Research On Deformation Damage And Dynamic Characteristics Of Slab Track In Subgrade-bridge Transition Zone In Severe Cold Regions

In the process of construction and operation of high-speed railway in China,it is inevitable for railways to cross rivers,natural valleys and other traffic arteries.In order to reduce land occupation and environmental impact,it is necessary to set up bridges.At the junction of subgrade and bridge in severe cold regions,it is easy to produce uneven deformation near the transition point,which leads to the irregularity of rail surface and structural damage.This is adverse for the safety and stability of railway operation.The existing studiesmainly focus on the generation mechanism,design method and control measures of foundation deformation,while studies on the damage characteristics of slab track caused by complex foundation deformation in severe cold regions are inadequate.Therefore,it is necessary to carry out research on the deformation damage and dynamic response of slab track caused by the foundation deformation in the subgrade-bridge transition of severe cold regions,which can provide theoretical guidance for the optimal design and maintenance of high-speed railway in China.In the thesis,based on the country strategy of building a strong transportation network,taking the CRTSIII slab track of high-speed railway in severe cold regions as the research object,the nonlinear damage model of slab track and the dynamic coupling model of vehicle-slab track-subgrade-bridge transition were established respectively by the method of finite element simulation.Then,the influence of complex deformation(cosine type frost heave deformation,half-cosine type frost heave deformation,half-cosine type settlement deformation,break angle type deformation,whole settlement of abutment,etc.)of the lower foundation in the subgrade-bridge transition zone and the combined action of multiple loads(temperature load and train load)on the deformation damage and dynamic characteristics of slab track were studied,respectively.Based on the static and dynamic results,the control standard of foundation deformation was proposed.The main research results and conclusions are as follows:(1)The existing design scheme of the subgrade-bridge transition of high-speed railway were summarized,and the adaptability of slab track in severe cold regions was compared from many aspects,thus the optimal design scheme CRTSIII slab track was determined as the research object.By deducing the constitutive relation of structural concrete,a subgrade-bridge transition-slab track refined model considering the structure internal reinforcements was established.Then,the law of structure stress and crack damage development was obtained.The seams between structural layers mainly occurred on both sides of the subgrade frost heave deformation peak.And it is the most unfavorable when the frost heave occurred in the middle of the track slab;when the frost heave amount was more than 15 mm,the failure crack of concrete would appear at the position of the frost heave wave peak,the beginning position of frost heave and the position of fasteners.Compared with the frost heave amount,the frost heave wavelength was the control factor for seam expansion.When the transition length of the half-cosine type frost heave deformation exceeded 15 m,the interlayer seams would be greatly reduced,and the structural damage was concentrated at the end position of the deformation.The structure was damaged at the beginning position of half-cosine type settlement deformation in the transition zone,and the interlayer seams at the end was the most serious.The damage of the upper surface of the composite plate and the base plate were most serious at the beginning position of the break angle type deformation in transition zone.When the deformation length was more than 15 m,the compatibility of deformation was good,and the seams between layers were less than 1.0mm.The whole settlement of abutment mainly affected the seams between composite slab and base plate,but had little effect on the damage.(2)Based on the slab track damage model,the influence of multiple loads on the deformation and damage of slab track was studied considering the complex operation environment in severe cold regions.Under the temperature load,both the damage of slab structure and seams between structural layers were small.Combined with the frost heave deformation,the negative temperature gradient would aggravate the seams between the base plate and subgrade,the composite plate and the base plate,and the propagation range of structural damage cracks.Under the combined action of temperature load and half-cosine type deformation,the slab structure was more prone to produce initial damage.Under the combined action of negative temperature gradient and break angle type deformation,the upper surface of composite slab and base plate would be tensile damaged.The train load had little influence on the stress of slab track.However,when it was combined with the subgrade frost heave deformation,the concrete damage of the base plate was intensified,and the seams at the lower part of the load position was compacted,but the "leverage effect" would increase the seams at the other side.At the end of the transition frost heave deformation or the beginning of the settlement deformation,the train load was the most unfavorable to the damage of the base plate.The train load had a great influence on the interlayer seams and the damage of slab track at the beginning of break angle type deformation.When the settlement amplitude of abutment was 3.6mm,there would be macro cracks in the base plate under the train load.(3)The dynamic coupling model of vehicle-slab track-subgrade-bridge transition zone was established,and the influence of different deformation types of the lower foundation and operation conditions on the dynamic indexes of the vehicle body was analyzed.The frost heave deformation of subgrade mainly affected the vertical wheel-rail force,vertical acceleration and sperling index of the train.With the increase of frost heave amount or the decrease of wavelength,it was more and more unfavorable to the safety of operation.When the train entered the deformation zone of transition,the vertical force of wheel rail begined to surge,which was greatly affected by the short wavelength.When the frost heave wavelength of the transition zone was 5m,the vertical force of wheel rail could reach 175.97 k N,exceeding the safety limit 170 k N.However,the wavelength variation of the half-cosine type settlement deformation and break angle type deformation had little effect on the wheel-rail force.The partial uneven deformation caused by the whole settlement of abutment would lead to the sudden change of vertical wheel-rail force and acceleration.When the settlement amplitude was 5mm,the sperling index was 2.75,which was close to the limit value of 3.0.It was necessary to pay attention to the stability of vehicle operation.(4)Based on the static and dynamic results of slab track under complex loads in the subgrade-bridge transition zone,the recommended values of deformation control for the lower foundation of the transition zone of high-speed railway in severe cold regions was proposed.According to the indexes of structural damage and interlayer seams,the standard of subgrade frost heave deformation was summarized as follow: when the frost heave wavelength was less than 5m,the recommended control value of frost heave was 1mm;when the wavelength was 5-10 m,the recommended control value of frost heave was 5mm;when the wavelength was 10m-20 m,the recommended control value of frost heave was 11mm;when the wavelength was more than 20 m,the recommended control value of frost heave was 14 mm.According to the indexes of structural damage,wheel unloading rate,sperling and interlayer seams,the deformation control standard of transition zone was put forward as follow: it was suggested that the half-cosine type deformation wavelength of subgrade-bridge transition zone was more than 20 m,and the deformation amount was less than 20 mm;and the control limit of break angle was not more than 1.1 ‰.According to the structural damage and sperling of stability index,ensuring the stability of train operation and avoiding the phenomenon of "vehicle bump",it was suggested that the whole settlement amplitude of abutment in subgrade-bridge transition zone should not exceed 3mm.There are 122 figures,41 tables and 156 references in this manuscript.