# Numerical Simulation and Engineering Application of Temporary Stress Field in Coal Mine Roadway
## 5 Analysis of Factors Influencing Stability of Surrounding Rock in Unsupported Areas  
The key to safe and efficient excavation lies in ensuring the stability of the surrounding rock in the unsupported area. Changes in the parameters of temporary support lead to variations in the stress-strain characteristics of the surrounding rock within the unsupported area. The primary parameters of temporary support include the length of the supported area, the length of the unsupported area, and the magnitude of the temporary support force. The length of the supported area determines equipment requirements, the temporary support force plays a pivotal role in controlling the surrounding rock, and the unsupported distance dictates the maximum spacing between excavation rows [86; 87; 88; 89; 90].  
Initially, the relationship between the temporary support force and roof strain in the unsupported area was investigated. It was observed that roof strain decreased with increasing temporary support force, indicating a corresponding increase in stress within the unsupported region. This parallels the behavior of permanent support (anchor support), where higher support forces enhance stress within the surrounding rock [91; 92; 93]. The optimum support force was defined as the force at which the roof strain approached zero. Through investigation, optimum support forces were determined for unsupported distances ranging from 1 m to 5 m as 13 MPa, 17 MPa, 20 MPa, 23 MPa, and 26 MPa, respectively (Figure 6). A strong linear relationship between unsupported distance and optimum temporary support force was identified (Figure 7). This relationship can accurately predict the required temporary support force in the unsupported area, providing valuable guidance for on-site support force settings.  
Second, an analysis of the roof strains at various unsupported distances in both the temporary support area and the unsupported area (Figure 8) reveals a decrease in roof strain within the temporary support area as the unsupported distance increases. This reduction can be attributed to the stress distribution in the unexcavated area transferring into the temporary support area. Furthermore, when the unsupported distance was less than 3 m, the roof strain in the unsupported area was lower than that in the temporary support area. There was no significant increase in roof strain in the unsupported area when the unsupported distance was less than 3 m. In comparison to the maximum unsupported roof distance of 2 m with permanent support, using temporary support allows for a maximum unsupported roof distance of 3 m, approximately 33% higher. This increase effectively enhances excavation efficiency [94; 95; 96].  
Figure 6: Influence of different temporary supporting forces on different empty roof spacing.  
Third, the evolution of roof strain in unsupported areas was examined concerning the length of the temporary support area. An inflection point was observed in the strain variation within the unsupported area relative to the length of the temporary support (Figure 9). Specifically, prior to this inflection point, there is no significant change in roof strain with an increasing length of the temporary support. However, after reaching this turning point, the roof strain increases notably with further extension of the temporary support. The turning points corresponding to unsupported distances of 1-5 m, illustrated in Figure 9, occur at temporary supporting area lengths of 17 m, 16 m, 15 m, 14 m, and 13 m, respectively. The total length of the temporary support area at the turning point, combined with the unsupported distance, is 18 m, suggesting that the combined length of the temporary support and unsupported areas should not exceed this limit. Furthermore, based on the conclusion in Figure 6, it can be inferred that the maximum allowable length for the temporary support area should not exceed 15 m [97; 98].  
Figure 8: Roof displacements conditions with different unsupported distance.  
Figure 7: Linear fitting relationship.