Embankment stabilization method, and embankment structure

Abstract

To realize an embankment stabilization method and an embankment structure that can effectively prevent landslide-like movements of embankment soil mass at low cost in the event of natural disasters such as record-breaking heavy rains and earthquakes.SOLUTION: A stability analysis is performed taking into account a lateral resistance of an embankment 5 so that a resistance of embankment soil mass is greater than a sliding force, a perforated pipe 8 is embedded along a sliding direction X, a dissipation region 9 in which excess pore water pressure generated during an earthquake or the like is dissipated is formed around the perforated pipe 8, a pseudo side wall 10 with high-strength lateral resistance is formed on the dissipation region 9, and the embankment 5 is divided into a plurality of embankment regions 5a, 5b by the pseudo side wall 10. And by making a ratio of a width dimension to a depth dimension of the embankment 5 smaller than when the pseudo side wall 10 is not present, a proportion of a lateral resistance which has a relatively large resistance out of resistance of the entire embankment is increased by the pseudo side wall 10, to increase an average strength of a sliding surface in the entire embankment to suppress landslide-like movements.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to an embankment stabilization method and an embankment structure, and more specifically to an embankment stabilization method that can prevent landslide-like movements (slide collapse) even in existing embankments due to natural disasters such as record-breaking rainfall and earthquakes, and an embankment structure that can prevent landslide-like movements of soil masses even in existing embankments. [Background technology]

[0002] In Japan, where natural disasters such as record-breaking heavy rains and earthquakes occur frequently, landslides are likely to occur on embankments due to these natural disasters, and various countermeasures have been proposed.

[0003] For example, Patent Document 1 proposes a landslide prevention method for a landslide mass consisting of a concave valley-filling embankment having side portions 101a, 101b and a bottom portion 102 as shown in FIG. 13, in which at least one resistor 103 is erected on the bottom portion 102 substantially parallel to the sliding direction x to form a pseudo side wall, which strengthens the lateral shear resistance of the landslide mass and prevents the landslide.

[0004] In Patent Document 1, the landslide mass is divided into multiple regions by resistor 103 which forms a pseudo side wall, and a slide surface is formed by bottom portions 102a, 102b and side portions 101a, 101b of each region, and resistor 103. The ratio w / d of the width dimension w to the depth dimension d of the mass on each divided slide surface is smaller than in the case where resistor 103 is not provided, and this increases the shear resistance of the entire embankment, thereby increasing the average resistance force per unit area of ​​the entire mass, thereby suppressing the sliding of the landslide mass.

[0005] Furthermore, Patent Document 2 proposes an earthquake-resistant reinforcement structure in which, as shown in FIG. 14, in a valley filling embankment 112 having an embankment slope 111, partition walls 113 made by adding cement-based solidification material or lime-based solidification material to the embankment and solidifying it are formed in multiple rows at predetermined intervals in a direction z perpendicular to the valley direction y.

[0006] In Patent Document 2, by reducing the individual width w of the valley filling embankment 112 in a cross section in a direction z perpendicular to the valley direction y of the valley filling embankment 112, the ratio of the length (depth d) of the side surface (natural ground and partition wall) with which the embankment is in contact is increased, thereby increasing the shear resistance of the entire embankment, thereby preventing deformation and sliding of the valley filling embankment 112.

[0007] Another known countermeasure of this type is groundwater drainage work, which aims to prevent landslide-like movements of the embankment by lowering the groundwater level.

[0008] For example, Patent Document 3 proposes a construction method as shown in FIG. 15. That is, for an existing embankment construction site in which a building 123 is constructed on an embankment 122 constructed on a ground 121, a casing 128 is inserted while drilling a hole from an end slope 126 of the embankment 122 using a pusher 127 so as to follow a water path (soil pipe) or its vicinity formed slightly above a boundary surface 124 between the ground 121 and the embankment 122 and below a groundwater level 125. Meanwhile, a drain cartridge of a double pipe structure consisting of an outer cylindrical pipe having a permeable cross section with a donut-shaped cross section and a gabion structure filled with aggregate, and an inner cylindrical pipe disposed in contact with the outer cylindrical pipe and draining groundwater is separately prepared. Then, this drain cartridge is pushed into the casing 128 while being connected as necessary, thereby forming an underground drainage channel 129, and then the casing 128 is pulled out.

[0009] In Patent Document 3, a large-diameter underground drainage channel 129 of 300 mm to 500 mm formed by connecting drain cartridges is provided to enable large amounts of groundwater to be drained outside the system in a short period of time, thereby ensuring the sliding resistance (bottom shear resistance) at the interface 124 between the ground 121 and the embankment 122 and suppressing landslide-like movements even if an earthquake occurs and pore water pressure rises suddenly.

[0010] Patent Document 3 also describes that for newly constructed embankment land, underground drainage channels can be formed in substantially the same manner as for the above-mentioned existing embankment land, and further describes that when the groundwater volume is large, multiple underground drainage channels can be installed in a radial or parallel pattern. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Patent No. 3773098 (Claim 1, paragraph

[0009] , Figures 2, 4, etc.) [Patent Document 2] JP 2007-239202 A (claims 1 to 4, paragraph

[0015] ) [Patent Document 3] JP 2022-130793 A (claims 1, 6, 9, paragraphs

[0071] -

[0080] ,

[0085] , figures 6-10, etc.) Summary of the Invention [Problem to be solved by the invention]

[0012] Following the mudslide disaster that occurred in Atami City, Shizuoka Prefecture in July 2021, the Land Development and Specific Embankment Regulation Act (hereinafter referred to as the "Embankment Regulation Act"), which comprehensively regulates dangerous embankments, etc., came into effect on May 26, 2023. In accordance with this Embankment Regulation Act, a disaster prevention manual for embankments, etc. (draft) has already been published.

[0013] This embankment regulation law will be applied two years after its enforcement date, after designating regulated areas based on basic surveys. In addition, according to the embankment disaster prevention manual (draft), in newly constructed embankments, it will be mandatory to implement countermeasures to prevent groundwater from accumulating in the embankment, which is expected to improve safety.

[0014] However, although there is an urgent need to identify dangerous embankments, especially large-scale embankments, and take safety measures quickly for existing embankments, the affected areas are so large that it is difficult to implement inexpensive and effective countermeasures using conventional methods.

[0015] In other words, the above-mentioned Patent Document 1 divides the valley fill embankment into multiple regions along the sliding direction x, reduces the ratio w / d of the width dimension w to the depth dimension d, and increases the lateral shear resistance, thereby attempting to suppress landslide-like movements that may occur due to earthquakes, etc. However, if one tries to apply this Patent Document 1 to an existing embankment, it is necessary to dig up the ground from the surface and bury the resistor 103 in the embankment.

[0016] However, in existing embankment construction areas, buildings such as houses and commercial facilities often already exist, and it is not easy to secure work space. For this reason, applying the construction method of Patent Document 1 to existing embankment construction areas is not realistic and difficult to put into practical use.

[0017] In addition, in Patent Document 2, by forming multiple rows of partition walls 113 at predetermined intervals in the direction z perpendicular to the valley direction y, the ratio w / d of the individual width w of the valley fill embankment 112 to the depth d of the embankment side where the embankment contacts is reduced, as in Patent Document 1, thereby increasing the lateral shear resistance and thereby preventing landslide-like movement in the embankment. However, in Patent Document 2, the partition walls 113 are formed in parallel with the construction of the embankment, making it unsuitable as a countermeasure for existing embankment.

[0018] Furthermore, in Patent Document 3, as described above, a large-diameter underground drainage channel 129 of 300 to 500 mm is provided along the water path, and when an earthquake occurs and pore water pressure rises suddenly, groundwater is drained from the underground drainage channel 129 in a short period of time, thereby forming a dissipation area for excess pore water pressure at the interface 124 between the ground 121 and the embankment 122, thereby ensuring bottom shear resistance and preventing landslide-like movements.

[0019] However, although Patent Document 3 attempts to suppress landslide-like deformation of the embankment by lowering the groundwater level and thereby dissipating excess pore water pressure over the entire boundary surface 124, the area in which excess pore water pressure can be dissipated is actually partial, and it can only be formed in a small, limited area around the underground drainage channel 129.

