How Does the 2023 Ministerial Regulation Govern Spread Footing Design?

A spread footing (shallow foundation) transfers the building load directly into the ground without piles. It is commonly used where the ground is stiff, such as in Eastern Thailand, the Northeast (Isan) or foothill areas. The Ministerial Regulation on Building Foundations and Ground Supporting Buildings B.E. 2566 (2023) (for an overview of the whole regulation, see The 2023 Foundation Ministerial Regulation Simply Explained) sets the principle that the allowable bearing pressure must not exceed one third of the ultimate bearing capacity of the foundation soil — equivalent to a factor of safety FS = 3.

Soil bearing capacity is obtained in two main ways: by calculation from the engineering properties of the soil found in the soil investigation, or by evaluation from field test results (for the basics, see What Is Soil Bearing Capacity?).

What Does the 200 kPa Threshold Mean in Practice?

The game-changer for spread footing designers is this condition: when the designer wants to use an allowable bearing pressure above 200 kPa (approx. 20 t/m²), the Ministerial Regulation requires the value to be confirmed by an in-situ plate bearing test (Plate Bearing Test) on the actual site. Calculation from boring results alone is not enough — what was once just good practice is now a legal condition.

In practical terms:

  • Projects on stiff ground that want smaller footings (using high bearing values) — book the plate bearing test into the schedule from the design stage.
  • Factories, warehouses and heavy machine foundations — high footing loads make these the most likely to hit this condition (see also the soil checklist before buying factory land).
  • If the value used is 200 kPa or less — design from soil investigation results and normal calculation; testing is not mandatory.
⚠️ Don't forget the case with no soil test at all

If a project has neither soil investigation results nor field test results, the Ministerial Regulation limits the design to presumptive bearing values, which are low and make footings much larger. Read more in No soil boring: what bearing values does the law allow?

The figure below sums up the 200 kPa dividing line in a single bar, together with a conceptual section explaining why a passed plate bearing test still cannot replace a soil investigation.

The 200 kPa bearing pressure threshold under the 2023 Foundation Ministerial Regulation, and the depth a plate bearing test reflects compared with an actual spread footing Two-panel figure. The left panel is a decision bar based on the Ministerial Regulation on Building Foundations and Ground Supporting Buildings B.E. 2566 (2023). The vertical axis is the allowable bearing pressure qa, increasing upward. In all cases FS = 3 applies, i.e. qa is no more than one third of the ultimate bearing capacity q ult. A thick line divides the bar at 200 kPa, or approx. 20 t/m². The lower green zone is qa up to 200 kPa: design from soil investigation results and calculation, no mandatory test. The upper orange zone is qa above 200 kPa: must be confirmed by an in-situ plate bearing test. A grey card below warns that with neither boring nor test results, only low presumptive bearing values may be used. The right panel is a conceptual soil section. A small test plate, Ø 0.3 to 0.75 m, width D, is placed at foundation level in a test pit; its orange dashed stress bulb reaches only about 2D deep. Beside it is an actual spread footing of width B, many times larger, whose blue dashed stress bulb reaches about 1.5 to 2B deep. Below the stiff upper layer is a soft layer that lies deeper than the plate's stress bulb but within the footing's stress bulb; red shading marks where the actual footing loads that soft layer. Conclusion: a plate bearing test cannot replace a soil investigation; both must be done together. 2D section: the 200 kPa rule and the depth the test plate "sees" Not to scale Criteria under 2023 Foundation Regulation Allowable bearing pressure qa of spread footing All cases: FS = 3 · qa ≤ qult / 3 qa → 200 kPa (≈ 20 t/m²) qa > 200 kPa Must be confirmed by Plate Bearing Test on site (legal requirement) qa ≤ 200 kPa Design from soil boring results + calculation (FS = 3) PBT not mandatory ! No boring/test results at all → only presumptive values allowed which are low, so footings get much larger How deep does the test plate "see" vs. an actual footing? Dashed = stress bulb · conceptual figure Test plate Ø 0.3–0.75 m Width D · placed at footing level Actual spread footing Width B — far larger ≈ 2D ≈ 1.5–2B Stiff Stiff Soft layer unseen by plate but within the footing's bulb Key: PBT can't replace boring — do both
Criteria under the 2023 Foundation Regulation: spread footings using qa above 200 kPa (≈ 20 t/m²) must be confirmed by a plate bearing test, and because the test plate reflects soil only to about twice the plate size, it must always be paired with a soil investigation (Diagram: SPN Soil Engineering)

What Is a Plate Bearing Test? (Short Version)

In short, a plate bearing test places a standard steel plate on the soil at foundation level and loads it in increments with a hydraulic jack, measuring the plate settlement at each increment. The result is the load–settlement curve of the actual soil at the footing location. The test follows DPT standard 1253-62 and ASTM D1195 / D1196, together with the criteria set by the design engineer. This article does not go into the equipment and procedure, because we already have a full guide at Plate Bearing Test: Testing the Load-Bearing Capacity of Soil.

Plate bearing test setup: a steel plate loaded by a hydraulic jack on an actual site
A plate bearing test at actual foundation level (Photo: SPN Soil Engineering)

Who Is Responsible, and When Should It Be Planned?

