Study On Mechanical Properties Of Cement Cinder Improved Soil Under Freeze-thaw Cycles

Liaoning is located in the northeastern part of China and belongs to seasonal frozen region.Compared with normal temperature soil,the physical and mechanical properties of seasonal frozen soil are unstable,which is greatly affected by seasonal change.Most of the road projects built in the seasonal frozen region suffer frost damage to varying degrees.For the improved soil roadbed fillers such as lime-modified soil and cement-modified soil,they often have good engineering properties at the beginning of the construction,but the physical and mechanical properties will be greatly reduced after several freeze-thaw cycles which will affect the use of the project.Therefore,road engineering in seasonal frozen zone should not only meet the requirements of traffic load,but also have certain frost resistance.Taking Fuxin-Zhangwu section subgrade engineering of Beijing-Shenzhen Passenger Dedicate as research background,freeze-thaw cycle test,triaxial test,CT scanning test and dynamic characteristic test of cement cinder improved soil are carried out by using GDS frozen soil dynamic and static triaxial test system,GDH2005B high and low temperature test system and GE Optima 520 medical CT.The mechanical properties of cement cinder improved soil under freeze-thaw cycles were studied.Through the study and analysis,the following results were obtained.The optimum mix ratio and curing age of cement cinder improved soil were obtained by carrying out strength and frost heave tests under different mix ratios and curing ages.The GM(1,1)model of frost heave rate is constructed by using grey theory.The frost heave law of cement cinder improved soil was predicted and its anti-freezing mechanism is analyzed.The CT scanning test of the cement cinder improved soil under different freeze-thaw cycles was carried out.The influence of freeze-thaw cycles on the internal structure of the improved soil was studied,and the development of improved soil pores under freeze-thaw cycles was obtained.Combined with the triaxial test results,the expression patterns and evolution laws of total damage variables under freeze-thaw-load conditions were obtained.CD tests under different confining pressures were carried out for improved soils with cinder under different freeze-thaw cycles by using the GDS frozen soil dynamic and static triaxial test system.The effects of freeze-thaw cycles on the evolution of the shear shrinking yield surface and shear dilation yield surface were analyzed.The ellipticl-parabolic double yield surface constitutive model was modified by introducing the freeze-thaw cycle influence factor,and the modified model was verified by experiments.The dynamic characteristics of the cement cinder improved soils under different freeze-thaw cycles were tested.The variation of dynamic parameters of the improved soils was analyzed,and a simplified calculation model of the damping ratio of the improved soils was established.The regression equation of the critical dynamic stress of the improved soil is established by using the multivariate fuzzy fitting method based on structural element,and the prediction model of the modified soil cumulative deformation is established based on the fuzzy critical dynamic stress.