KR102323225B1 - Repair and Strengthening Method for Wind Turbine Tower Flange Anchoring Foundations - Google Patents

Abstract

The present invention provides a reinforcement method for reinforcing a connection part between a lower part of a wind turbine tower and a concrete foundation, the concrete foundation drilling step of drilling a part of the concrete foundation to provide a space for installing an anchor bolt in the concrete foundation; An anchor bolt installation step of integrating the anchor bolt with the concrete foundation through a grouting operation after inserting the anchor bolt through the concrete foundation drilling step; a connecting member installation step of installing a connecting member for connecting the anchor bolt and the lower part of the wind turbine tower after the anchor bolt installation step; a connecting member welding step of welding one end of the connecting member to the lower part of the wind turbine tower and integrating the connecting member after the connecting member installation step; and an anchor bolt coupling step of fixing the connecting member connected to the concrete foundation with the anchor bolt after passing through the connecting member welding step.

Description

Repair and Strengthening Method for Wind Turbine Tower Flange Anchoring Foundations

The present invention relates to a reinforcement method for reinforcing the lower foundation of a wind turbine tower, and more particularly, a method for reinforcing the anchoring foundation of a wind turbine tower to improve the foundation performance by reinforcing the connection part between the lower portion of the wind turbine tower and the concrete foundation. is about

In general, when designing a wind turbine, the service life is considered to be 20 or 25 years, and therefore, safety factors are calculated based on the fatigue life of 20 or 25 years in various fatigue designs. In relation to the operation of the wind farm, when the service life is reached, it is necessary to review alternatives such as decommissioning, repowering, or simple lifetime extension. In the case of decommissioning, it means that the wind power generation business is no longer carried out in the relevant complex, and in this case, all facilities will be dismantled. Repowering is a business method to replace the existing wind turbine with the latest large wind turbine. In this case, the existing turbine is dismantled and demolished, and a new larger turbine is installed. Such re-powering has received a lot of attention as it can minimize the cost of building various licenses and related infrastructure required for the construction of power generation complexes. However, recently, power plant operators are very interested in simply extending the lifespan. In other words, if the safety and power generation performance of the current state of the wind turbine are evaluated and the safety is sufficient and the performance of the power generation facility also satisfies a certain level, the profit is maximized by not dismantling it and using it for another 5 to 10 years. In this case, by maximizing the profits from power generation while minimizing additional costs, the operator can obtain profits with minimal cost and effort.

However, the most problematic part in such life extension is the fatigue damage part, and in particular, the fatigue damage of the foundation is a task that must be solved. Since wind turbines are continuously exposed to high levels of thrust and wind forces, fatigue damage may accumulate in blades, foundations, and tower joints during long-term operation. Among them, the possibility of damage at the junction between the wind turbine tower and the concrete foundation is very high, and such damage has been reported a lot in the case of a wind turbine in operation.

As shown in FIG. 1 in relation to the damage to the foundation that has occurred in the existing domestic wind turbine tower, the separation between the lower part of the wind turbine tower and the concrete foundation occurs most frequently, and repair and reinforcement of the foundation where such separation occurs Failure to do so may result in deterioration of overall foundation stability. That is, (a) of FIG. 1 is a view showing a state in which a separation occurs at the junction of a wind turbine tower, (b) is a view showing a state in which the breakout of concrete occurs due to vibration caused by an applied load, (c) ) is a diagram showing how concrete powder is ejected due to pumping action, (d) is a diagram showing an increase in vertical vibration deformation of a wind turbine tower after a gap, and a state in which shear failure proceeds, (e) is a wind power It is a view showing a state in which power generation is stopped due to acceleration of vertical vibration of the turbine tower, and (f) is a view showing a state of repair by injecting grouting into the spaced part of the junction.

The repair method using grouting for the part where the separation occurs is generally widely used. This can be said to be a method of preventing additional damage by filling the space by injecting grouting and adhesive into the spaced part of the joint. However, since this method does not fundamentally increase the strength of the foundation joint, there is a high possibility that separation occurs again, and thus it is not a fundamental solution.

