ARMORFORM is Chosen to Protect

a High Volume Spillway

In the summer of 1995, A large coal company in West Virginia was in the process of upgrading an overflow spillway at their coal refuse slurry impoundment facility. The new spillway would need to be constructed directly over coarse coal refuse, and provide a safe means of transporting large volumes of water over a distance of approximately 1,700 feet. The bed slope of the spillway would vary from 1% to 10% with the 10% section generating flow velocity of over 20 feet per second and a corresponding shear stress of nearly 40 pounds per square foot during a severe storm event. It was obvious that a substantial form of erosion protection would be necessary to combat the potentially destructive forces that would be present during these hydraulic conditions.

The coal company enlisted the services of a local consulting engineering firm to design the spillway and confirm that the selected form of erosion protection would be adequate. Rock riprap was almost immediately ruled-out due to the large diameter required to resist the expected flow conditions, and the designer wanted a system that was less restrictive than large boulders. Although a properly installed (i.e. reinforced, freeze/thaw resistant, expansion joints, etc.) poured concrete spillway would provide sufficient hydraulic stability, it was believed that the cost would be higher than desired. With numerous, successful spillway projects under their belt, the engineering firm felt most comfortable in selecting ARMORFORM Articulating Block Mat (ABM).

Product Selection and Design

Due to the flow conditions that would be present at the coal refuse facility, the engineering firm determined that the ABM erosion protection would be required for the 40 foot wide bottom and both side slopes of the trapezoidal spillway. The “finished” average thickness requirement of the ABM will be 8 inches to produce individual block sizes of approximately 24 inches x 24 inches and a weight of 95 pounds per square foot. High strength, 3/8 inch diameter polyester cables, exhibiting a nominal breaking strength of 10,000 pounds will be inserted into the ABM at the factory. These cables will provide additional tensile strength to the system, as well as reinforcement during articulation.

Entrance point of the spillway. ABM mat is buried in a 10 feet deep trench at this location.

Completed spillway, looking downstream.