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Numerical Modeling in Geotechnical Engineering - Science topic

Numerical Modeling in Geotechnical Engineering is a fEM, DEM, FDM, etc
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how to define geosynthetics in SEEP to calculate its effect on drainage characteristics
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They must separate saturated and unsaturated soil from each other in their analyses, because the analysis of seepage of semi-saturated soils in a saturated state leads to wrong and unrealistic results. Such an error can be prevented by defining the permeability function in Geostudio software. Permeability changes linearly in the interval defined for this function and is considered constant outside this interval.
For this purpose, the Hydraulic Conductivity command must be selected from the Hydraulic Functions section. This will open the Conductivity Function window and users can apply their desired settings by editing the Function Number field
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There is an underground powerhouse structure in the Himalayan region. In this structure, rockbolts and steel ribs were installed.
The rockbolts have load holding capacity of 57 tons but due to improper installation and poor rockmass condition, the final load-holding capacity of the rockbolt varies between 30 tons to 57 tons.
The load is increasing on the underground structure and at several locations, rockbolts are failing because the load reached 45 tons.
At the same time, steel rib has a compression capacity of 1.06 MN/m2 but at a few steel ribs, it has reached 1.33 MN/m2.
What are the geotechnical risks involved in such a situation in this underground rockmass structure?
What corrective measures would be necessary to handle such a situation in this underground rockmass structure?
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Dear Vikalp Kumar Please do recommend my answer if helpful
Choosing the wrong type of rock bolt in an underground structure can lead to failure and compromise the stability and safety of the structure. Corrective measures should be taken promptly to address such issues. Here are some recommended corrective measures:
1. **Site Assessment and Evaluation:**
- Conduct a thorough assessment of the site, including geological conditions, rock type, stress distribution, and other relevant factors.
- Reevaluate the load-bearing capacity and structural requirements to ensure that the selected rock bolts are appropriate for the specific conditions.
2. **Engineering Analysis:**
- Engage geotechnical and structural engineers to perform a detailed analysis of the failure and determine the root causes.
- Assess the load-carrying capacity of the original rock bolts and identify any design flaws or miscalculations.
3. **Selection of Appropriate Rock Bolts:**
- Choose rock bolts that are suitable for the geological and structural conditions of the underground environment.
- Consider factors such as rock type, stress levels, and the required load-bearing capacity when selecting new rock bolts.
4. **Implementation of Monitoring Systems:**
- Install monitoring systems to continuously assess the performance and behavior of the rock bolts.
- Implement instrumentation such as strain gauges, displacement sensors, or other relevant devices to detect any signs of stress or movement.
5. **Reinforcement and Redesign:**
- Reinforce the failed rock bolt locations with additional support or alternative reinforcement methods.
- Redesign the structural support system if necessary, incorporating lessons learned from the failure.
6. **Quality Control and Assurance:**
- Implement stringent quality control measures during the installation of new rock bolts to ensure proper installation and adherence to design specifications.
- Regularly inspect and maintain the rock bolts to identify any potential issues before they escalate.
7. **Training and Education:**
- Provide training to personnel involved in the selection, installation, and monitoring of rock bolts.
- Ensure that the engineering and maintenance teams are aware of best practices and lessons learned from the failure.
8. **Documentation and Reporting:**
- Document the failure incident, including the identified causes and implemented corrective measures.
- Share this information within the organization and with relevant stakeholders to prevent similar mistakes in future projects.
9. **Continuous Monitoring and Feedback:**
- Establish a continuous monitoring and feedback system to track the performance of the structure over time.
- Regularly review the effectiveness of corrective measures and make adjustments as needed.
By taking these corrective measures, it is possible to address the issues caused by the wrong choice of rock bolts and enhance the stability and safety of the underground structure.
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I modeled a earth dam
I want to Simulation Rapid Drawdown of the earth dam at different rates with FLAC 2D software.
Who knows the FISH function or a way to do this simulation in FLAC2D software?
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In my idea, upstream is transient. I think that you make a model with different levels water in upstream,rapid drawdown is very difficult for modeling. The simulation is near the real.
1. The 3D analysis and estimation of transient seepage in earth dams through PLAXIS 3D software: neural network
Numerical study of Seepage for KORD-OLIYA dam and compare by using actual data
2.
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For example it is common that curve of (v) against (ln p) will be plot. Why don't we use e instead of v?
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The reason is the one described by Pedro Miguel Vaz Ferreira above. The specific volume is linked to total volumes and definition of volumetric strain is then straightforward. No effect on the CSSM parameters, other than that
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In Plaxis 3D, I have modelled a quai front consisting of cellular sheet pile walls as a continuous plate with interfaces. How can you find the interlock strength of such a construction? In theory the maximum interlock strength will occur at 67% of its height but this has not occurred where i try to find the results from the output.
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That is a good question.
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Hi all
Im modeling interaction of soil and reinforcement in abaqus. As you know there are two obtaining parameters for soil-reinforcement interface from direct shear test of soil and reinforcement:
1. Friction coefficient between these surfaces
2. Apparent cohesion (adhesion)
for simulating mentioned interaction in abaqus I used surface to surface contact algorithm.
Friction coefficient can be defined in Tangential behavior >> Penalty method, However I can not find any way to insert apparent cohesion of interface.
It should be mentioned that Intrinsic cohesion of soil inserted as a plastic property of soil in mohr - coulomb plasticity. But apparent cohesion between these two surfaces cannot be defined in mentioned part, because this property is related in both surfaces.(its not the plastic property of one material).
Im wondering to hear any suggestion.
Thanks for your attention beforehand.
Alireza Akbari
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Hi
I wanna model interaction between two different material(soil and reinforcement)in abaqus.
As I know when there is no penetration between these two parts, hard contact must be defined in normal behavior however in my simulation reinforcement penetrates in soil due to loading in normal direction so I think soft contact is required in normal behavior. right??
for this purpose linear relation must be defined but I don't have stiffness (coefficient between stress and over closure).
It should be noted I tried some different value for stiffness just to see effect of that, however the analysis didn't convergence at all.
I'm willing to hear your suggestions.
Best Regards
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Hi, Alireza!
