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Define Geosynthetics

Geosynthetic reinforcement such as Geotextiles or Geogrids, can be modeled in RS2.

In the following discussion the term Geosynthetic will be used to refer to all forms of flexible planar reinforcement, which are used in the form of fabrics, meshes, grids, strips, membranes, etc, to reinforce earthworks. This includes both synthetic (polymer) and metal (e.g. steel strip) reinforcement.

IMPORTANT NOTE!!!: in RS2, the modeling of Geosynthetic reinforcement has been grouped as a sub-category of Liner reinforcement. This has simplified some of the modeling procedures. However, the user should be aware of this use of terminology in RS2.

There are three general ways of modeling Geosynthetics in RS2, depending on whether or not you wish to consider slip at the interface of the Geosynthetic and the surrounding soil:

In all cases, the basic support properties (strength and stiffness) of the Geosynthetic are defined in the Define Liners dialog.

Modeling a Geosynthetic as a regular liner

No Slip - the simplest way to model a Geosynthetic, is to use the Add Liner option to apply a liner to a boundary. In this case, slip at the interface is not considered. The Geosynthetic is considered to be fully bonded to the soil, and no joint will exist at the interface. For this method:

  1. Define the location of the Geosynthetic by adding appropriate boundary(s). In most cases a Material boundary is most suitable (e.g. a single horizontal line segment).
  2. Define the strength and stiffness properties of the Geosynthetic with the Define Liner option.
  3. Use the Add Liner option to apply the liner (Geosynthetic) to the desired boundaries.

Modeling a Geosynthetic as a Composite Liner

Slip on one side - if you want to model a Geosynthetic where slip is allowed on one side, and the other side is fully bonded, you can use the Composite Liner option. A Composite Liner in RS2 allows you to include a single joint, between the soil and the liner. For this method:

  1. Define the location of the Geosynthetic by adding appropriate boundary(s). In most cases a Material boundary is most suitable (e.g. a single horizontal line segment).
  2. Define the strength and stiffness properties of the Geosynthetic with the Define Liner option.
  3. Define the properties of the joint with the Define Joint option.
  4. Define the overall properties of the composite liner (i.e. select the joint / liner combination), with the Define Composite option.
  5. Use the Add Liner option to apply the composite liner (Geosynthetic) to the desired boundaries.

Modeling a Geosynthetic as a Structural Interface

Slip on both sides - in the most general case, slip on BOTH sides of the Geosynthetic can be considered, by using the Structural Interface option. For this method:

  1. Define the location of the Geosynthetic by adding a Structural Interface boundary with the Add Structural Interface option.
  2. Define the strength and stiffness properties of the Geosynthetic with the Define Liner option.
  3. Define the properties of the joints on either side of the Geosynthetic, with the Define Joint option (i.e. the properties of the Geosynthetic/soil interface).
  4. Define the overall properties of the Geosynthetic (i.e. select the joint / liner / joint combination), with the Define Structural Interface option.
  5. If necessary assign the properties to the Structural Interface boundary with the Assign option.

NOTE: with the Structural Interface method, you do NOT use the Add Liner option to apply the liner to the boundary. The support element is implicitly included as part of the Structural Interface.

Defining Geosynthetic Properties

The strength and stiffness properties of a Geosynthetic are defined in the Define Liners dialog, as follows:

  1. Select Define Liners Define Liners icon from the toolbar or the Properties menu.
  2. In the Define Liners dialog set the Liner Type = Geosynthetic.
  3. Enter the following Geosynthetic properties. Note: properties are specified per unit width of material.

Tensile Modulus

The Tensile Modulus represents the elastic response of the Geosynthetic to a tensile load. It is equal to the slope of a force versus strain graph, per unit width of material. Strain is the elongation strain measured in the direction of the applied tensile force.

Material Type - Elastic

If the Material Type = Elastic, then the only property of the Geosynthetic which will be used in the analysis is the Tensile Modulus. The strength of the Geosynthetic will not be considered (i.e. there will be no upper limit to the tensile load which can be sustained by the Geosynthetic).

Material Type - Plastic

If the Material Type = Plastic, then you may enter values of Tensile Strength (peak) and Tensile Strength (residual).

  • The peak Tensile Strength determines the maximum load (force) which can be sustained by the Geosynthetic, per unit width of material.
  • If the peak Tensile Strength is reached, then the Geosynthetic will fail in tension, and the strength (force in the Geosynthetic) will revert to the residual Tensile Strength. If the Geosynthetic has no residual tensile strength then enter zero for this parameter.

Staged Properties

The properties of a Geosynthetic can be modified at different stages of a multi-stage model, with the Stage Liner Properties option in the Define Liner Properties dialog. This could be used, for example, to simulate a decrease in Geosynthetic strength or stiffness over time.

Any of the parameters in the Define Liner Properties dialog, can be increased or decreased by user-defined factors at different stages. For details about staging Geosynthetic properties, see the Stage Material Properties topic, as the general procedure for staging properties is the same.

Flexural Properties of a Geosynthetic

By definition in RS2, a Geosynthetic has zero flexural rigidity. If you need to model a geosynthetic with flexural rigidity (e.g. a stiff geogrid), then you will have to model this as a regular liner (i.e. Liner Type = Beam), and enter appropriate properties to simulate the flexural behaviour.

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