Settlement due to truck wheel load

[kxa]

I need to estimate the amount of settlement due to the wheel load and imact load of trucks on soil and road with 6” of crushed stone. Ground water is 3’ below and there is chance for some flooding. Is there any reference material that can help me with this? Thanks.

 

[ishvaaag]

The static settlement is an issue easy to deal with notionally with layers of elastic materials corresponding to the underground materials.

However, the problem of rutting is one dependent on many factors such

mechanical properties of the road layers
truck loads applied
frequency of the loadings
shape and pressure of the tire, contact area
speed of the vehicles

hence a number of special studies may be required to bracket the behaviour for your case.

If you would have well graded well compacted subgrades, reasonably drained and ample not tall shoulders, you could expect to keep rutting in the range of under 5 to 10 cm in persisten rains under even insistent very slow traffic of ordinary construction trucks; recompaction and regrading may then be needed to flatten any rutting of operations. But for wilderness roads nor proper subgrades nor the recompaction availability are surmised to be warranted, hence either you study your cases or you won't know.

Flooding can as well entirely disrupt the matrix of the soil; and it is on this disruption of the mechanical ability of the supporting ground (or engineered layers) that many roads and subservient structures are lost. Economical restrictions affect even to the most completely engineered road structures, and hence one of the modest characteristics as that described even more.

 

[Ron]

An estimate of the amount of subgrade deformation (rutting) can be done using elastic layer analysis. In this case you would only have a two layer system, the first layer being a crushed stone surface/base overlying some subgrade material, the second layer. You will need to know the resilient modulus of both materials, Poisson's ratio of both materials and the thickness of the first layer. The second layer is modeled as a semi-infinite layer, so the thickness is not necessary.

A free analysis program is available from the Washington State Department of Transportation. The program is called "Everstress" and will compute stresses and deformations at any point under or around the load.

Since it can be modeled as a two layer system, several textbooks cover this approach and it can be done by hand. Principles of Pavement Design by Yoder and Witczak is one such text.

 

[howardoark]

Tensar has a nice (and free) program for doing what you want to do - you need to put down a layer of geogrid (many people prefer high strength woven geotextiles but contractors don't like them because of maintenance issues) but that will certainly help with your rutting problem. Tensar will probably claim that the reduced gravel section will pay for the geogrid.

 

[oldestguy]

This seems like you are designing a pavement, right? If so, I have found in the past that criteria for pavement design generally is based upon an acceptable permanent deflection. I use 1/2 inch for a rut depth as the limit This is more appropriately done using some recognized pavement design method than computations for settlement.

These usually tie axle loads, repetitions, etc. to soil type and then result in a thickness for each of the layers. In such a case, I would ask of the nearest large municipality or large department of transportable as to what system they use.

If you are only looking for what happens say at a loading dock, then you might go for what is listed in reties above or a simple no impact foundation design, tied to settlement.

In closing, I'd have to say 6 inches of base course won't do much for you if your soil is capable of being softened any time of the year for most truck traffic.