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<br />There were a few sites visited where the bags had an ungainly appearance. In most cases,
<br />these were bags that were pumped so full that they looked like sausages. Other reasons for
<br />a poor appearance include inadequate attention to design, installation, preparation of the
<br />bed on which the mat is placed, or a combination of these factors.
<br />
<br />Early installations included bags with lengths of 4.6 m (15 feet) or more. In some cases, the
<br />bags were too long to fit properly into a compact mat. Use of shorter bags should help to
<br />minimize this problem in future installations.
<br />
<br />Specifications for grout bags for undermined areas at piers were also provided by the
<br />State of Maine Department of Transportation as follows:
<br />
<br />The underwater grout bags shall be fabricated based on the dimensions of the existing voids
<br />to be filled. Bags should be on the order of 900 mm to 1.2 m (3 to 4 ft) wide and 1.8 to 2.4
<br />m (6 to 8 ft) long. Bags shall be securely placed to form a perimeter bulkhead to partially fill
<br />and enclose the substructure void. Grout shall be pumped to uniformly fill the secured bag
<br />with sufficient restraint so as to not rupture the bag. Consecutive bag placement shall be in
<br />accordance with the manufacturer's requirements. At a minimum this will require: placement
<br />of reinforcing bar between successive layers, stitching together adjacent bags with an
<br />overlapping splice (where accessible), and covering holes left by grout and other inserts.
<br />
<br />NOTE: The State of Maine recommends stitching bags together for protection of
<br />undermined areas at piers. This procedure conflicts with the guideline provided by the State
<br />of Maryland in Tips for Concrete Bag Installation number 4.
<br />
<br />References
<br />
<br />Bertoldi, D.A., Jones, S.J., Stein, S.M., Kilgore, A.T., Atayee, A.T., 1996, "An Experimental
<br />study of scour protection alternatives at Bridge Piers,. FHWA-RD-95-187, Office of
<br />Engineering and Highway Operations R&D, McLean VA.
<br />
<br />Brown, SA, E.S. Clyde, 1989, "Design of Riprap Revetment," Hydraulic Engineering
<br />Circular No. 11, FHWA-IP-016, prepared for FHWA, Washington, D.C.
<br />
<br />Fotherby, L.M., 1997, "Footings, Mats, Grout Bags, and Tetrapods, Protection Method
<br />Against Local Scour at Bridge Piers," M.S. Thesis, Colorado State University.
<br />
<br />Holtz, D.H., Christopher, B.A., Berg, A. A. , 1995, "Geosynthetic design and Construction
<br />Guidelines," National Highway Institute, Publication No. FHWA HI-95-038, Federal Highway
<br />Administration, Washington D.C. May.
<br />
<br />Keown, M.P., 1983, "Streambank Protection Guidelines for Landowners and Local
<br />Governments," U.S. Army Corps of Engineers, Waterways Experiment Station, Vicksburg,
<br />MS.
<br />
<br />Lagasse, P.F., J.D. Schall, F. Johnson, E.V. Richardson, F. Chang, 1995, "Stream Stability
<br />at Highway Structures," Hydraulic Engineering Circular No. 20, FHWA-IP-90-014, FHWA,
<br />Washington, D.C.
<br />
<br />Maryland State Highway Administration, 1993, "Bridge Scour Notebook Supplement No.1,"
<br />MDSHA Office of Bridge Development, Bridge Hydraulics Unit, May.
<br />
<br />7.8
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