REINFORCEMENT STRUCTURES FOR TENSIONLESS CONCRETE PIER FOUNDATIONS AND METHODS OF CONSTRUCTING THE SAME

Abstract

A reinforced tensionless concrete pier foundation for supporting a tower and a method of constructing the same is provided, the foundation having an outer CMP and an inner CMP with an annular space therebetween in which a plurality of sleeved tower anchor bolts are embedded, and the pier foundation including at least one reinforcement structure that at least partly encircles the outer CMP to provide one or more of increased lateral stiffness, increased shear resistance and overturning (upset) moment capacity, reduced bending, displacement, and deflection of the top of the pier, and improved conditioning, containment, skin friction and lateral bearing capacity of the surrounding soil and/or rock substrate that supports the tensionless pier.

Claims

1-11. (canceled)

12. A tensionless concrete foundation for supporting a tower comprising a concrete pier in an excavation, said concrete pier including an outer pier CMP and an inner pier CMP having a smaller diameter than the outer pier CMP to define an annular space between the inner and outer pier CMPs when the CMPs are placed within the excavation, a plurality of sleeved tower anchor bolts embedded in said annular space and secured at their lower ends to an embedment ring adjacent a bottom of the concrete pier, the anchor bolts extending upwardly beyond an upper surface of the foundation, said upper surface including a tower base flange support surface configured to support a tower having a tower base flange that is secured against the support surface by the tower anchor bolts which are post-tensioned to keep the foundation under compression, and a reinforcement structure at least partly encircling the outer pier CMP, said reinforcement structure providing increased lateral stiffness, overturning resistance and lateral bearing capacity to the concrete pier, wherein the reinforcement structure is a plurality of buttress additions embodied as individual concrete blocks or reinforcements spaced around the outer perimeter of the pier foundation, said buttress additions increasing the overall load capacity and stiffness of the pier foundation.

13. The tensionless concrete pier foundation as set forth in claim 12, wherein the buttress additions are each approximately 4 ft wide, 5 ft long and 10 ft deep.

14. A tensionless concrete foundation for supporting a tower comprising a concrete pier in an excavation, said concrete pier including an outer pier CMP and an inner pier CMP having a smaller diameter than the outer pier CMP to define an annular space between the inner and outer pier CMPs when the CMPs are placed within the excavation, a plurality of sleeved tower anchor bolts embedded in said annular space and secured at their lower ends to an embedment ring adjacent a bottom of the concrete pier, the anchor bolts extending upwardly beyond an upper surface of the foundation, said upper surface including a tower base flange support surface configured to support a tower having a tower base flange that is secured against the support surface by the tower anchor bolts which are post-tensioned to keep the foundation under compression, and a reinforcement structure at least partly encircling the outer pier CMP, said reinforcement structure providing increased lateral stiffness, overturning resistance and lateral bearing capacity to the concrete pier, wherein the reinforcement structure includes pressure grouting around an outer perimeter of the foundation to provide soil stabilization and to expand the diameter of the cementitious materials horizontally supporting the pier.

15. A method of pressure grouting for soil stabilization around an existing tensionless concrete pier foundation to increase the lateral bearing capacity of the surrounding soil and increase the skin friction around the perimeter of the pier foundation, the method comprising: driving a grout emitting pipe to the desired soil depth adjacent the base of the foundation; and pressure grouting to several hundred psi at 5 ft intervals as the grouting pipe is lifted upwardly.

16-17. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] FIG. 1 shows a tensionless concrete pier foundation suitable for reinforcement with one or more reinforcement structures and methods according to the present invention.

[0041] FIG. 1A is a top view of the foundation shown in FIG. 1.

[0042] FIG. 2 is a cross-sectional side view of a tensionless concrete pier foundation reinforced with a post-tensioned collar in accordance with a first embodiment of the present invention.

[0043] FIG. 3 is a partial view of the components of a tensionless concrete pier foundation reinforced with a post-tensioned collar like that of the first embodiment shown in FIG. 2, and including a deep concrete floor addition in accordance with the present invention.

[0044] FIG. 4 is a cross-sectional side view of a tensionless concrete pier foundation reinforced with an extended base flange support (EBFS) repowering addition for supporting a larger tower in accordance with a second embodiment of the present invention.

[0045] FIG. 5 is a cross-sectional side view of a tensionless concrete pier foundation reinforced with a replacement base flange support (RBFS) repowering addition, also for supporting a larger tower in accordance with the second embodiment of the present invention.

