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Title: Erosion control of scour during construction. Report 1. Present design and construction practice
Authors: Hales, Lyndell Z.
Keywords: Construction practices
Construction projects
Sediment transport
Erosion control
Harbor structures
Hydraulic structures
Coastal structures
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.
Description: Technical Report
Abstract: It is frequently necessary to construct large engineering works of improvement in the surf and nearshore zone to protect harbor entrances, recreational beaches, and navigation channels. Shallow-water surface-gravity waves breaking on the structure during construction will cause bottom material to be suspended and transported from the region by longshore or other currents that may exist. This removal of material is often not compensated by an influx of additional material, and the result is a scour hole, or erosion, which usually develops along the toe of the structure. In order to ensure structural stability and functional adequacy of the works of improvement, any scour area must be filled with non-erosive material (sufficiently stable to withstand the environmental forces to which it will be subjected). This may result in additional quantities of material being required during construction which can potentially lead to substantial cost overruns. The objective of this study is to develop techniques to minimize and control scour during nearshore construction, and to predict the probable magnitude of scour that may result as a function of the wave climate. Most major stone structures require a foundation blanket for bearing surfaces to support the mass of the structure above, and to serve as scour protection during the actual construction. The thickness and design features of the blanket vary with location, but in general are on the order of 2 to 5 ft thick, extend beyond the toe of the structure from 5 to 25 ft, and are composed of quarry-run spoils. In recent years, a wide variety of plastic filter fabrics have been used on unconsolidated materials to prevent the settlement of heavier stone into the foundation. A layer of crushed stone or shell should be applied next in order to prevent puncture or tearing of the cloth by heavier stone. Foundation bedding materials should be placed ahead of the core construction at least 50 ft to prevent temporal scouring to undermine the working section. In those regions where, historically, vertical-walled structures have been built (sheet-steel pile, concrete pile, sheet-steel cellular units, bulkheads, etc.), these should be rehabilitated or rebuilt with sloped rubble-mound stone to dissipate wave energy along the structure. "Accelerated core placement" has been utilized successful ly in crossing scour holes susceptible to continuing scour. On major structures where the work will extend over more than a single construction season, no more stone should be placed than can be armored that season. Gabion units have been fabricated and placed in a continuous layer as foundation bedding material instead of a loose layer of crushed stone to ensure that the bedding material will be evenly distributed even after structure settlement. In emergency situations, scour has been minimized by filling ebb or flood channels with dredged material to allow construction operations to continue. Unique construction procedures have been applied in the State of Alaska which include working when soils are frozen or using ice block covered with soil to temporarily prohibit currents from scouring the work area during construction. The purpose of this report is to document the location and magnitude (regionally) of the problem of scour and erosion during construction of major structures in the coastal zone, and to review the present design and construction practices which are being applied in this regard. 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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