plaxis 2d vs wallap

[JSD1986]

I use wallap and plaxis essentially all day at work. I often compare the two for shoring wall designs. Typically I find the two are in general agreement ie similar bending, shear, deflections. In my experience plaxis shows higher strut loads - maybe 10-15% more.

I have just run a model and the strut loads in plaxis are over double. It is very strange as the bending moment and deflections are essentially the same.

The specific situation is: 10m cut depth, 600 dia secant wall with a prop at the top ie a capping beam with cross stuts at 13m centres.

Its doing my head in as I can comprehend how the bending moment and deflections could be the same ie same load acting on the wall but the strut loads are different by a factor of 2.

Has anyone experienced this? Any ideas?

Anyone interesting in looking at both the wallap and plaxis files?

For those who are unsure the peak shear load is essentially the strut load.

 

[JSD1986]

Thanks for the input, its more like Soil: g=20kN/m3; f'=37º, delta=19º
- Surcharge: 15kPa
- 4m of hydrostatic.


We build the shoring systems to, so in reality im going to go a mid value range and put some strain gauges on the struts and have a contingency to add a second row of bracing.

The query was more around the fact that how can the moment and deflection results be essentially the same but the shear diagram different.

i would assert that the integral of shear is moment and if the moment is the same then the shear should be the same which they are not.

 

[HENRYZAU]

To OP, Plaxis is a true 2-D plane strain model while Wallap is a pseudo 2-D model or a subgrade reaction model; which option did you use in Wallap? with soil arching or not? Are you comparing the total strut load or per meter run in two programs? your excavation width? 13m is strut horizontal spacing?

 

[Retrograde]

What is your deflection at the strut elevation for each method?

 

[JSD1986]

Forgot about this thread.

The answer was - strut EI was a factor of 100 too high which threw more load in that direction.

 

[yakpol]

You can verify force in the strut as an initial slope of the moment diagram.

 

[EireChch]

Yakpol, can you explain that more?