Climb inside the massive tunnel 60 feet below downtown L.A.

Ten weeks in and 60 feet beneath the streets of downtown Los Angeles, the miners have clawed through nearly 2,600 feet of earth.

At 5 a.m. on a cool Thursday morning, they gather in the construction yard for the start of another shift.

The moon, just starting to wane, hangs above the distant skyscrapers as the men stretch like athletes and huddle to hear the latest safety report.

The day before, they had been unable to dig. Gas — most likely methane — had been detected in the tunnel, and they had to wait for state inspectors to give them the OK.

“It’s all good now,” their foreman announces, “but we’ll still be monitoring, so be careful.”

Coolers in hand, hard hats and fluorescent vests reflecting the glare of the light towers, they clomp down seven flights of stairs into a large open pit, shored up by wooden timbers and crowded with vats of grout, portable trailers and man lifts.

The mouth of the tunnel gapes at them. The moon, the clouds and the city disappear as they enter.

In 2021, commuters will follow their steps, barreling through an S-shaped tunnel — the $1.75-billion Regional Connector project — 1.9 miles out of Little Tokyo, north to Bunker Hill and west to 7th and Flower streets.

The transit corridor will allow riders, for the first time, to travel from Long Beach to Azusa and Santa Monica to East L.A. without changing trains — filling a critical gap in Los Angeles’ subway system.

Construction workers will lay almost a mile of that tunnel through a methodical excavation of Flower Street, building the subway and then rebuilding the street. The rest, however, is being dug the hard way.

The miners, traipsing single file along a plank walkway, descend a gentle grade into the tunnel for nearly half a mile before reaching their destination: a 400-foot-long, 1,000-ton earth-chewing beast, known as the tunnel boring machine.

Sometimes called moles, sometimes sandhogs, the men — there are no women on this shift — belong to a tight confederacy. They can see themselves doing little else for a living. They like being left alone to do their job. They like the variety of challenges, the on-the-spot repairs. They like the community.

“There are no bad people down here,” said one miner. “We would throw them out if there were.”

Veterans of other tunnels, they have built passages for water to flow through the San Bernardino Mountains and under Lake Mead, and they look ahead to the possibility of digging beneath the streets of South Pasadena or in the Sacramento-San Joaquin Delta. For those willing to travel, the world is in play.

Tunnels are turning Earth into an ant farm with massive projects underway in London, New York, Hong Kong and Germany.

In Qatar, nearly 24 tunneling machines are digging a subway system for the 2022 World Cup, and in China, one company manufactures nearly 50 tunneling machines a year for that market alone.

As long as the world’s population continues to grow and cities become more congested, there will be a demand for tunnels and miners, says Richard McLane, chief mechanical engineer for the Regional Connector project.

“Why is tunneling so addicting?” McLane asks. “It’s like watching civilization in action. This is not a leaf spring for a Chevy Camaro that in 10 years will be in a junkyard. The work we do will last generations.”

All aboard the dirt-chewing machine

After a five-minute walk through the tunnel, the miners reach their destination and begin to spread out.

Inside the operator’s cab, a small air-conditioned box near the front of the tunneling machine, Scott Halsey faces a wall of monitors, one featuring video feeds of the conveyor belts, others relaying with rising and falling numbers the machine’s progress.

His hands are reflexively poised over rows of switches, dials, toggles and buttons lit red or green. He picks up the phone.

“OK, we’re good to go.”

Looking more like a computer technician than a miner, Halsey presses a series of buttons, and the numbers on the control panel begin to rise. Seventy feet ahead, far out of sight, the machine’s cutting head has begun to rotate.

Hydraulic jacks push the cutting head forward and exert a steady pressure against the earth.

The cutting head grinds through the earth at two rotations a minute, shaving and clawing at a dense wall of clay and silt compressed over millennia. Every minute it advances three inches.

Auger screws churn the excavated soil — softened by a foamy mixture of air, conditioner and water to a Play-Doh-like substance known as muck — and conveyor belts transport it back to the pit and an armada of dump trucks bound for Irwindale.

