JP2017031562A - Construction method of continuous underground wall - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a construction method for a continuous underground wall for readily constructing a continuous underground wall while preventing collapse of a groove wall during the construction work at a low altitude below a head.SOLUTION: In a construction method for a continuous underground wall, a scheduled excavation area S1 for an excavation groove G of a preceding element EA and an intermediate area S2 comprise a unit area. The construction method for a continuous underground wall includes a construction step in which ground improvement bodies 1 (1A, 1B) having the unit area inside are constructed for each of the unit areas. The following processes are performed in the construction step for each of the unit areas: forming a borehole GH in a ground; inserting a rod 12 into the borehole GH, the rod having a cylindrical tip rod 121, a nozzle 122, and an extension rod 123; spraying a liquid J from the nozzle 122 outward in a radial direction, the liquid containing a solidification material and water; and at the same time, rotating and lifting the rod 12 for constructing the ground improvement bodies 1 (1A, 1B) having a diameter greater than the borehole GH and strength greater than the ground.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an underground continuous wall construction method.

As an underground continuous wall construction method for building underground continuous walls made of reinforced concrete, etc., the underground continuous wall is divided into a leading element and a trailing element. It is generally known to construct the underground continuous wall by sequentially forming and then adding a succeeding element to the preceding element.
In this type of underground continuous wall construction method, as disclosed in Patent Document 1, reinforcing rods are poured into the excavation groove excavated by the excavator at an interval in the ground and concrete is placed. Then, after forming the preceding element, by inserting a reinforcing bar into the excavation groove obtained by excavating the ground etc. between the preceding elements with an excavator, and placing concrete to form the trailing element, The underground continuous wall is constructed.
This general underground continuous wall construction method is, for example, continuous underground in a ground including a soil layer or the like having a low fine particle content (for example, the content of soil particles having a particle size of less than 0.075 mm is about 35% or less). If it is adopted as a method for constructing a wall, a part of the groove wall of the excavation groove may collapse during excavation of the ground by the excavator or erection of a reinforcing bar. When the groove wall collapses, the excavator and the reinforcing bar are buried in the collapsed earth and sand, making it impossible to excavate or making it difficult to place concrete. In addition, if the groove wall collapses, the planned shape of the underground continuous wall cannot be secured, and the collapsed earth and sand accumulate on the bottom of the excavation groove to obtain the required bearing capacity for the underground continuous wall. There is also a risk that it will not be possible. For this reason, there is a need for an underground continuous wall construction method capable of constructing an underground continuous wall while protecting the groove wall in a ground including a soil layer having a high risk of groove wall collapse.

  Here, when it is necessary to protect the groove wall during the construction of the underground continuous wall, for example, prior to the construction of the underground continuous wall, two rows are arranged so as to sandwich the construction planned area of the underground continuous wall. It is common practice to construct a soil mortar column by the SMW method. Specifically, a base machine equipped with a large-diameter auger screw excavates the ground and mixes and stirs the original soil and mortar at the original position to form two rows of soil mortar columns. By protecting the groove wall of the excavation groove for the construction of the underground continuous wall with the two rows of soil mortar columns, the occurrence of the groove wall collapse during the underground continuous wall construction is suppressed.

JP-A-5-132927

By the way, in the underground continuous wall construction method for constructing the underground continuous wall by protecting the groove wall by the soil mortar column, the large base machine having a relatively large diameter and heavy auger screw for excavation and kneading. is necessary. In addition, a large crane is required when installing or carrying out this large base machine at a place where the underground continuous wall construction is planned.
However, there is a case where a large base machine or a large crane as described above cannot be used at a construction site where some structure exists above the planned construction site of the underground continuous wall, and a device is required.

  In the present invention, in view of such a situation, there is some structure above the planned construction site of the underground continuous wall, and in the region where the crane work is restricted, the groove wall during construction of the underground continuous wall An object of the present invention is to provide an underground continuous wall construction method capable of easily constructing an underground continuous wall while preventing collapse.

  For the above problem, in the underground continuous wall construction method according to one aspect of the present invention, the preceding elements are formed in the excavation grooves for the preceding elements excavated in the ground at intervals, and then adjacent to each other. Underground continuation in which a continuous element is formed by forming a trailing element in each excavation groove for a trailing element obtained by excavating the end of the preceding element and excavating an intermediate region between the preceding elements. A wall construction method, wherein a drilling planned area of the excavation groove for one of the preceding elements and an intermediate area of each are set as unit areas, and prior to excavation of the excavation groove for the preceding element, A boring hole extending in the vertical direction into the ground in the forming step for each unit region, including a forming step for forming the ground improvement body in which the unit region is located for each unit region; Forming and inserting a rod having a cylindrical tip rod, a nozzle provided on the tip end side of the tip rod, and an extension rod sequentially added to the base end side of the tip rod into the boring hole, The rod is rotated while ejecting a liquid containing solidification material and water radially outward from the nozzle, and the rod is pulled up to be larger in diameter than the boring hole and higher in strength than the ground. The ground improvement body is constructed.

According to the underground continuous wall construction method according to the one aspect, a planned excavation area of an excavation groove for one preceding element and an intermediate area between adjacent preceding elements are set as unit areas, respectively. Prior to excavation of the excavation groove, a ground improvement body in which this unit region is located is formed for each unit region. Then, in the creation process for each unit region, a rod formed by sequentially adding extension rods to the proximal end portion side of the distal end rod provided with the nozzle on the distal end portion side is inserted into the boring hole, The ground improvement body having higher strength than the ground is created by rotating and pulling up the rod while ejecting a liquid containing solidified material and water from the nozzle outward in the radial direction.
As a result, each excavation groove for the preceding element can be formed by excavating the ground improvement body already formed, and each excavation groove for the succeeding element is already formed with the already established ground improvement body. Can be formed by excavating the ends of the adjacent preceding elements. Therefore, for example, the strength of each ground improvement body is set appropriately higher than the surrounding ground according to the ability and construction method of the excavation equipment for excavating the ground improvement body and the preceding element, and the groove wall of each excavation groove Therefore, it is possible to prevent the groove wall from collapsing during construction of the underground continuous wall.
And even if there is some structure above the planned construction site of the underground continuous wall and the area where the crane work is restricted, a small-diameter boring hole that can be inserted with a rod with a small drilling machine is provided. Drilling and inserting the rod into the borehole while extending the rod, and rotating and pulling up the rod while spraying a liquid containing solidification material and water from the nozzle at the tip of the rod In addition, it is possible to build (create) a ground improvement body having a strength appropriately higher than that of the surrounding ground. It should be noted that the machine and method for forming the small-diameter boring hole for inserting the rod and the excavation groove depend on the height from the ground in the planned excavation area of each excavation groove to the structure existing above it. Thus, an appropriate machine and construction method may be employed.

  In this way, in the area where there is some structure above the planned construction site of the underground continuous wall and the crane work is restricted, the ground wall is prevented from collapsing during the construction of the underground continuous wall. An underground continuous wall construction method capable of easily constructing an intermediate continuous wall can be provided.

It is sectional drawing of the underground continuous wall E constructed | assembled by the underground continuous wall construction method in this embodiment. It is a top view of the underground continuous wall E. It is a figure which shows schematic structure of the ground improvement body formation apparatus in the said embodiment, and is also sectional drawing of the ground of the construction planned location of an underground continuous wall. It is a figure which shows schematic structure of the excavation apparatus in the said embodiment. It is a conceptual diagram for demonstrating an example of the underground continuous wall construction method in the said embodiment, and is the top view which showed the state in the middle of construction of a ground improvement body. It is the top view which showed the state which creation of the said ground improvement body was completed. It is a conceptual diagram for demonstrating an example of the creation process of the said ground improvement body, and is a figure which shows a boring hole formation process. It is a figure for demonstrating creation of the various ground improvement body (1st ground improvement body) for preceding elements. It is a figure which shows the state in the middle of the creation of the said 1st ground improvement body. It is a figure which shows the state which creation of the said 1st ground improvement body was completed. It is a figure which shows the state which completed the creation of each ground improvement body (2nd ground improvement body) for succeeding elements, and the creation process was completed. It is the figure which showed the state in the middle of excavation of the excavation groove for leading elements. It is the enlarged plan view which showed the state which excavation of the excavation groove for the preceding elements was completed. It is a figure for demonstrating a reinforcing bar construction process. It is a figure for demonstrating a concrete placement process, and is also a figure which shows the state which the formation of the preceding element was completed. It is an enlarged plan view showing the state where the formation of the preceding element is completed. It is the figure which showed the state under excavation of the excavation groove for a succeeding element. It is the enlarged plan view which showed the state which excavation of the excavation groove for succeeding elements was completed. It is a flowchart for demonstrating the setting procedure of the thin part thickness of the ground improvement body 1 and the formation diameter after the said ground improvement body excavation process. It is a figure which shows the relationship between the uniaxial compressive strength of a ground improvement body, and a thin part thickness. It is a figure which shows the modification of the cross-sectional shape of a ground improvement body. It is a figure which shows another modification of the cross-sectional shape of a ground improvement body.

