Bearing capacity and foundation design
Bearing capacity is the ground’s ability to support foundation loads without shear failure or excessive settlement. Engineers derive design values from ground investigation, laboratory and in-situ tests, and calculation methods appropriate to the foundation type — they are not universal “soil tables” contractors can apply from a website.
This page explains what bearing capacity means for clients reading a GI and foundation drawing. Deep explanation of testing and allowable pressures lives on the flagship soil-bearing-capacity-explained guide; foundation system choice on foundation-design-strategy. Mainline constructs to the issued bearing-aware design — we do not calculate or certify allowable bearing pressures.
Clients searching for a single kN/m² number for “clay” or “sand” will not find a responsible answer here — or anywhere without site data. This page exists to explain the process and where project values come from.
review Piling Contractors in Tonbridge and Piling Contractors in London.
When investigation is needed before you build
When GI quotes presumed bearing values or recommends foundation widths/depths; when an engineer widens strips or switches to rafts/piles after calculation; or when Building Control asks for design justification of foundation size.
It also appears when plate load or other in-situ tests are used to verify formation assumptions on site.
Formation proof testing (including plate load where specified) verifies assumptions; it does not license ignoring GI elsewhere on the plot. Use tests as the specification intends.
What investigation methods deliver
Ultimate bearing capacity relates to failure; serviceability is often governed by settlement. Soft, loose, or organic soils may “fail” settlement criteria long before classical bearing failure. Made ground complicates both.
GI may present indicative allowable pressures for preliminary use, with caveats. Final foundation sizes come from structural design using those parameters (and partial factors as required by the design codes in force on the project).
Plate load testing and related methods can support shallow foundation or platform verification when specified — see soil bearing and plate load service pages — but they do not replace a full GI on complex sites.
Presumed bearing values in older references are crude starting points only; modern design uses characteristic parameters and partial factors from the project codes. Width and embedment both influence capacity and settlement — narrowing a strip to “save concrete” can invalidate the calculation. Eccentric loads and moments need explicit design, not centred assumptions on sloping ground.
Service trenches cut near newly cast foundations can undermine edge bearing if dug carelessly — coordinate drainage digs with curing and inspection holds.
Think you might have bearing capacity and foundation design? A professional inspection will confirm the diagnosis.
Request Your QuoteMethod comparison
| Need | Owner page |
|---|---|
| Testing and bearing explained in depth | /guides/soil-bearing-capacity-explained |
| Choosing strip / raft / piles | /guides/foundation-design-strategy |
| Ground risk commercial narrative | /guides/ground-conditions-risk-explained |
| When piles are required | /guides/when-is-piling-required |
When scope usually expands
- GI states bearing recommendations or geotechnical parameters
- Foundation widths/depths justified by calculation
- Settlement criteria control foundation type
- Plate load or formation tests specified
- BC requesting design evidence for foundation size
How reports inform foundation and drainage design
Build foundations to the designed widths, depths, and reinforcement. Record formation inspections and any test results required by the specification.
Where plate load or similar tests are specified, protect the test location from trafficking before the test and record groundwater conditions at the time of testing.
Briefing checklist for GI
- GI bearing / strength / stiffness summary
- Structural foundation schedule
- Settlement criteria notes
- Formation test specification if any
- Escalation path for soft formation
From brief to design use
Step 1: Obtain GI parameters
What this step delivers: Designer has ground data.
Step 2: Engineer sizes foundations
What this step delivers: Drawings reflect bearing/settlement checks.
Step 3: Construct and verify formation
What this step delivers: As-built matches assumptions.
Step 4: Test if specified
What this step delivers: Plate load / other results filed.
What affects investigation scope and cost
Wider or deeper foundations, rafts, and piles all flow from bearing/settlement checks. Guessing bearing to avoid GI is a false economy. Rate intent: /groundworks-costs — no invented kN/m² prices here.
Project stages that rely on GI
- Clients reading GI bearing recommendations
- Tenders where foundation size changed after calculation
- Sites with plate load verification specified
- BC queries on foundation justification
Frequently asked questions
Can Mainline tell me the bearing capacity of my soil?
No. Bearing capacity is established through investigation and engineering calculation. We build the resulting foundations.
Are online soil bearing tables reliable for design?
Not for project design. They are crude conversation aids at best. Use site GI and an engineer.
What if formation looks softer than the GI suggested?
Stop, photograph, and ask the designer before concreting. Construction quality cannot invent missing bearing capacity.
Why did my neighbour’s foundation width differ on similar soil?
Loads, settlement limits, groundwater, and design codes/editions differ. Never copy a neighbour’s sizes without engineering.
How This Issue Is Normally Diagnosed and Repaired
Follow the typical path from problem identification through to resolution:
We provide these services across the UK, including
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Related Services
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Concrete FoundationsReinforced and mass concrete foundations and ground beams.
Related Topics
Related Groundworks Guides
Contact Us
Request Your QuoteBearing capacity and foundation design FAQ
Can Mainline tell me the bearing capacity of my soil?
No. Bearing capacity is established through investigation and engineering calculation. We build the resulting foundations.
Are online soil bearing tables reliable for design?
Not for project design. They are crude conversation aids at best. Use site GI and an engineer.
What if formation looks softer than the GI suggested?
Stop, photograph, and ask the designer before concreting. Construction quality cannot invent missing bearing capacity.
Why did my neighbour’s foundation width differ on similar soil?
Loads, settlement limits, groundwater, and design codes/editions differ. Never copy a neighbour’s sizes without engineering.
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Share your site details and priorities. We will outline a practical scope, likely timeline, and next steps.