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Modeling a Soldier Pile Wall with Raker Support

Modeling a Soldier Pile Wall with Raker Support

(OP)
Hi, I'm designing a soldier pile wall with raker support for a temporary 4m excavation in a medium dense silty sand (phi=30, c=0) using SAP2000 FEA software. The wide flange IPB section piles are to be buried in 1.0m height, 0.8m diameter cast in place reinforced piles below dredge line and the rakers are pinned UNP sections resting on 1m by 1m square footings of 0.5m height. Piles are to be placed with 3.0m spacing (Attached drawing).

I use Coloumb's theory for calculating lateral earth pressure diagram on piles, their concrete footings and the square footing that rakers rest on, as suggested by USS Steel Sheet Piling Design Manual, 1984. I use pined support at the button of each pile, assuming that it is the point of fixity of piles, (not sure if I'm doing it right though) and I use a rolled support in horizontal direction at the end of rakers, simulating square footing behavior, I then apply the resultant force of active, passive and friction force acting on square footing to this support in that direction (Attached drawing, The units shown are of KN and m).

1- Is there anything wrong about my assumptions on modeling the whole system or the soil pressure diagram?

2- I can find the required length of cast in place concrete pile below dredge line by simply doing external stability analysis, by taking moment of acting forces, including piles weight and their skin friction, about raker's resting point and putting M-R=M_D and solving for required depth of embedment of piles... but the question is, how can I find the point of fixity to put pinned support in my model? Does simply assuming that the pile is rotating about it's tail is a rational decision for you?

3- Does assuming a horizontal rolled support in rakers resting point and applying resultant horizontal forces on the square footing in that direction is a right procedure? If so, how do you think I can calculate the frictional horizontal force below square footing, without knowing exact vertical loading acting on it?

Unfortunately there is no thorough documentation about modeling raker supported soldier pile walls and many books just simply mention this type of supports without much talking about their behavior or design procedure or even about lateral earth pressure diagrams acting on them, so I will be thankful to you if you could help me complete designing my model.

RE: Modeling a Soldier Pile Wall with Raker Support

1) Look for Tergahzi and Peck's Apparent pressure diagrams for propped walls. It has been tested in the field and has produced more accurate results regarding the actual pressure seen by flexible walls.
2) The point of zero moment below the dredge line is where I would be placing the pinned support for the model. The canadian foundation engineering manual has information on determine that point for flexible cantilevered walls.
3) My feeling is your raker footing may be undersized. I neglect friction and only rely on passive pressures to restrain the raker.

Keep in mind the extreme uplift that is induced into your soldier piles from the raker. Your 1m deep plug likely won't have enough restraint. I know it seems odd to picture the soldier coming out of the ground but when you perform the force balance of the system the uplift is there.

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