Below, an embodiment of the underground continuous wall construction method concerning the present invention is described based on an accompanying drawing.
The underground continuous wall construction method according to an embodiment of the present invention includes a creation step of creating the ground improvement body 1 in advance in the underground continuous wall construction planned area, and excavating the inside of the ground improvement body 1 in the vertical direction to form the excavation groove G. The excavation process which forms reinforced concrete, the reinforcement bar construction process which builds a reinforcement bar in the excavation groove G, and the concrete placement process are included.
FIG. 1 shows a partial cross-sectional view of an underground continuous wall E constructed by the underground continuous wall construction method in the present embodiment, and FIG. 2 is a top view of the underground continuous wall E shown in FIG. 1 (viewed from the ground side). An enlarged plan view) is shown. FIG. 3 shows a schematic configuration of the ground improvement body generating apparatus 10 used in the underground continuous wall construction method in the present embodiment, and FIG. 4 shows a schematic configuration of the excavating apparatus 20 used in the present embodiment. 1 is also a vertical sectional view passing through the center line O of the underground continuous wall E shown in FIG.

  In this embodiment, the underground continuous wall E is a structural wall made of reinforced concrete, has a wall thickness t, is erected in the ground, and has an appropriate length in one horizontal direction, and is extended to the whole. As an example, the case of having a horizontally long rectangular cross section will be described. As shown in FIGS. 1 and 2, the underground continuous wall E is sequentially added to the preceding element EA formed at a predetermined interval in the horizontal extending direction and the shorter side of the preceding element EA adjacent to each other. The leading element EA and the trailing element EB are alternately arranged in a line. The leading element EA and the trailing element EB each have a rectangular cross section, the length in the short side direction corresponds to the wall thickness t of the underground continuous wall E, and the surface in the long side direction corresponds to the underground continuous wall E. It becomes a wall. In each figure, although the underground continuous wall E shows only the part of the horizontal direction one end side, it is extended | stretched by the same structure to the horizontal direction other end side.

  In this embodiment, the element width W, which is the length in the long side direction when the preceding element EA is completed (that is, before the succeeding element is added), is the element width W when the succeeding element EB is completed. It shall be the same. The leading element EA is partly excavated (cut) at the time of connection with the trailing element EB. For this reason, the width of the preceding element EA after being added is slightly shorter than the element width W of the succeeding element EB, as shown in FIG.

In this embodiment, a low-headed and narrow construction site directly under the existing railway viaduct, that is, a low-headed place where the railway viaduct B exists as an existing structure above the planned construction area of the underground continuous wall E. In addition, the following is an example of the construction of an underground continuous wall E made of reinforced concrete in a narrow place where it is difficult to secure sufficient work space around the ground side of the planned construction area. To do.
Specifically, it is assumed that the railway viaduct B in the planned construction area of the underground continuous wall E exists at a height of about 3 to 4 m from the ground. In the present embodiment, the existing structure is the railway viaduct B, and the underground continuous wall E will be described in a case where it is constructed at a low head and a narrow place directly below the railway viaduct B, but not limited to this. Any construction site may be used as long as some structure exists above the planned construction site of the underground continuous wall E and the crane work is restricted.
In the present embodiment, the ground including the planned construction area of the underground continuous wall E includes an upper layer G1 positioned on the ground side and a support layer G2 positioned below the upper layer G1, and the upper layer G1 is fine-grained. The fraction content is low (for example, the content of soil particles having a particle size of less than 0.075 mm is about 35% or less), and the support layer G2 has an appropriate strength. In the present embodiment, the underground continuous wall E is specifically constructed so that the lower end thereof reaches the support layer G2.

  First, the structure of the ground improvement body formation apparatus 10 and the excavation apparatus 20 used in the underground continuous wall construction method of this embodiment is demonstrated below with reference to FIG.3 and FIG.4.

  The ground improvement body creation device 10 is a device that forms the ground improvement body 1 (see FIG. 2) on the ground by a so-called high-pressure jet stirring method. The ground improvement body production | generation apparatus 10 is comprised including the main body 11 and the rod 12, as shown in FIG.

The main body 11 includes an injection liquid tank (not shown) for storing the injection liquid, and an ultrahigh pressure and a large flow rate (for example, pressure: about 20 to 40 MPa, discharge flow rate: 0.1 to 0.6 m ³ / And an ultra-high pressure pump (not shown) capable of being pumped in about a minute) and an air compressor (not shown). A grip portion 13 is attached to the front surface of the main body 11 for rotating the rod 12 around its axis and gripping the rod 12 so as to be lifted and lowered along the axis.

  The propellant is solidified milk as a liquid containing an appropriate solidifying material (for example, a self-hardening material such as cement) and water. In the present embodiment, the injection liquid will be described below as cement milk using cement as a solidifying material, but the solidifying material milk is not limited thereto. The solidified material milk is blended so that the uniaxial compressive strength qu of the ground improvement body 1 is within a predetermined strength range described later higher than the strength of the surrounding ground.

A pit (concave portion) 14 is formed at the planned location of the ground improvement body 1. The pit 14 is formed by digging a floor by a predetermined depth from the ground.
Here, the ground improvement body 1 is used for the first ground improvement body 1A as the ground improvement body 1 for the preceding element EA and the succeeding element EB (that is, in a region overlapping the planned construction region of the underground continuous wall E (that is, It is divided into a second ground improvement body 1B as the ground improvement body 1 of the intermediate region S2 (to be described later), and a plurality of them are formed. The local board improvement body 1 is formed with an appropriate cross-sectional shape so as to overlap with the adjacent ground improvement body 1 in plan view.
In the present embodiment, each of the ground improvement bodies 1 (1A, 1B) is formed to have a circular cross-sectional shape, and the formation diameter (outer diameter) of the first ground improvement body 1A is D3, and the second ground The formation diameter of the improved body 1B is D2. In addition, arrangement | positioning of the ground improvement body 1 (1A, 1B) in the construction plan area | region of the underground continuous wall E is explained in full detail behind.

  A guide hole GH, which is a small-diameter boring hole extending vertically in the ground, is formed in the pit 14 by a small hole drill (not shown) such as a rotary boring machine. For example, the guide hole GH is formed to a depth that reaches the boundary position between the upper layer G1 and the support layer G2. The rod 12 is inserted into the guide hole GH. Here, the inner diameter D1 of the guide hole GH is smaller than the formation diameter of the ground improvement body 1, that is, the outer diameter (D2 or D3) of the ground improvement body 1. The drilling rod of the drilling machine is appropriately divided into lengths, and is configured to be extended as appropriate. Therefore, the guide hole GH having an appropriate depth can be easily formed without using a crane or the like even in a low-headed and narrow place.

  When the ground improvement body 1 is created, slime-like kneaded soil (slime) rises through the gap between the rod 12 and the guide hole GH and stays in the pit 14. This slime is discharged into the slime storage tank 16 via a sand pump 15 installed in the pit 14.

  The rod 12 is sequentially added to a cylindrical distal end rod 121, an injection monitor 122 provided on the distal end side (lower end side) of the distal end rod 121, and a proximal end side (upper end side) of the distal end rod 121. And an appropriate number of extension rods 123. The upper end portion side of the rod 12 (that is, the upper end portion side of the extension rod 123 to be added last) protrudes from the ground and is gripped by the grip portion 13.

