Foundation for a Wind Turbine Utilizing a Slurry of Low Viscosity Grout

Abstract

A self-leveling grout provides a level surface for the disposition of a wind turbine base. The self-leveling grout is placed within the foundation grout trough as an initial slurry having a viscosity at ambient temperature approximately the same as the viscosity of known grout slurries utilized in turbine foundations. After placement in the grout trough, elevated temperature is applied to the grout slurry, which lowers the viscosity of the slurry such that the slurry becomes self-leveling and the top surface assumes a nearly perfectly level surface. Additional elevated temperature is applied which initiates the curing of the grout to the required compressive strength for supporting the turbine tower.

Description

BACKGROUND OF THE INVENTION

This invention relates to concrete foundations set within excavations or bore holes which are installed to support wind turbines. More particularly, this invention comprises an apparatus and method for configuring, installing, and setting the anchor bolts for a cylindrical foundation for a wind turbine.

U.S. Pat. Nos. 5,586,417 and 5,826,387, both by Henderson, disclose a foundation “which can be poured-on-site monolithically and is of cylindrical construction with many post-tensioned anchor bolts which maintain the poured portion of the foundation under heavy compression, even during periods when the foundation may be subject to high overturning moment.” Henderson's foundation is preferably in the shape of a cylinder, having an outer boundary shell and an inner boundary shell each formed of corrugated metal pipe. Between the outer boundary shell and the inner boundary shell elongated high strength steel bolts extend vertically up through concrete from a peripheral anchor plate, called an inbed plate, located near the bottom of the cylinder. The bolts extend upwardly from the inbed plate to a connecting plate or flange above the ground surface. The bolts extend through hollow tubes to prevent adhesion of the concrete to the bolts and thus allowing the tensioning of the bolts to the necessary pre-load. The foundation typically uses no rebar reinforcing steel. This design uses the mechanical interaction with the earth to prevent over turning instead of the mass of the foundation typically used by other foundations for tower structures. FIG. 1 schematically shows an embodiment of the Henderson foundation.

The “hollow tubes” of the known foundation are typically elongated plastic tubes which encase the bolts substantially through the entire vertical extent of the concrete and allow the bolts to be tensioned after the concrete has hardened and cured, thereby post-tensioning the entire concrete foundation. Alternatively, the elongated bolts can be wrapped in plastic tape, or coated with a suitable lubrication, which will allow the bolts to stretch under tension over the entire operating length of the bolt through the vertical extent of the concrete.

Henderson further discloses the post-stressing of the concrete in great compression by tightening the high strength bolts to provide heavy tension between a heavy top flange and the inbed plate at the bottom of the foundation, thereby placing the entire foundation under high unit compression loading. The bolts are tightened so as to exceed the maximum expected overturning force of the turbine tower on the foundation. Therefore, the entire foundation withstands various loads with the concrete always in compression and the bolts always in static tension.

The tensioning bolts in the Henderson foundation are preferably in side-by-side pairs, the pairs extending radially from the center of the foundation, forming an inner ring of bolts and an outer ring of bolts as shown in FIG. 2. As shown in FIG. 2, the inner ring of bolts define a circle having a slightly shorter diameter than a circle defined by an outer ring of bolts. The bolt pattern is, of course, determined by the bolt pattern on the mounting flange of the turbine tower to be installed on the foundation. A large number of bolts is typically used for this type of foundation. Typically seventy tensioning bolts are used in the inner ring and seventy tensioning bolts in the outer ring for a total of one hundred forty. In Henderson's foundation, the lower ends of the bolts are anchored to the inbed plate at the bottom of the foundation which may be constructed of several circumferentially butted and joined sections.

The following known procedure is typically followed in constructing the cylindrical foundation. A bore hole is drilled or excavated and an outer boundary shell of corrugated metal pipe (“CMP”) is set within the hole. Bolt bundles are lowered into the borehole. The bolt bundles typically comprise about thirty bolts, with each bolt weighing up to two hundred pounds per bolt. Workers are lowered into the CMP lined bore hole. Working from the bottom of the bore hole, the workers lift and/or position each individual bolt so it can be inserted into a template at the surface, which is suspended above the bore hole by a crane having a capacity of approximately 100 tons. Once each bolt is inserted into the template, a nut made up onto the threads extending above the template, such that the weight of each bolt is suspended by the template.

