JP5319266B2 - Ground reinforcement method and improved ground structure - Google Patents

Description

  The present invention relates to a ground reinforcement method capable of reinforcing a soft ground and an improved ground structure obtained by the ground reinforcement method.

  When building a house or retaining wall on soft ground, it is necessary to perform construction to reinforce the ground in advance. As one of the construction methods, a ground improvement pile is placed up to the support layer that exists under the soft ground layer, and the ground or the retaining wall that is constructed on the soft ground is supported by the ground improvement pile. There is.

  Examples of the construction method using the ground improvement pile as described above include a columnar improvement construction method and a small-diameter steel pipe pile construction method. The columnar improvement method is a method of injecting and stirring cement milk into the soil that constitutes the soft ground to build a ground improvement pile in the ground. The small-diameter steel pipe pile construction method is a construction method in which a steel pipe is driven into a support layer, the steel pipe is used as a ground improvement pile, and a load of a house or the like is supported at the tip of the steel pipe.

Furthermore, the technique which can be used also when the object ground is a very soft viscosity layer etc. is disclosed until now. For example, in Patent Document 1, the upper ends of a plurality of deep mixed improvement pillars formed at predetermined intervals in the vertical and horizontal directions as a structure base of a soft layer, layered soil is provided between a plurality of net-like reinforcing materials. A composite improved ground structure characterized by being connected by sandwiched surface reinforcing layers is disclosed. According to such a composite improved ground structure, it is said that a horizontal load at the time of an earthquake can be borne by a plurality of deep mixed improved pillars embedded in the ground.
JP-A-11-269860

However, in the composite improved ground structure disclosed in Patent Document 1, a deep mixed improved column (corresponding to the ground improved pile of the present application, hereinafter referred to as “ground improved pile”) and a surface reinforcing layer (the mattress-like structure of the present application). The contact area between the ground improvement pile and the mattress structure is a small area below the horizontal cross section of the ground improvement pile. It has become. Therefore, when a large load is applied downward in the vertical direction, the load is likely to concentrate locally, and the ground improvement pile may pierce the mattress-like structure and damage the mattress-like structure. .
Moreover, in the composite improved ground structure disclosed in Patent Document 1, the strength against the load in the horizontal direction is not sufficient. For example, when a horizontal load is applied to a ground improvement pile and a mattress-like structure due to an earthquake, etc., the vibration of one side is transferred to the other by the direct connection between the ground improvement pile and the mattress-like structure. Reportedly. However, since the vibration period of the ground improvement pile and the vibration period of the mattress-like structure are different, the vibration of the ground improvement pile is transmitted to the mattress-like structure, and an extra load is applied to the ground improvement pile. There was a risk that the pile would break.

  Therefore, an object of the present invention is to provide an improved ground structure that can withstand a load in the horizontal direction in addition to a load in the vertical direction, and a ground reinforcement method for obtaining the improved ground structure.

  The present invention will be described below. In addition, in order to make an understanding of this invention easy, the reference sign of an accompanying drawing is attached in brackets, However, This invention is not limited to the form of drawing.

  The first aspect of the present invention provides a load transmission having a larger area than the horizontal cross section of the ground improvement pile on each of the plurality of ground improvement piles (3, 3, 3) driven into the ground and having rigidity. A mattress-like structure in which a filling material (20) is filled in a substantially rectangular parallelepiped frame (10b) composed of a geotextile and a load transmission plate installation step for installing the plates (2, 2, 2) It is a ground reinforcement construction method provided with a mattress installation process which installs a thing (1) on a plurality of load transmission boards.

  In the present invention, the “load transmitting plate” may be a plate-like body having rigidity enough to withstand a load applied during use, and examples thereof include a steel plate or a concrete plate-like body. Can do. Moreover, the magnitude | size of a load transmission board can be determined suitably by the magnitude | size of the load concerning a ground improvement pile, the magnitude | size of the horizontal direction cross section of a ground improvement pile, etc.

