Study On Pore Water Distribution And Permeability In Kaolin Consolidation Process

During the excavation and support process of a foundation pit,the consolidation settlement of soil and the drainage of pore water are crucial for construction safety and deformation control.The pore water distribution and permeability of soil have long been topics of great concern in soil mechanics and geotechnical engineering,as they determine the engineering properties such as consolidation settlement of the soil.Indepth research on the pore water distribution and permeability of clay before and after consolidation is beneficial for theoretically assessing the deformation of foundation pits and the stability of soils.This study focuses on kaolin clay and conducts consolidation compression tests using a self-made consolidation permeameter,based on the principles of laboratory consolidation tests.The adsorption method,volumetric flask method,thermogravimetric analysis,and nuclear magnetic resonance(NMR)are employed to investigate the bound water content of kaolin clay.The NMR technique is used to explore the pore water distribution and forms during the consolidation compression process of kaolin clay.Permeability tests under different dry densities are conducted using the principle of unique corresponding pore ratios,and the theoretical permeability coefficient of kaolin clay is calculated based on the Terzaghi’s consolidation theory.The quantitative relationship between bound water content,pore ratio,and permeability coefficient is established using the Kozeny-Carman equation.The specific achievements are as follows:(1)A set of consolidation permeation containers is produced based on the principles of traditional consolidation compression tests and the requirements of NMR technology.According to the test results of the self-made consolidation permeation containers,the variation pattern of the consolidation compression curve of the specimens conforms to the variation pattern of laboratory consolidation compression tests,solving the technical problem of stress state and deformation changes during NMR scanning of the specimens.(2)The bound water content measured by thermogravimetric analysis,volumetric flask method,and NMR technique are similar,around 23%.The bound water content obtained from the isothermal adsorption test is 6% smaller than that measured by the other methods.(3)During the consolidation compression process of kaolin clay,the total pore water continuously decreases due to compression.When the pressure is below 100 k Pa,the mass fraction of free water rapidly decreases from 83% to 46%,while the mass fraction of bound water increases from 17% to 54%.When the pressure exceeds 100 k Pa,both free water and bound water decrease slowly,with bound water becoming the dominant component of pore water during this stage.(4)The theoretical permeability coefficient and the measured permeability coefficient during the consolidation compression process of kaolin clay decrease with the decrease of pore ratio,and they exhibit the same variation pattern.The difference in permeability coefficient between them is within the range of 1×10-4 when the pore ratio is greater than 0.95,and within the range of 2×10-5 when the pore ratio is less than 0.95.(5)Based on the experimental data,a method is proposed to substitute the bound water content for specific surface area in the Kozeny-Carman equation.The modified permeability coefficient is compared with the theoretical and measured permeability coefficients,showing a high degree of fit.This indicates that the modified method can serve as an effective tool for studying the permeability of kaolin clay during the consolidation process.