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Any simple test for estimation of Soil Bearing capacity
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elina.dutta2010
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PostPosted: Sun Mar 21, 2010 8:20 am    Post subject: Any simple test for estimation of Soil Bearing capacity Reply with quote

Dear Sefians,

Determination of bearing capacity of soil and depth of foundation for not so important building (two storey load bearing residential) in remote areas is a matter of concern especially for practising engineers starting their careers. The unfactored maximum pressure at the foundaion level due design load in the foundation for two storey brick masonry wall building may be around 5t/m2 (derived from 25kN/m on 0.5m wide strip footing). Soil experts may be able to suggest the bearing capacity by just seeing the site soil conditions.  Identify the type of soil and get the corresponding standard values will also be a crude method.

Laboratory testing of soil is possible, but may not be a feasible solution in this case. Is there any simple tests which can be done at site to determine the bearing capacity of soil? Some people say that wells in the neighbourhood of the site can give an idea of the soil stratum, and the depth of foundation.

If there are residential buildings (two storey) exist in the vicinity of 10-15 metres around the site (with foundation depth of around 0.6-0.7m), can we take that as an additional data for getting the confidence to fix the foundation depth?

Regards
Elina
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B.V.Harsoda
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PostPosted: Sun Mar 21, 2010 9:02 am    Post subject: Reply with quote

Miss Elina,

In practice S. B. C. is decided by visual observation of soil strata available in excavation of trial pits or foundation for small strcutures.In any book of building Constrution & also in N.B.C.Table for maximum safe bearing capacity of various soil & rock are given.

Simple method of field test for S.B.C. is METHOD OF DROPPING A WEIGHT, For this refer book Building Constrution By S.C. Rangwala.

Observation of near by existing building foundation depth is also helpful for decision.Due care shoud be taken in depth decision,considering  type of existing strcuture,our proposed sturucture & possibility of future  development of near by structures..

Best wishes

B. V. Harsoda
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PostPosted: Sun Mar 21, 2010 10:55 am    Post subject: SBC Resolution @ Site Reply with quote

SBC Resolution @ Site
Dear Eng Elina,

Well, agreed that for smaller buildings, laboratory may not help.

As suggested by Eng B. V. Harsoda ji, site pit may speak a lot about the subsoil nature.

Type of soil gives an excellent idea & that does not require any laboratory report.

One can use a transparent glass like any jar filled with water. Put small quantity of soil in that & stir well to dissolve by spoon for a couple of seconds.

Let the turbid water wait for hours till the soil settles to bottom & suspension remains in precipitation.

Bottom collection shall definitely tell about the apprx % of sand particles.

Near bottom minute particles shall give an idea about silt content.

Very minute particles contribution of water turbidity, shall advise about clay content.

Depth of moist soil as well as water table shall help in further assessment.

Higher contents of sand in combination of low amount of silt or clay helps.

Higher water table near the ground goes against BC.

Engineer has to understand the soil behaviour accordingly.

Loose soil can be visibly noticed.

Good soil can be noticed by walking on strata. Weight of person walking wearing the shoes or foot area contacting soil can be used to understand at least the static load sustainable. Jumping can further allow another assessment.

An Inquiry can also be made from the residents about soil type.

Local bodies responsible for construction may also be referred to.

Regards

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PostPosted: Sun Mar 21, 2010 1:01 pm    Post subject: Reply with quote

Dear Er Harsoda & Er Suraj Singh Sirs,

Thanks for the information. I personally have been exposed to only such projects where soil reports were available (you could say that I've been pampered in that). Thus, even after a decade in the design field, the thought of working with nothing other than visual inspection still makes me nervous.

As such, I would request you please to guide us on how to translate the qualitative impressions obtained from visual inspection of trial pits into a quantitative recommendation of SBC.

