Grouting Method

Abstract

A method is provided for securing an offshore structure 1 to a pre-driven foundation pile 5. The foundation pile 5 comprises a pipe that is driven into the seabed, and the offshore structure 1 has a leg 3 that is inserted into the foundation pile 5. The method involves applying grout to a first area A between the end of the leg 3 and the seabed. The grout is then allowed to harden before applying grout to a second area B, which is an annular area between the leg 3 and the foundation pile 5.

Description

[Technical field]

[0001] The present invention relates generally to a grouting method, more particularly to a method of applying grout to the feet of an offshore structure, and more particularly, but not exclusively, to a method of fastening an offshore structure to pre-driven foundation piles. [Background technology]

[0002] Offshore structures common to both the offshore wind and offshore oil and gas industries often include a structural jacket that supports a payload above the water surface. In the offshore wind industry, the payload is a wind turbine, and in the offshore oil and gas industry, the payload is often a processing and / or storage platform.

[0003] The structural jacket is secured to the seabed via one or more foundation piles, which often take the form of hollow tubes that are driven into the seabed. To secure the structural jacket to the foundation piles, and thus to the seabed, a cementitious material, commonly known as grout, is applied to the foundation. The grout is applied to fill the interfaces between each foundation pile and the respective legs of the jacket. The grout is then allowed to harden. Traditionally, the grout is applied via pipes or hoses from a pump unit above the water surface. Summary of the Invention

[0004] According to one aspect of the invention there is provided a method of fixing an offshore structure to a pre-driven foundation pile, the foundation pile comprising a pipe which is piled into the seabed surface and the offshore structure having a foot which is inserted into the foundation pile, the method comprising applying grout to a first area between an end of the foot and the seabed surface within the foundation pile, allowing the grout to at least partially harden and then applying grout to a second area, the second area being an annular area between the foot and the foundation pile.

[0005] The end of the leg may be generally referred to as the stub-in or stub-in portion of the leg.

[0006] The offshore structure can be configured to support a payload above the water surface. The payload can be attached to the offshore structure, for example, a jacket of the offshore structure, after grouting is completed. The payload can be or include a wind turbine or an oil and gas platform.

[0007] The method may be particularly advantageous where the payload is a wind turbine, where the offshore structure may be subjected to cyclic lateral loads, for example due to wind and / or wind turbine operation, and the present invention may result in a more reliable structure when subjected to such lateral loads due to the structural integrity of the foundation.

[0008] The legs or stub-ins may be inserted into the open ends of the foundation piles.

[0009] The offshore structure may comprise a plurality of foundation piles and the jacket may comprise a plurality of corresponding legs, each of which may be inserted into the open end of a respective foundation pile.

[0010] The method may include applying grout to all of the first regions of the plurality of foundation piles before applying grout to second regions of the plurality of foundation piles.

[0011] The grout applied to the first region can be left to harden, for example to a predetermined extent, before applying the grout to the second region. The grout applied to the first region can be left to harden until it sets or hardens, or is substantially hardened or hard, before applying the grout to the second region. The grout applied to the first region can be left to harden until it reaches final set, before applying the grout to the second region.

[0012] The grout applied to the region between the end of the leg and the seabed may be or may include a first grout. The grout applied to the annular region between the leg and the foundation pile may be or may include a second grout. The first grout may be different from the second grout, i.e., the first grout may have a different composition than the second grout. The first grout may be left to harden, for example to a predetermined extent, before applying the second grout.

[0013] The first grout may be left to cure for a predetermined period of time before applying the second grout, which may be determined based on the amount of first grout applied and / or the water temperature in the foundation pile.

[0014] The method can include testing the grout applied to the first region (i.e., the first grout), for example, to determine whether it has hardened. The method can include testing the grout applied to the first region (i.e., the first grout) prior to applying the grout to the second region (i.e., the second grout).

[0015] The grout or second grout can be applied to the second area until it fills or overflows the second area.

