# Instability Characteristics of and Control Techniques for Mudstone-Clay Composite Roof Roadways
## 4 Deformation and Instability Law and Prevention Technology of Double Soft Composite Roof
### Prevention Techniques for Roadway Deformation
#### 4.3.3 Analysis of Engineering Site Effects  
To analyze deformation patterns in surface and deep RSR, assess the support body's stress state, and identify abnormal deformation areas in the roadway, convergence monitoring was conducted on the experimental section's roadway surface. Displacement measurement stations were arranged near the excavation face, with each station containing two observation sections spaced 2 m apart and three measurement stations in total. Monitoring was performed using the \"cross measurement method\", as shown in Figure 19. In Figure 19, 'A', 'B', 'C' and 'D' represent the measurement points on the roof and floor of the roadway as well as on the left and right sides.  
The displacement observations for both sides and the top and bottom plates of the 18,511 th working face of the material roadway are shown in Figure 20. The roadway surface deformation during excavation, when supported by anchor rods and short anchor cables, exhibits the following patterns:  
1. Initial Excavation Impact Stage This stage occurs within 5 days after excavation, or within 10 m of the excavation face. Following roadway excavation, stress redistribution in the RSR creates stress concentration around the roadway, peaking in the shallow part and causing crack expansion in the shallow RSR. The low-strength mudstone-clay composite rock layer yields and enters a plastic state, resulting in significant shallow rock deformation. At this point, deformation rates are high for the roadway roof, floor, and sides. Monitoring shows that roof and floor deformation rates reach a maximum of 37 mm/d with 92 mm cumulative displacement, while side deformation rates peak at 32 mm/d with 73 mm cumulative displacement.  
Figure 19: Schematic diagram of roadway surface displacement observation method.  
Figure 18: Mudstone–clay composite roof support control scheme of material roadway at the 18,511 th working face.  
Exavation General Impact Stage  
This stage spans from 5 to 15 days after excavation, occurring 10 m-30 m from the excavation face. The plastic zone formed in the shallow mudstone-clay rock layer above the roadway and the coal bodies during initial excavation altered the stress state in the RSR, with stress concentration moving deeper. This results in decreased stress concentration, reduces support load, and improves the surrounding rock's stress state. During this period, deformation rates significantly decrease, with side convergence rates dropping from 32 mm/d to 4 mm/d, and the roof and floor's convergence rates decreasing from 37 mm/d to below 5 mm/d. The roof and floor maintain higher convergence rates and greater cumulative displacement compared to the sides.  
Excavation Affects Stability Stage  
After 15 days of roadway excavation, with the excavation face more than 30 m away, secondary reinforcement supports with long anchor cables were implemented on the roof. This combined support system of anchor rods, short anchor cables, and long anchor cables effectively controlled roadway deformation. The surrounding rock entered a stable stage, with deformation rates stabilizing at 23 mm/d. Excavation activities had minimal impact on roadway stability at this stage. Final measurements showed cumulative deformations of 141 mm for the roof and floor and 135 mm for the two sides. The stabilization of surrounding rock after 15 days and at 30 m of excavation demonstrates the effectiveness of the integrated support system in controlling deformation of the mudstone-clay composite roof roadway.