Republic of Korea Public Utility Model No. 20-2015-0001684

Accordingly, the present invention has been devised to solve the above problems, and an object of the present invention is to repair and reinforce the damage occurring at the junction between the wind turbine tower and the foundation. will provide

However, the technical problems to be achieved in the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned are clearly to those of ordinary skill in the art to which the present invention belongs from the description below. can be understood

The present invention was created to improve the problems of the prior art as described above, and as a reinforcement method for reinforcing a connection part between the lower part of a wind turbine tower and a concrete foundation, in order to provide a space for installing an anchor bolt on the concrete foundation Concrete foundation perforating step of perforating a part of the concrete foundation; An anchor bolt installation step of integrating the anchor bolt with the concrete foundation through a grouting operation after inserting the anchor bolt through the concrete foundation drilling step; a connecting member installation step of installing a connecting member for connecting the anchor bolt and the lower part of the wind turbine tower after the anchor bolt installation step; A connecting member welding step of welding one end of the connecting member to the lower part of the wind turbine tower after the connecting member installation step is integrated; and an anchor bolt coupling step of fixing the connecting member connected to the concrete foundation with the anchor bolt after passing through the connecting member welding step.

In addition, after the anchor bolt coupling step, the wind turbine tower fixing step of fixing while filling the space between the lower portion of the wind turbine tower and the concrete foundation by grouting; may be made to further include.

In addition, forming a plurality of holes along the periphery of the lower portion of the wind turbine tower and connecting a plurality of wires corresponding to the plurality of holes, a tensile force applying step of applying a tensile force while fixing the wires to the concrete foundation; further comprising can be done by

In addition, an additional reinforcement step of reinforcing while fixing the wind turbine tower to the concrete foundation by installing at least one support bar in the lower portion of the wind turbine tower in a diagonal shape; may be made to further include.

In addition, the connection member is manufactured in a wedge shape having an inclined surface, one end is welded to the wind turbine tower, both sides are formed to be inclined downward, and a bolt hole into which the anchor bolt is inserted is formed in a part of the bottom surface. can

In addition, the method further comprises a concrete foundation forming step of forming the concrete foundation by pouring concrete under the wind turbine tower, wherein the concrete foundation forming step forms a recessed space recessed downward from the upper surface of the concrete foundation, The recessed space may be formed along the circumference of the wind turbine tower.

According to an embodiment of the present invention, the repair and reinforcement method of the wind turbine tower can perform repair and reinforcement without the need to dismantle the concrete foundation, thereby reducing the construction period and cost, and extending the service life.

In addition, the possibility of damage to the foundation by using additional anchor bolts to increase the bearing capacity of the foundation joint of the wind turbine tower, which is difficult to respond to vibration and load with only the attachment strength between the lower part of the wind turbine tower and the concrete foundation. can reduce

However, the effects obtainable in the present invention are not limited to the above-mentioned effects, and other effects not mentioned will be clearly understood by those of ordinary skill in the art to which the present invention belongs from the following description. will be able

The following drawings attached to this specification illustrate preferred embodiments of the present invention, and serve to further understand the technical spirit of the present invention together with the detailed description of the present invention to be described later, so the present invention is described in such drawings It should not be construed as being limited only to
1 is a view showing an example of a conventional wind turbine tower foundation repair and reinforcement construction method.
Figure 2 is an overall flow chart of the wind turbine tower flange anchoring foundation repair and reinforcement construction method according to an embodiment of the present invention.
3 is a view showing a state in which a separation occurs between the wind turbine tower and the concrete foundation.
4 is a view showing the state of drilling the concrete foundation.
FIG. 5 is a view showing a state in which the anchor bolt is installed following FIG. 4 .
FIG. 6 is a view showing the installation of the connecting member for connecting the anchor bolt and the lower part of the wind turbine tower following FIG. 5 .
7 is a view showing a state in which the connection member is integrated by welding the lower part of the wind turbine tower.
8 is a view showing a state in which the connecting member is fixed with the anchor bolt.
9 is a view showing a state of fixing the gap between the wind turbine tower and the concrete foundation while filling.
10 is a view showing an embodiment in which the connecting member is coupled to the wind turbine tower.
11 is a view showing a state in which the support bar is installed in the wind turbine tower.
12 is a view showing an embodiment in which the connecting member is coupled to the wind turbine tower and the concrete foundation.
13 is a view showing a state of forming a recessed space in the step of forming the concrete foundation.

