# FLAC **URL:** https://forum.itascainternational.com/c/flac/7.md [Latest](https://forum.itascainternational.com/latest.md) · [Categories](https://forum.itascainternational.com/categories.md) · [Tags](https://forum.itascainternational.com/tags.md) --- ## [About the FLAC category](https://forum.itascainternational.com/t/about-the-flac-category/14)
**Author:** [@jhazzard](https://forum.itascainternational.com/u/jhazzard)\ **Replies:** 0
FLAC , Fast Lagrangian Analysis of Continua, is numerical modeling software for advanced geotechnical analysis of soil, rock, groundwater, and ground support in two dimensions. FLAC is used for analysis, testing, and des… --- ## [How to Start Post-Shake Consolidation After Compliant-Base Dynamic Analysis in FLAC2D?](https://forum.itascainternational.com/t/how-to-start-post-shake-consolidation-after-compliant-base-dynamic-analysis-in-flac2d/2386)
**Author:** [@EmirhanAltinok](https://forum.itascainternational.com/u/EmirhanAltinok)\ **Replies:** 5\ **Last updated:** [September 16, 2026, 5:46pm UTC](https://forum.itascainternational.com/t/how-to-start-post-shake-consolidation-after-compliant-base-dynamic-analysis-in-flac2d/2386 "2026-09-16T17:46:39Z")
Hello all, I am performing nonlinear dynamic effective-stress SSI analyses in FLAC2D 9.0 using PM4Sand and PM4Silt. The model includes two buildings represented by elastic beam elements. The earthquake motion is applied … --- ## [Bade distortion](https://forum.itascainternational.com/t/bade-distortion/2393)
**Author:** [@Milads](https://forum.itascainternational.com/u/Milads)\ **Replies:** 1\ **Last updated:** [June 18, 2026, 5:34pm UTC](https://forum.itascainternational.com/t/bade-distortion/2393 "2026-06-18T17:34:14Z")
I am seeing significant base distortion when applying a strong subduction-zone earthquake motion. The input is applied only in the horizontal direction, and the base is modeled as a compliant boundary. Increasing the bed… --- ## [Boundary conditions for soil block](https://forum.itascainternational.com/t/boundary-conditions-for-soil-block/2379)
**Author:** [@William](https://forum.itascainternational.com/u/William)\ **Replies:** 1\ **Last updated:** [April 22, 2026, 4:08pm UTC](https://forum.itascainternational.com/t/boundary-conditions-for-soil-block/2379 "2026-04-22T16:08:15Z")
Hello I am currently working with the automatic remeshing feature in FLAC2D. I want to model a soil block and allow it to fail towards the left. However, I am unsure how to properly define boundary conditions in the … --- ## [Zone Maximum Shear Strain Increment in Flac2D](https://forum.itascainternational.com/t/zone-maximum-shear-strain-increment-in-flac2d/2232)
**Author:** [@Miguel\_S](https://forum.itascainternational.com/u/Miguel_S)\ **Replies:** 5\ **Last updated:** [April 21, 2026, 2:24pm UTC](https://forum.itascainternational.com/t/zone-maximum-shear-strain-increment-in-flac2d/2232 "2026-04-21T14:24:03Z")
I am modeling a seismic site response analysis in FLAC2D, applying only the horizontal component of ground motion at the base. In the results, I can see the plot Maximum Shear Strain Increment, which I understand corresp… --- ## [Plotting disp-x relative to the bottom](https://forum.itascainternational.com/t/plotting-disp-x-relative-to-the-bottom/2358)
**Author:** [@Milads](https://forum.itascainternational.com/u/Milads)\ **Replies:** 2\ **Last updated:** [April 2, 2026, 7:33pm UTC](https://forum.itascainternational.com/t/plotting-disp-x-relative-to-the-bottom/2358 "2026-04-02T19:33:26Z")
How do I define an extra variable in FLAC v9 so I can plot x‑displacement relative to the base of the model? In FLAC v8 I used something like: ex\_30($iev, $jev) = xdisp($iev, $jev) - xdisp($iev, 1) What’s the equivalen… --- ## [Plastic hinge formation in Liner element](https://forum.itascainternational.com/t/plastic-hinge-formation-in-liner-element/2360)
