Evaluation of ballast compactness during the tamping process by using an image-based 3D discrete element method

Abstract

We investigated the dynamic behavior of a railway ballast layer during tamping operation by 3D Discrete Element simulations. The ballast layer was prepared with ballast grains that had a realistic shape and was measured by a laser scanner and modeled by clumped spheres using the dynamic optimization technique. Three types of sleeper models that were embedded in the ballast layer were prepared, and a series of tamping operations (lifting of the sleeper, insertion of vibrating tines and packing, pulling out of tines, and settling of the sleeper) were simulated in a realistic manner. The compaction underneath the sleeper mainly occurred during the insertion of tines and the packing process, while the tine insertion zone was eventually loosened after the tines were pulled out. The final porosity differs with different sleeper models and packing process periods. On the other hand, the coordination number (the number of inter-granular contacts per grain) drastically decreased during the insertion of the vibrating tines and the packing process; then, it recovered to the original value after the tines were pulled out. This change is important to identify the extent of ballast grain agitation due to the processes. The contact force network is sensitive to the applied loading and the place where the tines are inserted, and the resulting force network localization at the final state can be understood by the Coulomb's earth pressure theory. The degree of heterogeneity may be the key to the long-term stability of the ballast layer under repeated train wheel loading.

Evaluating Gyratory Compaction Characteristics of Unbound Permeable Aggregate Base Materials from Meso-Scale Particle Movement Measured by Smart Sensing Technology

“…A series of conventional impact compaction tests were conducted in the laboratory to obtain the optimal moisture content of UPAB materials with scaled gradations of 1–3% [ 39 ]. Previous studies revealed that the vertical stress level observed during field compaction and in-service periods is from 100 to 700 kPa [ 21 , 40 , 41 , 42 ]. The details of the orthogonal array testing along with the test design scheme are shown in Table 1 , which was obtained according to the principle of mixed-level orthogonal design.…”

Calibration for discrete element modelling of railway ballast: A review

“…The following column is the generation method, which describes the applied DEM software and the methods of creating the particles. The applied software includes 1) particle flow code (PFC) [82], 2) Yade [83], 3) extended discrete element method (EDEM), 4) dynamic optimization method [73], 5) BLOKS3D [84] and 6) LMGC90 [85].…”

“…Using the DEM models, the studies mainly concern the tamping frequency, compaction and performance after tamping, etc. [38,[67][68][69][70][71][72][73].…”

Experimental and Theoretical Evaluation of Side Tamping Method for Ballasted Railway Track Maintenance

“…The studies by Sysyn M. et al and Sysyn M. et al [30,31] allow to determine the differences in ballast compaction along the sleeper after vibration loading. Numerical simulation of ballast compaction and ballast porosity using discrete element method is shown in other papers [32][33][34][35]. Tamping operations, like sleeper lifting, tines insertion, vibrating and packing, their pulling, and sleeper settling were simulated in a realistic manner, which showed the decrease of inter-granular contacts number during the insertion of the vibrating tines and the packing process.…”