JP2024055743A - Debris flow prevention structures - Google Patents

Abstract

[Problem] To provide a structure capable of mitigating impacts from debris on a structure and maintaining its original shape when a debris flow occurs in a mountain stream where debris flow is expected to occur. [Solution] A debris-flow prevention structure (1) is constructed from a structure (2) constructed three-dimensionally on a flat foundation (11) constructed on a mountain stream bed (26), and tension members (13) that are erected between at least the ground on both sides of the mountain stream and the structure (2) and have ends on both sides fixed to the ground, and that bear impact forces from debris together with the structure (2) when a debris flow occurs, the structure (2) is constructed from a plurality of lower frame members (3) arranged in parallel in the width direction of the mountain stream on the foundation (11) and along the direction of the debris flow, front side vertical frame members (4) and rear side vertical frame members (5) that are joined to the upstream and downstream sides of the axial direction of each lower frame member (3) and stand up from the lower frame members (3), and connecting members (6) that connect at least the lower frame members (3, 3) adjacent to each other in the width direction of the mountain stream, and the tension members (13) are brought into contact with or connected to the structure (2) so that the lower frame members (3) can be moved axially relative to the foundation (11). [Selected Figure] Figure 1

Description

This invention relates to a debris flow prevention structure that is installed in mountain streams where debris flows are expected to occur, in order to dam the debris flows that may occur.

Structures that are installed (constructed) in mountain streams to dam debris flows can be broadly divided into two types: those that have a basic structure of a cable (tensile material) with both ends fixed to the riverbanks and a net connected to the cable (see Patent Documents 1 to 4), and those that have a basic structure of a structure made of framework materials assembled three-dimensionally on the riverbed to span both riverbanks and a net stretched on either the upstream or downstream side (see Patent Documents 5 to 7). A cable may also be used in conjunction with the structure (Patent Document 5). There are also examples of structures that are just structures without cables or nets (see Patent Documents 8 and 9).

In the former structure, the impact (kinetic energy) when the net catches soil or rocks is borne mainly as tensile force by the cable body and the anchoring parts at its ends, so its ability to catch soil or rocks is lower than that of the latter structure, which uses a structure in combination, and there is a possibility that either the cable or the anchoring parts will break when soil or rocks that cause an impact that exceeds the net's capacity are caught.

The latter structure is basically assembled from vertical members such as columns that are parallel to the direction of the debris flow, and horizontal members that connect adjacent vertical members across the width of the stream, and the net is stretched across the width of the stream, so the structure bears the impact when the net catches debris.

In the latter structure, when the legs of the vertical members are simply placed on the riverbed (Patent Document 7), even if connecting members are installed between the vertical members arranged in parallel in the direction of the debris flow, if the lower ends of adjacent vertical members in the width direction of the river are not connected, the lower ends of each vertical member arranged in the width direction of the river may slide independently on the riverbed in the event of an impact, and the structure may not be able to maintain its original shape. If the structure can no longer maintain its shape, collapse may begin from the point where it has lost its shape.

When the legs (lower ends) of the vertical members are fixed into a foundation such as concrete (Patent Documents 5, 6, 8, and 9), the overall stability of the structure is greater than when it is placed on a surface. However, when each vertical member receives an impact from soil or rocks directly or through a net, because each vertical member is restricted from moving (sliding), it is more susceptible to impact than if it were able to slide, and is more likely to sustain greater damage from the impact. For this reason, there is a high possibility that the vertical members will be damaged, and the shape of the structure may be compromised due to the damage.

Even if the vertical members arranged in parallel in the direction of the debris flow are connected to each other by horizontal members erected in that direction and the parallel vertical members are restrained (Figs. 7 and 8 of Patent Document 6), the vertical members are still structurally fixed to the foundation, so there is a high possibility that the vertical members will be damaged.

In the case of a configuration in which a structure and a cable are used together (Patent Document 5), in theory, the impact can be shared between the structure and the cable, which reduces the possibility of damage during an impact compared to when the structure or cable is used alone, and it is therefore thought that it is possible to improve the shape retention ability relatively compared to other examples.

Japanese Utility Model Application Publication No. 3-36021 (Claim 1, page 6, line 20 to page 13, line 10, Figures 1 to 13) JP-A-9-273137 (Claim 1, paragraphs 0008 to 0032, Figures 1 to 5) JP-A-10-60866 (Claim 1, paragraphs 0015 to 0032, Figures 1 to 4) JP 2009-52215 A (Claim 1, paragraphs 0048 to 0073, Figures 1 to 10) JP-B-58-51568 (Column 3, line 42 to Column 5, line 12, Figures 4 to 6) JP 2017-141568 A (paragraphs 0022 to 0030, Figures 1 to 8) JP 2021-28445 A (paragraphs 0013 to 0030, Figures 1 to 13) JP 2007-177467 A (paragraphs 0013 to 0039, Figures 1 to 8) JP 2022-39651 A (paragraphs 0022 to 0039, Figures 2, 3, 7 to 15)

However, in Patent Document 5, the vertical members are independently fixed (restrained) to the concrete foundation, and therefore, under restrained conditions, the impact when each vertical member receives soil or rocks is likely to be large, and there is a high possibility that it will be damaged.

In light of the above background, the present invention proposes a debris flow prevention structure that can absorb the impact that the structure receives from debris and maintain the structure's shape.

The debris flow prevention structure of the present invention is a three-dimensional structure constructed on a flat foundation on the riverbed of a river where a debris flow is expected to occur,
and tension members that are installed between the structure and the ground on at least both sides of the stream, with ends on both sides fixed to the ground, and that bear impact forces from debris when the debris flow occurs together with the structure,
The structure is provided on the foundation with a plurality of lower frame members arranged in parallel in the width direction of the stream and along the direction of the debris flow, front vertical frame members and rear vertical frame members that are joined to the upstream and downstream sides of the axial direction of each lower frame member and stand up from the lower frame members, and connecting members that are installed at least between the lower frame members adjacent in the width direction of the stream and connect the two lower frame members to each other,
The lower frame member directly or indirectly contacts the foundation so as to be relatively movable in the axial direction;
A constituent requirement of the present invention is that the tension member is in contact with the downstream side of any part of the structure so as to be able to bear the load that the structure receives from the soil and rocks toward the downstream side of the stream, while allowing the relative movement of the lower frame member on the foundation.

"Flat foundation constructed on the river bed" refers to a foundation 11 such as a concrete base or similar concrete slab that has a substantially flat upper surface (top surface) and is constructed generally in a flat shape on the river bed 26 in order to level the unevenness of the river bed 26. "Substantially" means that the entire surface does not necessarily have to be uniformly flat. The structure 2 is constructed on the foundation 11. "Construction" includes cases where some parts have been preassembled.