Once all of the bolts have been suspended from the template, the entire assembly is lifted out of the bore hole so the inbed plates may be placed at the bottom end of the bolts. As the assembly is lowered back into the bore hole, bands or rebar wraps are placed around the collective bolts to hold the bolts in position during the pouring of the concrete. FIG. 3 shows such an assembly suspended by a lifting frame which is connected to the template. The entire assembly is then lowered back into the bore hole and an inner boundary shell of CMP is lowered into the bore hole such that the bolts are extending upwardly through an annulus formed by the outer boundary shell and the inner boundary shell. Concrete is poured into this annulus around the upwardly extending bolts, with the template at the top of the bolts used to form a “grout trough” in the upper surface of the concrete. The upwardly facing ends of the bolts extend into the grout trough and, following the hardening of the concrete, the grout trough is filled with a high strength grout upon which the tower flange is placed.

As shown in FIG. 2, flange 14 of the turbine tower 10 is set upon the anchor bolts 16. Because flange 14 must be set nearly perfectly level, shims 5 (as shown in FIG. 5) are placed in the grout trough and the shims and flange leveled through laser leveling techniques. Once the shims are leveled, the high strength grout is poured into the grout trough and the flange 14 set down on the anchor bolts 16 and the grout allowed to set up.

Based upon the discussion above, it is clear that the integrity of this type of foundation is dependent upon the integrity of the anchor bolts and the ability to obtain sufficient preload in the bolts. The failure of a bolt creates a stress riser on the remaining bolts, leading to the potential failure of the entire foundation. The integrity of the steel anchor bolts can be compromised by corrosive attack. As described above, according to the current practice each anchor bolt is enclosed for most of its length within a PVC sleeve. However, because the outside diameter of the PVC sleeve is too large for the sleeve to enter the bolt hole of the flange of the tower structure, the sleeve typically terminates at approximately the top of the concrete foundation, with the bare metal of the anchor bolt extending above the sleeve, where the bolts extend through the flange and have a nut and bolt cap installed on the top side of the flange. As with the holes of the flange of the tower base, the bolt holes in the circular template are sized to accommodate the bolt diameter, but not the diameter of the PVC sleeve, so the tops of the bolt sleeves will generally be flush with the bottom of the grout trough formed by the circular template.

In order to prevent dehydration of the grout—thus adversely impacting the grout strength—it is a common practice to place water within the grout trough prior to the pouring of the grout slurry to keep the grout properly hydrated during the curing process. However, water placed in the trough will gravitate into the ends of the PVC sleeves which are flush with the bottom of the grout trough. In the current installation practice, a foam sleeve is typically placed around a portion of each bare bolt extending above the bottom of the grout trough, with each foam sleeve and held in place with duct tape. The length (or height) of the foam sleeve is sized to extend above the anticipated thickness of the grout layer within the grout trough. In the known practice, the tower flange is set on the grout before the grout sets so that the tower base may be leveled. It is hoped that the foam sleeve will prevent grout from adhering to the body of the bolt, such that when the grout fully cures the bolt may be tensioned and slide through the foam sleeve without damage to the grout. However, in reality the foam sleeve is likely so deformed by the flange of the tower base that the bolts will not slide freely through the sleeves once the grout cures.

If a low viscosity grout slurry is used as disclosed herein with the commonly used bolt sleeves, the flow properties of the slurry will cause it to flow into the annulus created by the PVC sleeve and the anchor bolt. Because of this problem, the use of low viscosity grouts, including epoxy grouts, has not been practical. However, the low viscosity grouts would otherwise be preferred because of the self-leveling which may be achieved with such a material. In particular, the use of a self-leveling grout slurry would eliminate the need for leveling shims and allow the grout to be poured and adequately cure before setting the flange onto the grout, as opposed to the current practice of setting and leveling the tower flange before the grout cures. The current practice requires the service of a high capacity crane for the initial setting of the tower flange and subsequently for the assembly of the complete turbine. However, if the tower flange can be placed at the same time as the other turbine tower components, the crane can be used more efficiently with less rigging up and rigging down time at each turbine tower installation.

Once the tower has been installed and a nut and bolt cap installed on the bolt ends extending above the tower flange, the annulus between the bolt and PVC is sealed, as illustrated in FIGS. 4 and 5. However, during the known installation method, the annulus between the bolt and the PVC sleeve is open thereby providing a pathway for water and other fluids to enter the annulus and be trapped between the PVC sleeve and the metallic bolt, forming a corrosion cell. Because of this opening, steps are usually taken to protect the bolt from corrosive attack and/or to seal the sleeve-bolt annulus during installation. Unfortunately, the currently practiced installation procedure aggravates the situation, because, as described above, the procedure typically includes pouring water in the grout trough to allow the grout to cure. This practice allows to water to accumulate at the top of the PVC sleeve, and potentially migrate into the sleeve-bolt annulus.

