Tunnel Project : Metro Rail Digs: Risky Business

One of James Monsees’ biggest professional thrills came the day he realized nobody noticed his work.

Monsees, an engineer, was working on a tunnel under the National Institutes of Health when a scientist approached him, concerned that explosions to dislodge rocks might interfere with sensitive experiments.

“When are you guys going to start blasting?” the scientist wanted to know.

“Three months ago,” Monsees replied.

Monsees, then helping to build the Washington subway, hopes to make a similarly small stir in Los Angeles.

He is chief tunnel engineer for a group of firms called Metro Rail Transit Consultants, which is advising the Southern California Rapid Transit District on how to build its subway.

The modest 4.4-mile subway, which the RTD hopes will be the first leg of an 18-mile run from downtown to the San Fernando Valley, will cost an estimated $1.25 billion, making it the costliest transportation project per mile ever built.

How well it will be built--and the extent to which Los Angeles residents will notice its construction--is a story that will not be fully known for years.

But if all goes well--which, as experts have noted, it seldom does in tunneling--the subway will come in on schedule and on budget, with a minimum of disruption, sometime in 1992.

Then four-car trains will take seven minutes to go from Union Station, through the Civic Center and financial district, to MacArthur Park.

Ground May Crumble

Monsees and his colleagues have already spent years building the subway in their heads.

They know that the ground here is soft and will not require blasting. But they also know that it presents other problems, chiefly that it may crumble as tunnelers bore through it.

It is certain that the soft ground will not stand unsupported as well as hard rock.

This relatively poor “stand-up time” means that the ground needs to be supported quickly as the tunnel is cut.

Tunnel workers could die, and buildings on the surface could be damaged, if the ground crumbles unchecked and fills the tunnel.

Subway builders have had a lot of practice avoiding such catastrophes. Their basic technology was developed 170 years ago by an engineer whose aim, like that of Metro Rail’s builders, was to relieve a traffic jam.

Marc Brunel wanted to build a vehicular tunnel under the River Thames to ease cart gridlock on the London Bridge, where merchants complained that produce wilted in the sun before they could move it to market.

But Brunel first had to solve the problem of how to keep the oozing, watery ground under the river from filling the tunnel as fast as it could be dug.

He chanced upon a solution at a London dockyard, where he picked up a piece of oak and observed a creature called a shipworm boring through it and simultaneously lining its hole with a secretion. Brunel designed a machine that would allow people to do a similar thing.

Called a shield, it was a rectangular assembly of cast-iron sections that could be lowered down a shaft. Workers could stand inside the shield, protected from cave-ins, and, through large openings at its front, remove the earth with picks and shovels.

Support in Brick

Other workers could stand behind them and, through large openings at the rear, line the tunnel with brick.

The shield could support the ground at the working face of the tunnel, and could be moved forward by screw jacks pressed against the end of the newly laid brick.

Brunel’s idea revolutionized soft-ground tunneling and made possible construction of the world’s first tunnel under a body of water.

The work was excruciatingly slow--400 yards in 18 years. But the tunnel had staying power; subway trains use it today.

During construction, Brunel worried all the time. “What anxiety, what fatigue both of mind and body,” he wrote of the round-the-clock effort. “Every morning, I say, ‘Another day of danger over.’ ”

Cause for Concern

He had cause to worry. His tunnel kept collapsing and filling with water. In one incident, six workers died. Most barely escaped with their lives.

Although safety has improved considerably since then, and tunnel shields have been radically refined, there is still plenty of reason for concern.

“There’s still a lot of art--and luck--to tunneling,” said Donald C. Jackson, a Washington-based consultant on the history of technology and engineering. “It’s not like here in the late 20th Century we can just crank this out.”

A current undersea project in Japan, for example, has claimed 34 lives. Fourteen workers died during the first 10 years of building the subway in Washington. In 1971, 17 workers were killed building a water tunnel in Sylmar.

“The history of modern tunnel building is replete with catastrophes and disasters,” according to a recent report by the Occupational Safety and Health Administration.

The leading cause of death is unsafe means of getting in and out of tunnels, followed by exposure to toxic or flammable gases, followed by ground collapses, the OSHA says.

Casual Attitudes

Those attracted to the work--known as “sandhogs” in the East; “tunnel stiffs” in the West--are, by reputation, hard-living boomers who travel from job to job and are somewhat casual about risks.

“You finally get to where you don’t pay much attention,” said Audrain Weatherl of Sacramento, a veteran tunnel stiff and an official of the Laborers International Union. “You drive your car a little faster and jump off of higher cliffs than do people who’ve been living in a real world.”

A relatively common hazard comes when unexpectedly heavy, waterlogged ground flows from the face of the tunnel and mires the shield.