"A three-dimensionally constructed structure" means that the entire structure 2 is constructed so that it has a length in the width direction of the stream, a height according to the expected size of the debris, and a thickness (depth) in the direction of the debris flow. The structure 2 basically has a length that essentially spans the entire width of the stream in the width direction, and a height that can receive the largest expected amount of debris. In more detail, as shown in Figure 1, the vertical distance of the length of at least the longer side of the front vertical frame member 4 and the rear vertical frame member 5, which are structural components, is the height of the structure 2, and the length of the lower frame member 3, which is placed facing the debris flow direction, is the thickness of the structure 2. "The width direction of the stream" is the axial direction (length direction) of the structure 2.

"Tension members installed at least between the ground on both banks of the stream and the structure 2" means that the tension members 13 are installed at least between the ground on both banks of the stream and the structure 2, including the tension members 13 installed between the ground on both banks via the structure 2 as shown in Figure 3-(b) and the tension members 13 installed between both sides of the structure 2 in the axial direction and the ground on the stream bank on that side as shown in Figure 14. In the former case, the tension members 13 located in the section of the structure 2 are mainly in contact with the structure 2 (claim 2), and in the latter case, the tension members 13 are connected to some part of the structure 2.

"Tension members whose ends on both sides are fixed to the ground" refers to the ends of the tension members 13 on both sides being fixed to the ground of the riverbank to the extent that the tensile force borne by the tension members 13 can be transmitted to the ground, as shown in Figure 3. Specifically, as shown in Figure 12, the anchor bodies 14, which are the fixing parts of the ends of the tension members 13, are inserted into the drilled holes 22 formed in the ground of the riverbank, and are embedded and fixed in the grout material 24 filled in the drilled holes 23, so that the tension members 15 are permanently fixed to the ground. The tension members 13 are made of materials that can introduce tensile force, such as PC steel and fiber-reinforced plastics. Both sides of the river are riverbanks.

The part of the tension member 13 on the structure 2 side may be connected (anchored) to any part of the structure 2 as shown in Figure 14, but as shown in Figures 3-(b) and 5, both ends of the tension member 13 in the longitudinal direction may be anchored to both banks of the stream, while the middle part (middle section) may contact the downstream side of any part of the structure 2 as described above (Claim 1). In the latter case, the tension member 13 is erected in the width direction of the stream while contacting the structure 2 on the downstream side of the stream, and is anchored to the ground of the stream bank at both ends, so that the structure 2 shares the impact force received from the earth and rocks together with the structure 2 and transmits it to the ground of the stream bank. Both ends of the tension member 13 are anchored to a degree that allows them to sufficiently resist the tensile force borne by the tension member 13.

"Tension member that bears the impact force from debris flow together with the structure" means that the tension member 13 shares the impact force from debris flow together with the structure 2. The ends of the tension member 13 on both sides of the bank are fixed to the ground, while the end on the structure 2 side is connected to or comes into contact with some part of the structure 2, so that the impact force that the structure 2 receives from debris flow together with the structure 2 is shared and transmitted to the ground of the riverbank. The tension member 13 bears the impact force transmitted from the structure 2 as a tensile force.

In particular, when the middle part of the tension member 13 contacts the structure 2, when the structure 2 is installed on the foundation 11, the tension member 13 allows the lower frame member 3 constituting the structure 2 to move relatively on the foundation 11, while contacting the downstream side of any part of the structure 2 so as to be movable relative to the structure 2 in the width direction of the stream, thereby bearing part of the impact force borne by the structure 2. The tension member 13 contacts, for example, the rear vertical frame member 5, etc. The relative movement of the lower frame member 3 is the relative movement of the structure 2 with respect to the foundation 11.

When the tension member 13 is connected to the structure 2 or when it is in contact with the structure 2, it is in a state where it shares part of the load borne by the structure 2 from the moment the structure 2 begins to move relative to the foundation 11. The load (impact force) that the structure 2 should bear is reduced by the amount of load borne by the tension member 13, so the damage that the structure 2 receives from earth and rocks is mitigated.

When the tensile member 13 comes into contact with the structure 2, the tensile member 13 allows the structure 2 to move relative to the foundation 11, so that when the structure 2 tries to slide (move relatively) on the foundation 11 toward the downstream side of the debris flow, the tensile member 13 bears a tensile force greater than normal. This tensile force that exceeds the normal tensile force corresponds to the load (impact force) that the structure 2 receives from the debris and is no longer able to maintain a stationary state. The tensile member 15 may not bear any tensile force under normal circumstances.

When the structure 2 receives an impact force from soil or rocks, the tension member 13 undergoes an elongation deformation in response to the impact force, whether it is connected to the structure 2 or in contact with the structure 2, and the amount of elongation deformation of the tension member 13 becomes the amount of sliding of the structure 2 relative to the foundation 11.

The fact that the structure 2 can slide on the foundation 11 when it receives an impact force from soil or rocks means that the impact force that occurs when the structure 2 slides is transferred to the tension member 15 without the structure 2 continuing to receive an impact force from soil or rocks that exceeds a certain magnitude. This also means that the structure 2 is not subjected to an impact force that would destroy it, and the load is transferred to the tension member 15.

Furthermore, the fact that the structure 2 can slide on the foundation 11 means that the kinetic energy possessed by the soil and rocks when impacted by the soil and rocks can be converted into thermal energy due to friction generated between the structure 2 and the foundation 11 when the structure 2 slides. Therefore, the structure 2 can consume the kinetic energy possessed by the soil and rocks as thermal energy, and therefore damage caused by the impact force is mitigated compared to when the structure 2 is restrained (fixed) on the foundation 11. Friction between the structure 2 and the foundation 11 occurs with the lower frame material 3.

The kinetic energy of the soil and rocks can be consumed more efficiently by providing a damping device 16 (claim 4) that generates a damping force when the tensile member 13 bears a tensile force from the soil and rocks in part of the tensile member 13 as shown in Figure 3-(b), improving the damage mitigation effect of the structure 2. The damping device 16 needs to be connected to the tensile member 13 in a state in which it can bear a tensile force greater than normal when the tensile member 13 bears the tensile force, and is therefore provided between the tensile member 13 and the anchor body 14 as shown in Figures 3, 5, and 13. The form of the damping device 16 is not important, and for example, an oil damper, a friction damper, or other energy absorbing device can be used.

