Gas injecting system

Abstract

A gas injecting system (10) for use with installing a foundation (100) having a body (12) for insertion into soil (200) in an insertion direction during installation. The body (12) having a toe (22) at its distal end (20). The toe (22) defining an aperture (24) into an internal cavity (18), wherein soil (200) is displaced laterally into a displaced soil suspension region (26) within the internal cavity (18) when the toe moves through the soil (200) during installation. The gas jetting system (10) comprises a plurality of outlets for injecting a gas into the displaced soil suspension region (26) for applying a lifting force to soil (200) suspended in the displaced soil suspension region (26) for reducing soil suspension pressure at the toe (22).

Description

GAS INJECTING SYSTEM

[0001] The present invention concerns a gas inj ecting system for use with installing a foundation, a foundation comprising the gas inj ecting system and a method for installing said foundation . In particular, the present invention concerns foundations , such as monopiles , that may be inserted into a soil for supporting wind turbines . The present di sclosure is particularly relevant to foundations and associated installation methods which use a gas inj ecting system comprising a plurality of outlets for inj ecting a gas to aid installation and embodiments can, in particular, be used in combination with liquid j etting systems to further enhance foundation installation ef ficiency .

[0002] Structural foundations are often installed by driving the foundation into the ground using a pile hammer to apply a series of axial impacts to drive the foundation down into the soil . As it is driven, soil is displaced by the foundation pile , thereby compressing the surrounding soil . However, as the foundation is driven deeper, the pressure increases whilst the area of lateral surfaces exposed to the soil also increases thereby increasing the axial load resi stance . As such, the forces required to continue installation and displace soil also increase .

[0003] With increased mechanical resistance to installation comes a requirement for high impact driving forces , and in turn, signi ficant mechanical requirements on the foundation itsel f to avoid its failure during installation . The noise generated by the impacts can be extremely high . In the case of of fshore installations , this poses a particularly signi ficant environmental hazard to marine li fe .

[0004] In this respect, the installation of foundations for offshore structures can cause detrimental physical and behavioural effects to marine wildlife. In recent years, significant efforts have been made to mitigate the noise generated during such installations. For instance, bubble curtains or pile-in-pile systems are often required to reduce the level of noise emitted from the piling location. However, the use of such noise mitigating measures adds considerable expense to the installation of offshore structures. Furthermore, this is a particular issue for larger foundations where the increased dimensions can render current noise mitigation options insufficient.

[0005] To address the above, research has been made into techniques for reducing installation resistance. One example is the use of electro-osmosis in clay type soils to reduce the pile driving resistance in offshore installations by attracting water in the soil towards the foundation body acting as a cathode and providing a lubricating effect over the lateral surfaces of the foundation body to allow installation to be achieved more easily.

[0006] In addition, jetting systems incorporated into the foundation have also been used to jet liquid to erode and break up soil. Jetting systems are particularly effective at tackling granular soils. In other arrangements, the liquid jetting is used to counteract compaction of the soil displaced by the advancing foundation toe. That is, the jets are used to create space at toe level for the soil to be displaced into by the toe for preventing soil from being squeezed outwards to counteract compaction. Such jetting systems can also be used in combination with electroosmosis to tackle stratified soils, which are composed of both, cohesive and granular layers. Electroosmosis can thereby beused to reduce outside wall friction in the cohesive layers, and the jetting can be used in both soil types to create space for the soil which is displaced by the toe. .

[0007] An effect of the above jetting methods is they act to form an annulus of liquid soil suspension around the interior wall of the foundation body. This forms a liquid channel which extends up from the toe of the foundation to the water table within the foundation' s interior cavity above the seabed. However, as the foundation's installation depth increases, the soil suspension pressure at the toe increases which acts to resist further soil displacement.

[0008] To address this issue, a pumping system described in the applicant's European patent EP 3,784,838 has been used for evacuating fluid from the interior cavity of the foundation. This acts to either lower the water table inside the pile and / or reduce the internal atmospheric pressure in the air above the water level. These mechanisms can act to reduce the soil suspension pressure at the toe. However, whilst effective, this solution requires typically electrically powered pumps mounted to the inside of the foundation. This introduces additional complexity and costs in terms of onshore / off shore logistics, mounting, extraction, umbilical handling, etc. At the same time, the technique is often limited to sufficiently deep-water applications.

