What is the minimum depth for a foundation?

50 cm below the natural ground level, after removal of topsoil and any disturbed soil (Clause 6.2.1).

What is the normal factor of safety against bearing capacity failure?

A minimum of 2.5 is used for static loads. This can increase to 3.0 or more depending on uncertainties and the importance of the structure (Clause 7.1.1).

What is the maximum allowable settlement for an isolated RCC footing on clay?

75 mm for total settlement and a differential settlement of L/1000 (Table 2).

Should I use this code for pile foundations?

No, this code is for shallow foundations (footings, rafts). For pile foundations, refer to the IS 2911 series.

IS 1904

: 1986

Code of practice for design and construction of foundations in soils (General requirements)

CurrentEssentialCode of PracticeBIMGeotechnical · Building Planning and Design

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This code outlines the general requirements for the design and construction of shallow foundations in various soil types. It provides guidelines on required site investigation, determination of safe bearing capacity, and permissible settlement limits for different types of structures.

Lays down general requirements for the design and construction of foundations for buildings and structures in different soil types.

Quick Reference Values

Minimum depth of foundation500 mm

Minimum Factor of Safety against bearing capacity failure2.5

Permissible total settlement for isolated foundations on sand50 mm

Permissible total settlement for isolated foundations on clay75 mm

Permissible total settlement for raft foundations on sand75 mm

Permissible total settlement for raft foundations on clay100 mm

Permissible differential settlement for steel structuresL/500

Permissible differential settlement for RCC structuresL/1000

Key Formulas

General Bearing Capacity Equation (Annex B) for determining ultimate bearing capacity

Practical Notes

The presumptive Safe Bearing Capacity values in Table 1 are for preliminary design and small projects only; a proper soil investigation as per IS 1892 is mandatory for most projects.

The effect of the water table is critical; its rise can reduce the bearing capacity by up to 50%. This must be accounted for in calculations (Clause 7.2.2).

Differential settlement is often more critical for structural safety and serviceability than total settlement. Pay close attention to the limits in Table 2.