www.sefindia.org

[pradeep joshiaaa]

" Bad geotechnical design is where you put the wrong parameters into the wrong analysis and get the wrong answer. Good geotechnical design is where you put the wrong parameters into wrong analysis

 and get the right answer. This is because in good design we asses how wrong our parameter determinations are and how wrong our analysis are and make a compensating correction based on precedent." 


Soil reports on which the tall structures are build , in INDIA , I have never seen the following key parameter's -


1. Dynamic shear modulus


2.Poisson's  Ratio.


3. Shear wave velocity.


4. Strain value.


5. Differential Settlement.


6. Liquefaction assement


7. soil improvement recommendations.


8. Calculation of subgrade modulus , which is only recommended , exact method is never given how it has been arrived upon.


9. structural engineers do not provide the exact load calculations to geotechnical engineers prior of submitting report


Differential Settlement are imp and resulting angular distortions which have to be limited w.r.t. evolving demands to safe guard the serviceability and stability of structure.


Horizontal acceleration can cause rocking of structure and the resulting structural overturning moments can produce significant cyclic vertical thurst on foundation element , this can in turn result in


 cumulative settlements with or without soil liqefication or other strength loss.


Acc. to Krinitzsky bearing capacity for seismic analysis , F.O.S is in range of 5-10, rather 2.5-3 used in our soil reports considering shear failure only.


Recommendation in IS:1893(2002) TABLE 1 - for increase in allowable bearing pressure it is not mentioned it's site soil specification such as when we can use increase in allowable bearing pressure-


(a) Massive crystalline bedrock and sedimentary rock that remain intact during E.Q.


(b) Dense soil to very dense granular soil.


( c) Heavenly over consolidated cohesive soil. 


For all other soil condition it cannot be used.


BEST METHOD


Interaction between geotechnical engineers and structural engineers for settlement and differential settlement of building , because geotechnical engineer can find settlement and diff settlement of


 building by means of 3d continuum based F.E. model were as structural engineer design raft by a more simple F.E. model using shell and spring element taking shear deformation into considerations.




Regard's


PRADEEP JOSHI


pradeepjoshiaaa@gmail.com (pradeepjoshiaaa@gmail.com)


PH-09968369045 





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