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|Title:||Erosion control of scour during construction. Report 8, Summary report|
|Authors:||Coastal Engineering Research Center (U.S.)|
Hales, Lyndell Z.
|Publisher:||Hydraulics Laboratory (U.S.)|
Engineer Research and Development Center (U.S.)
|Series/Report no.:||Technical report (U.S. Army Engineer Waterways Experiment Station) ; HL-80-3 rept.8.|
Abstract: When major stone structures such as jetties, breakwaters, or groins are erected in the coastal zone, they alter the existing tidal, wave-induced, or wind-driven currents that are in a dynamic equilibrium with the existing bathymetry. These altered currents and waves breaking on such structures under construction may change the existing bathymetry by causing bottom material to be suspended and transported from the region. This removal of material from around structures is often not compensated for by an influx of additional material, and the result is a scour hole that usually develops in the near vicinity of the toe of the partially completed structure. In order to ensure structural stability, any such scour area must be filled with nonerodible material (sufficiently stable to withstand the environmental forces to which it will be subjected) to allow construction to proceed to completion. This may result in significant additional quantities of material being required during construction that can potentially lead to substantial cost overruns. Four fundamentally different materials are presently being used to combat scour from wave-induced erosion around major stone structures. These are: (A.) A layer of crushed or quarry-run stone (graded or ungraded) placed as a foundation blanket on sandy or otherwise semiconsolidated foundations to prevent upward migration of loose materials and settlement of larger stone sizes. (B.) Fabricated gabion units placed underneath stone structures to form a continuous layer in lieu of a crushed stone foundation blanket. (C.) A wide assortment of synthetic filter fabrics placed underneath rock structures to prevent settlement into otherwise unconsolidated foundations. (D.) To a lesser extent, the use of Gobimats, particularly for toe protection of shore-connected structures such as seawalls or slope revetments. The objectives of this research were to develop techniques and knowledge for estimating resulting wave characteristics and wave-induced current fields in the vicinity of major coastal structures. Both analytical and laboratory experimental studies were conducted during the investigation. The analytical developments regarding wave heights and wave-induced currents were verified by the use of precise experimental studies of shore-connected breakwaters. Additional underlayer stability experimental studies were conducted for estimating the size of stone comprising the foundation bedding material which would remain stable under various wave conditions. A two-dimensional finite element numerical simulation model (FINITE) was developed by Houston and Chou (1984) that calculates wave heights under combined refraction and diffraction for both long and short waves approaching structures from any arbitrary direction. The wave equation solved governs the propagation of periodic, small amplitude surface gravity waves over a variable depth seabed. A computational scheme is employed that allows the solution of large problems with relatively small time and memory storage requirements, necessary for practical problem solutions. A generalized wave-induced current numerical model (CURRENT) was developed by Vemulakonda (1984) to estimate the magnitude of longshore currents and nearshore circulations in the vicinity of structures. This model retains the unsteady terms of the equations of motion, as well as advection and lateral mixing terms. Comparisons with known analytic solutions and experimental results provided good agreement. The model was successfully applied to a complex actual prototype field situation with reasonable results. NOTE: This file is large. Allow your browser several minutes to download the file.
|Rights:||Approved for public release; distribution is unlimited.|
|Appears in Collections:||Technical Report|
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