JP4712456B2 - Foundation reinforcement method - Google Patents

Description

  The present invention relates to a foundation reinforcing method for reinforcing a foundation of an existing structure.

  As a reinforcement method to reinforce the foundations of existing structures, etc., drilling the injection hole from the outer periphery of the existing foundation with a boring machine, installing the injection pipe and injecting chemicals such as water glass system around the existing pile A chemical solution injection method for strengthening the ground, a method for constructing a constrained solidified body around an existing pile by a high-pressure jet agitation method, etc. are known (for example, Patent Document 1).

However, the chemical solution injection method described above can only strengthen the ground, and a reliable and uniform ground reinforcement could not be expected. Moreover, in the method of constructing a constrained solidified body around an existing pile, there is a problem that an effective confined solidified body may not be constructed depending on construction conditions such as the space around the existing foundation and the topography.
JP 2003-155752 A

  The present invention has been made in order to solve the above-described conventional problems, and the problem is to provide a foundation reinforcing method capable of simultaneously achieving the strength improvement of the foundation of the existing structure and the prevention of liquefaction. is there.

  The foundation reinforcement construction method of the present invention is a construction method in which a steel pipe pile that also serves as an injection pipe for injecting grout directly under an existing foundation is press-fitted and installed using the existing foundation as a supporting body, and is constructed according to the following steps.

That is, the foundation reinforcing method of the present invention includes a excavation process for excavating and forming a work space in which a reinforcing pile made of a steel pipe is press-fitted into the soil immediately below the existing foundation, and a reinforcement in which the reinforcing pile is press-fitted with the bottom surface of the existing foundation as a bearing surface. Pile press-in process, grout injection process for injecting grout into the ground through the hollow part of the reinforcing pile, support member joining process for joining the support member supporting the bottom of the existing foundation to the reinforcement pile, and excavated work space And a backfilling process in which a reinforcing foundation for reinforcing an existing foundation is formed and backfilled. The reinforcing pile is made is foot joint and the injection steel pipe generally steel pipe with a grouting hole for injecting grout into the surrounding ground, the grout injection hole is inserted into the hollow portion of the injection steel pipe opening outside the reinforcing pile grout injection path which is characterized that you have communicated.

Further, in the basic reinforcing method of the present invention, it is desirable that the grout injection holes are formed radially from the axial center in the side portion of the steel pipe, and the packer ring is fixed to the outer periphery of the tip end portion of the injection steel pipe. Preferably it is.

  In the foundation reinforcing method of the present invention, the reinforcing pile can be installed adjacent to the existing pile.

According to the foundation reinforcing method of the present invention, the reinforcing pile can be installed directly under the existing foundation, so that the supporting force of the existing foundation can be increased. In addition, the reinforcing pile is formed by appropriately adding an injection steel pipe having a grout injection hole and a general steel pipe without an injection hole, so that the grout can be effectively injected at an arbitrary depth of the ground. Furthermore, since the grout injection hole is inserted into the hollow portion of the injection steel pipe and communicated with the grout injection path opened outside the reinforcing pile, the type of grout material can be changed for each injection path. A suitable grout material can be selected depending on the properties of the ground around each grout injection hole. And it is possible to accurately form an injection-consolidated portion of grout on the ground surrounding the reinforcing pile. Therefore, the ground around the reinforcing pile can be strengthened, and the frictional resistance of the reinforcing pile can be increased, so that the supporting force for the existing foundation of the reinforcing pile can be increased.

In addition, such a reinforcing pile can be formed by press-fitting a steel pipe having a predetermined length with the existing foundation as a supporting body. Therefore, the work space for excavation formation may be small, and the construction period can be shortened and the cost can be reduced .

  Furthermore, by installing the reinforcing pile adjacent to the existing pile, the surrounding ground of the existing pile can be improved and strengthened, preventing buckling of the existing pile (seismic strengthening) and increasing the bearing capacity of the existing pile. It becomes possible.

  According to the foundation strengthening method of the present invention, a pile foundation having high earthquake resistance can be constructed by installing a reinforcement pile immediately below an existing foundation without piles.

  The foundation reinforcement construction method of the present invention is a construction method in which a steel pipe pile also serving as an injection pipe for injecting grout directly under an existing foundation as described above is press-fitted and installed using the existing foundation as a supporting body, (1) excavation process, (2 ) Reinforcement pile press-in step, (3) Grout injection step, (4) Support member joining step, (5) Backfill step. The existing foundation can be effectively reinforced by sequentially performing these steps on the reinforced portions of the existing foundation to be reinforced. A preferred embodiment of the foundation reinforcing method of the present invention will be described by taking the reinforcement of the footing foundation 10 of the pier shown in FIG. 1 as an example. Fig.1 (a) is the schematic diagram which looked at the foundation 10 of the pier from the side, (b) is a corresponding plane schematic diagram. In FIG. 1, the ground F1 is a soft ground including, for example, an alluvial sand layer or a sand layer mixed with fine-grained soil, and a support layer F2 such as a rock is present at a predetermined depth. The pier 12 is constructed on such ground F1, and in the ground F1, four piles 16 are driven so as to reach the support layer F2 from the footing foundation 14 as shown in the plan view of FIG. ing.

