To calculate the minimum amount of bentonite clay required to seal around an outlet pipe you will need the following information.
1. Outlet pipe diameter (in feet)
2. Width of desired seal around the exterior of the pipe. We recommend a minimum of 3X the pipe radius (diameter divided by 2).
3. Length of desired seal (we recommend a MINIMUM of 5X the pipe radius
To calculate the required amount. First calculate the area of the circle described by the exterior boundary of the bentonite seal - So at minimum the circle area would be
Total Area =2*Pi*r^2 or Total Area = 2 x 3.141 x (3 x pipe radius)^2
Next, calculate the area of the pipe cross-section. Pipe Area = 2 x Pi x r^2 or Pipe Area = 2 x 3.141 x (pipe radius)^2
Now subtract the Pipe Area from the Total Area to find the area of the Bentonite Seal.
So, Seal Area = Total Area - Pipe Area
Next, multiply the Seal Area times the length of the seal. This yields cubic feet of bentonite.
To determine Tons of Bentonite required, divide the cubic feet of bentonite required by 28 (28 cubic feet per ton of granular bentonite).
See attached excel spreadsheet for calculator.