I recommend checking out this paper on the use of hard and soft contact implementations through the general finite-element software, Abaqus. You can jump directly into section 7.3, which is related to your concern. Below is the link.
Chapter Contact
I hope this helps. Good luck!
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Geological 3D modelling is becoming increasingly popular and every now and then there are articles about voxel based geological 3D models (e.g. )
While "classical" geological 3D models often consist of discrete surfaces that separate volumes of "homogeneous geology" from one another, in a 3D voxel model each voxel can contain different values and therefore 3D variability of ground properties can be represented. My question is if there are any approaches that deal with geotechnical 3D stability assessment of voxel based underground models?
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Dear Bryant Andrew Robbins, Muhammad Usman Arshid and
N. Bar
, thank you for your answers and I was not aware of these methods and software packages!
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Hi dear researchers
I connected a rigid body into the part of my structure by tie constraint and then I added displacement to rigid body, in static general step every thing is fine and these two part are connected during displacement but when i run this model in dynamic explicit step , tie constraint does not work properly and rigid body and structure become separate from each other during displacement at the beginning time of this step,could anyone help?
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Glad I can help, regarding why the error does not appear using Abaqus standard, I can't tell without checking the model. From what I understand, this particular type of error should appear regardless of the type of solver/step definition. If you're interested in pursuing this further, make a copy of your model with the explicit step (the one without the error) and replace the step with a general static step. If the error persists, refer to the manual.
Good luck!
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Hi researchers
I wanna model tensile test on geogrid in abaqus, so I added displacement to one side of geogrid and the other side of geogrid is constrained completely, everything seems normal but i want to see rupture in geogrid after run in visualization(deformed shape) but rupture doesn’t happen,I even made the displacement of geogrid really big(10 meters and more!) but rupture doesn’t happen and just elongation happend in deformed shape,I defined elastic and plastic part for property of geogrid .
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Thanks dear Pavan for your help,there are list of damage definitions in mechanical part of property,you mean that part? if yes, choosing which one of these damages type is suitable for geogrid?
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Hi engineers,I have a problem, I want to model geogrid by use of beam element however something seems wrong,the axial force in beam is not true in elastic equilibrium and after pullout test, I use the following code:
struct node 1 0,0.3
struct node 2 0.95,0.3
struct beam begin node 1 end node 2 seg ... prop 1
prop 1 syield=124e3 e=96e6 a=2e-3 i=0
int 1 as from node 1 to node 2 bs from 1,32 to 98,32
int 2 as from node 2 to node 1 bs from 98,31 to 1,31
int 1 kn=540e6 ks=54e6 fri=30.2 di=3 c=0
int 2 kn=540e6 ks=54e6 fri=30.2 di=3 c=0
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What is your meaning of the beam? I don't understand it
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I am searching the web for "Thrustpack" modeling software but haven't come across it. Is it open access? Are there any alternative open-access codes for forward kinematic modeling of thrust belts?
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Hi There! You should try the Andino, one of the most powerful modeling softwares, and it is available in full for free academic use,
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I simulated the shield driven-tunnel by FLAC 2D, in which step of numerical model must be applying the traffic loads of ground surface (20 Kpa)? the traffic loads of ground surface change along day and night
@steps:
1. elastic initial equilibrium.
2. elastic-plastic initial equilibrium.
3. Simultaneous with excavation and pre-installation lining.
*in which step influence the traffic loads is real? (interaction with ground above tunnel)
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I created longitudinal joints using solid element ( in Flac 2d software) but my results is not very interesting.
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I modeled a shallow tunnels in urban environments . Which method is suitable for considering the presence of water in the model?
1. specify pore pressures with the INITIAL pp command or WATER table command (in non CONFIG gw mode)
2. specify pore pressures with the INITIAL pp command (in CONFIG gw mode)
In each of the above two conditions which density must be defined?
Dry density or wet density or saturation density
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Hi colleagues,
Because of the complexity of modelling geogrid layers and their interfaces which can cause convergence problem in FE analyses, I have seen in practice they model the whole MSE wall system (eg a block 6m long and 5m high) with very dense or elastic material.
I couldn't pinpoint this in the literature or in guidelines and standards.
Do you know any reference that suggests this?
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Thank you Ahmed Hussein Olat !
That's an interesting piece of work.
However, what I am interested in particularly is the MSE walls.
There are complications in the response of the geogrid interface to the soil and the block in dynamic analyses.
Because of that, I haven't seen research that investigates the dynamic response of an MSE wall.
In industry, I've seen people modelling the whole MSE block (without modelling geogrid and interfaces) using an overly stiff material that at the end would act as an elastic block because of how stiff it is.
I was just wondering if there is anything in guidelines or research that address or recommend this approach.
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I need a large model say 100 x100 m with a mesh size of 0.05m. such a large model cannot be made in version 7. before upgrading to version 8, I need to confirm whether it is working in version 8 or not?
I have also tried trail version 8. it is also not working
if anyone has version 8, I can send you a file to check.
Thanks
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For interface elements in Plaxis 2019, the user is given a choice to choose between default stiffness values or to enter the values manually. The default values are not displayed. How can one calculate these default values?
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Damians et al. - Eauivalent interface properties to model soil-facing interactions 2015 may help you and provide you critical point which could be used to solve the raised issue.
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There are many published literature available on modeling of actual shape of geocell in FLAC3D. But there is no paper available on Plaxis 3D. Many people modeled it as a square or circular shape in Plaxis 3D but no one able to model it as the actual curve-linear shape. Is it a limitation of Plaxis 3D, in modeling thin curve shape?
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My pleasure
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the soil sample which we test in the lab ( disturbed or undisturbed) provide index and engineering properties. how can we predict entire ground behaviour by conducting lab tests?
  • even field tests and FE analysis provide results, but with some shortcomings.
  • how to relate lab, field and FE test results to predict accurate ground behaviour?
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The key thing about lab tests is consistency and thus comparability. The soil undergoes the same process every time, this means that theoretically you can send the same soil to different laboratories and get the same numerical output. This then means that you can classify the soil and compare it to other soils to get an idea of its behavior. However you are right you should not then carry out design without applying judgement about what the results mean. The site conditions, geological structure, where the samples come from, sampling quality etc all go into the interpretation of the results.
