Braun Intertec has provided vibration monitoring services on the Interstate-35E project through downtown St. Paul.

To investigate whether ground vibrations were within project specifications, we monitored blasting and construction activity for the Minnesota Department of Transportation.

Challenges

Ground vibrations caused by blasting can potentially damage older buildings and residential structures nearby. During I-35E construction, when vibration levels were approaching the specified limits, we suggested using a method of trench blasting that could reduce vibration levels.

Solutions

This trench blast method works by creating a vertical break between existing structures and the blasting. Trenches are blasted to be approximately 5 feet wide and 8-10 feet deep. The charge weights, hole spacings and burdens are also reduced to prevent excessive ground vibrations during the trench blasting. After the trenches were installed, production blasting proceeded.

The trench blast method, as described above, proved to be an effective method of controlling excessive ground vibrations. It also increased productivity to the contractor by eliminating the need for smaller blasts, which require much more time.

During the first construction phase of the I-35E project, we received a Grand Award from the Consulting Engineers Council (CEC) of Minnesota for our work with the Minnesota Department of Transportation. We were recognized for this innovative approach to vibration monitoring by devising the trench blast method.