[0020] Therefore, when applying Patent Document 3 to a large-scale embankment construction site, a large number of underground drainage channels 129 must be buried in parallel or radially along the boundary surface 124 or its vicinity, and since there are many existing embankment construction sites to be targeted, huge construction costs are required. In addition, the groundwater drainage work as in Patent Document 3 is a construction method based on the premise that excessive pore water pressure does not occur widely in the eroded part of the earth in the embankment from the viewpoint that the rise in pore water pressure can be avoided and the bottom shear resistance can be secured by lowering the groundwater level in the embankment, and has limitations as a countermeasure work. For this reason, in order to improve the effect as a countermeasure work, there is a risk that it will be necessary to use it in combination with deterrent pile work, etc., which will lead to further increase in construction costs, and therefore it cannot be said to be realistic as a preventive work.

[0021] The present invention has been made in consideration of the above circumstances, and aims to provide an embankment stabilization method that can effectively prevent landslide-like movement of embankment masses at low cost in the event of natural disasters such as record-breaking rainfall or earthquakes, even in existing embankments, and an embankment structure that can prevent landslide-like movement even in existing embankments. [Means for solving the problem]

[0022] The Fill Land Regulation Act mentioned above aims to ensure safety by imposing necessary restrictions on fill land which is prone to collapse during record-breaking rainfall and other such events. However, the larger the fill land, the greater the amount of groundwater it contains, making it more susceptible to excess pore water pressure during natural disasters such as earthquakes. Therefore, it is believed that this law will contribute to improving safety not only in the event of record-breaking rainfall, but also as an earthquake countermeasure.

[0023] The inventor then investigated embankments where landslide-like movements (sliding collapse) had occurred in the past due to earthquakes and discovered that in order to prevent landslide-like movements, it is more important to prevent the generation of excess pore water pressure than to lower the groundwater level.

[0024] That is, the inventors investigated the behavior of specific areas where landslide-like movements occurred in the 1978 Miyagi Prefecture Offshore Earthquake to determine whether similar landslide-like movements occurred again during the Great East Japan Earthquake in 2011. As a result, it was found that in some of the specific areas where drainage wells were installed after the Miyagi Prefecture Offshore Earthquake, landslide-like movements did not occur during the Great East Japan Earthquake.

[0025] In some of the above-mentioned specific areas, countermeasures have been taken by installing drainage wells at designated locations and burying drainage boreholes radially in the embankment from the drainage wells so that in the event of a rise in the groundwater level due to record-breaking rainfall, earthquakes, or other natural disasters, the drainage boreholes will be able to drain groundwater outside the system.

[0026] The Great East Japan Earthquake occurred under these circumstances. However, while no landslide-like movements occurred in the aforementioned areas where water-collection bore pipes had been buried, landslide-like movements did occur outside the aforementioned areas where water-collection bore pipes had not been buried.

[0027] The water collection bore pipe has the effect of draining groundwater outside the above-mentioned area where the water collection bore pipe is not buried, and the groundwater level outside the above-mentioned area should have dropped, but a landslide-like movement occurred outside the above-mentioned area. This is because if even a small amount of groundwater remains in the embankment, the groundwater cannot be quickly drained and depressurized even if the groundwater level (hydrostatic pressure) drops during an earthquake, so excess pore water pressure is generated, which is thought to be why a landslide-like movement occurred outside the above-mentioned area.

[0028] On the other hand, in some of the above mentioned areas, it is believed that the excess pore water pressure generated during the earthquake was dissipated as a result of groundwater flowing into the collection bore pipes and being rapidly drained, resulting in a state in which excess pore water pressure does not occur even if a small amount of groundwater remains. This is because excess pore water pressure is a phenomenon that occurs only when pressure is applied to groundwater and it cannot be rapidly drained.

[0029] Therefore, these field surveys show that landslide-like movements of the embankment cannot be sufficiently prevented in the "range where the groundwater level drops," as mentioned above, but can only be prevented in the "range where excess pore water pressure can be dissipated."

[0030] In this way, landslide-like movements of embankments can be suppressed only within the range where excess pore water pressure can be dissipated, i.e., in the dissipation area of ​​excess pore water pressure, by providing such a dissipation area along the sliding direction, a pseudo-side wall with high shear resistance is formed on the dissipation area, and this pseudo-side wall acts as a new lateral shear resistance. Therefore, it is believed that landslide-like movements can be effectively suppressed by constructing a pseudo-side wall by performing a three-dimensional stability analysis based on lateral resistance so that the resistance force of the embankment mass is greater than the sliding force, and by making the resistance force counter the sliding force.

[0031] In other words, by dividing the entire embankment into multiple embankment areas by pseudo side walls and forming pseudo side walls partially at the bottom of the embankment, landslide-like movement of the embankment can be effectively suppressed at low cost without having to form a dissipation area over the entire interface between the ground and the embankment.

[0032] By embedding a long tubular member with many openings formed in the longitudinal direction (hereinafter referred to as a "perforated pipe") in a specified position at the bottom of the embankment along the sliding direction, the perforated pipe can function in the same way as a water-collecting borehole pipe. Moreover, this perforated pipe can be easily formed by performing horizontal boring work directly from the end of the embankment, such as the slope of the embankment, and this makes it possible to take measures against landslides even in existing embankments where houses, commercial facilities, etc. have already been built, without the hassle of securing a work area.

[0033] The present invention has been made based on such findings, and the embankment stabilization method of the present invention is an embankment stabilization method for suppressing landslide-like movements of valley-filling embankments by embedding at least one long perforated pipe into the bottom of the embankment, and comprises carrying out a stability analysis taking into account the lateral resistance of the embankment so that the resistance force of the embankment mass is greater than the sliding force of the embankment mass when a natural disaster occurs, embedding the perforated pipe along the sliding direction based on the stability analysis, and forming a dissipation area in which excess pore water pressure that may be generated in the event of a natural disaster is dissipated. A pseudo side wall having high lateral resistance is formed around the perforated pipe and on the dissipation area, the pseudo side wall divides the entire embankment into a plurality of embankment areas, and the ratio of the width dimension to the depth dimension of the embankment is made smaller than when the pseudo side wall is not present. This increases the proportion of the lateral resistance, which has a relatively large resistance, out of the resistance of the entire embankment, thereby increasing the average strength of the slide surface in the entire embankment and suppressing landslide-like movements.

[0034] Here, the dissipation region includes not only a region where excess pore water pressure is no longer generated, but also a region where the excess pore water pressure is extremely reduced.

[0035] In addition, in the embankment stabilization method of the present invention, the dissipation zone is formed by rapidly draining and depressurizing the groundwater that has flowed into the perforated pipe due to the excess pore water pressure.

[0036] This creates a dissipation zone around the perforated pipe through which groundwater is rapidly drained, and by partially forming a dissipation zone at the bottom of the embankment, it is possible to efficiently prevent landslide-like movements of the embankment without having to create a dissipation zone over the entire interface between the bottom of the embankment and the ground.

[0037] In addition, since the area where excess pore water pressure dissipates is formed by rapidly draining groundwater, excess pore water pressure does not occur even if groundwater remains, which helps to prevent landslide-like movements.

[0038] In other words, the embankment stabilization method of the present invention is characterized in that the dissipation area has a function of suppressing the landslide-like movement.

[0039] Furthermore, the embankment stabilization method of the present invention is characterized in that the resistance force is used to resist the sliding force to suppress landslide-like deformation of the embankment.

[0040] By countering the sliding force in this way, landslide-like movement of the embankment can be effectively suppressed even if the shear resistance of the bottom of the embankment between the side part of the ground and the artificial side wall, or between the artificial side walls, is lost.

[0041] In addition, the embankment stabilization method of the present invention is characterized in that after drilling a hole in the embankment in the sliding direction to form a drilled hole, the perforated pipe is inserted into the drilled hole and the perforated pipe is embedded in the bottom of the embankment.

[0042] This makes it possible to carry out horizontal boring work from the end of the embankment, such as the embankment slope, on existing constructed land, and even if there are buildings such as houses or commercial facilities on the embankment, it is possible to carry out work on the existing embankment, making it possible to realize a construction method for preventing landslides at a relatively low cost.

