| The high-speed train has the advantages of stability,high speed and comfort,so it is often used as a means of transportation for people.High-speed trains,on the other hand,are fast and comfortable and require greater flexibility and platform stability.Gravel filling high resistance,stiffness and integrity,and are commonly used as construction materials for high-speed railway foundation.In seasonal frozen soil areas,gravel roadbed is prone to relatively large freeze-expansion deformation and melting sedimentation due to the thin soil grains.In order to improve this situation,researchers add cement to graded gravel to improve the frost heave and thaw settlement characteristics of the fillings.However,the climate in northern China is dry throughout the year and the temperature difference between the four seasons is large.The addition of cement makes the graded gravel filler prone to temperature shrinkage deformation due to temperature change and dry shrinkage deformation due to the reduction of moisture content.The subgrade has tiny cracks due to shrinkage deformation,and under the comprehensive influence of upper load and environment,the micro-cracks extend to the subgrade and form reflection cracks,which brings harm to the operation of highspeed railway.As a result,the dry shrinkage and temperature shrinkage characteristics of the coarse soil filling material on high-level railway ground have been improved,the research on crack resistance of high grade railway subgrade can provide reference for construction of high grade railway subgrade.Cement stabilized gravel subgrade material tends to shrink and deform in the process of use,which will harm the operation of high-speed railway lines.Fly ash material as a solid waste,the stock is large and the price is low,the secondary utilization of fly ash also meets the energy saving,low carbon,green construction technology,and fly ash as an amendment in the field of building materials is widely used.Therefore,we should make use of the quiet situation of Qingyang to conduct research based on relevant documents,the composition of subgrade filler is determined,and the filler improvement method is cement improvement and cement fly ash improvement.The mi physiological index of carbon nanotechnology and coagulants is determined by instant fibers and other materials made on the screen.The maximum dry density and optimum water content of each modified filler were determined by compaction test,which was convenient for the subsequent preparation of specimens.The mechanical properties and shrinkage properties of the improved packing were tested.The results show that the filling is much more plastic than concrete and tailings in terms of pressure resistance and bending.With no opposition to the minimum versiegende druckfestiges keit maherungen,with webwiderstand once u.The empirical analysis of dehnungs and druckverhaltnisses betonflachen shows an inactive or negative relationship between dehnverhaltnis and betongehalt or fly ash wage composition when changing.but cement fly ash can improve the tensile compression ratio and better crack resistance of the high iron base filler,while fly ash can improve the strength and crack resistance of the filler.Modified by temperature shrinkage test and packing maximum temperature shrinkage strain increases with temperature cycle to stabilise after.After three cycles,the sensitivity of the packing to temperature change decreases and the temperature shrinkage coefficient increases regularly.When coal ash is added,the maximum shrinkage strain and the average shrinkage coefficient are reduced,but when fly ash accounts for 28%,the temperature shrinkage strain increases compared with other cement fly ash improvement schemes.The concepts of strain loss rate α and strain recovery rate β were proposed by comparing the performance of different amendments in two temperature environments.A small amount of cement added to cement fly ash modified fillers can increase the strain recovery rate β of fillers and reduce the accumulation of micro-cracks,but this effect is not obvious at-20℃～ 30℃.The dry shrinkage test shows that the dry shrinkage performance of the modified filler with low content of 3% is good,and the dry shrinkage performance of the modified filler is further improved with the addition of fly ash.However,dry shrinkage performance of modified packing increased with the increase of cement content,when the dosage of fly ash is 1:4,dry shrinkage performance becomes poor packing.By analyzing the experimental results of mechanical and shrinkage characteristics,the mechanical and shrinkage deformation properties of each modified filler for high railway foundation are obtained.However,the failure of the crushed stone filler is the result of the comprehensive action of stress and strain,so the evaluation index to measure the cracking resistance of the filler by analyzing the strength or deformation is limited.Cracking resistance coefficient of dry shrinkage energy and temperature shrinkage energy can be effectively analyzed by combining the deformation and mechanical properties of the packing from the perspective of energy.However,in the real environment,the phenomena of drying and temperature shrinkage occur together,so the cracking resistance coefficient of drying and temperature shrinkage energy is further processed to obtain the comprehensive cracking resistance coefficient.After analyzing it,it is concluded that: In the two temperature ranges,the comprehensive cracking resistance coefficient of S3-F12 and S5-F20 fillers is large and the cracking resistance is good.However,due to the poor drying shrinkage performance of S5-F20 fillers,the dry shrinkage increases after the incorporation of fly ash,and the increase of the amount of cement in the fillers does not meet the requirements of low carbon and environmental protection of building materials.Therefore,it is recommended to use coarse particle fillers with cement content of 3%(the cement content can be appropriately increased when the temperature is very low and high in the region)and fly ash content of 12% ～ 15% in the Beijing-Tianjin-Hebei improve shrinkage and crack resistance of high-speed railway foundation. |
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