[0009] Embodiments of the present invention aim to provide an alternative technique of reducing soil suspension pressure in the context of installation of a monopile for a wind turbine, which is not reliant on the use of a pumping system. The configurations of the presented embodiments are cost- effective and robust.

[0010] According to a first aspect of the present invention, there is provided a gas injecting system for use with installing a foundation having a body for insertion into soil in an insertion direction during installation, the body having a toe at its distal end, and the toe defining an aperture into an internal cavity, wherein soil is displaced laterally into a displaced soil suspension region within the internal cavity when the toe moves through the soil during installation, wherein the gas jetting system comprises: a plurality of outlets for injecting a gas into the displaced soil suspension region for reducing soil suspension pressure at the toe.

[0011] In this way, a simple, cost-effective solution to reduce soil suspension pressure at the toe of a foundation, such as a monopile, is provided. The injected gas bubbles may act to cause a drag force on the liquid phase of the suspension, which in return lowers the suspension pressure at toe level. The gas injecting system can be retrofit or added to existing foundation comprising liquid jetting. Due to its simplicity, the gas injecting system can be designed as a sacrificial solution which remains within the monopile after the foundation is installed, which significantly simplifies offshore operations. The solution is inherently robust and has a low risk profile.

[0012] In embodiments, the plurality of outlets comprises nozzles or filter stones. The nozzles may be referred to herein as 'micro-nozzles' . In this way, the gas is injected in the form of a fine dispersion into the displaced soil suspension region, which increases the size of the region around the toe in which the reduction in soil suspension pressure is seen. Consequently, installation of the foundation is facilitated.

[0013] In embodiments, the gas injecting system further comprises a pressurised gas supply for supplying gas to the plurality of outlets.

[0014] In embodiments, the gas injecting system comprises a pressurised supply of liquid and gas for supplying a mixture of liquid and gas to the plurality of outlets. In this way, the liquid jetting velocity at the injection system is increased in comparison to a liquid supply which does not contains compressed gas, improving cutting power of the liquid jet and the removal of soil from the displaced soil region, while injecting gas at the same time to achieve the suspension pressure reduction effect at toe level.

[0015] In embodiments, the pressurised supply of liquid and gas comprises 0%-5% of compressed gas, and preferably 0.1- 5%. In this way, the balance between liquid and gas in the mixture is such that an optimum reduction in soil suspension pressure is achieved at the toe. In embodiments, the compressed gas is air or nitrogen. It will be understood that the gas fraction will be very small while the water is still at elevated pressure (e.g. 1% at 250bar) but will increase significantly while the jetting water is passing through the jetting nozzle due to the large pressure drop. For example, a small gas fraction of 1% can increase up to 20-70% during a pressure drop from 250 down to 10-lbar, respectively, assuming constant temperature. It will be understood that as the compressed gas expands while passing through the nozzle, it wants to cool down significantly. However, the weight ration and the very high specific heat of water means that this will only marginally cool down the jetting water and hence there is no risk of freezing and clogging the jetting nozzles .

[0016] In embodiments, the gas injecting system comprises a plurality of liquid nozzles for directing a jet of liquid into the displaced soil suspension region for displacing soil as the toe moves through the soil during installation. In this way, a liquid jet can displace or erode soil ahead of the toe and into the displaced soil suspension region, thereby preventing the soil in this region from becoming overly compressed. Accordingly, this acts to reduce the bearing resistance at the toe of the foundation.

[0017] In embodiments, the plurality of outlets is distributed around each of the liquid nozzles, such that the injected gas flows around the jet of liquid. In this way, a 'collar' or 'sleeve' of gas is created around the liquid jet which improves the reach of the liquid jet and its effectiveness in transporting soil away from the displaced soil suspension region. Dispersion of the gas through the displaced soil suspension region is also improved as a result of mixing the gas with the liquid jet.

[0018] In embodiments, each outlet is configured for forming a gas sleeve around the jet of liquid.

[0019] In embodiments, each outlet is upstream of the stream of the jet of liquid.

[0020] In embodiments, each outlet comprises a continuous gap enclosing the each of the liquid nozzles.

[0021] In embodiments, the gas injecting system comprises a pressurised liquid supply for supplying a liquid to the plurality of liquid nozzles.

[0022] In embodiments, the pressurised liquid supply is arranged to accommodate the pressurised gas supply. This isenabled as a result of the diameter of a pressurised gas supply piping being smaller than the diameter of piping of the pressurised liquid supply system, due to the compressibility of the gas .

