## 6 Conclusions  
This paper presents a twin-link stepping temporary support process for underground coal mine excavation roadways and develops a comprehensive set of twin-link stepping temporary support equipment, enabling simultaneous operations of drivage, support, and anchoring in underground coal mines. A comparison was conducted to evaluate the temporal and spatial advantages of the new operation process in contrast to the traditional excavation process. The new process has demonstrated the potential to reduce the duration of a single excavation cycle by nearly 50%. However, the repeated application of the twin-link stepping temporary support may potentially lead to roof damage in specific roadways, limiting its applicability. To address this, a numerical simulation approach using 3 DEC was employed to establish a comprehensive numerical model for repeated support during roadway excavation. The numerical simulations were conducted considering various factors such as burial depths of roadways, lithologies of the direct roof, and thicknesses of the direct roof, based on the twin-link stepping temporary support process. By analyzing the fragmentation range, displacement, and relative displacement between the direct roof and the basic roof, the range of repeatable roof support for the roadways was determined. Consequently, this study provides the necessary conditions for the implementation of the complete equipment of the twin-link stepping temporary support system. The proposed twin-link stepping temporary support process and the numerical simulation method for repeatable roof support in roadways address the significant deficiency \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Roadway Burial** & **Direct Roof** & \
\begin{tabular}{c} **Direct Roof** \\ **Thickness** \\ **Range** \\ \end{tabular} &
\begin{tabular}{c} **Repeatability of** \\ **Support** \\ \end{tabular} & **Applicability** \\ \hline
200 m & \
\begin{tabular}{c} sandstone \\ Sandy mudstone \\ mudstone \\ \end{tabular} &
\begin{tabular}{c} \textgreater{}0.8 m \\ \textgreater{}0.8 m \\ \textgreater{}1.0 m \\ \end{tabular} & & \\ \hline
500 m & \begin{tabular}{c} sandstone \\ Sandy mudstone \\ mudstone \\ \end{tabular} & \begin{tabular}{c} \textgreater{}0.8 m \\ \textgreater{}1.0 m \\ \textgreater{}1.3 m \\ \end{tabular} & \
\begin{tabular}{c} Repeatable \\ support \\ \end{tabular} &
\begin{tabular}{c} Applicable to the stepping \\ support process \\ \end{tabular} \\ \hline
800 m & \
\begin{tabular}{c} sandstone \\ Sandy mudstone \\ mudstone \\ \end{tabular} &
\begin{tabular}{c} \textgreater{}0.8 m \\ \textgreater{}1.2 m \\ \textgreater{}1.5 m \\ \end{tabular} & & \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Applicable Range of Stepping Temporary Roof Support Conditions. Figure 26: Schematic diagram of the applicable roadway range for stepping temporary support. of ineffective temporary support in underground excavation roadways, thereby greatly enhancing the safety and efficiency of underground coal mine excavation roadways. Furthermore, the new process, equipment, and research methods presented in this paper have the potential for application in similar operational roadways. Conceptualization, D.W. and R.L. ; methodology, J.C. and D.W.; software, H.J. ; validation, Y.S., D.W. and M.W. ; formal analysis, S.Z. ; investigation, S.Z. ; resources, M.W. ; data curation, R.L. ; writing--original draft preparation, D.W.; writing--review and editing, R.L. and Y.Q. ; visualization, H.J. ; supervision, M.W. ; project administration, S.Z. ; funding acquisition, M.W. All authors have read and agreed to the published version of the manuscript. This research was supported by Youth Found of the National Natural Science Foundation of China grant number 52104169 and China University of Mining and Technology (Beijing) Doctoral Talents Cultivation Fund for Top Innovative Talents, grant number BBJ2024062. Not applicable. The raw data supporting the conclusions of this article will be made available by the authors on request.