Presentations and Papers
Summary - Towards a Better Design Guideline of Sub-Ballast Materials for Filtration Purpose Under Cyclic Load
Presenter: Asadul Haque
In wet conditions, a sub-ballast interface between the ballast and formation soil protects migration of formation soils, reduces track settlement and allows water to drain without excessive pore water pressure development. In a clayey formation, fine mud like slurry is often generated at the formation-subballast interface as water enters into the formation and facilitates upward migration of fines (also known as mud pumping) under the cyclic load. Therefore, providing a sub-ballast interface that satisfies filtration requirements is very important in maintaining an acceptable track condition under the cyclic train loading. Filtration behaviour of sub-ballast materials at various piping ratios and permeability ratios under a cyclic load frequency of 1 to 13Hz were investigated in the laboratory. Turbidity of the effluent and permeability of the filtration system were measured at different time intervals. Test results showed that an increase in cyclic loading caused an increase in turbidity indicating that migration of formation soils was highly possible. Piping ratio of greater than 9 was found to be unsatisfactory to minimise migration of fines under a cyclic load frequency of 10 Hz and pressure of 70-140 kPa.
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