Experimental Study On Static Properties And Permeability Of The Graded Crushed Stone Filling On The Surface Layer Of Subgrade Bed

High speed and heavy load have inevitably become the current and future development trend of railway transportation,which puts higher requirements on the strength,deformation and drainage of the foundation bed.For graded crushed stone widely used in the surface of the foundation bed,its quality will directly affect the safety of the operation and the service life of the roadbed.On the one hand,the graded crushed stone filler will increase its fine particle content and grading due to external invasion or particle wear during the construction and operation phases.The rain environment will inevitably cause the mechanical properties of graded crushed stone to change.In this context,this article aims at grading crushed stone fillers.After conducting a large number of laboratory tests and understanding the basic physical properties,the static characteristics and permeability are analyzed and a permeability coefficient model for grading crushed stones is established.It provides important reference for the design of railway subgrade and disease prevention.The main findings are as follows:?1?Based on the large-scale static triaxial test,the variation of stress-strain curve,shear strength,modulus of elasticity and shear strength index of graded crushed stone is studied.The results show that with the increase of moisture content,the stress-strain curve of graded crushed stone changes from the strain softening type in unsaturated state to the strain hardening type in saturated state.The shear strength and modulus of elasticity increase with the increase of confining pressure and decrease with the increase of water content.In the range of fine content?3%to 10%?,the shear strength increases first and then decreases with the increase of fine content,and the influence of confining pressure decreases with the increase of fine content;when the water content is 6%,the change range of elastic modulus is 40 MPa to 80MPa;the cohesion increases with the increase of fines content,the internal friction angle decreases with the increase of fines content,and both decrease with the increase of moisture content.?2?Through experimental research on permeability under different conditions,it is found that there is a positive correlation between the permeability coefficient and the porosity ratio e and the average particle sized₅₀,and a highly linear correlation withe² andd₅₀ ²;there is a negative correlation between the permeability coefficient and the unevenness coefficient,which shows an exponential correlation relationship.Based on the significance analysis of the influencing factors of the permeability coefficient based on the orthogonal test method,the average particle size has the largest effect on the permeability coefficient of the graded crushed stone filler,followed by the non-uniformity coefficient and the weakest porosity ratio.?3?Based on the correlation analysis of various influencing factors of permeability coefficient,the improved permeability coefficient model formulas based on different Taisha-based models are obtained,and the different calculation models are verified and compared,and finally the calculation model of permeability coefficient for graded gravel is established.