EFFECTIVE STRESS 4

[eritrea]

could anyone please tell us what the difference is between the principle of effective stress and the law/rule of effective stress for we are confused to differentiate them very clearly .

 

[Riz]

U need to understand it from 1st principles.

If u consider sliding in a soil mass - it can occur in any plane. The stresses acting at any such point is inclined to the normal to the plane. Stresses thus evaluated are complex and have both normal and tangential component.

The principal plane is a plane acted upon by the normal stress only. And this stress is called Principal stress.

Therefore at every point considered in a soil mass there are three mutually orthogonal principal stresses.

A Mohr circle diagram and theory should be clear to u.

The resulting effective stresses are setup by stresses that control changes in volume and strength of a soil mass. Drainage conditions of a soil mass effects loads on it. The application of load on a saturated soil will be shared by the water and soil skeleton. Instances do exist ( depending on soil type ) where water in the soil voids carry the load and cause increase in pore water pressure or by the soil skeleton as particle contact stresses.

Terzaghi stated that the effective stress is equal to the total applied normal stress less pore water pressure. This is still valid.

Determination are from either consolidated undrained or drained tri axial shear tests.

Once u understand the above, the differentiation should become lot easier.

Books to check are:
G.N. Smith - Elements of Soil Mechanics &
M. J. Tomlinson - Foundation Design and Construction

 

[Qshake]

Well put Riz.

 

[Anotai]

The effective stress analysis is the method that analysis the stress in soil mass seperately between the soil skeleton stress and the pore water pressure. So , when you want to analysis of your problem in the effective stress approach you have to determine the strength of soil skeleton in the manner of drained strength. This approach is suitable when you analysis the long term behaviour of the soil mass because you treat that pore water is absolutely drain.

 

[lanlinfrac]

Thanks for Riz. Terzaghi efficitive law has been applied very well in soil mechanics. Many people, for example, Zimmerman, has deduced a thereotical equation for porous media, which porosity was introduced into it. I ever did some work in terms of well log, so I think Zimmerman equation is very well for analysis of porous media, especially for rock. What about you? Contact me later. Thank you.

 

[dgillette]

The original question was about "the difference...between the PRINCIPLE of effective stress and the LAW/RULE of effective stress." (Emphasis added.)

As far as I can tell, they are the same thing under a slightly different name.

What is the difference between Karl Terzaghi and Charles Terzaghi? Same guy, slightly different names at different times in his life. (In his earlier days of work in the US, he published under "Charles.")