The constitutive model and properties for geomembrane in the stability analysis

Question

Dear Plaxis, 
 I am conducting the stability analysis for a dam using the strength reduction method. There is a geomembrane between the stone and moraine layers, as shown below. i found that the critical slip surface will go through the geomembrane layer when using the Mohr-coulomb for the geomembrane. 
 But I read in the literatures that nonlinear strain softening behavior was usually observed for the geomembrane interface and several constitutive models (e.g., Duncan-Change hyperbolic model) have been proposed to simulate the geomembrane/soil interface behavior. I wonder if it is necessary to consider this strain-softening behavior of the geomembrane interface in the numerical modellings. What kind of constitutive model is the most appropriate for the geomembrane? 
 Thank you.

Vasileios Basas · Accepted Answer

Hi Jian, 
 I&rsquo;ve noticed that your geomembrane is modelled using thin soil clusters instead of a geogrid material. I&rsquo;ve found that interesting for two reasons: (a) geomembranes generally have a small thickness (typically up to 2mm) and (b) thin soil layers tend to produce a poor-quality mesh. Therefore, I would suggest using geogrid elements instead. Should you choose that, PLAXIS offers four available options for defining the material type of a geogrid: Elastic , Elastoplastic , Elastoplastic (N-&epsilon;) and Visco-elastic (time-dependent). 
 Also, geomembranes are not meant for reinforcement because their strength becomes mobilized rather easily (short mobilization distances). Therefore, an accurate simulation of the mechanical behaviour of the geomembrane and its corresponding interface should be of secondary importance in this case. However, as every case is different, you should apply your judgement, knowledge, and experience. 
 Regarding your question, a non-linear strain-softening behaviour is typically observed for interfaces between geotextiles and geomembranes (or other geosynthetics) and not so much for interfaces between soil and geosynthetics. Nevertheless, PLAXIS offers the option of assigning a specific material dataset directly to an interface, when the &ldquo; Custom &rdquo; option is selected. For instance, you may choose to model the interface using a strain hardening model, such as the Hardening Soil (which supersedes the Duncan-Chang model) or any other model for that matter.

The constitutive model and properties for geomembrane in the stability analysis

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