Experimental Study On Permeability Properties Of Graded Macadam In High Speed Railway Surface Layer Of Subgrade Bed

The permeability of the surface layer of the subgrade bed plays a very important role in the operation of high-speed railways.Graded crushed stone and cement stabilized crushed stone,as high-quality fillers,are widely used on the surface of high-speed railway subgrade bed.In the process of high-speed railway construction,the permeability coefficient of graded crushed stone or cement stabilized crushed stone is mainly obtained through experiments,which consumes a lot of manpower and material resources.Therefore,the accurate and rapid determination of the permeability coefficient of graded crushed stone and cement stabilized crushed stone is of great significance to the construction quality and schedule control of high-speed railways.Based on this,this paper conducted a large number of indoor permeability tests for graded crushed stone and cement stabilized crushed stone fillers to explore the influence of void ratio,grading parameters,cement content,etc.on its permeability coefficient.Through the analysis of the test data,a calculation model of the permeability coefficient considering the gradation characteristics and void ratio parameters is established.The main findings are as follows:（1）Through a series of graded crushed rock permeability tests,it is found that the permeability coefficient of graded crushed rock is positively correlated with its average particle size d₅₀ and void ratio,and negatively correlated with the uneven coefficient C_u;after analysis,It is found that the permeability coefficient is highly linearly related to d²₅₀ and e³,and has an exponential relationship with C_u.Through the significance analysis in the orthogonal test method,it is found that the average particle size d₅₀ has the greatest impact on the permeability coefficient of the graded crushed stone,followed by the void ratio e,and the non-uniformity coefficient C_u has the least impact on the permeability coefficient of the graded crushed stone.（2）Through the permeability tests of cement stabilized crushed stone,it is found that the permeability coefficient of cement stabilized crushed stone decreases with the increase of cement content,and when the cement content changes from 0%to 1%,the permeability coefficient decreases rapidly.When the amount continues to increase,the decrease in permeability coefficient decreases;the permeability coefficient of cement stabilized crushed stone is positively related to the void ratio and characteristic particle size,and is related to the square of the void ratio and the cubic d³₆₀ and d³₂₀ of the characteristic particle size.Linear correlation.（3）Through the analysis of the various factors affecting the permeability coefficient,and the improvement of the permeability coefficient model based on the Terzaghi and Hazen formulas,the improved permeability coefficient calculations for graded crushed stone and cement stabilized crushed stone are finally obtained model.The comparison and verification of the measured value of permeability coefficient and the calculated value of the model shows that the improved permeability coefficient calculation model has higher accuracy and can be used to guide on-site construction.