DESIGN OF FOUNDATIONS - PRESUMPTIVE BEARING CAPACITY VALUES FROM CODES.

For the design of foundations of lightly loaded structures and for a preliminary design of any structure the presumptive safe bearing capacity may be used. The presumptive safe bearing capacities of various types of soils are given in Table 2.2.

TABLE 2.2  PRESUMPTIVE SAFE BEARING CAPACITY ( IS: 1904-1961 )

Note 1. Compactness or loosenEss of non-cohesive matenais may be determined by driving a wooden picket of dimension 5cm x 5 cm x lOcm with a sharp point. The picket shall be pushed vertically into the soil by full weight of a person and if the penetration of the picket exceeds 20 cm, the loose state shall be asaumed to exist.

Note 2. No generalised values for presumptive safe bearing capacities can be given for these types of soils. In such area, adequate site investigation shall be carried out and expert advice shall be sought.

Note 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 presures and the movements continue for decades.

Note 4. The strength of made-up ground depends on the nature of the material, its depth and age, and the method used for consolidating it.

Note 5. The presumptive safe bearing values may be increased by an amount equal to weight of the material (virgin soil) removed from above the bearing level, that is, the base of the foundation.

Note 6. For non-coheisve soils, the presumptive safe bearing values shall be reduced by 50 percent if the water table is above or near the bearing surface of the soil. If the water table is below tje bearing surface of the soil at a distance at least equal to the width of the foundation, no such reduction shall apply. For intermediate depths of the water table, proportional reduction of presumptive safe bearing value may be made.

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