[0043] Thus, according to the embankment stabilization method of the present invention, the resistance force of the embankment soil mass is made to resist the sliding force, so that even in large-scale embankment construction, dissipation areas are partially formed in the embankment so that dissipation areas and non-dissipation areas (hereinafter simply referred to as "non-dissipation areas") where no dissipation areas are formed are arranged in an alternating row, making it possible to realize countermeasure work that can effectively suppress landslide-like movements at low cost without having to form dissipation areas over the entire interface between the ground and the bottom of the embankment.

[0044] The embankment structure according to the present invention is an embankment structure for suppressing landslide-like movements of valley-filling embankments by embedding at least one or more long perforated pipes in the bottom of the embankment, and is characterized in that a stability analysis is performed taking into account the lateral resistance of the embankment so that the resistance of the embankment mass is greater than the sliding force of the embankment mass when a natural disaster occurs, the perforated pipes are embedded in the sliding direction based on the stability analysis, a dissipation area in which excess pore water pressure that may be generated in the event of a natural disaster is formed around the perforated pipes, and pseudo side walls having high-strength lateral resistance are formed on the dissipation area so that the entire embankment is divided into a plurality of embankment areas by the pseudo side walls, and the ratio of the width dimension to the depth dimension of the embankment is made smaller than that in the case where the pseudo side walls are not present, thereby increasing the proportion of the lateral resistance having a relatively large resistance out of the resistance of the entire embankment, and increasing the average strength of the sliding surface in the entire embankment to suppress landslide-like movements.

[0045] The embankment structure of the present invention is also characterized in that the resistance force resists the sliding force, thereby suppressing landslide-like deformation of the embankment. Effect of the Invention

[0046] According to the embankment stabilization method of the present invention, at least one long perforated pipe is embedded in the bottom of the embankment to suppress landslide-like movements of valley-filling embankments, and a stability analysis is performed taking into account the lateral resistance of the embankment so that the resistance of the embankment mass is greater than the sliding force of the embankment mass when a natural disaster occurs, the perforated pipe is embedded along the sliding direction based on the stability analysis, a dissipation area in which excess pore water pressure that may be generated in the event of a natural disaster is dissipated is formed around the perforated pipe, and a pseudo side wall having a high strength lateral resistance is formed on the dissipation area, the entire embankment is divided into a plurality of embankment areas by the pseudo side wall, and By making the ratio of the width dimension to the depth dimension of the embankment smaller than when the pseudo side wall is not present, the proportion of the lateral resistance, which has a relatively large resistance, is increased by the pseudo side wall, and the average strength of the sliding surface of the entire embankment is increased to suppress landslide-like deformation. Since the excess pore water pressure is dissipated in the dissipation area, no landslide-like deformation occurs, and the pseudo side wall formed on the dissipation area has the same resistance as the soil mass as the side of the embankment, so that the pseudo side wall acts as a new lateral shear resistance surface, and the resistance of the embankment soil mass can counter the sliding force of the embankment soil mass even if a natural disaster occurs. In other words, even if the resistance of the bottom of the embankment is almost lost due to the excess pore water pressure generated during a natural disaster, the lateral resistance of the pseudo side wall formed in the embankment can effectively suppress landslide-like deformation of the embankment at low cost.

[0047] In addition, the dissipation area is formed by rapidly draining and decompressing the groundwater that has flowed into the perforated pipe due to the excess pore water pressure, so it is possible to efficiently suppress landslide-like movements of the embankment by partially forming a dissipation area at the bottom of the embankment without having to provide a dissipation area over the entire interface between the bottom of the embankment and the ground.

[0048] Furthermore, the dissipation area has a function of suppressing the landslide-like movement, and therefore, even if groundwater remains, excess pore water pressure does not occur in the dissipation area, thereby contributing to suppression of landslide-like movement.

[0049] In addition, since the resistance force is made to oppose the sliding force to suppress landslide-like movement of the embankment, even if the bottom shear resistance force of the embankment located between the side portion of the ground and the pseudo side wall, or between the pseudo side walls, is lost, landslide-like movement of the embankment can be effectively suppressed.

[0050] Furthermore, in the embankment stabilization method of the present invention, after drilling a hole in the embankment in the sliding direction to form an excavation hole, the perforated pipe is inserted into the excavation hole and the perforated pipe is embedded in the bottom of the embankment. Therefore, it is possible to easily embed a perforated pipe in an existing embankment directly from the end of the embankment, such as the embankment slope, by horizontal boring work. Therefore, even in existing embankments where buildings such as houses and commercial facilities exist, a working area can be secured without being obstructed by these buildings, and construction can be carried out at a relatively low cost.

[0051] Thus, according to the embankment stabilization method of the present invention, the resistance force of the embankment soil mass is made to resist the sliding force, and by partially forming dissipation areas in the embankment so that dissipation areas and non-dissipation areas are arranged alternately in a row, landslide-like movements can be effectively suppressed without forming dissipation areas over the entire interface between the ground and the bottom of the embankment, and the desired embankment stabilization method can be realized at low cost.

[0052] According to the embankment structure of the present invention, at least one long perforated pipe is embedded in the bottom of the embankment to suppress landslide-like movement of the valley-filling type embankment, and a stability analysis is performed taking into account the lateral resistance of the embankment so that the shear resistance of the embankment mass is greater than the sliding force of the embankment mass when a natural disaster occurs, and the perforated pipe is embedded in the embankment along the sliding direction based on the stability analysis, a dissipation area is formed around the tubular member in which excess pore water pressure that may occur in the event of a natural disaster is dissipated, and a pseudo side wall having high strength lateral resistance is formed on the dissipation area so that the entire embankment is protected against the shear resistance of the embankment mass when a natural disaster occurs. By dividing the embankment into multiple embankment areas by the pseudo side walls and making the ratio of the width dimension to the depth dimension of the embankment smaller than when the pseudo side walls are not present, the pseudo side walls increase the proportion of the lateral resistance, which has a relatively large resistance, out of the resistance of the entire embankment, thereby increasing the average strength of the slide surface in the entire embankment and suppressing landslide-like movements.Since the embankment structure is constructed using the above-mentioned embankment stabilization method, it is possible to obtain an embankment structure that can effectively suppress landslide-like movements not only in newly constructed embankments but also in existing embankments, even if natural disasters such as record-breaking rainfall or earthquakes occur.

[0053] Furthermore, the embankment structure of the present invention suppresses landslide-like movement of the embankment by using the resistance force to resist the sliding force, so that even if the bottom shear resistance of the embankment located between the side portion of the ground and the pseudo side wall, or between the pseudo side walls, is lost, the embankment can effectively suppress landslide-like movement of the embankment. [Brief description of the drawings]

[0054] [Figure 1] FIG. 1 is a perspective view that typically shows the internal structure of one embodiment (first embodiment) of an embankment structure constructed using an embankment stabilization method according to the present invention. [Diagram 2] FIG. 2 is a vertical cross-sectional view of a main portion of the embankment structure according to the present invention. [Diagram 3] FIG. 1 is a plan view showing a schematic diagram of an embankment structure according to a first embodiment. [Figure 4] FIG. 2 is a cross-sectional view of a main portion, which is a schematic view of an embankment structure according to a first embodiment of the present invention. [Diagram 5] FIG. 2 is a full view showing one embodiment of a perforated pipe. [Figure 6] This is a cross-sectional view of a main part of a conventional embankment structure that does not have a dissipation area. [Figure 7] This is a diagram to explain the collapse of an embankment mass that occurred on an embankment in Shiroishi City, Miyagi Prefecture, during the Great East Japan Earthquake. [Figure 8] FIG. 1 is a plan view showing a schematic diagram of a drainage well installed in an embankment. [Figure 9] FIG. 2 is a cross-sectional view of a main portion showing the internal structure of a second embodiment of an embankment structure constructed using the embankment stabilization method according to the present invention. [Figure 10] FIG. 2 is a schematic plan view of the embankment structure model of Example 1. [Figure 11] FIG. 11 is a schematic plan view of the embankment structure model of Example 2. [Figure 12] FIG. 13 is a schematic plan view of an embankment structure model of a comparative example. [Figure 13] FIG. 1 is a perspective view that illustrates a conventional landslide prevention method (Patent Document 1). [Figure 14] FIG. 1 is a plan view showing a conventional earthquake-resistant reinforcement structure for a valley filling embankment (Patent Document 2). [Figure 15] FIG. 1 is a schematic diagram showing an outline of a conventional groundwater drainage work (Patent Document 3). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0055] Next, an embodiment of the present invention will be described in detail with reference to the drawings.

