Pipeline case study (continued)

Since time was a critical issue the custom fabricated ABM panels were assembled immediately and the dirt work was commenced. Just a few days after the preconstruction meeting the custom fabricated ABM panels were delivered to the job site, and the now relocated creek was ready for armoring.

After grading was completed the creek was effectively “moved” to re bury the exposed pipeline. Also note that the electrical tower is now far away enough from the outer embankment to be out of the photograph.

Once the side slopes were graded to the desired angle, an “anchor” trench was cut at the top of each slope. This trench is located approximately 1 foot back from the top of the slope and its purpose is to provide an anchor or “toe-in” for the ARMORFORM mats. This anchor will help reduce the possibility of the mat from sliding down the slope, however, its primary function is to prevent scour at the top of the slope caused by water flowing outside of the creek’s banks when a flood occurs. A geotextile filter fabric supplied by Mirafi was installed directly over the subgrade to prevent the loss of fines when water passes through the open areas of the concrete mat. The ARMORFORM panels were then placed on top of the geotextile and temporarily held in place by placing sandbags around the edges. During the inflation process the sandbags are simply pushed off of the ABM as the injected grout thickens the mat.

The ARMORFORM panels were installed starting at the downstream end first. By working downstream to upstream, panels could be overlapped onto one another in the flow direction so that water could not infiltrate the system. Access to the project site was limited to 1 side of the creek, however, the armoring was required on both embankments. The work crews simply carried the light weight ABM panels across the creek and unrolled them into place. The grout was then pumped through a hose and into the ABM from the opposite side of the creek where the pump and the trucks delivering the concrete were located.

ABM panels being inflated on the inside embankment. Note the geotextile filter fabric on the slopes of the outer embankment in the foreground.

The installation of the ARMORFORM panels continued into its second day with just under half of the project completed. While the inflation of the panels continued, a dozier backfilled the anchor trenches of the mats that were installed the previous day. The second day of installation proved to be much more productive, and the project was completed in the early hours of the evening. The installation of the ARMORFORM panels went without a single glitch. Over 400 cubic yards of fine aggregate concrete was injected into the ABM panels in just 2 days, and the project was completed substantially under the amount budgeted by Colonial Pipeline.

As the inflation of the ARMORFORM mats continues into the second day a dozier can be seen in the background filling in the anchor trench of the mats installed the previous day. Note the change in the color of the concrete. The freshly pumped concrete in the foreground is dark gray, while the concrete that was installed the previous day has turned to a whitish color.