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I want Friction pile group efficiency data and I am unable to find anything about it. I want cohesion number of pile adhesion factor etc.?
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Prof. Gopal Ranjan Book is Good Read , Please refer to that
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Dear all,
What are the factors to be taken into consideration when modeling stone columns in FLAC 3D? Are there differences between the modeling of stone columns and piles?
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For using piles in FLAC 3D, alot of parameters of every pile element should be determined such as bending moment and shearing force.
If you use stone columns in FLAC 3D, only some parameters of stone zone should be determined, but bending moment and shearing force of every pile element can not be obtainedobtained and the infill materials of stone columns are totally different with that for RC piles.
Best regards,,,
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I want to do a three dimensional analysis of pile group in saturated silty sand using results of shaking table test .
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Plaxis 3D Foundation is very good for modelling a group of piles. See Attached file
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I modeled a Disconnected pile raft foundation system,
I used to pile as an embedded beam with plate (raft) both as an elastic material, but I'm not getting enough axial load in a pile. 350kPa loading(uniform) being used. Also, the connection of pile and raft and use of interfaces in the model.
The paper used for reference is attached below, also the plaxis pile.
please help with this, and I'm a student m.tech
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Hi,
I prefer beam element
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Greetings,
I was wondering what is the optimal way to connect the reinforcement at the top of the pile (the part that connects to the raft foundation):
-The pile bars are left straight and connected to the raft?
-Or the bars are bent in 45 degrees and then connected to the raft?
Because I've seen both cases
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If the pile is subjected to axial compression without any pull, both alternatives are okay. However, if the pile is subjected to pull, the second alternative ( the bars are bent in 45 degrees ) is better.
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How to calculate the natural frequency of various pile group systems or natural frequency of a single pile system? Does natural frequency formula for piled raft foundation system hold good for pile group system?
For soil layers, natural frequency is calculated using the formula
fn = Vs (2n-1)/4H where, Vs is shear wave velocity of soil and H is the depth of soil layer.
However, how to calculate the natural frequency of a pile group system or a single pile system? Is there any codes available for calculation of natural frequencies like IS 1893 that gives standard formula for calculation of time period of a structure?
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Natural frequencies and mode shapes can be obtained from existing engineering structures like pile group or single pile subjected to dynamic loading using a dynamic sensor. However, finite element analysis can be used to calculate the mode shapes and natural frequencies. A semi-empirical formula can be used, Nevertheless, modelling using the Finite element method is much more realistic and efficient. You can use the Plaxis 3D software package.
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Hi everyone;
I have never used the "pile group effect" reduction coefficient in any of my projects where I made a rock socket pile design calculations. Because I know that there is no literature acceptance on this subject, and I think that's the right calculation method to do.
But the government agency that I work with now has asked me to do so. What do you think about this request ? Do you use "pile group effect" in rock socket pile bearing calculations ?
Best regards
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Dear Yazgan,
The pile group effect is often wrongly treated. It should be differentiate two criterions: bearing capacity and settlements (ULS and SLS according to Eurocode 7). Bearing capacity of piles in a group is usually higher than of a single pile; various “theories” and formulas which reduce the pile bearing capacity in group are myth or superstition. In contrary, a pile in a group almost always settle more than a single pile. In the case of a pile socketed in rock the reduction of bearing capacity is not probable – it would be difficult to imagine a mechanism of such phenomenon. The settlement of piles in a group may be a bit higher, but in rock it should not be a problem. In my opinion you are right not using the pile group effect- on the basis of temporary knowledge.
Regards, Boleslaw Klosinski
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Hello. I'm modelling pile group and pile raft in plaxis. I have got pile raft results fine but I'm facing problems in pile group as I need to ignore the interface between cap and soil. What should be the appropriate way of modelling it?
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Dear Abbas,
Nice to know that you got good results for piled raft foundation but you are facing problems in pile group mainly concerns on ignoring the interface between cap and soil. This can be done easily, you identify soil elements which are covering just below the pile group. Then, define the separate soil model for these elements by assuming the interface factor as 1. I suggest you to read PLAXIS manual for further details in this regard. ok all the best..
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I need papers or just information about the use of t-z curves taking into consideration group effect in pile groups. I've learned Randolph suggest a Zm factor to estimate the increase in the settlements, but I just couldn't find the paper. The t-z curves, from what learned, have orginally come from the offshore industry, and they have some expertise in this subject, I've found much more easily papers related to the group effect in the py curves, the case for laterally loaded piles, but I know there is something in the literature for the case of axially loaded piles, if anyone can help, I appreciate.
