JP7841833B2 - Invert block - Google Patents

Description

This invention relates to a construction technique for preventing ground swelling within tunnels.

Depending on the stress conditions around the tunnel, upward pressure from the bottom can cause bulging or deformation of the road surface, potentially reducing the structural integrity of the tunnel.

Therefore, construction work is carried out to install an inverted arch-shaped structure in the ground at the bottom of the tunnel to withstand the upward pressure from below.

Regarding the technology for constructing inverts in tunnels, for example, the method described in Patent Document 1 (Japanese Patent Publication No. 2020-041381) is known.

Japanese Patent Publication No. 2020-041381

In tunnels, the installation of inverts is generally done using cast-in-place concrete. However, this method requires time for formwork setup and concrete curing, resulting in longer construction periods. This is particularly problematic when applied to tunnels on expressways already in use, as it prolongs lane closures.

Another construction method involves manufacturing precast inverts, transporting them into the tunnel, and installing them. However, this method is not only costly, but also difficult because the construction takes place inside the tunnel, limiting the size of the heavy machinery that can be used, and making it challenging to rotate the crane needed to lift and install the inverts.

This invention was made in light of the above-described technical background, and aims to provide a technology that enables tunnel bulging prevention construction to be carried out easily, in a short construction period, and at low cost.

To solve the above problems, the invert block of the present invention as described in claim 1 is an invert block installed in the ground at the bottom of a tunnel and forming an inverted arch shape along the circumference of the tunnel, and is composed of a plurality of steel elements that are elongated in shape and connected to each other in the axial direction on their longitudinal side and arranged to be long in the circumference of the tunnel, and these elements are integrally formed into a box shape consisting of an upper plate, a lower plate and side plates, and a gap is formed in the connecting opening formed on the longitudinal side of the element in which concrete poured into the inside of the box shape can flow from one element to the other, and a support member is installed to support an upward load , concrete is filled inside the box shape consisting of the upper plate, the lower plate and the side plates , and connecting plates are provided on the longitudinal side of the element that span the upper plates of both elements and the lower plates of both elements.

The invert block of the present invention described in claim 2 is characterized in that, in the invention described in claim 1, the connecting plate spanning the upper plates of both elements is attached to the lower surface of the upper plate of one element, extending over the entire length of the upper plate on its longitudinal side, so as to protrude from the upper plate, and the connecting plate spanning the lower plates of both elements is attached to the lower surface of the lower plate of one element, extending over the entire length of the lower plate on its longitudinal side, so as to protrude from the lower plate.

The invert block of the present invention described in claim 3 is characterized in that, in the invention described in claim 2, the connecting plate attached to the upper plate of one of the elements has a through hole, and the upper plate of the other element is attached from above so that a connecting bolt that passes through the through hole and screws into a nut can be tightened.

The invert block of the present invention described in claim 4 is characterized in that, in the invention described in claim 3, the through-hole is an elongated hole formed in the axial direction of the tunnel.

The invert block of the present invention described in claim 5 is characterized in that, in the invention described in claim 4, the element is provided with a short-direction side plate which is the side plate along the short direction of the element, and a closing plate is provided between two short-direction side plates of adjacent elements to close the gap formed according to the fastening position of the connecting bolt and the nut to the elongated hole.

The invert block of the present invention described in claim 6 is characterized in that, in the invention described in claim 5, the closing plate is welded to the outer surface of one of the short-side plates, with a portion of it protruding in the tunnel axial direction so as to overlap the short-side plate of the adjacent element.

The invert block of the present invention described in claim 7 is characterized in that, in the invention described in claim 2, a sealing material is attached to the upper surface of the connecting plate attached to the lower plate of one of the elements, thereby sealing the space between it and the other element.

According to the invert block of the present invention, the invert block is constructed and installed in the tunnel bottom ground simply by setting up multiple steel elements on-site and connecting them to each other via connecting plates. Therefore, by using the invert block of the present invention, it becomes possible to prevent ground swelling in tunnels in a short construction period, at low cost, and easily.

This is a plan view showing an invert block, which is one embodiment of the present invention, installed on the ground at the bottom of a tunnel by connecting two blocks along the circumferential direction of the tunnel through which vehicles pass. This is a cross-sectional view of the invert block shown in Figure 1, which is embedded in the ground at the bottom of the tunnel, and the lower half of the tunnel, taken from the circumferential direction of the tunnel. This is a cross-sectional view of the end portion in the installation direction and the element other than both ends of the invert block, which is one embodiment of the present invention. This is a cross-sectional view along the short direction of the element at the rear end in the installation direction, which is one of the two ends of the invert block that constitutes one embodiment of the present invention. This is an explanatory diagram showing the short-side plates of adjacent elements. (a) is an explanatory diagram showing the relationship between the short-side plate and the closing plate before adjacent elements are connected, and (b) is an explanatory diagram showing the relationship between the short-side plate and the closing plate after adjacent elements are connected. This is a plan view showing the flow direction of the concrete poured into the invert block shown in Figure 1. This is a cross-sectional view of Figure 7. Figure 1 shows a diagram illustrating the process of bringing in the excavation machine, which is one step in the continuous installation of the invert blocks along the axial direction of the tunnel. (a) is an explanatory diagram viewed from above, and (b) is an explanatory diagram viewed from a cross-sectional view of the tunnel along the axial direction. The following diagram shows the initial excavation process, with (a) being an explanatory diagram viewed from above and (b) being an explanatory diagram viewed from the axial cross-section of the tunnel. The following diagram shows the floor-laying machinery installation process, with (a) being an explanatory diagram viewed from above and (b) being an explanatory diagram viewed from the axial cross-section of the tunnel. The following diagram shows the excavation and bed preparation process, with (a) being an explanatory diagram viewed from a plan view and (b) being an explanatory diagram viewed from an axial cross-section of the tunnel. The following diagram shows the unloading and transport machinery installation process, with (a) being an explanatory diagram viewed from above and (b) being an explanatory diagram viewed from the axial cross-section of the tunnel. The following diagram shows the entry and exit process of the material transport vehicle, following Figure 13. (a) is an explanatory diagram viewed from above, and (b) is an explanatory diagram viewed from the axial cross-section of the tunnel. The following diagram shows the unloading process of the components, following Figure 14. (a) is an explanatory diagram viewed from above, and (b) is an explanatory diagram viewed from the axial cross-section of the tunnel. The following diagram shows the temporary placement process of the components, as shown in Figure 15. (a) is an explanatory diagram viewed from above, and (b) is an explanatory diagram viewed from the axial cross-section of the tunnel. The following diagram shows the component installation process, with (a) being an explanatory diagram viewed from above and (b) being an explanatory diagram viewed from the axial cross-section of the tunnel. The following diagram shows the backfill injection process, which follows Figure 17. (a) is an explanatory diagram viewed from above, and (b) is an explanatory diagram viewed from the axial cross-section of the tunnel. The following diagram shows the process of bringing in backfilling machinery, following Figure 18. (a) is an explanatory diagram viewed from above, and (b) is an explanatory diagram viewed from the axial cross-section of the tunnel. The following diagram shows the backfilling process, with (a) being an explanatory diagram viewed from above and (b) being an explanatory diagram viewed from the axial cross-section of the tunnel. The following diagram shows the compaction process, with (a) being an explanatory diagram viewed from above and (b) being an explanatory diagram viewed from the axial cross-section of the tunnel. The following diagram shows the process of removing heavy machinery and bringing in paving machinery, following Figure 21. (a) is an explanatory diagram viewed from above, and (b) is an explanatory diagram viewed from the axial cross section of the tunnel. The following diagram shows the temporary paving process, as shown in Figure 22. (a) is an explanatory diagram viewed from above, and (b) is an explanatory diagram viewed from the axial cross-section of the tunnel. The following diagram shows the temporary pavement removal and excavation process, with (a) being an explanatory diagram viewed from above and (b) being an explanatory diagram viewed from the axial cross-section of the tunnel. These diagrams illustrate the temporary pavement removal process, which is one step in pouring concrete into the buried invert blocks. (a) is an explanatory diagram viewed from above, and (b) is an explanatory diagram viewed from the axial cross-section of the tunnel. The following diagram shows the concrete pouring commencement process, following Figure 25. (a) is an explanatory diagram viewed from above, and (b) is an explanatory diagram viewed from the axial cross-section of the tunnel. The following diagram shows the concrete pouring process, following Figure 26. (a) is an explanatory diagram viewed from above, and (b) is an explanatory diagram viewed from the axial cross-section of the tunnel. The following diagram shows the temporary repaving process, which follows Figure 27. (a) is an explanatory diagram viewed from above, and (b) is an explanatory diagram viewed from the axial cross-section of the tunnel.