"Multiple lower frame members arranged on the foundation in parallel with the width direction of the stream and along the debris flow direction" means that multiple lower frame members 3 arranged in parallel with the width direction of the stream are arranged on the foundation 11 with their axial direction facing the debris flow direction. "Along the debris flow direction" basically means "the axial direction (of the lower frame members) faces the debris flow direction," but the axial direction does not necessarily have to match the debris flow direction. The structure 2 is constructed (installed) directly or indirectly on the foundation 11, so the lower frame members 3 are arranged (placed) directly or indirectly on the foundation 11.

By arranging the lower frame material 3 on the foundation 11 so that its axial direction is aligned with the direction of the debris flow, when the structure 2 receives an impact force from debris, it receives a force (load) in the axial direction of the lower frame material 3, which is the direction of the debris flow. In addition to the lower frame material 3 being in contact with the foundation 11 and being able to move freely relative to the axial direction, as described above, depending on the level of the impact force, the tensile material 13 can slide in the axial direction of the lower frame material 3 within the range in which it can stretch and deform.

"The front vertical member and rear vertical member that are joined to the upstream and downstream sides of each lower frame member in the axial direction and stand up from the lower frame member" refers to the front vertical member 4 being joined upward to the upstream end or a position close to the end of the lower frame member 3, and the rear vertical member 5 being joined upward to the downstream end or a position close to the end of the lower frame member 3. "Upward" does not necessarily mean vertically. The front vertical member 4 and rear vertical member 5 are joined directly to each other, or indirectly joined by installing an intermediate member such as the auxiliary member 10 described below between them.

The front vertical member 4 and the rear vertical member 5 are joined together directly or indirectly, as shown in Figure 1, and together with the lower frame member 3, form a unit frame 2A with a plane truss or a structure similar to a plane truss, and each unit frame 2A ensures a certain degree of shape retention (rigidity) against external forces (impact forces) in the direction of the debris flow. The structure 2 is made up of unit frames 2A made up of these lower frame members 3, connected by connecting members 6 installed in the width direction of the stream.

"Tie members that are installed at least between the lower frame members adjacent in the width direction of the stream and connect both lower frame members to each other" means that tie members 6 are installed at least between the lower frame members 3, 3 adjacent in the width direction of the stream, and if necessary, tie members 6 are also installed between at least one of the front vertical frame members 4, 4 and the rear vertical frame members 5, 5 adjacent in the width direction of the stream. Tie members 6 may be installed in units of adjacent lower frame members 3, 3, or they may be installed to span all of the lower frame members 3, 3.

"The lower frame member is in direct or indirect contact with the foundation so as to be freely movable relative to the axial direction" means that the lower frame member 3 placed on the foundation 11 is in direct contact with the foundation 11 so as to be freely movable relative to the axial direction of the lower frame member 3, or indirect contact via some intermediate material such as the adjustment material 15 described below. By the lower frame member 3 being in contact with the foundation 11 so as to be freely movable relative to the axial direction of the lower frame member 3, the structure 2 is in a state in which it can move relative to the axial direction of the lower frame member 3 when it receives an impact force from soil or rocks, as described above.

"The tension member is in contact with or connected to the structure so as to be able to bear the load that the structure receives from the soil and rocks toward the downstream side of the stream while allowing the lower frame member to move relatively on the foundation" means that while the tension member 13 is in contact with or connected to the structure 2, it does not restrict the relative movement of the structure 2 on the foundation 11, and the tension member 13 shares the load that the structure 2 receives from the soil and rocks. When the structure 2 moves (slides) relatively on the foundation 11, the tension member 13 stretches more than usual, and as described above, it bears a tensile force that is greater than usual.

When the tensile member 13 comes into contact with the structure 2, the tensile member 13 moves relative to the structure 2 while stretching as the structure 2 moves relatively on the foundation 11. When the tensile member 13 is connected to the structure 2, the tensile member 13 allows the structure 2 to move relative to the foundation 11 within the range in which it can stretch (expand).

"Contacting any part of the structure" means that the structure 2 comes into contact with the downstream side of the stream on the side of the structure 2 that receives impact force from soil and rocks and moves relative to the foundation 11, among the structural components such as the lower frame member 3, the front vertical frame member 4, or the rear vertical frame member 5 that make up the structure 2, or the receiving member 8 described below.

When the tension member 13 comes into contact with the structure 2, it is reasonable for the tension member 13 to be installed (stretched) over the entire axial length of the structure 2, so it is installed via all rear vertical frame members 5 or all front vertical frame members 4 that make up the structure 2, or the connecting members 6, or other support members 8 mentioned above. However, if the tension member 13 is installed with a partial extreme bend on a flat surface, the tension in the bent portion will be excessive, making the tension member 13 more likely to break.

Therefore, by placing the tensile member 13 in contact with the rear side (downstream side) of the structure 2 near the center of the width of the stream, and arranging it from near the center toward the upstream side of the stream toward both sides of the width of the stream, and arranging it in a curved shape on a plane as a whole (claim 2), it is possible to eliminate places where the tensile member 13 is extremely bent partially, and to avoid partial breakage of the tensile member 13. "On the whole" means that the tensile member 13 is arranged in a curved shape when viewed as a whole, excluding the end fixing parts (anchor bodies 14) on both sides, and includes arranging the tensile member 13 in a straight line between structural components adjacent in the width direction of the stream. "On a plane" means when viewed as a plan view.

In the case of contact, the tensile member 13 comes into contact with some part of the structural component, but if the tensile member 13 comes into contact with the structural component in such a way that it slips against the structural component at the contact point, frictional force due to sliding will be generated when the tensile member 13 moves relative to the structural component, and the tensile force bearing capacity of the tensile member 13 may decrease. To address this, rollers or pulleys can be connected to the contact points of the structural component with the tensile member 13 to prevent the tensile member 13 from sliding against the structural component, thereby suppressing the generation of frictional force and suppressing the decrease in the tensile force bearing capacity.

When the lower frame member 3 slides or attempts to slide on the foundation 11, depending on the level of impact force from the soil or the location of impact of the soil, it is expected that the structure 2 will attempt to tip over with the downstream end of the lower frame member 3 as a fulcrum. To prepare for such an event, a guide member (guide rail) such as the above-mentioned adjustment member 15 is fixed to the foundation 11, and the guide member is used to restrain the lower frame member 3 from floating up (claim 3), making it possible to prevent the lower frame member 3 (structure 2) from floating up.

When the lower frame member 3 has a flange that rests on the foundation 11, such as when an H-shaped steel is used for the lower frame member 3 as shown in Figure 2, the guide member (adjustment member 15) is formed in a shape that sandwiches both sides of the width of the flange from above and below together with the foundation 11 as shown in Figure 2-(c). The guide member does not need to be continuous in the axial direction of the lower frame member 3, and may be arranged partially in the axial direction as shown in Figure 1.

