RAMÓN CRONWELL SALAZAR MANRIQUE's Activities

Fully drained analysis

RAMÓN CRONWELL SALAZAR MANRIQUE — Tue, 16 May 2023 20:38:40 GMT

Dear PLAXIS support/coleagues,

In a project we are developing right now, we are running two kind of analysis: fully undrained and "fully drained". For the latter, we have some questions come up from the following statement:

First, a little description of our project:

1. In our project we have the installation of a Comb-wall (sheet piles + king piles) and then a dredging stage at the level -5.35. Because of the way of loading for these two stages, we are modeling them as UNdrained.

2. After dredging, we have a reclamation stage at +3.0, then the PVD's installation from that level and after that a pre loading stage. These stages are being modeled as drained.

3. Finally, the operation stage (after the removal of the surcharge) is also being modeled as drained.

The doubts/questions we have are the following:

a. For item 1, is it correct to model these stages as UNdrained and the following stages as drained?

b. The statement mentioned that in a fully drained analysis "This will give a reasonably accurate prediction of the final situation, although the precise loading history is not followed and the process of consolidation is not dealt with explicitly" then, when I perform a fully drained analysis: should "intermediate stages" be avoided and go through to the final stage? In our case, after the installation of comb-wall we have to go straight to the final situation: operation stage. How could I check the development of displacements during the intermediate stages?

c. The statement mentioned that the fully drained analysis can assess the settlements in the long term, in our case, besides the settlements we are interested in lateral displacements. Is fully drained analysis a good starting point in order to report preliminary results of lateral displacements?

We really appreciate your comments and supports.

Many thanks in advance.

Ramón Salazar,

Discontinued wall pile in PLAXIS 2 - Output forces

RAMÓN CRONWELL SALAZAR MANRIQUE — Wed, 12 Jan 2022 17:01:34 GMT

Dear Plaxis Support

When I model a discontinued pile wall, I enter the stiffness (axial and flexural) as the stiffness of the element divided by the distance, "s", between two of them. After the analysis I got the internal forces (bending moments, normal and shear forces) "per meter width". For pile design, should these forces multiply by the distance between them "s" or by its diameter "d"? or the values from output can be used directly for design.

I hope you can help me with this question.

Thanks for your support.

Ramón S.

Updated mesh analysis

RAMÓN CRONWELL SALAZAR MANRIQUE — Tue, 09 May 2023 22:06:43 GMT

Hi dear PLAXIS SUPPORT,

Currently, I am running a deformation analysis and I would like to take into consideration the second order effect in the structure I am evaluating. However, when I select updated mesh option in the general information, after running some construction stages the software delivers one of the two following warnings: "soil body seems to collapse..." or "deformation not compatible in STRESBL". This just happens when I run the model with the updated mesh option selected, in a normal analysis everything is ok.

This is the model I am running and the screenshot shows what I described above. The wall is a COMB-WALL comprised for king piles and sheet piles.

In order to get over this issue, Plaxis reference manual suggests the following:

But in my case, I need to compare the effects of first order analysis with the effects from the second one, If I increase the stiffness (like manual reference suggests) I am afraid that I will not be comparing the same model. Even, If I changed the stiffness, it would be very probably that the model still does not run.

Any comment or support?

Thanks in advance.

Ramón S.

Design approach 1 combination 2: DA1C2

RAMÓN CRONWELL SALAZAR MANRIQUE — Mon, 24 Apr 2023 16:52:42 GMT

Dear PLAXIS support

I'm designing a comb-wall (king piles+sheet piles). For the bearing piles (king piles) I have to check the embedment length of the wall using DA1C2. To do that, I'm using design approaches in PLAXIS 2D with load factors and material factors. After running the model, I obtain from the output the pressures diagrams from the interfaces both side of the wall passive and active. Then I get the rotation point ('pivot') in the wall and take moments over this point. Finally, I check that the moments developed by the passive side are higher than the moments caused by the active side or that, in the worst case, the sum of moments is zero. Is this procedure right? It seems to be right because It is the way to verify if we used LEM (Sum of moments over a pivot), but I'd like to know your opinion. Is there another way to check the embedment length of the wall using DA1C2?

Stresses acting on the wall after applying load/material factors

Sum of moments over a point of rotation (import from PLAXIS to Excel)

Verification

I represent the way of the pressure diagrams through known geometric figures, in order to make easier the sum of moments.

I really appreciate yor comments.

Best regards,

Ramón S.

