Tolerable Settlement of Pavement 1

[jpoha]

I have a roadway project in which subsurface soils included fill over organic soils over sand and gravel. Settlement from the organic soils has been calculated.

What are typical total and differential settlements that should be designed for? Different portions of the site will be preloaded, some will not. I want to recommend a hold time, in which settlements are allowed to occur under the new embankments before final paving.

 

[iandig]

It all depends on which specificaton you are working to.
Values are provided within the Specification for Highway Works (UK), as to the acceptble tolerences on a finished carriageway during construction. Once a pavement has been completed it should be periodically checked for compliance.
During the road pavement assessment, ruts or permenant deformation that exceeds 25mm is deemed to have caused a failure, however part of the assessment will be to determine where this failure has occured, i.e. in the flexible pavment material, sub-base or sub-grade.
Typically it is accepted that flexible pavements can take more deformation than structures, and often structures will have very generic total and differential settlement criteria, i.e. max 25mm total, less than 1:500 differential. If you base your design on these parameters then it should form a good starting point for the pavement.
Pavment design is based around using the actual values to come up with a design which meets the long-term requirements, and more and more the basis for this design looks at the effect of repeat loading as opposed to genereic strength/settlement testing. To be able to complete the design, you will need to know things like design life, MSA, etc..., it is not as straight forward as it first sounds and just looking at total allowable settlement may not provide a comprehensive design.

 

[BigH]

iandig - you are right to a degree. What you are discussing is the pavement crust details. What jpoha wishes to know is about short/medium/long term settlements of the pavement due to the settlements of the underlying embankment foundation - it is a question I asked several months ago. Basically, with embankments on soft soils that will settle under embankment loadings, it will be neigh on impossible to predict uniformity. We are building on such and even after a year, we are getting undulations - not due to heavy traffic (although there is some of that) but due to to the basal soils non-uniformly settling. It feels, at times, like a miniature roller coaster - ants would think so at least! Look up the previous post for some answers/points.