# Effect of Drying-Wetting Cycle and Vibration on Strength Properties of Granite Residual Soil
## 3 Test Results and Analysis
### Analysis of Unconfined Compression Strength Test Results
#### 3.2.2 Unconfined Compression Strength  
Figure 13 shows the relationship between UCS and the number of DW cycles and vibration time. The UCS decreases rapidly with an increase in the number of DW cycles and vibration time, the rate of decrease gradually slows down and eventually stabilizes and the trend of changes caused by vibration time is similar to that of [PERSON] et al. [29].  
Figure 12: Stress-strain curve of unconfined compression strength test.  
To further quantify the effect of DW cycles and vibration on the UCS, the degradation of UCS is calculated using Equation (5).  
\[\eta_{t,n}=\frac{\text{UCS}_{0,0}-\text{UCS}_{t,n}}{\text{UCS}_{0,0}}\times 100\% \tag{5}\]  
where \(\eta_{t,n}\) is the UCS degradation index after \(t\) minutes of vibration and \(n\)th DW cycles; UCS\({}_{0,0}\) is the UCS without DW cycles and vibration; and UCS\({}_{t,n}\) is the UCS after \(t\) minutes of vibration and \(n\)th DW cycles.  
The calculation results of \(\eta_{t,n}\) are shown in Table 4. It can be observed that the DW cycle and vibration have a significant degradation effect on the UCS, reaching a maximum of 81.1%. The initial DW cycles and vibration have the most significant impact, with \(\eta_{t,n}\) reaching 30.2% and 30%, respectively. When the vibration time increases from 5 min to 15 min, there is little change in \(\eta_{t,n}\), with an average increase of about 10%.  
Figure 14 presents the relationship between the UCS degradation index \(\eta_{t,n}\) and the DW cycle. The relationship is nonlinear for unvibrated specimens, while it is approximately linear for vibrated specimens. By substituting Equation (5) into the fitting formula, the USC under DW cycles and vibrations can be obtained, as shown in Equation (6).  
\[\text{UCS}_{v,n}=\left\{\begin{matrix}\text{UCS}_{0,0}(1-0.27n^{0.45}),v=0\\ \text{UCS}_{0,0}(0.74-0.1n+0.045 nv-0.45v),\frac{1}{3}\leq v\leq 1\end{matrix}\right. \tag{6}\]  
where \(v\) is the normalized vibration time, \(v=t/15\), where \(t\) is the vibration time, and 15 is the maximum vibration time; UCS\({}_{v,n}\) is the UCS under \(n\)th DW cycles and the normalized vibration time \(v\).  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{6}{c}{**UCS Degradation Index \(\eta_{t,n}\)/\%**} \\ \cline{2-7}
**Vibration Time/mins** & \multicolumn{6}{c}{**DW Cycles/Times**} \\ \cline{2-7}  & **0** & **1** & **2** & **3** & **4** & **5** \\ \hline
0 & 0.0 & 30.2 & 35.7 & 42.0 & 48.5 & 59.4 \\
5 & 30.0 & 41.2 & 45.5 & 57.5 & 69.8 & 75.2 \\
10 & 36.2 & 50.2 & 55.7 & 63.7 & 73.2 & 77.2 \\
15 & 43.5 & 47.7 & 54.0 & 67.7 & 76.5 & 81.1 \\ \hline \hline \end{tabular}
\end{table}
Table 4: \(\eta_{t,n}\) under DW cycles and vibrations.  
Figure 13: Unconfined compression strength change graph.  
Figure 15 shows a UCS comparison of the calculated and measured values for different vibration times under 0-5 DW cycles. The diagonal line is the contour line, where the measured values are equal to the predicted values. The data errors are all within 8%, indicating that the modified UCS formula has good accuracy.