[0016] The filling or flooding of the second region with grout may be determined acoustically and / or visually. The filling or flooding of the second region with grout may be determined using a remotely operated vehicle (ROV). The filling or flooding of the second region with grout may be determined using a density gauge or meter, for example an ultrasonic density gauge or meter or a nuclear density gauge or meter.

[0017] The method may include applying grout to a first region, for example from a water surface point, such as a vessel, via a first conduit extending through or along the legs. The first conduit may have a first outlet at or toward the bottom of each leg. The grout may be applied to a second region, for example from a water surface point, via a second conduit extending through or along the legs. The second conduit may have a second outlet at or toward the side of each leg.

[0018] The second outlet can be above the first outlet. The second outlet can be spaced apart from the first outlet. The second outlet can be spaced further from the seabed surface than the first outlet when the leg is located in the foundation pile. The second outlet can be rotationally offset from the first outlet.

[0019] The grout may be applied to a first area via a conduit extending from a water surface point. The conduit may be positioned such that an outlet of the conduit is at a first location within the foundation pile at or proximate the seabed. The grout may then be applied to a second area by raising the conduit such that the outlet is at a second location that is spaced farther from the seabed than the first location.

[0020] The conduit may include a rigid tube having a first open end for receiving the grout, a sidewall, and an outlet. The outlet may be located in the sidewall. The rigid body may have, for example, a second end opposite the first end. The second end may be a closed end. The outlet may be located in the sidewall proximate the closed end.

[0021] The conduit is preferably separate from the offshore structure and foundation piles, for example the conduit may be carried on board and deployed from a sea-going vessel, such as a supply ship.

[0022] The method can include applying a grout to a first region (i.e., the first grout) and then preparing a grout to be applied to a second region (i.e., the second grout). That is, the method can include applying the first grout, e.g., to the first region, and then preparing the second grout. The method can include allowing the first grout to harden, e.g., to a predetermined extent, and then preparing the second grout.

[0023] The composition of the grout can be prepared depending on the water temperature on the day of application.

[0024] The composition of the first grout and / or the second grout may be prepared depending on the water temperature on the day of application.

[0025] It is expressly intended that within the scope of this application, the various aspects, embodiments, examples, and alternatives described in the preceding paragraphs, claims, and / or the following description and drawings, in particular their individual features, may be employed individually or in any combination. That is, the features of all of the embodiments and / or any of the embodiments may be combined in any manner and / or combination, so long as such features are not incompatible. For the avoidance of doubt, the words "may", "and / or", "eg", "for example" and any similar words used herein should be interpreted as open-ended, such that any features recited similarly need not be present. Indeed, any combination of optional features is expressly contemplated, so long as it does not depart from the scope of the invention, whether or not those features are expressly claimed. The applicant reserves the right to modify any of the originally filed claims or to submit any new claims accordingly, including the right to amend any of the originally filed claims to depend on any other claim and / or to incorporate any feature of any other claim even if not originally claimed in that manner.

[0026] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0027] [Figure 1] FIG. 2 shows an offshore structure fixed to foundation piles. [Diagram 2] FIG. 2 shows the interface between the legs of the offshore structure and the foundation piles. [Diagram 3] A side view showing the stub-in portion of the leg of the offshore structure. [Figure 4] A schematic cross-sectional view showing the legs of an offshore structure inserted into a foundation pile. [Diagram 5] FIG. 5 is a diagram of the arrangement of FIG. 4 including an apparatus for applying grout. [Figure 6] FIG. 5 is a diagram of the arrangement of FIG. 4 including an alternative apparatus for applying grout. [Figure 7a] FIG. 7 is a schematic diagram showing the device of FIG. 6 in a first position. [Figure 7b] FIG. 7 is a schematic diagram showing the device of FIG. 6 in a second position. [Figure 8] FIG. 8 shows a part of the device of FIGS. 6 and 7. [Figure 9] FIG. 9 is a diagram showing a funnel-shaped guide for guiding the device of FIGS. 6 to 8 when in use. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] Referring now to FIG. 1, an offshore structure 1 is shown supporting a payload (not shown) on the surface of a body of water. In different examples, the payload (not shown) can be a wind turbine or an oil and gas platform. The offshore structure 1 comprises a jacket 2 having three legs 3. In this example, the legs 3 are interconnected by cross members 4. Each leg 3 has a body 3a and a stub-in portion 3b (as shown more clearly in FIG. 3 ). Each of the body 3a and the stub-in portion 3b is a hollow steel tube in this example. In other examples, the body 3a and the stub-in portion 3b of each leg 3 can have different materials and structures. In this example, the offshore structure 1 has three legs 3, but it will be understood that the offshore structure 1 can have any number of legs 3, including four legs 3.