The initial attempt at solving the anchor bolt corrosion problem was to paint the anchor bolts along the entire length. However, this solution is labor intensive and does not prevent liquid accumulation around the anchors. In addition, this protection method requires that the anchors be repainted periodically, as well as after re-tensioning the anchor if required in the particular application. The currently practiced method of protecting the anchor bolts is to seal the annulus between the top of the PVC sleeve and the bolt with a sealant, such as a silicon gel. The current practice also includes placing foam rings 32 or other material around the portion of the bolt extending above the PVC sleeve, so as to prevent adhesion of the grout to the bolt and to block the migration of water into the sleeve-bolt annulus. Typically, foam cylinders with longitudinal slits are placed around the bolts, with duct tape wrapped around each cylinder, and the cylinder pushed downwardly into contact with the top of the PVC sleeve. However, with the large number of bolts utilized in these types of foundations, it is time consuming and difficult to seal the top of each PVC sleeve with sealant and to install the foam cylinders or similar devices. If hurried, the annulus may not be adequately sealed to prevent the intrusion of water into the PVC-bolt annulus. Moreover, once the tower base flange is set upon the foam cylinders, the cylinders are greatly deformed. It is non-unlikely that when the anchor bolts are tensioned, the bolt does not slide through the foam cylinder, but that the deformed foam cylinder moves within the grout, potentially damaging the integrity of the grout.

The PVC sleeves, because of the outside diameter, displace, in totality, a significant volume of concrete in the foundation, thereby reducing the overall compressive strength of the foundation.

SUMMARY OF THE INVENTION

The present application is directed toward methods and apparatus which allow the utilization of a slurry of low viscosity, self-leveling grout, which results in a level surface for installing the base flange of a wind turbine tower. The self-leveling grout is placed within the foundation grout trough as an initial slurry having a viscosity at ambient temperature approximately the same as the viscosity of known grout slurries utilized in turbine foundations. After placement in the grout trough, elevated temperature is applied to the grout slurry, which lowers the viscosity of the slurry such that the slurry becomes self-leveling and the top surface assumes a nearly perfectly level surface. Additional elevated temperature is applied which initiates the curing of the grout to the required compressive strength for supporting the turbine tower.

A cover structure may be utilized in combination with the low viscosity grout slurry, where the cover structure may provide the heat transfer required to trigger the changes in the rheological properties of the grout slurry. The cover structure also provides protection from environmental conditions which might disturb the grout as is cures, such as rain, wind, hail, etc., and potentially disrupt the top surface of the grout.

In an embodiment of the disclosed invention, rather than utilizing PVC sleeves which terminate at the bottom of the grout trough, the present invention comprises anchor bolt packages comprising a sheath or sleeve which extends above the grout trough and, if desired, may partially extend inside the base flange of the wind turbine base. The sleeve may be manufactured from polypropylene, polyethylene or other materials having satisfactory mechanical properties, primarily that the material be capable of withstanding sufficient plastic deformation to cause the material to conform to the shape of the threads of the anchor bolts without failing. A tool, such as the swaging tool disclosed in the inventor's U.S. Pat. No. 7,975,519, may be used to crimp the polypropylene sleeve along the threads of the anchor bolt.

The use of the polypropylene sleeve and the swaging of the sleeve onto a portion of the bolt provides a bolt package (i.e. a bolt/sleeve combination) which has an overall diameter less than the overall diameter of the currently utilized bolt-PVC sleeve combination. This reduced diameter allows the bolt and crimped sleeve to extend through the bolt holes of the circular template, and into the bolt holes of the tower flange, which under the known apparatus and method, only a sleeveless bolt would extend. Because the crimped sleeve extends above the top of the grout trough, the encased bolts will not be exposed to water placed within the grout trough, or to a low viscosity grout slurry. In addition, because the top of the crimped sleeve extends above the level of the grout, the crimped sleeve prevents adhesion of the grout to the bolt, thereby allowing the bolt to move relative to the grout.