It is constructed on a foundation on the riverbed and has a structure with multiple lower frame members arranged along the direction of the debris flow, and tension members whose ends are fixed to both banks of the river. The lower frame members are in contact with the foundation so that they can move freely relative to the foundation in the axial direction, and the tension members are in contact with or connected to the structure while allowing the lower frame members to move relative to each other. This means that the tension members can share part of the load borne by the structure from the time the structure begins to move relative to the foundation. Therefore, the load (impact force) that the structure should bear can be reduced by the amount borne by the tension members, and damage to the structure from debris can be mitigated.

In addition, because the structure can slide on the foundation, the kinetic energy of the soil and rocks when they impact can be converted into thermal energy due to friction between the structure and the foundation as it slides, and the kinetic energy of the soil and rocks can be consumed as thermal energy, so damage caused by the impact force can be mitigated compared to when the structure is restrained (fixed) on the foundation.

This is a vertical cross-sectional view of the structure viewed in the width direction of the stream, showing an example of the configuration of a structure built on a foundation and the relationship between the tensile material placed downstream of the structure. 1, (b) is a cross-sectional view taken along line yy in FIG. 1, and (c) is an enlarged view of the dashed circle portion in (a). 2A is a longitudinal cross-sectional view showing the relationship between the structure shown in FIG. 1 and the debris flow, and the relationship between the end fixing portion (anchor body) and the tension member fixed to the ground, and FIG. 2B is a plan view showing the relationship between the structure and the tension member. 2A is a longitudinal sectional view showing an example of the structure different from the structure shown in FIG. 1, and FIG. 2B is a sectional end view taken along line xx of FIG. 5A is a plan view showing a state in which a tensile member is arranged on a plane in a curved state in contact with the downstream side of the structure shown in FIG. 4 . FIG. FIG. 6 is a plan view showing the structure of the structural body shown in FIGS. 4 and 5 excluding the cross members. 7A is an elevational view showing the arrangement of the cross members of the structure shown in FIGS. 4 to 6 as viewed from the upstream side, and FIG. 7B is a plan view of FIG. 1A is an elevational view showing an example of the configuration of the connection between the end of a tensile material body and an anchor body, which is an end fixing portion connected to it, and FIG. 1B is a plan view of FIG. 9A is a front view showing the fixing material shown in FIG. 8, FIG. 9B is a view taken along line xx in FIG. 9A, and FIG. 9C is a view taken along line yy in FIG. 9A is a front view showing the connecting material shown in FIG. 8, FIG. 9B is a view taken along line xx in FIG. 9A, and FIG. 9C is a view taken along line yy in FIG. 9A is a front view showing the anchor fixing material shown in FIG. 8, and FIG. 9B is a view taken along the line xx in FIG. FIG. 2 is a cross-sectional view showing an example of the overall configuration of a main body of an anchor body. FIG. 2 is a cross-sectional view showing a configuration example of a damping device. (a) is a plan view showing the end of the upper tensile material connected to the structure when the tensile material is arranged in two tiers, upper and lower, and (b) is a plan view showing the end of the lower tensile material connected to the structure. 14-(a) is a plan view showing a specific example of a connection portion between the tensile member and the structure in FIG. 14-(a), and FIG. 14-(b) is an elevation view of (a). (a) is an elevational view showing an outline of an example of installation of tension members when two tension members are arranged in parallel on the vertical plane when the tension members are arranged in two tiers, one above the other, and (b) is an elevational view showing an outline of an example of installation of tension members when two tension members are arranged so as to cross on the riverbank side on the vertical plane.

Figures 1 and 2 show an example of the configuration of a debris flow prevention structure 1 that includes a structure 2 constructed three-dimensionally on a foundation 11, such as a flat concrete plate constructed on the bed 26 of a stream where a debris flow is expected to occur, for installing (constructing) the structure 2 substantially horizontally on the bed 26, and tensile members 13 whose ends on both sides of the stream (river banks) are fixed to the ground on both sides of the stream.

The tension members 13 may be installed across the width of the stream between both banks with the structure 2 in between, or may be installed between both sides of the structure 2 in the axial direction (length direction) and the riverbanks on each side. In the former case, the tension members 13 contact the entire structure 2, and in the latter case, the tension members 13 are connected to both sides of the structure 2 in the axial direction. In either case, the tension members 13 bear the impact force from debris when a debris flow occurs together with the structure 2. The reference number 12 below the foundation 11 indicates a broken granite stone. The ends on both sides of the tension members 13 are anchor bodies 14, which are the fixing parts. Figures 1 to 7 show an example of the construction of the structure 2 when the tension members 13 contact the structure 2, and Figures 14 to 16 show an example of the construction of the structure 2 when the tension members 13 are connected to both sides of the structure 2 in the axial direction.

As shown in Figure 1, the structure 2 is constructed on a foundation 11 with multiple lower frame members 3 arranged in parallel in the width direction of the stream with their axial direction aligned with the debris flow direction, and a front vertical frame member 4 and a rear vertical frame member 5 which are joined to both axial ends or positions close to both ends of each lower frame member 3 and stand up from the lower frame members 4 as basic unit frames 2A. The structure 2 is constructed by erecting the following connecting members 6 between multiple unit frames 2A, 2A arranged in the width direction of the stream.

At least between the lower frame members 3, 3 adjacent in the width direction of the stream, a tie member 6 is installed and joined to both of them, connecting the lower frame members 3, 3 to each other in the width direction of the stream, as shown in Figures 4 and 6. The tie member 6 may also be installed between either or both of the front vertical frame members 4, 4 or the rear vertical frame members 5, 5 adjacent in the width direction of the stream.

As shown in Figures 1 to 3, on the upstream side between the adjacent front vertical frame members 4, 4, horizontal members 7 that directly block the debris are installed in parallel in the height direction and joined to both front vertical frame members 4, 4. The horizontal members 7 are arranged at appropriate intervals in the axial direction of the front vertical frame members 4 to allow gravel smaller than a certain size to pass through and block gravel larger than a certain size. The horizontal members 7 may also block driftwood that flows downstream along with the debris flow.

Figures 1 and 2 show an example in which the installation height of the cross member 7 from the foundation 11 is changed for each section divided into adjacent front vertical frame members 4, 4, and the impact force that the structure 2 receives from earth and stones is distributed to the adjacent front vertical frame members 4, 4 and also in the axial direction of the front vertical frame members 4. In this case, a step is provided between the cross members 7, 7 that are joined to one front vertical frame member 4 and are adjacent in the width direction of the stream. The cross member 7 is installed between the front vertical frame members 4, 4 that are adjacent in the width direction of the stream and is joined to both, so it also serves as the connecting member 6.