[0056] Fig. 1 is a perspective view showing the internal structure of an embodiment (first embodiment) of an embankment structure constructed using the embankment stabilization method according to the present invention. Fig. 2 is a vertical cross-sectional view of the main part of the embankment structure, Fig. 3 is a plan view of the main part of the embankment structure, and Fig. 4 is a horizontal cross-sectional view of the main part of the embankment structure.

[0057] 1 to 4, in this embankment structure, a valley consisting of side portions 1a, 1b having side inclination angles β1, β2 and a bottom portion 2 connected to the side portions 1a, 1b is formed on the ground 3, and an embankment 5 is constructed in the valley, thereby forming a valley-filling type embankment. The ground 3 has a bottom inclination angle θ (for example, 3° to 15°), and the embankment 5 is made slidable in the direction of the arrow X. In this first embodiment, a hollow soil pipe (water path) 7 is formed at the boundary between the ground 3 and the embankment 5 due to underground erosion over many years.

[0058] In this embankment structure, a long perforated pipe 8 is buried along the bottom surface 2 of the ground 3 from the end (slope) of the embankment 5 to the back along the sliding direction X. In the first embodiment, the perforated pipe 8 is buried along the bottom surface 2, but it is sufficient that the perforated pipe 8 is buried below the groundwater level WL and near the bottom surface 2.

[0059] As shown in FIG. 5, this perforated pipe 8 has many openings 8h formed in the longitudinal direction, and the groundwater in the embankment 5 flows into the openings 8h due to excess pore water pressure generated during natural disasters such as record-breaking rainfall or earthquakes, passes through the inside of the perforated pipe 8, and is rapidly drained outside the system.

[0060] The diameter of the perforated pipe 8 is not particularly limited, and perforated pipes 8 with a diameter of about 50 to 300 mm are usually used appropriately depending on the construction site. In addition, the material of the perforated pipe 8 is not particularly limited, and any material such as steel or resin can be used.

[0061] In Figure 5, the opening 8h is formed over the entire surface of the perforated pipe 8, but it is also preferable to block off one of the openings or to leave the areas near both ends non-perforated to prevent groundwater from flowing back out of the perforated pipe 8.

[0062] It is also preferable to lengthen the perforated pipe 8 by pressing both ends of a short perforated pipe to form female threads, and then connecting them via joint members having male threads formed by pressing. By lengthening the short perforated pipes by connecting them with joint members in this way, a perforated pipe 8 of a desired length according to the construction site can be easily obtained, and construction efficiency can be improved.

[0063] In this manner, in the first embodiment, the long perforated pipe 8 is buried in the bottom of the embankment, so that groundwater in the embankment around the perforated pipe 8 flows into the perforated pipe 8 through the opening 8h and is rapidly drained outside the system, forming a dissipation region 9 in which excess pore water pressure (which may occur during natural disasters such as earthquakes) dissipates around the perforated pipe 8. A pseudo side wall 10 having a high strength similar to that of the side portions 1a, 1b is formed on this dissipation region 9, and the entire embankment 5 is divided into two embankment regions 5a, 5b by the pseudo side wall 10.

[0064] In this first embodiment, a three-dimensional stability analysis is performed taking into account the lateral resistance of the embankment 5 so that the resistance of the embankment soil mass is greater than the sliding force that would occur in the event of a natural disaster such as record-breaking rainfall or an earthquake.As a result, pseudo side walls 10 with high-strength lateral resistance are formed on the dissipation area 9 to divide the entire embankment 5 into a number of embankment areas 5a, 5b, and the ratios W1 / D, W2 / D of the width dimensions W1, W2 to the depth dimension D of the embankment areas 5a, 5b are made smaller than the ratio W / D of the width dimension W to the depth dimension D when the pseudo side walls 10 are not present, thereby preventing landslide-like movement of the embankment.

[0065] FIG. 6 shows a cross-sectional view of a main part of a conventional embankment structure in which the dissipation area 9 is not formed.

[0066] In other words, when an embankment 5 is simply constructed in a valley in the ground 3 as in the conventional method, the side portions 1a, 1b of the embankment 5 have high-strength lateral shear resistance similar to that of a mass of soil, since no excess pore water pressure is generated in the side portions 1a, 1b even in the event of a natural disaster such as an earthquake.

[0067] On the other hand, in the embankment 5, soil particles usually flow out together with groundwater that has eroded into the ground due to years of rainwater, etc., and a hollow so-called soil pipe 7 is formed at the boundary surface between the bottom surface 2 of the embankment 5 and the ground 3 or in the vicinity thereof, or the soil becomes weak even if the soil pipe 7 is not formed. If an earthquake occurs in such a state, the structure of the embankment 5 collapses, and excess pore water pressure approximately equal to the weight of the soil mass on the bottom surface 2 is generated in the bottom surface 2 to which the soil mass load is applied, and the bottom shear resistance on the bottom surface 2 is almost lost. In addition, during record-breaking heavy rain, excess pore water pressure is generated due to an oversupply of groundwater or blockage of the soil pipe 7, and the bottom shear resistance on the bottom surface 2 is almost lost, as in the case of an earthquake. This causes shear failure in the embankment 5, which may lead to landslide-like deformation. In other words, a shear failure surface is generated in the embankment 5, and this shear failure surface causes sliding failure, inducing landslide-like deformation of the embankment.

[0068] Therefore, in order to prevent landslide-like movement of the embankment 5, it is desirable to artificially form high-strength lateral shear resistance surfaces within the embankment 5 to resist the shear failure surface.

[0069] In the first embodiment, a three-dimensional stability analysis is performed based on the side resistance of the embankment, and a perforated pipe 8 is buried in the bottom of the embankment 5 along the sliding direction X based on the stability analysis, and the excess pore water pressure generated during natural disasters is dissipated to form a dissipation area around the perforated pipe. Since the excess pore water pressure is dissipated in this dissipation area and landslide-like deformation is suppressed, the pseudo side wall 10 formed on the dissipation area 9 also forms a new side shear resistance surface with high strength similar to that of the soil mass.

[0070] By dividing the embankment 5 into a plurality of embankment regions 5a, 5b in this manner, the ratios W1 / D, W2 / D of the width dimensions W1, W2 and depth dimension D of the embankment regions 5a, 5b become smaller than the ratio W / D of the width dimension W and depth dimension D in the absence of the pseudo side wall 10. Since the side portions 1a, 1b have a large shear resistance similar to that of a mass of soil, and the pseudo side wall 10 also has a large shear resistance similar to that of a mass of soil, even if excess pore water pressure occurs in the bottom portions 2a, 2b sandwiched between the side portions 1a, 1b and the pseudo side wall 10, causing them to lose most of their shear resistance and become slippery, the side shear resistance of the entire embankment can be effectively exerted, thereby making it possible to effectively suppress landslide-like movements.

[0071] In addition, the total width Y of the dissipation region 9 in the direction perpendicular to the sliding direction X is preferably about 10 m (about 5 m for each side width Y1, Y2) for reasons described later, but is not particularly limited as long as the dissipation region 9 divides the embankment 5 into multiple regions so that the average strength at the sliding surface is greater than the sliding force.

[0072] Next, the method of stability analysis in the first embodiment will be described in detail, taking as an example a case where an earthquake occurs.

[0073] The landslide movement of the embankment 5 can be evaluated using the safety factor Fs shown in formula (1).

[0074] Fs = R / T … (1) Here, R is the resistance force and T is the sliding force.

[0075] As shown in formula (2), if the safety factor Fs is 1.0 or more, it can prevent landslide-like deformation of the embankment. On the other hand, as shown in formula (3), if it is less than 1.0, it may cause landslide-like deformation of the embankment, which may lead to sliding and collapse during an earthquake.