**Author:** [@Milads](https://forum.itascainternational.com/u/Milads)\ **Replies:** 1\ **Last updated:** [April 2, 2026, 7:18pm UTC](https://forum.itascainternational.com/t/plastic-hinge-formation-in-liner-element/2360 "2026-04-02T19:18:38Z")
I am modeling a sheet pile wall using liner elements in FLAC v9.6. Currently, I have assigned an elastic model to these elements, but I would like to know how to specify a plastic moment capacity so that a plastic hinge … --- ## [FLAC2D 8.1 Shell Element Issue](https://forum.itascainternational.com/t/flac2d-8-1-shell-element-issue/2356)
**Author:** [@New\_user](https://forum.itascainternational.com/u/New_user)\ **Replies:** 4\ **Last updated:** [March 23, 2026, 9:04pm UTC](https://forum.itascainternational.com/t/flac2d-8-1-shell-element-issue/2356 "2026-03-23T21:04:41Z")
I’m facing an error when I’m trying to solve the model. I created a axisynmetric model with a shell element. When I’m trying to solve the model, there is an error indicating me to assign the radius or perimeter for the… --- ## [Bulkhead wall modeling](https://forum.itascainternational.com/t/bulkhead-wall-modeling/2332)
**Author:** [@Milads](https://forum.itascainternational.com/u/Milads)\ **Replies:** 0\ **Last updated:** [February 20, 2026, 6:20pm UTC](https://forum.itascainternational.com/t/bulkhead-wall-modeling/2332 "2026-02-20T18:20:05Z")
I am planning to model a bulkhead wall on a slope using FLAC v9, and I’ve noticed that there are two possible structural elements to represent the wall. In previous projects, I used beam elements, but the FLAC manual als… --- ## [Output contour values via profile](https://forum.itascainternational.com/t/output-contour-values-via-profile/799)
**Author:** [@jwang](https://forum.itascainternational.com/u/jwang)\ **Replies:** 2\ **Last updated:** [February 19, 2026, 3:46pm UTC](https://forum.itascainternational.com/t/output-contour-values-via-profile/799 "2026-02-19T15:46:01Z")
A simple way is creating a profile (Plot-\>profile), select the item to create(e.g. xdisp ) and draw a line along the top surface, and then create a profile, in the profile window, right click on the plot, press ‘view dat… --- ## [Model won't reach equilibrium along interfaces and top](https://forum.itascainternational.com/t/model-wont-reach-equilibrium-along-interfaces-and-top/2312)
**Author:** [@AdamL](https://forum.itascainternational.com/u/AdamL)\ **Replies:** 1\ **Last updated:** [January 8, 2026, 2:54pm UTC](https://forum.itascainternational.com/t/model-wont-reach-equilibrium-along-interfaces-and-top/2312 "2026-01-08T14:54:32Z")
My current model is in MC with standard properties, and I’ve been unable to get the model to solve. I’m currently just using ‘model solve’, but I’m not sure if this is an issue with the model setup, properties, or if I s… --- ## [Short period amplification in site response](https://forum.itascainternational.com/t/short-period-amplification-in-site-response/2265)
**Author:** [@Milads](https://forum.itascainternational.com/u/Milads)\ **Replies:** 0\ **Last updated:** [November 5, 2025, 7:58pm UTC](https://forum.itascainternational.com/t/short-period-amplification-in-site-response/2265 "2025-11-05T19:58:47Z")
I am modeling a soil column for effective stress analysis, and the results show that the top 20 ft of the soil deposit is liquefying. I ran the model using a series of short-duration crustal motions and long-duration CSZ… --- ## [Expansion joint (or contraction joint) in FLAC3D](https://forum.itascainternational.com/t/expansion-joint-or-contraction-joint-in-flac3d/2216)
