Construction workers are drilling 35 holes and then filling them with concrete and grout to stabilize the road, which is built over layers of limestone that easily dissolves in water, creating cavities, said Charles Metzger, another PennDot spokesman.
``[Workers] are trying to create a boundary to prevent the sinkholes from spreading, and we are trying to prevent new ones from forming in the same place,'' Metzger said.
In all, three sinkholes have been discovered since Sept. 25, shortly after Tropical Storm Floyd. They are several feet apart and close to the foot of a bridge that runs over a tributary of Abrams Creek.
Also worrying PennDot officials are cavities that were discovered in the earth at one end of the bridge. They were first noticed during the summer, when work was begun to fill them in, but many more have been found since Floyd. A sinkhole was also found in the creek bed after the storm.
``All that water is getting into the earth and has caused more voids to occur,'' Blaum said. ``Our bridge engineers are out there and we are keeping a close eye on it. It's a matter of searching for the cavities and filling them in.''
Bob Norman, the public works director for Upper Merion, said township officials were concerned about the safety of the bridge, which is a major artery to the King of Prussia mall and other shopping areas.
``We could lose a bridge over this,'' Norman said.
The first sinkhole was filled, but the pavement buckled again on Oct. 2. Workers were injecting concrete into the hole Wednesday night when they noticed a depression in the roadway several feet away. As they drilled, they found a 50-foot cavity.
About half of Upper Merion has the type of limestone underground that causes the problem, Norman said. There are 10 sinkholes in Upper Merion, including one at the Valley Forge Memorial Gardens and another in the intersection of Church and Henderson Roads.