Soil Bearing Capacity Values as per IS 1904 — Complete Reference
Before a single brick is laid or a column is erected, the most fundamental question in any construction project is: "Can the soil carry the load?" The safe bearing capacity (SBC) of soil determines everything — foundation type, depth, size, and ultimately the safety of the entire structure. Overestimate it, and the building settles or collapses. Underestimate it, and you waste money on oversized foundations.
IS 1904:2021 (Code of Practice for Design and Construction of Foundations in Soils) and IS 6403 (Code of Practice for Determination of Bearing Capacity of Shallow Foundations) together provide the framework for bearing capacity assessment in India. This article gives you the ready-reference values and the methodology to determine SBC for your project.
Critical Rule: IS 1904 Table 1 values are presumptive bearing capacities — useful for preliminary design ONLY. For final design, actual SBC must be determined from soil investigation (bore log + lab tests) per IS 1892 and IS 6403.
Presumptive Bearing Capacity — IS 1904 Table 1
These values can be used for preliminary design and small structures (up to 2 storeys) where detailed soil investigation is not available. For anything larger, conduct a proper soil investigation.
| Soil Type | Safe Bearing Capacity (kN/m² or kPa) | Approx. in t/m² | Typical Depth (m) |
|---|---|---|---|
| Rock (hard) — intact | 3250 | 33 | Surface |
| Rock (soft/weathered) | 880 | 9 | Surface |
| Gravel, sand-gravel mix (dense) | 440 | 4.5 | 1.0-1.5 |
| Sand (coarse, dense) | 440 | 4.5 | 1.5 |
| Sand (medium, medium dense) | 245 | 2.5 | 1.5-2.0 |
| Sand (fine, loose) | 100 | 1.0 | 2.0+ |
| Clay (stiff) | 440 | 4.5 | 1.5 |
| Clay (medium) | 245 | 2.5 | 2.0 |
| Clay (soft) | 100 | 1.0 | 2.5+ |
| Black cotton soil | 130-150 | 1.3-1.5 | Below active zone (1.5-3.0m) |
| Filled-up ground | — | Not reliable | Requires investigation |
Important Disclaimer: These values are from IS 1904 Table 1 for preliminary assessment only. Actual SBC for design must be determined from site-specific soil investigation per IS 1892 (soil investigation) and IS 6403 (bearing capacity calculation). Using presumptive values for multi-storey buildings is not acceptable.
When Is Soil Investigation Mandatory?
IS 1892:1979 (Code of Practice for Subsurface Investigation) specifies when soil investigation is required:
| Project Type | Soil Investigation Required? | Minimum Bore Holes |
|---|---|---|
| Individual house (G, G+1) | Recommended but not mandatory | 1 bore hole |
| Residential building (G+2 to G+4) | Mandatory | 2 bore holes minimum |
| Multi-storey building (>G+4) | Mandatory | 1 per 500 m² of plot area, min 3 |
| Bridge/flyover | Mandatory | 1 per pier/abutment |
| Industrial building | Mandatory | 1 per heavy machine foundation + perimeter |
| Any structure on filled/soft ground | Mandatory | As per site conditions |
SPT Value and Bearing Capacity Correlation
The Standard Penetration Test (SPT) is the most common field test in India for estimating bearing capacity. IS 2131 specifies the SPT procedure. The N-value correlates to soil strength:
For Cohesionless Soils (Sand/Gravel)
| SPT N-value | Relative Density | Approx. SBC (kPa) | Foundation Type Suitable |
|---|---|---|---|
| 0-4 | Very loose | <50 | Pile foundation required |
| 4-10 | Loose | 50-100 | Raft or piles for heavy loads |
| 10-30 | Medium dense | 100-300 | Strip/isolated footings acceptable |
| 30-50 | Dense | 300-500 | Isolated footings, good bearing |
| >50 | Very dense | >500 | Excellent bearing for any structure |
For Cohesive Soils (Clay)
| SPT N-value | Consistency | Unconfined Compressive Strength (kPa) | Approx. SBC (kPa) |
|---|---|---|---|
| 0-2 | Very soft | <25 | <25 |
| 2-4 | Soft | 25-50 | 25-50 |
| 4-8 | Medium | 50-100 | 50-150 |
| 8-15 | Stiff | 100-200 | 150-300 |
| 15-30 | Very stiff | 200-400 | 300-500 |
| >30 | Hard | >400 | >500 |
Site Tip: SPT is the minimum investigation for any building foundation in India. For cohesive soils, also conduct UCS (Unconfined Compressive Strength) and consolidation tests for settlement prediction. Download SPT Test Report Format →
