International Dredging Review

International Dredging Review

On March 11 the cutterhead dredge Florida was digging next to the dike face of the Pier 400 Stage 1 in the Port of Los Angeles pumping to a spill barge a half mile away. A joint venture of Great Lakes Dredge and Dock and Connolly Pacific Pier 400 Constructors is on Stage 2 of a project with a combined worth of nearly $300 million to create 582 acres of land at the Port of Los Angeles for what will be the largest container terminal in the world. It involves digging 52 million cubic meters of material building 12 miles of rock dike and deepening eight miles of channel to a maximum of 81 feet.

A key to the success of this project is a unique and powerful marriage of equipment: the Florida and the spill barge. Powerful enough to pump sand 25000 feet without a booster the 34-inch Florida can be placed where necessary in the project and continue to feed the spill barge an elaborate discharge mechanism that swings like a dredge to accurately place the 20 million cubic meters of material to be dredged in this phase of the project. A cantilevered pipe extending 150 feet ahead of the barge allows it to do plus elevations without going aground.

On this day Matt Jack Quality Control Engineer is taking a visitor on a tour of the project. They board the survey boat Potomac River and boat operator Tom Decker welcomes them aboard. A long-time Great Lakes employee Decker is a “plank holder” (original crewmember) of the split hull hopper dredge Manhattan Island built by the company in 1978. As he shows the visitors onto the boat he points out a seal sunning on the dock in the company of three gulls and a pelican. El Nino has been hard on the seals this year by driving the fish away he explains

The spill barge working in 2.7 meters of water at the east end of the Stage 2 fill is spraying a fan of dark slurry onto an engulfed area where wading birds are foraging indicating that this area is rising above water level. It is connected to the dredge by 2000 feet of floating line 1500 feet of submerged line and 250 feet of shore pipe crossing the dike. Deckhand Joanne VanAnrooy ties off the boat and directs the visitors to the control room where Tom LaVera is monitoring the fill.

The discharge pipe comes aboard the barge at the center of the stern and the swinging spud is to port of the pipe. Swing anchors off the port and starboard bow allow the barge place the fill evenly. Two Hagglunds hydraulic winches rated at four tons linepull on a full drum swing the barge. A four-cylinder Detroit Diesel engine provides power to the winches.

A plot map on the bridge of the barge gives them an idea of where they are aided by a Trimble 4000 GPS unit. A base station at the main office sends DGPS corrections to all the floating units LaVera explains. Depths are measured with a lead line until the material breaks the surface at which time surveyors with backpack total stations walk the area.

The dikes are built in lifts to conserve rock explains Matt Jack. The first lift is built and filled then the next lift of rock is placed using the first lift and the fill as a base. To bring the dike to +4.6 meters elevation will require four lifts said Jack.

Stage 2 will create 362 acres north of and adjacent to the 220-acre Stage 1. Subcontractor Manson Construction and Engineering began dredging with the cutterhead Mr. Manson and clamshell dredges Haakon and Andrew in August 1997 to dig the trench for the dike placing 400000 cubic meters into the Stage 2 fill with their own spill barge. Connolly Pacific began placing rock for the dikes in July. The dikes are now at –3 meters and will be raised to +4.6. This portion is being expedited because the Port has a tenant wanting to begin building in this area. A temporary sand berm was placed to bring this area to the surface.

The Florida began dredging on November 1 1997 digging 800000 cubic meters of sand clay and rock to create the Cabrillo Shallow Water Habitat inside Angel’s Gate.

On December 22 she was moved to the east face of the Stage 1 fill and began pumping through the floating submerged and shore pipe to the spill barge.

The Potomac River navigates along the transportation corridor a strip of land where road and railroad access to Pier 400 will be built. Originally designed as an unbroken dike fears that enclosing the area would create a stagnant pond led to designing a break that will allow water to circulate. This break will be bridged. The Potomac River heads for the break passing the new Pier 300 where APL container cranes create a lacework against the sky. Several Connolly-Pacific barges loaded with rock from the quarries on Catalina Island are moored along the way. This is the rock used to build the dikes.

The boat cruises beside the corridor where sand is piled at elevation 28 feet. A paleo-channel (an ancient riverbed) runs through part of the project and contains fine material clays and silts explained Washington Bryan project engineer. In this area the solution was to surcharge over this channel with extra material to compact the bottom material. On the breakwater face of Stage 1 this riverbed was excavated and filled with quarry run material. That dike face which takes the waves from the harbor entrance was designed with larger rock.

Around the corner the Florida comes into view but the boat first heads to where the submerged discharge line breaks the surface next to the dike. A figure waiting on the pipe is Florida Captain Clay Holley. The boat noses up to the pipe and Holley steps aboard for a ride to the dredge. 1500 feet of submerged line in this area traverse the future shipping channel and South Turning Basin.

