Numerical Modeling in Geotechnical Engineering - Science topic

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

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.

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

That is a good question.

Dear Alireza Akbari

the following tutorials can help you:

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.

I hope this helps. Good luck!

Dear Bryant Andrew Robbins, Muhammad Usman Arshid and , thank you for your answers and I was not aware of these methods and software packages!

Alireza Akbari

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!

Pavan Kumar

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?

What is your meaning of the beam? I don't understand it

Hi There! You should try the Andino, one of the most powerful modeling softwares, and it is available in full for free academic use,

info@lateandes.com

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.

Thanks Alireza Rashiddel

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.

My pleasure

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.

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.

I uploaded the input file (*.inp). It is compressed.

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..

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

https://www.plaxis.com/support/tips-and-tricks/stress-relaxation-due-creep-concrete-structures/

where you can find the "official" methods to do that.

Bye

Luca

Hi,

There are MPM codes with different perspectives. For geotechnical analysis, in my opinion these are the main available codes:

Regards,

Fabricio

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.

Thank you Sir Karthigeyan . S Navid Kardani

Thank you for your interest Samuel J. Abbey , Which constitutive model do you recommend?

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

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.

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

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.

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).

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).

Please share me the best answer might you get...

You can read this paper

Unqualified comment: Such instruments are very intelligent and inherently wrong. Understand definitions. Calibrate it to communicable scale or calibrate/understand your "subject" limitations.

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

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..

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.

Согласен, наш ГОСТ для современной геотехники не годится

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??)...

Hello Nithin Sudersanan

The Mohr-Coulomb yield or failure criterion states that

τ_f = 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 τ_f increases also.

A purely cohesive soil with ϕ = 0 cannot harden.

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!

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.

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.

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.

I will try to help soon

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. 

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"

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.

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

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...

Hi,

also, you can have the results as a text file by using set log on command.

Also see the famous book

"Design of Small Dams"

Hi Shashank,

The PLAXIS software is very user friendly. You can your model easily in this software.

i have read that book. but, it's not useful for learning Abaqus

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.

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.

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.

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

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

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

Let's face it, sometimes it is utterly complicated to find the position of origin!

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:

 https://onlinecourses.science.psu.edu/stat506/node/9

Loads of thanks for the documentation; yet, I have not been signposted towards my desirable destination by them.

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.

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

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