External Load Calculation for Buried Conduit

EXTERNAL LOAD CALCULATIONS FOR DIRECT BURIED CONDUIT
DEFLECTION (∆X) IS THE RATIO OF THE INSIDE DIAMETER (LOADED)
VERSE THE INSIDE DIAMETER (UNLOADED) OF THE CONDUIT OR DUCT
(5% = 0.05). THE INSIDE DIAMETER (I.D.) CAN BE CALCULATED BY TAKING
THE OUTSIDE DIAMETER (O.D.) AND SUBTRACTING TWO (2) TIMES THE
WALL THICKNESS (t). I.D. = (O.D. - 2*t).
BEDDING SOIL MODULUS (E
1
) SHALL BE 2000 lb/in
2
FOR TYPE I SOIL AND
1000 lb/in
2
FOR TYPE III SOIL.
A DEFLECTION LAG FACTOR (D) OF 1.5 IS A COMMONLY USED VALUE.
A BEDDING CONSTANT (K) OF .1 IS A COMMONLY USED VALUE.
PIPE STIFFNESS (PS) OF THE CONDUIT OR DUCT IS EITHER
PREDETERMINED OR CALCULATED BY USING THE FOLLOWING
FORMULA:
PS = E*I/(0.149*r
3
)
PS = PIPE STIFFNESS (lb/in
2
)
E = MODULUS OF ELASTICITY IN TENSION (lb/in
2
)
I = MOMENT OF INERTIA (in
3
)
r = MEAN RADIUS (in)
MODULUS OF ELASTICITY (E) OF PVC FOR THE CONDUIT OR DUCT IS
EQUAL TO 500,000 lb/in
2
. HDPE CONDUIT OR DUCT MODULUS OF
ELASTICITY (E) IS EQUAL TO 150,000 lb/in
2
.
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