What are the relevant tests to determine geocells performance for the entire design life?

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The geocell market is growing rapidly. As a result, there is a large increase of manufacturers who produce geocells with different properties.

Therefore, How can an engineer choose the right geocell product for his design?

Lets discuus it further..

Problem #1 – How can I validate my design will not reach its failure point before the end of the design life? How can i ensure achieving this result at minimum cost?

Lets examine a load support incident to anwer this question.

We can see at the pic above that part of any vertical load on any of the cells is transferred to lateral load turning to hoop stress on the cell wall.

Therefore, the cell integrity is dependent on cell hoop stress. Consists of:

  1. Tensile Force on Geocell Strips
  2. Effective actual force on seam

 

Therefore the structural Engineering solution will consist of:

  1. Stresses cause strains on the designated structure.
  2. Calculate the accumulative strains (deformations) throughout the design life.
  3. Measure: Accumulative deformations < Calculated Failure Point.
  4. Calculated Failure Point is dependent on the application (1%-3%).

Problem #2 – Which Lab tests results can assure that my project will not fail prematurely?

There are couple of existing geocell stiffness tests to answer this question.

Elastic (Dynamic) Modulus Range:

  • Test ability to apply accumulated loads on geocell walls prior to plastic deformation

Plastic (Permanent) Modulus Range:

  • Verify that accumulated plastic deformation does not reach failure point during project design life.

Elastic (Dynamic) Modulus Test

  • Elasticity is tested by DMA (Dynamic Mechanical Analysis)
  • This method is widely used in the automotive, electronic, military and aero-space industries.
  • This test is adjusted to the needs of each specific industry. Lately, this method was adopted to geocells as well.

 

Plastic (Permanent) Deformation Test

  • Based on: ASTM D-6992 (SIM) –Stepped Isothermal Method, modified for geocells
  • Concept: Accelerate time by temperature  under typical applied geocell load per application type.
  • Note: The structural failure point is defined as the accumulated plastic deformation caused by the accumulated stresses applied to it.

Typical SIM comparison test

 

Problem #3 – How to evaluate the actual geocell strength?

Geocell Tensile Strength Test

  • Based on ISO 10319:2015; modified test specimen is in-situ product sample.
  • Test specimen must include the entire perforation pattern
  • if pattern is symmetric, then 1/2 the cell length
  • if not, then entire cell size.
  • Testing: a longitudinal force is applied at a constant strain rate (according to the relevant applications) – until the specimen yields.

Geocell Tensile Strength Test 

Geocell Seam Strength Test

  • Weld Splitting Test – based on
    ISO 13426-1 (Part 1 Method C).
  • Typical size of cell opening in field (cell width-to-length) creates an angle of 95⁰±7%. The test should simulate this opening angle.
  • Simulation of actual in-situ forces can be achieved by using a jig apparatus (shown in picture).

Geocell Seam Strength Test

To sum up,  our suggested approach is:

  1. Measure the forces applied on the Geocell in your design.
  2. Verify the Geocell Geometry is retained for the entire design life

Geocell Geometry Retained = Confinement Sustained

 

Hope you found the article useful, share with friends as well how to validate the geocell integrity is sustained for the entire design life.