<p>Sand-bentonite mixtures (SBMs) have been widely used as hydraulic barrier materials; however, their low tensile resistance limits their suitability for intermediate landfill cover applications. This study presents a novel experimental methodology for evaluating the tensile behaviour of biopolymer-modified SBMs under uniaxial tension. A custom-designed direct tensile test setup was developed to characterise the tensile response of dumbbell-shaped soil specimens under uniaxial loading. Digital image correlation was integrated with the test setup to capture displacements at multiple predefined gauge lengths, and a simple yet versatile strain extrapolation procedure was proposed to determine the tensile strain at failure within the localised failure region. SBMs containing different bentonite fractions were treated with varying dosages of guar gum and xanthan gum to evaluate the influence of biopolymer modification on tensile behaviour. The results showed that the tensile strength increased with sand content up to 65% owing to enhanced interparticle friction and mechanical interlocking, beyond which it decreased due to reduced matrix cohesion. Biopolymer addition significantly enhanced both tensile strength and tensile strain. At 2% dosage, guar gum and xanthan gum increased the tensile strength of SBM by up to 94% and 137%, and the tensile strain at failure by 174% and 156%, respectively. Based on mechanisms reported in previous studies, the improved tensile behaviour is attributed to the formation of interconnected biopolymer networks, which enhance particle bonding and interlocking. Comparative analyses between the direct tensile and split tensile strength tests showed excellent agreement (<i>R</i>² = 0.989), validating the reliability of the developed test setup.</p>