  In the present embodiment, a reinforcing method for reinforcing the reinforcing portions A to D of the bridge pier foundation 10 as described above will be described along the steps shown in FIGS. In each figure, (a) is a schematic diagram of the right half when the pier foundation 10 is viewed from the side, and (b) is a schematic plan view of the corresponding right half.

(1) Excavation process (see Fig. 2)
First, a primary excavation portion A between adjacent existing piles 16 and 16 of the footing foundation 14 is dug using a drilling machine such as a power shovel, and a work space A ′ is excavated so that the bottom surface of the footing foundation 14 is exposed. To do. At this time, the depth d from the bottom surface 14a of the footing foundation 14 to the bottom surface 18 of the work space A ′ is deeper than the length of the steel pipe described later, and pressing means such as a hydraulic jack for press-fitting the steel pipe can be installed. Drill to depth.

(2) Reinforcement pile press-in process (see Fig. 3)
Next, the reinforcing pile 20 is press-fitted into the ground F1 using the footing foundation 14 as a supporting body. The reinforcing pile 20 is formed by appropriately adding a plurality of steel pipes 22 having a predetermined length. The material and thickness of the steel pipe 22 are not limited as long as they have a desired strength. For example, a steel pipe having an outer diameter of STK400 of 50 to 300 mm and a thickness of 3 to 15 mm is preferably used. Can do. Further, the length of the steel pipe 22 is not particularly limited, but is preferably about 300 to 2000 mm in consideration of pressing means for press-fitting the steel pipe with the existing foundation as a supporting body and workability of press-fitting work.

  The steel pipe 22 is composed of a general steel pipe 22a and an injected steel pipe 22b as schematically shown in FIGS. 8 (a) and 8 (b). The general steel pipe 22 a is formed by fitting an inner pipe 26 with a protruding part 26 a at the tip of the outer pipe 24, and the protruding part 26 a can be inserted and connected to the other end side of the other steel pipe 22.

  In addition, the injected steel pipe 22b shown in FIG. 8 (b) is composed of an outer pipe 24 and an inner pipe 26 in the same manner as the general steel pipe 22a, and is further drilled radially from the axial center in the side portion of the outer pipe 24. A plurality of grout injection holes 28 are provided. Each grout injection hole 28 communicates with an injection path 32 such as a hose provided in the hollow portion 30 of the steel pipe 22, and grout G such as milk cement is passed through the injection path 32 from the outside of the press-fitted reinforcement pile 20. Can be injected. Note that a sealing material 36 such as a vinyl sheet or a rubber sheet may be wound so as to seal the injection hole 28 to prevent the injection hole 28 from being blocked by intrusion of ground water or earth and sand before the injection of grout.

  A packer ring 34 made of an iron bar or the like is fixed to the outer periphery of the outer end of the outer tube 24 of the injected steel tube 22b, and a gap e can be formed around the outer periphery of the outer tube 4 by press-fitting the injected steel tube 22b. Due to the gap e, it is possible to prevent the positional deviation or breakage of the sealing material 36 when the injected steel pipe 22b is press-fitted.

  The steel pipe 22 configured as described above is sequentially press-fitted into a predetermined position directly below the existing foundation 14 (in the middle portion of the existing piles 16 and 16 in FIG. 3B) to form the reinforcing pile 20. First, pressing means P such as a hydraulic jack, a post hammer or a bible hammer is installed at the upper end of the injected steel pipe 22b, and the injected steel pipe is introduced from the bottom surface 18 of the work space A 'into the ground F1 with the bottom surface 14a of the footing foundation 14 as a bearing surface. 22b is press-fitted. In addition, the front-end | tip part (opening part of the inner pipe | tube protrusion part 26a) of the injection | pouring steel pipe 22 initially press-fit is sealed by the appropriate method. Once the injection tube 22b is press-fitted to a predetermined depth, the pressing means P is once removed, the inner tube protrusion 26a of the general steel tube 22a is inserted into the upper end portion of the injection steel tube 22b, and the fitting portion is welded appropriately. The injection steel pipe 22b and the general steel pipe 22a are connected by the method. Subsequently, the pressing means P is again installed on the upper end of the general steel pipe 22a and the connected steel pipe 22 is press-fitted.

