Evaluation of Mechanical Parameters of Contaminated Road Base and Railway Ballast
This dissertation comprises two topics in the area of transportation geotechnics that focus on the evaluation of stiffness parameters of contaminated road base and railway ballast. The abstracts of these two studies are provided in the following two paragraphs. The performance of a flexible pavement depends on the mechanical characteristics of its unbound granular base layer. The mechanical characteristics such as stiffness and deformation resistance depend on many factors such as the material gradation, fines content, moisture content, physical properties of coarse aggregate and more. The base materials are often contaminated by the excessive fines that is caused by improper material handling, migration of fines from subgrade and the other reasons. The moisture content of base layers may alter during pavement construction and operation by exposure to excessive water and percolation of rainwater from pavement surfaces. In this research, the mechanical behaviors of contaminated base materials were evaluated to understand the effects on the performance of the pavements. Twelve different test sequences were performed with a combination of moisture contents from dry to wet of optimum moisture content and four different fines contents through laboratory and simulated field tests. An increase in moisture content was typically detrimental to the mechanical properties of the base material. However, the increase in the fines contents yielded mixed results. One of the major challenges associated with railway systems is the degradation of the railway tracks with time. The ballast that forms the major supporting structure of the railway track degrades mainly due to the application of train dynamic loads, changes in climatic conditions and interaction of ballast and the underlying subgrade. The contamination of the ballast (also known as ballast fouling) due to the penetration of clay, rock dust, coal or any other agent accelerates track degradation, and affects the stability of the ballast in particular and the track in general. In this research, the roles of fouling agents and moisture content were evaluated to understand the effects on the mechanical characteristics of ballast. Thirteen different tests sequences were performed with a combination of two different fouling agents at three degrees of fouling and three different moisture contents through simulated field tests. The fouling agents directly impacted the physical properties of ballast by replacing the void spaces in ballast by fine particles and disturbing the structural integrity of ballast particles. The effect of contamination on the performance of the ballast was highly dependent on the type of fouling agent. For clay-fouled specimens, the increase in the degree of fouling and the moisture resulted in significant reduction in the deformation resistance and load bearing strength.
Geophysical|Civil engineering|Transportation planning
Tamrakar, Prajwol, "Evaluation of Mechanical Parameters of Contaminated Road Base and Railway Ballast" (2017). ETD Collection for University of Texas, El Paso. AAI10256240.