This paper summarizes published investigations concerning the deviations from a standard of in-place density measurements of cohesionless soils. The effect of moisture content of the soil on in-place density measurements also was investigated. Discussions about methods of calibrating measuring devices and numerical values for test results are omitted. Some results are shown graphically. It is hoped the reader will be stimulated to consult the primary references if interested in more detail.
When a soil is physically sampled during the process of conducting an in-place density measurement, a shearing action of the soil is unavoidable. Cohesionless soils are sensitive to volume change during shear; dense sands tend to expand and increase in volume; loose sands tend to contract and decrease in volume. Thus, in general, measured in-place density of dense sand is found to be relatively low and for loose sand, it is found to be relatively high compared to control values; the opposite relationship was found for cohesionless coarse grain base course material. Any moisture present in such soils provides some cohesion and in turn alters the error involved in a density measurement.
A plot of measured values versus control values provides a means for adjusting the value measured in the field for a specific soil more closely toward the true (standard) value. All density measuring methods investigated require such correction plots. Moreover, specific plots for a given sand generally are not applicable to other sands of even slightly different character or water content. Each method requires a separate plot for each soil and each soil moisture condition.