# Effect of Drying-Wetting Cycle and Vibration on Strength Properties of Granite Residual Soil
## 4 Conclusions  
Through direct shear and UCS tests, the stress-strain curves, cohesion, internal friction angle and UCS of GRS were studied. Modified calculation formulas for shear strength and unconfined compression strength under DW cycles and vibration were proposed. The  
Figure 14: UCS degradation index vs. DW cycle.  
Figure 15: Comparison of measured and calculated values of UCS.  
proposed modified formulas enable the use of more accurate GRS mechanical parameters in numerical simulations, as opposed to the outdated parameters often found in geotechnical survey reports. Furthermore, the research provides specific mechanical parameter changes for considering soil in different influencing areas, such as areas affected only by DW cycles, areas affected only by vibrations and areas where the two factors intersect. By applying more precise grid mechanical parameters to these distinguishing regions, researchers can obtain more accurate simulation results. The following conclusions were drawn:  
1. The stress-strain curve of shear strength mainly exhibited strain-hardening characteristics. Due to the volume shrinkage caused by DW cycles and vibration, the shear compressibility of the sample increased with the number of DW cycles and the vibration time. The stress-strain curve of unconfined compression strength showed strain-softening characteristics, with a significant decrease in the stress peak due to DW cycles and vibration, and their combined effect shifted the stress peak forward in the stress-strain curve.
2. The cohesion decreased nonlinearly with the increase in the number of DW cycles and the vibration time, and the degradation of cohesion reached 58.6% under their combined effect, but the degradation effect was not simply additive. The compaction effect of DW cycles on the soil caused a fluctuating increase in the internal friction angle with the increase in the number of DW cycles. The influence of vibration on the internal friction angle decreased with the increase in the number of DW cycles.
3. The UCS rapidly decreased and then stabilized with the increase in the number of DW cycles and vibration time. The degradation effect of UCS due to DW cycles and vibration was significant, with a maximum degradation of 81.1%. Without vibration, the degradation of UCS increased nonlinearly with the number of DW cycles, while after experiencing vibration, the degradation of UCS increased linearly with the number of DW cycles.
4. Modified formulas considering the effects of DW cycles and vibration on shear strength and UCS were established. The calculated values of the two modified formulas were within a reasonable range of error compared to the measured values, indicating that the modified formulas can effectively predict the effects of DW cycles and vibration on shear strength and UCS.  
Investigation, D.C.; data curation, J.T.; writing--original draft, J.T.; writing--review and editing, D.C.; supervision, D.C.; project administration, D.C. All authors have read and agreed to the published version of the manuscript.  
The work in this paper was supported by the Natural Science Foundation of Fujian Province (No.: 2021J01010), the Key Program of Natural Science Foundation of Fujian Province (No.: 2021J02003) and China Railway Southern Group 2022 Science and Technology Innovation Program Topics (No.: 202208).  
Not applicable.  
The data are available and are explained in this article; readers can access the data supporting the conclusions of this study.  
The authors declare no conflicts of interest.