Study On Mechanical Properties And Constitutive Model Of Silty Clay Under The Condition Of Freezing And Thawing Cycles In Subgrade

Subgrade is an important component of road,is base bearing road surface load,in addition to solid and steady,it must be durable,resisting impact of various natural factors.Subgrade in frozen area permanently experiences alternate cooling and heating,and freezing and thawing cycle,which is an important factor resulting in mechanical property degradation of roadbed filling,further resulting in damage of subgrade.So,soil filled in road bed must resist freezing and thawing cycle,drying and watering cycle to ensure safe and smooth transportation in operational period.Because our country build,rebuild and expand numerous high-grade road and rural road in cold region,especially along with multiple influencing factors such as high frequency vehicle load,heavy load and seasonal freezing and thawing cycle,etc.,disease of roadbed is even more serious.However,we have not clearly known disease mechanism of roadbed under vehicle load in seasonal freeze soil region.This paper conducts mechanical property test of compacted powder clay aiming at typical roadbed filling,conducts load compacting property research and roadbed constitutive model research which embody the influence of freezing-thawing cycle through theoretical analysis and combining results of indoor experiment.Results help to deepen knowledge of mechanical property of compacted powder clay filled in roadbed of seasonal freeze soil region and provide data support for follow-up research;based on numerous dynamic triaxial experimental data,clarifies disease generating process and mechanism of roadbed under vehicle load in seasonal freeze soil region.Major conclusions drawn from this research:(1)Through thaw collapse experiment of different freezing temperature and water content,by analyzing concludes:thaw collapse coefficient increases as freezing temperature decreases,and has a good linear relation with absolute value of freezing temperature.The higher water content,the higher thaw collapse coefficient.(2)Freezing-thawing cycle has significant impact on thaw collapse coefficient,the most unfavorable condition of freezing soil thaw collapse is a cycle from No.3 to 6 cycle,where the thaw collapse coefficient is the highest.Then with number of cycle increasing,thaw collapse coefficient will decreases,and tend to be stable after twelve cycles.So this paper suggests that when conducting frozen earth engineering survey,thaw collapse coefficient provided for use of design shall be larger than that of No.1 cycle.If permitted,shall freeze and thaw original earth sample taken from site 3-6 times in constant temperature humidity chamber first,then measure thaw collapse coefficient according to procedure,so that estimation and calculation of sedimentation is more scientific and safe.(3)The settlement calculation relational expression proposed by this paper gives the formula calculating deformation of compacted soil body after thawing by considering thawed soil compression change law,influence of water content and number of freezing-thawing cycle on amount of compression.This formula is based on indoor experiment with high practical significance and pertinence.(4)Proposes flow associated double yield surface constitutive model aiming at soil body experiencing freezing-thawing cycle based on numerous triaxial compression experimental data.and the constitutive equation proposed is verified by programming to better reflect mechanical influence of freezing-thawing cycle on roadbed compacted powder clay,comparatively accurately predicting stress-strain relation of thawing earth,so it provides solid theoretical foundation for further researching intensity change of roadbed soil body in cold region.(5)Through dynamic triaxial experiment,it is found that as number of freezing-thawing cycle increases,dynamic cohesive force and dynamic friction angle of roadbed filling under different number of destructive vibration both decreases,so we think after repeated freezing-thawing cycle,voids within soil body gets larger,clearance between soil grains also gets larger.As number of destructive vibration increases,acting force between soil grains dissipates gradually,dynamic cohesion of soil body decreases,;as number of destructive vibration increases,relative motion between soil grains increases,dynamic internal friction angle of soil body decreases.(6)Freeze thawing and load induce damage in different mechanical mechanism,both interconnect,interact,must bring change of mechanical property to soil body in seasonal cold region during service life;joint action of freeze thawing and load can intensifies overall damage to soil body.This paper establishes damage evolution model of modulus of resilience of roadbed filling base on strain equivalence hypothesis created by professor Lemaitre,with its results better consistent with experimental data,showing damage based estimation of modulus of resilience is accurate,reasonable and feasible.This constitutive model is simple,with clear concept,needing no hypothesis,with high practical value.