The all-electric dredge Florida was refitted in the early 1980’s to work in the Los Angeles area where the Air Quality Control Board designates that all stationary construction equipment be electrically powered. After a ladder pump was installed on the 115-foot-long ladder in the course of the initial deepening of the channels the 34-inch dredge was powerful enough to pump the long distances required without booster pumps. During this project she will pump 18000 feet from the offshore entrance channel to the fill. During the building of the transportation corridor the longest discharge line was 12000 feet. With a 184-foot-long idler barge moored to the stern the Florida’s overall length is 450 feet allowing for a wide swing.

The Florida’s main pump is a Mobile Pulley double wall pump cast of Moballoy high-strength-alloy chrome iron. It is a 34-inch discharge/38-inch suction with a 72-inch four-vein impeller. The original lining lasted throughout the 25 million cubic yards pumped in Stage 1. “We anticipated good results but even we were surprised at how well it lasted” said Hannon Hairston chairman of Mobile Pulley & Machine Works.

The main pump drive is a 10000 hp 13200-volt Canadian General Electric motor. The ladder pump is a GIW 38×34-68 powered by a 2500 hp 750-volt Gulf Electroquip motor running through a Falk reduction gear. Shore power comes to the dredge via 15000 feet of heavy-duty cable deployed by two reel barges.

The visitors board the dredge and make their way to the lever room where leverman Jesse Gist is watching the crew below remove debris from the ladder pump. He speculates that the dredge might be in a shipwreck area as debris removed from the pump is increasingly broken sheaves and other deck equipment. Besides the line-of-sight view offered by the generous window Gist monitors the operation with the aid of three video cameras trained on the winches.

The cut is 22.9 meters deep 90 meters wide at the toe and 100 meters at the top of the slope he says. Positioning software written in-house by Don Fields displays the channel template overlaid in a different color by the pre-dredge survey. As the cutter moves into the material a real-time animation of the process is displayed so the leverman knows exactly where the cutterhead is at any time. This is especially critical digging beside the dike to avoid undermining it by getting too close.

The software will display real time Christmas tree position cutter position how far the dredge has moved since 7 a.m. swing speed tide and time of last tide reading ladder depth digging azimuth and GPS HDOP.

“Our best day on this job was 138000 cubic yards in 24 hours during Stage 1” he said. That was digging free flowing sand the entire day. So far on Stage 2 the best day was 64000 cubic meters he said.

Alex Meyer assistant project engineer sets up the dredge cuts and ensures proper dredge positioning. Hydrographic survey data provides a cross-sectional view of the material removed.

“The proximity of the post-dredge contour and the specified template is a tribute to the accuracy of GPS and the positioning software” he said.

A modular cubicle on the deck of the dredge serves as a survey control center where the engineers and surveyors process surveys and produce maps on the complete computer mapping equipment.

“AutoCad has been a great advancement in our mapping” said Jack. On the bathymetric maps the surveys for each day are color-coded. The survey boat is equipped with a DESO 15 dual frequency echo sounder Trimble 4000 GPS receiver and TSS heave pitch and roll sensor. Each morning they survey for the previous day’s dredging and process the maps in the survey control center on the dredge. He also updates the rates of the spill barge and plans when to move it.

“We can set up and survey any element below the water said surveyor Paul Moorhead. They use a total station to walk the fill above the water line. The tugs and spill barge need three meters of water he said.

Pier 400 Design Consultants did the planning for Stage 1 a joint venture of Frederic R. Harris Inc. and Moffatt Nichol Engineers. Because Stage 1 was totally funded by the Port of Los Angeles the Port contracted the entire planning process from conceptual studies through writing bid documents. Stage 2 with federal funding is managed by the Los Angeles District Corps of Engineers who did the engineering with oversight by the Port and the Pier 400 Design Consultants to assure consistency with the Port’s goals.

A major element of this project is the environmental mitigation. A 265-acre shallow water marine life habitat is being created inside the breakwater using contaminated material capped by clean material considered unsuitable for land reclamation.

The project was designed for a seismic event of 7.5 magnitude on the Richter scale. To this purpose the best material is being placed on the perimeter of the fill for seismic stability.

The entrance channel extends a 3 ½ miles beyond Angel’s Gate and is now at 65 feet. The Manson clamshell dredges Haakon and Viking which work off anchor wires rather than spuds will come in this spring to begin deepening the offshore channel to 81 feet. Material will be hauled to ocean disposal site LA-2 in bottom dump barges.

Stage 2 is scheduled for completion in the year 2003 and will provide 7150 lineal feet of wharf six berths a 1000-foot-wide shipping channel 1800-foot-diameter turning basin 50 feet of depth at the berths capacity for 16 shoreside cranes an on-dock intermodal container transfer facility and six working tracks to handle two intermodal trains simultaneously. The transportation corridor will provide direct access to the Alameda Corridor a dedicated thruway to major transportation arteries for truck and rail traffic.

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