Development of Comprehensive Subgrade Deflection Acceptance Criteria - Phase 3 Report

This report has presented the findings of Phase III of research conducted to aid in the development of subgrade deflection acceptance criteria for WisDOT. The reconfigured rolling wheel deflectomter (RWD), portable truck-mounted deflection measurement systems, and automated dynamic cone penetrometer (DCP) were utilized on subgrade construction projects throughout the 2000 construction season. Laboratory analysis of soil properties, including Proctor, CBR and unconfined compression tests, were also conducted. The research findings have validated the concept of using deflection testing results to identify areas of poor in-place stability within constructed subgrades. It is recommended that pilot implementations of deflection acceptance testing be conducted in conjunction with subgrade penetration testing and moisture controls until more data has been collected, especially in moisture sensitive fine grained soil types. The use of deflection acceptance testing, in conjunction with in-situ penetration tests, should provide the data necessary to determine if the in-place support capacity for a given soil is sufficient to provide a stable construction platform for subsequent paving operations. However, it is important to note that both the RWD and DCP test results are related to the moisture-density conditions at the time of testing. Soils that show acceptable results (i.e., low deflections) may subsequently weaken due to changes in moisture content, freezing/thawing, etc. In instances where subgrade acceptance is well in advance of base course application, subgrade moisture changes may result in decreased soil support