Lytton, Robert | Texas A&M University (original) (raw)
Papers by Lytton, Robert
Springer Proceedings in Physics 113
State surface approach is becoming much less popular nowadays since many elasto-plastic modellers... more State surface approach is becoming much less popular nowadays since many elasto-plastic modellers consider though it is useful as a simplified method in some practical problems, it can not be used to explain complex stress path dependency for unsaturated soils. Consequently, nearly all researchers used “normal compression lines at different suction levels” to develop their elasto-plastic models. In this paper,
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Transportation Research Record: Journal of the Transportation Research Board
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Materials and Structures
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Canadian Geotechnical Journal
When characterizing an unsaturated soil using the triaxial test apparatus, it is required to meas... more When characterizing an unsaturated soil using the triaxial test apparatus, it is required to measure the soil deformation during loading. Recently, a photogrammetry-based method has been developed for total and localized volume change measurements on unsaturated soils during triaxial testing. In this study, more in-depth discussions on the photogrammetry-based method are addressed, such as system setup, the measurement procedure, accuracy self-check, data post-processing, and differences from conventional image-based methods. Also, an application of the photogrammetry-based method on unsaturated soil deformation measurements is presented through a series of undrained triaxial tests with different loading paths. After testing, three-dimensional (3D) models of the tested soils at different loading steps were constructed based on the 3D coordinates of measurement targets on the soil surface. Clear barreling processes for soils during deviatoric loading were observed through the constru...
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International Journal of Pavement Engineering
A simple procedure is developed to account for the effects of aggregate physical properties (grad... more A simple procedure is developed to account for the effects of aggregate physical properties (gradation and shape characteristics) in predicting the cross-anisotropic properties of unbound granular layers. Variable confining pressure repeated triaxial tests were performed on six aggregate sources with three different gradations (coarse, intermediate and fine) and three different moisture contents (wet, optimum and dry). The experimental results were
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Acta Geotechnica
ABSTRACT Triaxial tests have been widely used to evaluate soil behaviors. In the past few decades... more ABSTRACT Triaxial tests have been widely used to evaluate soil behaviors. In the past few decades, several methods have been developed to measure the volume changes of unsaturated soil specimens during triaxial tests. Literature review indicates that until now it remains a major challenge for researchers to measure the volume changes of unsaturated soil specimens during triaxial testing. This paper presents a non-contact method to measure the total and local volume changes of unsaturated soil specimens using a conventional triaxial test apparatus for saturated soils. The method is simple and cost-effective, requiring only a commercially available digital camera to take images of an unsaturated soil specimen during triaxial testing from which accurate 3D model of the soil specimen is reconstructed. In this proposed method, the photogrammetric technique is utilized to determine the orientations of the camera where the images are taken and the shape and location of the acrylic cell, multiple optical ray tracings are employed to correct the refraction at the air-acrylic cell and acrylic cell–water interfaces, and a least-square optimization technique is applied to estimate the coordinates of any point on the specimen surface. The paper first discusses the theoretical aspects of the proposed method. An image analysis on a caliper was then used to evaluate the accuracy of photogrammetric analysis in the air. A series of isotropic compression tests on a stainless steel cylinder were used to demonstrate the procedure and evaluate the accuracy of the proposed method, while triaxial shearing tests on a saturated sand specimen were used to exam the capacity of the proposed method for measuring the total and localized volume changes during triaxial testing. Results obtained from the validation tests indicate that the accuracy for the photogrammetry in the air is about 10 µm. The average accuracy for single point measurements in the triaxial tests ranges from 0.056 to 0.076 mm with standard deviations varying from 0.033 to 0.061 mm. The accuracy for total volume measurements is better than 0.25 %.
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Journal of Materials in Civil Engineering
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Geotechnical Frontiers 2017, 2017
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E3S Web of Conferences, 2016
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Transportation Research Record Journal of the Transportation Research Board, Feb 2, 2015
The mechanical properties of granular materials are nonlinear and stress dependent. Several resea... more The mechanical properties of granular materials are nonlinear and stress dependent. Several researchers have identified cross-anisotropy as a better model for characterizing granular materials. However, determining cross-anisotropic material properties from the conventional triaxial setup has been extremely difficult. A laboratory testing protocol has been developed using theories of elasticity and the system identification method. The testing protocol is efficient and precise. Material properties determined with the testing protocol satisfy elasticity requirements. The cross-anisotropic material properties of four granular materials were determined. The material properties were entered into a finite element program, which was modified to accept these properties, to determine pavement response. Nonlinear crossanisotropic modeling was observed to eliminate tension zones predicted by isotropic models in granular layers. This is an important step because the presence of such tensile zones has required adjustments in layered pavement models to predict pavement performance on the basis of response parameters.