Plastic analysis vs Consolidation analysis

RAMÓN CRONWELL SALAZAR MANRIQUE — Wed, 22 Mar 2023 05:11:02 GMT

Dear PLAXIS support,

We have to run a deformation analysis. The cross section involved is the next

Geotechnical parameter (stiffness and strength) haven't been defined yet and they are being evaluated at this moment. Besides that, we have a preliminary schedule of the construction sequency. Our target is to estimate the deformations in the soil underneath the "old structure" caused by the construction our project (on the left side). The project consists in the expansio of a container yard and some preloading works have been considered in order to meet residual settlement requirements. Our questions are the following:

Under the considerations mentioned (highlighted in yellow): what kind of deformations analysis should be performed? Undrained plastic analysis, fully drained analysis or consolidation analysis? We would like to report a range of estimated deformations (lateral and vertical) in order to have a set of values to be compared during construction works and take some precautions if these values were out the estimated range.

I really appreciate your comments about this issue.

Sincerely,

Ramón Salazar

mobilized passive pressure

pasquale paldino — Sat, 09 Jul 2022 18:29:13 GMT

hy,

I need to determine the ratio between effective pressure (sigma_N to interface) and passive pressure (maximum resistence). For passive pressure i do not know how to calculate with plaxis (take sigma_v and calculate to hand maybe?) . Did someone ever resolve this situation?

Thanks a lot.

OCR - SIMULATION OF HISTORY_Consolidation Analysis HS-SS-SSC

RAMÓN CRONWELL SALAZAR MANRIQUE — Thu, 29 Dec 2022 08:12:20 GMT

Hello Everyone,

I am running a consolidation analysis with three soil models: HS, SS and SSC. The soil profile comprises a NC clay embedded between two sand layers.

I was reading PRACTICAL APPLICATION OF THE SOFT SOIL CREEP MODEL part I and I have the following doubts:

1. It is mentioned that one possibility to asign a correct OCR value is to leave the OCR equal to 1 in the initial conditions and start the calculation with a plastic nil step setting a given time interval. Questions are: Can this procedure do for any of the three soil models or it is just for SSC in order to define OCR value? If the procedure were only for SSC model what OCR value for SS and HS models should I enter as a input? What is the 'common' time interval to simulation of history?

2. If I am performing Gravity Loading as a method of initial stress generation, do I need to reset displacements to zero in the nil phase?

3. In the case I need to split primary consolidation settlement and secondary compression settlement I should perfom two analysis with both SS and SSC models. How does the way to obtain OCR (question 1) affect these two settlements?

Finally, I was checking the settlements values for a given period of time and the settlement obtained by HS is very lower than that obtained by SSC and quite lower than the obtained ones by SS. Is this correct? what is the most suitable soil model to model soft soils in a consolidation analysis?

I really appreciate you can help me with this questions.

Looking forward to your prompt reply

Greetings,

Ramón S.

Ask A Question II

Thu, 29 Dec 2022 08:12:22 GMT

Ask 10 questions in a forum.

PASSIVE RESISTANCE

RAMÓN CRONWELL SALAZAR MANRIQUE — Mon, 03 Oct 2022 00:13:14 GMT

Hi dear team PLAXIS support

I have some quetions, in the next picture you can see active and pasive pressure distributions over a wall.

About the last stament: How can I know the percentage of passive pressure mobilized related to the maximum earth pressure? Why does the stament establish that "only a small part of the maximum is mobilized"?

Is it possible obtain the maximum from PLAXIS? or Should I get it from an analytical way? In the figure before, is it correct my interpretation of the maximum passive earth pressure?

I really appreciate your comments.

Ramón Salazar

Soft soil in pseudo-static analysis

RAMÓN CRONWELL SALAZAR MANRIQUE — Fri, 16 Sep 2022 04:10:06 GMT

Hi, everybody

Currently, I'm running a pseudo-static analysis for the assesssment of a COMB-WALL (king pile + sheet pile). In the next figure you can see the model configuration

In green a very soft soil (MH)

In blue a sandy soil (SM)

In orange a the bearing stratum (GP)

In gray a quarry run (QR)

The fact is that when I'm running pseudo-static analysis (kh = +/- 0.24g) in the model the multiplier SumMstage not converge to 1 and I have to stop running because it is much time consumed. Then, I can't assess the behaviour of the COMB-WALL in this condition. Very soft soil is modelling with soft soil creep model. When I check out the deformations in output, the deformation in the very soft soil is extremely large, like the soil "fails". I have some questions:

1. Is it okay to model a very soft soil with SSC creep model when it is analyzing a retaining wall and not necessarily a settlement calculation or I should have used HS or HSS?

