Abstract
Generation of mud pumping is commonly triggered by a combination of three main factors such as excess fines, excess water, and cyclic loading. Excess fines particle is generated from depositing mechanisms (i.e., dust, waste material and ballast breakage) and fluidisation or internal erosion mechanism (i.e., subgrade degradation). Mud pumping phenomenon that is associated with ballast fouling has been widely discussed and is of interest among the railway engineers and researchers. However, subgrade degradation or fluidisation of subgrade layer induced mud pumping mechanism gained less attention from the researchers due to complexity of subgrade soil behavior. Various methods applicable in railway track's subgrade degradation assessment based on destructive and nondestructive test were comprehensively reviewed in this research paper. The assessment on subgrade mud pumping is based on migration of the subgrade fine mechanism including in-situ excavation test, particle size distribution test, ground penetrating radar (GPR) and physical modelling test. This paper summarizes the advantages and weaknesses of various assessment methods of subgrade degradation induced mud pumping and clarifies most effective method for repair and maintenance of railway track.
Highlights
The mechanism of mud pumping is a complex process, and real-time assessment of mud pumping must be carried on site to understand the loading and basic characteristics of ballasted railway track
In late 1950s, the researcher began to investigate the pumping of subgrade soils in pavement engineering context whereas; since 1980s the researcher began having interest in mud pumping in railway engineering context [20]
As pore water pressure development is the main influence on the dissipation of fine-grained particle of subgrade soil which causes the occurrence of mud pumping [26]
Summary
The mechanism of mud pumping is a complex process, and real-time assessment of mud pumping must be carried on site to understand the loading and basic characteristics of ballasted railway track. The conventional mitigation approach for mud pumping problems is to directly modify or replace the fouled section of rail tracks to improve the drainage system and bearing capacity. This repeated localised maintenance work is usually expensive as it does not completely solve the mud pumping problem [1,2,3]. From site investigation conducted by Selig and Waters [11] discovered on 76% contribution of fine sources is from ballast breakage or ballast aggregate deterioration which takes place during heavy freight load and high-speed train surpass the track same goes with ballast tamping during maintenance works [11,14,15]. Contamination frequently produced from train such leaking fuel tank, grease dropping and heavy metals Johan [18] which possibly occur due to rapid contact between wheel and rail or wheel and brake pad when braking [19]
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