JP2020084524A - Method for constructing underground structure - Google Patents

Abstract

To provide a method for constructing an underground structure, which is capable of efficiently constructing an underground structure using a ground improvement body.SOLUTION: A method of constructing an underground structure for constructing an underground structure 1 using a ground improvement body 3 comprises steps of constructing an underground hole filled with adjustment liquid mixed with excavated soil by drilling the ground with an excavation and agitating unit of a rotating drilling agitation device while supplying the adjustment liquid, building core material 2 in the underground hole, replacing a part of the adjustment liquid containing the excavated soil filling the underground hole with a cement-based solidifying liquid, and injecting compressed air at a bottom of the hole to generate an upward flow in the underground hole, and mixing and agitating the cement-based solidifying liquid and the adjustment liquid mixed with the excavated soil.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD The present invention relates to a method of constructing an underground structure for constructing an underground structure using a ground improvement body.

BACKGROUND ART Conventionally, a method of forming a ground improvement body made of soil cement in the ground and using it to construct a temporary mountain retaining wall or the like is widely known. For example, Patent Document 1 discloses a method of forming a ground improvement body constituting a soil cement structure with a small ground improvement apparatus.

Specifically, a drilling bit is provided in the vicinity of the lower end, and an exciter that transmits an exciting force is connected to the rod, and the rod is rotated while applying an up-and-down exciting force while drilling the ground. Cement milk is discharged from the tip of the rod, and excavated soil and cement milk are mixed and stirred to form a soil improvement body made of soil cement in the ground.

Japanese Patent No. 5443928

The method of Patent Document 1 can be said to be a method suitable for a case where the construction target area is located on a narrow site because the ground improvement body can be created using a small ground improvement device.

However, since the cement milk is discharged while drilling the ground, the mixture of the cement milk and the excavated soil begins to harden immediately after the stirring is completed. Therefore, for example, when trying to construct an underground structure including a core material in a ground improvement body, the core material must be quickly penetrated into the mixture of cement milk and excavated soil, and the building must be built. Incorporation work tends to be complicated.

Furthermore, when the underground structure is large in the depth direction, it takes time to assemble the core material, so hardening of the soil cement progresses and it cannot penetrate to a predetermined depth, and a high stop occurs. It is likely that it will be difficult to ensure high quality for underground structures.

The present invention has been made in view of the above problems, and its main purpose is to provide a method for constructing an underground structure, which is capable of efficiently constructing an underground structure using a ground improvement body. It is to be.

In order to achieve such an object, the method of constructing an underground structure of the present invention is a method of constructing an underground structure using a ground improvement body, while supplying a conditioning liquid, A step of boring the ground in the excavation and stirring section of the rotated boring and stirring device to construct an underground hole filled with the adjustment liquid containing the excavated soil, and a step of building a core material in the underground hole. , A step of replacing a part of the adjustment liquid of the excavated soil mixed with the cement-based solidifying liquid that fills the underground hole, and injecting compressed air at the bottom of the hole to generate an upward flow in the underground hole, And a step of mixing and stirring the cement-based solidifying liquid and the adjustment liquid mixed with the excavated soil.

According to the method for constructing an underground structure of the present invention described above, the core material can be built in the underground hole filled with the adjustment liquid mixed with the excavated soil in the state where the cement-based solidifying liquid is not mixed. .. As a result, the core material can be built without being restricted by the working time due to the hardening of the cement-based solidifying liquid, so that it is possible to increase the degree of freedom in the work of building the core material. In addition, it is possible to interrupt the work of building the core material in response to an unexpected situation, and it is possible to significantly improve the workability of the underground structure.

Further, by injecting compressed air at the bottom of the hole to generate an upward flow in the underground hole, the adjusting liquid mixed with the excavated soil and the cement-based solidifying liquid are mixed and stirred in the underground hole. Thereby, a homogeneous mixture in the height direction can be produced in the underground hole, and it becomes possible to secure high quality in the ground improvement body after curing.

In the method of constructing an underground structure of the present invention, in the step of building the core material, a core is added by adding a plurality of core material divided bodies in an underground hole filled with the adjustment liquid containing the excavated soil. Characterized by building and building timber.

According to the method for constructing an underground structure of the present invention described above, it is possible to efficiently construct a long underground structure in the depth direction even if the construction target area is located on a site with a head limitation. Become.

