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<br />Design Guideline 7 <br />Grout/Cement Filled Bags <br /> <br />Introduction <br /> <br />Grout/cement filled bags have been used to protect stream banks in areas where rip rap of <br />suitable size and quality is not available at a reasonable cosl. Guidelines for the use of bags <br />(sacks) as a streambank revetment can be found in Richardson et al. (HIRE) (1990), <br />Lagasse et al. (HEC-20) (1995) and Keown (1983). Grout/cement filled bags have also <br />been used as a countermeasure against scour at bridges. Historically they have been used <br />to fill in undermined areas around bridge piers and abutments. As scour awareness <br />increases, grout filled bags are being used to armor channels where scour is anticipated or <br />where scour is detected. Whether they are implemented in a post- or pre-scour mode, grout <br />bags are relatively easy to install and can shift to changes in the channel bed to provide <br />effective scour protection. <br /> <br />Design Guidelines <br /> <br />A precise quantitative factor of safety design procedure is not normally completed for the <br />design of grout filled bags. This type of design would be beneficial in determining the <br />hydraulic stability of the bags, but historically this has not been done for grout filled bags. It <br />would require a comparison of the hydraulic shear stress and the critical shear stress to <br />uplift the grout bag as is done with riprap using discrete particle analysis. Information on <br />hydraulic performance of grout bags at bridge piers can be found in Bertoldi et al. (1996) <br />and Fotherby (1992). More often, engineering judgment is used to select a bag size that will <br />not be removed by the flow and installation practices are more critical to the success of the <br />system. Guidelines for the use of grout filled bags for bridge scour reflect information <br />provided by the Maryland State Highway Administration (MDSHA). <br /> <br />Tips for Concrete Bag Installation (MDSHA): (see attached Sheets 1 -10) <br /> <br />1. It is preferable to place a single layer of bags instead of stacking. Filter Fabric should be <br />placed under single layered bags that have the potential to settle away from each other. <br />Guidelines on the selection and design of filter material can be found in Brown and Clyde <br />(HEC-11) (1989) and Holtz et al. (FHWA HI-95-D38) (1995). <br /> <br />2. If bags are stacked, overlap the joints of the preceding layer. <br /> <br />3. If possible, bags should be buried so that the top of the bag is at or below the stream <br />bottom (see Sheet 3 of 10). When filling a scour hole, keep the top of the bag at or <br />below the stream bottom, if possible (see SheetS of 10). <br /> <br />4. Do not tie bags together with reinforcing steel or by any other means. Allow bags to <br />settle to a state of equilibrium individually. (This differs from specifications <br />recommended by the State of Maine where stitching bags together is a recommended <br />procedure for protection of undermined areas at piers) <br /> <br />5. Excessively large bags, one side greater than 4.6 m (15 ft), are more susceptible to <br />undermining because they do not tend to settle or shift into place as scour develops. <br /> <br />7.3 <br />