Compaction quality control of earth fills using dynamic cone penetrometer

Quality control for compaction of earth fills is commonly performed by measuring the in situ density using the sand cone method. In situ density measurements from sand cone testing are highly operator-dependent; in addition, the test procedure is tedious and time-consuming. In this study, a dynamic cone penetrometer (DCP) was used to perform quality control (QC) of earthworks by measuring penetration resistance in compacted soil. DCP tests were performed on three test pads specially constructed using different soil types - clayey sand with gravel, clayey sand, and silty sand. The test results were expressed in terms of a dynamic penetration index (DPI), defined as the depth of penetration of the cone per hammer blow. Correlations are developed between DPI and compacted density for the three soil types considered. In order to meet the criterion of compacted density equal to or greater than 98% of the maximum density from a laboratory standard Proctor test, DPI values are found to range from 5 to 8 mm/blow, corresponding to 250 mm penetration of cone on tested soil types. The effect of the fall height of the hammer on the measured DPI is also studied by performing DCP tests for two fall heights, 575 and 450 mm. DPI values are found to increase by 11-26% when the height of the fall increases from 450 to 575 mm, for the highest energy level considered in the study. It is also found that DPI is very sensitive to the moisture content and in situ density of compacted layers. The DCP device provided quick test results and was simple to operate on any subgrade layer; hence, the frequency of QC tests can be increased, leading to an improvement in the overall quality of compaction of earthworks.