The following describes an embodiment of the present invention in detail with reference to the drawings. In the drawings illustrating the embodiment, the same reference numerals are generally used for identical components, and repeated descriptions are omitted.

Figure 1 is a plan view showing two invert blocks, one embodiment of the present invention, connected together along the circumferential direction of a tunnel through which vehicles pass, and installed in the ground at the bottom of the tunnel. Figure 2 is a cross-sectional view showing the invert blocks of Figure 1 embedded in the ground at the bottom of the tunnel and the lower half of the tunnel, viewed from the circumferential direction of the tunnel. Figure 3 is a cross-sectional view of the end portions of the invert block, one embodiment of the present invention, along the installation direction and the elements other than the end portions, along the short direction. Figure 4 is a cross-sectional view of the element at the rear end portion of the invert block, one embodiment of the present invention, along the short direction.

As shown in Figures 1 and 2, the invert blocks 10 of this embodiment are installed and buried in the ground at the bottom of the tunnel T, with two blocks connected in a reverse arch shape in the circumferential direction of the tunnel T. In this embodiment, the width of one invert block 10 corresponds to the width of one lane. Therefore, the invert blocks 10 of this embodiment are laid in the ground at the bottom of a tunnel T with two lanes (one-way traffic with two lanes on each side or two-way traffic with one lane on each side).

In the actual installation process, the invert blocks 10 are installed across the entire lane of one lane, and then the invert blocks 10 are installed across the entire lane of the other lane, connecting them to the existing invert blocks 10. Furthermore, in some tunnels, three or more invert blocks may be connected circumferentially around the tunnel T to form an inverted arch.

As shown in Figure 1, the invert block 10 has an elongated shape that extends in the circumferential direction of the tunnel T in which it is installed, and is composed of four steel elements 10e that are interconnected in the axial direction along their longitudinal side. These elongated elements 10e are installed along the circumferential direction of the tunnel T. Specifically, elements 10e-1 and 10e-4 located at both ends, and two elements 10e-2 and 10e-3 located between them, are installed along the circumferential direction of the tunnel T and are connected in parallel to each other in the axial direction (installation direction) of the tunnel T. Note that the number of elements 10e does not necessarily have to be four; two or more elements are acceptable.

The invert block 10 comprises an upper plate 10ts, a lower plate 10us, and side plates 10sf, each separated into elements 10e. That is, the invert block 10, when these elements 10e are integrated, forms a box-shaped hollow structure consisting of the upper plate 10ts, the lower plate 10us, and the side plates 10sf. The side plates 10sf consist of a longitudinal side plate 10sf-1 (located in the axial direction of the tunnel) and a short-direction side plate 10sf-2 (located in the circumferential direction of the tunnel). The elements 10e-1 and 10e-4 at both ends comprise an upper plate 10ts, a lower plate 10us, a longitudinal side plate 10sf-1, and a short-direction side plate 10sf-2. Furthermore, elements 10e-2 and 10e-3 are equipped with an upper plate 10ts, a lower plate 10us, and a short-side plate 10sf-2. These upper plate 10ts, lower plate 10us, and side plate 10sf are welded to each other for each element 10e.

Figures 2 and 8 (described later) show the invert blocks 10 embedded in temporary pavement. Details leading up to the temporary pavement will be described later, but in this embodiment, the temporary pavement consists of a subgrade RB formed on the invert blocks 10, with a pavement layer L (a layer in which the lower subbase L1 (crushed stone), upper subbase L2 (grade-adjusted crushed stone), base layer L3 (coarse-graded asphalt concrete), and surface layer L4 (dense-graded asphalt concrete) are sequentially layered on top of the subbase RB.

Here, as shown in Figures 3 and 4, inside the connecting opening 10ea of the element 10e, which is formed on the longitudinal side where the elements 10e are connected, ribs 10eb are welded perpendicular to the upper and lower plates 10ts and 10us, extending along the longitudinal direction and facing each other. A support member 11 is installed on this rib 10eb to support loads from above. As shown in Figure 2, the support member 11 is truss-shaped, generating compressive force from the load from above, but less susceptible to bending moment. Furthermore, the truss shape creates gaps between the support members 11, thereby connecting the internal spaces of each element 10e that constitute the hollow invert block 10.

Furthermore, the support member 11 does not need to be truss-shaped; for example, it can be a vertical grid shape, or any other structure that supports loads from above and creates a space where the insides of the elements 10e are interconnected (more specifically, a space large enough for concrete to be poured in a later step to flow from one element 10e to the other).

