Theoretical And Experimental Research On Dynamic Properties Of Fly Ash Soil Subjected To Freeze-Thaw Cycles

Experiment study to dynamic strength and dynamic properties of roadbed filling. In order to reduce and prevent occurring of the frost heave in seasonal forst region, this paper discusses the frozen process and cause of formation of highways through to investigate and monitor to roadbed deformation, especially freeze-thaw cycles, often cause severe problems from long-term frozen heaves and thaw settlements and physical and mechanical properties as well as mechanism damage of roadbed.In this thesis, the dynamic triaxial instrument of DTC-306 is used to make cyclic triaxial test of silty clay under dynamical loading by load control. The influence of vehicle cyclic load to the deformation of roadbed deformation is researched. On the basis of various parameters and data offered in the test, utilize common finite element procedure ABAQUS to set up the three-dimensional finite element model of the dynamic triaxial sample, simulate the dynamical deformation behavior of silty clay roadbed under cyclic load. Through a lot of contrast analysis to the cyclic triaxial test relation data, the reliability of the model is validated. Then the paper researched on the relationship between dynamic deformation and the influence factors such as cyclic load's magnitude, confining pressure, frequency, the number of cyclic load, different load wave and puts forwards to some suggestions to experiment of dynamic strength and dynamic properties of roadbed filling. Triaxial tests on composite material from easy liquefaction fly ash and easy freezing silty clay according to dry weight (1:2) are conducted to investigate the dynamic properties of fly ash soils and silty clay for roadbed filling. Fly ash soils potential for (l)underwater fills, (2)light weight structural fills, (3)higher stability, (4)frost resistance, (5)higher strength liquefaction resistance. Therefore, the present investigation describes the behaveioral aspect of soils mixed with fly ash to improve the load bearing capacity of soil. Silty clay is higher of dynamic strength than fly ash soils at range from 100KPa to 200KPa of confining pressure. The addition of fly ash played an important role in the development of shear strength parameters c andφof fly ash soils. Then since the dynamic strength of silty clayare low at relatively high confining stresses levels of 300KPa. The dynamic modulus of fly ash soils is higher than silty clay atε_d=5%, N_f =10 ,but maximumdynamic modulus of fly ash soils and silty clay is relatively stability.Triaxial tests were carried out on fly ash soils and silty clay samples after every freeze-thaw cycles, in order to analyze dynamic properties of its. The results of investigation show that dynamic strength of silty clay decreases ranges from 52% to 75% after 3 freeze-thaw cycles at confining pressure of 300KPa. The effects of parameters such as confining pressure cyclic stress ratio on dynamic strength of silty clay. Dynamic strength of fly ash soils is higher from about 40% to 60% than silty clay's subjected to 8 freeze-thaw cycles at confining pressure and deviator stress of fly ash soils also increased with an increase in confining pressure. Dynamic modulus of fly ash soils can be increased by 28.6% in comparison with silty clay's. Therefore, the gain in liquefaction and freeze-thaw resistance of fly ash soils(l :2) is more pronounced at confining pressure of 300KPa and fly ash addition in soil can also be effectively used as the base materials for the roads.Although variable confining pressure dynamic triaxial tests are made on the two kinds of soils after 8 freeze-thaw cycles. The authors obtain that the variety law between the dynamic strength and the number of circular of dynamic load and the number of freeze-thaw cycles. Test results show the relationship curves of the dynamic stress-strain and the dynamic elastic modulus-elastic strain, the dynamic modulus and the number of freeze-thaw cycles. After 3 freeze-thaw cycles, its dynamic strength and dynamic modulus reach stability. The mathematics model of dynamic module damage in freeze-thaw cycles are also put forward. This model can predict the dynamic strength and the greatest dynamic module of fly ash soil after 8 freeze-thaw cycles. The numerically computational results demonstrate that the simulating values with this model can approach to experiment values where it ranges from -3.13% to 0.75% and from 0.117% to 2.5% in the case of dynamic strength, moreover ranges from 0.71% to -5.26% and from 0.417% to 5.01% in the case of dynamic module damage. This model can preferably evaluate the service life of fly ash soil roadbed subjected to freeze-thaw cycles. It can reduces numerous and complicated of the dynamic triaxial tests. It has laid a theoretical foundation for design of roadbed in seasonal frost region.The results of investigation show that the dynamic properties of fly ash soils(l :2) is better than silty clay after 3 freeze-thaw cycles. Based on the evidence, it is concluded that the fly ash soils has superiority as roadbed filling in season frost region. This study also benefits the effective use of fly ash and cost effective method for soil properties. The value of society and economy can be increased by the addition of fly ash in soils.