Project Details

The Glory hole Spillway - Whiting, Vermont

Wet-Mix Shotcrete Construction for a Major Northeast Hydro Energy Supplier

At Harriman Lake in Whiting, Vermont the Glory Spillway was in dire need of shotcrete construction repairs and was a perfect candidate for a wet mix process shotcrete application. The glory spillway, known as the “glory hole,” is one of only three in the world and would be a large undertaking because it’s difficult to access opening is so large that four Greyhound buses could fit side-by-side down the outlet.

The outlet’s critical function is to control the flow of water from the lake as an overflow mechanism for the earthen-dammed lake. Over the years, severe concrete deterioration caused by freeze-thaw damage required the hydro energy supplier to undertake a critical repair program. The consequences of a faulty spillway and soil erosion of the earthen dam would be catastrophic. An overflow of high water would result in major flooding and the destruction of homes and businesses residing downstream.


Knowles Industrial Services was contracted to perform an inspection as well as to perform this work under the maintenance agreement with the hydro energy supply company, due to the many unknowns associated with the required repair effort. Moving forward with the project, safety was a major concern due to the unique methods required to access the spillway.

Concrete Repair in Motion

The first major step in beginning the work at the Glory Hole Spillway was getting access into the dam to begin stripping out the damaged concrete. Knowles’ team created an elaborate staging system along the sides of the dam’s curved concrete walls that was both safe and effective. From there, they began the process of removing the deteriorated concrete and laying down reinforcement structures before they began to apply new concrete.

Once the structures were in place as a new foundation, Knowles used a 4” shotcrete placement pipe to apply the wet-mix shotcrete. Placement and finishing is similar to poured concrete, but has a much fast application process and is easier to maneuver the pump and pipe on the curved-wall structure.

Finally, the team had to repair the freeze-thaw damaged pier, that was porous and brittle. New forms were chosen to replace the old pier due to depth of repair and cold temperatures. These two major repairs completed phase 1 of the spillway project.

The Benefits of Wet-Mix Shotcrete in Concrete Repair

As a concrete repair contractor, Knowles knew that wet-mix shotcrete would make the most sense for a project like the Glory Spillway. First of all, time was of the essence and by using this method they were able to complete the repairs in a quarter of the time it would have take for the conventional methods of form and pour.

Due to the many curved surfaces, traditional methods would make forms difficult and expensive for such a massive project. The structure and position of the spillway required staging that prevented conventional forms of concrete to be poured. Even if the staging was not in the project zone, crane access was not possible for setting forms and placing concrete into the spillway’s newly reinforced foundation.

Responsibilities to Client Needs, Customers Satisfaction

Knowles believes that in all business climates, owners need to take advantage of every opportunity to keep costs down by finding innovative methods to solve a problem and bring their goods to market at the lowest possible cost. Due to the accelerated schedule of the project, our team worked diligently to complete the repairs in half the time it would usually take. With these shotcrete repairs, we have alleviated the urgency of a spillway overflow issue, allowing the hydro energy supplier to continue to service their customers.

Safety and efficiency is always a priority for our company and even with this unique project we were able to meet our stringent standards and goals. For more information on this project, contact the Knowles Engineering Group.