JP2011236675A - Underwater foundation construction method and outer shell section structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a construction method of an underwater foundation of which center-of-gravity position can be adjusted so that it becomes a stable floating body while being towed, without unnecessarily increasing the weight of a sidewall and a floor slab of the underwater foundation, and an outer shell section structure.SOLUTION: A plurality of outer shell members 7 are continuously arranged along a top face 25 of a side wall 5 provided around the bottom slab 3 of a caisson 1, and the outer shell members 7 and the side wall 5 are fixed by a PC steel 11 to install an outer shell section structure 14. The caisson 1 with the outer shell section structure 14 installed is moved to water surface and arranged by putting a weight body 39 such as seawater, sand or ballast into the inside 37 thereof, to adjust the center-of-gravity position of the caisson 1. Thereafter, the caisson 1 is towed up to a position above an installation planned position and filling sand 45 is put into the inside thereof to immerge the caisson 1 at the installation planned position and place upper floor concrete 47. Thereafter, water is poured into the inside 49 of the caisson 1 and tensioning force of the PC steel 11 is released to remove outer shell members 7 from the top face 25 of the side wall 5, and then the PC steel 11 projecting from the side wall 5 is cut off.

Description

  The present invention relates to an underwater foundation construction method and an outer shell structure.

  Conventionally, when a structure such as a bridge is constructed on the water, it has been necessary to construct a foundation for supporting a bridge girder, a pier, and the like on the bottom of the water. Gravity caisson has been often used for the foundation. For example, as shown in the prior art of Patent Document 1 and Patent Document 2, at the time of construction, a foundation body of a circular vessel shape or a hollow structure is manufactured at a land dock, and towed as a floating structure from the dock to the construction site, The foundation body was sunk by throwing sand and filling water at the installation site.

  However, the bottom plate and side wall thickness required to function as a gravity-type foundation after the site was set up, the position of the center of gravity became shallower from the water surface during towing, and it was not stable as a floating body. In order to function as a stable floating body during towing, measures such as increasing the thickness of the side walls and floor slabs of the foundation body to increase the weight and deepening the center of gravity from the water surface were necessary.

JP 2009-203664 A JP-A-2005-330718

  However, when the weight of the foundation main body is increased, the thickness of the side wall or floor slab becomes larger than the thickness necessary for functioning as a foundation, which may be uneconomical. In addition, it was necessary to improve the grade of the hoist and the like, which led to an increase in construction costs.

  The present invention has been made in view of the above-described problems, and its purpose is to increase the center of gravity so that a stable floating body can be obtained during towing without unnecessarily increasing the weight of the side wall or floor slab of the underwater foundation. To provide an underwater foundation construction method and outer shell structure that can be adjusted in position.

  In order to achieve the above-described object, the first invention is an underwater foundation construction method for constructing an underwater foundation by sinking a caisson having a bottom plate and a side wall provided around the bottom plate. A step (a) of providing an outer shell structure configured by arranging an outer shell member along the side wall on the upper surface of the side wall of the caisson; and a weight body disposed in the caisson moved to the water surface. A step (b) of adjusting the position of the center of gravity, a step (c) of towing the caisson above the planned installation position, and a step (c) of sinking the caisson to the planned installation position, and removing the outer shell member from the caisson An underwater foundation construction method comprising the step (d) of:

  The outer shell member is provided so that the top of the caisson is on the water surface. In step (d), water is poured into the caisson before removing the outer shell member of the caisson.

  In the first invention, in the step (a), the outer shell member is inserted into a hole penetrating in the height direction, and one end is attached to the fixing portion on the side wall and the other end is attached to the fixing portion on the top portion of the outer shell member. In the step (d), it is desirable to release the prestress due to the PC steel material at the other end, remove the outer shell member, and then remove the PC steel material protruding from the side wall in the step (d).

  The outer shell portion structure is constituted by, for example, a plurality of outer shell members made of a precast member, which are continuously arranged along the side wall.

  In the first invention, an outer shell structure is provided on the upper surface of the side wall of the caisson so that the outer shell member is arranged along the side wall, and seawater, sand, ballast, etc. are provided inside the caisson moved to the water surface. Place the weight body and so on. This makes it possible to adjust the position of the center of gravity so that the floating body is stable during towing without increasing the weight of the side walls and floor slabs more than necessary.

  According to a second aspect of the present invention, there is provided an outer shell structure comprising a caisson having a bottom plate and a side wall provided around the bottom plate, wherein an outer shell member provided on the upper surface of the side wall is arranged along the side wall. And is inserted into a hole penetrating the outer shell member in the height direction, pre-formed with a PC steel material having one end attached to the fixing portion on the side wall and the other end attached to the fixing portion on the top portion of the outer shell member. The outer shell structure is characterized in that stress is introduced.

