AASHTO Nongravity Cantilevered Walls - Soldier Piles w/ Timber Lagging Embedded in Rock 1

[WBell]

I am developing a MathCAD worksheet to provide a design check for temporary shoring using soldier piles and timber lagging. I have a copy of AASHTO 2010 and would like to develop the solution for the configuration shown in Figure 3.11.5.6-2, which is for a discrete vertical wall element embedded in rock (see attachment).
The free body diagram shown in the figure shows the earth pressure distributions above and below the dredge line and the resultant forces, which I am able to use for the solution of the embedment depth, D; however, there is a force, F shown at the base of the rock socket which is defined in the spec. as "force at base of nongravity cantilevered wall required to provide force equilibrium (kip/ft)", which can be solved for, but I am not sure how to evaluate the capacity of the rock socket to safely distribute the force into the surrounding material, which in this case is the rock.

Your comments and suggestions are appreciated.

 

[r13]

required to provide force equilibrium

Doesn't that mean "sum forces and moment at the bottom equal to zero"?

 

[BridgeSmith]

I had the same dilemma the first time I used the diagram for a design. It turns out that the force "F" doesn't actually exist. It's only there to make the numbers work for the model. The method itself is a simplified linear approximation of a non-linear analysis, so as I understand it, it never works out where the forces and moments can both be in equilibrium at the same time.

It's as retired13 alluded to - you find the embedment depth where the sum of the moments equals zero, and you add a force at the point where you summed the moments in order to satisfy the sum of the forces equal to zero.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[PEinc]

Read about Wayne C. Teng's Simplified Method for cantilevered sheeting on Page 359 in Foundation Design, 1962. Teng calls the force "C" and calculates the overturning moment about the tip of the sheeting where he applies the force. Therefore, C does not enter into the moment calculation.

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