The Ameron International Corp.’s Water Transmission Group received the Steel Tank Institute--Steel Plate Fabricators Assn.’s 2009 Pipeline Project of the Year Award. The 144-in. inside diameter Arrowhead Tunnel Project, which, for more than a decade, was subject to delays due to extremely difficult tunneling and groundwater conditions, was completed in late 2009.
The Arrowhead Tunnel System, which is now in service, is capable of doubling the water delivery capacity (up to 650 million gal per day) from the east branch of the California State Aqueduct to Southern California (the Colorado River Aqueduct and Diamond Valley Lake), bringing water to a part of the state where it has historically been in short supply.
Challenges aside, this project presented an opportunity for Ameron to put its engineering, design and fabrication capabilities to the ultimate test. Specified as a two-pass tunnel lining system, the project called for a dual containment tunnel lining structure with the annular space between the two liners grouted with cement mortar. The initial outer liner is a precast reinforced concrete segmental tunnel designed to withstand all ground loads and water infiltration during construction.
For the final inner liner, Ameron manufactured a rigid-wall composite steel-and-concrete pipe that was designed to withstand external heads of up to 1,200 ft (520 psi), a maximum internal pressure of 80 psi and tunnel depths that ranged from 800 to 1,590 ft beneath the San Bernardino Mountains. Since the tunnel system is constructed in the middle of several fault lines, the design criteria required the 144-in.-diameter tunnel liners to survive an earthquake of up to 8.0 magnitude. It is believed that this project is unique due to its large 12-foot-diameter and exposure to 1,200 ft of external pressure.
Before a single pipe section of the rigid-wall composite steel-and-concrete tunnel liner was installed, Ameron worked closely with the Metropolitan Water District’s engineers and conducted more than eight months of critical testing and analysis, which included:
• Assessment of the best available sources of course and fine aggregates;
• Creep and shrinkage testing conducted concurrently with compressive strength and modulus tests;
• Additional project specific long-term concrete and creep testing ;
• Structural analyses of the composite wall, with various preliminary reinforcement schemes; and
• Load deflection tests on two test pipe sections, manufactured with the final proposed reinforcement, to verify the composite wall designs. This was done to ensure the pipe would not be compromised during handling and installation.
During manufacturing of the liner, the steel cylinders were hydrostatically tested and the weld seams were radiographically tested to ensure the water-tightness of the composite-wall liner. The joint welds required to seal the composite steel-and–concrete tunnel liner inside the tunnel were tested in conformance with the ASME pressure vessel code. Further hydrostatic testing was conducted after the installation was completed as a final quality check before the tunnels were put into service.
It took nearly 10 years, and more than 2,500 pieces of the 144-in.-diameter composite-liner pipe, to complete the East and West tunnels. The lengths of the East and West tunnels total approximately 30,000 and 20,000 ft long, respectively. They are now an integral part of the Metropolitan Water District of Southern California’s critical Inland Feeder pipeline.
Source: Ameron International Corp.
