Effects of reinforcement arrangements on load transfer in spring-based trapdoor tests

Five spring-based trapdoor tests allowing continuous displacement during both fill placement and localised static loading were conducted. Quartz sand was used as the test fill. Biaxial geogrids with and without ribs, having two different reinforcement stiffnesses, were used as reinforcement materials. Test results show that when two low-stiffness geogrid reinforcement layers were used, higher reinforcement spacing ratios (defined as the ratio of the reinforcement spacing between two reinforcement layers to the trapdoor width) induced more stable and efficient load transfer generally. Consequently, an optimum value of 0.3 and a worst-case value of 0.1 for the reinforcement spacing ratio were obtained and considered as representatives of two low-stiffness reinforcement layers for comparison with a single high-stiffness reinforcement layer, where their total reinforcement stiffnesses were approximately same. Generally, the inclusion of two low-stiffness reinforcement layers induced more stable load transfer. More importantly, compared with a single high-stiffness reinforcement layer, two low-stiffness reinforcement layers with the optimum reinforcement spacing ratio enhanced load transfer and induced less overall tensile forces, whereas the reinforcement arrangement with the worst reinforcement spacing ratio induced similar load transfer efficiency and overall tensile forces.