What is the difference between Pile Driving Prediction (PDA) and a Vibratory Driving Prediction (VDP)?

A Pile Driving Prediction (PDP) and a Vibratory Driving Prediction (VDP) are both pre-installation analyses that simulate whether a pile can reach its target depth with a chosen installation system, but they model fundamentally different physical processes. Impact driving generates discrete stress waves through hammer blows, while vibratory driving applies continuous cyclic motion, which means the soil interaction models, software tools, and output parameters differ significantly between the two methods. The sections below unpack how each prediction works, when to use each one, and how they can complement each other on the same project.

How does impact pile driving prediction work?

Impact pile driving prediction simulates the interaction between a hammer, pile, and soil for each individual blow using one-dimensional stress-wave analysis. For every penetration level, the model calculates how a stress wave travels down the pile after impact, how the soil resists that wave, and what permanent set the pile achieves per blow. The result is a complete picture of the installation process from start to target depth.

The core output of a Pile Driving Prediction (PDP) covers more than just whether the pile reaches its final depth. A well-executed prediction simultaneously addresses:

Blow count versus penetration depth: how many blows per unit of penetration are needed at each stage
Maximum compressive and tensile stresses: to verify pile integrity throughout driving
Energy transfer: how efficiently the hammer delivers energy into the pile
Refusal risk: at which depth further penetration may become practically impossible
Installation time: total blow count and estimated duration
Fatigue loading: the cumulative stress cycles generated during the full installation

The soil model used in a PDP is typically derived from CPT data, SPT results, or laboratory testing. A key concept is Soil Resistance to Driving (SRD), which accounts for the fact that dynamic soil resistance during installation differs from static bearing capacity. Friction fatigue, the progressive reduction of shaft friction as the pile advances, is also incorporated to reflect realistic conditions at depth.

Importantly, a reliable impact driving prediction is not a single calculation. It is an iterative process in which initial assumptions are tested against monitoring data during installation, then refined through back-analysis to improve future predictions. This learning loop, moving from ground investigation through prediction, installation monitoring, and signal matching back to an updated soil model, is what turns a driveability study into a technically defensible engineering tool.

How does vibratory driving prediction differ in its approach?

A Vibratory Driving Prediction (VDP) differs from an impact prediction because a vibratory hammer does not generate discrete stress waves. Instead, it imposes continuous cyclic displacement, velocity, and acceleration on the pile. The soil response to this type of loading cannot be described by the same models used for impact driving, which means the entire simulation framework must be rebuilt around a different physical mechanism.

In vibratory driving, the soil reaction is a function of displacement, velocity, and acceleration simultaneously. Simple linear constants for spring stiffness and damping, which work reasonably well for impact models, are insufficient to capture the real interaction under cyclic loading. Back-analysis of monitored vibratory installations has shown that the relationships between these parameters are more complex and must reflect the specific loading character of a vibro hammer.

One practically important distinction involves soil type. In granular soils, the cyclic motion temporarily disrupts grain contact and reduces shear resistance, allowing the pile to advance significantly under the combined static weight of the hammer and pile. In cohesive soils, residual strength remains higher, and each cycle must generate enough displacement to produce plastic behavior. If the vibration amplitude is too small, the soil response stays largely elastic and little permanent penetration occurs. This is not the same as liquefaction, though liquefaction can further ease penetration in saturated granular conditions.

The VDP must also account for soil modelling for pile driving simulations using a vibro hammer, which requires dedicated calibration. Because vibratory installations are less frequently monitored and back-analyzed than impact-driven ones, the soil models carry greater uncertainty, and engineering judgment plays a larger role in interpreting the results.

What types of piles and projects suit each method?

Impact driving prediction is suited to projects where piles are installed blow by blow into soil or rock, making blow count a meaningful measure of progress and resistance. Vibratory driving prediction applies when a vibro hammer is used, typically to advance piles more quickly through granular soils before switching to an impact hammer for final set, or as the sole installation method where conditions allow.

