JP4926293B1 - Ground improvement method - Google Patents

Abstract

[PROBLEMS] To prevent liquefaction of the surrounding ground of a columnar solid formed by the ground improvement method, and even when the columnar solid does not reach the hard ground in the liquefied ground, Providing a ground improvement method that can prevent columnar consolidated bodies from collapsing and rising.
An excavator having a drilling head provided at the tip and an agitating blade provided above the drilling head is used to excavate the ground to form a drilling hole, and below the drilling head. The first grout 11 is discharged from the first discharge port 7 formed in the lower part 5 b of the excavation hole 5 to be mixed with the ground 13, and is formed on the stirring blade 3 toward the side 5 a of the excavation hole 5. 2 Excavation process in which the second grout 12 is pressurized and press-fitted into the ground 13 on the side 5a of the excavation hole 5 from the discharge port 9, and the second grout 12 press-fitted in the excavation process is injected into the ground 13 to form an excavation hole And a consolidation step of integrally solidifying the first grout 11 discharged to 5 and the second grout 12 injected into the ground 13.
[Selection] Figure 2

Description

  The present invention relates to a ground improvement method for strengthening a soft ground by injecting grout into the ground, and more particularly to a ground improvement method suitable for maintaining the effect of soil improvement of a soil layer that is liable to liquefy during an earthquake.

  Conventionally, when constructing a structure on soft ground, a pile foundation method for placing the pile in the ground and supporting the load of the structure by the support force of the pile, or a ground improvement method for injecting grout into the ground Is generally used.

  The pile foundation method is classified into a pile foundation method for supporting piles and a pile foundation method for friction piles. First, the support pile supports the pile by reaching the hard ground below the soft ground. Support piles need to be driven to deep hard ground, and it is necessary to excavate deeper than friction piles to be placed on shallow soft ground. Increase. The friction pile is supported by the peripheral friction force between the pile and the surrounding ground in the soft ground above the hard ground. The construction cost for placing the friction pile is lower than that for placing the support pile, but if the frictional force between the pile and the surrounding ground is lost due to liquefaction of the ground, the pile may collapse in the ground. There is also a possibility that the pile will be lifted by buoyancy in the ground.

  On the other hand, the ground improvement method strengthens the ground by injecting grout into the soft ground instead of placing piles in the ground. In the ground improvement method, grout such as cement-based material is injected into the ground, and the earth and sand in the ground are mixed and consolidated. In the ground improvement method, a columnar consolidated body is formed in the ground so that the columnar consolidated body has the same function as a pile and supports a structure. The ground improvement construction method is used in place of the pile foundation construction method when it is an environment that does not allow the generation of the driving sound of the ready-made pile or when the placement space of the ready-made pile cannot be secured. As with the pile foundation method, the ground improvement method requires a suitable excavation depth when a columnar solid is formed until it reaches the hard ground, and therefore the construction cost generally increases. The ground improvement method is the same as the pile foundation method even when the columnar solid body does not reach the hard ground, but at the same time, the construction cost is low, but the columnar solid body may collapse or float due to liquefaction of the soft ground. There is a problem that there is.

  In order to prevent the columnar consolidated body from collapsing and rising when the columnar consolidated body does not reach the hard ground, a ground improvement method disclosed in Patent Document 1 has been proposed. The ground improvement method disclosed in Patent Document 1 is to inject grout into the surrounding ground of the columnar consolidated body, and mix and solidify the earth and sand in the surrounding ground to strengthen the surrounding ground. is there.

JP-A-62-72810

  The present invention prevents the liquefaction of the surrounding ground of the columnar solid body in the ground formed by the ground improvement method, and the columnar solid body does not reach the hard ground in the liquefied ground. Even if it exists, it is providing the ground improvement construction method which can prevent the collapse | collapse of a columnar solidified body and levitation at low construction cost.

  In order to solve the above-mentioned problem, the present inventor, forcibly pressurizing the grout to the side of the excavation hole, press-fitting the grout into the ground, and stirring and mixing with the excavation sediment in the excavation hole A ground improvement method to solidify with the ground was proposed.

