Exposed Pipeline is Once Again Protected Thanks to ARMORFORM

A once buried pipeline that is now exposed can be of serious concern. When Colonial Pipeline found out that a 16” diameter pipeline that had once been buried well beneath Raccoon Creek in North Georgia was now exposed they required immediate action.

In December of 1995, shortly after the exposed pipeline was discovered, Colonial Pipeline had a crucial decision to make. The pipeline obviously needed to be re buried. The options were to close the pipe, refit it and re bury it below the now relocated creek bottom or to simply move the creek back to its original position. The first option appeared to be the easiest thing to do, however, shutting down the pipeline would cause serious down time and there was no guarantee that the creek would not relocate itself again and cause the pipeline to be re exposed. Upon further inspection of the site it was discovered that the outer bank of the creek was now less than 20 feet away from a 500,000 volt electrical tower! It was obvious that the creek would have to be moved.

It was decided to relocate a 250 feet long curved section of the creek in order to re bury the exposed pipeline and to protect the electrical tower. The creek would have to be moved over 40 feet thus creating a much sharper bend than that which was formed naturally, and there was evidence in the surrounding terrain that the creek frequently overtopped its banks. It was obvious that there was the potential for a serious erosion problem. Hard armoring of the creek’s embankments would be necessary.

 

Once it was decided what needed to be done Colonial Pipeline was faced with another problem. The application of the hard armor system would have to be done without dewatering the site. Since it was an active creek, flow conditions of 2 feet deep at velocities of 5 fps were expected during the construction. Any type of poured concrete or shotcrete was immediately ruled out. Rip rap seemed to be the obvious solution, but very large stones would be needed and it was feared that the sized of the stone would lower the capacity of the creek and cause more water to spill out of its banks. It was decided that an articulated concrete block mat, or ACB, would be the best possible solution. ARMORFORM® Articulating Block Mat (ABM)

 

A preconstruction meeting was held at the project site with Colonial Pipeline and ARMORFORM representatives present. It was determined that the creek should retain its current sectional area. The creek would be relocated by cutting from the inside embankment and filling the outside embankment. Final geometry would be trapezoidal with a bottom width of 20 feet, a depth of 12 feet, 1.5:1 side slopes and a bed slope of approximately 1%. It was also estimated that a discharge of 7,000 cfs would be experienced frequently. This volume of water equates to a unit discharge of over 180 cfs/ft at a velocity of over 16 fps. Since the application area is in a sharp curve, additional shear stresses can also be expected. The size of ARMORFORM ABM that was chosen is a 6” thick mat.

Exposed 16” diameter pipeline caused by the natural relocation of Raccoon Creek.

A 500,000 volt electrical ower is dangerously close to the the edge of the creek’s outer embankment.