Hereinafter, with reference to the accompanying drawings, embodiments of the present invention will be described in detail so that those of ordinary skill in the art can easily implement them. However, since the description of the present invention is merely an embodiment for structural or functional description, the scope of the present invention should not be construed as being limited by the embodiment described in the text. That is, since the embodiment may have various modifications and may have various forms, it should be understood that the scope of the present invention includes equivalents capable of realizing the technical idea. In addition, since the object or effect presented in the present invention does not mean that a specific embodiment should include all of them or only such effects, it should not be understood that the scope of the present invention is limited thereby.

The meaning of the terms described in the present invention should be understood as follows.

Terms such as “first” and “second” are for distinguishing one component from another, and the scope of rights should not be limited by these terms. For example, a first component may be termed a second component, and similarly, a second component may also be termed a first component. When a component is referred to as being “connected” to another component, it may be directly connected to the other component, but it should be understood that other components may exist in between. On the other hand, when it is mentioned that a certain element is "directly connected" to another element, it should be understood that the other element does not exist in the middle. Meanwhile, other expressions describing the relationship between elements, that is, “between” and “immediately between” or “neighboring to” and “directly adjacent to”, etc., should be interpreted similarly.

The singular expression is to be understood as including the plural expression unless the context clearly dictates otherwise, and terms such as "comprises" or "have" refer to the described feature, number, step, action, component, part or these It is intended to indicate that a combination exists, and it should be understood that it does not preclude the possibility of the existence or addition of one or more other features or numbers, steps, operations, components, parts, or combinations thereof.

All terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs, unless otherwise defined. Terms defined in the dictionary should be interpreted as being consistent with the meaning of the context of the related art, and cannot be interpreted as having an ideal or excessively formal meaning unless explicitly defined in the present invention.

Figure 2 is an overall flow chart of the wind turbine tower flange anchoring foundation repair and reinforcement construction method according to an embodiment of the present invention, Figure 3 is a view showing a state in which the separation occurs between the wind turbine tower and the concrete foundation, Figure 4 is a view showing the state of drilling the concrete foundation, FIG. 5 is a view showing the installation of the anchor bolt following FIG. 4, and FIG. 6 is a view showing the anchor bolt and the lower part of the wind turbine tower following FIG. It is a view showing a state of installing the connecting member for connection, FIG. 7 is a view showing a state in which the connecting member is welded to the lower part of the wind turbine tower to be integrated, and FIG. 8 is the connecting member fixed with the anchor bolt 9 is a view showing a state of fixing while filling the gap between the wind turbine tower and the concrete foundation, and FIG. 10 is a view showing an embodiment in which the connecting member is coupled to the wind turbine tower. 11 is a view showing a state in which the support bar is installed in the wind turbine tower, FIG. 12 is a view showing an embodiment in which the connecting member is coupled to the wind turbine tower and the concrete foundation, and FIG. 13 is It is a view showing a state of forming a recessed space in the step of forming the concrete foundation.

2 to 13, as a reinforcement method for reinforcing the connection part between the lower part of the wind turbine tower and the concrete foundation, the concrete foundation forming step (S50), the concrete foundation drilling step (S100), the anchor bolt installation step ( S200), a connecting member installation step (S300), a connecting member welding step (S400) and an anchor bolt coupling step (S500) may be included. The wind turbine tower flange anchoring foundation repair and reinforcement method of the present invention is not limited to the above construction method, and according to the site situation or conditions, the connection member 400 can be installed, and the anchor bolt 300 can be installed after welding. It can be applied and modified.

The concrete foundation forming step (S50) is a step of forming the concrete foundation 200 by pouring the lower part of the wind turbine tower 100 with concrete. The concrete foundation forming step (S50) may support the wind turbine tower 100 by pouring the lower part of the wind turbine tower 100 with concrete. The concrete foundation forming step ( S50 ) forms a recessed space (S) recessed downward from the upper surface of the concrete foundation ( 200 ), and the recessed space (S) may be formed along the circumference of the wind turbine tower ( 100 ). The step of forming the recessed space (S) may be omitted depending on the construction method.