The high-pitch whir of the cutting head echoes inside the tunneling machine along with the drone of the conveyor belts, motors driving the hydraulics, the hammering of the grease pumps and the occasional air-horn blast from an arriving locomotive that runs through the tunnel ferrying supplies and equipment.

“We’re mining,” Halsey says.

Halsey first stood at this console in 2004 when he took his inaugural run into Boyle Heights under Mariachi Plaza for the Gold Line. Never having operated equipment so demanding, he remembers shaking with adrenaline.

He and his wife live on a cul-de-sac in Santa Clarita, but he has done his share of traveling for the job, most recently to Washington where he experienced history from 130 feet deep, tunneling under the Potomac River (“that George Washington crossed”) and near the airfield where Obama’s helicopter was hangared.

That soil, he says, was the best he has ever found: clay with layers of sand.

Halsey is a member of the International Union of Operating Engineers Local 12 and earns nearly $50 an hour, not counting overtime. He got his start in tunnels almost 20 years ago when he was in his early 30s, having worked road maintenance after graduating from Sylmar High School.

With its heavy machinery, cranes, loaders and excavators, the underground world was a big kid’s dream, he says.

But the work could be hazardous. Carbon monoxide and diesel soot choked tunnels. Cave-ins left men running for their lives, and bosses cut corners as they drove their crews harder and faster.

The ancient Persians pioneered tunneling techniques for transporting water, and the Romans added fire-quenching — heating subterranean rock with fire and dousing it with cold water to encourage cracking — to the engineer’s repertoire.

Los Angeles was once considered an unlikely place for such grand ambitions, the soil deemed too gassy, too unpredictable.

A methane explosion in a water tunnel in Sylmar in 1971 killed 17 miners. In 1985, underground gas accumulated in a clothing store at 3rd and Fairfax streets, and when it blew up, nearly two dozen people were injured, leaving many to question the wisdom of building a regional subway system.

Gas wasn’t the only problem for the city’s first underground. In 1994 as Red Line crews burrowed beneath Hollywood, its star-studded boulevard sank 10 inches, and two years later, the 101 Freeway dropped nearly four.

Not long after, a new style of tunneling machine came on the scene as the Metropolitan Transit Authority built the Gold Line.

By keeping steady pressure on the earth while excavating, operators minimized subsistence and heaving — sinking and bulging — the twin evils of tunneling, and with the miners enclosed in a capsule the diameter of the tunnel, dangerous gases could more easily be vented.

With the old equipment, the ground might move as much as an inch and a half, McLane says. On this project, he says, sensors have picked up movement of no more than 0.16 inches.

Men as moles

After 20 minutes, Halsey has excavated five feet. He pushes a button on the console labeled “Ringbuilding,” and Jesus Ruiz and his crew take over.

Six prefabricated segments — up to 8,000 pounds each — have been hauled into the tunnel by a locomotive, and Ruiz, operating the erector, a circular crane that moves like the hands of a clock, positions the segments and a keystone around the circumference of the tunnel.

“Retract,” shouts a ring builder, and Ruiz toggles a joystick on the remote hanging off his chest, bringing a segment into alignment.

Moving gracefully, each step orchestrated by habit, the miners scramble over and under the erector, leveraging themselves against a network of ladders, catwalks, angle irons and tread plates. Impact guns slam segment bolts into the adjoining segments, and after 20 minutes, they are done. Halsey can start mining again.

So it goes for each 10-hour shift, this back-and-forth between mining and ring building. Some miners extend water lines, electrical conduits, ventilation duct and tracks for the locomotive. Another oversees a continuous injection of grout between the rings and the tunnel boring machine.

This is the excitement of the job, says Halsey: moving along without interruption. “This is what gets my blood going.”

By 8 a.m., they have built three rings, and the city above them — drivers rushing to work, cubicle jockeys jaywalking for lattes — is unaware of the activity underfoot.

Standing at the console, thumb and forefinger on the dials, Halsey monitors the balance between the amount of dirt the machine excavates and the amount of dirt that, according to McLane’s calculation, can be removed with the minimum of subsistence. If one exceeds the other, the whole enterprise could come to a stop.

