How many days of concrete age does each pile test need?

Short answer: bored piles wait ~7 days (Seismic), several weeks per the specification (PDA) and ~21–28 days (Static). Driven piles can be seismic-tested after driving, but PDA and Static must wait for Soil Setup first.

The waiting time before testing is the period between casting the concrete (or completing pile driving) and the day testing can start. It varies with the type of test and the type of pile. The table below summarizes common practice for pile testing as a starting point for planning; actual figures follow the project specification.

← Scroll to see the full table →

Summary of waiting times before each pile test method
Test methodBored pileDriven pileReason / Soil Setup
Seismic Integrity TestUsually ~7 days or more after castingCan be tested once driving is complete and the pile head is cut (concrete already cured at the factory)Concrete must be hard enough for the wave velocity to stabilize, so depth can be calculated accurately
Dynamic Load Test (PDA)Wait until the concrete can withstand impact, usually several weeks per the specificationUsually ~7 days or more after driving, to allow Soil SetupConcrete must take the impact without the pile head breaking + soil around the pile must recover
Static Load TestUsually wait until design strength is reached, ~21–28 days, or until cylinder/cube strength results meet the criterionWait for Soil Setup per engineerMust carry a test load of about 2–3 times the design load (per specification) + soil recovery
⚠️ These figures are common practice, not fixed rules

The waiting times in the table are common practice. Actual waiting times must follow the project specification and the design engineer, who sets them according to the pile type, concrete strength and soil conditions of each job.

Bored piles after concrete casting, with pile heads prepared before reaching the required age for pile testing
Bored piles must wait for the concrete to gain strength, and the pile heads must be prepared before the test team arrives on site (Photo: SPN Soil Engineering)

The diagram below turns the table into a timeline. Follow each method's bar to see on which day it changes from grey to solid. The upper panel is for bored piles (counted from the casting date) and the lower panel is for driven piles (counted from the date driving is completed).

Conceptual chart of concrete age in days against when each pile test method can start, shown separately for bored piles counted from the casting date and driven piles counted from the date driving is completed Two stacked panels share one time axis from zero to forty-two days. The upper panel is for bored piles, counted from the casting date, with a conceptual example curve (not actual values) of concrete compressive strength increasing with age. A horizontal dashed line marks the design strength per the specification, and a light orange band from twenty-one to twenty-eight days marks when concrete usually reaches design strength. Below the curve are three timeline bars: grey means testing should not yet be done, hatched means testing may start per the specification or cylinder/cube test results, and solid means testing is possible per common practice. The Seismic Integrity Test can start about seven days or more after casting, once the wave velocity in the concrete is stable enough to calculate depth accurately. The Dynamic Load Test, or PDA, must wait until the concrete can withstand impact, usually several weeks per the specification, and the pile head must be strengthened as specified. The Static Load Test usually waits until the concrete reaches design strength, around twenty-one to twenty-eight days, or until confirmed by cylinder/cube strength results. The lower panel is for factory-cured prestressed concrete driven piles, counted from the date driving is completed; the constraint is soil recovery, or Soil Setup, not concrete age. Seismic testing can be done once driving is complete and the pile head is cut. PDA by restrike usually waits seven days or more after driving for the soil to recover, and Static waits for Soil Setup as specified by the engineer. The bottom strip notes that the figures are common practice and that the project specification and design engineer govern, that cylinder/cube strength results should be checked before testing bored piles, and that in sand the Soil Setup effect is smaller than in clay, so the waiting time may be shorter. Concrete age (days) vs when each pile test can start Not to scale Do not test yet Start per spec / cube results Testable per common practice Bored pile From casting date (day 0) 21–28 days Design strength (spec) Concrete strength curve Conceptual example not actual values Strength → 0 7 14 21 28 35 42 Age (days) Concrete strength rises with age Each test loads differently so waits differ Seismic Integrity Integrity check Too early ~7 days+ · stable wave velocity, accurate depth Dynamic (PDA) High-energy impact Too early Usually weeks · per spec + pile head strengthened Static Load Test Load 2–3× design load Below design strength 21–28 days Design strength Driven pile (factory prestressed) From end of driving · limit is Soil Setup, not concrete age 0 7 14 21 28 35 42 Days after driving Seismic Integrity Factory-cured concrete Testable after driving + head cut Dynamic (PDA) Restrike Soil recovery ~7 days+ after driving · Soil Setup (soil-dependent) Static Load Test Full soil recovery Soil recovery Wait for Soil Setup per engineer 1 Follow project spec Figures are common practice 2 Check cubes first confirm that pile's strength 3 Sand: shorter wait Setup is strong in clay
Conceptual timeline: bored piles can be seismic-tested at about 7 days or more, PDA usually after several weeks per the specification, and Static at about 21–28 days; for driven piles, PDA/Static wait for Soil Setup, ~7 days or more — the concrete strength curve is a conceptual example, not actual values; actual figures follow the project specification and the design engineer (Image: SPN Soil Engineering)

