
The Los Angeles County Sanitation Districts are working on a new tunnel to carry wastewater to the ocean in an endeavor titled the Clearwater Project. This will be created using a tunnel boring machine, or TBM, which will travel under public streets along a 7-mile path, starting at the Joint Water Pollution Control Plant in Carson (next to the 110 fwy) and going underneath Harbor City and San Pedro. This $700 million project was created to replace two existing tunnels that are part of the joint outfall system. One of the existing tunnels is 60 years old, and the other is 80 years old. Water that comes to the plant is treated, and then sent to the ocean via these tunnels.
Despite their age, the two existing tunnels cannot be inspected or repaired, because they are still continuously used. In addition, they are not built to current seismic standards, and pass over two fault lines. The capacity of the tunnels was almost met twice during major storms. Once the new tunnel is created, the older tunnels will be kept as backups.
While construction for the project began in 2019, the actual tunneling will begin in July, after a launch event on April 15. It will start in Carson and end at Royal Palms Beach in 2026. Along the way, it will go under Figueroa Street, Harbor Regional Park, North Gaffey Street, Capitol Drive and Western Avenue.
The TBM should reach North Gaffey Street near the end of 2021, said Russ Vakharia, supervising engineer of construction management.
“It’ll take several months to get the machine launched,” Vakharia said. “We got to go … across Harbor Park for quite a ways, and then onto San Pedro.”
While the existing tunnels follow a straightforward path, the new tunnel will have more than 30 curves.
“The purpose of that is to try to keep it under public-right-of-way,” Vakharia said. “[This is] to minimize the impact on the public, per the public’s request.”
To minimize above ground impact, once the TBM begins its journey underground, it will not be emerging until it finishes at Royal Palms Beach. However, there will be several machines monitoring the project, including monitors above ground, which will monitor whether the TBM is moving the ground above.
The dirt that is removed from the tunnel will have to be taken out through the TBM’s initial entrance shaft. The farther the TBM goes, the longer the removal will take, and the more the wiring attached to the machine will need to be extended.
“Because there’s only one shaft in Carson, near Figueroa and Lomita boulevards, everything has to come out that shaft,” Vakharia said. “As they go further, the logistics in terms of time to get segments in, and people in and out, plus dirt out, will increase for sure.”
A slurry made of bentonite helps lubricate the head of the TBM, and then the bentonite is mixed with dirt, and sent back up the shaft. Once it goes back up the shaft, it is treated, and the bentonite and dirt are separated. The bentonite is sent back to continue to lubricate the TBM, and the dirt is either disposed of, or sold if Dragados, the contractor the districts are using, can find a buyer for it.
The TBM will not be remote operated, it will be manned all the time it is in operation. Vakharia said it will probably be used 20 to 24 hours a day, five days a week. Dragados estimates it will be able to tunnel 45 to 50 feet a day.
“The contractor always has a crew down there,” Vakharia said. “Even though the machine is very automated and all, there’s always an operator there and then there are other people in there doing various other tasks.”
The Sanitation Districts have dug other tunnels before but have usually used simpler tunnel machines. This project is more complex, partially because of the many curves the tunnel will have, and the length of the tunnel. Many other tunneling jobs are straight, and only one or two miles. In addition, the TBM must go through a variety of ground, ranging from soft ground to rock. Ordinarily, the districts would use two different machines for different types of ground.
“We’re using one machine from one shaft to minimize the surface impact,” Vakharia said. “So that machine has to be versatile.”
Another challenge is that the entire tunnel will be below groundwater, meaning the TBM will need to function under significant earth and water pressures.
The TBM was built in a Herrenknecht factory in Germany, where it was tested, then sent to the plant in pieces. It is 21.5 feet in diameter, completely electric and has a head that turns, with individual pieces on the head that cut as well. The tunnel itself will be 18 feet in diameter, because as it tunnels, the TBM leaves behind pre-made concrete rings 5 feet long, which form the inside of the tunnel.
The different sections of the TBM are so heavy that they will be placed into the shaft with a crane one at time, and then welded together inside. It also pulls behind it more than 750 feet of trailing gear, which includes ventilation for the workers, power cables, transformers, pumps, piping and safety equipment.
“You have to support the entire crew with the trailing gear, and the entire tunneling operation,” Vakharia said. “It’s like a moving, underground city.”
The various parts of the TBM were sent to the plant in 90 truckloads. This was slowed somewhat by the pandemic, as it was being manufactured last spring, when COVID-19 was at its height.
“There were some factory shutdowns, logistic issues and all that did delay some of the parts being procured and delivered,” Vakharia said. “The ports have been really backed up, LA and Long Beach, so even some of the parts that came from elsewhere were held up.”
There are other things that must be done inside the tunnel after the TBM is finished, such as the placing of a secondary steel where the tunnel crosses earthquake faults. However, there will not need to be any more concrete work.
The plant has various contingency plans for different problems, such as if the machine breaks down.
“It’s the contractor’s responsibility to maintain the machine,” Vakharia said. “There’s a lot of moving parts, and it’s [a] pretty high-tech machine, so depending on what the situation is, they always have mechanics and other people who are technically qualified, plus the manufacturer of the machine is available to provide support also.”
If the TBM were to run into an unexpected oil deposit, or some other type of contaminant, there is a plan in place.
“If we run into abandoned oil well or something like that, which is not shown in the drawings, we don’t think there’s anything there, we’ve done scans and all, then there is a procedure for stopping the mining and removing that,” Vakharia said. “We don’t anticipate that, but it’s always possible that there’s something out there that wasn’t shown on the drawings from a long time ago.”