Fouled Ballast and Geotechnical Asset Management of Retaining Walls
The objective of this thesis is to submit my work on two transportation geotechnics problems: unsaturated characteristics of fouled ballast and asset management for mechanically stabilized earth (MSE) walls. Ballast is the layer of aggregates that support railroad track; aggregates are used because of their high strength and because they are free-draining materials. Fouling occurs when fine-grained materials intrude into the ballast, which impedes drainage, reduces strength, and increases settlement. This reduces the service life of the track and can result in train derailment. Researchers have studied ballast degradation for years; however, there has been limited research in the unsaturated characteristics of fouled ballast. This is likely because the relatively large aggregate limits the use of conventional soil testing and modeling. Therefore, this research focused on establishing the experimental and numerical results of unsaturated fouled ballast. This is the first time these types of measurements have been conducted for the railroad industry. Fouled ballast is an inherently unsaturated material. Establishing fouled ballast soil water retention curves is an important step in the experimental design and constitutive models to replicate field conditions. The results show that clay and coal fouling materials have similar water retention characteristics, despite having significantly different soil properties. The long-term goal of this research is to improve the ability of nondestructive methods to identify fouled ballast in situ. The MSE study will provide the Kansas Department of Transportation (KDOT) with an asset management program for MSE walls. MSE walls have been standing since the 1970s with little or no management after completing a wall unless it fails. Asset management techniques are a cost-effective way to show when maintenance is needed. There are many ways that an asset management program can be implemented. This study gives special consideration to other state departments of transportation and federal programs. Fourteen categories were selected as identifiable MSE elements for inspection and monitoring. The analytical hierarchy process method was used for a systematic weighting system for each category, along with additional risk-based factors determined by the MSE age, height, and average annual daily traffic. The new asset management system was used for 19 MSE walls in Kansas. The results show that two walls should be reinspected and closely monitored based on current deterioration. The most common defect was vegetation, which should be removed from the wall, but it does not significantly impact performance. A cost estimator tool was used so that KDOT can track the performance of the structure and tie deterioration to asset depreciation. This tool will give KDOT the ability to manage their MSE assets and therefore have a better return on investment in corrective actions.
fouled ballast, SWRC, asset management, MSE walls
Radnor, W. (2022). Fouled ballast and geotechnical asset management of retaining walls (Unpublished thesis). Texas State University, San Marcos, Texas.