Which test directly measures the shear strength of soil in a simple and common manner?

The Direct Shear Test is specifically designed to measure the shear strength of soil in a straightforward and effective manner. This test involves applying a horizontal shear force to a soil sample confined between two halves of a shear box. The sample is subjected to normal loads, allowing the determination of shear strength as the applied shear force reaches the point of failure. This set-up allows for direct observation of the failure surface and provides significant insight into the soil's shear parameters, such as cohesion and friction angle, which are crucial for understanding the stability of soil under various loading conditions.

The Unconfined Compression Test does measure the compressive strength of a soil sample but does not directly assess shear strength. Similarly, the Consolidation Test focuses on response to vertical loading and the time-dependent settlement of saturated soil, rather than shear strength. The California Bearing Ratio Test evaluates the strength of subgrade soil for road design and does not measure shear strength directly but rather provides an empirical measure of a soil’s support capability under load. Therefore, the Direct Shear Test remains the most direct and applicable method for evaluating shear strength in various civil engineering contexts.