Thursday, December 6, 2018

The curious case of the recent Howard Street sinkhole

Baltimore's Howard Street is an extreme case of divided responsibilities: There is a CSX owned tunnel a few feet below the street, and above the tunnel but below the pavement a BGE gas line. Electricity runs in City owned conduits under the sidewalks but is filled with BGE cables. Howard Street also covers powerful underground data lines feeding a big switching facility in the old Murdock building at Lexington Street. MTA owns rail tracks embedded on the surface for the light rail trains. The City owns the street and also the water and sewer below it.
New sgements of track are welded into place where
sinkhole work had been performed at Howard and
Lexington (Photo: Philipsen)

In such a situation it is quite disruptive if somebody discovers that in some sections there is no base and no soil holding up the pavement and that the pavement itself is all that's holding up the street.

This is exactly what a MTA  track maintenance crew discovered last Sunday when they investigated a dip in the road running there between the tracks that had them concerned. They peered into a cavity several feet large with an exposed water and gas line visible in the glow of the flashlight. With heavy buses and trains running over the street, the discovery had immediate repercussions for transit riders. The road was closed and trains and buses stopped.  A bus bridge was established to ferry riders between Camden Station and Mt Royal Avenue on a parallel route. 
Fortunately, CSX determined that the tunnel wasn't affected and kept its trains running.

Of course, the MTA discovery also brought out the City transportation folks, BGE and DPW to see what was going on.

A few drillings and a subsurface camera revealed only what was already known, considerable cavities but little insight regarding the cause. Often leaky water or sewer lines are the culprits which wash out soil and fill under roadways, but no defect utility lines were detected. "It must have been the heavy rains" city engineers determined and proceeded cleaning out stormdrains for good measure.
As frequently the case on these emergency repairs, a few workers work and
many others watch. (Photo: Philipsen)
And like any dentist, they began filling the cavities. Instead of amalgam they used a gravel concrete slurry. The method of building up a base underneath existing pavement doesn't represent the usual  industry standard, but it may well do the trick and wont easily wash away again. At this point only work on the concrete encased "embedded" track is left to do before the roadway can be opened again. MTA contractors discovered poor track embedment on the other end of the block as well and busted it up for a new fill as well, making best use of the order of concrete that is needed anyway. A pretty clear dip on the southbound track just south of Saratoga, though, will remain for the time being. And, in a rare case of prudent coordination, BGE is also on site doing maintenance on the conduits, using the street closure as an opportunity.

With all the activity, the originally anticipated re-opening date of Tuesday came and went. Maybe now it will be Friday until the bi trains rumble down Howard Street again.
This dip will stay in place (Photo: Philipsen)

 MTA identified the same section of Howard Street as the target for a comprehensive fix next year. The MTA wants to rip the worn tracks out and realign them so that they don't swerve as from running  with traffic on the side to traffic running in between. The work is part of a comprehensive track upgrade on the aging system and may give Howard Street once again a traffic free pedestrian area between Saratoga and Lexington Street. However, this is depending on a new TIGER grant which had not yet been awarded and isn't certain. Details would still be worked out if the grant is sure. Even if there is no grant, after nearly 30 years in service, the MTA will have to replace Howard Street tracks to get them into a state of good repair.

On July 18, 2001 at 3:07 pm a spectacular tunnel fire in the CSX tunnel under Howard Street brought all of downtown to a standstill and resulted in a special FEMA report about the incident. City and CSX argued for a long time about the question whether a 40in water main above the tunnel had leaked into the tunnel, causing the tanker derailment or whether the line damage was caused by the derailed tanker burning at very high temperatures. In 2005 NTSB finally blamed CSX for likely causing the accident that cost a total of $12 million. City and CSX were blamed for poor records of the location of utilities and the previous track repairs.

If the current fix holds, the vigilance of the MTA track inspectors prevented another debacle which could have easily arisen from the sinkhole.
Still busting up unrelated track embedment on
Thursday (Photo: Philipsen)

Klaus Philipsen, FAIA

BGE work on electric lines using the
opportunity for maintenance
(Photo: Philipsen)

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