[0076] Fs ≧ 1.0 … (2) Fs<1.0 …(3) In order to ensure a sufficient margin of safety against landslide-like movements of the embankment 5, it is preferable to perform a stability analysis so that the modified safety factor Fs' shown in equation (4) satisfies equation (5).

[0077] Fs′=R / (f T) …(4) Fs′≧1.0 …(5) Here, f is a partial safety factor, which is set, for example, to about 1.2 to 2 depending on the degree of uncertainty in the lateral resistance force estimation. By satisfying formula (5), the embankment can ensure a sufficient degree of stability against natural disasters.

[0078] Incidentally, even in the case where a valley-filling embankment 5 is simply formed in the ground 3 as in the conventional case, as described above, the side portions 1a, 1b of the embankment 5 have high-strength lateral shear resistance similar to that of a mass of soil, since no excess pore water pressure is generated in the side portions 1a, 1b of the embankment 5 even in the event of an earthquake.

[0079] In this case, the shear resistance forces τ1 and τ2 at the side portions 1a and 1b can be expressed by formulas (6) and (7), respectively.

[0080] τ1=Z1cosβ1·tanφ1+c1·A1…(6) τ2=Z2cosβ2·tanφ2+c2·A2…(7) Here, Z1 and Z2 are the weights of the soil masses on side portions 1a and 1b, φ1 and φ2 are the angles of internal friction of the soil masses on side portions 1a and 1b, β1 and β2 are the side inclination angles of side portions 1a and 1b, c1 and c2 are the adhesive forces of the soil masses on side portions 1a and 1b, and A1 and A2 are the areas of side portions 1a and 1b.

[0081] On the other hand, since soil pipes 7 have formed at the bottom 2 due to long-term underground erosion and soil particles are thought to be flowing out, the adhesive force c3' of the soil mass at the bottom 2 can be regarded as "0." Therefore, the shear resistance force τ3' at the bottom 2 under normal conditions can be expressed by equation (8).

[0082] τ3′=Z3′cosθ·tanφ3′…(8) However, if the time that has elapsed since the construction of the embankment is short, a stability analysis can be performed taking into account the cohesive strength c3' of the soil mass.

[0083] Here, Z3' is the weight of the soil mass at the bottom portion 2, and φ3' is the internal friction angle of the soil mass at the bottom portion 2.

[0084] Therefore, in a conventional embankment structure (see Fig. 6), the resistance force R of the entire embankment is expressed by equation (9).

[0085] R = R1 + R2 + R3 ' ... (9) Here, R1 and R2 are expressed by formulas (10) and (11), and R3' is expressed by formula (12) where A3' is the area of ​​the bottom portion 2.

[0086] R1 = τ1 · A1 … (10) R2 = τ2 · A2 … (11) R3′=τ3′·A3′…(12) On the other hand, the sliding force T of the embankment soil mass is expressed by equation (13).

[0087] T = Z sinθ … (13) Here, Z is expressed by formula (14).

[0088] Z = Z1 + Z2 + Z3' ... (14) Therefore, by conducting a stability analysis of the embankment in advance and constructing the embankment 5 so that the resistance force R and the sliding force T satisfy the above formula (2), it is possible to prevent landslide-like movements under normal circumstances.

[0089] On the other hand, when an earthquake occurs, the shear resistance force τ3' of the bottom part 2 can be expressed by formula (15) since excess pore water pressure occurs in the vicinity of the soil pipe 7, including the bottom part 2, during an earthquake, where the excess pore water pressure is Ue'.

[0090] τ3′=(Z3′cosθ-Ue′)tanφ3…(15) Then, an excess pore water pressure Ue' is generated at the bottom surface 2, which is approximately equal to the weight Z3' of the soil mass on the bottom surface 2, and since the adhesion force c3' of the soil mass can be regarded as 0 as mentioned above, the shear resistance τ3' is almost lost, and τ3' ≒ 0.

[0091] Therefore, in a conventional embankment structure, the resistance force R during an earthquake is expressed by equation (16), and since the area A3 of the bottom portion 2 corresponds to the entire bottom area of ​​the embankment 5, the resistance force R is significantly reduced, and the embankment 5 may be at risk of undergoing a landslide-like movement.

[0092] R = R1 + R2 … (16) Therefore, in this first embodiment, a pseudo side wall 10 is provided and the embankment 5 is divided into two embankment areas 5a, 5b to increase the proportion of the lateral resistance, which has a relatively large resistance force, out of the resistance force of the entire embankment, thereby optimizing the embankment structure to strengthen the average strength of the sliding surface of the entire embankment and suppress landslide-like movements.

[0093] That is, when a pseudo side wall 10 is provided as in the first embodiment (see FIG. 4), the shear resistance force τ3 of the bottom portion 2a during an earthquake is expressed by equation (17), and the shear resistance force τ4 of the pseudo side wall 10 is expressed by equation (18).

[0094] τ3 = (Z3 cosθ - Ue) tan φ3 … (17) τ4=Z4cosβ4·tanφ4+c4·A4…(18)

[0095] Here, Z3 is the weight of the soil mass at the bottom surface 2a, Ue is the excess pore water pressure generated at the bottom surface 2a, φ3 is the internal friction angle of the soil mass at the bottom surface 2a, Z4 is the weight of the soil mass at the pseudo side wall 10a on the opposite side of the side surface 1a, φ4 is the internal friction angle of the soil mass at the pseudo side wall 10a, c4 is the adhesive force of the soil mass at the pseudo side wall 10a, and A4 is the area of ​​the pseudo side wall 10a.

[0096] Furthermore, by providing a pseudo side wall 10 on the dissipation area 9 so that the safety factor Fs defined by the resistance force R and the sliding force T satisfies the above formula (2), and more preferably the above formula (5), the sliding force T can be made to counteract the resistance force R, thereby effectively preventing landslide-like movement of the embankment 5 even if an earthquake occurs.

[0097] The above stability analysis has been explained for the banking area 5a, but it goes without saying that the same applies to the banking area 5b formed by the side portion 1b, the bottom portion 2b and the pseudo side wall 10b.

[0098] The embankment stabilization method according to the first embodiment was developed after the inventor investigated embankments that had experienced landslide-like movements in past earthquakes and analyzed the causes. The details of how this was done are described below.

[0099] During the 1978 Miyagi Prefecture offshore earthquake, a large slope in Midorigaoka 1-chome, Shiroishi City, Miyagi Prefecture, where embankment construction was underway at the time, collapsed, causing a landslide-like movement.

[0100] However, during the Great East Japan Earthquake in 2011, the upper area of ​​the district again experienced major landslide-like movements, but the lower area was spared.

[0101] Figure 7 is a schematic diagram showing the reclaimed land in Shiroishi City, Miyagi Prefecture after the Great East Japan Earthquake in 2011.

[0102] After the 1978 Miyagi Prefecture offshore earthquake, the use of this embankment 11 was changed from residential to a park, and at that time, the following drainage wells were installed.

[0103] That is, in the lower areas P, P' of the embankment 11, two collection wells 13a, 13b suspended by hanging members 12a, 12b were placed at predetermined locations to drain groundwater flowing in the embankment 11 as a landslide prevention measure, and numerous collection bore pipes 14a..., 14b... were buried in the embankment 11 radially from each collection well 13a, 13b toward the upstream side of the sliding surface. In addition, drainage bore pipes 15a, 15b were buried in the embankment 11 downstream of the collection wells 13a, 13b, and the groundwater that passed through the drainage bore pipes 15a, 15b was collected in a collection basin 17 via protective retaining walls 16a, 16b and was constructed so that it was drained outside the system.

[0104] Under these circumstances, the Great East Japan Earthquake occurred in 2011, but while no landslide-like movements occurred in the lower areas P and P' where the water collection bore pipes 14a..., 14b... were buried, landslide-like movements occurred in the upper area Q where the water collection bore pipes were not buried. In other words, the drop in the groundwater level should have extended not only to the lower areas P and P' where the water collection bore pipes 14a..., 14b... were buried, but also to the upper area Q where the water collection bore pipes 14a..., 14b... did not reach, but because landslide-like movements occurred only in the upper area Q, it was found that the drop in the groundwater level had a limited and not very large impact on the landslide prevention measures of the embankment.