[0046] FIG. 6 is a cross-sectional side view of a tensionless concrete pier foundation reinforced with a soil condition improvement collar in accordance with a third embodiment of the present invention.

[0047] FIG. 7 is a cross-sectional side view of a tensionless concrete pier foundation reinforced with buttress additions in accordance with a fourth embodiment of the present invention.

[0048] FIG. 7A is a top view of the tensionless concrete pier foundation shown in FIG. 7.

[0049] FIG. 8 is a cross-sectional side view of a tensionless concrete pier foundation reinforced with pressure grouted soil stabilization in accordance with a fifth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0050] It is to be understood that the embodiments described herein are disclosed by way of illustration only. It is not intended that the invention be limited in its scope to the details of construction and arrangement of components set forth in the following description or illustrated in the drawings. Also, in describing the preferred embodiments, specific terminology will be resorted to for the sake of clarity. It is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar purpose.

[0051] A tensionless concrete pier foundation like that disclosed in the '417 patent is shown in FIGS. 1 and 1A. The concrete pier foundation, generally designated by reference numeral 10, includes an inner corrugated metal pipe (CMP) 12 (the “inner pier CMP”), an outer CMP 14 (the “outer pier CMP”) and a plurality of tower anchor bolts 20, 21 fitted within sleeves 30. The tower anchor bolts 20, 21 are secured at their lower ends to an anchor or embedment ring 22 and are nutted at their upper ends by nuts 18 against a tower base connection flange 301 upon which a tower 32 is supported. The center area 17 surrounded by the inner CMP 12 may be backfilled with soil or other material with the upper surface having a concrete floor 19. A top view of the foundation (without the tower) is provided in FIG. 1A.

[0052] Broadly, and as claimed in the '417 patent, the tensionless pier foundation 10 is an upright cylindrical structure of cementitious material having upper and lower ends, the lower end being embedded within an excavation and the upper end for supporting a tower. At least one set of tower anchor bolts, and preferably two sets of tower anchor bolts 20, 21, are disposed in the upright structure and spaced about a central axis thereof. The lower ends of the bolts are secured to the embedment ring 22 adjacent the lower end of the foundation, and the upper ends project upwardly from the upper end of the foundation. The bolts are shielded against bonding with the cementitious material by sleeves 30. The tower base flange 301 is fitted tightly upon the upper surface of the upright structure. The tower base flange has openings formed therethrough through which the threaded upper ends of the tower anchor bolts 20, 21 are slidingly received. A plurality of nuts 18 are threaded onto the bolt upper ends and tightened downwardly upon the tower base flange sufficiently to place the bolts under heavy tension. As a result, the entire upright cylindrical structure is placed under heavy post-compression. Reference is made to the '417 and '947 patents for a more detailed disclosure of the structure and construction of the basic pier foundation 10 shown in FIGS. 1 and 1A.

[0053] As shown in FIG. 2, the present invention is directed to a reinforced tensionless concrete pier foundation generally designated by reference numeral 100. Like the pier foundation 10 shown in FIG. 1, the reinforced tensionless concrete pier foundation 100 includes an inner pier CMP 12, an outer pier CMP 14, and a plurality of elongated tower anchor bolts 20, 21 embedded within sleeves 30 within the annular area between the inner and outer pier CMPs 12, 14.

[0054] According to the first embodiment of the reinforced tensionless concrete pier foundation 100 as shown in FIG. 2, the pier foundation is reinforced with a structural post-tensioned collar generally designated by reference numeral 110. The collar 110 can be added during original construction or as a retrofit to an existing pier, and increases the stiffness and load-bearing capacity of the foundation.

[0055] The outer perimeter of the post-tensioned collar 110 is defined by an outer collar CMP 112 that surrounds the outer pier CMP 14 to create an annular space generally designated by reference numeral 114 between the outer pier CMP 14 and the outer collar CMP 112. The annular space 114 is filled with concrete, preferably 6000 psi concrete. As used herein, “concrete” is intended to refer to any combination of aggregate, including various aggregate sizes, water and a binding cementitious material such as Portland cement and the like, which may or may not include optional strength and/or consistency additives, and which hardens upon cure as is known in the concrete and masonry fields.