Field tests tend to be more expensive than lab tests, especially large volume field tests. Due to variations in field equipment and field conditions the results from field tests can also be more variable making comparisons between sites more difficult. However you are right, field tests are really useful for ensuring that the results from the lab can be interpreted in relation to what is happening in the field.
Computational models can be carried out... but they will be meaningless without a source of parameters for the grounds behavior (lab or field). Computational models in this respect can be problematic as their sophistication can generate blind faith in the output even where the initial parameters have no basis in reality.
Irrespective of the approach or tools that are used, judgement and interpretation are the most important elements of the process.
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Geotechnical Engineering is a branch of Civil Engineering that deals with the behavior of earthen materials and how they interact with man-made elements such as foundations, and infrastructure.
The practice of forensic geotechnical engineering is the application of geotechnical engineering to answer questions pertaining to a conflict in the legal system.
Geotechnical engineers must apply science and engineering within the rules
and practice of the legal system In order for their work to be effective in representing reality.
Forensic Geotechnical Engineering involves analysis of a project, site conditions, or construction from a geotechnical standpoint. Analyses of failures connected with geotechnical and geological origin to improve professional practice, codes of analysis and design as well as practice. These analyses are performed to check the calculations and engineering assumptions during and/or after the construction of a project to provide quality assurance or address issues that arise during or after construction.
Common issues that may arise that a forensic geotechnical analysis can help with include:
  • Expansive Soils Related problems
  • Collapsible Soils related problems
  • Settlement of Shallow and Deep Compacted Fill Soils
  • Pavement excessive Settlement and Failures
  • Slope Stability Failures
  • Embankment Failure
  • Foundation Failures
  • Excavation Failures
  • Others
For more readings on forensic geotechnical engineering:
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Having done a good deal of this kind of work, it is important to understand that this is more than just technical exercise. It is important to understand the standard of care and local practices by which the performance is judged. The American Consulting Engineers Council has an excellent publication on this topic: https://docs.acec.org/pub/18803059-a2fd-2d06-cc39-a6d1dd575265.
It is also important to understand the roles of all parties to the case. Failures are seldom the result of a single error or oversight, but often are the result of a perfect storm of factors involving multiple parties from the initial investigation, design assumptions, owner inputs, contracting limitations, information sharing, construction practices, etc.
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Hi everyone,
As we know, the formulas of the natural frequencies and their corresponding mode shapes for the uniform linear elastic soil (without damping) on the rigid bed are as follows [1]:
f_n = (2n - 1)vs / (4H)
vs = sqrt(G/ρ)
φ_n = sin((2n - 1)πz / (2H))
where f_n is the natural frequency of the corresponding mode in Hertz, φ_n is the mode shape of the corresponding mode, n is the mode number, H is the depth of the soil column, vs is shear wave speed, and z is the height from the rigid bed.
I create the finite element model (FEM) of soil using the commercial finite element (FE) program Abaqus/CAE 6.14-2 x64. The soil was modeled according to the geometric properties using the C3D8. It has a depth of over 50 meters and a horizontal distance of over 100 meters. The soil element size is 2 meters. The total model consisted of 62500 soil elements. Fig. 1 shows the 3D of the soil model. The unit weight of soil is taken 15 kN/m^3, Young’s modulus is 1000 kN/m^2, Poisson’s ratio is 0.35, Cohesion is 5 kN/m^2.
In order to closely match the theoretical solution, some assumptions have been made for the modeled soil. The soil rests on the rigid bed, modeled as boundary conditions restraining the bottom against translations and rotations at all directions. Further, the outer nodes of the model at the same level (Y equal) are tied using the MPC-Tie constraint to move together.
According to the theoretical formulas mentioned above, the first and second natural frequencies of soil column are obtained 0.0786 Hz and 0.2357 Hz, respectively. Nevertheless, the FE results do not conform to this order as the mode number. The first twenty-two natural frequencies of the soil FEM are shown in Fig. 2. The selected 3D mode shapes of the soil FEM are illustrated in Fig. 3. As can be seen in Fig. 1 and Fig. 2, the 1st frequency of the model occurs at mode numbers 1 and 2 and in two horizontal directions perpendicular to each other. This result is consistent with the theoretical results. However, the 2nd mode shape as the model occurs in modes 11 and 12, which is contrary to the theoretical results. Interestingly, the behavior of other mode shapes of the soil model is also strange.
Why do the order of the fundamental mode shapes and their frequencies of the soil FEM differ with theoretical values? Should further assumptions be made to fully simulate the FEM with the theoretical soil model?
The figures and the Abaqus/CAE FEM file are attached.
Thanks a lot in advance.
References
[1] Steven L. Kramer. Geotechnical Earthquake Engineering. Pearson Prentice Hall, 1 edition, 1996.
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I uploaded the input file (*.inp). It is compressed.
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In modelling a retaining structure in PLAXIS, earth pressures are calculated using 'cross section' and '(sigma-xx)' commands. But how to calculate earth pressure at particular node point which are selected along height of retaining wall?
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HI, ..as per finite element method earth pressure is calculated at various integration points within the element. you have to find the stress obtained from the integration point i.e. closer to the node point in which you want to know earth pressure..
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Please note that reduction of stiffness does not lead to any change in stress or strain. Therefore, the behavior of structure would not be changed just by stiffness reduction of the section.
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In the formulation of fem or mdf, if the model is equilibrated no effects is visible if the stiffness is changed with elastic based constitutive model (i'm not speaking on plasticity failure criteria)
Please refer to
where you can find the "official" methods to do that.
Bye
Luca
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Dear RG users,
I am wondering if there are good research topics related with industries need on “Wastewater threatment facilities” and “Solid waste landfills” considering only Geotechnical aspects.
I am looking forward for your messages.
Best Regards
Bekir S.F.
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It is very important topic and really we and our planet is in need of such importance researches
Best Regards
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Dear RG users,
I am looking to investigate the Material Point Method in Geotechnical applications. Do you know any available software for this purpose? It can be etiher commercial or open source. Looking forward for your answers.
