Phenomenon of Mud Pumping in Rail Tracks
Fundamental Concepts and Practical Implications
Distinguished Professor Buddhima Indraratna
Over the years, rapid urbanization has led to an increase in the demand for faster and sustainable heavy-haul rail service worldwide. With increasing axle loads of trains, the subgrade foundation experiences higher cyclic excess pore water pressures. At high axle load exceeding say 30 tonnes, the yielding of soft subgrade soil can occur, causing significant softening and undrained failure. In certain cases, fluidization of the soil (slurry) may occur, especially if the water content approaches the liquid limit of the soil, and the fluidized soil will pump-up rapidly (hence the term, mud pumping) towards the overlying substructure, adversely affecting the shear strength and permeability. While this phenomenon is commonly reported beneath heavy haul tracks, the underlying mechanism of subgrade fluidization under cyclic loads has not been given adequate attention. In this presentation, some critical studies investigating the mechanisms of mud pumping will be presented, including: (i) an experimental programme to investigate the mechanisms of subgrade fluidization; (ii) modelling mud pumping based on the novel approach CFD/LBM-DEM coupling; and (iii) site investigations and testing. The test results indicate that under adverse combination of cyclic loads, the excess pore water pressure increases rapidly in low-medium plasticity soils that are more prone to mud pumping. It is accompanied by a redistribution of moisture along with the depth of the specimen, where the water content increases towards the top layers while the bottom layers tend to densify (cyclic consolidation). When the moisture content reaches the liquid limit of the subgrade, the specimen transforms to a fluid-like state with a dramatic reduction in stiffness. Advanced computer simulations demonstrate that increased hydraulic gradients cause a reduction of inter-particle contact areas thus destabilizing the soil fabric. The presentation will also show some ongoing efforts towards deeper understanding of this complex geo-hydrodynamic phenomenon of mud pumping through extensive site investigations and laboratory-based testing.
About the speaker
Currently, Buddhima Indraratna is a Distinguished Professor of Civil Engineering and the Director of Transport Research Centre, at University of Technology Sydney. Formerly, he was a Distinguished Professor and the Founding Director of Australian Research Council’s Training Centre for Rail Infrastructure at the University of Wollongong. He is also an Honorary Distinguished Professor at the Asian Institute of Technology, Thailand, Indian Institute of Technology, in Assam and Harbin Institute of Technology in Harbin, China.
Education, Awards and Recognitions:
Buddhima is a Civil Engineering graduate from Imperial College, London. Since his PhD at University of Alberta in 1987, his contributions to geotechnical and railway engineering have been acknowledged through numerous national and international awards, including 1st Ralph Proctor Lecture and 4th Louis Menard Lecture of the International Society of Soil Mechanics and Geotechnical Engineering. He also delivered the 2009 EH Davis Memorial Lecture of the Australian Geomechanics Society for contributions to Theory and Practice of Geomechanics. For his pioneering contributions, he was honoured with the 2009 Business and Higher Education award by the Australian Commonwealth, 2011 Engineers Australia Transport Medal and 2015 Australia-New Zealand Railway Technical Society’s Outstanding Individual Award. His numerous international awards include Thomas Telford Premium by the Institution of Civil Engineers (UK), Robert Quigley Award by the Canadian Geotechnical Society, and the Medal of Excellence for life-time contributions by the International Association of Computer Methods and Advances in Geomechanics.
Research Leadership, Publications and Supervision:
Buddhima currently leads numerous projects worth over $ 1.5 million per year. He has been a consultant to various infrastructure organisations worldwide, and a former United Nations expert representing Australia. He has published over 850 papers including 12 books, over 450 journal papers, and more than 70 invited Keynote papers in all continents. So far, he has supervised over 100 PhD and Master’s graduates and over 40 Postdoctoral Fellows. He is the Chair of the Ground Improvement Advisory Board of Inst. of Civil Engineers, UK, and the Chief Editor of the Journal of Ground Improvement.
Buddhima is a Fellow of the prestigious Australian Academy of Technological Sciences and Engineering (FTSE), Fellow of the Institution of Engineers Australia (FIEAust), Fellow of American Society of Civil Engineers (FASCE), Fellow of Australasian Institute of Mining and Metallurgy (FAusIMM), and Fellow of the Geological Society of UK (FGS). He is a Chartered Professional Engineer of Australia, United Kingdom, and Sri Lanka.
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