Detection of local instabilities caused by plastic deformations of cohesive soils in the substructure / subsoil of railway tracks (EPIB1.2)

• Applicant: Professor Dr.-Ing. Christian Moormann, Ph.D.
• Subject Area: Geotechnics, Hydraulic Engineering
• Term: from 2017 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 321258667

The aim of the proposed project is to detect as early as possible and reliably local instabilities caused by plastic deformations of cohesive soils in the substructure / subsoil of railway tracks. As far as it becomes possible to identify typical dynamic additional stimulations regarding the wheel-rail forces concerning frequency and amplitude as indicators of the presence of local instabilities, this could be used in a simple manner for practical applications to analyze the continuous records of the acceleration of the axle-box, even with regular trains, to identify local instabilities in an early stage and to integrate this method into the railway maintenance management.To achieve this overall objective, the impact of local instabilities in the subsoil / substructure on the wheel-rail forces shall be evaluated by numerical simulations using a calibrated subrade-subsoil interaction model developed by the sub-project EPIB 1.2 applied for hereby. From the dynamic components of the wheel-rail forces, which can be evaluated in the later practice by the acceleration of the axle-box, the current form of a local instability can be identified and appropriate measures can be taken early. As part of the proposed work package EPIB 1.2 therefore indicators for the presence of local instabilities shall be identified by using a dynamic continuum model for the simulation of the typical system response of the dynamically stressed superstructure, substructure and subsoil. Based on this the valuation basis for the overall goal of a screening indicator for such local instabilities will be provided.The geotechnical accurate numerical simulation of these issues is challenging, since in such a simulation model the dynamic behavior and the load distribution in the superstructure, in the substructure and in the subsoil as well as the wave propagation in the soil layers must be represented realistically. It is intended to simulate the overall system in a complete three-dimensional model for the implementation of fundamental studies. The description of soil behavior under dynamic loads and at small strains is crucial for the simulation. The physical modeling will be realized by applying a hypoplastic constitutive model with intergranular strains for non-cohesive soils and a hyperplastic constitutive model for cohesive soils.To calibrate the model appropriate investigations in situ (field measurements) carried out by work package EPIB 2 will be back-analyzed. Since the dynamic wheel-rail forces are determined by the geometry of the loaded track correlated with the stiffness ratios and the vehicle-side parameters, the model must represent a correspondingly long track section.

• DFG Programme: Research Grants