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Structural design of test piles vs working piles
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Damodara Bhat
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PostPosted: Mon Aug 10, 2020 3:09 pm    Post subject: Re: Structural design of test piles vs working piles Reply with quote

durgaprasad wrote:
Dear Er. S.P.Srinivasan ,


Thanks a lot for your reply.

Yes your observations are correct and this is a practical problem from one of our ongoing project at ENNORE-CHENNAI.

We have started installation of test pile considering load factor of 1 on test load. Our aim will be achieved even if structural failure occurs at test load. However this should not be the case because at that point geotechnical capacity of pile shall be developed to its ultimate capacity and still we will be having the partial safety factors of materials (concrete and RF) to allow for the additional load on pile before it reaches to its ultimate structural capacity.

With this we are keen to know the test results and surely will come back to forum with all details.

Thanks and regards,
Durga Prasad Kulhari



spsvasan wrote:
Dear Er.Durga Prasad

Yours is a peculiar case. The safe load on the pile is quite high, probably because of the considerable frictional forces developed for a 32m long pile

The very high pile capacity makes it difficult to design for 2.5 times safe load on pile

The pile diameter cannot be changed for the initial test pile. We can modify only the pile concrete strength and reinforcement. It is impossible to design the pile for a load factor of 1.5 for the load for initial test. In your case, you will have to reduce the load factor.

I am worried about adopting a loadfactor of 1, since the pile will be close to its structural failure stage. I think inputs from any Professor who has carried out several  tests upto failure on rcc columns should be obtained before taking a call on a load factor of 1.

If concrete strength is taken as M50 and 6% reinforcement is provided, a load factor of 1.25 can be achieved.

Concrete grade M50 is to be achieved with a slump of about 150mm. This will require a good mix designer.

Bar congestion will have to be avoided by avoiding laps in the top portion of the pile. This may be ok since the required pile capacity will go on reducing as we go down, due to side friction. hence in the top portion there may be only curtailment of rods and not any lapping

Very careful planning of the initial pile load test will be required

If this is a realtime problem, I request you to kindly come back to the forum after the test is over with the test results and the problems faced by you. We will all learn.

Regards
S.P.Srinivasan





durgaprasad wrote:
Dear Sefian,

I wish to discuss the structural design philosophy for initial test piles and working piles. In my understating reinforcement for initial test piles will be higher then working piles.  
Request you all to go through the case study below and provide the valuable feedback/suggestions.

1.0 CASE : As per soil data : 500 dia 32M long pile : Safe load 245MT and as per project spec test load is 2.5 times of safe load.

2.0 GENERAL :  As per cl. 6.1 of "IS 2911 (Part 1/Sec 1) : 2010" The pile shaft should have adequate structural capacity to withstand all loads (vertical, axial or otherwise) and moments which are to be transmitted to the subsoil and shall be designed according to IS 456.

3.0 Initial Test pile : Test pile has to transfer the 2.5 times the safe load. Hence test pile's structural design has to be done for vertical load of 612.5MT (2.5*245*1). Here partial safety factor for load is taken as 1 because its a test load and probability of increasing is zero.

4.0 Working pile : Pile has to transfer the safe load. Hence working pile's structural design has to be done for vertical load of 367.5MT (245*1.5). Here partial safety factor for load is taken as 1.5 based on Table 18 of IS 456:2000.

5.0 Structural design of piles : Based on above para 3 & 4 it is noted that reinforcement requirements for initial test pile will be higher then working pile. Piles may be designed as per cl 39.3 of IS 456 considering short axially loaded members in compression because buckling is prevented by soil.

I thank you very much for reading and valuable feedback/suggestions.

Thanks & regards,
Durga Prasad
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badamsundararao
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PostPosted: Sat Aug 22, 2020 5:38 pm    Post subject: PILE DESIGN Reply with quote

dear friend,

     While designing Pile itself,You are considering a Factor of safety of 2.50 to 3,hence I feel that,there is no need to consider additional reinforcement for Test piles. Seniors may give their Expert opinion on this.
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Damodara Bhat
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PostPosted: Sun Aug 23, 2020 9:02 am    Post subject: Re: PILE DESIGN Reply with quote

badamsundararao wrote:
dear friend,

     While designing Pile itself,You are considering a Factor of safety of 2.50 to 3,hence I feel that,there is no need to consider additional reinforcement for Test piles. Seniors may give their Expert opinion on this.
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francis chacko
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PostPosted: Sun Aug 23, 2020 10:43 am    Post subject: ADDITIONAL REINFORCEMENT FOR TEST PILES Reply with quote

NO ADDITIONAL REINFORCEMENT IS REQUIRED
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natarajan_alagesan
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PostPosted: Mon Aug 24, 2020 6:34 am    Post subject: Re: PILE DESIGN Reply with quote

Damodara Bhat wrote:
badamsundararao wrote:
dear friend,

     While designing Pile itself,You are considering a Factor of safety of 2.50 to 3,hence I feel that,there is no need to consider additional reinforcement for Test piles. Seniors may give their Expert opinion on this.




For initial pile load test, reinforcement to be provided for either maximum vertical load to be tested or maximum pull out load to be tested.
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jaweed_darbar
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PostPosted: Wed Aug 26, 2020 4:38 am    Post subject: Reply with quote

please refer to IS:2911 (Part 4) - 1985.

In conclusion it can be stated that there are 2 types of tests to ascertain pile capacity ( safe bearing load ).
A) Initial Test is done on the test pile, & loaded upto 2.5 times of the design load. This pile is NOT used in the structure.
B) Routine Test is done on working pile and loaded upto 1.5 times the design load. This pile can be  used in the structure provided it passes the criteria successful parameters.

In both type of tests , the reinforcement and concrete quality shall be the same as that of working pile.


jaweed darbar
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