Magical Charts for Effective E': Removing the Smoke and Mirrors

The Proceedings of the Thirty-Seventh Annual Meeting of the Highway Research Board, Washington, D.C., January 6-10, 1958, included an important milestone in the history of underground pipe design: the birth of the Iowa formula for flexible pipe deflection including the modulus of soil reaction, E', at the hands of the late Professor M. G. Spangler and Emeritus Professor R. K. Watkins. Little did they know that their vision would turn into widespread confusion leading to a plethora of opinions, methodologies, and charts and graphs among various segments of the pipe industry and the design engineers. For nearly six decades, the "body of knowledge" has been flooded with hundreds of manuscripts on E'. In spite of the deluge of published "solutions," there has been no unified agreement among authors, pipe manufacturers, design engineers, specification writers, standard writing bodies, utilities, and regulatory agencies. Writers have debated about a) what factors of the pipe-soil system govern the choice of E'; b) whether E', which is not a fundamental soil property that is measured either in a laboratory or in situ, can be replaced with constrained soil modulus, Ms, which is measured in a laboratory procedure; c) how native soils have an impact; d) what role does the fundamental geotechnical principle that effective confining pressure has the most influence on the soil modulus play in translating this phenomenon to the depth of soil controlling the value of E'; e) to what extent the relative stiffness ratio of the pipe to the bedding controls E'; f) are the horizontal or vertical deflection being calculated; g) are prism load or Marston's load being used; h) is there a need for a shallow cover correction factor; and many other questions. Most of the "solutions" result in, at best, a "feel good" attitude on the part of the design engineer. The bottom line is that all the fancy academic exercises, models, finite element analyses, MathCAD engines, excel workbooks, equations, and graphs are not useful if the final shape of the installed pipe is not measured before acceptance; serious problems surface; and will be met in court. In the final analysis, the three most important factors are the pipe soil stiffness ratio, the pipe shape control, and the neglected orphan on the job-inspection. This paper presents a historical overview of the lessons not yet learned by pipeline engineers and makes a strong case for modern tools such as laser profiling.

Language

  • English

Media Info

  • Media Type: Web
  • Features: References;
  • Pagination: pp 699-711
  • Monograph Title: Pipelines 2014: From Underground to the Forefront of Innovation and Sustainability

Subject/Index Terms

Filing Info

  • Accession Number: 01536261
  • Record Type: Publication
  • ISBN: 9780784413692
  • Files: TRIS, ASCE
  • Created Date: Aug 4 2014 3:01PM