sheet pile retaining wall to resist guardrail impact load

huangyhg

sheet pile retaining wall to resist guardrail impact load
we are designing a steel sheet pile retaining wall that will be used as temporary shoring for construction of a bridge foundation, during which it will retain about a 6 ft. depth of cut. it will be left in place after construction is complete and will then serve as a permanent retaining wall to retain about 3 ft. of soil with an existing roadway directly adjacent to the top of the wall.
we need to provide guardrail, either with ground mounted posts directly in front of the wall (like less than 1 foot away), or mounted directly to the sheet piling. which of these two options we go with will be dictated by how much room we ultimately have.
for the second case above we plan to design a concrete cap that will encase the top of the exposed sheeting and mount the guardrail to this, and use a 10 kip design load applied to the top of the post, per aashto std. specs. for highway bridges.
for either case, in the permanent wall condition i would appreciate any thoughts or suggestions on what effective length (horizontal) of the sheet piling can be used in design for resisting the impact load transferred from the post. i.e. what equivalent line load can be used for designing the sheet piling? aashto has some numbers to use for distributing impact loads to concrete walls, but nothing for steel sheeting.
thanks in advance for your help.
due to having a rigid concrete cap, the effective area of the sheet pile to resist the force will be more that not having a cap at all.
the conservative approach will be-
the load tends to travel at 45 degrees from the origin. so, consider twice the depth of the cap as the effective width at the top of the piling just below the cap. from here on, you can again apply the 45 degree formula to calculate the effective with at the bottom of the piling.
all these assumung that you have enough embedment of the piling in the soil to resist the 10 kips thrust!
if it is a reinforced cap, i would tend to use more like 5 times the width of the cap plus impact width.
csd