According to the present invention, since the core material is built in the underground hole filled with the adjustment liquid mixed with the excavated soil in the state where the cement-based solidifying liquid is not mixed, the work resulting from the hardening of the cement-based solidifying liquid The core material can be built without being restricted by time. As a result, it is possible to increase the degree of freedom regarding the work of building the core material and significantly improve the workability, and it is possible to efficiently construct an underground structure.

It is a figure which shows the outline of the underground structure in embodiment of this invention. It is a figure which shows a mode that the underground hole is constructed|assembled in the ground in Embodiment of this invention (the 1). It is a figure which shows a mode that the underground hole is constructed|assembled in the ground in Embodiment of this invention (the 2). It is a figure which shows a mode that the core material is built in the underground hole in embodiment of this invention (the 1). It is a figure which shows a mode that the core material is built in the underground hole in embodiment of this invention (the 2). It is a figure which shows a mode that a part of adjustment liquid of excavated soil mixing which fills an underground hole in embodiment of this invention is replaced with a cement type solidification liquid. It is a figure which shows a mode that the adjustment liquid of the excavated soil mixing and the cement type solidification liquid which mix and agitate which fills an underground hole in embodiment of this invention are mixed and stirred. It is a figure which shows the construction procedure of the core material of the mountain retaining pile which carried out the test construction by the construction method of the underground structure in embodiment of this invention. It is a figure which shows the result of the uniaxial compressive strength calculated|required by the uniaxial compression test which carried out the test construction by the construction method of the underground structure in embodiment of this invention.

The present invention is a method for constructing an underground structure such as a mountain retaining pile or a supporting pile using a ground improvement body, and among them, it is suitable when the construction target area is located on a site with a head limitation. Is the way. In the present embodiment, as an underground structure, a mountain retaining pile having a core material penetrating a ground improvement body is taken as an example, and the details thereof will be described.

As shown in FIGS. 1(a) and 1(b), the mountain retaining pile 1 is an underground structure formed in a columnar shape, and in the present embodiment, a ground hole H having a cross-sectional diameter of about 400 mm to 800 mm is formed. It is composed of a built-in core material 2 and a ground improvement body 3 formed in the underground hole H so as to include the core material 2. The core material 2 includes an air supply hose 4 and a solidified liquid supply hose 5 Is fixed. The cross-sectional diameter of the underground hole H is not necessarily limited, and for example, a cross-sectional diameter of 800 mm or more may be adopted.

The core material 2 is configured by connecting a plurality of core material divided bodies 21 in series in the longitudinal direction, and the core material divided body 21 has a sectional width of about 250 to 400 mm in the present embodiment. Long steel material such as H-section steel is used. These are detachably connected by bolt connection via a gusset plate 22 arranged so as to straddle the adjacent flanges while being arranged in series in the longitudinal direction. The sectional width of the core material divided body 21 is not necessarily limited, and for example, a sectional width of 400 mm or more may be adopted.

The core material dividing body 21 is not necessarily limited to the long steel material, and any long material may be adopted as long as it is a material having rigidity enough to function as the core material of the mountain piles 1. .. The member length of the core material divided body 21 may be set to any value. For example, when the construction target area has an empty space limitation, a suitable material may be appropriately set according to the height thereof. ..

Further, the number of the core material divided bodies 21 used to form the core material 2 may be appropriately determined according to the required length of the core material 2. Therefore, when the total length of the pile retaining pile 1 to be constructed is short and it is not necessary to connect a plurality of core material divided bodies 21, only one core material divided body 21 may be used as the core material 2.

In addition, in order to hold two air supply hoses 4 and one solidified liquid supply hose 5 in the core material divided body 21, as shown in FIGS. 1 and 4, one side of the web is provided with an air supply hose. An air supply hose gripper 41 for fixing 4 and a solidification liquid supply hose gripper 51 for fixing the solidification liquid supply hose 5 are installed. Further, only the air supply hose gripper 41 for fixing the air supply hose 4 is installed on the other surface.

Note that the air supply hose gripper 41 and the solidification liquid supply hose gripper 51 may have any shape as long as they can grip the air supply hose 4 and the solidification liquid supply hose 5, respectively. ..

