JP2012092520A - Construction method for preventing surface failure of slope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To relatively easily and rapidly prevent a surface failure of a slope by providing a complementary construction method which can be applied even to the slope in precipitous mountains kept in a natural state and making carrying-in of large-size equipment difficult and which can prevent the surface failure while leaving vegetation as-is.SOLUTION: A plurality of iron base pipes 20, which each have a large number of strainer holes 24 formed in a dispersed manner on a peripheral wall of a pipe body and which each structurally have a leading end sharpened, are driven at each of a plurality of spots on a slope from a ground surface in directions different from one another. Back ends of the iron base pipes exposed on the ground are bundled and fastened together by a binding fitting 22, a wire and the like.

Description

  The present invention relates to a method for preventing the collapse of the surface layer of the slope. More specifically, the surface layer is formed by directly driving a hollow steel pipe having a large number of strainer holes and closed ends into the slope while leaving the slope vegetation intact. This is related to complementary measures to prevent collapse.

  Among natural disasters that occur in Japan, landslide disasters occur frequently and cause great damage to human lives and property. In particular, slopes and slopes are the most disasters, and about 90% of them are said to be surface failure. For this reason, it is extremely important to prevent the collapse of the surface layer in order to preserve the slope. Vegetation that protects the surface layer is said to be effective in preventing this surface layer collapse.

  By the way, in the surface layer collapse, the depth of the tree roots or a slightly deeper soil layer loses mechanical stability such as cohesion and adhesion due to the infiltration of precipitation and the resulting groundwater, and along the basement rock. It is a phenomenon that suddenly collapses in the form of peeling or sliding. Therefore, the presence or absence of vegetation, the type of vegetation, and its management status are presumed to be greatly involved in these surface layer collapses.

  The slope stabilization effect by vegetation is considered to be the dispersion effect of rainfall and the effect of preventing erosion of the ground surface, the top-soil binding effect by the root system, and the pile effect by the vegetation invading the basement rock. Therefore, establishing a slope stabilization method using the vegetation root system is considered to be the most economical countermeasure method in addition to greatly helping to preserve many slopes and slopes in Japan and to protect local ecosystems. However, there are few studies that systematize how surface vegetation is related to slope stability.

  Explain the case study of the field survey on the slope stability effect of vegetation. For example, as for the unconsolidated layer ground, as a result of surveys conducted at two locations on the coastal terraces of the Shikoku Muroto Peninsula and the Neji Plateau in the Kushiro region, the effects of forest vegetation on preventing the unconsolidated layer from eroding and preventing surface collapse It is clear that there is. As for the rock mass, the result of the survey in Shichimune Town in Gifu Prefecture showed that there was little damage to the broadleaf trees even when the topography and geological conditions were the same during the typhoon No. 8 and No. 7 in 1998. It was found that the slope stabilization effect of broad-leaved trees, whose roots are strong, is high, and that the species and forest care are important.

However, a detailed study has revealed that there are special ground characteristics that impede slope stability due to vegetation. In particular, Typhoon No. 4 that traversed the Japanese archipelago in August 1998 caused many slope failures in the southern part of Fukushima Prefecture (Shirakawa region) and the northern part of Tochigi Prefecture. Paying attention to this slope failure, it was found that the collapse surface is thin, and the root system does not extend deeply vertically but constitutes a special surface ground that extends only in the slope direction. This decay is referred to as “root system layer decay” (see Non-Patent Document 1). Its characteristics are as follows.
(1) Collapse thickness is very thin with less than 1m (2) Slope slope is steep and around 40 ° (3) Topography and geology where surface water and groundwater are likely to gather (4) Directly under the surface layer with root system The basement rock is distributed and the Nc value changes suddenly from 2 or less to 50 or more. (5) There is no fissure where the root system enters the basement rock immediately below the surface layer. And so on.