The recessed space (S) may be a space formed by sailing down from the upper surface of the concrete foundation 200 . In an embodiment, the recessed space S may be a space integrally formed along the circumference of the wind turbine tower 100 . Alternatively, in another embodiment, the recessed space S may be formed of a plurality of space cells arranged at regular intervals along the circumference of the wind turbine tower 100 . Specifically, the process of forming the recessed space (S) in the concrete foundation forming step (S50) is to install the Steel bar (31) and the Anchor (32) in a part of the concrete foundation 200 around the wind turbine tower 100 and , It can be formed while installing the formwork 33 on the edge, pouring the concrete 34 on the set part, and reinforcing it using the Anchor exposed to the top.

The concrete foundation drilling step (S100) is a step of drilling a part of the concrete foundation 200 in order to provide a space for the anchor bolt 300 installation in the concrete foundation 200 (10). Specifically, in the concrete foundation drilling step (S100), a plurality of perforations 10 of a size set at a set interval are formed while enclosing the perimeter of the wind turbine tower in the ground or concrete foundation 200 where the wind turbine tower 100 is installed. to accommodate the anchor bolt 300 .

The anchor bolt installation step (S200) is a step of integrating the anchor bolt 300 into the concrete foundation 200 through a grouting operation after inserting the anchor bolt 300 through the concrete foundation drilling step (S100). Specifically, in the anchor bolt installation step (S200), the anchor bolt 300 is installed in the perforation 10, and for fixing the anchor bolt 300, the space portion of the hole in which the anchor bolt 300 is embedded is grouted and finished. Thus, the anchor bolt 300 can be firmly fixed.

The connecting member installation step (S300) is a step of installing the connecting member 400 for connecting the anchor bolt 300 and the lower part of the wind turbine tower 100 after the anchor bolt installation step (S200).

The connecting member 400 is manufactured in a wedge shape having an inclined surface, one end is welded to the wind turbine tower 100, both sides thereof are formed to be inclined downward, and the anchor bolt 300 is inserted into a part of the bottom surface of the bolt hole. (70) may be formed.

Specifically, the connecting member 400 installed in the connecting member installation step (S300) is manufactured in a wedge shape having an inclined surface, and one end of the connecting member 410 is welded while supporting the lower portion of the wind turbine tower 100. and both sides are formed to be inclined downward from both sides of the coupling part 410 to form a support part 420 that supports and transmits the load applied to the coupling part 410, and the bottom surface to which they are connected is the coupling part 410 and the fixing part 430 in which the bolt hole 70 to which the anchor bolt 300 is fixed is formed in a part of forming the lower part of the support part 420.

That is, the fixing part of the connecting member may be in close contact with the wind turbine tower 100 , respectively, and the coupling part may be in close contact with the concrete foundation 200 while connecting the wind turbine tower 100 and the concrete foundation 200 .

The connecting member welding step (S400) is a step of integrating one end of the connecting member 400 by welding it to the lower part of the wind turbine tower 100 after the connecting member installation step (S300). In an embodiment, the welding step (S400) of the connecting member is installed by welding the bent upper end of the connecting member 400 to the lower part of the wind turbine tower 100, and the other bent portion of the connecting member 400 is welded to the concrete base 200 ) while fixing each of the wind turbine tower 100 can be supported.

Alternatively, in another embodiment, the concrete foundation 200 may have a recessed space (S) recessed in its upper surface. The recessed space S may be located between the wind turbine tower 100 and the perforation 10 . In an embodiment, the recessed space (S) may be formed as a single space surrounding the circumference of the wind turbine tower (100). Alternatively, in another embodiment, the recessed space (S) may be composed of a plurality of space cells arranged at regular intervals along the circumference of the wind turbine tower (100).

The connection member 400 may be located above the recessed space (S). For example, a portion of the fixing part 430 of the connecting member 400 may vertically overlap the recessed space (S). That is, the outer part of the fixing part 430 vertically overlapping with the perforation 10 may be supported by the concrete foundation 200, but the inner part of the fixing part 430 vertically overlapping with the recessed space S is concrete. It cannot be supported by the foundation 200 . However, after welding the lower end of the coupling portion 410 of the connecting member 400 to the wind turbine tower 100 using the recessed space (S), the recessed space (S) can be filled with concrete. When the recessed space S is filled with concrete, the inner portion of the fixing part 430 may be supported by the concrete. In addition, by being coupled to the wind turbine tower 100 as well as the upper end of the coupling unit 410, the coupling force between the connecting member 400 and the wind turbine tower 100 may be improved.

