Volume No. 9 Issue No.: 1 Page No.: 216-223 July-September 2014

 

A CONCEPTUAL MODEL FOR THE LOSS OF DYNAMIC SHEAR-STRENGTH OF THE TURBIDITY CURRENT IN THE ENVIRONMENT OF CARBONATE COMPENSATION DEPTH

 

J. Rajaraman* K. Thiruvenkatasamy1 and S. Narasimha Rao2

1. Department of Harbour and Ocean Engineering , AMET University, Kanathur, Chennai (INDIA)
2. IIT Madras and Dredging Corporation of India, Madras, Tamil Nadu (INDIA)

 

Received on : December 25,2013

 

ABSTRACT

 

A turbidity current is a current of rapidly moving, sediment-laden, water moving down a slope through water or another fluid. The current moves because it has a higher density than the fluid through which it flows. The driving force of a turbidity current is from its sediment which renders the turbid water denser than the clear water above. The deposit of a turbidity current is called a turbidite. Turbidity currents are an example of density or gravity currents. Turbidity currents are characterized by a well-defined front, also known as head followed by a larger known as the body of the current. A turbidity current is a suspension current in which the interstitial fluid is a liquid (generally water). When turbidity current approaches carbonate compensation depth due to environmental changes, it slows down. The shear strength of the turbidity current is also reduced. In this paper the interaction between filled fluid space and particles is illustrated through a conceptual model involving hypocycloid. The hypocycloid is a curve produced by a fixed point p on the circumference of a small circle of radius b rolling around the inside of a large circle of radius a > b. The particle circle with radius b rotates inside a fluid circle with radius a geo-technically a particle of radius b is inside a fluid environment of radius a. The geo-technical behavior of the sediments in suspension depends on a /b ratio which is discussed at length in the full paper. When the particle laden slow turbidity current reaches CCD (Carbonate Compensation Depth) all carbonate derived particles are dissolved. The particle contact points with other particles decreases in number. Due to this environmental change the shear strength which depends upon number of particle to particle contacts decreases with decreasing number of contact points. Already dissolved calcium carbonate of any type is no longer a frictional material or cementing material. The slow current (the final stage turbidity current) reaches Abyssal plain which contains only sand, silt and clay with other oozes. At this stage the sediment shear strength is controlled by coaxial component of shear strength (pure shear) and non coaxial component of shear strength (simple shear).

 

Keywords : Abyssal plain, Carbonate Compensation Depth (CCD), Dynamic shear strength, Hypocycloid, Turbidity current

 

 

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