Mobile Port Project Requires Massive Underground Electrical Installations

By Jeff Griffin, Senior Editor | September 2009 Vol. 64 No. 9

Vaults, duct banks and feeders in the underground system are like spokes from the hub of a wheel going out from the center to various locations and substations, said Hensley.

The project was designed to be completed in phases, beginning with underground work, followed by substations, cable pulling, termination and installation of lighting.

"To support the fully grounded installation, all distribution cable was placed underground in 42 miles of PVC conduit," Hensley said. "The electrical engineer made the decision to use Schedule 40 PVC glue joint pipe in the specs for the high durability and the wall thickness to be able to handle the friction of the wires being pulled. At just over 2,000 feet, the crane feeders were the longest."

Conduit duct banks were installed first so site paving could take place.

"All conduits were installed in open trench," said Doug Beasley, project manager, R.B. Baker Construction. "Seven excavators were in operation at one time, including two Volvo 330s, and one each Volvo 290, Volvo 460, Caterpillar 325, Komatsu 200 and Komatsu 300."

Trench depths ranged from four to 25 feet with water a continuing problem.

"Because the terminal is within arm's reach of Mobile Bay," Beasley explained, "water was encountered in any cut beyond three to four feet in depth. For water issues, we used well pumping systems, thousands of feet of sock pipe and multiple trash pumps."

Special PVC

One hundred percent of the Cantex conduit installed was four and five inch diameter Schedule 40 PVC pipe in 20 foot sections. All electrical duct banks were stacked in PVC chair supports with rebar cage surrounding the entire duct bank totally encased in 3,000 psi red dye concrete.

"The project," Beasley said, "required a lot of coordination with owner supplied materials, including the cranes which were shipped from overseas and had to be transferred to the wharf for operations. The first stage was to install power to the cranes and next, power to the buildings. The facility included new administration and maintenance buildings which were not part of our contract, and that required a lot of coordination."

RJ Baggett Inc., Mobile, was the subcontractor that performed all excavating and concrete operations associated with the electrical work and other areas of the site, including all concrete pads for the substations, reefer areas, inbound and outbound gates and K rail barriers.