The tip rod 121 and the extension rod 123 are each configured by, for example, a double tube including an outer tube and an inner tube. In the present embodiment, the case where the tip rod 121 and the extension rod 123 have a double tube structure will be described as an example. However, the present invention is not limited to this, and a structure such as a triple tube can be appropriately employed.
In the present embodiment, the swivel 17 having a jet liquid inlet and a compressed air inlet is connected to the upper end of the extension rod 123 to be added last, and a coupling (not shown) is connected to the lower end side of the tip rod 121. ) Is connected to the injection monitor 122. The distal end rod 121 and the extension rod 123 and the extension rods 123 and 123 are appropriately connected via a joint.
The tip rod 121 and the extension rod 123 have an inner pipe communicating with the jet liquid inlet of the swivel 17 to form a flow path for the jet liquid, and a gap between the inner pipe and the outer pipe is connected to the compressed air inlet of the swivel 17. It communicates and becomes a flow path of compressed air.

  The spray liquid in the spray liquid tank of the main body 11 is pumped into the inner tube of the rod 12 through the ultrahigh pressure pump and the spray liquid inlet of the swivel 17. Further, the compressed air from the air compressor of the main body 11 is pumped to the flow path between the outer tube and the inner tube of the rod 12 via the compressed air inlet of the swivel 17.

The injection monitor 122 includes an injection liquid injection nozzle (not shown) that communicates with the inner tube of the rod 12 (tip rod 121) and a compressed air injection nozzle (not shown) that communicates with the aforementioned compressed air flow path. Prepare. That is, a jet liquid jet nozzle and a compressed air jet nozzle are provided on the tip end side of the rod 12.
The tip of the spray liquid spray nozzle opens outward in the radial direction at a part of the outer peripheral surface of the spray monitor 122. Moreover, the front-end | tip of a compressed air injection nozzle is opening the radial direction outward around the injection liquid injection nozzle. By injecting compressed air from around the injection liquid injection nozzle, the injection liquid can be efficiently injected. In the present embodiment, the injection monitor 122 corresponds to a “nozzle” according to the present invention.

  When the ground improvement body generating apparatus 10 is operated to create the ground improvement body 1, first, the extension rod 123 is sequentially added so that the injection monitor 122 is positioned near the lower end of the guide hole GH. In this state, the high pressure pump and the air compressor of the main body 11 are driven, and the high pressure injection liquid and the compressed air are pumped into the rod 12, whereby the high pressure injection is performed from the injection liquid injection nozzle of the injection monitor 122. The liquid is continuously jetted outward in the radial direction of the guide hole GH, and compressed air is jetted from the compressed air jet nozzles around the jet liquid jet nozzle. As a result, a jet flow J in which the jet liquid and the compressed air are mixed is formed. Further, the rod 12 is rotated by the grip portion 13 while jetting the jet stream J. At this time, the ground around the jet monitor 122 is cut by the pressure of the jet stream J, and the excavated soil and the jet liquid are stirred and kneaded to improve the ground. Accordingly, the bottom of the soil improvement body 1 made of soil mortar, which is configured to be able to inject the jet stream J including the solidified material and water outward from the injection monitor 122 in the radial direction, is larger than the guide hole GH. It is formed.

  Subsequently, the jet stream J is continuously ejected, and the rod 12 is driven to rotate upward by the grip portion 13 and is pulled upward in the vertical direction indicated by an arrow in FIG. The rod 12 is pulled up until the jet stream J is injected near the pit 14 (for example, the bottom surface). During this lifting, the rod 12 rises with the swivel 17. Therefore, for example, the injection of the jet stream J is temporarily stopped at an appropriate timing until the swivel 17 is positioned in front of the bottom of the railway viaduct B, and an appropriate number of extension rods protruding from the ground among the extension rods 123. After removing 123 and reconnecting the upper end of the uppermost extension rod 123 to the swivel 17, the jet stream J may be restarted. In this way, a cylindrical ground improvement body 1 having a diameter larger than that of the guide hole GH and having a length reaching the boundary surface between the upper layer G1 and the support layer G2 is formed (see FIG. 9 described later). .

  Thereafter, the uniaxial compressive strength qu of the ground improvement body 1 gradually increases, and as the age period of the ground improvement body 1 becomes longer, the rate of strength increase becomes gradual and substantially falls within a predetermined strength range. The predetermined strength range of the uniaxial compressive strength qu will be described in detail later.

Next, the excavator 20 will be described with reference to FIG.
The excavation device 20 excavates the ground improvement body 1 formed by the ground improvement body creation device 10 in the vertical direction (excavation direction indicated by an arrow in FIG. 4) to form the excavation groove G.
For example, the excavator 20 is horizontally arranged so as to project forward on the top of the leader 22, a base machine 21 having an endless track and capable of self-propelled, a column-shaped leader 22 supported by the base machine 21, and standing upright. An auxiliary crane 23 to be attached, an excavator 24, and an elevating unit 25 that elevates and descends along the leader 22 are configured.

  The base machine 21 has an endless track and is configured to be self-propelled. The base machine 21 is provided with a winch 26 for lifting the auxiliary crane 23. The wire rope 27 drawn out from the winch 26 is stretched over a guide pulley of the auxiliary crane 23 and connected to a lifting tool 28 located below the tip of the auxiliary crane 23. The auxiliary crane 23 can lift or suspend heavy objects such as the excavator 24 through the lifting tool 28 by winding or sending the wire rope 27 by the winch 26.

  The excavator 24 has a plurality of (two in the figure) cutter drums 29 that can rotate around an axis extending in the horizontal direction to excavate the ground or the like at the tip, and have a slot with a horizontally long rectangular cross section (that is, This is a so-called horizontal multi-axis continuous wall excavator capable of forming the excavation groove G). In parallel with excavation by the excavator 24, an appropriate stabilizing liquid (for example, stabilization mud containing bentonite) having a density larger than that of water is supplied from the treatment plant (not shown) into the excavation groove G that is being formed. The In the following description, the case where the stabilizing liquid has a density higher than that of water will be described as an example. However, the present invention is not limited thereto, and water may be used as the stabilizing liquid as described later.

  The elevating part 25 is configured to be able to ascend or descend while gripping one end side (upper end side) of a plurality of cylindrical sludge reverse rods 25a connected in series. The reverse rod 25 a is connected to the excavator 24 as appropriate with its lower end extending to the vicinity of the cutter drum 29 in the excavator 24. That is, one end side of the reverse rod 25 a is held by the elevating unit 25 and the other end side is connected to the excavator 24.

When excavating the ground improvement body 1 by operating the excavator 20, for example, while operating the excavator 24, the wire rope 27 is sent out by the winch 26, and the elevating unit 25 is lowered to vertically move the ground improvement body 1. Drill in the downward direction. When the lifting unit 25 is lowered to the vicinity of the ground, the lifting unit 25 is lifted while the excavator 24 is held (lifted) by the auxiliary crane 23 while releasing the grip of the reverse rod 25a by the lifting unit 25. Let Then, after the reverse rod 25a is appropriately added and the reverse rod 25a thus added is gripped by the elevating unit 25, the excavator 24 is lowered again by the winch 26 and the elevating unit 25 to continue excavation.
The excavator 20 supplies the stabilizing liquid into the excavation groove G in parallel with the excavation. At the same time, when a suction pump (not shown) connected to the reverse rod 25a is started, the muddy water formed by mixing the stable liquid and the excavated soil generated by excavating the ground improvement body 1 is opened at the lower end of the reverse rod 25a. It is sucked from the section and discharged out of the excavation groove G. The discharged muddy water is appropriately processed at the processing plant (not shown) and separated into a stable liquid and residual soil. Thereby, it is possible to recover the stable liquid from the muddy water. Then, the recovered stable liquid is supplied again into the excavation groove G, and thereafter circulated between the processing plant (such as a stabilization liquid tank) and the excavation groove G.

  In this way, the excavator 20 supplies the stable liquid into the excavation groove G when the excavation groove G is formed, and discharges the excavated sediment generated in the ground improvement body 1 to the outside of the excavation groove G together with the stable liquid, The discharged stable liquid is supplied again into the excavation groove G and is circulated. That is, the excavator 20 circulates the stabilizing liquid by a so-called reverse circulation method or the like.

