Flow through and Volume Change Behavior of a Compacted Expansive Soil Amended with Natural Biopolymers

Abstract

Natural biopolymers offer a sustainable alternative for improving soil behavior due to their inert nature, small dosage requirement, and applicability under ambient temperatures. This research evaluates the efficacy of natural biopolymers for ameliorating an expansive soil by using a 0.5% dosage of cationic chitosan, charge-neutral guar gum, and anionic xanthan gum during compaction. The results of laboratory investigations indicate that the flow through and volume change properties of the expansive soil were affected variably. The dual porosity, characterized by low air entry due to inter-aggregate pores (AEV1 of 4 kPa) and high air entry due to the clay matrix (AEV2 of 200 kPa) of the soil, was healed using chitosan and guar gum (AEV of 200 kPa) but was enhanced by the xanthan gum (AEV1 of 100 kPa and AEV2 of 200 kPa). The s-shaped swell–shrink path of the soil comprised structural (e from 1.23 to 1.11), normal (e from 1.11 to 0.6), and residual stages (e ranged from 0.6–0.43). This shape was converted into a j-shaped path through amendment using chitosan and guar gum, showing no structural volume change, with e from about 1.25 to 0.5, but was reverted to a more pronounced form by xanthan gum, with e from 1.5 to 1.32, 1.32 to 0.49, and 0.49 to 0.34 in the three stages, respectively. The consolidation behavior of the soil was largely unaffected by the addition of biopolymers such that the saturated hydraulic conductivity decreased from 10−9 m/s to 10−12 m/s over a void ratio decrease from 1.1 to 0.6. At a seating stress of 5 kPa, the swelling potential (7.8%) of the soil slightly decreased to 6.9% due to the addition of chitosan but increased to 9.4% and 12.2% with guar gum and xanthan gum, respectively. The use of chitosan and guar gum will allow the compaction of the investigated expansive soil on the dry side of optimum.