Venice Beach Micro-Tunnel
HK and Geneva Pipe and Precast team up for high-profile project
Once a bohemian enclave for drifters, artists and immigrants, the seaside community of Venice in Los Angeles gradually evolved into an iconic L.A. scene, visited by millions of tourists annually and frequented by locals for its beach and bustling promenade. In 1960, to manage the growth of Venice and the surrounding area, the city’s Department of Public Works (DPW) constructed a 48-inch force main sewer. Now, more than 60 years later, it’s time to revisit that essential infrastructure.
According to a DPW report, the new force main sewer is needed, “to avert a potential sewage spill that could occur, resulting from an overflow or failure” of the existing force main. There is no backup for the aging force main sewer, which conveys wastewater to the Hyperion Treatment Plant nearby. “Without additional capacity, there is risk of an overflow of sewage into city streets and surface waters,” according to the DPW.
After years of location studies, community education about the need for the sewer and extensive planning, construction began in 2015 and is scheduled for completion summer 2021. The new force main sewer will run in parallel to the current system.
The Micro-Tunneling Solution
The many months of detours and disruption caused by a conventional open trenching sewer project would be out of the question in such a densely packed, high profile part of the city, so DPW went with the optimal solution: micro-tunneling. The sewer originates at the Venice Pumping Plant, travels near the beach front and crosses under Marina del Rey.
Geneva Pipe and Precast supplied 1,710 linear feet of 72” diameter Class V precast concrete jacking pipe for micro-tunneling along the route. The jacking pipe acts as a casing pipe for the 54” pressurized force main. Ensuring a watertight fit for the jacking pipe are Hamilton Kent’s O-Ring gaskets.
Heather Christensen, technical marketing manager for Geneva Pipe and Precast, said that micro-tunneling provides a variety of benefits in a densely populated area like Venice.
“It is a specific type of trenchless installation,” Christensen said. “The benefit with micro-tunneling is that you can do it under groundwater, and rather than opening a huge trench to go through downtown Venice, blocking traffic, rerouting and having all these detours, they can tunnel it. And because they are close to the beach, the groundwater was, in certain areas, 15 feet over the pipe. Through the marina it was 20 to 30 feet over the pipe. It’s faster and safer, and when you start adding in the costs of traffic delays and detours it could very well be a cheaper alternative too.”
The Hamilton Kent O-ring gasket plays a significant role in this scenario. Geneva Pipe and Precast sent its joint design to Hamilton Kent, where Pardeep Sharma, director of Innovation, evaluated the design and determined the ideal gasket specifications based on the stretch of the gasket on the spigot and the sealing of the joint once the joint is closed.
“The joint was designed to meet 50 psi requirements,” Sharma said. “In a confined O-ring groove, the gasket will not displace under pressure. It is a simple design and easily mathematically modeled. This is an excellent jointing method and commonly used for high-pressure prestressed concrete pipe.”
Meeting the 50 psi was a critical requirement, Christensen said. “Conventional open trench pipe with the traditional bell and spigot generally meets about 13 psi, which is what the standard requires for a straight connection,” she said, “so adjusting the joint design to have a confined O-ring gasket allows for higher pressure resistance, which is of course critical in this instance where they are tunneling under the groundwater.”
Geneva Pipe and Precast uses self-consolidating concrete to produce its micro-tunneling pipe. The O-ring fits into a confined groove and a steel band wraps around the joint. The result is a super-smooth surface from the SCC, and pipes that can withstand the pressure, with the steel band helping to disperse much of the jacking force around the pipe.
The micro-tunneling pipe came from the Geneva Pipe and Precast plant in Washington, Utah, 410 miles from the site. Kody Mangum, sales manager, said that the continuous 1,710 foot run is the longest single drive that the company has produced. Vertical and horizontal curves in the route added additional complexity to the calculations.
“We delivered the last of the pipe between February and November, 2020,” Mangum said. “As far as the gaskets, we didn’t hear of any problems, complaints, leakages or any issues, so I consider it successful in that regard,” Mangum said. He also credited Hamilton Kent with a big save during the installation phase.
“We went down and did a site visit late September and early October and everything was going good,” Mangum said. “Then about two weeks later they called and they were out of gaskets, and if we didn’t get them more gaskets by Friday of that same week, they were going to be shut down. If you have to stop the tunneling machine, it’s a huge deal, but Hamilton Kent stepped up. They air freighted the gaskets from Canada – and they were there on time. With that short notice and a quick turnaround time, it was phenomenal,” he said. “It was a great job. Awesome customer service.”