In the present embodiment, the inner dimension (groove thickness t1, see FIGS. 13 and 18 described later) of the excavation groove G formed by one vertical excavation is the wall of the underground continuous wall E. The inner dimension (groove width W1) in the long side direction of the excavation groove G formed by one excavation in the vertical direction, corresponding to the thickness t, is the length in the long side direction of the preceding element EA and the succeeding element EB. This corresponds to a certain element width W (that is, t1 = t, W1 = W). Thus, in this embodiment, the excavator 20 is configured to be able to form an excavation groove G having an opening shape that is substantially equal to the cross-sectional shape of each element EA, EB upon completion of one excavation (1 gut). ing.
Here, in this embodiment, the groove width W1 (= element width W) of the excavation groove G is larger than the inner diameter D1 of the guide hole GH and smaller than the formation diameter D3 of the first ground improvement body 1A (that is, D1). <W1 <D3).

Next, arrangement | positioning of the ground improvement body 1 in the construction plan area | region of the underground continuous wall E is explained in full detail with reference to FIG.5 and FIG.6. FIG. 5 is a plan view showing a state during the formation of the ground improvement body 1 (after the formation of the first ground improvement body 1A), and FIG. 6 is a state where the formation of the ground improvement body 1 is completed (second ground improvement body). It is the top view which showed the state after the creation of 1B.
In this embodiment, the ground improvement body 1 is divided into two types of a first ground improvement body 1A for the preceding element EA and a second ground improvement body 1B for the following element EB.
Here, the preceding element EA is formed in the excavation groove G (see FIG. 13 described later) for the preceding element EA excavated at a certain interval in the ground. On the other hand, after the leading element EA is formed, the trailing element EB excavates the short side end portion of the preceding element EA adjacent to each other and the intermediate region S2 between the adjacent preceding elements EA (FIG. 15 and FIG. It is formed in each excavation groove G (see FIG. 18 described later) for the succeeding element EB obtained by excavating (see FIG. 16). The planned excavation area S1 of the excavation groove G for one preceding element EA and one intermediate area S2 are set as unit areas for the formation of the ground improvement body 1, respectively.

As shown in FIG. 5, the first ground improvement body 1A for the preceding element EA is disposed so that a planned excavation area (that is, a unit area) S1 of the excavation groove G for the preceding element EA is located therein. Has been.
On the other hand, as shown in FIG. 6, the second ground improvement body 1B for the trailing element EB is arranged so that the area between the adjacent excavation scheduled areas S1 for the preceding element EA is located inside the second ground improvement body 1B. Yes. In other words, in the state after the preceding element EA is completed, the second ground improvement body 1B is arranged so that one intermediate area (that is, unit area) S2 between the adjacent preceding elements EA is located inside. Yes.
Thus, the ground improvement body (1A, 1B) 1 is arranged for each unit area so that the unit area (S1 or S2) is located inside prior to excavation of the excavation groove G for the preceding element EA. The ground improvement bodies 1 adjacent to each other are formed by overlapping a part thereof. That is, the first ground improvement body 1A and the second ground improvement body 1B are formed so as to partially overlap each other. The overlapping length in the wall thickness direction of the underground continuous wall E in the overlapping portion of the ground improvement body 1 is set to be larger than the wall thickness t.

  In the present embodiment, the creation diameter D2 of the second ground improvement body 1B is set to be smaller than the creation diameter D3 of the first ground improvement body 1A. That is, the horizontal cross-sectional area of the ground improvement body 1 (1B) formed corresponding to the intermediate area S2 is the ground improvement body 1 (corresponding to the planned excavation area S1 of the excavation groove G for the preceding element EA). It is set to be smaller than the horizontal sectional area of 1A).

Next, referring to FIG. 1, FIG. 2, FIG. 7 to FIG. 18, an embodiment of the underground continuous wall construction method according to the present invention will be described with reference to a general boring device (not shown) and the above ground improvement body. The case where the creation device 10 and the excavation device 20 are used will be described in detail.
In the following description, for convenience of explanation, it is assumed that after the first ground improvement body 1A for the leading element EA is first formed, the second ground improvement body 1B for the trailing element EB is formed, and thereafter First, an example will be described in which the preceding element EA is all formed, and finally the trailing element EB is formed to construct the underground continuous wall E. Further, the groove width W1 of the excavation groove G, the thickness t1 of the excavation groove G, the formation diameter D3 of the first ground improvement body 1A, and the formation diameter D2 of the second ground improvement body 1B are determined as appropriate, and the ground improvement The uniaxial compressive strength qu of the body 1 (1A, 1B) is a predetermined material that is set according to the period from when the formation of the ground improvement body 1 is completed until the excavation groove G can be formed in the ground improvement body 1 Description will be made on the assumption that an age day (for example, material age 42) is set to fall within a predetermined strength range higher than the strength of the surrounding ground.

  In the present embodiment, the underground continuous wall construction method includes a process for creating the ground improvement body 1 using a high-pressure jet agitation method, a drilling process using a horizontal multi-axis excavator 24, and a reinforcing bar building process. And a concrete placing process. 7 to 11 show the creation process, FIGS. 12 and 13 show the excavation process of the excavation groove G for the leading element EA, FIG. 14 shows the reinforcing bar erection process, and FIG. 15 and FIG. FIG. 17 and FIG. 18 show the excavation process of the excavation groove G for the trailing element EB.

  In the creation step, first, the first ground improvement body 1A is created. In this creation, as shown in FIG. 7, first, in a planned formation place of the first ground improvement body 1A (excavation planned area S1 for the preceding element EA), a floor is dug by a predetermined depth from the ground, and a concave shape is formed. A pit 14 is formed. Then, by a small drilling machine (not shown) as the boring device, it extends in the vertical direction into the ground so that the axial center substantially coincides with the central axis X1 extending in the vertical direction of the planned excavation area S1. A guide hole GH for guiding the rod 12 is formed to a depth reaching the boundary position between the upper layer G1 and the support layer G2. Since the drilling machine is small and the drilling rod is appropriately divided into lengths, it can be easily carried in, installed, and installed by a handcart, etc. even in a low-headed and narrow construction site. In addition to being able to carry out, the guide hole GH can be drilled to a desired depth.

  Next, after completion of the drilling of the guide hole GH, as shown in FIG. 8, the ground improvement body generating device 10 is arranged so that the axis of the gripping portion 13 substantially coincides with the axis (X1) of the guide hole GH. To do. Since the ground improvement body generating apparatus 10 is relatively small like the drilling machine for the guide hole GH, it is disposed at a predetermined position by a hand cart or the like. Thereafter, the rod 12 is inserted into the guide hole GH, and the extension rod 123 is sequentially added until the injection monitor 122 is positioned near the lower end of the guide hole GH. In this state, the rod 12 is driven to rotate while injecting a jet stream J, which is a mixture of a solidified material, water-containing injection liquid, and compressed air, from the injection monitor 122 outward in the radial direction. While pulling up at a predetermined pulling speed (for example, 10 min / m). Here, for example, the discharge pressure of the spray liquid is set to about 38 MPa, and the discharge flow rate is set to about 190 L / min. The rod 12 is pulled up until the jet stream J is injected near the pit 14 (for example, the bottom surface). At the time of this lifting, the extension rod 123 such as the uppermost portion is sequentially removed so that the swivel 17 does not interfere with the bottom surface of the railway viaduct B. As a result, as shown in FIG. 9, a cylindrical first ground improvement body having a construction diameter D3 larger than the guide hole GH and a length reaching the boundary surface between the upper layer G1 and the support layer G2. Create 1A. Thereafter, in the planned excavation area S1 for the adjacent preceding element EA, the next first ground improvement body 1A is created in the same procedure as in FIGS. This is sequentially repeated to complete the creation of the first ground improvement body 1A as shown in FIG. Accordingly, the planned excavation area S1 of the excavation groove G for the preceding element EA is located inside each first ground improvement body 1A.

  Next, the formation of the second ground improvement body 1B is sequentially performed in the same manner as the formation of the first ground improvement body 1A. In this construction, each guide hole GH is formed so that its axis is substantially coincident with a central axis X2 extending in the vertical direction of the intermediate region S2 (in other words, an axis passing through the center of adjacent central axes X1). . As a result, the intermediate region S2 is located inside each second ground improvement body 1B, and as shown in FIG. 11, the first ground improvement body 1A and the second ground improvement body 1B are integrally formed. Improved body groups are formed. Then, the ground improvement body production | generation apparatus 10 is carried out and a creation process is completed. Thus, in this embodiment, the ground improvement bodies 1 (1A, 1B) are arranged in a line along the construction direction of the underground continuous wall E.

