FLAC

FLAC is an analysis package developed by Itasca Consulting Group, Inc. This software utilizes explicit finite difference formulation to simulate a multitude of geotechnical problems in the geotechnical, civil and mining industries.

The UCSD soil models UCSDSAND3 and UCSDCLAY have been integrated into FLAC as user-defined constitutive models (UDM). These material models are capable of simulating the essential dynamic response characteristics of cohesionless and cohesive soils respectively. Additional references can be found here. Example of 1D site response analysis is provided below (for illustration purposes). Download links of the soil models (full version) are on the bottom of this page.

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1D Seismic Site Response Examples

 

Example 1

Example 1 is a 10-m deep saturated medium sand soil stratum subjected to base shaking (El Centro motion).

Input files:
Project file: example1_elcentro.prj
Data file: (Coming soon!)
Input motion: elcentro.txt
Results (including comparison with FLAC3D): example1_elcentro.pdf

Example 2

Example 2 is a 10-m deep saturated medium sand soil stratum subjected to base shaking (scaled Rinadi motion).

Input files:
Project file: example2_rrsmv1.prj
Data file: (Coming soon!)
Input motion: rrsmv1.txt
Results (including comparison with FLAC3D): example2_rrsmv1.pdf

Example 3

Please follow the steps below to download, install, and run the FLAC example.

Step 1: Download and Installation

1) If you do not have FLAC 8 installed, please visit http://www.itascacg.com/software to download a 32-bit installation file. A demo version is available which allows UDM. This installation may require a restart.
2) Download FLAC_Example.rar (coming soon!) (10 MB, updated 9/12/2017)
3) Unzip all files in the FLAC_example.rar to a desired location. The zip file includes the material models (modelucsdclay005.dll, modelucsdsand3005.dll), and an excel sheet interface (1D_Seismic_Site_Response_Example.xlsm).
4) Please move files modelucsdclay005.dll and modelucsdsand3005.dll (contained in the above Example file) to the "models" folder which can be found in the FLAC installation folder "\Itasca\FLAC800\Exe32\plugins\models".
5) Update FLAC_location.txt with the location of the FLAC installation.

Step 2: Run 1D_Seismic_Site_Response_Example

1) Open 1D_Seismic_Site_Response_Example.xlsm. If prompted please enable macros. This Excel sheet makes use of macros to generate input files for FLAC and run the analysis.
2) Update the material and analysis parameters shown on the Excel sheet and then click "Create Input and Run" to start the analysis in FLAC.
3) "View Results" can be used to load the output for previously completed runs.

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Model Performance

Below are some sample responses using the UCSD soil models. Click images to see full sized versions. Click here for a comparison with PM4Sand.

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UCSDSAND3 - Saturated:

Soil Column Model in FLAC	Pore Pressure Time History
Shear Stress vs. Shear Strain	Shear Stress vs. Confinement

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UCSDSAND3 - Dry:

Soil Column Model in FLAC

Shear Stress vs. Shear Strain

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UCSDCLAY:

Soil Column Model in FLAC

Shear Stress vs. Shear Strain

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Usage of UCSDSAND3 and UCSDCLAY

For information on how to use the soil models UCSDSAND3 and UCSDCLAY in FLAC, please click here.

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DLL Files of UCSD Soil Models

Full version of UCSDSAND3 model (for FLAC 8.0)

64 bit: modelucsdsand3005_64.dll (updated 4/23/2021); Please upload to the FLAC models folder
(Typically C:\Program Files\Itasca\FLAC800\exe64\plugins\models)

Full version of UCSDCLAY model (for FLAC 8.0)

64 bit: modelucsdclay005_64.dll (updated 3/9/2021); Please upload to the FLAC models folder
(Typically C:\Program Files\Itasca\FLAC800\exe64\plugins\models)