  The cause of the root layer collapse is the pile effect (drawing resistance effect), which is another prevention effect, although the tight binding effect, which is one of the root collapse prevention effects, is secured from the topography, geology, and vegetation status. ) Cannot be exhibited at the boundary between topsoil and basement rock. In addition, the root system collapse occurred on the slope of the catchment topography, and many spring holes were observed at the boundary between the topsoil and the basement rock on the collapsed surface, and the concave structure of the basement rock was observed at the top of the collapse. Therefore, it can be judged that slip occurred at the boundary between the root system layer and the basement rock due to the concentration of groundwater and generation of pore water pressure due to heavy rain.

  It was found that not only the low welded pyroclastic flow deposit ground in Shirakawa but also weathered granite and mudstone ground are likely to cause such root system collapse. As weathered granite ground, we investigated the Suzuka Mountains (forestation) in Shiga Prefecture and Mt. According to this, clear-cutting was once performed, soil runoff occurred, and root system layer collapse occurred repeatedly in the Suzuka Mountains, which is a cedar plantation. On the other hand, Mt. Tajin, where the evergreen virgin forest remains, has good surface soil development and no root system collapse. The topography and geology are similar to those of the Suzuka Mountains, but it is clear that once the surface ground flows out due to the difference in vegetation, it is clear that the surface layer will repeatedly collapse, and the importance of potential vegetation to create a good surface structure Became clear.

  Thus, vegetation that protects the ground surface is extremely important in preventing the collapse of the slope. However, managing vegetation effectively is a laborious and time consuming process. In addition, the slope stabilization effect by vegetation is limited on the ground where root system collapse is likely to occur.

  By the way, drainage pipes are conventionally used to reinforce slopes of unstable sediments such as banking / cutting related to railways and roads, and slopes of residential land development sites (see Patent Document 1). This is to discharge water through the inside of the pipe by driving or inserting a pipe having a plurality of drain holes in the peripheral surface into the slope of an unstable earth and sand part. Since the main purpose is to discharge excess water in the ground, the pipe needs to have a certain thickness and length. For example, in Patent Document 1, an outer diameter of about 60 mm and a length of about 3.6 m are used. For drainage, the pipe is installed so as to be substantially horizontal or inclined so that the outer end exposed to the outside faces downward.

  Using such a long and long drainage pipe, it is possible to secure a long-term drainage channel in the ground, but the construction work on the slope requires a driving machine, and an artificially limited unstable slope that can carry in equipment. Only applicable to However, in many cases, it is a natural slope, and a steep mountain slope where it is difficult to carry in equipment is desired to prevent the slope from collapsing. At present, such slope stabilization can only be relied on vegetation. However, as mentioned above, effective management of vegetation requires enormous effort and time, and is effective in nurturing the root system of trees. There is no way. There are also grounds where vegetation alone is insufficient.

JP 2003-155737 A

Hideaki Inagaki "Root System Collapse" Soil and Foundation, Vol.50, No.5 (2002)

  The problem to be solved by the present invention can be applied even to steep mountain slopes that are in a natural state and difficult to carry in large-sized equipment, and a complementary construction method that prevents surface layer collapse while leaving vegetation intact. It is to be able to prevent the surface layer collapse of the slope relatively easily and quickly.

  The present invention is a steel pipe having a structure in which a large number of strainer holes are distributed and formed on the peripheral wall of the pipe body, and the tip is sharpened, at a plurality of points on the slope, a plurality of pipes at each point, driven from the surface in different directions, It is a surface layer collapse prevention construction method characterized by bundling and fastening the rear ends of iron pipes exposed on the ground. This “iron pipe” is a small-diameter pipe that has a suction function that can easily be driven into the ground, has mechanical strength that can withstand the driving, and can reduce the underground pore water pressure. In the present invention, it is called “iron root” because it is like an artificial root that mimics the function of a tree root.

  The iron pipe used here typically has a length of 1.0 to 1.5 m and a diameter of 10 to 20 mm, and a large number of strainer holes formed in the peripheral wall of the pipe body have a diameter of 2 to 6 mm, It is perforated in the 3-4 direction of the circumference at intervals of 5-15 cm in the length direction. Such iron root pipes are driven from the ground surface, for example, by 2 to 6 pieces per point, and the rear ends of the iron pipes exposed on the ground are bundled and tied together by a wire.

