Use of Dynamic Cone Penetration and Clegg Hammer Tests for Quality Control of Roadway Compaction and Construction

Abstract

Soil compaction quality control presently relies on the determination of the in-place compacted dry unit weight, which is then compared with the maximum dry unit weight obtained from a laboratory compaction test. The Indiana Department of Transportation (INDOT) requires that the in-place dry unit weight for compacted soil be over 95% of the laboratory maximum dry unit weight. In order to determine the in-place dry unit weight, INDOT engineers generally use nuclear gauges, which are hazardous and also costly because of the required safety precautions. Thus, several alternative tests such as the Dynamic Cone Penetration Test (DCPT) and the Clegg Hammer Test (CHT) were introduced as testing tools for soil compaction quality control. However, no reliable correlations are available in the literature to employ these tests for soil compaction quality control. The main objectives of this research were to evaluate the use of the DCPT and the CHT results to develop criteria for soil compaction quality control. A number of DCPTs and CHTs was performed on Indiana road sites, in a test pit, and in the soil test chamber at Purdue University. Since soil compaction varies from place to place, a statistical approach was applied to account for the compaction variability in the development of the criteria for soil compaction quality control. Based on the DCP tests performed on several INDOT road sites, as well as in the test pit at Purdue University, and the requirement that the in-place dry unit weight of the fill material be over 95% of the laboratory maximum dry unit weight, minimum required DCP blow counts (NDCP)req were proposed for soils belonging to three groups of the AASHTO (American Association of State Highway and Transportation Officials) soil classification system. For the DCPT, the minimum required blow count for 0-to-12 inch penetration, (NDCP)|0~12” associated with an RC of 95% for A-3 soil varied from 7 to 10; it is a function of the coefficient of uniformity. For A-1 soil and A-2 soils except those containing gravel, the (NDCP)|0~12” was a function of the optimum moisture content. For silty clays, the minimum required blow counts, (NDCP)|0~6” and (NDCP)|6~12” were a function of the plasticity index and the soil percentage passing the #40 sieve. Since the relationship of Clegg Impact Value (CIV) with relative compaction exhibited considerable variability, no criterion for CHT was proposed. Dynamic analyses hold promise in forming the basis for interpretation of the DCPT and CHT results since predictions of the penetration process (DCPT) and accelerations (CHT) for sand under controlled conditions were very reasonable.