JP7574372B2 - Compression device and compression method for rock surrounding an underground structure, and underground structure integrated with the rock - Google Patents

Description

The present invention relates to an apparatus and method for compressing the rock surrounding an underground structure.

There is a known technology that improves the earthquake resistance of foundations by integrating the ground around an underground structure with the foundation. Patent Document 1 discloses a method of forming a foundation with ground reinforcement, in which perforations are formed radially around the foundation, reinforcing materials are fixed into the perforations, and the ends of the reinforcing materials are fixed to the main body of the foundation.

Special Publication No. 5-40085

According to the method described in Patent Document 1, the ground can be integrated with the foundation via reinforcing materials. Therefore, the foundation can be substantially expanded and a large bearing capacity can be obtained. Depending on the type of underground structure, it may be necessary to improve the water impermeability of the surrounding ground. Compressing the rock around the underground structure may be one solution to such various requirements. The object of the present invention is to provide a device for compressing the rock around an underground structure.

According to one aspect of the present invention, the apparatus includes a plurality of strands extending radially from an underground structure into the rock mass, and a plurality of anchors for tensioning the plurality of strands and compressing the rock mass inside the outer ends of the plurality of strands . The plurality of strands are provided only in the upper half region of the underground structure.

The device of the present invention can compress the rock surrounding an underground structure.

FIG. 1 is a conceptual diagram of a first embodiment. FIG. 2 is a perspective view of an underground structure and a strand according to the first reference embodiment. FIG. 13 is a conceptual diagram of a modified example of the first embodiment. FIG. 13 is a conceptual diagram of a second reference embodiment. FIG. 13 is a conceptual diagram of a third embodiment. FIG. 13 is a conceptual diagram of a modified example of the third embodiment. FIG. 13 is a conceptual diagram of a fourth embodiment. FIG. 13 is a conceptual diagram of a modified example of the fourth embodiment. FIG. 13 is a conceptual diagram of a further modified example of the fourth embodiment. FIG. 1 is a conceptual diagram of a first embodiment. FIG. 11 is a conceptual diagram of a modified example of the first embodiment. FIG. 13 is a conceptual diagram of a second embodiment. FIG. 13 is a conceptual diagram of a modified example of the second embodiment. FIG. 13 is a conceptual diagram of a further modified example of the second embodiment. FIG. 13 is a conceptual diagram of a third embodiment. This is the result of a 3D FEM analysis of rock mass.

Below, several embodiments and reference forms of the device and method for compressing the rock surrounding an underground structure of the present invention will be described with reference to the drawings. Unless otherwise specified, the following description is directed to an existing underground structure, but can also be applied to a newly constructed underground structure.

(First embodiment)
In this embodiment, a caisson pile that is constructed deep underground will be described as an example of an underground structure. The aboveground structure supported by the underground structure is a bridge pier, but may be a building or other structure. The caisson pile is a roughly cylindrical underground structure embedded in bedrock. FIG. 1 shows a conceptual diagram of this embodiment. FIG. 1(a) shows a plan view of the underground structure 1, and FIG. 1(b) shows a cross-sectional view taken along line A-A in FIG. 1(a). FIG. 2(a) shows a perspective view of the underground structure 1, the aboveground structure 2, and the strand S, and FIG. 2(b) shows a perspective view of the strand S. A plurality of strands S are provided along the periphery of the underground structure 1. The strands S are circumnavigated at a position radially away from the underground structure 1, and a bedrock R is interposed between the strands S and the underground structure 1. The strands S extend inside a guide hole (not shown) drilled in the bedrock R. The strand S is made of PC steel (PC cable), but may be a cable made of aramid fiber, carbon fiber, or the like. The strand S is provided horizontally at approximately equal intervals at multiple depth levels of the bedrock R. The strand S at each depth level is composed of multiple divided strands S1, S2 that surround the entire circumference of the underground structure 1 in a circular shape. In this reference embodiment, two divided strands S1, S2 that surround half the circumference of the underground structure 1 are provided at each depth level. The number of divided strands is not limited, and the lengths of the divided strands may be different from each other. One strand S may go around the entire circumference of the underground structure 1. In other words, as long as at least one strand S is provided along the side of the underground structure 1 at each depth level and the strand S surrounds the entire circumference of the underground structure 1 in a circular shape, the number and length of the strands S are not limited.

