Soil strengthening of age-old-designed railway tracks Research Paper

Soil strengthening of age-old-designed railway tracks - Research Paper Example Superstructure consists of rails, fastening, and sleepers, and sub-structure consists of ballast, sub-ballast, and sub-grade. This research assignment studies the functions of substructure in track operation. Railroad substructure receives dynamic load from train movement and behaves according to the principles and laws of soil mechanics. Soil performance under loading in soil mechanics is governed by two characteristics: strength and deformation (STRATIGRAPHICS n.d.). Strength refers to the shear strength properties, and deformation refers to settlement. The proper functioning of substructure is characterized by the bearing capacity which implies that shear stresses caused by the cyclic loading has to be lower than the soil’s undrained shear strength value, and at the same time settlement will not develop plastic behavior in the soil. After a number of years of operation, instability of both super and sub structures is caused by the shear failure and plastic settlement of sub -grade. There are many factors that may contribute to the loss of soil-strength. Among them, poor drainage, and trapped water in ballast pockets play significant roles. According to Harry Cedergreen, drainage represents a significant issue for railroad construction and maintenance; stability and low maintenance cost can only exist when adequate drainage is provided (Cedergren 1989, p. 364). Sub-grade failure in railroad jargon is called â€Å"soft track† (Australian Rail Track Corporation a 2001). Soft track includes ballast failure, top formation failure, shallow sub-grade failure, embankment failure, and landslide failure. Water is one of the several contributors that cause these failures. The scope of this assignment is to study methods... The response to the cyclic loading of rail track is an interaction of superstructure and substructure. Ballast, sub-ballast, and sub-grade relates to substructure. Decades of operation bring structural changes of substructures. The sub-grades of the old existing rail tracks require rehabilitation to satisfy proper functioning and meet current technical operational standards. The scope of this assignment is to find the rehabilitation approach for the existing tracks of Australia. The solution must account that improvement of substructure by dismantling the railways is not an option due to the transport collapse, which is accompanied by financial losses. Rehabilitation of the existing railway is not a sheer issue that relates to Australia only; it is also a significant issue for the European countries, Canada, and USA. CSX Rail Line in Milstead, Alabama, USA faced excessive ballast settlement and soil pumping problems due to the poor sub-grade conditions. Moreover, Tallapoosa River run s parallel to the rail line. The rehabilitation of the track included raising the track, undercutting and removing the existing ballast, and use of filter fabric over the exposed sub-ballast, which was followed by a layer of Geogrid