The present invention relates generally to vibratory pile drivers. More particularly, the invention relates to increasing the penetration depth of a vibratory pile driver using a dynamic pile end piece that is capable of displacing ground material at the pile head end during the driving action.
The most common foundation type in the offshore wind industry is the monopile. The foundation of a monopile is a large steel open-ended tube with diameters ranging from 2 to 16 meters, and wall thicknesses ranging from 5 to 20 centimetres. These foundation piles are installed into the ground with an impact hammer. The depth of installation typically ranges from 25 up to 40 meters into the ground. This depth is reached by striking the top of the pile with an impact hammer. By these strikes the pile penetrates the ground.
The impact hammer creates high noise levels underwater of up to 220 dB in the immediate proximity of the pile. Restrictions by several European governments have been stated on the level of this noise. The strictest regulations are the regulations stated by the German government, which allow a maximum noise level of 160 dB SEL (Sound Exposure Level) at 750 meters distance from the source. Other countries are expected to follow these requirements, which include The Netherlands, The United Kingdom, Denmark, Sweden, Norway and Belgium. In order to comply with these regulations, noise mitigation measures have to be taken. These countries have planned to install large amounts of wind turbines in the North Sea in the coming 15 years.
Several forms of noise mitigations have been developed and deployed since these regulations where stated. The most common used noise mitigations are a bubble curtain around the pile, which absorbs the sound produced by the hammer, and a noise mitigation screen, which is in fact a large round cofferdam in which the foundation pile is placed during installation, where this cofferdam is pumped dry so no direct contact between the water and the pile exist. Several other mitigation measures have been implemented, which all prevent the sound from propagating further into the water. These mitigation measures cost an average of three hundred thousand euros for each foundation pile installation. This is approximately 15% of the total foundation costs.
One attempt to not exceed the maximum sound level while installing a foundation pile includes using a vibratory hammer that is able to install a foundation pile to a certain depth without exceeding the maximum sound level. However the vibratory hammer is not capable of installing the pile to the required penetration depth of 25 to 40 meters deep. The depth which is typically reached with a vibratory hammer in the North Sea is anywhere between 5 and 20 meters. To reach the required depth an impact hammer is used after the use of a vibratory hammer. This once more requires the use of noise mitigation measures, therefore rendering this combination not profitable.
The soil resistance, which prevents the pile form penetrating the soil, has two components. The first is the resistance of the soil along the wall of the pile, outside and for an open ended steel pile also the inside. This resistance is called the ‘shaft resistance’ and is caused by the friction between the pile wall and the soil particles. The second is the resistance of the soil underneath the pile head end. When the pile penetrates the soil, the soil has to be pushed away to make room for the pile to enter. This resistance is called the ‘tip resistance’. During vibratory driving in sand, the soil type commonly found in the North Sea, the shaft resistance is low compared to the tip resistance. Friction fatigue of the soil is considered responsible for this. A vibratory hammer typically vibrates with a frequency of 10 Hz to 30 Hz and with the amplitude of the pile and hammer, which are rigidly connected, of 0 to 10 millimetres in the vertical plane. During vibratory driving the soil around the shaft is shaken by these motions and the soil experiences a high number of loading cycles, up to 1×105 to 10×105 loading cycles are applied to the pile and soil around the pile during the time it takes to install the pile. These loading cycles cause fatigue in the soil. The frictional strength reduces by 80% to only 20% of its initial value. However the soil underneath the pile at the time of installation does not experience this large number of loading cycles because the pile enters new soil every time it penetrates further into the ground. Also, the shear strength of sand is, compared to other soil types such as clay, very high which in turn causes a high tip resistance in this type of soil. The combined shaft- and tip resistance of the pile during installation is the total resistance. The majority of this resistance, in hard sandy soils, such as the North Sea, is the tip resistance. This follows from pile driving predictions and measurements taken during pile installations with a vibratory hammer. What is needed is the reduction of the high tip resistance, where the pile could be installed to the full-required penetration depth with a vibratory hammer, while meeting noise reduction requirements.
To address the needs in the art, a foundation pile end piece is provided that includes a ring-shape connection housing, where a proximal end of the ring-shape connection housing is configured to secure to a bottom end of a foundation pile, a moveable tip, where a distal end of the ring-shape connection housing is configured to fixedly hold the moveable tip, where the moveable tip is disposed to oscillate transversely with respect to a central axis of the ring-shape connection housing, where the moveable tip is configured to displace soil from the bottom end of the foundation pile according to actuation of the oscillation.
According to one aspect of the invention, the actuation of the oscillation can include electromagnetic actuation, mechanical actuation, hydraulic actuation, electromechanical actuation, pneumatic actuation, or piezoelectric actuation.
