Pedologic Based Subgrade Characterization for Low-Volume Pavement Design

174 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1993.Subgrade soils play an integral part in pavement performance. The nature and properties of subgrade soils must be considered in structural pavement design. Many highway agencies, particularly agencies that administer "local" or low-volume pavements, do not have the resources to conduct comprehensive subgrade evaluation programs. This research investigates the use of soil index properties, obtained from County Soil Surveys published by the Soil Conservation Service, to estimate the subgrade resilient modulus for structural pavement design. Such a procedure allows highway agencies to evaluate subgrade soils in the absence of comprehensive subgrade characterization programs.Soils and nondestructive pavement testing data from five counties in Illinois are used in the research. A pedologic based classification system is used to consider subgrade soils. Soil property information is given in County Soil Surveys based on the soil's pedologic classification. Procedures are developed to account for the effects of soil horizonation on estimates of subgrade resilient modulus. Soil property based estimates of subgrade modulus are compared to modulus estimates backcalculated from pavement surface deflections. These comparisons are used to develop methodologies for adjusting pedologic based modulus estimates to "design" values for use in pavement design. A sensitivity analysis is performed on current flexible pavement design procedures to determine the effect of subgrade modulus on required pavement thickness. The results of the sensitivity analyses are used to assess the feasibility of using pedologic based subgrade characterization methodologies in routine pavement design.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD