Vibratory offshore pile driving offers a potential solution for reducing the underwater noise generated during the installation of foundation piles compared to using impact hammers. Existing noise prediction models are specifically tailored to impact pile driving scenarios. This paper introduces a novel methodology for underwater noise predictions during vibratory pile driving. A non-linear driveability model is utilised to derive realistic non-linear interface friction forces, which are then incorporated into a noise prediction model. The study emphasises the significance of integrating a driveability analysis, revealing substantial differences from traditional models that assume perfect contact between the pile and soil. The authors argue that the proposed model provides more realistic outcomes when considering smooth driving without refusal, in contrast to traditional models designed for impact piling. The results illustrate noticeable deviations in pressure levels and seabed vibrations between the linear and presented methods at the driving frequency and its superharmonics. Furthermore, the research demonstrates that the noise field is highly sensitive to variations in system dynamics and excitation spectrum during driving, using both small- and large-diameter monopiles as examples. This research contributes to developing more effective driving techniques to reduce underwater noise pollution and facilitate sustainable offshore wind turbine installations.

Offshore wind energy holds significant promise as a solution in the energy transition. However, installing offshore pile foundations can generate substantial levels of underwater noise, posing potential risks to marine life. This paper examines the influence of asymmetric impact forces and pile inclination on producing underwater noise and seabed vibrations based on cases of a small- and large-diameter monopile. The study focuses on scenarios involving inclined and eccentric forces and tilted piles. The analysis reveals that non-symmetrical conditions significantly impact the sound pressure levels around the ring frequency of the pile due to various noise generation mechanisms. However, it is observed that the vertical component of the impact force predominantly contributes to the generation of underwater noise, primarily due to its considerably higher amplitude.

Gentle Driving of Piles (GDP) is a new technology for the vibratory installation of tubular (mono)piles. Its founding principle is that both efficient installation and low noise emission can be achieved by applying to the pile a combination of axial and torsional vibrations. Preliminary development and demonstration of the proposed technology are the main objectives of the GDP research programme. To this end, onshore medium-scale tests in sand have been performed on piles installed using both impact and vibratory driving methods (including GDP). After presenting the development of a purpose-built GDP driving device and the geotechnical characterisation of the site, this paper covers the execution of GDP installation tests. Focus is on the installation performance of GDP-driven piles, which is discussed with the aid of structural and ground monitoring data. The comparison between piling data associated with GDP and standard axial vibro-driving points out the potential of the proposed installation technology, particularly with regard to the beneficial effect of the torsional vibration component. The findings of this study encourage further development of the GDP method and its future extension to offshore full-scale conditions.

Due to the growing demand in offshore wind, increasing numbers of foundation piles are planned to be installed in the coming decades. Monopiles driven by impact hammers have a large environmental impact on aquatic life. Vibratory pile driving is a promising alternative that generates less noise nuisance. Despite the lower levels of noise expected, modeling of noise radiation from vibratory piling is still required due to the large size of the foundation piles used nowadays and the changes in the radiated spectrum of the noise. The existing models used to assess the noise emission are calibrated against impact piling and are not accurate when it comes to noise radiation from vibratory installation. Existing models either represent the sediment as an acoustic fluid or, when the seabed is modelled as elastic medium, they couple the soil and pile displacements fully at their interface. The effect of both these assumptions on the radiated noise still needs to be verified in vibratory pile installation. Additionally, the effect of the secondary noise path, i.e. noise channeling into the seawater via the soil, is expected to play a more significant role in vibratory pile driving because more energy is concentrated at the lower frequencies. In this paper, a pile-water-soil model to predict the noise emission due to vibratory pile driving is developed which describes the soil as an elastic medium and allows the pile to move relative to the soil during the pile driving process. To maintain a computationally efficient solution method, the effect of friction is linearized via a spring connection between soil and pile. Finally, a study is conducted and the effect of the slip on the noise emission is studied in detail for the first time.

In the original publication, Eqs. (11) and (17) are published incorrectly, and this has been corrected as follows: (Formula presented.) The original article has been revised.

This paper presents a computationally efficient mode-matching method to predict the relative axial motion of two elastic rods in frictional contact. The motion is of the stick-slip type and is non-uniform along the rods. The proposed method utilizes the piecewise linearity of the problem in time and space. The original set of nonlinear partial differential equations describing the dynamics of the coupled system is first reduced to a system of linear, per time interval, ordinary differential equations by means of modal decomposition. The global modes are used for one of the two rods, while for the other rod, different modes are identified per time interval based on the regions in stick or slip phase. Subsequently, the system response is obtained by combining the piecewise linear solutions. A comparison of the solution method proposed with standard numerical techniques shows its advantage both in terms of computational time and accuracy. Numerical examples demonstrate the capability of the method to analyse cases involving either harmonic- or impact-type forces that drive the relative motion. Although the discussion in this paper is limited to the one-dimensional configuration, the approach is generic and can be extended to problems in more dimensions.

In the next decade, an increasing number of offshore windfarms is planned to be installed, the vast majority of which to be founded on monopiles. Traditionally, the driving of piles is performed by impact hammers, however, due to the environmental impact, alternatives such as vibratory driving become more important. Current models to assess the underwater noise from pile driving are tuned to impact pile driving and are less accurate for vibratory pile driving. A major difference is that in vibratory pile driving, the driving is continuous and energy is concentrated at lower frequencies. The assumption of perfect contact between pile and sediment is questionable since it is known that slippage will occur. This paper presents a model for underwater noise calculations in which the effect of pile-soil slip is taken into consideration. A subsystem approach is used to separate pile from the fluid-soil domain. The latter is modelled as an acoustic fluid layer over an elastic half-space. The dynamic stiffness of the fluid-soil domain is calculated based on distributed body forces over a cylindrical surface. To allow the pile-soil slip condition, the interface condition of perfect vertical contact is relaxed and replaced by a dynamic'friction' spring. The paper shows that especially at low frequencies, that contain most energy in vibratory pile driving, the allowance for sliding contributes significantly to the pressure levels in the fluid.

A novel pile-driving technique, named Gentle Driving of Piles (GDP), that combines axial low-frequency and torsional high-frequency vibrations has been developed and tested recently. During the experimental campaign, several piles were installed onshore, making use of the GDP shaker. Besides those, a number of additional piles were installed using conventional pile-driving techniques, i.e. impact piling and axial vibratory driving. After the completion of the installation phase, the installed piles have been subjected to impact hammer tests with the following goals. First, the in-situ dynamic properties of the pile-soil system have been identified. Second, the post-installation soil state has been investigated, along with its evolution in time for each pile driving scenario. Preliminary analyses, of the data collected during the impact tests show dissimilar trends in the overall dynamic response between the piles installed with impact hammer and those installed with the axial and the GDP shakers.This observation suggests a difference in the post-installation dynamic behaviour of the pile-soil systems related to different pile-driving techniques. In this paper, a first attempt is made to identify the differences in the overall pile-soil dynamic behaviour of the piles installed by means of the three different pile-driving techniques.