Effect of confining pressure and frequency on the deformation of ballast

Abstract

Increasing the speed and frequency of trains with the same static axle weight imparts higher dynamic axle loads more frequently. When this occurs on existing track which has not been designed for such loading there can be increased rates of ballast degradation, characterised by unacceptable deformation and lateral spread, leading to more frequent requirements for track maintenance. Recent studies carried out at the University of Wollongong highlighted that confining pressure and frequency have a significant influence on the permanent deformation and degradation of ballast. However, confinement required to keep the deformation and degradation of the ballasted track to an acceptable limit will depend on the train speed (frequency). In this context, a series of cyclic triaxial tests was conducted on latite basalt samples having an initial confining pressure of 120 kPa. After every 25 000 cycles, the confining pressure was decreased in steps to simulate the drop of confining pressure during heavy traffic. This test procedure was adopted to replicate the influence of train speed on the stability of ballast. Test results indicated that both the frequency and confining pressure have a significant influence on the permanent deformation of ballast. Resilient modulus is found to increase with an increase in confining pressure and number of cycles, but to decrease with increasing frequency. The results also showed that the ballast layer requires a minimum level of confinement for preventing an excessive amount of track deformation. An empirical equation is formulated to determine the required confining pressure and resilient modulus of the ballast layer for an allowable limit of track deformation at a given train speed.

Effect of increase in load and frequency on the resilience of railway ballast

“…For instance, the longest and heaviest train in Western Australia had a gross weight of nearly 100,000 tonnes and a length exceeding 7 km with as many as 682 wagons hauled by eight locomotives (Railway Gazette, 2001). The effect that the magnitude of the cyclic load (q max,cyc ), the confining pressure (σ 3 ′) and load frequency (f) has on the accumulative plastic deformation of granular materials has been studied in the past (Raymond and Williams, 1978;Indraratna et al, 2014;Suiker and de Borst, 2003;Werkmeister et al, 2004;Lackenby et al, 2007;Thakur et al, 2013;Sun et al, 2014;D'Angelo et al, 2017). Englund (2011) carried out cyclic triaxial tests with an increasing deviator load on unbound road material, and also studied the permanent deformation by evaluating the elastic modulus.…”

Deformation behaviour of gap-graded fouled ballast evaluated by a 3D discrete element method

“…Therefore, a small suction pressure is not sufficient in the experiments conducted. The effects of confining pressure on the deformation characteristics of railway ballast can be found in Lackenby et al (2007) and Thakur et al (2012).…”

Optimizing the Compaction Characteristics and Strength Properties of Gravelly Soils in terms of Fine Contents

“…Actually, the mechanical behaviors of coarse-grained soils are determined by various factors, such as moisture content, grain gradation, fine content, origin of soil particles, and crushing effect [12][13][14][15][16][17]. Cao et al [12] conducted a largescale triaxial test on crushed tuff gravelly soils under optimum moisture condition and saturated condition.…”