A question project owners and contractors ask all the time is: “How much load does the law allow a single pile to carry?” This article builds on The 2023 Foundation Ministerial Regulation Simply Explained and digs into the part engineers and site supervisors use most: turning a pile's "ultimate" capacity into a "value that can be safely used in design".
What is the difference between ultimate resistance and allowable resistance?
The Ministerial Regulation separates these two terms clearly. Ultimate resistance of a pile is the maximum load the pile can carry before failure, calculated from a soil investigation report or estimated from test results. Allowable resistance of a pile is the value that can actually be used safely in design.
The gap between the two is the factor of safety (FS). The more accurate the method used to determine capacity, and the lower its uncertainty, the higher the proportion the law allows (i.e. a lower FS). That is why the 40/50/40 figures differ from method to method.
How does Clause 24 set the 40/50/40 criteria?
For vertically loaded pile foundations with a soil investigation report, or with pile resistance tests carried out at or near the construction site, Clause 24 of the Ministerial Regulation sets the allowable resistance as follows:
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| Method of determining pile capacity | Applicable up to | Approx. equivalent FS |
|---|---|---|
| Calculated from the foundation soil investigation report | 40% of ultimate resistance | ~2.5 |
| Static method (static load test) | 50% of ultimate resistance | ~2.0 |
| Dynamic method (dynamic load test, PDA)* | 40% of ultimate resistance | ~2.5 |
*Dynamic results must come from tests calibrated against the static method · FS values are a conceptual comparison to aid understanding; the figures set by law are the percentages in the table
Hypothetical example: if a pile has an ultimate resistance of 100 t, a value calculated from the soil investigation report may be used up to 40 t, a static load test value up to 50 t, and a calibrated PDA value up to 40 t. If the allowable value exceeds 40 t per pile, the assessment must follow what the engineer responsible for the design and calculations certify under Clause 25.
The 3D model below places the source of each of the three values on three piles, to show that each method's cap stems from a different level of data reliability.
Why a static load test earns 50%
A static load test applies real load to the pile head in increments while measuring settlement, so it best reflects the true capacity of that pile in the actual ground. Uncertainty is low, so the law allows a higher proportion than other methods. Read more about the test procedure in Static Pile Load Test: Testing Pile Capacity by the Static Method
Why soil-based calculation and the dynamic method get 40%
Calculation from a soil investigation report relies on soil parameters and theoretical formulas, which carry the natural variability of the soil layers. The dynamic method (PDA) measures stress waves during driving and back-calculates pile capacity; it is fast and can test many piles, but the law requires it to be calibrated against the static method and limits the allowable value to 40%. Read more in Dynamic Load Test (PDA Test) for Pile Capacity and A Guide to Reading PDA Test Results
📌 Which standards these tests follow: dynamic pile testing refers to DPT 1252-51 and ASTM D4945-26, while the static method refers to ASTM D1143/D1143M-20e1 together with DPT 1251 (referenced via DPT 1106-64 clause 6.1). The percentage criteria used in design, however, follow the 2023 Foundation Ministerial Regulation.
What does Clause 25 require for piles carrying more than 40 t each?
The Ministerial Regulation also splits pile capacity assessment by the size of the load carried:
- Not more than 40 t per pile — the allowable resistance is assessed as prescribed by the Minister, on the advice of the Building Control Committee, by notification in the Royal Gazette
- More than 40 t per pile — the allowable resistance is assessed as certified by the engineer who carried out the design and calculations (civil engineer)
In practice, piles designed to carry more than 40 t each usually need pile testing to confirm capacity before the engineer signs off. This is where the choice of test method (static or dynamic) directly affects both budget and schedule.
The figure below plots the hypothetical example above as a chart, with the 40 t-per-pile line from Clause 25. In this example the static load test value crosses that line, so it must be certified by the engineer responsible for the design and calculations.
How should you choose a test method to fit the legal criteria?
Since the law allows 50% for static testing but only 40% for dynamic testing, many projects combine the two — a static load test on a few representative piles to obtain a high reference value, and dynamic testing (PDA) to check large numbers of piles economically. A comparison of pros and cons is in Dynamic vs Static Load Test: Which Should You Choose?
⚠️ Caution: the 40/50/40 figures are the maximum caps the law allows, not values that must always be used. Choosing the pile capacity, depth, size and number of piles for a given project is the responsibility of the design engineer in charge, who must consider soil conditions, building loads and site-specific factors together. This article is general information, not project-specific design advice.
Summary: how much load can a pile carry by law
Clause 24 of the 2023 Foundation Ministerial Regulation clearly sets the allowable resistance of piles: 40% when calculated from a soil investigation report, 50% from a static load test, and 40% from a calibrated dynamic test. The different figures reflect each method's accuracy. Clause 25 separates piles of not more than and more than 40 t each, with high-capacity piles requiring certification by the design engineer. Understanding these criteria helps project owners budget correctly for pile testing and be confident that reports submitted to the authorities comply with the law.