Retrofitting of Existing Railway Tracks Using Micropiles as a Ground Improvement Technique: Finite-Element and Genetic Programming Approach

Indian Railways has the fourth largest railway network in the world. Today, there is an urgent need for enhancing the capacity of tracks for which replacement of old tracks with new ones in a time bound manner for the vast and busy network is a challenging task. To overcome this challenge, micropiles are proposed as an alternative tool to reinforce the existing railway subgrade without removing the existing track and without blocking existing traffic. In this study, suitability of micropiles as a ground improvement method for the existing railway track was assessed. Micropiles were modelled along the sides of the track in various orientations. A complete parametric study varying the geometrical parameters of the micropile under static and realistic moving train load conditions was performed using Finite Element Method (FEM) software. Three-dimensional numerical models with variations in length, diameter, inclination and spacing of micropiles was also performed. The results of FEM analyses were utilized as an input to the Genetic Programming (GP) model. The GP analysis output generates empirical equations for the prediction of track performance with micropile parameters as an input variable. The GP analysis resulted in empirical equations for the prediction of track performance, with the micropile parameters as input variables. The input variables were: length, diameter, spacing, and inclination of the micropile. These empirical equations can be utilized to predict the performance of the track for different reinforcement conditions. The empirical equations by GP have been used to develop a design methodology and a flowchart illustrating the overall design steps is generated. This design methodology can be adopted for practicing civil engineers to perform the upgradation of the existing tracks.