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foundation in black cotton soil
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ibarua
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PostPosted: Mon Aug 03, 2009 8:15 am    Post subject: foundation in black cotton soil Reply with quote

3rd Aug 2009

Two queries:

1. As there will be not much use in locating the bulbs of the u/r piles within the black cotton soil, will there be not considerable difficulties in constructing the piles with the bulbs at 10+ meters frm the GL?

2.  What is the guarantee that the bulbs will be formed correctly (as per design assumptions) at +10m. below GL without caving in of the soil?

About 30 years ago, we had recovered 2 u/r piles after construction, They did not look much like the piles we had designed and thought we had got constructed. After this experience, we have been avoiding the use of u/r piles on our projects.

Indrajit Barua.



On Mon, 03 Aug 2009 praveerkum wrote :
Quote:
The provision of under reamed piles is the best
foundation for this type of expansive soil, the size ,
no. of bulbs , tem size can be calculated based on
emprical data and equations as developed By CBRI
Roorkee.
with warm regards
Praveer Kumar


On Thu, Jul 30, 2009 at 4:46 PM, manish_del
<forum@sefindia.org (forum@sefindia.org)> wrote:

Quote:
Respected members,

We are designing an industrial building in Gujarat.
There is black cotton soil upto 10m depth. The soil
investigation report suggests providing stabilized
macadam layer at 2m depth (this is 800mm layer of 40mm
stone soling mixed with moorum and sand), on which
isolated footings can be rested, taking SBC of 12t/m2.
Is this approach correct? Has anyone used such a
mechanism before? The other alternative is to provide
under-reamed piles. Which option would be better?
Quote:

Thanks in advance,

Manish Shah.








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suraj
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PostPosted: Mon Aug 03, 2009 10:04 am    Post subject: Soil Stabilisation Is Suggested In Comparison To Piling Reply with quote

Input parameters:The depth of expansiove soil is 10 m
The expansive soil is medium class
The porosity of soil is 70%
Liquid limit is considerably high
The water table is non existing in June month
Column reaction is 60 T
OHT is 20 T
Proposed bulding is pre engineered

Soil report:Recommendation for 800 mm depth of graded matric macadem @ 2 m from NGL

Observations:Below foundation, expansive soil strata  remains 10-2.8 is 7.2 m
Keeping in view the possible rise of water table & consequently capillary rise may not be considerable in this case.

Span of the pre engineer building is 20 m quiet normal
OHT crane of 20 T gives  a little concern
Soil improvement shall provide 10 to 15 T SBC
Provision of isolated footings with grade or foundation connections should work successfully
Sufficent depth of the RCC stub with proper volume for bolts hole grouting is required
Backfill should be imported garded fill or desert fill
Adequate concrete protection is required
Ground flooring at plinth should be concrete to be toped with epoxy flooring
Expansive soil from the building surrounding needs removal for at least 5 m from building lines to be placed with graded fill so that water is kept drained off

Piling can also be carried out but is not a preferred solution in this case.

Regards
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PostPosted: Mon Aug 10, 2009 2:55 am    Post subject: Reply with quote

Basic Data provided are as follows:
Free swell index- 50 to 80%
Liquid limit- 40 to 70.
Column to column distance -20m
Maximum column Reaction-70mt.


I would like to have the Differential Free swell index of the soil rather than Free swell Index. Depending upon value of the differential free swell index, the degree of expansiveness can be approximately determined.
Degree of expansiveness is low if DFS is less than 20.
Degree of expansiveness is moderate if DFS percent varies from 20 to 35.
Degree of expansiveness is high if DFS percent varies from 35 to 50.
Degree of expansiveness is very high if DFS percent is greater than 50.
These data are available in Appendix A of IS: 2911(part-3)
Unfortunately no such details data are available for interpretation of Free Swell Index. The soil is considered to be problematic if the Free swell index is above 50%. In this case Free swell index varies to 50% to 80% which indicates soil is certainly expansive but the degree of expansiveness cannot be ascertained. But the liquid limit comes to our rescue. The Indian black cotton soils usually show a liquid limit varying from 40 to 100%. The Indian black cotton soils also have a degree of expansiveness from high to very high because of high percentage of montomorillonite which has surface electrical charge to attract water.
In this case liquid limit varies from 40 to 70 percent. Hence it can be considered that the soil has moderate to high degree of expansiveness.
I would have preferred to have two more data before I hazard a suggestion regarding foundation.
     The depth upto which this property continues ? Though the hard strata is at 10 m depth ,it might so happen that at a sallow depth say at 2.5m  to 3 m,the clay might have contained non-expansive characteristic. In that case removal of top expansive soil would have been the best solution. In case of Indian black cotton soil it is usually observed that Kankar and murrum is found below black cotton soil.
     Measurement of swelling pressure as per IS: 2720 (part XLI) should have been carried out to determine whether the load in column is adequate to counter the upward soil pressure. Nevertheless there are some empirical formulas available to calculate swelling pressure of the soil from the void ratio and plasticity index of the soil,Viz:
Ps=2.7-24(Ei/Pi)
Ps=swelling pressure in kg/sqcm
Ei=Initial void ratio.
Pi=plasticity Index in form of percentage.
The swelling pressure helps in determining whether a particular column (lightly loaded) in the structure is getting uplifted by swelling pressure. In other words column loads should counter the upward swelling pressure. Therefore it is undesirable to guess a very low Safe Bearing Capacity of soil and design the foundation without proper study of soil parameters. Low bearing capacity gives a large base area of footing which leads to higher upward pressure while the column load remains constant.

Now let us come back to the problem in hand. The good news is that water table is not encountered upto depth of 10m when the soil investigation is carried out in the month of June(Rainy season).Now what we have to take care that surface water due to rain fall should not find its way to foundations of building.
My suggestions are as follows:
1)     End bearing pile is not preferred considering the cost factor. Definitely it is a costly proposition.
2)     Underreamed pile is not preferred because forming a bulb at such a deeper depth of around 9m is not easy. The flap of the reamer may not act properly at such a high depth. Formation of proper bulb is doubtful.
3)     Hence go for Isolated footing/combined footing as per the load requirement. In the excavated pit, provide three layers of WEDGE SHEAR ELEMENT. Each layer of wedge shear element shall be 25cm thick comprising of 150mm to 200mm of basalt rock with sand and lime in proportion of 10:1. Over three layers of wedge shear elements provide P.C.C. OF 1:4:8 ratios of 100 mm thick and cast your footing over it. This arrangement shall give safe bearing capacity of 20t/sqm.
4)     Construct compound wall, cover the entire plot with good soil to a height of 500 mm (min). This overburden pressure shall add to Safe bearing capacity of soil.
5)     Provide concrete apron of 5m width all around the building to prevent percolation of surface water to under the floor the building. The 5m is based on assumption that horizontal coefficient permeability of soil is 50% of vertical coefficient of permeability.
6)     Replace the back cotton soil under the floor with non expansive soil with proper compaction. Do not submerge the floor area with water for compaction of filled up soil. Submerged water does not help in compaction of soil under the floor. Rather entrapped water shall create problem at a later date.

I was involved in construction of G+ 3 storied constructions to be used for residential purpose involving above method. Construction completed sometimes in 2001, performance is reported to be good.













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Last edited by P.K.Mallick on Mon Aug 10, 2009 6:10 pm; edited 2 times in total
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PostPosted: Mon Aug 10, 2009 7:19 am    Post subject: Reply with quote

Dear Er.Mallick,
Your suggestion for the footing of an industrial building over B.C soil is very interesting. Is it possible to attach a sketch explaining the description since all the description will be put into or translated in the form of a sketch which will be easily understood by people like me?

Thanks in advance.