A method of utilizing a low viscosity grout may comprise the following steps. Once the cement foundation has set, the foundation surface is blown free of any loose material. The components of the epoxy grout, comprising a base component and a catalyst component, are mixed together and pumped into the grout trough. The base component and catalyst are mixed in a sealed mixer which prevents entrainment of air bubbles in the grout slurry. The rheological properties of the low viscosity grout are such that when initially catalyzed and at ambient temperature, the viscosity may be generally in the range of viscosities normally observed for grout slurries as the slurry is pumped into the grout trough. Once the grout is in place, a cover structure is erected over the grout trough, covering all of the pumped in grout slurry. The cover structure will typically be constructed in arc length segments which are joined together to form a circular structure. The cover structure has a top surface and sides which, when joined together, cover the top of the grout trough and enclose it on the outward side of the grout trough and the inward side of the grout trough. The cover structure comprises heat generating means, such as resistance heat elements, heat lamps or burners. Utilizing the heat generating means, the temperature under the tent structure is raised to 120 degrees Fahrenheit and held at this temperature for approximately two hours. At this elevated temperature, the grout remains ungelled and the viscosity of the grout slurry decreases to approximately 100 centipoise. At this viscosity, the grout becomes self-leveling such that the top surface of the grout will be sufficiently close to being perfectly level. In addition, with a grout of this low viscosity for this period of time, the grout will be able to penetrate the concrete foundation. After two hours, the temperature is brought up to 180 degrees Fahrenheit and held at the elevated temperature for two hours, during which time the epoxy grout gels and hardens. The heat is thereafter turned off and the grout allowed to cool for twenty-four hours, with the protective cover, or other protective cover, maintained over the foundation for protection. An acceptable grout formulation is an epoxy grout manufactured by the Polyset Company of Mechanicville, N.Y.

The advantage of the above procedure is that all of the turbine components can be installed with a single crane set, thereby speeding up the erection of the turbine while reducing the cost of equipment and manpower. In addition, utilization of the disclosed procedure allows the foundation bolts to be shortened by approximately eight inches each, which saves approximately $400 per installation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the foundation of Henderson following installation of the anchor bolts.

FIG. 2 shows a completed foundation, showing an inner ring of anchor bolts and an outer ring of anchor bolts with a tower base attached.

FIG. 3 shows the prior art method of placing the anchor bolts, where all of the anchor bolts are lowered into the borehole with the prior art grout template.

FIG. 4 shows front view of a portion of a tower foundation, with the tower base flange begin lowered onto the anchor bolts.

FIG. 5 shows a portion of a grout trough, prior to the lowering of the tower base, showing the existing method of protecting the bolt-sleeve annulus with foam sleeves and utilizing shims for leveling the tower flange.

FIG. 6 shows a cross section of a portion of the base flange, grout, anchor bolt and PVC sleeve of a prior art foundation.

FIG. 7 shows a cross section of a portion of the base flange, grout, anchor bolt and sleeve according to the present invention.

FIG. 8 shows a portion of an embodiment of an anchor bolt according to present invention showing how the sleeve is swaged around some of the threads of the anchor bolt.

FIG. 9 shows an embodiment of a cover structure which may be used to apply heat to the grout mixture and protective the uncured grout.

FIG. 10 shows an embodiment of a cover structure utilizing a control unit for applying heat.

FIG. 11 shows a section of the cover structure shown in FIGS. 9 and 10, showing a heating element which may be utilized.

FIG. 12A shows a sectioned side view of the cover structure shown in FIGS. 9 and 10.

FIG. 12B shows a sectioned front view of the cover structure shown in FIGS. 9 and 10.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Prior Art Bolt Protection Devices

Referring specifically to the figures, FIG. 1 depicts an embodiment of a known foundation 100 utilized for installation of a relatively tall vertical structure, such as a wind turbine. It is to be appreciated that while the disclosed method and apparatus may be utilized to obtain a foundation 100 such as that depicted in FIG. 1, the procedure for obtaining the foundation is entirely different from the known methods. Foundation 100 comprises a bore hole 120, an outer boundary shell 140 and an inner boundary shell 160, each typically fashioned of corrugated metal pipe (“CMP”), set within the bore hole hole. An inner ring 180 of bolts 16 and an outer ring 200 of bolts 16 are disposed within the annulus formed between the outer boundary shell 140 and the inner boundary shell 160, with the bolts 16 anchored at the lower end of the bore hole 120 to an inbed plate 220. The annulus between the outer boundary shell 140 and the inner boundary shell 160 is filled with concrete 240 and the portion of the bore hole 120 inside the inner boundary shell 160 typically filled with loosely compacted soil 260.

FIG. 2 generally depicts the base 10 of a wind turbine set upon a foundation 12. Base 10 comprises a flange 14, by which the base is attached to foundation 12 with anchor bolts 16. As shown in FIG. 2, the anchor bolts 16 may be placed in side-by-side pairs, the pairs extending radially from the center of the foundation 12 forming an inner ring of bolts and an outer ring of bolts. The bolt pattern is, of course, determined by the bolt pattern on the mounting flange 14. Each anchor bolt 16 has a corresponding nut 18 which is used to secure the base 10, and to apply tension to the bolt. The exposed portion of each bolt 16 is usually protected with a bolt cap 19.

