Study on the substantial increase in the seismic stability of reinforced soil structures by preloading and prestressing

通过对桥墩结构缩尺模型的静力循环加载试验和振动台试验，研究了预压和预应力显著提高加筋土结构抗震稳定性的基本机理。根据研究人员的建议，三年前在九州博多车站附近已经建造了一座土工织物加固砾石铁路桥的原型桥墩。在固定到预应力条件之前，在垂直方向上对用若干水平土工织物层加固的结构的砾石回填进行预加载。模型试验结果表明，只要保持足够大的预应力，加固结构在地震荷载条件下变得非常坚固。当输入地震荷载为振幅为700 gals的长周期均匀正弦波，其频率与结构的固有频率几乎相同时，结构顶部的近共振响应高达2，000 gals。即使在这种情况下，结构只表现出有限的循环横向位移与一些残余的垂直压缩。提出了一种在结构出现沉降时保持预应力的方法，经验证是有效和实用的。对试验结果进行了土工分析，以发展设计方法。

The basic mechanism of substantial increasing the seismic stability of reinforced soil structures by preloading and prestressing was studied by performing static cyclic loading tests and shaking table tests on small-scaled models of pier structures. Based on the proposal of the researchers, a prototype bridge pier for a railway bridge of geotextile-reinforced gravel has already been constructed near the Hakata station in Kyushu three years ago. The gravel backfill of the structure that was reinforced with a number of horizontal geotextile layers was preloaded in the vertical direction before having been fixed to prestressed conditions. The model test results showed that reinforced structures become very strong under seismic loading conditions as far as a sufficiently large prestress was maintained. When the input seismic load was a long period of uniform sinusoidal waves with an amplitude of 700 gals at a frequency that was nearly the same with the natural frequency of the structure, the nearly-resonance response at the top of the structure was as high as 2,000 gals. Even in that case, the structure exhibited only a limited amount of cyclic lateral displacement with some residual vertical compression. A method for maintaining prestress when the structure is exhibiting settlement was examined and found effective and practical. Geotechnical analysis of the test results was made for developing the design method.