Regards,

Abhijeet Oundhakar
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PostPosted: Sun Mar 21, 2010 2:11 pm    Post subject: Any simple test for estimation of Soil Bearing capacity Reply with quote

Dear Madam,
 
there is no shortcut for estimate of the SBC of soil. It is advisable to consult a competent getechnical engineer for the type of foundation, founding level, SBC of the soil.
 
visual inspection  by experienced engineer can help reinforce the advise of the geotechnical engineer.
 
cheers
 
amarjeet singh


On Sun, Mar 21, 2010 at 2:32 PM, bharsoda <forum@sefindia.org (forum@sefindia.org)> wrote:
Quote:
  Miss Elina,

In practice S. B. C. is decided by visual observation of soil strata available in excavation of trial pits or foundation for small strcutures.In any book of building Constrution & also in N.B.C.Table for maximum safe bearing capacity of various soil & rock are given.

Simple method of field test for S.B.C. is METHOD OF DROPPING A WEIGHT, For this refer book Building Constrution By S.C. Rangwala.

Observation of near by existing building foundation depth is also helpful for decision.Due care shoud be taken in depth decision,considering type of existing strcuture,our proposed sturucture & possibility of future development of near by structures..

Best wishes

B. V. Harsoda







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PostPosted: Sun Mar 21, 2010 3:44 pm    Post subject: Any simple test for estimation of Soil Bearing capacity Reply with quote

Dear Sefian
Existing practices in any area certainly throws light. At the site while excavating , the ease or difficulty with which excavation is being possible also gives the idea. At a minimum depth of 0.9 m , we can check the strength of soil by dropping brick or stone and checking the depth of indentation . Some times if soil is too hard excavation of 0.9 m also becomes difficult. In that case 0.75 m may also be considered for small buildings.

A K JHA
Superintending Engineer,
C.P.W.D.
09312836256

--- On Sun, 21/3/10, elina.dutta2010 <forum@sefindia.org> wrote:

Quote:

From: elina.dutta2010 <forum@sefindia.org>
Subject: [SEFI] Any simple test for estimation of Soil Bearing capacity
To: general@sefindia.org
Date: Sunday, 21 March, 2010, 1:50 PM

Dear Sefians,

Determination of bearing capacity of soil and depth of foundation for not so important building (two storey load bearing residential) in remote areas is a matter of concern especially for practising engineers starting their careers. The unfactored maximum pressure at the foundaion level due design load in the foundation for two storey brick masonry wall building may be around 5t/m2 (derived from 25kN/m on 0.5m wide strip footing). Soil experts may be able to suggest the bearing capacity by just seeing the site soil conditions. Identify the type of soil and get the corresponding standard values will also be a crude method.

Laboratory testing of soil is possible, but may not be a feasible solution in this case. Is there any simple tests which can be done at site to determine the bearing capacity of soil? Some people say that wells in the neighbourhood of the site can give an idea of the soil stratum, and the depth of foundation.

If there are residential buildings (two storey) exist in the vicinity of 10-15 metres around the site (with foundation depth of around 0.6-0.7m), can we take that as an additional data for getting the confidence to fix the foundation depth?

Regards
Elina






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manishpatel
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PostPosted: Mon Mar 22, 2010 6:03 am    Post subject: Reply with quote

Dear Sefians,

The SBC of a soil depends on many parameters, when you change the loading conditions the SBC will be different for changed size of foundation or for different type of foundations as well. If you are aiming for supporting heavy loads, the soils at even far greater depth also comes in picture due to increased size of pressure bulb, the soil at surface or just below foundation level may not give correct picture to judge the overall soil underneath, so proper soil investigation is a must before arriving at final decision,There is no way to judge the SBC in visual examination only, and it should not be tried for heavier loads atleast.
Regards
Manish
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PostPosted: Mon Mar 22, 2010 6:44 am    Post subject: Soil Properties Reply with quote

Soil Properties
Dear Eng Abhijeet Oundhakar
It is agreed in principle that there is no alternative without soil testing for the required parameters but as said, for smaller houses & on good known soil, it is also not mandated always to repeat the test for soil exploring by bore holes when an experienced person knows about the soil performance in the concerned area.