Furthermore, connecting plates 10ed and 10ef are provided at the points where the elements 10e are connected, so as to span both elements 10e. Specifically, a connecting plate 10ed, which has an elongated hole (not shown) formed in the axial direction (installation direction) of the tunnel, is attached to the lower surface of the upper plate 10ts of one element 10e, extending along the entire length of the upper plate 10ts so as to protrude from the upper plate 10ts. Also, a connecting plate 10ef, which has a sponge-type sealing material 10ee attached to its upper surface, is attached to the lower surface of the lower plate 10us of one element 10e, extending along the entire length of the lower plate 10us so as to protrude from the lower plate 10us. Therefore, the protruding portions of the connecting plates 10ed and 10ef overlap with the upper plate 10ts and lower plate 10us of the other element 10e, so that the connecting plates 10ed and 10ef are positioned to span both elements 10e. Furthermore, a connecting bolt 10eg is attached to the upper plate 10ts of the other element 10e so that it can be tightened from above, passing through the aforementioned elongated hole formed in the connecting plate 10ed and screwing into the nut 10ec.

Thus, the connecting bolt 10eg passes through an elongated hole formed in the connecting plate 10ed, which is elongated in the axial direction (installation direction) of the tunnel. This elongated hole acts as an adjustment allowance, allowing the connecting bolt 10eg to be screwed into the nut 10ec without being affected by the misalignment in the installation direction when connecting the elements 10e. In other words, since the fastening position of the connecting bolt 10eg and the nut 10ec with respect to the elongated hole can be adjusted, depending on the ground conditions in which the elements 10e are installed, when they can be installed in close contact, the connecting bolt 10eg and the nut 10ec can be screwed into the elongated hole at the position in the close contact state. When the elements 10e cannot be installed in close contact and are misaligned in the installation direction, the connecting bolt 10egt and the nut 10ec can be screwed into the elongated hole at the position in the misaligned state. However, if it is not necessary to consider the misalignment in the installation direction when connecting the elements 10e, a round hole with a diameter through which the connecting bolt 10eg can pass may be formed in the connecting plate 10ed instead of an elongated hole.

When the elements 10e are installed in close contact, only small gaps are formed between the upper plates 10ts, lower plates 10us, and short-side plates 10sf-2 of both elements 10e. However, when the elements 10e are installed offset from each other in the installation direction, gaps equal to the offset are formed between the upper plates 10ts, lower plates 10us, and short-side plates 10sf-2. These gaps (the small gap formed when the elements 10e are installed in close contact, and the gap corresponding to the offset formed when the elements 10e are installed offset from each other) are closed by the connecting plate 10ed between the upper plates 10ts, by the connecting plate 10ef between the lower plates 10us, and by the closing plate 10eh (described later) between the short-side plates 10sf-2.

Furthermore, the sealing material 10ee is designed to be compressed (for example, compressed to less than 1 mm) by being pressed down from above by the lower plate 10us of the other element 10e when the two elements 10e are connected, thereby creating a seal.

Therefore, by screwing the connecting bolt 10eg into the nut 10ec, the two adjacent elements 10e are connected to each other via the upper connecting plate 10ed, and the sealing material 10ee of the lower connecting plate 10ef is crushed and sealed, making it difficult for soil and sand to enter the hollow invert block 10 from the outside.

Furthermore, the sealing material 10ee may also be provided along its entire length on the upper surface of the connecting plate 10ed, which is attached to the upper plate 10ts.

Support bolts 15 are attached to the lower plate 10us of element 10e, protruding downwards. These support bolts 15 adjust the height of element 10e by inserting a base 16 between the lower end of the support bolt 15 and the ground when element 10e is installed on the ground. They are provided at both ends of the element 10e in the longitudinal direction.

Furthermore, nuts 17 that engage with the support bolts 15 are fixed by welding to the holes through which each support bolt 15 passes through the lower plate 10us of element 10e.

Element 10e-1 (starting end element), located at the end of the invert block 10 and the first element installed when the invert block 10 is formed, is provided with two support bolts 15 at each of its longitudinal ends, for a total of four bolts. The other elements 10e-2, 10e-3, and 10e-4 are provided with one support bolt 15 at each of their longitudinal ends, for a total of two bolts. This is because element 10e-1 needs to be stabilized with four support bolts 15 because it is the first element to be installed, whereas elements 10e-2, 10e-3, and 10e-4 are connected sequentially to the existing elements 10e-1, 10e-2, and 10e-3, respectively, and can be stabilized with two support bolts 15. However, the number of support bolts 15 is not limited to the four or two bolts mentioned above, and any number greater than or equal to that shown in this embodiment is acceptable. In the illustration, the support bolts 15 on elements 10e-2, 10e-3, and 10e-4 are shown at both ends in the longitudinal direction, on the side facing the element installation direction. However, their position is not necessarily limited to this; for example, they could be on the opposite side of the element installation direction.

As shown in Figure 3, the support bolt 15 on the opposite side of the element installation direction of the initially installed element 10e-1 (the support bolt 15 shown on the left side of element 10e-1 in Figure 3) is located at the back, making it difficult for an operator to reach it through the connection opening 10ea. Therefore, the support bolt 15 at this location is housed within a bolt hole H4 that penetrates the element 10e vertically, and a wrench hole (such as a hexagonal wrench hole) is formed in its head. A long wrench (such as a hexagonal wrench) is inserted from the top of the bolt hole H4 to rotate the support bolt 15 and adjust the height of element 10e-1.

Furthermore, as also shown in Figure 3, the support bolt 15 located on the element installation side of element 10e-1 (the support bolt 15 shown to the right of element 10e-1 in Figure 3), and the support bolts 15 of elements 10e-2 and 10e-3 located between element 10e-1 and element 10e-4 (the element located at the end of the invert block 10 and the last element installed when the invert block 10 is formed: the terminal element) (the support bolts 15 shown for elements 10e-2 and 10e-3 in Figure 3) are positioned so that they can be rotated from the connection opening 10ea, as they are within reach of the worker by reaching through the connection opening 10ea.

Furthermore, as shown in Figure 4, the support bolt 15 of element 10e-4 is positioned to rotate from the gap between element 10e-4 and the ground, because when element 10e-4 is connected to the adjacent element 10e-3, it becomes impossible for an operator to reach through the connection opening 10ea. In this case, as shown in the figure, the support bolt 15 is screwed in from below the bottom plate 10us upwards so that the head 15a of the support bolt 15 (i.e., the part that rotates the support bolt) is between element 10e-4 and the ground.

Here, the structure of the side plate 10sf of the invert block 10 will be explained using Figures 5 and 6. Figure 5 is an explanatory diagram showing the short-side plate of adjacent elements, and Figure 6 is an explanatory diagram showing the relationship between the short-side plate and the closing plate of adjacent elements; (a) shows the adjacent elements before connection, and (b) shows the adjacent elements after connection.

