IS 6403:1981 is the Indian Standard (BIS) for determination of bearing capacity of shallow foundations. This code provides a methodology for calculating the ultimate bearing capacity of soils under shallow foundations based on shear failure criteria. It covers both general and local shear failure conditions and includes modifying factors for foundation shape, depth, load inclination, and the effect of the water table. The code also gives guidance on estimating bearing capacity from in-situ tests like SPT and plate load tests.
Provides methods and guidelines for calculating the ultimate and safe bearing capacity of shallow foundations on various types of soils.
Key bearing capacity factors, shape/depth/inclination factors, settlement limits, and field test correlations for shallow foundations.
| Reference | Value | Clause |
|---|---|---|
| Bearing Capacity Factor, Nc (φ=0°)— For general shear failure in cohesive soils (undrained). | 5.14 | Cl. 5.1.2 (Table 1) |
| Bearing Capacity Factor, Nq (φ=0°)— For general shear failure in cohesive soils (undrained). | 1.0 | Cl. 5.1.2 (Table 1) |
| Bearing Capacity Factor, Nγ (φ=0°)— For general shear failure in cohesive soils (undrained). | 0.0 | Cl. 5.1.2 (Table 1) |
| Bearing Capacity Factor, Nc (φ=30°)— For general shear failure. | 30.1 | Cl. 5.1.2 (Table 1) |
| Bearing Capacity Factor, Nq (φ=30°)— For general shear failure. | 18.4 | Cl. 5.1.2 (Table 1) |
| Bearing Capacity Factor, Nγ (φ=30°)— For general shear failure. | 22.4 | Cl. 5.1.2 (Table 1) |
| Shape Factor, sc (Square/Circle) | 1.3 | Cl. 5.1.3 (Table 3) |
| Shape Factor, sq (Square/Circle) | 1.2 | Cl. 5.1.3 (Table 3) |
| Shape Factor, sγ (Square) | 0.8 | Cl. 5.1.3 (Table 3) |
| Depth Factor, dq = dγ (for φ > 10°)— D=depth, B=width of footing. | 1 + 0.1(D/B)tan(45+φ/2) | Cl. 5.1.3 |
| Inclination Factor, ic = iq— α is load inclination from vertical in degrees. | (1 - α/90)² | Cl. 5.1.3 |
| Inclination Factor, iγ— α is load inclination, φ is friction angle (both in degrees). | (1 - α/φ)² | Cl. 5.1.3 |
| Mobilized Cohesion (Local Shear)— Use c' and φ' in BC equations for local shear failure. | c' = (2/3)c | Cl. 6.1 |
| Mobilized Friction (Local Shear)— Use c' and φ' in BC equations for local shear failure. | tan(φ') = (2/3)tan(φ) | Cl. 6.1 |
| Water Table Correction Factor, W'— Applied to γ term if water table is at or above footing base. | 0.5 | Cl. 5.1.4 |
| Max Settlement (Isolated, RC, Sand) | 50 mm | Cl. 8.2 (Table 2) |
| Max Settlement (Isolated, RC, Clay) | 75 mm | Cl. 8.2 (Table 2) |
| Max Settlement (Raft, RC, Sand) | 75 mm | Cl. 8.2 (Table 2) |
| Max Settlement (Raft, RC, Clay) | 100 mm | Cl. 8.2 (Table 2) |
| Max Differential Settlement (Sand)— L is c/c distance between columns or length of deflected part. | L/300 or 25 mm | Cl. 8.2 (Table 2) |
| Settlement from PLT (Clay)— Sf/Sp: foundation/plate settlement; Bf/Bp: foundation/plate width. | Sf/Sp = Bf/Bp | Cl. 9.1.4 |
| Settlement from PLT (Sand)— Bf and Bp are foundation and plate widths in metres. | Sf = Sp * [(Bf(Bp+0.3))/(Bp(Bf+0.3))]² | Cl. 9.1.4 |
BIM-relevant code. See the BIM Hub for ISO 19650, IFC, and LOD/LOIN frameworks used alongside it.
| Parameter | IS Value | International | Source |
|---|---|---|---|
| Design Safety Approach | Global Factor of Safety (typically 2.5 to 3.0) | Partial Factors of Safety (e.g., γ_R,v = 1.4 on bearing resistance for Design Approach 1) | EN 1997-1 |
| Bearing Factor Nq (for φ=30°) | 18.4 | 18.4 (from formula e^(π tanφ) tan²(45+φ/2)) | EN 1997-1 |
| Bearing Factor Nγ (for φ=30°) | 22.4 (from Vesic) | 20.1 (from formula 2(Nq-1)tanφ) | EN 1997-1 |
| Shape Factor s_q (Square Footing, φ=30°) | 1.2 (for φ>10°) | 1.5 (from formula 1 + sinφ) | EN 1997-1 |
| Shape Factor s_γ (Square Footing) | 0.8 | 0.7 (from formula 1 - 0.3 B'/L') | EN 1997-1 |
| Treatment of Eccentricity 'e' | Use effective width B' = B - 2e | Use effective width B' = B - 2e | EN 1997-1 |
| Inclination Factor i_q (Load Inclination α) | i_q = (1 - α/90°)^2 | i_q = (1 - H/(V+A'c'cotφ'))^m (more complex) | EN 1997-1 |