Antonios Zervos

Discretization of Gradient Elasticity Problems Using C 1 Finite Elements

Strain-gradient theories have been used to model a variety of problems (such as elastic deformation, fracture behavior and plasticity) where size effect is of importance. Their use with the finite element method, however, has the drawback that specially designed elements are needed to obtain correct results.

Improving the performance of railway tracks through ballast interventions

Maintenance and eventual renewal of a ballasted track constitute major operational costs for a railway network. Thus, significant benefits would accrue from a more robust track design having a longer service life and reduced maintenance requirements. This paper presents the results from a laboratory study and explores the potential to achieve this through improving the ballast grading and reducing the ballast shoulder slope. Cyclic loading tests were carried out on a section of track representing one sleeper bay in plane strain, in the Southampton Railway Testing Facility. A cyclic load representing a 20 tonne axle load was applied at 3 Hz for at least 3 million cycles, during which measurements of permanent and resilient vertical deflection were made. Certain interventions are found to result in lower rates of permanent settlement and different resilient ranges of movement. Supplementary measurements to determine longitudinal pressure, ballast breakage and attrition, and shoulder slope movement were used to explore the mechanisms responsible for the observed improvements in ballast bed performance. It is concluded that the use of finer ballast gradings and a shallower shoulder slope have the potential to reduce maintenance requirements.

Modelling of ground-borne vibration when the train speed approaches the critical speed

When trains run on soft ground, large deflections of the track and vibration of the ground can occur when the train speed approaches the speed of Rayleigh waves in the ground. Modelling is helpful to understand and mitigate such critical velocity effects. Here, a three-dimensional time-domain model of a load moving on a track and ground has been developed with the finite element software ABAQUS. This allows nonlinear soil properties to be considered. In order to validate the approach, the vibration of the track and ground induced by a high speed train is compared with those from the site measurements carried out in the late 1990s at Ledsgard, Sweden. Due to the particularly soft soil at this site, it is necessary to adopt a nonlinear soil model due to the large deflections induced by the high-speed train. It is shown that using a linear model based on the small strain soil parameters leads to results which underestimate the displacements. Laboratory test data allow the nonlinear characteristics to be obtained. These have previously been used by various authors in an equivalent linear model. Here this approach is compared with a fully nonlinear model.

Data set for "Modelling the effects of trafficking and tamping on scaled railway ballast in triaxial tests"

Data for the paper Aingaran, S., Le Pen, L., Zervos, A., & Powrie, W. (2018). Modelling the effects of trafficking and tamping on scaled railway ballast in triaxial tests. Transportation Geotechnics.

Data to accompany "A Review and Evaluation of Ballast Settlement Models using Results from the Southampton Railway Testing Facility (SRTF)"

Data to support: Abadi, Taufan et al (2016) A review and evaluation of ballast settlement models using results from the Southampton Railway Testing Facility (SRTF). Procedia Engineering, 143, 999-1006.