Polymers keep deforming under sustained load, so a geogrid holding a wall for decades keeps elongating after construction and can rupture at loads well below its short-term strength. Creep is measured in long-term load tests, often accelerated with temperature, and turned into a creep reduction factor for design. Polyester creeps much less than polypropylene or HDPE, which is why it is favored for heavily loaded reinforcement.
Creep factor on the HDPE grid is close to 3, so the polyester grid works out cheaper per unit of design strength.
Creep data cannot be borrowed from another product, even one of the same polymer; resin and processing both change it.
Also heard as
- creep strain
Related terms
LTDS
Long-term design strength: reinforcement strength left after reductions for creep, installation damage and aging.
Reduction factor
Number that divides a geosynthetic's index strength to allow for creep, installation damage or degradation in service.
Uniaxial geogrid
Geogrid with its strength concentrated in one direction, used to reinforce walls and steep slopes.
Reinforcement
Using the tensile strength of a geosynthetic to hold soil together so it can stand steeper or carry more load.