Determination of elastic constants for geosynthetics using in-air biaxial tension tests
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Date
2018
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Montana State University - Bozeman, College of Engineering
Abstract
Geosynthetics are polymeric membranes used for structural reinforcement for many geotechnical applications such as reinforced pavement. Geosynthetics have been shown to increase the service life of roadways in a variety of field tests. The knowledge of geosynthetics and design methodologies could be improved with a better understanding of geosynthetic material properties. To better understand how geosynthetics perform in field loading situations, geosynthetic tensile resilient material properties are needed. The properties of geosynthetics of interest for this thesis are the resilient tensile modulus of elasticity and Poisson's Ratio (elastic constants) in both material directions. Modulus of elasticity has been traditionally calculated using wide-width uniaxial tests, which is a poor representation of field loading conditions due to the unrestrained sides of the material. Biaxial tension tests are a better representation of field loading conditions and thus were implemented for determination of elastic constants pertaining to different geosynthetic materials. Biaxial tension tests were performed on cruciform shaped samples using a custom device built by the Western Transportation Institute at Montana State University to test geosynthetic samples. A biaxial testing procedure was created using conclusions from a uniaxial testing program implemented to examine the resilient response of geosynthetics after being subjected to four types of loading (cyclic stress relaxation, monotonic stress relaxation, cyclic creep and monotonic creep) over different durations of time. The conclusions of the uniaxial testing program, the available literature and ASTM D7556 were synthesized to create a biaxial testing procedure. Biaxial tension tests were performed in three modes of loading to simulate loading conditions and loadings where a geosynthetic experiences loading in both directions simultaneously. The biaxial tension tests generated stress and strain data used to calculate the elastic constants of six biaxial geogrids and two woven geotextiles. The elastic constants were calculated using an orthotropic linear elastic constitutive model with a least squares approximation. The elastic constants calculated for each geosynthetic material were shown to represent the resilient behavior of geosynthetics in different field loading situations with more realistic boundary conditions than previous uniaxial tests used to characterize the resilient response of geosynthetics.