The split strands S1 and S2 are connected to each other and tensioned by the fixing device 10. The fixing devices 10 are provided in the same number as the split strands S1 and S2, and connect the opposing ends of the split strands S1 and S2 to each other. The type of fixing device 10 is not particularly limited, but as an example, the fixing device described in Patent No. 3439403 can be used. This fixing device 10 is an integrated device of two sleeves that hold the ends of the PC steel, and is embedded in concrete so that the tension of the PC steel can be transmitted to the concrete. In order to install and tension the fixing device 10, a pit 3 that accommodates the fixing device 10 is provided in the rock mass R on the side of the underground structure 1. Two pits 3 are provided at 180° intervals and open to the ground. The strands S and the fixing devices 10 constitute the device 100 for compressing the rock mass surrounding the underground structure of this reference embodiment.

The installation of the device 100 is carried out according to the following procedure. First, a pit 3 is excavated to house the fixing device 10. Next, guide holes are excavated from the side of the pit 3. The guide holes are excavated by flexible boring, starting from one of the pits 3. This forms guide holes that go around the entire circumference of the underground structure 1. Next, strands S are inserted into each guide hole. The ends of the two strands S1, S2 are placed opposite each other in each pit 3, and these ends are connected by the fixing device 10. After that, the strands S1, S2 are tensioned by the fixing device 10.

The fixing device 10 applies tension to the strand S. The tension tightens the strand S, compressing the rock mass R between the underground structure 1 and the strand S, and as shown by the white arrow in FIG. 1, the underground structure 1 is pressed radially toward the rock mass R. Due to the compressive force acting on the rock mass R, the rock mass R is embraced by the underground structure 1 or integrated with the underground structure 1. In other words, by applying a compressive force to the rock mass R that presses the underground structure 1 radially inward, a ring-shaped rock mass region or embracement region (hereinafter referred to as the integrated region R1) that is integrated with the underground structure 1 is formed between the underground structure 1 and the strand S, and the rock mass R behaves as if it were a part of the underground structure 1.

According to this embodiment, the same effect as expanding the foundation itself can be expected, and seismic reinforcement work can be streamlined. Conventionally, when expanding the foundation itself, it was necessary to excavate the surrounding bedrock, build a new reinforced concrete foundation, and integrate it with the existing foundation. In contrast, with this embodiment, it is only necessary to install the strand S using the construction procedure described above, so large-scale excavation or installation of reinforced concrete structures is not required, making it possible to reduce construction costs and shorten construction time.

This reference embodiment can also be applied to a newly constructed underground structure 1. In this case, it is preferable to first construct the underground structure 1 and then install the strand S. This makes it possible to more reliably form an integrated region R1 of the bedrock R surrounding the underground structure 1. However, if the integrity and adhesion between the underground structure 1 and the surrounding bedrock R can be sufficiently ensured, it is also possible to install the strand S first, or to construct the strand S and the underground structure 1 simultaneously.

Figure 3 is a view similar to Figure 1, showing a modified example of the first reference form. In this modified example, the caisson piles are omitted, and the pier is embedded in bedrock R. Therefore, in this modified example, the underground structure 1 is the pier. By integrating the bedrock R around the pier with the pier, the same effect as providing a foundation around the pier can be obtained. Since the caisson piles can be omitted in this modified example, it is possible to reduce construction costs and shorten the construction period.

