The Sandhogs

Larry McCloy, construction superintendent for The Sandhogs had to make a decision: Should he call off tomorrow's press conference and shut down construction? Planned to celebrate the tunnel's having reached the center of the river, the press conference was to be a major public-relations event. But two engineers had warned McCloy that predicted flood conditions and leaking joints in the new tunnel's temporary metal lining might pose danger.

The Situation

The Sandhogs had attained a nearly legendary reputation for superiority in tunnel construction. In a business typified by unexpected delays and late completions, the Sandhogs had finished almost every tunnel on schedule. Even more impressive to people in an industry where fatal construction accidents are frequent, the Sandhogs had never had a fatal accident. The Sandhogs attributed their singular record mainly to the exceptional skills of their foremen, who had earned the reputation of being able to solve any problem that a construction project could throw at them. Time and again, the foremen had overcome serious challenges. The Sandhogs also attributed their excellent record to their careful adherence to written procedures. They did everything by the book. No tests were omitted, no details overlooked.

This tunnel was being pushed through muck in the bed of the Columbia River. The top of the tunnel was only a few feet below the river bottom. Each extension began with the advance of a massive hydraulic ram that drove itself through the muck. Then workers moved in and erected a temporary metal lining (TML), bolting the new wall segments to those installed previously. The joints between TML segments contained gaskets, which are flexible rings that compress and render the joints water-tight when the bolts are tightened. Later, forms would be set up inside the TML and a permanent concrete wall would be poured.

Or, at least the joints were supposed to be water-tight. The joints had been leaking almost since the project began. At first there had just been occasional trickles. But the trickles had become more frequent over time; and a year ago in March and again June, there had been really serious flows of water that the workers had labeled "gushers." These gushers had forced The Sandhogs to shut down work and to bring in pumps until they stopped the flows of water. Each time a leak had occurred, including the two gushers, The Sandhogs had succeeded in eliminating the leakage by retightening the bolts that held the TMLs together, and there seemed to have been no permanent harm.

People had advanced several theories about this leaking. One theory held that the workers had grown increasingly careless over time, with the result that they made assembly errors more and more often. The Sandhogs had tried to address this concern by emphasizing need for assembled surfaces to be clean and the importance of testing the tightness of every bolt with a torque wrench.

A second theory held that TMLs didn't have enough bolts holding them together, so the joints were not stiff enough and the bolts tended to loosen over time. The Sandhogs tried to address this by increasing the torque level that each bolt had to meet. Nevertheless, the leakage had not only continued but become more frequent. Midwest Casting's engineers said that the new torque requirement might actually be exacerbating the problem by imposing uneven pressures on the gaskets between TMLs.

A third theory held that the gaskets didn't have enough resilience. Although laboratory tests said they exceeded the design specifications, they were a new plastic material rather than the traditional rubber. Anything new may have unexpected deficiencies.

A fourth theory held that the TMLs were too thin, causing them to flex too much. Two years ago, when construction started, The Sandhogs were using thicker TMLs. But the engineers at Midwest Casting, the firm supplying the TMLs, had recommended shifting to a stronger alloy that could be thinner, lighter, and faster to assemble on site, thus making it easier to meet the construction schedule. This change might explain why leakage became more frequent about 16 months ago.

Unfortunately, there was no way to go back and replace TMLs that were in place if they were too thin or their gaskets were inadequate or they needed more bolts. At best, Midwest Casting could change the TML design when they produced the next batch of TMLs. There were enough TMLs already on site for another five or six months of work.

A fifth theory laid the blame on the spring melt. In March a year ago, when the first gusher occurred, one of the engineers, Roger Bonjovi, speculated that this gusher was somehow related to the strong river currents or the high water level. The winter snows had been melting and water levels were high, and this gusher had erupted about 36 hours after the river level began to rise. However, the spring-melt theory couldn't account for a second gusher that occurred in June, after the water levels had receded and the current slowed.

Like Bonjovi, some of the engineers, both within the Sandhogs and at Midwest casting, are worried that the leaks might foretell more serious risks. The gushers seem especially ominous. Not knowing the cause of the leaks means that they cannot assess the risks realistically. They speculate that whatever has been causing the leaks might be capable of actually rupturing the TML, say by fracturing a joint. They also find disturbing the escalation in leakage over time. A couple of the engineers have put together a graph showing the frequencies of leaks. (See Figure 1. There was just one gusher in March and a second one in June.)

