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The 11-mile-long pipeline is being built in a tunnel that was excavated by three tunnel boring machines. Tunneling rather than cut-and-cover trenching means fewer impacts to land surfaces and the surrounding communities.
Since the pipeline route covers a range of geology from soft to very hard rock material, the contactor used two types of tunneling machines to excavate the majority of the tunnel. . |
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This hard rock tunnel boring machine excavated approximately two miles of the tunnel. The machine was 400 feet long, including trailing gear that supported the tunneling operation. |
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The boring machine entered the pipeline tunnel at the San Vicente Portal to start its work. An art contest for local school children celebrated the start of the tunneling effort. |
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The front of the machine was a rotating cutterhead that matched the diameter of the tunnel. As the cutterhead turned, hydraulic cylinders gripped the rock and a second pair of hydraulic cylinders pushed the cutters into the rock. |
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For other portions of the tunnel, a digger shield tunneling machine was used. Here, a crane lowered the digger shield machine into the Central Shaft.
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The digger shield used a pick and paddle apparatus at the front of the machine to excavate approximately eight miles of the tunnel. |
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As the machines advanced underground, concrete segments were erected behind it to stabilize and secure the tunnel walls. |
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The rock and dirt material excavated by the tunneling machines was removed from the tunnel in haul trains.
Some short sections of the tunnel contained rocks too hard for the tunnel machines to excavate, so controlled blasting was needed. |
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This is the view inside a portion of the excavated tunnel from the Slaughterhouse Shaft. The tunnel is 12 feet in diameter. |
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After more than four years of tunnel excavation work, a significant milestone was achieved in September 2009 when crews completed all 11 miles of tunneling for the pipeline. |
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Pipe installation is the second major construction phase of the project. Steel pipe sections are 50 feet long, 8.5 feet in diameter and weigh 17 tons. More than 1,000 pipe segments will be used to build the pipeline.
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Some of the pipe segments used to build the pipeline are delivered and stored near the San Vicente Portal.
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Pipe segments are moved into the tunnel by a crane at the Central Shaft and San Vicente Portal locations. |
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The pipe enters the tunnel from the bottom of the shaft. When each segment reaches its destination inside the tunnel, crews precision-fit the pipe to the adjacent pipe segment while it is braced securely against the tunnel walls. |
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Once pipe is installed in the tunnel, crews pump in grout to fill the space between the pipe exterior and the tunnel walls. This ensures the steel pipe stays in place and is protected from corrosion. |
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A grout plant at the Central and West shafts produce grout on site. The system pumps grout into the tunnel through a pipe and hose system.
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To protect the pipe during the grout work, eight-foot-tall aluminum beams are placed in a crossed position inside the pipe.
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The final step for pipe installation is applying a cement mortar lining to the inside of the pipe to further protect it from corrosion. A wire brush tool at the end of this rotating device cleans the pipe interior before the mortar lining is applied. |
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Water in the pipeline will be moved with an assist from San Vicente Pump Station, located near the San Vicente Portal. In an emergency, the pump station will be able to move approximately 300 million gallons of water each day from San Vicente Reservoir. |
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From the pump station, water will be pumped up to the new surge control facility on a hilltop near the San Vicente Dam. The surge control facility enables water to flow by gravity through the San Vicente Pipeline to the Water Authority’s Second Aqueduct, 11 miles away. It also protects the pipeline in case of a sudden pressure surge in the pipe. |
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All work for the San Vicente Pipeline is scheduled to be complete in summer 2010.Once complete, the pipeline will operate with the San Vicente Pump Station and Surge Control Facility to deliver water from San Vicente Reservoir to the southern portion of the county in an emergency. |