[0023] According to a second aspect of the present invention, there is provided a foundation comprising the gas inj ecting system described above .

[0024] According to a third aspect of the present invention, there is provided a method of installing a foundation for a wind turbine , the foundation as described above . The method comprising inserting a toe of the foundation into soil ; forcing a body of the foundation in an insertion direction; directing a j et of liquid to a displaced soil suspension region within the internal cavity to displace soil as the toe moves through the soil ; and inj ecting gas into the displaced soil suspension region for reducing soil suspension pressure at the toe .

[0025] In embodiments , the method further comprises supplying the inj ection system with liquid for inj ection into the displaced soil region for transporting soil away from the displaced soil region .

[0026] I llustrative embodiments of the present invention will now be described with reference to the accompanying drawings in which :Figure 1 shows a sectioned isometric view of a foundation compri sing a gas inj ecting system according to an illustrative embodiment of the invention;Figure 2 shows a sectioned isometric view of a foundation compri sing a gas inj ecting system according to an illustrative embodiment of the invention;Figure 3 shows a cross sectional view through a foundation comprising a liquid j etting noz zle with a gas j etting system according to an illustrative embodiment of the invention;Figure 4 shows a cross sectional view of a liquid noz zle according to an illustrative embodiment of the invention;Figure 5 shows a monopile installation comprising a gas inj ecting system for inj ecting gas and liquid into soil according to embodiments of the invention; andFigure 6 shows installation of a foundation comprising a gas inj ecting system according to an illustrative embodiment of the invention .

[0027] Figure 1 shows a sectioned isometric view of the distal end region of a foundation according to a first embodiment of the invention . In this embodiment , the foundation is a monopile 100 of a wind turbine , which is to be inserted into soil , such as a seabed, during installation .

[0028] The foundation comprises a hollow tubular body 12 having an exterior lateral surface 14 , and an interior lateral surface 16 that defines an interior cavity 18 in the form of a bore . The distal end 20 of the body 12 comprises a toe 22 , which defines an aperture 24 .

[0029] During installation, the toe 22 is inserted into the soil 200 , and the body 12 of the monopile 100 is forced into the soil 200 . I f using a pile hammer to install the monopile , the monopile 100 of the present disclosure requires a lower pile driving force compared with the pile driving force applied during installation of conventional monopiles , for at least the reasons that are explained in more detail below . Indeed, in many scenarios , the monopile 100 may be installedunder its own weight or with additional ballast only, without the need for pile-driving . Due to the lower installation resistance , less noise can be generated .

[0030] As the toe 22 penetrates through the soil 200 , soil 200 is displaced into a displaced soil suspension region 26 immediately ahead of the toe and / or in the internal cavity 18 adj acent to the toe at the distal end of the foundation . In this respect , liquid j etting acts to erode the soil below the foundation' s toe on the inside of the pile wall . The eroded soil forms a soil suspension with the water influx from the j etting . The soil below the toe is displaced into this cavity / annulus and is also broken up by the water j ets and merges into the soil suspension . The suspens ion inside the pile will rise above the seabed level with a soil suspension filled annulus 28 formed as an annulus around the interior surface of the monopile extending from the displaced soil suspension region 26 up to the water table , separating the interior surface from the soil 200 in the seabed . The soil suspension level inside the foundation can, for example , rise up to 5- 10m above seabed level . The internal water table height and the suspension level / unit weight inside the foundation will govern the suspens ion pressure at toe level . Optionally, the distal end 20 of the body 12 may also comprise a radially inward- facing tapered surface for directing displaced soil toward the internal cavity 18 .

[0031] In order to lower the soil resistance resulting from the soil suspension pressure associated with the soil suspension filled annulus 28 (e . g . stabilising the soil below toe and which causes elevated soil stresses acting on the outer pile wall ) , a gas inj ecting system 10 according to the first embodiment is provided on the monopile 100 for reducingthe soil suspension pressure at the toe 22, to be described below .

[0032] As shown in Figures 1 and 2, the interior of the internal cavity 18 of the monopile 100 is provided with a gas injection system 10 at the toe 22. The gas injection system comprises a plurality of outlets that may be connected to one or more feed pipes 30 that each extend distally down the interior surface 16 for injecting a gas into the displaced soil suspension region 26 during installation. In one embodiment, the plurality of outlets is provided on an injection manifold provided at the toe 22. In this embodiment, at least one feed pipe 30 may be connected to the injection manifold to deliver gas to the plurality of outlets .

