Moisture-Strength-Constructability Guidelines for Subgrade Foundation Soils Found in Indiana

摘要

Soil moisture is an important indicator of constructability in the field. Construction activities become difficult when the soil moisture content is excessive, especially in fine-grained soils. Change orders caused by excessive soil moisture during construction projects drive up construction costs for INDOT and cause unexpected delays. To alleviate these problems and minimize change order costs associated with having unexpectedly high soil moisture conditions at the time of construction, a methodology was developed to allow INDOT engineers to estimate in situ soil moisture conditions early in the design phases of projects. The soil moisture prediction methodology is based on results from soil moisture flow simulations carried out using the HYDRUS-1D software. The soil moisture flow simulations in HYDRUS-1D required i) weather data, ii) groundwater table data and iii) in situ soil hydraulic (saturated and unsaturated) and index property data. These data were collected for all the counties in Indiana from five different sources: i) Indiana Department of Transportation (INDOT), ii) Indiana Geological Survey (IGS), iii) United States Department of Agriculture’s (USDA’s) Soil Survey Geographic (SSURGO), iv) the Department of Natural Resources (DNR) and v) Indiana State Climate Office (Iclimate). The results obtained from initial soil moisture flow simulations were first validated using field measurements from six IGS test sites located in Indiana where soil property data and continuous in situ soil moisture measurements at multiple depths were available for up to 3 years (2011-2014). Good agreement was observed between moisture content measurements and predictions. After validation of the developed moisture prediction methodology, ten-year moisture content simulations using HYDRUS 1D were performed for typical profiles in each county in Indiana using as input weather data from the iclimate database, groundwater data from DNR database and soil properties from IGS, INDOT and the SSURGO databases. Yearly results from these ten-year soil moisture flow simulations were then overlapped to ascertain how the profiles of the in situ soil moisture content within the depth of interest varied monthly within this period of time in each county. Using the results of these simulations for typical soil profile(s) for each county, a constructability criteria was developed that is based on determining how the in situ soil moisture content deviates from the optimum soil moisture content obtained from standard Proctor compaction tests (these are often performed by INDOT in routine projects). Recommendations are made for in situ soil moisture constructability assessment that can be implemented by INDOT in pilot projects and further refined as needed.