  The outer shell part structure is configured, for example, by continuously arranging a plurality of outer shell members made of precast members along side walls. And the fitting part which fits with another outer shell member is provided in the continuous part of the outer shell member which continues with the other outer shell member. Also, a fitting portion that fits with the side wall is provided on the lower surface of the outer shell member.

  The outer shell structure of the second invention is provided on the upper surface of the side wall of a caisson having a bottom plate and a side wall provided around the bottom plate. As a result, a space surrounded by the outer shell structure, the bottom plate and the side wall is formed, ensuring the buoyancy required to make the foundation a floating body, while ensuring seawater, sand and ballast to become a stable floating body during towing It is possible to adjust the position of the center of gravity by placing a weight body such as the like. In addition, by introducing prestressing with PC steel, the caisson and the outer shell member can be integrated more effectively, and the outer shell member itself can be effectively improved in bending rigidity and bending strength, thereby enabling stable towing.

  ADVANTAGE OF THE INVENTION According to this invention, the construction method and outer shell structure of an underwater foundation which can adjust a gravity center position so that it may become a stable floating body at the time of towing, without increasing the weight of the side wall and floor slab of an underwater foundation more than necessary can be provided. .

Vertical sectional view of the caisson 1 with the outer shell structure 14 installed Enlarged view of range A shown in FIG. Horizontal sectional view of outer shell structure 14 Enlarged view of range C shown in FIG. The figure which shows the process of constructing the caisson 1 and arrange | positioning the outer shell member 7 The figure which shows the process of fixing the outer shell member 7 to the caisson 1 The figure which shows the process of arrange | positioning the weight body 39 in the inside 37 of a caisson 1, and adjusting a gravity center position. The figure which shows the process of towing caisson 1 and sinking it to the planned installation position The figure which shows the process of pouring water into the inside 49 of caisson 1 The figure which shows the process of removing the outer shell member 7 from the caisson 1

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a vertical sectional view of the caisson 1 in which the outer shell structure 14 is installed. FIG. 2 is an enlarged view of a range A shown in FIG. FIG. 3 shows a horizontal sectional view of the outer shell structure 14. 3 is a cross-sectional view taken along arrows BB shown in FIG. FIG. 4 is an enlarged view of a range C shown in FIG.

  As shown in FIG. 1, the caisson 1 includes a bottom plate 3, a side wall 5, and the like. The bottom plate 3 is, for example, circular, and the side wall 5 is provided on the outer periphery of the bottom plate 3. An outer shell structure 14 is installed on the upper surface 25 of the side wall 5 of the caisson 1.

As shown in FIG. 3, the outer shell portion structure 14 includes a plurality of outer shell members 7. As shown in FIGS. 1 and 3, the outer shell structure 14 is configured by continuously arranging a plurality of outer shell members 7 along the side wall 5 on the upper surface 25 of the side wall 5 of the caisson 1. The outer shell member 7 is, for example, a precast member made of ultra high strength fiber reinforced concrete. Here, the ultra high strength fiber reinforced concrete is a concrete having a high compressive strength, a material in which steel fiber, carbon fiber, glass fiber, vinylon fiber, or the like is mixed in a mortar. For example, the compressive strength is 100 to 250 N. / Mm ² , bending tensile strength is 10 to 40 N / mm ² , and tensile strength is 5 to 15 N / mm ² .

  As shown in FIG. 2, a shear key 17 is provided at a boundary portion 21 between the outer shell member 7 and the side wall 5. The shear key 17 includes a convex portion 17 a provided on the upper surface 25 of the side wall 5, which is a fitting portion, and a concave portion 17 b provided on the lower surface 27 of the outer shell member 7. In the shear key 17, the convex part 17a and the recessed part 17b are fitted. The shear key 17 may be provided over the entire length of the boundary portion 21 or may be provided at a predetermined interval.

  As shown in FIG. 2, at the boundary portion 21, a water stop structure 23 is provided inside and outside the outer shell structure 14 (outer shell member 7) with the shear key 17 interposed therebetween. The water stop structure 23 is installed over the entire length of the boundary portion 21. The water stop structure 23 is a swollen rubber or the like.

