Analysis And Research On The Performance Of Subgrade Filling Material Under The Condition Of Freezing And Thawing Cycles

Tianjin belongs to the coastal area and distributes widely the marine sedimentary soft soil.And the landform is mainly the beach and the lagoon.Because Tianjin is located in the seasonal frozen and higher water table area,the road structure is subject to thawed and frozen that causing frost heaving and frost boiling of road.At present,in order to improve the service level of road and prolong the service life of the road,our country generally adopts the method of adding lime to improve the characteristics of subgrade filling.Therefore,the research that the characteristics of the subgrade filling under the freeze-thaw cycle not only helps to guide the entity engineering construction,but also can save resources and reduce costs.Considering the realistic meaning and economic efficiency,the study have great research value.In this paper,the physical and mechanical indexes and the improvement measures of marine soft soil are mainly analyzed accord indoor test point,and according to the comparison and analysis of lime modified soil and soil,it is found that the method of improving the subgrade by adding lime can improve effectively the physical and mechanical parameters of subgrade filling.According to frost heave test,the frost heaving characteristics of soil and lime modified soil were studied under closed condition and open conditions,and the influence of water content,cooling temperature,degree of compaction,and ash ratio was analyzed on frost heaving characteristics.And through comparative analysis,the lime can effectively suppress the frost heaving of subgrade.The soil and lime modified soil ware studied under freezing and thawing according static tri-axial compression,unconfined compressive strength test and california bearing ratio,and the effects of freezing and thawing cycles were analyzed on strength and stability of soil.The results show that the strength,stability and freezing and thawing resistance of the lime modified soil is better.The dynamic characteristics of lime modified soil under freezing and thawing cycles were studied by dynamic tri-axial compression,and the effects of dynamic stress amplitude,freeze-thaw cycles,cooling temperature and confining pressure are analyzed on the cumulative plastic deformation of the soil.The prediction model of cumulative plastic deformation was established under dynamic stress and number of freeze-thaw cycles.And basing on the analysis of accumulated plastic deformation,the effects of number of freeze-thaw cycles,cooling temperature and confining pressure were analyzed on the critical dynamic stress,and the conclusion that the critical dynamic stress of the soil is less than 80KPa and the critical dynamic stress of lime modified soil is between 150KPa and250KPa is summarized.On the basis of the standard value MR of dynamic resilient modulus of subgrade in standard condition,subgrade soil modulus reduction coefficient K_?under the freeze-thaw cycle and the humidity adjustment coefficient K_S of resilient modulus of subgrade were introduced.Therefore the dynamic resilient modulus of subgrade is obtained under the influence of freezing thawing cycle and soil moisture.The resilient modulus of lime modified soil is respectively 70.18KPa and 58.48KPa on the top and bottom surfaces of subgrade work area,so it meet the requirements of resilient modulus of subgra.The stress and strain of lime modified soil under the freeze-thaw cycle were simulated and analyzed by the finite element software ANSYS,and it is find that lime can not only inhibit effectively the occurrence of subgrade frost heave phenomenon,but improve the stability and strength of subgrade.