Bearing Capacity Calculator — Geotechnical Tool

Results

Factors

Charts

CFEM Resistance Factors

Soil Reference Data

Bearing Cap. Factors Reference Table

su Methods

Report

ULS Design

SLS / Settlement

Drained analysis — effective stress (φ' > 0) — CFEM 2023 Eq. 10.1

Undrained analysis — total stress (φ_u = 0, use s_u) — CFEM 2023 Eq. 10.6

Foundation adequacy check

Applied pressure vs governing q_allow. Required width = min. B for a square footing at current load P and FoS.

Parameter	Symbol	Value	Formula / Source

q_ult vs Footing Width B — Drained & Undrained

q_allow vs Embedment Depth D_f

q_ult vs Friction Angle φ' (drained)

Parameter Sensitivity — Drained q_ult

Each row shows the effect of independently varying a single input parameter by ±10% from its current value. The bar represents relative influence — a longer bar means that parameter has a larger effect on drained q_ult. Use this to identify which inputs most warrant careful site investigation.

High sensitivity (>60%) Moderate (30–60%) Low (<30%)

Parameter	Base value	+10% q_ult	−10% q_ult	Sensitivity

CFEM 2023 Table 10.1 — Bearing capacity factors N_c and N_q from Meyerhof (1963) and N_γ from Davis and Booker (1971). Highlighted row = current φ' in calculator. N_γ interpolated at current roughness setting shown at right.

N_γ formulas — Davis & Booker (1971) — CFEM eq.10.4/10.5

Smooth: N_γ ≈ 0.0663 · e^0.1623φ (φ > 10°)
Rough: N_γ ≈ 0.1054 · e^0.1675φ (φ > 10°)
Intermediate: linear interpolation (tool only — not explicit in CFEM)
N_c = (N_q − 1)cotφ — eq.10.2
N_q = e^πtanφ · tan²(45 + φ/2) — eq.10.3
φ = 0: N_c = 2+π = 5.14, N_q = 1, N_γ = 0 — eq.10.6–10.8

Current φ' interpolated values

—

φ (°)	N_c	N_q	N_γ rough	N_γ smooth	N_γ at current roughness

Geotechnical resistance factors (φ_gu, φ_gs) from CFEM 2023 Table 6.2, based on 2019 CHBDC calibration (Fenton et al. 2016). NBCC recommends these same values. Apply as: R_factored = φ_gu × q_ult.

Degree of Understanding

Low

Limited representative data — extrapolation from nearby/similar sites, conventional models

Typical

Typical site investigation + conventional prediction models → typical confidence

High
Extensive project-specific investigation + demonstrated models → high confidence

Shallow Foundations

Limit State	Method	Low	Typical	High
Bearing ULS (φ_gu)	Analysis	0.45	0.50	0.60
Bearing ULS (φ_gu)	Scale model test	0.50	0.55	0.65
Sliding — frictional ULS (φ_gu)	Analysis	0.70	0.80	0.90
Sliding — frictional ULS (φ_gu)	Scale model test	0.75	0.85	0.95
Sliding — cohesive ULS (φ_gu)	Analysis	0.55	0.60	0.65
Sliding — cohesive ULS (φ_gu)	Scale model test	0.60	0.65	0.70
Passive resistance ULS (φ_gu)	Analysis	0.40	0.50	0.55
Settlement / lateral mvmt SLS (φ_gs)	Analysis	0.70	0.80	0.90
Settlement / lateral mvmt SLS (φ_gs)	Scale model test	0.80	0.90	1.00

Source: CFEM 2023, Table 6.2 — Canadian Foundation Engineering Manual, 5th Edition (2023), Canadian Geotechnical Society. Values from Fenton et al. (2016) reliability calibration as adopted in the 2019 CHBDC.

The s_u value computed from the selected method is fed directly into the undrained bearing capacity calculation above. Select the method in the left panel.

UU Triaxial Test

No drainage during consolidation or shear. Measures in-situ state directly but sensitive to sample disturbance. B ≥ 0.95 required for saturation.

BS EN ISO 17892-8:2018; Head (1998)

CU Triaxial Test

Consolidated to in-situ stress then sheared undrained. More reliable for disturbed samples. Derives both φ_u and φ'. Standard for glacial till.

BS EN ISO 17892-8:2018; Atkinson (2007)

CPT / CPTu (Nkt)

s_u = (q_t − σ_v0) / N_kt. N_kt = 10–20, typically 12–15. Must be calibrated locally. Continuous profiling identifies heterogeneity.

Lunne et al. (1997); Robertson (2009) CanGeoJ 46(11)

SPT — Stroud (1974)

s_u ≈ 4.5 · N₆₀ (kPa) for stiff clays and tills. Factor of 2 uncertainty typical. Preliminary use only.

Stroud (1974) ESPT Stockholm Vol.2:2, 367–375

Pocket Penetrometer (PP)

Hand-held gauge measures unconfined compressive strength q_u directly in the field. Dial reads 0–4.5 TSF (Humboldt H-4215 or equivalent). s_u = q_u/2 = PP reading × 47.88 kPa. Factor of 2 variability is common; use for soil classification and consistency checks only, not final design.