[0056] The collar 110 preferably includes shear steel embedded within the concrete, such as an inner collar CMP 116, which is placed between the outer collar CMP 112 and the outer pier CMP 14 before the concrete is poured. Because the inner collar CMP 116 can be set in one piece, as contrasted with the placing and tying of individual shear steel rebars as was done according to previously known construction methods, the inner collar CMP 116 not only increases the shear resistance in the collar but also expedites collar construction.

[0057] The collar 110 also preferably includes sleeved radially-extending horizontal tensioning bolts 118 that connect the collar 110 to the pier 10 and, when post tensioned after concrete pour and set, provide tension steel and lateral stiffness for minimizing bending of the collar and enable the collar to share the overturning (upset) loads otherwise borne by the concrete pier alone.

[0058] The structural post-tensioned collar 110 can also support soil and rock anchor additions 140 that extend vertically through the collar and into the underlying soil and/or rock substrate 142 to increase the overturning resistance, load-bearing capacity, and lateral stiffness of the tensionless pier foundation. The soil and rock anchor additions 140 are typically bolts which are secured against an upper surface 146 of the concrete collar with nuts 144.

[0059] To provide additional stiffness to the pier foundation according to the first embodiment, the inner pier CMP 12 is filled with concrete from the top to the depth of the collar, preferably on the order of about 5 ft deep, to form a deep concrete floor addition 150 as shown in FIG. 3. The deep concrete floor addition 150 in the center area of the pier provides structural bending resistance and prevents distortion of the top of the tensionless pier 10 while also providing the floor for the foundation.

[0060] According to a second embodiment of the present invention, the reinforcement structure for the tensionless concrete pier foundation 10 includes a repowering addition generally designated by reference numeral 210A in FIG. 4 and by reference numeral 210B in FIG. 5, and referred to generically herein, when appropriate, as repowering addition 210. The repowering addition 210, when added to an existing tensionless concrete pier foundation 10, enables the existing pier foundation to support a larger tower than that for which the foundation was originally constructed.

[0061] The repowering addition shown in FIG. 4 is an extended base flange support (EBFS) repowering addition 210A and is suitable for modifying an existing tensionless concrete pier foundation 10 to support a somewhat larger tower while still utilizing the existing tower anchor bolts 20, 21. The EBFS repowering addition 210A includes a repowering addition CMP 216 that surrounds the outer CMP 14 of the pier 10 to define an annular space 218. The annular space 218 is approximately 2 ft wide and 6 ft deep, and is filled with concrete to form a repowering collar generally designated by reference numeral 220.

[0062] The EBFS repowering addition 210A further includes lateral reinforcing bolts 228, a tower base insert 230, and an auxiliary ring of tower anchor bolts 121. The lateral reinforcing bolts 228 extend across the annular space 218 and couple the EBFS repowering addition CMP 216 to the inner and outer pier CMPs 12, 14. The tower base insert 230 has openings that receive both the existing tower anchor bolts 20, 21 and the auxiliary tower anchor bolts 121 and acts to provide a wider, or extended, support surface on the upper surface of the repowering collar to accommodate the tower base flange 232 of a larger tower 233. The auxiliary tower anchor bolts 121 extend vertically through the concrete of the repowering addition collar 210A, generally parallel with the outer pier CMP and the repowering addition CMP, and are coupled to the tower base flange 232 through the insert 230.

[0063] To support much larger towers, the repowering addition can be configured as a replacement base flange support (RBFS) repowering addition 210B, as shown in FIG. 5. The RBFS repowering addition 210B also includes a repowering addition CMP 316 but one that is larger in diameter than that used with the EBFS repowering addition in order to create an annular space 318 between the RBFS repowering addition CMP 316 and the outer pier CMP 14 that is about 4 feet wide and 6 feet deep. Further, the RBFS repowering addition provides a stand alone support surface for the tower connection flange 332 of the much larger tower 333. The support surface provided by the RBFS repowering addition 201B is spaced outwardly from, and functionally replaces, the existing tower base support surface for the tower connection flange 301 and is supported by repowering addition tower anchor bolts. The repowering addition tower anchor bolts 327, which are generally 1.5 inch bolts 7 ft in length, extend vertically through the concrete of the repowering addition collar, generally parallel with the outer pier CMP and the repowering addition CMP. Like the EBFS repowering addition, the RBFS repowering addition also includes tensioning lateral reinforcing bolts 328 that extend across the annular space 318 between the repowering addition CMP 316 and the outer pier CMP 14, and into the annular concrete ring formed between the inner and outer pier CMPs. Both the smaller EBFS and the larger RBFS repowering additions allow a tower having a commensurately larger diameter to be connected to the existing foundation for retrofitted repowering, saving the cost and time required to remove the original foundation and construct a new foundation.

