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。断层中部上部和下部出现较大的应力降，应力在1 ~ 1.5s内单调下降。2.利用DEM分析研究了由于走滑断层在地下层中剪切带的发展。在不同元素的沉积物模型中，首先观察到从基底断层发育的断层浴侧向上凹的剪切带，然后观察到螺旋状剪切。螺旋形剪切（Riedel剪切）通过沉积物模型传播并破坏表面。随着基底位移的增大，地表发育了与基底断层呈低角度走向的剪切带。这些剪切的几何形状和顺序与沙箱试验中观察到的一致。研究表明，船形构造（断裂两侧基底断裂发育的剪切带）和里德尔剪切的发育，是由于地壳运动产生的应力和伴随侧向剪切的垂直面内沿着剪切作用的结果。3.走滑断层模型试验表明，通过用不同性质的地层物质置换部分模型沉积物，基底断层引起的模型沉积物滑移位置和滑移量发生了变化。4.采用三维有限元法对桩的地震反应进行了分析。非线性材料特性和相互作用被纳入。结果表明，数值分析较好地模拟了桩-土体系的实际工作特性，并适当考虑了材料的非线性，动、静分析给出了不同的地面应变。

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.