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foundation in black cotton soil
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sdec.in
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PostPosted: Sat Aug 01, 2009 5:30 am    Post subject: foundation in black cotton soil Reply with quote

Dear Manish

We have successfully used soil replacement by good soil/moorum, to a depth where stable soil is found, in sites with highly swelling soils in some projects at Indore and it has worked even better than under reamed piles in terms of economy and time of execution.Unfortunately we were not able to find many agencies willing to work with Lime and I personally feel stabilisation of soil with lime piles would work out to be most economical in such situations.

best regards

Sangeeta Wij
Quote:
----- Original Message -----
From: drnsmani (forum@sefindia.org)
To: general@sefindia.org (general@sefindia.org)
Sent: 30 July, 2009 11:08 PM
Subject: [SEFI] Re: foundation in black cotton soil


Dear Er Manish Shah,

We have used under-reamed piles in such situations. But as Er Mallick has pointed out, without the soil information, it may be difficult to suggest a suitable solution.

One more interesting observation. In swelling soil, single storey buildings will be more affected than two storey buildings, because of the light weight.

Best wishes
Subramanian
P.K.Mallick wrote:      manish_del wrote:  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?

Thanks in advance,

Manish Shah.


What is the depth of water table?
what is the minimum load and maximum load in columns of structure?
What is the liquid limit of soil at different depth?
What is the differential free swell index of soil at different depth ?






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manish_del
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PostPosted: Sat Aug 01, 2009 8:35 am    Post subject: foundation in black cotton soil Reply with quote

Dear Sir,

Thanks for your response.

Water table has not been met up to depth of 10m, when soil investigation was done in month of June.
The soil is medium expansive in nature, with free swell index varying from 50-80%.
The liquid limit varies from 40 to 70 at different bore-hole locations.
The structure is PEB steel structure with 20m span, with 20 ton capacity EOT cranes in some areas. The maximum column reaction would be about 60-70 MT.

Thanks and regards,

Manish Shah.



From: P.K.Mallick [mailto:forum@sefindia.org]
Sent: Saturday, August 01, 2009 7:15 AM
To: general@sefindia.org
Subject: [SEFI] Re: foundation in black cotton soil


P.K.Mallick wrote:        
manish_del wrote:    
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?

Thanks in advance,

Manish Shah.
    



What is the depth of water table?
what is the minimum load and maximum load in columns of structure?
What is the liquid limit of soil at different depth?
What is the differential free swell index of soil at different depth ?
    



The logic behind asking those questions is to ascertain whether it is expansive soil and If it expansive,what is the degree of expansiveness. All the black soils are not expansive soil.




P.K.Mallick
p.k.mallick1962@gmail.com (p.k.mallick1962@gmail.com)

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ergdr
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PostPosted: Sat Aug 01, 2009 5:31 pm    Post subject: foundation in black cotton soil Reply with quote

I have worked extensively in black cotton soil areas at Indore and Jabalpur and have provided under ream pile foundation in groups of 2 to 5 piles with pile cap below the columns.Even buildings not designed for EQ loads have worked well on such foundations. The buildings have been 4 to 6 storied both residensial and commercial,with spans up to 12 meters also.So you can try this.
Er.G.D.Rao
--- On Thu, 30/7/09, P.K.Mallick <forum@sefindia.org> wrote:
Quote:

From: P.K.Mallick <forum@sefindia.org>
Subject: [SEFI] Re: foundation in black cotton soil
To: general@sefindia.org
Date: Thursday, 30 July, 2009, 10:40 PM

      manish_del wrote:                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?

Thanks in advance,

Manish Shah.
     

What is the depth of water table?
what is the minimum load and maximum load in columns of structure?
What is the liquid limit of soil at different depth?
What is the differential free swell index of soil at different depth ?
     


P.K.Mallick
p.k.mallick1962@gmail..com

     



     

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PostPosted: Sat Aug 01, 2009 6:13 pm    Post subject: foundation in black cotton soil Reply with 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?

Thanks in advance,

Manish Shah.








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rahul.leslie
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PostPosted: Sun Aug 02, 2009 4:32 am    Post subject: Footing bearing stress Reply with quote

Dear SEFI’ans,

I haven’t under stood the implication of clause 34.4 of IS:456-2000, dealing with bearing pressure.