“There’s really only one damned thing you can do then,” Weatherl said. “You’ve got to mine that ground out by hand until you can get up (over the shield) and free it.

“Any time a man has to go above the shield and work in a little tunnel he’s made, that thing could cave in and kill everybody at most any time because, if (the ground) was good, it wouldn’t have set down on the shield in the first place.”

“A lot of people think these tunnel stiffs are crazy,” Weatherl added. “Maybe we are.”

Engineers like Monsees work to limit dangers that will take workers by surprise. But they cannot banish them. In Los Angeles, they have spent five years trying to detail their vision of the subway on charts. But, in the end, they have chafed against unknowns, and their charts carry a lot of question marks.

Like surgeons performing biopsies, they have reached into the earth with borings and extracted ground along the route of the proposed tunnel. But their samples have been intermittent, and they can speak with authority only about ground conditions they have actually seen and tested.

“There are bound to be surprises,” said Robert Vogel, curator of civil engineering at the Smithsonian Institution. “Tunneling is unlike building a bridge or a building, where you’re building in the air; it’s all there, and there are no mysteries. To a certain extent (in tunneling), you’re working blind.”

Tunneling is different in another way too, he said. “You are not really constructing. You are taking apart. Your end product is the removal of material, not the assembly of material. . . . In other words, you are producing a void.”

Monsees is fascinated with underground work precisely because it is uncertain. “You don’t always have exact knowledge and exact equations of everything you want to do,” he said.

Careful Examination

To limit the uncertainty, engineers get the most out of their samples. They shear them, bake them, compress them and push on them until they fail. They even eat some. Clay for instance, is said to taste like butter.

And they go down to tunnel depth to take a look first hand.

Monsees, equipped with a flashlight and screwdriver, was lowered down a couple of 30-inch diameter shafts so that he could see what the ground looked like at the 55-foot tunnel depth and poke it as much as he liked. It was “pretty good stuff,” he said.

Most of the ground at that depth is expected to be what geologists--but nobody else--would call rock. “It’s a soft rock,” Monsees said. “It’s not like concrete or something.”

“In engineering terms,” he added, “it’s really a very hard, stiff soil--a sandstone or silt stone which has been partially cemented and will tend to behave pretty much as a continuum.”

Matter of Stability

A fingernail is enough to scrape off a layer of the stuff. But Monsees said it is sufficiently stable that it will not move much when the tunneling shield cuts through it. It could probably stand without arch support for days or even weeks.

But one segment of the planned tunnel is “tricky,” Monsees said. That is between 5th and Hill streets and 7th and Flower streets, where the tunnel goes under the largest buildings on the route and through the least stable soil.

Much of this segment lies in the ancestral bed of the Los Angeles River, which, according to historical records, repeatedly flooded what is now downtown Los Angeles, depositing boulders and cobbles in the river’s narrows and rapids and much finer sediments in its broader, calmer waters.

“As you go through (these sands and gravels) you don’t hold everything perfect, so there is some movement of the ground towards the tunneling machine,” Monsees said.

The movement has to be stopped before its effects reach buildings on the surface and damage them by causing abrupt settlement.

In case of such trouble, there won’t be much time to react. But there is a plan.

Ready on the Surface

Workers on the surface will stand ready to inject a mixture of fine sand with a lot of water and a little cement into the ground above the tunnel. This mixture, injected under pressure through pipes, “enlarge(s) gradually, displacing and compacting the surrounding soil,” said Ralph B. Peck, professor emeritus of foundation engineering at the University of Illinois.

The mixture, called grout, should stabilize the ground under buildings like the Jewelry Mart, whose footings are about 27 feet above tunnel depth, engineers said.

The RTD’s real estate department has obtained temporary easements for a dozen such buildings to allow contractors to drill in advance a series of 60- to 70-foot-long holes from basements and alleyways to form a sort of umbrella pattern over the tunnel path.

By the time the tunnel reaches these buildings, Monsees said, “the holes will be put in. The . . . pipes will be in place. The pumps will be ready. The mix will be there. And . . . we’ll have settlement instruments that will tell us if the ground is starting to move. As soon as we get an indication that we’re starting to get some movement, we start pumping.”

Most of the work in modern tunneling is done by a digging device housed at the front of a steel tube.

The tube, slightly larger than the diameter of the finished tunnel, is a shield. Like Brunel’s, it protects workers from cave-ins by supporting earth at the tunnel’s working face.

The digging device at its front is designed to fit local soil conditions. Sometimes it is a series of carbide bits that grind rock. For Metro Rail, it will most likely be a backhoe-type shovel.

Workers assemble segments of the tunnel’s circular lining inside the shield. The shield’s operator, who sits near the tunnel’s face, moves the machine forward by pressing jacks against the end of the newly assembled liner segment.

