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Results

Zerkleinerungs- und Setzungsvorgänge bei Eisenbahnschotter.
Degradation and settlement processes in ballast beds.

During the first funding period, the Discrete Element Method (DEM) was successfully applied for the simulation of granular beds consisting of breakable bodies. A methodology was developed, which allows constructing realistically shaped stones and to conduct further analyses with these stones. Up to now, these analyses were limited to spheres or disks made of breakable material [LM05, LGV06] or irregularly shaped but unbreakable stones [LM07]. Thus, with the results of this project it is now possible to investigate the processes in ballast beds with consideration of particle breakage.

Zerkleinerungs- und Setzungsvorgänge bei Eisenbahnschotter.
Material modelling as system of bonded particles.

The simulation results were evaluated by comparison with published experimental results [Die03, HB97, LID00, MC94]. The failure of strong rock is qualitatively very well represented. Also, good quantitative prediction of uniaxial and moderately threeaxial strength is obtained. Advantageous in using the DEM is the fact that the failure results solely from the loading state, and no initialization of cracks is necessary. Likewise, multiple fractures are possible. By an extension of the particle bond laws that is intended for the current funding period the quantitative prediction of multiaxial strength shall be further improved.

Literature
Zerkleinerungs- und Setzungsvorgänge bei Eisenbahnschotter.
Tangent planes used to define the shape of macro-bodies.

[LM05] W. L. Lim und G. R. McDowell. Discrete element modelling of railway ballast. Granular Matter, 7:19–29, 2005.

[LGV06] S. Lobo-Guerrero und L. E. Vallejo. Discrete element method analysis of railtrack ballast degradation during cyclic loading. Granular Matter, 8:195–204, 2006.

[LM07] M. Lu und G. R. McDowell. The importance of modelling ballast particle shape in the discrete element method. Granular Matter, 9:69–80, 2007.

[Die03] M. S. Diederichs. Rock fracture and collapse under low confinement conditions. Rock Mechanics and Rock Engineering, 36(5):339–381, 2003.

[HB97] E. Hoek und E. T. Brown. Practical estimates of rock mass strength. International Journal of Rock Mechanics & Mining Sciences, 34(8):1165–186, 1997.

[LID00] F. Lekarp, U. Isacsson und A. Dawson. State of the art. I: Resilient response of unbound aggregates. Journal of Transportation Engineering, 126(1):66–75, 2000.

[MC94] C. D. Martin und N. A. Chandler. The progressive fracture of lac du bonnet granite. International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts, 31(6):643–659, 1994.