Carlon External Load Calculation for Buried Conduit User Manual

EXTERNAL LOAD CALCULATIONS FOR DIRECT BURIED CONDUIT

Gross Automation [phone] · www.carlonsales.com · [e-mail]

EXTERNAL LOADS ON DIRECT BURIED PVC OR HDPE CONDUIT OR DUCT
FALL INTO TWO CATEGORIES, DEAD LOADS (EARTH LOADS) AND LIVE
LOADS. DEAD LOADS ARE BASED ON THE WEIGHT OF THE COLUMN OF
SOIL ABOVE THE BURIED CONDUIT OR DUCT. LIVE LOADS ARE FROM
DIFFERENT SOURCES SUCH AS HIGHWAYS, AIRPORT RUNWAYS OR
RAILWAYS. LIVE LOADS HAVE LITTLE EFFECT ON CONDUIT
PERFORMANCE EXCEPT AT SHALLOW DEPTHS (4’ OR LESS FOR
HIGHWAY LOADS).

THE TOTAL LOAD IS THE SUMMATION OF THE DEAD LOADS AND OF THE
LIVE LOADS. THE TOTAL LOAD SHALL BE LESS THAN THE LOAD
(MAXIMUM LOAD) REQUIRED TO CHANGE THE INSIDE DIAMETER OF THE
CONDUIT OR DUCT BY ARBITRARY DATUM OF 5% DEFLECTION. THIS
DEFLECTION, CAUSED BY THE TOTAL LOAD, IS FAR BELOW THAT WHICH
WOULD CAUSE DAMAGE TO THE PVC WALL OF THE CONDUIT OR DUCT.

THE MAXIMUM LOAD (W) CAN BE CALCULATED WITH THE FOLLOWING
FORMULA:

1

W = [∆∆∆∆X *(0.149*PS + 0.061*E

)]/[D*K]

W = MAXIMUM LOAD (lb/in2)

∆∆

∆∆

X = DEFLECTION (%/100)

PS = PIPE STIFFNESS (lb/in2)

E_ = BEDDING SOIL MODULUS (lb/in2)

D = DEFLECTION LAG FACTOR

K = BEDDING CONSTANT

25701 Science Park Drive

Cleveland, Ohio 44122

216-464-3400

1-800-3CARLON (322-7566)

www.carlon.com

EXTERNAL LOAD CALCULATIONS FOR DIRECT BURIED CONDUIT

Gross Automation [phone] · www.carlonsales.com · [e-mail]

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).

1

BEDDING SOIL MODULUS (E
1000 lb/in

2

FOR TYPE III SOIL.

) SHALL BE 2000 lb/in2 FOR TYPE I SOIL AND

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:

3

PS = E*I/(0.149*r

PS = PIPE STIFFNESS (lb/in

E = MODULUS OF ELASTICITY IN TENSION (lb/in

)

2

)

2

)

I = MOMENT OF INERTIA (in3)

r = MEAN RADIUS (in)

MODULUS OF ELASTICITY (E) OF PVC FOR THE CONDUIT OR DUCT IS
EQUAL TO 500,000 lb/in2. HDPE CONDUIT OR DUCT MODULUS OF
ELASTICITY (E) IS EQUAL TO 150,000 lb/in2.

EXTERNAL LOAD CALCULATIONS FOR DIRECT BURIED CONDUIT

Gross Automation [phone] · www.carlonsales.com · [e-mail]

THE MOMENT OF INERTIA (I) EQUALS THE WALL THICKNESS (t) CUBED,
DIVIDED BY TWELVE (12). I = t3/12.

THE MEAN RADIUS (r) EQUALS THE OUTSIDE DIAMETER (O.D.) MINUS
THE WALL THICKNESS (t) DIVIDED BY TWO (2). r = (O.D. - t)/2

2

PIPE STIFFNESS FOR DB60 IS EQUAL TO 60 lb/in

AND FOR DB120 IS
EQUAL TO 120 lb/in2. 4” SCHEDULE 40 CONDUIT WILL HAVE A PIPE
STIFFNESS OF 346 lb/in2 (MINIMUM WALL THICKNESS).

MATERIALS SUITABLE FOR FOUNDATION AND EMBEDMENT ARE
DEFINED ACCORDING TO THE UNIFIED SOIL CLASSIFICATION SYSTEMS
(USCS) IN ASTM D2487, “STANDARD METHOD FOR CLASSIFICATION OF
SOILS FOR ENGINEERING PURPOSES”. BEDDING SOIL MODULUS (E

1

)
SHALL BE 2000 LB/IN2 FOR CLASS IA AND IB SOILS AND 1000 LB/IN2 FOR
CLASS III SOIL. CLASS IA MATERIALS PROVIDE MAXIMUM STABILITY AND
PIPE SUPPORT FOR A GIVEN DENSITY DUE TO ANGULAR INTERLOCK OF
PARTICLES. CLASS III MATERIALS PROVIDE LESS SUPPORT FOR A
GIVEN DENSITY THAN CLASS I MATERIALS. HIGH LEVELS OF
COMPACTIVE EFFORT MAY BE REQUIRED UNLESS MOISTURE CONTENT
IS CONTROLLED.

DEAD LOAD (DL) IS EQUAL TO THE UNIT WEIGHT OF THE BACKFILL (γ)
TIMES THE HEIGHT OF COVER (H) DIVIDED BY 144.

DL = γγγγ * H/144

2

DL = DEAD LOAD (lb/in

)

25701 Science Park Drive

Cleveland, Ohio 44122

216-464-3400

1-800-3CARLON (322-7566)

www.carlon.com