Halsey makes small adjustments, but he also knows that the earth can be fickle. At this depth and location, it has at times become sticky and gummed up the screw augers that carry the muck to the conveyor belts. “It’s all about what Mother Nature throws at you.”

Mother Nature was not kind to them during the first month of tunneling as they clawed through the sand and gravel deposits of the ancient floodplain of the Los Angeles River. Five feet took them nearly two and a half hours as they advanced under the Japanese Village Plaza in Little Tokyo.

When they finally hit the silt and clay, a stratum of earth known as the Fernando Formation, they broke out in song. ABBA provided the melody:

We mined all night,

and we could not find …

Fernando.

By then they were under 2nd Street with few obstacles in their way. Up ahead, at Hill Street, they will come within six feet of the Red Line tunnel, and as they close in on the station at 2nd and Hope streets, they will have a target to hit and can be off by no more than four inches.

The Romans drilled vertical shafts at close intervals and used plumb lines to keep their tunnels going where they wanted. A laser navigation system keeps the city’s miners on track. Halsey fine-tunes the pitch and the yaw of the tunneling machine by moderating the pressure applied by the hydraulic jacks.

Money, pride, ego, reputation

Early afternoon, and the work has assumed an easy rhythm. A dusty haze drifts through the tunnel. The miners fill water bottles from Igloo coolers and grab foil-wrapped plates of chicken or leftover spaghetti that they’d been warming on the electric motors that drive the hydraulics.

After replacing a gasket on the erector, repairing an overhead crane, cleaning a clogged port for the grout and clearing an overloaded hopper, they have the tunneling machine grinding away, like a finicky car finally on track.

“It’s the technology of a 747 in a 22-foot diameter tube,” says Halsey.

Drawing on the loose coils of a chain winch, Jose Bautista muscles a fresh 50-gallon drum of tail-skin grease under pumps that will push it between the tunneling machine and the concrete rings. Bautista, 22, is an apprentice mechanic, his father a supervisor on the day shift.

Bautista graduated from Bishop Amat Memorial High School and enrolled in automotive and diesel classes at Universal Technical Institute. He started working at a Dodge dealership for $11 an hour but found himself fast in debt with student loans.

Now he wakes at 3 a.m. for work, a small sacrifice for $29.85 an hour. He hopes to have his loans paid off in four years.

Outside the tunnel, Alex Barajas, who recently turned 22, helps load and unload the trucks that deliver the tunnel rings. His father, a foreman on the night shift, tried to discourage him from the tunnels, but a $100 award for every A wasn’t enough to keep him in school.

When he was younger, Barajas used to unlace his father’s mining boots at the end of a shift, and he would visit his father at tunneling projects around the country. “Without even knowing it, I was encouraging him to become a miner,” says his father.

Halsey too tried in vain to turn away his son, who is now an oiler in Las Vegas servicing the construction cranes.

At 3:05, Halsey thumbs the red button to stop the tunneling machine’s advance. He has finished the last five-foot push for the day. Outside the operator’s cab, Ruiz is shouting to his crew.

“Looks like he is going to try to get in the 10th ring build,” Halsey says.

Miners are not paid by the ring or the foot. There are no bonuses, so what’s at stake for finishing this ring? Halsey knows. “Pride and ego and reputation,” he says.

The day shift’s best day in the tunnel was back in March, when nothing broke down and the soil stayed easy. They advanced by 14 ring builds, 70 feet total, nearly 7,000 tons of muck, giving them the edge on the swing shift after being tied at 13 1/2 rings.

“Yeah, there’s competition, and now we’re the best,” Halsey says. “Only don’t tell them that. It will only start trouble.”

At 3:30, with no whistle, no horn, the miners pack up their gear, pass the swing shift heading in and crowd aboard the locomotive to hightail it out of the tunnel.

Outside, they squint into the sun and check their phones. The sky is blue, speckled with clouds. The sounds of the city serenade them.

To see more photos, video and graphics, go to latimes.com/tunnel.

thomas.curwen@latimes.com

Twitter: @tcurwen