A STUDY ON WAVE-INDUCED LIQUEFACTION OF SANDY SEA BED AND SEDIMENT TRANSPORT

砂质海床波致液化及沉积物迁移研究

基本信息

批准号：
06650577
负责人：
MAENO Yoshihiko
金额：
$ 1.28万
依托单位：
NIHON UNIVERSITY JUNIOR COLLEGE
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1994
资助国家：
日本
起止时间：
1994 至 1996
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-06650577/
关键词：
Liquefaction Sediment transport Seabed Coastal Environment Measurement Drifted Sand Effective Stress Pore Pressure

项目摘要

The effective stress and pore pressure in the surf zone were directly measured to study the relation with the stress, and the wave condition and other factors, and to evaluate the bottom elevation change from the effective stress data. From the careful observation and analysis of the measured data during this period the followings are found.(1) The pore pressure and effective stress appears to respond to the water surface elevation without any time lag. The measured area is always attacked by breaking waves and the sand there is anticipated to be loose. Then, the pressure on the bottom transmits almost simultaneously to the pore presssure inside the soil. Both the pore pressure and effective stress show larger variation when the short waves with large wave steepness pass.(2) The mechanism of liquefaction in the surf zone seems to be different from that outside the surf zone. The large effective stress drop and strong flow in the onshore direction when the wave crest passes are the possible cause for the sand movement in the surf zone.(3) The water depth change estimated from the effective stress records agrees well with the measured depth change. This leads to the following three conclusions (i) The effective stress in sea bed is closely related to liquidization of sand and then to sand movement. (ii) The sea bottom elevation change can be evaluated from the effective stress in the sand. (iii) The effective stress sensor was proved to be useful in estimating local and temporal sediment transport.(4) The currents going offshore were observed when the sea level was low. The effective stress varied corresponding to these currents. The averaged effective stress over 50 minutes drops sharply at low tide. The shallower water depth may be a possible cause, and the exact reason for this is still being studied. The ground water level near the coast is likely to affected by the long waves and tidal changes.

直接测量冲浪区的有效应力和孔压力，以研究与应力以及波浪条件和其他因素的关系，并评估有效应力数据的最低升高变化。从在此期间对测量数据进行仔细的观察和分析。（1）孔隙压力和有效应力似乎对水面高度响应而没有任何时间滞后。测得的区域始终会被破坏的波浪攻击，预计那里的沙子会松动。然后，底部的压力几乎同时传输到土壤内部的孔隙压力。当较大波浪陡度的短波传递时，孔隙压力和有效应力都显示出更大的变化。（2）冲浪区域中液化的机理似乎与冲浪区外部的液化机制不同。当波峰通过时，在陆上方向上的较大有效应力下降和强烈的流动是冲浪区砂运动的可能原因。（3）从有效应力记录中估计的水深变化与测量的深度变化非常吻合。这导致了以下三个结论（i）海床的有效应力与沙子的液化密切相关，然后与沙子运动有关。（ii）可以根据沙子的有效应力评估海底高度变化。（iii）事实证明，有效的应力传感器可用于估计局部和颞沉积物的运输。（4）当海平面较低时，观察到了近海的电流。有效应力变化与这些电流相对应。在低潮时，在50分钟内平均的有效应力急剧下降。较浅的水深度可能是可能的原因，而确切的原因仍在研究中。海岸附近的地下水位可能会受到长浪和潮汐变化的影响。