Evaluation Of Load Transfer Mechanisms Between Soil And Geogrid Using Transparent Soil

Download or read book Evaluation of Load Transfer Mechanisms Between Soil and Geogrid Using Transparent Soil written by Xin Peng (Ph. D.) and published by . This book was released on 2017 with total page 614 pages. Available in PDF, EPUB and Kindle. Book excerpt: The increasing use of different types of geosynthetics in the design of reinforced soil retaining structures and of stiffened roadways require proper evaluation of the mobilization of load-transfer mechanisms between soil particles and geosynthetics. Compared to other planar geosynthetics, geogrids develop a soil-interlocking interaction that leads to the mobilization of different types of resistance from different rib elements. The resistance mobilized by the different rib elements ultimately determine the mechanical responses for both: (1) the ultimate pullout resistance; and (2) the confined geogrid stiffness. Geogrids with different aperture shapes involve rib elements along different orientations. Different rib orientations, as well as different rib dimensions, may lead to different load transfer mechanisms. The contributions of the different mechanisms have been difficult to be quantify and evaluate using conventional experimental techniques. In this study, a new experimental approach involving the use of transparent soil with laser aided imaging, was developed to visualize and quantify load-transfer mechanisms between soil particles and geogrids with different geometric characteristics. Laser beams with up to 350 mW output power and with a wavelength of 638 nm were adopted to allow tracking the transparent soil particles at a plane perpendicular to the soil-geogrid interface. The collimated beam resulted in well-defined individual particles in the selected plane of the soil model. High-definition cameras were used to track the displacement fields of both the confined geogrid specimen and the soil particles within the laser-illuminated plane. Digital Image Correlation (DIC) techniques, as well as other image-processing approaches were used to define the displacement fields based on images captured during the tests. Using this experimental approach, a series of investigations were conducted based on soil-geosynthetic interaction (SGI) tests: (1) experimental evaluation of the confined performance of geogrids with different geometric characteristics; (2) load transfer modeling of the soil-geogrid interaction using both biaxial and triaxial geogrids. The experimental evaluation illustrated the impact of the geometric characteristics of geogrids (e.g. aperture shapes, aperture sizes, and rib dimensions), on the mobilization of load transfer between soil particles and geogrid specimens. Specifically, the digitally-collected data allowed determination of: (a) geogrid displacement profiles, (b) load-displacement relationships of geogrid specimens, (c) soil stiffening along the loading direction, and (d) the development of shear bands. Using the proposed testing configuration, the experimental results allowed the comparison between the response of triaxial geogrids and that of the biaxial geogrid. Load transfer models of soil-geogrid interaction were developed. They involve independent modeling for (1) longitudinal ribs, and (2) transverse or diagonal ribs of the geogrid specimen. The models developed in this study were validated using the results from tests conducted using the selected biaxial and triaxial geogrids. Good agreement was observed between the experimental measurements and model predictions. The load transfer models also allowed the evaluation of the interference between different load transfer mechanisms during the SGI tests conducted using the biaxial geogrid as a part of this study. In addition, the difference between the load transfer mechanisms developed in the biaxial geogrid and those developed in the triaxial geogrids was evaluated and quantified in this study. Overall, the triaxial geogrids tested as a part of this study showed a higher load transfer efficiency than the biaxial geogrid along the loading direction. This was probably attributed to the comparatively uniform unit tension distribution exhibited by the triaxial geogrids in relation to that of the biaxial geogrid used in this study. The governing component of the resistance mobilized at low displacement levels in the test conducted using the selected biaxial geogrid was the resistance developed by the longitudinal ribs. Instead, at high displacement levels and until pullout failure, the relative contributions of the transverse ribs were larger than those of the longitudinal ribs. The most relevant component of the resistance mobilized throughout the entire tests conducted using the triaxial geogrids as a part of this study, both under low and large displacements, was found to be the resistance developed by the diagonal ribs, with their relative contributions particularly high during the early stages of the tests. In the tests conducted using different triaxial geogrids, the relative contributions of the resistance from different rib components were found to depend on the geometric characteristics of the geogrids. Overall, the conclusions addressed from this study provide valuable insight into identifying the impact of the geometric characteristics of geogrids on the load transfer mechanisms between soil particles and geogrids.