Structural Design of Buried Pipes

Owners of buried pipes - states, cities, and corporations - are responsible for the buried pipes - the guts of their infrastructures. For engineers who write the specifications, this manual is an overview of the essentials for designing buried pipes. Pipe - Pipes are varied and are changing as technology advances. Pipes are rigid (clay and concrete); and flexible (metal, plastic, composite) and are lined, coated, encased, non-circular; and are subjected to widely varying conditions. Design includes service life, risk, mitigation, etc. The basics of pipe design are strength and pipe stiffness. Soil - The structural mechanics of buried pipes is not simply the mechanics of a pipe under pressure - internal or external. In many cases, soil contributes more to structural performance of a conduit than does the pipe. Soil holds the pipe in shape and alignment. It supports much of the external load. In the case of flexible pipe, the soil is the conduit - a tunnel - in which the flexible pipe is a leak-proof liner. The basics of soil design are soil strength and soil stiffness. Pipe-soil interaction - In the design of pipe-soil interaction, embedment soil must be correctly selected and properly placed and compacted. Important embedment considerations are: 1. Selection - drainable, compactable, resistant to soil slip and excessive compression 2. Compaction - adequate strength at soil slip (both when soil is dry and when wet); and adequate stiffness (low compressibility) 3. Deflection - both ring deflection and longitudinal pipe defection which are controlled primarily by soil deflection 4. Inspection - of soil quality and of soil placement during construction Tests - Tests and inspections are important elements of pipe, soil, and installation.