The research program described in this paper investigates the influence of magnitude of horizonta... more The research program described in this paper investigates the influence of magnitude of horizontal toe compliance on the performance of 1/6-scale reinforced soil retaining walls at end of construction and during subsequent staged surcharge loading. The walls were 1.2 m high and were constructed with a very stiff horizontal toe support, a free support and with two different spring arrangements resulting in horizontal reaction stiffness values falling between these two limiting conditions. The data showed that the wall performance was sensitive to the range of toe boundary stiffness conditions investigated. As horizontal toe stiffness increased the following observations were made: a) wall deformations decreased but the displacement mode changed from uniform translation to rotation about the toe; b) the toe carried progressively more of the total horizontal earth force acting at the back of the facing column, and; c) strains in the reinforcement layers were attenuated, particularly at...
ABSTRACT Current practice to quantify the load transfer capacity between soil and geosynthetic re... more ABSTRACT Current practice to quantify the load transfer capacity between soil and geosynthetic reinforcement materials in the anchorage zone of a wall, slope, or embankment is to carryout laboratory pullout tests. In a recent paper, the authors described a novel large pullout box with a transparent bottom. Geogrid specimens up to 2000 mm in length were embedded in a transparent fused quartz soil and the specimens subjected to constant rate-of-displacement in-air testing and in-soil pullout testing under a range of normal stress. Displacement–time histories over the entire area of each reinforcement specimen were measured using the digital image correlation (DIC) technique applied to sequential images captured by a row of cameras located directly below the test apparatus. Opaque particles were also mixed with the transparent soil particles so that horizontal displacement of the soil in the planes immediately above and below the geogrid specimens could be tracked. The difference in horizontal displacement response corresponds to the relative shear displacement between the soil and geogrid that is responsible for load transfer during pullout. These results demonstrate the utility of the experimental methodology using the transparent fused quartz material as a successful analog to a natural sand soil for the investigation of granular soil–geogrid interaction. The example data is a necessary precursor to the development of interface shear models for load transfer in the anchorage zone of geogrid reinforced soil structures.
Geosynthetic reinforced soil walls and slopes are now a mature technology in geotechnical enginee... more Geosynthetic reinforced soil walls and slopes are now a mature technology in geotechnical engineering. Nevertheless, the mechanisms of soil-geosynthetic interaction are not fully understood for pullout of a geogrid material in the anchorage zone of a reinforced structure. It is also difficult to quantify the interactions between the geogrid and the soil. A new strategy to overcome these difficulties is to use a pullout box with a transparent glass bottom, a transparent soil, and non-contact measurement technology. This paper describes such a pullout box apparatus which is used in combination with a recently developed transparent granular soil. Embedded geogrid specimens are visible through the transparent bottom of the box and the surrounding soil. The displacements of the geogrid and seed (target) particles placed in the transparent soil are tracked using digital images captured by a row of synchronized cameras located below the apparatus. Digital processing is carried out using the Digital Image Correlation (DIC) technique to quantify the in-situ displacement of the geogrid specimen and surrounding soil. The displacements are used to compute continuous longitudinal strain profiles in the geogrid specimen over the duration of each pullout test and relative shear displacements between the geogrid and the soil. Also reported are lessons learned to improve the method of clamping geogrid specimens at the front of the pullout box which are also applicable to conventional pullout box equipment.
The paper describes a new transparent granular soil that can be used for laboratory geotechnical ... more The paper describes a new transparent granular soil that can be used for laboratory geotechnical modeling purposes. The transparent soil consists of fused quartz particles in combination with a mixture of two mineral oils as pore fluid. The solid particles and the matching liquid have the same refractive index. The soil has important advantages with respect to transparency, stability, health safety, and utility over glass and silica gel materials. The transparent soil is also inexpensive compared to silica gel-fluid materials that have been used in the past. Conventional laboratory shear box, triaxial compression, and permeability tests were carried out to demonstrate that the mechanical properties and hydraulic permeability of the transparent soil are typical of granular soils with angular particles.
