Shallow foundation bearing is the ability of the ground just beneath a footing, pad or raft to carry the load placed on it without shearing and without settling more than the structure can tolerate. You work it out by finding the ultimate bearing capacity from soil strength and footing geometry, applying a safety factor or Eurocode 7 partial factors, then checking settlement. In UK practice, settlement usually decides the footing size, not the capacity.
This guide sets out what counts as a shallow foundation, how bearing capacity is calculated, why settlement often governs, and where the UK’s prescriptive shortcuts stop working. It is written for engineers, technicians and project managers at consultancies and construction firms who need to get this right and move on.
TL;DR
- A foundation is shallow when its embedment depth is no more than about its width (Df ≤ B), or in looser usage up to roughly twice its width.
- Ultimate bearing capacity comes from cohesion, overburden and self-weight terms; a factor of safety (typically 2.5 to 3.0 with BS 8004-style practice) gives the allowable value.
- In the UK, settlement limits frequently size the footing, particularly on clay, so a capacity check alone is not enough.
- Approved Document A suits simple domestic ground; trees, slopes, a high water table or heavy loads call for site investigation and full Eurocode 7 design.
- If your team is stretched, we can embed engineers to produce review-ready foundation calculations to UK standards.
Table of Contents
- What counts as a shallow foundation
- The two ideas behind bearing
- How to calculate ground bearing capacity
- Why settlement usually governs
- Eurocode 7 and the move away from BS 8004 habits
- When Approved Document A is enough, and when it is not
- Water, drainage and the details around the footing
- Our perspective: what we see on shallow foundation packages
- Choosing the foundation type once capacity is known
- Getting foundation design support without hiring
- FAQ
- Sources
What counts as a shallow foundation
The usual geotechnical definition is that the foundation width B is equal to or greater than its embedment depth Df, so Df ≤ B. The FHWA shallow foundations circular gives that definition and also notes a looser rule of thumb, where shallow foundations bear at less than about two times the width (Df ≤ 2B). The same idea appears in these online soil mechanics lecture notes.
The practical meaning is simple. The load reaches the soil through the base of the footing, and the soil’s resistance along the sides is small compared with what sits under it. That is the opposite of a pile, where shaft friction does much of the work.
The four common types
Shallow foundations are normally grouped as:
- Pad (isolated) footings under individual columns.
- Strip (continuous) footings under load-bearing walls.
- Ring foundations, used for circular structures such as tanks and chimneys.
- Mats or rafts, which spread the whole building load across a single slab.
Concretemetric lists the same four types as the primary shallow forms. Pad foundations are square, rectangular or circular slabs that transmit column load to the ground, and they are the type most often meant when someone says “design the footing”.
The two ideas behind bearing
The University of the West of England’s geotechnical notes put the design logic plainly: a foundation, shallow or deep, must have an adequate factor of safety against collapse, and its settlements must stay tolerable. Everything else follows from those two criteria.
- Ultimate bearing capacity (qu or qf) is the pressure at which the ground fails in shear.
- Allowable bearing capacity (qs) is the pressure you permit, after applying a safety factor, so that both shear failure and excessive settlement are avoided.
The distinction matters in conversation too. When a client asks “what is the bearing capacity of the ground?”, the honest answer is “ultimate or allowable, gross or net, and at what settlement?”
How to calculate ground bearing capacity
For a strip footing, the general expression given by UWE is:
qf = cNc + qoNq + 0.5γBNγ
Here c is cohesion, qo is the initial overburden stress at founding level (γ × Df), B is the footing width, γ is the unit weight of the soil, and Nc, Nq and Nγ are bearing capacity factors that depend on the soil’s angle of internal friction (UWE). Each term has a physical meaning:
- cNc is the contribution from the soil’s cohesion, dominant in undrained clay.
- qoNq is the contribution of the soil surrounding the footing, which acts as a surcharge. Founding deeper increases it.
- 0.5γBNγ is the contribution of the soil’s own weight beneath the footing, which grows with width and matters most in granular soils.
Square, rectangular and circular footings, inclined loads and eccentricity all modify this basic form with shape, depth and inclination factors. A 2024 study of depth factors in combination with the N-factors shows that refining these equations is still an active research topic, which is a good reason to state in your calculation which method you used.
A worked illustration of the safety factor
Take a 0.6 m wide strip founded 0.75 m down in soil with a unit weight of 18 kN/m³. The overburden is qo = 18 × 0.75 = 13.5 kPa. Suppose your chosen method and the site investigation parameters give a net ultimate capacity of 300 kPa. With a factor of safety of 3.0, the net allowable pressure is 100 kPa.