[0029] The offshore structure 1 is anchored to the seabed by fastening to foundation piles 5, which in this example are hollow steel pipes pre-pile driven into the seabed. The stub-in portion 3b of each leg 3 is received within an open end 50 of the respective foundation pile 5. A cementitious material in the form of grout is used to at least substantially fill the remaining area or volume between the stub-in portion 3b and the foundation pile 5 (particularly formed from areas A and B shown in Figures 4 to 6), thereby anchoring the jacket 2 to the foundation pile 5.

[0030] 2, there is shown the interface between the jacket 2 and the foundation pile 5 with the stub-in portion 3b inserted into the foundation pile 5. Between the body 3a and the stub-in portion 3b of each leg is a flange 30a. The flanges 30a extend radially. When the respective stub-in portion 3b is located within the respective foundation pile 5, the flanges 30a abut a rim at the open end 50 of the foundation pile 5. The position of the flanges 30a on the legs 3 defines the amount of insertion of the legs 3, and in particular the stub-in portion 3b, into the foundation pile 5. The flanges 30a are pierced by overflow outlets 35b (shown more clearly in FIG. 4) to allow excess grout to overflow during the grouting operation, as described further below.

[0031] 3, the stub-in portion 3b of the leg 3 is shown. At the end of the stub-in portion 3b distal to the flange 30a is a tapered end 30b. The end 30b may be integral with the tubular portion of the stub-in portion 3b or may be formed by a cap inserted into the end of the stub-in portion 3b. The end 30b comprises a number of circumferentially spaced radially extending fins 31b. The geometry of the end 30b is configured to facilitate positioning of the stub-in portion 3b within the respective foundation pile 5 and thus to make it easier to insert the leg 3 into the foundation pile 5.

[0032] A sidewall 32b extends between the flange 30a and the end 30b. In this example, the stub-in portion 3b has a plurality of shear keys 33b located along the length of the sidewall 32b between the flange 30a and the end 30b. The shear keys 33b are preferably formed from ridges or ridges in the surface of the stub-in portion 3b. The shear keys 33b are configured to resist relative translational movement between the stub-in portion 3b and the foundation pile 5 after the leg 3 is grouted to the foundation pile 5 in order to better secure the leg 3 to the foundation pile 5.

[0033] Referring now to FIG. 4, as discussed above, when the stub-in portion 3b is positioned within the foundation pile 5, the flange 30a acts as a stop to limit the depth to which the stub-in portion 3b extends into the open end of the foundation pile 5.

[0034] In some examples, the underside of the flange 30a has a circumferentially extending seal 34b in the form of an elastomeric O-ring that is configured to seal against the free end 50 of the foundation pile 5. Radially inward of the circumferentially extending seal 34b is the overflow outlet 35b mentioned above.

[0035] 4 shows the dredge line D, which is the elevation of the seabed surface within the foundation pile 5 after the piling operation has been performed. In this example, the dredge line D is below the surrounding seabed surface (not shown), but alternatively, it can be at the same elevation as or above the seabed surface. As shown, the leg 3 is inserted into the foundation pile 5 such that the end 30b is spaced apart from the seabed surface within the foundation pile 5 (i.e., spaced apart from the dredge line D).

