Theses and Dissertations at Montana State University (MSU)
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Item In-plane shear behavior of geosynthetics from bias biaxial tests using digital image correlation(Montana State University - Bozeman, College of Engineering, 2019) Schultz, Emily Christine; Chairperson, Graduate Committee: Steven PerkinsGeosynthetics are polymeric membranes used for structural reinforcement of soils in a variety of roadway and foundation applications, many of which create biaxial loading on the geosynthetic. Orthotropic linear elastic models have been used to represent geosynthetic behavior at working load levels for engineering design purposes. Typically, the models rely on index parameters obtained from test methods that do not represent the biaxial field loading conditions. Proper calibration of these models requires load-strain data obtained from tests that have controlled stress and strain boundaries such as biaxial tension tests. Previously at Montana State University, Haselton (2018) successfully used a custom biaxial device to perform biaxial tension tests on cruciform shaped geosynthetic specimens, producing a partial set of resilient elastic constants for two woven geotextiles and six biaxial geogrids. To complete the set of elastic constants by determination of the in-plane shear modulus, another mode of loading was necessary. Literature from biaxial shear tests of architectural membranes suggested cutting the cruciform shaped samples with the principal material directions on a 45-degree bias, which causes the sample to shear when the cruciform axes are unequally loaded. This test mode was successfully implemented with the existing biaxial device to determine the resilient in-plane shear modulus using an orthotropic linear elastic model. Full-field strain measurements were captured using digital imaging correlation (DIC) software available at Montana State University. DIC was shown to produce equivalent strain measurements to the mechanical instrumentation (LVDTs) used by Haselton, enabling a combined dataset. The full-field DIC strain measurements were then used to validate Haselton's assumption regarding the region of uniform strain and to identify the region of uniform strain for data collection in this thesis. DIC also showed reasonably pure biaxial tension in the cruciform samples, validating the elastic constant derivations for both Haselton and this thesis.Item Determination of elastic constants for geosynthetics using in-air biaxial tension tests(Montana State University - Bozeman, College of Engineering, 2018) Haselton, Henry Nathaniel; Chairperson, Graduate Committee: Steven PerkinsGeosynthetics 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.Item Evaluation of full-scale laboratory models of geosynthetic reinforced pavement systems(Montana State University - Bozeman, College of Engineering, 1998) Fogelsong, Macgregor L.Item Instrumentation of a geosynthetically reinforced roadway(Montana State University - Bozeman, College of Engineering, 1996) Lapeyre, Joseph AndrewItem Evaluation of transverse behavior of geosynthetics when used for subgrade stabilization(Montana State University - Bozeman, College of Engineering, 2013) Morris, Zachary Lee; Chairperson, Graduate Committee: Steven PerkinsState departments of transportation (DOTs) routinely use geogrids and geotextiles for subgrade stabilization. There is a general consensus between state DOTs concerning the effectiveness of these geosynthetics for this application; however, there is a lack of understanding and agreement with respect to the material properties of the geosynthetics that most directly relate to performance. A full-scale field study using geosynthetics as subgrade stabilization was conducted to analyze the performance and transverse behavior of 14 reinforced test sections under vehicular loads. Insight into the mechanisms of support that geosynthetics provide was determined based on strain gage and LVDT measurements, and transverse rut profiles. Mechanical properties of geosynthetics were compared to truck passes at the transition from lateral confinement to membrane support as well as at failure to evaluate which properties best predicted field performance. The properties evaluated included wide-width tensile strength, cyclic tensile modulus, resilient interface shear stiffness, junction strength, and aperture stability modulus. The behavior of geosynthetics was primarily characterized by when they started to transition from lateral confinement to membrane support. The results indicate that in general, the geosynthetics transitioned between truck pass 80 to 300 at a corresponding average elevation rut of about 1.7 inches, or between 1.7 to 3.1 inches of apparent rut. Failure was defined as 3 inches of elevation rut, and in general, the geosynthetics that transitioned to membrane support before truck pass 80 to 300 failed early. The results from the field study indicate that junction strength and stiffness, and wide-width tensile strength at 2% and 5% strain may be the most pertinent mechanical properties of geogrids, and surface friction may be the most pertinent property of geotextiles, for estimating field performance when used for subgrade stabilization applications with 10 to 12 inches of base aggregate, CBR strength values between 1.5 to 2.2, and elevation ruts less than 3.0 inches (or less than 5.4 inches of apparent rut).Item Development of a test protocol for cyclic pullout of geosynthetics in roadway base reinforcement(Montana State University - Bozeman, College of Engineering, 2009) Holley, Timothy Michael; Chairperson, Graduate Committee: Steven PerkinsGeosynthetics, or manmade materials used in soils engineering, have successfully been used as base reinforcement of pavements for over 40 years. Use of geosynthetics can result in cost savings by allowing the aggregate base layer to be reduced in thickness and/or the service life of the pavement to be extended. Design methods for this type of reinforcement have typically been developed by individual manufacturers for specific products. These methods are not widely used by state transportation agencies because 1) they are proprietary, 2) they are empirically based, and 3) they lack compatibility with the current national trend towards mechanistic-empirical pavement design procedures. This project was initiated to develop testing methods to determine one of the critical material properties needed for mechanistic-empirical base-reinforced pavement design, namely, the resilient interface shear stiffness. This property describes the interaction, in particular the shear stiffness, between the geosynthetic and the surrounding aggregate. This new test protocol closely mimics vehicular load patterns, resulting in design parameters pertinent to the use of the geosynthetics to reinforce the base course. A study was conducted to evaluate the repeatability of these tests and to develop a standardized test method. Specific parameters under investigation include load pulse and rest period duration, embedment length of the geosynthetic, and differences in results using different soils and types of geosynthetics. Some parameters seemed to have little effect on values of resilient interface shear stiffness, while others vastly impacted the results. Load pulse and rest period durations did not affect output results significantly. Maintaining a constant confinement or shear stress during the test duration produced higher repeatability and correlated well to the adapted resilient modulus equation. Three-aperture length tests on polyester geogrid also correlated well with this equation, however repeatability was moderately low. Polypropylene geogrid and a woven geotextile confined in Ottawa sand displayed low correlation to this equation. During testing, very small displacements occur, and therefore, every effort should be made to ensure that these measurements are accurate and not skewed by electrical noise and interference.