Interaction between tiered cantilever retaining walls
Interaction between tiered cantilever retaining walls
(OP)
Hi all -
Long time listener, first time caller :)
I'm trying to find some advice / help / reference with respect to the attached problem, where the passive wedge asssociated with upper wall (Wall A) extends over the active wedge of the lower wall (Wall B). The design approach needs to be an Ultimate Limit State one. The uprights are timebr poles with the embedded portion encased in concrete. Upright spacing is at 1.2 metre centres.
Does anyone have any advice / reference sources etc etc
Do any of these options sound reasonable:
1. Designing Wall A as if wall B didn't exist (i.e. as a 4.8m high wall with 1 in 2.5 (v:h) toe slope. This would however require huge poles and big embedment depths
2. Look at what percentage of Pp is overlapping Pa and add this percentage of Pp into the loads applied to Wall B (say as a traffic load)
3. Treat the embedded portion of Wall A as a strip footing with applied load and look at how a Boussinesq type bulb would extend laterally from Wall A to Wall B, and add additional load to Wall B
Thanks in advance
Long time listener, first time caller :)
I'm trying to find some advice / help / reference with respect to the attached problem, where the passive wedge asssociated with upper wall (Wall A) extends over the active wedge of the lower wall (Wall B). The design approach needs to be an Ultimate Limit State one. The uprights are timebr poles with the embedded portion encased in concrete. Upright spacing is at 1.2 metre centres.
Does anyone have any advice / reference sources etc etc
Do any of these options sound reasonable:
1. Designing Wall A as if wall B didn't exist (i.e. as a 4.8m high wall with 1 in 2.5 (v:h) toe slope. This would however require huge poles and big embedment depths
2. Look at what percentage of Pp is overlapping Pa and add this percentage of Pp into the loads applied to Wall B (say as a traffic load)
3. Treat the embedded portion of Wall A as a strip footing with applied load and look at how a Boussinesq type bulb would extend laterally from Wall A to Wall B, and add additional load to Wall B
Thanks in advance





RE: Interaction between tiered cantilever retaining walls
RE: Interaction between tiered cantilever retaining walls
Also I would add a line or strip load to the loading of Wall B to account for the axial load of wall A. Check your embedment depths, usually we see buried depth that is about 1.2 to 1.4 times the exposed height.
RE: Interaction between tiered cantilever retaining walls
ka=0.333 & gamma = 16kN/m^3, so I calculate the active earth pressure for Wall A as 18.43kN per pole 0.5 x ka x gamma x height^2 x spacing). 18.43kN applied laterally to the top of Wall B with a lever arm of at least 3 metres will require some reasonable upgrading of pole size and embedment.
Ron - what is the worst condition?
Cheers
RE: Interaction between tiered cantilever retaining walls
EIT
RE: Interaction between tiered cantilever retaining walls
For the scenario attached, the following was calulated:
Pp = 0.5 x kp x gamma x Embedment^2 x spacing (138.24 kN per pole)
% of Pp that overlaps or extends beyond Wall b = 35%
Therefore, 48.4kN per pole additional load applied to Wall B.
Kp was simply taken as (1+sin30)/(1-sin30), so there was no cohesion component.
RE: Interaction between tiered cantilever retaining walls
RE: Interaction between tiered cantilever retaining walls
RE: Interaction between tiered cantilever retaining walls
EIT
RE: Interaction between tiered cantilever retaining walls
Kieran
RE: Interaction between tiered cantilever retaining walls
Has anyone tried the method as attached?
RE: Interaction between tiered cantilever retaining walls
FixedEarth - This seems to be slightly different than the method you proposed previously but I thought you have suggested the method as GNK attached. Any reason for using one or the other?
EIT
RE: Interaction between tiered cantilever retaining walls
I need to correct one assumption I made about the axial load caused by the upper wall. I believe the load path goes to the pole tip of the upper wall. We can then draw a 1:0.5 (V:H) and see where it intersects the lower wall. Not likely to be critical, but we also need to check for the global slope stability of the two wall system in static and if applicable in seismic region, the pseudo-static condition.
Given the generous setback distance between the two walls and the short exposed heights, I do not see it as very critical situation. By choosing embedded walls, you have eliminated a lot of additional analysis.
RE: Interaction between tiered cantilever retaining walls
We've already looked at static and seismic slope stability. Also, the timber uprights have been designed giving consideration to static and seismic loading.
Seismic loading does however raise another issue, being how the wall interaction occurs under seismic loading, but that's definitely starting to get into the realm of over-thinking the problem.
RE: Interaction between tiered cantilever retaining walls