Steel is primarily used for the structural components 2, such as the lower frame 3, but precast concrete members may also be used, and the structural components 2 may be constructed of reinforced concrete or a composite structure with steel. The drawing shows an example in which the structural components 2, except for the cross members 7, are steel such as H-shaped steel. The cross members 7 are made of steel pipes that are resistant to deformation due to the impact force of earth and rock collisions, but the shape of the structural components, including the cross members 7, is not important. When the structural components 2 are made of steel, the connections are primarily welded or bolted, as shown in the figure.

The upper parts of the front vertical member 4 and the rear vertical member 5 may be joined directly to each other, but in order for the rear vertical member 5 to fulfill the function of preventing the front vertical member 4 from tipping over when subjected to impact forces from soil and rocks, it is reasonable for the upper part of the rear vertical member 5 to be joined to the axial middle part of the front vertical member 4, as shown in Figures 1 and 3-(a). In this case, there is also the advantage that the bending moment generated in the front vertical member 4 can be efficiently borne by the rear vertical member 5 as an axial force. "Upstream side" refers to the upstream side (front side) of the stream. Similarly, hereinafter, "downstream side" refers to the downstream side (rear side) of the stream.

A support member 8 is joined to the rear (downstream) side of the front vertical frame member 4 so that it can be erected in the width direction of the stream, with tension members 13 in contact with the structure 2 as shown in Figures 1, 4, and 5, and is supported directly or indirectly by the lower frame member 3. A support member 9 is placed below the support member 8 as shown in Figure 4 to support the support member 8 directly or indirectly by the lower frame member 3, and is joined to the lower frame member 3 or the rear vertical frame member 5. The support member 9 pairs with the front vertical frame member 4 in the width direction of the structure 2.

In the example shown in Figure 1, in order to stably support the receiving material 8 on the structure 2 and ensure the rigidity of the structure 2 as a whole, a reinforcing member 10 is installed between the upper end of the front vertical frame member 4 and the middle part of the receiving material 8, and both ends of the reinforcing member 10 are joined to the front vertical frame member 4 and the receiving material 8. Also in Figure 1, the receiving material 8 is joined in the direction of the debris flow to a connecting member 6 joined downstream above the joint between the front vertical frame member 4 and the rear vertical frame member 5, and a support member 9 is installed between the middle part of the receiving material 8 and the lower end of the rear vertical frame member 5.

Figure 4 shows an example in which the lower end of the support material 9 is joined to a tie material 6 joined to the downstream side of the lower frame material 3, and the upper end of the support material 9 is joined to a tie material 6 joined to the downstream side below the receiving material 8. In the example shown in Figure 4, a reinforcing material 10 is installed between the bottom of the joint between the front vertical frame material 4 and the rear vertical frame material 5 and a position near the downstream side of the lower frame material 3.

As shown in Figures 1 and 2-(c), the lower frame member 3 is in direct or indirect contact with the foundation 11 so as to be freely movable relative to the foundation in the axial direction of the lower frame member 3. The tension member 13 contacts or is connected to the downstream side of any part of the structure 2 so as to be able to bear the load that the structure 2 receives from the soil and stones toward the downstream side of the stream, while allowing the lower frame member 3 to move relative to the foundation 11. In the case of contact, the tension member 13 contacts the structure 2 so as to be freely movable relative to the width direction of the stream. In the case of connection, the structure 2 can slide on the foundation 11 within the range in which the tension member 13 stretches when it receives an impact force from the soil and stones.

Figure 2-(c) shows an example in which an adjustment material 15 is fixed onto the foundation 11 with an anchor bolt or the like to adjust the degree of load (frictional force) that the structure 2 receives from soil and rocks when the lower frame material 3 starts to slide. By fixing the adjustment material 15 onto the foundation 11, it is possible to adjust the static frictional force when the lower frame material 3 starts to slide on the foundation 11, making it easier or harder to slide.

In the example shown in Figure 2-(c), a sliding member 31, which rests directly on the adjustment member 15 and has a width greater than the width of the lower flange of the lower frame member 3, is integrated with the bottom surface of the lower flange of the lower frame member 3, which uses an H-shaped steel. At the same time, a retaining portion 15a is integrated with both sides of the width of the adjustment member 15, which, together with the main body of the adjustment member 15, sandwiches both sides of the width of the sliding member 31 from above and below, preventing the sliding member 31 from floating up as it slides on the adjustment member 15. In this case, the static friction force is determined by the coefficient of friction between the sliding member 31 and the adjustment member 15.

The interlocking portions 15a may be partially and dispersedly arranged at intervals in the axial direction of the adjustment material 15 as shown in FIG. 1, but may also be formed continuously. The interlocking portions 15a, 15a on both sides of the width of the adjustment material 15, or the adjustment material 15 having interlocking portions 15a, 15a, act as a guide member (guide rail) that guides the sliding movement on the adjustment material 15 while preventing the lower frame material 3 from lifting up from the foundation 11.

Figure 3-(a) shows how the tension members 13, 13 are arranged in two tiers, one above the other, on the structure 2, and how both tension members 13, 13 are in contact with the structure 2, and how the anchor bodies 14, which are the end fixing parts of the tension members 13, are fixed to the ground on both sides (river banks) of the stream. Figure 3-(b) shows how the tension members 13 on the upper tier shown in (a) are installed (placed). The anchor bodies 14 are connected to both ends of the tension members 13 in the longitudinal direction, as shown in Figures 3-(b) and 5. A detailed example of the connection between the anchor bodies 14 and the tension members 13 will be described later. Figure 3-(a) also shows how the structure 2 is placed directly on the foundation 11, or indirectly via the above-mentioned intermediate adjustment material 15, in a state in which it can slide freely on the foundation 11, depending on the level of impact force from soil and rocks.

The lower frame member 3 of the structure 2 is placed directly on the foundation 11 or on the adjustment member 15, or the sliding member 31 described above is placed on the foundation 11 or on the adjustment member 15. Therefore, when a horizontal force that exceeds the static friction force between the bottom surface of the lower frame member 3 and the foundation 11 or adjustment member 15 acts on the structure 2 in the direction of the arrow in Figure 3, the structure 2 slides on the foundation 11 or on the adjustment member 15. The bottom surface of the lower frame member 3 is the bottom surface of the lower flange of the H-shaped steel described above.

Figure 3-(b) shows the tension member 13 placed in a curved shape on a plane while contacting the downstream side of the structure 2. The tension member 13 is placed in a plane so that it does not have any extreme bends, so that it can share the impact force that the structure 2 receives from the earth and rocks together with the structure 2 and distribute the force in the length direction.