  As described above, the general steel pipe 22a and the injected steel pipe 22b are appropriately added, and the reinforcing pile 20 is formed by press-fitting in sequence to a desired depth, for example, the support layer F2.

(3) Grout injection process (see Fig. 4)
In this step, grout G is injected into the surrounding ground of the reinforcing pile 20 from the outside through the injection path 32 to the reinforcing pile 20 that has been press-fitted by adding a predetermined number of steel pipes 22. The grout material is not particularly limited, and examples thereof include a composition in which silica colloid, fine particle slag, fine particle cement and the like are mixed as a main material and an appropriate hardening agent and hardening accelerator are mixed, and cement milk. Such a grout material is injected into the surrounding ground from each injection hole 28 formed in the injection steel pipe 22b constituting the reinforcing pile 20.

  The grout G that has reached the injection hole 28 from the outside via the injection path 32 presses the wound sealing material 36 and fills the ejection gap e from the injection hole 28. After that, it penetrates into the surrounding ground in the radial direction by external pressure. For example, in the gap e1 formed between the packer rings R1 and R2, when the grout g1 injected into the distal end side of the reinforcing pile 20 is ejected from the injection hole 28, the grout g1 passes through the gap e1 along the arrow y. It rises until it is blocked by the packer ring R2 and fills the gap e1. Then, since it penetrates into the surrounding ground radially as indicated by an arrow x by the applied pressure, the periphery of the gap e1 can be reliably reinforced with the grout g1. According to such a grout injection method, not only the type of grout G but also the injection timing can be appropriately adjusted depending on the properties of the ground, such as injecting grout g2 after waiting for consolidation of grout g3. it can.

  The grout G is preferably injected over a wide range so as to include the adjacent existing piles 16 and 16. Thus, by strengthening the ground around the existing pile 16, the supporting force of the existing pile 16 can be increased and the earthquake resistance can be enhanced. In addition, it is desirable to select a suitable grout material for each injection hole 28 (or for each injection steel pipe 22b) in accordance with the presence or absence of groundwater and the properties of the soil. For example, in soil such as clay soil, suspension type or solution type quick setting grout material g1 is suitable, and in soil such as sandy soil, ultrafine cement is suspended to provide excellent permeability. It is preferable to inject a long-grown grout material g2 having the same.

(4) Support member joining step (see FIG. 5)
The upper end portion of the reinforcing pile 20 in which the grout injection has been completed as described above and the bottom surface 14a of the footing foundation 14 are substantially separated by the length of the pressing means P. In this state, the reinforcing pile 20 is footed. Does not support the foundation 14. Therefore, the supporting member 38 is joined to the upper end portion of the reinforcing pile 20, and the supporting member 38 is brought into close contact with the bottom surface 14 a of the footing foundation 14 to support the footing foundation 14 with the reinforcing pile 20. The support member 38 is not particularly limited as long as it has the same strength as the steel pipe 22 that can fill the gap between the press-fitted reinforcement pile 20 and the bottom surface 14a of the footing foundation, but the same steel pipe as the outer pipe 24 of the steel pipe 22 is used. The footing foundation 14 can be supported by fixing the steel pipe to the upper end of the reinforcing pile 20 by welding or the like.

(5) Backfill process (see Fig. 6)
Next, the work space A ′ is backfilled to return the primary excavation part A to the original state. However, after the reinforcing foundation for reinforcing the footing foundation 14 is formed, the work is refilled. For example, a reinforcing material such as foamed mortar or mortar includes the reinforcing pile 20 and is poured and consolidated so as to bury part of the footing foundation 14 to obtain the reinforcing foundation 40. In addition, a reinforcing bar 40 or an angle may be incorporated in an appropriate region of the work space A ′ to form the reinforcing foundation 40.

  The steps (1) to (5) described above are repeated for the reinforcing areas A to D between the existing piles 16 and 16, and four reinforcing piles 20A to 20D are installed as shown in the plan view of FIG. And the existing foundation 10 whole of the pier 12 can be reinforced by strengthening the surrounding ground with grout G.

  In the pier foundation 10 reinforced in this way, the reinforcing pile 20 is press-fitted and formed in the middle position of the existing pile 16 to the same depth as the existing pile 16 (which reaches the supporting ground F2). And the reinforcing pile 20 are integrally injected so that the surrounding ground is consolidated and strengthened, so that it is much more reliable and uniform than the conventional chemical injection method or high-pressure jet agitation method. A reinforcing effect can be obtained.

  The present invention is not limited to the above-described embodiment, and can be modified without departing from the gist of the present invention.