FIG. 3 depicts a bolt assembly 20 comprising a plurality of anchor bolts 16 being lifted in preparation for being placed within a relatively deep excavation prepared for construction of the foundation 12. The anchor bolts 16 typically used for wind turbines are approximately thirty feet in length, and usually have outside diameters of 1¼ inch or 1⅜ inch. Each anchor bolt 16 is partially enclosed within a “hollow tube” or sleeve 22. The sleeve is typically an elongated plastic tube fabricated from polyvinyl chloride (“PVC”) which encases the bolt 16 substantially through the entire vertical extent of the concrete and allows the bolt to be tensioned after the concrete has hardened and cured, thereby post-tensioning the entire concrete foundation. The bolts 16 comprising bolt assembly 20 are secured at the end by circular template 23, which is attached to a lifting assembly 24 and lifted by crane 26.

FIG. 5 shows a close view of a portion of the grout trough 28 before grout has been poured or base flange 14 has been placed. Grout trough 28 is formed as follows: when the concrete is poured, circular template 23, which remains attached to lifting assembly 24 and held in place by crane 26, holds the bolt assembly 20 in place. Concrete is poured up around circular template 23, thereby forming an inner ring groove in the top of the foundation 12 known as the grout trough 28. Before grout 30 is placed in grout trough 28, a sealing member 32 comprising foam, plastic or other material, is placed around each bolt 16. Sealing member 32 is typically cylindrical in shape, having a circular opening and longitudinal slit cut through from the outside edge to the circular opening so the sealing member may be placed around each bolt 16. The sealing member 32 often has duct tape wrapped around it to secure it to the bolt 16. Also shown in FIG. 5 is a leveling block 5 which is used, in combination with a number of other leveling blocks contained within the grout trough, to properly level the base flange 14. It is to be appreciated that the placement of leveling block 5 immediately adjacent to sealing members 32, which is not an uncommon occurrence in the prior art installations, inhibits the uniform deformation of the sealing members as the base flange 14 is lowered into the grout trough 28, resulting in the non-uniform deformation discussed below.

FIG. 4 depicts a portion of a prior art foundation 12 after the grout has been poured and cured, but before flange 14 has been set upon the foundation and nuts 18 made up onto bolts 16. As shown in FIG. 5, flange 14 will be set on top of the grout 30 contained within grout trough 28.

FIG. 6 shows a cross section of a portion of the base flange 14, grout layer 30, and sleeve 22 of a prior art anchor bolt installation for a wind turbine, where sleeve 22 contains bolt 16. As shown in FIG. 6, the top of sleeve 22 is generally flush with the bottom 34 of grout trough 28. It is to be appreciated that before grout 30 is placed within grout trough 28, the top of sleeve 22 is exposed to whatever liquids may enter the grout trough, such as water which may be placed in the grout trough to provide for hydration of the grout. An annulus 36 is formed between bolt 16 and sleeve 22, which provides a potential path for water or other liquids, such as low viscosity grout, to travel along the length of bolt 16.

As can be seen in FIG. 6, sealing member 32 is substantially deformed once engaged by base flange 14. It is to be appreciated that FIG. 4 shows an idealized view of the deformed sealing member 32, in which the deformation has been uniform. In actuality, it is expected that the deformation will not be uniform because, for example, of obstructions which may inhibit uniform deformation such as the leveling block 5 shown in FIG. 5. It is also to be appreciated that the deformed sealing member 32 displaces more volume than the non-deformed sealing member. Because each bolt requires the sealing member, a typical installation may have ninety-six of the deformed sealing members 32 in the grout trough 28, thereby reducing the overall volume of grout which may be placed, resulting in a final grout pack with less strength than one having less grout displacement. It is also to be appreciated that once the grout 30 sufficiently cures, tension will be applied to each anchor bolt 16 by the tightening of a nut at the top of base flange 14, causing the bolt to move relative to the grout. Ideally, sealing member 32 would remain stationary, allowing bolt 16 to slide through the sealing member 32. However, deformation of sealing member 32 reduces the ease with which anchor bolt 16 will slide through the sealing member, potentially causing sealing member 32 to also move, potentially damaging the surrounding grout 30.

