Explanation of the Influence of Sodium Chloride Solution on Volume Deformation and Permeability of Normally Consolidated Clays.

Tongwei Zhang,Shijun Wang

doi:10.3390/ma12101671

Abstract

The marine clays located in the Southeast area of China are characterized by their higher water content, higher compressibility and higher salinities. This soil is mainly composed of illite/montmorillonite interlayer minerals. Previous research has shown that the saline water significantly influences the liquid limit and other physical characteristics of the clays. As the desalination of pore water occurs as a result of freshwater or rainfalls, the physical and mechanical behaviors of the soft marine clays changes, and this can lead to potential hazards for infrastructure. Therefore, it is essential to understand the effects of chemistry variations and to predict the long-term foundation deformations. Based on previous works, the deformation behavior of artificial soils corresponding to a mixture of kaolinite and bentonite (the mass ratios of bentonite were 0%, 5%, 10% and 20%) was further discussed in a ln(1 + e)-logp’ system. The permeabilities of the samples mixed with different concentrations of sodium chloride solutions were compared based on oedometer tests. The micro-structures in the samples were investigated by SEM (scanning electronic microscopy) tests. The declining trend of a newly defined volume compression index Ccv and swelling index Csv with pore water salinity and e0/eL was observed when the initial void ratios e0 of the samples were close. The permeability coefficient k and the slopes Ck = e/logk of the mixtures increased with the ionic concentrations. Finally, the changes in volume deformations and permeabilities induced by sodium chloride solution are discussed based on ‘suction pressure’ and initial void compression at micro-level. This paper proves that the influences of salinity on the mechanical behavior of clays are mainly attributable to the interaction between diffused double layers, and these findings are helpful for improving the constitutive model of soft clays when taking pore water chemistry changes into consideration.

Highlights

The hydro-chemo-mechanical coupling effect of very active soils has drawn increasing attention with regard to the geotechnical problem of soil-environment interactions and the synthesis of composite materials
The Ccv and Csv of B5%K95%, B10%K90% and B20%K80% significantly decreased with the increase in salt solution, and the decrements of Ccv and Csv depending on salinities were larger when the bentonite content increased
To better understand the salinity effect on the volume compression and swelling behavior of clays, oedometer tests and SEM (Scanning electronic microscopy) tests were conducted on four artificial clays

Summary

Introduction

The hydro-chemo-mechanical coupling effect of very active soils has drawn increasing attention with regard to the geotechnical problem of soil-environment interactions and the synthesis of composite materials. The pore water chemical effect on compacted bentonite is of significant importance in the buttering of waste landfills and repositories for high levels of radioactive waste (HLW). Salinity variations in pore water can change the engineering properties of marine. Materials 2019, 12, 1671 clays [2]. Since the economic development of this region and the springing up of substantial infrastructure projects, the mechanical behavior of marine clay in relation to the environment has been drawing increasing attention. Marine clays are deposited in sea regression environments, and high water salinity and montmorillonite content are their main characteristics [2]

Methods

Results

Conclusion