Soil bearing capacity

Geotechdata.info - Updated 28/06/2015 

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Allowable bearing capacity: The maximum pressure that can be applied to the soil from the foundation so that the two requirements are satisfied:

1. Acceptable safety factor against shear failure below the foundation
2. Acceptable total and differential settelement

Ultimate bearing capacity: The minimum pressure that would cause the shear failure of the supporting soil immediately below and adjacent to the foundation.

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Typical values of soil bearing capacity

For preliminary design purposes, BS 8004 [1] gives typical values of allowable bearing capacity which should result in an adequate factor of safety against shaer failure without accounting for the setllemenet criteria [2].

Soil type	Bearing value (kPa)	Remarks
Dense gravel or dense sand and gravel	> 600	Width of foundation not less than 1 m. Water table at least at the depth equal to the width of foundation, below base of foundation.
Dense dense gravel or medium dense sand and gravel	200-600	-
Loose gravel or loose sand and gravel	< 200	-
Compact sand	> 300	-
Medium dense sand	100 - 300	-
Very stiff boulder clays and hard clays	300 - 600	Susceptible to long term consolidation settelement
Stiff clays	150 - 300	-
Firm clays	75 -150	-
Soft clays and silts	< 75	-
Very soft clays and silts	-	-

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Ultimate bearing capacity for shallow foundations according to Terzaghi

The utimate bearing capacity for shallow foundations can be calculated using the relation proposed by Terzaghi [3]:

and the net ultimate bearing capacity:

With the bearing capacity factors:

	factor for surcharge
	factor for cohesion
	factor self-weight [4]
	factor self-weight [5]

and

B, L, D	Width, Length and Depth of foundation,
	cohesion, effective frinaction angle and effective unit weight

In case of a rectangular foundation, the terms of the above relations should be multiplied by the respective shape factors as follows [6]:

In case the loads are not applied vertically, additional factors should be also considered for inclined loads.

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SpreadSheet for Soil Bearing capacity: Free download

Geotechdata_Bearing_Capacity.xlsx

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 REFERENCES

1. BS 8004: (1986): Code of practice for foundations
2. Craig, R. F. (1986), Soil Mechanics, 4th ed., ISBN 0-412-38430-2
3. Tezaghi, K. (1943): Theoretical soil mechanics, John Wiley and sons, New York
4. Hansen, J. B. (1968): A revised extended formula for bearing capacity. Danish Geotechnical Institute Bulletin, No. 28
5. Meyerhof, G. G. (1963). Some recent research on the bearing capacity of foundations. Canadian geotechnical journal Vol. 1 No. 1
6. Terzaghi, K. and Peck, R. B. (1967): Soil mechanics in engineerin practice (2nd ed). John Wiley and Sons, New York

Citation :
Geotechdata.info, Soil Bearing capacity, http://geotechdata.info/parameter/bearing-capacity.html (as of April 15, 2015).

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Other soil parameters

• » Angle of friction
• » Cohesion
• » Dry unit weight
• » Young's modulus
• » Void ratio
• » Soil Permeability coefficient
• » Soil porosity

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