CFEM 2023 §4; Humboldt H-4215

SHANSEP Method

s_u/σ'_v0 = S · OCR^m. S ≈ 0.20–0.30; m ≈ 0.80. Accounts for stress history. Best practice for OC glacial tills.

Ladd & Foott (1974) JGED ASCE 100(GT7), 763–786

Field Vane (FVT)

Apply Bjerrum (1972) correction: s_u = μ · s_u,vane. μ depends on plasticity index. Not suitable for gravel-bearing tills.

Bjerrum (1972) ASCE Purdue Conf. Vol.II, 1–54; ASTM D2573

Plasticity Correlation

s_u/σ'_v0 ≈ 0.11 + 0.0037·I_p for NC (Skempton 1957). For OC: multiply by OCR^0.8. Index test only.

Skempton (1957); Jamiolkowski et al. (1985) ICSMFE Vol.1

Pressuremeter (SBP)

Horizontal stress-strain from borehole expansion. Derives s_u from limit pressure. Expensive; specialist use for major structures.

Mair & Wood (1987) CIRIA/Butterworths

Computed su from selected method

—

Calculating…

Reference values from CFEM 2023 and standard geotechnical literature. Click any φ' row to pre-fill the friction angle slider. E-modulus ranges are indicative — select representative values based on site-specific testing.

Friction Angle φ' — Typical Ranges by Soil Type

USCS	Soil Description	φ' min (°)	φ' typical (°)	φ' max (°)	Notes
SP	Poorly graded sand, loose–medium	28	30	34	Increases with density
SP	Poorly graded sand, dense	30	33	37	Dense to very dense
SW	Well-graded sand, medium	30	32	36	Well-graded, medium dense
SW	Well-graded sand, dense	33	35	40	Dense; angular particles higher
SM	Silty sand	25	28	33	Depends on fines content
GW/GP	Gravel (well- or poorly-graded)	33	36	42	Angular gravel higher
GW	Dense angular gravel	37	40	45	Well-graded, angular particles
ML	Silt, low plasticity	22	25	30	Drained; use s_u for undrained
CL	Lean clay	22	26	30	Effective friction angle (drained)
CH	Fat clay, high plasticity	20	24	28	Lower than CL; sensitive to OCR
Till	Glacial till (sandy)	30	34	40	Highly variable; site-specific
Till	Glacial till (gravelly)	34	38	44	Dense; angular particles

Elastic (Young's) Modulus E — Typical Ranges for Settlement Analysis

Soil Type	Condition	E min (MPa)	E typical (MPa)	E max (MPa)	Notes
Soft clay	Normally consolidated	1	3	10	High compressibility; consolidation governs
Stiff clay	Overconsolidated	15	40	100	Much stiffer below pre-consolidation pressure
Silt, low plasticity	Medium dense	5	15	40	Highly variable; drainage-dependent
Loose sand (SP)	Uncemented	10	25	50	Increases with confinement
Medium dense sand	SP / SW	25	50	100	Use drained E' for long-term settlement
Dense sand	SP / SW	50	100	200	E ≈ 2–4 × q_c (CPT) for coarse-grained
Gravel (loose–med.)	GP / GW	50	100	200	Hard to sample; rely on in-situ tests
Dense gravel	GW angular	100	200	400	High stiffness; plate load test recommended
Glacial till (sandy)	Dense	50	120	300	Highly variable; pressuremeter preferred
Glacial till (gravelly)	Dense to very dense	100	250	600	Can approach rock stiffness when cemented
Soft rock / shale	Weak / weathered	200	1000	5000	Use intact E_i with RQD reduction

Sources: CFEM 2023 §10.9 & §10.12; Bowles (1996) Foundation Analysis and Design; Mayne & Poulos (1999); Lunne et al. (1997). φ' values assume drained effective-stress conditions. For undrained analysis of fine-grained soils use s_u directly. E values are guidance only — always confirm with site-specific investigation (CPT, PMT, plate load test, or laboratory triaxial).

ULS bearing check per CFEM 2023 §6 / NBCC 2020. WSD (factor of safety) always shown. LRFD check activates when DL + LL are entered in the Design section.

Working Stress Design (WSD) —

LRFD ULS — CFEM Eq. 6.1 Ψ × φ_gu × R̂_u ≥ 1.25DL + 1.50LL N/A

LSD parameters

—

Elastic settlement per CFEM 2023 Eq. 10.18 — Boussinesq stress integration beneath footing centre over compressible layer H. B&B: Burland & Burbidge (1985) for coarse-grained soils. SLS resistance check per CFEM Eq. 6.2.

Settlement calculation

—

SLS Check — CFEM Eq. 6.2 φ_gs × R̂_s ≥ DL + LL N/A

Notes: Settlement uses total service load P (unfactored). LRFD SLS check activates when DL + LL entered. Elastic: Boussinesq σ_z integrated from 0 to H using Fadum (1948) corner-influence superposition. B&B: Burland & Burbidge (1985) — coarse-grained soils; N₆₀ input via SPT su section. R̂_s is back-calculated as the load that produces δ_allow settlement. Allowable differential settlement typically 50–75% of total — engineer to verify.