In addition, the connecting member 400 may further include a fixing protrusion 80 protruding downward from a portion of the lower portion of the fixing portion 430 . The fixing protrusion 80 may be located in the recessed space (S). The fixing protrusion 80 may be in contact with the bottom surface of the recessed space (S). Accordingly, the fixing protrusion 80 may perform a function of supporting the connecting member 400 until the concrete is filled. In addition, the fixing protrusion 80 may be formed with irregularities in the lower portion. Accordingly, when the recessed space (S) is poured with concrete, the frictional force with the concrete can be increased.

The anchor bolt coupling step (S500) is a step of fixing the connecting member 400 connected to the concrete foundation 200 after passing the connecting member welding step (S400) while integrating with the anchor bolt 300 . Specifically, in the anchor bolt coupling step (S500), the connecting member 400 connected to the concrete foundation 200 is integrated into the anchor bolt 300 after the connecting member welding step (S400) is passed, and the method is the anchor bolt 300 ) while fastening the upper part with a nut 60 or the like, the anchor bolt 300 can be fixed to the connection member 400 .

The wind turbine tower flange anchoring foundation repair and reinforcement method according to an embodiment of the present invention may further include a wind turbine tower fixing step (S600), a tensile force application step (S700), and an additional reinforcement step (S800).

The wind turbine tower fixing step (S600) is a step of fixing the spaced space generated between the lower part of the wind turbine tower 100 and the concrete foundation 200 by grouting and filling after the anchor bolt coupling step (S500).

In the tensile force application step (S700), a plurality of holes are formed along the periphery of the lower portion of the wind turbine tower 100 and connected with a plurality of wires 30 (not shown) corresponding to the plurality of holes, and the wire 30 is connected to the concrete foundation. It is a step of applying a tensile force while fixing to (200). Specifically, the tensile force application step (S700) is controlled through appropriate distribution of the pressure or load applied to the wind turbine tower through adjustment of the tensile force of the wire while winding and unwinding the wire using a winding member such as a winch or a winder. possible.

The additional reinforcement step (S800) is a step of reinforcing while fixing the wind turbine tower 100 to the concrete foundation 200 by installing at least one support bar 50 in the lower portion of the wind turbine tower 100 in a diagonal shape. Specifically, in the additional reinforcement step (S800), the support bar 50 is hydraulically manufactured, the hydraulically driven support bar 50 is installed, and the wind force is also applied to the load or pressure acting in the horizontal direction due to an earthquake or strong wind. It may be possible to actively cope with the flow of the turbine tower 100 .

More specifically, the hydraulic jack, which is one embodiment of the hydraulic type, is provided between the separated holder support members to elevate the holder support member. That is, the hydraulic jack may be inserted between the upper and lower leg portions of the holder support member to adjust the length of the leg portion while connecting the leg portions. The hydraulic jack actuator may be connected to the hydraulic jack to provide hydraulic pressure to the hydraulic jack for driving the hydraulic jack. That is, the hydraulic jack actuator may extend the length of the hydraulic jack by providing hydraulic pressure to the hydraulic jack or discharge the hydraulic pressure to reduce the length of the hydraulic jack while stretching and relaxing the leg portion. In addition, as an example of the hydraulic jack, a pneumatic cylinder and a hydraulic cylinder method are mainly used. Specifically, the pneumatic cylinder is also called a compressed air cylinder, and converts the energy of compressed air into mechanical reciprocating linear motion. it is a device

In the present invention, a winding member such as a winch or a winder or a support bar hydraulic jack can be operated through a controller (not shown) linked to any one of a mobile terminal, etc., a Wi-Fi communication module, a Bluetooth communication module, and a Zigbee communication module.

That is, the operator can use the winding member or the hydraulic actuator by adopting any one of a Bluetooth communication module, a Wi-Fi communication module and a Zigbee communication module, but it is not limited to the above method and can be used by selecting the best method. .

According to an embodiment of the present invention, the repair and reinforcement method of the wind turbine tower 100 can perform repair and reinforcement without the need to dismantle the concrete foundation 200, thereby reducing the construction period and cost, and extending the service life. .

