Dynamic Response And Permanent Deformation Of Subgrade Induced By Heavy Truck Load In Deep Seasonally Frozen Region

The frozen soil are widely distributed in China, freeze-thaw cycle and heavy truck load are main causes of subgrade diseases causing pavement destroyed in these regions. However, there are few researches on the dynamic responses of pavement and subgrade induced by heavy truck and stability evaluation of long-term heavy truck load in seasonally frozen soil regions at home and abroad. Additonnaly, our country is in the new periods of highway constructions and many of them are distributed in seasonally frozen regions (especially in deep seasonally frozen regions), so the effective evaluation of long-term performance and stability of subgrade in these regions and the control of subgrade and pavement diseases are the bottlenecks of highway development and the technical problems faced by scientific workers.Therefore, employing laboratory test, field monitoring, theoretical analysis and numerical simulation, especially according to the coupling effect of seasonal freeze-thaw action and heavy truck load, this paper investigated dynamic parameters of the frozen and thaw soil induced by heavy truck load, dynamic interaction of heavy truck-surface course-base course-subgrade, dynamic responses of subgrade induced by heavy truck load, and permanent deformation of subgrade induced by long-term heavy truck load. The main contents and results are as fellows.(1) According to the features of freeze-thaw cycles and heavy truck load, adopting the low temperature dynamic triaxial test, the paper investigated the effects of water content, numbers of freeze-thaw cycle, loading frequency, negative temperature and confining pressure on dynamic parameters of the frozen soil. Meanwhile, the effects of water content, numbers of freeze-thaw cycle, and loading frequency on dynamic parameters of the thawed soil by employing the normal triaxial test were studied. In the paper, the relationships between dynamic stress and strain were described by equivalent linearization model, the backbone curves of the frozen and thaw soil were fitted by improved Hardin Hyperbolic Model, and the effects on the maximum shear modulus, maximum damping ratio, the relationships between shear strain and shear modulus and damping ratio were studied.(2) According to the characteristics of highway traffic system, the dynamic interaction simplified analysis models of heavy truck-surface course-base course-subgrade in seasonally frozen regions based on some reasonable hypothesis were developed, which included typical heavy truck model in highway, surface course-base course-subgrade dynamic model, surface course-base course-subgrade dynamic model in spring thawing and normal periods. The dynamic interaction of heavy truck model and surface course-base course-subgrade model was realized by taking surface roughness as systematic excitation and taking tire point contact model and improved elastic roller model as contact. Finally, dynamic equations of system were solved using Wilson-θmethod.(3) Based on the theory of the second term, the program DATPS was developed for investigating the dynamic interaction of heavy truck- surface course-base course-subgrade in deep seasonally frozen regions, and the validation of the model and reliability of program were verified by the test and simulated results. The effects of driving factors and road factors on tire ground pressure and pavement dynamic displacement were investigated by program DATPS, and the time histories of dynamic compressive stress time histories of top base were obtained.(4) The propagation law and distribution characteristic of dynamic compressive stress of the subgrade soil induced by the three axles heavy truck with different speed and weight were studied by field monitoring. Based on principle of virtual work, taking the dynamic compressive stress time history caculated by simplified model of the dynamic interaction of heavy truck-surface course-base course-subgrade model as the input of load, viscoelastic dynamic finite element models of base course-subgrade-ground verified by the field monitoring data were built. Then the effects of traffic type, rear axle load, running speed, highway grade and thawing depth on distribution law of subgrade dynamic stress during normal and spring thawing periods were analyzed by numerical simulation method.(5) Consided the freeze-thaw cycle and heavy truck load, the permanent strain model were established and the model parameters obtained by the consolidated undrained triaxial test and dynamic triaxial test under cyclic load. Refered to stress ratio as a link and based on the fourth term, the effect of traffic type, rear axles load, running speed and subgrade thickness on the permanent deformation induced by long-term heavy truck load were investigated by the numerical method. Hereby, the prediction formula of subgrade permanent deformation induced by long-term heavy truck load was established.