Wheel Load Stress Distribution and Different Soild Types

[foreng]

I am looking for a reference that deals with stress distribution as it relates to different soil types. I have read that a load applied to the surface of a material such as crushed rock, can yield stresses on a subgrade at depth of up to 1/2 of that of some other materials (i.e sand). I am looking for some way to quantify this relationship in order to assess the cost benefit of using a more expensive
road ballast on a soft clay subgrade (i.e. less material of higher quality).

 

[BigH]

You might consider, as a first recourse, using layered elastic theory. It is readily available (see Poulos and Davis' book Elastic Solutions for Soil and Rock Mechanics. Secondly, it is well covered in Yoder and Witczak's Principals of pavement Design, Second Edition, Chapter 2. Tensar corp has a computer program available that will let you see what varying thicknesses of mateials having different rigidness values (structural number approach if I remember right). It also permits you to incorporate tensar grids for increasing the rigidity of a layer and to hence reduce the thickness. Remember that it may be wise in any event to use a separation geotextile to prevent punching of ballast into the soft clay. On our project we use a sand layer but we have relatively high embankments. You sound like you are trying to use the soft clay inherently as a subgrade itself - with subbase/base and . . . above.

 

[Ron]

foreng...I agree with BigH....use elastic layer analysis. One that's available in the public domain is ELSYM5. It's easy to use and the algorithms are the same as most of the other ELA programs.

Using different material properties, this allows you to compute orthogonal stresses at any point below or near the load. Very useful in pavement analysis.

Yoder and Witzcak is a good reference. If you use that one, I think the elastic layer technique is only good for two layers, so you will have to go further to evaluate more materials.

 

[BigH]

Ron - they have section on 3 layers.

 

[Ron]

BigH...thanks...see, never trust your memory!!

 

[BigH]

That's I who should have posted that! Trouble is that most of my good references are back in Toronto and I am here in India - so I must rely more on the peanut than most!