Question

Describe the concept of Effective Stress

Answer 1

When some load is applied on a soil mass , due to this if the load is large the movement of particles would take place and they come close to each other .If there is presence of water then the water movement also takes place . All of these things can be understand by the concept of effective stress analysis .

Total Stress,   ,

To find out the total stress at a Point O , given in the image attached :

Total stress is a measurable paramter and it can be measured by pressure cell .

Total stress consists of Two parts i.e : EFFECTIVE STRESS and PORE WATER PRESSURE . In this we are only going to discuss about EFFECTIVE STRESS .

We can not directly measure the effective stress , It is FOUND OUT by the DIFFERENCE of TOTAL STRESS and PORE WATER PRESSURE .

EFFECTIVE STRESS = TOTAL STRESS - PORE WATER PRESSURE

Suppose we have soil , we are considereing a plan which have soil particles and some load P that is being applied on top of that surface , these pores have water in them . Due to the applied force P there would interparticles forces which are going to be developed inside the particles . And we resolve those and take components of that in the normal and conventional direction . Therefore , Normal Component is N and Tangential Component is T . And the area of pores is Aw . After that if take the vertical equilibrium of this force , we have : Dicussed in the images attached

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