Effect of natural fiber reinforcement on strength response of alkali activated binder treated expansive soil: Experimental investigation and reliability analysis

Expansive soil possesses high swelling-shrinkage potential owing to moisture instability, resulting in loss of geomechanical strength. In this study, an effort is made to improve the shear strength properties of expansive soil by combined effects of alkali activated binder (AAB) with chemically treated hemp (THF) and coir fiber (TCF). AAB is produced by the reaction between alkaline binder of sodium silicate and sodium hydroxide in aluminosilicate precursors of Class-F fly ash and slag at various proportions. The effect of varying dosages of THF, TCF, and slag/fly ash ratio in the AAB soil mixture on compressive shear, tensile, and flexural strength is evaluated through a series of geotechnical characterization tests. It is observed that THF-AAB-soil shows higher interfacial bonding with strong interlocking density and tensile cracking resistance compared to TCF. Furthermore, in order to effectively consider the uncertainties associated with the design of subgrade for foundations, reliability indices against unconfined compressive strength and split tensile strength are predicted using Monte Carlo simulation through a non-linear regression model developed from experimental results. The study shows that the optimum dosages of fly ash-slag and fiber reinforcement are essential factors for controlling the swelling of expansive soil as well as improving its tensile strength.