JP6901928B2 - Pile construction method - Google Patents

Description

The present invention relates to a method of constructing piles.

Conventionally, when constructing a cast-in-place pile, first, a hole is drilled at the construction position of the pile. Then, after the pre-assembled reinforcing bar cage is built in the hole, concrete or mortar is cast to create a pile. Further, when constructing a ready-made pile manufactured in a factory or the like, there are a construction method in which a hole is drilled in advance and a ready-made pile is built in the hole, and a construction method in which the ready-made pile is driven into the ground by impact. Machines are often used to drill holes in the ground, and typical methods include the earth drill method, the all-casing method, and the reverse method.

When constructing cast-in-place piles, if the hole wall collapses after drilling the ground, the drilled soil may accumulate at the bottom of the hole, making it impossible to secure the vertical bearing capacity required for the pile. In order to ensure the quality of piles, it is necessary to prevent the collapse of the hole wall after drilling. As a construction method for preventing the collapse of the hole wall over the entire length of the hole, an all-casing construction method in which a cylindrical casing tube is press-fitted into the ground by a casing press-fitting device and the inside of the casing is excavated with a hammer grab is common.

In addition, a method of preventing the collapse of the hole wall by using a ground improvement body without using a casing has also been proposed. FIG. 12 is a diagram showing a method of preventing the hole wall from collapsing by using the ground improvement body 103. In the method shown in FIG. 12, as shown in FIG. 12A, a solid ground improvement body 103 is formed on the ground 101. Then, as shown in FIG. 12B, the inside of the solid ground improvement body 103 is excavated to form the drilled portion 105. Then, as shown in FIG. 12 (c), a pile 107 is constructed in the drilled portion 105 (see, for example, Patent Document 1).

Furthermore, if the ground is contaminated by substances that are harmful to the human body or the environment, or if the groundwater in the ground is contaminated, the pollutants will spread in addition to the hole wall stabilization measures when constructing piles, etc. Preventive measures are required. The guidelines of the Soil Contamination Countermeasures Law provide some examples of pile construction methods.

As the first example, a casing is installed up to the semi-impermeable layer to block the groundwater, the soil at the place where the casing is installed is removed by excavation, etc., and then the groundwater in the casing is collected and replaced or purified. There is a method of constructing a pile in the casing (see, for example, Non-Patent Document 1). As a second example, a casing is installed up to the semi-impermeable layer to block groundwater, the soil at the place where the casing is installed is removed by excavation, etc., and then the place where the casing is installed is filled with an impermeable material. There is a method of pulling out the casing and constructing a pile at a place filled with a water-impermeable material (see, for example, Non-Patent Document 2).

Japanese Unexamined Patent Publication No. 2016-217119

Guidelines for Investigation and Measures Based on the Ministry of the Environment Soil Contamination Countermeasures Law (Revised 2nd Edition), Appendix 12_19 Guidelines for Investigation and Measures Based on the Ministry of the Environment Soil Contamination Countermeasures Law (Revised 2nd Edition), Appendix 12_21

When a hole is drilled by the casing method and a pile is constructed in the hole while stabilizing the hole wall with the casing, a number of casings corresponding to the number of piles to be constructed is required. Further, in order to construct a cast-in-place pile, a casing is installed in advance, the inside of the casing is excavated to construct the cast-in-place pile, and then the casing is removed by a machine for removing the casing, so that the process is congested. However, it is complicated.

In the method of stabilizing the hole wall using a solid ground improvement body, since the ground improvement body is also created in the planned pile construction area, it is necessary to drill the inside of the ground improvement body prior to the pile construction. is there. At this time, since the ground improvement body is solidified by cement or the like and has greater strength than general ground, it is necessary to use a large machine for drilling and it takes time. In addition, since the earth and sand generated by the drilling of the ground improvement body generally contains cement, the pH is high and it is classified as construction sludge, so that the cost required for disposal increases.

Even when it is necessary to take measures to prevent the spread of pollutants contained in the ground or groundwater in the ground, in the example shown in the guidelines of the Soil Contamination Countermeasures Law, a casing is used to block the groundwater, so a hole is made in the casing. Similar to the method of stabilizing the wall, there is a problem that the number of casings corresponding to the number of piles to be constructed is required.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to construct piles that can be rationally constructed in a small number of steps while surely stabilizing the hole wall and stopping groundwater. To provide a method.

In order to achieve the above-mentioned object, the present invention comprises a step a of creating a tubular ground improvement body in the ground so that the lower end reaches the cohesive soil layer, and a plan view of the tubular ground improvement body. A step b of constructing a pipe so that the lower end reaches a layer below the cohesive soil layer is provided in a pile construction planned area located inside, and the step a comprises an outer casing and an inner casing. After press-fitting the casing pipe of the heavy pipe structure until it reaches the cohesive soil layer, the lower end of the casing pipe is provided by an improved rod provided between the outer casing and the inner casing while rotating and pulling up the casing pipe. This is a pile construction method characterized in that it is carried out by a high-pressure jet stirring method in which a jet is jetted from the vicinity and stirred with earth and sand.

According to the present invention, it is not necessary to construct a pile in a range where the strength is higher than that of the original ground by creating a ground improvement body as in the conventional method, or to pull out the casing from the ground after the pile is constructed. , Can rationally construct piles. In addition, since the improved body is cylindrical, a large amount of construction sludge containing cement is not generated as compared with the case of constructing a columnar improved body, and various types required for the construction of the ground improved body. Material can be reduced.

