If you've driven down Market Street in Portsmouth past the State Pier in the last few weeks, you have probably noticed the large yellow structure being assembled. This is a set of forms that will be used to cast segments of the four towers on the bridge.
In the rendering below, I've outlined one of these segments. There are 80 of these in all. The segments are hollow to allow the counterweights to drop within.
In the photo at the top, and in the one below, you can see workers assembling the internal section of the mold for the first segment. Part of the external form is also visible on the right in the below photo. The second photo below is of some of the other external form sections.
Once these forms are in place, a rebar cage that has been pre-assembled on the ground will be lifted into place. This will sit outside of these forms with a minimum clearance of 3 inches between the form and the steel. The rest of the external forms will then be assembled around it, and concrete poured. Since so many of these cages will be required, jigs have been constructed of welded angle steel. Below, you can see the rebar cage still sitting on the jig. This particular cage has a large void in it (at the left of the photo) where a door will go. This is the at the bottom of the tower, and will allow access to the machine rooms. The second photo shows the lifting frame that will be used to hoist the rebar cages into place.
Once the initial tower segment has been cast and cured, it will be transferred to the other half of the structure. Here's why the structure is so tall: the next segment of the tower will be cast directly on top of the previous segment. Below is a photo of the setup that allows for this. Remember that the segments are hollow. The completed segment will be lowered onto the pads seen at each of the four corners about a quarter of the way up from the bottom of the photo. All of the structure above that level will be inside of the completed segment. The top of that segment will be flush with the platform at the top of the photo. The forms for the next segment can then be assembled with the completed segment serving as the bottom form, and the new segment cast such that it mates perfectly with the one below it. This process is known as "match casting". Once the new segment cures, the previous one will be set aside, the new one lowered into this position, and the next one cast on top of it. And so on, until each tower is complete.
There will be tubes cast into each segment that extend from the base to the top of the tower. These will house post-tensioning continuity tendons - essentially steel rods that will be tensioned after they are inserted in order to hold all of the tower segments together. Like a truss rod on a guitar, if that means anything to you. The plastic tube in the cage below will form the void for one of these tendons.
Finally, as each segment is ready to be moved to the tower position, it will be carefully transferred to this creeper. This will allow it to be moved to a barge, and floated to the position of the tower. Remember that each segment is cast on top of the previous one, so it would very difficult to replace one if damaged. This creeper keeps the platform very steady as it moves over uneven terrain.
The first of the 10-ft diameter drilled shafts has been completed. You can see it in center of the photo below.
Here, it's being checked to be sure that it is positioned in the right place. Tolerance is 3 inches. This shaft extends 103 ft below this top lip.
The next step is to lower these rebar cages into the shaft. They are constructed in chunks so they can be transported by truck.
The large rebar cage from the dock is lifted into place. The smaller cage is already in the shaft (I missed that).
In the next few photos, you can see that the two cages are connected together using shaft couplings on the vertical bars. Each of these has 32 bolts that need to be torqued. This takes some time, and was ongoing when I left the site.
Meanwhile, work has begun preparing another of the shafts for drilling. The pipe that will guide the rock drill is not in place yet (visible is a larger temporary pipe). Overburden is beging removed with an auger in order to get to solid rock. The rock in this location slopes 45 degrees relative to the shaft, so setting the guide is trickier. Here you can see the auger bit on the drill. The second photo shows some workers next to it for scale.
On the Portsmouth side, work is progressing on the temporary trestle. No drilling over there, yet.
Some odds and ends: a plaque on the existing bridge, and another interested party.
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.
The new bridge will be a concrete structure with a center lift span. It will carry both a road deck and a railroad deck, like the existing bridge. An important and innovative difference is that the lift span will have only one level. The rails will be embedded in the roadway, and the span will be lowered to the height of the rail deck to allow passage of a train. Trains are infrequent - twice a year or so - and this will allow for a much higher default clearance under the bridge when it's in the road configuration. This will mean fewer openings.
Here's a photo of the existing bridge, followed by a rendering of the new bridge with the deck in the road configuration. Both are from essentially the same perspective:
So that brings us to the start of construction. The first step is the construction of temporary trestles from the shore on each side of the river to the locations of the two towers. These are being built using steel piles (pipe, essentially). These were delivered by rail. Here are a photos of one of the trains crossing the causeway at Great Bay, between Newfields and Stratham, and of the delivery to the State Pier in Portsmouth, where the staging work is being done.
The pipes are cut to length and welded end-to-end to create the piles. You can see a cutting torch in the first of these photos, and a welding rig in the second.
Here, a pile is being lowered into place on the trestle extending from the Portsmouth side into the river.
The trestle section from Market Street to the pier is already complete, and the one on the Kittery side is much further along. Note also the temporary railroad crossing that has been constructed between the pier and Market St.
Over the next two or so years, the Sarah Mildred Long Bridge, which connects Kittery, ME and Portsmouth, NH will be replaced. During the replacement of the Memorial Bridge, I spent countless hours taking photos to document that important project. (A selection can be found here: http://www.ericreuterphotography.com/memorial-bridge.html.) Thanks to this body of work, I've been granted access to document the replacement of the Sarah Long Bridge. This blog will provide an ongoing photographic essay on the project.
I'm grateful for the support of MaineDOT and Cianbro on this project, but am not affiliated with either. This should not be construed as an official source of information on the project.