Short for long-term design strength, it is found by dividing ultimate tensile strength by reduction factors for installation damage, creep and chemical or biological degradation, each taken from testing or conservative defaults. Creep usually takes the biggest bite, so polyester grids keep a larger share of their ultimate strength than polyolefin grids. Wall and slope designs then apply a further safety factor to LTDS.
LTDS on that grid is under half its ultimate once creep is in, so don't size it off the roll label.
Also heard as
- long-term design strength
- Tal
Related terms
Reduction factor
Number that divides a geosynthetic's index strength to allow for creep, installation damage or degradation in service.
Creep
Slow, continuing stretch of a geosynthetic under a constant load over time.
Installation damage
Loss of geosynthetic strength caused by placing, spreading and compacting fill on it.
Reinforcement
Using the tensile strength of a geosynthetic to hold soil together so it can stand steeper or carry more load.