  The second aspect of the present invention is a plurality of ground improvement piles (3, 3, 3) driven into the ground, and is installed on the ground improvement piles and has an area larger than the horizontal cross section of the ground improvement piles. In addition, a load transmitting plate (2, 2, 2) having rigidity and a filling material (20) in a substantially rectangular parallelepiped frame (10b) which is installed on the plurality of load transmitting plates and is configured by geotextiles. And an improved ground structure (50) comprising a mattress-like structure (1) filled with.

According to the ground reinforcement method of the first aspect of the present invention, it is possible to provide an improved ground structure capable of withstanding a horizontal load in addition to a vertical load.
Moreover, the existing ground improvement pile left when the building structure was demolished can be used effectively, and an improved ground structure with further increased strength can be obtained. Many existing ground improvement piles that are left when building structures are dismantled are designed by considering only the load in the vertical direction. However, due to the revision of the Building Standard Law, when designing an improved ground structure, it is essential to consider not only the vertical load but also the horizontal load. Therefore, when existing ground improvement piles are used as the foundation of a new building or improved ground structure, the standards stipulated by law are often not satisfied. According to the ground reinforcement method of the first aspect of the present invention, an improved ground structure having a structure capable of withstanding a load in the horizontal direction can be obtained. Even it can be used effectively.

  According to 2nd this invention, it can be set as the improved ground structure which can be equal to the load of a horizontal direction in addition to the load of a vertical direction.

  Hereinafter, the present invention will be described based on embodiments shown in the drawings. However, the ground reinforcement method of the present invention is not limited to these embodiments.

  The ground reinforcement method of the present invention includes a load transmission plate installation step and a mattress installation step. Each step will be described in detail with reference to FIGS.

  1 to 5 are a top view and a cross-sectional view schematically showing a part of the process in the ground reinforcement method of the present invention. In each drawing of FIGS. 1-5, (a) is a top view, (b) is sectional drawing of the perpendicular direction containing the broken-line part shown to (a). In Fig.1 (a) and FIG.2 (a), in order to make intelligible the positional relationship of a load transmission board and a ground improvement pile, it has shown so that the ground improvement pile under a load transmission board can be seen through. In FIG. 1 to FIG. 5, the same reference numerals are given to the same components as those shown in other drawings. Further, some symbols are omitted in order to prevent the drawings from becoming complicated.

<Load transmission plate installation process>
The load transmission plate installation process has a larger area than the horizontal cross section of the ground improvement piles 3, 3, 3 on each of the plurality of ground improvement piles 3, 3, 3 driven into the ground and has rigidity. This is a process of installing the load transmission plates 2, 2, 2. More specifically, as shown in FIG. 1, load transmission plates 2, 2, 2 are installed on the ground improvement piles 3, 3, 3 at the bottom of the depression 101 formed in the ground 100. In order to install the load transmission plate 2 substantially horizontally or to fill the gap between the top end of the ground improvement pile 3 and the load transmission plate 2, the load transmission plate 2 and the ground improvement pile 3 are Sand, mortar, concrete or the like is preferably interposed.

  The ground improvement pile 3 that can be used in the present invention is not particularly limited, but it is preferable to use an existing pile before performing the ground reinforcement method of the present invention because resources can be used effectively. Examples of existing piles include PC piles, RC piles, pre-tensioned centrifugal force prestressed concrete piles (PHC piles), cast-in-place piles, and deep mixed treated piles. In addition, when using an existing pile, the pile head of the pile is often damaged. Therefore, after repairing the pile head and making the top end of the existing pile substantially horizontal, It is preferable to install.

  Existing piles are designed with consideration only for the load in the vertical direction, and many are not considered for the load in the horizontal direction. Therefore, it was difficult to obtain an improved ground structure that satisfies the standards defined by the current law using existing piles. However, according to the ground reinforcement method of the present invention, as will be described in detail later, an improved ground structure having a structure capable of withstanding a load in the horizontal direction can be obtained, so that existing piles can be used effectively.

