SHEAR BEHAVIOR AT THE SOIL–CONCRETE INTERFACE OF AGAROSE-TREATED SAND

Abstract

Soil–structure interface behavior governs shear transfer mechanisms in many geotechnical systems. This study investigates the soil–concrete interface shear behavior of agarose-treated sand considering the combined effects of fines content and curing time. Direct shear interface tests were conducted under normal stresses of approximately 10.4, 20.8, and 31.2 kPa to evaluate peak shear strength, interface adhesion, interface friction angle (δ), and interface friction ratio (δ/φ). The results show that curing time significantly enhances interface shear resistance due to progressive development of biopolymer bonding with substantial strength gain occurring during the first 14 days of curing and the most pronounced increase observed within the first 7 days. Fines content exhibits a non-monotonic influence where moderate fines (5–15%) improve interface strength through enhanced packing and bonding while excessive fines (35%) reduce frictional contribution despite increased adhesion. Increasing agarose content enhances adhesion but may reduce frictional resistance due to particle coating effects. A key finding is the identification of a transition in interface behavior from friction-dominated to adhesion-controlled mechanisms effectively characterized by the interface friction ratio (δ/φ). These findings provide practical insight for the design of soil–structure interfaces particularly in foundation systems and support the use of biopolymer stabilization as a sustainable ground improvement method.