LABORATORY TEST STUDY ON MOISTURE MIGRATION WITHIN MUCKY CLAY UNDER UNIDIRECTIONAL FREEZING IN CLOSED SYSTEM

The freezing-induced moisture migration within saturated soft mucky clay with high moisture content in closed system is an important factor that affecting the frost heave rate. This pape aims to gain a better understanding of the effect of cooling temperature on moisture migration within coastal soft clayey soil. It carries out the unidirectional freezing tests of Shanghai Quaternary marine mucky clay in closed system. Different cooling temperatures of - 5 to - 20 ℃ are set. It measures the amounts of frost heave and the temperatures of samples along the direction of temperature gradient. From the variation of frost front with time,the critical temperature gradient,the water inflow flux and velocity are derived. The results show that the heights of frost front at different cooling temperatures are a function of time. It is expressed as X(t)=t(at+b)^-1. A ratio value of the decrease of the temperature gradient in the frozen zone to the critical temperature gradient can be used to estimate the onset of moisture migration. The critical temperature gradient increases linearly with the decrease of cooling temperature. In the period of moisture migration,the water inflow velocity increases first and then decreases with time. Correspondingly,the water inflow flux-time curve gradually turns to linear from "S-shaped" as the cooling temperature decreases. The results of critical temperature gradient and cooling temperature,and the fitting formula of height of frost front on time,have great significance to predict the starting time of moisture migration during the unidirectional freezing process in closed system at a certain cooling temperature. This paper can promote the quantitative study of moisture migration within soft clayey soil with high moisture content under unidirectional freezing in closed system. It can be a valuable reference for the early warning of frost heaving during artificial ground freezing construction in coastal areas.