Goshen continues to investigate underground vaults
Posted: 08/29/2013 at 8:22 pm
By: Nick Wesman
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Goshen City Building Maintenance Manager, Jeff Halsey, patchs a sidewalk coring at 225 S. Main Street Thursday, Aug 29.† (Photo Supplied)
This photograph shows a coring from the sidewalk above that went down into a vault at 205-207 S. Main Street in Goshen Thursday, Aug 29.† The vertical white rod was sent through the void into the basement and then located in the basement by the inspector.(Photo Supplied)
This photograph shows a bore hole at 136 S. Main St, inspected with a bore hole camera Thursday, Aug. 29 in Goshen.† Shows some settlement of the subgrade beneath the sidewalk, but it was so minimal that it poses no risk. (Photo Supplied)
City inspectors were able to gain access to many of the underground vaults and could easily determine whether the voids were structurally sound or needed to be shored.
Others, however, had foundation walls previously constructed that prevented investigators the access needed to be able to look through them.
For those vaults, the Redevelopment Commission brought in Blood Hound Inc. with ground-penetrating radar (GPR) in order to get a better idea of which vaults are already filled in and which might still be empty.
The GPR provided a non-destructive method of getting a clearer picture on which of the inaccessible vaults were empty and which were filled.
Blood Hound set up its equipment in the downtown area and canvassed the 110 sites needing the GPR over a period of about a week and a half.
The equipment surveyed two-foot grids, meaning that readings were taken every two feet at varying depths.
“It was trying to look at different segments and see, do I see an inconsistency or a void at this level,” city utilities engineer Dustin Sailor said.
“Where I’m at right now is, we’ve sent out letters to people who had some kind of foundation wall out front and we could not determine if there was anything out past that wall,” Sailor explained.
“The ground-penetrating radar, in some of those cases, said we still see something here that’s not consistent with other samples we’ve taken.”
What the GPR found were 15 additional locations that need further investigation to determine whether or not a void is indeed present.
That number seemed a bit high to Sailor, but does not necessarily indicate that all 15 of those sites feature a void.
“I think 15 is more than I had anticipated they’d find,” he said. “Now, whether the 15 end up being empty, in actuality, that’s something different.”
“Based upon the other stuff that (the GPR) made a determination on, there’s probably a void there,” he continued.
“But the other problem is they calibrate on hard ground, where they know there’s no void,” Sailor continued, so there’s a possibility that the void could already be filled but with a different material that was inconsistent with the material used in calibration.
The next step, then, was to drill a quarter inch hole in the concrete at those 15 sites and drop a fiberglass rod down the hole to see if there is in fact a void or if it’s simply been filled in with some other kind of material.
Even if some of the vaults are empty, Sailor does not anticipate another incident like last summer’s where the owner of Dew Drop Inn fell through the sidewalk above an empty vault.
Goshen continues to work with building owners to help complete the task of reinforcing the vaults and filling them in.
A current city program allows building owners with empty vaults to enlist the help of the city to ease some of the burden of handling the work.
Sailor explained that building owners are responsible for constructing a foundation wall, if one is not already present, and the city will then provide for the cost of the backfill.
Then, through Goshen’s sidewalk program, the owner and city will split the cost of replacing the sidewalk.
The fact that the GPR did end up finding a handful of sites with potential voids justifies the city’s hiring of Blood Hound, Sailor said.
“To me, the ones that we can’t get access to are of more concern than the ones you can, because you can’t see,” he explained. “If you can’t see, you don’t know what the conditions are.”