With Best regards,
T.Rangarajan.
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PostPosted: Mon Aug 10, 2009 1:39 pm    Post subject: Reply with quote

Hi All,

Excellent suggestion by ER Mallick. Since he has applied it himself(this is the difference between a professor and practitioner) and found it to be successful, others can also emulate it.

Under-reamed piles should not be used in sands also, especially when the  water table is high. Normally the effect of drying will be felt till about 3m below G.L.

Regards
Subramanian
P.K.Mallick wrote:
Basic Data provided are as follows:
Free swell index- 50 to 80%
Liquid limit- 40 to 70.
Column to column distance -20m
Maximum column Reaction-70mt.


I would like to have the Differential Free swell index of the soil rather than Free swell Index. Depending upon value of the differential free swell index, the degree of expansive can be approximately determined.
Degree of expansiveness is low if DFS is less than 20.
Degree of expansiveness is moderate if DFS percent varies from 20 to 35.
Degree of expansiveness is high if DFS percent varies from 35 to 50.
Degree of expansiveness is very high if DFS percent is greater than 50.
These data are available in Appendix A of IS: 2911(part-3)
Unfortunately no such details data are available for interpretation of Free Swell Index. The soil is considered to be problematic if the Free swell index is above 50%. In this case Free swell index varies to 50% to 80% which indicates soil is certainly expansive but the degree of expansiveness cannot be ascertained. But the liquid limit comes to our rescue. The Indian black cotton soils usually show a liquid limit varying from 40 to 100%. The Indian black cotton soils also have a degree of expansiveness from high to very high because of high percentage of montomorillonite which has surface electrical charge to attract water.
In this case liquid limit varies from 40 to 70 percent. Hence it can be considered that the soil has moderate to high degree of expansiveness.
I would have preferred to have two more data before I hazard a suggestion regarding foundation.
     The depth upto which this property continues ? Though the hard strata is at 10 m depth ,it might so happen that at a sallow depth say at 2.5m  to 3 m,the clay might have contained non-expansive characteristic. In that case removal of top expansive soil would have been the best solution. In case of Indian black cotton soil it is usually observed that Kankar and murrum is found below black cotton soil.
     Measurement of swelling pressure as per IS: 2720 (part XLI) should have been carried out to determine whether the load in column is adequate to counter the upward soil pressure. Nevertheless there are some empirical formulas available to calculate swelling pressure of the soil from the void ratio and plasticity index of the soil,Viz:
Ps=2.7-24(Eli/Pi)
Ps=swelling pressure in kg/sqcm
Ei=Initial void ratio.
Pi=plasticity Index in form of percentage.
The swelling pressure helps in determining whether a particular column (lightly loaded) in the structure is getting uplifted by swelling pressure. In other words column loads should counter the upward swelling pressure. Therefore it is undesirable to guess a very low Safe Bearing Capacity of soil and design the foundation without proper study of soil parameters. Low bearing capacity gives a large base area of footing which leads to higher upward pressure while the column load remains constant.

Now let us come back to the problem in hand. The good news is that water table is not encountered upto depth of 10m when the soil investigation is carried out in the month of June(Rainy season).Now what we have to take care that surface water due to rain fall should not find its way to foundations of building.
My suggestions are as follows:
1)     End bearing pile is not preferred considering the cost factor. Definitely it is a costly proposition.
2)     Underreamed pile is not preferred because forming a bulb at such a deeper depth of around 9m is not easy. The flap of the reamer may not act properly at such a high depth. Formation of proper bulb is doubtful.
3)     Hence go for Isolated footing/combined footing as per the load requirement. In the excavated pit, provide three layers of WEDGE SHEAR ELEMENT. Each layer of wedge shear element shall be 25cm thick comprising of 150mm to 200mm of basalt rock with sand and lime in proportion of 10:1. Over three layers of wedge shear elements provide P.C.C. OF 1:4:8 ratios of 100 mm thick and cast your footing over it. This arrangement shall give safe bearing capacity of 20t/sqm.
4)     Construct compound wall, cover the entire plot with good soil to a height of 500 mm (min). This overburden pressure shall add to Safe bearing capacity of soil.
5)     Provide concrete apron of 5m width all around the building to prevent percolation of surface water to under the floor the building. The 5m is based on assumption that horizontal coefficient permeability of soil is 50% of vertical coefficient of permeability.
6)     Replace the back cotton soil under the floor with non expansive soil with proper compaction. Do not submerge the floor area with water for compaction of filled up soil. Submerged water does not help in compaction of soil under the floor. Rather entrapped water shall create problem at a later date.

