roadways has transformed from traditional shed supports to bolt supports [16; 17; 18]. [PERSON] et al.