  The slope surface layer prevention method according to the present invention includes a plurality of iron pipes having a plurality of strainer holes, driven from the surface in different directions, and binding the rear end of the iron pipe exposed to the ground. Therefore, it is possible to simulate the effect of the roots of the tree, thereby enabling complementary measures to prevent surface collapse while leaving the surrounding vegetation intact. The iron pipe pipes laid here can prevent the surface layer from collapsing by the binding effect and the pile effect on the ground. In addition, since many strainer holes are distributed in the iron pipe, the effect of reducing excessive pore water pressure occurs, and at the boundary between the root system layer and the basement rock due to the concentration of groundwater and generation of pore water pressure due to heavy rain. It is possible to prevent the occurrence of slippage.

Explanatory drawing which shows one Example of the surface layer collapse prevention construction method of the slope concerning this invention. Explanatory drawing which shows an example of the iron pipe used by this invention.

  An example of a slope to which the present invention construction method is applied is schematically shown in FIG. This is a cross section of a mountainside with some vegetation. The surface layer 12 covers the inner basement rock 10. The basement rock 10 may be a bedrock that does not have cracks, and may not have roots, or may have cracks and roots. The surface layer 12 is formed of topsoil.

  The trees form a tough root system 16 that spreads the net in the hillside topsoil. The root system 16 enhances the topsoil binding effect. Furthermore, in the case of basement rocks with cracks, the roots develop in the depth direction and enter the cracks. The planted root that has entered the crack becomes like a pile, and the slope stabilization effect is enhanced. However, in the case of basement rocks without cracks, the development of the root system in the depth direction is hindered, the pile effect due to rooting does not work, and the sliding surface 14 with reduced shear strength is directly above the basement rock (basement rock 10 and surface layer 12). It appears that root system layer collapse occurs. Such a situation in which root layer collapse is likely to occur is characterized by the topography and geology where the collapse thickness is as thin as less than 1 m, the slope is steep and around 40 degrees, and surface water and groundwater are likely to gather.

  Therefore, in the method of the present invention, the iron pipe 20 is driven from the surface of the steel pipe 20 at a plurality of points on the slope in different directions, and the rear ends of the steel pipes exposed on the ground are bundled together. Fastening is performed using the binding hardware 22 or the like.

  An example of the iron pipe used here is shown in FIG. A represents a plane, B represents a longitudinal section thereof, and C represents a cc section. The iron pipe 20 has a structure in which a large number of strainer holes 24 are dispersedly formed on the peripheral wall of the pipe body, and the sharpened tip portion 26 is sharply closed like a blade by being crushed from two opposite directions. Typically, the tube body has a length of 1.0 to 1.5 m and a diameter of 10 to 20 mm, and a large number of strainer holes 24 formed on the peripheral wall of the tube body have a diameter of 2 to 6 mm and a total circumference of 3 It is perforated in the length direction of 5 to 15 cm in the 4 directions. In order to facilitate driving, the tip portion 26 is sharpened as described above. As shown in FIG. 2, it is preferable that the structure is flattened by crushing from both sides because it can be manufactured at low cost, but a structure in which a cone-shaped tip member is separately manufactured and mounted may be used. In addition, it is preferable to galvanize the surface of the iron pipe for rust prevention.

  In actual construction, since the iron pipe 20 to be driven is small in diameter and short, an operator can carry it in even in a mountainous area where a transport vehicle or the like cannot enter. Bring the iron pipe 20 into the construction site and drive it directly into the ground with a hammer. At that time, for example, 2 to 6 iron pipes 20 are driven in various directions from the horizontal direction or slightly upward to the vertical direction. Then, the rear ends of the iron pipes exposed on the ground surface are bundled and fastened. For fastening, a band-shaped binding metal fitting 22 may be used, but may be bound with a wire (for example, a wire in which a stainless wire is twisted) or a wire. Wires and wires can more easily respond to changes in various situations such as the number of iron pipes and driving angle.