Why must the concrete gain strength before a pile is tested?

Because each method applies very different forces to the pile, from a light tap (Seismic) to a high-energy impact (PDA) to an actual load several times the design load (Static), so each needs a different concrete age. Concrete strength is the ability of the concrete to carry load, and it increases with age after casting.

Seismic Test (~7 days) — wait for the wave velocity to stabilize

Interpreting a Seismic Integrity Test uses the wave velocity in the concrete to calculate the position of reflections. Young concrete still has low strength and an unstable wave velocity, which leads to errors in the calculated depth. General practice is therefore to wait about 7 days or more after casting, so the wave velocity approaches its normal value.

Driven piles, on the other hand, are produced in a factory and cured to strength before delivery to site, so they can be seismic-tested once driving is complete and the pile head is cut, without waiting for concrete age on site.

PDA (usually several weeks) — the concrete must withstand impact

A Dynamic Load Test (PDA) uses a drop weight or pile hammer to strike the pile head with high energy. If the bored pile concrete is not yet strong enough, the pile head may break during the test, so testing must wait until the concrete reaches the strength specified by the engineer, which usually takes several weeks, longer than for a Seismic Test. The pile head must also be prepared, for example by fitting a steel sleeve or recasting the head to the required strength.

PDA testing strikes the pile head with high energy; the concrete must be strong enough that the pile head does not break
PDA strikes the pile head with high energy — bored pile concrete must gain enough strength first, or the pile head risks breaking during the test (Photo: SPN Soil Engineering)

Static Load Test (~21–28 days) — must carry the full test load

A Static Load Test applies an actual load to the pile head, typically up to 2–3 times the design load as required by the specification. Bored piles therefore usually have to wait until the concrete reaches design strength, generally around 21–28 days, or until confirmed by compressive strength results of cylinder or cube specimens from that pile.

A Static Load Test applies an actual load to the pile; the concrete must reach design strength before testing
A Static Load Test applies an actual load several times the design load, so it must wait for the concrete to reach full strength (Photo: SPN Soil Engineering)

What is Soil Setup, and why must driven piles wait before capacity is measured?

Soil Setup is the increase in pile load capacity with time after driving, as the disturbed soil around the pile gradually recovers. The effect is pronounced for driven piles in clay, such as the Bangkok soft clay layer, and it is an issue many people overlook.

During driving, the soil around the pile is severely disturbed and the pore water pressure rises, making the strength of the soil around the pile temporarily lower than normal. Over time the excess pore water pressure dissipates and the soil recovers, so the pile load capacity steadily increases. This phenomenon is called Soil Setup (or Soil Freeze). For how this effect is measured by restriking, see Restrike Test and Soil Set-up

In practice:

  • If PDA or Static testing is done immediately after driving, the measured capacity is usually lower than the actual long-term capacity. The pile may appear not to meet the criterion even though its long-term capacity may be sufficient.
  • Project specifications therefore often set a minimum waiting time after driving (commonly 7 days or more, depending on soil type) before load capacity testing.
  • In sand this effect is much smaller than in clay and the waiting time may be shorter. In some soil layers the reverse can occur, with capacity decreasing over time (Relaxation), which the engineer must assess from restrike results.
💡 Why restrike gives higher values than End of Drive

This is why a PDA test by Restrike (re-driving after a waiting period) usually gives higher capacity than measurement at the end of driving (End of Drive), especially in clay, and better reflects the actual service capacity.