The invert block 10 is equipped with separate side plates 10sf (longitudinal side plate 10sf-1, transverse side plate 10sf-2) for each element 10e. Between the transverse side plates 10sf-2 of adjacent elements 10e, a gap is formed corresponding to the fastening position of the connecting bolt 10eg and nut 10ec in the elongated hole formed in the connecting plate 10ed, as described above (see Figure 6(a)).

If this gap is left as is, soil and sand will enter the hollow invert block 10, and concrete will leak out through the gap when it is poured in a later step. Therefore, as shown in Figures 5 and 6(a), a closing plate 10eh is provided to close the gap formed between the two short-side plates 10sf-2 when the elements 10e (in this case, element 10e-1 and element 10e-2) are connected.

This closing plate 10eh is welded to the outer surface of the side end of the short-side plate 10sf-2 of one element 10e (element 10e-2 in the illustration), with a portion of it overlapping the short-side plate 10sf of the adjacent element (element 10e-1 in the illustration) in the tunnel axial direction. This ensures that the gap formed when two elements 10e (in this case, elements 10e-1 and 10e-2) are connected is closed by the closing plate 10eh. It is desirable that, after connecting two elements 10e, the gap between the other element 10e (in this case, element 10e-1) and the closing plate 10eh be welded or sealed with a pre-installed sealing material.

Now, in Figure 1, multiple (two in this case) H-shaped steel piles 12 are erected. These piles 12 serve both as support posts for guardrails separating the two lanes and as main piles for sheet piles used during ground excavation (sheet piles acting as retaining walls when excavating the ground for the installation of the invert blocks 10). Therefore, the elements 10e constituting the invert blocks 10 have recesses formed to avoid interference with the piles 12.

Furthermore, as shown in Figure 1, elements 10e-1 and 10e-4 located at both ends of the invert block 10 in the installation direction (tunnel axis direction) have connecting holes 13 formed in the upper plate 10ts, with nuts fixed to the inside. These connecting holes 13 are for connecting adjacent invert blocks 10 via connecting plates (not shown). That is, by screwing a bolt through a through-hole formed in the connecting plate into the nut in the connecting hole 13, the connecting plate is fixed to the invert block 10. Then, by bolting the same connecting plate to an adjacent invert block 10, the adjacent invert blocks 10 are connected via the connecting plates. Note that the connecting holes 13 may be located in only one place, rather than multiple locations as in this embodiment.

Furthermore, as shown in Figure 2, each element 10e is provided with two lifting fittings 14 at two locations along its longitudinal direction on the upper plate 10ts. These fittings allow the element 10e to be suspended by a wire from a crane (such as a crawler crane) and installed on the ground at the bottom of the tunnel T.

Furthermore, as shown in Figures 1, 3, and 4, each element 10e is provided with a grout injection hole H3 for injecting grout between the element 10e and the ground when installed in the tunnel bottom ground, thereby filling the void between the element 10e and the ground. This grout injection hole H3 is cylindrical, penetrating the element 10e vertically (i.e., isolated from the hollow internal space). Therefore, grout injected from the upper grout injection hole H3 passes through the cylindrical grout injection hole H3 and fills the space between the element 10e and the ground.

As shown in Figure 1, the upper plate 10ts of the invert block 10 has concrete pouring holes H1 for pouring concrete into the hollow interior in a subsequent process, and concrete blowing holes H2 for blowing out the poured concrete.

As shown in the figure, the concrete placement hole H1 is formed at one location on the upper plate 10ts of the invert block 10 when it is installed in the ground at the bottom of the tunnel T (near the center on the side opposite the side wall of the tunnel T where it is installed). The concrete blowout holes H2 are formed at two locations on the upper plate 10ts of the invert block 10 when it is installed in the ground at the bottom of the tunnel T (at the corners on the side wall side of the tunnel T where it is installed). Note that the number and location of the concrete placement holes H1 and concrete blowout holes H2 are not limited to the example shown in this embodiment. However, it is desirable that the concrete blowout holes H2 be formed at the corners on the side wall side of the tunnel T where it is installed so that the air inside can be smoothly discharged during concrete placement.

In this embodiment, the invert block 10, composed of four (even) elements 10e, has the concrete pouring hole H1 formed in element 10e-2, one of the two elements 10e (10e-2, 10e-3) located in the central part. However, if there is an even number of elements 10e and these elements 10e are installed with a slope in the axial direction of the tunnel T, it is desirable to form the concrete pouring hole H1 in the element 10e located at the lower position among the two elements 10e located in the central part. In the case of an invert block 10 composed of an odd number of elements 10e, the concrete pouring hole H1 is formed in the element 10e located in the center.

Furthermore, concrete pouring holes H1 may be formed in two or more locations (i.e., at least one on the side opposite the side wall of the tunnel T where it will be installed is sufficient), and concrete blowout holes H2 may be formed in three or more locations (i.e., at least two on both sides of the side wall of the tunnel T where it will be installed are sufficient).

Furthermore, in a subsequent process, concrete is poured with the invert block 10 embedded in the ground at the bottom of the tunnel T. Therefore, as shown in Figure 2, connecting pipes P are attached upwards to the concrete pouring hole H1 and the concrete blowout hole H2. This allows for concrete pouring into and blowing out of the invert block 10 simply by exposing the connecting pipes P from the ground where the invert block 10 is embedded. A detachable cap (not shown) is attached to the tip of the connecting pipe P to prevent soil and sand from entering the pipe when concrete is not being poured.

In this embodiment, the connecting pipe P is a steel pipe with a diameter of approximately 6 inches, and has the same diameter as the pressure pipe (a pipe attached to a concrete pump truck for pumping concrete) that is connected via a joint when concrete is placed in a subsequent process. However, the diameter of the connecting pipe P is determined according to the diameters of the concrete placement hole H1 and concrete discharge hole H2, and the diameter of the pressure pipe, and is not limited to 6 inches in this embodiment.

Here, the flow of concrete when pouring concrete into the invert block 10 in the subsequent process (the process after installing the invert block 10) will be explained using Figures 7 and 8. Figure 7 is a plan view showing the flow direction of the concrete poured into the invert block in Figure 1, and Figure 8 is a cross-sectional view of Figure 7.

As described above, the concrete pouring hole H1 is formed at a lower position on the upper plate 10ts of the invert block 10 when it is installed in the ground at the bottom of the tunnel T, and the concrete blowout hole H2 is formed at a higher position on the upper plate 10ts of the invert block 10 when it is installed in the ground at the bottom of the tunnel T.