The uniaxial compressive strength qu of soil improvement body 1, for example, about 570kN / m ² next to the age of 28 days, about 790kN / m ² next to the age of 42 days, then, the strength increase rate becomes gentle , Approximately within a predetermined strength range higher than the surrounding ground (for example, about 500 to about 1000 kN / m ² ). The lower limit value of the predetermined strength range is set higher than the strength of the surrounding ground of the ground improvement body 1, and the upper limit value of the predetermined strength range is set according to the excavation force of the excavator 20 that forms the excavation groove G. The In addition, as will be described later, the jet liquid (solidified milk) is blended so that the uniaxial compressive strength qu of the ground improvement body 1 on a predetermined material age falls within the predetermined strength range.
In the present embodiment, prior to excavation of the excavation groove G for the preceding element EA, the ground improvement body 1 (1A, 1B) in which the unit area (S1, S2) is located is replaced with the unit area (S1). , S2), and in each of the unit regions, the rod 12 is inserted into the guide hole GH and the cement milk is sprayed radially outward from the spray monitor 122 while the rod is inserted. 12 is rotated, and the rod 12 is pulled up to create the ground improvement body 1 (1A, 1B) having a diameter larger than that of the guide hole GH and higher in strength than the ground.

Next, in the excavation process of the ground improvement body 1, for example, all the excavation grooves G for the leading element EA are formed.
Specifically, the excavator 20 is arranged so that the axis of the excavator 24 substantially coincides with the central axis (that is, X1) in the extending direction of the first ground improvement body 1A. Thereafter, the cutter drum 29 is positioned in the vicinity of the upper end portion of the first ground improvement body 1A so that excavation is possible. The period from the completion of the creation of the first ground improvement body 1A to the time when the excavation device 20 is arranged and the excavation groove G can be formed in the first ground improvement body 1A is, for example, about 1 month to 1 month. Since it takes about half, the uniaxial compressive strength qu of the first ground improvement body 1A at the start of excavation is within the predetermined strength range. In this state, the excavator 24 is lowered by the winch 26 or the lifting unit 25. Thereby, the excavation groove G in which the groove center is aligned with the axial center of the first ground improvement body 1A starts to be formed. Then, as shown in FIG. 12, the excavator 24 descends until the cutter drum 29 penetrates the support layer G2. As a result, it has a groove width W1 smaller than the formation diameter D3 of the first ground improvement body 1A and a groove thickness t1 that substantially matches the wall thickness t of the underground continuous wall E, and the center of the groove is the first ground improvement body 1A. The excavation groove G that is formed together with the central axis (X1) in the extending direction of the steel and reaches the support layer G2 is formed. Each of the four groove walls in the long side direction and the short side direction constituting the excavation groove G is formed by the excavation surface of the first ground improvement body 1A. Thereafter, the excavation of the excavation groove G is sequentially repeated in the adjacent excavation planned area S1 to complete the formation of the excavation groove G for the preceding element EA as shown in FIG.
Here, the 1st ground improvement body 1A in which the excavation groove G was formed along the central axis (X1) turns into a hollow improvement body, and has a thin part in which the wall thickness becomes the minimum in an appropriate place. In addition, the thin part thickness (hereinafter referred to as the thin part thickness) T (T3) and the creation diameter D (D3) setting procedure, the thin part thickness T and the uniaxial compressive strength qu of the first ground improvement body 1A The relationship will be described in detail later.

  In parallel with the excavation, a stable liquid is supplied into the excavation groove G. At the same time, a suction pump (not shown) is activated, and the muddy water composed of the excavated earth and sand and the stabilizing liquid in the excavation groove G is sucked and raised from the tip opening of the reverse rod 25a for discharging mud. It guides to a screening part (illustration omitted), and discharges outside the excavation groove G. Moreover, a screen part removes excavation earth and sand from muddy water suitably, and collects a stable liquid. Then, the recovered stable liquid is supplied again into the excavation groove G and is circulated between the stable liquid tank and the excavation groove G. Thus, the excavation groove G is excavated to an appropriate depth while stabilizing the groove wall of the excavation groove G.

  Next, in the reinforcing bar erection process for the leading element EA, as shown in FIG. 14, approximately rectangular reinforcing bar ridges 30 formed in advance in each excavation groove G are sequentially added on the ground side. Build. This erection is performed until the lowermost reinforcing bar 30 reaches the bottom of the excavation groove G. It is assumed that the excavation groove G is filled with the stabilizing liquid used in the excavation process as it is when the reinforcing bar is installed.

  After the reinforcement is built, in the concrete placing process, for example, the excavation groove G is filled with the stabilizing liquid, and the tremi pipe is placed in each excavation groove G so that its lower end is located at the bottom of the excavation groove G. insert. Then, concrete is poured into the excavation groove G from the lower end opening of the tremi pipe, and the stabilizing liquid is appropriately discharged, and the concrete is cast into each excavation groove G as shown in FIGS. To do. Thereby, the preceding element EA is formed in each excavation groove G for the preceding element EA.

Next, as shown in FIGS. 17 and 18, the subsequent element EB is sequentially formed in the same manner as the formation of the preceding element EA, for example.
In detail, the excavator 20 is disposed so that the axis of the excavator 24 is substantially coincident with the central axis (that is, X2) in the extending direction of the second ground improvement body 1B, and the excavator 24 is lowered. Thereby, the excavation groove G in which the groove center is aligned with the axial center of the second ground improvement body 1B starts to be formed. In this excavation, the excavator 24 excavates (cuts) the short-side end portions of the adjacent preceding elements EA and excavates an intermediate region S2 between the adjacent preceding elements EA, so as to The excavation groove G is obtained. Thereby, it has the groove width W1 larger than the formation diameter D2 of the second ground improvement body 1B and the groove thickness t1 substantially coincident with the wall thickness t of the underground continuous wall E, and the groove center is defined as the second ground improvement body 1B. An excavation groove G that is formed in alignment with the central axis (X2) in the extending direction and reaches the support layer G2 is formed. Of the groove walls constituting the excavation groove G, the two groove walls in the short side direction are respectively formed by excavation (cutting) surfaces at the short side end of the preceding element EA. Of the groove walls constituting the excavation groove G, the two groove walls in the long side direction consist of the excavation surface of the first ground improvement body 1A at both ends, and the second ground for the other portions. It consists of the excavation surface of the improved body 1B. Thereafter, the excavation of the excavation groove G is sequentially repeated in the planned excavation area including the adjacent intermediate area S2, and the formation of the excavation groove G for the trailing element EB is completed as shown in FIGS. In addition, the width | variety of the reinforcing bar 30 is set suitably smaller than the element width W of the preceding element EA, and it is comprised so that the reinforcing bar 30 may not be cut at the time of cutting of a short side edge part.
Here, the 2nd ground improvement body 1B in which the excavation groove G was formed along the central axis (X2) has a thin part where the wall thickness becomes the minimum in an appropriate place. In addition, the setting procedure of the thin part thickness T (T2) and the formed diameter D (D2) and the relationship between the thin part thickness T and the uniaxial compressive strength qu of the second ground improvement body 1B will be described in detail later. .

  Next, as with the preceding element EA, in each excavation groove G for the succeeding element EB, a reinforcing bar 30 is added and built, and concrete is placed using a tremi pipe, and FIG. 1 and FIG. As shown in FIG. 2, the leading element EA and the trailing element EB are alternately arranged in a line, and the construction of the underground continuous wall E having the wall thickness t is completed.

By the way, considering the drilling performance by the excavator 20, the construction efficiency (drilling efficiency) is higher when the strength of the ground improvement body 1 is suppressed to a low strength. Therefore, in the present embodiment, the construction of the low strength ground improvement body 1 is realized by devising the composition of the spray liquid. In the present embodiment, in consideration of the construction efficiency of the excavation groove G by the excavator 20 while setting it higher than the surrounding ground, the uniaxial compressive strength qu of the ground improvement body 1 is a predetermined age (for example, material age). in day 42), within a predetermined intensity range (for example, it sets to fit about 500 kN / m ² in the range of about 1000 kN / m ^2). The predetermined material age is set according to a period from when the formation of the ground improvement body 1 is completed to when the excavation hole BH can be drilled in the ground improvement body 1. In addition, the range (predetermined strength range) of about 500 kN / m ² to about 1000 kN / m ² with respect to the uniaxial compressive strength is the ground improvement body 1 determined according to the excavating force of the excavator 20 and the strength of the ground. This corresponds to an allowable strength range R1 described later.