[0105] In this way, if even a small amount of groundwater remains, excess pore water pressure will be generated by an earthquake, but the reason why the embankment masses did not move in the lower areas P, P' is that groundwater flowed into the water collection bore pipes 14a..., 14b... and was rapidly drained, resulting in no excess pore water pressure being generated around the water collection bore pipes 14a..., 14b..., or the generation of excess pore water pressure was suppressed and extremely reduced, and therefore an excess pore water pressure dissipation area was formed around (nearby) the water collection bore pipes 14a..., 14b..., where the excess pore water pressure has dissipated.

[0106] In other words, landslide-like movements of embankment soil masses cannot be sufficiently prevented in the "range where the groundwater level falls," and can only be prevented in the "range where excess pore water pressure can be dissipated." Incidentally, in the March 2022 Fukushima offshore earthquake in Sendai City, which experienced a seismic intensity of lower 5, many landslide-like movements occurred again in embankments that had been treated only with restraining works such as restraining piles. This is thought to be because the behavior of excess pore water pressure was not sufficiently reflected in the landslide prevention measures.

[0107] In the above-mentioned lower areas P and P', the tip spacing T of the water collection bore pipes 14a..., 14b... is approximately 10 m. Therefore, based on the results of a field survey in Shiroishi City, Miyagi Prefecture, it is considered that if the tip spacing T of adjacent water collection bore pipes 14a..., 14b is approximately 10 m, excess pore water pressure will be dissipated.

[0108] As a method of constructing such a collection well, as shown in Figure 8, a valley-filling embankment 15 is excavated from the surface of the earth to provide a number of collection wells 16a, 16b, 16c at prescribed locations, horizontal boring is carried out from inside the collection wells 16a, 16b, 16c to bury collection borehole pipes 17a..., 17b..., 17c... radially in the embankment, and each of these collection wells 16a, 16b, 16c is connected by drainage borehole pipes 18a, 18b.

[0109] However, when deep vertical wells are dug to form the water collection wells 16a, 16b, and 16c, and water collection boring work is performed from the water collection wells 16a, 16b, and 16c, the drilling capacity of the water collection boring work is about 50 m. Therefore, water collection boring pipes 17a..., 17b..., 17c..., which are shorter than the embankment area, must be buried radially in the embankment from the water collection wells 16a, 16b, and 16c throughout the entire area of ​​the embankment 15, and further the water collection wells 16a, 16b, and 16c must be connected with drainage boring pipes 18a and 18b, which not only increases the construction cost but also makes it difficult to secure a work area in areas densely populated with buildings such as houses and commercial facilities, making it unrealistic and practically difficult to carry out the work.

[0110] In the first embodiment, therefore, the landslide-like movement of the embankment can be suppressed within the range where the excess pore water pressure can be dissipated, and a pseudo side wall 10 having the same strength as the soil mass can be formed on the dissipation area 9. Therefore, a three-dimensional stability analysis of the embankment is performed taking into account the above-mentioned lateral resistance, and a long perforated pipe 8 having the same function as a water collection boring pipe is buried in the lower part of the embankment along the sliding direction X of the embankment 5, and a pseudo side wall 10 is formed on the dissipation area 9 to divide the embankment 5 into two embankment areas 5a and 5b. As a result, the ratios W1 / D and W2 / D of the width dimensions W1 and W2 to the depth dimension D are made smaller than the ratios W / D in the case where the pseudo side wall 10 is not provided, thereby increasing the lateral resistance of the entire embankment and effectively suppressing the landslide-like movement.

[0111] Moreover, this perforated pipe 8 can be easily formed by performing horizontal boring work directly from the end of the embankment, such as the slope of the embankment 5, so that it is easy to secure a working area even in existing embankments where houses, commercial facilities, etc. have already been built, and construction can be carried out relatively inexpensively.

[0112] In addition, in the embankment construction site in Shiroishi City, Miyagi Prefecture (see FIG. 7), the excess pore water pressure was dissipated with a tip interval T of about 10 m as described above, so the total width Y of the dissipation area 9, which is perpendicular to the sliding direction, is preferably set to a width Y1 of about 5 m on one side of the pseudo side wall 10a on the dissipation area 9 and a width Y2 of about 5 m on the other side of the pseudo side wall 10b, and therefore the total width Y of the dissipation area 9 is preferably set to about 10 m. However, in order to prevent landslide-like deformation of the embankment, it is important that the embankment 5 be divided into a plurality of embankment areas 5a, 5b by the pseudo side walls 10 so that the average strength on the sliding surface is greater than the sliding force, and so long as the total width Y is such, it is not particularly limited.

[0113] The above embankment structure is obtained by carrying out the following construction procedure on an existing embankment.

[0114] First, a boring machine is installed at the end of the embankment 5, such as the slope of the embankment, at a position corresponding to the bottom of the embankment 5. Then, the boring machine is driven to drill a hole in the embankment along the sliding direction by horizontal boring, forming an excavated hole. Then, a long perforated pipe 8 with many openings 8h formed in the longitudinal direction is inserted into the excavated hole, the casing of the boring machine is removed, and then appropriate post-processing is performed, making it easy to carry out the work.

[0115] According to this embankment stabilization method, a stability analysis is performed based on the lateral resistance of the embankment so that the resistance force R of the embankment mass is greater than the sliding force T of the embankment mass when a natural disaster occurs. Based on the stability analysis, a perforated pipe 8 is embedded along the sliding direction X, a dissipation region 9 in which excess pore water pressure that may occur in a natural disaster is dissipated is formed around the perforated pipe 8, and a pseudo side wall 10 having high strength lateral resistance is formed on the dissipation region 9. The entire embankment 5 is divided into a plurality of embankment regions 5a, 5b by the pseudo side wall 10, and the ratios W1 / D, W2 / D of the width dimensions W1, W2 and the depth dimension D of the embankment 5 are set to the values ​​obtained when the pseudo side wall 10 is present. By making the ratio W / D smaller than that when it is not applied, the proportion of lateral resistance having a relatively large resistance R out of the resistance R of the entire embankment 5 is increased by the pseudo side walls 10, and the average strength of the sliding surface in the entire embankment 5 is increased to suppress landslide-like deformation. Therefore, since the excess pore water pressure is dissipated in the dissipation area 9, no landslide-like deformation occurs, and since the pseudo side walls 10 formed on the dissipation area 9 have the same resistance R as the soil mass, just like the side of the embankment, the pseudo side walls 10 act as new lateral shear resistance surfaces, and even if a natural disaster occurs, the resistance R of the embankment soil mass can counter the sliding force T of the embankment soil mass. In other words, even if the resistance R of the bottom surface part 2 of the embankment 5 is almost lost due to the excess pore water pressure generated during a natural disaster, the lateral resistance of the pseudo side walls 10 formed in the embankment 5 can effectively suppress landslide-like deformation of the embankment 5 at low cost.

[0116] In addition, since the dissipation area 9 is formed by rapidly draining and decompressing the groundwater that has flowed into the perforated pipe due to the excess pore water pressure, it is possible to efficiently prevent landslide-like movements of the embankment by partially forming a dissipation area at the bottom of the embankment without having to provide a dissipation area over the entire interface between the bottom of the embankment and the ground.

[0117] In addition, the dissipation region 9 has a function of suppressing landslide-like movements, and therefore, even if groundwater remains, excess pore water pressure does not occur, which contributes to suppressing landslide-like movements.

[0118] Furthermore, the resistance force R is made to resist the sliding force T to suppress landslide-like movement of the embankment 5, so that even if the bottom shear resistance of the embankment between the side portions 1a, 1b of the ground 3 and the pseudo side walls 10, or between the pseudo side walls 10, is lost, the landslide-like movement of the embankment 5 can be effectively suppressed.

[0119] Furthermore, in this embankment stabilization method, after drilling a hole in the embankment 5 in the sliding direction X to form an excavation hole, a perforated pipe 8 is inserted into the excavation hole and the perforated pipe 8 is embedded in the bottom of the embankment 5. Therefore, it is possible to easily embed a perforated pipe in an existing embankment directly from the end of the embankment, such as the embankment slope, by horizontal boring work. Therefore, even in an existing embankment where buildings such as houses and commercial facilities exist, a work area can be secured without being obstructed by these buildings, and construction can be carried out at a relatively low cost.

