# Applicable Conditions of Room-and-Pillar Mining Goal Treatment Methods under a Traffic Load
## 4 Engineering Case Analysis
The parameters presented in Table 8 were included in Formula (2), and the tensile stress of the roof under traffic load conditions was calculated to be 0.283 MPa. This value was then included in Formula (3), and the calculated K was 2.47, which is greater than 1.5. It was therefore necessary to check the strength of the coal pillar and base plate. After the parameters were included in Formulas (4) and (5), the compressive stress of the coal pillar under traffic load conditions was determined to be 13.867 MPa, and the strength of the coal pillar was 15.845 MPa. After these parameters were included in Formulas (6) and (7), the values of K were 1.14 and 1.66, respectively. As the safety factor of the coal pillar was 1.14, the coal pillar may be unstable under traffic load conditions in this road section. Therefore, grouting treatment should be performed in the goat area under this road section. Referring to the analysis process of the treatment methods in K1631 + 985-K1632 + 035, the remaining sections to be treated were analyzed, and the treatment methods for each section are presented in Table 10. As can be observed from Table 10, the K1626 + 400-K1626 + 500, K1627 + 945-K1628 + 433, and K1631 + 985-K1632 + 035 sections need to be treated by grouting because they failed the calculations of the roof or coal pillar strength values. The grouting treatment is presented in Figure 8. However, K1633 + 000-K1633 + 160 and K1627 + 145-K1627 + 423 passed the calculation of the load disturbance depth, so it was only necessary to adopt the method of laying a geogrid on the subgrade for treatment purposes. The geogrid is presented in Figure 9. In one year of operation following these calculations, none of the above-mentioned road sections collapsed. The subsidence of the treated grouting and geogrid sections was monitored by level for one year, once every half month, and a total of 25 periods of subsidence monitoring data were obtained. Taking the K1631 + 985-K1632 + 100 grouting treatment section and the K1627 + 145-K1627 + 423 geogrid-laying treatment section as examples, the treatment effects of the two methods were evaluated. The subsidence of each section is presented in Figures 10 and 11. As can be observed in Figure 10, following one year of grouting treatment for K1631 + 985-K1632 + 100, the subsidence trend in the middle and both sides of the subgrade gradually tended to become smooth over time, which is in line with the subsidence trend of the normal subgrade. The values of the middle and both sides of the subgrade were \(-\)17.94, \(-\)14.25, and \(-\)14.57 mm, respectively, which met the subsidence requirements of the subgrade following construction. It can be observed in Figure 11 that the subsidence trend of K1627 + 145-K1627 + 423, at the middle and both sides of the subgrade, gradually tended to become smooth over time after laying the geogrid for one year, which agrees with the subsidence trend of the normal subgrade. The subsidence values of the middle and both sides of the subgrade were \(-\)10.25, \(-\)8.24, and \(-\)7.91 mm, respectively, which met the subsidence requirements of the subgrade following construction. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Pile Number Range**} & **Traffic-Disturbance-Depth-Check Calculation** & **Roof-Strength-Check Calculation** & **Coal-Pillar-Strength-Check Calculation** & **Base-Plate- Strength-Check Calculation** & **Treatment Method** \\ \hline K1626 + 400–K1626 + 500 & Fail & Fail & No need to check & No need to check & Grouting treatment \\ K1627 + 145–K1627 + 423 & Pass & No need to check & No need to check & No need to check & Laying geogrid \\ K1627 + 945–K1628 + 433 & Fail & Pass & Fail & No need to check & Grouting treatment \\ K1631 + 985–K1632 + 100 & Fail & Pass & Fail & No need to check & Grouting treatment \\ K1633 + 000–K1633 + 160 & Pass & No need to check & No need to check & No need to check & Laying geogrid \\ \hline \hline \end{tabular}
\end{table} 
Table 10: Analysis of treatment methods for each road section.