How to calculate sheet pile deflection and ground settlement?

[neaveyoung]

Recently i'm doing a calculation involved the cantilever sheet pile for temporary earth retaining structure. Actually my excavation depth is 2 meter and the embedment depth is 2.1 meter. I get the max. bending moment =42 kNm/m. Now my question is how to get the:-
1) Lateral deflection.
2) Adjacent ground settlement.

Thanks.

 

[Doc08]

You can either utilize structural mechanics: model the sheet pile as a catilever loaded by a triangular load distribution with the point of fixity occuring about 0.5 to 1m below the dredge line (this would be a reasonable approximation), or simply use a computer program such as PYwall by Ensoft or LatPilePro by Tsoft.

 

[neaveyoung]

Thanks for your help. But can i get the free spread sheet? and i still finding how to calculate ground settlement caused by this temporary earth retaining structure. i refer the Braja M.Das -Principles of Geotechnical Engineering but there are no more example for me to refer.

 

[moe333]

A paper by Clough and O'Rourke “Construction Induced Movements of Insitu Walls” provides lateral and vertical settlement estimates adjacent to various types of retaining structures based on distance, soil type, wall stiffness, etc.

American Society of Civil Engineers (1990), Design and Performance of Earth Retaining Structures, Lambe & Hansen, ASCE Geotechnical Special Publication 25, “Construction Induced Movements of Insitu Walls.”

 

[vulcanhammer]

Most of the newer sheet pile programs (like SPW 911) calculate deflection of sheet pile walls, cantilever and anchored alike.

http://www.vulcanhammer.net

http://www.vulcanhammer.info

 

[DRC1]

Bowles as well as several other references (see the US Steel Sheetpiling manual on Slideruleera's website) dicuss deflection and settlement. As a rough approximation I have done as doc08 suggests. For settlement in a granular material, AS AN APPROXIMATION, you can calculate the area of a trianle behind the sheet with a back slope equal to phi. Then calculate the area of the deflected shape and the orginal vertical line. Reduce the first area by the second area and recompute your new height. The difference between this and the orginal ground is your settlement. I will be the first to tell you there are better methods in the cited texts.

 

[neaveyoung]

Could you draw out the diagrams? because i'm still not very clear about the first area, second area as well as back slope equal to phi. Thanks.

 

[DRC1]

I don't have access to a scanner right now. Let me try to explain again, and if it is still not clear, let me know and I will figure out how to attach a sketch.

The basic principle is simple. Actually too simple as the actual response is much more complicated, but it gives a good approximation.

A failure plane will develop in the retained soil that will start at the sheet where it meets the limit of excavation (the dredge line or mud line) This extends upward to the surface at angle equal to phi (the friction angle of the soil) from the horizontal. This is the failure plane. Compute the volume of the triangle formed by the vertical (undeflected) sheeting line, the top of ground and the failure plane.

Next computed the deflected shape of the sheet. Now draw a straight vertical line from the point of zero deflection and a horizontal line between the top of the deflected sheet and the vertical line. The vertical line represents the undeflected sheet and the horizontal line is the top of ground for the deflected sheet. Compute the area between these three lines.

Okay the first area represents the the volume of soil retained between the wall and the failure plane prior to movement. As the wall deflects, the wedge of soil will move down the failure plane, filling the deflected shape. Thus if we recompute the area bounded by the failure plane and the vertical (undeflected) sheet, we will find it has been reduced by the area required to compute the deflected shape. Knowing the value of the reduced area between the vertical line and the failure plane we can compute the reduced height of the triangle. The difference between the orginal height and the reduced height is your settlement.

Any Questions? Great! Clear as Mud? Thought so. Let me know if you followed this.