Best Regards
Bekir SF
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Hi,
There are MPM codes with different perspectives. For geotechnical analysis, in my opinion these are the main available codes:
Regards,
Fabricio
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Dear RG Users,
I have gained an interest in studying static liquefaction phenomena, however, I constantly see some other terms. Are there any other names that are being used for it? Ex: flow liquefaction.
Also, we have a fully automated triaxial (stress path) apparatus built by Geocomp Co.
Do you know any gap in the literature related with static liquefaction? I am open to any type of research ideas from physical to numerical modelling.
Thank you.
Best Regards,
Bekir
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Dear Bekir Firincioglu,
Static liquefaction is all related to critical hydraulic gradient. when the submerge unit weight of soil become equal to unit weight of water then their might be possibility of liquefaction. Its a critical analysis of fully saturated soil under a steady seepage. You could collect data regarding seepage and hydraulic gradient. However its a very important parameter to irrefutable the safety of earthen dams, earth embankment ect.
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Which model estimates behavior of soils accurately among HS, HS - cap and hybrid hyperbolic?.
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Hello everyone,
  • What type of failure mechanism do you expect to occur in a slope composed of fissured clays?
  • Does the fissure properties influence the overall behavior?
  • Can you expect it to act similar to a disintegrated rock mass?
  • What type of numerical method would you choose to simulate the behavior?
I am particularly interested in fissures in the soil mass and not on the surface such as shrinkage or tension cracks. Also, you can see an example photograph attached.
Thank you for your interest.
Regards,
Bekir SF
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Thank you for your interest Samuel J. Abbey , Which constitutive model do you recommend?
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Hello to all RG users,
I am currently searching for softwares to anaylze the behavior of discontinuous media such as rock masses. It would be a lot better if they are especially developed for Geotechnical Engineering applications. I am also aware that discrete element solutions such as UDEC and 3DEC would do the work. Are there any other softwares for the particular field? I am interested in Discrete Element Method (DEM) and Discontinuous Deformation Analysis (DDA) but I am also open to any other methodologies and softwares. Please keep in mind that they should be used on Geotechniques.
Thank you
Regards
Bekir SF
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I recommend the ITASCA software such as (UDEC, PFC, 3DEC). They are designed specifically to anaylze the behavior of discontinuous media such as rock masses Bekir Salih Firincioglu
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Hello RG users,
I am wondering if there are some new methodologies that have been developed over the past few years. It should be based on solid materials and not fluids. Also, there has to be a software to generate models and it would be perfect if it allows assigning different material strength criterions.
Looking forward to hear from you.
Regards,
Bekir SF
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Numerical methods are techniques to approximate the governing equations in the mathematical models. Common numerical methods include finite element method, spectral method, finite difference method, and finite volume method.
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Hello everyone,
this is the second draft of my Question, I'll keep refining it until it becomes readable, coherent and goes to the point. Thanks for the entries and the suggestions already offered. This is part of my Ph.D. studies, dealing with remote sensing techniques and numerical modelling of deforming slopes. The question popped out once I completed a run of simulations using a combination of 2D and 3D trajectory analysis software (Rocfall and Rockyfor3D, and I'm planning to add RocPro3D to the recipe as well).
In a Ritchie's video (from Ritchie 1963, see attached image for reference, I do actually love it), on the CD that comes with the book ROCKFALL, Characterization and Control (TRB), he says how angular momentum, and increased rotational velocity, is one of the most important factor controlling the run-out of falling blocks, if a rock stays close to the slope, and start to roll faster and faster, is very likely to end up further away from the bottom of the slope, even compared to other geometrical/physical properties. And he mentions also how falling rocks tend to rotate perpendicular to their major axis, which is a minor issue for equidimensional blocks (spheres, blocks) but it can be fundamental for elongated blocks (e.g. fragments of columnar basalt).
The real case scenario I'm testing the models with, is a relatively small rockfall. Its vertical drop is about 15 m in a blocky/columnar weathered granite, the transition zone is resting at approximatively 45 degrees, covered in medium sized blocks (10 cm to 1 m across section), the deposition zone is about 25 m away from the vertical wall, confined by a 3 m height crushed rock embankment. The energy line for this event is extremely high (around 80 degrees), because is constrained by the rocktrap. I'll add some maps, maybe some screenshots, to hide some sensible information.
In the simulations that I have run (in ecorisQ's Rockyfor3D) it looks like the column-like boulders (having a very evident major axis, the base is .4 m x .8 m, while the height is 1.8 m) travel farther than any other class of rocks (I got 3 classes, small spheres 50 cm in diameter, large cubes 1 m by side, and column-like), even the ones larger in dimension and volume/mass, but with all 3 axis of comparable length. You can observe the results in the maps attached to the question. Img02 has been computed with cubical blocks. Img03 with elongated block.
The value of the pixels farther away from the bottom of the slope, the ones that overtopped the rocktrap, upon investigation, in GIS, show a value of indicatively 0.05 (%). Following some consideration in the ecorisQ manual they should be considered outliers, and practically tolerable.
My question is: how do I have to interpret this effect? Is it due to the rigid body approach? If everything else stay the same, mass should be the primary factor for controlling the horizontal travel distance right? Why I do find smaller block travelling farther? It might be a negligible difference given the extremely low likelyhood for those blocks to get there, but does it tell me something I don't get about how the numerical model works?
Is there a way to visualise angular momentum/rotational velocity in that software? AND, most importantly, is the way the problem has been formulated valid?
I really appreciate any help and any idea you can share about it. I'm very appreciative of the time you will spend regarding my problem. I'll probably keep adding details as they are needed. Thanks again
Kind Regards,
Carlo Robiati, PhD student in Camborne School of Mines, UK
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as observed by Matthew:
"At 3:36 in the video is states "the only shape that has a marked effect upon the way a rock rolls is demonstrated by this elongated piece of columnar basalt. Its length gives it eccentric action." By this I think they mean it inhibits its ability to roll. If you have ever tried to roll a fireplace sized log down a natural slope, you will have observed the difficultly that is being referred to."
An elongated rock (or log) is unable to change direction as easily as the natural slope changes aspect which cause it to wobble or bounce and slow its momentum. Not sure how/if you can model that effect.
Elongated rocks also have more of a tendency to break apart as they travel down a slope.