Specifically, the tension member 13 is placed at the rear (downstream) side of the structure 2 near the center in the width direction of the stream, and is erected so as to draw a curve from near the center to both sides in the width direction of the stream toward the upstream side of the stream. When the structure 2 receives an impact force from earth and rocks and slides on the foundation 11, the tension member 13 stretches more than normal, bears the tensile force of the stretch, and transmits it to the ground through the anchor body 14. The tension member 13 draws a convex curve toward the downstream side at the axial middle of the structure 2.

When viewed in the width direction of the stream, Figures 3-(a) and (b) also show a situation in which a damping device 16 is connected between the parts of the tensile member 13 located on both sides of the structure 2 and the anchor bodies 14 fixed to the ground on both banks, which generates a damping force corresponding to the impact force (tensile force) when an impact force from soil or rocks is received. A detailed example of the damping device 16 and the anchor bodies 14 will be described later.

Figure 4 shows another specific example of the structure 2. In this example, the lower end of the front vertical frame member 4 is joined to the upstream end or a position close to the end of the lower frame member 3, the lower end of the rear vertical frame member 4 is joined to the downstream end or a position close to the end, and the upper end of the rear vertical frame member 4 is joined to the axial middle part of the front vertical frame member 4. Here, the support member 8 is joined to a position above the joint between the rear vertical frame member 5 and the front vertical frame member 4, and is installed horizontally in parallel with the lower frame member 3.

The upper end of the support member 9 is joined to the downstream end or near the end of the receiving member 8 to support the receiving member 8 on the lower frame member 3. In this example, since a tie member 6 is installed above the downstream side of the lower frame member 3 and below the downstream side of the receiving member 8, the top and bottom of the support member 9 are joined to the tie members 6, 6, and the receiving member 8 is joined to the tie member 6. The lower end of the support member 9 may be joined to the rear vertical frame member 5, and the upper end of the support member 9 may be joined to the receiving member 8. In addition, an auxiliary member 10 is installed below the joint between the front vertical frame member 4 and the rear vertical frame member 5 and the upstream side of the joint between the lower frame member 3 and the rear vertical frame member 5, and both ends are joined to both.

Figure 5 shows a specific example of the relationship between the structure 2 shown in Figure 3-(a) and the upper tensile member 13. The upper tensile member 13 shown in Figure 3-(a) is located on the downstream side (rear side) of the structure 2 near the center of the stream's width, and is located on the upstream side of the stream near both sides of the stream's width, and is arranged so that it is curved in a plane.

"Curved" also includes the case where the tension members 13 are arranged in a polygonal shape overall in the width direction of the stream within the section of the structure 2. Figure 5 also shows the arrangement of the tension members 13 on the lower level shown in Figure 3-(a). The tension members 13 on the lower level are arranged curved like the tension members 13 on the upper level, and are also partially bent and arranged in a polygonal shape that is smaller than the upper level.

As shown in Figure 5, the tension members 13 are positioned downstream of the structure 2 near the center of the stream's width, and as they move toward both sides of the width, they are positioned upstream of the structure 2. This can also be achieved by aligning the upstream end of the receiving member 8, with which the tension members 13 directly or indirectly come into contact, with the front vertical frame member 4, while varying the length of the receiving member 8. However, in this case, the length of each receiving member 8 will differ for each position in the stream's width, and it will be necessary to change the position of the support member 9 that supports the receiving member 8.

In contrast, changing the contact position of the tension member 13 while standardizing the length of all receiving materials 8 regardless of the position in the width direction of the stream is possible by connecting contact members 17 such as pulleys (idlers) or rollers, which contact the tension members 13 at different positions for each receiving material 8, to the receiving materials 8 as shown in Figure 5, and changing the connection position to the receiving material 8 depending on the position in the width direction. The section of the contact member 17 where the tension member 13 comes into contact is mainly formed in a curved shape.

When a tensile force is applied to the tension member 13 in advance, the tension member 13 is arranged in a straight line between the receiving members 8, 8 adjacent in the width direction of the stream, but is arranged in an approximately curved line on a plane for the entire structure 2. When the contact member 17 is a pulley or the like, there is an advantage that the frictional force generated between the tension member 13 and the contact member 17 can be suppressed when the tension member 13 tries to move relative to the contact member 17, as compared to when the tension member 13 slides against the contact member 17. In order to have the tension member 13 share part of the impact force from the moment the structure 2 receives the impact force from the soil and rocks, it is reasonable to apply a tensile force to the tension member 13 in advance, but this is not necessarily required.

Figure 6 shows the relationship between the lower frame members 3 and the connecting members 6 that are installed between the lower frame members 3 and 3 adjacent to each other in at least the width direction of the stream of the structure 2 shown in Figure 5 and connect the two lower frame members 3 and 3 to each other. The connecting members 6 are placed at upstream and downstream positions on the lower frame member 3 as shown in Figure 4-(a) and are joined to the lower frame member 3.

Figure 4 shows an example in which a tie 6 is also placed directly below the downstream side of the support member 8. Specifically, as shown in Figure 6, the tie 6 consists of fixed tie 61 that is pre-joined onto each lower frame member 3, etc., and connecting tie 62 that is installed on-site between fixed tie 61, 61 fixed to adjacent lower frame members 3, 3, etc., and joined to the fixed tie 61. "Pre-joined" means before the structure 2 is finally constructed on-site, and mainly refers to joining at a factory.

The lower frame members 3 with the fixed ties 61 integrated into them are arranged on-site on the foundation 11 at intervals in the width direction of the stream, and connecting ties 62 are erected between the fixed ties 61, 61 of the lower frame members 3, 3 adjacent in the width direction and joined to both fixed ties 61, 61.

Horizontal braces 18, 18 are installed crossing each other between the joint between the lower frame member 3 and the upstream fixed tie member 61 and the joint between the lower frame member 3 adjacent to that lower frame member 3 and the downstream fixed tie member 61, as shown in FIG. 6. The horizontal braces 18, 18 ensure horizontal rigidity in two directions between the adjacent unit frames 2A, 2A, and ensure the integrity of the adjacent unit frames 2A, 2A, including the lower frame member 3. The horizontal braces 18 may also be installed between adjacent structural components other than the lower frame member 3.

Figure 7-(a) shows an example of the installation of a horizontal member 7 different from that shown in Figure 2. Like the connecting member 6, the horizontal member 7 is made up of a fixed horizontal member 71 that is joined in advance to the front vertical frame member 4 that is joined to the lower frame member 3 (unit frame 2A) that is the base of the structure 2, and a connecting horizontal member 72 that is erected on-site between fixed horizontal members 71, 71 that are fixed to adjacent front vertical frame members 4, 4 and joined to both fixed horizontal members 71, 71.

