Deadman Design for sloped anchor 1

[RFreund]

This is a two part question:

Part 1 is generic - how would you design the attached deadman.
Part 2 should the passive resistance of a deadman anchor be only the hieght of the pressure diaphragm that is equal to the height of the anchor or should you use the entire height of the pressure diaphragm?

Background:
This is an anchor for an erosion control mat that utilizes tendons.

Thank you in advanced.

EIT

 

[RFreund]

I really should have named this Deadman for Erosion Control. It may have been a more attractive topic.

EIT

 

[RFreund]

Ok, what about this question:

For a deadman anchor, bowels appears to use the resistance of the full passive pressure:
F=0.5*Pp*g*d^2
shouldn't the resistance be:
F=Pp*g*d*h

Where d is the depth to the bottom of the anchor and h is the height of the anchor?


EIT

 

[PEinc]

No. The first equation is the total net passive pressure per LF of deadman width. Pp should actually be (Kp-Ka). The second equation is only the magnitude of the net passive pressure at a depth of d (below OG) times some undefined anchor height, h. I never saw this used for design.

F = 0.5*Pp*g*d^2 = 0.5 x d x (Pp x gamma x d) = the area of the net passive pressure triangular distribution = net passive pressure per LF of deadman width.

http://www.PeirceEngineering.com

 

[RFreund]

Thanks for the response.

I think I may have confused some variables in my questions so I have attached a sketch to clarify.

I agree that there is passive and active however I have not shown the active. Also yes these equations are per linear foot. Can you look at the sketch and see if you think Eqn 1 or Eqn 2 is correct?

Also when you say you have never seen this used for design are you referring to the deadman equations? If so what design equations are typically used? This appears to be the equations given by Bowels who does say that there are some more complex equations given in the USS sheet piling design manual but that they may not be warranted as the precision is not that much better.

EIT

 

[PEinc]

I have never seen anyone design a deadman using the 2nd equation in your third posting above or the first equation in your fourth posting. I have always used the second equation in your fourth posting. Pp = 1/2 x gamma x Kp x d^2

http://www.PeirceEngineering.com

 

[RFreund]

Ok, I guess it makes sense to use the 'full depth' of the pressure diagram because you have the full weight of that mass of soil.

Thanks again.

EIT

 

[PEinc]

I also check for bearing of the deadman load against the deadman itself. Because you may have a high passive resistance available due to great deadman depth, you don't want to have too high of a bearing pressure on the deadman. You don't want to have a small deadman punch horizontally through the soil.

http://www.PeirceEngineering.com

 

[RFreund]

Yes thanks good point. I was going to ask that in my previous post but I figured it would be a good check anyway.

Any thoughts on my original post regarding the deadman being pulled out at an angle toward the surface?

EIT

 

[PEinc]

I never installed or designed a deadman that was pulled at an upward angle. I probably would look at the vertical and horizontal components as you did. Vertical would be resisted by the deadman weight and soil overburden.

http://www.PeirceEngineering.com