Next, the setting procedure of the thin part thickness T (T1, T2) and the formed diameter D (D3, D2), the thin part thickness T (T1, T2) and the uniaxial compressive strength qu of the ground improvement body 1 The relationship will be described.
FIG. 19 is a flowchart for explaining a procedure for setting the thin portion thickness T and the forming diameter D, and FIG. 20 is a view showing the relationship between the uniaxial compressive strength qu and the thin portion thickness T.

  The setting procedure of the thin part thickness T and the forming diameter D is roughly divided into two procedures, STEP1 and STEP2. In STEP 1, the range of the thin part thickness T satisfying the predetermined condition is set, and in STEP 2, the final thin part thickness T and the formation diameter D are set, and the ground improvement body 1 for the purpose of protecting the groove wall is set. Determine construction specifications. Below, each STEP is explained in full detail.

  In STEP1, as shown in FIG. 19, in STEP11, the groove width W1 and the groove thickness t1 of the excavation groove G are determined according to the element width W and wall thickness t of the required elements (EA, EB). Next, in STEP 12, when the dimensions of the excavation shape are W1, t1, and the value of the uniaxial compressive strength qu of the ground improvement body 1 is changed, the necessary safety factor Fs for the collapse of the groove wall of the excavation groove G is set. The satisfactory thin part thickness T is calculated using, for example, a three-dimensional cylindrical sliding method. As a result, as shown in FIG. 20, a relational line Lin1 between the thin portion thickness T satisfying the necessary safety factor Fs and the uniaxial compressive strength qu of the ground improvement body 1 is obtained. In the present embodiment, the necessary safety factor Fs is set to 1.5. Note that the calculation method is not limited to the three-dimensional cylindrical sliding method, and for example, an appropriate method such as a proto-jakonov method or a finite element method can be used.

Next, in STEP 13, the allowable strength range R1 of the ground improvement body 1 is set based on the excavation force of the excavator 20 and the strength of the ground. Here, the lower limit value R1min of the allowable strength range R1 is set to about 500 kN / m ² that is higher than the strength of the surrounding ground, and the upper limit value R1max of the allowable strength range R1 is set to about 1000 kN / and m ^2. This allowable strength range R1 is an example of drilling strength by the excavator 20 in the present embodiment, and can be determined as appropriate according to the excavation force of the excavator to be employed.
Further, for example, based on the vertical inclination of the excavation groove G and the ground improvement body 1, the dimensional accuracy of the excavation groove, the construction accuracy of the excavation groove G and the ground improvement body 1 such as the formation accuracy of the ground improvement body 1, and the like. The minimum wall thickness Tmin, which is the minimum wall thickness that can be constructed, is set. Here, the minimum wall thickness Tmin = 50 mm.
In STEP 14, a safe wall thickness range R2 is set based on the allowable strength range R1 of the ground improvement body 1 and the necessary safety factor Fs. Specifically, in the relationship line Lin1 between the thin portion thickness T and the uniaxial compressive strength qu of the ground improvement body 1 shown in FIG. 20, the thin portion corresponding to the lower limit value R1min and the upper limit value R1max of the allowable strength range R1, respectively. A lower limit value and an upper limit value of the thickness T are obtained. In FIG. 22, the lower limit value R2min of the safety wall thickness range R2 is 120 mm, and the upper limit value R2max of the safety wall thickness range R2 is 200 mm. The required safety factor Fs can be satisfied by setting the thin portion thickness T within the safety wall thickness range R2 (that is, R2max ≧ T ≧ R2min). Here, as can be seen from FIG. 20, when the uniaxial compressive strength qu is small, the required safety factor Fs can be satisfied by increasing the thin portion thickness T. When the uniaxial compressive strength qu is large, the thin portion thickness Even if the length T is small, the necessary safety factor can be satisfied.
In this way, the thickness T of the thin wall portion is determined by the allowable strength range R1 of the ground improvement body 1 determined according to the excavation force of the excavator 20 and the strength of the ground, and the necessary safety factor for the groove wall collapse of the excavation groove G. It is determined within the safety wall thickness range R2 determined based on Fs.

Moreover, the thin part thickness T is specifically set within the minimum wall thickness Tmin determined according to the construction accuracy of the excavation groove G and the ground improvement body 1 in the safety wall thickness range R2. There is a need. For this reason, in STEP 15, it is determined whether or not the minimum wall thickness Tmin is equal to or less than the upper limit value R2max of the safe wall thickness range R2. In the case of R2max ≧ Tmin (STEP 15: YES), in STEP 16, a construction wall thickness range R3 that is a range equal to or larger than the minimum wall thickness Tmin in the safety wall thickness range R2 is set. The thin part thickness T can be determined within the construction wall thickness range R3 (that is, R2max ≧ T ≧ Tmin), and the process proceeds to the next STEP2. In this embodiment, since the lower limit value R2min (= 120 mm) of the safety wall thickness range R2 is larger than the minimum wall thickness Tmin (= 50 mm), the construction wall thickness range R3 coincides with the safety wall thickness range R2.
When the upper limit value R2max of the safe wall thickness range R2 is smaller than the minimum wall thickness Tmin (STEP 15: NO), for example, the ground is set so that the minimum wall thickness Tmin is at least equal to or lower than the upper limit value R2max of the safe wall thickness range R2. The construction accuracy may be improved by lowering the minimum wall thickness Tmin by, for example, more strictly managing the positioning of the rod 12 of the improved body building apparatus 10 and the excavator 24 of the excavator 20 (STEP 15 ′).

In STEP2, first, in STEP21, an appropriate thin part thickness T is determined within the construction wall thickness range R3. Next, in STEP 22, for the first ground improvement body 1A, the above-determined thin portion thickness T can be secured in the four groove walls in the long side direction and the short side direction (all directions) constituting the excavation groove G. A formation diameter D (D3) of the ground improvement body 1 is determined. On the other hand, with respect to the second ground improvement body 1B, the formation diameter D (D2) of the ground improvement body 1 that can secure the determined thin wall thickness T in the two groove walls in the long side direction constituting the excavation groove G. To decide.
Specifically, in the present embodiment, the thin portion thickness T is determined within the construction wall thickness range (= safe wall thickness range R2) R3, that is, within a range of 120 mm to 200 mm. The creation diameter D3 of the first ground improvement body 1A was set to be smaller than the creation diameter D2 of the second ground improvement body 1B.
Here, the construction cost of the ground improvement body 1 increases as the creation diameter D (D2, D3) increases. However, considering the overall construction accuracy at the construction site, the creation diameter D has a margin. Can be installed.
In this way, the final thin wall thickness T (T3, T2) and the creation diameter D (D3, D2) are set, and the construction specifications of the ground improvement body 1 for the purpose of protecting the groove wall are determined. To do.

According to the underground continuous wall construction method according to this embodiment, the planned excavation area S1 of the excavation groove G for one preceding element EA and one intermediate area S2 between the adjacent preceding elements EA are unitized. Prior to excavation of the excavation groove G for the preceding element EA, the ground improvement body 1 (1A, 1B) in which the unit area is located is formed for each unit area. Then, in the creation process for each unit region, the rod 12 formed by sequentially adding the extension rod 123 to the proximal end side of the distal end rod 121 provided with the injection monitor 122 on the distal end side is inserted into the guide hole GH, The ground improvement body 1 having higher strength than the ground is created by rotating and pulling up the rod 12 while jetting the jet stream J containing the solidified milk from the jet monitor 122 in the guide hole GH radially outward. doing.
Accordingly, each excavation groove G for the leading element EA can be formed by excavating the ground improvement body 1A that has already been created, and each excavation groove G for the subsequent element EB has been already created. It can be formed by excavating the improved bodies 1A and 1B and the short-side ends of the adjacent preceding elements EA that are already formed. Therefore, for example, each excavation groove is simply set to a strength higher than that of the surrounding ground according to the capability and construction method of the excavator 20 for excavating the ground improvement body 1 and the leading element EA. Since stabilization of the groove wall of G can be aimed at, collapse of the groove wall during construction of the underground continuous wall can be prevented.
And even if there is some structure above the planned construction site of the underground continuous wall E and the crane operation is restricted, the rod 12 of the ground improvement body building device 10 is simply attached by a small drilling machine. A small diameter guide hole GH that can be inserted is excavated, the rod 12 is sequentially inserted into the guide hole GH, and the jet stream J is sprayed to rotate and pull up the rod. It is possible to construct (create) a ground improvement body 1 having a strength appropriately higher than that of the ground. The machine and the method for forming the guide hole GH and the excavation groove G are different from each other according to the height from the ground in the planned excavation area of each excavation groove G to the structure existing above it. Thus, an appropriate machine and construction method may be employed.

