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Soil Bearing Capacity Calculator
Calculate soil bearing capacity using Terzaghi & Meyerhof methods. Get allowable pressure, safety factors & foundation recommendations. Free geotechnical tool.
Soil Bearing Capacity Calculator
Estimate soil bearing capacity for different soil types and moisture levels. Includes safety factor and maximum safe load calculation. Free geotechnical calculator.
Range: 1.5-5.0 (typical 2.0-3.0)
Enter to calculate maximum safe load
Enter to calculate maximum safe load
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- This is a BASIC ESTIMATOR only. Actual bearing capacity MUST be determined through professional soil testing and geotechnical analysis.
- Always consult a qualified geotechnical engineer before construction.
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📚 In-Depth Guide
This calculator is part of a comprehensive guide
Soil Bearing Capacity Calculator — Complete Geotechnical Guide
Estimate ultimate and allowable bearing capacity for isolated, strip, and raft foundations using Terzaghi, Meyerhof, and IS 6403 methods. Includes settlement checks for safe geotechnical design.
How Soil Bearing Capacity is Determined
Ultimate bearing capacity (qult) is the maximum pressure per unit area at which the soil beneath a footing will shear and fail — the classic Terzaghi failure mechanism where a punching or general shear wedge forms under the footing and the surrounding soil heaves. The allowable bearing capacity (qa) divides this by a factor of safety (typically 2.5–3.0) to account for uncertainties in soil data, load estimation, and construction variability.
However, ultimate capacity is only half the story. In many soils — particularly soft clays, loose sands, and fills — the foundation will reach intolerable settlement long before shear failure. IS 1904 limits isolated footing settlement to 25 mm and differential settlement to 20 mm for buildings on sand; for raft foundations, 65 mm total and 25 mm differential. Serviceability often governs in soft soils even when the bearing capacity safety factor is comfortable.
Field investigation informs the design: the Standard Penetration Test (SPT) N-value correlates empirically to bearing capacity and relative density of sand; the Cone Penetration Test (CPT) gives continuous stratigraphy; laboratory triaxial and direct shear tests measure the cohesion c and friction angle φ needed for Terzaghi / Meyerhof equations. Never rely on table values alone for structural foundations — always verify with site-specific borings or trial pits.
Design Checklist
Bearing Capacity Formulas
q_ult = c·Nc + q·Nq + 0.5·γ·B·Nγ
where q = γ·Df (overburden pressure)Nc, Nq, Nγ are Terzaghi bearing capacity factors (functions of φ). For square footings: 1.3cNc + qNq + 0.4γBNγ. For circular: 1.3cNc + qNq + 0.3γBNγ. Valid for general shear only (dense sand / stiff clay).
q_ult = c·Nc·Fcs·Fcd·Fci
+ q·Nq·Fqs·Fqd·Fqi
+ 0.5·γ·B·Nγ·Fγs·Fγd·FγiF_s = shape, F_d = depth, F_i = inclination correction factors. IS 6403 recommends Meyerhof factors with Indian practice modifications. More versatile than Terzaghi — handles inclined loads, sloped ground, and eccentric loads.
q_a = q_ult / FOS (typically FOS = 3.0)
P_safe = q_a × A_footing
A_footing = column load / q_aNet bearing capacity: q_net = q_ult − γDf. For existing footings already embedded, use net values. For new footings, use gross q_ult / FOS. Always check both gross and net to be conservative.
S_i = q·B·(1−μ²)/E_s · I_w
S_i ≤ 25 mm (isolated), ≤ 65 mm (raft)μ = Poisson ratio (0.3 sand, 0.45 clay), E_s = soil modulus (MPa), I_w = influence factor (shape/rigidity). Consolidation settlement in clay: S_c = Cc·H/(1+e₀) × log[(σ₀+Δσ)/σ₀]. Consolidation often governs over shear in soft clays.
Soil Types — Typical Bearing Capacities
| Soil Type | Allowable SBC (kPa) | SPT N-value | φ (degrees) | Behaviour |
|---|---|---|---|---|
| Hard / dense rock (basalt, granite) | 3000–10000 | N/A (rock) | — | Elastic — no shear failure; settlement negligible |
| Soft rock (sandstone, limestone) | 600–3000 | N/A | — | Elastic; check for jointing and dissolution features |
| Dense sand / gravel (well graded) | 300–600 | > 50 | 38–45° | General shear; settlement in mm range; water table critical |
| Medium-dense sand | 150–300 | 10–50 | 30–38° | Moderate bearing; settlement in 25–50 mm range |
| Loose sand / fill | 50–150 | < 10 | < 30° | Local/punching shear; settlement often governs; liquefaction risk |
| Stiff clay (cu > 100 kPa) | 150–300 | 15–30 | φ = 0 for undrained | Undrained bearing controls short-term; consolidation long-term |
| Medium clay (cu 50–100 kPa) | 75–150 | 5–15 | φ = 0 undrained | Significant consolidation settlement; needs surcharge timing |
| Soft clay (cu < 50 kPa) | < 75 | < 5 | φ = 0 undrained | Settlement governs; piled or raft foundation usually required |
Source: IS 1904:1986, BS EN 1997-1:2004, NAVFAC DM-7. Tabulated values are for preliminary design only; site-specific investigation is mandatory for all structural foundations.
History of Geotechnical Engineering
Charles-Augustin de Coulomb publishes his earth pressure theory, including the wedge failure mechanism and the equation τ = c + σ tan φ (cohesion + friction), which remains fundamental to soil mechanics two and a half centuries later. Coulomb was designing retaining walls for French military fortifications.