  Some of the installed steel pipes stay on the surface depending on the driving direction, but some of them penetrate the sliding surface 14 between the surface layer 12 and the basement rock 10 having a thickness of about 1 m, and the basement rock Reach 10 At this time, since the present invention is a driving method, the soil layer around the iron pipe is not loosened, and the iron pipe is not clogged. Since multiple iron pipes 20 are bound at the rear end, the topsoil bondage effect appears even if it stays on the surface layer, and when it reaches the basement rock through the sliding surface, the surface layer slides down Suppresses Further, since the iron pipe 20 is subjected to strainer processing, it is possible to extract and reduce excessive pore water pressure that causes surface layer collapse. By these effects, root system layer collapse can be particularly prevented. In addition, the flow of groundwater on the slope is often a pipe flow, and many iron root pipes can be driven in various directions, so the effect of removing excessive groundwater pressure is high.

  In addition, the iron pipe used in the present invention is driven in an arbitrary direction between the horizontal direction or a slightly upward direction and a vertical direction, and unlike the prior art that drains groundwater, it simply removes the underground pore water pressure. It has a function. Therefore, even the small diameter as described above functions sufficiently.

Therefore, this invention construction method has the following features.
(1) Since this iron pipe is long and heavy enough to be carried by manpower even on steep slopes, it can be constructed by manpower, and can be constructed in any narrow place or steep slope. Because it is a very simple countermeasure, it is also economical. In addition, since the iron pipe is driven during construction, the surrounding soil layer does not loosen and clogging does not occur.
(2) Since the iron pipe is subjected to strainer processing, excessive pore water pressure that causes surface layer collapse can be eliminated. Moreover, since the iron pipe can be driven in various directions, the effect of removing excessive pore water pressure is great.
(3) Since the iron pipe is driven through the sliding layer to the base rock, the pile effect can suppress the unstable surface soil of the surface layer like the tensile resistance of the root.
(4) Since the vegetation can be kept as it is, measures can be taken to protect the slope ecosystem. Moreover, it has a rapid effect.
(5) Since it can also be driven into unbroken basement rocks, it can solve the problem of root system layer collapse, which is not effective with natural roots.

  As can be seen from the above, the method of the present invention can be used for both base rocks with cracks and base rocks without cracks. In the case of basement rocks with cracks, the roots of the trees enter the cracks and exert a pile effect, but when the vegetation is sparse, it is supplemented with vegetation until the vegetation becomes dense by driving iron pipes It becomes. In the case of unbroken basement rocks, the iron root pipe is driven into the basement rock to exert a pile effect, thereby preventing root system collapse.

DESCRIPTION OF SYMBOLS 10 Basement rock 12 Surface layer 14 Sliding surface 16 Root system 20 Iron pipe 22 Bundling bracket 24 Strainer hole 26 Sharpened tip

Claims (3)

  A number of strainer holes are distributed and formed on the peripheral wall of the pipe body, and steel pipes with a sharpened tip are driven from the surface of the ground at multiple points on the slope in different directions and exposed to the ground. A method for preventing the collapse of the surface layer of a slope, which is characterized by bundling and fastening the rear ends of a steel pipe.   The iron pipe to be used has a length of 1.0 to 1.5 m and a diameter of 10 to 20 mm, and a number of strainer holes formed in the peripheral wall of the pipe body have a diameter of 2 to 6 mm and 3 to 4 directions on the entire circumference. The method for preventing surface collapse of a slope according to claim 1, wherein the method is perforated at intervals of 5 to 15 cm in the longitudinal direction.   The surface layer of the slope according to claim 1 or 2, wherein 2 to 6 iron pipes are driven from the ground surface at one point, and the rear ends of the iron pipes exposed on the ground are tied together and tied together with a wire. Collapse prevention method.

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