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Dear Edno,
The pile foundation are designed based on various method, the one as you looking for t-z curves based design is done based on API code for pile foundation design. so i suggest you to read from API code about the t-z method. I also attached the paper related to your topic for your ready reference. ok all the best in your research..
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I'm investigating group effect in piles with RS Pile. For lateral loads, the software calculates reduction factors for the py curves to take into account the group effect, but for axial loads, the user must input a coeffient himslelf. I'm having dificulties to find how to calculate such coeffient, would anyone recomend me a method or point a direction?
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Dear Mt. Arsoy,
Thanks for the reply. It is very good to know that even at lower displacement levels, the group efficiency is valid. I have found some expressions especific for tzqz curves, but not the one I need yet (if it is of your interest, this video is a good one, https://www.youtube.com/watch?v=gIqPPB5BOoU ). If I don't suceed at finding the factor I need, I'll defenetely use group efficiency, so thanks again!
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I am going to model a pile group in liquefiable soil. Although this phenomena should be really modeled as a 3D problem, I want to model this problem in 2D state due to simplification. If employing 2D model for this problem is correct, how can I obtain the 3D results from this modelling? In my opinion I guess that I should work on the stiffness of piles. Do you have any suggestion about the equivalent stiffness of pile groups under seismic loads in 2D modeling?
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So Flac 3D gives good results.
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In order to calculate it I consider the influence of the load that the raft carries and the influence of the load that the pile group carries.
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I am modelling pile group in plaxis 3D. i have information about soil and pile but no idea about cap.please guide me about properties of cap in plaxis.
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You can use the following equation to find that 
E= 4700 SQRT (f'c)
depending on the compresive strength of the concrete (f'c) that you are using
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What is the difference between free-head pile group and fixed-head pile group?
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Dear Hasan,
As I understand a pile is called fixed headed, if its deflection at the head is restricted by integrating the head of the pile into a pile cap. However, a pile whose deflection is not contained at the head by a pile cap is considered as a free head pile. So, group of piles which are connected by a pile cap can be called as a fixed head pile group and which are not connected are called a free head pile group.
Regards
Sravan MV
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What is the most effective software for dynamic analysis of "soil-structures" such as piled raft or pile group foundation? Is Flac3D Suitable for that?  
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Hi Maryam,
Plaxis 3D, ABAQUS, ANSYS and FLAC 3D are suitable software with adequate soil models. 
What you need to be mindful of, is the boundary conditions at the limits of your model. This is to ensure the wave propagate outward and doesn’t come back into the mode, i.e. energy is not trapped. In Abaqus you model it yourself. PLAXIS define a viscous boundary condition, and you can’t impose displacement. When you finish the analysis in PLAXIS you will find that the model has undergone rigid body displacement. This is not terrible if you are not interested in displacements.
If you decide to use Abqus, then send me your problem (if it is seismic loading on building, machine foundation etc.)  and I will tell you how to model the radiating boundary condition.
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A foundation resting on soil reinforced by floating stone or sand columns?
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You have several methods. One is the one Keller recommends for computing the equivalent overall mechanical parameters using Priebe's method. You can find it here: http://www.getec-ac.de/download/en/pdf/GT07-13E.pdf
Another way is to use any FEM analysis and consider the stone columns as such, with proper interaction with the adjacent soil.
A third method, if you intend to have a gradual change of mechanical parameters from the column axis to the soil, is to use the thermal dependence trick, namely consider a homogeonous medium with parameters variable with temperature so that a 0 degrees you have soil parameters and at 1 degree you have the stone column parameters.  You control the linear variation in the zones with temperatures between 0 and 1, you have the columns in the zones with 1 degree and the rest of the soil remains at 0. If you want to pursue this path I can give you additional info.
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I am trying to simulate the dynamic behavior of a pile group. In my model, pile and soil are modeled by beam and solid elements, respectively.
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One way is to model your piles with solid elements as well. If you decide not to follow this approach then your problem is to manage capturing the boundary conditions between the piles and the soil especially when tension applies at the interfaces. Given that you want to study the dynamic behavior of a pile-soil interaction problem you will need to use some advanced numerical features. The most realistic way to go is to generate a 3D model and solve it as a contact problem. Many researchers model the soil with springs which of course is more simplistic. In your case, if you insist in coupling beams and solids, you will have to make sure that the degrees of freedom for the case of the two different dimensionality type of elements, is compatible, while the mesh of your solids should always follow the mesh of your beams (common nodes). In this case (beams and solids) you will have stiffness overlapping given that the beam elements are 1D and solid elements are 3D, thus the geometrical representation of your system will not be exact.