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foundation in black cotton soil
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manish_del
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PostPosted: Thu Jul 30, 2009 4:15 am    Post subject: foundation in black cotton soil Reply with 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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vikram.jeet
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PostPosted: Thu Jul 30, 2009 11:53 am    Post subject: foundation in black cotton soil Reply with quote

UR piles foundation would be best option for 10m deep black cotton soil
layer.

vikramjeet

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suraj
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PostPosted: Thu Jul 30, 2009 2:49 pm    Post subject: Foundation On Black Cotton Soil Reply with quote

Eng Manish has raised a very practical & technical question linked to the fundamentals of the foundation engineering involving soil engineering. It is often that we highly educated engineers keep off the in depth studies of the soil engineering after qualifying the examination & the studies made during the education too are just for the purpose of getting through the examination. In the field, we leave the head ache of the soil exploration on to the soil engineers who are generally from the basic science fields in general.

Well, the question is relevant to the weakest soil designated Black Cotton which is known to all us as Clay. The properties & the conduct of this type of cohesive soil on coming in contact with water or moisture swells it to even 300degrees C while on drying, it develops crack in octagonal or hexagoinal form visible to eyes.

The buiding as described is Industrial must be having long spans & usually 12 to 15 m high. The soil bearing capacity SBC at 2 m depth cannot be more than a maximum of 5 T/sqm not acceptable for the proposed foundations. It is also not practicable to remove the soil upto 10 m. The Soil engineer's recommendation to improve the soil at 2 m from NGL placing 800 mm thick graded permeable layer shall definitely result in 15 to 20 T/sqm. But, provision of isolated footings alone is not a foolproof solution. Since the whole information about the building is unknown, further comments cannot be given.
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Suraj
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P.K.Mallick
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PostPosted: Thu Jul 30, 2009 5:09 pm    Post subject: Re: foundation in black cotton soil Reply with quote

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.

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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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Dr. N. Subramanian
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PostPosted: Thu Jul 30, 2009 5:38 pm    Post subject: Re: foundation in black cotton soil Reply with quote

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.

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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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pravin.pai
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PostPosted: Fri Jul 31, 2009 7:19 am    Post subject: foundation in black cotton soil Reply with quote

Dear Mr. Shah:
 
I remember having done some pipe-rack structures for Bombay High oil near Uran, way back in 1988-90. That time the firm I was working with had taken an opinion from IITB and they had suggested a process called as "Soil Stabilization" wherein you excavate the soil from founding level upto a certain depth (I do not remember the value now) and well mix it with lime (if I remember correctly 10 - 15%) and then refill the same - below the founding level. This stabilizes the soil. Actually black cotton soil swells when it gets moist (swelling pressure can be as high as 0.7 T/sqm) and this pressure reverses when it gets dry. So if you have light structures like pipe-rack, suddenly after a night's rain when you go to site the next morning you will find your footings have all risen above the ground - imagine what a shock you will receive!!
 
Regards
Pravin Pai


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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shireeshpatil
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PostPosted: Fri Jul 31, 2009 8:09 am    Post subject: Soil Stabilizing Reply with quote

Dear Mr. Shah,

I will suggest go for pile foundation. You are going to design a industrial building, where heavy loads may arise in the life of building at that time soil stabilization will not sustain. Pile foundation way may be costlier than stabilization but building life is more important. You can use end bearing piles for the same.

Thank & Regards

SHIREESH PATIL
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althaap
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PostPosted: Fri Jul 31, 2009 3:11 pm    Post subject: foundation in black cotton soil Reply with quote

Mr.shah

better provide under-reamed piles.


with regards,


T.Dhuraipandi

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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mks
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PostPosted: Fri Jul 31, 2009 6:28 pm    Post subject: Re: foundation in black cotton soil Reply with quote

Dear Sirs

In my opinion,  soil stabilization and UR piles both are the solution for this case. But the selection should be done according to colmn load, depth of water table,   differential free swell index of soil, etc as sighted by Mallick Sir.

Regards

Mithilesh

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.

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P.K.Mallick
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PostPosted: Sat Aug 01, 2009 1:44 am    Post subject: Re: foundation in black cotton soil Reply with quote

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.

Posted via Email


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.

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