Pipeline stress level

Pipeline stress level of 20% or less of the specified minimum yield strength of the live pipe ... 

If data are not available on the effects of time, temperature, and strain rate on modulus, creep tests can be performed at various stress levels as a function of temperature over a reasonable period of time. In this regard, reasonable is a relative term. For applications like rockets and missiles, data obtained over a time period of 4-5 sec to an hour provide the essential information. For structural applications, such as pipelines, data over a period of years are required. 

When the top level of a fresh (very) soft clay deposit is below the water table, a sand layer can very gently be installed upon it by means of a spraying pontoon. This will increase the stress and improve the self-weight consolidation process. Such a sand layer will allow for access of light equipment or for the deposition of subsequent sand layers by means of land pipelines, using the advantage of gentle slopes realised by hydraulic fill (see Section 9.1.3.5 and 9.1.3.6). 

Earthquake shaking may trigger the liquefaction of saturated loose cohesionless soils. The liquefaction process increases the pore water pressure in the ground to a level where the effective stress approaches zero at which point the soil loses entirely its shear strength. A separate section in this chapter presented and discussed methods of analyzing and designing pipelines buried in liquefiable soils. 

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