Therefore, as shown in Figures 7 and 8, when concrete C is poured into the invert block 10 from the concrete pouring hole H1 formed in element 10e-2 (more specifically, the connecting pipe P attached to the concrete pouring hole H1), the concrete C flows from directly below the concrete pouring hole H1 through the gap in the support member 11 to the other elements 10e-1, 10e-3, and 10e-4, filling the hollow structure by pushing out the air inside through the concrete blowing hole H2. Then, when the concrete C is blown out from the highest concrete blowing hole H2 (more specifically, the connecting pipe P attached to the concrete blowing hole H2), it can be inferred that the entire interior of the invert block 10 has been filled with concrete C.

As shown in Figure 8, the tips of the connecting pipes P attached to the concrete pouring hole H1 and the connecting pipes P attached to the concrete blowing hole H2 are located at the boundary between the base layer L3 and the upper subgrade L2 that constitute the pavement roadbed L (i.e., the boundary between the subgrade layer (lower subgrade L1, upper subgrade L2) and the asphalt layer (base layer L3, surface layer L4)). Therefore, when pouring concrete C into the embedded invert block 10 in a subsequent process, the two layers of the surface layer L4 and base layer L3 (i.e., the asphalt layer) should be peeled off to expose the tips of the connecting pipes P, the cover should be removed, and the connecting pipe P attached to the concrete pouring hole H1 should be connected to the pumping pipe from the pump truck via a joint (not shown).

By attaching connecting pipes P to the concrete pouring holes H1 and concrete discharge holes H2 in this manner, when pouring concrete into the invert block 10, it is only necessary to peel off the asphalt layers L3 and L4 to expose the tips of the connecting pipes P. This eliminates the need to remove the subgrade RB to expose the invert block 10 itself, thus simplifying the concrete pouring process.

In this embodiment, the lower subbase L1, upper subbase L2, base layer L3, and surface layer L4 are sequentially stacked to form the pavement subbase L, and the tip of the connecting pipe P is located at the boundary between the base layer L3 and the upper subbase L2. However, the composition of the pavement subbase L and the position of the connecting pipe P's tip are not limited to this. In other words, the pavement subbase L is formed from the subbase layer and the asphalt layer stacked on top of the subbase layer, and the tip of the connecting pipe P only needs to be at or below the boundary between the subbase layer and the asphalt layer (i.e., below the asphalt layer). If the tip of the connecting pipe P is below the boundary between the subbase layer and the asphalt layer, when pouring concrete C into the invert block 10, the surface layer L4 and base layer L3 (i.e., the asphalt layer) and a portion of the subbase layer are peeled off to expose the tip of the connecting pipe P.

Here, the area to be stripped of the temporary pavement may be the entire area where the invert blocks 10 for concrete placement are embedded, or it may be just the area around the connecting pipe P. However, when constructing a highway, it is desirable to strip the temporary pavement over the entire area where the invert blocks 10 for concrete placement are embedded. When constructing a general road, it may be sufficient to strip only the temporary pavement around the connecting pipe P.

As described above, the invert block 10 of this embodiment is composed of four elongated steel elements 10e that are interconnected axially along their longitudinal sides, and has a hollow structure with an upper plate 10ts, a lower plate 10us, and a side plate 10sf. A support member 11 is installed inside the connection opening 10ea formed on the longitudinal side where the elements 10e are connected, allowing the internal spaces of both elements 10e to communicate and supporting loads from above.

Therefore, by simply installing four steel elements 10e on-site and connecting them to each other, the invert block 10 is constructed and installed in the ground at the bottom of the tunnel. This avoids the lengthy construction period associated with installing inverts using cast-in-place concrete, and eliminates the increased costs and difficult installation work associated with transporting and installing precast inverts into the tunnel.

Therefore, by using the invert block 10 of this embodiment, it becomes possible to perform tunnel bulging prevention construction in a short construction period, at low cost, and easily.

Next, the process for installing the invert block 10 described above into tunnel T will be explained using Figures 9 to 24. Here, as an example, we will describe the case where the invert block 10 is installed under one lane in a tunnel T that is a one-way tunnel with two lanes in each direction.

Figure 9 is an explanatory diagram showing the excavation machine delivery process, which is one step in the continuous installation of the invert blocks shown in Figure 1 along the axial direction of the tunnel; Figure 10 is an explanatory diagram showing the initial excavation process following Figure 9; Figure 11 is an explanatory diagram showing the floor-laying machine delivery process following Figure 10; Figure 12 is an explanatory diagram showing the excavation and floor-laying process following Figure 11; Figure 13 is an explanatory diagram showing the unloading and transport machine delivery process following Figure 12; Figure 14 is an explanatory diagram showing the entry and withdrawal process of the material transport vehicle following Figure 13; Figure 15 is an explanatory diagram showing the material unloading process following Figure 14; Figure 16 Figure 15 is an explanatory diagram showing the temporary placement of components, Figure 17 is an explanatory diagram showing the component installation process, Figure 18 is an explanatory diagram showing the backfill injection process, Figure 19 is an explanatory diagram showing the backfilling machinery delivery process, Figure 20 is an explanatory diagram showing the backfilling process, Figure 21 is an explanatory diagram showing the compaction process, Figure 22 is an explanatory diagram showing the heavy equipment removal and paving machinery delivery process, Figure 23 is an explanatory diagram showing the temporary paving process, Figure 24 is an explanatory diagram showing the temporary pavement removal and excavation process, Figure 23. In these drawings, (a) is an explanatory diagram viewed from above, and (b) is an explanatory diagram viewed from the axial cross-section of the tunnel.

First, as shown in Figure 9, one lane is designated as a restricted zone where general vehicle traffic is restricted in order to lay the invert blocks 10, while the other lane is designated as a traffic lane where general vehicle traffic is permitted. Then, a trailer 21 equipped with a backhoe (for example, a 0.45-class backhoe) 20 is brought in from the traffic lane into the restricted zone, and the backhoe 20 is unloaded and transported into the restricted zone (excavation machine transport process). The trailer 21 then exits the tunnel from the end of the restricted zone (the end opposite the entrance).

In this embodiment, a backhoe is used as the heavy machinery for excavating the ground, but a hydraulic excavator other than a backhoe may also be used.

Next, as shown in Figure 10, a dump truck (for example, a 10-ton dump truck) 22 is moved from the traffic lane into the restricted area and then reversed to the loading position for the excavated soil. Then, the backhoe 20 is used to excavate the soil in the restricted area and load it onto the dump truck 22 (initial excavation process). Once the dump truck 22 has loaded the specified weight of soil, it exits the tunnel from the end of the restricted area.

