Xuyan Liu's Communities Activities

Safety analysis: failure mechanism slope stability with high load on crest

Xuyan Liu — Wed, 29 Nov 2023 11:32:58 GMT

Hey!

I'm running a slope stability check in Plaxis 2D and got a bit confused how Plaxis works to find the failure surface.

I have a slope 1:2 inclination and distributed load is applied slightly away from the crest of 57 kPa. First we tried it in Geosuite stability and got a circular failure surface like this. The slip surface is circular and overlaps with the line load for only a small distance.

Then I tried in Plaxis 2D with Hardening soil model and got failure surface like this.

The surface in Plaxis is quite different from the one returned by Geosuite and it seems like the failure surface of slope stability problem reached into the failure surface of bearing capacity problem. The slip surface includes the entire distance of the line load.

When I reduced the load to 20 kPa in Plaxis, the failure surface looks like this

So I'm wondering how Safety analysis in Plaxis is conducted? Does it consider different failure mechanisms at the same time and concluded on the most critical slip surface, instead of considering only slope stability? As in different failure mechanisms are not considered independently?

Thanks a lot for help!

Plate forces output results Qmax,Qmin,Q?

Xuyan Liu — Wed, 15 Nov 2023 13:49:20 GMT

Hi everyone,

I'm looking at output variables for plate element. There is Qmin,Qmax,Q (same for N,M), corresponding to in python manual Q_envelopmin2D,Q_envelopemax2D, Q2D. I'm a bit unsure about what Qmax and Qmin are. Anyone has an explaination to the difference between them? Thanks a lot!

How to input geogrid material properties in Plaxis

Xuyan Liu — Mon, 30 Oct 2023 11:16:21 GMT

Hey folks!

I'm thinking to use geogrid to model geosynthetic in my Plaxis and am a bit unsure how to create geogrid material model. I'm looking at Miragrid GX 110/30 with manufacturing info as below. I'd like to include the long term effect of the material (as in degrade/weakened over time). So I'm guessing elastic model would not be ideal. Could anyone share a thought how I can use the info from the manufacturer in Plaxis for geogrid? Thanks a lot in advance!

Plaxis geogrid result weird

Xuyan Liu — Mon, 30 Oct 2023 15:09:22 GMT

Hey folks!

I've read a bit in (+) Geogrids as a soil reinforcement? Modelling in PLAXIS? - GeoStudio | PLAXIS Forum - GeoStudio | PLAXIS - Bentley Communities regarding the geogrid. But I still couldn't manage to have a reasonable result.

I have my geogrid in orange color and the interface is not using any strength reduction (Rinter=1). The geogrid is about 500 mm above the dark grey concrete pillers. No boundary conditions given to the geogrid it self (no tutorials apply boundary conditions on geogrid). Updated mesh is selected.

But when I checked my result, the settlement of the soil is not much reduced and the axial force of the geogrid is weird.

Material properties for geogrid is

I'm not sure what's done wrong here. Anyone has a clue or suggestion? Thanks a lot!

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Mon, 30 Oct 2023 15:09:24 GMT

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N2N anchor-plate connection

Xuyan Liu — Wed, 18 Oct 2023 14:10:13 GMT

Hey guys!

I'm wondering about the connection between a N2N anchor and a plate, if it is automatically created as rigid. If you see the red circle part, that the connection between my strut and sheet pile wall and they will be in reality welded together. So I want to model this welded connection in Plx as well. Is this automatic in Plx to set the connection between the N2N anchor and the plate elements to be rigid? (I read in manual that between N2N anchor and embedded beam, it's automatic) Or do I need to use a "Connection" element to model the welding myself? But it doesn't let me to create a connection between N2N anchor and plate.

Thanks a lot for help!

Equivalent length for FE anchor and N2N anchor

Xuyan Liu — Tue, 17 Oct 2023 08:38:37 GMT

Hey!

I've always been a bit confused about how to set the equivalent length of FE and N2N anchors.

What I understand by far is that a FE anchor usually used when it's symmetrical excavation and the equivalent length is half of the excavation length. While a N2N anchor can be used to as an alternative when the structure is supported in multiple directions and the equivalent length of the N2N anchor needs to be adjusted accordingly. Is this correct?