As shown in FIG. 4, the air supply hose 4 is composed of a pipe member through which the compressed air A can flow, and has a base end portion connected to an air compressor 81 installed on the ground and an air injection pipe 6 at the tip end portion. Is installed. The shape and material of the air supply hose 4 may be any hollow material that allows gas to pass therethrough. An air flow meter 82 is installed between the air supply hose 4 and the air compressor 81 so that the flow rate of the compressed air A supplied to the air injection pipe 6 can be measured.

On the other hand, the solidification liquid supply hose 5 is composed of a pipe member through which the cement-based solidification liquid C can flow, and its base end is connected to the solidification liquid supply device 91 installed on the ground, and the solidification liquid discharge pipe is provided at the tip. 7 is installed. The solidification liquid supply device 91 manages the composition and flow rate of the cementation solidification liquid C to be supplied to the solidification liquid supply hose 5, and supplies a predetermined amount of the cementation solidification liquid. The solidification liquid supply hose 5 may have any shape and material as long as it is a hollow material that allows liquid to pass therethrough.

As shown in FIG. 1B, the air injection pipe 6 installed in the air supply hose 4 and the solidification liquid discharge pipe 7 installed in the solidification liquid supply hose 5 respectively have an air injection port 61 and a solidification liquid discharge port 71. It is provided. The numbers of the air injection ports 61 and the solidified liquid discharge ports 71 may be any number as long as they are paired, for example, two or four, but in the present embodiment, both are provided and the air injection ports are provided. The air injection pipe 6 and the solidification liquid discharge pipe 7 are arranged so that the port 61 and the solidification liquid discharge port 71 are located below the lower end of the core material divided body 21 that constitutes the lowermost end of the core material 2.

Then, as shown in FIG. 7B, the air injection pipes 6 installed on each of the two air supply hoses 4 have a total of four air injection ports 61 compressed in four directions in a plan view of the underground hole H. The injection directions are adjusted so that the air A can be injected. Further, as shown in FIG. 6( b ), the solidified liquid discharge pipe 7 installed in the single solidified liquid supply hose 5 has two solidified liquid discharge ports 71 which are cement-based in a direction parallel to the web of the core material 2. The orientation is adjusted so that the solidified liquid can be discharged.

As shown in FIGS. 6(a) and 7(a), the ground improvement body 3 has an adjustment liquid W1 containing a mixture of excavated soil and excavated soil when excavating the underground to construct an underground hole H. The cement-based solidifying liquid C of a predetermined amount is mixed, stirred, and then cured to form a hardened cement cement, which is formed into a columnar shape.

Here, the adjusting liquid W1 mixed with the excavating soil is a mixture of the excavating soil and the adjusting liquid W which are generated at the time of boring the ground when the adjusting liquid W is used for boring the ground. In order to have a function of protecting the hole wall of the intermediate hole H, a function of discharging excavated soil when the ground is drilled, and a function of being hardened by being mixed and stirred with the cement-based solidifying liquid C, the ground of the construction target area is combined. It is a liquid whose specific gravity and viscosity are adjusted and controlled according to its properties.

Therefore, the adjustment liquid W may be any liquid that has the above-mentioned three functions, such as bentonite muddy water or a polymer-based aqueous solution to which a dispersant is added.

The method for constructing an underground structure including the mountain retaining pile 1 having the above configuration will be described below in detail together with the details of the hole drilling stirring device 10, the gate crane 20 and the core material gripping device 30 used during construction. To do.

≪First step≫
As shown in FIG. 2, a drilling stirrer 10 described below is installed at a predetermined position in the construction target area of the mountain retaining pile 1, and the ground is adjusted to a predetermined depth via the drilling stirrer 10 while supplying the adjusting liquid W. The hole is drilled until it reaches, and the underground hole H, as shown in FIG. 3, in which the inside of the hole is filled with the adjusting liquid W1 containing the excavated soil is constructed.

At the planned construction position of the Yamadome pile 1, before starting the drilling with the drilling agitation device 10, after the mouthpiece P penetrates from the ground surface to protect the hole wall, the inside of the mouthpiece P is Excavate in advance. Note that the mouth pipe P does not necessarily have to be applied, and if the work ground is strong, for example, it is sufficient to perform maintenance only by digging and laying an iron plate. Further, when starting the drilling work to construct the underground hole H, the drainage pipe S for draining the excavated soil generated by the drilling using the adjusting liquid W is used as the underground hole H. Install near the mouth of the hole.

