Dynamic analysis of dynamic cone penetration test for subgrade compaction assessment

In practice, soil compaction quality assessment 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. Most DOTs typically require that the in-place dry unit weight for compacted soil be over 95% of the laboratory maximum dry unit weight obtained from Standard Proctor compaction test results. Nuclear gauges may be used to determine the in-place dry unit weight, however, they are potentially hazardous and require safety precautions. Other tests, such as the Dynamic Cone Penetration Test (DCPT), can be used for soil compaction quality assessment. The main objectives of this research were to develop criteria for soil compaction quality assessment for different soils based on DCPT results. A number of DCPTs were performed on Indiana road sites, in a test pit, and in the soil test chamber at Purdue University. Since soil compaction varies spatially, a statistical approach was applied to the test measurements in the development of the criteria for soil compaction quality control. Based on the results of DCP tests performed on INDOT road sites and the requirement that the in-place dry unit weight of the fill material be over 95% of the laboratory maximum dry unit weight obtained from standard Proctor compaction tests, correlations that can be used to obtain the minimum required DCP blow count (NDCP)req were proposed for soils belonging to three groups of the AASHTO (American Association of State Highway and Transportation Officials) soil classification system. A series of tests were performed in the laboratory to determine the matric suction in compacted silty clays for different compaction conditions. Based on the results of the tests performed in this research and those available in the literature, a method was proposed that can be used to estimate the shear strength and small-strain shear modulus of compacted silty clays. A dynamic analysis, accounting for the increase in shear strength and stiffness due to matric suction in compacted soils, was used to predict DCPT results, which were then compared with DCP blow counts measured in the field. The results of this study are very useful for facilitating the use of DCPT as a tool for compaction quality control