Paving Thickness

[barthamm]

I need to know what thickness of asphalt pavement would typically be needed for a heavy vehicle area. The area is a coal yard for a boiler plant and the traffic will be coal trucks weighing up to 80,000 lb when loaded. The subgrade is 6" of compacted chrushed stone.

I have a specification that calls out 2" base layer, with 1.5" of wearing layer. Is this adequate, or are thicker layers needed?

Thanks

 

[ishvaaag]

Your taffick looks heavy and you should design in accord with the requirements of heavy traffic. Unfortunately I have not here a book lent by my brother (a civil engineer, I am an architect), but the designs for heavy traffic were invariably thicker and more engineered in layers than yur description shows. The typical sections of diverse construction are normalizaed in Spain according to traffic, and so must be in other countries. Look for one such source.

 

[Ron]

You don't mention the frequency of traffic nor the design life. Both are necessary to assess the section you are addressing. Your total structural layer of 3.5 inches of asphalt over a 6-inch thick structural base course is likely adequate. I would prefer a thicker base course, as it is more appropriate and cost effective to build the section from the bottom, up. You could then reduce the asphaltic concrete layer thicknesses to compensate.

You must also consider water table depth and environmental conditions in this design. Give us a bit more info and perhaps we can help a bit more.

Ron

 

[emmgjld]

Ron lists some information required for a Road Section design/analysis. In addition,You have not given information regarding the subgrade soils and longterm soil moisture predictions for the upper subgrade and aggregate base.

For an analysis, using the AASHTO or Asphalt Institute (AI) methods, the Resiliant Modulus of the subgrade and aggregate base materials must be determined. Several methods are availible, the Hveem-Carmany (R value) and the CBR are common. (I have a preference for the Hveem-Carmany method.)

For the clayey soils and bedrocks I am used to, the section you described section is light and could have a useful life of less than 6 months. However, If the site has very sandy or gravelly soils or a competent bedrock which will not rapidly degrade, your section may be sufficient.

Whether or not you go with a relatively thick or thin Asphalt Layer, proper analysis and preparation of the subgrade soils is very important.

 

[Jim6758]

I agree with Emmgjld. Your proposed section would be considered light for this area where we deal with highly expansive clays. Drainage should also be a consideration. A poorly drained sub-grade will have a substantial adverse effect on your pavement structure.