<Drilling stirrer 10>
As shown in FIG. 2, a boring and stirring device 10 used when boring the ground in a construction target area includes a moving mechanism 11 composed of a caterpillar, a pedestal portion 12 movable by the moving mechanism 11, and a pedestal portion. A leader 13 supported by 12 so as to extend in the vertical direction, an oscillating device 14 installed movably in the vertical direction along the reader 13, and a rod 15 whose head is connected to the oscillating device 14. The excavation stirring unit 16 attached to the tip of the rod 15, the adjustment liquid supply device 17 that supplies the adjustment liquid W discharged from the tip of the excavation stirring unit 16 to the inside of the rod 15, and the rotational force is applied to the rod 15. The rotating device 18 is provided.

The vibration generator 14 is a device that generates a vertical vibration force by rotating an eccentric weight, and is installed so as to be vertically movable along the reader 13. The vibration generating device 14 may be any device as long as it can generate a vibration generating force capable of transmitting a vibration including at least one component in the vertical direction or the horizontal direction with respect to the rod 15.

The rotating device 18 grips the peripheral surface of the rod 15 with a rod gripping portion (not shown) provided inside thereof, and applies a rotational force in the forward direction or the reverse direction about the axis of the rod 15 to the rod 15. The device is located below the vibration generating device 14 and is vertically movable along with the vibration generating device 14 along the reader 13.

The rod 15 is composed of a hollow single tube, is erected with its head supported by the vibrating device 14, and is connected to the adjusting liquid supply device 17 via a swivel 151 installed in the middle part. At the same time, the excavation and stirring unit 16 is connected to the tip.

The excavation and agitation unit 16 is attached to the shaft portion 161, which is connected to the rod 15, the excavation blade main body 162 which is attached so as to extend laterally in the vicinity of the tip end portion of the shaft portion 161, and the excavation blade main body 162. And a drill bit 163. Further, a tip bit 164 is attached to the tip of the shaft portion 161, and an adjustment liquid discharge port (not shown) is provided.

The adjustment liquid supply device 17 includes a plant 171 for producing the adjustment liquid W described above, and an adjustment liquid supply pipe 172 for supplying the produced adjustment liquid W to the rod. In the present embodiment, the specific gravity of the adjusting liquid W is adjusted and managed in consideration of the properties of the ground so that the adjusting liquid W1 mixed with excavated soil that fills the underground hole H has a specific gravity of about 1.5.

When the excavation and agitation unit 16 of the hole agitation agitation device 10 having the above-described configuration is operated in a state where the excavation agitation unit 16 penetrates into the overexcavated mouth pipe P, the oscillating device 14 applies vertical vibration to the excavation agitation device 16 and the rotation device 18 causes It rotates forward about the axis of the rod 15. At the same time, the adjustment liquid W supplied from the adjustment liquid supply device 17 and flowing down the hollow portion of the rod 15 is discharged from the adjustment liquid discharge port provided at the tip of the shaft portion 161 of the excavation and stirring unit 16.

As a result, as shown in FIG. 3, the ground is excavated by the excavation bit 163 and the tip bit 164 provided in the excavation and agitation unit 16 to form the underground hole H, and the underground hole H is also excavated. The soil and the adjusting liquid W are mixed and stirred, and the underground hole H is filled with the adjusting liquid W1 containing the excavated soil.

The boring work using the boring agitator 10 is performed while sludge is discharged through the mud discharge pipe S together with the excess adjustment liquid W1 containing the excavated soil. Further, when removing the excavation and agitation unit 16 after constructing the underground hole H, the excavated soil stored at the bottom of the hole is fluidized and lifted up, and the adjustment liquid for mixing the excavated soil in the height direction inside the underground hole H. In order to make the specific gravity of W1 uniform, as shown in FIG. 3, the rod 15 is pulled out while being rotated about the axis thereof as in the case of excavation.

<<Second step>>
Next, as shown in FIGS. 4 and 5, in the underground hole H filled with the excavated soil mixture adjusting liquid W1, the core material divided body 21 is hung and added to build the core material 2, The core material 2 is built in a predetermined position of the hole H.

In the present embodiment, the gate-type crane 20 capable of hoisting the core material divided body 21 and the core material divided body 21 inserted in the underground hole H can be grasped for the work of building the core material 2. The core material holding device 30 is used.

