Road settlement
Road settlement
(OP)
is there any method to find the settlements occur on roads constructed on reclaimed land areas (i.e Ports) and the compaction depth required for a heavy vehicle road when preparing the subgrade of the road? most of the pavement design methods doesn't explain it deeply. please can anyone help me since i'm in a tight situation..





RE: Road settlement
Traffic loads can cause additional compaction, but that influence is usually only in the upper 12 to 18 inches.
Traditional pavement design methods still apply; however, I would suggest elastic layer analysis down to the point of your potentially compressible layer.
You need to consider a higher modulus material as your fill, in order to "bridge" the softer soils. Unfortunately higher modulus usually means greater compaction and higher unit weights. To counteract this, I have specified cellular concrete fill, which has a unit weight of about half that of soil, for such applications. I designed a truck haul road for a paper mill over a reclaimed swamp area about 20 years ago. Worked fine. Also designed a high modulus fill without reduced weight for a similar application but almost all car traffic for a municipal street, about 25 years ago. Both lasted at least their anticipated design lives.
I used a conventional flexible pavement section for both applications, above the high modulus fill.
RE: Road settlement
it is necessary to provide proof that the road will get deformed due to the traffic. i tried using the Westergaard's formula to find the stress variation due to traffic. the results were that up to 0.5m the stresses are high and from then onwards the stresses are not that high.
RE: Road settlement
Your Westergaard analysis is as expected. Pavement loads dissipate quickly with depth.
RE: Road settlement
A couple of things - make sure you have some drainage provisions - the dredged sand will be wet and will want to drain when placed unless it has "lost" its moisture during transport, etc.
Secondly, and assuming that the placed fills are wholly or partly above the existing ground, the outer perimeters of the dredged sand layers need to be of a material that will help confine the dredged sand if the sand has a potential to "run". I have seen "clay' being used but the problem with this, unless you have some drainage holes through it, that the clay will act making the structure act as a bathtub which raises the groundwater level within the fills. I had wanted to use prefabricated wick drains laid horizontally to act as rainwater infiltration outlets through the clay confining zone but client and engineer didn't see the need. Time will tell, I guess.
On compaction, with dredged sand, think of checking the compaction of the previous lift rather than the lift you are placing as an acceptance criterion.
Another "toy" that might be considered is to mix in a couple of percent cement in the compacted sand layer - to increase the strength for the heavy loads. Mixing it with sand and a farm harrow is easily done as we did with a mix of fly ash and sand.
RE: Road settlement
RE: Road settlement
RE: Road settlement
As for settlement calculations, you can use Boussinesq method or the simple 60 degree approximation method. The Atterberg tests will give you liquid limit value and this will enable you to approximate Cc which wil give you settlement magnitude.
I have seen few failed pavements, they are not pretty nor are they cheap to fix.
RE: Road settlement
Sand compression (elastic) will occur quickly, as already mentioned. That said, whatever you would calculate using the "gravity turn on" approach, I'd consider an additional 20 percent of this value to occur after the initial compression. Duncan's settlement manual (Virginia Tech CGPR) gives parameters for long-term compression of granular soils.
I agree that the traffic loading is moot below 2 ft or so. That said, if the soils below 2 ft are weak, you'll have a heck of a time actually getting specified compaction. Geotextile and open-graded aggregate may be needed to get a firm-enough base for specified compaction.
All posts above represent good advice, just don't want to retype what's already been credited to the knowledgable.
f-d
¡papá gordo ain't no madre flaca!
RE: Road settlement
Can more info on the site situation be presented to help clarify this part?
RE: Road settlement