STRUCTURALMECHANICS

OF

BURIED PIPES

Boca Raton London New York Washington, D.C.CRC Press

Reynold King WatkinsUtah State University

Logan, Utah

Loren Runar AndersonUtah State University

Logan, Utah

2000 CRC Press LLC

2000 CRC Press LLC

b = angle of soil shear plane.

Forces, Pressures, and StressesP = external pressure on the pipe or tank,P' = internal pressure,p = vacuum in the pipe or tank,Q = concentrated force,W = surface wheel load,g = unit weights,s = direct (normal) stress,t = shearing stress.Subscripts refer to directions of forces and stresses.

Properties of Materialsc = cohesion of soil,E = modulus of elasticity of pipe (tank) material,S = allowable stress (strength) of material,g = unit weight of material,n = Poisson ratio,j = soil friction angle.

'2000 CRC Press LLC

CONTENTS

Chapter

1 Introduction 2 Preliminary Ring Design 3 Ring Deformations 4 Soil Mechanics 5 Pipe Mechanics 6 Ring Stresses 7 Ring Deflection 8 Ring Stiffness 9 Non-circular Cross Sections 10 Ring Stability 11 Encased Flexible Pipes 12 Rigid Pipes 13 Minimum Soil Cover 14 Longitudinal Mechanics 15 Thrust Restraints 16 Embedment 17 Parallel Pipes and Trenches 18 Special Sections 19 Stress Analysis 20 Plastic Pipes 21 External Hydrostatics 22 Buried Tanks and Silos 23 Flotation 24 Leaks in Buried Pipes and Tanks 25 Long-Span Structures 26 Non-circular Linings and Coatings 27 Risers 28 Analysis of Buried Structures by the Finite Element Method 29 Application of Finite Element Analysis to a Buried Pipe 30 Economics of Buried Pipes and Tanks Appendix A: Castigliano's Equation

Appendix B: Reconciliation of Formulas for Predicting Ring Deflection

Appendix C: Similitude Appendix D: Historical SketchAppendix E: Stress Analysis Appendix F: Strain Energy Analysis

2000 CRC Press LLC

PREFACE

Buried pipes are an important medium of transportation. Only open channels are less costly to construct.On the average, pipelines transport over 500 ton-miles of product per gallon of fuel. Gravity systemsrequire no fuel for pumping. Ships transport 250 ton-miles per gallon. Rails transport 125 ton-miles pergallon. Trucks transport 10 ton-miles per gallon. Aircraft transport less than 10 ton-miles per gallon offuel.

Buried pipelines are less hazardous, and less offensive environmentally than other media of transportation.They produce less contamination, eliminate evaporation into the atmosphere, and generally reduce loss anddamage to the products that are transported.

The structural mechanics of buried pipes can be complicated -- an interaction of soil and pipe each withvastly different properties. Imprecisions in properties of the soil embedment are usually so great thatcomplicated analyses are not justified. This text is a tutorial primer for designers of buried structures --most of which are pipes. Complicated theories are minimized. Fundamentals of engineering mechanicsand basic scientific principles prevail.

"Science is understanding gained by deliberate inquiry." -- Philip Handler

ACKNOWLEDGMENT

Gratitude is expressed to Becky Hansen for her patient and expert preparation of manuscript.

2000 CRC Press LLC

2000 CRC Press LLC