[0120] According to this embankment structure, a stability analysis is performed taking into account the lateral resistance of the embankment 5 so that the resistance force R of the embankment mass is greater than the sliding force T of the embankment mass when a natural disaster occurs, and based on the stability analysis, a perforated pipe 8 is embedded along the sliding direction X, and a dissipation region 9 that dissipates excess pore water pressure that may occur in the event of a natural disaster is formed around the perforated pipe 8. Furthermore, a pseudo side wall 10 having high strength lateral resistance is formed on the dissipation region 9, so that the entire embankment 5 is divided into a plurality of embankment regions 5a, 5b by the pseudo side wall 10, and the width dimensions W1, W2 and depth dimensions of the embankment 5 are set to be equal to or larger than the width dimensions W3, W4, and the depth dimensions T of the embankment 5 are set to be equal to or larger than the width dimensions W5, W6, and the width dimensions T of the embankment 5 are set to be equal to or larger than the width dimensions T of the embankment 5. By making the ratios W1 / D and W2 / D to the slope D smaller than the ratio W / D when the pseudo side wall 10 is not present, the pseudo side wall 10 increases the proportion of the lateral resistance, which has a relatively large resistance force R, out of the resistance force R of the entire embankment, thereby increasing the average strength of the slide surface in the entire embankment and suppressing landslide-like movements.Since the embankment structure is constructed using the above-mentioned embankment stabilization method, it is possible to obtain an embankment structure that can effectively suppress landslide-like movements not only in newly constructed embankments but also in existing embankments, even if natural disasters such as record-breaking rainfall or earthquakes occur.

[0121] In addition, since the resistance force R resists the sliding force T and suppresses the landslide-like movement of the embankment 5, even if the bottom shear resistance of the embankment 5 located between the side portions 1a, 1b of the ground 3 and the pseudo side walls 10, or between the pseudo side walls 10, is lost, the landslide-like movement of the embankment 5 can be effectively suppressed.

[0122] Furthermore, after an excavation hole is formed in the existing embankment 5 from the end of the embankment slope in the sliding direction X, the tubular member 5 is inserted into the excavation hole and the perforated pipe 8 is buried in the embankment 5. Therefore, the perforated pipe 8 can be easily buried by horizontal boring work, which is suitable for countermeasure work on an existing embankment.

[0123] FIG. 9 is a cross-sectional view of a main part of the internal structure showing a second embodiment of an embankment structure constructed using the present embankment stabilization method.

[0124] In other words, in this second embodiment, a large number of perforated pipes 21... similar to those in the first embodiment are buried under an embankment 22, and dissipation regions 23... are formed around each of these perforated pipes 21..., and dissipation regions 23... and non-dissipation regions 24... which have no dissipation regions are formed alternately.

[0125] Even in such large-scale existing embankments, dissipation areas 23... are lined up at predetermined intervals so that dissipation areas 23... and non-dissipation areas 24... are formed alternately in the embankment 22, and since the individual shear resistance of these dissipation areas 23... is increased, the lateral shear resistance of the embankment as a whole is increased, thereby making it possible to effectively suppress landslide-like movement of the embankment even in the event of natural disasters such as record-breaking rainfall or earthquakes.

[0126] In other words, in this second embodiment as well, the resistance force R of the embankment soil mass is made to resist the sliding force T, so that dissipation areas 23... and non-dissipation areas 24... are arranged alternately in a row by partially forming dissipation areas 23... in the embankment 22, so that landslide-like movements can be effectively suppressed without forming dissipation areas over the entire interface between the ground and the bottom of the embankment, and the desired embankment stabilization method can be realized at low cost.

[0127] The present invention is not limited to the above-mentioned embodiment. The above-mentioned embodiment is also an example of the embankment stability analysis method, and it goes without saying that various stability analysis methods can be applied. For example, in the case of record-breaking heavy rain, if excess pore water pressure can be generated due to an excess supply of groundwater to the soil pipe or blockage of the soil pipe, it goes without saying that a stability analysis method suitable for the event can be used.

[0128] In the above embodiment, the perforated pipes 8, 21 are embedded directly from the end of the embankment such as the embankment slope by horizontal boring work, but if a work area can be secured, they may be excavated from the ground surface.

[0129] Furthermore, although the present invention is an embankment stabilization method suitable for existing embankments, it goes without saying that it can also be applied to new embankment construction sites.

[0130] Next, examples of the present invention and comparative examples will be described in detail. EXAMPLES

[0131] An embankment structure model was constructed in which a pseudo side wall was formed in the center of the valley-fill embankment, and a simulation was performed to evaluate the stability of the embankment.

[0132] FIG. 10 is a schematic plan view of the embankment structure model of the first embodiment.

[0133] This embankment structure model has a concave shape with a width dimension of the slope at the bottom of the embankment of a total length W of 180m, a depth dimension D1 of the center of 6m, a depth dimension L1 of 100m, a depth dimension D2 of both side parts of 4m, a depth dimension L2 of 50m, and further, an inclination angle (side inclination angle) β (β1, β2) of the side parts of the embankment set to 70°. In this embankment structure model, the bottom inclination angle θ is 15° and inclined from the slope 51 toward the upper depth of the embankment, the embankment is slidable in the direction of the arrow X, and the outer periphery EA of the embankment is formed in a parabolic shape. In the figure, CL is a contour line of the bottom of the embankment, which is drawn at intervals of 5m from the embankment slope 51.

[0134] In this Example 1, a perforated pipe 8 (diameter 50 mm) with a total length of 100 m was formed in the center of the bottom of the embankment along the sliding direction X to the position of the depth dimension L1 of the embankment, the total width Y of the dissipation area 9 was set to 10 m (one side widths Y1, Y2 were each 5 m), and the inclination angle β (β3, β4) of the pseudo side wall was set to 70°, thereby constructing an embankment structure model divided into two by the pseudo side wall.

[0135] Table 1 shows the specifications of this embankment structure model.

[0136] [Table 1]

[0137] For this embankment structure model, under the soil conditions shown in Table 2, the groundwater level was set 3 m below the ground surface, and the sliding force T and resistance force R were calculated using the formulas shown in the above embodiment.The safety factors Fs and Fs' (partial safety factor f = 1.5) were obtained from the sliding force T and resistance force R, and the stability of the embankment was evaluated.

[0138] [Table 2]

[0139] The soil mass weights Z1, Z2, and Z3 are calculated based on the unit volume weight of the embankment and the unit volume weight underwater, with the weight above the groundwater level being the wet weight and the weight below the groundwater level being the submerged weight, respectively.

[0140] As a result, the sliding force T was 151,804kN, the resistance R1 of the side part 1a was 73,124kN, and the resistance R2 of the pseudo side wall facing the side part 1a was 168,310kN. In addition, when an earthquake occurs, excess pore water pressure is generated and the bottom shear resistance is lost, so the resistance R3 of the bottom part is R3 = 0.

[0141] Therefore, the resistance R is R=R1+R2=241,434kN, and the safety factor Fs is Fs=R / T=1.590, which ensures Fs≧1.0 and confirms that landslide-like movements can be prevented. Even when the partial safety factor f is set to 1.5, the safety factor Fs′ is Fs′=R / f T=1.060, which confirms that landslide-like movements can be prevented with a sufficient margin.

[0142] In this Example 1, the stability of the embankment was evaluated for the side portion 1a, the pseudo side wall, and the bottom portion between these side portion 1a and the pseudo side wall. However, it goes without saying that similar results can be obtained when the stability of the embankment is evaluated for the other side portion 1b, the pseudo side wall, and the bottom portion between these side portion 1b and the pseudo side wall. EXAMPLES

[0143] An embankment structure model was constructed in which the entire valley-fill embankment was divided into three parts by pseudo-side walls, and a simulation was performed to evaluate the stability of the embankment.

[0144] FIG. 11 is a schematic plan view of the embankment structure model of the second embodiment, and the shape of the embankment is the same as that of the first embodiment.

[0145] In this Example 2, an embankment structure model was constructed which was divided into three parts, with end blocks 52a, 52b at both ends and a central block 53 sandwiched between the end blocks 52a, 52b.