The ground improvement method according to claim 1 of the present invention is to form a drilling hole by excavating the ground using an excavator provided with an excavation head at the tip and provided with a stirring blade above the excavation head. While lifting the head from the excavation hole, the first grout is discharged from the first discharge port formed below the excavation head to the lower side of the excavation hole, and the rotation of the stirring blade is temporarily stopped . An excavation process in which a second grout is press-fitted into the ground on the side of the excavation hole from a second discharge port formed in the stirring blade toward the side, and the second press-fitted in the excavation process And a consolidation step of integrally solidifying the first grout injected into the ground and discharging the first grout into the excavation hole and the second grout injected into the ground. To do.

  The ground improvement construction method according to claim 2 of the present application is the ground improvement construction method according to claim 1, wherein, in the consolidation step, the second grout injected into the ground forms an intrusion hole in the ground. A part of the 2 grout is pressed into the ground from the penetration hole into the ground and solidified, and the second grout is solidified in the penetration hole.

The ground improvement method according to claim 3 of the present application is the ground improvement method according to claim 1 or 2 , wherein in the excavation step, the excavation head is lowered while the excavation head is lowered in the process of forming the excavation hole. The second grout is pressurized and press-fitted into the ground on the side of the excavation hole.

The ground improvement construction method according to claim 4 of the present application is the ground improvement construction method according to any one of claims 1 to 3 , wherein the second grout pressurized to 1 to 10 MPa in the excavation step is the second ground. It is characterized by being press-fitted from the discharge port.

The ground improvement construction method according to claim 5 of the present application is the ground improvement construction method according to any one of claims 1 to 4 , wherein in the excavation step, at least cement and water as the first grout and the second grout. The second grout having a consolidation strength equal to or higher than the consolidation strength of the consolidated body obtained by mixing the first grout and the earth and sand is used from the second discharge port. It is characterized by being press-fitted.

  The ground improvement construction method of the present invention can prevent liquefaction of the ground by forming a solid consolidated body by solidifying the second grout in a vein shape in the ground. Moreover, the ground improvement construction method of the present invention can prevent the columnar solid body from collapsing and rising by integrally solidifying the first grout and the second grout. Furthermore, since the ground improvement method of the present invention locally injects the second grout, the amount of grout used can be reduced, and since it does not require mixing with the surrounding ground of the columnar consolidated body, the time required for construction can be reduced. It can be shortened.

It is a front view which shows the ground in which the ground improvement construction method to which this invention was applied was constructed, and the structure on the ground. It is an enlarged front view which shows the condition where grout discharges and press-fits from an excavation head and a stirring blade. It is an enlarged plan view which shows the condition where grout press-fits from a stirring blade. (A) is a front view which shows the excavation process of a ground. (B) is a front view showing the discharge and press-fitting process of grout. (C) is a front view which shows the completion of construction of a ground improvement construction method. It is an enlarged front view which shows the condition of the ground which constructed the ground improvement construction method.

  Hereinafter, as an embodiment for carrying out the present invention, a ground improvement method for increasing the strength of a soft ground by injecting grout into the ground will be described in detail with reference to the drawings as an example.

  FIG. 1 is a front view showing a ground on which a ground improvement method is applied by applying the present invention and a structure on the ground. FIG. 2 is an enlarged front view showing a state in which grout is discharged and press-fitted from the excavation head and the stirring blade. FIG. 3 is an enlarged plan view showing a situation in which grout is press-fitted from the stirring blade.

  As shown in FIG. 2, the excavator 1 used for the ground improvement method is provided with the excavation head 2 at the tip of the excavation rod 17 that enters the excavation hole 5 from the ground, and the excavation rod 17 rotates above the excavation head 2. A stirring blade 3 is provided as a shaft. The excavation head 2 and the agitating blade 3 may have an integral structure, or the excavation head 2 and the agitating blade 3 may be in a separated position.