(Second Reference Form)
FIG. 4(a) shows a perspective view of an underground structure 1, a ground structure 2, and a strand S in the second reference embodiment, and FIG. 4(b) shows a perspective view of the strand S. Here, the differences from the first reference embodiment will be mainly described. The configurations, effects, etc. that are not described are the same as those of the first reference embodiment. The strand S extends in a spiral shape around the underground structure 1. Although not shown, both ends of the strand S are fixed to a fixing device 10 supported by the bedrock R and tensioned. One end of the strand S may be extended to the bedrock R outside the pit 3 as shown by the line 11, and the end may be fixed with grout. Since both ends of the strand S are at the same angular position when viewed vertically, only one pit 3 needs to be provided. The angular positions of both ends of the strand S may be different from each other. For example, if the angular positions of both ends of the strand S are 180 degrees different, two pits 3 are provided as in the first reference embodiment. The number of turns of the strand S is approximately equivalent to the number of stages of the strand S in the first reference embodiment, and can be set appropriately taking into consideration the required earthquake resistance, costs, and construction period. In this reference embodiment, two fasteners 10 are required regardless of the number of turns of the strand S, so the number of fasteners 10 can be reduced. Also, only one pit 3 is required, so construction costs can be reduced.

Figure 4(c) is a view similar to Figure 4(b) showing a modified example of the second reference form. The strand S has a spiral portion 12 that spirally surrounds the underground structure 1, an upper connection portion 13 that is connected to the upper end of the spiral portion 12 and extends diagonally downward, and a lower connection portion 14 that is connected to the lower end of the spiral portion 12 and extends diagonally upward. The fixing device 10 is provided in the pit 3 and connects the lower end of the upper connection portion 13 to the upper end of the lower connection portion 14. In this modified example, both ends of the strand S are connected by a single fixing device 10, so the number of fixing devices 10 can be further reduced.

(Third Reference Form)
FIG. 5(a) shows a perspective view of an underground structure 1, a ground structure 2, and a strand S in the third reference embodiment, FIG. 5(b) shows a perspective view of the strand S, and FIG. 5(c) shows a plan view of the strand S. In FIG. 5(c), the upper strand S is shown over its entire length, but the middle and lower strands S are shown only in end regions 16 on both sides. Each strand S surrounds the entire circumference of the underground structure 1 in a circular shape. Each strand S crosses at an intersection 15, and the end regions 16 from the intersection 15 to both ends 17 extend obliquely upward toward both ends 17 located on the ground. The end regions 16 extend approximately linearly when viewed in the vertical direction. Both ends 17 of the strand S are supported by the anchorages 10. In other words, the number of anchorages 10 is twice the total number of the strands S. The anchorages 10 are supported by rock masses and supporting structures on the ground. By tensioning the strand S at the anchorages 10 on both sides, a compressive force is applied to the rock mass R to press the underground structure 1 radially inward, providing the same effect as in the first embodiment. In addition, since there is no need to provide a pit 3 in this embodiment, it is possible to reduce construction costs and shorten the construction period.

In this reference embodiment, three strands S are provided at different depth levels. In the vertical direction, the parts of the three strands S surrounding the underground structure 1 follow the same path in a plane, and have the same radius from the center C of the underground structure 1. The intersections 15 are offset from each other by 120 degrees, preventing interference between the anchoring parts 10. The number of strands S is not limited to three, but it is preferable to arrange the intersections 15 at equal intervals. As in the first reference embodiment, it is preferable to provide the strands S only in the upper half of the underground structure 1. The length of the end region 16, i.e., the length from the intersection 15 to both ends 17, varies depending on the installation depth level of the strands S. Specifically, the deeper the strand S is installed, the longer the end region 16 is. This makes it possible to align the gradient of the end region 16 between the strands S.

Construction is carried out as follows. First, guide holes are excavated from above ground. The guide holes are excavated by adjustable boring. The guide holes extend downward from above ground to a specified depth level, circle the entire circumference of the underground structure 1, and then extend upward to above ground. Next, strands S are inserted into each guide hole. Both ends 17 of the strands S are exposed above ground, and both ends 17 are connected to the fixing devices 10. The strands S are then tensioned by the fixing devices 10.