In another aspect of the invention, the moveable tip includes a cone-shape moveable tip. Here, the actuation of the cone-shape moveable tip includes mechanical actuation, where the mechanical actuation includes an eccentrically weighted arm configured to oscillate the cone-shape moveable tip when operated on by motor-driven vibration, or hammering. In one aspect, the current embodiment further includes lubrication ports disposed proximal to the foundation pile bottom end, an outer wall of the cone-shape tip, or the foundation pile bottom end and the outer wall of the cone-shape tip, where the lubrication ports are disposed to output lubrication between soil and the cone-shape moveable tip, the foundation pile, or the cone-shape moveable tip and the foundation pile. Here, the lubricant can include fresh water, seawater, air, and mud. Further, the lubricant ports are disposed to output grouting after installation of the foundation pile. In another aspect the current embodiment further includes a load sensor and accelerometer, where the load sensor and accelerometer are disposed to measure a resistance force between the moveable tip and soil surrounding the moveable tip.
According to another aspect of the invention, the moveable tip includes an array of the moveable tips arranged around the ring-shape connection housing forming a closed circular moveable tip array at the foundation pile bottom end. In one aspect, the closed circular moveable tip array includes a plurality of moveable elements arranged around the closed circle, where a gap is disposed between the foundation pile and soil that is adjacent to the foundation pile according to soil displacement by the actuation of the array of moveable tips. Here, the current embodiment further includes lubricant ports proximal to the gap or the bottom end of the moveable tips, where the lubricant ports output lubricant to the foundation pile walls. In one aspect of the current embodiment, the lubricant can include fresh water, seawater, air, and mud. In another aspect, the lubricant ports are disposed to output grouting after installation of the foundation pile. In yet another aspect of the current embodiment, each moveable tip includes a spring loaded moveable tip, where each spring loaded moveable tip pivots about a separate axis that is tangential to the circumference of the ring-shape connection housing, where each moveable tip is configured to displace soil radially inward and radially outward with respect to the foundation pile bottom end. According to one aspect of the current embodiment, each movable tip is actuated by mechanical actuation, where the mechanical actuation includes a hammer driven cam arm configured to oscillate a spring loaded moveable tip. In another aspect of the current embodiment, each movable tip includes a self-oscillating moveable tip, where the self-oscillation includes an articulating arm connected to the ring-shape connection housing at a proximal end and a tip element connected to the articulating arm at a distal end, where the articulating arm includes a shape memory material, or the self-oscillation is actuated according to actuation selected from the group consisting of electromagnetic actuation, mechanical actuation, hydraulic actuation, electromechanical actuation, pneumatic actuation, and piezoelectric actuation. The current embodiment further includes lubricant ports disposed output lubricant to the foundation pile walls. Here, the lubricant can include fresh water, seawater, air, and mud. Further, the lubricant ports are disposed to output grouting after installation of the foundation pile.
According to one aspect of the invention, the moveable tip includes a force sensor, where the force sensor is configured to measure a soil resistance force along the tip.
To further address the needs in the art, a foundation pile end piece is provided that includes a connection housing, where the connection housing is fixedly connect to a foundation pile bottom end using connection actuators, where the connection actuators include actuators fixedly connected to an inner wall of the foundation pile, where the actuators are disposed to extend and retract radially with respect to the foundation pile inner wall, a movable tip, where the moveable tip includes a ring-shape tip having a diameter that is smaller than an inner diameter of the foundation pile, where the moveable tip is connected to the connection actuators, where the moveable tip is configured to move soil from the foundation pile bottom end during installation of the foundation pile according to operation of the actuators.
The current invention is directed to the installation of foundation piles. According to one embodiment, the invention facilitates the installation of foundation piles with or without the use of a vibratory hammer. By adding the invention to the bottom part of the pile, the soil is cut, scraped, and pushed away from the pile bottom end and displaced to the surrounding soil to eliminate or reduce the high tip resistance from underneath the pile. According to different embodiments of the invention, the moveable tip device is actuated by the motions generated by a vibratory hammer, electromagnetic actuation, mechanical actuation, hydraulic actuation, electromechanical actuation, pneumatic actuation, piezo electric actuation, thermally activated bimorph actuation, thermal expansion, shape memory materials, or chemical actuation configured to induce oscillations in a vertical direction. The oscillating vertical motions are transformed by the device underneath the foundation pile bottom end into lateral, rotating, or lateral and rotating motions of the scraper.
In another embodiment the lateral, rotating, or lateral and rotating motions of the scraper are directly induced by electromagnetic actuation, mechanical actuation, hydraulic actuation, electromechanical actuation, pneumatic actuation, piezo electric actuation, thermally activated bimorph actuation, thermal expansion, shape memory materials, or chemical actuation. The current invention enables penetration of the foundation pile into the soil according to the force of the weight of the foundation pile and possibly combined with the weight of the vibratory hammer.
