Track behaviour: the importance of the sleeper to ballast interface

Abstract

The aim of this research is to develop a fuller understanding of the mechanical behaviour of the
sleeper/ballast interface, related in particular, to the forces applied by high speed tilting trains on
low radius curves. The research has used literature review, field measurements, and laboratory
experiments on a single sleeper bay of track. Theoretical calculations are also presented.

Field measurements are carried out using geophones to record time/deflection for sleepers
during passage of Pendolino trains on the West Coast Main Line. Calculations are presented to
quantify normal and extreme magnitudes of vertical, horizontal and moment (VHM) loads on
individual sleepers.

Results from laboratory experiments, on the pre-failure behaviour of the sleeper to ballast base
contact area, show that lateral load/deflection behaviour is load path dependent and relations are
determined for improved computer modelling of the sleeper/ballast interface. Further test results
are used to establish the failure envelopes for combined VHM loading of the sleeper/ballast base
contact area. Tests show that the sleeper/ballast base resistance at failure occurs at a load ratio
(H/V) of about 0.45 (24°) at 2 mm of displacement tending to 0.57 (30°) at greater
displacements. In addition, measurements from pressure plates within the testing apparatus are
used to describe the development of confining stress within the ballast during 100 cycles of
vertical load. The development of confining stress is assessed with reference to a finite element
model of the laboratory apparatus and it is shown that the earth pressure ratio moves towards the
active condition for peak load and the passive condition at minimum load per cycle.

The contribution to lateral resistance of the crib ballast and varying sizes of shoulder ballast is
also established and it is found that the shoulder and crib resistance can best be characterised by
taking the mean resistance over a range of deflection from 2 mm to 20 mm. Calculations are
presented, supported by the experimental data, to quantify the resistance from different sizes of
shoulder ballast and a chart is presented which can be used as the basis for shoulder
specification in practice.

More information

Identifiers

ORCID for Louis Le Pen: orcid.org/0000-0002-4362-3895

ORCID for William Powrie: orcid.org/0000-0002-2271-0826

Catalogue record

Export record