Figure 6 is a diagram similar to Figure 5 showing a modified example of the third reference form. Each strand S surrounds almost the entire circumference of the underground structure 1 in a circular shape. However, unlike the third reference form, each strand S does not completely surround the periphery of the structure 1. Since the three strands S are arranged at 120 degrees offset from each other, the underground structure 1 is surrounded by at least two strands S at any angular position relative to its center C. The end region 18 extends obliquely upward from the end of the part of each strand S that surrounds the periphery of the structure 1 toward both ends 17 located above ground. The fixing device 10 is shared by both ends 17 of each strand S. The end region 18 is provided on the same side of the fixing device 10. In other words, the end region 18 is located between the underground structure 1 and the fixing device 10. This makes it possible to minimize the part of the underground structure 1 that is not surrounded by the strands S and to minimize the laying distance of the strands S. As with the third reference embodiment, the deeper the strand S is installed, the longer the end region 18 is. In this modified example, the number of fasteners 10 is reduced compared to the third reference embodiment, allowing for further cost reductions.

(Fourth embodiment)
FIG. 7 is a view similar to FIG. 5 of the fourth reference embodiment. Here, the differences from the first reference embodiment will be mainly described. The configuration, effects, etc. that are omitted are the same as those of the first reference embodiment. In this reference embodiment, three strands S are provided. Each strand S partially surrounds the underground structure 1 in the circumferential direction, and both ends 17 are installed on the ground. Each strand S has an arc-shaped portion 19 that surrounds the underground structure 1 in an arc shape within a range of 120 degrees, and the three strands S are shifted from each other by 120 degrees. Therefore, the entire circumference of the underground structure 1 is surrounded by three strands S. The number of strands S is not limited to three, and may be two or four or more. Although not shown, multiple strands S may be provided at multiple depth levels. Each strand S has end regions 20 connected to both ends of the arc-shaped portion 19. The end regions 20 extend obliquely upward from the ends of the arc-shaped portion 19 toward both ends 17 located on the ground. The end region 20 extends in a generally straight line when viewed in the vertical direction. The fixing devices 10 are provided on both ends 17 of the strand S. In this reference embodiment, the length of the end region 20 also varies depending on the installation depth level of the strand S. The deeper the strand S is installed, the longer the end region 20 is. This allows the gradient of the end region 20 to be uniform between the strands S. In this reference embodiment, the length of each strand S is shorter than in the third reference embodiment, and the range in which the strand S curves is limited, making it easier to drill the guide hole and install the strand S. In addition, the three strands S can be constructed in parallel, which is advantageous in terms of shortening the construction period. In order to apply a compressive force evenly to the rock mass R, it is preferable to perform the tensioning work for the three strands S simultaneously.

Figure 8 is a view similar to Figure 7 of a modified example of the fourth reference form. The strands S are provided at different depth levels. The configuration of the strands S at each depth level is the same as in the fourth reference form. As in the modified example of the third reference form, the fixing device 10 is shared by both ends 17 of the three strands S. Since the number of fixing devices 10 is reduced, further cost reduction is possible. In addition, even if the number of stages of the strands S increases, the number of fixing parts 10 remains constant, so it is easy to prevent interference between the fixing parts 10 on the ground.

