| The disease of high-speed railway subgrade in seasonally frozen soil region mainly occurs in the superficial position of the structure.Therefore,the optimization and protection of the surface layer of subgrade bed becomes the key for the prevention and control of freezing damage.The physical and mechanical properties of the surface layer are very important for the long-term stable operation of the high-speed railway line.On the one hand,considering the poor water stability of fine-grained soil in graded crushed stones,it is easy to produce subgrade hazard such as mud pumping and frost heave deformation under the coupling effect of train load,freeze-thaw climate and atmospheric precipitation.It is necessary to further optimize and improve the serviceability and structural form of the surface layer of subgrade bed.On the other hand,the full-section asphalt mixture strengthening layer can effectively improve the environmental adaptability of the surface layer of the subgrade bed in seasonally frozen soil region.It is necessary to further study the serviceability and the law of freeze-thaw deterioration of the reinforced layer.Therefore,it is of great significance to systematically study the physical and mechanical properties of surface layer of subgrade bed and surface reinforced layer and reveals the mechanical properties of interlayer contact.The research is important to guide the hazard control and structure optimization of high-speed railway subgrade in seasonally frozen soil region.Based on the National Natural Science Foundation Project,"Study on the serviceability and durability of strengthened layer of asphalt concrete with rubber particles located above subgrade bed of high-speed railway,(52172347)" was studied in this thesis.Static and dynamic tests,freeze-thaw cycle durability tests and low-temperature environment adaptability tests were carried out based on the physical and mechanical properties of the composite structure for the subgrade bed modified by rubber powder.Finally,through theoretical calculation and interlayer contact mechanics analysis,the serviceability and interlayer contact characteristics of rubber powder modified composite subgrade bed were systematically studied.The main research work included the following four aspects:(1)The effects of long-term freezing–thawing cycles on frost resistance and mechanical damage deterioration of cement-stabilized macadam were considered.Three different cement contents(3%,5%,and 7%)and removal of two different fine particle sizes(0.1 and 0.25 mm)of cement-stabilized macadam were studied and analyzed.It was recommended that the cement content is 5%,and the fine particles below 0.1mm should be removed.If the surface layer of the subgrade bed had higher permeability requirements,fine particles with a size below 0.25 mm could be removed.Meanwhile,the prediction model of freeze-thaw durability damage deterioration was established by combining the macroscopic test with the damage development of structural micro unit,and the prediction ability of the model based on small samples test was evaluated.(2)The frost heave and thawing settlement and the mechanical characteristics of strength and toughening for cement-stabilized macadam mix with rubber powder were revealed.Based on the vertical full scale model test of frost heave and thawing settlement,the incorporation of rubber powder could inhibit the frost heave deformation of graded gravel and cement-stabilized macadam.According to the deterioration of freeze-thaw strength,the characteristic coefficient of strength and toughening,and the nonlinear mechanical evolution characteristics of cement-stabilized macadam mix with rubber powder.It could be seen that the material’s frost resistance and strength and toughening characteristics were obviously improved when the equivalent volume replacement level of rubber powder was greater than 30% below 1.7mm.The new pressure film technology was used to measure the interlayer stress distribution of the cement-stabilized macadam to subgrade filling under static load pressure test.The problem of local stress concentration between layers was alleviated.(3)Based on the dynamic cyclic loading test,the fatigue characteristics and deformation evolution law of the cement-stabilized macadam mix with rubber powder were mastered.Under the loading control mode of splitting fatigue with the same stress ratio,the fatigue resistance of cement-stabilized macadam was gradually strengthened with the increase of rubber powder content.The dynamic stress-strain relationship and damping specific energy dissipation law of cement-stabilized macadam mix with rubber powder were revealed by taking different dynamic stress amplitudes and rubber powder content levels as test variables.When the equivalent volume replacement level of rubber powder under 1.7mm was 30%,the cumulative plastic deformation was minimum value and the damping ratio was maximum value.The semi-logarithmic function model could be used to establish the cumulative plastic deformation calculation model of cement-stabilized macadam mix with rubber powder under cyclic load,which had a high degree of fitting and matching.(4)The environmental adaptability of asphalt mixture modified by rubber powder in seasonally frozen soil region and its contact effect with the surface layer of subgrade bed were determined.Through DMA dynamic mechanical analysis and asphalt basic performance index tests,it was suggested that the particle size of rubber powder should be 60 mesh or 80 mesh,and the dosage should be between 18% and25%.SBS/ rubber powder mixed modified asphalt could be considered as 3% SBS content;16% rubber powder content,particle size 80mesh;aromatic oil 4% and stabilizer 3‰.Through in-depth analysis of the mechanical properties of asphalt mixture modified by rubber powder,it was found that SBS/ rubber powder modified asphalt mixture had better environmental and climate adaptability in seasonal frozen soil regions,while dry modified asphalt mixture did not adapt to the requirements of seasonal freezing area climatic environment service.Based on the research results of cement-stabilized macadam and the calculation theory of interface contact mechanics of composite layered structures,the interlayer contact relations of rubber powder modified composite subgrade bed structures and the mechanical characteristics of cooperative work between structures were analyzed.When selecting the reinforced asphalt mixture with better low temperature service performance in seasonally frozen soil region,the surface layer of cement-stabilized macadam subgrade bed with strong and toughened should be selected.Therefore,the new structure of "waterproof closed anti-cracking reinforced layer+ strong and toughened subgrade bed surface" can be used as a technical solution to optimize composite surface layer of subgrade bed in seasonally frozen soil region,so as to improve the serviceability of the subgrade structure. |
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