NoDigTech Sleeve Structural Strength Calculator

AWWA Manual 11 chapter 6

qa = (1/FS){(32 * Rw * B' * E' * EI / D^3)^ 1/2}

Symbol Explanation Value  
qa allowable buckling pressure (psi)    
FS design factor 

= 2.5 for (h/D) >= 2


= 3.0 for (h/D) < 2

h = height of ground surface above top of pipe (in)

D = diameter of pipe (in)




Rw water  bouyancy factor = 1-0.33(hw/h), 


hw = height of water surface above top of pipe (in)


(for hw = h)

B' empirical coefficient of elastic support (dimensionless)

= 1 / (1 + 4 e^(-0.065 H) )

where H  = height of fill above pipe (ft)

D pipe diameter (in)  
E modulus of elasticity 3*10^7 for steel [psi]  
I transverse moment of inertia per unit length of pipe wall 1.t^3/12

t is the thickness of pipe wall [in]

E' modulus of soil reaction lb/in^2 (psi) 2000


The allowable buckling pressure must be greater or equal the real buckling pressure calculated form the water column, the dead and live loads above the pipe.
qa1= Gamma w * hw + Wc / D + WL / D


Symbol Explanation Value  
Gamma w specific weight of water 0.0361 lb/cu in
hw height of backfill above conduit (ft)

= H

Wc vertical soil load on pipe per unit length (lb/ft) w * Hc * Bc

w unit weight of fill (lb/cu ft)

Hc height of fill above top of pipe (ft)

Bc = D Diameter of pipe (ft)

D pipe diameter    
WL live load on the conduit for a 10 ft height cover = 1100 psf = 7.6389 psi

t: thickness of sleeve wall needed to withstand the load:
t: thickness of sleeve wall needed for 100 yrs service life:  


  • 5 psi ----> 11.53' of water load

  • 11.53' is entered  for water load in the formula

  • for 100 years service-life 0.01" was added to the calculated value 

  • calculate requested t 

  • compare thickness t requested with thickness tg (Gauge of metal sheet available in the market)


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