  The load transmitting plate 2 that can be used in the present invention has a horizontal cross-sectional area that is larger than the horizontal cross-sectional area of the ground improvement pile 3, and has a rigidity that can withstand a load applied during use. Any shape may be used. Specific examples include steel plates and concrete plate-like bodies. The thickness of the load transmitting plate 2 and the size of the horizontal cross section can be appropriately determined depending on the size of the load applied to the ground improvement pile 3 and the size of the horizontal cross section of the ground improvement pile 3.

<Mattress installation process>
In the mattress installation process, a mattress-like structure 1 in which a filling material 20 is filled in a substantially rectangular parallelepiped frame 10b made of geotextile is installed on a plurality of load transmission plates 2, 2, 2. It is a process.

  In the mattress installation process, first, as shown in FIG. 2, a wooden frame 102 along the side surface of the depression 101 is installed in the depression 101.

  After the installation of the wooden frame 102, as shown in FIG. 3, the frame 10a having the upper surface opened inside the wooden frame 102 (denoted separately from the frame 10b having the upper surface closed (see FIG. 5)). Are installed on the plurality of load transmission plates 2, 2, 2 installed in the load transmission plate installation step. From the viewpoint of applying a certain amount of pulling resistance between the frame body 10a and the load transmission plate 2, it is preferable to interpose sand or the like between the frame body 10a and the load transmission plate 2.

  The frame body 10a is composed of a geotextile, and includes a bottom surface 11, side surfaces 12a, 12b, 12c, and 12d (only two surfaces (side surfaces 12a and 12c are shown in FIG. 3B)) and the frame body 10b. It consists of upper surface pieces 13a, 13b, 13c, and 13d that are part of the upper surface 13 (see FIG. 5).

  The bottom surface 11 has a substantially rectangular shape, and side surfaces 12a, 12b, 12c, and 12d (hereinafter, collectively referred to as “side surface 12”) are integrated on four sides thereof. The method of integrating these is not particularly limited, and may be configured by one geotextile, or may be configured by connecting a plurality of geotextiles using a conventionally known method. Moreover, it is preferable that adjacent side surfaces (12a and 12b, 12b and 12c, 12c and 12d, 12d and 12a) are also integrated, respectively, and these can be connected using the conventionally well-known method. Further, the upper surface piece 13a is opposite to the bottom surface 11 of the side surface 12a, the upper surface piece 13b is opposite to the bottom surface 11 of the side surface 12b, and the upper surface piece 13c is opposite to the bottom surface 11 of the side surface 12c. On the opposite side of the bottom surface 11, upper surface pieces 13d are integrated. The method of integrating these is not particularly limited, and may be configured by one geotextile, or may be configured by connecting a plurality of geotextiles using a conventionally known method.

  After installing the frame body 10a, as shown in FIG. 4, the filling material 20 is filled into the frame body 10a to a predetermined height. What comprises the filling material 20 is not specifically limited, Well-known things, such as a crushed stone, can be used. The size of the crushed stone constituting the filling material 20 is not particularly limited, but a soil material containing 50% or more by weight of soil having a particle size of 2 cm or more (Geotechnical Foundation Geotechnical Engineering Standards “ “Classification method” (from JGS0051-2000) is preferable. The soil material measuring method is based on JIS A1204 “Soil Grain Size Test Method”. By using the above earth material as the crushed stone constituting the filling material 20, the friction between the crushed stones is increased, and the shear resistance exerted when the mattress-like structure 1 is loaded from above can be increased. it can.

  The filling amount of the filling material 20 can be appropriately determined according to the planned size of the mattress-like structure 1. The size of the mattress-like structure 1 is not particularly limited, but the length or width is preferably about 10 m to 100 m, and more preferably about 5 m to 20 m. Further, the height is preferably about 30 cm to 200 cm, and more preferably about 40 cm to 100 cm.

