Hi Eng-Tips:
A recent failure returned a consultant report. The failure on a typical bridge approach and the work was less than a year or two old. The consultant called the failure, "Shallow, sloughing failure" and told the contractor how to fix it. Contractor and consultant opined, "Well, of course it failed! We had four rain events in August!"
I'm the annoying fellow that then had to ask, "Just how many rain events did you consider in design?"
Well, I know the answer!
Returning to the original design, we captured the soil properties used in preliminary design. PHi=30, c=50. For the geometries, all was well in global stability. For the infinite slope equation (the form with cohesion), all was well, but. . .
When we considered seepage parallel to the slope, things went wonky. For top-down saturation to depth 18-inches, safety factor went to unity.
Bam! Just like the field observations.
So, to all - How many of you all set water filled tension cracks in infinite slope design? Cracks to what depth? We don't use cracks, we just make them consider a few feet of top-down saturation?
LA county requires 4 ft of top-down saturation!
Clearly, if it's free-draining embankment this is moot.
Seems to me, we are overlooking this area of slope stability and it's hitting our maintenance budgets!
f-d
ípapß gordo ainÆt no madre flaca!
A recent failure returned a consultant report. The failure on a typical bridge approach and the work was less than a year or two old. The consultant called the failure, "Shallow, sloughing failure" and told the contractor how to fix it. Contractor and consultant opined, "Well, of course it failed! We had four rain events in August!"
I'm the annoying fellow that then had to ask, "Just how many rain events did you consider in design?"
Well, I know the answer!
Returning to the original design, we captured the soil properties used in preliminary design. PHi=30, c=50. For the geometries, all was well in global stability. For the infinite slope equation (the form with cohesion), all was well, but. . .
When we considered seepage parallel to the slope, things went wonky. For top-down saturation to depth 18-inches, safety factor went to unity.
Bam! Just like the field observations.
So, to all - How many of you all set water filled tension cracks in infinite slope design? Cracks to what depth? We don't use cracks, we just make them consider a few feet of top-down saturation?
LA county requires 4 ft of top-down saturation!
Clearly, if it's free-draining embankment this is moot.
Seems to me, we are overlooking this area of slope stability and it's hitting our maintenance budgets!
f-d
ípapß gordo ainÆt no madre flaca!