Macro- and micromechanical interactions between the geogrid and granular aggregates considering particle shape effects are essential for the performance of reinforced soil structures under cyclic normal loading (CNL). Crushed limestone and spherical granular media were mixed to obtain samples with different overall regularities (OR = 0.707, 0.774, 0.841, 0.908, and 0.975). Direct shear tests under CNL were conducted at various overall regularities, normal loading frequencies, and waveforms. Consistent with experiment tests, a discrete-element method (DEM) simulation was performed, incorporating authentic particle shapes obtained through three-dimensional (3D) scanning technology. The results showed that the macroscopic interface shear strength and volume change decreased with an increase in the overall regularity and normal loading frequency. The interface shear strength and deformation under the square waveform are bound to be higher than that under other waveforms. The coordination number, porosity, and fabric anisotropy were used to explain the macroscopic interface shear behavior in relation to the overall regularity. A higher coordination number and stronger contact force were observed with a decrease in the overall regularity. As the overall regularity decreased, the interface integrity and stability became stronger, with the result that the reinforced soil structure can withstand a larger principal stress deflection. Through experimental and DEM analyses, the underlying explanation for the effect of particle shape on the mechanical interaction of reinforced soil was revealed.

In this study, laboratory aging experiments are conducted to examine the aging effect on the interface shear behavior between soil and geomembrane. In the first stage, the geotechnical index and shear strength parameters of the soils are determined through laboratory experiments. The second stage focuses on examining the shear strength behavior of soil-geomembrane interfaces. The study examines commonly used geomembranes in the world, such as high-density polyethylene and thermoplastic polyolefin. Different synthetic waste leachates prepared in laboratory conditions are used to simulate real field conditions. The aging effects of geomembranes are examined by subjecting them to different pore liquids in the curing pool for 16 months. The surface deformations and roughness of the geomembranes used in the experiments are analyzed using scanning electron microscopy and optical profilometer. The study evaluates the effects of soil properties, pore liquids, and aging on the geomembrane surfaces. Soils with more coarser grains exhibited higher interface friction angles. It has been determined that the interface friction angles were significantly adversely affected by all curing liquids. Acidic mine drainage was found to have the most detrimental effect on the interface friction angles of geomembranes, while coal combustion product leachate caused minimal damage. The results from optical profilometer and scanning electron microscopy analysis aligned with the interface direct shear test results, further supporting the findings from the experiments. The study has shown that the design interface friction resistances are not sufficient for geomembranes exposed to chemicals in the long term. This aspect should be taken into consideration when creating design parameters.

The interface shear behaviour between the geomembranes and soils was studied. Sand/ bentonite (80/20), crushed sand, river sand, crushed gravel, and river gravel were used in this study. Polyvinyl chlorides were cured in the 0.5 molar saltwater and high-density polyethylene was cured in municipal solid waste leachate for eight months. Direct shear experiments were performed using cured GMs. This study recommends the use of crushed gravel in projects that use polyvinyl chloride and high-density polyethylene. The interface friction angles, which were exposed to the effects of saltwater and municipal solid waste leachate, decreased even after eight months, and this reduction effect should be considered in future projects. When designing projects involving GMs exposed to MSW leachate, particularly in landfills, potential damage over time should be considered, and appropriate design parameters should be selected. Failure to do so can lead to disasters that cause the loss of life and property.

The interface shear behaviour between the geomembranes and soils was studied. Sand/ bentonite (80/20), crushed sand, river sand, crushed gravel, and river gravel were used in this study. Polyvinyl chlorides were cured in the 0.5 molar saltwater and high -density polyethylene was cured in municipal solid waste leachate for eight months. Direct shear experiments were performed using cured GMs. This study recommends the use of crushed gravel in projects that use polyvinyl chloride and high -density polyethylene. The interface friction angles, which were exposed to the effects of saltwater and municipal solid waste leachate, decreased even after eight months, and this reduction effect should be considered in future projects. When designing projects involving GMs exposed to MSW leachate, particularly in landfills, potential damage over time should be considered, and appropriate design parameters should be selected. Failure to do so can lead to disasters that cause the loss of life and property.