# Cross-Section Shape and Asymmetric Support Technology of Steeply Inclined Thick Coal Seam Roadway
## 1 Introduction  
Steeply inclined coal seams (dip angles between 35\({}^{\circ}\) and 55\({}^{\circ}\)) are widely distributed in China, accounting for approximately 20% of the national total proven reserves [1, 2, 3]. However, compared with near-horizontal coal seams, the coal-forming environment and geological occurrence conditions of steeply inclined coal seams are complex, with extremely high mining difficulty and frequent safety hazards [4; 5; 6]. Especially, the deformation of steeply inclined coal seam roadways often exhibits asymmetry and significant magnitude, and even overall instability of the roadway may occur [7; 8; 9]. Therefore, alleviating the asymmetric deformation of steeply inclined coal seam roadways and ensuring the stability of surrounding rock are of great practical significance for the safe and efficient mining of steeply inclined coal seams. Many scholars have conducted extensive research on the asymmetric deformation and failure mechanism and control technology of steeply inclined coal seam roadways, from the aspects of surrounding rock stress distribution characteristics [10], interlayer shear slip deformation mechanism [11], the roof deformation law, and surrounding rock support technology [12]. [PERSON] et al. [13]. revealed that under the influence of high horizontal stress, lithological variations, and weak coal-rock interfaces, the roof and floor of such roadways exhibit extensive failure, with stability compromised when the roadway strike is perpendicular to the maximum principal stress direction. [PERSON] et al. [14] found that the roof instability of the mining roadway shows asymmetric arc-shaped breaking, and the shear slip of the triangular broken body is the main reason for the deformation and failure of the two sides. The severely damaged area is located at the upper part of the side corner, and the breaking at the upper middle part of the roof is the trigger point for surrounding rock instability. [PERSON] [15] proposed an asymmetric support scheme based on the asymmetric characteristics of roadway stress and deformation, which has a significant effect on maintaining the surrounding rock stability. [PERSON] et al. [16]. found that changing the cross-sectional shape of the roadway can weaken the degree of local stress concentration in the surrounding rock, which is an effective way to control steeply inclined coal seam roadways. The above studies have explored the failure mechanism of steeply inclined coal seam roadways at the mechanical level. Further practice has found that the coal seam thickness and coal seam dip angle are the two most key geological factors determining the stability of the engineering-scale surrounding rock. From the perspective of the coal seam thickness, practice has shown that for thin and medium-thick coal seams, using inclined roof trapezoidal and inclined roof special-shaped roadway cross-sections [17] and asymmetric coupling support technology [18] can conform to the force of inclined coal and rock layers, prevent interlayer shear [19], and effectively alleviate asymmetric deformation. In thick and extra-thick coal seams, due to the absence of stable coal-rock interfaces for inclined-roof roadway formation, uniform support schemes based on symmetric cross-sectional shapes [20], such as rectangular [21] and arch, are adopted [22], and high-strength bolt-mesh-cable [23] is used to improve the overall support strength to maintain the stability of the surrounding rock. However, while uniform reinforcement effectively controls the deformation of the surrounding rock in roadways, there is an over-engineering in low-deformation zones. Existing studies have carried out in-depth research on the failure mechanism of steeply inclined coal seam roadways and proposed asymmetric roadway cross-sectional shapes and asymmetric support technologies for thin and medium-thick coal seams, which have achieved good results in engineering practice and have important practical significance.