Monday, August 29, 2016

Why it took less time to fix a sinkhole in 1997

Last Wednesday the always chipper mailman Tony who delivers the office mail, looked somewhat beaten: "Just when you thought it can't get any worse, there comes another hit".

Indeed, Wednesday, and without much warning, came the day when on-call contractor Spiniello had figured out how to cross the Howard Street light rail tracks with its temporary sewer bypass of a twin set of 24" pipes and obtained all necessary permits (hard to tell which took longer). 
Drilling rigs and cranes (photo ArchPlan)

The resulting construction needed to get this accomplished is astounding in its complexity and scope, and yes, it required the complete closure of Franklin Street as well. 

The last time Franklin Street had to be closed for a sinkhole was on November 9,  1997, when the intersection of Franklin and Park disappeared and a severed gas line exploded and set the hole on fire for five hours, forcing evacuations all around. But after a few weeks pipes were sutured, the hole filled, the road paved and traffic could flow again. This time it is worse and one of the reasons is the quick patchwork that was too common 20 years ago. 

Now the arterial route 40 corridor is fully severed in the eastbound direction at Mulberry and Greene Street and in the westbound direction at Franklin and Park. All traffic get routed around the 1 block (eastbound) and two block (westbound) closure. The closures will be in effect for some time to come. To get under the tracks, a tunnel boring machine will be used that will be placed on the on Franklin west of Howard Street.The boring has to pass under the tracks and some pretty deep utilities running on Howard Street, but above the CSX tunnel under Howard Street, which is pretty deep down at this point. The way I understand it, the borings will be about 24' under the street level and accordingly, the hole in which to assemble the boring machine has to be that deep as well.
Shoring the pit with steel plates (photo ArchPlan)
Shoring the pit with steel plates (photo ArchPlan)

 Before one can dig a hole that deep in between buildings and with the prospect of extensive work at the bottom of the hole, it has to be shored up. To this end, 14 piles had to be driven into the ground, or more precisely, placed into drilled holes. When the pit gets excavated, metal sheets will slide down between the flanges of the piles and shore up the soil. The drilling and placing of the piles took until Friday evening, since then excavation is taking place. The pit on the east side of Howard was dug much faster, just lifting the boring machine out again, apparently requires less elaborate shoring.
The matter is quite reminiscent of the tunnel work envisioned for the Red Line, just this time on a much smaller scale and only temporary.
A big excavator ready to dig the 25' deep pit
(photo ArchPlan)

Once the boring machine is operational, it will drill those holes, one after the other (it can't back up, so it must be reset by crane, I suppose). Then the pipes can be pushed through, they need to be connected with the surface pipes that by then will have been waiting for this moment for more than two months. One all the pipes are connected the big sewer diversion from the 54" broken main at Mulberry Street can finally occur which will allow the actual repair work in the sinkhole to finally begin.
Utility work worldwide: In Baltimore on Time & Materials
(photo ArchPlan)

The big question I had was, wether is the sewage going all this time and wouldn't there have been an easier more direct detour with a fix in the hole much earlier? If I understand it correctly, the broken pipe still carries the sewage in its bottom half while the top is blown. If the loads grow bigger than the bottom can carry, it spills. As for the direct fix with a mini detour, that isn't being considered because that sewer main is shot over a much longer distance with many other places where the street shows already signs of being washed out. So the plan is to fix the whole length, bless their heart, with a plastic liner that essentially creates a new pipe inside the brittle old one.

What business owners, tenants and residents in the area probably care most about is: How long will it take and when will Franklin be reopened? From what I gathered, if the borings work as planned, Franklin will be reopened with two westbound lanes in four weeks at the earliest. The sinkhole fix will go through the rest of the year, probably into 2017.  The Center Street sewage pipe is fixed, but workers for phone and electric are still in the ground doing their things. So that will also still be about a month.

Meanwhile DOT traffic engineers will review the area with a field visit this week to see how traffic flow can be improved. 

The 1997 caused the vacant building at the northwest corner of Oark and Franklin to be demolished, it's foundations weakened. So far, the new crop of sinkholes hasn't threatened any buildings yet. And there were no fires yet, either. 

Klaus Philipsen, FAIA

The article is compiled from inquiries to a DPW Inspector, several Spiniello supervisors, a superintendent and City DOT.
Diagram of a lined pipe

Injection of plastic liner

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