This paper aims to investigate the interfacial strength characteristics, particularly the residual strength, of a high-density polyethylene smooth geomembrane (GMB-S)/nonwoven geotextile (NW GTX) interface using a novel ring shear apparatus under high normal stresses and two specimen conditions. A total of eight normal stresses (from 50 kPa to 2308 kPa) and two specimen conditions (dry and submerged at ambient temperature) are considered in this study. The reliability of using the novel ring shear apparatus to study the strength characteristics of the GMB-S/NW GTX interface was demonstrated by conducting a series of direct shear experiments with a maximum shear displacement of 40 mm and ring shear experiments with a shear displacement of 10 m. The peak strength, post-peak strength development, and residual strength determination method of the GMB-S/NW GTX interface are explained. Three exponential equations suitable for characterizing the relationship between the post-peak friction angle and the residual friction angle of the GMB-S/NW GTX interface are established. This relationship can be used with the relevant apparatus (i.e., an apparatus with deficiencies in executing large shear displacement) in determining the residual friction angle of the high-density polyethylene smooth geomembrane/nonwoven geotextile interface.

A novel multifunctional ring shear apparatus is introduced in this paper, which is developed for investigating the interface strength characteristics of liner systems in various waste containment and other facilities. Annular specimens with a 300-mm inner diameter and a 500-mm outer diameter are tested by the apparatus. This apparatus consists of four components: (1) the vertical loading system, (2) the torsional shearing system, (3) the multifunctional shearing box, and (4) the process control and data acquisition system. The advantages of this apparatus are as follows: (1) The specimen can be tested both in displacement control and stress control, during which the normal stress is maintained or varied as needed. (2) The maximum normal stress and shear stress that can be loaded are 2.39 and 2.59 MPa, respectively. (3) The shear displacement is unlimited and the real-time shear displacement of each interface in the liner system can be obtained. (4) Special nail plate panels are developed for clamping different types of geosynthetics. A new adaptive telescopic pressure plate device is also developed for testing other materials, such as the clay layer and sand layer, and adapting to its compression deformation without lateral deformation. The performance of the apparatus is comprehensively evaluated by the conventional shear mode experiment and mode switching shear experiment of the textured geomembrane/geotextile interface and the conventional shear experiment of the composite liner system.

Buried high-density polyethylene (HDPE) pipes are widely used in solid waste landfills, heap-leach mining pads, large earth dams, and other infrastructures. Large earth pressures and elevated temperatures in these applications can lead to the failure of HDPE pipes, resulting in pipes plugged in the drainage system and increases in the leachate level. High leachate levels contribute to landslides in landfills. Based on the theory of elasticity, a plane strain pipe-soil interaction model was developed to investigate the deformation characteristics of HDPE pipes while considering the influence of temperature. Analytical solutions were obtained under perfectly smooth and fully bonded interfaces. The solutions and calculated results were verified using the Höeg formula and the results of laboratory tests. The results show that the Höeg formula is applicable to pipes with a standard dimension ratio (SDR = nominal diameter/wall thickness) greater than 40. In contrast, the analytical solutions obtained in this paper are relatively accurate for calculating the deformation characteristics of pipes when the SDR of the pipes is less than 40, as in the case of most landfills. A parametric analysis was conducted, and implications for landfills were analyzed. Furthermore, simplified equations were derived for landfill design, and preliminary suggestions were provided regarding the waste height control and temperature regulations in landfill operations. To ensure the safety and stability of HDPE pipes and to avoid environmental damage, the maximum waste temperature of the landfill should be regulated under a certain waste height, and the waste height should be controlled against a given maximum waste temperature. According to the simplified equations, the security of the drainage system can be evaluated with monitored waste height and temperature, and pipes plugged in the drainage system could be avoided.