  After filling and compacting the filling material 20 to a predetermined height, as shown in FIG. 5, the upper surface of the frame body 10 a is closed, and the frame body 10 b including the upper surface 13 composed of a geotextile integrated with the side surface 12. And Thereafter, the wooden frame 102 is removed. As a specific example of the method of forming the upper surface 13, a method of forming the upper surface 13 by connecting the upper surface pieces 13a, 13b, 13c, and 13d or another geotextile is prepared, and the upper surface pieces 13a, 13b are prepared. , 13c, and 13d to form the upper surface 13 by coupling. As a connection method in these cases, a known method can be used.

  Examples of the geotextile that can be used in the present invention include Tensor (registered trademark) manufactured by Mitsubishi Plastics Corporation.

<Improved ground structure>
According to the ground reinforcement method of the present invention, the improved ground structure of the present invention can be obtained through the steps described above. Hereinafter, the improved ground structure of the present invention will be described with reference to FIG.

  FIG. 6 is a diagram schematically showing the improved ground structure 50 of the present invention. (A) is a top view, (b) is a vertical sectional view including the broken line portion shown in (a). In addition, in (a), it has shown so that what was equipped below may be seen through. The same components as those in FIGS. 1 to 5 are denoted by the same reference numerals, and description thereof will be omitted as appropriate.

  The improved ground structure 50 of the present invention includes a plurality of ground improvement piles 3, 3, 3, load transmission plates 2, 2, 2 installed on the ground improvement piles 3, 3, 3, and a plurality of load transmission plates The mattress-like structure 1 is provided so as to be in contact with the upper surfaces of 2, 2, and 2. And on the improved ground structure 50, as shown in FIG. 6, the foundation 40 and pillar 30 of a building structure can be installed and constructed.

  When a building structure is built on the improved ground structure 50, a load is applied to the improved ground structure 50 in the vertical direction via the foundation 40 and the pillar 30. Since the mattress-like structure 1 provided in the improved ground structure 50 can withstand and exert a shear resistance when a load is applied from above, it can contribute to the reinforcement of the ground. Further, since the ground improvement pile 3 is provided below the mattress-like structure 1, the load applied from the top of the mattress-like structure 1 can be transmitted to the ground improvement pile 3. The ground structure 50 can withstand a greater vertical load. Furthermore, the load transmission plate 2 is provided between the mattress-like structure 1 and the ground improvement pile 3, so that the improved ground structure 50 can withstand a larger vertical load and the horizontal direction. It can withstand load. Below, the effect acquired by providing the load transmission board 2 is demonstrated in detail.

  When the mattress-like structure 1 is installed directly on the ground improvement pile 3, the area of the contact surface between the mattress-like structure 1 and the ground improvement pile 3 is the horizontal break of the ground improvement pile 3. The area becomes smaller than the area. Therefore, when a large load is applied vertically downward from the top of the mattress-like structure 1, the load is locally concentrated, and the ground improvement pile 3 pierces the mattress-like structure 1 so that the mattress-like structure 1 is pierced. There is a risk of damaging the structure 1. In the improved ground structure 50, the stress acting between the mattress-like structure 1 and the ground improvement pile 3 is dispersed by interposing the load transmission plate 2 between the mattress-like structure 1 and the ground improvement pile 3. Therefore, the mattress-like structure 1 can be prevented from being damaged. Therefore, the improved ground structure 50 can withstand a larger vertical load by providing the load transmitting plate 2.

