FCAB Rules 41Chapter IV · Structural Materials and Control

Section 41 · Foundations. Section 43(2), 57(2)(m)

(1)

The foundations of every building shall be so constructed as to sustain the combined dead load of the building and the super-imposed load and to transmit those loads to the sub-soil in such a manner that the pressure on the sub-soil shall not exceed the safe pressure specified below:

S.No.	Type of rocks and Soil	Presumptive safebearing capacity	Remarks
	(a) Rocks-	Kg/cm2
1.	Rocks (Hard) without lamination and defects for example,granite trap and diorite	33	..
2.	Laminated rocks, for example, stone and lime stone in soundcondition	16.5	..
3.	Residual deposits of shattered and broken bedrock and hardshale, cemented material	9	..
4.	Soft rock	4.5	..
	(b) Non-cohesive soils -
5.	Gravel, sand and gravel, compact and offering high resistanceto penetration when excavated by tools.	4.5	See note 1.
6.	Coarse sand, compact and dry	4.5	Dry mean that the ground water level is at a depth not lessthan the width of foundation below the base of the foundation.
7.	Medium sand, compact and dry	2.5	..
8.	Fine sand, silt (dry lumps easily pulverised by the fingers)	1.5	..
9.	Loose gravel or sand gravel mixture; loose coarse to mediumsand dry.	2.5	See note 1.
10.	Fine sand loose and dry	1	..
	(c) Cohesive soils -
11.	Soft shale, hard or stiff clay in deep bed, dry	4.5	This ground is susceptible to long term consolidationsettlement.
12.	Medium clay, readily indented with a thumb nail	2.5	..
13.	Moist clay and sand clay mixture which can be indented withstrong thumb pressure	1.5	..
14.	Soft clay, indented with moderate thumb pressure	1	..
15.	Very soft clay which can be penetrated several centimetreswith the thumb	0.5	..
16.	Black cotton soil or other shrinkable or expensive clay indry condition (50 per cent saturation)	..	See note 2. To be determined after investigation.
	(d) Peat -
17.	Peat	..	See notes 2 and 3 to be determined after investigation.
	(e) Made up ground -
18.	Fills or made up ground	..	See notes 1 and 4. To be determined after investigation.

Note 1 : Compactness or looseness of non-cohesive materials may be determined by driving a wooden picket of dimensions x 5 centimetres x 5 centimetres x 70 centimetre with a sharp point. The picket shall be pushed vertically into the soil by the full weight of a person and if the penetration of the picket exceeds 20 centimetres, the loose state shall be assumed to exist.Note 2 : No generalised valves 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 pressures 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 methods used for consolidating it.Note 5 : The presumptive safe bearing values may be increased by amount equal to weight of the material (virgin soil) removed from above the bearing level that is, the base of foundation.Note 6 : For non-cohesive soils, the presumptive safe bearing value shall be reduced by 50 per cent, if the water table is above or near the bearing surface of the soil. If the water table is below the bearing surface of the foundation no such reduction shall apply. For intermediate depths of the water table, proportional reduction of the presumptive safe bearing value may be made.

(2)

The loads shall not cause such settlements of the building or any part of the building as may impair its stability.

(3)

For building 3 storey high, foundation shall be designed after making standard tests or establishing the safe bearing pressure of the soil and the foundations shall be taken down to such a depth or so constructed as to render the building immune from damage, from upheaval and movement due to seasonal variations in the content of the moisture in the ground.

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