  As shown in FIG. 2, the excavation head 2 includes an excavation blade 4 and a first discharge port 7 downward. The excavation head 2 is configured to excavate the ground 13 by rotating around the excavation rod 17. However, the excavation head 2 is not limited to this and may excavate the ground 13 by vibration or impact given from the excavation blade 4. . The excavation blade 4 may have a rectangular parallelepiped shape, a semicircular shape, a cone shape, or the like.

  As shown in FIG. 3, the stirring blade 3 extends from the center 1 a of the excavator 1 in the excavation direction to the side 5 a of the excavation hole 5. Two wing-like plates 6 are provided symmetrically with respect to 1a. The stirring blade 3 may be of any configuration as long as it extends from the center 1a of the cross section in the excavation direction of the excavator 1 toward the side 5a of the excavation hole 5, and is constituted by a single blade plate 6. It may be a shape constituted by three or more wing plates 6, a pillar, a spiral blade, or the like. As shown in FIG. 3, the stirring blade 3 includes a second discharge port 9 toward the side 5 a of the excavation hole 5.

  As shown in FIG. 2, the first discharge port 7 discharges the first grout 11 from the first tubular body 8 provided inside the excavation rod 17. The first discharge port 7 is provided in the center 1a of the cross section in the excavation direction of the excavator 1 in the excavation head 2 shown in FIG. 3 toward the lower part 5b of the excavation hole 5 as shown in FIG. The first discharge port 7 may have a shape of a press-fitting nozzle. The first discharge port 7 may be provided at any position as long as it faces the lower part 5b of the excavation hole 5, and is provided at a side end (not shown) of the excavation head 2 in the excavation direction of the excavator 1. Also good.

The first grout 11 discharged from the first discharge port 7 has a predetermined fluidity and is stirred and mixed with the earth and sand generated by excavation so that the consolidation strength becomes 0.5 to 6.0 N / mm ^2. Use a cementitious material.

  As shown in FIG. 2, the second discharge port 9 press-fits the second grout 12 from the second tubular body 10 provided inside the excavation rod 17. The second discharge port 9 is provided on the end surface 3 a of the stirring blade 3 toward the side 5 a of the excavation hole 5. The second discharge port 9 may have a shape of a press-fitting nozzle, or may be provided only on the end surface 3 a of the single stirring blade 3. The second discharge ports 9 may be provided at a plurality of locations on the stirring blade 3.

  The second grout 12 that is press-fitted from the second discharge port 9 uses a cement-based material that has fluidity necessary for pouring into the ground 13 and can obtain a predetermined strength. The second grout 12 may use water glass. The second grout 12 may be blended with bentonite, water glass, sulfuric acid band, or the like as an adhesive or strength enhancer. The consolidated strength of the second grout 12 itself may be equal to or higher than the consolidated strength obtained by mixing the first grout 11 and the ground 13.

  4A to 4C are front views showing the construction process of the ground improvement method. In the present invention, the first grout 11 is discharged while the excavation head 2 is lifted from the excavation hole 5 and the second grout 12 is press-fitted, and the second grout 12 is injected into the ground 13 and discharged into the excavation hole 5. It is a ground improvement construction method comprising a consolidation step of solidifying integrally with the first grout 11.

  In the excavation process of the present invention, first, the excavation rod 4 is rotated about the excavation rod 17 shown in FIG. 2 and is made to enter the ground 13 as shown in FIG. 13 is excavated to form an excavation hole 5. Next, the excavation head 2 is pulled up to the ground as shown in FIG. 4B while rotating the stirring blade 3 shown in FIG. At this time, in the excavation process shown in FIG. 4B, the first grout 11 is discharged from the first discharge port 7 to the lower part 5b of the excavation hole 5 and mixed with the earth and sand as shown in FIG. At this time, the first grout 11 may be discharged by the pressure difference in height between the ground and the first discharge port 7, or may be further pressurized and discharged. Further, as shown in FIG. 3, the second grout 12 is pressurized and press-fitted from the second discharge port 9 toward the side 5 a of the excavation hole 5. The second grout 12 may be subjected to a pressure capable of forming the penetration hole 14, for example, a pressure of about 1 to 10 MPa. In addition, unlike the normal injection pressure, the second grout 12 can be penetrated into the ground 13 by forcibly applying a high pressure, and finger characteristics can be ensured.

