Assessing subgrade strength using an instrumented dynamic cone penetrometer |
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Authors: | Jong-Sub Lee Sang Yeob Kim Won-Taek Hong Yong-Hoon Byun |
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Affiliation: | 1. School of Civil, Environmental and Architectural Engineering, Korea University, 145, Anam-ro, Seongbuk-gu, Seoul 02841, South Korea;2. School of Agricultural Civil & Bio-Industrial Engineering, Kyungpook National University, 80 Daehak-ro, Buk-gu, Daegu 41566, South Korea;3. Institute of Agricultural Science & Technology, Kyungpook National University, 80 Daehak-ro, Buk-gu, Daegu 41566, South Korea |
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Abstract: | Subgrade strength is an important aspect to be considered when designing unsurfaced roads and working platforms for pavement structures. Furthermore, dynamic cone penetration tests are used to characterize the subgrade strength. However, the results of dynamic cone penetration tests, including the penetration depth per blow, can be affected by transferred energy and the verticality of the cone penetrometer. The objective of this paper is to characterize the subgrade strength using an instrumented dynamic cone penetrometer (DCP). The instrumented DCP includes a load cell and an accelerometer, located on the cone tip, and measures the dynamic responses of force and velocity over elapsed time. Weathered soil is compacted with three different dry unit weights in a square-shaped container for lab-scale dynamic cone penetration tests. Using instrumented and standard DCPs, several dynamic cone penetration tests are performed, and the dynamic cone penetration index (DCPI) is recorded along the depth profiles. Based on the dynamic responses at the cone tip of the instrumented DCP and the principles of energy conservation, the dynamic cone resistance is suggested as a new strength index. The experimental results show that the dynamic cone resistance increases with the depth of the instrumented DCP, providing a reliable subgrade strength profile in the soil. In addition, the correlation between the DCPI obtained from the instrumented DCP and the dynamic cone resistance suggests that the dynamic cone resistance is more sensitive than the DCPI for stiff soil. Based on the correlation values of the dynamic cone resistance obtained from the instrumented DCP, the internal friction angle and California bearing ratio values can be estimated with a high degree of reliability. This study demonstrates that use of the instrumented DCP may be a promising in situ testing method for the reliable characterization of subgrade strength. |
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Keywords: | Corresponding author at: School of Agricultural Civil & Bio-Industrial Engineering, Kyungpook National University, 80 Daehak-ro, Buk-gu, Daegu 41566, South Korea. CBR DCP Dynamic cone resistance Instrumented DCP Subgrade strength |
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