Lake Mead, approximately 50 miles from Las Vegas, Nevada, is the main source of fresh water to Las Vegas Valley, and one of the world’s largest subaqueous pressure pipelines was installed under Lake Mead’s Boulder Harbor. The original intake structure, Intake No 1, which was built by the Bureau of Reclamation, and the associated water supply system, has been supplying water to the Valley since the early 1960’s. The demand for water in Las Vegas has been growing due to tourism expansion and 7% annual residential growth rate. To meet the increased water supply demand, the Southern Nevada Water Authority (SNWA) has embarked on a 2 billion dollars capital improvement plan to expand the existing 400-mgd water supply system. The expansion includes the Lake Mead Intake No. 2 Project, which runs parallel to the original intake.

The 144-inch diameter, 3600-ft. long Reinforced Concrete Cylinder Pipe (RCCP) subaqueous pipeline, the Bay Aqueduct, is part of SNWA’s Lake Mead Intake No. 2 Project. The Bay Aqueduct was designed for a nominal flow of 600 mgd with a peak flow of 800 mgd, an internal pressure of 160 psi under normal conditions, an extreme pressure of 300 psi, 80 ft. of external water head and up to 20 feet of soil cover at the banks. This 144- inch diameter RCCP Bay Aqueduct, which runs from Saddle Island to the mainland under Lake Mead’s Boulder Harbor, may be the largest subaqueous water pressure pipeline in the world. CH2M Hill engineers designed the 144-inch diameter RCCP Bay Aqueduct. Because of the demanding design and installation conditions, CH2M Hill and SNWA have only considered the rigid wall RCCP option for this project. Ameron International’s Water Transmission Group, manufactured the RCCP at its plant in Rancho Cucamonga, California. Lake Mead Constructors (LMC) installed the subaqueous pipeline.

• A 5/8 inch thick steel cylinder.
• A deep double gasketed joint to allow for testing and settlement after installation and dewatering. The joint was designed for a joint lap of 6.5 inches to allow for a minimum straight pull of 2.5 inches and a minimum joint deflection of 1.5 inches.
• Each cylinder and joint ring assembly were hydrostatically tested to 160 psi in the plant.
• Three reinforcing cages, an inside cage in the concrete lining, an intermediate cage over the steel cylinder, and an outer cage.
• A 12-inch thick concrete wall with 6000 psi strength.
• Manufactured and shipped in 16.67-ft. standard lengths weighing 60 tons per section.
• LMC joined three pipe sections together on shore to form 50-ft. long assemblies weighing 180 tons per assembly.
• A special corrugated grout bands to allow for grouting the exterior joint space from inside the pipe after dewatering.
• An internal welded butt-strap restraint system installed after dewatering..
• Special color markings in the joint and exterior spring lines of the pipe to establish the limits of the joint stab and backfill limit for the divers during installation.
• Precast concrete saddles for placing over the pipe after backfilling up to the springline to counteract buoyancy after dewatering.

Hydrostatic Joint Tests: Two test pipe sections were assembled in the plant with a controlled inside joint gap of 3.75 inches (1.25 inch joint gap in the fully inserted position) to allow a straight 2.5 inch pull. The spigot of the assembled joint had two grooves and two gaskets, which allowed testing between the gaskets through two 1/4 inch tapped holes 180 degrees apart. A water hose and a pressure gauge were connected to the bottom test hole and a connection and bleed valve was connected to the top test hole. The system was pressurized to 45 psi for 10 minutes with no pressure drop. A portable “power pac” was used to adjust the joint gap. The test was repeated with a 1.25-inch gap on onside and a 2.75-inch gap on the other side for a total deflection of 1.5 inches. The system was pressurized for 8 minutes with no pressure drop. The joint was deflected in additional 1/2-inch increments until the joint leaked when the gasket disengaged from the bell on one side. The total joint deflection was 3 inches before the joint leaked. The hydrostatic joint testing results verified that the specification requirements of a minimum 2 1/2-inch straight pull and a minimum of 1 1/2-inch deflection were met and exceeded.

Structural Testing: The purpose of the structural testing was to verify the structural and radial tension performance of the pipe. Two test pipe sections were each instrumented with two horizontal and two vertical deflection monitors. In addition, a radial tension monitor was installed at the invert near the bell. The test pipe was positioned in the D-load (3-edge bearing) machine, which is equipped with two hydraulic jacks that press the head beam against the pipe. A data logger was connected to the deflection and radial tension monitors and a pressure transducer was connected to the hydraulic pressure system of the jacks. The data logger would instantaneously measure the transducer pressure and corresponding applied load and the vertical and horizontal deflection and radial tension movements of the pipe. Load/deflection curves indicate that the deflection is in the elastic range up to a load of 20 kips/ft. The 0.01-inch crack was observed at a load of 21 kips/ft.

The maximum load which could be applied was 27.5 kips/ft. The apparent radial tension movements up to a load of 20 kips/ft were negligible. The radial tension crack was observed at a load of approximately 20 kips/ft. The theoretical D-load capacity for the test pipe was 15 kips/ft. Although the 3-edge bearing load (D-load) is a very severe loading condition, the structural tests have verified that the proposed 144-inch RCCP can safely withstand the design loads and validated the design assumptions.

Grout Band Tests: Two of the test pipe sections were assembled and used to test the proposed corrugated steel grout band and gasket assembly. A total of eight trial tests were conducted until the design of the grout band and grout-pumping procedure was finalized and approved. This is the first time for this type of grout band application.

Precast Concrete Saddle Fit Up Test: The test pipe sections were used to check and verify installation. Lake Mead Constructors (LMC) installed the Bay Aqueduct in over 80 feet of water with both soil and rock trenching and bedding preparation completed ahead of pipe installation. LMC joined three pipe sections together on land to form 50-ft. long assemblies. The assemblies, with temporary bulkheads attached at both ends, were rolled over by means of a cable and winch set-up to the launch way saddles, and then the assembly was launched through a rail and cable system on a ramp to the water. The assemblies were floated and pulled with a tug to the laying barge.

The pipe assembly was picked up with a hoisting frame with one of the bulkheads removed and lowered into place. The joints were pulled together by pumping water out through the remaining bulkhead to form a vacuum that eased the joint to its final position. The joints were tested during installation and grout bands placed into position. The backfilling was placed up to the pipe springline, at which point large precast concrete saddles were placed over the pipe to counteract buoyancy, and backfilling was completed. After dewatering the line, the exterior joint space was grouted from the interior of the pipe through small grouting nozzles. Interior steel butt-straps were welded across the joint for restraint and shotcrete reinforced with wire mesh was applied over the interior surface of the butt-strap to fill the interior joint spaces.

Bay Aqueduct Completion

The installation and successful testing of the RCCP Bay Aqueduct was completed in December of 1999. The pipeline was hydrostatically tested at 220- psi pressure. This rugged RCCP subaqueous pipeline met the challenge of very difficult installation conditions. The design and construction versatility of concrete pressure pipe is demonstrated on the Southern Nevada Water Project. Whether it’s a subaqueous line, a tunnel, or a downtown main, concrete pressure pipe can meet your needs.

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