  In the excavation process of the present invention, the excavation head 2 is pulled up to the ground while rotating the agitating blade 3 and flowing the excavation earth and sand in which the excavation head 2 is buried, so that the excavation is easy. Further, since the excavation head 2 is pulled up by rotating the stirring blade 3 while discharging the first grout 11 from the first discharge port 7, the excavation soil and the first grout are extracted in the excavation hole 5 when the excavation head 2 is pulled up. 11 can be mixed with stirring. Furthermore, since the 2nd grout 12 is press-fitted from the 2nd discharge port 9 provided in the end surface 3a of the rotating stirring blade 3, all directions of the cross section of an excavation direction with respect to the ground 13 of the side 5a of the excavation hole 5 The 2nd grout 12 can be penetrated into.

  In the excavation process of the present invention, when the second grout 12 is press-fitted, the rotation of the agitating blade 3 is temporarily stopped, so that it is locally concentrated on the ground 13 on the side 5a of the excavation hole 5 at the stopped position. Then, the second grout 12 can be injected. In the excavation process of the present invention, when the second grout 12 is press-fitted while rotating the stirring blade 3, the rotation of the stirring blade 3 is not stopped, so that the construction efficiency is improved.

  In the excavation process of the present invention, excavation of the ground 13, lifting of the excavation head 2, agitation and mixing of the first grout 11 and excavated soil and press-fitting of the second grout 12 can be performed by a series of operations, and efficient construction is performed. It becomes possible.

  In the consolidation step of the present invention, as shown in FIG. 2, the second grout 12 is pressurized and press-fitted toward the side 5 a of the excavation hole 5, and the second grout 12 is injected laterally into the ground 13. In the consolidation step of the present invention, the second grout 12 injected under pressure against the ground 13 pushes the soil particles and enters the ground 13 to form the penetration holes 14. Thereafter, the second grout 12 is finely press-fitted into the ground around the penetration hole 14 formed by the ground 13 in a pulse shape.

  FIG. 5 is an enlarged front view showing the situation of the ground 13 on which the ground improvement method is applied. As shown in FIG. 5, the consolidation step of the present invention increases the branching portion of the surrounding ground 13 through the penetration hole 14 into which the second grout 12 has penetrated as far as the ground 13 toward the back of the ground 13. Pressed in finely. By consolidating the second grout 12, a vein-like solid body 16 is formed, and it is possible to increase the frictional force with the soil particles in a wide range and prevent liquefaction of the soft ground.

  In the consolidation step of the present invention, as shown in FIG. 2, the second grout 12 is locally injected into the ground 13 on the side 5 a of the excavation hole 5 to form the ground 13 on the side 5 a of the excavation hole 5. Therefore, it is possible to easily prevent liquefaction of the soft ground without requiring mixing of the earth and sand and the second grout 12. Since the second grout 12 is locally injected, the amount of the second grout 12 used can be reduced as compared with the case where the ground 13 around the excavation hole 5 and the second grout 12 are mixed as a whole. it can. Therefore, an increase in construction cost required for the ground improvement method can be suppressed. Moreover, since the press-fitting of the second grout 12 into the earth and sand constituting the ground 13 around the excavation hole 5 does not require time, the construction period can be shortened.

  In the consolidation step of the present invention, the second grout 12 is consolidated at the penetration hole 14 and the first grout 11 is consolidated at the drilling hole 5 at substantially the same timing. Further, as shown in FIG. 5, the columnar solid body 15 of the excavation hole 5 is integrally formed via a pulse-shaped solid body 16 and a boundary 14 b between the excavation hole 5 and the penetration hole 14.

