New video, below, shows how explosions are used to test the bedrock for the new Highway 43 bridge in Winona.

Bridge engineers use “pile load testing”  to find out how much weight and resistance the ground will bear. It not only saves time and money, but helps design a bridge that will sit securely on the bedrock, below the river.

The statnamic test used in the video is one part of this process.

Winona Bridge Statnamic Test

How load testing works: 

It begins with digging and pounding.

Two different kinds of piles are put into the ground:

• A hollowed shaft, which is filled with rebar and concrete. It goes 30 to 50 feet below the bedrock to create a solid pillar that can assess how much weight and sway the ground will bear.
• A steel pipe that is hammered into the ground. Since the bedrock is about 100 to 150 feet below the river, these pipes are welded together end-to-end to reach that length.

Once the piles are in, they’re tested two different ways.

• Pile Dynamic Analysis, with gauges affixed to the top of the pile to read the pressure put on it when hit with a pile driver.
•  A Statnamic test (shown in videos), which involves accelerating a heavy weight by setting off a controlled combustion reaction. This shows how much resistance the pile can take.

Once the data is collected for the bridge design, the piles are cut off two feet below the river bed.