[0036] With the stub-in 3b located within the foundation pile 5, area A is shown between the end 30b and the dredge line D within the foundation pile 5. Additionally, annular area B is shown between the side wall 32b and the inner wall 51 of the foundation pile 5. During a grouting process (described below), grout is brought into areas A and B. Once areas A and B are filled, grout overflows from the annular area B through outlet 35b. Seal 34b is configured to prevent grout from leaking from a point or area other than outlet 35b.

[0037] It will be understood that in this example, in the case of a jacket 2 having several legs 3, each leg 3 has a configuration according to FIG.

[0038] To secure the legs 3 to the foundation piles 5, the seabed is preferably dredged prior to installation of the foundation piles 5. One or more foundation piles 5 are then piled to a desired depth into the seabed such that an open end 50 of each pile 5 protrudes above the seabed. The jacket 2 is then lowered towards the seabed and each stub-in portion 3b is positioned within the open end 50 of each foundation pile 5. The jacket 2 is lowered until each flange 30a abuts the respective open end 50, defining areas A and B. Grout is then applied to areas A and B, as described below.

[0039] Referring now to Figure 5, the configuration of Figure 4 is shown with a grout application device installed inside. In this example, a first conduit 6a extends from the top of the jacket to a first outlet 60a at the bottom of the end 30b. A grout pump or material supply (e.g., a hopper or storage tank) can be connected to the first conduit 6a, for example, at a point above the water surface, to supply grout to the first conduit 6a. A second conduit 6b extends from the top of the jacket to a second outlet 60b at the side wall 32b of the stub-in portion 3b. A grout pump or material supply can be connected to the second conduit 6b, for example, at a point above the water surface, to supply grout to the second conduit 6b. Each of the conduits 6a, 6b extends along the inside of the leg 3 between the water surface and the respective outlet 60a, 60b.

[0040] In use, to apply grout to the volume shown between the stub-in portion 3b and the foundation pile 5, the grout composition is prepared above the water surface and conveyed along the first conduit 6a to the first outlet 60a. The grout is conveyed until area A is filled.

[0041] Preferably, a predetermined volume of grout is delivered to region A. The predetermined volume is based on a known diameter of the foundation pile and a defined distance between the seabed surface (i.e., the dredge line) and the stub-in portion 3b in the foundation pile 5. In another example, the first conduit 6a and / or the second conduit 6b may be equipped with a sensor that detects when the grout in region A reaches a certain height, for example along the length of the first conduit 6a and / or the second conduit 6b, corresponding to a desired depth of region A. Alternatively, the filling of region A may be determined by using a pressure sensor or transducer located in either the first conduit 6a or the second conduit 6b or in the volume represented by region A. The filling of region A may be determined acoustically, for example by an acoustic sensor on a remotely operated vehicle (ROV) or on the legs 3.

[0042] Once area A is filled, the pump unit is turned off and the grout filled area A is allowed to harden to a predetermined degree.

[0043] Once the grout filled area A has hardened to a predetermined extent, the grout is conveyed along the second conduit 6b to the second outlet 60b. The grout is conveyed until area B is filled.

[0044] In this example, the filling of area B is identified by the presence of grout at the overflow outlet 35b. However, it will be appreciated that instead of providing an overflow outlet 35b, the filling of area B can be determined acoustically, for example by an acoustic sensor on the remotely operated vehicle (ROV) or on the legs 3. Alternatively, the filling of area B can be determined by using a pressure sensor or transducer located either on the stinger 7 or in the volume represented by areas A and B. In the absence of an overflow outlet 35b, when area B is filled, a pressure rise can be detected if the pump unit P is still operating. In another example, a predetermined volume of grout is delivered into area B based on the known dimensions of the stub-in portion 3b and the foundation pile 5. Such an example can be advantageous to prevent grout from spilling out if the flange 30a is not provided.

[0045] In this example, the grout composition conveyed along the first conduit 6a and the grout composition conveyed along the second conduit 6b are the same.