Between the step a and the step b, a step c of excavating the unimproved ground inside the tubular ground improvement body to the bottom of the ground improvement body may be further provided.
In the present invention, since the pile construction site located in the unimproved ground inside the tubular ground improvement body is the same as the original ground, drilling is easy. Further, by using the tubular ground improvement body, it is possible to prevent the hole wall of the hole excavated in the unimproved ground from collapsing and to surely stabilize the hole wall.

When the step c is provided, a step d of filling the bottom of the tubular ground improvement body with a water-impermeable material may be further provided between the steps c and the step b.
As a result, the groundwater can be stopped so that the groundwater does not move to the outside from the space surrounded by the ground improvement body and the impermeable material, and the diffusion of pollutants can be prevented.

When the step c is provided, it is desirable to further include the step e of filling the cement-based material between the tubular ground improvement body and the pile after the step b.
As a result, it is possible to eliminate the gap between the ground improvement body and the pile and secure the peripheral frictional force. Further, when a steel pipe pile is used, corrosion can be prevented.

In the step b, if necessary, the planned pile construction area is drilled to the lower layer, and the pile is constructed.
In the step b, for example, a ready-made pile may be constructed.
Alternatively, in the step b, a reinforcing bar cage may be installed in the drilled hole, concrete may be cast, and a cast-in-place pile may be constructed.
When driving ready-made piles by the driving method, the deep digging method, the rotary penetration method, etc., it is not necessary to drill holes in the layer below the cohesive soil layer. When driving ready-made piles by the pre-boring method or when driving cast-in-place piles, the planned pile construction area is drilled to a layer below the cohesive soil layer before the piles are driven.

In the step a, the tubular ground improvement body more and reclamation child by high-pressure injection stirring method, may be applied to cylindrical soil improvement material in a short period of time.

According to the present invention, it is possible to provide a pile construction method that can be rationally constructed with a small number of steps while surely stabilizing the hole wall and stopping the groundwater.

The figure which shows each process for constructing the ready-made pile 23 on the uncontaminated ground 1a. The figure which shows the horizontal cross section of the uncontaminated ground 1a in each process shown in FIG. The figure which shows each process for constructing a tubular ground improvement body 11. The figure which shows the structure and operation of the casing pipe 29 The figure which shows the other construction method of the ready-made pile 23 and the construction method of a cast-in-place pile 55. The figure which shows each process for constructing the ready-made pile 23 on the contaminated ground 1. The figure which shows the horizontal cross section of the contaminated ground 1 in each process shown in FIG. The figure which shows the process of drilling a pile construction planned area 25 The figure which shows the construction example of the cast-in-place pile 55 The figure which shows each process for constructing the ground improvement body 11a using the self-propelled construction machine 60. The figure which shows the structure and operation of a casing pipe 67 The figure which shows the method of preventing the collapse of a hole wall by using a ground improvement body 103.

Hereinafter, the first embodiment of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a diagram showing each process for constructing a ready-made pile 23 on the uncontaminated ground 1a. FIG. 1A is a diagram showing a process of creating a ground improvement body 11 on a non-contaminated ground 1a, and FIG. 1B is a diagram showing a process of excavating an unimproved ground 13 inside the ground improvement body 11. FIG. 1 (c) shows a process of placing a ready-made pile 23 in a planned pile construction area 25, and FIG. 1 (d) shows a cement-based material 27 filled between the ground improvement body 11 and the ready-made pile 23. It is a figure which shows the process to perform.

FIG. 2 is a diagram showing a horizontal cross section of the uncontaminated ground 1a in each step shown in FIG. 2 (a) is the arrow A1-A1 shown in FIG. 1 (a), FIG. 2 (b) is the arrow A2-A2 shown in FIG. 1 (b), and FIG. 2 (c) is the arrow shown in FIG. 1 (c). A3-A3 and FIG. 2 (d) are views showing a cross section by arrows A4-A4 shown in FIG. 1 (d).

FIG. 3 is a diagram showing each process for constructing the tubular ground improvement body 11. FIG. 3A is a diagram showing a state in which the casing pipe 29 is press-fitted, FIG. 3B is a diagram showing a state in which the casing pipe 29 is press-fitted, and FIG. 3C is a casing pipe 29. FIG. 3D is a diagram showing a state in which the casing pipe 29 has been pulled up.

FIG. 4 is a diagram showing the configuration and operation of the casing pipe 29. FIG. 4A is a vertical cross-sectional view of the casing pipe 29 at the position of the improved rod 41. FIG. 4B is a horizontal cross-sectional view in a state where the casing pipe 29 is press-fitted into the uncontaminated ground 1a, and is a view showing a cross section by arrows B1-B1 of FIG. 3A. FIG. 4 (c) is a horizontal cross-sectional view in a state where the casing pipe 29 is pulled up from the uncontaminated ground 1a, and is a view showing a cross section by arrows B2-B2 of FIG. 3 (c).

As shown in FIG. 1, a sand layer 3a, which is a non-contaminated soil layer, exists on the surface layer of the non-contaminated ground 1a. Below the sand layer 3a, there are a cohesive soil layer 5, a sand layer 7, and a support layer 9, which are uncontaminated soil layers.

