How is pile fatigue calculated with AllWave-VDP?

AllWave-VDP calculates pile fatigue during vibratory driving by tracking the cumulative stress cycles generated at each depth increment throughout the full installation process. The software uses one-dimensional stress-wave analysis based on the Method of Characteristics, combined with a depth-dependent soil fatigue model that accounts for the local loading history at every point along the pile shaft. The sections below answer the most common technical questions engineers ask when running a fatigue check with AllWave-VDP.

What inputs does AllWave-VDP need to calculate pile fatigue?

AllWave-VDP requires three categories of input to calculate pile fatigue: a complete pile geometry and material specification, a vibratory hammer definition, and a soil resistance profile derived from ground investigation data. Together, these inputs allow the software to simulate the stress state at every depth increment for every vibration cycle during installation.

On the pile side, you need cross-sectional dimensions, wall thickness, material grade, and the pile’s elastic and mass properties. For the hammer, the software uses a hammer library that covers eccentric moment, operating frequency, bias weight, and clamping force. On the soil side, CPT data is the preferred input because it provides the continuous resistance profile needed to build a realistic Soil Resistance to Driving (SRD) model. SPT and laboratory data can supplement or replace CPT data where necessary.

The soil model must also capture friction fatigue, the reduction in local shaft resistance as the pile tip advances past a given soil horizon and that horizon accumulates more loading cycles. Without a friction fatigue model, the SRD profile will be unrealistic, particularly for long piles where upper soil layers experience thousands of cycles before the pile reaches its target penetration.

How does AllWave-VDP model stress cycles during vibratory driving?

AllWave-VDP models stress cycles by propagating one-dimensional stress waves through the pile at each vibration cycle and recording the resulting compressive and tensile stress amplitudes as a function of depth and penetration. Because the vibratory hammer operates continuously at a fixed frequency, the software accumulates these cycles over the full installation trajectory rather than treating each blow as an isolated event.

A vibratory hammer operating at 23 Hz produces roughly 10,000 cycles in approximately seven minutes of driving. The software tracks how many of those cycles each soil layer along the shaft has experienced. Soil near the pile tip has been loaded for only a short time, while soil high on the shaft has undergone the full cycle count. This depth-dependent loading history is what makes AllWave-VDP’s approach physically realistic compared to models that apply a uniform residual strength across the entire shaft.

The stress amplitude at any given depth is not constant throughout installation. As the pile penetrates deeper, the boundary conditions change: the effective SRD profile shifts, the hammer-pile interaction evolves, and the stress wave reflections from shaft and toe resistance change in character. AllWave-VDP recalculates the stress state at each penetration step, giving your team a complete picture of how stress cycles build up from the start of driving to final set.

Which fatigue standard or damage rule does AllWave-VDP apply?

AllWave-VDP generates stress cycle output that is compatible with standard fatigue damage accumulation methods, most commonly the Palmgren-Miner linear damage rule combined with S-N curves specified in the applicable design standard. The software itself produces the stress range and cycle count data; the fatigue damage calculation is then performed against the S-N curves defined in standards such as DNV-ST-0126, ISO 19902, or EN 1993-1-9, depending on the project specification.

This separation between stress cycle prediction and damage assessment is intentional. Different projects reference different standards, and pile material grades carry different S-N classifications. By outputting the stress history in a format that feeds directly into a damage calculation, AllWave-VDP keeps the fatigue workflow flexible without locking engineers into a single code.

For offshore steel piles, the relevant S-N curve is typically selected based on weld classification, corrosion environment, and whether the pile is in air, seawater with cathodic protection, or free corrosion. Your team applies the appropriate curve to the cycle counts and stress ranges that AllWave-VDP reports, then sums the partial damage fractions across all penetration steps to obtain the total installation fatigue damage.

How does pile fatigue from driving differ from in-service fatigue?

Driving fatigue and in-service fatigue differ in their source, frequency, and distribution along the pile. Driving fatigue accumulates during installation from high-frequency, high-amplitude stress cycles generated by the hammer, concentrated near the pile head and varying with depth as the pile penetrates. In-service fatigue accumulates over the operational life of the structure from environmental loads such as waves, wind, and current, which typically govern stress at the mudline and at structural connections.

