Being built on the shore of the Cooper River here, the Hugh K. Leather- man Sr. Terminal had some 4.5 million metric tons of rock imported from Newfoundland to create a 23-foot elevation and the total site foot- print of 248 acres. During the design phase, a prime concern for the engineers was the projected shifting of the rock due to the site and also the river’s currents. Upon review of new data, it was determined that the concrete pipe initially selected for the stormwater runoff system was not capable of providing the joint performance that was required to handle the anticipated settlement of the created site. “One of the biggest issues was the very poor soil and the anticipation of as much as a foot of settlement after construction,” stated Stuart Timmons, P.E., water resources engineer for Infrastructure Consulting & Engineering, PLLC (ICE) (Columbia, SC) “The settlement of 12 inches over 25 years is not something that you typically see on a major infrastructure project like this one. That was definitely a key factor we were always designing around and looking at ways that would better suit those conditions. It was the number one challenge we had to overcome.” The South Carolina Port Authority (SCPA) is building the terminal, which is the only permitted new container terminal on the U.S. Eastern and Gulf Coasts. Since receiving the final permit approvals in 2007, the Port has completed demolition, site preparation, containment wall construction, and design activities for the first phase of the terminal on the Cooper River, site of the Charleston Naval Base from 1901 until 1996. The new terminal is on schedule to open in March 2021. Phase One construction of the terminal began in August 2019 and included the construction of the site improvements, buildings and canopies, the Port Access Road and Tidewater Road extensions, the wharf, and the purchase of five ship-to-shore cranes and 25 gantry cranes. The $700 million terminal will boost capacity in the Port by 50 percent. Another $300 million was spent to dredge the river to a depth of 52 feet to accommodate the draft of post-Panamax container ships, making it the deepest harbor on the East Coast. Currently, the Leatherman Terminal is one of the top five largest con- struction projects in the State of South Carolina. The port is a key com- ponent of the SCPA plan to enhance economic development in the state and for the Southeast region of the United States. SCPA, established by the state’s General Assembly in 1942, owns and operates public seaport and intermodal facilities in Charleston, Dillon, Georgetown and Greer. As an economic development engine for the state, Port operations facilitate 225,000 statewide jobs and generate nearly $63.4 billion in annual economic activity STORMWATER DRAINAGE SYSTEM DESIGNED TO HANDLE UNDERGROUND SHIFTING Project at Port of North Charleston Wins Industry Honor
“To limit the settlement at the site the imported stone was brought in to surcharge the site via barges and ships to promote settlement before construction began,” Timmons explained. “Settlement has always been a huge driving force of this project. And so, when we started to think about the problems settlement could cause, we looked into using a flex- ible pipe system. That way as the site settled the pipe could move with it as opposed to a rigid pipe being affected by a shearing force with the differential settlement. With the poor soils and the higher groundwa- ter, we recommended using polypropylene pipe. It’s a slightly stiffer pipe and better suited for the terminal’s conditions plus the joints for the polypropylene pipe are double gasketed. The idea was that with the settlement conditions anticipated, a double gasketed connection at the joints would help prevent any sort of sepa- ration and would be the best product for us to go forward with. We presented this to the Port and they liked the idea. Also, the stone that was brought on site was perfect backfill material for the pipe. So, a lot of things just fell into place that made the polypropylene pipe the most suitable option for our stormwater system.” In order to mitigate joint separation and possible exfiltration and even infiltration, Timmons and his team specified HP Storm Polypropylene Pipe fromAdvanced Drainage Systems, Inc. (ADS) (NYSE: WMS) as the storm drain conveyance pipe for the entire project. This was due to secure joint performance, the pipe’s inherent ability to flex with the soil, and provide strength while also being easy to handle. As a result
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csengineermag.com
december 2020
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