Waiting period for MSE walls
Waiting period for MSE walls
(OP)
I understand that in some states they allow MSE designs with a bearing pressure greater than the bearing capacity, IF the contract agrees to build the wall to a height where the pressure and capcity are equal and then wait 30 days. From what I understand the assumed capacity is then increased by the weight of the material that was placed in stage 1 allowing the new overall bearing capacity to accomodate stage 2 or even stage 3 of wall height.
Has anyone else heard of this process?
Does this process make sense, if so why?
Thanks!
Has anyone else heard of this process?
Does this process make sense, if so why?
Thanks!





RE: Waiting period for MSE walls
What doesn't make sense if the notion of bearing capacity related to MSE walls. Fundamental to the design of MSE walls is internal, external and global stability. You must show appropriate safety factors for these three failure modes at the instant of completion. Global stability is actually the purer form of bearing capacity. I mean what process is used to determine the "bearing capacity" of an MSE wall? You can't use the typical rational equations, 'cause they are based on boundary conditons that are not available on the MSE wall. Would you use "L" as the foundation width (i.e., the length of the reinforcement strips)? O.K. that'd be fine. Would you use the equations for an infinitly long footing? O.k. that makes sense too. What's your depth of burial? 20 ft on one side and zero feet on the other (e.g., for a 20 ft tall MSE)?
I don't buy it. Terzaghi's equiations (Meyerhof?) just don't fit the boundary conditons. Why force the square peg into the round hole?
f-d
¡papá gordo ain’t no madre flaca!
RE: Waiting period for MSE walls
RE: Waiting period for MSE walls
I tend to agree with fattdad on MSE wall bearing capacity but that is a long discussion. Regardless of method, there can be short term and long term strength characteristics to deal with soft foundations and constructing a wall too fast has the same problem as constructing a levee too fast and risking a quick foundation failure on a soft foundation. The concept is pretty basic and piezometers are usually installed to measure pore pressures and allow the surcharge to continue when the pressures stabilize.
This method may be overdone at times as I have seen it prescribed without piezometer monitoring and as just a "wait 30 days" criteria. Some of the foundation soils do not appear to be that sensitive in my opinion but it is a conservative way to avoid a possible situation without doing all the work necessary to define the problem. Just the way it goes in real life occasionally.