What sieve should samples for liquid limit and plastic limit tests pass through?

The correct choice for the sieve that samples for liquid limit and plastic limit tests should pass through is No. 40, which has a sieve opening of 0.425 mm. This specification is important because the test procedures for determining the plasticity characteristics of soils require a consistent and specified grain size to ensure reliable measurements and reproducible results.

By using a sieve that retains particles larger than 0.425 mm, the results might be skewed due to the presence of larger particles that can affect the moisture retention properties of the soil. The plastic limit and liquid limit tests are designed to assess the transition between the plastic and the liquid states of soil, which is critical for understanding how various soils behave under different moisture conditions. Therefore, the use of the No. 40 sieve ensures that the material is uniform and consistent, leading to accurate and valid test outcomes.

In summary, adhering to the specified size of the particles helps maintain the integrity of the test results, which is why No. 40 is specified for these particular tests.