[0146] Here, the end blocks 52a, 52b have an embankment depth dimension D of 4m, width dimensions W3, W4 of 55m, and a total length L3 of the perforated pipe 8a (diameter 50mm) of 90m, with the perforated pipe 8a formed at the bottom along the sliding direction X, and the dissipation areas 9a, 9b have a side width Y1 of 5m and a pseudo side wall inclination angle β (β3) of 70°.

[0147] The central block 53 has a depth D of 5m and a width W5 of 50m, and the total length L3 of the perforated pipe 8a (diameter 50mm) is 90m like the end blocks, and the perforated pipe 8a is formed at the bottom along the sliding direction X. The dissipation areas 9a and 9b have a side width Y2 of 5m and a pseudo side wall inclination angle β (β3) of 70°. The total width Y of the dissipation areas 9a and 9b is 10m like the first embodiment, because the side widths Y1 and Y2 are each 5m.

[0148] Table 3 shows the specifications of the embankment structure in Example 2.

[0149] [Table 3]

[0150] For this embankment structure model, the groundwater level was set 3 m below the ground surface under the same soil conditions as in Example 1, and the stability of the embankment was evaluated using the same method as in Example 1.

[0151] As a result, the sliding force T of the end block 52a was 83,146 kN, the resistance R1 of the side portion 1a was 73,124 kN, and the resistance R2 of the pseudo side wall facing the side portion 1a was 115,641 kN. Furthermore, since excess pore water pressure is generated during an earthquake and the bottom shear resistance is lost, the resistance R3 of the bottom portion of the end block 52a is R3=0.

[0152] Therefore, the resistance force R is R = R1 + R2 = 188,765kN, so the safety factor Fs is Fs = R / T = 2.270, and it is confirmed that Fs ≥ 1.0 can be ensured and landslide-like movements can be prevented. Even when the partial safety factor f (= 1.5) is taken into consideration, as in Example 1, the safety factor Fs' is Fs' = R / f T = 1.514, and it is confirmed that landslide-like movements can be prevented with a sufficient margin.

[0153] Needless to say, the end block 52b also provides the same results as the end block 52a.

[0154] In addition, the sliding force T of the central block 53 was 129,601 kN, and the resistance forces R4 and R5 of the opposing pseudo side walls were both 115,641 kN. And, since the bottom part between the pseudo side walls loses its bottom shear resistance due to excess pore water pressure generated during an earthquake, the resistance force R6 of the bottom part of the central block 53 is R6=0.

[0155] Therefore, the resistance force R is R=R4+R5=115,641+115,641=231,282kN, so the safety factor Fs is Fs=R / T=1.785, and it was confirmed that Fs≧1.0 can be ensured and landslide-like deformation can be prevented. Even when the partial safety factor f is set to 1.5 as in Example 1, the safety factor Fs' is Fs'=R / f T=1.190, and it was confirmed that landslide-like deformation can be prevented with a sufficient margin.

[0156] That is, it was confirmed that even in this embankment structure model divided into three, all of the end blocks 52a, 52b and the central block 53 can suppress landslide-like deformation of the embankment.

[0157] As a comparative example, the stability of the embankment was also evaluated in a case where no perforated pipe was embedded in the bottom of the embankment and no pseudo side wall was formed.

[0158] FIG. 12 is a schematic plan view of an embankment structure model of a comparative example, and the shape of the embankment is the same as that of the first embodiment.

[0159] For this embankment structure model, the stability of the embankment was evaluated using the same method as in Example 1 under the same soil conditions as in Example 1, with the groundwater level set 3 m below the ground surface.

[0160] As a result, the sliding force T was 379,393 kN, the resistance forces R1 and R2 of the side parts 1a and 1b were both 73,124 kN, and the resistance force R3' of the bottom part 2 under normal conditions before the earthquake was 348,446 kN.

[0161] Therefore, the resistance force R under normal conditions is R = R1 + R2 + R3' = 494,694 kN, and the safety factor Fs is Fs = R / T = 1.304, which shows that the embankment structure model in the comparative example is also capable of preventing landslide-like movement of the embankment under normal conditions.

[0162] On the other hand, when an earthquake occurs, excess pore water pressure is generated and the bottom shear resistance is lost, so the resistance force of the bottom part R3' is R3' = 0. Therefore, during an earthquake, the resistance force R is R = R1 + R2 = 146,248 kN, and the safety factor Fs is Fs = R / T = 0.385, which is significantly less than 1.0, and it was found that it is difficult for the embankment to prevent landslide-like movement during an earthquake.

[0163] From the above, it was confirmed that landslide-like movements of embankments can be effectively prevented by performing stability analysis of the embankment and installing pseudo-side walls with high strength lateral shear resistance in the embankment. [Industrial Applicability]

[0164] Stability analysis is carried out taking into account lateral resistance so that the resistance of the embankment mass is greater than the sliding force, and at least one perforated pipe is buried at the bottom of the valley-fill embankment to form a dissipation area in which excess pore water pressure can dissipate. This reduces the ratio of each width and depth dimension of the embankment and increases the proportion of lateral shear resistance, which has a relatively large shear resistance, out of the shear resistance of the entire embankment, thereby increasing the average strength of the slide surface and preventing landslide-like movement of the embankment. [Explanation of symbols]

[0165] la, 1b side part 2 Bottom part 3 Ground 5 Embankment 8, 21 Perforated pipe (tubular member) 8h opening 9, 23 Dissipation region 10 False sidewall

Claims

1. A method for stabilizing embankments, comprising embedding at least one long tubular member having a number of openings formed in the longitudinal direction at the bottom of the embankment to suppress landslide-like movements of the embankment in a valley, comprising: Conduct a stability analysis taking into account the lateral resistance of the embankment so that the resistance of the embankment will be greater than the sliding force of the embankment in the event of a natural disaster; embedding the tubular member along a sliding direction based on the stability analysis; A dissipation region in which excess pore water pressure that may occur during a natural disaster is dissipated is formed around the tubular member, A pseudo side wall having high strength lateral resistance is formed on the dissipation area, and the pseudo side wall divides the entire embankment into a plurality of embankment areas; An embankment stabilization method characterized by increasing the proportion of the lateral resistance, which has a relatively large resistance force, out of the resistance force of the entire embankment by making the ratio of the width dimension to the depth dimension of the embankment smaller than when the pseudo side wall is not present, thereby increasing the average strength of the slide surface of the entire embankment and preventing landslide-like movements.

2. 2. The embankment stabilization method according to claim 1, wherein the dissipation area is formed by rapidly draining and depressurizing groundwater that has flowed into the tubular member due to the excess pore water pressure.

3. 3. The embankment stabilization method according to claim 1, wherein the dissipation area has a function of suppressing the landslide-like movement.

4. 3. An embankment stabilization method according to claim 1, wherein said resistance force is applied against said sliding force to suppress landslide-like deformation of said embankment.

5. 3. An embankment stabilization method as claimed in claim 1 or claim 2, characterized in that after drilling a hole in the embankment in the sliding direction to form a hole, the tubular member is inserted into the hole and the tubular member is embedded in the bottom of the embankment.

6. An embankment structure for suppressing landslide-like movements of a valley-filling embankment by embedding at least one or more long tubular members having a number of openings formed in the longitudinal direction at the bottom of the embankment, A stability analysis is carried out taking into account the lateral resistance of the embankment so that the resistance force of the embankment mass is greater than the sliding force of the embankment mass in the event of a natural disaster, and the tubular members are embedded in the embankment along the sliding direction based on the stability analysis. A dissipation region is formed around the tubular member to dissipate excess pore water pressure that may occur during a natural disaster; Furthermore, a pseudo side wall having high strength lateral resistance is formed on the dissipation area, and the entire embankment is divided into a plurality of embankment areas by the pseudo side wall; An embankment structure characterized by making the ratio of the width dimension to the depth dimension of the embankment smaller than when the pseudo side wall is not present, thereby increasing the proportion of the lateral resistance, which has a relatively large resistance force, out of the resistance force of the entire embankment, through the pseudo side wall, thereby increasing the average strength of the sliding surface of the entire embankment and preventing landslide-like movements.

7. 7. The embankment structure according to claim 6, wherein said resistance force resists said sliding force to suppress landslide-like deformation of said embankment.

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