Analysis of Lightweight Deflectometer Test Based on In Situ Stress and Strain Response
Publication: Journal of Geotechnical and Geoenvironmental Engineering
Volume 135, Issue 2
Abstract
The lightweight deflectometer (LWD) is gaining acceptance and popularity as an in situ spot-testing device for quality control/quality assurance of earthwork compaction. Little research has been conducted to investigate the stress–strain response within the soil during LWD testing. Similarly, little research has been performed to examine the appropriateness of using homogeneous, isotropic, linear elastic half-space theory to estimate soil modulus from LWD results. With this aim, an array of vertical stress and strain sensors was placed within the soil to measure the stress–strain response during LWD loading. Measured in situ stress values matched well with stresses predicted using homogeneous, isotropic, linear elastic half-space theory. In situ stress data revealed that the contact stress distribution between the soil surface and loading plate is a function of the soil type. Measured in situ strain values did not correspond well with strains predicted using homogeneous, isotropic, linear elastic elasticity. An exponentially increasing modulus function was required to match experimental with theoretical elastic strains. The results indicate that the commonly used form to predict is inappropriate if the goal is to extract constitutive soil properties. Analysis of strain data suggests the LWD depth of influence (measurement depth) is 0.9–1.1 times the plate diameter.
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Acknowledgments
This research was supported by the National Science Foundation (NSFCMS-0327509); their support is greatly appreciated. The writers would like to thank Dr. Joseph Labuz for his help with earth pressure cell calibration and Olson Instruments, Wheat Ridge, CO for their help in designing and fabricating the LWD. The writers would also like to thank Dr. Nils Ryden, Dr. Robert Rinehart, Mr. John Siekmeier, and Dr. John Berger for their contributions and feedback, and Dr. David White for providing index properties on the soils tested.
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Information & Authors
Information
Published In
Journal of Geotechnical and Geoenvironmental Engineering
Volume 135 • Issue 2 • February 2009
Pages: 199 - 208
Copyright
© 2009 ASCE.
History
Received: Feb 28, 2007
Accepted: Mar 27, 2008
Published online: Feb 1, 2009
Published in print: Feb 2009
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