2. Could a very soft soil fail when acting a inertial force due to the dynamic loading? What can I do in order to allow the model runs completely? Without a complete running I can't assess the forces acting in the COMB-WALL.

3. I have tried to run the model eliminating the very soft soil when a pseudo-static analysis is performing, considering that the "soils fails" and then it does not contribute any passive resistance to the COMB-WALL. The assumption is conservative but, is this correct?

I hope you can help me with these questions

Ramón S.

Soft soil improvement

RAMÓN CRONWELL SALAZAR MANRIQUE — Fri, 16 Sep 2022 05:07:09 GMT

Hi everybody,

Next questions are about modelling of drains and stone columns.

PVD Drains.

1. Improvement with PVD can be modelled as a material with a equivalent vertical permeability according to Chai et. al equation

or following the recommendations of Predicted and observed behaviour of soft clay foundations stabilised with vertical drains (Indraratna):

Questions are: is it necessary to draw the drains in the model when vertical equivalent permeability is used? what modelling is more appropiate to use?

Stone columns

1. In plain strain model we can simulate stone columns as a material which is drawing like walls?

Question is: how can I simulate vibro-sustitution/compaction in PLAXIS 2D? is it enough with give the stone colum material a high phi value? or should the stiffness and resistance parameters of the soils surrounding the stone columns modify (improved somehow)?

Thanks!

Ramón S.

Undrained shear strength in consolidation analysis

RAMÓN CRONWELL SALAZAR MANRIQUE — Thu, 17 Mar 2022 12:53:07 GMT

Dear PLAXIS SUPPORT,

I'd like to know how I can get the undrained shear strength (Su) after a pre load (surcharge) stage in a consolidation analysis. I'm using Soft Soil Creep model and type of drainage is "undrained A". Is it possible to obtain this parameter from PLAXIS output? Theoretically, after a surcharge is applied, this parameter should improve, how PLAXIS does this calculation?

I really appreciate your prompt answer.

Best regards,

Ramón S.

Reclamation works in PLAXIS 2D

RAMÓN CRONWELL SALAZAR MANRIQUE — Sun, 13 Mar 2022 23:52:46 GMT

Dear PLAXIS Support,

Recently, We've been running PLAXIS 2D for reclamations works in quay and containers yard areas for marine ports. I have the followings questions and doubts which I'd like to clarify in order to make better settlements estimations.

1. I've been running the dredging stages in PLASTIC analysis and once they were done I would follow it with reclamations works (or filling) using a CONSOLIDATION analysis. Is that correct?

2. How can I differentiate immediate settlements from consolidation settlements in the outputs and in the curves? Usually, the subsoil profile (of the projects that we've evaluated) was represented by a granular material layer (meanly sands) above a compressible clay or mud layer which lays above a stiffer soil or rock.

3. In the case of an impervious layer (rock or stiffer clay) at the bottom of the subsoil profile, should "boundary y = min" be closed during analysis? in the case of a pervious layer (gravel) should it be opened? In general, is it necessary to open all or some boundaries during consolidation analysis to allows the drainage?

4. Which is the best way to model stone columns and PVD's in the case of these analysis? We've been modelling this elements as a materials. In the case of stone columns, we've been drawing each element one by one, while for PVD's, we've been using de "kve" (equivalent vertical permeability, Chain 2001).

I hope you can help us with your comments.

Best regards,

Ramón Salazar

Consolidation analysis

RAMÓN CRONWELL SALAZAR MANRIQUE — Tue, 15 Feb 2022 00:43:21 GMT

Dear PLAXIS SUPPORT,

I have two questions that I'd like to be repplied.

1. When we pre load a compressible layer in order to accelerate the primary consolidation, after that we remove the surcharge, is it neccesary to change the secondary compression index, Cα, by the secondary compression index after surcharge, C'α? to calculate secondary compression settlements. Hand calculations suggests the use of this index (The Mesri Method, 1997), how PLAXIS take into account this situation?

2. How can I check the maximun surcharge height that I can apply in one particular phase without cause a shear failure in the soft soil layer?

I hope you can help me with this questions.

Best regards,

Ramón Salazar

Passive Earth Force

RAMÓN CRONWELL SALAZAR MANRIQUE — Tue, 14 Dec 2021 22:26:07 GMT

How can I get from PLAXIS the mobilized earth passive pressure in orden to calculate the earth resistance ratio?

I appreciate your help.

Best regards,

Ramón Salazar