  • Design engineer — decides the bearing pressure used in the design, and therefore whether the project falls under the testing requirement, as well as the number of test points, their locations and the maximum test load.
  • Project owner — responsible for procuring the test and allowing time in the schedule, because the test must be performed at actual foundation level and is usually tied to when excavation opens up.
  • Testing provider — must deliver a test report signed and certified by an engineer, so the designer can use it in the calculations and the building permit application (see what a complete report contains in the legally compliant soil investigation report checklist).

A common mistake is realizing the test is needed only after the design is finished or the site has already been excavated, which halts work while waiting for results. The better approach is for the designer to specify the testing requirement from the preliminary design stage and locate the test points together with the soil boring plan.

The sequence that keeps the site from stopping to wait for results is to mark the test points in the plan from the design stage, then open the test pits to foundation level following the same plan as the boreholes, as shown below.

3D model of planning plate bearing tests together with the soil investigation from the design stage, on a factory or warehouse site Conceptual 3D view of a factory or warehouse construction site, with the soil block cut away to show the section: laterite on top, stiff clay below, and weathered rock at the bottom, which is typical of Eastern Thailand. On the ground surface, the spread footing layout is shown as a rectangular grid. There are three soil boreholes: the front one has a drill-rig tripod and the borehole is visible through all layers in the section; the other two are marked by borehole pegs. At two footing locations, pits are opened down to foundation level for plate bearing tests: a steel plate sits on the pit floor, and a hydraulic jack pushes up against a steel beam resting on timber cribbing, with kentledge blocks as reaction. The front pit is cut away to show the inside. An orange dashed line on the section marks foundation level. A panel on the right shows four steps: one, preliminary design — the designer selects qa and plans the soil investigation; two, if qa exceeds 200 kPa, specify the plate bearing test in the plan, including number of points, locations and maximum test load; three, excavate to foundation level and test — the project owner procures the work and must allow time in the schedule; four, the engineer-signed report supports the calculations and the building permit application. A note states that this is a conceptual figure and the number and location of test points are set by the design engineer. 3D model: plan PBT with soil boring from the design stage Not to scale BH-2 BH-3 Footing layout (grid) Sized for designer's qa 3 PBT test pit Excavated to footing level Steel plate + jack + kentledge BH-1 1 Soil boring (BH) Shows layers over full depth Footing level Test plate sits here Section: Laterite Stiff clay Weathered rock PBT planning sequence Done with the boring plan 1 Preliminary design Designer selects qa Plan soil boring (BH) 2 qa > 200 kPa Specify PBT in plan: no. of points, locations and max. test load 3 Excavated to footing level → Run PBT as planned Owner procures · allow time 4 Engineer-signed report Supports calculations → Building permit application Common mistake Found out after design/excavation → Work stops for test results Conceptual No./location of test points Set by design engineer
Conceptual figure of planning plate bearing tests together with soil boreholes on a factory site, from the designer selecting qa to the engineer-signed report for the building permit application — the number and location of test points are set by the design engineer (Diagram: SPN Soil Engineering)

Plate Bearing Test vs. Soil Investigation: Can One Replace the Other?

← Scroll to see the full table →

IssueSoil investigation (Soil Boring)Plate Bearing Test
What you getSoil layers over full depth, SPT, samples for laboratory testingActual load-bearing behavior of the soil at foundation level
Depth reflectedFull borehole depthOnly the shallow zone under the plate (about 2× the plate size)
Used forDesigning all foundation types; choosing the foundation typeConfirming high bearing pressures for spread footings
Legal statusMandatory for building categories specified in the Ministerial RegulationMandatory when using values above 200 kPa

In short, they are not interchangeable but complementary — soil investigation tells you the whole soil profile for design, while the plate bearing test proves the value you actually want to use when the legal condition applies. Projects that fall under the rule therefore usually need both (for which building categories require a soil investigation, see the Ministerial Regulation summary).

Why Is a Soil Investigation Still Needed After a Passed Plate Bearing Test?

The test plate is only 0.3–0.75 m across, so the load spreads into the soil as a stress bulb only about twice the plate size deep. An actual footing is many times wider than the plate, so its stress bulb reaches much deeper. If a soft layer lies deeper than the plate can "see", the test result will look good, yet the actual footing can still settle due to that soft layer (see the section in the 200 kPa threshold section). Soil layer data over the full depth from boreholes is therefore something the designer must always check alongside.

Summary

The 2023 Foundation Ministerial Regulation upgrades the plate bearing test from an "option" to a "requirement" for spread footings designed with an allowable bearing pressure above 200 kPa under the FS = 3 principle. Anyone designing factories, warehouses or buildings on stiff ground who wants to get the most out of their footings should put this test in the schedule from the outset and plan it together with the soil investigation, to get complete data on both counts. See the full scope of plate bearing test and soil investigation services at Soil Investigation and Testing Services.

📌 Disclaimer

This article summarizes the Ministerial Regulation for general understanding only. It is not legal or engineering advice for any specific project. For practical use, refer to the official text of the Ministerial Regulation as published in the Royal Gazette and consult the licensed engineer for your project.