Ground reinforcement method

Abstract

To provide a ground reinforcement method that can reduce an amount of excavated soil and crushed stone while maintaining a high subsidence suppression effect.SOLUTION: A ground reinforcement method comprises: a root excavation process S1 of excavating the ground to construct a root excavation surface B with a surface shape corresponding to a bottom shape of a building's foundation A; a primary laying process S2 of laying base granular material 1 on the root excavation surface B and compacting to construct a primary granular material layer C; a placing process S3 of disposing a plurality of strip-shaped reinforcing sheets 2 in parallel on the primary granular material layer C so that they partially overlap in a width direction; a temporary fixing process S4 of anchoring both longitudinal ends of the reinforcing sheets 2 to the ground to construct a temporary fixed end E; a secondary laying process S5 of laying the base granular material 1 on the reinforcing sheets 2 and compacting to construct a secondary granular material layer D; and a fixing process S6 of pouring concrete onto the temporary fixed end E to fix it to the ground. In the secondary laying process S5, tension is applied to at least one of the plurality of reinforcing sheets 2 by the load of the base granular materials 1 laid in recesses of the reinforcing sheets 2.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a ground reinforcement method, and more particularly to a ground reinforcement method that can reduce the amount of excavated soil and crushed stone while maintaining a high subsidence suppression effect. [Background technology]

[0002] When the site where a detached house or other structure is to be built has soft ground, ground reinforcement methods are implemented to improve the bearing capacity of the ground. Patent Document 1 discloses a ground reinforcement method for reinforcing soft ground by laying reinforcing sheets made of strip-shaped spunbond nonwoven fabric on the ground so that they overlap in the perpendicular direction and fixing both ends of the reinforcing sheets to the ground. This ground reinforcement method is carried out in the following steps: (1) excavating the ground, (2) laying and compacting crushed stone, (3) laying a reinforcing sheet on top of the crushed stone, (4) temporarily securing the ends of the reinforcing sheet with anchors, (5) laying crushed stone on top of the reinforcing sheet and compacting it, (6) securing the ends of the reinforcing sheet with concrete, and (7) backfilling. When laying the reinforcing sheet, to prevent it from sinking due to the building load, workers pull on the edges of the reinforcing sheet, applying longitudinal tension (prestress) to the sheet, and then anchor it in place. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-116156 Summary of the Invention [Problem to be solved by the invention]

[0004] The prior art has the following drawbacks: <1> Because this construction method involves manually pulling the reinforcing sheet longitudinally to apply prestress, it is necessary to flatten the crushed stone layer onto which the sheet is laid and the excavation surface below it. Therefore, when applying this method to the foundation of a structure with underground beams at the bottom (Figure 11), the excavation surface must be set not at the bottom of the foundation (a), but at a depth from the bottom of the underground beam (b) to ensure the thickness of the crushed stone layer, and the excavation must be flat. As a result, the amount of excavated soil and crushed stone required is greater than the required performance by an amount equivalent to the thickness of (ab), which increases the cost of disposing of the removed soil and the cost of procuring crushed stone. <2> Since the reinforcing sheet is tensioned manually, there is a limit to the tension that can be applied. <3> The task of pulling the reinforcing sheet and anchoring it while maintaining tension is highly difficult and places a great physical strain on workers.

[0005] An object of the present invention is to provide a ground reinforcement method that solves the above-mentioned problems of the conventional technology. [Means for solving the problem]

[0006] The ground reinforcement method of the present invention comprises a root excavation process in which the ground is excavated to construct a root excavation surface with a surface shape corresponding to the shape of the bottom of the building foundation; a primary laying process in which base granular material is laid on the root excavation surface and compacted to construct a primary granular material layer; a laying process in which multiple strip-shaped reinforcing sheets are arranged in parallel on the primary granular material layer so that they overlap partially in the width direction; a temporary fixing process in which both longitudinal ends of the reinforcing sheets are anchored to the ground to construct temporary fixed ends; a secondary laying process in which base granular material is laid on the reinforcing sheets and compacted to construct a secondary granular material layer; and a fixing process in which concrete is poured on the temporary fixed ends to fix them to the ground, characterized in that in the secondary laying process, tension is applied to at least one of the multiple reinforcing sheets by the load of the base granular material laid in the recesses of the reinforcing sheet.

[0007] In the ground reinforcing method of the present invention, the reinforcing sheet may be made of a woven fabric in which the tensile strength of the wires in the longitudinal direction is greater than the tensile strength of the wires in the width direction.

[0008] In the ground reinforcing method of the present invention, in the temporary fixing step, the longitudinal ends of the reinforcing sheet may be wrapped around fixing bars made of synthetic resin to anchor them to the ground.

