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Lequefaction of Seabed deposits and its effects on the submarine Iandslide and stability of marine structures.

海底沉积物液化及其对海底滑坡和海洋结构稳定性的影响。

基本信息

批准号：
60302065
负责人：
ISHIHARA Kenji
金额：
$ 6.4万
依托单位：
The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Co-operative Research (A)
财政年份：
1985
资助国家：
日本
起止时间：
1985 至 1987
项目状态：
已结题

项目摘要

The cyclic stresses induced in the seabed deposit due to overhead travelling waves are characterized by the rotation of principal stress direction. To simulate such stress conditions in the laboratory tests, the existing triaxial torsion shear test apparatus was revamped and remodeled and multiple series of tests were conducted on hollow cylindrical specimens of Toyoura sand. The results of tests disclosed that the cyclic shear strength of the sand is lowered by 20-30%, if the continuous rotation of principal stress is imparted, as compared to the strength obtained in the cyclic stress application without rotation of principal stress direction.The second prime subject was to provide a basic body of information on the possible reduction in shear strength of under-consolidated clay extant in the sea bottom. Several series of triaxial shear tests were performed on clay samples prepared under different degrees of under-consolidation. The results of tests disclosed the fact that a sharp red … More uction in shear strength can encountered if the extant seabed deposit is under-consolidated. This findings appear to prove the occurrence of lange-scale lendslides on gentle slopes in the ocean bottom.The third item of the present study was to see the effects of the cyclic deformation of seabed deposit due to the travelling wave on underwater driven piles. The current design of piling considers only forces coming fromthe impulse of waves near the sea surface. It appears highly probable that, in addition to this force, there should be forces on piles exerted from the deformation of surrounding ground due to the wave transmission. The analysis results in this context disclosed that the contribution from the seabed deformation to the bending moment in piles is insignificant as compared to the moment induced by the impulsive forces of waves overhead. However, when the soil surrounding the piles is to be checked against failure, the cyclic shear stress induced by wave itself is as significant as the cyclic stress imparted from the piles to the soil being considered.The fourth item of the study was an attempt to monitor insitu pore water pressures in the seabed deposits. Three pieces of piezometers were embedded, on the seabed surface and at 2.5m and 3.5m deep sand deposits, in the area of Shimizu harbor. The results of observation indicated that the transmission of wave-induced stress through the seabed deposits is governed largely by the deformation characteristics of soils. This fact indicated, in turn, that the deformation and stability of the seabed soils is dominated significantly by the magnitude of pore water pressures induced by the ocean waves. Less

海底沉积物中由架空行波引起的循环应力具有主应力方向旋转的特征。为了模拟室内试验中的这种应力条件，对现有的三轴扭剪试验装置进行了改造和改造，并对Toyoura砂中空圆柱形试件进行了多系列试验。试验结果表明，与在没有主应力方向旋转的情况下施加循环应力时获得的强度相比，如果施加主应力方向连续旋转，砂体的循环抗剪强度降低了20-30%。第二个主要课题是提供海底存在的欠固结粘土抗剪强度可能降低的基本信息。对不同欠固结程度下制备的粘土试样进行了一系列三轴剪切试验。试验结果揭示了这样一个事实，即如果现有的海底沉积物固结不足，则会遇到更大的抗剪强度下降。这一发现似乎证明了海底缓坡上存在大规模的滑坡。本研究的第三个项目是观察行波引起的海底沉积物循环变形对水下打桩的影响。目前的桩结构设计只考虑来自海面附近波浪冲击的力。除了这种力之外，很可能还存在由于波的传播而引起的周围地面变形对桩施加的力。在此背景下的分析结果表明，海底变形对桩身弯矩的贡献与架空波浪冲力引起的弯矩相比微不足道。然而，当对桩周土体进行失稳校核时，波浪本身引起的循环剪应力与桩向土体传递的循环应力一样重要。该研究的第四个项目是试图监测海底沉积物中的原位孔隙水压力。在清水港区的海床表面和2.5m和3.5m深的沙层处分别埋设了三块压电计。观测结果表明，波浪应力在海底沉积物中的传递在很大程度上取决于土壤的变形特性。这一事实反过来表明，海底土壤的变形和稳定性在很大程度上取决于海浪引起的孔隙水压力的大小。少