Comparison of Density-Based and Modulus-Based In Situ Tests for Earthwork Quality Control

Abstract

A series of density-based and modulus-based quality control tests were performed to evaluate and compare the performance of a number of in situ testing methods for control of soil compaction. This paper highlights the results from the study that focus on three in situ testing tools for compaction control: the lightweight deflectometer (LWD), the dynamic cone penetrometer (DCP), and the nuclear density gauge (NDG). In situ tests conducted using these tools were performed during construction of an embankment built with a coarse-grained soil in a series of lifts. Comparison of the in situ test results shows that that there is a notable variability in measured soil properties for each of the testing methods that were performed. All three in situ tests showed an increasing trend in the measured properties from pass-to-pass of the compactor, which indicates the suitability of these tests for proper control of the compaction process. However, the soil moduli measured by the LWD and DCP correlated poorly to the NDG dry unit weights. This lack of agreement was likely caused by a variety of factors, including variations in the tested soil volume between these devices and variations in the local moisture content and matric suction conditions. The effect of soil moisture content was shown to be particularly significant when interpreting the results of LWD and DCP tests, and the usefulness of multivariate regression analyses was explored for including this effect.