<Gate type crane and core material gripping device>
As shown in FIG. 4, the portal crane 20 includes a pair of leg portions 201 that are arranged in parallel at a distance, and a beam portion 202 that connects upper end portions of the leg portions 201. The leg portion 201 is provided with traveling means 203 such as a wheel at the lower end thereof and an expansion/contraction device 204 such as a hydraulic jack, and is configured to be expandable/contractible in the height direction as shown in FIGS. 4 and 5. ing.

Further, the beam portion 202 is provided with a lifting machine 205 such as a hoist capable of suspending the core material divided body 21 via a wire or the like, and the lifting machine 205 has a length direction of the beam section 202. It is installed so that it can be moved in the horizontal direction.

Therefore, the portal crane 20 is installed so that the axis of the beam portion 202 is parallel to the diameter direction of the underground hole H in the vertical plane, and the lifting machine 205 is appropriately moved to the beam section 202 so that the lifting machine 205 is installed. It is possible to make the axis of the suspended core material 21 coincide with the axis of the underground hole H. In addition, the core material divided body 21 in a state of being suspended by the lifting machine 205 is arranged in the underground hole H by the expansion and contraction of the pair of leg portions 201 by the expansion and contraction device 204 and the winding or unwinding of the wire included in the lifting machine 205. It is possible to hang or hang.

On the other hand, the core material gripping device 30 is installed on the ground surface and holds and releases the pedestal 301 having a hole having a diameter larger than the underground hole H in the center and the core material divided body 21 inserted into the through hole. Possible chuck member 302. Note that the core material gripping device 30 may have any shape as long as it can grip the core material 20.

The construction method and the construction method of the core 2 using the portal crane 20 and the core gripping device 30 described above are as follows. As shown in FIGS. 4 and 5, first, the core material holding device 30 is installed so as to surround the underground hole H on the ground surface, and the axis of the beam portion 202 is in the diametrical direction of the underground hole H and in the vertical plane. Install the portal crane 20 so that it is parallel to.

Next, the hoisting machine 205 of the portal crane 20 suspends the core material division body 21 to align the core material division body 21 and the underground hole H with each other, and to hang the core material division body 21 in the underground hole H. Thereafter, the vicinity of the upper end of the core material dividing body 21 is grasped by the chuck member 302 of the core material grasping device 30, and then the core material dividing body 21 is removed from the lifting machine 205.

Then, the lifting machine 205 of the portal crane 20 suspends the new core material division body 21, and the position adjustment is performed so that the lower end thereof faces the upper end of the core material division body 21 gripped by the core material gripping device 30. After that, the two are abutted against each other and connected by bolt bonding using the gusset plate 22. In addition, any joining means such as welding may be employed to connect the core material divided bodies 21 to each other.

After that, the connected core material divided body 21 was suspended by the gate crane 20, the grip by the core material grasping device 30 was released, and the connected core material divided body 21 was suspended to a predetermined depth, and then connected. The core material gripping device 30 grips the vicinity of the upper end portion of the core material divided body 21, and a new core material divided body 21 is added by the procedure described above.

The above-described operation of adding the core material divided bodies 21 is repeated until the core material 2 constructed by connecting the core material divided bodies 21 has a required length. In addition to the work of adding the core material divided body 21, the air supply hose 4 and the solidification liquid supply hose 5 are respectively utilized by using the air supply hose gripper 41 and the solidification liquid supply hose gripper 51. Fix it to 21. By these operations, the core material 2 having a desired length is built in the underground hole H with the air supply hose 4 and the solidification liquid supply hose 5 installed.

When the core material 2 is built, when the viscosity of the adjusting liquid W1 mixed with the excavated soil stored in the underground hole H is high and the penetration resistance acts on the core material 2, air is supplied from the air compressor 81. Compressed air A may be jetted from the air jet pipe 6 via the hose 4 to reduce the penetration resistance acting on the core material 2. Further, when the construction target area does not have an empty head restriction, the core material 2 formed by adding the core material divided bodies 21 to each other on the ground may be built in the underground hole H. A suitable method may be appropriately selected according to the environment.

≪Third process≫
After the core material 2 is built in the underground hole H filled with the adjustment liquid W1 containing the excavated soil, as shown in FIGS. 6(a) and 6(b), the adjustment liquid mixed with the excavated soil is filled with the adjustment liquid W1. A part of W1 is replaced with the cement-based solidifying liquid C.