In the example shown in Figure 7, a connecting cross member 72 is erected on-site between adjacent fixed cross members 71, 71, and to ensure workability when joining the two fixed cross members 71, 71, end plates 71a are joined to both axial ends of the fixed cross member 71, and end plates 72a are joined to both axial ends of the connecting cross member 72. Stiffeners 71b, 72b for stiffening are joined to the end plates 71a, 72a.

In addition, in order to improve workability in particular in the joining process, as shown in Figure 7-(b), the surface of the end plate 71a of the fixed cross member 71 and the surface of the end plate 72a of the connecting cross member 72 are inclined from both outer sides in the width direction of the front vertical frame member 4 toward the center from the downstream side to the upstream side. "Inclination from both outer sides in the width direction of the front vertical frame member 4 toward the center" can also be said to be an inclination from both axial ends of the fixed cross member 71 toward the center.

By providing this inclination to the surfaces of the end plates 71a, 72a, the connecting cross member 72, which has end plates 72a, 72a joined to both ends, can be inserted between adjacent fixed cross members 71, 71 from the upstream side to the downstream side, and the end plate 72a of the connecting cross member 72 can be placed on the end plate 71a of the fixed cross member 71, making it easier to join them using bolts or the like.

In this case, even if the fixed beam 71 and the connecting beam 72 are manufactured with a precision that allows the end plate 72a to overlap the end plate 71a without any gaps, the upstream gap between the end plates 71a, 71a of the adjacent fixed beams 71, 71 is large, so the end plates 72a, 72a of the connecting beam 72 can be inserted between the end plates 71a, 71a without contacting (sliding) with the end plates 71a, 71a. The end plates 72a, 72a are joined by bolts or the like that pass through both the end plates 71a, 71a while overlapping them.

In addition, because the surfaces of the end plates 71a and 72a are inclined, when the connecting cross member 72 receives an impact force from soil or rocks, a reaction force can be expected in a direction perpendicular to the surface of the end plate 71a from the end plate 71a of the fixed cross member 71 on which the end plate 72a overlaps. Therefore, the impact force (load) received by the connecting cross member 72 from soil or rocks can be transmitted to the fixed cross member 71 through the end plates 72a and 71a without relying on the shear force of the bolts, so the impact force received by the fixed cross member 71 and the connecting cross member 72 can be borne by the entire structure 2 through the front vertical frame member 4 without causing damage to the bolts.

Figure 8 shows an example of a connection between the end of the main body of the tensile member 13 and the anchor body 14 of the end fixing part which is connected to it and fixed to the ground on both sides of the stream. Since the anchor body 14 is fixed (anchored) to the ground, the end of the tensile member 13 is indirectly fixed to the ground by being connected to the head 141 of the anchor body 14 exposed above ground. Figure 8 shows how the head 141 of the anchor body 14 shown in Figure 12 is fixed to the anchor fixing material 20 described below.

In the example shown in Figure 8, the end of the tensile member 13 is connected to the fixing member 19 shown in Figure 9, while the connecting member 21 shown in Figure 10 is connected to the anchor fixing member 20 shown in Figure 11, which is connected to the head 141 of the anchor body 14, and the fixing member 19 is connected to this connecting member 21. The end of the tensile member 13 is fixed to the fixing member 19 by a fixing device 131 such as a nut.

The connecting material 21 has a connecting plate 21a connected to the anchor fixing material 20, and a fixing plate 21b which is integral with the connecting plate 21a and to which the fixing material 19 connected to the tensile material 13 is indirectly connected, and the rods 22, 22 to which the fixing material 19 is connected are connected to the fixing plate 21b in a state where they protrude toward the tensile material 13. Here, in order to stably transmit the tensile force from the tensile material 13 to the connecting material 21, the rods 22, 22 and the fixing plates 21b, 21b are arranged in parallel in the width direction (thickness direction) of the tensile material 13. The rod 22 is connected to the fixing plate 21b by a fixing device 221 such as a nut.

The anchor fixing material 20 has a fixing plate 20a to which the head 141 of the anchor body 14 is fixed by a fixing device 142 such as a nut, and a connecting plate 20b that protrudes from the fixing plate 20a toward the connecting material 21 and is integrated with the fixing plate 20a, and the connecting plate 21b of the connecting material 21 is connected to the connecting plate 20b so as to be rotatable around either axis or any axis.

As shown in FIG. 9, the fixing material 19 is assembled from rod insertion portions 19a, 19a through which the parallel rods 22, 22 of the connecting material 21 are inserted, a tension material insertion portion 19b through which the tension material 13 is inserted, and a reaction material 19c integrated with both of these. As shown in FIG. 8, the fixing material 19 is connected to the rods 22, 22 so that the axial position of the rod 22 can be freely adjusted, and by adjusting the connection position, it is possible to apply initial tension to the tension material 13 and adjust the tension. The rod 22 is inserted through a hole formed in the rod insertion portion 19a, and the tension material 13 is inserted through a hole formed in the tension material insertion portion 19b.

Figure 12 shows the entire anchor body 14. The section below the head 141 of the anchor body 14 is inserted into a drilled hole 23 formed in the ground, the drilled hole 23 is filled with grout material 24, and a tensile force is applied in the axial direction from the head 141 side with the tip fixing part 143 of the anchor body 14 fixed in the grout material 24. In this state, as shown in Figure 8, the head 141 is fixed to the anchor fixing material 20 on the ground, so that the anchor body 14 applies a compressive force to the ground and maintains its fixed state. The plate to which the head 141 of the anchor body 14 in Figure 12 is fixed is replaced with the fixing plate 20a of the anchor fixing material 20 in Figure 8.

The anchor fixing material 20 is installed on the ground surface or supported by a fixed body 25 such as a constructed reinforced concrete structure, and the reaction force of the tensile force of the anchor body 14 borne by the anchor fixing material 20 is borne by the fixed body 25.

Figure 13 shows a specific example of the damping device 16 shown in Figure 3. The damping device 16 shown here has a structure in which a thick plate 161, the cross-sectional area of which changes in the axial direction, is connected to any part of the tensile member 13 that is stretched by a tensile force and moves relative to the anchor body 14 fixed to the ground, while a tubular member 162 in which the plate 161 is inscribed is disposed on the outer periphery of the tensile member 13.

The plate 161 has a tapered shape in which the cross-sectional area in the direction perpendicular to the axial direction of the tensile member 13 gradually expands from the side where the tensile force is applied to the opposite side. In FIG. 13, the side where the tensile force is applied is the tensile member 13 side. The tubular member 162 is divided into a small diameter section 162a on the side where the cross-sectional area of the plate 161 is smaller, a large diameter section 162b on the side where the cross-sectional area is larger, and an intermediate section 162c in which the plate 161 is inscribed under normal conditions. The plate 161 moves in the axial direction of the tensile member 13 in response to the elongation of the tensile member 13, but the tubular member 162 is insulated from the tensile member 13 and absolutely fixed so as not to follow the tensile member 13, and only the plate 161 moves relative to the tubular member 162.

