Relief Sewer Project Wins Award

February 2010 Vol. 65 No. 2

One of the first sections replaced included bursting and replacing 3,938 feet of existing 12-inch VCP with 18-inch VCP. Soil conditions in the area proved to be one of the biggest challenges. The original pipe to be burst was bedded in a soft, dry, silty sand material and installed in a trench width ranging from 3 to 5 feet depending on depth. Existing trench depths range from 10 to 20 feet deep. Dry, dense soil conditions adjacent to the existing trench and the existing sewer pipe alignments, among other minor obstacles, caused some production issues. However, pipe bursting has proven to be a cost effective process for upsizing capacity deficient sewers with VCP.

Static bursting with VCP
Static bursting equipment has evolved from a cable-pulled bursting head to a more sophisticated system that uses a system of interlocked rods to pull the bursting head. The rigid rods do not stretch under heavy pulling as a cable would. This becomes particularly crucial when bursting with sectional pipes such as No-Dig VCP. Mission Clay Products first introduced No-Dig vitrified clay jacking pipe in 1992. Manufactured from 100 percent natural materials, VCP is a blend of clays, shale and slate. For this particular project in Phoenix, the bursting equipment was designed and assembled for the specific purpose of bursting the existing VCP and towing in the new, non-restrained joint VCP.

PEC worked closely with utility contractor Kiewit Western, Omaha, NE, to develop an innovative approach to increase the capacity deficiencies with minimal socio-economic impact. The pipe handling, assembly and bursting plan worked very well when put into operation. Launch and receiving pits were located in areas where existing manholes were to be replaced. The manholes were located at approximately 400-foot intervals. The pits were adequately shored with trench boxes to stabilize the walls of the pit. This provided a safe environment for workers and ample room for equipment and pipe.