At head of title: National Cooperative Highway Research Program.

"Resilient modulus indicates the stiffness of a soil under controlled confinement conditions and repeated loading. The test is intended to simulate the stress conditions that occur in the base and subgrade of a pavement system. Resilient modulus has been adopted by the U.S. federal highway administration as the primary performance parameter for pavement design. We thank those who prepared these papers, the reviewers who provided anonymous peer reviews, and those who participated in the symposium. We hope this STP encourages more work to improve the testing standard and the value of the Resilient Modulus test."

Field and laboratory testing programs were conducted to develop models that predict the resilient modulus of subgrade soils from the test results of DCP, CIMCPT, FWD, Dynaflect, and soil properties. The field testing program included DCP, CIMCPT, FWD, and Dynaflect testing, whereas the laboratory program included repeated load triaxial resilient modulus tests and physical properties and compaction tests. Nine overlay rehabilitation pavement projects in Louisiana were selected. A total of four soil types (A-4, A-6, A-7-5, and A-7-6) were considered at different moisture-dry unit weight levels. The results of the laboratory and field testing programs were analyzed and critically evaluated. A comprehensive statistical analysis was conducted on the collected data. The results showed a good agreement between the predicted and measured resilient modulus from the various field test methods considered. The DCP and CIMCPT models were enhanced when the soil moisture content and dry unit weight were incorporated. The results also showed that, among all back calculated FWD moduli, those back calculated using ELMOD 5.1.69 software had the best correlation with the measured Mr. Finally, the Mr values estimated using the approach currently adopted by the LADOTD were found to correlate poorly with the measured Mr values.

This report contains 27 papers that serve as a testament to the state-of-the-art of civil engineering at the outset of the 21st century, as well as to commemorate the ASCE's Sesquicentennial. Written by the leading practitioners, educators, and researchers of civil engineering, each of these peer-reviewed papers explores a particular aspect of civil engineering knowledge and practice. Each paper explores the development of a particular civil engineering specialty, including milestones and future barriers, constraints, and opportunities. The papers celebrate the history, heritage, and accomplishments of the profession in all facets of practice, including construction facilities, special structures, engineering mechanics, surveying and mapping, irrigation and water quality, forensics, computing, materials, geotechnical engineering, hydraulic engineering, and transportation engineering. While each paper is unique, collectively they provide a snapshot of the profession while offering thoughtful predictions of likely developments in the years to come. Together the papers illuminate the mounting complexity facing civil engineering stemming from rapid growth in scientific knowledge, technological development, and human populations, especially in the last 50 years. An overarching theme is the need for systems-level approaches and consideration from undergraduate education through advanced engineering materials, processes, technologies, and design methods and tools. These papers speak to the need for civil engineers of all specialties to recognize and embrace the growing interconnectedness of the global infrastructure, economy, society, and the need to work for more sustainable, life-cycle-oriented solutions. While embracing the past and the present, the papers collected here clearly have an eye on the future needs of ASCE and the civil engineering profession.

This synthesis report will be of interest to pavement and geotechnical design and research engineers, geologists and engineering geologists, and related laboratory personnel. It describes the current practice for measuring in situ mechanical properties of pavement subgrade soils. The tests conducted to measure the mechanical properties of soil strength and stiffness are the primary topics, and these are discussed in the context of design procedures, factors affecting mechanical properties, and the variability of measurements. Information for the synthesis was collected by surveying U.S., Canadian, and selected European transportation agencies and by conducting a literature search. This TRB report provides information on existing and emerging technologies for static and dynamic, and destructive and nondestructive testing for measuring in situ mechanical properties of pavement subgrade soils. Correlations between in situ and laboratory tests are presented. The effects of existing layers on the measurement of subgrade properties, and soil spatial and seasonal variability are discussed. Most importantly, the use of soil properties in pavement design and evaluation are explained. New applications or improvements to existing test methods to support the use of mechanistic/stochastic-based pavement design procedures are also explained.