[0009] In the ground reinforcement method of the present invention, in the temporary fixing step, the longitudinal ends of the reinforcing sheet may be bent widthwise together with the fixing bar, and anchored to the ground in a state that follows the unevenness of the primary granular material layer. [Effects of the Invention]

[0010] The ground reinforcement method of the present invention has at least one of the following effects. <1> The reinforcing sheet can be laid along the unevenness of the bottom surface of the foundation, and tension can be applied to the reinforcing sheet afterwards by applying pressure or compacting the base granular material. This allows the granular material layer to be of a uniform thickness along the bottom surface of the foundation, significantly reducing the amount of excavated soil and base granular material required compared to conventional technology (Figure 12). As a result, the amount of work required in the excavation process can be reduced, and the costs of disposing of the removed soil and procuring crushed stone can be significantly reduced. <2> The reinforcing sheet is sandwiched between the primary and secondary granular material layers with unevenness that corresponds to the shape of the bottom surface of the foundation, which improves the frictional force of the reinforcing sheet between the granular material layers and thereby provides a high subsidence prevention effect. <3> Since the reinforcing sheet is tensioned by the load of the base granular material, a large tension can be applied to the reinforcing sheet without relying on human force. <4> There is no need to anchor the reinforcing sheet under tension, so the physical burden on workers is reduced. [Brief explanation of the drawings]

[0011] [Figure 1] An explanatory diagram of the ground reinforcement method according to the present invention [Figure 2] Basic diagram [Figure 3] Root cutting process diagram [Figure 4] Illustration of the primary laying process [Figure 5] Illustration of the installation process [Figure 6] Anchor bar illustration [Figure 7] Temporary fixing process [Figure 8] Illustration of the secondary laying process [Figure 9] Illustration of the fixation process [Figure 10] Explanatory diagram of Example 2 [Figure 11] Explanatory diagram of the prior art [Figure 12] Illustrative diagram of the present invention DETAILED DESCRIPTION OF THE INVENTION

[0012] The ground reinforcement method of the present invention will be described in detail below with reference to the drawings. In the present invention, the term "concrete" is used to include mortar. [Example]

[0013] [Ground reinforcement method] <1> Overall configuration (Figure 1) The ground reinforcement method of the present invention is a method for increasing the bearing capacity of the ground by extending a reinforcing sheet 2 within a layer of base granular material 1 placed under foundation A on a building site and constructing a composite structure of base granular material 1 and reinforcing sheet 2. The ground reinforcement method of the present invention includes at least a root cutting step S1, a primary laying step S2, a laying step S3, a temporary fixing step S4, a secondary laying step S5, and a fixing step S6. One feature of the ground reinforcing method of the present invention is that it is possible to apply tension to the reinforcing sheet 2 not by human power but by the load of the base granular material 1 laid on the reinforcing sheet 2.

[0014] <1.1> Basics (Fig. 2) The foundation A according to the ground reinforcement method of the present invention is a mat foundation made of reinforced concrete. The foundation A has an underground beam A1 that protrudes continuously from the bottom surface. The underground beam A1 is a structure that complements the cut of the beams in the above-ground portion and reinforces the foundation A. Note that the shape and structure of the underground beam A1 are not important in the present invention.

[0015] <1.2> Reinforcement sheet The reinforcing sheet 2 used in the ground reinforcing method of the present invention is a strip-shaped sheet having a predetermined tensile strength. In this example, "UV-fir (registered trademark)" manufactured by Geofarm Co., Ltd. is used as the reinforcing sheet 2. UV-fir is a special 2m wide sheet woven with high-tensile vinylon fiber (tensile strength: 3600N / 5cm or more) for the warp and polypropylene flat yarn (tensile strength: 1800N / 5cm or more) for the weft. By combining high-tensile fiber for the warp and general-purpose resin fiber for the weft, it is possible to obtain a sheet that is strong in the tensile direction yet relatively inexpensive. However, the reinforcing sheet 2 is not limited to UV-fir, and other known strip-shaped sheets may be used as long as they can ensure the required tensile strength and scientific stability.

[0016] <2> Root pruning process (Figure 3) The excavation step S1 is a step of excavating the ground and constructing an excavation surface B. In detail, the excavation step S1 is carried out as follows, for example. Based on the construction drawings (root cutting drawings), the ground is excavated to a specified depth using heavy machinery such as a backhoe. At this time, the part corresponding to the underground beam A1 is excavated in a trench shape deeper than the bottom surface of the main body of the foundation A, thereby constructing a root cutting surface B with a surface shape corresponding to the shape of the bottom surface of the foundation A. In the conventional technology, during the root excavation process, the entire surface was excavated to a uniform depth based on the depth of the bottom surface of the underground beam, resulting in a relatively large amount of soil being removed. In contrast, the ground reinforcement method of the present invention excavates the ground to match the bottom shape of foundation A, thereby significantly reducing the amount of soil discharged.

