Assessment of Creep Reduction Factors of High-Density Polyethylene Geogrids Using Conventional and Stepped Isothermal...

Area of Science:

• Geotechnical Engineering
• Materials Science

Background:

• Long-term creep behavior of geosynthetics, specifically high-density polyethylene (HDPE) geogrids, requires further clarification for reinforced-soil structures.
• Existing research has not fully addressed the influence of different failure criteria on creep performance or validated creep reduction factor (RFCR) estimations and the stepped isothermal method (SIM).

Purpose of the Study:

• To investigate the long-term creep behavior of HDPE geogrids using conventional tests and SIM.
• To evaluate the applicability of SIM for accelerated creep testing and validate RFCR estimation methods.
• To determine the most reliable design criterion for long-term creep performance.

Main Methods:

• Creep behavior of HDPE geogrids was assessed using conventional creep tests (ISO 13431) and the stepped isothermal method (SIM) (ASTM D6992).
• Master curves were developed under load levels of 40-60% of ultimate tensile strength.
• Creep reduction factors (RFCR) were calculated using 20% creep strain and creep rupture criteria for a 100-year design life.

Main Results:

• SIM results aligned with conventional tests initially but showed higher creep strains beyond 1000 hours due to HDPE's thermal sensitivity.
• RFCR values for a 100-year design life were 3.04 (combined data) and 2.43 (block-shift analysis) based on the 20% creep strain criterion.
• The creep rupture criterion yielded a lower RFCR of 2.30, indicating the 20% strain limit is more conservative.

Conclusions:

• The 20% creep strain limit is a more conservative and reliable criterion for estimating long-term design strength in HDPE geogrids.
• The stepped isothermal method (SIM) is confirmed as applicable for accelerated creep evaluation of HDPE geogrids.
• Practical guidance is provided for selecting appropriate RFCR values in reinforced-soil structure design.