Next, as shown in Figure 11, a trailer 21 equipped with a small backhoe (for example, a 0.1-class backhoe) 23, which serves as the floor-setting machine, is brought in from the traffic lane into the restricted area. The backhoe 23 is then lowered between the backhoe 20 and the excavated area (the area excavated by the backhoe 20) S (floor-setting machine delivery process). Since the trailer 21 cannot proceed through the restricted area due to the backhoe 20 in front, safety is ensured by a speed control vehicle (not shown) introduced into the traffic lane, which regulates the speed of following general vehicles. The trailer 21 then exits the restricted area into the traffic lane and out of the tunnel when it is ahead of the speed control vehicle.

Next, as shown in Figure 12, the backhoe 20 excavates the soil in the restricted area and loads it onto the dump truck 22. Simultaneously, a small backhoe 23 is used to level the excavated area S (excavation and leveling process). Once the dump truck 22 has loaded the specified weight of soil, it exits the tunnel from the end of the restricted area.

Next, as shown in Figure 13, a trailer (not shown) equipped with a crawler crane (e.g., a 4.9-ton lifting crawler crane) 24, which serves as unloading and transporting machinery, is brought in from the traffic lane into the restricted area. The crawler crane 24 is lowered in front of the excavated area S (on the opposite side of the direction in which excavation and bed preparation are being carried out in the excavated area S) (unloading and transporting machinery installation process). Since the trailer cannot proceed through the restricted area due to the excavated area S ahead, safety is ensured by a speed control vehicle (not shown) introduced into the traffic lane, which regulates the speed of following general vehicles. The trailer exits the restricted area into the traffic lane and leaves the tunnel when it is ahead of the speed control vehicle. During this time, the excavation and bed preparation process (see Figure 12) continues.

Next, as shown in Figure 14, a dump truck (e.g., a 4-ton dump truck) 25, which is used as a material transport vehicle and loaded with element 10e, is moved from the traffic lane between the excavated area S of the restricted zone and the crawler crane 24, and then reversed to near the crawler crane 24 (material transport vehicle entry and reversal process). During this time, the excavation and bed preparation process (see Figure 12) continues.

Next, as shown in Figure 15, the elements 10e loaded onto the dump truck 25 are unloaded using the crawler crane 24 (component unloading process). During this time, the excavation and bed preparation process (see Figure 12) continues.

Next, as shown in Figure 16, the unloaded elements 10e are temporarily placed in front of the excavated area S (temporary placement of components). During this time, the excavation and bed preparation process (see Figure 12) continues. Furthermore, the dump truck 25 carrying the elements 10e cannot proceed through the restricted area because of the excavated area S ahead. Therefore, safety is ensured by a speed control vehicle (not shown) introduced into the traffic lane, which regulates the speed of following general vehicles. The dump truck exits the restricted area into the traffic lane and exits the tunnel when it is ahead of the speed control vehicle. During this time, the excavation and bed preparation process (see Figure 12) continues.

Next, as shown in Figure 17, the crawler crane 24 is used to install the unloaded elements 10e into the excavated area S (member installation process). That is, as shown in the figure, the longitudinal direction of the elements 10e is oriented in the direction of the tunnel circumference, and the crawler crane 24 installs the elements 10e along the axial direction (installation direction) of the tunnel T. Then, the expansion and contraction of the support bolts 15 is adjusted to align the heights of the four elements 10e, and the connecting bolts 10eg are screwed into nuts 10ec to connect the elements 10e, forming an integrated invert block 10 (see Figures 3 and 4).

As mentioned above, in this embodiment, four elements 10e are installed to form a single invert block 10. The axial length of the tunnel T formed by these elements 10e is, for example, 3m. However, this length varies depending on the number of elements 10e installed and their widths, and is not limited to 3m. During this time, the excavation and bed preparation process (see Figure 12) continues.

Here, the tasks of installing (mounting) the elements 10e, aligning the heights of the installed elements 10e, and connecting the elements 10e with aligned heights to form the invert block 10 may be performed on an element 10e-by-element basis, or they may be performed collectively on all elements 10e constituting the invert block 10.

More specifically, the invert block 10 may be formed by repeatedly installing each element 10e one by one, aligning their heights, and connecting them. Alternatively, the invert block 10 may be formed by repeatedly installing each element 10e that constitutes the invert block 10, aligning their heights, and then connecting all the elements 10e at once. Alternatively, all the elements 10e that constitute the invert block 10 may be installed at once, the heights of all the elements 10e constituting the invert block 10 may be aligned at once, and all the elements 10e constituting the invert block 10 may be connected at once to form the invert block.

Next, once one invert block 10 has been formed, grout (backfill material) G is injected between the invert block 10 and the installation ground, as shown in Figure 20 (backfill injection process). In this embodiment, a rapid-strength type grout G, which exhibits excellent early strength development and reaches high strength in a short time, is used. However, other types of grout may also be used.

In this process, first, to prevent the injected grout G from flowing out, a spill-prevention wall W made of concrete panels (plywood) or the like is erected on the side of the invert block 10 (specifically, the side of element 10e-4 on the tunnel axial end side and the side of the invert block 10 on the tunnel side wall side), and sandbags D are placed outside the spill-prevention wall W to prevent it from collapsing. Then, a dump truck (for example, a 2-ton dump truck) 26 loaded with grout G and grout pumping equipment GE such as a pump for pumping the grout G is brought into the restricted zone, and the grout G is injected between the bottom surface of the invert block 10 and the installation ground through the grout injection holes H3 (see Figures 1, 3, and 4) provided in each element 10e. In this embodiment, the grout is injected after one day's worth of construction. However, the timing of grout injection is not limited to after one day's worth of construction, and other injection timings are also possible. Furthermore, the components used to prevent the collapse of the runoff prevention wall W may be other than sandbags D.

Furthermore, between the backfill material injection process and the backfilling process described later, connecting pipes P (see Figures 2 and 8) are attached to the concrete pouring holes H1 and concrete blowout holes H2 formed in each element 10e. A cap (not shown) is placed over the end of the connecting pipe P to prevent soil from entering. However, the connecting pipes P are not shown in Figures 18 to 24. During this time, the excavation and base preparation process (see Figure 12) continues.

Next, once the grout has hardened, the runoff prevention wall W and sandbags D are removed, and as shown in Figure 19, a backhoe (for example, a 0.45 class backhoe) 27 for backfilling with subgrade material and a compaction roller 28 for compacting the backfilled subgrade material are brought into the restricted area (backfilling machine delivery process). During this time, the excavation and subgrade preparation process (see Figure 12) continues.

