Berms in Shoring design

[Doc08]

Anyone knows of a reference that addresses the subject of a berm in front of a retaining/shoring wall. How is it accounted for ? how to determine the required size of a berm to insure stability ? What is the effect on the passive resistance of the soil (Kp) ? (Kp) can account for slope in front of the wall but cannot account for the presence of a berm.

 

[DRC1]

Berms are usedin shoring design, although this was prevelent before tie backs. Prior to tiebacks, Rakers were used to support walls to install the raker a berm was left to suppport the wall.
The charts for Caraquot & Kerseill (in Pile buck as well as many other references have charts for negative slopes that will give you Kp. If your berm has a significantly wide flat top before it slopes off, a Cullmen's solution will give you a better answer.
I have used berms for walls, and they do not generateany where near as much passive pressure as level gruond.

Good Luck

 

[Doc08]

Thanks DRC1, I appreciate your response.

I am looking for a way to quantify the reduction in Kp due to the presence of a berm + a slope and from there translate that into an equivalent spring. The means to do that when a slope is present is indeed available through coulomb, caquot and keriesel, etc... but not for the berm.

There is a procedue described in Bowles and a similar one in the NAVFAC manual for a footing on a slope with or without a berm. This procedure produces reduced bearing capacity factors (Nc, Nq, Nq), which is allright. One of the required parameters is the ratio of the berm to the footing's width (b/B) and embedment depth to footing width (Df/B). In principle it looks as if I could apply this to a shoring problem but the difficulty lies in deciding on the width parameter (B) to be used in the formula. Perhaps one way would be to use an approach similar to what is used when calculating a factor of safety against a bearing capacity failure in front of the wall (e.g. terzaghi). It would be nice to have something else to compare and consider.

cheers.

 

[DRC1]

Bearing capacity is the shear restiance to a vertical load along a failure surface. I don't know if that would be applicable to a retaining wall. I would advocate either a traditional hand solution or again using the Cullman solution or trial wedge, find Pph and then find the triangular pressure distribution that yields that valure and solve for Kp.