Comparative assessment of expansive soil stabilization by commercially available polymers

Abstract

The objective of this study was to determine the effectiveness of commercially available polymer soil stabilizers in expansive soil swell reduction relative to quicklime and Class C fly ash. A survey of state departments of transportation within the Mountain-Plains region of the USA (Colorado, Montana, North Dakota, South Dakota, Utah, Wyoming) was conducted to define the state-of-practice in expansive soil mitigation, from which lime and fly ash were identified as the most used soil stabilizers. Four commercially available polymers were tested for comparison with lime and fly ash. Untreated and treated soils were classified, and tested for swelling pressure, swelling potential, unconfined compressive strength, and hydraulic conductivity (k). Relative to untreated soil, polymer treatment was less effective at reducing the swelling potential (70% reduction) and increasing unconfined compressive strength (46 kPa increase) of a highly expansive soil relative to lime (100% reduction, 1260 kPa increase) and fly ash (97% swelling potential reduction, 380 kPa increase in UCS). However, lime and fly ash treatments resulted in a 52,000- and 1,100-times increases in k, respectively, while polymer resulted in only a 2-times increase in k relative to the untreated soil (k = 2.9 × 10-11 m/s). Polymer was also shown to be effective at reducing k to below 1.9 × 10-12 m/s when used as a spray-on coating. The results of this study illustrate that polymers reduce swell in expansive soils by mechanisms that are different than lime and fly ash.