Metro Rail’s two tunneling contractors can choose between putting up precast concrete liner segments as they dig, or constructing a lining of steel ribs and timbers and putting a concrete lining on top of that later.

Most U.S. contractors favor the ribs-and-timbers method, Monsees said, and the inside of their tunnels under construction look like the inside of barrels.

Four-Foot Segments

“They . . . do it in four-foot segments,” he said. “They erect a steel ring. Set in four feet worth of boards. . . . Erect another steel ring. Shove forward and just . . . keep going.”

Working three shifts around the clock, they are expected to make 50 feet a day.

The soil they remove, called “muck,” will be carried out of the tunnel shield on a conveyor belt, then dumped into a muck train.

The train will carry it to the end of the tunnel, where workers called muckers will transfer it to dirt brokers, who will sell it where they can.

Tunnel shields cost millions and take months to build. “It’s not like walking into a dealership and buying a Chevrolet,” Monsees said. “No two tunnels are exactly the same.” The troublesome clay of Mexico City forced Monsees to design a shield with flaps that could be extended from the front for extra protection against cave-ins during a sewer tunnel project.

Monsees doesn’t think flaps will be needed here, “but we won’t know for sure until we get out there and try.”

Variety of Tasks

Monsees also has worked on underground missile silos and on planning for tunnels to store nuclear wastes. To him, one tunnel is about as interesting as the next.

But other engineers are drawn specifically to subways. Many of them have worked together on one or more of the modern American subways--in San Francisco, Washington, Miami, Atlanta and Baltimore. In fact, each of these subways represents a subtle refinement of what was learned from the last, in part because each was designed by the same circle of people.

Monsees works for a leading civil engineering firm--Parsons Brinckerhoff Quade & Douglas--that has had a hand in subways since the turn of the century. Its founder, William Barclay Parsons, was credited with designing and building the first 21 miles of the New York City system.

No one engineer will get credit for Metro Rail. The heroic days of the past are gone, said Emory L. Kemp, director of the program for the history of science and technology at West Virginia University. “It’s much more anonymous now.”

Monsees is part of a huge team of engineers. Parsons Brinckerhoff is one of four engineering or architecture firms advising the RTD on subway design in a joint venture. Three large construction firms are advising the RTD on how to manage the construction. Still other companies will build Metro Rail.

Choices Limited

The engineers on a project like Metro Rail function much like architects designing buildings. But they don’t have too many grand choices.

The shape of the tunnel is usually a foregone conclusion. Tunnels are customarily circular in part because of the way tunneling shields move forward: They tend to roll slightly as they advance. A shield could be designed to build a horseshoe-shaped tunnel with a flat bottom. But because of the machine’s tendency to roll, the flat bottom might wind up on the side. With a circle it doesn’t matter.

Interior diameters--17 1/2 feet here--are dictated by the size of the trains.

Tunnel depths--between 50 and 60 feet for Metro Rail--are determined by a variety of factors:

The alignment has to be deep enough to allow trains to run safely underneath footings of tall buildings. But stations cannot be placed too deeply without ignoring a powerful money-saving incentive to keep massive station excavations shallow. And tunnels cannot be dipped sharply to dodge footings, then climb sharply to enter shallow stations, because subway trains will not perform well on sharp grades.

Key Design Factor

The main challenge for the engineer is designing the tunnel lining--also known as a ring--in such a way that it has a symbiotic relationship with the ground it passes through.

A well-designed lining will compress slightly in response to the ground’s weight, rather than bend and lose its shape. The very earth that surrounds it presses in on it and keeps it from losing its shape.

Sandhogs have a saying to describe the relationship. “The ring supports the ground,” they say. “But the ground supports the ring.”

In Los Angeles, two factors--methane gas and the threat of earthquakes--complicated lining design.

Methane gas cannot be seen or smelled, but it can blow up. In an effort to prevent this during construction, workers called “sniffers” will carry sensing devices to detect the gas, which explodes when it mixes with air in certain known proportions. Ventilation is planned to keep the mixture well below its lower explosive limit.

To prevent methane explosions after construction, the tunnel needs to be sealed against the gas. Engineers decided to require that the linings of stations and tunnels be wrapped with high-density polyethylene to keep the methane out.

Earthquake Concern

To respond to earthquakes, they wanted a flexible lining.

“People tend to think of the ground as being a solid or permanent,” Monsees said. “But when an earthquake wave comes through, the ground actually goes through a wave motion.”

The tunnel is subject to “snaking” as it follows the “earth wave.” Also, probably because the wave comes from the side, the tunnel goes into an “ovaling mode, where an original circle gets bent into an oval,” he said.

“The whole goal is to build it in such a way that it can follow these ground movements . . . and return right back to its shape.”

Monsees built a mathematical model to test the effect of the wave on the 8-inch-thick lining he helped design and found that it was resilient.

