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- Unsaturated soils Mechanics, Constitutive modeling on unsaturated soils, Triaxial test on unsaturated soils, Applicat... moreUnsaturated soils Mechanics, Constitutive modeling on unsaturated soils, Triaxial test on unsaturated soils, Application of Photogrammetry on engineering projects, Ice-rich cut slope protection, and Frost heave behavior of granular materials.edit
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... 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, measurement procedure, accuracy self-check, data postprocessing,
and differences from the 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, threedimensional
(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 constructed 3D models at different axial
strain levels. Soil volume changes and volumetric strain non-uniformities during isotropic and
deviatoric loadings were extracted based upon detailed analyses on different soil layers. Through
a full-field strain distribution analysis, a shear band evolution process was captured for the soil
during deviatoric loading at a low confining stress. The photogrammetry-based method proved to
be very powerful for in-depth soil deformation characteristics investigation.
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, measurement procedure, accuracy self-check, data postprocessing,
and differences from the 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, threedimensional
(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 constructed 3D models at different axial
strain levels. Soil volume changes and volumetric strain non-uniformities during isotropic and
deviatoric loadings were extracted based upon detailed analyses on different soil layers. Through
a full-field strain distribution analysis, a shear band evolution process was captured for the soil
during deviatoric loading at a low confining stress. The photogrammetry-based method proved to
be very powerful for in-depth soil deformation characteristics investigation.
Research Interests:
Research Interests:
In the past, full-field deformation of unsaturated soils during triaxial testing has never been reported due to lack of a measurement method. In this paper, a photogrammetry-based method was presented to investigate the deformation of an... more
In the past, full-field deformation of unsaturated soils during triaxial testing has never been reported due to lack of a measurement method. In this paper, a photogrammetry-based method was presented to investigate the deformation of an unsaturated soil during triaxial testing. Measurement targets were attached to the surface of an unsaturated cylindrical specimen. With the newly developed photogrammetry-based method, the three-dimensional coordinates of these targets are accurately determined to monitor soil deformation during triaxial testing. Soil deformation non-uniformity was extracted based on the movements of those measurement targets on specimen surface. It was found that an unsaturated soil deformation under shear load was not uniformly distributed.
Research Interests:
Recently, a novel photogrammetry-based method has been developed for unsaturated soil deformation measurements during triaxial testing. This method provides a simple and cost effective alternative to the conventional double-wall cell... more
Recently, a novel photogrammetry-based method has been developed for unsaturated soil deformation measurements during triaxial testing. This method provides a simple and cost effective alternative to the conventional double-wall cell method. In this study, a validation test on a saturated sand specimen was conducted to evaluate the accuracy of the newly developed photogrammetry-based method. A sensitivity analysis was also carried out on the impact of the system parameters (i.e. cell wall thickness, refractive indices of water and cell wall) on the overall measurement accuracy. The refractive index of water was found to have the most significant impact on overall measurement accuracy of the photogrammetry-based method.
Research Interests:
To investigate unsaturated soil behavior during consolidation under K0 condition, a new undrained oedometer cell with matric suction measurement ability was developed based upon modifications on a conventional oedometer. A high-suction... more
To investigate unsaturated soil behavior during consolidation under K0 condition, a new undrained oedometer cell with matric suction measurement ability was developed based upon modifications on a conventional oedometer. A high-suction tensiometer was equipped to monitor matric suction variation during loading under undrained condition. Soil volume change during testing was recorded by a local displacement transducer. To validate the performance of this new oedometer cell, an undrained oedometer compression test was performed on an unsaturated soil specimen. Some preliminary results were obtained which included soil suction and volume variation during K0 loading. Test result indicated that the proposed system is very efficient and suitable to be utilized for unsaturated soil behaviors evaluation.
Research Interests:
Suction-controlled triaxial tests have been widely used to characterize unsaturated soils. However, this type of test requires sophisticated and therefore expensive equipment, and is very time consuming because of the low permeability of... more
Suction-controlled triaxial tests have been widely used to characterize unsaturated soils. However, this type of test requires sophisticated and therefore expensive equipment, and is very time consuming because of the low permeability of unsaturated soils. Only a few research universities can afford the equipment, which limits the advancement and implementation of unsaturated soil mechanics. This paper proposes a new triaxial testing system for unsaturated soils based upon minor modifications on the conventional triaxial test apparatus for saturated soils. Instead of controlling suction, high-suction tensiometers are adopted to monitor matric suction variations during constant water content triaxial testing. Also, a photogrammetry-based method is used to measure volume changes of unsaturated soil specimens during triaxial testing. To evaluate the capabilities of the proposed testing system, a series of constant water content triaxial tests were performed on unsaturated soils with different moisture content. Matric suction and volume variations during testing were monitored by the high-suction tensiometers and the photogrammetry-based method, respectively. New methods were also proposed to analyze the test results. Analysis results showed that the proposed system is cost effective and efficient for unsaturated soil characterization.