Foundation Type Selection Guide
| SBC (kPa) | Suitable Foundation | Typical Structure |
|---|---|---|
| >300 | Isolated footings | Multi-storey RCC frame |
| 150-300 | Combined/strip footings | Low-rise buildings |
| 100-150 | Raft foundation | Load-bearing masonry, light structures |
| 50-100 | Raft or piled raft | Any structure with ground improvement |
| <50 | Pile foundation only | Multi-storey on soft soil |
Black Cotton Soil — Special Considerations
Black cotton soil (expansive clay) is found across central and southern India (Maharashtra, Karnataka, Madhya Pradesh, Telangana). It poses unique challenges:
| Problem | Cause | IS Code Solution |
|---|---|---|
| Swelling in wet season | Montmorillonite clay absorbs water, expands | Foundation below active zone depth (IS 2720 Part 40) |
| Shrinkage in dry season | Clay loses water, shrinks, causing cracks | Under-reamed piles (IS 2911 Part 3) |
| Differential settlement | Non-uniform moisture changes | Plinth beam/grade beam mandatory |
| Low SBC | High plasticity reduces strength | Soil replacement or lime/cement stabilization |
Rule for Black Cotton Soil: Foundation depth must be below the "active zone" — the depth to which seasonal moisture changes occur. This is typically 1.5-3.0m in most Indian regions. Use under-reamed piles (IS 2911 Part 3) for individual buildings as the most reliable solution.
Permissible Settlement Limits — IS 1904
Even if bearing capacity is adequate, excessive settlement can make a structure unusable. IS 1904 limits:
| Structure Type | Max Total Settlement | Max Differential Settlement |
|---|---|---|
| Isolated footing on sand | 50 mm | 0.0015L (angular distortion) |
| Isolated footing on clay | 75 mm | 0.0015L |
| Raft on sand | 75 mm | 0.002L |
| Raft on clay | 100 mm | 0.002L |
Where L = length between columns or walls. Angular distortion of 1/500 to 1/666 (0.0015-0.002) is the limit to prevent cracking in infill walls and finishes.
Frequently Asked Questions
What is the bearing capacity of normal soil in India?
There's no single answer — it depends entirely on soil type. Medium sand: ~245 kPa (~2.5 t/m²). Medium clay: ~245 kPa. Soft clay: ~100 kPa. Hard rock: >3250 kPa. Always conduct a soil investigation for actual values.
What SBC is needed for a 4-storey building?
Minimum 150-200 kPa for isolated footings with reasonable footing sizes. Below 150 kPa, consider raft foundation or piles. A geotechnical engineer should verify based on actual column loads and soil profile.
Can I build on black cotton soil?
Yes, with proper precautions: under-reamed piles (IS 2911 Part 3), foundation below active zone, plinth beams, and proper drainage to prevent water accumulation near foundations. Many cities in Maharashtra and Karnataka are entirely on black cotton soil.
What tests determine bearing capacity?
SPT (Standard Penetration Test, IS 2131) for preliminary values. Plate Load Test (IS 1888) for direct measurement. Laboratory tests: UCS, triaxial, consolidation (IS 2720 series) for detailed analysis. CBR (IS 2720 Part 16) for pavement subgrade.
Download QA/QC Templates
| Template | Download |
|---|---|
| SPT Test Report | Excel / PDF ↓ |
| Excavation Inspection Checklist | Excel / PDF ↓ |
| Foundation Checklist | Excel / PDF ↓ |
| Plate Load Test Report | Excel / PDF ↓ |
| Soil Investigation Register | Excel / PDF ↓ |
Related Resources
- IS 1904 — Foundation Design Code
- IS 6403 — Bearing Capacity of Shallow Foundations
- IS 2911 — Pile Foundation Design
- All Soil & Foundation QA/QC Templates (16 formats)
- Construction Cost Calculator — Includes foundation cost estimation
References
- IS 1904:2021 — Design and Construction of Foundations in Soils — General Requirements
- IS 6403:1981 — Determination of Bearing Capacity of Shallow Foundations
- IS 1892:1979 — Code of Practice for Subsurface Investigation for Foundations
- IS 2131:1981 — Method for Standard Penetration Test for Soils
- IS 1888:1982 — Method of Load Test on Soils
- IS 2720 (Parts 1-41) — Methods of Test for Soils
- IS 2911:2021 — Code of Practice for Design and Construction of Pile Foundations