When the Port of Anchorage, Alaska, began operations in 1961, about 38,000 tons of marine cargo moved across its single berth. In 2003, more than 4 million tons of material moved across the port's greatly expanded five-berth terminal. This equates to nearly five tons of goods for every man, woman and child in Alaska. The surge in activity and growth can be attributed, in large part, to a natural disaster that had devastating effects on the state and two other ports but led the Port of Anchorage to become the dominant marine facility in the state.
In 1964, an earthquake and the tsunami it generated destroyed the two ports that served South-central Alaska at the time. Luckily, the Port of Anchorage sustained only minor damage and was back in operation within a matter of days. As a result, all the materials shipped to rebuild the state came through the Anchorage facility. The port has been experiencing increased activity ever since.
Today, the port serves an important role in stimulating economic development and the movement of goods into and out of South-central Alaska. The port facilitates the movement of containerized freight, iron and steel products, wood products, bulk petroleum and cement, and many other commodities. Continued growth and demand have required further expansion, and the port is now in the middle of what has become the largest near-term marine transportation project in the United States.
The Port of Anchorage Intermodal Expansion Project Takes Shape
The Cook Inlet near the Port of Anchorage, Alaska, is attracting attention as it is now the center of an estimated $230 million dock expansion. The Port of Anchorage Intermodal Expansion Project (PIEP) is a major transportation infrastructure project to assure that the Port maintains market dominance by accommodating larger ships, having the ability to unload containers using better and bigger cranes and ensuring continued service to city businesses, citizens and the state with transportation links to meet the increased demand for these services.
The project will greatly expand the current 100-acre port by another 83 acres. The port's road and rail access will be extended and the terminals for cruise ships, ferries, barges and buses will be expanded. Docks will be widened to allow 100-foot cranes to operate and the harbor will be deepened by 10 feet, allowing access to 1,000-foot container ships. This expansion will improve and expand cruise ship, container ship, bulk material and petroleum handling as well as help accommodate the 200 percent increase in activity projected over the next 20 years. The project is estimated to take six years to complete.
Prospective Designs
A development proposal was submitted by Peratrovich Nottingham & Drage Inc. outlining the construction of a dock based on their open-cell system technology. Their model utilized sheet pile membranes to create a bulkhead that would hold nine million tons of compacted gravel when completed. This would allow for a land-based installation and a cost savings of over 30 percent compared to traditional designs. This design had been successfully implemented at neighboring Port Mackenzie and other areas in Alaska.
Another option was provided by the engineering firm originally contracted to complete this dock project, Tryck Nyman Hayes Inc. They had developed a design for a pile-supported dock similar to current West Coast ports. In this traditional design, the dock would be supported by piles driven deep into the ocean floor.
Settling on a Stable Plan
Stability issues played a pivotal role in selection of a design because the region is prone to massive earthquakes. This area of Alaska experienced the second largest recorded earthquake in history in 1964, which registered a 9.2 on the Richter scale. The earthquake itself caused less damage than the numerous tsunamis and landslides that resulted from the quake.
To be able to withstand a large earthquake, it was essential that the new port incorporate certain design features into the construction. San Francisco, another city familiar with earthquakes and the safeguards necessary to prepare for them, had designed its docks to withstand a magnitude 7.5 earthquake. In comparison, the new port in Anchorage would be designed to withstand a magnitude 9.0 earthquake, almost 800 times more intense. For this to be accomplished, the new dock needed to be designed with a good understanding of the subsurface conditions and ground environment. To gain this understanding, a $1.25 million geotechnical investigation was ordered to collect more data on the strength and stiffness of the seabed near the Port of Anchorage.
A Call to California
In the summer of 2003, the Federal Maritime Administration hired a team headed by Koniag Services Inc. who contracted Gregg Drilling and Testing Inc., of Long Beach, California, to test and sample the soil in the Port of Anchorage. Gregg was selected, in part, because of their past experience with over-water drilling in California ports and at Folsom Dam. These jobs had come within budget and the met the demanding timeframes required. Also, previous contractors were impressed with the knowledge and skill of the operators and the professionalism of the company.
Several challenges faced the Gregg team. First, the trip to Anchorage was over 2,500 miles each way and men and equipment would have to be transported quickly and economically. The job was planned for the summer of 2003 and would last approximately one month with a crew of six operators working 24/7 while the weather permitted. Second, the Cook Inlet experiences tidal fluctuations of up to 36 feet in a number of hours, causing most drilling boats or barges to be grounded. Therefore, Gregg was charged with the job of finding a different kind of work platform for this project that was independent of the sea level. In addition, it was estimated that as many as 40 seabed locations would have to be sampled so the work platform chosen would have to be highly portable.