[0033] As shown in Figure 3, the gas injecting system 10 according to an embodiment of the invention is fitted to an interior cavity 18 of the monopile 100, with the monopile 100 comprising a liquid jetting system 221 for jetting liquid from nozzles provided at the toe 22 to erode soil ahead of the toe 22 and form the soil suspension filled annulus 28. The gas injected by the gas injection system 10 disperses through the displaced soil suspension region in the form of gas bubbles 34. The gas bubbles 34 rise upwards to the sea surface from the soil suspension region within the internal cavity 18 of the body 12. A drag force acting on the gas bubbles 34 creates an upwards, or lifting, force on the on the liquid phase of the suspension. As a result, the upwards force on the soil 200 suspended in the displaced soil suspension region 28 and in soil suspension 32 lowers the soil suspension pressure in the toe region.

[0034] Moreover, the gas bubbles 34 inj ected by the gas inj ecting system 10 into the displaced soil suspension region 26 will expand as they ascend to the sea surface , due to the reducing pressure exerted by the surrounding water as the depth of the bubbles reduces . The soil suspension pressure is reduced by a greater extent , as the associated drag ef fect increases . This is illustrated in Figure 3 , where it is shown that the gas bubbles 34 expand in si ze the closer the gas bubbles 34 ascend to the sea surface . Due to the introduction of gas bubbles 34 into the soil suspension 32 , the soil suspension 32 occupies a greater volume within the internal cavity 18 of the monopile 100 when compared with the volume of the soil displaced from the soil suspension filled annulus (water column) 28 . This is emphasised in Figure 3 by the di f ference in the level of the soil suspension 32 within the internal cavity 18 of the monopile 100 and the level of the soil 200 around the exterior surface 14 of the monopile 100 .

[0035] As a consequence of the reduction in soil suspension pressure , soil stresses and mechanical resistance to the installation of the monopile 100 are reduced . In the first embodiment , reduction of the pressure in the soil suspension region 26 at the toe is achieved without the need to lower the water table inside the bore of the foundation using extraction pumps or water level control systems , and there is no requirement for atmospheric pressure to be reduced inside the bore above the sea level . As such, the resulting solution is both simple and cost-ef fective , avoiding the need for complex of fshore installation of technology that would otherwise be required to achieve a reduction in soil suspension pressure in the toe region .

[0036] In an embodiment , the plurality of outlets of the gas inj ection system 10 may comprise noz zles 36 . The noz zles 36may be connected to respective one or more feed pipes 30 for directing the gas towards the toe 22 in an insertion direction. Advantageously, the shape of the nozzles 36, and particularly the profile of the axis of each of the nozzles 36, is such that the exit velocity of the gas is greater than the velocity of the gas supplied through each of the one or more feed pipes 30. In further embodiments, the injection system may comprise micronozzles that can be used to inject very small and precise amounts of gas into the displaced soil suspension region 28. In further embodiments, the plurality of outlets of the gas injection system 10 may comprise filter stones that can be used to control the size of the gas bubbles 34. The filter stones are a porous material, which have pore sizes which affect the sizes of the gas bubbles 34 that are dispersed through the filter.

[0037] The gas delivered through the one or more feed pipes 38 is supplied to the gas injection system 10 by a pressurised gas supply 40 on an installation vessel 102. In embodiments, the pressurised gas supply 40 delivers a gas, such as air.

[0038] Figure 4 shows a cross-sectional view of a liquid nozzle for directing a jet of liquid to the displace soil suspension region 28 during installation of the foundation according to a further embodiment. In this embodiment, the gas injection system 10 comprises a plurality of liquid nozzles 36 each having a central portion 42 for directing a jet of liquid to the displaced soil suspension region 28 during installation of the monopile 100 for displacing soil 200 into the soil suspension filled annulus 28. A pressurised liquid supply delivers liquid to each of the nozzles 36 via a respective liquid feed pipe 44 extending distally down the interior surface 16. In embodiments, the pressurised liquid supply delivers a hydraulic fluid, such as water.