[0017] <3> Primary laying process (Figure 4) The primary laying step S2 is a step of constructing the primary particle layer C. In detail, the construction is carried out as follows, for example. The base granular material 1 is spread on the root cut surface B and leveled to a uniform thickness. In this example, C40 crushed stone is used as the base granular material 1. However, the base granular material 1 is not limited to crushed stone, and can also be sand or gravel. The spread base granular material 1 is sufficiently compacted using a vibrating roller or vibro rammer, etc., to form the primary granular material layer C. In this example, the thickness of the primary granular material layer C is 100 mm. However, depending on the shape of the root cutting surface B, some of the base granular material 1 on the inclined surface may flow downward, making the layer thickness on the inclined surface thinner than that on the flat surface.

[0018] <4> Installation process (Figure 5) The laying step S3 is a step of laying the reinforcing sheet 2 on the primary particle layer C. In detail, the construction is carried out, for example, as follows. The starting end (fixed edge 21) of the rolled reinforcing sheet 2 is wrapped around two fixed bars 3, and a temporary fixed end E is constructed by driving the fixed bars 3 into the primary granular material layer C with an anchor pin 4. The roll of reinforcing sheet 2 is unrolled and laid across the primary particle layer C, and the reinforcing sheet 2 is laid over the primary particle layer C. It is desirable to lay the reinforcing sheet 2 in the direction of the short side of the building. When the reinforcing sheet 2 is laid across, the reinforcing sheet 2 is given some slack in the portion where it straddles the unevenness on the primary particle layer C. That is, for example, in a recess in the primary particle layer C corresponding to the underground beam A1 of the foundation A, the bottom surface of the reinforcing sheet 2 is not brought into contact with the bottom surface of the recess, and a small space F is secured between the reinforcing sheet 2 and the recess. The subsequent reinforcing sheet 2 is laid adjacent to the previously laid reinforcing sheet 2 in the same manner as above. At this time, the subsequent reinforcing sheet 2 is made to overlap the previous reinforcing sheet 2 by a certain width (300 mm or more in this example). The same procedure is repeated to cover the upper part of the primary particle layer C with a plurality of reinforcing sheets 2.

[0019] <4.1> Fixing bar (Fig. 6) The fixing bar 3 is a rod-shaped body around which the fixing edge 21 of the reinforcing sheet 2 is wound. The length of the fixing bar 3 corresponds to the width of the reinforcing sheet 2. In this example, the fixed bar 3 is a polyethylene square bar measuring 8 mm x 10 mm x 2,000 mm, made from recycled wire coating material. Polyethylene square bars are highly strong yet lightweight and have a certain degree of flexibility, and do not corrode underground, making them ideal for the fixing bars 3. In addition, because their cross-sectional shape is rectangular, the reinforcing sheet 2 can be sandwiched between the two fixing bars 3 in a planar manner and held securely in place. However, the fixing bar 3 is not limited to a square bar made of polyethylene, but may be a deformed steel bar, a steel pipe, or the like.

[0020] <5> Temporary fixing process (Figure 7) The temporary fixing step S4 is a step of temporarily fixing the fixing edge 21 of the reinforcing sheet 2 to the ground. In detail, the work is carried out as follows, for example. The fixed edge 21 at the tip end of the laid reinforcing sheet 2, i.e., the fixed edge 21 on the side where the anchor pin 4 was not driven in during the laying process S3, is wrapped around two fixed bars 3, and the fixed bar 3 is driven into the primary granular material layer C with the anchor pin 4 to create a temporary fixed end E. The same operation is carried out for all the fixed edges 21. The reinforcing sheet 2 that does not straddle the uneven portion of the primary particle layer C may be tensioned by manual pulling as in the prior art. Furthermore, the temporary fixing may be carried out after each row of reinforcing sheets 2 is laid, rather than being carried out all at once after all the reinforcing sheets 2 have been attached.

[0021] <6> Secondary laying process (Figure 8) The secondary laying step S5 is a step of constructing the secondary particle layer D. In detail, the construction is carried out as follows, for example. The base granular material 1 is spread on the reinforcing sheet 2 stretched on the primary granular material layer C and spread to a uniform thickness. However, the base granular material 1 is not spread on the temporary fixing end E, but is left exposed. The spread base granular material 1 is sufficiently compacted using a plate compactor or the like to form a secondary granular material layer D. In this example, the thickness of the secondary granular material layer D is 100 mm. However, depending on the shape of the root cut surface B, some of the base granular material 1 on the inclined surface of the reinforcing sheet 2 may flow downward, causing the layer thickness on the inclined surface to be thinner than the layer thickness on the flat surface.