I was involved in construction of G+ 3 storied constructions to be used for residential purpose involving above method. Construction completed sometimes in 2001, performance is reported to be good.











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PostPosted: Mon Aug 10, 2009 3:24 pm    Post subject: Reply with quote

thirumalaichettiar wrote:
Dear Er.Mallick,
Your suggestion for the footing of an industrial building over B.C soil is very interesting. Is it possible to attach a sketch explaining the description since all the description will be put into or translated in the form of a sketch which will be easily understood by people like me?

Thanks in advance.

With Best regards,
T.Rangarajan.


I would certainly attach the sketches.

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PostPosted: Tue Aug 11, 2009 8:35 pm    Post subject: Reply with quote

There are so many suggestions are posted for the proposed footing over the black cotton soil.
Suggestion are given to improve the bearing capacity of soil like:
1.Soil is mixed with LIME.
2.Stone coulmns.
3.Soil is mixed with cement+lime mix.ie chemical treatment.
4.As from the engineer removal of soil to 2 m depth and fill with aggregate+sand+ moorum. In this I can add the GEOTEXTILE FABRIC in between each layer as it will improve the BC further
5.Er.Mallick has given a wonderful solution with the LIVE example.
6.Also we can add PILE WITH RAFT FOUNDATION.

Now I want to suggest another technique ie use of VIRENDEEL GIRDER SYSTEM as discussed earlier in the forum under the link:

www.sefindia.org/forum/viewtopic.php?t=4792

I am attaching the procedure with a sketch(Since I do not have the AUTOCAD I drew with the help of MS WORD-So the sketch is to understand the description). As there is no W.T it is easy to build and no problem without  bulb  for the under reamed piles as the skin friction and end bearing will take care of the loads.

Any comment or suggestion is welcome.

T.Rangarajan.



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PostPosted: Wed Aug 12, 2009 3:01 am    Post subject: Reply with quote

In continuation of my previous suggestion, the following alternate is possible in the transverse direction of 20 m. As it is important to connect all the columns in both the x and y direction in PLAN instesd of Virendeel system, the two columns spaced at 20 m can be connected by means of STUB COLUMNS. The STUB COLUMNS MAY BE IN bRICK OR RR MASONRY OR RCC COLUMNS OR EVEN A 12" PILE SPACED AT 10'C/C AND CONNECTED BY  PLINTH BEAM AT FLOOR LEVE and a GRADE BEAM at ground level.. The pile depth may be from 10' to 15' as it is going to support the load from FFL to the top of pile.

T.Rangarajan.
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PostPosted: Wed Aug 12, 2009 9:43 am    Post subject: Reply with quote

Dear all,
The following link gives a fair idea about the foundation. It is from HINDU magazine containing one page.

http://www.thehindu.com/thehindu/pp/2009/01/17/stories/2009011750360400.htm

T.Rangarajan.
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PostPosted: Mon Sep 12, 2016 11:25 am    Post subject: Reply with quote

Dear Mallick Sir,

I read this very interesting concept you shared years ago.

Could you kindly upload a sketch?

Best,

Abhishek

P.K.Mallick wrote:
thirumalaichettiar wrote:
Dear Er.Mallick,
Your suggestion for the footing of an industrial building over B.C soil is very interesting. Is it possible to attach a sketch explaining the description since all the description will be put into or translated in the form of a sketch which will be easily understood by people like me?

Thanks in advance.

With Best regards,
T.Rangarajan.


I would certainly attach the sketches.
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