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Transportation Research Record, 1991
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Ndt E Int, 1992
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Journal of Materials in Civil Engineering, Feb 1, 2013
ABSTRACT A controlled-strain repeated direction tension (RDT) test is useful for characterizing a... more ABSTRACT A controlled-strain repeated direction tension (RDT) test is useful for characterizing asphalt mixtures and assessing fatigue cracking accompanied by plastic deformation. The strain curve in a loading cycle of the controlled-strain RDT test is a standard haversine wave with only a tensile portion, whereas the stress curve has a tensile portion and a compressive portion (quasi-compression) because of the viscoelastoplastic nature of the asphalt mixture. Usually the material properties in the tensile stress portion (the tensile properties) are used, while those in the compressive stress portion (the quasi-compressive properties) are neglected. This leads to nonnegligible errors in estimating the dissipated strain energy (DSE) and characterizing the damage (such as cracking and permanent deformation) generated in the material. The objective of this paper is to obtain complete material properties and accurate amounts of dissipation and storage of energy of this test method as the foundation of damage characterization. This paper provides methods to simulate the stress and strain for the tensile and compressive stress portions separately so as to determine the tensile and quasi-compressive properties, respectively. The difference between the tensile and quasi-compressive properties is investigated using statistical analysis. It is found that the tensile properties of an asphalt mixture are different from the quasi-compressive properties due to the crack opening and closure within each loading cycle. The DSE calculated using both the tensile and quasi-compressive properties is larger compared to the traditional method using only the tensile properties, indicating an underestimation of the damage by the traditional method. In addition, the recoverable strain energy (RSE) is investigated to examine the ability of an asphalt mixture to store and recover energy. A new perspective in terms of the integration method is provided to determine the actual amount of the RSE in a loading cycle. DOI: 10.1061/(ASCE)MT.1943-5533.0000586. (C) 2013 American Society of Civil Engineers.
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Proceedings of the Seventh Workshop on Multidimensional Signal Processing, 2000
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... 5. Report Date February 2009 Published: December 2009 6. Performing Organization Code 7. Auth... more ... 5. Report Date February 2009 Published: December 2009 6. Performing Organization Code 7. Author(s) Arif Chowdhury, Joe W. Button, and Robert L. Lytton 8. Performing Organization Report No. ... by Arif Chowdhury Assistant Research Engineer Texas Transportation Institute ...
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Springer Proceedings in Physics 113
State surface approach is becoming much less popular nowadays since many elasto-plastic modellers... more State surface approach is becoming much less popular nowadays since many elasto-plastic modellers consider though it is useful as a simplified method in some practical problems, it can not be used to explain complex stress path dependency for unsaturated soils. Consequently, nearly all researchers used “normal compression lines at different suction levels” to develop their elasto-plastic models. In this paper,
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Materials Evaluation
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Transportation Research Record: Journal of the Transportation Research Board
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Transportation Research Record: Journal of the Transportation Research Board
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Materials and Structures
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Canadian Geotechnical Journal
When characterizing an unsaturated soil using the triaxial test apparatus, it is required to meas... more When characterizing an unsaturated soil using the triaxial test apparatus, it is required to measure the soil deformation during loading. Recently, a photogrammetry-based method has been developed for total and localized volume change measurements on unsaturated soils during triaxial testing. In this study, more in-depth discussions on the photogrammetry-based method are addressed, such as system setup, the measurement procedure, accuracy self-check, data post-processing, and differences from conventional image-based methods. Also, an application of the photogrammetry-based method on unsaturated soil deformation measurements is presented through a series of undrained triaxial tests with different loading paths. After testing, three-dimensional (3D) models of the tested soils at different loading steps were constructed based on the 3D coordinates of measurement targets on the soil surface. Clear barreling processes for soils during deviatoric loading were observed through the constru...
