When is a larger apparatus required during a sand cone test?

In the context of performing a sand cone test, larger apparatus is necessary when dealing with particles larger than 1.5 inches. This is because the test is designed to determine the in-place density of soil, and larger particles can impact the accuracy and effectiveness of the measurement if the apparatus is not appropriately sized. The equipment used must accommodate the size of the soil particles being tested to allow for an accurate assessment of density without interference from larger aggregates.

When particles exceed this size, standard equipment may become inefficient for measuring the volume displacement accurately, resulting in unreliable data. Therefore, using a larger apparatus ensures that the test can accommodate the size of the particles and accurately reflect the soil's condition and characteristics.

The other options either indicate sizes that do not necessitate the use of larger equipment or incorrectly suggest that size does not matter at all, which could compromise the test results.