By Kery Murakami
PostGlobe
On Beacon Hill, Christine Miller-Panganiban said she was doing a little gardening in her front yard a couple of Sundays ago, when she noticed a mysterious hole. She stuck her shovel down. It didn’t feel the bottom.
Her husband got a piece of tubing seven feet long. Still they couldn’t feel the bottom. Only when she looked down it with a flashlight did she find that it went down 21 feet. “Oh my God,” she thought, and more when she realized that suddenly there was a deep void that now only went down and down, but extended under her house.
The hole was apparently created when Sound Transit was boring the tunnel for the new light rail line. On Monday, Sound Transit spokesman Bruce Gray acknowledged the agency has found seven underground voids caused by its boring machine within a couple of blocks east of the future Beacon Hill station, though the one in Miller-Panganiban’s front yard was the only one visible from the surface. Aside from causing concern in the neighborhood, he said testing for them and filling them would cost the agency up to $1 million.
Gray said what happened was this: The machine digging the tunnel hit a layer of sand, and like an hourglass, the sand flowed into the tunnel, leaving an empty gap under the earth.
Sound Transit engineers filled the void with concrete, but after looking for more voids, they found a second one at the side of the house. That was filled, too, and Gray said six of the seven have now been filled. The agency has been drilling into the ground in what’s believed to be the sandy area looking for other voids. And though Gray said Sound Transit engineers believe Miller-Panganiban’s home is now structurally sound, Sound Transit plans to drill more holes to see if there are any more voids under her home.
Sound Transit moved quickly, Miller-Panganiban said. But she still isn’t comforted. “If there was one, you can think that maybe it was some random event, but now that there are seven, I don’t feel comfortable at all.”
Gray said there’s no cause for concern. Sound Transit believes it’s narrowed down areas where there might be voids by analyzing data collected during the boring work. The amount excavated from the tunnel has remained constant, except for a few areas where more material was taken out of the tunnel. The agency is testing those areas looking for voids and should be finished by the end of the week. Additionally, he said the agency looked at its excavation readings for the entire line and found no indications of voids elsewhere.
There are a number of questions still unanswered, besides whether more voids exist on Beacon Hill. Gray said engineers don’t know yet why the hole appeared in front of Miller-Panganiban’s home, but not the other six voids. But Gray said the agency has been checking all along to see if there have been any signs of the ground’s sagging over the sandy section. No indications have been found, and the tunnel itself seems to be on solid ground, he said.
Still, all the testing and filling of the voids have had a price tag – albeit a fraction of the $305 million budgeted to build the line around Beacon Hill.
Gray said Sound Transit knew where there were layers of sand along the route. Still, the machine hit the sandy areas, anyway. Gray said, “We’re not able to know to the inch where the sand flows ended.”