How should the pile testing schedule be planned to avoid delays?

Build the testing wait time into the program from day one, and test in batches by casting or driving date rather than waiting for every pile to be finished. Practical guidelines:

  1. Build testing wait times into the program from the start — a common mistake is planning foundation work to follow immediately after piling, forgetting to allow time for testing, which delays the whole project.
  2. Test in batches — there is no need to wait for every pile. Test the first zone once it reaches the required age while piling continues in other zones.
  3. Coordinate with the test team in advance — book the test slot as soon as the casting/driving completion dates are known, so the team can be on site as soon as the piles reach the required age.
  4. Prepare pile heads before the test day — cut the pile heads, grind the surface or strengthen the pile heads as required for each test, so the test team's trip is not wasted.
  5. Check cylinder/cube strength results before booking the team — confirm that the concrete in that batch meets the specified criterion, especially before PDA and Static testing.

The 3D view below shows a site where bored piles were cast in batches on different days. Labels show the concrete age of each batch, and symbols on the pile heads show which tests can be carried out today.

3D model of a bored pile site cast in batches on different days, each batch labeled with its concrete age and colored by the tests possible today, with a cylinder/cube compressive strength testing station Conceptual 3D view of a bored pile site on a soil block cut away to show a section. The piles are divided into four batches arranged in casting order from left to right, each with three piles and a label showing concrete age. The leftmost batch, aged 21 to 28 days, is dark blue, with pile-head symbols for Seismic, PDA and Static once cylinder/cube strength results meet the criterion. The second batch, several weeks old, is orange and can be tested by Seismic and PDA once the concrete can withstand impact per the specification. The third batch, 7 days or older, is light blue and can be seismic-tested, with an engineer tapping a pile head with a hammer. The rightmost batch, less than 7 days old, is grey and not yet tested, with a frame suspending a hopper that feeds concrete through a tremie pipe into the steel casing of the pile cast today, which counts as day 0 of that batch. The lower left corner is a sampling station for cylinder and cube specimens, color-coded by batch, beside a compression testing machine. The right panel summarizes the basic rules from the article: Seismic at about 7 days or more once the wave velocity is stable; PDA usually after several weeks per the specification because the pile head must withstand impact; Static at about 21 to 28 days once the concrete reaches design strength; check specimen compressive strength results before testing; driven piles can be seismic-tested after driving and head cutting, but PDA and Static must wait for Soil Setup, usually seven days or more; and actual figures follow the project specification and the design engineer. 3D model: bored pile batches of different ages, different tests possible Not to scale 21–28 days Several weeks ≥ 7 days < 7 days Casting order: first batch → latest Cast earlier = older concrete → more test methods possible Cast today = day 0 of this pile Seismic tap OK Batch reached ~7 days Pile-head symbols: light blue = Seismic Orange ring = PDA · blue frame = Static Cylinder/cube strength testing Specimens by batch Results meet spec before booking PDA / Static Basic rules (bored piles) < 7 days · not yet tested Young concrete Wave velocity not stable Seismic · ~7 days+ Wave velocity stable Accurate depth PDA · usually weeks Head must take impact Per spec + head strengthened Static · ~21–28 days Design strength reached Carries 2–3× test load Check specimen strength before every test That pile's cubes meet spec Driven pile (factory-made) Seismic: after driving + head cut PDA/Static: Soil Setup ~7 days+ Actual figures: project spec/engineer Conceptual, not actual layout
Conceptual 3D model: batches younger than 7 days are not yet tested, batches 7 days or older can be seismic-tested, batches several weeks old (per specification) add PDA, and batches 21–28 days old add Static once cylinder/cube results meet the criterion — not an actual layout; actual figures follow the project specification and the design engineer (Image: SPN Soil Engineering)

For an overview of which test methods apply to each type of pile, read the complete guide to pile testing methods, and see the criteria for how many piles need to be tested

📌 Note

This article provides general engineering knowledge. All waiting times (7 days, 21–28 days) are common practice. The actual waiting time, minimum concrete age and test method must follow the specific project specification and the judgment of the licensed design engineer; this is not design advice for any particular pile.