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[mayank016]

Dear All,
I have situation which needs kind guidance of all esteemeed members, In one of the WTP Sites at odisha we have conducted 2 Nos Initial pile tests each of 500 dia 12M length pile and 500 dia 15M length of the pile. The results are 11mm deflection is reached for 500 mm dia 12m length of the pile at a load of 92.5 MT Loading (Considering safe load of 39 MT provided in soil report). Both the tests of 500mm dia of 12m length of pile shows same results.
However when 500 dia 15m length of pile was tested with loading intervals of 21MT at 84 MT the test pile shows vertical deflecition of 15mm and for other 500 dia 15m length of pile the 17mm delflection is reached at 84MT.
Is it possible that 15m length of pile has low load carrying capacity then 12m length of the pile ?all 4 tests are done at hardly 70-80 meters of interval and soil borelog suggests more or less uniform profile of soil throughout the campus.

[vikram.jeet]

Generally
if Pile depth is more - there is increase in Load carrying  capacity due to added skin friction plus better point bearing base pressure from deeper strata :-

Reasons of decreased capacity in this case could be :-

Negative skin friction effect

Poor bearing  deeper strata - generally not possible but highly remote possibility

Errors in readings

Change of equipments

[shailesh_gandhi]

This could be due to construction issues like not cleaning of the pile borehole bottom properly or soil collapse during concreting resulting in a zone of weak concrete. You may do a Pile Integrity test to check the pile.


Prof. S.R.Gandhi

Visiting Professor in Civil Engineering
IIT Gandhinagar - 382 055

+91-7046404444
Former Professor in Civil Engineering, IIT Madras
Former director, SVNIT Surat











On Sun, May 11, 2025 at 3:26 PM mayank016 <forum@sefindia.org (forum@sefindia.org)> wrote:

[deepakattingal]

Safe load mentioned in the report will be based on the soil parameters ( N) value if it was not hard rock. Have we ensured that we got the same soil profile at termination?Regards,
 
Deepak. R
+91 8281592907









On Sun, 11 May 2025 at 5:22 PM, shailesh_gandhi <forum@sefindia.org (forum@sefindia.org)> wrote:

[quote]            This could be due to construction issues like not cleaning of the pile borehole bottom properly or soil collapse during concreting resulting in a zone of weak concrete. You may do a Pile Integrity test to check the pile.


Prof. S.R.Gandhi

Visiting Professor in Civil Engineering
IIT Gandhinagar - 382 055

+91-7046404444
Former Professor in Civil Engineering, IIT Madras
Former director, SVNIT Surat











On Sun, May 11, 2025 at 3:26 PM mayank016 forum@sefindia.org (forum@sefindia.org))> wrote:

      --auto removed--

Posted via Email

[shenoy]

Dear Mayank,

The soil profile shown in 2 boreholes are very similar (Surprisingly very very similar), So theoretically for the same diameter piles theoretically are expected to undergo same settlement under the same load, if the pile lengths are same.
Now comes the length of the pile. If the soil profile is same, does it mean more the length of the pile the more is the Load transfer capacity? The Answer is- need not be always. There are theoretical reasons and Practical Reasons.
The theoretical reasons being

1. There are Two parts of the transfer capacity of a pile ( only in case of friction piles). First part, the due to the peripheral surface friction and the second part due to the end bearing area. If the length of the pile increases, the first part is likely to increase. But there is no guarantee that the second part will increase. It depends on the nature of the soil and its SBC where the end of the pile rests., if the SBC is less at the end bearing, a longer pile may give less total Transfer capacity.
2. The effect of water table. Was the Water level Same while casting and while the tests were being done ? Water being lubricant, the surface friction may reduce. So if the Longer piles were tested when WT was high, it can effect the transfer capacity. This is possible near the coastal areas affected by tides.
3. Negative skin friction is a gradually, but slowly, acting downward load on piles that need to be considered (to be added ) to the other loads expected, if the soil around is newly filled, but not well compacted. When natural consolidation happenes, the soil on the periphery of the pile, due to friction, can pull the pile down while going down. The effect of this natural consolidation during the pile load test (which may be completed just in 2 to 3 days, may not be much. So the Negative skin friction may not be the culprit. If it were there it would have been there for both the sets of piles.


