Vu Ngo's Activities

Threshold limits of excess pore pressure during reclamation

Vu Ngo — Tue, 13 Sep 2022 04:54:09 GMT

Good morning,

To control stability of the boundary bund during reclamation we observe the settlement rate and and excess pore pressure (EPP) in control area (generally initiated at the slope side). The threshold limit of EPP can be defined by incremental ratio B= delta(u)/ delta (sigma) and also a site-specific experience, i.e., EPP= 60~70kPa.

But what should be the threshold for the middle area to ensure that the loading is not so fast? As the bund was already constructed one and haft years, EPP under the bund was already dissipated and will not be high during reclamation as shown in the picture. However, there will be an threshold for the middle area, I think, but which should be the condition to defined the threshold?

If anybody have idea, please give me the suggestion!

Thank you and have a nice day,

Is that corrected to set the LineDisplacement ux,start,ref= 0.5m at the bottom boundary in Plaxis 2D seismic analysis?

Vu Ngo — Fri, 16 Apr 2021 02:49:42 GMT

Hi all,

As explained in communities.bentley.com/.../how-to-prescribe-a-dynamic-displacement, the amplitude of the motion is double when body wave reaches a free surface due to impossibility of transmitting stresses and therefore ux,start,ref= 0.5m to account for that. However, it's still a question when the result shows peak acceleration is about half and one time of input signal at the bottom and the surface, respectively. In Plaxis version 2011 the displacement is only set as 0.01 to convert cm to m for input SMC file. Something is still not clear for me to understand the above explanation and to decide the input in our project case. Would anybody explain me more clearly?

Thank you!

Can Plaxis coupling tool be used in another structural types?

Vu Ngo — Mon, 03 May 2021 05:09:14 GMT

Dear all,

Yep, it can be used for buildings where structural and geotechnical problems are usually analyzed independently. It seems that the tool couldn’t be used for other types of structures such as deep open pile-deck where pile and soil interacted in term of spring. However, this beam spring model is not enough where the soil response needs to be considered and we need geotechnical model too. So, is there any way to use this coupling tool in this case?

Thank you very much.

Load in embeded beam row

Fadi Haddad — Thu, 12 Nov 2020 14:27:23 GMT

Hi All, I have please an urgent question concerning embedded beam row in Plaxis 2D.
I defined an embedded beam row with a certain spacing (6 m). In the output I am getting internal forces, which are as example Moment in kN.m/m. Is that the complete load in the embedded beam or should I multiply it by the spacing?

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Mon, 31 May 2021 10:35:00 GMT

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Would Plaxis model consider the P-delta effect for a structural member?

KC Chan — Thu, 29 Apr 2021 05:37:06 GMT

If I use Plaxis model to analysis a foundation with pile and clay material, would the model consider the P-delta effect?

Embedded beam row skin resistance input value clarification

Nitharshan — Wed, 28 Apr 2021 09:54:05 GMT

Hi all and Dennis Waterman Rushan Gizzatullin

For the embedded beam row, we have provided skin resistance value in the material data set as kN/m based on the length of the pile. Embedded beam row is connected with soil using springs with axial, lateral and base resistance factors.

I have provided linear start 0 and 200 kN/m at then end for the skin resistance with zero weight of the pile and out plane spacing is 1.5m , i got max skin as 133.3 kN/m/m ( which is 133.3*1.5 => nearly 200 kN.m)

Let's consider the case this pile in cohesionless soil with length less than the critical depth of the pile, we have used A ks σv tan(δ) to calculate the skin friction where A is the surface area, ks is the factor depending on pile material , σv is the average vertical stress and tanδ is the friction angle between soil and pile. In plaxis 2D skin resistance is kN/m (per length) so we need to multiply only by the perimeter in that equation and provide the value.

My question is here we have ks and tan(δ) value which is depend on the soil pile interaction so if we provide the value for skin resistance P δv in the above equation (where P is the perimeter) is correct or do we need to multiply by ks and tan(δ) and then provide the value? i thought since there is the interaction factor between pile and soil this value would be covered by that factor.

I hope you understand my question. If so plz reply.

Thanks.

Liquefaction Analysis on Plaxis

Marcus Delfino — Tue, 04 May 2021 18:46:01 GMT

Hello,

Good afternoon.

I am working on my Master's dissertation with Liquefaction Analysis from Earthquake Loading and I have three questions about my modeling.

1) What should be the correct dynamic boundaries to use on this modeling? I am simulating a field without any lateral constraint. Should I use for xmin and xmax, free field? And for ymin: should i use Compliant Base or Viscous?

2) From simulations that I already did: it took a lot of time to be concluded. Is there any way to decrease the time needed to calculate? And, in most of the cases, the value of pore pressure peaked positive values. What is the reason about it?

3) How can I install drains on this soil to decrease the excess of pore pressure? I already tried to use the Drain tool but it was in vain.

Thank you so much.

Dynamic Analysis Using max Step and Substep

Tolgahan Feyizoglu — Thu, 29 Apr 2021 09:27:11 GMT

I am running a earthquake analysis. Earthquakes time is 35 sec. I consider the differences for using max step=3500, sub step=1 and using max step=1, substep=3500. What is the difference between this 2 situation. What is the effective numbers of step and sub step for analysis? Earthquake records has accelaration value for each 0.01 sec.

Unit of Acceleration

ZAID ALFARHAN — Sat, 27 Mar 2021 13:29:46 GMT

kindly look to the screenshot. I have El centro earthquake acceleration in "g" unit , and my project unit in "m" and "days" , So I used scaled value 9.8 to transform the multiplier to m/s2 units ..

but it seems the displacement of the soil is so high, it is about 800 mm while the maximum acceleration of input motion is 3.4 m/s2 or 0.34 g ,,,,,

and when I used another acceleration record in m/s2 directly without scaled value (because already in m/s2) I got so lower displacement it is 80 mm while the maximum acceleration 2 m/s2

- is it wrong to use scaled value to transform the multiplier?

best regards