EMBODIMENTS OF THE PRESENT INVENTION

FIG. 7 shows a cross section of a portion of the base flange 14, grout 30′, and sleeve 38 which results by application of the prevent invention. In contrast to the installation shown in FIG. 6, it can be seen in FIG. 7 that the crimped sleeve 38 does not terminate at the bottom 34 of the grout trough 28 as with the prior art structure, but rather extends upwardly through and past the space in which low viscosity grout 30′ will be placed. The crimped sleeve 38 will partially penetrate the bolt hole 13 of base flange 14 once the base flange is placed over the upwardly extending bolts 16′ as shown in FIG. 7. This feature prevents the top of crimped sleeve 38 from being exposed to the liquids which may be placed within grout trough 28. The use of crimped sleeve 38 as the protective sleeve for bolt 16′ is a substantial departure from the present use of PVC sleeve 22, and allows the use of low viscosity grout 30′ according to the invention described herein. It is to be appreciated that the term “low viscosity grout” is utilized to describe the flow characteristics of the grout slurry during a portion of the construction phase of the foundation. Once the “low viscosity grout” cures, it will have comparable compressive strength to the conventional cured grout and suitable for the service required for a wind turbine foundation.

The critical distinction between the crimped sleeve 38 shown in FIG. 7 from the sleeve 22 shown in FIG. 6 is that the wall thickness of the crimped sleeve is substantially reduced, and the tolerance between the internal diameter of the crimped sleeve and the outer diameter of the bolt threads is substantially reduced, resulting in an external diameter of the crimped sleeve which is smaller than possible with the thicker-walled PVC sleeves. This reduced diameter allows the crimped sleeves 38 to extend into the bolt holes 13 of the base flange 14. For example, a crimped sleeve comprising polypropylene sleeves has a closer tolerance than the available PVC, such that the crimped sleeves may have a clearance of 20 thousands of an inch between the internal diameter of the crimped sleeve and the outer diameter of the anchor bolt threads.

As shown in FIG. 7, this smaller outside diameter of the crimped sleeve 38 allows a portion of the sleeve to be disposed within the holes 13 in the base flange 14. In contrast, the known installations utilize PVC sleeves 22 which terminate at the bottom 34 of the grout trough 28 as shown in FIG. 5, rather than extending into the base flange 14 of the wind turbine because the external diameters of commonly available PVC sleeves 22 are too large to be inserted within the holes of the flange.

As shown in FIG. 7, and in greater detail in FIG. 8, the top of the crimped sleeve 38 is “swaged” such that a portion of the sleeve conforms to the threads of the anchor bolt 16′. The swaging serves several purposes. First, the swaging retains the crimped sleeve 38 on the anchor bolt 16′ such that nuts are not required to retain the sleeve on the anchor bolt during transportation. This characteristic allows the anchor bolts 16′ to be shipped without nuts, which reduces manpower required for placing the nuts on the bolts for transportation and removing of the bolts upon arrival.

The swaging further inhibits the flow of liquids into the annulus between the crimped sleeve 38 and the anchor bolt 16′, although it is to be appreciated that the exposure of the sleeve end to liquid is reduced or eliminated, because of the capability of placing the top of the crimped sleeve 38 above the grout trough 28 and partially within the base flange 14 once the tower base is installed. It has been found that swaging approximately two inches of the top of the crimped sleeve 38 forms a sufficient length of “crimps” 17 (i.e., portions of the sleeve 38 which conform to the shape of individual threads 21) to form an interference fit which adequately inhibits liquid penetration into the sleeve-bolt annulus.

It has been found that sleeves 38 comprising polypropylene, or similar materials, have the desired mechanical properties for swaging the sleeve material such that it conforms to the shape of the threads. The mechanical properties of the polypropylene are such that the material has a “memory” and retains the crimps 17 once the swaging operation has been completed. U.S. Pat. No. 7,975,519 discloses a swaging tool which may be utilized to swage the polypropylene sleeve 38. It is also to be appreciated that when the anchor bolts 16′ are tensioned by the tightening of the nuts 18, the mechanical properties of the sleeve material are such that upon tensioning of the anchor bolt 16′, the material will plastically deform and the crimps 17 will relax and allow relative movement of the anchor bolt with little resistance such that the anchor bolts 16′ may be properly preloaded.

FIGS. 9 through 12 show a cover structure 50 which may be utilized to apply heat to the slurry of the low viscosity grout 30′. FIGS. 9 through 12 show a portion of the foundation after the anchor bolts 16′ have already been set within cement 240 and a slurry of the low viscosity grout 30′ is introduced into the grout trough 28. For simplicity, polypropylene sleeves 38 are not shown in these figures, but it should be understood that the anchor bolts 16′ are contained within the polypropylene sleeves as described above.

