Civil Engineering ETDs

Publication Date

7-2-2012

Abstract

Resilient modulus (Mr) is a laboratory determined parameter, where a cylindrical specimen is subjected to dynamic axial stresses under confining stresses, while axial deformations are measured. By definition Mr is the ratio of the peak axial stress to the corresponding recoverable axial strain. Currently, there are two accepted laboratory testing protocols for determining Mr, namely AASHTO T 307 and NCHRP 1-28A. These two standards differ from one another in ways that are known to affect Mr, namely in location of load and deformation transducers. One focus of this study is the determination of resilient modulus for an A-6 subgrade soil at varying moisture conditions (± 2-3% relative to optimum). Specimens of 2.8 inch and 4 inch diameters are reconstituted using modified proctor compaction. Resilient modulus values are determined using internal and external deformation measurement techniques. Comparative analyses are performed, and based on the results, a multivariate regression equation has been developed which estimates resilient modulus as a function of gravimetric moisture content and maximum cyclic axial stress for this soil. A second focus of this study is aimed at addressing the potential for reducing the time and complexity required to determine Mr of a cohesive fine-grained subgrade soil. An experimental study is conducted, where unconfined dynamic testing is performed. In this study, load pulse forms and durations differ from standardized tests. Test sequence durations are also reduced. Resilient Modulus values determined from this alternate testing experiment match well with values determined from the standardized test results. Alternate and Standard Mr values are within 15% of each other for 35 of 40 test comparisons, with an average magnitude difference of 9%.

Keywords

Shear strength of soils--Measurement, Pavements--New Mexico--Subgrades--Testing, Soils--New Mexico--Testing, Soil moisture--Measurement.

Document Type

Thesis

Language

English

Degree Name

Civil Engineering

Level of Degree

Masters

Department Name

Civil Engineering

First Committee Member (Chair)

Taha, Mahmoud

Second Committee Member

Ng, Tang-Tat

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