The research program described in this paper investigates the influence of magnitude of horizonta... more The research program described in this paper investigates the influence of magnitude of horizontal toe compliance on the performance of 1/6-scale reinforced soil retaining walls at end of construction and during subsequent staged surcharge loading. The walls were 1.2 m high and were constructed with a very stiff horizontal toe support, a free support and with two different spring arrangements resulting in horizontal reaction stiffness values falling between these two limiting conditions. The data showed that the wall performance was sensitive to the range of toe boundary stiffness conditions investigated. As horizontal toe stiffness increased the following observations were made: a) wall deformations decreased but the displacement mode changed from uniform translation to rotation about the toe; b) the toe carried progressively more of the total horizontal earth force acting at the back of the facing column, and; c) strains in the reinforcement layers were attenuated, particularly at...
ABSTRACT Current practice to quantify the load transfer capacity between soil and geosynthetic re... more ABSTRACT Current practice to quantify the load transfer capacity between soil and geosynthetic reinforcement materials in the anchorage zone of a wall, slope, or embankment is to carryout laboratory pullout tests. In a recent paper, the authors described a novel large pullout box with a transparent bottom. Geogrid specimens up to 2000 mm in length were embedded in a transparent fused quartz soil and the specimens subjected to constant rate-of-displacement in-air testing and in-soil pullout testing under a range of normal stress. Displacement–time histories over the entire area of each reinforcement specimen were measured using the digital image correlation (DIC) technique applied to sequential images captured by a row of cameras located directly below the test apparatus. Opaque particles were also mixed with the transparent soil particles so that horizontal displacement of the soil in the planes immediately above and below the geogrid specimens could be tracked. The difference in horizontal displacement response corresponds to the relative shear displacement between the soil and geogrid that is responsible for load transfer during pullout. These results demonstrate the utility of the experimental methodology using the transparent fused quartz material as a successful analog to a natural sand soil for the investigation of granular soil–geogrid interaction. The example data is a necessary precursor to the development of interface shear models for load transfer in the anchorage zone of geogrid reinforced soil structures.
Geosynthetic reinforced soil walls and slopes are now a mature technology in geotechnical enginee... more Geosynthetic reinforced soil walls and slopes are now a mature technology in geotechnical engineering. Nevertheless, the mechanisms of soil-geosynthetic interaction are not fully understood for pullout of a geogrid material in the anchorage zone of a reinforced structure. It is also difficult to quantify the interactions between the geogrid and the soil. A new strategy to overcome these difficulties is to use a pullout box with a transparent glass bottom, a transparent soil, and non-contact measurement technology. This paper describes such a pullout box apparatus which is used in combination with a recently developed transparent granular soil. Embedded geogrid specimens are visible through the transparent bottom of the box and the surrounding soil. The displacements of the geogrid and seed (target) particles placed in the transparent soil are tracked using digital images captured by a row of synchronized cameras located below the apparatus. Digital processing is carried out using the Digital Image Correlation (DIC) technique to quantify the in-situ displacement of the geogrid specimen and surrounding soil. The displacements are used to compute continuous longitudinal strain profiles in the geogrid specimen over the duration of each pullout test and relative shear displacements between the geogrid and the soil. Also reported are lessons learned to improve the method of clamping geogrid specimens at the front of the pullout box which are also applicable to conventional pullout box equipment.
The paper describes a new transparent granular soil that can be used for laboratory geotechnical ... more The paper describes a new transparent granular soil that can be used for laboratory geotechnical modeling purposes. The transparent soil consists of fused quartz particles in combination with a mixture of two mineral oils as pore fluid. The solid particles and the matching liquid have the same refractive index. The soil has important advantages with respect to transparency, stability, health safety, and utility over glass and silica gel materials. The transparent soil is also inexpensive compared to silica gel-fluid materials that have been used in the past. Conventional laboratory shear box, triaxial compression, and permeability tests were carried out to demonstrate that the mechanical properties and hydraulic permeability of the transparent soil are typical of granular soils with angular particles.
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Papers by Fawzy Ezzein