An earth dam was modeled in FLAC 2D. During the soil-fluid coupled seismic analysis, negative excess pore pressure (show in in Figure) develops at phreatic surface which eventually affects the deformation pattern of the model. The seepage analysis was performed prior to dynamic analysis and hence the phreatic surface was defined. Flow vectors were also uniform at the end of static seepage analysis. No examples in the manual discusses the coupled seismic analysis. So, I request to clarify me the likely causes for the development of negative excess pore water pressure in this case. Thank you
All the material ( foundation, shell and core) was modeled using PM4Sand model. The permeability in the core region was set to a low value to make it impervious.
I suggest that you change the permeability and check its effect on pore pressure buildup.
Second, I wonder if the PM4Sand parameters are calibrated for the core materials.
In reality a seismic event can cause liquifaction in granular soils, the pore pressure reaches a stage where internal friction between particles reaches zero. In this state the soil under load will collapse. It's important you get speciaist geotechnical advice on the materials you use in a seismic area that may cause liquifaction.
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