Next, as shown in Figure 20, a dump truck (e.g., a 4-ton dump truck) 29 loaded with backfill soil (subgrade material) is moved from the traffic lane into the restricted area and introduced between the backhoe 27 and the compaction roller 28. The backhoe 27 then transfers the subgrade material from the dump truck 29 onto the invert blocks 10 (i.e., interconnected and integrated elements 10e) to backfill that section (backfilling process). In Figure 20 and the following Figure 21, the symbol ES indicates the subgrade material, which is the backfill soil. The dump truck 29, now empty after the subgrade material has been transferred, moves from the restricted area to the traffic lane and exits the tunnel. During this time, the excavation and subgrade preparation process (see Figure 12) continues. Furthermore, while the illustration shows backfilling after installing the number of elements 10e required to form one invert block 10, it is also possible to backfill after installing the number of elements 10e required to form multiple invert blocks 10.

Next, as shown in Figure 21, the subgrade material ES is compacted with a compaction roller 28 to form the subgrade RB (Figure 22) (compaction process). During this compaction process, the subgrade material ES is compacted, so the surface of the formed subgrade RB is lower than the surrounding road surface (see Figure 22). During this time, the excavation and subgrade preparation process (see Figure 12) continues.

For example, if the restricted zone is opened to general traffic on Saturdays and Sundays, and Monday through Friday is considered one work unit, then the processes described above, from the excavation and bed preparation process (Figure 12) to the compaction process (Figure 21), are repeated sequentially from Monday to Thursday to form a continuous invert block structure in which the invert blocks 10 are continuously installed along the axial direction of the tunnel. These are then embedded in the roadbed RB, which is made of compacted roadbed material ES. Here, adjacent invert blocks 10 are connected by screwing bolts through through holes formed in the connecting plates into nuts in the connecting holes 13, as described above, to ensure that their heights are aligned.

Furthermore, the work unit and the process within each work unit are not limited to those described in this embodiment and can be freely configured.

After the final compaction process on Thursday (Figure 21) is completed, as shown in Figure 22, various excavation equipment other than the compaction roller 28 is removed from the tunnel, and paving equipment such as the asphalt finisher 33 is brought in (excavation equipment removal and paving equipment arrival process). Depending on the progress of the work, as shown in Figure 22, the backfilled excavated area S may contain areas where invert blocks 10 are embedded and areas where they are not.

Next (in this embodiment, on Friday), as shown in Figure 23, temporary paving is carried out on the excavated area S, which was excavated from Monday to Thursday (temporary paving process). This is done to minimize the impact on general traffic caused by one-way traffic for construction, as the restricted zone is opened to general vehicles on Saturday and Sunday, as mentioned above. In this embodiment, temporary paving is carried out by forming a pavement layer L on top of the subgrade RB, by sequentially stacking the lower subgrade L1, upper subgrade L2, base layer L3, and surface layer L4. After the temporary paving is completed, the paving heavy machinery that was brought in is removed and the restricted zone is opened.

Next (in this embodiment, on the following Monday), as shown in Figure 24, the temporary pavement in the excavated area S where the invert blocks 10 are not embedded is removed using the backhoe 20 (temporary pavement removal process). Then, the processes described above, from the excavation and base preparation process (Figure 12) to the compaction process (Figure 21), are repeated sequentially from Monday to Thursday. Furthermore, after the final compaction process on Thursday (Figure 21), the excavation equipment removal and paving equipment delivery process (Figure 22) is carried out, and on Friday, the temporary paving process (Figure 23) is performed.

Once multiple consecutive invert blocks 10 (continuous invert block structure) have been embedded in part or throughout one lane of tunnel T as described above, the next process involves pouring concrete into the embedded invert blocks 10. Therefore, the process of pouring concrete into the invert blocks 10 will now be explained using Figures 25 to 28.

Figure 25 is an explanatory diagram showing the temporary pavement removal process, which is one step in pouring concrete into the buried invert block; Figure 26 is an explanatory diagram showing the concrete pouring commencement process following Figure 25; Figure 27 is an explanatory diagram showing the concrete pouring execution process following Figure 26; and Figure 28 is an explanatory diagram showing the re-temporary pavement process following Figure 27. In these drawings, (a) is an explanatory diagram viewed from above, and (b) is an explanatory diagram viewed from the axial cross-section of the tunnel.

First, as shown in Figure 25, the temporary pavement is removed using a backhoe (for example, a 0.45 class backhoe) 30 as an excavation machine, exposing the tips of the connecting pipes P attached to the concrete pouring holes H1 and concrete blowout holes H2 (temporary pavement removal step). As mentioned above, in this embodiment, the tip of the connecting pipe P is located at the boundary between the base layer L3 and the upper subgrade L2 that constitute the pavement roadbed L. Therefore, the two layers (asphalt layers) of the surface layer L4 and base layer L3 are removed, while the two layers (subgrade layers) of the upper subgrade L2 and lower subgrade L1 are not removed. However, in Figures 25 to 27, the surface layer L4, base layer L3, upper subgrade L2, and lower subgrade L1 are not shown.

As mentioned above, the area of temporary pavement to be peeled off to expose the tip of the connecting pipe P may be limited to the area around the connecting pipe P, or it may be the entire area where the invert block 10 for concrete pouring is embedded. Here, however, the latter peeling area is used.

Furthermore, in this embodiment, when pouring concrete into the existing invert block 10, as shown in Figure 25 and Figures 26 and 27 described below, each of the processes from the excavation and base preparation process (Figure 12) to the compaction process (Figure 21) is performed in parallel within different ranges. In this way, by performing the concrete pouring into the buried existing invert block 10 and the installation and burying of the invert block 10 in the unexcavated area in parallel within mutually different ranges, it becomes possible to complete the series of operations in a shorter construction period.

Now, after the tip of the connecting pipe P is exposed in the temporary pavement removal process shown in Figure 25, the mixer truck 31, which transports ready-mix concrete, and the concrete pump truck 32, which docks with the mixer truck 31 to receive the ready-mix concrete into a hopper and pumps the concrete through a pumping pipe 32a using an equipped pump (not shown), are introduced into the restricted zone, as shown in Figure 26. Furthermore, the caps on the tips of the connecting pipes P attached to the concrete placement holes H1 and concrete discharge holes H2 are removed, and the pumping pipe 32a of the concrete pump truck 32 is connected to the connecting pipe P attached to the concrete placement hole H1 (in this case, the connecting pipe P of the invert block 10 buried closest to the concrete pump truck 32) using a joint. Then, concrete placement into the invert block 10 begins (concrete placement start process). Once the mixer truck 31 has loaded the required amount of ready-mix concrete into the hopper of the concrete pump truck 32, it exits the tunnel and moves out into the traffic lane.

In this embodiment, high-flow concrete is used as the concrete to be poured. High-flow concrete requires less water than ordinary concrete and has high fluidity, ensuring that it reliably fills every corner of the invert block 10 without the need for vibration or compaction. However, it is also possible to use other types of concrete, such as ordinary concrete or fluidized concrete, as the concrete to be poured.

