An ongoing photo essay documenting the replacement of the Sarah Mildred Long Bridge
The trestle on the Kittery side is complete, and preparations are being made to begin construction of the towers and intermediate supports for the bridge. The towers will require several 10-ft diameter bore holes that will extend to 35 ft below the bedrock at the bottom of the river. Here, test bores are being done on the Kittery side.
Looks back up the hill, we can see the drilling apparatus being assembled. It's the blue thing.
In order to drill the10-ft diameter shafts, guides must be set up. These are 10-ft diameter pipes that will extend from above the water to the bedrock below. Drilling from there down will be done with an auger. These guides are being assembled from smaller sections. You can see a worker welding sections together below. Note that the welder stays in one place while the pipe rotates on rollers. One one end of the pipe are carbide teeth that will dig about 12 inches into the rock to hold it in place.
The intermediate bridge supports won't require such elaborate bases. These will be constructed in coffer dams that have been erected along the sides of the trestles. This view from above shows two of the dams (boxes formed from sheet piles), and a crane ready to start dredging material from within the dams. The concrete will be poured with water in the dams, but it's important that the rock surface at the bottom be completely clean of sediment.
More in a couple of weeks when boring begins.