  For example, in the above embodiment, the reinforcement of the footing foundation 14 having the existing pile 16 has been described. However, as shown in FIG. The pile foundation 42 having the reinforcing pile 20 can be obtained by applying the foundation reinforcing method of the present invention as shown in FIG.

  In addition, when the soft ground F3 exists between the foundation construction ground F1 and the support ground F2 as shown in FIG. 10, the reinforcing pile 20 is press-fitted adjacent to the existing pile 16, and the grout G is put into the soft ground F3. By injecting, it is possible to increase the pile effect of the reinforcing pile 20 and increase the supporting force of the existing pile 16 and the reinforcing pile 20.

  As mentioned above, although the aspect of embodiment was demonstrated to the example of the footing foundation, the foundation reinforcement construction method of the present invention is not limited to the aspect of the foundation such as the footing foundation, and can sufficiently withstand as a bearing body when press-fitting a steel pipe. If so, the present invention can be applied to any type of foundation (for example, cloth foundation, caisson foundation, etc.) that supports any type of structure or structure.

  The foundation reinforcement method of the present invention is extremely useful as a foundation reinforcement method to reinforce the foundation of a structure built on soft ground, increasing the bearing capacity of existing foundations with reinforcement piles, and the ground when an earthquake occurs due to grouting. The prevention of liquefaction can be achieved at the same time. The foundation reinforcing method of the present invention can be applied to any type of foundation that supports a structure portion or a structure. Among them, it can be suitably used for reinforcing a footing foundation of a pier or a foundation of a building.

It is a schematic diagram explaining the structure of the foundation of the pier which is one embodiment. (A) is a side view, (b) is a plan view. It is explanatory drawing which shows the excavation process of the reinforcement construction method which reinforces the foundation of the pier of FIG. 1, (a) is a side surface schematic diagram (only one side), (b) is a plane schematic diagram. It is explanatory drawing which shows the reinforcement pile press-in process following FIG. FIG. 4 is an explanatory view showing a grout injection process following FIG. 3. It is explanatory drawing which shows the supporting member joining process following FIG. It is explanatory drawing which shows the backfilling process following FIG. It is a plane schematic diagram of the foundation of the bridge pier after reinforcement completion. It is a schematic diagram explaining the structure of a reinforcement pile. (A) is sectional drawing explaining the shape of a general steel pipe, (b) is sectional drawing explaining the shape of an injection steel pipe. This is another embodiment, in which only the footing foundation having no existing pile is reinforced. (A) is the side surface schematic diagram which shows before reinforcement, (b) is the side surface schematic diagram which shows after reinforcement. It is another aspect, and shows an example of reinforcement when soft ground F3 exists partially. (A) is the side surface schematic diagram which shows before reinforcement, (b) is the side surface schematic diagram which shows after reinforcement.

Explanation of symbols

10: Foundation of bridge pier 12: Pier pier 14: Footing foundation 16: Existing pile 18: Bottom of work space 20: Reinforcement pile 22: Steel pipe 22a: General steel pipe 22b: Injection steel pipe 24: Outer pipe 26: Inner pipe 28: Injection hole 32: Injection path 34: Packer ring 36: Seal 38: Support member 40: Reinforcement foundation 42: Pile foundation A: Primary excavation part A ': Primary work space G: Grout (grout consolidation part) F1: Foundation construction ground F2: Support ground F3: Soft ground

Claims (4)

An excavation process for excavating and forming a work space in which a reinforcing pile made of steel pipe is press-fitted into the soil directly under the existing foundation;
Reinforcement pile press-in process for press-fitting the reinforcement pile with the bottom surface of the existing foundation as a bearing surface;
A grout injection step of injecting grout into the ground through the hollow portion of the reinforcing pile;
A support member joining step of joining a support member supporting the bottom surface of the existing foundation to the reinforcing pile;
A backfilling step for forming and reinforcing a reinforcing foundation for reinforcing the existing foundation in the excavated working space;
The reinforcing pile is made is injected steel and general steel pipe and the joint legs including a grout injection hole for injecting the grout into the surrounding ground,
Basic Retrofit grout injection path wherein the grouting holes opening outside of the reinforcing pile is inserted into the hollow portion of the injection steel pipe characterized that you have communicated. 2. The foundation reinforcing method according to claim 1, wherein the grout injection holes are formed radially from an axial center in a side portion of the injected steel pipe. The foundation reinforcement construction method according to claim 1 or 2, wherein a packer ring is fixed to the outer periphery of the tip end portion of the injected steel pipe. Basic Retrofit according to any one of claims 1 to 3, installing the reinforcing piles adjacent to existing pile.

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