He was not surprised.

“The soil you’ve taken out is usually more stiff than the liner you’ve put back in,” he said. “The thin liner just rides along.”

‘There’s still a lot of art--and luck--to tunneling.’

--Donald C. Jackson,

Washington-based consultant

TUNNEL TIMETABLE The tentative schedule for building Metro Rail’s shell: Metro Rail’s Union Station (Under the tracks behind Amtrak’s Union Station)

Pile Driving: April, 1988 Excavation: May, 1988 Shell Completed: Sept., 1990

Fifth and Hill Station

Pile Driving: Aug., 1987 Excavation: Jan., 1988 Shell Complete: Feb., 1990

Seventh and Flower Station

Pile Driving: Sept., 1987 Excavation: Nov., 1987 Shell Complete: Feb., 1990

Wilshire-Alvarado Station

Pile Driving: Sept., 1987 Excavation: Nov., 1987 Shell Complete: Feb., 1990

Tunneling from Union Station to Fifth and Hill, including Civic Center Station

Pile Driving: June, 1987 Station Excavation: July, 1987 Shaft Excavation: Nov., 1987 Tunnel Excavation: Jan., 1988 Completion: April, 1990

Tunneling from Seventh and Flower to Wilshire and Alvarado

Shaft Excavation: July, 1987 Tunnel Excavation: Oct., 1987 Tunnel Complete: July, 1989

Tunneling from Fifth and Hill to Seventh and Flower

Shaft Excavation: Sept., 1987 Tunnel Excavation: Jan., 1988 Tunnel Complete: May, 1989

DESIGNING THE SUBWAY Those overseeing Metro Rail design and construction for the RTD: James A. Strosnider, director of construction for Metro Rail, is in overall charge of building the subway. Strosnider handles contractor safety, quality control, cost control and scheduling. He helped build San Francisco’s BART, Atlanta’s MARTA, an extension of Boston’s subway, and the Morgantown, W. Va. people mover. He managed engineering and construction for New Jersey Transit, and headed design and construction in northern New Jersey section of the northeast corridor rail improvement project, which refurbished lines from Boston to Washington. James E. Crawley, director of engineering for Metro Rail, supervised design of the subway’s alignment, tunnels and stations. Crawley was deputy project manager for a joint venture of Deleuw, Cather & Co. and the Ralph M. Parsons Co., consultants to the city of Los Angeles in building the second-level roadway at Los Angeles International Airport. Crawley was project manager for a firm developing an Orange County rail transit plan, which voters rejected. William J. Rhine, design director for Metro Rail operating systems, oversees trains and what powers them, fare collection, safety, security and communications. He was director of engineering for BART, safety director for the federal Urban Mass Transit Administration, and, as manager of NASA’s Apollo guidance and navigation office, supervised design of the system that carried astronauts to the moon and back. Melvin L. Polacek directs a joint venture that serves as RTD’s construction management consultant. The joint venture known as PDCD consists of the Ralph M. Parsons Co., Dillingham Construction Co. and Deleuw, Cather & Co. Polacek, of Parsons, was construction manager for the government’s strategic petroleum reserve project, worked on subways in Baltimore, Washington and Atlanta, and helped start the northeast corridor rail improvement project. William H. George of Deleuw, Cather is a deputy construction manager for PDCD. His duties include reviewing designs to make sure Metro Rail can be built as planned and processing design changes necessary to complete the work. George was a resident engineer on the Washington subway and was manager of construction operations on the northeast corridor rail improvement project. Henry C. Scott of Dillingham Construction is a deputy construction manager for PDCD, supervising the work of its resident engineers, who are assigned to monitor each contract at the work site. Resident engineers answer to project engineers on Strosnider’s staff at the RTD. Scott supervised construction of segments of BART and the Washington subway. Howard J. Chaliff is project director of the joint venture that serves as RTD’s design consultant for Metro Rail. The joint venture, known as Metro Rail Transit Consultants, or MRTC, consists of Parsons Brinckerhoff Quade & Douglas, Daniel Mann Johnson & Mendenhall, Harry Weese & Associates and Kaiser Engineers. Chaliff, of Parsons Brinckerhoff, had a key role in supervising the design of the Atlanta subway. Krishniah N. Murthy of Parsons Brinckerhoff heads design of Metro Rail’s physical facilities for MRTC. He was a project manager for several design and construction jobs on the Atlanta subway and has also designed bridges and highways in this country and tunnels and industrial structures in India. Alan Dale of Kaiser Engineers oversees design of Metro Rail’s trains, power systems, signals, communications equipment and fare collection devices for MRTC. He had similar duties for the consultant on Miami’s aerial rapid transit system and served as chief engineer for the firm that supplied subway cars to BART and the Washington system.