The clause 34.4 is: “The bearing pressure on the loaded area shall not exceed the permissible bearing stress in direct compression multiplied by a value equal to sq.root(A1/A2) but not greater than 2”. It says that the permissible bearing stress is

0.45 * fck * minimum.of (sq.root(A1/A2) & 2)

If I assume square footing and a square column, with b as column width and B as footing width, that makes it

0.45 * fck * minimum.of (B/b & 2)

The formula continues saying: “A1 = supporting area for bearing of footing, which in sloped or stepped footing may be taken as the area of the lower base of the largest frustum of a pyramid or cone contained wholly within the footing and having for its upper base, the area actually loaded and having side slope of one vertical to two horizontal ...”.

It explains that the base area is calculated from a truncated pyramid of side slope 1V:2H, starting from the column base to the bottom of the footing, provided the footing is larger than the pyramid thus assumed.

Assuming that the footing is larger , and being square as assumed above, the pyramid’s base dimension will be (b+4*d), d being the depth of the footing. And then the equation becomes

0.45 * fck * minimum.of ((b+4*d))/b & 2)

So far so good... but...

1) How does one find the ‘bearing pressure’ to be compared with the ‘permissible bearing stress’ obtained above?

2) Clause 34.4.1 says “Where the permissible bearing stress on the concrete in the supporting or supported member would be exceeded, reinforcement shall be provided for developing the excess force, either by extending the longitudinal bars into the supporting member...”. Further, clause 34.4.3 says “Extended longitudinal reinforcement or dowels of at least 0.5 percent of the cross-sectional area of the supported column...”. How is this significant when the minimum reinforcement to be provided in a column is 0.8% (see clause 26.5.3.1 a) which anyway exceeds 0.5%?

3) Doesn’t the thickness of footing have any effect on the allowable bearing? Since the term

minimum.of ((b+4*d))/b & 2)

in equation above, the limit of 2 puts that a depth d greater than b/4 has no significance.

Regards,
Rahul Leslie

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PostPosted: Sun Aug 02, 2009 6:39 am    Post subject: foundation in black cotton soil Reply with quote

2/8/2009

The problem with black cotton soil is that apart from its low shear strength, it is very prone to shrinkage upon withdrawal of moisture.

Providing stabilized macadam layer at 2.0 metre depth may not be helpful, as the pressure bulb under the footing would exend to a depth of 2*b, where 'b' is the width of the footing.

Constructing under-reamed files of length of about 10m. or more (assuming pile cut off level to be at 2 m. below ground)is no easy task: (1) the bulbs have to rest on soil with SPC 0f 12-15 t /sq.m.; and  (2) how does one ensure that the bulbs do get formed in accordance with what is shown on drawings without cave-ins in the bores at depths greater than 10m. below ground?

The solution may be to go in for bored RCC piles. But do consult a competent geo-technical specialist in this regard.

Indrajit Barua.


On Thu, 30 Jul 2009 manish_del 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?

Thanks in advance,

Manish Shah.








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thirumalaichettiar
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PostPosted: Sun Aug 02, 2009 4:58 pm    Post subject: Reply with quote

UNDER reamed pile is best option as stated by Er.Vikram jeet and the first proposal is the method of improving the BC of doil. It is good to use the GEOTEXTILE fabric in addition to the aggregate filling. The stone column with the proposed aggregate mixed with sand and moor um id good but I hope the cost of the UR pile will certainly work out as an economical solution.

Er.T.Rangarajan.
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PostPosted: Mon Aug 03, 2009 4:34 am    Post subject: Re: foundation in black cotton soil Reply with quote

praveerkum wrote:
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> 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?

Thanks in advance,

Manish Shah.








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PostPosted: Mon Aug 03, 2009 4:58 am    Post subject: Under-reamed piles Reply with quote

While selecting under reamed piles you have to be very careful for selection of appropriate dia of pile, length and bulbs.  It is preferred to adopt higher dia of pile (400-500 mm), with suitable no. of bulbs (preferably 2) based on column reactions.  As small dia of pile will lead to large pile group and pile cap, leading to uneconomical solution.
ajay
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PostPosted: Mon Aug 03, 2009 5:55 am    Post subject: Reply with quote

I'm sorry my posting to another subject (of mine) somehow found destiny here.... Please ignore my above posting...

Rahul Leslie
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