[0039] In this embodiment, each of the plurality of outlets are located upstream of the liquid nozzles and are distributed around each of the liquid nozzles, such that the injected gas flows around the jet of liquid. The plurality of outlets comprise a peripheral portion 46 distributed around the central portion 42. In an embodiment, the feed pipe 30 for delivering the gas may be enclosed, or accommodated, within the liquid feed pipe 44, such that a single pipe can be used to deliver gas and liquid to the one or more liquid nozzles 36. The peripheral portion 46 comprises a manifold 48 to distribute the gas around the central portion 42, such that the gas from the pressurised gas supply 40 flows around a jet of the liquid. For example, a continuous ring gap for delivering air may be provided, for forming an air sleeve around the jet of liquid jetted from the central portion 42. This air sleeve may act to enhance the jetting efficiency, thereby allowing the jet to reach further because of the air sleeve. In other embodiments, compressed air may be fed into the jetted water before it enters the nozzle.

[0040] Figure 5 illustrates a foundation comprising the liquid nozzles shown in Figure 4. The liquid nozzles are configured to direct pressurised liquid jets downwardly ahead of the body 12 in the insertion direction. The cutting action of the jets from the one or more nozzles 36 forms circumferential cuts into the soil 200 ahead of the body 12. Accordingly, a cut into the soil 200 is created by the plurality of liquid nozzles, which excavates the soil 200 ahead of the body 12 and transports it away through the displaced soil suspension region 26 in the soil suspension filled annulus 28 to reduce the force required to install the monopile 100. As each of the nozzles 36 can jet a liquid andinject a gas, the gas injected from the nozzles 36 can forms a curtain, collar or sleeve around the jetted liquid which enables the effectiveness and reach of the liquid jets to be increased. The dispersion of the injected gas is also enhanced by the turbulence generated by the jetted liquid. That is, the air sleeve acts to enhance the reach of the jet and promotes a better dispersion of the air in the water. In addition, a more compact arrangement of nozzles can also be achieved as separate nozzles for the liquid and the gas are not required.

[0041] In this connection, the injection system is arranged such that the gas is injected into the displaced soil suspension region in the form of a mixture comprising a liquid, for transporting soil away from the displaced soil suspension region, and the gas. Beneficially, the injection system of the present disclosure is used to reduce the installation resistance of monopile foundations, such that the monopile 100 can be installed without using a pile hammer. This is achieved by reducing soil stress at the toe 22 of the monopile 100 by reducing the soil suspension pressure that is created by the mostly downwards facing liquid jets on the inside of the monopile at the toe 22. Moreover, by injecting the gas into the displaced soil suspension region 26, the soil suspension pressure is reduced, as described above. This is illustrated in Figure 5, where it is shown that the liquid jets displace the soil 200 ahead of the toe to form the soil suspension filled annulus 28.

[0042] In an alternative embodiment, a mixer is provided on an installation vessel 100, or the supply vessel, for preparing a mixture of gas and liquid, as shown in Figure 6. The mixer combines a liquid, such as sea water, with a gas from a compressor or from a gas storage supply provided onthe installation vessel 100 or the supply vessel . Once the liquid and gas have been combined in the mixer, the pressurised mixture supply is delivered through the one or more feed pipes 30 for supplying the mixture to the inj ection system . In this embodiment , the liquid and the gas are mixed before being delivered through the one or more feed pipes 30 to the noz zles 36 , thereby eliminating the need for additional feed pipes to deliver both the liquid and the gas separately .

[0043] In one embodiment , the mixer 102 is configured to mix compressed nitrogen into the liquid at the mixer 102 , such that 0%-5% of the mixture comprises compressed gas . Preferably, the mixer 102 is configured to mix compressed nitrogen into the liquid, such that 0 . 5- 1 % of the mixture comprises compressed air .

[0044] During installation of the monopile 100 , the body 12 of the monopile 100 is lowered by a crane 104 on an installation vessel 100 towards the soil 200 , as illustrated in Figure 6 . As the body 12 is lowered further, the toe 22 penetrates axially downward in the insertion direction through the soil 200 .

[0045] Soil 200 ahead of the toe is eroded by the water j ets and also forced radially inward as the toe moves through the soil 200 . These actions displace the soil 200 into the soil suspension laterally adj acent to the distal end 20 of the body 12 of the monopile 10 in the displaced soil suspension region 26 at the bottom of the internal cavity 18 . As the one or more noz zles 36 of the present disclosure act to inj ect a gas into the soil suspension 32 , this acts to reduce the soil suspension pressure within the internal cavity 18 , as described above .

