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Safe bearing capacity of soil - Local shear failure?

 
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BenjaminLucas
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PostPosted: Tue May 12, 2020 10:44 am    Post subject: Safe bearing capacity of soil - Local shear failure? Reply with quote

we are constructing, designing projects for government at Rajasthan. Soil investigation for all projects is being done. Most of the soil consultants are working out SBC for General and local shear and then averaging as per para 5.2.1.1 of is 6403. For example in one case  as as per soil investigation report void ratio is generally about 0.65 with soil with cohesion of 33 KPa and phi as 24 degree .omegle discord xender

In this connection i am having certain doubts and i will be grateful if same can be clarified.

1. can this approach be used even if n is more than 40 and the soil is c - phi soil , as the above para of code is for cohesionless soil. If no, than what criteria should be used.

2. Even if soil is cohesion less soil with n value more than 20, still local shear to be checked as void ratio is more than 0.55.

3. Also i am having doubt that void ratio evaluation is not being done correctly. As soil investigation is done more than six months back to reject the findings are there any alternate way to check the void ratio. As other parameters like sieve analysis, shear strength parameters, moisture content. dry density etc have been worked out.  
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es_jayakumar
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PostPosted: Wed May 13, 2020 1:49 pm    Post subject: Reply with quote

You can discern the type of failure, based on N value, making use of the table given below. I hope, this can be used for any type of soil.

E S Jayakumar



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es_jayakumar
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PostPosted: Sat May 23, 2020 2:47 am    Post subject: Reply with quote

Though not much related to the query, I will illustrate how the interpolation for a case between general shear failure and local shear failure is done, for a cohesion-less soil.
Suppose, your N value is 20. Calculate phi from Fig. 1 of IS : 6403, or using Wolff formula, phi = 27.1+0.3N-0.00054N2. It comes to 330. From the above table, if N>30, it is general shear failure and if N<5, it is local shear failure. Our case is in between and hence have to interpolate for the phi value to be used in the SBC equation.
For N = 30, phi = 330 (general SF)
For N = 5, phi = 2/3 x 33 = 220 (local SF).
Interpolating for N = 20, we get phi = 28.600.    [ 33-(33-22)*(30-20)/(30-5)]

E S Jayakumar
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