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<br />Supplemental Observations on Grout Bags (MDSHA) <br /> <br />Design of Bags <br /> <br />Bags should be designed and constructed as flat mats, 0.9 m to 1.2 m (3 to 4 feet) wide and <br />about 0.3 m (1 foot) thick. The bag lengths should be on the order of 1.2 m to 2.4 m (4 to 8 <br />feet). Bags should not be filled to the point that they look like stuffed sausages, since they <br />will be much more vulnerable to undermining and movement, and will not fit properly into the <br />mat. <br /> <br />Both the designer and the installer should understand how the mat is expected to perform. <br />Each bag should be independent of other bags so that it is free to move; however, the bag <br />should be snugly butted against adjoining bags to minimize gaps in the mat. This concept <br />will result in a semi-fiexible mat that will be able to adjust to a degree to changes in the <br />channel bed. The mat should not be constructed as a rigid monolithic structure. It would be <br />helpful to have a pre-construction conference with the designer, contractor and the State <br />inspector. <br /> <br />The bags should be sized and located in accordance with the SHA Standards for the <br />particular type of foundation and condition of scour. It is recommended that the type of grout <br />bag installation and its design be reviewed by an engineer with experience in evaluating <br />scour at bridges. <br /> <br />Installation <br /> <br />Careful attention should be given to preparation of the bed on which the bags are to be <br />placed. Where the bed is uneven, such as might occur in scour holes, best results <br />will be obtained by planning for a sequence of placement of the bags so that each <br />bag adds to the support of the other bags. This is particularly important in locations <br />where several layers of bags are to be placed. It is unlikely that detailed plans will be <br />developed for such locations, and the integrity of the installation will depend on the skill of <br />the persons placing the mal. If the bed is highly irregular, appropriate modification of the <br />bed and removal of obstacles should be accomplished prior to placement of the bags. <br /> <br />Each bag should butt up firmly against its neighbor to provide a tight seal and to minimize <br />the occurrence of gaps between bags. Particular attention should be given to obtaining this <br />tight seal between the foundation and the first row of bags. <br /> <br />For piers, the bags should extend to a distance of 1.5 to 2 times the pier width on both sides <br />as well as upstream of the pier nose and downstream of the pier end. <br /> <br />For abutments, the best results are obtained for most locations by placing the bags the full <br />length along the upstream wingwall, abutment backwall and downstream wingwallto form a <br />solid mal. As an interim guide, the mat width for abutments is recommended to be on the <br />order of 1.8 m to 2.4 m (6 to 8 feet), depending upon the particular site conditions. This <br />arrangement provides for a smooth streamlined design that locates the ends of the mat <br />away from the main stream current or thalweg. Of course, there are a wide variation of <br />conditions at abutments and each location needs to be designed for the site conditions. <br /> <br />7.6 <br />