The cement-based solidification liquid C is supplied from the solidification liquid supply device 91 to the solidification liquid discharge pipe 7 through the solidification liquid supply hose 5 installed along the core material 2, and the solidification liquid discharge port of the solidification liquid discharge pipe 7 is supplied. It discharges from 71 in the vicinity of the hole bottom of the underground hole H.

In addition to the supply of the cement-based solidifying liquid C, the excavated soil mixing adjusting liquid W1 corresponding to the supply amount of the cement-based solidifying liquid C is discharged through the sludge pipe S. At this time, since the solidification liquid discharge pipe 7 is arranged at the lower end of the core material 2 as described above, the cement-based solidification liquid C is added to the excavated soil mixing adjustment liquid W1 discharged from the mouth of the underground hole H. Are rarely mixed.

The setting position of the solidification liquid discharge pipe 7 is such that when the cement-based solidification liquid C is discharged into the underground hole H, the cement-based solidification liquid W1 is discharged from the mouth of the underground hole H to the cement-based solidification adjusting liquid W1. The lower end of the core material 2 does not necessarily have to be provided as long as the liquid C does not substantially coexist.

<<Fourth step>>
After discharging a predetermined amount of the cement-based solidifying liquid C into the underground hole H, the compressed air A is directed toward the hole wall near the hole bottom of the underground hole H, as shown in FIGS. The cement-based solidifying liquid C and the adjusting liquid W1 mixed with the excavated soil are mixed and stirred by injecting and using the upward flow generated in the underground hole H by this.

The compressed air A is supplied from the air compressor 81 to the air injection pipe 6 through the air supply hose 4 installed along the core material 2, and the air injection port 61 of the air injection pipe 6 extends from the hole H to the hole H. It is jetted toward the hole wall near the bottom. The injected compressed air A rises as continuous bubbles and rises in the underground hole H. As a result, the cement-based solidifying liquid C separated in the underground hole H and the adjustment liquid W1 mixed with the excavated soil are mixed and stirred in the height direction, and uniformly mixed in the height direction of the underground hole H. It becomes a mixture.

In addition, the injection amount and the injection time of the compressed air A may be appropriately adjusted according to the viscosities of the two so that the cement-based solidifying liquid C and the adjustment liquid W1 mixed with the excavated soil are homogeneously mixed in the underground hole H. Good. The injection amount is preferably 500 L/min or more and 2000 L/min or less, and the injection time is preferably 5 minutes or more and 20 minutes or less.

When the cement-based solidifying liquid C and the adjusting liquid W1 mixed with the excavated soil are homogeneously mixed in the height direction of the underground hole H to form a mixture, the injection of the compressed air A is stopped and the mixture is hardened to cure the soil cement. The ground improvement body 3 which is a hardened body is created. Thereby, the soil improvement body constructed by the conventional method, that is, the soil cement hardened body obtained by hardening the mixture obtained by mixing and stirring the excavated soil and the cement-based hardening liquid by drilling the ground while discharging the cement-based hardening liquid. It becomes possible to construct the similar ground improvement body 3, and the mountain retaining pile 1 including the core material 2 in the ground improvement body 3 as shown in FIG. 1 is constructed.

According to the method for constructing an underground structure, the core material 2 is built in the underground hole H filled with the adjustment liquid W1 containing the excavated soil before the cement-based solidifying liquid C is mixed, The work time for building the core material 2 is not restricted by the work time due to the hardening of the cement-based solidifying liquid C. Therefore, the core material 2 including the plurality of core material divided bodies 21 can be adopted for the mountain retaining pile 1, and the core material 2 can be constructed and built while utilizing the underground hole H to add the core material divided bodies 21. ..

As a result, even if the construction target area of the mountain retaining pile 1 is a site with a limited head, it is possible to construct the mountain retaining pile 1 that is long in the depth direction with high quality. Further, in response to an unexpected situation, it is possible to interrupt the work of building the core material 2, and it is possible to greatly improve the workability of the mountain retaining pile 1.