[0046] In this connection, during installation, the liquid jets break up the soil 200 to form a dense soil slurry, referred to as the soil suspension 32, for upward sediment transport. This moves soil 200 relatively upward from the displaced soil suspension region 26 and hence avoids the soil 200 in this region from becoming overly compressed. As such, the build-up of resistance to further soil displacement at the toe 22 is minimised. At the same time, a proportion of the jetted water drains downward to balance the negative pore pressure as the soil 200 dilates in the displaced soil suspension region 26. This further acts to reduce the bearing resistance at the toe 22. The shape and direction of the nozzles 36 may be configured to control the tangential, vertical, and horizontal spread of the high pressure fluid flow for optimising the above effects. For example, it is envisaged that the nozzles 36 may be provided with a flat square shape, similar to that provided on high pressure car washing nozzles, for creating a jetting fan.

[0047] It will be understood from the present disclosure that the installation of the monopile 100 may be performed without the use of a pile hammer as a result of the reduction in suspension pressure achieved in embodiments of the present invention. For example, the monopile 100 may be installed only under its own weight or with the aid of an additional ballast, rather than requiring pile-driving.

[0048] It will be understood that the embodiments illustrated above show applications of the invention only for the purposes of illustration. In practice the invention may be applied to many different configurations, the detailed embodiments being straightforward for those skilled in the art to implement. For example, the gas injection system maybe provided as a separate tool which may be coupled to the foundation of a wind turbine, such as a monopile.

[0049] In this connection, for example, it will be understood that embodiments of the invention may be used in combination with other methodologies to facilitate foundation installation. For example, the air injection may be used in combination with a pumping system to support the water level control .

[0050] Furthermore, in other embodiments, additives may be added to jetted water to work in combination with the air injection system. For example, a foaming agent may be added to the jetted water to produce a suspension 'foam' as air is injected. This may act to further increase the air fraction within the suspension. Such a foaming agent would preferably be biodegradable.

Claims

CLAIMS1 . A gas inj ecting system for use with installing a foundation having a body for insertion into soil in an insertion direction during installation, the body having a toe at its distal end, and the toe defining an aperture into an internal cavity, wherein soil i s displaced laterally into a displaced soil suspension region within the internal cavity when the toe moves through the soil during installation, wherein the gas inj ecting system comprises : a plurality of outlets for inj ecting a gas into the displaced soil suspension region for reducing soil suspension pressure at the toe .2 . The gas inj ecting system according to claim 1 , wherein the plurality of outlets comprises noz zles or filter stones .3 . The gas inj ecting system according to any preceding claim, further comprising a pressurised gas supply for supplying gas to the plurality of outlets .4 . The gas inj ecting system according to claim 1 or 2 , further comprising a pressurised supply of liquid and gas for supplying a mixture of liquid and gas to the plurality of outlets .

5. The gas inj ecting system according to claim 4 , wherein the pres surised supply of liquid and gas comprises 0%-5% of compressed gas .

6. The gas inj ecting system according to any one o f claims 1 to 3 , further comprising a plurality of liquidnozzles for directing a jet of liquid into the displaced soil suspension region for displacing soil as the toe moves through the soil during installation.

7. The gas injecting system according to claim 6, wherein the plurality of outlets are distributed around each of the liquid nozzles, such that the injected gas flows around the jet of liquid.

8. The gas injecting system according to claim 6 or 7, wherein each outlet is configured for forming a gas sleeve around the jet of liquid.

9. The gas injecting system according to any of claims 6 to 8, wherein each outlet is upstream of the stream of the jet of liquid.

10. The gas injecting system according to any of claims 6 to 8, wherein each outlet comprises a continuous gap enclosing the each of the liquid nozzles.

11. The gas injecting system according to any one of claims 6 to 10, further comprising a pressurised liquid supply for supplying a liquid to the plurality of liquid nozzles .

12. The gas injecting system according to claim 11, wherein the pressurised liquid supply is arranged to accommodate the pressurised gas supply.13 . A foundation comprising the gas inj ecting system according to any one of claims 4 to 12 .14 . A method of installing a foundation according to claim 13 , the method comprising : inserting a toe of the foundation into soil ; forcing a body of the foundation in an insertion direction; directing a j et of liquid to a displaced soil suspension region within the internal cavity to displace soil as the toe moves through the soil ; and inj ecting gas into the displaced soil suspension region for applying a li fting force to soil suspended in the displaced soil suspension region for reducing soil suspension pressure at the toe .

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