A few of Midwest Casting's engineers have formed an informal task force to redesign the TMLs and, especially, the joints between TMLs. This task force has so far come up with 43 design proposals. Laboratory tests on one design, a so-called capture-lip joint, have demonstrated that it is "a good thing."

Larry McCloy, The Sandhogs' superintendent of construction, disagrees with these engineers, both about the risks posed by the leaks and about the desirability of design changes. McCloy has concluded that he can accept the occurrence of some leakage and he worries that design changes might harbor worse problems. Joe Cullister, Midwest Castings' liaison engineer for the tunnel project, agrees with McCloy. McCloy and Cullister have discussed the leakage with The Sandhogs top management, who have agreed that the current situation is acceptable. Explains McCloy,

Although leaks have been frequent, there had been no gushers since last June. None of the leaks, even the two gushers, caused long-term damage, and we've had no trouble stopping them. All we've had to do is readjust a few bolts. Our experience shows that the TML design has enough safety factors to make some joint leakage acceptable.

Since some leakage is accepted and indeed expected, it is no longer a serious anomaly that we have to eliminate. Building a tunnel always involves uncertainties. We work on these projects because we like the challenges they present and we accept the risks that go with those challenges. If we would try to eliminate every little anomaly, we'd never complete a tunnel.

The main thing is not to introduce sudden changes in the way we do things. Abrupt changes escalate the risks. We need to stick with procedure and to modify procedure only when we are certain that a change will be an improvement. Since we aren't sure what is causing these leaks, we can't be sure that a change will be an improvement.


The Decision

Two of The Sandhogs’ engineers, Roger Bonjovi, and Arnie Thomas, have gone to see Larry McCloy and told him that they are recommending that The Sandhogs immediately halt construction on the tunnel and cancel the press conference scheduled for tomorrow. They explained that they are deeply concerned about the effects of the record warm temperatures that have moved in over the northwestern United States and Canada, extending as far east as the Rocky Mountains. The weather bureau is predicting that the abnormal warmth will continue for some time, producing a rapid spring melt with consequent flooding. The Columbia River will bear the brunt of this runoff.

Bonjovi and Thomas reminded McCloy that the first gusher occurred during the spring melt last year. This year, the weather forecasters are saying that the record high temperatures are going to make the water levels and floods much, much worse. If strong river currents were a factor last year, they are going to be a much bigger factor this year. Perhaps the strong currents will recarve the river bottom and subject the tunnel to pressures outside its design parameters. In fact, if the river really acts up, it could rupture the tunnel. The uncertainties are too great for The Sandhogs to do more work on the tunnel until the water levels subside, say three or four weeks from now.

The press conference was scheduled months ago. The Governors of Oregon and Washington as well as all four Senators will be in the tunnel, at the construction face, when The Sandhogs' CEO announces that they have reached the middle of the river. All the major television stations will be covering the event; they have laid their cables and set up other equipment inside the tunnel. Because so much equipment is already inside, it is too late to move the press conference outside the tunnel, but it will be a public relations disaster if a gusher cuts loose during the press conference!

After Bonjovi and Thomas left, McCloy consulted his chief engineer, Bob Hunt. Hunt said he thought that Bonjovi and Thomas were probably being too cautious. Afterall, the second gusher last year had occurred long after the spring melt so the connection to the spring melt isn't obvious. But at the same time, he cannot rule out the possibility that Bonjovi and Thomas might be right.

McCloy has also considered calling his boss, The Sandhogs CEO. But he thinks that wouldn't be the smartest phone call he ever made. All the dignitaries involved in the press conference, including the CEO, are already en route to the construction site. With the television crews already setting up, there would be no way to mask a cancellation and he would have to give a very convincing explanation. The project is already close to breakeven. If he halts construction until the spring melt ends, The Sandhogs would lose over a $1 million a day, not counting interest costs. He figures that shutting down would most likely be his last decision as a construction superintendent.

Should McCloy call off the press conference inside the tunnel and shut down construction until after the spring melt?




Created by Bill Starbuck 10/97