≪Unconfined compressive strength test of underground structure≫
The results of the compressive strength test performed on the mountain retaining pile 1 constructed to confirm the workability of the method for constructing an underground structure described above will be described below. The test object was a mountain retaining pile 1 having a cross-sectional diameter of 750 mm, a design body length of 13.5 m, and a ground improvement body 3 having a design strength of 1.0 kN/m ² . In addition, although the construction target area of the above-mentioned underground structure is assumed to be a site with an empty head restriction, the mountain retaining pile 1 for confirming the following workability is constructed in the construction target area without an empty head restriction. There is.

In manufacturing the mountain retaining pile 1 to be tested, first, the ground was drilled while supplying the adjusting liquid W to construct an underground hole H having a cross-sectional diameter of about 750 mm and a total length of about 14 m. The adjusting liquid W used when drilling the ground has a specific gravity of 1.01 so that the adjusting liquid W1 containing the excavated soil stored in the underground hole H after construction has a specific gravity of about 1.5 (in-hole average). The bentonite mud water that was adjusted and managed was adopted. Further, the adjustment liquid W1 mixed with excavated soil is in a state in which approximately 20 to 30% by weight of excavated soil is mixed.

Next, a core material 2 having a member length of 13.5 m connected in advance on the ground is constructed in the underground hole H in which the adjustment liquid W1 mixed with the excavated soil is stored, and this is made into the underground hole H by a lifting machine. I built it. As the core material 2, H-section steel having a cross-sectional width of about 400 mm was adopted. In addition, the replenishment work of the core material division body 21 in the underground hole H under the construction target area with the head limitation is carried out over 3 days as shown in, for example, FIGS. 8(a) to 8(c), It is assumed that a total of 7 pieces will be added, 3 pieces on the 1st day, 2 pieces on the 2nd day, and 2 pieces on the 4th day.

Then, in the underground hole H in which the core material 2 was built, a part of the stored adjustment liquid W1 containing excavated soil was replaced with the cement-based solidifying liquid C. As the cement-based solidifying liquid C, a cement-based solidifying liquid containing blast furnace cement type B as a main material was adopted.

Then, the compressed air A whose injection amount is adjusted to about 1000 L/min is injected in two directions toward the hole wall in the vicinity of the hole bottom of the underground hole H, and bubbles rising from the hole bottom toward the hole mouth are continuous. Generated. By the upward flow generated by the bubbles, the adjusting liquid W1 mixed with excavated soil and the cement-based solidifying liquid C were mixed and stirred for about 10 minutes.

After preparing a mixture of the adjusting liquid W1 mixed with excavated soil and the cement-based solidifying liquid C in the underground hole H, an unconsolidated sample and a sample without core are collected from the mixture, and the unconsolidated sample is a material The uniaxial compressive strength test was carried out on the 28th day and the sample after core removal on the 56th day.

For the unconsolidated samples, cores were collected from the ground surface 3 in the depth direction from the ground surface in the range of 0 m, 6 m, 10 m, and 14 m, and three cores were collected from each of the 12 test samples. A uniaxial compression test was performed, and an average value of uniaxial compression strength was calculated in each of the above four ranges. The core-removed samples are collected from the ground surface 3 in the depth direction from the ground surface in the range of 2 to 4 m, 5 to 7 m, 9 to 11 m, and 11 to 14 m, and three cores are collected. A uniaxial compression test was performed on each of the 12 test bodies, and an average value of uniaxial compression strength was calculated in each of the four ranges.

As shown in FIGS. 9(a) and 9(b), in both of the unconsolidated sample and the sample without core, the average value of the uniaxial compressive strength exceeds the designed strength of 1.0 kN/m ² in each of the above four ranges. You can see how it is being expressed. As a result, when the core material 2 is built in the underground hole H in a state where the adjustment liquid W1 mixed with the excavated soil is filled, and then a part of the adjustment liquid W1 mixed with the excavated soil is replaced with the cement-based solidifying liquid C. Also, by utilizing the upward flow generated in the underground hole H by injecting the compressed air A, the adjustment liquid W1 mixed with the excavated soil and the cement-based solidifying liquid C are mixed and stirred, so that the height direction is increased. It can be seen that it is possible to create a homogeneous and sound ground improvement body 3.

Further, it is possible to carry out the work of building the core material 2 for several days, and it is possible to construct a sound mountain retaining pile 1 satisfying the design strength while improving the workability.

Needless to say, the method of constructing an underground structure of the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.

