Effects Of Fines Content And Moisture Content On Mechanical Properties Of Graded Crushed Stone

The foundation bed is the most direct and main load bearing part of the subgrade structure,and its main function is to bear the static load generated in the process of track laying and the long-term cyclic load generated by train operation.In addition,the subgrade bed is also affected by the complex environment?such as rain,surface water,etc?.Among them,the surface layer of foundation bed is the area bearing the greatest impact of train dynamic load and environment in the subgrade structure.The study of mechanical properties of graded crushed stone as a widely used coarse soil filler on the surface of subgrade bed provides a useful reference for the structural design of subgrade bed,and further enrishes the understanding of the engineering properties of graded crushed stone filler.The effects of fines content and moisture content on strength and deformation characteristics of graded crushed stone were studied by static and dynamic triaxial tests in laboratory.Based on the analysis of experimental data,the main research work and conclusions are as follows:?1?Considering the relationship between fines content and coarse grain soil structure and the requirement of engineering specifications on fines content of graded crushed stone of foundation bed surface,4 kinds of fines content graded crushed stone were designed:0%,5%,10%and 20%.The compaction test and infiltration test were carried out on the graded crushed stone.With the increase of fines content,the maximum dry density of soil after compaction first increases and then decreases,and the shape of compaction curve gradually presents inverted"S"shape.The permeability coefficient decreases with the increase of fines content,and its order of magnitude decreases from 10^-2 to 10^-5.The addition of fines content can improve the compaction effect of graded crushed stone and obtain higher dry density,but at the same time reduce the permeability of soil.?2?Through the static triaxial test,the stress-strain relationship of graded crushed stone under the action of static load was analyzed,and the influence of the fines content and moisture content on the peak strength,strength index,initial elastic modulus and pore pressure was studied.With the increase of fines content,the peak strength of soil increases first and then decreases.After the soil is saturated,except for 10%fines content,the peak strength of other soil increases.The pore pressure produced of graded crushed stone by shear is mainly negative pore pressure,so the total stress moire circle moves to the right to obtain the effective stress moire circle,but the obtained strength index has different variations due to the variation of negative pore pressure.In the optimal moisture content,the initial elastic modulus increases with the increase of fines content,but after saturated,the initial elastic modulus first decreases and then increases,and reaches the minimum value at 10%fines content.The pore pressure curve can be divided into three parts:increasing,decreasing and stabilizing.Since water is more difficult to compress than gas,the pore pressure generated is not buffered,and the pore pressure of soil changes more after saturat.The strength and pore pressure under the optimal moisture content and saturation state were compared,and the influence of pore pressure on the strength was discussed.?3?The effects of fines content and moisture content on cumulative plastic deformation and dynamic pore pressure were studied through dynamic triaxial test.Under the optimal moisture content,the cumulative plastic deformation curve of graded crushed stone will go through the process of deformation stabilization,attenuation and rapid failure,and the plastic deformation will increase with the increase of dynamic stress.In the saturated state,the cumulative deformation of 5%and 10%fines content did not show a rapid failure state,and the plastic deformation decreased with the increase of dynamic stress in part of the cumulative plastic deformation curve.The cumulative plastic deformation of 0%fines content under the optimal moisture content and saturation state before rapid failure tends to be stable,and the dynamic stress it bears is also relatively high,and its dynamic stability is relatively good.Barksdale model was used to fit the cumulative plastic deformation curve to obtain the fitting parameters a and b,and it was further found that a and b had a good linear relationship.The dynamic pore pressure curve corresponding to the larger dynamic stress will have the change rule of step-down,which is more and more obvious with the increase of dynamic stress and vibration times.Under the condition of saturation,the dynamic pore pressure of graded crushed stone with fines increases first and then decreases with the increase of dynamic stress,and with the increase of fines content,the dynamic pore pressure is closer to the confining pressure when it reaches the peak point.The effect of pore pressure on cumulative plastic deformation is discussed,and it is found that when the difference between dynamic stress increment and corresponding dynamic pore pressure is small,the effective confining pressure increase can enhance the anti-deformation ability of soil.