Experimental Study On Cyclic Cumulative Rehabilitation Of Railway Settlement

Because of the rapid development of high-speed railway all over the world in recent years,with the increase of train speed and the increase of freight load, which puts forward higher requirements for the rail line structures. The structure under rail line is mainly composed of ballast and subballast, and its permanent strength and deformation under train traffic loadings are related to the two filling materials themselves directly. The granular material,which is the weakest and the most unstable part in the whole structure, is the main source of the track deformation. Under the condition of the large number of train wheel moving load cycles, the granular material under high-speed railway slab track can be crushed and the dynamic subsidence may be obtained. When the water enters may also cause mud pumping, leading to serious subsidence, sleeper slab warping and cracking. The excessive settlement of high-speed railway subgrade will adversely affect the durability of railway structures and the comfort and safety of trains, therefore the uplift of track structures will be demanded to restore the vertical alignments of the railway.This paper carried out large-diameter static triaxial test on subballast and ballast specimens,the influence of some key parameters, such as gradation, compaction degree and loading conditions on specimen's strength and deformation behaviors are discussed based on the test data. In this paper, a discrete element program BLOKS3D is presented, which can be used to simulate the static triaxial test based on t polyhedral particles. This paper presents the experimental results of cyclic triaxial testing and postcyclic triaxial testing on individual ballast and subballast materials. Also, to investigate mechanical behavior at the ballast/subballast interface, cyclic tests were performed on composite specimens consisting of the upper half ballast layer and underlying half subballast layer. These cyclic tests indicated that the existence of the ballast/subballast interface depresses the development of permanent axial or volumetric deformation at the interface zone, and this effect vanishes as the initial compaction and confining pressure increase. Postcyclic failure tests show that the ballast/subballast interface zone's strength is close to that of the ballast material but lower than that of the subballast material.According to the dynamic uniaxial test and postcyclic failure test on polyurethane specimen and the combination specimen of polyurethane and subballst,the evolution process of deformation and mechanical properties of two kinds of specimens under cyclic loading can be obtained, and the static strength characteristics of the combination specimen of polyurethane and subballst can also be obtained. Loading-unloading test, single point excitation test, simulation of train running test and simulation of the fatigue test of 1 train load with a great number cycles,which are carried out on full scale high-speed railway ballastless track subgrade physical model test device. The experimental results show that it is feasible to apply the polymer injection technology to rehabilitate subgrade of high-speed railway ballastless track, the dynamic stability and durability of track-subgrade system can basically meet the technical requirements of ballastless track subgrade.