[0046] In the case of an offshore structure 1 with multiple legs 3 housed within respective foundation piles 5, in this example each leg 3 has the configuration of Figure 5. In such a case, area A of each leg 3 is filled with grout. This is done by connecting each of the first conduits 6a to a grout pump or material supply, either sequentially or simultaneously, and supplying grout via the first conduits 6a to each respective first area A. The grout is left to harden to a predetermined extent before area B is filled.

[0047] Although it has been described that the grout compositions delivered along the first conduit 6a and the second conduit 6b, i.e., filling areas A and B, are the same, this is not necessarily the case. Instead, area A may be filled with a first grout composition and area B may be filled with a second grout composition that is different from the first grout composition.

[0048] 6-8, there is shown another apparatus for applying grout to an offshore structure 1 with its legs 3 inserted into a foundation pile 5. In particular, this apparatus is for filling the areas A and B mentioned above with grout. In this example, a stinger or needle 7 extends from a vessel V (FIGS. 7a, 7b) above the water surface. Flange 130a differs from flange 30a in that, in addition to the overflow outlet 135b, it has a further hole in the form of an inlet 131a for receiving the stinger 7. The stinger 7 extends into the volume shown between the stub-in portion 3b and the foundation pile 5.

[0049] As shown most clearly in Figures 7a and 7b, the stinger 7 comprises a flexible conduit or hose 70 having a first end 70a connected to a grout source, in particular a pump unit P on board the vessel V, and a second end 70b connected to a rigid pipe 71. The rigid pipe 71 is made of steel in this example. The flexible conduit 70 is hoisted by a crane C on board the vessel V, but may additionally or alternatively be on a reel or spool. The flexible conduit 70 may be not only a conduit for the grout but also support the weight of the rigid pipe 71, or alternatively the rigid pipe 71 is suspended on a tether and a separate conduit is provided to feed the grout to the rigid pipe 71. For example the rigid pipe 71 may be suspended on a chain, with the grout being fed to the rigid pipe 71 by a hose.

[0050] 8, the rigid tube 71 has a first open end 710 which connects to the flexible conduit 70 and a second closed end 711 opposite the first end 710. A sidewall 712 of the rigid tube 71 has an outlet 72 for grout, in this example proximal to the closed end 711. The closed end 711 is preferably provided by a welded cap, but may also be crimped closed or plugged.

[0051] Markings or markings 73 are provided along the length of the rigid tube 71 on the exterior surface of the sidewall 712. In this example, the markings or markings 73 indicate the distance from the center of the outlet 72 to distinct points along the length of the rigid tube 71. Such markings 73 indicate the depth to which the outlet 72 has been inserted into the volume between the stub-in portion 3b and the foundation pile 5.

[0052] Alternatively, the indicia 73 may indicate the distance from the closed end 711 to a discrete point along the length of the rigid tube 71 .

[0053] A grouting operation using the apparatus of Figures 6 to 8 is carried out as shown in particular in Figures 6, 7a and 7b. A stinger 7 is connected to a pump unit P and lowered from a vessel V towards the seabed S (Figures 7a and 7b). A rigid pipe 71 is placed via the inlet 131a and lowered into the volume shown between the stub-in portion 3b and the foundation pile 5.

[0054] In a first stage, the stinger 7 is lowered to a first position P1, shown in dashed outline in FIG. 6 and also shown in FIG. 7a. In the first position P1, the closed end 711 is located at or proximate to the dredge line D in the foundation pile 5. To reach this position, the stinger 7 can be lowered until the tension in the tether is reduced. The reduction in tension in the tether indicates that the stinger 7 is attached to the seabed. The stinger 7 can then be optionally raised slightly above the seabed. The pump unit P is then used to convey the grout along the stinger 7 to the outlet 72. The grout is conveyed until the area A is filled. Preferably, a predetermined volume of grout is conveyed into the area A. The predetermined volume is based on a known inner diameter of the foundation pile 5 and a defined distance between the seabed surface (i.e. the dredge line) and the stub-in portion 3b in the foundation pile 5. In another example, the stinger 7 and / or the stub-in portion 3b may be equipped with a sensor that detects when the grout in region A reaches a certain height along the length of the rigid tube 71 corresponding to a desired depth in region A.