  In the present invention, even when the ground 13 around the columnar solid body 15 is liquefied, the vein-shaped solid body 16 formed on the ground 13 that is not liquefied behind the liquefied ground 13. Frictional force is generated. As shown in FIG. 5, the columnar solid body 15 and the pulse-shaped solid body 16 are integrally formed via the boundary 14 b between the excavation hole 5 and the penetration hole 14. The frictional force thus transmitted is transmitted to the columnar consolidated body 15. As a result, it is possible to prevent the columnar solid body 15 from collapsing and rising by the frictional force transmitted from the pulse-shaped solid body 16 to the columnar solid body 15. Further, as shown in FIG. 1, when a plurality of columnar consolidated bodies 15 are formed, the pulse-shaped consolidated bodies 16 shown in FIG. 5 are formed on the ground 13 with a high density by the plurality of columnar consolidated bodies 15. Therefore, the columnar consolidated body 15 can be more securely prevented from collapsing and rising.

  In the consolidation step of the present invention, before the first grout 11 and the second grout 12 are consolidated, a part of the second grout 12 is connected to the first grout 11 via the boundary 14b between the penetration hole 14 and the excavation hole 5. Mix. In the present invention, the cement strength of the cementitious material used as the second grout 12 is equal to or higher than the consolidation strength of the first grout 11 and the ground 13 mixed. Thereby, the strength after consolidation of the second grout 12 is equal to or higher than the strength after consolidation of the first grout 11, and the columnar solid body formed by the first grout 11 in which a part of the second grout 12 is mixed. It is possible to avoid a decrease in the strength of 15.

  In the present invention, the first discharge port 7 is communicated with a ground grout supply facility (not shown) by a first tube 8, and the second discharge port 9 is communicated with a ground grout supply facility (not shown) by a second tube 10. Is done. Thereby, this invention can adjust the compounding ratio of the cement-type material used as the 1st grout 11 and the 2nd grout 12 according to the condition of the ground 13, and responds to the condition of the ground 13 flexibly. be able to.

  In the excavation process of the present invention, the second grout 12 is discharged when the excavation head 2 is lifted after excavation. However, the excavation head 2 is lowered to the excavation hole 5 during excavation. Alternatively, the second grout 12 may be discharged.

DESCRIPTION OF SYMBOLS 1 Excavator 2 Excavation head 3 Agitation blade 4 Excavation blade 5 Excavation hole 6 Wing plate 7 1st discharge port 8 1st pipe body 9 2nd discharge port 10 2nd pipe body 11 1st grout 12 2nd grout 13 Ground 14 penetration Hole 15 Columnar solid body 16 Pulse-shaped solid body 17 Drilling rod

Claims (5)

The excavator is provided with an excavation head at the tip and provided with an agitating blade above the excavation head to excavate the ground to form an excavation hole. The first grout is discharged from the first discharge port formed below to the bottom of the excavation hole, and the rotation of the stirring blade is temporarily stopped, and the stirring blade is formed toward the side of the excavation hole. A drilling step of pressurizing and press-fitting the second grout from the second discharge port into the ground on the side of the drilling hole;
The second grout press-fitted in the excavation step is injected into the ground, and the first grout discharged into the excavation hole and the second grout injected into the ground are integrally consolidated. A ground improvement method characterized by comprising a tying step. In the consolidation step, a penetration hole is formed in the ground by the second grout injected into the ground, and a part of the second grout is pressed into the ground from the penetration hole into the ground and consolidated. The ground improvement method according to claim 1, wherein the second grout is consolidated in the penetration hole. In the excavation step, the second grout is pressurized and pressed into the ground on the side of the excavation hole from the second discharge port while lowering the excavation head in the process of forming the excavation hole. The ground improvement construction method according to claim 1 or 2 . The ground improvement method according to any one of claims 1 to 3 , wherein in the excavation step, the second grout pressurized to 1 to 10 MPa is press-fitted from the second discharge port. In the excavation step, a cement-based material in which at least cement and water are kneaded is used as the first grout and the second grout, and the consolidation strength of the consolidated body obtained by mixing the first grout and earth and sand. The ground improvement method according to any one of claims 1 to 4 , wherein the second grout having the above-described consolidation strength is press-fitted from the second discharge port.

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