  In this way, in the area where there is some structure above the planned construction site of the underground continuous wall and the crane work is restricted, the ground wall is prevented from collapsing during the construction of the underground continuous wall. An underground continuous wall construction method capable of easily constructing an intermediate continuous wall can be provided.

Moreover, in this embodiment, it was set as the structure which supplies a stable liquid in the excavation groove G at the time of formation of the excavation groove G, and at the time of reinforcement reinforcement construction. Thus, the excavation groove G can be excavated to an appropriate depth and a reinforcing bar can be built in a state in which the groove wall of the excavation groove G is more reliably stabilized.
In addition, for example, a method is generally known in which, while directly excavating an excavation groove in the ground, a stabilizing liquid is supplied to suppress the collapse of the groove wall. However, even with this construction method, when the groundwater level of the ground is relatively high, or when there is a temporary imbalance between the amount of stable liquid supplied to the excavation groove and the suction amount by the excavator, There is a high possibility that the groove wall will collapse. On the other hand, in this embodiment, since the ground improvement body 1 is created prior to the step of forming the excavation groove G, the risk of collapse of the groove wall of the excavation groove G can be completely eliminated.

  In addition, by creating the ground improvement body 1 that covers the planned excavation area S1 of the excavation groove G for the preceding element EA, both horizontal end portions of the planned excavation area of the excavation groove G for the subsequent element EB are also formed at the same time. be able to. For this reason, in the present embodiment, the horizontal cross-sectional area of the ground improvement body (second ground improvement body 1B) 1 created corresponding to the intermediate area S2 is set in the planned excavation area S1 of the excavation groove G for the preceding element EA. It is set to be smaller than the horizontal cross-sectional area of the corresponding ground improvement body (first ground improvement body 1A) 1 created. That is, in this embodiment, D2 is set to be smaller than D3. Thereby, the creation range of the ground improvement body 1 can be narrowed, and the creation cost of the ground improvement body 1 can be lowered.

  Moreover, in this embodiment, the ground improvement body 1 is a structure which is simply arranged in a line along the construction direction of the underground continuous wall E. Therefore, compared with the general construction method that constructs two rows of soil mortar columns by the SMW method so as to sandwich the planned construction area of the underground continuous wall E, the construction period required to create the ground improvement body is shortened. Can do. In addition, in the above general construction method, considering the excavation ability of the excavation groove by the excavator, the soil mortar column is adjacent to the completed line of the underground continuous wall E or has a slight clearance from the completed line. In any case, after excavation of the trench, earth and sand remained between the completed line and the outer periphery of the ground improvement body, and it was necessary to remove this residual earth and sand in a subsequent process. In the underground continuous wall construction method according to the embodiment, the above removal work is not necessary.

In the present embodiment, the thickness T of the ground improvement body 1 after the formation of the excavation groove G is determined within the safety wall thickness range R2 determined based on the allowable strength range R1 and the necessary safety factor Fs. Yes. Thereby, collapse of a groove wall can be prevented more reliably.
Furthermore, in this embodiment, the thin wall thickness T is a construction wall thickness that is within a minimum wall thickness Tmin determined in accordance with the construction accuracy of the excavation groove G and ground improvement body 1 in the safety wall thickness range R2. It is determined within the range R3. Thereby, the thin part thickness T can be set in consideration of construction accuracy.

  Moreover, in this embodiment, the uniaxial compressive strength qu of the ground improvement body 1 is set according to the period until it becomes possible to form the excavation groove G in the ground improvement body 1 after the creation of the ground improvement body 1 is completed. It is set so as to be within a predetermined strength range on a predetermined material age day. Thereby, when forming the excavation groove G in the ground improvement body 1, the uniaxial compressive strength qu can be reliably set within the intended strength range.

Further, in the present embodiment, the lower limit value of the predetermined strength range is set higher than the strength of the surrounding ground of the ground improvement body 1, and the upper limit value of the predetermined strength range is the excavation of the excavator 20 that forms the excavation groove G. It is set according to the force. Thereby, the uniaxial compressive strength qu on the predetermined age of the ground improvement body 1 is set higher than the surrounding ground, and the construction efficiency of the excavation groove G by the excavator 20 is set to ensure a low strength. Therefore, prevention of groove wall collapse and improvement in construction efficiency of the excavation groove G can be achieved at the same time. In the present embodiment, the predetermined intensity range has a lower limit value (lower limit value R1mim of allowable intensity range R1) of about 500 kN / m ² and an upper limit value (upper limit value R1max of allowable intensity range R1) of 1000 kN / Although the case of the m ² and described by way of example, not limited to this and can be suitably determined according to the intensity of the drilling force and surrounding soil of the excavation device 20.

In the present embodiment, the local ground improvement body 1 (1A, 1B) has been described as being formed with a circular cross-sectional shape at the time of completion. The shape can be appropriately adopted without limitation.
For example, as shown in FIG. 21, each board improvement body 1 (1A, 1B) may have a semicircular cross-sectional shape. In this case, for example, each ground improvement body 1 (1A, 1B) is arranged so that the side surface extending in the vertical direction of the first ground improvement body 1A and the side surface extending in the vertical direction of the second ground improvement body 1B are aligned. Good. Although not shown in the drawings, the shape is not limited to a circle or a semicircle, and may be a fan shape, a ribbon shape that is inverted at the center of a fan shape and integrated with two fan shapes, or a rectangular shape. There may be. In the case of a rectangular shape, for example, in the creation for each unit region, the guide holes GH may be provided at a plurality of locations. Moreover, each board improvement body 1 (1A, 1B) may be formed integrally by partially overlapping a plurality of small ground improvement bodies.

In the present embodiment, the horizontal cross-sectional area of the second ground improvement body 1B is set to be smaller than the horizontal cross-sectional area of the first ground improvement body 1A. The horizontal section of the body 1A may be substantially coincident, or may be set to be large.
In addition, the first ground improvement body 1A and the second ground improvement body 1B are similar to each other, but are not limited to this, and different types of cross-sectional shapes (circular, semicircular, fan-shaped, ribbon-shaped, rectangular) , Dumplings, etc.) may be employed. For example, as shown in FIG. 22, as the first ground improvement body 1A, a dumpling-like cross-sectional shape in which a plurality of circles are partially overlapped and integrated is adopted, and as the second ground improvement body 1B, a circular shape is adopted. A cross-sectional shape may be adopted.
Further, different types of shapes and sizes of the first ground improvement bodies 1A may be adopted, and the same applies to the second ground improvement bodies 1B.
Moreover, in this embodiment, although the 1st ground improvement body 1A and the 2nd ground improvement body 1B shall be each arrange | positioned by the fixed space | interval (pitch), it is not restricted to this, You may arrange | position at unequal intervals. Good.

  Moreover, in this embodiment, although the local board improvement body 1 demonstrated each extending from the ground surface to the support layer G2, it is not restricted to this. For example, when buried objects such as pipes have already been buried so as to cross the planned construction area of the underground continuous wall E, for the appropriate number of ground improvement bodies 1 located in the buried part, What is necessary is just to extend from the lower end vicinity to the support layer G2. In this case, the rod 12 may be pulled up in the creation process until the jet stream J is injected near the lower end of the pit buried object.

  Further, in the present embodiment, for convenience of explanation, the first ground improvement body 1A is created, and then the second ground improvement body 1B is created. However, the ground improvement body 1 is constructed in units of this. Not limited to. For example, when the horizontal direction length of the underground continuous wall E is long, the first ground improvement body 1A and the second ground improvement body 1B may be created for each of the small sections as appropriate.