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International Journal of Pavement Engineering
A simple procedure is developed to account for the effects of aggregate physical properties (grad... more A simple procedure is developed to account for the effects of aggregate physical properties (gradation and shape characteristics) in predicting the cross-anisotropic properties of unbound granular layers. Variable confining pressure repeated triaxial tests were performed on six aggregate sources with three different gradations (coarse, intermediate and fine) and three different moisture contents (wet, optimum and dry). The experimental results were
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Acta Geotechnica
ABSTRACT Triaxial tests have been widely used to evaluate soil behaviors. In the past few decades... more ABSTRACT Triaxial tests have been widely used to evaluate soil behaviors. In the past few decades, several methods have been developed to measure the volume changes of unsaturated soil specimens during triaxial tests. Literature review indicates that until now it remains a major challenge for researchers to measure the volume changes of unsaturated soil specimens during triaxial testing. This paper presents a non-contact method to measure the total and local volume changes of unsaturated soil specimens using a conventional triaxial test apparatus for saturated soils. The method is simple and cost-effective, requiring only a commercially available digital camera to take images of an unsaturated soil specimen during triaxial testing from which accurate 3D model of the soil specimen is reconstructed. In this proposed method, the photogrammetric technique is utilized to determine the orientations of the camera where the images are taken and the shape and location of the acrylic cell, multiple optical ray tracings are employed to correct the refraction at the air-acrylic cell and acrylic cell–water interfaces, and a least-square optimization technique is applied to estimate the coordinates of any point on the specimen surface. The paper first discusses the theoretical aspects of the proposed method. An image analysis on a caliper was then used to evaluate the accuracy of photogrammetric analysis in the air. A series of isotropic compression tests on a stainless steel cylinder were used to demonstrate the procedure and evaluate the accuracy of the proposed method, while triaxial shearing tests on a saturated sand specimen were used to exam the capacity of the proposed method for measuring the total and localized volume changes during triaxial testing. Results obtained from the validation tests indicate that the accuracy for the photogrammetry in the air is about 10 µm. The average accuracy for single point measurements in the triaxial tests ranges from 0.056 to 0.076 mm with standard deviations varying from 0.033 to 0.061 mm. The accuracy for total volume measurements is better than 0.25 %.
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Journal of Materials in Civil Engineering
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Geotechnical Frontiers 2017, 2017
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E3S Web of Conferences, 2016
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Transportation Research Record Journal of the Transportation Research Board, Feb 2, 2015
The mechanical properties of granular materials are nonlinear and stress dependent. Several resea... more The mechanical properties of granular materials are nonlinear and stress dependent. Several researchers have identified cross-anisotropy as a better model for characterizing granular materials. However, determining cross-anisotropic material properties from the conventional triaxial setup has been extremely difficult. A laboratory testing protocol has been developed using theories of elasticity and the system identification method. The testing protocol is efficient and precise. Material properties determined with the testing protocol satisfy elasticity requirements. The cross-anisotropic material properties of four granular materials were determined. The material properties were entered into a finite element program, which was modified to accept these properties, to determine pavement response. Nonlinear crossanisotropic modeling was observed to eliminate tension zones predicted by isotropic models in granular layers. This is an important step because the presence of such tensile zones has required adjustments in layered pavement models to predict pavement performance on the basis of response parameters.
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Transportation Research Record, 1991
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Ndt E Int, 1992
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Journal of Materials in Civil Engineering, Feb 1, 2013
ABSTRACT A controlled-strain repeated direction tension (RDT) test is useful for characterizing a... more ABSTRACT A controlled-strain repeated direction tension (RDT) test is useful for characterizing asphalt mixtures and assessing fatigue cracking accompanied by plastic deformation. The strain curve in a loading cycle of the controlled-strain RDT test is a standard haversine wave with only a tensile portion, whereas the stress curve has a tensile portion and a compressive portion (quasi-compression) because of the viscoelastoplastic nature of the asphalt mixture. Usually the material properties in the tensile stress portion (the tensile properties) are used, while those in the compressive stress portion (the quasi-compressive properties) are neglected. This leads to nonnegligible errors in estimating the dissipated strain energy (DSE) and characterizing the damage (such as cracking and permanent deformation) generated in the material. The objective of this paper is to obtain complete material properties and accurate amounts of dissipation and storage of energy of this test method as the foundation of damage characterization. This paper provides methods to simulate the stress and strain for the tensile and compressive stress portions separately so as to determine the tensile and quasi-compressive properties, respectively. The difference between the tensile and quasi-compressive properties is investigated using statistical analysis. It is found that the tensile properties of an asphalt mixture are different from the quasi-compressive properties due to the crack opening and closure within each loading cycle. The DSE calculated using both the tensile and quasi-compressive properties is larger compared to the traditional method using only the tensile properties, indicating an underestimation of the damage by the traditional method. In addition, the recoverable strain energy (RSE) is investigated to examine the ability of an asphalt mixture to store and recover energy. A new perspective in terms of the integration method is provided to determine the actual amount of the RSE in a loading cycle. DOI: 10.1061/(ASCE)MT.1943-5533.0000586. (C) 2013 American Society of Civil Engineers.
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Proceedings of the Seventh Workshop on Multidimensional Signal Processing, 2000
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... 5. Report Date February 2009 Published: December 2009 6. Performing Organization Code 7. Auth... more ... 5. Report Date February 2009 Published: December 2009 6. Performing Organization Code 7. Author(s) Arif Chowdhury, Joe W. Button, and Robert L. Lytton 8. Performing Organization Report No. ... by Arif Chowdhury Assistant Research Engineer Texas Transportation Institute ...
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