An engineer must have a capacity to talk to soil about its nature by looking at its conduct that requires about a couple of observation months including passage of wet & dry seasions. All soils exhibit their defined structures that definitely are seen during such observations. For example, a good snady soil well graded in absence of high water table would definitely show a good capacity. Similarly, an engineer can differentiate among different soils types. Even, soil technician would observe all such parameters in addition to testing either by plate bearing capacity or to find value of N etc.

Too small house owner may not be in a capacity to afford soil testing but engineer may assist self to understand the soil & conclude based on ones working experience predicted conduct of soil. Many reports understood by engineers from considerable size projects shall help design engineer to understand the soil behaviour provided, engineer also accompanies the soil technician. Just reading the report & adopting the recommendation cannot help. Even the syllabus of post graduation would not help in this regard, howsoever, so done on soil mechanics. It is therefore, suggested that an engineer must look into soils of different types practically to know more & not just depend on reading test reports. It is an experience that pays in long run.

Regards

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IntPE(India)Suraj Singh FIE Civil
Engineering & Arbitration

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bijay sarkar
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PostPosted: Mon Mar 22, 2010 7:10 am    Post subject: Reply with quote

A beautifull write-up by Shri Suraj Singh Sir.  Mere printed results may not suffice to decide some civil engineering parameters like soil.  Though soil testing is being done for such small storied buildings in and around city areas,  thousands of other buildings in semi-urban area are also safely standing for several decades with some assumption for soil parameters & foundation depth.  For so many buildings even in city areas, foundation depth for such two storied buildings is taken as 0.75m or around and SBC considered is around 8 t/m2 to 15 t/m2 based on some visual inspection.


with regards,


Bijay Sarkar

M-9748510409

Kolkata
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vikram.jeet
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PostPosted: Mon Mar 22, 2010 7:33 am    Post subject: Any simple test for estimation of Soil Bearing capacity Reply with quote

SBC without performing geo-tech investigatioin for small buildings

I think this is very pertinent querry because in remote areas/Villages, far away
from cities, the facilities of soil investigation ,that too for small works, may cost
the low cost project very dearly(owner'thinking) and tendency of the owners
is to skip this by relying on the judgement of the engineer/designer.

National Building Code,though, provides sbc value for soils based on  
observation for small load bearing works, but confidence of a designer
always lies with the soil report.

The methods given by the highly experienced sefi members like
P Eng Sh Suraj Singh ji,Sh AK Jha ji , Sh BV Harsoda ji for having
judgement of sbc are quite informative and definately helpful.

I think in situations where soil reports are not available , the tendency  
of designer will definately be on conservative assumption, which
sometimes offsets the costs saved by avoiding the soil tests.

However keeping in view the practicality of situation in subject cases,there
is no option but to assume net sbc and precutions to be provided in form of
Notes in foundation drawings , such as under:
(though a scape goat option but something better than nothing)

1 Foundations are designed for a net SBC= - - - Tonne/sqm at - - -
meters below EGL (Assumed as per site information)
2 Foundations must rest on Firm strata capable of above stated sbc.
If firm strata is not met at indicated founding level, the foundations shall
be placed deeper under intimation to the designer.

3 Foundation level shall be approved by an experienced site engineer
(Civil)
4 The Foundation details are NOT valid for following soil stratas and
separate foundation details shall be needed
a) Filled -up-soil area
b) Strata in the vicinity of a water body like canal, Nallah , River,
Marshy area
c) Black cotton soil /expansive soils area.
d)Areas susceptible to flooding

Net Sbc in the range of 6.0 tonne/m2 to 8.0 tonne/m2 could be assumed  
based on informations for areas having low water table,
otherwise 60% to 75% of above values in high water table areas in absence
of soil reports .---may be conservative but could be at par also.

STILL, Soil Testing , a must for any project ,big or small as that
removes the guess work involved apart from providing informations
of strata beneath ,upto pressure bulb influence zone.

regards

vikramjeet












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