Now the Practical reasons.
1. Two piles can not be cast , chipped, prepared and tested 100% equal and similar in all aspects. Was there any particular order in which the piles were tested ? Were the equipment calibrated? Were the kentledge beam  or kentledge ledge  ( load reaction system used to apply the test load against a pile's top) Same ? The Jack used was the same? The increment of load same? The dial gauges were same? The age of concrete for the pile same? The head preparation same?
2. If the distance between the supports for the reaction load is less, the Reaction load may start pulling the pile down and the dial gauges may show wrong readings. The initial Readings at Zero Loading itself will be wrong.
3. If the Supports for the reaction load sink(s) the readings will be wrong, which is likely in your case single the reaction load you would have assemble would be more expectation of  more transfer capacity of longer piles. If the Jack and dialguages were not symmetrically arranged, there could be tilting of the reaction load platform, surface settlements, which can affect the dial readings.
4. The longer piles, if buckle and the dial Guage, by chance, is on the compression side, it may ‘show’ more settlement of pile.  
Recording errors.

There could be multiple reasons for your observations and inferences.
Now basically I have certain doubts. It is told that (Considering safe load of 39 MT provided in soil report) Why the piles are being tested for 92.5 MT ? is it to know the transfer capacity of piles for 12 mm settlement ? Generally they are being tested for a Test load 1.5 times the design load and be happy when the settlement at the Test load is less than 12 mm.
If the Soil profile is the same, What was the need for you to drive some piles to longer depths? That too for 84 MT for longer piles  which is less than 92.5 MT for shorter piles ?


- Dr Premanand Shenoy

[glnp12]

I agree with Prof. Gandhi,
There will be many uncertainties, during field test of piles.  
PIT will show any abnormal quality.
For test piles, it is advisable to have CSL tubes, and check for overall quality. Now that is not possible for existing piles.  
Prabhakar G.
Associate Director (Civil), NPCIL Mumbai.
--
  This could be due to construction issues like not cleaning of the pile borehole bottom properly or soil collapse during concreting resulting in a zone of weak concrete. You may do a Pile Integrity test to check the pile.Prof. S.R.GandhiVisiting Professor in Civil EngineeringIIT Gandhinagar - 382 055+91-7046404444Former Professor in Civil Engineering, IIT MadrasFormer director, SVNIT SuratOn Sun, May 11, 2025 at 3:26â&euro;¯PM mayank016 forum@sefindia.org)> wrote:    --auto removed--

Posted via Email

[Arvind Kumar Jaiswal]

Dear Friend,


Following answers are required before a conclusion can be drawn:


1. What are the design criteria of pile? I mean is it a) Full end bearing b) Full friction or c) part friction cum part end bearing d) Design load, e) deflection assumed etc f) Mix of pile g) etc


2. What is the load testing method and load increase adopted by you at site commensurate to 1 a), 1 b) and 1 c)


3. What is the graph you have plotted? 


Once these are known then only some inferences can be drawn...


with warm regards...
Arvind Kumar Jaiswal





On Sun, 11 May, 2025, 3:26 pm mayank016, <forum@sefindia.org (forum@sefindia.org)> wrote:

[lagnajit das]

Standard Penetration Test SPT.  
On Sat, 17 May, 2025, 8:14 pm Arvind Kumar Jaiswal, <forum@sefindia.org (forum@sefindia.org)> wrote:

[quote]            Dear Friend,


Following answers are required before a conclusion can be drawn:


1. What are the design criteria of pile? I mean is it a) Full end bearing b) Full friction or c) part friction cum part end bearing d) Design load, e) deflection assumed etc f) Mix of pile g) etc


2. What is the load testing method and load increase adopted by you at site commensurate to 1 a), 1 b) and 1 c)


3. What is the graph you have plotted? 


Once these are known then only some inferences can be drawn...


with warm regards...
Arvind Kumar Jaiswal





On Sun, 11 May, 2025, 3:26 pm mayank016, forum@sefindia.org (forum@sefindia.org))> wrote:

      --auto removed--

Posted via Email

[sundararajulu]

Sent from my iPad

[quote]On May 17, 2025, at 9:42 AM, Arvind Kumar Jaiswal <forum@sefindia.org> wrote:

            Dear Friend,


Following answers are required before a conclusion can be drawn:


1. What are the design criteria of pile? I mean is it a) Full end bearing b) Full friction or c) part friction cum part end bearing d) Design load, e) deflection assumed etc f) Mix of pile g) etc


2. What is the load testing method and load increase adopted by you at site commensurate to 1 a), 1 b) and 1 c)


3. What is the graph you have plotted?


Once these are known then only some inferences can be drawn...


with warm regards...
Arvind Kumar Jaiswal





On Sun, 11 May, 2025, 3:26 pm mayank016, forum@sefindia.org)> wrote:

      --auto removed--

Posted via Email

[hemraj chanchal]

Posted via Email