Does it mean, if I have a non-symmetrical excavation, for example in the figure below, I should use N2N anchor instead of FE anchor (or is it possible to use FE anchor as well)? And for this N2N anchor, I don't need to consider anything regarding equivalent length?

Thanks a lot for help!

Plaxis python get maximum Utot for a plate

Xuyan Liu — Mon, 02 Oct 2023 13:44:56 GMT

Hey,

I'm following the script in (+) Output scripting example: get maximum bending moment - GeoStudio | PLAXIS Wiki - GeoStudio | PLAXIS - Bentley Communities to get maximum total displacement of the plate. The script I use is here

x_left=32

IDsSLS=[]
UtotSLS=[]
Mmax2SLS=[]
Mmin2SLS=[]

IDsULS=[]
UtotULS=[]
Mmax2ULS=[]
Mmin2ULS=[]

xy=[g_o.Phases[4]]
# for all phases, starting from the second phase (Phase_1)
for phase in xy:
#initialize defaults:
maxM = 0.0
xAtMaxM = 0.0
yAtMaxM = 0.0
minM = 0.0
xAtMinM = 0.0
yAtMinM = 0.0

# obtain result tables
plateX = g_o.getresults(phase, g_o.ResultTypes.Plate.X, 'node')
plateY = g_o.getresults(phase, g_o.ResultTypes.Plate.Y, 'node')
plateUtot = g_o.getresults(phase, g_o.ResultTypes.Plate.Utot, 'node')
#print(len(plateX))

# determine minimum and maximum bending moment:
for x, y, M, Utot in zip(plateX, plateY, plateM,plateUtot):
#is it on the left wall (with small numerical tolerance)?
if abs(x - x_left) < 1E-5:
if Utot > maxUtot:
maxUtot = Utot*100
xAtMaxUtot = x
yAtMaxUtot = y
if Utot < minUtot:
minUtot = Utot*100
xAtMinUtot = x
yAtMinUtot = y

if phase.InputSettings.LoadingType=="TotalMultipliers":
IDsULS.append(phase.Identification)
UtotULS.append(maxUtot)
Mmin2ULS.append(minM)
else:
IDsSLS.append(phase.Identification)
UtotSLS.append(maxUtot)
Mmin2SLS.append(minM)

print( "{}: ".format( phase.Name ) +
"Utotmax = {:.5f} cm at Y={:.5f} m; ".format(maxUtot, yAtMaxUtot) +
"Utotmin = {:.5f} cm at Y={:.5f} m".format(minUtot, yAtMinUtot) )

But when I compare what I got from the script and what's in Plx output, some numbers are not the same. Script returns max.Utot is 0.0010244 m but Plx output is 1.198e-3. I'm not sure what's wrong in my code here?

Thanks a lot for help!

Plaxis snaplinear is not working

Xuyan Liu — Sun, 01 Oct 2023 15:04:45 GMT

Hi guys,

I'm trying to create geometry in python and it's not exactly standard rectangles or anything. So when I add points to the lines, the point may not be accurately sitting on the line (not snap to the line) if I use python to create points with coordinates (e.g., x=0.324453,y=9.87089). So I hope to use command snaplinear to snap the point to the line. And I tested with reference script

# Alternative 1
point_g = g_i.point(0, 0)
# Creates multiple objects, the last one is the Line object ([-1])
line_g = g_i.line((0.001, 0), (1, 1))[-1]

g_i.snaplinear(point_g, line_g)

But it doesn't seem to snap the point to the line. Did I misunderstand the command or? If I'm looking at the wrong command, which command should I use then to snap points to the line?

Thanks a lot for help in advance!

Quick way of export Mstage or Msf plot or data?

