PE piping is considered a "flexible" pipe indicating it can withstand relatively large (e.g., 5%) deflection over its diameter.
However, since its flexibility is directly proportional to its Dimension Ratio (outer diameter divided by the minimum wall thickness), different installation requirements may be necessary for different DR values to achieve successful and economical installations. The depth of cover and anticipated surface loads also affect the particular PE pipe design and installation requirements.
The weight of the earth, as well as surface loads above the pipe, produce soil pressure on the pipe. The weight of the earth or "earth load" is often considered to be a "dead-load", whereas surface loads are referred to as "surcharge loads" and may be temporary ("live loads") or permanent. When surcharge loads are of short duration they are usually referred to as "transient" loads." The most common live load is vehicular load. Other common surcharge loads include light structures, equipment, and piles of stored materials or debris. Design procedures and formulas are available for calculating the vertical soil pressure due to both earth and surcharge loads, which may then be used for calculating deflection and for evaluating the pipe's vulnerability to wall crushing and buckling.