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Calculating the pile load capacity for Bored Cast in situ piles as per Is 2911 (part1/Sec2):2010

 
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reena_secton
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PostPosted: Sat Jun 29, 2019 8:48 am    Post subject: Calculating the pile load capacity for Bored Cast in situ piles as per Is 2911 (part1/Sec2):2010 Reply with quote

Calculating the pile load capacity for Bored Cast in situ piles as per Is 2911 (part1/Sec2):2010

IS code has recommended 2 methods for calculating the ultimate capacity of piles for vertical loads as below

1. Cl B-1 Qu= Ap(0.5DγNγ + PD Nq)+Σ KiPDitanδAsi
2. Cl B-4.1 Qu= 13N(L/B)Ap + NAS/0.50

We have a soil report in which the capacity has been calculated based on Eq(1) by conducting SPT test. The consultant has calculated the capacity using eqn.1 & also using the equation 2 but instead of 13 he has used 40 which is for Driven cast in situ piles. Te soil sample is medium & fine sand (20% silt) with N value 70. water table effect accounted. N value has been corrected for overburden & dilatancy. The φ value corresponding to N has been taken as 40o

When we use Eq 1 the pile capacity is getting as 280t where as if eqn 2 is used we get the value as 83t (after reducing the capacity with FOS). For finding the capacity only end bearing has been considered and skin friction neglected.

1.Which formula is to be used for finding the pile capacity.
2. In equation 1 do we have to reduce the value of φ for finding the bearing capacity factors.
3. Why this much difference in values in 2 equations
4. Is any modifications to be done
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es_jayakumar
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PostPosted: Wed Jul 03, 2019 2:50 pm    Post subject: Reply with quote

It will be apt if you can attach any available calculation. Why is the shaft skin resistance neglected ? The N value of 70 indicates very hard soil. Is this value available at pile tip only ? More details are required to fix the problem.

E S Jayakumar
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reena_secton
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PostPosted: Wed Jul 03, 2019 3:59 pm    Post subject: Reply with quote

I will update the details tomorrow once I reach office
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reena_secton
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PostPosted: Thu Jul 04, 2019 10:41 am    Post subject: Calculating the pile load capacity for Bored Cast in situ piles as per Is 2911 (part1/Sec2):2010 Reply with quote

N value from a depth of 7.00m is more than 50. This N-70 is at tip. No calculation is available. Only capacity is written in the soil report.
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es_jayakumar
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PostPosted: Sun Jul 07, 2019 2:16 pm    Post subject: Reply with quote

A model calculation of end bearing pile load capacity is attached.
The capacity of bored cast-in-situ pile is less than (taken approximately 1/3) that of driven precast pile. That is how the coefficient of 40 for driven pile got reduced to 13 for a cast in situ pile, in Meyerhoff formula.

E S Jayakumar



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reena_secton
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PostPosted: Mon Jul 08, 2019 4:36 am    Post subject: Calculating the pile load capacity for Bored Cast in situ piles as per Is 2911 (part1/Sec2):2010 Reply with quote

Sir,
     Thank you for the reply.
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es_jayakumar
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PostPosted: Mon Jul 08, 2019 5:36 am    Post subject: Reply with quote

You are welcome Er. Reena.
Now you work out the pile capacity in your case, with the available data (dia of pile, bore-log details etc. were not provided by you) vis--vis the recommendation given by the consultant and post it here, for further clarifications.

E S Jayakumar
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