**Author:** [@MiguelN](https://forum.itascainternational.com/u/MiguelN)\ **Replies:** 5\ **Last updated:** [October 18, 2025, 11:22am UTC](https://forum.itascainternational.com/t/expansion-joint-or-contraction-joint-in-flac3d/2216 "2025-10-18T11:22:05Z")
Hi everyone, I have a question. How can I model an expansion joint in a tunnel using FLAC3D? Is it sufficient to assign different IDs to the structural elements, or is there another recommended approach? I’m uncertain be… --- ## [Cable Element Simulation](https://forum.itascainternational.com/t/cable-element-simulation/2244)
**Author:** [@New\_user](https://forum.itascainternational.com/u/New_user)\ **Replies:** 3\ **Last updated:** [October 6, 2025, 3:09pm UTC](https://forum.itascainternational.com/t/cable-element-simulation/2244 "2025-10-06T15:09:43Z")
How to use the cable element to reinforce soil? I don’t want the cable pulled out of the soil. I want to reinforce the soil zones by bonding the cable and soil together. How can I do this? I try not to assign propert… --- ## [Modified Cam Clay Model](https://forum.itascainternational.com/t/modified-cam-clay-model/2245)
**Author:** [@New\_user](https://forum.itascainternational.com/u/New_user)\ **Replies:** 1\ **Last updated:** [October 6, 2025, 1:47pm UTC](https://forum.itascainternational.com/t/modified-cam-clay-model/2245 "2025-10-06T13:47:55Z")
I’m using FLAC2D. In my model, I consider the Modified Cam-Clay Model for clay. At the same time, I also have Mohr-Coulomb Model for sand. I use some code from the example “isotropic consolidation modified cam caly”. … --- ## [Rayleigh damping in Id soil column](https://forum.itascainternational.com/t/rayleigh-damping-in-id-soil-column/2240)
**Author:** [@Milads](https://forum.itascainternational.com/u/Milads)\ **Replies:** 2\ **Last updated:** [October 1, 2025, 1:43pm UTC](https://forum.itascainternational.com/t/rayleigh-damping-in-id-soil-column/2240 "2025-10-01T13:43:37Z")
Is there an example or step-by-step tutorial on calculating Rayleigh damping parameters for a 1D soil column in effective stress site response analysis? I would like to add a small amount (0.5%) of mass- and stiffness-pr… --- ## [Export extra variable log in a CSV or text file](https://forum.itascainternational.com/t/export-extra-variable-log-in-a-csv-or-text-file/2239)
**Author:** [@Milads](https://forum.itascainternational.com/u/Milads)\ **Replies:** 1\ **Last updated:** [September 26, 2025, 3:54pm UTC](https://forum.itascainternational.com/t/export-extra-variable-log-in-a-csv-or-text-file/2239 "2025-09-26T15:54:29Z")
How can I export extra variables to a CSV or text file for the seismic site response results? I tried using the commands below, but they did not work. I would like the output to be written horizontally, with each column… --- ## [Transition from creep to "static" analysis](https://forum.itascainternational.com/t/transition-from-creep-to-static-analysis/2231)
**Author:** [@agapanto](https://forum.itascainternational.com/u/agapanto)\ **Replies:** 1\ **Last updated:** [September 8, 2025, 2:46pm UTC](https://forum.itascainternational.com/t/transition-from-creep-to-static-analysis/2231 "2025-09-08T14:46:47Z")
Hi all, I work with FLAC v.8 and I’m running a creep analysis by using a cvisc consitutive model. At the end of the modeled time, which I input with the crdt command, I’d like to stop the creep (i.e, time-dependent) an… --- ## [Joining Structural Nodes - Recursive Rigid Link Error](https://forum.itascainternational.com/t/joining-structural-nodes-recursive-rigid-link-error/2210)