The numbers here are illustrative, not design values. The point is the sequence: ultimate first, then a safety factor, then a comparison with the actual applied pressure. The UWE notes describe typical factors of 2.5 to 3.0 in line with BS 8004 recommendations, chosen so that both shear failure and settlement are limited.
Gross, net and allowable are not the same number
One of the commonest slips in checked calculations is mixing definitions. Gross ultimate capacity includes the overburden; net ultimate capacity subtracts it. One educational summary of the topic expresses gross as net plus γDf. Say which one you are quoting, and compare like with like against the applied load, including the weight of the footing and any backfill.
Why settlement usually governs
Students learn bearing failure. Practitioners spend their time on settlement. A paper from Cambridge’s geotechnical group opens by stating that the design of shallow foundations is dominated by settlement rather than bearing capacity, so being able to predict settlement at a given factor of safety is central.
The common misconception, according to the structural engineers behind Concretemetric’s guidance, is that a foundation only needs to not break. In reality most shallow foundations are sized to limit settlement, in order to prevent cracking in masonry and damage to finishes, and that often needs larger footings than the capacity check alone would suggest.
In UK practice, clay is the usual culprit. It can have ample ultimate capacity and still move too much. Typical project criteria sit around 25 mm total and 20 mm differential settlement, though the acceptable figure depends on the structure and what it carries, so take it from the project specification and the structural engineer, not from a rule of thumb.
A practical sequence for any footing:
- Establish ground conditions from the site investigation.
- Size the footing on bearing resistance.
- Calculate settlement under the relevant loading and compare it with the tolerable limit for the superstructure.
- Enlarge, deepen or change the foundation type if settlement fails, then recheck both.
Eurocode 7 and the move away from BS 8004 habits
Many UK engineers trained on the allowable-pressure approach: calculate qu, divide by 2.5 or 3, done. Current design is carried out to Eurocode 7 (BS EN 1997-1) with the UK National Annex, which permits only Design Approach 1. That approach requires several limit states, each with its own set of partial factors, to be satisfied for the structure.
Two practical points from the literature:
- For a pad on soft clay, one worked comparison reports that Combination 2 nearly always governs in DA1 provided the loading is substantially permanent, with Combination 1 acting mainly as a check.
- The partial factors are applied to actions, material properties and resistances in different combinations, which is more involved than older empirical methods. We have written separately about how UK Eurocode 7 partial factors are applied, including the input versus output factoring question.
The cultural shift is the harder part. A calculation that quotes only an allowable bearing pressure and a factor of safety will not satisfy a checker expecting ULS and SLS verifications under DA1.
When Approved Document A is enough, and when it is not
For simple domestic builds, the prescriptive route in Approved Document A is a valid shortcut that avoids full Eurocode 7 calculations. It gives tabulated strip foundation widths based on ground type and wall load. Commonly quoted minimums put the underside of a footing at 450 mm below finished ground level in the UK, and practical guides quote about 900 mm in shrinkable clay subsoils. Treat those as starting points to confirm against the current document and the local building control body, not as design values.
The prescriptive route stops being safe when any of these appear:
- Trees near the footing on shrinkable clay, where NHBC Standards Chapter 4.2 guidance on depth increases comes into play.
- Sloping ground or proximity to an embankment or a retaining wall.
- A high water table.
- Made ground, soft or variable strata, or old workings.
- Loads above the domestic range, such as point loads from steel frames, or a heavy extension on an older house.
The research behind this article makes the same point: any variation such as trees, slopes or high water tables demands professional geotechnical analysis to avoid costly settlement later. Firms scaling up often miss the moment a job crosses that threshold, and the change from simple rules to full limit state verification lands on someone’s desk late.
Presumed bearing values: use with caution
Tables of presumed bearing capacity are tempting. A trial pit guide for domestic groundworks offers field descriptions with approximate capacities, for example strong rock needing a hammer to break at over 600 kN/m². Such tables suit preliminary planning only. They do not account for a high water table, which can roughly halve the permissible capacity, and a boot impression is no substitute for SPTs, plate bearing tests or laboratory data when you must justify safety factors under Eurocode 7.