Figure 9 is a conceptual diagram showing a further modified example of the fourth reference form, in which Figure 9(a) is a plan view, Figure 9(b) is a plan view showing only the underground structure 1 and two strands S, and Figure 9(c) is a cross-sectional view taken along line A-A in Figure 9(a). In this reference form, the underground structure 1 is rectangular. Each strand S surrounds one side of the underground structure 1 and the two adjacent sides in a U-shape. Four U-shaped strands S are arranged at 90 degrees offset from each other. Each strand S mainly compresses a semicircular area surrounded by the underground structure 1 and the curved part of the U-shape. Thus, as shown in Figure 9(a), a semicircular integrated region R1 is formed on each side of the underground structure 1, which is radially wide at the center and radially small at the corners. As shown in Figure 9(c), multiple stages of strands S are provided, and the configuration of the strands S at each depth level is the same. The end region 21 is inclined toward the ground, as in the third and fourth reference forms. The ends of the strands S located above ground are supported by the fixing devices 10, and the strands S are tensioned by the fixing devices 10. According to this embodiment, a rectangular underground structure 1 can achieve the same effect as a circular underground structure 1. The shape of the underground structure 1 is not limited to a rectangle, and can be applied to polygonal underground structures 1.

(First embodiment)
FIG. 10 is a conceptual diagram showing the first embodiment, in which FIG. 10(a) shows a plan view of the underground structure 1, and FIG. 10(b) shows a cross-sectional view along line A-A in FIG. 10(a). Here, the differences from the first reference embodiment will be mainly described. The configurations, effects, etc. that are not described are the same as those of the first reference embodiment. A plurality of strands S extending horizontally at different depth levels are provided. At each depth level, eight strands S extend horizontally from the underground structure 1, and a total of four stages of strands S are provided. The eight strands S extend radially at equal intervals from the underground structure 1. Along the side wall of the underground structure 1, the same number of pits 3 as the strands S of each stage (eight in this embodiment) are provided. The fixing device 10 is fixed to the underground structure 1. The other end of the strand S is inserted into a guide hole (not shown) drilled from the side wall of the pit 3, and is fixed to the bedrock R by grout G. In this embodiment, unlike the above-mentioned reference embodiments, the rock mass R is compressed by the compressive force of the strand S, not by the hoop effect due to the tension of the strand S. As in the first reference embodiment, the integrated region R1 is an annular region roughly concentric with the underground structure 1. Since the pit 3 is provided along the side wall of the underground structure 1, this embodiment is advantageous in cases where the site area is limited.

Figure 11 is a diagram similar to Figure 10, showing a modified example of the first embodiment. In this embodiment, the underground structure 1 is rectangular. Each strand S extends in a direction perpendicular to each side of the underground structure 1, and also extends from the four corners of the underground structure 1 at angles of 45 degrees to these strands S. Since the length of the strands S is constant, the integrated region R1 has a rectangular shape with rounded corners.

Second Embodiment
FIG. 12 is a conceptual diagram showing the second embodiment, in which FIG. 12(a) is a plan view and FIG. 12(b) is a cross-sectional view taken along line A-A in FIG. 12(a). Here, the differences from the first reference embodiment will be mainly described. The configurations, effects, etc. that are not described are the same as those of the first reference embodiment. A plurality of strands S extend obliquely downward from the aboveground structure 2 supported by the underground structure 1 in a direction away from the underground structure 1. A circular support 31 that covers the periphery of the pier is provided at the top of the underground structure 1, and a plurality of fasteners 10 are provided on the support 31, which is a part of the aboveground structure 2. The lower end of the strand S is fixed to the bedrock R by grout G, and the strand S is tensioned by the fasteners 10. A horizontal component of tension is applied to the bedrock R radially from the underground structure 1. This horizontal component of tension compresses the bedrock R around the underground structure 1 toward the underground structure 1, achieving the same effect as the first embodiment. In this embodiment, a compressive force can be applied to a wide area in the vertical direction without providing multiple stages of strands S, so the number of strands S and fasteners 10 can be reduced.

The above-ground structure 2 has a prestressing means 32 that applies a circumferential prestress to the support 31. The support 31 receives a radially outward force due to the tension of the strand S. To counter this force, a circular PC steel wire extending along the support 31 is arranged inside the support 31, and tension is applied to the PC steel wire by a fixing device (not shown). The diameter of the support 31 is larger than the diameter of the underground structure 1, and the fixing device 10 is arranged radially outward from the side of the underground structure 1. For this reason, the strand S can be arranged at an angle closer to the vertical direction, and the strand S can be fixed to the bedrock R even if the bedrock R is at a deep level. In addition, the strand S resists the overturning moment during an earthquake, improving earthquake resistance.

