Investigation On Testing Apparatus For Frozen Soils With Raidal Thermal Gradient And Deformation Failure Characteristics Of Frozen Hollow Cylinder Under Uniaxial Compression

The investigation on deformation strength mechanism and the correspondingshearing failure characteristics of frozen soils could better understand the interactionbehaviors between frozen soil and engineering and predict the stabilities of frozenstructures both in artificial freezing engineering and permafrost regions. Both the thermalgradient and average temperature are the significant factors controlling themacro-mechanical properties and deformation of frozen soils. In present paper, theresearch emphasis is put on the deformation and failure characteristics of frozen hollowcylinder with radial thermal gradient. The macro uniaxial compression and micro fissuremeasurement experiments were carried out on two categories soils under varioustemperatures and thermal gradient using the self-developed apparatus for frozen soils withradial thermal gradient, and some interesting phenomenon were observed.The apparatus for frozen soils with radial thermal gradient consists of loadingequipment with a load precision of0.05KN, a displacement precision of0.18mm, and acell pressure precision of10kPa, surrounding environmental controlling device with aprecision of±0.5℃, freezing and temperature controlling device with a precision of±0.05℃. The experimental results indicated that the the target freezing temperature couldbe achieved less than12h, and the distribution defromation measred precison couldapproach0.001. In addtion,the measred mean density for speciemnt is2.02g/cm3with atolerance of1%and the mean water content is21.24%with a tolerance of0.56%based onthe two ends compaction method alternatively.The stress-strain curves for frozen hollow cylinder (FHC) with thermal gradient wassimilar with that for frozen hollow cylinder with uniform temperature, and that allpresented strain—softening characteristics. The peak strength and elastic modulus forfrozen hollow cylinder decreased as thermal gradient increased, in other word, the thermalgradient presented weakening effects to the frozen hollow cylinder with thermal gradient.The peak strength of frozen Silty Clay (FSC) is higher than that for frozen Clay(FC). Theaxial strain at peak stress decreased as the thermal gradient increased, but the shearingangel between the maximum stress and sliding surface shown an increase trend as thermalgradient increased. The thermal gradient leaded to an abvious enhancement of ductile characteristics. The stress-strain could be described by113a b c2, and the11model parameters are closely related to the thermal gradient.Here, we proposed the deformation variable of S to describe the micro fissures andholes development in certain cross sections with maximum lateral deformation and thevariation of S stands for the radial non-uniform deformation. The micro measurementresults shown that the relationship between deformation variable of S and radial distancesatisfied parabolic equation for frozen hollow cylinder with uniform temperature, but thatincreased lineally for frozen hollow cylinder with radial thermal gradient. Thisphenomenon implies that the place of micro fracture appearance moved towards the highertemperature sides from the thermal gradient.