To study the interaction between sand particles and geogrids, pullout tests were performed on one type of geogrid in Pingtan medium sand. The sand motion around the ribs was captured by high-resolution digital camera and CCD camera. The images were analysed with the aid of digital photography measurement and micro-image analysis. Microscopic particle motion and displacement fields around the transverse ribs were then obtained to verify the macro behaviour of the sand–rib interaction. It was found that the thickness of shear band increases with the normal stress applied, and the shear zone is asymmetrical to the soil–rib interface. A near wedge shape shear zone was observed by analysing the shear strain around the ribs, which indicated that a punching shear failure mechanism may be applicable to the tested geogrid in medium-dense sand. Comparison of various models for bearing capacity of geogrids shows that the size and shape of bearing members should be considered in the calculation of bearing resistance of geogrids.
Adequate waste disposal is currently under high demand in Australia, due to a rapid growth in population. Australia’s scarcity and cost for the use of clays (most commonly used landfill liner material) have resulted in a search for alternative materials to achieve satisfactory performance in landfill design. This study explored liquid limit and hydraulic conductivity (HC) of coal composites for potential landfill liner use. Brown coal (lignite) was mixed with polyacrylamide (PAM) or sodium bentonite (Bt) to investigate liquid limits (LL), HC, and swelling behaviour. Each additive was subject to distilled water and sodium chloride solution (50 g/l) to investigate the effects of pore fluid chemistry. The addition of 2 wt% PAM resulted in approximately 82 percentage point (pp) increase in the LL of lignite with distilled water and 76 pp increase with 50 g/l sodium chloride (NaCl) solution. The HC of lignite also decreased by more than two orders of magnitude as the PAM content increased. The swell index of lignite composites increased with the addition of PAM. This exploratory study has found the unique property of brown coal and its composites that the LL, HC and swell index do not deteriorate significantly in the presence of highly concentrated electrolyte solution (50 g/l NaCl). Such distinct properties will be beneficial over currently used landfill liner materials.