Figure 13 is a view similar to Figure 12, showing a modified example of the second embodiment. This modified example is similar to the second embodiment, except that the diameter of the support part 31 is smaller than the diameter of the underground structure 1. Because the support part 31 is small, the strand S can be installed even when there is limited space on the site.

Figure 14 is a view similar to Figure 12, showing a further modified example of the second embodiment. This modified example is similar to the second embodiment, except that the support portion 31 is divided in the circumferential direction for each strand S. In this modified example, the material amount of the support portion 31 can be reduced.

Third Embodiment
FIG. 15 is a conceptual diagram showing the third embodiment, in which FIG. 15(a) is a plan view and FIG. 15(b) is a cross-sectional view taken along line A-A in FIG. 15(a). In this embodiment, the underground structure 1 is, for example, a cylindrical underground tank, and the strand S is installed mainly for the purpose of increasing the water impermeability of the rock mass R around the tank. In this embodiment, the underground structure is newly constructed and is installed together with the strand S. The structure of the tank is not limited, but may be, for example, an underground cavity formed by excavating a rock mass and having a reinforced concrete body or a metal liner installed therein. In this embodiment, a plurality of horizontally extending strands S are provided at different depth levels in a plurality of stages (a total of four stages in this embodiment). A plurality of strands S (eight in this embodiment) are provided at equal intervals in each stage. One end of the strand S is fixed to the rock mass R with grout G, and the other end of the strand S is connected to a fixing device 10. The fixing device 10 is provided inside the underground structure 1, but may be provided outside the underground structure 1.

The construction is carried out according to the following procedure. First, the rock mass R is excavated to form a cylindrical cavity that will become the tank. Next, guide holes are drilled horizontally and radially from the side wall of the cavity. Next, the strands S are inserted into the guide holes. A plurality of strands S are provided that extend radially from the cavity inside the rock mass R. Next, grout G is injected into the guide holes, and the ends of the strands S are fixed to the rock mass R with the grout G. Next, a fixing device 10 is provided on the side wall of the cavity, and the strands S are tensioned. As a result, the rock mass R inside the radial outer end of the strands S is compressed in the radial direction. The rock mass R has an extremely large number of discontinuous surfaces such as joints and cracks. For this reason, in a tank with such a structure, there is a possibility that liquid inside the tank will leak from the side wall of the tank and penetrate and diffuse into the rock mass R. By applying a compressive force to the rock mass R, the discontinuous surfaces and cracks in the rock mass R can be closed, improving the water impermeability. Before tensioning the strands S, grout material may be injected into the cracks in the rock mass R. This further improves the water-tightness of the rock mass R.

In addition, in this embodiment, a plurality of other strands (hereinafter referred to as vertical strands S3) extending vertically and a second fixing device 33 for tensioning the vertical strand S3 are provided. The vertical strand S3 extends vertically inside the rock mass R inside the radially outer end of the strand S. The lower end of the vertical strand S3 is fixed to the rock mass R by grout G. A plurality of second fixing devices 33 are provided on the ground structure 2 and tension the plurality of vertical strands S3. This compresses the rock mass R above the lower end of the strand S. The horizontally extending strand S applies a radial compressive force to the rock mass R, so it is effective against discontinuous surfaces and cracks extending vertically, but a compressive force in the direction of closing these does not efficiently act on discontinuous surfaces and cracks extending horizontally. The vertical strand S3 compresses the rock mass R vertically, so it is effective against discontinuous surfaces and cracks extending horizontally. The construction procedure for the vertical strand S3 is as follows. First, a guide hole is drilled vertically from the ground. Next, the strand S is inserted into the guide hole. Next, grout G is injected into the guide hole, and the tip of the strand S is fixed to the bedrock R with the grout G. Next, a second fixing device 33 is installed on the ground, and the strand S is tensioned. This causes the bedrock R above the lower end of the strand S to be compressed vertically.