It is fortunate that the rockfall trap is effective for each of your simulations and not dependent on this issue.
good luck
Dave
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Hello RG users,
The rocks are recrystallized limestones and dolomites and physically in various conditions such as in some areas the outcrop is fresh and intact, in some areas it is lightly or highly decomposed and weathered, even somewhere there are residual soils. Also, some areas contain discontinuities and some not.
Assume that I have the plain 3D geometry. I simply cannot assume that the whole area is homogeneous and has same characteristics.
My question is How can I efficiently represent such varying conditions (heterogeneity) in a 3D model based on FEM, DEM, FDEM etc. ? Is there any software capable of doing it?
Thank you!
Best Regards,
Bekir SF
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Dear Bakir,
You have distinct weathering zones in your bench slope. So, you can define these zones in your model as a starting point. You can use GSI for estimating material properties of these zones. Since you do not have any defined joint sets, as you said, you can apply RS2 or RS3, both are FEM analysis program. Your slope dimension seems greather than REV size of your rock mass. Therefore, you can model your slope using continuum approach. Your bench slope is more prone to circular or non-circular failure mechanisms rather than discontunity controlled slip failures, such as plane, wedge or toppling.
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Hello RG users,
I was wondering how can I determine the exact location of expected wedge, planar or toppling falures in rock slopes. Assume that I have already done kinematical analyses and results indicate such possible failure mechanisms. In this case, How can I possible know the location of the wedges etc. to prevent such an instability?
Thank you
Best Regards
Bekir SF
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I don't think using a probabilistic approach is the right thing to do. The most dangerous and statistically processed direction of cracks is not the same. The safety factor is very sensitive to the orientation of the cracks and changing the orientation by 5-10 degrees can change the safety factor several times. Enough odnogo adverse combination that basically the ledge collapsed. The analysis of field measurements of cracks and the choice of the most critical combinations is necessary. Also, it is possible to analyze already accomplished collapses (on what systems of cracks they occurred).
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Dear RG users,
I would like to model fractures in 3D and integrate it into my model. Which may be Finite Element Method (FEM) based, Discrete Element Method (DEM) based or a hybrid (FDEM) based.
I am particularly interested in rock masses so in this case; modeling discontinuities. However, any suggestions that can be used to model fracture systems will be very much appreciated. If your suggestion is software based please tell the name of it.
Thank you,
Bekir SF
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This can be done using RS3 Rocscience. But it is important to remember that the statistically processed parameters of cracks are not the same as the most dangerous ones. A single unfavorable combination (very far from the result of statistical processing) is enough to collapse the slope. This analysis can also be performed in the programs Rocscience (Dips and Swedge).
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I am currently doing a research on modelling Longitudinal Deformation Profiles using Plaxis 3D 2016. Firstly, I needed to set up a staged construction of a circular tunnel excavation deep underground where the stress field is uniform (isotropic). According to Plaxis Reference Manual, I made the calculation type for the initial phase calculation type to 'field stress', inputted the negative field stresses in the model explorer, and fully fixed all the deformation boundaries. Yet, the deformations heat graph, attached in this question, only captured the deformations of the tunnel wall surface.
I also did a check by using K0 (non uniform stress) calculation type, and I was able to get a decent heat graph of the radial wall deformations, which can be observed from the attached image.
What could be the cause of the deformation graph for the uniform stress model? What can I do to have the correct set up for the model? I would appreciate any input. Cheers.
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Please share me the best answer might you get...
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Please give your suggestions how to model the individual cell of a geocell. Which type of element is to be used.
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Just for confirming that whether vibrating wire earth pressure cell (rst instrument)provides accurate result or not, I put 2 kPa pressure (taking weight of a sample and divided by its area)in one sensor but in data acquisition system it shows only around 0.8 kPa. I have calibrated all the five sensors using the calibration file provided by the provider. What would be the possible solution to get proper value?
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Unqualified comment: Such instruments are very intelligent and inherently wrong. Understand definitions. Calibrate it to communicable scale or calibrate/understand your "subject" limitations.
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Hi, I am new to COMSOL, and would like to know if there is an expression/operation or function I can apply or plot in COMSOL that will return the Time Period / Frequency / Wavelength information from the following Displacement/Time Graph attached below?
The 3 coloured displacement components are w, u & v, z, x and y componenets respectively displaced due to pressure and shear waves.
I wish to find the difference in the time period and frequency response of various structures to an induced earthquake.
Thank you,
MM
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quick&dirty field analysis ;-) : the blue signal is a pretty clean ~3.3 Hz sine (~30 peaks/9 sec). the red one contains at the first sight the 3.3 Hz component and a second frequency pretty close to it (3.3+/- 0.2Hz), you can see the resulting interference (beating T~5 sec). the green has a baseline, as Claudio said, get rid of it, and FFT to find the harmonics. My stomach feeling tells me you'll find a mix of the ~3.3Hz main and another 2 relevant additional frequencies, each with significantly smaller amplitude... regards
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I am looking for software that could be used in 3D modeling geosynthetic encased stone columns.
Thank you.
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I feel both PLAXIS3D and FLAC3D is good in simulating your problem but PLAXIS3D is very easy to use as compared to FLAC3D. PLAXIS3D based literature related to your problem is available, so i recommend you to collect those paper and use effectively in your work..All the best in your research..
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Dear researchers/engineers
I was reviewing a report of a dam monitoring during construction. considering a specific piezometer, it is installed at time t1 and elevation z1. but the casing datum is z2 (near 15 meters above z1). the overburden pressure is zero until t3 days after installation. after t3 the B-value is calculated 1.350. B-value is calculated by this formula : [the piezometric pressure (read at time t4 - initial read)]/[overburden pressure (gamma * elevation at t4 - z2)]
the first thing comes to mind as an issue is without overburden pressure there's an increase in piezometric pressure.
can anyone suggest anything?
Thanks
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Thanks Dear John for sharing this. that was useful. the important thing about this dam (the one in my question) is there's no water behind the dam and not situated in impounding phase.
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How can I use Plaxis undrained A to model the behavior of the material.
After the calculation of pore pressure shear strength decreases. If I have a test in situ with the same shear strength for the entire layer. How do I use Plaxis to calculate the shear strength of the type of behavior undrained A? How do I find the minimum value where the pore pressure is maximum?
