SAFE BEARING CAPACITY VALUES OF DIFFERENT SOILS & ROCKS

Values of Safe Bearing Capacity

The safe bearing capacity of soil should be determined on the basis of soil test data or by performing some field test such as Standard penetration test or Plate load test etc.

However, in the absence of soil test data, the values of safe bearing capacity (S.B.C) as given in the following table may be used as a guide for preliminary analysis.

RECOMMENDED VALUES OF SAFE BEARING CAPACITY FOR PRELIMINARY ANALYSIS

Sl. No

TYPE OF ROCK OR SOIL

SAFE BEARING CAPACITY

(kN/m2)

(kg/cm2)

ROCKS

1 Rocks (hard) without lamination and defects, for example granite, trap and diorite 3300 33
2 Laminated rocks, for example sand stone and lime stone in sound condition 1650 16.5
3 Residual deposits of shattered and broken bed rock and hard shale, cemented material 900 9
4 Soft rock 450 4.5

NON-COHESIVE SOILS

5 Gravel, sand and gravel mixture, compact and offering high resistance to penetration when excavated by tools. (Refer Note 5) 450 4.5
6 Coarse sand, compact and dry (with ground water level at a depth greater than width of foundation below the base of footing) 450 4.5
7 Medium sand, compact and dry 250 2.5
8 Fine sand, silt (dry lumps easily pulverized by fingers) 150 1.5
9 Loose gravel or sand gravel mixture; loose coarse to medium sand, dry (Refer Note 5) 250 2.5
10 Fine sand, loose and dry 100 1

COHESIVE SOILS

11 Soft shale, hard or stiff clay in deep bed, dry 450 4.5
12 Medium clay, readily indented with thumb nail 250 2.5
13 Moist clay and sand clay mixture which can be indented with strong thumb pressure 150 1.5
14 Soft clay indented with moderate thumb pressure 100 1.0
15 Very soft clay which can be penetrated several centimeters with the thumb 50 0.5
16 Black cotton soil or other shrinkable or expansive clay in dry condition (50 percent saturation) (Refer Note 2) To be determined after site investigation
17 Peat (Refer Note 2 & 3)
18 Fills or made up ground (Refer Note 4 & 5)

Notes

  1. Values given in the above table can be adopted for design of unimportant and lightly loaded structures only.
  2. No generalized values for safe bearing capacities can be given for these types of soils. In such area, adequate site investigation is required to be carried out and expert advice should be sought.
  3. Peat may occur in a very soft spongy condition or may be quite firm and compact. While ultimate bearing capacity may be high in the compact cases, very large consolidation settlements occur even under small pressures and the movements continue for decades.
  4. The strength of made up ground depends on the nature of the material, its depth and age and methods used for consolidating it.
  5. Compactness or looseness of non-cohesive material may be determined by driving a wooden picket of dimension 5 cm x 5 cm x 70 cm with a sharp point. The picket is pushed vertically into the soil by full weight of a person and if the penetration of the picket exceeds 20 cm, then it considered as loose state.
  6. The safe bearing capacity value may be increased by an amount equal to weight of the material removed from above the bearing level that is the base of foundation.
5 Comments

Add a Comment

Your email address will not be published. Required fields are marked *