A SIMPLIFIED FRAMEWORK FOR EVALUATING UNSATURATED SOIL SHEAR STRENGTH USING FILTER PAPER METHOD

Soil in an unsaturated state governs the performance of embankments, foundations, pavements, and slopes, where changes in suction significantly influence strength and stability. Conventional suction-controlled shear tests are expensive, time-consuming, and impractical for routine use. This study proposes a simplified methodology that integrates the Filter Paper Method with direct shear testing to estimate matric suction and corresponding shear strength under constant water content conditions. The Soil Water Characteristic Curve was derived using Whatman Grade-42 filter paper and fitted with van Genuchten and Fredlund-Xing models through non-linear regression. Shear tests revealed that shear strength parameters increase non-linearly with matric suction, confirming classical unsaturated soil behavior. Experimental results were compared with semi-empirical predictive models, showing good agreement at low suctions and slight overestimation at high suctions, corrected by calibrating fitting parameters. The approach offers a cost-effective and practical alternative to complex suction-controlled methods, making it suitable for geotechnical design and soil characterization in partially saturated conditions.