Studies on Soil Fluidization Mechanism and Sediment Suspension under Wave Action

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Project title

Code/計畫編號

NSC86-2611-E019-027

Translated Name/計畫中文名

海域地形變遷---子計畫六：波浪引起之非凝聚性海床不穩定現象與交互作用---(I)波浪作用下海床液化反應機制與漂沙現象研究

Project Coordinator/計畫主持人

Shiaw-Yih Tzang

Funding Organization/主管機關

National Science and Technology Council

Department/Unit

Department of Harbor and River Engineering

Website

https://www.grb.gov.tw/search/planDetail?id=286047

Year

1997

Start date/計畫起

01-08-1996

Expected Completion/計畫迄

31-07-1997

Bugetid/研究經費

520千元

ResearchField/研究領域

土木水利工程
海洋科學

本計畫為海工學門海岸空間利用第六子題『海域地形變遷』整合計畫之一子計畫,三年期計畫全程研究範圍主要為海床在波浪作用下其力學反應,特別是其不穩定反應之物理特性及與波浪之交互作用對波場與海床附近流場之影響。最後將針對影響海域地形變遷最關鍵之懸浮漂沙活動與海床反應關聯做深入研究,並期望提出適當之漂沙濃度水深分布模式。本年度為第一年計畫,主要重點是『波浪作用下海床液化反應機制與漂沙現象研究』。本研究先以理論分析共振液化時之力學機制,並分就二維平行孔穴與圓柱孔穴探討共振波動特性與孔穴水流動壓力分布,接著再以Tzang(1992)之實驗結果探討砂質土壤與沈泥質土壤在波浪作用下之同步反應,並深入探討沈泥質土壤反應之特性表面液化現象。研究結果顯示共振液化機制可合理描述實驗室之試驗結果,而沈泥質之特性反應顯示細顆粒底床在波浪作用時,不能完全用孔彈性理論(Poro-elasticity)描述,且表面液化現象不僅與邊界層水動力特性有關,且往往造成較明顯之懸浮漂沙現象。最後並以分析結果建立實驗配置以進行下一階段之實驗研究計畫。 This project is one of the sub projects of the Coordination Project entitled "Geomorphologic Changes in Marine Areas". The three-year term project focuses on the subject regarding seabed responses under water wave actions, especially on the mechanisms of instability and their interactions. Detailed studies will be performed to find out the link between the suspended sediment transport and the seabed instability. It is expected in the last a reasonable model of sediment concentration profiles with considerations of seabed characteristics under wave actions is to be proposed for engineering applications. Present report is for the first-year project which studied the mechanism of soil fluidization and suspended sediment transport in and near cohesionless seabeds. The study began with the theoretical analysis of the mechanism of the seabed fluidization due to cavity resonance. The cavity configurations consisted of a 2-D crack and a cylindrical type and the characteristics of resonant waves and the induced pore pressures were discussed. Afterwards, based on the experimental data by Tzang (1992), the instantaneous responses of a sandy and a silty seabeds and the surface fluidization mechanism in the silty seabed were analyzed in detail. These studies illustrated that the proposed cavity resonance model could reasonably explain the seabed fluidization observed in the laboratory set-ups. The fine-grained silty seabeds would respond to wave actions slightly different from sandy seabeds, thus their behaviors did not totally follow poro-elasticity theory. In particular, the associated phenomenon of surface fluidization exclusively found in the silty beds are related to the hydrodynamic characteristics in the boundary layers at water-seabed interface. It usually resulted in more significant sediment suspensions. Based on the mentioned analyses, an experimental set-up was preliminarily executed for next step experimental studies.

Keyword(s)

波浪
孔隙水壓
海床
不穩定性
懸浮漂沙濃度
Wave
Pore pressure
Seabed
Instability
Suspended sediment concentration

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Studies on Soil Fluidization Mechanism and Sediment Suspension under Wave Action

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