WTI

Measurement and Evaluation of Subgrade Soil Parameters: Phase 1 - Synthesis of Literature

Primary Investigator Contact Information

External Project Contact(s)

Report(s)

1. Measurement and Evaluation of Subgrade Soil Parameters: Phase I – Synthesis of Literature
   1. Dr. Robert Mokwa, P.E. and Michelle Akin
   2. 4W2409_Final_Report.pdf

Project Objective

The objective of this project is to conduct a comprehensive literature review of the state of the practice pertaining to testing and evaluation of subgrade soils.

Project Abstract

A critical component of the pavement design involves a thorough and reliable characterization of the subgrade; i.e., the foundation of the pavement riding surface. A number of laboratory and insitu methods are available to characterize the strength and stiffness of subgrade soils. The Montana Department of Transportation (MDT) uses the Resistance value (R-value) testing method, which can yield unsatisfactory or inconsistent results with some of the soils present in the state. MDT is interested in exploring alternative investigatory techniques that are more suited to the state’s soil conditions. AASHTO is in the process of adopting a new pavement design method known as the mechanistic-empirical pavement design guide (MEPDG). Upon implementation, this mechanically based design approach will be used by all state highway agencies for layer thickness calculations. A key material property to be used in design will be the resilient modulus (Mr) value, which either can be obtained from laboratory testing or can be backcalculated from measured in-situ deflection data. The determination of a representative Mr value for a given subgrade, considering seasonal variations and testing intricacies, is not an easy or straightforward task. There is no currently recognized or unified general approach for using the correlations. Most are site or region specific, and often do not account for important variations in soil type and consistency. Adding to the confusion are the various modifications, adjustments, and simplifications that have been proposed as improvements to the laboratory resilient modulus test method. There is a considerable amount of published information, both historic and recent, that needs to be synthesized before the Department may be ready to proceed with an efficient, useful, and productive testing program. This project will assist MDT in the selection of appropriate and representative subgrade design parameters for use in mechanistic-based pavement design procedures. The first phase of the study will focus on a comprehensive study and synthesis of available technical literature. The second phase of work (if deemed necessary) will focus on laboratory and field testing of selected subgrade soils from Montana sites.

Task Descriptions

1. Survey State Department of Transportation
   1. To evaluate the current state-of-the-practice, researchers will analyze the information collected during the literature review and develop a series of succinct survey questions that can be submitted to appropriate state department of transportation personnel across the U.S.
2. Report and Presentation
   1. The outcome of this evaluation will include a written compilation of succinct, timely, and practical information on subgrade testing methods. The research report will focus on methods and correlations that can be used in the mechanistic design approach for estimating soil modulus parameters.
3. Literature Review
   1. Researchers will conduct a literature review to collect and synthesize applicable published information related to subgrade soil testing and the use of test results to develop parameters for use in mechanistic pavement design methods.
4. Project Oversight
   1. This task includes project management activities, including budget and schedule, administrative tasks, and communications with MDT.

Milestones, Dates, Schedule

Student Involvement

False

Relationship to Other Research Projects

False

Technology Transfer Activities

False

Transportation Research Board Keywords

Subgrade soil, mechanistic-empirical pavement design guide, resistance testing, resilient modulus (Mr) value

Partners

Montana Department of Transportation