What specification is required for sand used in the sand cone method?

In the sand cone method, sand needs to have specific characteristics to ensure accurate results when determining the in-place density of soil. The requirement that sand be uniformly graded and free of fines is essential for several reasons.

Firstly, a uniformly graded sand reduces the variability in measurements by providing consistent particle sizes. This uniformity allows for more predictable behavior when the sand is poured into the voids left by the excavated soil. If the sand contained varying particle sizes or was graded poorly, it might not fill the voids consistently, leading to inaccurate density calculations.

Secondly, the absence of fines (particles smaller than 0.075 mm) is crucial because fines can retain water and lead to packing differences that add uncertainty to the measurements. Fines can also fill voids in the sand and disrupt the intended density measurements by altering the packing characteristics of the sand used in the test.

Thus, using sand that is uniformly graded and free of fines helps minimize variables that could potentially skew the results, ensuring a more reliable and repeatable assessment of the soil density being tested.