**Author:** [@EmirhanAltinok](https://forum.itascainternational.com/u/EmirhanAltinok)\ **Replies:** 3\ **Last updated:** [September 8, 2025, 6:54am UTC](https://forum.itascainternational.com/t/joining-structural-nodes-recursive-rigid-link-error/2210 "2025-09-08T06:54:25Z")
Hi everyone, I am trying to model a 5-story building with 9 column axes in FLAC2D. For this, I created all structural members (columns, beams, and slabs) using the structure beam create by-line command. After completing… --- ## [1D soil column for deep site response analysis](https://forum.itascainternational.com/t/1d-soil-column-for-deep-site-response-analysis/2226)
**Author:** [@Milads](https://forum.itascainternational.com/u/Milads)\ **Replies:** 2\ **Last updated:** [September 4, 2025, 6:04pm UTC](https://forum.itascainternational.com/t/1d-soil-column-for-deep-site-response-analysis/2226 "2025-09-04T18:04:42Z")
When running a 300-ft deep one-dimensional site response analysis, does it matter if we use only one zone in the horizontal direction, or is it beneficial to include multiple zones since the profile is so deep? --- ## [Multi directional shaking effect](https://forum.itascainternational.com/t/multi-directional-shaking-effect/2225)
**Author:** [@Milads](https://forum.itascainternational.com/u/Milads)\ **Replies:** 0\ **Last updated:** [September 3, 2025, 8:45pm UTC](https://forum.itascainternational.com/t/multi-directional-shaking-effect/2225 "2025-09-03T20:45:55Z")
I am modeling a seismic site response analysis as a 1D soil column in FLAC2D, applying only the horizontal component of ground motion at the base. Should I apply a scaling factor to the resulting Ru profile to account fo… --- ## [Post liquefaction residual strength](https://forum.itascainternational.com/t/post-liquefaction-residual-strength/2214)
**Author:** [@Milads](https://forum.itascainternational.com/u/Milads)\ **Replies:** 2\ **Last updated:** [August 28, 2025, 5:13pm UTC](https://forum.itascainternational.com/t/post-liquefaction-residual-strength/2214 "2025-08-28T17:13:38Z")
I am running a 1D seismic site response analysis with FLAC 2D v8.1 and would like to know whether it is possible to extract the post-liquefaction residual strength directly from the model. I am using the PM4Sand and PM4S… --- ## [Deformation at the free field boundary](https://forum.itascainternational.com/t/deformation-at-the-free-field-boundary/2205)
**Author:** [@song](https://forum.itascainternational.com/u/song)\ **Replies:** 2\ **Last updated:** [August 15, 2025, 1:42am UTC](https://forum.itascainternational.com/t/deformation-at-the-free-field-boundary/2205 "2025-08-15T01:42:21Z")
I have a dynamic/seismic FLAC model with liquefied material at the free boundary. I have used free boundary and this is large lateral deformation at the free boundary (liquefied here), what is the cause and how I can pre… --- ## [Ground Water Table Setting](https://forum.itascainternational.com/t/ground-water-table-setting/2191)
**Author:** [@New\_user](https://forum.itascainternational.com/u/New_user)\ **Replies:** 4\ **Last updated:** [August 14, 2025, 9:58pm UTC](https://forum.itascainternational.com/t/ground-water-table-setting/2191 "2025-08-14T21:58:33Z")
I want to create a slope model where the groundwater is 1m below the slope surface. How can I do this in FLAC 2D? --- ## [Short-Period Spike in PSA from Plastic Hardening Model](https://forum.itascainternational.com/t/short-period-spike-in-psa-from-plastic-hardening-model/2192)