Impact driving predictions are commonly used for:

Offshore monopiles and jacket foundations for wind energy structures
Driven steel pipe piles and H-piles for port and marine infrastructure
Precast concrete piles in building and civil engineering projects
Any installation where final bearing capacity is verified through blow count at set

Vibratory driving predictions are particularly relevant for:

Sheet piles and tubular piles in granular soils where speed of installation matters
Offshore projects where a vibro hammer is used for initial penetration before impact driving takes over
Projects in loose to medium-dense sands where vibratory methods are efficient
Situations where minimizing noise and vibration impact on the surrounding environment is a project requirement

In practice, many offshore and nearshore projects use both methods in sequence. A vibro hammer advances the pile to a certain depth, and an impact hammer completes the installation. This is precisely the scenario where running both types of prediction on the same project adds the most value.

Can both predictions be run on the same pile installation project?

Yes, running both a PDP and a VDP on the same project is not only possible but often recommended when the installation plan involves a combination of vibratory and impact driving. Each prediction covers the phase of installation it is designed for, and together they give your team a complete view of the full installation process.

A well-documented example of this combined approach involves a monopile with a diameter of 4.5 m and a total length of 40.5 m. A vibratory hammer advanced the pile to approximately 25 m penetration, where early refusal occurred. An impact hammer then completed the installation to around 31.5 m. By running both types of prediction beforehand and monitoring the actual installation, it became possible to compare the original CPT-based soil model against signal matching results from both the vibratory phase and the impact restrike phases. The installation itself became a calibration experiment for both driveability and capacity assessment.

This combined workflow reflects a broader principle: the most powerful approach is not an isolated prediction but a closed learning loop. The sequence runs from ground investigation and an initial soil model, through driveability prediction, installation monitoring, signal matching and back-analysis, to an updated soil model that feeds into the experience database and improves the next prediction. A deviation between prediction and reality is not just an error to explain. It is information that makes future models more accurate.

What software tools are used for each type of prediction?

AllWave-PDP is used for impact driving predictions, and AllWave-VDP is used for vibratory driving predictions. Both are part of the AllWave Software Package, which simulates stress-wave phenomena in piles and covers both installation methods as well as pile test simulation.

AllWave-PDP models the full hammer-pile-soil interaction for impact driving. It includes a hammer library, supports input from CPT, SPT, and laboratory data, and generates output covering blow count versus penetration, maximum tensile and compressive stresses, energy transfer, pile displacement, and shaft friction distribution with depth. The software can also produce stress cycle data as input for fatigue analysis, which is particularly relevant for offshore steel piles.

AllWave-VDP applies the same stress-wave framework but with soil models adapted to the cyclic loading mechanism of a vibro hammer. Because the physical interaction differs, the soil resistance parameters, damping relationships, and penetration criteria are formulated differently from those used in AllWave-PDP. The software allows engineers to simulate blow rate, penetration rate, and soil response under vibratory conditions and to compare predictions against monitored installation data.

Both tools are built on the Method of Characteristics, a numerical approach to one-dimensional wave equation solutions with a long development history in pile engineering. The underlying methodology traces back to decades of research and field validation, and the current software versions reflect accumulated experience from impact and vibratory installations across a wide range of soil conditions and pile types.

How We Support Your Drivability Predictions

We provide drivability studies for both impact and vibratory pile installation, using AllWave-PDP and AllWave-VDP to deliver predictions that are grounded in site-specific soil data and validated against real installation experience. Our approach treats every prediction as the starting point of a learning loop, not a one-time calculation.

When you work with us on a drivability study, we can support your project with:

Impact driving predictions (PDP) covering blow count, pile stresses, energy transfer, refusal risk, and fatigue loading
Vibratory driving predictions (VDP) with soil models calibrated for cyclic loading conditions
Combined PDP and VDP studies for projects using both installation methods in sequence
Installation monitoring and signal matching to compare predictions against measured data and update the soil model
Back-analysis and post-analysis reporting that turns installation data into a technical asset for future projects
Independent technical review of existing drivability studies for risk assessment or project verification

Whether you are planning an offshore wind foundation, a port structure, or a land-based driven pile project, accurate drivability predictions reduce installation risk and help your team make informed decisions before the first blow or vibration cycle. Contact us to discuss your project and find out how we can support your installation planning.