Figure 15 (c) shows the arrangement of the strand S, vertical strand S3, and pit 3 when the tank is already installed. One end of the strand S is fixed to the underground structure 1, and the fixing device 10 is provided at the radially outer end of the strand S. This is because it is difficult to arrange the fixing device 10 on the side of the tank when the tank is already installed. The construction procedure of this modified example is as follows. First, a pit 3 is provided on the radially outer side of the tank, and a guide hole is excavated from the side wall of the pit 3. Next, the strand S is inserted into the guide hole, and the end of the strand S is fixed to the side of the tank with grout G. Next, a fixing device 10 is provided on the side of the pit 3, and the strand S is tensioned. As a result, the rock mass R inside the radially outer end of the strand S is compressed in the radial direction. The vertical strand S3 is constructed in the above-mentioned manner.

Although not shown in the figure, the strand S and the vertical strand S3 can be installed to a depth deeper than the underground structure 1. Since the bedrock R directly below the underground structure 1 is compressed, the possibility of liquid leakage from the bottom of the underground structure 1 can be reduced.

(Analysis example)
A three-dimensional FEM analysis of the rock mass R was performed for the first embodiment shown in FIG. 10. FIG. 16(a) shows a three-dimensional FEM analysis model of the underground structure 1, the aboveground structure 2 supported by the underground structure 1, and the rock mass R. A horizontal load was applied to the aboveground structure 2 at the position shown in the figure, and the horizontal displacement of the aboveground structure 2, the underground structure 1, and the rock mass R was obtained. The horizontal force simulates the horizontal force during an earthquake. The analysis was performed for a case where no strand S was arranged (comparative example), a case where 10 strands S were arranged from the top to the bottom of the underground structure 1 (Example 1), and a case where 5 strands S were arranged only on the top of the underground structure 1 (Example 2). FIG. 16(b) is a contour diagram of the displacement in Example 1, where light colors indicate large displacement and dark colors indicate small displacement. From this, it can be seen that the rock mass R around the underground structure 1 behaves almost the same as the underground structure 1. This is believed to be because, as described above, the compressive force acting on the rock mass R causes the rock mass R to be embraced by the underground structure 1 or to be integrated with the underground structure 1. It is believed that similar results can be obtained for the other embodiments and reference forms.

Figure 16 (c) shows the relationship between horizontal load and displacement in the comparative example and in Examples 1 and 2. The displacement is the horizontal displacement at the center of the top of the underground structure 1. In Examples 1 and 2, the displacement is reduced compared to the comparative example, and it can be seen that the earthquake resistance performance of the foundation is improved. On the other hand, there is no significant difference between Example 1 and Example 2. Example 2 not only reduces the number of strands S and anchors 10, but also halves the depth of the pit 3, making it more advantageous than Example 1 in terms of reducing construction costs and shortening the construction period. Therefore, it is preferable to install the strands S only in the upper half of the underground structure 1.

REFERENCE SIGNS LIST 1 Underground structure 2 Aboveground structure 3 Pit 10, 33 Anchorage 12 Spiral section 13 Upper connection section 14 Lower connection section 32 Prestressing means 100 Compression device G Grout R Rock S Strand S1, S2 Split strand S3 Other strand (vertical strand)

Claims (12)