In order to construct the ready-made pile 23 on the non-contaminated ground 1a, first, as shown in FIGS. 1A and 2A, a tubular ground improvement body 11 is constructed on the non-contaminated ground 1a. It is assumed that the lower end portion 15 of the ground improvement body 11 penetrates the sand layer 3a, which is a non-contaminated soil layer, and reaches the cohesive soil layer 5, which is a non-contaminated soil layer. The penetration depth 57 of the ground improvement body 11 into the cohesive soil layer 5 is about 0.5 m or more. As shown in FIGS. 3 and 4, the ground improvement body 11 is constructed by using the casing pipe 29.

As shown in FIG. 4A, the casing pipe 29 has a double pipe structure having an outer casing 35 and an inner casing 37. The casing pipe 29 has a shape in which the tip of the outer casing 35 is located below the tip of the inner casing 37, and the bottom plate 39 is provided at the position of the tip of the inner casing 37. The casing pipe 29 is made of steel.

Further, as shown in each figure of FIG. 4, an improved rod 41 is provided between the outer casing 35 and the inner casing 37. As shown in FIG. 4A, a nozzle 43 is provided at the tip of the improved rod 41. The tip of the improved rod 41 penetrates the bottom plate 39, and the nozzle 43 is arranged at a height between the tip of the outer casing 35 and the tip of the inner casing 37. As shown in FIG. 4C, the improved rod 41 having the nozzle 43 is arranged at two locations between the outer casing 35 and the inner casing 37 in a plan view. The nozzle 43 is provided on the rear side of the improved rod 41 in the direction of rotation of the casing pipe 29, that is, in the direction of arrow C2 shown in FIG. 4 (c).

In order to form the ground improvement body 11 using the casing pipe 29, first, as shown in FIGS. 3 (a) and 4 (b), the casing pipe 29 is designated by the arrow C1 by using the all-turning construction machine 31. While rotating in the indicated direction, it is lowered in the direction indicated by the arrow D and press-fitted into the uncontaminated ground 1a. At this time, the jet 45 is not injected from the nozzle 43. As shown in FIG. 3B, the press-fitting of the tubular casing pipe 29 is completed when the tip 33 of the casing pipe 29 reaches the penetration depth 57 of the cohesive soil layer 5. If the casing pipe 29 is short, press-fit it while connecting the casing pipe 29 with a pin or the like.

Next, as shown in FIG. 3C, the casing pipe 29 is rotated in the direction indicated by the arrow C2 and raised at a constant speed in the direction indicated by the arrow E by using a crane or the like to start from the uncontaminated ground 1a. Pull up. At this time, a supply pipe from a cement milk plant or a high-pressure pump (not shown) is connected to the improved rod 41. Then, as shown in FIG. 4C, the jet 45 composed of high-pressure cement milk and compressed air is injected from the nozzle 43 in the circumferential direction of the casing pipe 29 and rearward in the rotational direction of the casing pipe 29. ..

When the casing pipe 29 is rotated while being pulled up at a predetermined speed, the jet 45 is jetted in a circular shape, and inside the tubular excavation range formed at the time of press-fitting the casing pipe 29, the jet 45 causes high-pressure cement milk and The compressed air and the earth and sand of the sand layer 3a are agitated (high-pressure jet agitation method). Then, as shown in FIGS. 3 (c) and 4 (c), a tubular ground improvement body 11 having a predetermined thickness is created. The ground inside the ground improvement body 11 remains as unimproved ground 13. As shown in FIG. 3D, the pulling up of the casing pipe 29 is completed when the ground improvement body 11 is constructed over the entire length from the ground surface to the cohesive soil layer 5. When a plurality of casing pipes 29 are connected at the time of press fitting, the injection of the jet 45 may be temporarily interrupted at the time of pulling up to disassemble the casing pipe 29.

As shown in FIGS. 1A and 2A, a tubular ground improvement body 11 is formed on the uncontaminated ground 1a, and after the strength of the ground improvement body 11 is developed, the inside of the ground improvement body 11 is developed. As shown in FIGS. 1B and 2B, the unimproved ground 13 is excavated to the bottom 17 of the ground improvement body 11. Excavation is carried out by the earth drill method or the hammer grab method. Since the sand layer 3a and the cohesive soil layer 5 contained in the unimproved ground inside the ground improvement body 11 are uncontaminated soil layers, the excavated soil in the process shown in FIG. 1 (b) can be disposed of as construction-generated soil. Is. Groundwater pumped up during excavation can also be treated normally. If care is taken to stabilize the hole wall of the excavated space 21, water, bentonite muddy water, or the like may be injected into the excavated space 21 after excavation.

Next, as shown in FIGS. 1 (c) and 2 (c), the planned pile construction area 25 (FIG. 1 (b)) located inside the ground improvement body 11 in a plan view is made of concrete or steel. The ready-made pile 23 is driven. The ready-made pile 23 penetrates the cohesive soil layer 5 and the sand layer 7 and reaches the support layer 9. The N value of the support layer 9 is approximately larger than 30.

The ready-made pile 23 is driven by, for example, a driving method in which a pile is installed by applying a blow by a hammer or a vibration by a vibro hammer. In addition, a middle digging method in which piles are installed while excavating the planned pile construction area 25 using the hollow portion of the ready-made pile 23, and a rotary penetration method in which a pile is installed in the planned pile construction area 25 by applying a rotational force. It may be cast by such as.

