# Instability Characteristics of and Control Techniques for Mudstone-Clay Composite Roof Roadways
## 2 Engineering Background  
According to China Coal Network data, total coal production reached 4.71 billion tons in 2023, representing a 3.4% year-on-year increase. Shanxi, Inner Mongolia, and Shaanxi Provinces account for 70% of total coal production, characterized by shallow-buried coal seams, abundant reserves, and superior coal quality. Shanxi Province, ranking first in annual coal production in China, faces challenges in certain areas due to shallow burial depths, significant roadway roof deformation, and frequent anchor rod and cable detachment [32]. It is important to note that the occurrence of mudstone-clay composite roofs in coal mines is not unique to China. Similar geological conditions have been reported in other coal-producing regions worldwide. For example, within the clay rock structure of the Maritsa East lignite basin in Bulgaria, all samples are composites [33]. These rock formations are prone to weathering and softening when exposed to water and humidity, leading to roof instability and deformation in underground coal mines. In Australia'sBowen Basin, a major coal-producing region, the presence of weak clay layers within the roof strata has been identified as a significant challenge for maintaining roadway stability [34]. The clay layers, often associated with mudstone and siltstone, undergo swelling and softening when exposed to water, resulting in roof delamination and failure. This study focuses on Xiegou Coal Mine of Shanxi Xishan Jinxing Energy Co., Ltd., located in Shuozhou, Shanxi Province, China. As a representative case, with its geographical location shown in Figure 1a. Figure 1b details the drilling sampling and roof deformation measurement area of the 18,511 th working face in Xiegou Coal Mine. An exploration of the working face reveals shallow-buried coal seams with limited shale development on the inclined roof, predominantly composed of mudstone. In the RSR support system, the mudstone layer, being a difficult-to-control soft rock, is combined with the even clay layer to form a characteristic double soft composite roof. The exploration revealed that single or multiple layers of clay are distributed in different positions directly above, forming complex mudstone-clay structures. To analyze the clay distribution characteristics directly in the mudstone top, an on-site drilling exploration was conducted at positions 1-5 located 7-8 m above the material roadway as shown in Figure 1b. The detection results identified four categories of clay containing composite roof structures: 1  a single mudstone structure; 2  mudstone-clay composite structure; 3  mudstone-clay-mudstone combination structure; and 4  mudstone-clay composite structure with multiple clay layers, as illustrated in the bar chart in Figure 1c. The working face's direct water source originates from the overlying Shanxi Formation sandstone fissure aquifer. Due to the shallow coal seam's burial and developed roof structure with weathered fissures, roof fissure water frequently gathers on roadways through surface excavation precipitation or shallow groundwater recharge. During the rainy season, this leads to increased dampness and moisture in the roadway roof. RSR deformation measurement stations were established at positions 1-3 along the belt roadway as shown in Figure 1b. The measurements, illustrated in Figure 1d, reveal roof deformations of 240 mm and 300 mm at measuring points 2 and 3, respectively. Particularly, measuring  
Figure 1: Test site and roof characteristics. point 1 shows a deformation of 140 mm during the dry season. The significantly larger roof deformation during the rainy season poses increased challenges for roadway support. Clay layers alter roof mechanical properties, change rock mass deformation and failure characteristics, and complicate roadway support requirements.