Thrust Block Bearing Area at a Pipe Bend (AWWA M41)
Resultant thrust at a bend T = 2 P A sin(theta/2) and the bearing face Ab = T / (allowable soil bearing), AWWA M41. An 8 in main (OD 8.625), 100 psi, 90-degree bend, 2000 psf soil -> T 8,263 lb, Ab 4.13 ft^2; a 45-degree bend halves the thrust (the sin(theta/2) term). Use the test/surge pressure. A design aid; the engineer of record governs.
Formula and source
A = (pi/4) OD^2; T = 2 P A sin(theta/2); Ab = T / (allowable soil bearing).
The AWWA M41 thrust-block resultant-thrust and bearing-area method for a pipe bend, by name.
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