The current invention is presented in two useful forms that include a cone-shape tip, and a ring-shape tip, where the cone shape tip has a single moveable tip, and the ring-shape tip has multiple moveable tips arrayed around the ring. According to one embodiment, the single cone-shape movable tip is useful for relatively small diameter foundation piles, for example less than approximately 1 meter. In another embodiment of the invention, the ring-shape movable tip is suitable for foundation piles having diameters greater than approximately 1 meter.
According to embodiments of the current invention, multiple variations of the devices can be connected to the bottom end of the foundation pile.
Feccentricweight=m·e·ω2,
where:
Regarding the ring-shape moveable tip embodiments, three exemplary variations are provided that include a ring-shaped array of elements that are oscillated by an additional vibratory hammer on top of the foundation, a ring-shaped array of self-oscillating elements, and a self-oscillating ring.
In one embodiment, the invention includes a plurality of moveable tips arranged in a circular pattern around the ring-shape connection housing forming an interconnected array of moveable tip devices in a circle, where the tip array has approximately the same diameter and wall thickness of the pile under which they are installed. As an example, the number of devices that are installed to form a closed circular array underneath time pile are determined as follows: number of devices equals the length of the inner circumference of the pile divided by the width of one device.
Regarding the transfer of the vertical oscillating motion of the foundation pile to the oscillating motion of moveable tip, some exemplary ways of transferring the vertical oscillating motion to the transverse oscillating motion of the moveable tip include using a rigid direct connection, and by matching the moveable tip frequency to the applied frequency of the foundation pile driven by the vibratory hammer.
For the rigidly connected embodiment, the piston is rigidly connected to the foundation pile. The ring-shape housing is slidably fitted to the pile. By this loose connection the housing is capable of moving up and down in the vertical direction. When the foundation pile moves vertically up and down, a displacement of piston occurs according to the displacement of the pile. This displacement is not adopted by the housing, since it is not rigidly connected to pile, causing a rotating motion of moveable tip, which is connected to both the tip housing by the moveable tip axis and the piston by the actuation axis. The rotating motion of the moveable tip revolves around the moveable tip axis.
Regarding the vibrating at resonant frequency, the piston is not connected to the foundation pile, where the cam arm is connected to the movable tip by the moveable tip axis. In this example, the system formed by the piston, the moveable tip, the moveable tip axis, the actuation axis, the cam arm and spring are configured to have a matching frequency to the frequency applied to the foundation pile by the vibratory hammer. For example, this matching frequency is calculated with the combined masses of the piston, the moveable tip, the moveable tip axis, the actuation axis, the cam arm and the spring (mtotal) and the spring constant of the spring (kspring) and of the soil pressing against the moveable tip (ksoii) according to the following formula:
In this example, the system resonates in its own frequency. The piston is guided by the housing. The spring balances the oscillating motions of the system, and prevents unwanted motions and accelerations.
Turning now to a further embodiment of the current invention, where
In a further embodiment of the invention,
As discussed above, the fluid lubrication alleviates wall friction between the foundation pile wall and the surrounding soil. According to the current invention, the fluid is injected through the gap between the movable tip machine and the foundation pile and/or through nozzles in the cone. The fluid is disposed to flow upward along the outside of the foundation pile wall to reduce friction.
The present invention has now been described in accordance with several exemplary embodiments, which are intended to be illustrative in all aspects, rather than restrictive. Thus, the present invention is capable of many variations in detailed implementation, which may be derived from the description contained herein by a person of ordinary skill in the art. All such variations are considered to be within the scope and spirit of the present invention as defined by the following claims and their legal equivalents.
This application is a 371 of PCT application PCT/EP2017/062717 filed on May 25, 2017. PCT application PCT/EP2017/062717 claims the benefit of US Provisional application 62/341214filed on May 25, 2016.
Filing Document | Filing Date | Country | Kind |
---|---|---|---|
PCT/EP2017/062717 | 5/27/2017 | WO | 00 |
Publishing Document | Publishing Date | Country | Kind |
---|---|---|---|
WO2017/203023 | 11/30/2017 | WO | A |
Number | Name | Date | Kind |
---|---|---|---|
3645345 | Olsen | Feb 1972 | A |
4271915 | Bodine | Jun 1981 | A |
4403665 | Bodine | Sep 1983 | A |
4527637 | Bodine | Jul 1985 | A |
4615400 | Bodine | Oct 1986 | A |
20060021447 | Hecht | Feb 2006 | A1 |
20120073107 | Koecher | Mar 2012 | A1 |
Number | Date | Country |
---|---|---|
WO 2017043709 | Mar 2017 | WO |
Number | Date | Country | |
---|---|---|---|
20190292745 A1 | Sep 2019 | US |
Number | Date | Country | |
---|---|---|---|
62341214 | May 2016 | US |