Experimental Study On Packing Characteristics Of Gravel Filling Subgrade

Coarse soil can be found everywhere in nature with a rich reserve.It has the characteristic of good compression, strong water permeability and high shear strength. It also has the ability of not liquefying under the load of earthquake easily. Thus comes to an widely application in civil engineering. For example,it is used in railway or highway embankment, earth-rock dam, artificial island and soft foundation treatment of sand-gravel cushion and so on.Base on the basic characteristic of particle packing,many experimental sutdy on coarse soil are taken out.Conclusions are made below.(1) According to coarse soil filling subgrade which maximum particle size is26.5mm.the law of interference index varying with filling level in the condition of multilevel continuous dense gradation was analyzed. Study shows that particle group of different sizes can be classified into three categories. They are interference function mainly particle (skeleton particle), filling function certainly (transition particle) particle and filling function mainly particle (packing particle) particle.(2) In the condition of gap gradation, it shows from the reference curve of the deficient particle fraction and the interference index that as the deficient particle fraction increase, the interference index form a linear reduction.When the deficient particle size varies from4.75mm to0.3mm,the interference index fall to zero.(3) Experiment shows that the traditional principle of volume filling is still suitable for the situation of fine particle bringing an interference to skeleton particle voids.Thus the dense gradation design method based on general volume filling is formed.(4) The particle size boundary experiment method of skeleton structure of coarse soil based on particle filling effect is designed.The soil structure pattern of graded crushed stone of high speed railway surface layer of subgrade is analyzed.It shows that as for coarse soil, the lower limit gradation of particle size boundary is1.18mm.That is, dense skeleton or voids structure is the one that particle which size larger than particle size boundary reacting as skeleton and the others having the filling function.suspending dense structure is the one which has more fine particle in upper limit and median gradation forming interference to particle skeleton structure inevitably.(5) The packing density increase with the ratio of cylinder diameter and particle size.When the ratio is more than4.70,the packing density tends to be stable. The variability of the parallel test data increase when the ratio decreases. (6)The pounding test of coarse soil shows that when the difference of particle size between the transfinite particle and the non-transfinite particle, the voids that between transfinite particle and non-transfinite particle have a large proportion in the solid volume of transfinite particle. It can not be ignored. Modified value is unexpectedly large using the modified formulas of the maximum dry density when the compaction test has transfinite particle following the law of’soil test procedure in railway project’. Based on the geometric analysis plane model of the binary particle packing and introducing the coefficient of same size sphere packing clearance percentage, the modified method of the maximum dry density when the compaction test has transfinite particle is improved. The calculated value is more approached to the measured value.