Shrinkage and cracking characteristics of Benggang soil under the condition of controlling height-diameter ratio

Abstract: Shrinkage and cracking of Benggang soil often occur and vary significantly in different soil layers during water evaporation. That is because there are the hydrophilic clay minerals (kaolinite and hydromica) in the special soil with stratification after natural geological evolution. This study aims to clarify the influence of height-diameter ratios on soil shrinkage and cracking characteristics. The Benggang soil was selected in the Wuli Town, Tongcheng County, Hubei Province of China. 10 groups of height-diameter ratio were then designed for the experiment. The soil samples were configured as supersaturated mud, where the water evaporation was accelerated using low-speed wind fans. The soil morphologies before and after dehumidification were characterized at a fixed position. Digital image processing was also utilized to carry out a quantitative analysis. Therefore, the shrinkage and cracking mechanism of Benggang soil were addressed under the condition of controlling the height-diameter ratio. The results are listed as follows. 1) There was the strongest radial shrinkage and cracks development in the transition layer, whereas, the weakest in the sandy layer among the four layers of Benggang soil. The transition and sandy layers were then defined as the lower soil adjacent to the soil layer in the vertical section. The less difference between the two soil layers was contributed to the stability and bearing capacity of Benggang soil, thereby relieving the collapse of the Benggang wall. 2) The samples with a smaller height-diameter ratio developed significant cracks, but the radial shrinkage was not outstanding. By contrast, there was no crack in the samples with a larger height-diameter ratio, but the radial shrinkage was significant. Among them, the specific critical values of the height-diameter ratio for the four soil layers during the transition from the drying cracking to radial shrinkage state were achieved, 0.147-0.160, 0.160-0.183, 0.160-0.183, and 0.134-0.147, respectively. 3) The crack parameters and radial shrinkage ratio were similar, but the axial shrinkage ratio increased as the thickness of the soil layer increased, particularly when the height-diameter ratio was the same, even though the height and diameter were different. More importantly, the crack morphology developed more complex from the topsoil to the transition layer, but the sandy layer remained unchanged. 4) The shrinkage water content gradually increased with the increase of height-diameter ratio, whereas, the crack water content gradually decreased. The difference between them was then represented by the tensile strength of soil during the dehumidification. Correspondingly, the degree of shrinkage and cracking, the width-diameter ratio, and the radial shrinkage ratio increased with the increase of the height-diameter ratio, whereas the rest parameters showed a decreasing trend. Therefore, there was the most significant influence of height-diameter ratio on the shrinkage and cracking characteristics in the transition layer, whereas, the least influence was found in the sandy layer. The finding can also provide strong theoretical support to reveal the collapse mechanism of Benggang soil for higher stability in construction projects.