  Further, when the mattress-like structure 1 is installed directly on the ground improvement pile 3, when a horizontal load is applied due to an earthquake or the like, the vibration of the mattress-like structure 1 causes the ground improvement pile 3 to vibrate. To be told. However, since the vibration period of the mattress-like structure 1 and the vibration period of the ground improvement pile 3 when a horizontal load is applied are different, the vibration of the mattress-like structure 1 is transmitted to the ground improvement pile 3. If it is done, an excessive load will be applied to the ground improvement pile 3, and the ground improvement pile 3 may be broken. In the improved ground structure 50, the load transmission plate 2 is interposed between the mattress-like structure 1 and the ground-improved pile 3, so that the horizontal load (vibration) is transferred from the mattress-like structure 1 to the ground-improved pile 3. ) Is difficult to transmit, and therefore has high strength against horizontal loads. The difficulty in transmitting the load in the horizontal direction between the mattress-like structure 1 and the ground improvement pile 3 is that the frictional force acting between the mattress-like structure 1 and the load transmission plate 2 is large. It depends. Thus, since the improved ground structure 50 can endure a load in the horizontal direction, the existing pile can be effectively used as the ground improved pile 3 as described above.

  In the description of the present invention so far, the embodiment in which three load transmission plates and three ground improvement piles are respectively provided below the mattress-like structure has been described, but the number of these is particularly limited. is not. Further, in the description of the present invention so far, the embodiment in which one load transmission plate is installed between the mattress-like structure and one ground improvement pile has been described as an example. The form is not limited. By installing a plurality of load transmission plates in the vertical direction between the mattress-like structure and one ground improvement pile, horizontal load transmission between the mattress-like structure and the ground improvement pile Can be made more difficult to communicate.

  Although the present invention has been described in connection with the most practical and preferred embodiments at the present time, the present invention is not limited to the embodiments disclosed herein, The present invention can be changed as appropriate without departing from the scope or spirit of the invention that can be read from the claims and the entire specification, and a ground reinforcement method and an improved ground structure accompanying such changes are also included in the technical scope of the present invention. It must be understood as a thing.

It is the upper side figure and sectional drawing which show a part of process in the ground reinforcement construction method of this invention roughly. It is the upper side figure and sectional drawing which show a part of process in the ground reinforcement construction method of this invention roughly. It is the upper side figure and sectional drawing which show a part of process in the ground reinforcement construction method of this invention roughly. It is the upper side figure and sectional drawing which show a part of process in the ground reinforcement construction method of this invention roughly. It is the upper side figure and sectional drawing which show a part of process in the ground reinforcement construction method of this invention roughly. It is the top view and sectional drawing which show schematically the improved ground structure of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Mattress-like structure 2 Load transmission board 3 Ground improvement pile 10a Frame body with open top surface 10b Frame body 11 Bottom surface 12 Side surface 13 Top surface 20 Filling material 30 Column 40 Foundation 50 Improved ground structure 100 Ground 101 Depression 102 Wood frame

Claims (4)

On each of the plurality of ground improvement piles driven into the ground, a load transmission plate installation step of installing a load transmission plate having a larger area than the horizontal cross section of the ground improvement pile and having rigidity, and
A mattress-like structure in which a mattress-like structure in which a filling material is filled in a substantially rectangular parallelepiped frame made of geotextile is installed on the plurality of load transmission plates, and
Do not connect the ground improvement pile and the load transmission plate, do not connect the load transmission plate and the mattress-like structure,
Ground reinforcement method. The ground reinforcement construction method according to claim 1, wherein a plurality of the load transmission plates are installed in a vertical direction in the load transmission plate installation step. A plurality of ground improvement piles driven into the ground, a load transmission plate installed on the ground improvement piles, having a larger area than the horizontal cross section of the ground improvement piles and having rigidity, and a plurality of the load transmissions A mattress-like structure that is installed on a board and is filled with filling material in a substantially rectangular parallelepiped frame made of geotextile, and
The ground improvement pile and the load transmission plate are not connected, and the load transmission plate and the mattress-like structure are not connected,
Improved ground structure. The improved ground structure according to claim 3, wherein a plurality of the load transmission plates are installed in a vertical direction between the mattress-like structure and the ground improvement pile.

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