Scenes of shaft drilling

From ODOT-

The drilling of the shafts is a facinating activity to watch! Here are some rare close-up scenes.

This worker standing next to the drill bit or auger illustrates just how large it is.

When crews first lower the drill into the target, they have to measure the distance from the auger to the walls of the shaft, ensureing that it is no more than three inches.



While watching the auger come out of the ground, we see the siltstone that is left on the machine that crews will need to clean off.

This shaft, in the center of the river, has been cleared of all earth debris.

Crews dish up a menu of specialized concrete mixes

From ODOT-

The concrete suppliers and specialists at the Willamette River Bridge are mixing up the standard components of concrete to deal with the complexity of the project. They designed 17 mixes to build the recently completed southbound structure. The arches, the drilled shafts, the columns and the deck all needed concrete specific to each function.

The mix for the bridge deck is made of high-performance concrete, which includes a special fiber additive. This fiber helps the concrete resist stresses placed on it, significantly reducing the risk of cracking. The fibers are evenly distributed throughout the concrete to form a secondary matrix of support.

Even though the drilled shafts forming the piers supporting the bridge were surrounded by rock, there was a chance that the concrete could leak into the river before it hardened. To ensure this would’t happen, our team created a mix for the piers that includes a special anti-washout additive to keep the concrete contained within the rock socket.

The two footings on the banks of the river require a lot of concrete — nearly 500 cubic yards each. The more massive the concrete structure, the more heat is generated while it cures. The more heat, the more the concrete expands and then shrinks as it sets, which can create cracks. So we designed a special mix for the riverbank piers to minimize heating and reduce cracking.

The point where the arches meet in the river and the first 23 feet of the arch ribs themselves required a concrete mix capable of flowing almost like water, then self-consolidating without vibration, filling every nook and cranny within the form.

The special concrete designed, mixed and placed resulted in a strong, beautiful southbound bridge. We’ll repeat our success as we build the new northbound bridge.

Supporting the bridge columns, Part 2

From ODOT-

In our last post, I told you about using a large drill to create deep shafts for the foundation of the bridge. Here’s what happens next.



Engineers determine how deep to drill each hole based on the strength of the rock required to support the column. The average depth of the shafts for the northbound Willamette River Bridge is 35 feet, but two are as deep as 70 feet



Once the drill reaches the required depth of the shaft, a steel rebar-reinforcing cage is lowered into the hole. These cages weigh between 13,000 and 28,000 pounds.

Crews lower one of the steel rebar-reinforcing cages into the drilled shaft before filling it with concrete.

With the steel cage installed, concrete is poured into the hole and allowed to cure.

Workers pump concrete into the drilled shaft to form the shaft for the columns that will soon follow.

The process of drilling and pouring the bridge shafts take a little over three months from the time the drill is moved onto the site until all 22 shafts are drilled and poured.

Supporting the bridge columns, Part 1

From ODOT-

In addition to two graceful arches supporting the bridge, the new northbound Willamette River Bridge will have nine columns, supported by 22 drilled shafts filled with concrete, which create the foundation for the columns.



The team surveyed and staked column locations before clearing and constructing cofferdams at each site. Next, crews built platforms to accommodate a large drill rig near each cofferdam.



The drill rig can drill to a depth of 200 feet, though for this project, the average depth is 35 feet. The bit or auger attached to the drill rig varies in size, but is typically 8 feet in diameter and 6 feet long. Once the drill is positioned, the drilling takes one to two days per shaft.

The drill rig positioned beside the cofferdam is ready to drill one fo the two shafts at this site.

Initial drilling is usually through soft material, which is removed from the hole. To prevent soil from falling back into the hole, workers insert a temporary steel casing (below) before pouring the shaft.