Which field test is commonly used to estimate in situ soil density?

The sand cone test is a standard field method used to estimate the in situ soil density. This test involves digging a small hole in the ground, collecting the displaced soil to measure its volume, and then filling the hole with dry sand from a calibrated container. By determining the volume of the hole and the weight of the sand required to fill it, engineers can calculate the density of the soil in place.

This method is especially reliable because it directly measures the soil in its existing state, capturing the effects of natural compaction and moisture content. As a result, the sand cone test provides an accurate representation of the soil's density at the specific location, which is essential for various geotechnical assessments and construction quality control.

Other options like the plasticity index test and Proctor compaction test are more focused on laboratory evaluations of soil properties and compaction characteristics rather than in situ density measurements. The California bearing ratio test assesses the strength of the soil but does not provide direct information about the density of the soil in the field.