Research on The Establishment of An Earthquake Response Analysis Scheme and The Improvement in Damping Performance of A New Type of Seismic Isolation System Composed of Piles Covered by Pipes and Partial Soil Improvement with Damping Devices

第一年，在试验场地采用常规技术，采用4根直径600mm、长度2.5m的土水柱改造，构建面积为2.4m × 2.4m、高度为1.0m的方形基础块（CF），并进行强制振动试验。次年，在CF以东6m处，采用与上年相同的工艺，新建同尺寸基础块，并通过改变侧面的条件进行强制振动试验。试验最后阶段（基础侧面沟槽深度0.8m），在新基础块（IF）沟槽内回填阻尼复合材料，进行强制振动试验。阻尼材料是沥青、碎石和废轮胎头的混合物。实验结束后，继续进行地震观测。试验、地震观测和模拟分析的主要新发现如下：中频比CF能更好地定量阐明阻尼性能和减振性能。首先，从强迫振动试验的结果来看，与CF相比，中频下单位激振力的响应位移在主导频率下降低了约30%；从2004年包括新潟县地震在内的32次地震观测资料推测的传递函数中，证实了中频比CF的响应减小更大。但其减小率还没有达到强制振动试验的程度。这是由于基础块的尺寸小，侧面的输入也小。

In the initial year, a foundation block (CF) with a square area of 2.4m x 2.4m and with a height of 1.0m was structured by a conventional technique on the experiment site improved by four soil cement columns (diameter:600mm, length:2.5m), and forced vibration tests were conducted. In the next year, a new foundation block of the same size was constructed 6m to the east of CF by the same technique as the previous year, and forced vibration tests were conducted by changing the conditions of the side surface. At the last stage of this test (the trench depth of the side surface of foundation was 0.8m), a damping composite material was backfilled into the trench of the new foundation block (IF), and forced vibration tests were performed. The damping material is a mixture of asphalt with crushed stones and scrap tire tips. After the experiment, the earthquake observation has been continued. The main new findings obtained from the tests, the earthquake observation and the simulation analyses of them are as follows:The IF could quantitatively clarify damping performance and vibration reduction better than the CF. First of all, from the result of the forced vibration tests, it was confirmed that in the case of IF, the response displacement per unit of excitation force was reduced approximately 30% at the dominant frequency, being compared to the case of CF. Next, more response reduction was confirmed in the IF than the CF from the transfer functions, which were presumed from the data of earthquake observations of 32 waves including the Mid Niigata Prefecture Earthquake in 2004. However, its decrease ratio was not to the extent of the case of forced vibration tests. It is attributed to the small sizes of foundation blocks and the small inputs from the side surfaces.