After placing the ready-made pile 23, as shown in FIGS. 1 (d) and 2 (d), the cement-based material 27 is filled between the ground improvement body 11 and the ready-made pile 23. The cement-based material 27 is, for example, fluidized soil, cement milk, mortar, concrete, or the like.

In the first embodiment, the tubular ground improvement body 11 is created. As a result, when constructing the ready-made pile 23, it is not necessary to excavate the ground improvement body in the planned pile construction area 25 as in the conventional case, or to pull out the casing from the ground after the construction of the ready-made pile 23. Can be constructed. Further, as compared with the case of constructing the columnar ground improvement body, the volume of the unimproved ground 13 does not generate a large amount of construction sludge containing cement, and the construction of the ground improvement body 11 is performed. Various materials required can be reduced.

In the first embodiment, by using the tubular ground improvement body 11, it is possible to prevent the hole wall of the hole excavated in the unimproved ground 13 from collapsing and to surely stabilize the hole wall. Further, by constructing the tubular ground improvement body 11 by the high pressure injection stirring method, the ground improvement body 11 can be constructed in a short period of time.

The construction method of the ready-made pile 23 in the non-contaminated ground 1a is not limited to the above-mentioned one, and the ready-made pile may be driven without excavating the unimproved ground inside the ground improvement body 11 or excavated in advance. A pre-boring method may be applied in which a ready-made pile 23 is built in the hole. In addition, cast-in-place piles may be placed on the uncontaminated ground 1a instead of ready-made piles.

FIG. 5 is a diagram showing another construction method of the ready-made pile 23 and a construction method of the cast-in-place pile 55. FIG. 5A is a diagram showing an example in which a ready-made pile is driven without excavating the unimproved ground inside the ground improvement body 11. In the example shown in FIG. 5A, after the ground improvement body 11 is driven into the uncontaminated ground 1a, the driving method is performed in the planned pile construction area located in the unimproved ground inside the ground improvement body 11 in a plan view. The ready-made pile 23a is driven by the middle digging method, the rotary penetration method, or the like.

FIG. 5B is a diagram showing an example of constructing a ready-made pile 23 by applying a pre-boring method. When the pre-boring method is applied, the process shown in FIG. 5 (b) is added between the process shown in FIG. 1 (b) and the process shown in FIG. 1 (c) among the construction procedures shown in FIG. To do.

In the step shown in FIG. 5B, after the step shown in FIG. 1B, a hole is drilled in the planned pile construction area 25 located inside the ground improvement body 11 in a plan view. Since the unimproved ground 13 inside the ground improvement body 11 has already been excavated in the process shown in FIG. 1 (b), in the process shown in FIG. 5 (b), the unimproved ground 13 penetrates the cohesive soil layer 5 and the sand layer 7. The hole 47 that reaches the support layer 9 is drilled. The diameter 49 of the hole 47 shall correspond to the diameter of the ready-made pile 23 to be constructed. The hole 47 is drilled by an all-around turning excavation method, an earth drill method, a TBH method, or the like. Since the cohesive soil layer 5, the sand layer 7, and the support layer 9 are non-contaminated soil layers and do not contain cement or the like, the excavated soil in the process shown in FIG. 5 (b) can also be disposed of as construction-generated soil. Is.

After drilling a hole 47 in the planned pile construction area 25, a ready-made pile 23 is placed in the hole 47 as shown in FIG. 1 (c), and the ready-made pile 23 is formed as shown in FIG. 1 (d). A cement-based material 27 is filled between the ground improvement body 11 and the ground improvement body 11.

5 (c) and 5 (d) are views showing a construction example of the cast-in-place pile 55. In the example shown in FIG. 5B, a case where a hole 47 is drilled in the planned pile construction area 25 to construct the ready-made pile 23 has been described, but after the hole 47 is drilled in the planned pile construction area 25, the ready-made pile 23 is constructed. Cast-in-place pile 55 may be constructed instead of pile 23. When constructing the cast-in-place pile 55, after the step shown in FIG. 5 (b), instead of the steps shown in FIGS. 1 (c) and 1 (d), the steps shown in FIGS. 5 (c) and 5 (d) are shown. Perform the steps shown.

In the process shown in FIG. 5C, a reinforcing bar cage 51 assembled in advance in another yard is installed in the space 21 inside the hole 47 and the ground improvement body 11. The reinforcing bar cage 51 has a length from the tip of the hole 47 to the surface of the earth.

After that, as shown in FIG. 5D, concrete 53 is placed in the hole 47 and the space 21. A tremie pipe or the like is used for placing the concrete 53. In the step shown in FIG. 5D, first, the concrete 53 is placed in the portion of the hole 47, that is, the portion up to the lower end of the ground improvement body 11, and then the concrete 53 is placed in the space 21 inside the ground improvement body 11. Set up.

Also in the example described with reference to FIG. 5, piles can be rationally constructed as compared with the conventional method, as in the first embodiment. Further, by using the tubular ground improvement body 11, it is possible to prevent the hole wall of the hole excavated in the unimproved ground 13 from collapsing and to surely stabilize the hole wall.

Next, the second embodiment will be described in detail.
FIG. 6 is a diagram showing each process for constructing a ready-made pile 23 on the contaminated ground 1. FIG. 6A is a diagram showing a process of creating a ground improvement body 11 on a contaminated ground 1, and FIG. 6B is a diagram and a diagram showing a process of excavating an unimproved ground 13 inside the ground improvement body 11. 6 (c) shows a step of filling the bottom 17 of the ground improvement body 11 with the impervious water-permeable material 19, and FIG. 6 (d) shows a step of placing a ready-made pile 23 in the planned pile construction area 25. FIG. 6 (e) is a diagram showing a step of filling the cement-based material 27 between the ground improvement body 11 and the ready-made pile 23.