[0064] According to a third embodiment of the present invention, the reinforcement structure for the tensionless concrete pier foundation 10 includes a soil condition improvement collar generally designated by reference numeral 400 as shown in FIG. 6. The soil condition improvement collar can be added to an existing tensionless concrete pier foundation or be constructed concurrently with a new pier construction.

[0065] The soil condition improvement collar 400 includes a soil improvement CMP 416 that surrounds the outer pier CMP 14, being about 4-5 feet larger in diameter, and is about 5-6 feet deep, to define an annular space 418 that is filled with concrete, preferably 3000 psi concrete. The resulting soil condition improvement collar acts to improve the integrity of the surrounding ground material, i.e., the soil and/or rock substrate, to reduce pier movement and soil cracks at the surface.

[0066] According to a fourth embodiment of the present invention shown in FIGS. 1 and 7A, the reinforcement structure for the tensionless concrete pier foundation 10 includes buttress additions 500. The buttress additions 500 may be added as part of a new pier construction, to retrofit an existing pier foundation, or to support future repowering of the tower or turbine supported on the foundation.

[0067] The buttress additions 500 are preferably formed as individual concrete blocks or reinforcements, either precast or cured in place, each approximately 4 ft wide, 5 ft long and 10 ft deep, that are spaced around the outer perimeter of the pier foundation 10. The buttress additions 500 increase the overall load capacity and stiffness of the pier foundation while also providing deep-level soil improvement. Further, the buttress additions require less concrete than do fully encircling reinforcement collars, and the buttress additions do not interfere with, or require encasement of, the electrical conduits which facilitates ease of construction.

[0068] According to a fifth embodiment shown in FIG. 8, the present invention includes the stabilizing of a tensionless pier foundation 10 by pressure grouting 600 the surrounding soil to increase the load capacity of the pier foundation by expanding the diameter of the cementitious materials horizontally supporting the pier. According to the method, a grout emitting pipe or tube 602 is driven to the desired soil depth adjacent the base of the foundation 10, followed by pressure grouting to several hundred psi at 5 ft intervals as the grouting pipe is lifted upwardly. Pressure grouting in this way can be performed immediately after construction or years later to improve the pier's resistance to lateral movement. Pressure grouting for soil stabilization also increases the lateral bearing capacity of the surrounding soil and increases the skin friction around the perimeter of the pier foundation.

[0069] The present invention is also directed to a method of constructing a post-tensioned reinforcement collar for a tensionless concrete pier foundation having inner and outer pier CMPs as shown in the '417 patent. The outer perimeter of the collar is bounded by a collar CMP and the collar is secured to the inner and outer pier CMPs with a plurality of lateral reinforcing bolts that extend through the three CMPs, spanning the annular spaces between the inner and outer pier CMPs and between the outer pier CMP and the collar CMP. The lateral reinforcing bolts are nutted both outside the collar CMP and inside the inner pier CMP and can include an upper set of lateral reinforcing bolts near the top of the CMPs and a lower set of lateral reinforcing bolts near the bottom of the inner pier and collar CMPs.

[0070] According to the method, when constructing a new tensionless pier foundation, the lateral reinforcing bolts of the post-tensioned collar are added before the foundation concrete is poured. The concrete for the tensionless pier can be poured monolithically or a plurality of pours may be placed separately. The bolts are nutted against the inner pier CMP and the collar CMP to retain post-tension loads after both pier and collar concrete cure.

