AUTHOR=Hussaini Syed Khaja Karimullah , Sweta Kumari 

TITLE=Application of Geogrids in Stabilizing Rail Track Substructure

JOURNAL=Frontiers in Built Environment

VOLUME=6

YEAR=2020

URL=https://www.frontiersin.org/journals/built-environment/articles/10.3389/fbuil.2020.00020

DOI=10.3389/fbuil.2020.00020

ISSN=2297-3362

ABSTRACT=<p>Large-scale direct shear tests were conducted to assess the performance of geogrid-reinforced ballast-sub-ballast interface followed by triaxial tests to explore the deformation and degradation response of geogrid-reinforced ballast under cyclic loading. While the direct shear testing was performed at applied normal stresses (σ<sub><italic>n</italic></sub>) ranging from 20 to 100 kPa and rate of shearing (<italic>S</italic><sub><italic>r</italic></sub>) from 2.5 to 10.0 mm/min, the cyclic triaxial tests were performed to capture the role of loading frequency (<italic>f</italic>) ranging from 10 to 40 Hz. Fresh granite ballast and sub-ballast with mean particle size (<italic>D</italic><sub>50</sub>) of 42 and 3.5 mm, and five geogrids having different aperture shapes and sizes (<italic>A</italic>) were used in this study. The tests results indicated that the behavior of ballast-sub-ballast interface is highly influenced by σ<sub><italic>n</italic></sub> and <italic>S</italic><sub><italic>r</italic></sub>. The friction (φ) and dilation angles (ψ) of unreinforced and geogrid-reinforced ballast-sub-ballast interface is found to reduce from 67.96 to 47.82° and 14.56 to 3.34° with the increase in σ<sub><italic>n</italic></sub> and <italic>S</italic><sub><italic>r</italic></sub>. Marsal's Breakage (<italic>B</italic><sub><italic>g</italic></sub>: an index to quantify the breakage of ballast) of unreinforced ballast was found to increase from 2.84 to 6.69% with the increase in σ<sub><italic>n</italic></sub> and <italic>S</italic><sub><italic>r</italic></sub>. However, the inclusion of geogrids significantly enhanced the friction angle (φ), reduced the extent of dilation angle (ψ), and minimized <italic>B</italic><sub><italic>g</italic></sub>. The interface efficiency factor (α) and <italic>B</italic><sub><italic>g</italic></sub> were found to be a function of <italic>A/D</italic><sub>50</sub> ratio. Accordingly, a model is developed using multiple linear regression analysis to predict the values of φ, ψ, and <italic>B</italic><sub><italic>g</italic></sub> in terms of the input parameters σ<sub><italic>n</italic></sub>, <italic>S</italic><sub><italic>r</italic></sub>, and <italic>A/D</italic><sub>50</sub> ratio. The results from triaxial tests indicate the deformation and degradation behavior of ballast under cyclic loading conditions to be influenced by the loading frequency (<italic>f</italic>). The extent of <italic>l</italic><sub><italic>d</italic></sub> and <italic>S</italic><sub><italic>v</italic></sub> of unreinforced ballast increases from 5.48 to 28.32 mm and 20.13 to 45.40 mm with the increase in <italic>f</italic>. The value of <italic>B</italic><sub><italic>g</italic></sub> increased from 4.3 to 11.69% when the value of <italic>f</italic> was increased from 10 to 40 Hz. Similarly, the extent of lateral and vertical deformation of ballast was found to be a function of <italic>A/D</italic><sub>50</sub> ratio.</p>