The first stage of mineral extraction in opencast mines involves the removal of overburden, which is dumped as multi-bench dump slopes. The most significant factor in determining the dump’s slope stability is shear strength. The shear strength parameters, cohesion, and angle of internal friction contribute to the material’s shear strength. These parameters can be obtained from the shear stress versus normal stress plot. Usually, the most common method used in laboratories to determine the peak shear stress is the direct shear test. In the present study, an in-situ direct shear apparatus is fabricated with two varying shear box sizes, large scale (60 cm × 60 cm × 30 cm) and small scale (30 cm × 30 cm × 30 cm), and tested with a normal stress of 150 kPa over dumps of iron ore mines, Odisha, India. The same material is collected and examined in a laboratory using the conventional direct shear apparatus with a shear box of 30 cm × 30 cm × 30 cm at dry and 8% moisture content at a normal stress of 150 kPa. In all conditions, the peak shear stress is compared. It is found that at laboratory, the peak shear stress is 194 kPa and 185 kPa for dry and at 8% moisture content, respectively. In the in-situ condition, the peak shear stress is 193 kPa and 245 kPa for the small and large-scale direct shear tests, respectively. The higher peak shear stress can be due to the presence of more boulders in the large-scale in-situ direct shear test.