Research Interests:
Beaver Slide is on the Dalton Highway near 177.8 km (110.5 mi), and it is downhill when heading north. The road gradient is approximately 11% and the road prism is on a side hill. Each year, there are soft spots that usually appear in... more
Beaver Slide is on the Dalton Highway near 177.8 km (110.5 mi), and it is downhill when heading north. The road gradient is approximately 11% and the road prism is on a side hill. Each year, there are soft spots that usually appear in late April and remain all summer, which are also called “frost boils” by engineers at the Alaska Department of Transportation and Public Facilities (AKDOT&PF). The frost boils have resulted in extremely unsafe driving conditions and frequent accidents. Past repair efforts indicate conventional road construction methods do not work. A new type of geosynthetic wicking fabric has been recently developed that has a high specific surface area (consequently high wettability and high capillary action) and high directional permittivity. Preliminary laboratory tests indicate it has great promise as a cost-effective means to solve the frost heave-related problems on northern road systems. This study verifies the effectiveness of the wicking fabric to mitigate frost boils in Alaskan pavements. A test section was built at the Beaver Slide area of the Dalton Highway with installation of two layers of wicking fabric. The test section was instrumented with moisture and temperature sensors to measure the temperature and moisture variations for two years. Results were analyzed to evaluate the effectiveness of the wicking fabric to mitigate the frost boils in Alaskan pavements.
Read More: http://ascelibrary.org/doi/abs/10.1061/(ASCE)MT.1943-5533.0000828
Read More: http://ascelibrary.org/doi/abs/10.1061/(ASCE)MT.1943-5533.0000828
Research Interests:
Triaxial tests have been widely used to evaluate the soil behavior. In the past few decades, several methods have been developed to measure the volume changes of unsaturated soil specimens during triaxial tests. Literature review... more
Triaxial tests have been widely used to evaluate the soil behavior. 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 noncontact 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 theory of 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. Based upon the analysis of the test results, some conclusions are drawn.
This paper presents a noncontact 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 theory of 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. Based upon the analysis of the test results, some conclusions are drawn.
Research Interests:
Nowadays, direct measurement of matric suction on unsaturated soils in laboratory is still a great challenge for researchers. In this study, two new high-suction tensiometers were designed and fabricated based on commercial pressure... more
Nowadays, direct measurement of matric suction on unsaturated soils in laboratory is still a great challenge for researchers. In this study, two new high-suction tensiometers were designed and fabricated based on commercial pressure transducers. Ceramic discs with air-entry value of 15 bar were used as the filter for those tensiometers. The design, fabrication, saturation, and calibration process are addressed in details. Also, the maximum attainable suctions were determined to be at around 1100 kPa through free evaporation tests. A series of tests was conducted to evaluate the performance of these tensiometers. Compared with existing high-suction tensiometers, these newly developed high-suction tensiometers were proved to be robust and reliable for measuring matric suction on unsaturated soils.
Research Interests:
Research Interests:
ABSTRACT The resilient modulus (M(R)) of base course material is an important material input for pavement design. Although extensive research efforts have been directed toward M(R) characterization and modeling, less effort has been spent... more
ABSTRACT The resilient modulus (M(R)) of base course material is an important material input for pavement design. Although extensive research efforts have been directed toward M(R) characterization and modeling, less effort has been spent on factors important for cold-region pavements. Most M(R) values of granular base materials available in the database of the Alaska flexible pavement design software were obtained from in-service roadways through nondestructive testing and backcalculation. The predictive models provided in the current Mechanistic-Empirical Pavement Design Guide cannot be confidently applied to Alaska materials because of the peculiar conditions for material properties and climatic differences. Hence, a systematic study was carried out to investigate the resilient behavior of granular base materials obtained from all three regions in Alaska, as presented in this paper. Effects of temperature, freeze-thaw cycle, and moisture and fines contents on the M(R) of Alaska base materials were experimentally evaluated, from which equations for M(R) prediction were developed and compared with those based on the Long-Term Pavement Performance data.