# Effect of Drying-Wetting Cycle and Vibration on Strength Properties of Granite Residual Soil
###### Abstract  
Granite residual soil (GRS) exhibits favorable engineering properties in its natural state. However, a hot and rainy climate, combined with vibrations generated during mechanical construction, can cause a notable decrease in its strength. In this study, the evolution of stress-strain curves and strength parameters (cohesion \(c\) and internal friction angle \(\phi\)), unconfined compression strength (UCS) under drying and wetting(DW) cycles and vibration were investigated by means of direct shear test and UCS test. Furthermore, modified formulas for calculating shear strength and UCS under DW cycles and vibration were proposed, and their accuracy was verified. The results are as follows: The stress-strain curve of shear strength exhibits strain-hardening characteristics, and the shear compressibility of the sample increases with the number of DW cycles and vibration time. However, the stress-strain curve of UCS shows strain-softening properties, and the peak strength shifts forward with the number of DW cycles and vibrations. With the increase in the number of DW cycles and the vibration time, \(c\) shows a non-linear degradation, with a maximum degradation of \(58.6\%\). \(\varphi\) fluctuates and increases due to the densification effect of DW cycles, but the influence of vibration on \(\varphi\) decreases with the increase in the number of DW cycles. UCS rapidly decreases and gradually stabilizes after DW cycles and vibration, with a maximum degradation of \(81.1\%\). This study can serve as a reference for the stability analysis of GRS pits subjected to long-term influences of hot and rainy climates and mechanical vibration, providing valuable insights for future research. granite residual soil; drying-wetting cycle; vibration; strength deterioration +
Footnote †: journal: Applied Sciences  
the effects of DW cycles, resulting in an increase in cohesion with the number of DW cycles. After four DW cycles, the cohesion doubled while the internal friction angle slightly decreased. The mechanical properties of GRS are closely related to changes in microstructure and cracks [4]. Several studies have analyzed the effects of DW cycles on the macro-mechanical behaviors from the changes in microstructure and cracks. [PERSON] et al. [16] investigated the correlation among the development of cracks, shear strength degradation and DW cycles in GRS and proposed a calculation formula for crack depth and strength degradation. [PERSON] et al. [17] found that exponential decreases in effective cohesion and effective internal friction angle occur with the increase in the number of DW cycles, using trianxial consolidation undrained tests. With the help of computer tomography, nuclear magnetic resonance and scanning electron microscopy it was demonstrated that the fracture evolution and a transition in particle and pore structure led to fatigue damage of soil structure, resulting in the attenuation of the mechanical properties of GRS. The mechanical properties of GRS are also significantly affected by mechanical vibrations during subway and tunnel construction [18; 19; 20; 21; 22]. Indoor tests of simulating soil sample disturbance mainly use sample vibration and sample extrusion. Since a vibration test can quantitatively control parameters such as vibration time, this method is more used for disturbance research. Commonly used vibration methods include the shaking table [23; 24], the GDS dynamic triaxial instrument [25; 26] and the vibrating sieve machine [27; 28]. These methods destroy the original structure between soil particles through vibration and obtain disturbed samples. Currently, the research on vibration affecting the mechanical and compression properties of soils mainly focuses on silt clays and soft clays. [PERSON] et al. [23] simulated the disturbance of soft soil using an indoor shaking table and determined that the unconfined compression strength (UCS) decreases with increasing vibration time. Additionally, the slope of the consolidation compression curve increases before yielding. [PERSON] et al.