For example, in the present embodiment, the mountain retaining pile 1 is taken as an example of the underground structure using the ground improvement body 3, but any underground structure using the ground improvement body 3 may be adopted. Good. For example, when constructing a support pile as an underground structure, the design strength of the ground improvement body 3, the structure of the tip portion of the core material 2, and the like may be appropriately changed to secure a desired vertical support force.

In addition, in the present embodiment, the H-shaped steel is adopted for the core material divided body 21, and a plurality of these are connected by bolt joining using the gusset plate 22 to construct the core material 2. Any connection method may be used. For example, when a steel pipe is adopted as the core material dividing body 21, it may be connected by a steel pipe screw joint, and the core material dividing body 21 and the joining method suitable for the underground structure to be constructed are adopted. The suitable core material 2 may be constructed.

Further, in the present embodiment, two air supply hoses 4 and one solidification liquid supply hose 5 are installed for the core material 2, but the numbers thereof are not limited to this, and may be increased or decreased as appropriate. May be. Further, although the air supply hose 4 and the solidified liquid supply hose 5 are fixed to the core material 2 and left on the mountain retaining pile 1 after construction, the air supply hose 4 and the solidification liquid supply hose 5 are detachably installed to the core material 2, The air supply hose 4 and the solidification liquid supply hose 5 may be reusable.

Therefore, the air supply hose 4 and the solidified liquid supply hose 5 may be separated from the core material 2 and inserted into the underground hole H at appropriate timings before and after the core material 2 is built. It is preferable to use an auxiliary tool for inserting the air supply hose 4 and the solidification liquid supply hose 5 into the underground hole H. As the auxiliary tool, for example, an auxiliary rod material such as a rod material or a single pipe may be adopted, and the air supply hose 4 and the solidified liquid supply hose 5 may be placed along the auxiliary rod material and inserted into the underground hole H.

Further, in the present embodiment, when the core material 2 is built in the underground hole H filled with the adjustment liquid W1 for excavated soil, the air injection pipe 6 of the air supply hose 4 is installed so as to smoothly build the core material 2. More compressed air A was injected. However, for example, the solidification liquid supply hose 5 may be connected to the air compressor 81, and the compressed air A may be jetted from the solidification liquid discharge pipe 7 of the solidification liquid supply hose 5.

Further, in the present embodiment, the underground hole H is constructed by using the hole agitating device 10, but it is not necessarily limited to this, and the ground is drilled while the adjusting liquid W is supplied, and the excavated soil is excavated. Any excavating device may be adopted as long as the underground hole H filled with the mixed adjusting liquid W1 can be constructed.

1 Yamadome pile (underground structure)
2 core material 21 core material division body 22 gusset plate 3 ground improvement body 4 air supply hose 5 solidification liquid supply hose 6 air injection pipe 61 air injection port 7 solidification liquid discharge pipe 71 solidification liquid discharge port 81 air compressor 82 air flow meter 91 Solidifying liquid supply device 10 Drilling stirring device 11 Moving mechanism 12 Pedestal part 13 Leader 14 Vibration generator 15 Rod 151 Swivel 16 Excavation stirring part 161 Shaft part 162 Excavation blade body 163 Excavation bit 164 Tip bit 17 Adjustment liquid supply device 18 Rotation device 20 Gate type crane 201 Leg 202 Beam 203 Traveling means 204 Telescopic device 205 Lifting machine 30 Core material gripping device 301 Frame 302 Chuck member

A Compressed air S Sewage sludge pipe P Hole wall protection pipe W Conditioning liquid W1 Conditioning liquid mixed with excavated soil

Claims (2)

A method of constructing an underground structure using a ground improvement body, comprising:
While supplying the adjustment liquid, a step of drilling the ground in the excavation stirring unit of the rotated drilling stirring device, and constructing an underground hole filled with the adjustment liquid containing the excavated soil,
A step of building a core material in the underground hole,
A step of replacing a part of the adjusting liquid of the excavated soil mixed with the cement-based solidifying liquid to fill the underground hole;
A step of injecting compressed air at the bottom of the hole to generate an upward flow in the underground hole, mixing and stirring the cement-based solidifying liquid and the adjustment liquid mixed with the excavated soil,
A method for constructing an underground structure, comprising: The method for constructing an underground structure according to claim 1,
In the step of building the core material, the core material is constructed and built by adding a plurality of core material divided bodies in the underground hole filled with the adjustment liquid containing the excavated soil. The method of constructing an underground structure.