Existing Railroads on Shrink-Swell Soils: Field Monitoring, Laboratory Tests, and Numerical Simulation
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ASCE. Shrink-swell soils (also known as expansive soils) lie into the category of problematic soils. These kinds of soils expand significantly their volume during wetting, and suffer large contractions while drying. The dominant clay minerals in shrink-swell soils correspond to smectite and their structure is characterized by multi-layer sheets. Upon wetting, water molecules penetrate easily into these structures and induce large volume expansions (i.e. around 3 to 4 times the initial volume); the reverse situation is observed during drying. Railroads on shrink-swell soils are subjected to huge solicitations associated with the volume changes of the subgrade due to weather variations. The highly permeable ballast layer exacerbates the problem, which generally leads to unacceptable uneven settlements. At the beginning of this research, the mechanisms behind the observed railroad problems on expansive soils, as well as the associated (possible) remedial solutions were unclear. Previous literature studies have covered (some) topics improving ground conditions for newly-built railroads on expansive soils. However, few studies explored the expansive soil problems in existing railroads. This is because operating rail lines allow (very) short window time for the monitoring, field investigation, construction, and other related activities. The goal of this study is to gain a better understanding in this field. In this paper, a summary of the typical problems caused by shrink-swell soils in railroads is presented. Then, the main components of the railroad test site selected for this study are discussed. Afterwards, the main results of the field campaign, and numerical simulations, including some laboratory tests are presented. Finally, possible solutions for existing railroads in expansive soils are discussed.