FIG. 7 is a diagram showing a horizontal cross section of the contaminated ground 1 in each step shown in FIG. 7 (a) is the arrow F1-F1 shown in FIG. 6 (a), FIG. 7 (b) is the arrow F2-F2 shown in FIG. 6 (b), and FIG. 7 (c) is the arrow shown in FIG. 6 (c). F3-F3, FIG. 7 (d) is a diagram showing a cross section by an arrow F4-F4 shown in FIG. 6 (d), and FIG. 7 (e) is a diagram showing a cross section by an arrow F5-F5 shown in FIG. 6 (e).

As shown in FIG. 6, a sand layer 3 which is a contaminated soil layer exists on the surface layer of the contaminated ground 1. Below the sand layer 3, there are a cohesive soil layer 5, a sand layer 7, and a support layer 9, which are uncontaminated soil layers.

In order to construct the ready-made pile 23 on the contaminated ground 1, first, as in the first embodiment, the high-pressure injection agitation method using a casing pipe having a double pipe structure is used, and FIGS. As shown in a), a tubular ground improvement body 11 is created in the contaminated ground 1. It is assumed that the lower end portion 15 of the ground improvement body 11 penetrates the sand layer 3 which is a contaminated soil layer and reaches the cohesive soil layer 5 which is a non-contaminated soil layer. The penetration depth 57 of the ground improvement body 11 into the cohesive soil layer 5 is about 0.5 m or more.

As shown in FIGS. 6 (a) and 7 (a), after the tubular ground improvement body 11 is formed on the contaminated ground 1 and the strength of the ground improvement body 11 is developed, FIGS. 6 (b) and 7 are shown. As shown in (b), the unimproved ground 13 inside the ground improvement body 11 is excavated to the bottom 17 of the ground improvement body 11. Excavation is carried out by the earth drill method or the hammer grab method. Since the unimproved ground 13 contains a sand layer 3 which is a contaminated soil layer, the excavated soil in the process shown in FIG. 6 (b) and the groundwater pumped up by the excavation are contaminated. Therefore, it will be strictly managed and carried out to a designated disposal site in accordance with the law for proper disposal. After the excavation to the bottom 17 is completed, the inside of the ground improvement body 11 may be washed.

Next, as shown in FIGS. 6 (c) and 7 (c), the bottom 17 of the ground improvement body 11 is filled with the impermeable material 19. As the poorly permeable material 19, a material having a water permeability coefficient of 1 × 10E-6 cm / s or less after solidification, such as fluidized soil, bentonite mortar, cement milk, and mortar, is used. Further, the casting thickness 59 is set to about 0.5 m or more in consideration of the construction accuracy.

When careful attention is paid to stabilizing the hole wall of the excavated space 21 and preventing the diffusion of contamination between the space 21 and the outside, even if water or bentonite muddy water is injected into the space 21 after the impermeable material 19 is cured. Good.

After that, as shown in FIGS. 6 (d) and 7 (d), concrete is formed in the planned pile construction area 25 (FIGS. 6 (c) and 7 (c)) located inside the ground improvement body 11 in a plan view. A ready-made pile 23 made of steel or steel is driven. The ready-made pile 23 penetrates the impermeable material 19, the cohesive soil layer 5 and the sand layer 7 and reaches the support layer 9. The N value of the support layer 9 is generally larger than 30.

The ready-made pile 23 is driven by, for example, a driving method in which a pile is installed by applying a blow by a hammer or a vibration by a vibro hammer. In addition, a middle digging method in which piles are installed while excavating the planned pile construction area 25 using the hollow portion of the ready-made pile 23, and a rotary penetration method in which a pile is installed in the planned pile construction area 25 by applying a rotational force. It may be cast by such as.

After placing the ready-made pile 23, as shown in FIGS. 6 (e) and 7 (e), the cement-based material 27 is filled between the ground improvement body 11 and the ready-made pile 23. The cement-based material 27 is, for example, fluidized soil, cement milk, mortar, concrete, or the like.

In the second embodiment, the tubular ground improvement body 11 is created. As a result, when constructing the ready-made pile 23, it is not necessary to excavate the ground improvement body in the planned pile construction area 25 as in the conventional case, or to pull out the casing from the ground after the construction of the ready-made pile 23. Can be constructed. Further, as compared with the case of constructing the columnar ground improvement body, the volume of the unimproved ground 13 does not generate a large amount of construction sludge containing cement, and the construction of the ground improvement body 11 is performed. Various materials required can be reduced.

In the second embodiment, by using the tubular ground improvement body 11, it is possible to prevent the hole wall of the hole excavated in the unimproved ground 13 from collapsing and to surely stabilize the hole wall. Further, the unimproved ground 13 inside the tubular ground improvement body 11 is excavated, and the bottom 17 of the ground improvement body 11 is filled with the poorly permeable material 19, so that the ground improvement body 11 and the poorly permeable material 19 are formed. The groundwater can be stopped so that the groundwater does not move between the space 21 surrounded by the space 21 and the outside, and the diffusion of pollutants can be prevented.

