Seismic design of retaining walls

[killswitchengage]

Hello my friends

I am conducting an analysis on the stability of a sheet pile wall under seismic conditions . the software indicates the resultant vertical force acting on the SSP is directed upward meaning the SSP is being lifted from the ground . Is this normal to you ? What should i do to remediate this issue , i am thinking of simply verifying the uplift bearing capacity of the wall .

thank you

 

[ATSE]

Your results are not normal.
If the wall-soil interface was frictionless, then the resultant would be horizontal (quick easy check).
Since you are checking seismic condition, I assume this is a permanent sheet pile wall.

 

[killswitchengage]

Yeah its permanent.
The soil profile consists of a heterogeneous fill 3 m deep underlying a sandy clayey layer and some silty clay to a depth of 8.8 m and then clayey shale with no carbonates all the way to 25 m. The shale is pretty bad and platy with 22° effective angle of friction and 14 kpa effective cohesion ( some passages are quiet stiff but mostly the shale is broken to pieces ) and the middle layer has very little cohesion no samples for testing were recuperated . Water table is at the foot of the slope.

At the front of the slope a building is being constructed and i have only have about 7 m of ROW ( as a matter of fact soil was cut for the building and since the slope started moving they gave way to those 7 m but its still moving )

 

[r13]

I suggest to double check on the software's user manual for interpretation of outputs.

 

[killswitchengage]

That i did , nowhere there is mention of such a case . Only commentary the software writes is : the wall is working on uplift -500 Kn/m.

 

[r13]

I've seen this before.

 

[killswitchengage]

Yea it should not be possible to get a negative resultant force

 

[r13]

It depends on where you get that reported negative force. On the wall, the applied load creates horizontal and downward components, then the reactive/resisting forces are horizontal and vertical as well, but with directions reversed. If the software assumes positive force pointing down, then after execution, it will report negative vertical force on the wall. Does the program includes friction of the wall? If so, you might want to turn that feature off.

 

[killswitchengage]

yea it does include friction of soil/wall interface as delta. I am not quiet convinced that a 11.8 soil active pressure could be below the passive pressure .

 

[r13]

Did you turn the feature off, or assign/override the default friction coefficient (set to zero).

 

[killswitchengage]

i am not at work right now but will try asap

 

[killswitchengage]

Hi i've changed the inclination to both active and passive pressures and it does make a difference as all resultant vertical forces are positive except in the case of seismic phase

 

[r13]

Can you provide the diagrams indicating the resultant forces/pressures?

 

[r13]

Does the program consider vertical inertia force? If it does, how it handles/report the effect?

 

[killswitchengage]

Thank you r13 for your active assistance
i have managed to find a solution to the problem , still the pile depth became 29 m instead of the 18 m that's enough for static situations
Does this make any sense ?

 

[ATSE]

Use different software or write your own spreadsheet. No software is better than bad software.
Surprisingly, the market has not produced a robust software package for complex retaining walls.
And I'm happy to be proved wrong on this point.
There's more than one software package that just can't handle anything but plain vanilla cantilever walls.

 

[r13]

I couldn't say it is making sense or not, as there are many unknown factors. I think it is the time to take another route, as suggested by ASTE, to check the accuracy of the program you are using.

 

[PEinc]

The soil profile consists of a heterogeneous fill 3 m deep underlying a sandy clayey layer and some silty clay to a depth of 8.8 m and then clayey shale with no carbonates all the way to 25 m. The shale is pretty bad and platy with 22° effective angle of friction and 14 kpa effective cohesion

I don't believe that you ever indicated the exposed height or retained soil height of the sheet pile wall. With clayey shale at 8.8 meters down, you could have serious trouble installing the SSP. Check the N-values and RQD's for the closest borings to see if SSP can be installed (if not already installed). Whether the pile depth is 18 or 29 meters, this is much lower than the 8.8 meter depth to shale. SSP cannot be driven through bedrock. Maybe you are designing the wrong type of wall.

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