A plurality of strands extending radially from an underground structure within the bedrock;
and a plurality of anchors for tensioning the plurality of strands and compressing the rock mass inside the outer ends of the plurality of strands ;
A compression device for compressing rock surrounding an underground structure, wherein the plurality of strands are provided only in the upper half area of the underground structure . The compression device according to claim 1, wherein the strands extend horizontally from the underground structure, one end of each of the strands is fixed to the bedrock or the underground structure, and the fixing devices are provided on the underground structure or bedrock located on the other end side of the strands. A plurality of strands extending radially from an underground structure within the bedrock;
and a plurality of anchors for tensioning the plurality of strands and compressing the rock mass inside the outer ends of the plurality of strands;
the plurality of strands extend horizontally from the underground structure, one end of each of the plurality of strands is fixed to a rock mass or the underground structure, and the plurality of fixing devices are provided in the underground structure or the rock mass located on the other end side of the plurality of strands;
A compression device for compressing rock surrounding an underground structure, comprising: a plurality of other strands extending vertically inside the rock inside the outer ends of the plurality of strands; and a plurality of other fasteners that tension the plurality of other strands and compress the rock inside the outer ends of the plurality of strands. A plurality of strands extending radially from an underground structure within the bedrock;
and a plurality of anchors for tensioning the plurality of strands and compressing the rock mass inside the outer ends of the plurality of strands;
the plurality of strands extend horizontally from the underground structure, one end of each of the plurality of strands is fixed to a rock mass or the underground structure, and the plurality of fixing devices are provided in the underground structure or the rock mass located on the other end side of the plurality of strands;
A compression device for the rock surrounding an underground structure , the compression device being provided in the rock on the side of the underground structure and having a pit for accommodating the fastener. The compression device according to claim 3 , further comprising a pit provided in bedrock on the side of the underground structure to accommodate the anchoring device. The compression device according to claim 1, wherein the strands extend obliquely downward from an aboveground structure supported by the underground structure in a direction away from the underground structure, the lower ends of the strands are fixed to bedrock, and the fixing devices are provided on the aboveground structure. A plurality of strands extending radially from an underground structure within the bedrock;
and a plurality of anchors for tensioning the plurality of strands and compressing the rock mass inside the outer ends of the plurality of strands;
the plurality of strands extend obliquely downward from a ground structure supported by the underground structure in a direction away from the underground structure, lower ends of the plurality of strands are fixed to bedrock, and the plurality of fixing devices are provided on the ground structure;
A compression device for compressing rock surrounding an underground structure, comprising: a support portion for the plurality of strands provided on the above-ground structure; and a prestressing means for applying a circumferential prestress to the support portion. A plurality of strands extending radially from an underground structure within the bedrock;
and a plurality of anchors for tensioning the plurality of strands and compressing the rock mass inside the outer ends of the plurality of strands;
the plurality of strands extend obliquely downward from a ground structure supported by the underground structure in a direction away from the underground structure, lower ends of the plurality of strands are fixed to bedrock, and the plurality of fixing devices are provided on the ground structure;
A compression device for compressing rock surrounding an underground structure , comprising support portions for the plurality of strands provided on the above-ground structure, the support portions being divided circumferentially for each of the strands. Providing a plurality of strands extending radially from an underground structure within the rock mass;
and tensioning the plurality of strands by a plurality of anchors to compress the rock mass inside the outer ends of the plurality of strands ;
A method for compacting rock surrounding an underground structure , wherein the plurality of strands are provided only in an upper half area of the underground structure . The compression method according to claim 9, further comprising injecting grout into the rock cracks before tensioning the strands. Bedrock and
an underground structure embedded in the bedrock;
A plurality of strands extending radially from the underground structure inside the rock mass;
and a plurality of anchors for tensioning the plurality of strands and compressing the rock mass inside the outer ends of the plurality of strands;
An underground structure integrated with bedrock, wherein the plurality of strands are provided only in the upper half area of the underground structure. An underground structure as described in claim 11, wherein when a horizontal load is applied to a ground structure supported by the underground structure, the difference in displacement between the rock mass surrounding the upper half region of the underground structure and the upper half region is smaller than the difference in displacement between the rock mass surrounding the lower half region of the underground structure and the lower half region.

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