Free field

Question

Hello Sir; 
 Do I need to add a dummy plate when I use the Free field and complain base? If I use drift correction it gave a mistake and I need to deactivate it? And How can I model these boundaries in the plaxis ?

Stefanos Papavasileiou · Answer

Dear Ashraf, 
 When using the free-field elements, it is not needed to add any plate elements, apart from the interfaces required. 
 However, using a dummy plate you can inspect In Output the input signal as it is being applied on the model boundary. 
 It is not exactly clear what error you get when using the drift correction. For a correct drift correction, note that the phase time interval should be the same as the input signal&rsquo;s time interval, otherwise, the integration of the accelerations and velocities with the drift correction will not give a correct drift correction at the end of the phase. 
 The available dynamic model boundaries in PLAXIS are mentioned in the article below (and our reference manual): https://communities.bentley.com/products/geotech-analysis/w/plaxis-soilvision-wiki/45984/on-the-use-of-dynamic-boundary-conditions 
 If you have issues with a specific project, feel free to submit a service request so that we can assist you in mode detail: https://apps.bentley.com/srmanager/ProductSupport

Stefanos Papavasileiou · Answer

Dear Ashraf, 
 Based on the picture, the lateral boundaries should be set to Free-field and the bottom boundary to None. 
 Note that typically for earthquake analysis, setting the bottom to None means that there is a very high impedance contrast between the layer above the model bottom boundary (included in the model) and the one under (the one not included), e.g. a soft soil layer over a rigid bedrock. This will result in a full reflection of downward propagating waves. 
 Another possibility, depending on the model, is to use the bottom boundary set to Compliant base, which is simulating the continuation of waves into the seep soil with minimum reflections. 
 For more information please check our Reference manual as well as the article attached in my previous reply.

Stefanos Papavasileiou · Answer

Dear Sir or Madam, 
 Please read the following article about it: https://communities.bentley.com/products/geotech-analysis/w/plaxis-soilvision-wiki/45985/fixed-and-compliant-base-what-input-motion-is-required 
 Interfaces are required on the bottom and lateral boundaries when using the free-field elements in dynamic analysis. They do not need to be activated, only generated to assist in the definition of the free-field boundaries. 
 I recommend you also follow this training: https://learn.bentley.com/app/VideoPlayer/LinkToIndividualCourse?LearningPathID=113626&CourseId=132352&MediaID=5020454