Search

Creep Rupture vs. Strain-Limited Creep - Analytical and Practical Comparison

Bernardi, Michael / Lostumbo, John

Continued deformation under a constant load, also known as creep, is a property of polymer geosynthetics that must be taken into consideration when determining the allowable long-term design strength. The geosynthetic's long-term design strength is used in design for reinforcement applications such as retaining walls, steep slopes and embankments. Currently, two ASTM Standard tests exist to determine the reduction factor due to creep (RFCR), and both tests may yield significantly different results. The older of the two tests, ASTM D5262, also known as the Conventional Test, is considered a strain-limited load test where the RFCR is a function of the maximum creep strain of the geosynthetic over a given period of time, usually the design life of the structure. The second test, ASTM D6992, is a creep rupture test using the Stepped - Isothermal Method (SIM), which provides an accelerated means of defining the creep rupture behavior of polymer geosynthetics. As a first objective, the paper will briefly describe the test methods and point out the differences in the approaches used to define the reduction factor. This will shed some light on the reasons why significantly different values may be obtained. The second objective of the paper is to present typical creep-related specifications, prepared by the engineering community as well as specifying agencies, and demonstrate the impact on the long-term design of the geosynthetic, depending on which approach, creep rupture or strain-limited creep, is used.