# Stability and Control of Surrounding Rock of a Trapezoidal Roadway Retained with Hard Roof Cutting
## 1 Introduction  
Recently, hard top-cutting and gob-side roadway retention has been widely used in the coal mining process due to its advantages of improving the coal recovery rate and reducing the occurrence of strong mine pressure on the working face [1, 2, 3]. After top-cutting, thestability of the roof and deformation characteristics of the surrounding rock are significantly different from those of the un-roofed roadway. The control mechanism and technology of the surrounding rock are also significantly different from those of the uncut roadway [4; 5; 6]. Trapezoidal roadways in inclined coal seams have unique asymmetric deformation due to their irregular shape [7; 8; 9; 10]. Furthermore, influenced by top-cutting, the stability changes of the trapezoidal roadway and the deformation of the surrounding rock become more complicated. Therefore, clarifying the stability characteristics of the trapezoidal top-cutting roadway and understanding the deformation characteristics and control mechanisms of the surrounding rock are important foundations for top-cutting and gob-side roadway retention in trapezoidal roadways with a hard roof. Experts and scholars in the mining field have conducted much research on top-cutting and gob-side roadway retention, focusing mainly on the structural characteristics, parameters and surrounding rock control technology. Based on the Roof Cut Short-Arm Beam Theory, [PERSON] and [PERSON] et al. established a mechanical model of the roof short-arm beam for top-cutting and analyzed the rules for the evolution of its roof structure [11; 12]. [PERSON] et al. proposed the concepts of the \"pressure-bearing structure\" and \"pressure-relief structure\" in the top-cutting roof, and analyzed the influence of the fracture position and motion state of the roof on the deformation of the surrounding rock [13]. [PERSON] et al. used the pre-split blasting method to conduct research on top-cutting and roadway retention of the soft-hard composite roof, and determined top-cutting parameters such as top-cutting height, top-cutting angle and borehole spacing [14]. [PERSON] and [PERSON] et al. used the hydraulic fracturing method to carry out top-cutting and gob-side roadway retention in a high mining face, and designed parameters such as deep and shallow drilling depth, pre-mining face hydraulic fracturing location, and so on [15; 16]. [PERSON] et al. studied the applicability of dense drilling for top-cutting to relieve pressure in the process of gob-side roadway retention, and determined key parameters [17]. [PERSON] et al. proposed the use of \"constant resistance and large deformation bolts (cables) + cable reinforced roadside support + dense individual support alongside the roadway\" to control the surrounding rock in gob-side roadway retention [18]. [PERSON] and [PERSON] et al. have studied the feasibility of high-strength bolting and grouting in controlling the stability of surrounding rock in a deep top-cutting roadway [19; 20]. For a thick and hard main roof, [PERSON] et al. proposed an integrated top-cutting and gob-side roadway retention for rock control technology, consisting of \"high-strength top-cutting anchor cable reinforcement + blasting pre-split pressure relief + strong support of monolithic column + U-shaped steel and metal mesh for gangue prevention\" [21]. [PERSON] et al. proposed that the selection of support for the roadway should take into account both geomechanical and ventilation criteria as well as minimum movement distances [22]. The ideas and methods of the above research results can be a reference for this study. However, the stability and control of the surrounding rock in a trapezoidal roadway retained with hard roof cutting is less complicated. The theoretical models and control techniques proposed in the results cannot effectively guide similar engineering practices, and more specific work is urgently needed.