Max Line Pressure for a Thrust Block (AWWA M41)
The highest test/surge pressure a thrust block of a given bearing-face area restrains at a bend.
Example
You enter
- Bearing-face area (ft²) 6.2
- Pipe outside diameter (in) 8.625
- Bend angle (deg) 90
- Allowable soil bearing (psf) 2000
You get
- Max pressure (psi) 100
- Max thrust the soil takes 8267 lb
Checked against published worked examples from: EBAA Iron.
Details, formula, and sources
ScopeP = Ab x soil / (Sf x 2 A sin(theta/2)), Sf ~1.5. A 6.2 ft^2 block on an 8 in main (OD 8.625) at a 90-degree bend in 2,000 psf soil holds about 100 psi. Answers 'how much pressure can this block take' instead of the area from a set pressure; compare against the test/surge pressure. Checks the bearing face only; the engineer of record governs.
Formula or tableA = (pi/4) OD^2; max_thrust = bearing_area x soil / Sf; max_pressure = max_thrust / (2 A sin(theta/2)). The inverse of Ab = Sf x 2 P A sin(theta/2) / soil, Sf ~1.5.
Source and editionThe AWWA M41 thrust-block resultant-thrust and bearing-area method for a pipe bend, by name, solved for the pressure.
Free accessThe resultant-thrust T = 2 P A sin(theta/2) and the bearing-area check are the standard published AWWA thrust-restraint relations.
What governsEstimate. AHJ and licensed professional govern.
API field namesbearing_area_ft2, od_in, bend_deg, soil_bearing_psf, max_pressure_psi, max_thrust_lb
- Max thrust from soil max thrust = bearing area x allowable soil bearing / Sf, Sf ~1.5 (input)AWWA M41 / DIPRA; EBAA Connections PD-1
- Pressure ceiling P = max_thrust / (2 A sin(theta/2)), A = (pi/4) OD^2AWWA M41
- Design pressure compare against the test/surge pressure and use a geotechnical soil valuescope of this tile