Dynamic response of a transition zone on

Projekt:

Quantifying complex track stiffness response

Sammanfattning:
This report for project TRV 2016/106277 presents the development of numerical methods to study the effect of strain accumulation from cyclic loading on the dynamic response of
a railway system. The work is a follow up on the project TRV 2015/108250 – Modelling deformations below high-speed rail. The following advances are made, which are in line with the recommendations of the previous project:

• Stiffness degradation based on experimental data is implemented in the constitutive model for cyclic accumulation of strain in soft soils: Creep-Sclay1Sc;

• The boundary value level analyses are now considering 2D longitudinal sections with moving train loads;

• The analyses now incorporate quasi-static cyclic accumulation modelling and time-domain dynamic analyses for a single train passage before and after simulating 100 000 load cycles.
Subsequently a transition zone is studied numerically where an embankment is overlaying a soft clay that is prone to settlements from cyclic loading and a competent stiff soil. The train
loads are simulated by moving four spring loaded point loads (one for each axle), which require some changes in the Tochnog Professional Finite Element code. Special care was taken to
convert the characteristics of the dynamic load to appropriate input parameters for the cyclic accumulation model. It is demonstrated that for the boundary value problem considered the
period for cyclic loading in the soft clay below the embankment is associated to the distance between the bogeys. Furthermore, the maximum deviatoric stress amplitude reduces with
depth rather quickly. The transition zone is studied for axle loads of 60 kN spaced following the X2000 passenger
carriage configuration for two train velocities, i.e. 10 m s−1 and 50 m s−1 using the cclic strain accumulation model with and without stiffness degradation. The results indicate that the
second train passage after cyclic degradation resulted in lower induced stress amplitudes, for both models. The effect of the stiffness degradation linked to destructuration in the clay is
limited for the studied cases where the deviatoric loading amplitude for cyclic accumulation was modest. Larger values for the deviatoric loading amplitude proved to be leading to numerical
stabilities issues. The measurable project impact is itemised below:
- Improved constitutive model for strain accumulation of soft sensitive clay;
- The resulting analysis method will be used in the follow up project in conjunction with the sensitivity analyses framework;
- All calculations can be performed with the Tochnog Professional Finite Element code, which since January 2020 is free to use for all. This dramatically improves market adaptation.
Keywords: strain accumulation, time effects, high-speed rail, soft soils, transition zones

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Författare: Dijkstra & Tahershamsi
Utgivare: CHALMERS UNIVERSITY OF TECHNOLOGY
Utgivningsdatum: 2020-12-31
Diarienummer: TRV 2016/106277
Antal sidor: 48
Språk: Engelska
Kontaktperson: Johan Jonsson, IVta2