Research On Mechanical Properties Of Fiber-curing Agent Reinforced Fillers Of Heavy Haul Railway In Seasonal Frozen Soil Areas

Heavy freight transportation is one of the main directions of railway transportation development for many countries.The typical load characteristics of Heavy-haul Railway trains,such as heavy load,large transportation capacity and long operation time of trains,make the existing railway subgrade often suffer from diseases.The quality of fillers is very important for the railway subgrade.Therefore,it is an urgent problem to adopt effective reinforcing methods to ensure the fillers retain excellent filling characteristics.In view of this,this paper selects the natural filler and fiber-curing agent modified filler of Bazhun heavy haul railway as the research object.Throughing the physical model test,the static and dynamic triaxial test considering of freeze-thaw cycles and 8-shaped specimen tensile test,the effects of different influencing factors and improved parameters on the settlement characteristics,static strength and deformation characteristics,tensile strength and dynamic permanent deformation characteristics of the two kinds of fillers were systematically studied.The conclusions are helpful to evaluate the applicability and effectiveness of the fiber-curing agent improvement measures applied to the actual subgrade engineering,and to provide experimental and theoretical references for preventing subgrade diseases in seasonal frozen regions.The details of main contents and progress of the present paper are listed as follows:(1)According to the filling process of the on-site railway subgrade,the small subgrade models are constructed,and the stress distribution law and vertical settlement characteristics of different models are studied by applying graded static load on the top of the subgrade.The research shows that the attenuation rate of the stress along the depth of modified model is faster than that of the model constructed with natural filler,and the greater the load acting on the top of the subgrade,the stronger the diffusion capacity of the fiber to the load.Under the higher external load,the settlement deformation of modified model is also studied,as the load increases,the sedimentation rate gradually decreases.From the perspective of controlling and reducing the subgrade settlement,the fiber-curing agent improvement method has the potential to keep the subgrade surface with minimize settlement deformation.(2)Based on the static triaxial compression test results,the stress-strain characteristics,strength characteristics and improvement effect of natural fillers and improved fillers considering freeze-thaw cycles are studied and analyzed.Initial elastic modulus and ultimate principal stress difference are selected as model parameters to verify the applicability of strain hardening failure characteristics of natural filler to hyperbolic model.At the same time,the applicability of strain softening model to the improved filler was verified by selecting the initial elastic modulus and residual strength as model parameters.The empirical formula of static strength model of filler considering multi-factor interaction was established by analyzing the influence of various factors and different improved parameters.The failure strength,initial shear modulus and residul strength of two kinds of fillers exponentially decrease with the increase of freeze-thaw cycles.But the mechanical strength and capacity of freeze-thaw resistance for improved filler are significantly better than that of natural filler.(3)By using an improved 8-shaped mold,the direct tensile test of the natural and modified fillers considering freeze-thaw cycles was carried out,and the tensile curve characteristics and tensile strength were discussed around the different influencing factors and modified parameters.The fiber-curing agent improvement method transforms the brittle failure mode of natural filler into flexible failure,and significantly enhance the tensile stiffness,peak tensile strength and residual strength.The peak tensile strength exibihits an unimodal form as the fiber content and water content change,and a nonlinear growth trend with increase of dry density,fiber length and curing agent content.The progressive failure characteristics of fiber during tensiling can be described by the shear stress-strain model of fiber-soil interface considering three parameters.The fiber-curing agent improvement measure increased the tensile strength of natural filler by about 1.9 times under different freeze-thaw cycles,and the capacity of freeze-thaw resistance of natural filler was greatly modified in terms of tensile properties.(4)In view of the dynamic stability of two kinds of fillers,the dynamic triaxial tests considering freeze-thaw cycles and constant amplitude and long-term reciprocating loads were carried out.The development laws of dynamic strength,critical dynamic stress and cumulative plastic strain-vibration times of fillers with different influencing factors were emphatically discussed.Based on the test results,the critical dynamic stress under different influencing factors was extracted by numerical fitting method,and the critical dynamic stress models of two fillers were established with respect to multi-factor changes.Then,the normalized dynamic strength empirical models were proposed by analyzing the normalized characteristics of dynamic strength with respect to static strength.The results also show that after three and nine freeze-thaw cycles,the dynamic stress levels of natural filler were increased by about 1.9 times and 2.4 times respectively,which effectively improves the capacity of freeze-thaw resistance of natural filler in terms of dynamic stability.