[0055] In this example, once area A is filled, the stinger 7 is then raised by crane C and the grout filled area A is left to harden to a predetermined degree, which can be determined based on the water temperature and the known hardening rate of the grout.

[0056] The stinger 7 may be raised to a second position P2, shown in solid outline in Figure 6 and also shown in Figure 7b. The second position P2 is above the first position and above area A. In some instances, as described further below, the stinger 7 is removed from the foundation pile 5 and moved to another foundation pile 5 of the offshore structure 1 to repeat the application of grout to area A.

[0057] After the grout filled area A has hardened to a predetermined extent, the stinger 7 is moved to a second position P2.

[0058] Next, with the stinger 7 in the second position P2, the pump unit P is used to convey grout along the stinger 7 to the outlet 72 to fill region B. The grout is conveyed until region B is filled.

[0059] In this example, the filling of area B is identified by the presence of grout at the overflow outlet 135b. However, it will be appreciated that instead of providing an overflow outlet 135b, the filling of area B can be determined acoustically, for example by an acoustic sensor on the remotely operated vehicle (ROV) or on the legs 3. Alternatively, the filling of area B can be determined by using a pressure sensor or transducer located either on the stinger 7 or in the volume represented by areas A and B. In the absence of an overflow outlet 135b (or if the overflow outlet 135b is restricted), when area B is filled, a pressure rise can be detected if the pump unit P is still operating. In another example, a predetermined volume of grout is delivered into area B based on the known dimensions of the stub-in portion 3b and the foundation pile 5. Such an example can be advantageous to prevent grout from spilling out if no flange 130a is provided.

[0060] 9, there is shown a funnel guide 8 which guides the stinger 7 through an inlet 131a in the flange 130a into the volume between the stub-in portion 3b and the foundation pile 5. The funnel guide 8 has a conical portion 80 which tapers towards the inlet 131a. In this example, a sleeve 81 is connected to the conical portion 80 and which is configured to be inserted into the inlet 131a.

[0061] In an example, the funnel guide 8 may be integrally formed with the flange 30a or 130a.

[0062] In use, the funnel guide 8 is used to provide a larger target area for the stinger 7, and in particular its rigid tube 71. This aids in positioning the stinger 7 through the inlet 131a as it is lowered towards the seabed surface.

[0063] Those skilled in the art will appreciate that numerous variations to the above-described embodiments are envisaged without departing from the scope of the present invention.

[0064] Those skilled in the art will also appreciate that combinations of any number of the features described above and / or illustrated in the accompanying drawings provide distinct advantages over the prior art and thus such combinations are within the scope of the invention as described herein. [Configuration 1] 1. A method of securing an offshore structure to a pre-driven foundation pile, the foundation pile comprising a pipe that is piled into a seabed surface, the offshore structure having a leg that is inserted into the foundation pile, the method comprising applying grout to a first area between an end of the leg and the seabed surface within the foundation pile, allowing the grout to at least partially harden, and then applying grout to a second area, the second area being an annular area between the leg and the foundation pile. [Configuration 2] 2. The method of claim 1, wherein the offshore structure comprises a plurality of foundation piles and the jacket comprises a plurality of corresponding legs, each leg being inserted into an open end of a corresponding foundation pile. [Configuration 3] 3. The method of claim 2, further comprising applying the grout to the first regions of all of the plurality of foundation piles before applying the grout to the second regions of the plurality of foundation piles. [Configuration 4] 4. The method of any one of claims 1 to 3, wherein the grout applied to the first region is allowed to harden to a predetermined extent before applying the grout to the second region. [Configuration 5] 5. The method of any one of claims 1 to 4, further comprising testing the grout applied to the first area to determine whether it has hardened to a predetermined degree prior to applying the grout to the second area. [Configuration 6] 6. The method of any one of claims 1 to 5, wherein the grout is applied to the second area until it floods the second area. [Configuration 7] 7. The method of claim 6, wherein overflow of grout from the second region is detected acoustically and / or visually. [Configuration 8] 8. The method of any one of claims 1 to 7, wherein the grout is applied to the first area via a first conduit extending from a water level point through or along the leg, the first conduit having a first outlet at or towards a bottom of the corresponding leg, and the grout is applied to the second area via a second conduit extending from the water level point through or along the leg, the second conduit having a second outlet at or towards a side of the corresponding leg. [Configuration 9] 8. The method of any one of claims 1 to 7, wherein grout is applied via a conduit extending from a water surface point, the method including applying grout to the first region by positioning the conduit such that an outlet of the conduit is positioned at or proximate to the seabed within the foundation pile, and grout is first applied to the annular region by raising the conduit such that the outlet is positioned at a second location spaced further from the seabed than the first location. [Configuration 10] 10. The method of any one of claims 1-9, wherein the grout applied to the first region comprises a first grout and the grout applied to the second region comprises a second grout. [Configuration 11] 11. The method of embodiment 10, wherein the first grout and the second grout have substantially the same or corresponding compositions. [Configuration 12] 12. The method of any one of claims 10 to 11, wherein the first grout and the second grout have different compositions. [Configuration 13] 11. The method of claim 10, further comprising providing the second grout after applying the first grout to the first area. [Configuration 14] 14. The method according to any one of claims 10 to 13, wherein the composition of the first grout and / or the second grout is prepared according to the water temperature on the day of application.

