Effects of freeze-thaw cycle on permeability and compression properties of aeolian soil-bentonite mixture
Authors: Chen Cong , Peng Wenming , Li Jian , Luo Qixun , Jiang Bingnan , Yu Yanyang , Liu Enlong 
Published: July 2023

Abstract

Since all the soil materials within 200 kilometers of the proposed dam site are aeolian sedimentary soil, the permeability is not in line with the engineering performance of the core dam materials. Moreover, in the construction of a large core dam in a high altitude area, the core wall dam materials will be subjected to repeated freeze-thaw action during the winter construction of the dam, resulting in changes in the particle distribution and particle connection inside the filled dam materials. Thus, the engineering properties and filling quality of dam materials are changed. Therefore, in this paper, two types of bentonite were used to improve the existing aeolian soil material, and the aeolian soil-Na/Ca-bentonite mixture (ANB/ACB) with different bentonite content (0%, 2%, 4%, 8%, 16%, 32%) was subjected to different freezing through particle separation test, variable head permeability test and consolidation compression test. The influence of the number of thawing cycles (0, 1, 5, 10) on the permeability and compression properties was studied. The test results show that: (1) the increase of bentonite content, the inhomogeneity coefficient, curvature coefficient and clay content of ANB/ACB increase gradually, and the inhomogeneity coefficient, curvature coefficient and clay content of ACB are greater than those of ANB under the same bentonite content,(2)the continuous incorporation of Na/Ca-bentonite, the permeability coefficient of ANB/ACB decreases, and the decreasing trend is gradually becoming slight; the permeability coefficient of ANB increases gradually after the freeze-thaw cycle, while the permeability coefficient of ACB decreases with the increase of freeze-thaw times when the bentonite content is high;(3) the increase of consolidation normal stress, the compression coefficients of ANB and ACB decrease rapidly, and their decreasing rates also decrease gradually. Meanwhile, under the same normal stress condition, the compression coefficient (av) of ANB/ACB decreases gradually with the increase of bentonite content, and increases gradually with the increase of freeze-thaw cycles; and (4) the compression index of ANB/ACB gradually increases with the continuous incorporation of bentonite content, and with the increase of bentonite content, the compression index of ACB develops from roughly equal to that of ANB to that of ACB greater than that of ANB. At the same time, the effect of the freeze-thaw cycle on the compression index of ACB/ANB is deteriorating, and the first freeze-thaw cycle has the greatest effect on the compression index of both ACB and ANB. In addition, the effects of bentonite content and freeze-thaw effect on the mixed soil samples are analyzed from the microscopic scale through electron microscope scanning. It is found that the addition of bentonite increases the proportion of fine particles in the mixed soil samples, while the freeze-thaw cycle effect changes the pore structure and particle size of the soil samples. This study provides scientific support for dam construction and design in plateau areas where aeolian soil is widely distributed.