<p>Soil shrinkage characteristics are critical in engineering projects due to its change in volume during drying. Factors such as soil composition, specimen shape, and additives may influence the anisotropic shrinkage behaviour of soil specimens. Due to these variations, a thorough understanding of the anisotropic shrinkage behavior becomes essential for ensuring the long-term stability of geotechnical and geoenvironmental structures, such as landfill cover. Therefore, the current study examines the effects of specimen shape and bamboo biochar (BB) amendments on the shrinkage behavior of CL and SM soils. The specimens were prepared in cylindrical and cuboidal shapes with varying (0, 1, 2, 3.5 and 5%) BB contents and subjected to air drying. The changes in specimen dimensions (vertical, lateral and longitudinal) and weights were meticulously measured at regular intervals using a digital Vernier caliper and electronic balance. The 5% BB addition reduced volumetric shrinkage by 9.15% in cuboidal and 11.12% in cylindrical specimens for CL soil, and by 7.24 and 8.32%, respectively, for SM soil. This shows that cylindrical specimens experienced greater volumetric shrinkage as compared to cuboidal specimens, indicating an anisotropic nature of soil shrinkage. Furthermore, the cylindrical specimens exhibited higher bulk and dry density as compared to the cuboidal specimens. The shrinkage characteristics curves showed lower void ratio for cylindrical specimens in the zero shrinkage zone than the cuboidal specimens due to better particle packing and uniform stress distribution. The void ratio was noted to be increased with biochar increment, and the maximum increase was obtained in cuboidal specimens at 5% BB content. Thus, the results demonstrate that both specimen shapes and BB amendment significantly influence the anisotropic shrinkage behavior of CL and SM soils.</p>