## 3 Results and Discussion
### Load Carrying Capacity  
The load values corresponding to the characteristic points of the specimens are shown in Table 6. Because positive and negative bearing capacities are asymmetric, the values in the table are the average values of the positive and negative load values. In this paper, the geometric mapping method is selected to determine the yield point of the specimen, as shown in Figure 11. The Y point determined by the method of Figure 11 is the yield point. The ultimate point is defined when the horizontal bearing capacity of the descending section of the specimen backbone curve drops to 0.85 times the peak load, or the horizontal bearing capacity does not drop to 0.85 times peak load, but the specimen can no longer withstand the load. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{
\begin{tabular}{c} **Specimen** \\ **Number** \\ \end{tabular} } & \multicolumn{4}{c}{**Characteristic Point Bearing Capacity (kN)**} \\ \cline{2-6}  & **Crack Load** & **Yield Load** & **Peak Load** & **Ultimate Load** & **Yield Ratio** \\ \hline RFSW-1 & 68.980 & 102.091 & 137.961 & 117.267 & 0.74 \\ CGSW-2 & 66.052 & 96.394 & 128.525 & 109.246 & 0.75 \\ CGSW-3 & 62.716 & 93.427 & 120.905 & 102.769 & 0.77 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Characteristic point bearing capacity of the specimens. Figure 11: Geometric mapping method. In Figure 11, Point O represents the origin point, Point A represents the peak point, Point Y represents the yield point, and Point B, C and D represent the auxiliary point. Besides, F\({}_{\rm m}\) represents the peak load, F\({}_{\rm y}\) represents the yield load, \(\Delta_{\rm u}\) represents the ultimate displacement, \(\Delta_{\rm m}\) represents the peak displacement, and \(\Delta_{\rm y}\) represents the yield displacement. Table 6 shows that with the increase in the coal gauge replacement rate, the load values at the characteristic points of the three specimens decrease. Horizontal ultimate bearing capacity of specimen RFSW-1 is the largest. Compared with specimen RFSW-1, the peak load of specimens CGSW-2 and CGSW-3 decreases by 6.8% and 12.4%, respectively, while the yield load decreases by 5.6% and 8.5%, respectively, indicating that the increase in the coal gauge replacement rate will reduce the horizontal bearing capacity of the concrete shear wall specimens. This is because the strength of spontaneous combustion coal gangue is between natural coarse aggregate and light aggregate, and the destruction surface of spontaneous combustion coal gangue is generally along its joint surface. So, the joint surface has become the weak link of spontaneous combustion coal gangue. On one hand, the strength of the joint surface is lower than the overall strength. On the other hand, with the increasement of the mortar strength, the aggregate strength will be even lower than the mortar strength. Thus, the concrete strength is controlled by the mortar to the aggregate. Above all, even if the amount of cement is increased, it is not significant to improve the strength. The strength of the concrete not only depends on the distribution of the joints of the spontaneous combustion coal gangue aggregate, but also relates to the strength along the direction of the joint. Therefore, the horizontal bearing capacity of coal gangue concrete shear wall is lower than that of the ordinary concrete shear wall, and with the increase of coal gangue replacement rate, the horizontal bearing capacity gradually decreases. The yield ratio, defined as the ratio of the yield load to the peak load, can reflect the strength reserve capacity of the structure. A small yield ratio indicates the safety of the specimen, but if the yield ratio is too small, the strength cannot be fully utilized, and the material is wasted. According to Table 6, the larger the replacement rate of coal gangue is, the larger the yield ratio of the specimen is, indicating that the strength reserve capacity becomes worse.