I have looked on the safety factor undrained A =  safety factor undrained B but I do not understand what is written in the manual: (s-s3) = 2cu. How can I check this condition?
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Согласен, наш ГОСТ для современной геотехники не годится
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Do you happen to know why the mobilized dilation angle was calculated via the equation-B dropped in the attachment in lieu of the equation-A? Cap-Yield (Cysoil) Model {FLAC3D-5.0}
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I know it is a little bit late to answer this but, just in case someone else has the same doubt:
It seems it is only a trigonometric trick...
at the end you compute x=ATAN(sqrt(SIN(x)^2/COS(x)^2))
so: x=ATAN(TAN(x)).
I'm not sure if numerically this is faster or better, afterwards they change the signe if sin(x) is negative. In my opinion it is easier to apply "asin(sin(x))".
In addition, In plaxis they set the values equal to zero if the mobilized dilation is negative but in flac they don't... Again I have no idea why they use a negative dilation angle (what is the physical meaning of it??)...
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The Mohr-Coulomb plasticity model in Abaqus need cohesion yield stress as function of plastic strain to model the hardening behavior of the material.  Please help by explaining the procedure to generate the function. The abaqus manual explains only the theoretical part, as per the description, from the experimental data of triaxial test, I am not able to generate the required function. Is it possible to develop the function with the help of triaxial test data? Any alternate methods are there to find the same?
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Hello Nithin Sudersanan
The Mohr-Coulomb yield or failure criterion states that
τf = c + σ*tan ϕ
Generally, for a specified soil c and ϕ do not change with plastic strain provided the soil remains in the same state. Thus, for a normally consolidated soil c will be almost zero and ϕ will be about 30 deg.
However, c and ϕ will change if the soil becomes overconsolidated. Thus, c and ϕ will be functions of overconslidation ratio and not necessarily functions of plastic strain. You may derive this functional relations using a series of triaxial tests.
With respect to hardening. A material like soil hardens if its shear strength increases. Thus, for an M-C material the hardening parameter may be taken to be the normal stress σ because as it increases τf increases also.
A purely cohesive soil with ϕ = 0 cannot harden.
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Dear all,
I have calculated Fine content (Silt+Clay), Liquid Limit, Plastic Limit, Plasticity Index, Mean grain size, SPT value for soil samples. I need to obtain Clay % for my study. Kindly suggest a suitable empirical formula to calculate clay % from the above available parameters.
Thanks you.
Ashok
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No such empirical formula exits to obtain Clay % from Fine content (silt+clay). The A-line in the plasticity chart enables you to see if the majority of (silt+clay) fraction is clay if it plots above the A-line and silt if it plots below the A-line. However, it could be organic soils as well!
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Hello!
I am carrying out the Slope Stability Analysis of a Highway Slope using 2D Limit Equilibrium Analysis in SLIDE (rocscience package). I was wondering if it is necessary to check the model for FOS & critical surface of the analysed slope (highway slope not embankment) for drained & un-drained case. Or if the drained & un-drained case check should be carried out in analysis highway slope.
Your support shall be highly appreciated.
Thanking you in advance.
Sumit
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The type of analysis depends on the type of soils, on groundwater flows and hydrogeological conditions.
For granular soils (i.e sand or gravel), the slope must be checked only in drained conditions.
For cohesive soils (i.e.clay and silts), there are two possibility. If the soils are dry the slope must be checked only in drained conditions. If the soils are saturated or with groundwater flow the slope must be checked in both undrained and drained conditions.
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Dear sir/madam,
I'm carrying out some research using SLIDE (rocscience) tool for modeling of Slope Failure. During my work, I'm facing some challenges in its numerical modeling & analysis.
I shall be highly thankful to you if could lend me some fraction of your valuable time to read the short 2 paged MS Word file attached herewith.
FYI: The word file contains the challenges I'm facing at the moment.
Thanking you in advance.
Sumit.
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Hi Sumit,
Glad to see you're making progress. In looking at the summary table of the offset distances vs. factors of safety. You'll note that the methods that show varying factors of safety are those that satisfy force equilibrium. The example from SLIDE shows that the Spencer's and GLE/M-P methods have a similar trend (a portion where the factor of safety drops below previous values and then comes back up - interesting to see the difference in the two methods too). I'd have to dig into the forces on the slices in your model to really review but I'd say it's likely due to how much external force from your 10 meter wide load is acting on the failure plane. That is, look at each analysis and see how much of the failure plane is below the external load. I'd suspect the number of slices (and hence the amount of force) on each failure plane below the external load is slightly different hence you're getting different factors of safety.
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i have come a cross a number of models that are used to predict ballast plastic strain; any particular recommedation on the most realistic model ?
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thank you Aliasger for your answer. i know that this is the ideal situation, however this will require many tests to trial different confinement stress levels which will be extremely costly to commission a uni or a lab to carry this out. Therefore i prefer using an existing model From the literature which giving that it can provide a good estimation.
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Currently, I am working on unsaturated soil mechanics applied to slope stability, I read about  ICFEP (general code for geotechnical analysis with a wide range of capabilities) developed by Potts & Zdravkovic and their team.
Is anyone working with ICFEP?, I am looking for experiences using this program.
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I will try to help soon
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Suppose in a basin we have a dam and we want to naturalize the flow at the outlet of the basin. What are the ways for naturalization of streamflow, so that the dam effect can be neglected. I have a long series of streamflow record prior to the dam construction.
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This has everything to do with the design of the outflow channel.  The channel must be shaped and dimensioned to mimic natural outflows corresponding to precipitation events.  Factors such as the nature of the inflow channel and incident precipitation directly on the reservoir surface will alter the flow regime and must be accounted for.  While you can mimic the flow, there will be a delay imposed by the reservoir.  The out flow rate will be driven by the levels in the reservoir and the configuration of the outflow channel.  Depending on the size of the reservoir and associated watershed, creating an effective discharge structure to mimic flows that would have occurred without the presence of the reservoir can be quite challenging. 