When the plate 161 receives a tensile force acting on the tensile member 13 and moves from the intermediate section 162c to the small diameter section 162a inside the tubular member 162, the plate 161 tries to forcefully spread the intermediate section 162c and the small diameter section 162a of the tubular member 162, creating a mechanism that generates a damping force according to the frictional force and the hysteretic absorption energy during the plastic deformation of the tubular member 162. However, since the damping device 16 shown in FIG. 13 is merely an example, the form of the damping device 16 is not important.

Figures 14-(a) and (b) show an example of the connection of the tensile member 13 to the structure 2 when the tensile members 13, 13 are arranged in two tiers, upper and lower, as shown in Figure 3, and the ends of the tensile members 13 on the structure 2 side are connected (fixed) to the upper and lower sides near both axial sides of the structure 2. (a) shows an example of the connection of the tensile member 13 on the upper tier to the structure 2, and (b) shows an example of the connection of the tensile member 13 on the lower tier to the structure 2. In the example of Figure 14, the ends of the tensile members 13 are connected to the support members 9 of the structure 2, but the connection position of the tensile members 13 is not important. The tensile members 13 may be arranged in three or more tiers in the height direction of the structure 2.

The end of the tension member 13 on the side of the structure 2 is connected (coupled) so as to be rotatable around a horizontal axis 2a and a vertical axis 2b supported on any part of the structure 2 as shown in Figure 15, so that no bending moment acts on it when it is displaced relative to the structure 2. A detailed example of the end of the tension member 13 on the side of the structure 2 in Figure 14 is shown in Figure 15-(a), and its elevation is shown in (b).

In FIG. 15, the end of the tension member 13 on the anchor body 14 side is connected directly to the connecting member 21 with a fixing device 131 such as a nut without the need for a fixing member 19, so a sleeve 13a with a male thread is connected integrally to the end of the tension member 13 on the structure 2 side, just like the sleeve 13a connected integrally to the end. This sleeve 13a is connected to an upstream connecting member 13b supported by a horizontal shaft 2a supported on any part of the structure 2 so that the tensile force from the tension member 13 can be transmitted.

The upstream connecting member 13b is connected to the downstream connecting member 13c, which is supported on a vertical axis 2b supported on another part of the structure 2, so that it can rotate freely around the horizontal axis 2a. The tension member 13 is connected to the structure 2 so that it can rotate freely around the horizontal axis 2a and the vertical axis 2b, so that it can rotate freely around an axis in any direction.

In the example shown in Figure 15 (a) and (b), a pin is supported as a vertical shaft 2b between brackets 9a, 9a that are arranged in parallel in the vertical direction and protrude from, for example, the upstream side of a support material 9 located downstream of the structure 2, and a downstream connecting material 13c is supported on this vertical shaft 2b.

The tension members 13, 13 are arranged in two tiers, so that the upper tier tension members 13 are connected to brackets 9a, 9a protruding from the top of the support member 9, etc., as shown in FIG. 14, and the lower tier tension members 13 are connected to brackets 9a, 9a protruding from the bottom of the support member 9, etc.

Figure 16-(a) shows an example of the installation of tension members 13, 13 when two tension members 13, 13 are arranged parallel to each other when two tension members 13, 13 are arranged in two tiers, one above the other, on the structure 2, and (b) shows an example of the installation of tension members 13, 13 when two tension members 13, 13 are arranged crossing each other on the riverbank side.

1... Debris flow prevention structures,
2: Structure, 2A: Unit frame, 2a: Horizontal axis, 2b: Vertical axis,
3: Lower frame material, 31: Sliding material,
4: Front vertical frame member, 5: Rear vertical frame member,
6: Tie material, 61: Fixed tie material, 62: Connection tie material,
7: horizontal member, 71: fixed horizontal member, 71a: end plate, 71b: stiffener, 72: connecting horizontal member, 72a: end plate, 72b: stiffener,
8: receiving material, 9: supporting material, 9a: bracket, 10: auxiliary material,
11... Foundation, 12... Broken granite,
13: tension member, 131: fastener, 13a: sleeve, 13b: upstream connecting member, 13c: downstream connecting member,
14: anchor body, 141: head, 142: fixing device, 143: tip fixing portion,
15: Adjustment material; 15a: Locking portion;
16: Damping device, 161: Plate, 162: Cylindrical member, 162a: Small diameter section, 162b: Large diameter section, 162c: Intermediate section,
17...contact material,
18...Horizontal brace,
19: fixing member, 19a: rod insertion portion, 19b: tension member insertion portion, 19c: reaction member,
20: anchor fixing material; 20a: fixing plate; 20b: connecting plate;
21: connecting material, 21a: connecting plate, 21b: fixing plate, 22: rod, 221: fixing tool,
23 ... drilling, 24 ... grout material,
25... object to be fixed,
26...River bed.

Claims (4)

A three-dimensional structure is constructed on a flat foundation built on the riverbed of a stream where debris flow is expected to occur.
and tension members that are installed between the structure and the ground on at least both sides of the stream, with ends on both sides fixed to the ground, and that bear impact forces from debris when the debris flow occurs together with the structure,
The structure is provided on the foundation with a plurality of lower frame members arranged in parallel in the width direction of the stream and along the direction of the debris flow, front vertical frame members and rear vertical frame members that are joined to the upstream and downstream sides of the axial direction of each lower frame member and stand up from the lower frame members, and connecting members that are installed at least between the lower frame members adjacent in the width direction of the stream and connect the two lower frame members to each other,
The lower frame member is in direct or indirect contact with the foundation so as to be relatively movable in the axial direction,
A debris-flow prevention structure characterized in that the tension member is in contact with or connected to any part of the structure so as to be able to bear the load that the structure receives from the debris toward the downstream side of the stream while allowing the relative movement of the lower frame member on the foundation. The debris flow prevention structure described in claim 1, characterized in that the tension members contact the downstream side of the structure near the center of the width of the stream, are arranged from near the center toward both sides of the width of the stream toward the upstream side of the stream, and are arranged in a curved shape overall in a plane. The debris flow prevention structure described in claim 1, characterized in that the lower frame material is restrained from rising by an adjustment material fixed to the foundation. The debris flow prevention structure according to any one of claims 1 to 3, characterized in that a damping device is interposed in a part of the tension member, which generates a damping force when the tension member bears the tensile force caused by the debris.

Images