Photogrammetry for digital reconstruction of railway ballast particles – A cost-efficient method

André Paixão,Ricardo Resende,Eduardo Fortunato

doi:10.1016/j.conbuildmat.2018.10.048

Abstract

Ballast aggregate is a natural material widely used in railway lines. Its mechanical properties and particle geometry are meticulously defined using well-established standards and characterisation procedures. Though extensively validated, these procedures have some limitations: they are operator dependent; only provide major particle dimensions; do not inform on surface colour; nor allow for advanced particle wear analysis or particle-based simulations. This work presents a cost-efficient photogrammetry method for 3D reconstruction of ballast particles, as an alternative to the significantly expensive laser scanning. It produces digital models of equivalent or higher quality, allowing for advanced and automated particle geometry analyses. Particle meshes produced here are shared among researchers.

Highlights

The conventional railway track consists of a superstructure and a substructure, which includes the sub-ballast layer and the foundation, the upper part of which is usually referred as capping layer
The behaviour of these elements under the cyclical action originated by rail circulation is relatively complex, with the ballast layer assuming a predominant role (UIC, 2008)
This layer directly receives loads transmitted by the sleepers and its main function is to distribute these loads, reducing stresses transmitted to bottom layers and guaranteeing the track’s horizontal stability

Summary

– INTRODUCTION

The conventional railway track consists of a superstructure (rails fastening systems, sleepers and ballast) and a substructure, which includes the sub-ballast layer and the foundation, the upper part of which is usually referred as capping layer. Image resolution is 0.05 mm, and accuracy is at least 0.04 mm, permitting the scanning of surfaces with detail and texture of objects of relatively small dimensions, as is the case of ballast particles In this method an external reference system is not necessary, as the point cloud localization is obtained with the aid of retroreflective targets, consisting of adhesives placed in the object or in the surrounding area, forming an irregular pattern.

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Findings

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