[0071] A preferred sequence of the method steps for construction of a new tensionless concrete pier foundation with a reinforcement collar in accordance with the present invention may be summarized as follows: [0072] 1. Drill or dig excavation to include center pier area to a first depth and outer collar area to a second depth less than the first depth. [0073] 2. Place outer pier CMP 14 into center pier area of excavation. [0074] 3. Slurry annular space 117 (see FIG. 3) between excavation perimeter in center pier area and outer pier CMP 14 to bottom of outer collar area. [0075] 4. Place inner pier CMP 12 into center pier area of excavation. [0076] 5. Pour concrete plug at bottom of inner CMP 12. The depth of the concrete plug can be increased to provide shear resistance. [0077] 6. Backfill lower part of region 17 inside inner pier CMP 12 to about 5 ft from the top of the foundation with uncompacted soil. [0078] 7. Place tower anchor bolts 20, 21 secured to the embedment ring 22 placed at the bottom of the pier. [0079] 8. Drill soil and/or rock anchor additions vertically into underlying substrate of outer collar area. [0080] 9. Place outer collar CMP 112 into outer collar area to create annular space between outer collar CMP 112 and outer pier CMP 14. [0081] 10. Bolt bottoms of outer collar CMP and inner and outer pier CMPs with lower lateral reinforcing bolts. [0082] 11. Place inner collar CMP on top of lower lateral reinforcing bolts. [0083] 12. Bolt tops of outer collar CMP and inner and outer pier CMPs with upper lateral reinforcing bolts. [0084] 13. Pour concrete in the annular space between inner and outer pier CMPs. [0085] 14. Pour concrete into annular collar space. [0086] 15. Pour concrete floor with high strength concrete to depth of about 5 ft. [0087] 16. After concrete cure, post-tension lateral steel reinforcing bolts and soil and/or rock anchors, install tower base flange over top of the tower anchor bolts and post tension tower anchor bolts.

[0088] While the concrete pours have been identified as separate steps, the concrete may be poured monolithically depending upon the specific construction sequence that is followed in a particular instance. In addition, the annular space between the outer perimeter of the excavation in the outer collar area and the outer collar CMP is also backfilled prior to completion of the foundation.

[0089] The post-tensioned collar can also be added to an existing tensionless pier foundation for retrofit or repowering with a larger turbine. The preferred method of adding the post-tensioned collar as a retrofit includes removing the floor as well as the soil within the cylindrical space defined by the inner pier CMP to the depth of the collar, and drilling holes for insertion of the horizontally-extending lateral bolts through the inner pier CMP, the annular concrete ring between the inner and outer pier CMPs, the outer pier CMP, the annular space between the outer pier CMP and the collar CMP, and the collar CMP. The bolts are inserted through the drilled holes and nutted against the inner surface of the inner pier CMP and against the outer surface of the collar CMP during post tensioning. In such a retrofit construction, the deep concrete floor addition can be incorporated within the retrofit collar addition by pouring the deep concrete floor after the concrete in the annular space between the collar CMP and the outer pier CMP has been poured and cured and the bolts post tensioned, effectively replacing the previously existing floor and soil fill which was removed to install the retrofit collar.

[0090] As already noted herein, the post-tensioned collar may also include soil and/or rock anchor additions which are placed within drilled holes prior to concrete pour in the collar. According to a preferred method of installation, rock anchors are installed in drilled holes, such as percussion drilled holes, and are grouted to within a few inches below the bottom of the collar while the upper end of the rock anchor bolt extends to the design height above the collar. Soil anchors can be auger cast or driven piles which are drilled to the design depth with a sleeved centralized bolt. The piles are backfilled with concrete or grout, and terminated a few inches below the bottom of the collar with the sleeved bolt extending above the top of the collar to the design height. Both the rock and the soil anchors are then post-tensioned after concrete pour and cure.

[0091] The present invention may also include soil anchor additions formed as helical anchors that are drilled to the design depth with a tube or bolt being central to the helices. An upper end of the tube or bolt extends to the design height above the collar. Helical anchors of this type can be pressure grouted, if required, to increase anchor capacity.

[0092] As a further alternative, displacement anchors having a centralized sleeved bolt secured near the top thereof can be drilled and grouted to design depth with the displacement section of the anchor terminating inches below the bottom of the collar and with the upper end of the central sleeved bolts extending to the design height above the collar for post tensioning.

[0093] The present invention is also directed to a method of installing repowering additions having tower anchor bolts. The tower anchor bolts extend through the repowering addition collar and are sleeved in like manner as has been described in connection with the rock and/or soil anchor bolts, also being post-tensioned after concrete pour and cure.

[0094] The foregoing descriptions and drawings should be considered as illustrative only of the principles of the invention. The invention may be configured in a variety of ways and numerous applications of the present invention will readily occur to those skilled in the art. Therefore, it is not desired to limit the invention to the specific examples disclosed or the exact construction and operation shown and described. Rather, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.