In the second embodiment, the ground improvement body 11 can be constructed in a short period of time by forming the tubular ground improvement body 11 by the high-pressure injection stirring method.

The method of constructing the ready-made pile 23 in the contaminated ground 1 is not limited to the above-mentioned one, and a pre-boring method of building the ready-made pile 23 in a hole excavated in advance may be applied. When the pre-boring method is applied, a step of drilling a hole in the planned pile construction area 25 up to the support layer 9 is added to the construction procedure shown in FIG. FIG. 8 is a diagram showing a process of drilling a hole in the planned pile construction area 25. The step shown in FIG. 8 is provided between the step shown in FIG. 6 (c) and the step shown in FIG. 6 (d) in the construction procedure shown in FIG.

In the step shown in FIG. 8, after the step shown in FIG. 6C, a hole is drilled in the planned pile construction area 25 located inside the ground improvement body 11 in a plan view. Since the unimproved ground 13 inside the ground improvement body 11 has already been excavated in the process shown in FIG. 6B, the impermeable material 19, the cohesive soil layer 5, and the sand layer 7 are formed in the process shown in FIG. A hole 47 that penetrates and reaches the support layer 9 is drilled. The diameter 49 of the hole 47 shall correspond to the diameter of the ready-made pile 23 to be constructed. The hole 47 is drilled by an all-around turning excavation method, an earth drill method, a TBH method, or the like. Since the cohesive soil layer 5, the sand layer 7, and the support layer 9 are non-contaminated soil layers and do not contain cement or the like, the excavated soil in the process shown in FIG. 8 can be disposed of as construction-generated soil.

After drilling a hole 47 in the planned pile construction area 25, a ready-made pile 23 is placed in the hole 47 as shown in FIG. 6 (d), and the ready-made pile 23 is formed as shown in FIG. 1 (d). A cement-based material 27 is filled between the ground improvement body 11 and the ground improvement body 11.

In the example shown in FIG. 8, the case where the hole 47 is drilled in the planned pile construction area 25 to construct the ready-made pile 23 has been described, but the cast-in-place pile may be constructed instead of the ready-made pile 23. FIG. 9 is a diagram showing a construction example of the cast-in-place pile 55. When the cast-in-place pile 55 is constructed by drilling a hole 47 in the planned pile construction area 25, after the step shown in FIG. 8, instead of the steps shown in FIGS. 6 (d) and 6 (e), FIG. 9 The steps shown in (a) and 9 (b) are performed.

In the process shown in FIG. 9A, the reinforcing bar cage 51 assembled in advance in another yard is installed in the space 21 inside the hole 47 and the ground improvement body 11. The reinforcing bar cage 51 has a length from the tip of the hole 47 to the surface of the earth.

After that, as shown in FIG. 9B, concrete 53 is placed in the hole 47 and the space 21. A tremie pipe or the like is used for placing the concrete 53. In the step shown in FIG. 9B, first, the concrete 53 is placed in the portion of the hole 47, that is, the portion up to the upper end of the impermeable material 19, and then the concrete 53 is placed in the space 21 inside the ground improvement body 11. Place.

Also in the example described with reference to FIGS. 8 and 9, piles can be rationally constructed as compared with the conventional method, as in the second embodiment. Further, by using the tubular ground improvement body 11, it is possible to prevent the hole wall of the hole excavated in the unimproved ground 13 from collapsing and to surely stabilize the hole wall. Further, the unimproved ground 13 inside the tubular ground improvement body 11 is excavated, and the bottom 17 of the ground improvement body 11 is filled with the poorly permeable material 19, so that the ground improvement body 11 and the poorly permeable material 19 are formed. It is possible to stop the groundwater so that the groundwater does not move to the outside from the space 21 surrounded by the space 21 and prevent the diffusion of pollutants.

Next, a third embodiment will be described.
FIG. 10 is a diagram showing each process for constructing the ground improvement body 11a using the self-propelled construction machine 60 and the casing pipe 67. FIG. 10A is a diagram showing a state in which the casing pipe 67 has been transported, FIG. 10B is a diagram showing a state in which the casing pipe 67 is ready for press fitting, and FIG. 10C is a casing pipe. FIG. 10 (d) is a diagram showing a state in which the press-fitting of 67 is completed, FIG. 10 (d) is a diagram showing a state in which the casing pipe 67 is pulled up, and FIG. 10 (e) is a diagram showing a state in which the casing pipe 67 is completed in pulling up. is there.

FIG. 11 is a diagram showing the configuration and operation of the casing pipe 67. FIG. 11A is a vertical cross-sectional view of the casing pipe 67 at the positions of the high-pressure pipes 73 and 75, and is an enlarged view of the range G shown in FIG. 10D. FIG. 11B is a horizontal cross-sectional view in a state where the casing pipe 67 is press-fitted into the uncontaminated ground 1a, and is a view showing a cross section by arrows I1-I1 of FIG. 11A. 11 (c) is a horizontal cross-sectional view of the ground improvement body 11a, and is a view showing a cross section by arrows I2-I2 of FIG. 11 (c).

In the first and second embodiments, the tubular ground improvement body 11 is constructed by using the full swivel construction machine 31 and the large-diameter casing pipe 29 shown in FIG. 3, but in the third embodiment, the tubular ground improvement body 11 is constructed. The ground improvement body 11a is constructed by using the self-propelled construction machine 60 shown in FIG. 10 and the casing pipe 67 having a small diameter.