Xuyan Liu — Mon, 02 Oct 2023 05:47:51 GMT

Hi guys,

I'm trying to export Mstage and Msf plots from Plx using Python. The one way I've found on forum is

step=[]

Msf=[]

plt.figure()

for phase in MsfPhases:

step_x=[]

Msf_x=[]

for c,s in enumerate(phase.Steps[::10]):

step_x.append(c)

Msf_x.append(s.Reached.SumMsf.value)

plt.plot(step_x,Msf_x,label=phase.Identification)

step.append(step_x)

Msf.append(Msf_x)

But this is super slow. I see that there's been similar questions posted on forum from earlier. So I'm wondering a few things:

1. I haven't found any way we can use python command (e.g. _tabulate or _getresults) to get the Msf-table. Is there a python command to get the table directly in python instead of copy-paste to Excel?

2. Or is there any python command to generate the Msf-plot (similar to g_i.structureplot, g_i.plot) and export/save the plot afterwards?

I guess either of these two methods would be much faster than the code above.

Thanks a lot for help!

Prestress on N2N anchor

Xuyan Liu — Tue, 26 Sep 2023 15:59:04 GMT

Hey guys,

I'm currently running a simulation where the sheet pile wall is anchored by -2.5 m below the terrain. The soil geometry is imported from AutoCAD.dxf file. The anchor props. are Elastic, Lspacing=4, EA=294000kN.

and I apply a prestress of +100 kN (in tension).

1. The stage where the anchor is activated with pretension does not run through. (It worked fine without prestress). Then I check the output, the deformation of the anchor is super weird, it got compressed.

I'm a bit uncertain what's going on. I thought maybe +100kN was compressive prestress and I changed it to -100kN, but still it won't run through. Anyone knows where I got it wrong?

2. If in the actual project, each anchor will have 10 kN prestress, and I have Lspacing=4 in Plx, what prestress should I apply? 10kN or 40 kN or 2.5kN?

3. Does N2N anchor have to be used together with grout or other stuff? Can I just simply use a N2N anchor and fix its anchored end as shown in the picture?

4. Regarding fail message for anchoring stage, sometimes it is load advancement sometimes it is soil collapse. I've read on Plx forum that it can be numerical issue and I adjust the numerical setting as given in (+) Pre-stressed anchors - GeoStudio | PLAXIS Forum - GeoStudio | PLAXIS - Bentley Communities. But it didn't work when prestress is increased higher to 100 kN (worked when it was 50 kN). What could be other reason that my achnor can'r be prestressed?

Thank you very much for help!

Python scripting: interfaces got split in stages, how do I activate selected interfaces?

Xuyan Liu — Wed, 20 Sep 2023 10:57:35 GMT

Hey guys,

I'm now working on a small case where a plate in inserted in two layers of soil. The soil and plate models are also imported from .dxf file.

The plate is imported as a whole line and I created the plate as well as the interfaces as a whole line, in the script below:

The plate and the interfaces are stored in their own list "plates[]" and "posinterfaces[]"/"neginterfaces[]". But when it comes to the staged construction, the plate and interfaces are split by the soil layer

I can't really use the posinterfaces[] or plates[] to activate the plate and the interfaces, as shown in the script here. Instead, I have to use the two commented lines to activate the plate and the interfaces.

Got two questions here:

1. How can I use the plate[] and posinterfaces[] lists that I create myself to activate these elements in the staged construction? Do I have to use g_i.Plates? Or is there a smarter way to realise what I want here? The reason I want to use self-created lists is such that I can activate only the elements I want to activate without having to know their id in g_i.Plates when there are more plates in the model (the example I show here is very simple). Say, if I have two plates, then I know the order they are saved in my list "plates[]". But if I have to use g_i.Plates, I'll have to first know which is saved in which g_i.Plates[1?2?...]

2. Didn't find in the mannual how can I activate for example only positive interfaces? Because if I use g_i.Interfaces, it's all interfaces. Is there anything like g_i.PosInterfaces?

Thanks a lot in advance!

Plaxis python tool failed to run

Xuyan Liu — Sat, 16 Sep 2023 13:47:32 GMT

Hi guys,

I'm trying to open the scripting reference or python interpreter in Plaxis (both 2D and 3D). But I got error message

and then my plaxis would just show

Any one could figure out what is it? I've used python scripting before with plaxis with other version of Plx and different laptop and had no problem. Does it have anything to do with the installation or? Thanks a lot for help in advance!

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Sat, 16 Sep 2023 02:33:45 GMT

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