BRE470 Reference
BR 470 (BRE 2004)

Design Reference Tables

Quick reference for BRE470 design parameters

Tracked piling rig on working platform
Table A1 — Bearing Capacity Factor Nγ

Values of Nγ for use in bearing resistance calculations. Interpolate for intermediate values.

φ'd (°)Nγ
25°10.9
30°22.4
35°48
40°109
45°272
50°763
Table A2 — Punching Shear Coefficient Kp·tanδ

Values for the platform material. Used in platform thickness calculations.

φ'd (°)Kp·tanδ
35°3.1
40°5.5
45°10
Table A3 — Loading Factors (γq)

Partial factors applied to characteristic loading values.

LoadingNo PlatformWith Platform
Case 12.01.6
Case 21.51.2

Case 1: Operator UNLIKELY to aid recovery from imminent failure — standing, travelling, crane mode, lifting precast pile, handling casings/cages.

Case 2: Operator CAN control load safely — installing casing, drilling, extracting auger/casing, travelling with fixed mast and fixed load close to surface.

Table B1 — Characteristic cu from Description

Undrained shear strength based on qualitative description of cohesive subgrade.

QualityRange (kPa)cuk (kPa)
Very soft< 2010
Soft20 – 4020
Firm40 – 7540
Stiff75 – 15080

Note: Very soft subgrade (cu < 20 kPa) is outside the valid range for this design method.

Table B3 — Typical φ' for Platform Material

Based on particle strength and compaction level. Material with φ' < 35° is unsuitable.

Particle Strengthqc (MPa)Poor CompactionHeavy Compaction
Weak< 25UnsuitableUnsuitable
Medium25 – 5035°40°
Strong> 5035°45°
Shape Factor Equations
Cohesive shape factor:sc = 1 + 0.2 × (W / L)
Granular shape factor:sγ = 1 - 0.3 × (W / L)
Punching shape factor:sp = 1 + (W / L)
Bearing capacity (cohesive):Nc = (2 + π) = 5.14
Key Design Formulas

Cohesive Subgrade — Bearing Resistance

R = cu × Nc × sc

Granular Subgrade — Bearing Resistance

R = 0.5 × γ's × W × Nγs × sγ

Unreinforced Platform Thickness (Cohesive)

D = √(W × (qd - cu·Nc·sc) / (γp·Kp·tanδ·sp))

Unreinforced Platform Thickness (Granular)

D = √(W × (qd - 0.5·γ's·W·Nγs·sγ) / (γp·Kp·tanδ·sp))

With Geosynthetic Reinforcement

Additional resistance = 2 × Td / W
where Td = Tult / 2
Reinforcement Verification Factors

When using reinforcement, the unreinforced platform at the same thickness must also satisfy reduced loading:

ConditionFactor
Case 1 (ignoring reinforcement)1.25
Case 2 (ignoring reinforcement)1.05
Minimum Requirements
Minimum platform thickness: Lesser of 0.5 × W or 300 mm
Minimum cover to reinforcement: 300 mm
Rounding: Round up to nearest 25 mm
Edge distance: Minimum half machine width from platform edge
Access ramps: Extra 50% of design thickness

Important: This tool implements the routine design calculations from BRE470 Appendix A. It is intended for preliminary design purposes. All designs must be reviewed and approved by a competent geotechnical engineer. Slopes greater than 1 in 10 require specialist design not covered by this guide. The design method contains simplifying assumptions and cannot fully represent actual soil behaviour.