The casing pipe 67 shown in FIGS. 10 and 11 has a weight and length that can be mounted on a vehicle. The casing pipe 67 has a smaller diameter than the casing pipe 29 shown in FIGS. 3 and 4, and has a diameter of, for example, about 1.5 to 2 m. The length of the casing pipe 67 is, for example, five times or more the diameter. As shown in FIG. 11A, the casing pipe 67 has a double pipe structure having an outer casing 69 and an inner casing 71. The casing pipe 67 is provided with a bottom plate 89 at the positions of the tips of the outer casing 69 and the inner casing 71. The casing pipe 67 is made of steel.

As shown in FIGS. 11A and 11B, bits 85 are provided on the inner peripheral surface side of the tip of the outer casing 69 at predetermined intervals in the circumferential direction. Stabilizers 87 are provided on the inner peripheral surface side slightly above the tip of the inner casing 71 at predetermined intervals in the circumferential direction. A high-pressure pipe 73 and a high-pressure pipe 75 are provided between the outer casing 69 and the inner casing 71.

As shown in FIG. 11A, a nozzle 81 is provided at the tip of the high-pressure pipe 75. The nozzle 81 is arranged so as to penetrate the bottom plate 89. As shown in FIG. 11B, the high-pressure pipe 75 having the nozzle 81 is arranged at two locations between the outer casing 69 and the inner casing 71 in a plan view.

Further, as shown in FIG. 11A, a pair of nozzles 77 are provided at the tip of the high-pressure pipe 73. The pair of nozzles 77 are arranged on the same vertical line at predetermined intervals. The nozzle 77 is arranged so as to penetrate the outer casing 69 slightly above the bit 85. As shown in FIG. 11B, the nozzles 77 are arranged at two locations between the outer casing 69 and the inner casing 71 in a plan view.

In order to form the ground improvement body 11a using the casing pipe 67, first, as shown in FIG. 10A, the casing pipe 67 is transported to a predetermined position by using the self-propelled construction machine 60. The self-propelled construction machine 60 is, for example, a rough terrain crane 61 in which a leader 63 is installed. The casing pipe 67 is gripped and transported by the guide portion 65 and the rotary drive portion 66 provided on the leader 63.

After completing the transportation of the casing pipe 67, the outriggers are projected to fix the position of the self-propelled construction machine 60. Then, as shown in FIG. 10B, the leader 63 is installed in the vertical direction by the rough terrain crane 61 to prepare for press-fitting the casing pipe 67.

Next, as shown in FIG. 10 (c), the casing pipe 67 is lowered while rotating in the direction indicated by the arrow H1 using the rotary drive unit 66 of the reader 63, and rotary drilling is press-fitted into the uncontaminated ground 1a. .. At this time, the jets are not injected from the nozzle 77 and the nozzle 81 shown in FIG. 11A. The press-fitting is completed when the tip of the casing pipe 67 reaches the penetration depth of the cohesive soil layer 5. As shown in FIG. 11B, when the casing pipe 67 is press-fitted, the excavated portion 93a by the casing pipe 67 main body and the surplus excavated portion 93b formed by the stabilizer 87 provided on the inner peripheral side of the inner casing 71 are formed. The excavation range 93 is formed.

Next, as shown in FIGS. 10 (d) and 11 (a), the casing pipe 67 is rotated at a constant speed while being rotated in the direction indicated by the arrow H2 by using the rotation drive unit 66 of the reader 63, and the casing pipe 67 is raised at a constant speed. Pull up from the contaminated ground 1a. At this time, a supply pipe from a cement milk plant or a high pressure pump (not shown) is connected to the high pressure pipe 73 and the high pressure pipe 75. Then, as shown in FIG. 11A, the jet 83 made of high-pressure cement milk and compressed air is jetted downward from the nozzle 81 provided in the high-pressure pipe 75.

Further, as shown in FIG. 11A, a jet 79 composed of high-pressure cement milk and compressed air is injected from a pair of nozzles 77 provided in the high-pressure pipe 73. Of the pair of nozzles 77, the upper nozzle 77 injects the jet 79 radially outward of the casing pipe 67 and diagonally downward. From the lower nozzle 77, the jet 79 is ejected obliquely upward and outward in the radial direction of the casing pipe 67. The pair of jets 79 are cross jets that intersect on the outside of the outer casing 69.

When the casing pipe 67 is rotated while being pulled up at a predetermined speed while injecting the jet 79 and the jet 83, as shown in FIGS. 11A and 11B, the excavation range formed at the time of press-fitting the casing pipe 67 is formed. The outside of 93 is cut by a pair of jets 79, which are cross jets, to a position where the jets 79 intersect with each other to form a widening portion 91. Then, inside the new excavation range 95 formed by the excavation range 93 and the widening portion 91, the high-pressure cement milk and compressed air and the earth and sand of the uncontaminated ground 1a are agitated by the jet 79 and the jet 83. High-pressure injection stirring method). Then, as shown in FIGS. 11A and 11C, a tubular ground improvement body 11a having a predetermined thickness is created in the excavation range 95.

As shown in FIG. 10 (e), the pulling up of the casing pipe 67 is completed when the ground improvement body 11a is constructed over the entire length from the ground surface to the cohesive soil layer 5. As shown in FIGS. 10 (e) and 11 (c), the ground inside the ground improvement body 11a remains as unimproved ground 13.

