On cyclic accumulation models for degradation of railway foundations
This thesis aims at identifying a proper sensitivity analysis method in geotechnical Finite Element Analysis (FEA) for optimal use of advanced constitutive soil models. For this purpose, first the viscoplastic Creep-SCLAY1S model is evaluated for a boundary value problem. The objective was ultimately addressed by implementing two Global Sensitivity Analysis (GSA) methods for quantifying the uncertainties of Creep-SCLAY1S. The common GSA method of Sobol was benchmarked against Experimental design in a lab-scale numerical model of Constant Rate of Strain (CRS). The Sobol method has proven to be computationally expensive for sensitivity analysis of advanced constitutive models using FEA. The spatial sensitivity measures of Sobol and Experimental design indicate that they are not altogether distinct. Thus, Experimental design represents a more feasible approach by using less resources, such as computational time and required storage. Furthermore, temporal Sensitivity Analysis (SA) has demonstrated the importance of the entire time domain spectrum, particularly for factor fixing purposes.
The second part of the study proposes a revised strain accumulation model that has been validated using new data on Swedish natural clay for cyclic loads with low amplitude. The model presented herein offers a strong basis for the accurate prediction of strain accumulation in soft clays beneath embankments subjected to a significant number of loading cycles. In general, the knowledge gained in this research contributes to a better understanding of comprehensive numerical models in Geotechnics and can be a helpful prior to inverse modelling, data assimilation, and Random Finite Element Method (RFEM).
Natural soft clay
Global Sensitivity Analysis
Cyclic accumulation models
Chalmers, Arkitektur och samhällsbyggnadsteknik, Geologi och geoteknik
Using experimental design to assess rate-dependent numerical models
Soils and Foundations,; Vol. 62(2022)
Artikel i vetenskaplig tidskrift
Towards rigorous boundary value level sensitivity analyses using FEM
IOP Conference Series: Earth and Environmental Science,; Vol. 710(2021)
Paper i proceeding
Tahershamsi, H., Ahmadi Naghadeh, R., Zuada Coelho, B., Dijkstra, J. Low amplitude strain accumulation model for natural soft clays below railways
The natural ground is a critical yet overlooked aspect of railway systems that can lead to degradation. With limited field measurements, the use of models is a preferred method for predicting the behaviour of railway structures over the long term. A model has been developed in this thesis by which to predict strain accumulation in soft natural clays by analysing their behaviour under cyclic loading through laboratory testing.
This thesis also aims to provide an efficient experimentation method using models. Existing models are becoming increasingly complex to be able to capture the physical problems with high precision. Of special value are statistical techniques that are used in this study to carefully assess these complex models. In addition, these statistical techniques are the very first steps with which to improve the design of railway systems by collecting suitable data. Collecting and studying suitable data can lead to significant improvements in the system, potentially revitalising the railway industry through a chain reaction initiated by quality improvement techniques.
Deformationer på spår-platta grundlagd på pålar i lös lera
Trafikverket (2015/108250), 2016-02-01 -- 2019-02-15.
Quantifying complex track stiffness response
Trafikverket (TRV2016/106277), 2017-08-15 -- 2020-04-30.
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5276
EA, Hörsalsvägen 11, Chalmers
Opponent: Dr. Marti Lloret-Cabot, Department of Engineering, Durham University, United Kingdom