During vibratory driving, stress amplitudes can be large and the cycle count reaches thousands within minutes. The stress distribution is governed by the wave equation mechanics: the pile behaves as a dynamic system, not a statically loaded column. In service, the loading is lower in frequency but extends over years or decades, and the governing stress location is usually determined by the structural configuration rather than the installation mechanics.

The practical consequence is that driving fatigue and in-service fatigue must be assessed separately and then combined. The total fatigue damage fraction at any weld or cross-section is the sum of the installation contribution and the operational contribution. For offshore monopiles and large-diameter tubular piles, driving fatigue can consume a meaningful portion of the total fatigue life, which is why running an AllWave-VDP fatigue check early in the design process matters: it informs whether the pile geometry, hammer selection, or installation sequence needs adjustment before fabrication begins.

When should engineers run a fatigue check with AllWave-VDP?

Engineers should run a fatigue check with AllWave-VDP at three points in a project: during preliminary design, before finalizing the installation specification, and after any significant change to the hammer, pile geometry, or soil model. Running the check only at the end of design is a common mistake that leads to late-stage redesigns or constrained hammer choices on site.

Preliminary design stage: Use AllWave-VDP to screen candidate pile geometries and hammer options for fatigue risk before committing to a wall thickness or steel grade. A geometry that looks adequate for static capacity may accumulate excessive driving fatigue at a critical weld location.
Installation specification stage: Confirm that the selected hammer, operating frequency, and driving sequence keep cumulative fatigue damage within the allowable fraction. This is also the stage to define any driving interruption criteria or maximum blow rate limits.
After model updates: If ground investigation data is revised, if a different hammer becomes available, or if the target penetration changes, rerun the fatigue check. The stress cycle output is sensitive to all three of these variables.

For offshore wind foundations, regulatory frameworks and certification bodies increasingly require documented fatigue assessments that cover the installation phase explicitly. Running AllWave-VDP as part of the AllWave software package workflow gives you the traceable, documented output needed to satisfy those requirements.

What does the AllWave-VDP fatigue output report include?

The AllWave-VDP fatigue output report provides stress cycle data as a function of both depth along the pile and penetration depth during installation. The core output includes the stress range at each calculation node for each penetration step, the cumulative number of cycles at each depth, and the resulting stress history that feeds into the damage calculation.

Typical report content covers:

Stress range versus depth profiles at selected penetration increments, showing where peak tensile and compressive stresses occur along the pile shaft
Cumulative cycle counts at each depth node, reflecting the local loading history based on how long that soil horizon has been in contact with the vibrating pile
Maximum stress amplitudes during the full installation, identifying the depth and penetration step at which the highest stress ranges occur
Input to S-N damage calculation: the stress range and cycle count data formatted for use with the applicable fatigue standard
Sensitivity results where multiple hammer or soil scenarios have been run, allowing comparison of fatigue exposure across different installation strategies

The report also connects to the broader driveability output from AllWave-VDP, so your team can review fatigue alongside blow count, penetration rate, and pile stress limits in a single consistent analysis framework. This integrated view is important when optimizing the installation: reducing driving fatigue often involves trade-offs with penetration rate or hammer efficiency that only become visible when all outputs are assessed together.

How We Support Vibratory Driving Prediction and Fatigue Analysis

We developed AllWave-VDP as part of our broader AllWave software package, drawing on decades of experience in pile driveability prediction, stress-wave analysis, and offshore installation engineering. When your project requires a fatigue check during vibratory driving, we can support you in the following ways:

Full AllWave-VDP fatigue analysis: We run the complete vibratory driving prediction, including stress cycle output, SRD modelling based on your CPT data, and friction fatigue modelling that reflects the actual loading history at each depth
Hammer and pile optimization: We assess multiple hammer configurations and pile geometries to identify the combination that minimizes driving fatigue while maintaining a practical penetration rate
Integration with installation monitoring: We combine pre-installation predictions with real-time monitoring data during driving, then perform back-analysis to validate and update the soil model, turning each installation into a calibration point for future predictions
Fatigue damage reporting: We deliver documented output compatible with DNV, ISO, and EN standards, supporting certification and independent review requirements
Soil modelling from CPT data: We build the SRD profile directly from your ground investigation data, applying our friction fatigue model to produce a physically realistic resistance profile for both prediction and post-analysis

Whether you need a standalone fatigue check or a full drivability study covering impact and vibratory driving, our team can provide the analysis your project requires. Contact us to discuss your pile installation challenge and find out how AllWave-VDP can support your design and installation planning.