# Experimental PIV Radial Splitting Study on Expansive Soil during the Drying Process
## 3 Results and Discussion  
### PIV Radial Splitting Test Results  
As shown in Figure 3, the load-displacement curve of the radial splitting test of the undisturbed and remolded expansive soils with different initial water contents during the process of drying can be divided into four stages. The OA section was formed by the stress concentration of the upper and lower pressure heads at the contact part of the specimen. The AB section, in which the stress was transmitted into the specimen, was similar to the linear stage of the uniaxial compression test curve, which showed good linear characteristics. In the BC section, after the peak value was reached, the specimen began to display obvious cracks and the curve decreased rapidly. In the CD section, the specimen had a large radial splitting crack. The specimen then exhibited some residual strength. As the stress increased, the crack continued to expand until it penetrated the specimen, eventually leading to the complete destruction of the specimen. The load-displacement curves of the specimens with different water contents all showed a strain-softening phenomenon, and this phenomenon became increasingly significant with decreasing water content. The ultimate load decreased with increasing water content. The reasons for the above phenomenon were as follows: During the drying process of the soil, the water content decreased, the suction increased, and the expansive soil shrank, which led to an increase in the splitting strength of the expansive soil. The undisturbed specimens, with 20% water content, showed no obvious softening after the peak value in the load-displacement curve because of the higher water content, and the displacement required to reach the peak strength was greater, requiring continued compression to provide the plastic deformation necessary to break the samples. The above test phenomenon was inconsistent with the test results obtained by [PERSON] at al. [35], due to the different production methods of the specimens. The crack propagation process and the displacement vector field of the splitting failures of the undisturbed and remolded specimens with different water contents are shown in Figures 4 and 5, respectively. Darker colors in the figures indicate greater displacement and greater deformation results in more obvious cracks. After the load passed through the approximately linear AB section, no obvious cracks appeared when the peak stress point B was reached; small cracks primarily appeared at the top and bottom of the samples. After point B, the load decreased to point C and the splitting crack appeared on the splitting surface; then, the load dropped sharply to point D. The crack development diagrams and the displacement vector fields of points B, C, and D are shown in Figures 4a-e and 5a-e, respectively. Figure 3: Load–displacement curves: (**a**) undisturbed specimens; (**b**) remolded specimens. Figure 4: \(Cont.\)  
From the displacement vector field of the undisturbed specimen, it could be seen that the plasticity of the soil caused the specimen to undergo compression deformation at point B; however, no obvious cracks appeared and the displacement was primarily concentrated on the top of the undisturbed specimen. There were obvious cracks at point C after the peak value. The deformation of the undisturbed specimens with water contents of 7.5%, 17.5%, and 20% was primarily concentrated in the right half of the specimen, and the deformation developed with the crack to the lower right; the above phenomenon may have been caused by an uneven specimen or by stress concentration when the specimen was in contact with the pressure plate. The deformation of the undisturbed specimen with a water content of 11% was primarily concentrated at the top of the sample. The deformation of the undisturbed specimen with a water content of 15% was primarily concentrated in the left half of the specimen, and the deformation developed with the crack to the lower left.