The cover structure may comprise a plurality of individual sections 52. The cover structure 50 comprises a plurality of apertures 54 which are sized to fit over the upwardly facing ends of anchor bolts 16′ The cover structure 50 may further comprise a fan 56 which evenly disperses heat throughout the cover structure. FIG. 10 shows a cover structure 50 placed over the grout trough 28 after the slurry of low viscosity grout 30′ has been introduced into the trough.

FIG. 11 shows a bottom view of an individual section 52 of the cover structure 50, with cover plate 62 removed. The individual sections 52 may comprise heater elements 58. Heater elements 58 may be resistance-type heating elements which receive current from a controller 60. Controller 60 may be controlled with a programmable controller to provide current at particular magnitudes for pre-selected times to provide a desired temperature sequence for controlling the rheological properties of the low viscosity grout 30′. The cover structure may further comprise a thermostat (not shown) so that the controller 60 may make temperature corrections to adjust the temperature within the cover structure 50 as necessary to achieve the desired rheological properties.

A method of utilizing a low viscosity grout may comprise the following steps. Once the cement foundation has set, with a grout trough 28 formed in the top surface of the concrete, the foundation surface is blown free of any loose material. The components of the low viscosity grout 30′, comprising an epoxy base component and a catalyst component, are mixed together in a slurry and pumped into the grout trough. The epoxy base component and catalyst are mixed in a sealed mixer which prevents entrainment of air bubbles in the grout slurry. The rheological properties of the low viscosity grout are such that when initially catalyzed and at ambient temperature, the viscosity may be generally in the range of viscosities normally observed for grout slurries as the slurry is pumped into the grout trough.

Once the low viscosity grout 30′ is in place, a cover structure 50 is erected over the grout trough 28, covering all of the pumped in grout. The cover structure 50 will typically been constructed in arc length sections 52 which are joined together to form a continuous structure, such the circular structure shown in the figures. The cover structure 50 has a top surface and sides which, when joined together, cover the top of the grout trough 28 and enclose it on the outward side of the grout trough and the inward side of the grout trough. The cover structure comprises heat generating means, such as resistive heat elements 58, heat lamps or burners.

With one embodiment of low viscosity grout 30′, the heat generating means is utilized to raise the temperature under the cover structure to approximately 120 degrees Fahrenheit. This temperature is held approximately constant for approximately two hours. At this elevated temperature, the slurry of low viscosity grout 30′ remains ungelled and the viscosity of the grout slurry decreases to approximately 100 centipoise. At this viscosity, the low viscosity grout slurry 30′ becomes self-leveling such that the top surface of the grout slurry will be sufficiently close to being perfectly level to provide a suitable landing surface for the tower flange 14. After about two hours, the temperature is brought up to approximately 180 degrees Fahrenheit and held at the elevated temperature for two hours, during which time the grout gels and hardens. The heat is thereafter turned off and the grout allowed to cool for twenty-four hours, with the cover structure 50 remaining in place over the foundation for protection.

Other grout formulations might be utilized so long as the grout possesses the rheological properties described above. In other words: (1) an initial slurry viscosity at ambient temperature which is approximately the same as the viscosity of known grout slurries utilized in turbine foundations; (2) a lower viscosity of triggered by application of an initial elevated temperature or a chemical catalyst at which viscosity the grout slurry is self-leveling, the top surface assuming a nearly perfectly level position; and (3) a temperature “trigger” or catalyst which initiates the curing of the grout to the required compressive strength for supporting the turbine tower.

When it comes time for erection of the tower base 10, the cover structure 50 is removed from the foundation. Foundation nuts 18 are made up on both the inside ring 180 of anchor bolts 16′ and outside ring 200 of anchor bolts, and equipment for placing the anchor bolts at the desired tension is put into position. The tower base 10 is positioned on the anchor bolts 16′ with several nuts 18 installed to prevent bounce-off. At this point, a half-inch bead of fast setting epoxy may be placed on the outside peripheral edge of the grout trough, while simultaneously a half-inch bead of fast setting epoxy is placed on the inside peripheral edge of the grout trough, to form an outer ring and inner ring of bedding epoxy. This bedding epoxy is a very fast set and cure catalyzed epoxy with a five minute open time and 5,000 plus psi compressive strength in one hour. While not an essential element of the present invention, the bedding epoxy does allow the correction of any deviation in the tower flange 14 to insure 100 percent tangency to the cured grout, because tower base flanges are held to less than 0.020 deviation in the flange. The tower base 10 is set down on the uncured bedding epoxy and nuts 18 are installed and run down on the anchor bolts 16′. After the midsection of the tower is installed, the bedding epoxy is cured to at least the compressive strength of the foundation concrete. The anchor bolts 16′ are thereafter tensioned to the desired amount before the installation of the upper tower section.