  As shown in FIG. 3, a shear key 33 is provided in a continuous portion where the outer shell members 7 are continuous, that is, a portion of the vertical joint 29. As shown in FIG. 4, in the portion of the vertical joint 29, one side portion 30 a of the outer shell member 7 and the side portion 30 b of the other outer shell member 7 arranged continuously face each other. The shear key 33 includes a convex portion 33a provided on the side portion 30a, which is a fitting portion, and a concave portion 33b provided on the side portion 30b. In the shear key 33, the convex portion 33a and the concave portion 33b are fitted. The shear key 33 may be provided over the entire length of the vertical joint 29 or may be provided at a predetermined interval.

  As shown in FIG. 4, in the vertical joint 29, a water stop structure 31 is provided inside and outside the outer shell structure 14 (outer shell member 7) with the shear key 33 interposed therebetween. The water stop structure 31 is installed over the entire length of the vertical joint 29. The water stop structure 31 is a swollen rubber or the like.

  As shown in FIGS. 1 and 2, a dead anchor type fixing unit 15 is provided near the upper end of the side wall 5. A fixing tool 13a is embedded in the fixing unit 15, and a space is provided below the fixing tool 13a. The side wall 5 is provided with a sheath tube 9b that penetrates the convex portion 17a of the upper surface 25 in the height direction and reaches the fixing tool 13a. The sheath tube 9b and the fixing unit 15 are provided at a predetermined interval in the circumferential direction of the side wall 5. These can be provided separately from the convex portion 17.

  As shown in FIG. 1 and the like, the outer shell member 7 is provided with a haunch 19 as a widened portion at the base. In addition, a fixing tool 13 b is disposed on the top 16. The outer shell member 7 is provided with a sheath tube 9a which is a hole portion penetrating in the height direction. The sheath tube 9 a is provided at a predetermined interval in the circumferential direction of the outer shell structure 14.

  As shown in FIG. 1 and FIG. 3, the outer shell structure 14 includes a sheath tube 9 a provided on the outer shell member 7 and a sheath provided on the side wall 5 by aligning the concave portion 17 b with the position of the convex portion 17 a on the side wall. It installs in the upper part of the side wall 5 of the caisson 1 so that the pipe | tube 9b may connect. A PC steel material 11 is inserted into the communicating sheath tube 9a and sheath tube 9b. One end of the PC steel material 11 is attached to a fixing tool 13 a embedded in the side wall 5. Further, the other end is attached to the fixing tool 13 b disposed on the top 16 of the outer shell member 7. Prestress is introduced into the PC steel material 11, and the caisson 1 and the outer shell structure 14 are integrated by the prestress of the PC steel material 11.

  Next, a method for constructing the underwater foundation by sinking the caisson 1 shown in FIG. 1 will be described. FIG. 5 is a diagram illustrating a process of constructing the caisson 1 and arranging the outer shell member 7. In the process shown in FIG. 5, first, the caisson 1 in the state shown in FIG. Further, the outer shell member 7 in the state shown in FIG. 5 is carried into the dock.

  Next, the outer shell member 7 is disposed on the upper surface 25 of the side wall 5 by fitting the convex portion 17a of the side wall 5 and the concave portion 17b of the outer shell member 7 with a dock. At this time, as shown in FIG. 2, the sheath tube 9 a provided on the outer shell member 7 and the sheath tube 9 b provided on the side wall 5 are communicated. Further, a water stop structure 23 is provided at a boundary portion 21 between the side wall 5 and the outer shell member 7.

  In the step shown in FIG. 5, as shown in FIG. 3, the plurality of outer shell members 7 are continuously arranged along the upper surface 25 of the side wall 5. At this time, as shown in FIG. 4, the convex part 33a of the side part 30a of the outer shell member 7 and the concave part 33b of the side part 30b of the continuous outer shell member 7 are fitted. Further, a water stop structure 31 is provided at the vertical joint 29.

  FIG. 6 is a diagram illustrating a process of fixing the outer shell member 7 to the caisson 1. In the process shown in FIG. 6, first, the PC steel material 11 is inserted into the sheath tube 9a and the sheath tube 9b, and the lower end portion of the PC steel material 11 is fixed to the dead anchor type fixing tool 13a. And the prestress by PC steel material 11 is introduce | transduced, and the fixing tool 13b attached to the upper end part of PC steel material 11 is crimped | bonded to the top part 16 of the outer shell member 7. FIG. The outer shell member 7 and the side wall 5 are fixed by prestress introduced by the PC steel material 11. In the process shown in FIG. 6, all the outer shell members 7 are fixed to the side wall 5, thereby completing the installation of the outer shell structure 14 on the caisson 1.

