# Research on Rock Strength Test Based on Electro-Hydraulic Servo Point Load Instrument
## 5 Conclusions  
In this paper, the self-developed electro-hydraulic servo point load instrument was used to conduct point load test research on three rock samples at different loading rates. The following conclusions were obtained by analyzing the internal stress state of rock samples at different loading rates, the effect of loading rate, and dimensional changes on different I\({}_{\rm s(50)}\), and establishing the empirical conversion equation between I\({}_{\rm s(50)}\) and uniaxial compressive strength. 1. The tensile and compressive stresses in the loading-axis direction of the three rock samples under the action of point load increased with the increase in the loading rate. The difference in stress distribution of the rock samples brought by the influence of the loading rate was mainly reflected in the compressive stresses, and the compressive stresses were mostly influenced by the loading rate near the center of the loading axis of the rock samples. 2. With the increase in loading rate, I\({}_{\rm s(50)}\) tends to increase, and when the loading rate increases to a certain range (0.5-1.0 kN/s), the growth of I\({}_{\rm s(50)}\) tends to level off, and the influence of loading rate on I\({}_{\rm s(50)}\) value is greatest at size 40\({}^{3}\) mm\({}^{3}\). I\({}_{\rm s(50)}\) solved using methods I, III, and IV have obvious size effect, while I\({}_{\rm s(50)}\) solved using method \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Rock Sample** & **Size Range (mm\({}^{3}\))** & **Loading Rate (kN/s)** & **\(I_{\rm s(50)2}\) (MPa)** & **\(R_{\rm c}\) (MPa)** & **Relationship Formula** \\ \hline Fine-crystalline granite & 30\({}^{3}\)–40\({}^{3}\) & 0.5 & 12.316 & 206.920 & \(R_{\rm c}=16.80I_{s(50)2}\) \\ Coarse-crystalline granite & 30\({}^{3}\)–40\({}^{3}\) & 0.5 & 8.514 & 130.450 & \(R_{\rm c}=15.32I_{s(50)2}\) \\ Silstone & 30\({}^{3}\)–40\({}^{3}\) & 1.0 & 3.986 & 58.200 & \(R_{\rm c}=14.60I_{s(50)2}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 10: Empirical conversion formulas for the three rock samples. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Author** & **Fitting Relationship** & **Rock Type** \\ \hline [PERSON] et al. [35] & \(R_{c}=17.4I_{5(50)}\) & Sandstone \\ [PERSON] and [PERSON] [36] & \(R_{c}=16I_{5(50)}\) & Granite \\ [PERSON] and [PERSON]. [37] & \(R_{c}=(12.5\sim 14.9)I_{5(50)}\) & Granite \\ [PERSON] and [PERSON] [38] & \(R_{c}=(23\sim 25)I_{5(50)}\) & Granite (fresh, weathered) \\ [PERSON] and [PERSON] [39] & \(R_{c}=18I_{5(50)}\) & Granite \\ [PERSON] and [PERSON], M.Z.A. [40] & \(R_{\rm c}=11.08I_{5(50)}\) & Silstone, limestone, dolomite \\ [PERSON] and [PERSON], L.N.Y. [14] & \(R_{c}=20I_{5(50)}\) & Silstone \\ [PERSON] et al. [41] & \(R_{\rm c}=16.08I_{5(50)}\) & Sandstone, mudstone \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Conversion relationship between I\({}_{\rm s(50)}\) and uniaxial compressive strength. II has no obvious size effect, so it is more reasonable to use I\({}_{\rm s(50)}\) solved using method II to predict the uniaxial compressive strength of the rock. 3. The I\({}_{\rm s(50)}\) solved by method II is more reasonable and reliable for fine-crystalline granite, coarse-crystalline granite, and siltstone in the size range 30\({}^{3}\)-40\({}^{3}\) mm\({}^{3}\) at loading rates of 0.5, 0.5, and 1.0 kN/s. 4. An empirical conversion relationship between I\({}_{\rm s(50)}\) and uniaxial compressive strength was proposed for the three rock samples used in this analysis, and the strength conversion coefficients of 16.80, 15.32, and 14.60 were obtained for fine-crystalline granite, coarse-crystalline granite, and siltstone specimens, respectively. It indicates that the high-strength rock has a higher conversion coefficient than the low-strength rock. Conceptualization, X.Z. and L.Q. ; formal analysis, X.Z. and L.Q. ; funding acquisition, F.W. ; investigation, Z.W. and J.W. ; methodology, F.W. and L.Q. ; data curation, Y.C. and Z.W. ; resources, J.W. and Z.W. ; validation, Y.C. and X.Z. ; visualization, J.W. ; writing--original draft, X.Z.