[0022] <6.1> Applying tension to the reinforcing sheet In the secondary laying step S5, when the base granular material 1 is spread on the reinforcing sheet 2, the load of the base granular material 1 is applied to the loosened part of the reinforcing sheet 2, and the base granular material 1 falls into the recessed part of the primary granular material layer C. Here, since both ends of the reinforcing sheet 2 are fastened to the ground by the temporary fixing ends E, a tensile force due to the load of the base granular material 1 is applied to the reinforcing sheet 2. Furthermore, by compacting the base granular material 1 after spreading it out, a tensile force is further applied to the reinforcing sheet 2 . The ground reinforcement method of the present invention has a structure in which the reinforcing sheet 2 is sandwiched between the primary granular material layer C and the secondary granular material layer D with unevenness that corresponds to the bottom shape of the foundation A, so that the friction force between the granular material layer and the reinforcing sheet 2 is large and the effect of suppressing the settlement of the building is high.

[0023] <7> Fixation step (Figure 9) The fixing step S6 is a step of fixing the temporary fixing end portion E to the ground. In detail, the work is carried out as follows, for example. Concrete is poured onto the temporary fixing end E (the part where the fixing edge 21 wrapped around the fixing bar 3 is temporarily fixed with the anchor pin 4) and hardened to form the fixed concrete 5. This allows the tension applied within the reinforcing sheet 2 to be maintained. After the fixing step S6, the secondary particle layer D is backfilled and the foundation is constructed, but these steps are not features of the present invention and will not be described in detail here. [Example]

[0024] [Example of fixed edge bent widthwise] Depending on the shape of the bottom surface of the foundation A, the primary granular material layer C below the fixed edge 21 may be partially depressed in the width direction. In this example, the fixing bar 3 is made of a bendable polyethylene material, so the fixing bar 3 can be bent in the width direction along with the wrapped fixing edge 21 and anchored in place along the slope of the primary granular material layer C (Figure 10). [Example]

[0025] [Example of laying reinforcing sheets perpendicular to each other] In the first embodiment, the plurality of reinforcing sheets 2 are arranged in parallel in only one direction, but the plurality of reinforcing sheets 2 may be laid one on top of the other so as to be perpendicular to each other. [Explanation of symbols]

[0026] S1 Root cutting process S2 Primary laying process S3 installation process S4 Temporary fixing process S5 Secondary laying process S6 Fixed process A. Basics A1 underground beam B Root cutting surface C Primary particle layer D Secondary particle layer E Temporarily fixed end F space 1. Base Granules 2 Reinforcement sheet 21 Fixed edge 3 Fixed bar 4 anchor pins 5 Fixed concrete

Claims

1. a root cutting process of excavating the ground and constructing a root cutting surface having a surface shape corresponding to the bottom shape of the foundation of the building; A primary laying step of laying and compacting base granular material on the root cutting surface to construct a primary granular material layer; a laying step of arranging a plurality of strip-shaped reinforcing sheets in parallel on the primary particle layer so that they partially overlap in the width direction; A temporary fixing process in which both longitudinal ends of the reinforcing sheet are anchored to the ground to construct temporary fixed ends; a secondary laying step of laying base granular material on the reinforcing sheet and rolling it to form a secondary granular material layer; and a fixing step of pouring concrete onto the temporary fixing end portion to fix the temporary fixing end portion to the ground. The foundation includes an underground beam that protrudes continuously from the bottom surface, In the root cutting process, a groove corresponding to the underground beam is formed, By the laying step, at least a part of the reinforcing sheet falls into the groove to form a recess, and a space is formed between the bottom surface of the recess and the primary particle layer in the groove, In the secondary laying step, the load of the base granular material laid in the recess of the reinforcing sheet presses the recess into the space, thereby applying tension to at least one of the plurality of reinforcing sheets. Ground reinforcement method.

2. 2. The ground reinforcing method according to claim 1, wherein the reinforcing sheet is made of a woven fabric in which the tensile strength of the wires in the longitudinal direction is greater than the tensile strength of the wires in the width direction.

3. 2. The ground reinforcing method according to claim 1, wherein in the temporary fixing step, longitudinal ends of the reinforcing sheet are wrapped around fixing bars made of synthetic resin to anchor the reinforcing sheet to the ground.

4. The ground reinforcement method described in claim 3, characterized in that in the temporary fixing process, the longitudinal ends of the reinforcing sheet are bent in the width direction together with the fixing bar, and anchored to the ground while following the unevenness of the primary granular material layer.

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