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es_jayakumar General Sponsor
Joined: 24 Nov 2011 Posts: 1408 Location: Cochin
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Posted: Sun Jan 31, 2016 3:07 pm Post subject: |
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A small Excel sheet prepared to verify the adequacy of the thickness of the raft provided for a slab type raft foundation, based on punching shear criterion, is enclosed.
E S Jayakumar
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Design of Raft Thickness.xls |
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SADATCHARAMOURTHY SEFI Member
Joined: 20 Jun 2009 Posts: 4
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Posted: Thu Feb 25, 2016 5:19 am Post subject: |
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Dear mohd_arastu
It's my humble request to send me your Excel sheet of Raft design on my below mail ID.
My Email ID is sadatcharamourthy@yahoo.com
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ynagaraju SEFI Member
Joined: 25 Apr 2016 Posts: 2
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Posted: Mon Apr 25, 2016 2:57 pm Post subject: Re: Excel sheet of Raft design |
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Dear mohd_arastu
It's my humble request to send me your Excel sheet of Raft design on my below mail ID.
My Email ID is archiedesigners1@gmail.com
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monikabothra SEFI Member
Joined: 31 Jan 2016 Posts: 2
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Posted: Sat Apr 30, 2016 12:17 pm Post subject: Raft / Strap Design |
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Dear mohd_arastu
It's my humble request to send me your Excel sheet of Raft design on my below mail ID.
My Email ID is monikabothra@ymail.com
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prash1730 SEFI Member
Joined: 02 Jul 2008 Posts: 5
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Posted: Sat Nov 07, 2020 2:45 pm Post subject: |
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Dear mohd_arastu,
Thanks a lot for preparing a spreadsheet spreadsheet for raft design. Request you to send a copy of the same to prash1730@gmail.com
Best regards,
PNP
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VPandya General Sponsor
Joined: 09 Nov 2009 Posts: 842
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Moosewala SEFI Member
Joined: 06 Aug 2020 Posts: 7
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Posted: Mon Jan 03, 2022 12:47 pm Post subject: |
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Sir,
Can we use the emperical formulas as given by E. Bowles using bearing capacity https://snaptube.cam/ of soil to calculate modulas of subgrade reaction? if yes, To what extent the values should be assumed to be appropriate ?
Regards.
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vikram.jeet General Sponsor
Joined: 26 Jan 2003 Posts: 3839
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Posted: Tue Jan 04, 2022 5:42 am Post subject: |
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STRUCTURE AND GEOTECHNICAL COMBINE
MODULUS OF SUBGRADE REACTION
The modulus of subgrade reaction is very important soil/rock parameter.
MODULUS K = (LOAD/AREA) /( CORRESPONDING SETTLEMENT)
Generally for field tests on 75cm circular plate , pressure for 1.25mm Settlement is taken .
Then K = p/0.125 MPA/cm = 10p / 0.125 kg/cm2/cm
P is the pressure for a settlement of 1.25mm on plate
REFER IS 9214 FOR DETERMINATION OF K VALUE
USEFUL SOIL DATA (AS PER SP-7, NBC OF INDIA)
COHESION LESS SOIL
LOOSE SOIL
RELATIVE DENSITY < 20%
SPT N VALUE (BLOWS/30CM) < 10
MODULUS OF SUBGRADE REACTION K 15000KN/m3(DRY,MOIST)
MOD OF SUBGRADE REACTION K 9000 kN/m3 (Submerged state)
MEDIUM SOILS
RD 20% TO 70%
SPT N VALUE 10 TO 30
K (DRY/MOIST) - 15000 - 47000 KN/m3
K (Submerged state) - 9000 - 29000 kN/m3
DENSE SOILS
RD> 70%
SPT N VALUE >30
K (DRY/MOIST) - 47000 - 180000 kN/m3
K (Submerged) 29000 - 108000 kN/m3
ALL ABOVE DATA IS FOR COHESION LESS SOILS
USEFUL SOIL DATA (AS PER SP-7 )
COHESIVE SOILS
SOFT TO VERY SOFT SOILS
SPT N VALUE < 4
UNCONFINED COMPRESSIVE STRENGTH - NOT GIVEN , MUST BE SMALL
MODULUS OF SUBGRADE REACTION K - NOT GIVEN
MEDIUM SOILS
SPT N VALUE 4 TO 8
UNCONFINED COMPRESSIVE STRENGTH Not given , but seems < 100 kN/m2 , since stiff values are given in range 100 - 200 kN/m2.
K value - not given , but seem < 27000 kN/m3 looking at range of stiff values
STIFF SOILS
SPT N VALUE 8 TO 15
UCS 100 - 200 KN/m2
Modulus of subgrade reaction K value 27000 kN/m3
VERY STIFF SOILS
SPT N VALUE > 15
UCS 200 - 400 KN/m2
Mod of subgrade reaction K value 27000 to 54000 kN/m3
HARD SOILS
SPT N VALUE > 15
UCS > 400 KN/m2
Mod of subgrade reaction K 54000 to 108000 kN/m3
UCS VALUES AND K VALUES ARE ON SQ PLATE 300X300MM
AV LOAD INTENSITY TO BE LESS THAN (ULTIMATE BC/2)
FOR MORE INFO REFER SP7 CHAPTER 6 ANNEXURE B
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vikram.jeet General Sponsor
Joined: 26 Jan 2003 Posts: 3839
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Posted: Tue Jan 04, 2022 5:45 am Post subject: |
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MODULUS OF SUBGRADE REACTION
EMPIRICAL FORMULA FOR CALCULATING MODULUS K
K= 0.65 {(Es*B^4)/(E I)}^(1/12) * Es/(1 - u^2) * 1/B
Approximately K can be taken as
K = 0.65 * Es/(1 - u^2) * 1/B
(1/12 the power term taken as nearly unity)
Es - Modulus of Elasticity of soil
E - Young's modulus of foundation material
u - Poisson ratio of soil
B - Foundations width
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vikram.jeet General Sponsor
Joined: 26 Jan 2003 Posts: 3839
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Posted: Tue Jan 04, 2022 5:47 am Post subject: |
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MODULUS OF SUBGRADE REACTION
FOR RIGID FOUNDATIONS :
MODULUS K = ( Average contact pressure)/(average settlement )
The ultimate BC = SBC* FOS
MODULUS K =( SBC * FOS) /(PERMISSIBLE SETTLEMENT)
The formula given by Foundation Design book by BOWELS is based on this.
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