Claims

1. 1. A method of securing an offshore structure to a pre-driven foundation pile, the foundation pile including a pipe that is driven into a seabed surface, the offshore structure having a leg that is inserted into the foundation pile, the method comprising: applying grout to a first region between an end of the leg and the seabed surface within the foundation pile, allowing the grout to at least partially harden, and then applying grout to a second region, the second region being an annular region between the leg and the foundation pile, the method further comprising determining whether the grout applied to the first region has hardened to a predetermined degree based on water temperature and a known hardening rate of the grout, prior to applying the grout to the second region, wherein the grout is applied to the second region when it is determined that the grout applied to the first region has hardened to the predetermined degree.

2. The method of claim 1, wherein the pre-driven foundation piles comprise a plurality of foundation piles and the offshore structure comprises a plurality of corresponding legs, each leg being inserted into the open end of a corresponding foundation pile.

3. The method of claim 2 , comprising applying the grout to the first regions of all of the plurality of foundation piles before applying the grout to the second regions of the plurality of foundation piles.

4. A method according to any one of claims 1 to 3, wherein the grout applied to the first area is allowed to harden to a predetermined extent before applying the grout to the second area.

5. The method of any one of claims 1 to 4, wherein the grout is applied to the second area until it floods the second area.

6. The method of claim 5 , wherein overflow of grout from the second region is detected acoustically and / or visually.

7. 7. The method of any one of claims 1 to 6, wherein the grout is applied to the first area via a first conduit extending from a water level point through or along the leg, the first conduit having a first outlet at or towards the bottom of the corresponding leg, and the grout is applied to the second area via a second conduit extending from the water level point through or along the leg, the second conduit having a second outlet at or towards the side of the corresponding leg.

8. 7. The method of any one of claims 1 to 6, wherein grout is applied via a conduit extending from a water surface point, the method comprising applying grout to the first area by positioning the conduit at a first location such that an outlet of the conduit is positioned at or proximate to the seabed in the foundation pile, and grout is applied to the annular area by first raising the conduit so that the outlet is positioned at a second location spaced further from the seabed than the first location.

9. The method of any one of claims 1 to 8, wherein the grout applied to the first area comprises a first grout and the grout applied to the second area comprises a second grout.

10. The method of claim 9 , wherein the first grout and the second grout have substantially the same or corresponding compositions.

11. The method of claim 9 , wherein the first grout and the second grout have different compositions.

12. 10. The method of claim 9, comprising preparing the second grout after applying the first grout to the first area.

13. The method according to any one of claims 9 to 12, wherein the composition of the first grout and / or the second grout is prepared depending on the water temperature on the day of application.

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