Strip Mall Savior

Tunneling machine helps a contractor replace lateral lines and restore sewer service to businesses.
Strip Mall Savior
Jim Voudy (left) and John Mahana (right) of Roddie Underground Construction help guide the 6.5-foot-diameter corrugated steel casing into place as Gustavo Barajas lifts it with the Gradall excavator.

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Sand leeching into a corroded 4-inch cast iron lateral caused sewage backups into a restaurant (which had to close), a check cashing service, and a bank on one block of a Santa Cruz, Calif., strip mall. High groundwater enabled sewage to wick up through the sand and the mall’s communal concrete floor, leaving wet spots in the check cashing and bank carpets.

For more than a year and as often as three times per month, local mechanical contractor Geo. H. Wilson tried clearing the 130-foot line with cutters on cable machines. As the health department and tenants’ patience expired, Wilson called subcontractor Roddie Underground Construction in San Martin. The company has a reputation for replacing sewer lines in difficult situations.

“The lateral ran north from the restaurant to the bank, turned 90 degrees under it, and ran out to the sanitary sewer,” says Roddie foreman John Mahana. “However, the bank refused to let us work inside, so we had to reroute the lateral out the south end of the mall.” He used a UB-40 tunneling machine from RODDIE in Columbia Falls, Mont., to install a 4-inch HDPE lateral under the mall without affecting customer access.

Touchy work

Mahana, Jim Voudy and Gustavo Barajas worked mornings and evenings before the establishments opened and after they closed. They also erected a chain link fence and placed barricades to isolate the work zone.

From a manhole, Mahana televised the pipe using a GatorCam3+ from Radiodetection, and took sonde measurements to plot the line’s location. Two drop ends from the bank and one from the check cashing service tied into the lateral at the common wall separating the two establishments. The restaurant had one drop cap for the lavatory and one for the kitchen.

“Documentation was very difficult because of the concrete walls and floor,” Mahana says. “I wound up measuring off the walls and doing lots of complicated geometry to plot the course and grade correctly.” The machine had to drill at a 1.7 percent grade to intercept the drop caps and maintain grade to the sanitary sewer.

Underground Service Alert identified the 6-inch water main, and gas, power and communication lines running under the sidewalk in front of the restaurant and into the parking lot. Mahana’s team used an Aquatech B15 combination truck from Keith Huber to excavate five 3- to 4-foot-deep potholes to document the numerous utilities, then backfilled the holes and replaced the concrete in the sidewalks. The work took two days.

Rock solid

To excavate the 7.5-foot-diameter, 7-foot-deep launch pit on the far side of the sidewalk in line with the restaurant’s front door, the team dug a trench around the perimeter with the combo truck to verify that it was free of utilities, then they dug out the center with a TBO15 Takeuchi mini excavator. Soil was stockpiled in another secure area in the well-lit parking lot.

“If the drilling machine moves 1/8 inch, it has to be reset,” says Mahana. “To prevent that from happening, we steady it inside a 6.5-foot-diameter corrugated steel casing.”

Barajas used a rented Gradall excavator to lower the casing into the pit, then the crew poured two-sack slurry in the annular space. (The mix was soft enough to be hand excavated later if necessary.) After the slurry set, Barajas lifted the 2,600-pound drilling machine off the trailer with the Gradall and lowered it into the pit. Mahana secured the frame of the machine to the casing with jacking plates.

To access the drop ends, the crew entered the check cashing service early in the morning and removed a 18- by 18-inch-square slab of 10-inch-thick concrete with multiple layers of rebar. “It took one hour to saw out the 300-pound piece using a hydraulic chain saw with an 18-inch diamond chain powered by the pump on the combo truck,” says Mahana. “Then we pried up the chunk, lifted it onto a wheelbarrow, and took it outside.”

After hydroexcavating down 3 feet to the tie-ins, the team repeated the process in the restaurant, which opened at 11 a.m. While Voudy and Barajas fused three 40-foot sticks of polyethylene pipe with a pulling head for the 90-foot run from the pit upstream to the common wall, Mahana drilled the pilot hole.

Optic guided

Mahana used a forward-reverse joystick to advance or retract the machine’s dual hydraulic rams. After he loaded a 3-foot-long hollow lead tube with slanted tip, 40 tons of thrust pushed it through a flexible seal in the casing and into the soil. “The soil displaced easily, so we didn’t need a boring auger,” he says.

Mahana repeated the jacking process with more hollow tubes until they reached the destination. To follow the programmed route, the guidance system used a camera on a surveyor’s level focused on an LED target visible inside the lead tube. The level, mounted on an independent adjustable support, set the height, grade and direction.

An image of the target on a monitor enabled Mahana to steer the lead tube with a joystick and maintain the target in the level’s cross hairs, which represented the desired line and grade. He made approximately one course correction per foot.

When the lead tube arrived at the check cashing excavation, Voudy replaced it with the pulling head, then monitored the pipe’s progress. The machine pulled the greased pipe through the tunnel at 1 foot per minute. Rollers and plastic sheeting under the pipe protected the carpets, and plywood panels protected the walls. As the tube sections emerged, Mahana disconnected them and handed them up to Barajas.

Pull two, connect three

The next day, the team excavated an entry pit at the sewer, welded a 10-foot length of pipe to a 40-foot stick, and turned the machine around to repeat the drilling process for the downhill shot. “The new line reversed the flow and removed the bank from the picture,” says Mahana.

On the last day, the crew connected the lateral to the sewer with a cut-in wye, fused the two pipe ends in the pit, and attached the polyethylene pipe to the cast iron lines from the bank with PVC SDR 35 and transition couplings. “The machine’s ability to drill at specific grades made this project possible,” says Mahana.

The overall job took two weeks and ended the mall’s sewer problems.



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