  Further, in the present embodiment, for the sake of convenience of explanation, it has been described that the formation of the succeeding element EB is started after all the leading elements EA are formed after the creation process is completed, but the present invention is not limited thereto. Similar to the above construction, the leading element EA and the trailing element EB may be appropriately formed for each small section.

  Further, in the present embodiment, for the sake of convenience of explanation, it has been described that after completion of the excavation process for all the preceding elements EA, the process proceeds to the reinforcing bar construction process, and then proceeds to the concrete placing process. The unit of work for formation is not limited to this. For example, after excavation, rebar construction, and concrete placement are completed for each preceding element EA, construction of the next leading element EA is carried out or divided into small sections as appropriate, and construction is performed for each small section. It is good to do. The same applies to the succeeding element EB.

  Further, in the present embodiment, the leading element EA and the trailing element EB are formed by sequentially adding and building the reinforcing bar rods 30 formed in advance in the excavation groove G and placing concrete. Although the case where it was an element made from reinforced concrete was demonstrated as an example, it is not restricted to this. For example, the material to be placed is not limited to concrete but may be a cement-based material. For example, soil mortar may be placed. In addition, each element (EA, EB) is not limited to one made of a reinforcing bar and a cement-based material. For example, in each excavation groove G, concrete members or steel members formed in advance are sequentially added. After erection, it is formed by filling cement-based materials such as concrete, mortar, cement paste and soil mortar between the groove wall of each excavation groove G and the erected concrete member or steel member. It may be a thing. In this case, as the cement-based material, it is preferable to use a material in which breathing is suppressed by using various admixtures.

  Further, in the present embodiment, after the excavation groove G is formed, the excavation groove G is filled with an appropriate stabilizing liquid having a density larger than water (for example, stabilization mud containing bentonite) as it is. Not limited to this. In the case where the groundwater level in the construction planned area of the underground continuous wall E is low, for example, simply filling the excavation groove G with fresh water is sufficient between the freshwater head in the excavation groove and the groundwater head. In some cases, it is possible to ensure a sufficient head differential. Thereby, each element EA, EB can be constructed without attaching fine particles of stabilizing mud on the surface of the reinforcing bar in the reinforcing bar building process and the placing process of cement-based material such as concrete.

  In addition, since the ground improvement body 1 is set to have a higher strength than the surrounding ground, when the groundwater level in the construction planned area of the underground continuous wall E is low, the excavation groove G is being formed and thereafter. In this process, there is a case where the risk of collapse of the groove wall can be completely eliminated without using a stabilizing liquid in the excavation groove G. Therefore, in the present embodiment, when the excavation groove G is formed, a stable liquid is supplied into the excavation groove G. However, depending on the ground conditions such as the groundwater level in the construction planned area of the underground continuous wall E, However, the present invention is not limited to this, and there may be a case where a stabilizer is not required. In this case, the construction method for forming the excavation groove G may be an appropriate construction method that can be constructed at a low construction site and in a narrow construction site.

  In the present embodiment, the size of the excavation groove G for the preceding element EA and the size of the excavation groove G for the subsequent element EB are described as being the same. However, the present invention is not limited to this, and may be different. . In the present embodiment, the excavation groove G for each element (EA, EB) is formed by one excavation (one gut) in the vertical direction. You may form by excavating. For example, in the modified example shown in FIG. 22, the excavation groove G for one preceding element EA is formed by, for example, 3 guts.

  In the present embodiment, the underground continuous wall E has been described as extending in one horizontal direction, that is, linearly. However, the present invention is not limited to this, and the underground continuous wall E may be extended so as to be curved. In addition, the underground continuous wall E is not limited to having a horizontally long rectangular cross section, and an appropriate cross sectional shape such as an arc-shaped cross section having a predetermined wall thickness can be applied. Moreover, the underground continuous wall E may have a hollow structure, for example, may be formed in a cylindrical shape.

  Further, in the present embodiment, the excavator 20 has been described using a so-called horizontal multi-axis excavator 24, but the present invention is not limited to this, and the excavator 20 exists above the ground in the planned excavation area of each excavation groove G. Depending on the height to the existing structure, for example, an appropriate continuous wall excavator such as a bucket type can be employed.

  Moreover, although the railway viaduct B was mentioned as an example of the existing structure which exists above the construction plan area | region of the underground continuous wall E, an existing structure is not restricted to the railway viaduct B, What kind of thing may be sufficient. The construction site is a low-headed and narrow place, but is not limited to this, a place where there is a sufficient distance to the existing structure above the planned construction area of the underground continuous wall E, It may be a place where there is no structure above or a place where a sufficient space can be secured even though the head is low.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not restrict | limited to the said embodiment, A various deformation | transformation and change are possible based on the technical idea of this invention.

DESCRIPTION OF SYMBOLS 1 ... Ground improvement body (1st ground improvement body, 2nd ground improvement body), 10 ... Ground improvement body formation apparatus, 11 ... Main body, 12 ... Rod, 13 ... Holding part, 14 ... Pit, 15 ... Sand pump, 16 ... slime storage tank, 17 ... swivel, 20 ... excavator, 21 ... base machine, 22 ... leader, 23 ... auxiliary crane, 24 ... excavator, 25 ... lifting part, 25a ... reverse rod, 26 ... winch, 27 ... wire Rope, 28 ... Suspension tool, 29 ... Cutter drum, 121 ... Tip rod, 122 ... Injection monitor (nozzle), 123 ... Extension rod, 261 ... Tip drilling rod tube, 262 ... Drilling bit, 263 ... Extension drilling rod tube, B ... Railway viaduct (existing structure), BH ... excavation hole, D1 ... inner diameter of guide hole, D2 ... creation diameter of second ground improvement body, D3 ... creation diameter of first ground improvement body, E ... underground connection Connecting wall, EA ... preceding element, EB ... trailing element, G ... excavation groove, G1 ... upper layer, G2 ... support layer, GH ... boring hole (guide hole), J ... jet flow, R1 ... allowable strength range, R2 ... Safety wall thickness range, R3 ... construction wall thickness range, S1 ... planned excavation area, S2 ... intermediate area, t ... wall thickness, t1 ... groove thickness, W ... element width, W1 ... groove width

Claims (6)

After forming the preceding element in each excavation groove for the preceding element excavated at a distance in the ground, excavating the end of the preceding element adjacent to each other and excavating the intermediate region between the preceding elements An underground continuous wall construction method for constructing an underground continuous wall by forming a downstream element in each excavation groove for the subsequent element obtained,
A drilling planned area of the excavation groove for one of the preceding elements and one intermediate area are each set as a unit area,
Prior to excavation of the excavation groove for the preceding element, including a creation step of creating, for each unit region, a ground improvement body in which the unit region is located,
In the creation process for each unit region,
Forming a borehole extending vertically in the ground,
Inserting a rod having a cylindrical tip rod, a nozzle provided on the tip end side of the tip rod, and an extension rod sequentially added to the base end side of the tip rod into the boring hole,
The rod is rotated while ejecting a liquid containing solidification material and water radially outward from the nozzle, and the rod is pulled up to be larger in diameter than the boring hole and higher in strength than the ground. An underground continuous wall construction method for creating the ground improvement body.   The underground continuous wall construction method according to claim 1, wherein the ground improvement bodies are arranged in a line along a construction direction of the underground continuous wall.   The underground continuous wall construction method according to claim 1 or 2, wherein the ground improvement body for the intermediate region and the ground improvement body for the preceding element are partially overlapped with each other.   In each of the excavation grooves, rebar bars formed in advance are sequentially added and built, and a cement-based material is placed to form the leading element or the trailing element. The underground continuous wall construction method according to any one of the above. In each of the excavation grooves, concrete members or steel members formed by dividing in advance are built in order,
The cemented material is filled between the groove wall of each excavation groove and the built-in concrete member or steel member to form the preceding element or the trailing element. 5. The underground continuous wall construction method according to any one of 4 above. The ground improvement body after the formation of the excavation groove has a thin wall portion whose wall thickness is minimized,
The thickness of the thin wall portion is the allowable strength range of the ground improvement body determined according to the excavation force of the excavator that forms the excavation groove and the strength of the ground, and the necessary safety factor for the collapse of the groove wall of the excavation groove The underground continuous wall construction method according to any one of claims 1 to 5, wherein the underground continuous wall construction method is defined within a safety wall thickness range determined on the basis of.