Study on Reinforcement Mechanism in Geosynthetic Reinforced Soil and Its Applicability to Soil Structures for Irrigation

In order to develope cost-effective practical methods that can protect and mitigate hazards caused by overflow-induced and earthquake-induced slope failures of soil irrigation structures, a new type of reinforcement technology combined with geosynthetic reinforced soil and a soil bag system was proposed. A new type of reinforcement technology combined with geosynthetic reinforced soil and a soil bag system was proposed to develop cost-effective practical methods that can protect and mitigate hazards caused by overflow-induced and earthquake-induced slope failures of soil irrigation structures. First, a series of laboratory tests with a pile of soil bags and tensile-reinforced soil and simulations were conducted to understand the stress-strain characteristics of geosynthetic-reinforced soil. As a result, it was found that the tensile-reinforcement mechanism in developing strength was associated with deformation of backfill materials, and strongly influenced by the deformation modes and particle sizes of backfill materials. Moreover, the sliding resistance of a pile of soil bags against lateral loading can be significantly improved by stacking soil bags inclined with the inner end placed lower than the front end, similar to a masonry wall. Second, shaking table tests and hydraulic overflow-induced collapse tests were conducted in a full-scale model to validate the effectiveness of the newly designed reinforcement technology. Shaking table test results showed that slippage among bag-to-bag interfaces easily occurred in a horizontal stacked soil bag slope. On the other hand, the soil bag slope stacked inclined were stable against lateral seismic loads. Furthermore, slope facing with soil bags that have a geosynthetic reinforcement tail significantly increased substantial seismic stability. As far as erosion resistance against overflow, a slope face reinforced by soil bags with a geosynthetic sheet embedded as a tail in the embankment was very stable against temporary flooding at high overflow levels required in the field. Finally, in the field tests, it was confirmed that the construction procedures were not only simple, but also didn't need heavy machineries and costly materials (i.e., concrete and steel). This rehabilitation technology also could be successfully applied to the small earth dam damaged by the 2008 Noto Peninsula earthquake. In the pratical design, the Multiwedge method was applied for stability design of reinforced slopes. Simulation results showed that this method could be expressed the effect of the stack inclined method, and connections between soil bags and tails. It's concluded that, the reinforcement technology proposed in this study is a simple and cost-effective technology to prevent the collapse of the downstream slope by natural disasters. This method can be applied to small earth dams as well as canals, road embankments, railways, river dikes, etc.