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I'm trying to calculate safety factor and displacement of deep excavation.both models represent different value,Which one is more reliable?and I want to know the reason of this difference.
thank you colleagues 
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Dear Poormousavian,
The MC model dose not consider the strain-dependent stiffness behavior or the small train characteristics that invole high stiffness modulus at small strain levels of soil. The MC model only uses a single Young's modulus and dose not also distinguish between loading and unloading stiffnesses. In the HS model, soil stiffness is calculated much more accurately by using three different stiffnesses (triaxial loading secant stiffness, triaxial unloading/reloading stiffness and oedometer loading tangent stiffness). The MC model represents Young's modulus of soil in the in situ stress state. On the other hand,  the HS model represents its three moduli at the reference pressure, and these moduli at the in situ stress state are automatically calculated as a function of the current stress state.
I suggest this paper:
"Evaluation of Constitutive Soil Models for Predicting Movements Caused by a Deep Excavation in Sand"
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Bhim,
Did you initialize the cam clay mean effective stress by using the corresponding function? Read the constitutive models manual / Cam clay. There is also an example at the end, which shows that you need to initialize the mean effective stress by using the corresponding function.
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I am looking for different data on soil themomechanical behaviour for numerical modelling calibration.
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Hi Ana Vieira
1. Odeometer-Type Pressure Plate Apparatus
2. Humility Measurement- Dew Point Method, Filter Method, Osmotic Method, Dynamic Dew Point Method
3. Thermocouple Pshycometers
4. High Air Entry MAtaterial- (Tensiometers, Axis Translation
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Dear all,
Can you recommend methods, materials or some recent works you know for defining the interface of soil-structure problems (in this case retaining walls).
Particularly I am using OpenSees for FE analysis and I want to define the interface along the wall as elastic perfectly plastic material (EPP) and toward the wall as elastic with no tension (ENT). Can you advise how can I obtain best values for these material parameters (young modulus of EPP, yield strain of EPP how it can be related to friction angle of soil-wall interface and young modulus of ENT)?
any advice, suggestion is truly appreciated especially best approach/material for modeling the friction between soil and wall.
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hello dear friend
for your work Opensees is a good choice but abaqus is better than that.
if you use abaqus your work is going to easy and better results.
but in opensees for this issue you can use: Contact or Spring and Tie
and if you see the papers the software they used are:
Flac (is low use of it)
Plaxis ( almost is the high range of using this software because in the codes of the Plaxis all your requirements is available and is specific software for Geotechnical Problems)
and Abaqus software...
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I want to printout node position in FLAC 2D, that is coordinates (x,y).
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Hi,
also, you can have the results as a text file by using set log on command.
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Hello, 
I am going to carried out a serie of Triaxial and Oedometer scale test, I need to verify which of these material will exhibit a better mechanical behavior under different confining Pressure. What kind of recommendations or suggestions can you give me to analize the results?. Or what kind of response would you expect?.
Thanks
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Also see the famous book
"Design of Small Dams"
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Most of the articles I've gone through validated their results from PLAXIS so I want some expert advice to use PLAXIS which is a geotechnical engineering software based on Finite Element Method and reasons to justify its superiority over other FEM based geotechnical engineering softwares available.
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Hi Shashank,
The PLAXIS software is very user friendly. You can your model easily in this software.
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i want to catch the pdf about Abacus geotechnical.
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i have read that book. but, it's not useful for learning Abaqus
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Please find enclosed the attachment. {FLAC3D}
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This has nothing to do with FLAC. This error is related to your operating system evoked by your command. There could be a missing file. You might need to install the operating system again or restore your computer.
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Additionally, in FLAC2D, the IDs associated with gridpoints and/or zones, for which the history commands are being invoked, illustrate in the working screen automatically. 
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Dear Navid,
FLAC 3D version 5 doesn't have this ability. Instead you can see the zones and gridpoints information by putting your mouse pointer on them and looking at "Information" window in "Control Panel" pane.
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I am trying to numerically model coupled phenomena of  loss of moisture, alteration of strength and hydraulic conduction properties and heat migration in soft soils subjected to evaporative flux. I seek suggestions about appropriate modelling package selection for this task.
Thank you.
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At the first time, you need consider some simple assumption. then, you can simulate your model. My suggestion is FLAC2D software, because you can model temperature and hydraulic condition in model. You can also write some FISH function for having more accurate model.
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I need some information about the new version of the program (2015) as it has changed a bit.
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hello everyone, when i run Midas GTS NX with axisymmetric model for consolidation analysis. i saw this error "Error encountered in Modified Cam Clay model, tension stress is applied in element..." Who know about that? thanks
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As it is seen in literature, the ADE with a (dS/dt) is used to model a reactive transport. However, how it can be modeled if nitrate as one solute is stuck by another solute (e.g. nanoparticles)? in this case part of nitrate is adsorbed by soil particles and another part by nano.
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It goes even beyond: Nitrate adsorbed to nano may be adsorbed to soil because nano adsorbs to soil. I know just one code capable of modelling co-transport and co-sorption. (You may consult: Totsche K.U., Knabner P. & Kögel-Knabner I. 1996. The modelling of reactive solute transport with sorption to mobile and immobile sorbents - Part II: Model discussion and numerical simulation. Water Resour. Res. 32, 1623-1632.). Kai Totsche is a Professor at Jena University in Germany
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FLAC2D:
def ps3d ; put 3D principal stresses
; into ex_1,2,3
loop i (1,izones)
loop j (1,jzones)
$sdif = sxx(i,j) - syy(i,j)
$s0 = 0.5 * (sxx(i,j) + syy(i,j))
$st = 4.0 * sxy(i,j)^2
$rad = 0.5 * sqrt($sdif^2 + $st)
$si = $s0 - $rad
$sii = $s0 + $rad
section
if szz(i,j) > $sii then
; ---- szz is minor p.s. ----
ex_1(i,j) = $si
ex_2(i,j) = $sii
ex_3(i,j) = szz(i,j)
exit section
end_if
if szz(i,j) < $si then
; ---- szz is major p.s. ----
ex_1(i,j) = szz(i,j)
ex_2(i,j) = $si
ex_3(i,j) = $sii
exit section
end_if
; ---- szz is intermediate ---
ex_1(i,j) = $si
ex_2(i,j) = szz(i,j)
ex_3(i,j) = $sii
end_section
end_loop
end_loop
end
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Hi. In connection with my first question, I was wondering why the following functions went haywire! Is it any problem in the loop I defined?
