Development of the methods of safety evaluation in land improvement facilities

1. 采用柱形破坏概念定义了地基渗流破坏的安全系数。通过改变板桩设置深度和挖土宽度，分析了二维集中流情况下的极限水头。结果表明，开挖宽度越小，设置深度越深，对渗流稳定性的影响越大。此外，还表明，当各向异性比为：2时，地面稳定性降低。考虑到材料的拉伸破坏通常发生在其特性发生变化时，因此认为土体引起的破坏与此类似。本文对某小土坝地基进行了三轴压缩试验，考察了不同含水量条件下竖向裂缝的产生情况，结果表明竖向裂缝的发生时间较早，试验含水量较低。因此，当水库水位上升时，可能发生水力压裂。对两轴应力作用下的楔形插入技术进行了研究。在含河卵石和碎石两种类型的混凝土中，各破碎能均由荷载开启位移测量得到。结果表明，与单轴应力情况相比，含河卵石混凝土的破坏能减小，且含碎石混凝土的破坏能大于含河卵石混凝土的破坏能。此外，对实测数据采用了多直线近似法。软化曲线形状各不相同，杨氏模量减小，压应力比增大。本文提出了一种考虑动力强度、n值、中位粒径、细粒含量等土壤参数空间变异性和地震发生统计特征的围垦堤防液化概率计算方法。应用该方法，对砂土压实桩的可靠性设计进行了探讨，为地基抗液化加固提供了依据。结果表明，为了使总成本最小，确定了最佳换砂率

1. Safety evaluation in seepage flow The safety factor to the seepage failure of the foundation ground is defined by using the prismatic failure concept. The limit water head is analyzed in case- of two dimensional concentrated flow by varying the setting depth of sheet piles and the width of digging of ground. As a result, it is clarified that the smaller the width of digging and the deeper the setting depth is, the more decreasing the stability to the seepage becomes. In addition, it is also shown that the stability of the ground decreases when the ratio ofanisotopic:2. Hydraulic fracturing in fill material Considering the tensile failure generally occurs in the material when its character changes, soil is thought to cause a similar mannec Tri-axial compression tests are conducted on samples taken from a foundation in a small earth dam to examine the generation of the vertical crack with varying water content As a result, it is confirmed that a vertical crack occurs at a considerably … More early stage and lower water content in the experiment, so it suggests the hydraulic fracturing possibly occurs when reservoir water level rises.3. Safety evaluation in concrete structures The wedge insertion technique under two axial stresses is performed. In two types of concrete with river gravel and crushed stone, each breaking energy is obtained from the measurement of load-opening displacement As a result it is clarified that the breaking energy decreases compared with the case of the uniaxial stress, and the one with crushed stone is larger than that with the river gravel. In addition, the multi straight line approximation method is applied from the measurement data. It is also shown that the shape of softening curve differs each other, and the Young's moduli decrease, increasing in the compressive stress ratio.4. Reliability design of reclamationtlvke A calculation method of probability of liquefaction in reclamation dyke is proposed considering the spatial variability of soil parameters for the dynamic strength, N-values, median grain size, fine contents and the statistical characteristics of the earthquake occurrence. Using this method, the reliability design of the sand compaction piles is discussed for the ground improvement against the liquefaction. As a result, it is shown that the optimum sand replacement rate is determined so as to minimize the total cost Less