Experimental Study On Gradient-dependent Deformation And Fracture Behavior Coupled Thermo-hydro Process In Saturated Soil Subjected To Freeze-thaw

The freezing method is the most important construction method in the city's watery soft and unstable soil layer.After the permanent structure of the underground project is formed,the frozen soil curtain will be thawed naturally?or manually?.Due to the nonuniformity of the freezing temperature field,the frozen-thawed soil exhibits a significant gradient characteristic.Water pressure gradually recovers after thawing of frozen soil curtain.The soil prepared by freezing with a constant thermal gradient(F_nonuin)and thawing under uniform temperatures(T_uni)gradually deforms and settles under the simultaneous action of overlying load and water pressure?hydraulic-mechanical coupling?,which controls the interaction mechanism between soil and structure and commands the load of permanent structure during the operation period of underground engineering by changing the contact properties of stratum and permanent construction.Therefore,considering the saturation conditions of the soil,it is of great academic and engineering value to study the law of deformation and crack evolution of saturated soil treated under F_nonuin-T_uniunder the action of hydraulic-mechanical coupling.In this paper,the law of deformation and fracture evolution of saturated soil treated under F_nonuin-T_uniis systematically studied through the independently developed compression visualization test device in the process of freezing-thawing under pressure?water-heat-force coupling environment?.The structure pressure chamber combined with semicircular stainless steel and transparent polycarbonate observation window is adopted to collect the digital photograph automatically;Pneumatic loading is used to control the radial heat flow of the sample;the initial gradient characteristics of saturated soil is achieved by freezing with a constant thermal gradient and thawing under uniform temperatures.The experimental results show that the temperature control effect of the newly developed deformation visualization test system in the process of freezing-thawing is good,and the deformation capture is accurate and reliable.Under undrained conditions,the pore pressure of saturated soil samples increases after freezing and thawing under pressure,which indicates that the it has a tendency to shrink;digital image analysis shows that:in the initial stage of hydraulic-mechanical coupling loading,the localized area and maximum lateral deformation position of the sample vary with heterogeneity and it tends to stabilize in late period;the effect of water pressure on the localized area and the location of the maximum radial deformation is greater,but the effect of freeze-thaw temperature is not significant.The results of CT scan test confirm that freezing causes moisture migration and redistribution within the sample.Near the the middle and lower part of the sample in high temperature position,multiple layers of segregated ice appear,resulting in a water-rich crack accumulation area after freezing and thawing.As the water pressure increases,the major cracks begin to appear inside the sample,and the volume,body surface area,and shape parameters of the major cracks increase as the water pressure increases.