Design of Retaining Wall.
Design of Retaining Wall.
(OP)
I have a retaining wall located in front of the sheet piles as shown in the attached PDF, how much soil/lateral pressure do I consider in designing the retaining wall? To the point, how do I design the retaining walls? The sheet piles are already existing.






RE: Design of Retaining Wall.
RE: Design of Retaining Wall.
If you refer to the sketch, the client would like to raise the ground level in front of the existing sheet pile. The retaining wall is there to retain the backfill between the front of the sheet pile and back of the retaining wall (distance x as indicated in the sketch). FYI, sheet piles were designed to retain the soil behind.
RE: Design of Retaining Wall.
Don Phillips
http://worthingtonengineering.com
RE: Design of Retaining Wall.
Thus, when your pressure "line" intersects the face of the existing sheet piling, there really isn't any physical intersection. Thought of another way - use a differnet horizontal scale for your pressure diagram and you could conceivably have a full triangular load to the bottom within the space between the walls.
Another way to think about this is that lateral earth pressure is similar to the lateral pressure of water in a vessle....only soil creates lateral pressure about 0.33 times the vertical soil weight while water is 1:1. Suppose you had the space filled with water. The lateral water pressure would be higher at the bottom than 1 foot off the bottom, despite the sheet pile wall behind.
RE: Design of Retaining Wall.
Second, keep in mind that the stiffest element ends up attracting the load, therefore it would be wise to design the concrete wall without considering this comparatively flexible sheeting as a limiter for active soil pressure behind the concrete wall. Passive pressure between the sheeting and concrete wall will be required to stabilize the sheeting regardless.
Since the development of passive soil pressure is roughly 3 times that of active soil pressure, one could argue that the passive zones needed in front of the sheeting would simply serve to transfer the active pressure to the stiffer concrete wall over time.
RE: Design of Retaining Wall.
I think also to get a feel of the problem physical dimensions should be included in your layout so that we may have a feel of the size of the job and the sort of soil conditions e.g. sand or granualar filling and perhaps clay backfill against the sheet piles ?
RE: Design of Retaining Wall.
Most of what you mentioned, I agree. However, refer to my sketch, you see the failure wedge line defines how much x distance is required to get full lateral pressure. There is difference between water and soil. Water is frictionless, however, soil is not (except some frictionless soil). In my case phi is around 30 degree. I am very positive that if the x distance is very less, the retaining wall will not see full lateral pressure (based on triangular diagram - Ka*gamma*H). I am trying to find H1 (H2 > H1 in my case) based on failure wedge line in respect to x distance (however, there is not failure wedge in case of water). The weight of the soil above the failure wedge line detects the soil lateral pressure. If x very less than H (height of retaining wall), I am not sure if the retaining wall will see the full lateral pressure.
RE: Design of Retaining Wall.
RE: Design of Retaining Wall.
I'm not suggesting that the earth pressure isn't less. What your diagram indicated, and what I was questioning, was that the intersection of your lateral stress line and the sheet piling indicated the point at which the lateral pressure becomes constant below that intersection.
I don't believe it does simply for the fact that your stress line was drawn based upon an arbitrary horizontal scale and thus the intersection is an arbitrary point in space and has no relevence.
I agree that with a smaller gap between the walls that intuitively the soil pressure would be less than with no sheet piling there. I just don't know how it is affected and KBVT's suggestion to get a geotech involved might be a good step.