In the third embodiment, a tubular ground improvement body 11a is formed on the uncontaminated ground 1a, and after the strength of the ground improvement body 11a is developed, the first embodiment and the example described with reference to FIG. 5 are used. In the same manner as above, the ready-made pile 23 and the cast-in-place pile 55 are constructed in the planned pile construction area located inside the ground improvement body 11a in a plan view.

When the ground improvement body 11a is created by the method of the third embodiment, the same effect as that of the first embodiment can be obtained.

The method for creating the ground improvement body 11a using the self-propelled construction machine 60 and the small-diameter casing pipe 67 described in the third embodiment is when the ground improvement body 11a is created on the contaminated ground 1 shown in FIG. Can also be applied to. After constructing the ground improvement body 11a on the contaminated ground 1 shown in FIG. 6 using the self-propelled construction machine 60 and the casing pipe 67 having a small diameter, the second embodiment and FIGS. 8 and 9 have been described. If the ready-made pile 23 and the cast-in-place pile 55 are constructed in the same manner as in the example, the same effect as that of the second embodiment can be obtained.

The method of creating the ground improvement body is not limited to the above. In the first and second embodiments, the casing pipe for the high-pressure injection stirring method may be press-fitted by rotary drilling instead of rotary press-fitting. Further, in the first to third embodiments, the jet injection direction when pulling up the casing pipe does not have to be the direction shown in FIGS. 4 (c) and 11 (a). Further, a tubular ground improvement body may be created by a mechanical stirring method instead of the high pressure injection stirring method.

In the first to third embodiments, the piles are constructed so that the lower end reaches the support layer 9, which is a layer below the cohesive soil layer 5, but the lower end may not reach the support layer. At this time, the pile is supported by the frictional force between the layer below the cohesive soil layer 5 and the pile.

Although preferred embodiments of the present invention have been described above with reference to the accompanying drawings, the present invention is not limited to such examples. It is clear that a person skilled in the art can come up with various modifications or modifications within the scope of the technical idea disclosed in the present application, and these also naturally belong to the technical scope of the present invention. Understood.

1 ………… Contaminated ground 1a ………… Non-contaminated ground 3, 3a, 7 ………… Sand layer 5 ………… Cohesive soil layer 9 ………… Support layer 11, 11a ………… Ground improvement body 13 ………… Unimproved Ground 15 ………… Lower end 17 ………… Bottom 19 ………… Impermeable material 21 ………… Space 23, 23a ………… Ready-made pile 25 ………… Planned pile construction area 27 ………… Cement-based material 29… …… Casing pipe 31 ………… Full swivel construction machine 33 ………… Tip 35, 69 ………… Outer casing 37, 71 ………… Inner casing 39, 89 ………… Bottom plate 41 ………… Improved rod 43, 77, 81 ………… Nozzle 45, 79, 83 ………… Jet 47 ………… Hole 49 ………… Diameter 51 ………… Reinforcement basket 53 ………… Concrete 55 ………… Cast-in-place pile 57 ………… Deep foundation 59 ………… Thickness 60 ………… Self-propelled construction machine 61 ………… Rough terrain 63 ………… Leader 65 ………… Guide part 66 ………… Rotary drive part 67 ………… Casing pipe 73, 75 …… … High-pressure pipe 85 ………… Bit 87 ………… Stabilizer 91 ………… Widening part 93, 95 ………… Excavation range 93a ………… Excavation part 93b ………… Excavation part 101 ………… Ground 103 ………… Ground Improved body 105 ……… Drilling part 107 ……… Pile

Claims (8)

Step a of creating a tubular ground improvement body in the ground so that the lower end reaches the cohesive soil layer,
Step b of constructing a pile in the planned pile construction area located inside the tubular ground improvement body in a plan view so that the lower end reaches the layer below the cohesive soil layer.
Equipped with
In the step a, a casing pipe having a double pipe structure composed of an outer casing and an inner casing is press-fitted until it reaches the cohesive soil layer, and then the casing pipe is rotated and pulled up between the outer casing and the inner casing. A method of constructing a pile, which is carried out by a high-pressure jet stirring method in which a jet is jetted from the vicinity of the lower end of the casing pipe to stir with earth and sand by an improved rod provided in the casing pipe. The shape is such that the tip of the outer casing is located below the tip of the inner casing, and the nozzle of the improved rod is arranged at a height between the tip of the outer casing and the tip of the inner casing. The pile construction method according to claim 1, which is a feature. 1. A claim 1 is characterized in that, between the step a and the step b, a step c of excavating the unimproved ground inside the tubular ground improvement body to the bottom of the ground improvement body is further provided. Alternatively, the pile construction method according to claim 2. The method for constructing a pile according to claim 3 , further comprising a step d of filling the bottom of the tubular ground improvement body with a poorly permeable material between the step c and the step b. The pile construction according to claim 3 or 4 , further comprising a step e of filling a cement-based material between the tubular ground improvement body and the pile after the step b. Method. The method for constructing a pile according to any one of claims 1 to 5 , wherein in the step b, the planned pile construction area is drilled to the lower layer to construct the pile. The pile construction method according to any one of claims 1 to 6 , wherein a ready-made pile is constructed in the step b. The pile construction method according to claim 6 , wherein a reinforcing bar cage is installed in the drilled hole, concrete is cast, and a cast-in-place pile is constructed in the step b.

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