High Strength Design

High Strength Design

Designing for long term reinforcement requires consideration of a number of points. This Tech Note outlines the requirements for high strength designs.

There are two aspects to the design of Reinforcement Geosynthetics, the design method, and the material design strengths. Further down on this page is a input form for a design. Please return the form with your design inquiry.

LTDS Partial Factors of Safety*
Partial Factor of Safety   K - Series Geogrids HS - Series Geotextiles
Creep 10,000
FSCR 1.67 1.67
Sand, Silt,
and Clay
FSID 1.02 to 1.05 1.17 to 1.10
20 mm well
graded Gravel
FSID 1.15 to 1.03 1.35 to 1.14
65 mm Crushed
FSID 1.25 to 1.05 1.40
Chemical FSCD 1.10 1.10
Biological FSBD 1.00 1.00
Joint** FSJNT 1.00 1.00
* Values shown are used in the determination of LTDS for Layfield Plastic's products. Other design methods may vary from these guidelines.
** A value of 1.00 indicates that a joint is not included in the direction of reinforcement.

Allowable Tensile Strength TALL

Layfield recommends that the Allowable Tensile Strength, TALL, used in your designs should be the Long Term Design Strength, LTDS, divided by a global factor of safety, FSUNC. This formula helps to account for uncertainties in the geometry of the structure, fill properties, reinforcement properties, and externally applied loads. The typical range for FSUNC is from 1.3 to 1.5 (FHWA / AASHTO Guidelines). Temperature is not included as a factor of safety but tests shold be carried out if site specific temperatures are of concern.

Long Term Design Strength

Long Term Design Strength (LTDS) is the strength in the Reinforcement Geosynthetic at the end of the service life of a soil reinforcement application. The LTDS is determined by the Ultimate Tensile Strength of the Reinforcement Geosynthetic divided by partial factors of safety.

Partial Factors of Safety are values that focus on specific phenomena which may adversly affect the performance of the Reinforcement Geosynthetic. Selection of appropriate values can be obtained by direct experimentation and measurment, or by using default values for the various applications. The Geosynthetic Reserach Institute provides Standard Practice GT7 and GG4 on "Determination of the Long Term Design Strength" for HS woven geotextiles and Geogrids repectively.

Partial Factors of Safety