In drained Direct Shear (DS) test, how to find soil stress path to reach failure(i.e. CSL)?

In a drained Direct Shear (DS) test, the soil stress path to reach failure (i.e., Critical State Line, CSL) can be determined through the following steps:

1. Preparation of the Sample: The soil sample is prepared and placed in the shear box apparatus. The sample is consolidated under a normal stress.

2. Application of Shear Stress: The shear stress is applied gradually while maintaining the normal stress constant. The drainage valves are kept open to ensure that the test is drained, i.e., no pore water pressure is developed.

3. Measurement of Shear and Normal Stresses: The shear stress and normal stress are measured at regular intervals. The shear stress is increased until the soil sample fails.

4. Plotting the Stress Path: The stress path is plotted on a graph with the vertical axis representing the shear stress and the horizontal axis representing the normal stress. The path starts from the initial point (the normal stress at the start of the test) and ends at the failure point (the shear stress at failure).

5. Determination of the CSL: The Critical State Line (CSL) is the line on the stress path graph that represents the state at which the soil is about to fail. It is determined by drawing a line through the points of peak shear stress for a series of tests conducted at different normal stresses.

Remember, the exact procedure and calculations may vary depending on the specific conditions of your test and the type of soil being tested. Always refer to the relevant soil mechanics literature or guidelines for the most accurate methods.