  Since the ultra high strength fiber reinforced concrete constituting the outer shell member 7 has high density, it becomes a member excellent in salt damage resistance even when used in seawater. Moreover, since the ultra high strength fiber reinforced concrete has a high compressive strength, a high prestress can be introduced by the PC steel 11 while being a thin member. The prestress by the PC steel material 11 is effective for improving the bending rigidity and the bending strength of the outer shell member 7 itself as well as enhancing the integrity of the caisson 1 and the outer shell member 7.

  FIG. 7 is a diagram illustrating a process of adjusting the position of the center of gravity by placing and placing a weight body 39 such as seawater, sand, or ballast in the interior 37 of the caisson 1. In the process shown in FIG. 7, the caisson 1 in which the outer shell structure 14 is installed is moved to the water surface. Then, a weight body 39 such as seawater, sand, ballast, or the like is placed in the inside 37 of the caisson 1 so as to adjust the position of the center of gravity deeper from the water surface. FIG. 7 shows an example in which water is injected into the interior 37. Thereby, the caisson 1 functions as a stable floating body in the water 35. Then, in a state where the caisson 1 is stable as a floating body, the tow is towed above the planned installation position.

  The outer shell structure 14 is installed in a ring shape on the upper surface 25 of the side wall 5 of the caisson 1. Therefore, as shown in FIG. 7, when a water level difference occurs inside and outside the outer shell structure 14, it is compressed to the vertical joint 29, which is the connecting portion of the outer shell member 7, due to the ring effect due to external water pressure. A force acts, which is advantageous for ensuring the integrity of the outer shell members 7 and the waterproofness.

  FIG. 8 is a diagram illustrating a process of towing the caisson 1 and sunk it at a planned installation position. In the process shown in FIG. 8, the filling sand 45 is put into a portion surrounded by the bottom plate 3 and the side wall 5, and the caisson 1 is set on the rubble 43 of the water bottom 41. Further, the upper floor concrete 47 is placed above the filling sand 45 to complete the body of the underwater foundation.

  As shown in FIG. 8, in the present embodiment, the top 16 of the outer shell structure 14 is on the water even after the caisson 1 is set. In the step shown in FIG. 8, the upper floor concrete 47 is placed to complete the body of the underwater foundation. Thereafter, as shown in FIG. 9, water is poured into the inside 49 of the caisson 1 to adjust the water level inside and outside to eliminate the water pressure from the outside, so that the outer shell structure 14 can be easily removed.

  FIG. 10 is a diagram illustrating a process of removing the outer shell member 7 from the caisson 1. In the process shown in FIG. 10, first, the fixing tool 13 b (FIG. 8, etc.) at the top 16 of the outer shell member 7 is removed using a hydraulic jack or the like, and the prestress due to the PC steel rod 11 is released. Then, the outer shell member 7 is sequentially lifted upward and removed. Further, the PC steel bar 11 protruding from the side wall 5 is removed, and the construction of the underwater foundation is completed.

  Thus, in the present embodiment, the outer shell structure 14 having a shape along the side wall 5 is fixed to the upper surface 25 of the side wall 5 of the caisson 1. Thereby, the buoyancy required to make the caisson 1 a floating body can be secured in the space surrounded by the bottom plate 3 and the side wall 5 of the caisson 1 and the outer shell structure 14. In addition, by arranging a weight body 39 such as seawater, sand, or ballast in the interior 37, the position of the center of gravity of the caisson 1 can be adjusted, and a low center of gravity for stabilizing the entire floating body can be realized. In addition, by introducing prestress by the PC steel material 11, the integrity of the caisson 1 and the outer shell member 7 is improved, and it becomes effective in improving the bending rigidity and bending strength of the outer shell member 7 itself, and stable towing is achieved. It becomes possible.

  In the present embodiment, a shear key 33 and a water stop structure 31 are provided on the vertical joint 29 which is a continuous part of the outer shell member 7 as necessary. Further, a shear key 17 and a water stop structure 23 are provided at a boundary portion 21 between the side wall 5 of the caisson 1 and the outer shell member 7. By providing the shear key, the outer shell structure 14 integrally resists the external water pressure, and when the outer shell member 7 is sequentially installed on the side wall 5, the member can be easily aligned. Become. Moreover, by providing the water stop structure, water leakage from the vertical joint 29 and the boundary portion 21 can be prevented. Furthermore, by providing the haunch 19 at the base of the outer shell member 7, the outer shell member 7 is stabilized during installation or when an external force is applied.

  In the present embodiment, the PC steel material 11 is only passed through the sheath tube 9a and the sheath tube 9b, and is not filled with grout or the like. If the tension | tensile_strength of PC steel material 11 is released after canceling a water pressure, the outer shell member 7 can be extracted and removed. Since the outer shell member 7 has excellent durability as described above, it can be reused repeatedly after removal.

