External Load Design Calculator

Introduction 

This calculator was developed in accordance with the equations and procedures found in the Handbook of PVC Pipe Design and Construction. The user is encouraged to reference the document if more information on external load calculations is needed. Conservative assumptions have been used to provide a conservative design with appropriate safety factors. Designers are responsible for the proper use of this program for all projects.

The formula used to calculate deflection is called the Modified Iowa Equation and is as follows:

Iowa equation

Where:

  • ∆Y/D = percent vertical pipe deflection, dimensionless
  • K = bedding factor, dimensionless
  • DL = deflection lag factor, dimensionless
  • P = vertical soil pressure due to prism load, psi
  • W’ = live load, psi
  • PS = pipe stiffness, psi
  • E’ = modulus of soil reaction, psi

External Load Design

Nominal Size 4 in.

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Pipe Stiffness, PS 129 psi

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Unit Weight of Soil, w 120 lb/ft3

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Please input Your Unit Weight of Overburden.

Height of Fill above Top of Pipe, H 10 ft

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Please input Depth of Burial.

Bedding Constant, K 0.100

figure

Deflection Lag Factor, DL 1.0

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Please input time lag factor.

Modulus of Soil Reaction, E' 1,000 psi

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Soil Type - Pipe Bedding Material
(Unified Classification System)
E' for Degree of
Compaction of Bedding, PSI
Dumped Slight, < 85% Proctor, < 40% relative density Moderate, 85%-95% Proctor, 40%-70% relative density High, >95% Proctor, >70% relative density
Fine-Grained Soils (LL > 50) Soils with medium to high plasticity, CH, MH, CH-MH No data available; consult a competent soils engineer; otherwise, use E' = 0 No data available; consult a competent soils engineer;
otherwise, use E' = 0
Fine-Grained Soils (LL < 50):, Soils with medium to no plasticity, CL, ML, ML-CL, with less than 25% coarse-grained particles
Fine-Grained Soils (LL < 50): Soils with medium to no plasticity, CL, ML, ML-CL, with more than 25% coarse-grained particles Coarse-Grained soils with fines: GM, GP, SW, SP, contain more than 12% fines
Coarse-Grained Soils with Little or No Fines: GW, GP, SW, SC, contain less than 12% fines
Crushed Rock
psi
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Please enter E'b

Live Load, W' None

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Please enter custom Live Load
If you have any questions, please click here to contact the Regional Engineer covering your area.