Flexible Pavement - Uniform Load

[balochile]

I have been asked to perform some pavement capacity calculations at a Port in Australia.

The majority of pavements are on reclaimed land, with the pavement consisting of dredged sand placed over a layer stiff clay with an asphalt wearing course.

I am able to ascertain capacities for wheel loads as there is an abundance of literature from the road construction industry.

However the port handles a large quantity of bulk cargoes which are stockpiled on the pavement. Some of this material is quite dense (eg Mineral Sands with density of 2.5t/m3). I need to calculate the maximum stockpile height allowable for the different cargo densities. Unfortunately I cannot locate much information on the effect of this type of load on flexible pavements.

My initial impression is that stockpiling of material on the pavement will not cause failure but rather excessive settlement of the pavement.

Does anyone have any idea of the methodology for this type of analysis or who can refer me to any relevant literature.

 

[ishvaaag]

If the containers come there on wheels certainly the amount of them that need be stockpiled before attaining the local solicitations appearing under the wheel sets that the trucks carrying them will develop will be big.

So you have a foundation problem more than a pavement problem. You need to investigate the allowable compressive strength for the wanted plan loads at the surface, on which a limit to the short and long term settlements will have a say.

For the overall settlements the whole array of the stockpiled containers need be considered. The elastic part you may analyze like a set of flexible footings on two layers of soil, in Boussinesq-like way. Then you can use the part affecting the clays to see what midterm and longterm settlements can be expected.

If the thickness of the sand layer is small and such layer is itself competent, you may pass your loads by a 1/2 rule expansion or so to the underlying clay layer and use just such layer for all these analyses, which may be convenient. This of course assumes the sand layer won't be controlling the strength, and that given its small thickness the sand layer won't affect much settlement.

 

[BigH]

Good points, again, by ishvaaag. Balochile - just a thought, why not use roller compacted concrete for the pavement. I understand that they are using this quite a bit in new/rehab port construction rather than asphalt. Still have to respond to storage problems, but the RCC should give better longer term performance.

 

[Focht3]

I've dealt with a similar problem in the Port of Houston - Vulcan/ICA import site near the Greens & Buffalo Bayou confluence. Vulcan/ICA wanted to stockpile crushed limestone base coming from the Yucatan peninsula in Mexico via custom super-Panamax cargo ships. As I recall, the ships carried 80,000 U.S. tons each, and could unload in as little as 16 hours!

Vulcan/ICA wanted to put the rock in very tall piles - 65+ feet high (roughly 20 meters). The weight of the pile was too great, and the problem was really a bearing capacity/slope stability issue. We ended up recommending a maximum stockpile height of about 45 feet (~14 meters.)


Asphalt pavement won't do much for the stability of big bulk cargo stockpiles - try to get them to stockple it somewhere else!




Please see FAQ731-376 by [blue]VPL[/blue] for tips on how to make the best use of Eng-Tips Fora.

 

[GeoPaveTraffic]

I agree with Focht3. I don't believe the pavement has anything to do with the allowable stockpile height, i.e. the answer is the same with or without the asphalt or roller compacted concrete. The real question is how much movement of the pavement is the owner willing to accept? Because the pavement will move when the ground supporting it settles from the stockpile.

The pattern of settlement will vary with an asphalt (flexible) pavement when compared to concrete, but the ultimate settlement will be very similar and in either case the pavement will fail relatively quickly.

Options might consist of deep dynamic compaction or another type of ground improvement prior to paving in areas where the cargo will be stockpiled.

Good Luck.

 

[BigH]

In my post where I suggested RCC - this is for the pavement only. No where did I imply that RCC would be appropriate for storage areas, In fact, it was indicated that storage was a separate issue.

There are two aspects that need to be handled. First is the storage. As has been pointed out, settlements of the storage areas will occur under heavy loads and, in fact, there might be shear distress. The storage areas should be properly delineated in the port area design - i.e., where they will occur, etc. Storage areas should not be allowed to run to the whims of the operators - they should be clearly identified. Necessary measures to ensure adequate stability against shear distress must be addressed in the storage areas - similarly should settlement govern. This is as per Focht3 and GeoPaveTraffic.

The other point is the pavement structure - where the loading/unloading vehicles will travel. In this, I was suggesting that RCC might offer better durability - not that it would provide anything as to the stability (shear and settlement) of storage.