In addition to drilling and sampling, it was determined that Cone Penetration Tests (CPT) would be used to provide a continuous soil behavior type profile of the expansion area. The CPT would provide a rapid, reliable and economical means of determining soil stratigraphy, relative density, strength and hydro geologic information without generating soil cuttings. Also, since it would be important to analyze soil behavior and liquefaction potential in response to dynamic loading from earthquakes, ice, vibrating machine foundations, waves and wind, seismic tests were required with the cone penetrometer in a few of the locations. Various other sampling methods including standard penetrations tests (SPT), Shelby tube and piston samplers would all be used at some of the sampling locations — some as many as 200 feet below the ocean floor.
In order to meet the challenge of finding an appropriate work platform, Gregg Drilling used a jack-up drilling platform similar to those used for near-shore oil drilling and capable of working in water up to 83 feet deep. Seacore of Cornwall, England, provided Gregg with their Skate III “jack-up” rig for the project. The Skate III is designed for rapid assembly and easy transportation with pontoons that double as containers for the jack-up legs and other components. The rig has a jacking capacity of 100 tons with a deck load capacity of 25,000 pounds and can be easily transported to near-by locations via tugboat.
In two weeks, the rig was shipped from California to Alaska, assembled and ready for use. Gregg Drilling mounted their equipment on this platform, and with crews of five to six people working around the clock, completed in-situ soil testing and sampling in little over a month.
Cone Penetration Tests (CPT) conducted in 39 locations provided a continuous soil behavior type profile of the expansion area. Basically, this test would show weaker versus stronger soil stratums and where they were located underground. This was accomplished by pushing a cone penetrometer at the end of a series of rods, attached to a data acquisition system, into the subsurface at a constant rate using a hydraulic ram. The cone penetrometer uses electronic load cells to measure tip resistance and sleeve friction, while a small transducer behind the tip measures pore water pressure.
Many other sensors such as resistivity, ultraviolet and seismic geophones can be added to the cone penetrometer. For this project, liquefaction potential of the soil was critical and seismic geophones built into the cone allowed operators to measure the velocity of shear waves at varying depths in the soil.
In addition to CPT, sampling methods employed allowed geologists to collect 190 samples from 20 different locations. Many of these were taken from 100 to 200 feet below the ocean floor. All samples were sent to Terracon Consulting for further evaluations by professional geologists and geotechnical engineers who were looking for firm and stable soils to support the large structures of the port expansion.
Because this project was completed in such a short time-frame and with an interesting piece of equipment, the job quickly attracted the attention of the Alaska Department of Transportation. For nearly 30 years, the Alaska DOT has been contemplating a bridge across the Knik Arm linking the crowded Anchorage bowl with the largely undeveloped Matanuska-Susitna (Mat-su) side. The proposed bridge would eliminate the current two-hour drive circling the Knik Arm from the Port of Anchorage to Port MacKenzie. The state acted quickly to retain Gregg Drilling and mobilize the same equipment directly from the port so work could begin immediately.
In the middle of August, Gregg Drilling began site investigation in the two nautical miles that stretch between Carin Point and Port MacKenzie. Gregg Drilling was asked to drill a number of boreholes and collect samples in the often rough waters of the Knik Arm. Drilling conditions included clays, hard silts, loose flowing sands, gravels, cobbles and a few boulders. Due to such variance in soil types, further work was required to gain a full understanding of the subsurface conditions. A CPT sounding was conducted to determine a continuous soil profile and a seismic CPT sounding was performed to a depth of 224 feet below the mud line.
By the end of August, drilling became difficult as a mixture of bad weather and complicated drilling conditions plagued the crew. Work was postponed until the middle of September, allowing the rig to move to areas of deeper water where more favorable tides were present. By the end of September, a total of seven boreholes had been drilled in the ocean floor spanning the Knik Arm. Samples and CPT data taken from the area will provide engineers with design parameters and allow planners to narrow cost estimates for the proposed bridge.
Heading Home
With the end of September approaching, it was time for Gregg’s drillers and engineers to head back home to warmer climates. Anticipation builds for port and bridge planners as Anchorage awaits test sample results and designs for a truly ambitious construction project.
Gregg Drilling & Testing, Inc. became an NDA member in 2000. Since 1985, Gregg Drilling & Testing has offered a wide range of drilling and cone penetration testing (CPT) services for environmental and geotechnical site investigation and remediation. Across America, on- or off-shore, their experienced personnel and extensive resources allow them to solve the most complex technical problems and save time and money, without sacrificing quality. Visit their Web site at www.greggdrilling.com for more information and to find an office near you.
RESOURCES
Contracted by:
Federal Maritime Administration
Drilling Contractor:
Gregg Drilling & Testing, Inc.
Location: Long Beach, CA
Tel: 562-427-6899
Fax: 562-427-3314
Web site: www.greggdrilling.com
![[ Drill Bits ]](../images/drillbits_biglogo.gif)
Building a Stable Future From the Ground Up