# Development Characteristics and Mechanism of Crack in Expansive Soil under Wet-Dry Cycling
## 6 Conclusions  
This study analyzes the development characteristics of cracks in specimens of expansive soil under the influence of wet-dry cycles. The analysis is conducted through indoor tests on expansive soil and direct shear tests. It examines the evolution of cracks and the response of shear strength indicators of expansive soil to various factors, both  
Figure 13: Schematic diagram of crack evolution process in different thicknesses of expansive soil samples.  
quantitatively and qualitatively. The objective is to reveal the mechanism behind crack evolution in specimens of expansive soil. The main findings are as follows:  
(1) The evolution of cracks in expansive soil exhibits an initial increase followed by stabilization with increasing wet-dry cycles, a phenomenon more pronounced in highly expansive soils. As cycles progress, the tensile forces from the surrounding soil drive lateral crack expansion, with average width increments of 0.5 mm for moderately expansive and 0.8 mm for highly expansive soil samples;  
(2) The influence of initial moisture content on the crack ratio of expansive soil is intimately linked to its expansive properties. In moderately expansive soils, this influence diminishes with additional wet-dry cycles. In contrast, pronounced swelling and shrinkage are observed only in highly expansive soil samples with an initial moisture content exceeding 35%;  
(3) Compaction significantly affects the crack count and length in expansive soils. At 90% compaction, the numbers of cracks in moderately and highly expansive soil samples drop by 71.4% and 68.8%, respectively, compared to those at 80% compaction, with a roughly 50% reduction in total crack length. Yet, as the sample height changes, the soil's expansion and contraction behavior during wetting and drying becomes more intricate, with an overall reduction in crack count and length but an increase in crack density and average width.  
(4) The shear strength of expansive soil is highly sensitive to wet-dry cycling. The cohesion of samples with an initial moisture content of 35% declines from 41.2 kPa to 20.3 kPa as the cycle count escalates, while the angle of internal friction fluctuates with an overall downward trend. The development of cracks under wet-dry cycling is identified as the cause of strength degradation, which correlates linearly with the crack ratio (R2 > 0.91).  
Conceptualization, Y.Z.; methodology, Y.Z.; validation, H.Z.; data curation, Y.Y. and M.O.; writing--original draft preparation, Y.Z.; writing--review and editing, Y.Z.; supervision, G.W.; funding acquisition, G.W. All authors have read and agreed to the published version of the manuscript.  
The work described in this paper was fully supported by a grant from the Title of the Excellent Young Scientist Project for Scientific Research from the Education Department of Hunan Province in 2023 (Project Number: 23B1040), National Key Research and Development Program Project (Project Number: 2019 YFC1509800), List of Key Technological Projects in the Transportation Industry, Ministry of Transportation, Year 2022 (Reference Number: 2022-MS5-125), and the Guangxi Key Research and Development Plan (Reference Number: AB23075184).  
Not applicable.  
The data that support the findings of this study are available from the corresponding author upon reasonable request.  
Author [PERSON] was employed by the company Guangxi Transportation Science and Technology Group Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.