Study on deformation of subsurface layer by faulting and mitigation of damage to structures due to fault displacement

取得了以下研究成果。1.根据观测到的强震记录，直接估算了2000年鸟取县西武地震的应力变化历史。断裂带的中上部和下部应力降较大，在1-1.5 S范围内单调下降。2.利用DEM分析方法研究了走滑断裂引起的次表层剪切带的发育。在不同元素的沉积模式中，首先观察到的是从断层浴侧的基底断层发育的凹形向上剪切带，然后是螺旋形的剪切。螺旋面切变(Riedel切变)通过沉积物模型传播，并破坏了表面。随着基底位移的增大，地表发育与基底断层夹角较小的剪切带。这些剪切剂的几何形状和顺序与沙箱试验中观察到的一致。认为船形构造(断层两侧基底断裂发育的剪切带)和Riedel剪切力的形成归因于膨胀应力和垂直面上的剪切与横向剪切的共同作用。3.走滑断层模型试验表明，用不同性质的底质代替部分模型沉积物，可改变基底断裂引起的模型沉积物中滑动的位置和数量。4.对桩的地震反应进行了三维有限元分析。考虑了材料的非线性性质和相互作用。结果表明，数值分析较好地模拟了桩-土体系的实际工作性状，适当考虑了非线性材料特性，动、静力分析给出了不同的地基应变。

The following research results were obtained. 1. Stress change history of the 2000 Tottori-ken Seibu earthquake was estimated directly from the observed strong motion records. It was hind that the large stress drop occurred in the upper central part and lower part of the fault and that the stress dropped monotonically within 1-1.5 s. 2. Development of shear bands in the subsurface layer due to strike slip fault was examined using DEM analysis. In the sediment model of distinct elements, concave-upward shear zones which developed from the basement fault on bath sides of the fault were observed first and were followed by a helicoidally shaped shear. The helicoidally shaped shear (Riedel shear) propagated through the sediment model and broke the surface. With increasing basement displacement, shear zone striking at lower angle to the basement fault developed at surface. The geometry and sequence of these shears agreed with those observed in sandbox tests. It was hind that the development of ship shape structures (shear zones which developed from the basement fault on both sides of the fault) and Riedel shears was attributable to the stress due to dilatancy and the shear in the vertical plane along with the lateral shear. 3. Model tests of strike slip fault showed that the location and amount of slip farmed in model sediments due to basement fault changed by replacing part of the model sediment with ground material which had different properties. 4. 3-D finite element analyses were carried out to investigate the seismic response of piles. Nonlinear material properties and interaction were incorporated. It was shown that the numerical analysis simulated fairly well the actual behavior of pile-soil system with proper consideration of nonlinear material property and that the dynamic and static analyses gave different ground strain.