Once concrete placement begins as shown in Figure 26, the concrete pumping pipe 32a of the concrete pump truck 32 is sequentially connected to the connecting pipes P attached to the concrete placement holes H1 of each embedded invert block 10, and the concrete is pumped and placed.

When pouring concrete into each invert block 10, the connecting pipe P attached to the two concrete discharge holes H2 from which concrete is discharged first should be capped to prevent leakage as soon as the concrete begins to discharge. The other connecting pipe P attached to the concrete discharge hole H2 should also be capped as soon as the concrete begins to discharge. Once both connecting pipes P attached to the concrete discharge holes H2 are capped, the connecting pipe P attached to the concrete pouring hole H1 should also be capped.

In this way, as shown in Figure 27, concrete is poured into the embedded invert blocks 10 (concrete pouring execution step) to create the invert. Here, as mentioned above, the installation and burial of the invert blocks 10 and the pouring of concrete into the existing embedded invert blocks 10 are carried out in parallel. However, since the invert is created by pouring concrete into the invert blocks 10, in the final stage, these processes are no longer carried out in parallel, and only the pouring of concrete into the existing invert blocks 10 is performed.

Then, after pouring concrete into all the embedded invert blocks 10 to create the invert, the detached base layer L3 and surface layer L4 are sequentially stacked on top of the upper subgrade L2, as shown in Figure 28, and temporary paving is performed (temporary paving step). Here, if the temporary pavement is detached only around the connecting pipe P, in the temporary paving, instead of sequentially stacking the base layer L3 and surface layer L4, for example, coarse-grained asphalt concrete may be used to fill the detached area. Note that the connecting pipe P is not shown in Figure 28. Furthermore, temporary paving is performed in the excavated area S used to bury the invert blocks 10 (see Figure 23).

In this way, concrete is poured into the invert blocks 10 embedded in one lane of tunnel T, thereby creating an invert. Once the invert is created by embedding the invert blocks 10 (Figures 9-24) and pouring concrete (Figures 25-28) throughout one lane of tunnel T, the same process is repeated for the other lane. Therefore, a continuous invert block structure, consisting of multiple invert blocks 10 arranged in a series (two series in this embodiment) along the axial direction of the tunnel, is installed. Then, two invert blocks 10 (two inverts) facing each other in the circumferential direction of tunnel T form an inverted arch shape along the circumferential direction of tunnel T (see Figure 2). When installing the invert blocks 10 in the other lane, they are fastened with bolts to the opposing invert blocks 10 in the lane where concrete has already been poured.

Finally, the entire area of tunnel T, which has been temporarily repaved, is stripped, and the final finishing step, permanent paving (paving with the original thickness), is carried out, completing the entire process.

The invention made by the present inventors has been specifically described above based on embodiments. However, the embodiments disclosed herein are illustrative in all respects and are not limited to the disclosed technology. That is, the technical scope of the present invention should not be interpreted restrictively based on the description of the embodiments above, but rather in accordance with the claims, and includes all equivalent technologies to those described in the claims and all modifications that do not depart from the essence of the claims.

The above description focuses on the installation of the invert block of the present invention in a tunnel already in use, but it can also be installed in newly constructed tunnels.

10 Invert block 10e Element 10ea Connection opening 10eb Rib 10ec Nut 10ed Connection plate 10ee Sealant 10ef Connection plate 10eg Connection bolt 10eh Closure plate 10sf Side plate 10sf-1 Longitudinal side plate 10sf-2 Shortitudinal side plate 10ts Top plate 10us Bottom plate 11 Support member 12 Stake 13 Connecting hole 14 Lifting bracket 15 Support bolt 16 Base 17 Nut 20 Backhoe 21 Trailer 22 Dump truck 23 Backhoe 24 Crawler crane 25 Dump truck 26 Dump truck 27 Backhoe 28 Compaction roller 29 Dump truck 30 Backhoe 31 Mixer truck 32 Concrete pump truck 32a Pressure pipe 33 Asphalt finisher C Concrete D Sandbag ES Subgrade material G Grout (backfill material)
GE Grout pumping equipment H1 Concrete placement hole H2 Concrete blowout hole H3 Grout injection hole H4 Bolt hole L Pavement subgrade L1 Lower subgrade L2 Upper subgrade L3 Base layer L4 Surface layer P Connecting pipe RB Subgrade S Excavated area T Tunnel W Runoff prevention wall

Claims (7)

An invert block installed in the ground at the bottom of a tunnel, forming an inverted arch shape along the circumferential direction of the tunnel,
It is composed of multiple steel elements that have an elongated shape, are interconnected along their longitudinal side in the axial direction, and are arranged to extend along the circumference of the tunnel, and these elements are collectively formed into a box shape consisting of an upper plate, a lower plate, and side plates.
A gap is formed in the connecting opening on the longitudinal side of the element, allowing concrete poured into the box-shaped interior to flow from one element to the other, and a support member is installed to support the load from above .
Concrete is filled inside the box-shaped structure consisting of the upper plate, the lower plate, and the side plates.
On the longitudinal side of the element, a connecting plate is provided that spans the upper plates of both elements and the lower plates of both elements.
An invert block characterized by the following features. The connecting plate that spans the upper plates of both elements is attached to the lower surface of the upper plate of one of the elements, extending along the entire length of the upper plate on the longitudinal side, so as to protrude from the upper plate.
The connecting plate that spans the lower plates of both elements is attached to the lower surface of the lower plate of one of the elements, extending along the entire length of the longitudinal side of the lower plate so as to protrude from the lower plate.
The invert block according to claim 1, characterized in that it is as described above. The connecting plate attached to the upper plate of one of the elements has a through hole formed in it.
On the other element, the upper plate is fitted with a connecting bolt that passes through the through hole and screws onto a nut, which can be tightened from above.
The invert block according to claim 2, characterized in that it is as described above. The aforementioned through-hole is an elongated hole formed in the axial direction of the tunnel.
The invert block according to claim 3, characterized in that it is as described above. The element is provided with a short-side plate which is the side plate along the short-side direction of the element,
Between the two short-side plates of the mutually adjacent elements, a closing plate is provided to close the gap formed according to the fastening position of the connecting bolt and the nut to the elongated hole.
The invert block according to claim 4, characterized in that it is as described above. The closing plate is welded to the outer surface of one of the short-side plates, with a portion of it protruding in the tunnel axis direction so as to overlap the short-side plate of the adjacent element.
The invert block according to claim 5, characterized in that it is as described above. A sealing material is attached to the upper surface of the connecting plate, which is attached to the lower plate of one of the elements, to seal the gap between it and the other element.
The invert block according to claim 2, characterized in that it is as described above.