Design and construction of soil reinforced structures using composite reinforcement systems: modern and cost effective alternatives for high walls and slopes

摘要

The innovative concept discussed deals with the possibility to combine geogrids and steel mesh together to build high Mechanically Stabilized Earth (MSE) walls or slopes. The study stems from the need to analyze when a more efficient use of the reinforcements will work in favor of the overall project's economy, which is often looked at as a function of the material cost only. Results on existing structures indicate that, as structures achieve relevant heights (above 10 m), there is a large potential for cost effectiveness in using wire mesh and grids combined, in place of a 100% geogrids or a 100% steel mesh reinforcement solution only. In high MSE walls or slopes the steel higher flexural rigidity makes it suitable to work as the preformed facing component of the reinforcement system. Additionally, the steel shorter tail can provide the function of secondary reinforcement. The benefit of the geogrid system as the primary reinforcement is evident, achieving the material a higher strength at moderately low cost with relatively simple installation requirements. However, the interaction of the steel mesh and geogrids when used for soil reinforcement needs to be looked at, since these materials are characterized by a different structural response under load. Geogrids are mostly characterized by a time-load sensitive response (creep), and by elongations at break higher than those obtained for the steel mesh which, on the contrary, is primarily characterized by a constant rigid elasto-plastic response. Research has shown that some combined reinforcement configurations have the benefit to be only minimally affected by the different structural response, therefore a simplified design model can be used for a realistic failure prediction. Some numerical methods (Bishop, Janbu, working stress "displacement" method) for slope stability analysis, were implemented in a computer software to provide a simplified numerical model. The software allows to enter any type of soil and reinforcement mixed geometry. The numerical examples presented show how different geometries can provide a different degree of reinforcement effectiveness.