Laserfiche WebLink
<br />6. Small bags, no side greater than 1.5 m (5 ft) , tend to settle and conform to the bottom. <br /> <br />7. The bag placed directly in front of the nose of the pier should be the width of the <br />exposed portion of the pier (See Sheets 8 and 10 of 10). This is the area with the <br />greatest turbulence. Overlapping of bags is important here. Any open gaps between <br />bags can allow sediment under the bags to be eroded causing undermining of the bags. <br />Geotextile fabric at this location would also help eliminate the possibility of <br />undermining. Similarly, no gaps should be allowed to form between the bags and the <br />front face of the footing. <br /> <br />8. The concrete bags should cover the stream bottom around the pier for a distance of 1.5 <br />times the width of the exposed portion of the pier or a minimum of 1.8 m (6 ft) whichever <br />is greater. <br /> <br />9. Use a cutoff wall along the entrance and trail end of the concrete bags that extend <br />across the entire stream channel, if possible. <br /> <br />10. Where there is a potential for continued scour along newly installed concrete bags in a <br />wide stream channel, use a cutoff wall or a fabric hinge to protect the bags against <br />undermining. <br /> <br />Concrete Bag Installation and Grouting of Undermined Area at Piers and Abutments <br />(MDSHA): (see Sheets 2 and 6 to 10 of 10) <br /> <br />1. Depending on the depth of the undermining, place one concrete bag or stack several <br />layers of concrete bags along the face of the abutment or pier in front of the undermined <br />area <br /> <br />2. Once the venVfill pipes have been installed and the bags are filled, pump the grout into <br />the undermined area. Cut the venVfill pipes flush with the top of the bags after the <br />pumping operation is complete. Debris could get caught up on these pipes and cause <br />additional scour if left exposed. <br /> <br />3. Adequate venting of the water to be displaced in the undermined area is importanl. The <br />water must be able to escape as it is displaced by the grout pumped into the cavity. A <br />1.2 m (4 ft) maximum spacing of the venVfill pipes is recommended. <br /> <br />4. It is important to keep the nozzle buried in the grout during pumping. This is to reduce <br />the amount of mixing of the grout and the water to be displaced. <br /> <br />5. Debonding jackets should be placed around piles to preventthA grout from adhering to <br />the piles if the added weight from the grout would cause a significant reduction in the pile <br />capacity. <br /> <br />6. If possible, clean out unstable material along the bottom of the undermined area prior to <br />filling with groul. This would reduce the amount of loose sediment discharged through <br />the vent pipes. <br /> <br />7. Pumping grout in the undermined area under a footing is not an underpinning for the <br />footing. This is done only to fill the void area and stop the fill material located behind the <br />footing from settling into the void area resulting in settlement of the roadway behind the <br />structure. <br /> <br />7.4 <br />