  In the present embodiment, a plurality of outer shell members 7 are arranged on the side wall 5 in the step shown in FIG. 5 and then fixed by the PC steel material 11 in the step shown in FIG. The fixing work with the PC steel material 11 may be performed in parallel. Moreover, the side wall 5 and the outer shell member 7 should just be a structure which has the hole which can insert PC steel material 11, and a sheath pipe | tube is installed as needed. A haunch 19 of the outer shell member 7 is also provided as necessary.

  In this embodiment, the outer shell member 7 is a precast member made of ultra high strength fiber reinforced concrete. However, the outer shell member 7 can be constructed on site, and the material is other than ultra high strength fiber reinforced concrete. It is also conceivable to use the above. Furthermore, although the outer shell portion structure 14 is formed by a plurality of outer shell members 7, it may be formed by one outer shell member.

  In the present embodiment, as shown in FIG. 8 and the like, the case where the top portion 16 of the outer shell structure 14 is on the water surface after the caisson 1 is set is described. The position of the top 16 is not limited to this. Depending on the construction method of the foundation and its form, there may be a case where the position of the top 16 is lower. In this case, since the water 35 flows into the caisson 1 during the settling process, water injection into the interior in the process shown in FIG. 8 becomes unnecessary.

  In the present embodiment, the substantially circular caisson 1 is used, but the underwater foundation construction method of the present invention can also be applied to the case of using other shapes of caissons. Further, the configuration of the underwater foundation main body is not limited to that shown in FIG. 8, and the filling of the filling material 45 and the placement of the upper floor concrete 47 in the process shown in FIG. 8 are performed as necessary.

  As mentioned above, although embodiment of this invention was described referring an accompanying drawing, the technical scope of this invention is not influenced by embodiment mentioned above. It is obvious for those skilled in the art that various modifications or modifications can be conceived within the scope of the technical idea described in the claims, and these are naturally within the technical scope of the present invention. It is understood that it belongs.

1 ... Caisson 3 ......... Bottom plate 5 ......... Side wall 7 ......... Outer shell member 9a, 9b ......... Sheath tube 11 ......... PC steel 13a, 13b ......... Fixing tool 17, 33 ......... Shear key 21 ......... Boundary part 23, 31 ......... Water stop structure 25 ......... Top surface 29 ......... Vertical joint 37, 49 ......... Inside

Claims (7)

An underwater foundation construction method for constructing an underwater foundation by sinking a caisson having a bottom plate and a side wall provided around the bottom plate,
A step (a) of providing an outer shell structure formed by arranging an outer shell member along the side wall on the upper surface of the side wall of the caisson;
Placing a weight body inside the caisson moved to the water surface and adjusting the position of the center of gravity (b);
(C) towing the caisson to a position above the planned installation position, and sinking the caisson at the planned installation position;
Removing the outer shell member from the caisson (d);
An underwater foundation construction method characterized by comprising: The outer shell member is provided such that the top of the caisson is on the water surface when set up,
The method for constructing an underwater foundation according to claim 1, wherein in the step (d), water is poured into the caisson before the outer shell member of the caisson is removed. In the step (a), a PC is inserted into a hole penetrating the outer shell member in the height direction, and one end is attached to the fixing portion of the side wall and the other end is attached to the fixing portion at the top of the outer shell member. Introducing prestress with steel,
2. The PC steel material protruding from the side wall is cut after releasing the prestress by the PC steel material at the other end and removing the outer shell member in the step (d). How to build an underwater foundation.   The method for constructing an underwater foundation according to claim 1, wherein the outer shell part structure is constituted by a plurality of outer shell members made of a precast member arranged continuously along the side wall. A caisson having a bottom plate and a side wall provided around the bottom plate, an outer shell part structure provided on an upper surface of the side wall and configured by arranging an outer shell member along the side wall,
Prestress is introduced by a PC steel material that is inserted into a hole that penetrates the outer shell member in the height direction, and has one end attached to the fixing portion on the side wall and the other end attached to the fixing portion on the top of the outer shell member. An outer shell structure characterized by that. A plurality of outer shell members made of precast members are continuously arranged along the side wall,
The outer shell structure according to claim 5, wherein the outer shell member is provided with a fitting portion that fits with the other outer shell member at a continuous portion continuous with the other outer shell member. .   The outer shell structure according to claim 5, wherein a fitting portion that fits with the side wall is provided on a lower surface of the outer shell member.

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