# Experimental PIV Radial Splitting Study on Expansive Soil during the Drying Process
## 1 Introduction  
The characteristics of expansive soil include water absorption expansion, water loss shrinkage and repeated expansion and shrinkage deformation [1], water immersion bearing capacity attenuation, and dry shrinkage crack development. The properties of expansive soil are extremely unstable. Expansive soil is prone to shrinkage and cracking during the drying process, leading to strength and permeability problems that exist widely in water conservancy projects and geotechnical engineering, including foundation pits and cracks at the bottom of channels and slopes. Such problems are closely related to the tensile strength of the soil [2; 3; 4]. As a result of seasonal and climatic influences, the structure of expansive soils change, which directly changes the strength of the soil. Because the strength of expansive soils is an important parameter that can determine the stability of projects such as buildings and slopes, it is essential to analyze the factors influencing the soil strength. During drying, the strength of an expansive soil is affected by its water content and dry density. [PERSON] et al. [5] performed drying-wetting cycle tests on remolded samples of expansive soil, and their results showed that the drying-wetting cycles changed the soil microstructure. [PERSON] et al. [6] concludedthat the strength of an expansive soil first increases and then stabilizes with the number of drying-wetting cycles. By analyzing the change in the pore volume, [PERSON] et al. [7] found that drying-wetting cycles destroy the intergranular connection and soil structure, resulting in an attenuation of the soil strength. Using laboratory tests, [PERSON] et al. [8], [PERSON] et al. [9], and [PERSON] et al. [10] found that the strength of expansive soils is affected by overconsolidation. [PERSON] [11] pointed out that cracks, as structural characteristics of overconsolidated soil, affect the strength of cohesive soils. [PERSON] [12] stated that when the stress on the soil exceeds the peak value of its shear strength, the crack tip causes greater stress concentration and soil damage. [PERSON] et al. [13; 14] examined the hydromechanical behavior of expansive soils related to suction and the suction history and investigated the strength and stress-strain behavior of expansive soils under suction control using triaxial shear tests. [PERSON] et al. [15] used the resistivity method to measure the crack depth of an expansive soil slope. [PERSON] et al. [16] used the discrete element method to study the microstructure of expansive soils, considering the influence of different confining pressures on the internal cracks of specimens. [PERSON] et al. [17] investigated the entire process of crack development in expansive soils under the action of water and external forces, using computerized tomography scanning combined with physical experimental parameters to reveal the effect of crack development on the macroscopic deformation of expansive soils. [PERSON] et al. [18] used image analysis techniques to quantify dry cracks on the surfaces of specimens. However, there are few comparative studies concerning tensile strength and crack development during the drying processes of undisturbed and remolded expansive soils. Therefore, further study is necessary to identify the relevant change rule and its internal mechanism. In general, soil crack development is closely related to the tensile strength of the soil. Methods of measuring the tensile strength of soil primarily include the direct tens test [19; 20; 21], the radial splitting test [22; 23], the bending beam test [24], and the ring specimen method [25]. The use of the radial splitting test to perform tensile strength tests is feasible because of its simplicity and ease of operation [26]. In addition, particle image velocimetry (PIV) technology has become a well-established technique in the field of geotechnical model tests and displacement field calculations. [PERSON] et al.