def install
pnt = zone_head
loop while pnt # null
_geref = 11.6e6 ; reference tangent shear mod
_keref = 25e6 ; reference tangent bulk mod
_Pa = 100e3 ; reference pressure
m = 1
z_extra (pnt, 1) = _geref*(((z_sig1(pnt)+z_sig2(pnt)+z_sig3(pnt))/3)/_Pa)^m ; elastic shear modulus
_ge = z_extra (pnt, 1)
z_extra (pnt, 2) = _keref*(((z_sig1(pnt)+z_sig2(pnt)+z_sig3(pnt))/3)/_Pa)^m ; elastic bulk modulus
_ke = z_extra (pnt, 2)
pnt = z_next(pnt)
end_loop
end
@install
pro bu @_ke sh @_ge
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Would you please utter how the axes and the origin can be exhibited in FLAC3D in the exact position? I dropped the photo.
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Let's face it, sometimes it is utterly complicated to find the position of origin!
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I would like to reliability analysis of the few geotechnical properties. Most of these properties will be derived from laboratory experimentation on the field specimen. I would like to know how to decide the sample size or no of experiments which will simulates the population with same mean and standard deviation.
If I assumed confidence interval of 95% with normal distribution, how shall i proceed further for deciding sample size.    
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Anurag -
I'm not sure what you are asking.  With known standard deviation for a population, for each design and data type, with good data, an acceptable standard error, say for a mean, is mathematically related to the sample size.  People generally want to know what sample size is needed for a given confidence interval about a mean, which is based on standard error, and that is where the usual 'formulas' are used, relating population standard deviation (which is fixed but unknown) to standard error of mean, proportion, or total (which is a function of standard deviation and sample size).   A standard deviation needs to be "guessed" from other information, such as related studies or a pilot study. 
So from a known, fixed standard deviation, a given sample size will attain a given standard error.   The standard error is made smaller with larger sample sizes. 
It sounds as if you want to know how much information is needed to estimate a standard deviation of a population so that you can proceed with estimating, say, the standard error of a mean.  If that is what you want to know, then perhaps you should estimate such a population standard deviation with incrementally increasing sample sizes until your estimated standard deviations stabilize.
Perhaps that was not what you were asking, but it was my impression.
Cheers - Jim
PS -  Penn State usually has good information online, for the 'usual formulas,' so I searched for and attach here the following, as an example:
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1. Inasmuch as the harnessing of kinematic hardening with the intention of considering the Bauschinger effect in soils under cyclic and reversed types of loadings would be sine qua non, I was wondering why the model, called HS-Small in PLAXIS program which is somehow akin to the aforesaid model in FLAC3D, had being invoked for conducting the dynamic and seismic analyses whereas the isotropic hardening rule was utilized in it.
2. Could you be kind enough to demystify the procedure whereby the mobilized friction angle in example 1-9 was calculated? In this regard, what are the chief reasons behind why _num equals 200 and xtable (1,_num+1) is equal to 0.1?
3. In the friction hardening section associated with the FLAC3D manual in connection with the Cap-Yield (Cysoil) Model, I have been perplexed by the parameter called β having the forthcoming descriptions:
FLAC2D-8.0: “β is a user-defined calibration factor, which can depend on the value of confinement (in triaxial test modelling) or in-situ confining stress (in field scale modelling).”
FLAC3D-5.0: “β is a calibration factor.”
I am enthusiastically curious how the above-mentioned parameter was supposed to be calculated. Additionally, this is to inform you that the correct form of the equation for assessing the plastic shear strain (Eq. 1.313, FLAC3D) subsequent to rectifying one mishap is attached here.
Thanks a bunch!
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Loads of thanks for the documentation; yet, I have not been signposted towards my desirable destination by them.
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Is the technique of geosynthetic-encased stone columns in soft clay applicable really? And is it possible to make geosynthetic around a stone column technically?
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Please have a look at the following articles:
1.Almeida, M.S.S., Hosseinpour, I., Riccio, M., and Alexiew, D. (2015). “Behavior of Geotextile-Encased Granular Columns Supporting Test Embankment on Soft Deposit.” Journal of Geotechnical and Geoenvironmental Engineering, 141(3), 04014116.
2.Mohapatra, S.R., Rajagopal, K., and Sharma, J. S. (2016). “Large direct shear load test on geosynthetic encased granular columns.” Geotextiles and Geomembranes 44(3), 396-405.
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The geological map of my study area has exactly 66 classes. For further analysis would be great to have less categories, grouped between the geotechnical properties. Does anyone can help me? 
I'm not a expert in Geology.
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hi pedro. 66 classes is pretty much, difficult task! however, there is a good approach used for decades in austria and described in detail in the "Guideline for the Geotechnical Design of Underground Structures with Conventional Excavation." you can download the guideline for free from the homepage of the austrian society for geomechanics. if you need any help applying the guideline to your problem, just let me know. i used the approach in my master thesis, but the thesis is in german, sorry. alexander
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Good night im actually using FLAC for earth dams design on the material creation tool the software asks me for shear and bulk modulus how can i calculate this modulus or if you can, bring me some soil materials tables with those modulus
regards
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Hi,
from elasticity theory, one has
K = E/(3(1-2v))
G = E/(2(1+v))
M = E(1−v)/((1+v)(1−2v))
where
E: Young's modulus, v: Poisson's ratio, K: bulk modulus, G: shear modulus, M: stiffness modulus (under oedometric conditions = vertical compression without lateral  displacement).
The elastic properties of soil depend on the strain amplitude. Estimates can be found for example, in B.M. Das "Advanced Soil Mechanics", 3rd ed., Taylor & Francis, 2008
In a homogeneous isotropic halfspace of soil with horizontal ground surface, you may estimate Poisson's ratio from
v = (1-sin y)/(2-sin y)
where y: angle of internal friction, and -1 < v < 0.5 has to be satisfied. This equation uses elasticity theory and Jaky's formula for the stress ratio:
sx/sz = 1-sin y
where sx: horizontal stress, sz: vertical stress.
Regards