Water, drainage and the details around the footing
Groundwater is the variable that most often undoes a footing that looked fine on paper. It reduces effective stress, softens clays and can undermine excavations before concrete is poured. Site drainage, surface water falls and the way thresholds and openings are detailed at slab level all affect what the ground sees over the building’s life. Specification notes on flush sill drainage detailing show how a small junction decision at slab level can trigger rework, which is worth remembering when you coordinate level-sensitive details with the foundation design.
On the civil side, a sound foundation design should be read alongside the site’s drainage strategy. Our guide to a drainage strategy report that wins planning approval explains how surface water and foul proposals are documented.
Our perspective: what we see on shallow foundation packages
We work as remote civil and structural engineers embedded in UK consultancies’ workflows, so we see foundation calculations at the point where they are handed over for checking. Three patterns recur.
The calculation answers the wrong question. A pad is sized for bearing, the settlement check is missing, and the checker returns it. We build the settlement check into the same package from the start, because it is the check that tends to change the footing size.
The ground information is thinner than the design assumes. We would rather flag an assumption on the face of the calculation, with the parameter, its source and what would change if it were wrong, than let a presumed value pass as a measured one.
The route is not stated. Whether a job follows Approved Document A or full Eurocode 7 under Design Approach 1 should be written at the top of the calculation, with the reason. It saves a review cycle.
Our outputs are aligned to UK standards and Eurocodes and arranged so your engineer can review them quickly. The client relationship stays yours throughout, and the work is covered by NDA protection.
— Mohammed
Choosing the foundation type once capacity is known
Bearing results narrow the choice:
| Situation | Likely shallow option | What to check |
|---|---|---|
| Load-bearing masonry walls, firm ground | Strip footing | Width from Approved Document A or calculation, depth for frost and shrinkage |
| Isolated column loads, moderate ground | Pad footing | Bearing, settlement, punching shear, eccentricity |
| Closely spaced columns or weak ground | Raft or mat | Differential settlement, stiffness, slab reinforcement |
| Circular tank or chimney | Ring foundation | Edge pressures, overturning |
| Poor ground at depth, heavy loads | Consider deep foundations | Whether a shallow solution can meet settlement limits |
Where pads or strips need reinforcement, drawing quality matters as much as the calculation. Our Eurocode 2 checklist for reinforced concrete drawings covers the points that avoid rework between calculation and detailing.
Getting foundation design support without hiring
Foundation packages tend to arrive in bunches: several extensions, a small frame and a retaining wall in the same fortnight. Hiring a permanent engineer for a peak is a poor fit. We provide remote engineering support that slots into your workflow, from structural calculations and reports to civil and drainage design and CAD and BIM drawings. Projects can kick off within 48 hours, and there are no recruitment fees. You can see how this works in practice in our structural calculation support case for a UK consultancy.
We do not publish prices, so to discuss capacity, scope and terms please get in touch through our website.
FAQ
What is the recommended depth for a shallow foundation?
By definition, embedment is no more than about the foundation width, or up to roughly twice the width in looser usage. In UK housing, the practical minimum is commonly quoted as 450 mm below finished ground level, and deeper in shrinkable clay or near trees. The final depth comes from the ground investigation and the design route you follow.
How do you calculate ground bearing capacity?
Find the ultimate capacity from soil strength (c and φ), the footing geometry and overburden, then apply a factor of safety or Eurocode 7 partial factors to get a design value. Finally check that settlement is within tolerance for the structure. The strip footing equation is qf = cNc + qoNq + 0.5γBNγ.
What are the four types of shallow foundation?
Pad (isolated) footings, strip (continuous) footings, ring foundations and mats or rafts. Each spreads the superstructure load to the ground at shallow depth, and the choice depends on load pattern, spacing and ground quality.
Can I rely on presumed bearing capacity tables?
Only for preliminary planning. Tables ignore site-specific factors such as a high water table, and formal design needs measured data from trial pits, SPTs or plate tests to justify the safety factors Eurocode 7 requires.
Sources
- FHWA Geotechnical Engineering Circular No. 6: Shallow Foundations
- UWE: Bearing capacity
- Geoengineer.org: Chapter 9, Bearing Capacity of Shallow Foundations
- Structville: Design of Pad Foundation
- Concretemetric
- Cambridge: Bearing capacity and settlement of circular shallow foundations
- Springer: Depth factors in bearing capacity of shallow foundations
- ResearchGate: Evaluating Foundation Design Concepts of Eurocode 7 and 8
- Squote: Strip Foundation Design
- Squote: Trial Pits for Domestic Groundworks
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