Henry Darcy publishes his law of flow through porous media (Q = kAi), establishing the mathematical framework for groundwater flow and consolidation. Darcy's Law underpins all seepage, drainage, and pore-pressure analysis in geotechnical engineering.
Probable year of the first systematic use of the Standard Penetration Test (SPT) in the United States, developed by engineers at the Raymond Concrete Pile Company. The SPT N-value remains the most widely used in-situ soil test globally, correlating to bearing capacity, relative density, and liquefaction susceptibility.
Karl von Terzaghi publishes Erdbaumechanik (Soil Mechanics), founding soil mechanics as a scientific discipline. He introduces effective stress (σ' = σ − u), consolidation theory, and the first rigorous bearing capacity analysis. Terzaghi is universally regarded as the "father of soil mechanics."
Terzaghi publishes Theoretical Soil Mechanics, including his landmark bearing capacity equations (q_ult = cNc + qNq + 0.5γBNγ) for strip footings with general shear failure. George Meyerhof later extends these (1951, 1963) to include shape, depth, and inclination factors, creating the IS 6403 framework used today.
Eurocode 7 (EN 1997) is developed and published, harmonising geotechnical design across Europe with a limit-state design approach (ULS + SLS) replacing allowable stress design. Partial factors replace global FOS = 3; Design Approach 1/2/3 offers alternative load-resistance factoring. Most European countries now use EC7 as the primary geotechnical design code.
Codes & Standards
IS 6403:1981 — Code of Practice for Determination of Bearing Capacity of Shallow Foundations (India)
The primary Indian standard for bearing capacity calculations. Adopts Meyerhof's general formula with shape, depth, and inclination correction factors. Covers strip, isolated, and raft foundations; includes SPT-based correlations for sand and SPT-to-cu correlations for clay. Mandatory for Indian construction.
EN 1997-1:2004 — Eurocode 7: Geotechnical Design (Europe)
The European limit-state geotechnical design standard. Replaces global FOS with partial factors on soil strength and structural loads. Design Approaches 1, 2, and 3 give alternative partial factor sets. Annex D provides analytical bearing resistance formulae equivalent to Meyerhof. Used across 30+ European countries.
ASCE 7-22 & NAVFAC DM-7 (USA)
ASCE 7-22 provides load combinations for geotechnical design; NAVFAC DM-7 (Design Manual 7, Naval Facilities Engineering Command) is the US reference manual for soil mechanics and foundation engineering, with comprehensive bearing capacity tables, SPT correlations, and settlement charts widely cited in US practice.
Soil Bearing Capacity Myths vs Facts
If the soil doesn't sink when you walk on it, it can take any building load
Soil failure is not visible underfoot — a person exerts about 30 kPa (standing) to 150 kPa (stiletto heel), while a 10-storey building exerts 150–300 kPa over its full raft area. Soil that feels solid underfoot may be soft clay capable of only 50–75 kPa allowable pressure. Always investigate with borings — visual inspection cannot determine bearing capacity.
A higher FOS (factor of safety) is always safer
Increasing FOS beyond 3.0 increases foundation size and cost but does not improve safety if settlement governs. In soft clays, serviceability (settlement ≤ 25 mm) often controls long before shear failure. An oversized shallow footing on soft clay will still settle excessively. The correct response to poor soil is to change the foundation type (piles, raft), not simply raise FOS.
The water table depth has no effect once foundations are above it
The water table reduces effective stress in the soil below it, potentially halving the bearing capacity contribution of the depth term (qNq) and the width term (0.5γBNγ) if the water table is at or above footing level. IS 6403 requires correction factors for water table position. Even seasonal water table fluctuation must be considered — design for the worst-case water level.
SPT N-values directly give allowable bearing capacity
SPT N-values are correlated empirically to bearing capacity (e.g., Terzaghi & Peck chart, IS 6403 Table 1), but these correlations have wide scatter bands (±50%). The same N=20 value in a fine-grained or gravelly sand will give very different actual bearing capacity. SPT N-values are a screening tool; detailed laboratory tests (triaxial, consolidation) are needed for final design of important structures.
Frequently Asked Questions
What is the typical allowable bearing capacity of ordinary residential soil in India?▾
What is the difference between gross and net bearing capacity?▾
Why is a factor of safety of 3 commonly used for foundations?▾
What is punching shear failure vs general shear failure?▾
How does the water table depth affect the bearing capacity calculation?▾
What is the minimum depth of a foundation as per IS 1080?▾
When is a raft (mat) foundation required instead of isolated footings?▾
What is the safe bearing capacity of black cotton soil?▾
How do I choose between Terzaghi and Meyerhof bearing capacity methods?▾
What is the relationship between SPT N-value and bearing capacity per IS 6403?▾
What causes differential settlement and how can it be prevented?▾
How do I account for seismic effects on soil bearing capacity?▾
References
- IS 6403:1981 — Code of Practice for Determination of Bearing Capacity of Shallow Foundations, BIS
- IS 1904:1986 — Code of Practice for Design and Construction of Foundations in Soils: General Requirements, BIS
- Terzaghi, K. (1943) — Theoretical Soil Mechanics, John Wiley & Sons
- Meyerhof, G.G. (1963) — "Some Recent Research on the Bearing Capacity of Foundations," Canadian Geotechnical Journal 1(1):16–26
- EN 1997-1:2004 — Eurocode 7: Geotechnical Design — Part 1: General Rules, CEN
- Das, B.M. (2021) — Principles of Foundation Engineering, 9th Ed., Cengage Learning
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Design Safe Foundations with Confidence
Estimate allowable bearing capacity, check settlement limits, and size your footings accurately — backed by IS 6403, Terzaghi, and Meyerhof methods.