Thickness Slab on-grade for haul trucks

[01399559]

Currently I'm looking for info on designing a concrete slab on grade.

The slab will have dimension of 35ft by 20ft, and will be sitting on compacted soil. The slab requires to be able to handle loaded haul trucks of an aproximate 800 tons.

Can somebody help me with the steps on how to find the required thickness of the slab.

Thanks

Ramon Diaz de Leon

 

[PSlem]

How many trucks per year will be needed.

 

[msquared48]

CRSI has a table for slab-on-grade design based on the psf seen, reinforcing and thickness. Goes up to 3500 psf. Also has several references in the notes to search out too.

Mike McCann
McCann Engineering

 

[msucog]

is it cost effective to design a 35x20 rigid pavement area? i guess if you don't have a point of reference to start from, then going through the process will help.

here's the UFC(NAVFAC) link i fall back on pretty regularly since the info is reliable and is fairly straight-forward reading most of the time.

http://www.wbdg.org/ccb/browse_cat.php?o=29&c=4

in particular, see "UFC 3-250-12N Design: Pavements". there's a few other references on that link that get a little more in to the nuts and bolts of it all.

to tackle pavement design, i typically like to know the anticipated subgrade conditions, EALs, traffic type (tractor trailers and what configuration, forklift, box truck, etc), turning conditions, driving lanes, life/performance expectancy, etc. it can get pretty in depth at times. for your situation, i would think that it would be more cost effective to pull a safe number out of the air based on the surrounding conditions (i assume that there's pavement of some sort around/leading up to your 35x20 area). for example, if there's asphaltic concrete leading up to this concrete area and the ac pavement is 4" base course and 2" ac, then 8" of concrete should be well to the safe side (unless this happens to be a dumpster pad which could be an entirely different animal to deal with).

hopefully, my ramblings will help. good luck.

 

[01399559]

Around 110, 000 trucks per year

 

[miecz]

The PCA Publication "Concrete Floors on Ground" has a design method for slabs with axle loads.

 

[csd72]

Pay close attention to your joints this is where most pavements fail.

 

[cvg]

800 ton haul trucks are huge! My previous experience working in an open pit coal mine the coal haulers were maxed out at about 250 tons capacity. Including the tractor and hauler weight, maybe 300 tons GVW. I would question if 8" concrete or 4" asphalt can handle this. I would think that for this weight and number of trips you would be closer to a 30" thick structural section (including your aggregate base course). Maybe you can strengthen the base using soil cement or cement treated base to reduce thickness a bit.

 

[PSlem]

There is a PCA curve which shows number of load repetitions per year based on stress ratio. So for 110,000 reps the stress ratio has to be less than 55%. This is determined by front and rear axles. Unfortunately the nomographs I have stop at 65K axle loads and a 10" slab.

 

[cvg]

you may want to look at methods used for designing airport aprons and taxiways for jumbo jets. Seems that the magnitude of the loads may be similar. Last large aircraft apron / taxiway project I worked on the concrete paving was 20" PCC with 4" agg base under that and another 6" of compacted subgrade (100% of max density) under that for a total structural thickness of 30" Slab edges were thickened to 24"

 

[msucog]

i wasn't necessarily saying that 4" base + 8" concrete would work...i was trying to point out that someone should look at what is around this one area (the truck isn't going to fly in and land on the 35'x20' area). and yes, now that i look at it closer, 800 tons is big (about a CAT 797 mining truck or so). for a 35'x20', hell, put 1.5-2' of concrete. if you're dealing with equipment like that, you're only talking about ~$1300 for each 6". it all depends on what you're doing with the 35'x20' area and whether you want to fuss around with a couple thousand dollars worth of concrete (when you could realistically use up some of that trying to design something).

 

[fattdad]

I would think that the fundemental requirements for the solution would be subgrade modulus, number of axles, number of tires per axle and contact area of each tire. I would seem meaningless to ask a bunch of geotechnical engineers (myself included) who are schooled on pavement design (assuming for the most part highway traffic) to assist without this information.

You driving these Leibherr (sp) trucks? They make them down the road from me in Virginia and they're HUGE!

f-d

¡papá gordo ain’t no madre flaca!

 

[concretemasonry]

With a truck that sizw (800 ton) and knowing the typical wheel configuration, you may be looking at the 200-300 ton loads on the edges and corners. You probably have only 4 load points from a prctical standpoint. That slab is not much bigger than the truck if you can actually get the entire truck in the little slab. You need special permits just to move the tires from A to B.

The most economical approach is to over-do the slab thinkness since the incremental thickness cost is so minimal in comparison to the long term benfits of rigidity. Then you are just left with the soil/base properties and any transitions to other sections of access.

I assume this slab is contiguous with a scale, crusher or dumphouse with significant foundations below grade.