While the above is a description of various embodiments of the present invention, further modifications may be employed without departing from the spirit and scope of the present invention. Thus the scope of the invention should not be limited according to these factors, but according to the following appended claims.

Claims

1. A method for using low-viscosity grout in the installation of a wind turbine foundation, the method comprising the steps of: providing a plurality of anchor bolts within a generally vertical excavation;cementing the anchor bolts within the excavation wherein a top surface of the cement comprises a grout trough;introducing a slurry of low-viscosity grout into the grout trough, the slurry of low-viscosity grout comprising the rheological properties of having a first viscosity at ambient temperature and a second viscosity at a first elevated temperature, wherein the first viscosity is higher than the second viscosity, and the grout self-levels to a level surface at the first elevated temperature;allowing the low-viscosity grout to cure to an acceptable compressive strength; andsecuring a base flange to the anchor bolts.

2. The method according to claim 1 wherein each of said anchor bolts is disposed within a sleeve extending substantially along the length of the anchor bolt, the method further comprising the step of obstructing an opening between an interior wall of the sleeve and a surface of the anchor bolt such that the low-viscosity grout cannot enter into a space between the interior wall of the sleeve and the surface of the anchor bolt.

3. The method according to claim 2 wherein the opening between an interior wall of the sleeve and a surface of the anchor bolt is obstructed by providing a swaged upper end of said sleeve conforming substantially to a surface of said anchor bolt.

4. The method according to claim 1 wherein the slurry of low viscosity grout comprises an epoxy, and further comprising the steps of mixing a base component of said grout and a catalyst component of said grout prior to introducing the slurry of low viscosity grout into the trough.

5. The method according to claim 1 further comprising the step of heating the slurry of the low viscosity grout further, such that the slurry hardens to a grout having an acceptable compressive strength to support the weight of the base flange in a level position.

6. The method according to claim 5 further comprising the step of allowing the grout to cool prior to securing the base flange.

7. The method according to claim 1 wherein heat is applied to the slurry of low-viscosity grout by a cover structure comprising heating elements.

8. The method of claim 7 wherein the cover structure comprises means for evenly distributing heat about the slurry of low viscosity grout.

9. The method of claim 7 wherein the cover structure comprises a plurality of arc length sections.

10. A foundation for supporting a wind turbine comprising: a plurality of anchor bolts disposed within a vertical excavation;a cement disposed within the vertical excavation such that a substantial portion of a length of each of said plurality of anchor bolts is embedded within the cement, the cement having an upper surface defining a trough; anda grout disposed within said trough, the grout initially introduced into the trough as a slurry having the rheological properties of having a first viscosity at ambient temperature and a second viscosity at a first elevated temperature, wherein the first viscosity is higher than the second viscosity, and the grout slurry is self-leveling to a level surface at the first elevated temperature.

11. The foundation according to claim 10 further comprising a sleeve extending substantially along the length of an anchor bolt, the sleeve preventing contact between the anchor bolt and the cement, the sleeve comprising a swaged upper end such that the upper end of the sleeve conforms substantially to a surface of the anchor bolt.

12. The foundation according to claim 10 wherein the trough is an annular trough.

13. A method of constructing a foundation for a wind turbine tower, comprising the following steps: providing a plurality of anchor bolt packages within a generally vertical excavation, wherein each anchor bolt package comprises an anchor bolt and a polypropylene sheath extending along a substantial portion of the exterior of the anchor bolt;cementing the anchor bolts within the excavation wherein a top surface of the cement comprises a grout trough with upwardly extending ends of the anchor bolt packages extending above the grout trough;introducing a low-viscosity grout slurry into the grout trough, the low-viscosity grout slurry comprising the rheological properties of having a first viscosity at ambient temperature and a second viscosity at a first elevated temperature, wherein the first viscosity is higher than the second viscosity, and the grout is self-leveling to a level surface at the first elevated temperature;allowing the low-viscosity grout slurry to cure to an acceptable compressive strength, the grout slurry curing to a hardened grout having a perfectly level top surface;lowering a base flange onto the level top surface of the hardended grout; andsecuring a base flange to the upwardly extending ends of the anchor bolt packages.

14. The method according to claim 13 wherein heat is applied to the slurry of low-viscosity grout by a cover structure comprising heating elements.

15. The method of claim 14 wherein the cover structure comprises means for evenly distributing heat about the slurry of low viscosity grout.

16. The method of claim 14 wherein the cover structure comprises a plurality of arc length sections.

17. The method of claim 14 wherein the cover structure comprises control means for adjusting the temperature within the cover structure.