In addition, an anchor bolt 300 is additionally attached to the base joint of the wind turbine tower, which is difficult to respond to vibration and load with only the attachment strength using the connection member 400 between the lower part of the wind turbine tower 100 and the concrete foundation 200. By increasing the bearing capacity, the possibility of damage to the foundation can be reduced.

The detailed description of the preferred embodiments of the present invention disclosed as described above is provided to enable any person skilled in the art to make and practice the present invention. Although the above has been described with reference to preferred embodiments of the present invention, it will be understood by those skilled in the art that various modifications and changes can be made to the present invention without departing from the scope of the present invention. For example, a person skilled in the art may use each configuration described in the above-described embodiments in a way that is combined with each other. Accordingly, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

The present invention may be embodied in other specific forms without departing from the spirit and essential characteristics of the present invention. Accordingly, the above detailed description should not be construed as restrictive in all respects but as exemplary. The scope of the present invention should be determined by a reasonable interpretation of the appended claims, and all modifications within the equivalent scope of the present invention are included in the scope of the present invention. The present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein. In addition, claims that are not explicitly cited in the claims may be combined to form an embodiment, or may be included as new claims by amendment after filing.

10: perforation
30: wire
31 : Steel bar
32 : Anchor
33 : formwork
34: concrete
50: support bar
60: nut
70: bolt hole
80: fixing protrusion
100: wind turbine tower
200: concrete foundation
300: anchor bolt
400: connecting member
410: coupling part
420: support
430: fixed part

Claims (6)

As a reinforcement method for reinforcing the connection part between the lower part of the wind turbine tower and the concrete foundation,
A concrete foundation drilling step of drilling a part of the concrete foundation in order to provide a space for the anchor bolt installation in the concrete foundation;
An anchor bolt installation step of integrating the anchor bolt with the concrete foundation through a grouting operation after inserting the anchor bolt through the concrete foundation drilling step;
a connecting member installation step of installing a connecting member for connecting the anchor bolt and the lower part of the wind turbine tower after the anchor bolt installation step;
a connecting member welding step of welding one end of the connecting member to the lower part of the wind turbine tower and integrating the connecting member after the connecting member installation step; and
An anchor bolt coupling step of fixing the connecting member connected to the concrete foundation by integrating with the anchor bolt after the connecting member welding step;
Concrete foundation forming step of forming the concrete foundation by pouring concrete under the wind turbine tower; further comprising,
The concrete foundation forming step forms a recessed space recessed downward from the upper surface of the concrete foundation, and the recessed space is formed along the perimeter of the wind turbine tower,
The connecting member is manufactured in a wedge shape having an inclined surface, a coupling portion welded to the lower portion of the wind turbine tower;
a support portion formed to be inclined downward from both sides of the coupling portion to support a load applied to the coupling portion;
a fixing part in which a bolt hole into which the anchor bolt is inserted is formed in a portion while forming a lower part of the coupling part and the support part; and
and a fixing protrusion formed to protrude from a lower portion of the fixing part and to come into contact with the bottom surface of the recessed space; and
The connecting member welding step is,
In the process of welding one end of the connecting member to the lower part of the wind turbine tower, the lower end of the coupling part can be welded to the wind turbine tower using the recessed space.
The method according to claim 1,
Wind turbine tower flange anchoring, characterized in that it further comprises; after the anchor bolt coupling step, a wind turbine tower fixing step of fixing while filling the gap between the lower part of the wind turbine tower and the concrete foundation by grouting. Foundation repair and reinforcement construction method.
The method according to claim 1,
Forming a plurality of holes along the periphery of the lower portion of the wind turbine tower and connecting a plurality of wires corresponding to the plurality of holes, a tensile force applying step of applying a tensile force while fixing the wires to the concrete foundation; Wind turbine tower flange anchoring foundation repair and reinforcement method, characterized in that.
The method according to claim 1,
An additional reinforcement step of reinforcing while fixing the wind turbine tower to the concrete foundation by installing at least one support bar in the lower portion of the wind turbine tower in a diagonal shape; Wind turbine tower flange anchoring foundation repair, characterized in that it further comprises a reinforcement technique.
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