**Author:** [@EmirhanAltinok](https://forum.itascainternational.com/u/EmirhanAltinok)\ **Replies:** 2\ **Last updated:** [August 10, 2025, 7:48pm UTC](https://forum.itascainternational.com/t/short-period-spike-in-psa-from-plastic-hardening-model/2192 "2025-08-10T19:48:35Z")
Hi everyone, I performed a zone test to compare the Plastic Hardening model in FLAC2D with the HS-Small model in Plaxis 2D. To do this, I set up a 1D single-column soil model composed of 5 zones, representing a 5-meter-… --- ## [Estimating Center of Frequency in Rayleigh damping - Embankment Dam](https://forum.itascainternational.com/t/estimating-center-of-frequency-in-rayleigh-damping-embankment-dam/1924)
**Author:** [@MHD\_N](https://forum.itascainternational.com/u/MHD_N)\ **Replies:** 2\ **Last updated:** [July 22, 2025, 4:37pm UTC](https://forum.itascainternational.com/t/estimating-center-of-frequency-in-rayleigh-damping-embankment-dam/1924 "2025-07-22T16:37:58Z")
Hi, I am trying to estimate the Center of Frequency for a dam. I have followed the example below, where the geometry was defined, and the shear modulus, bulk modulus, and density properties were assigned to different r… --- ## [Strange PSA Amplification in FLAC Plastic Hardening vs Plaxis HS-Small in 1D Model](https://forum.itascainternational.com/t/strange-psa-amplification-in-flac-plastic-hardening-vs-plaxis-hs-small-in-1d-model/2128)
**Author:** [@EmirhanAltinok](https://forum.itascainternational.com/u/EmirhanAltinok)\ **Replies:** 3\ **Last updated:** [June 18, 2025, 3:08pm UTC](https://forum.itascainternational.com/t/strange-psa-amplification-in-flac-plastic-hardening-vs-plaxis-hs-small-in-1d-model/2128 "2025-06-18T15:08:01Z")
Hi all, I’m running a 1D site response analysis consisting of 8 horizontal layers. The top 7 layers are modeled using PM4Sand and PM4Silt, and the bottom layer (Layer 8) uses the Plastic Hardening (PH) model in FLAC2D, … --- ## [Strange PWP Ratio Response in 1D Analysis Compared to 2D Version](https://forum.itascainternational.com/t/strange-pwp-ratio-response-in-1d-analysis-compared-to-2d-version/2094)
**Author:** [@EmirhanAltinok](https://forum.itascainternational.com/u/EmirhanAltinok)\ **Replies:** 4\ **Last updated:** [May 27, 2025, 11:51am UTC](https://forum.itascainternational.com/t/strange-pwp-ratio-response-in-1d-analysis-compared-to-2d-version/2094 "2025-05-27T11:51:54Z")
Hello all, I am currently performing a 1D site response analysis using FLAC 2D. My model consists of eight soil layers: the top seven layers are defined with PM4Sand and PM4Silt, while the bottom (eighth) layer is model… --- ## [Fish function for strain](https://forum.itascainternational.com/t/fish-function-for-strain/2101)
**Author:** [@agapanto](https://forum.itascainternational.com/u/agapanto)\ **Replies:** 1\ **Last updated:** [May 23, 2025, 2:04pm UTC](https://forum.itascainternational.com/t/fish-function-for-strain/2101 "2025-05-23T14:04:02Z")
Hi everyone, I’m trying to implement a FISH function in FLAC 2D v.8 to compute the total strain at each gridpoint, based purely on geometric deformation of the mesh. My intention is to monitor the increase in deformatio… --- ## [FISH function for elastic modulus increment with confining pressure](https://forum.itascainternational.com/t/fish-function-for-elastic-modulus-increment-with-confining-pressure/1996)
**Author:** [@agapanto](https://forum.itascainternational.com/u/agapanto)\ **Replies:** 2\ **Last updated:** [March 18, 2025, 2:37pm UTC](https://forum.itascainternational.com/t/fish-function-for-elastic-modulus-increment-with-confining-pressure/1996 "2025-03-18T14:37:45Z")
Hi all, I’d like to initialize a non linear distribution of elastic moduli in my FLAC slope model. In particular, I would like to vary the moduli according to the confining pressure (sig2). I’m therefore trying to writ… [Next page](https://forum.itascainternational.com/c/flac/7.md?page=1)