JP7517054B2 - Anchor members and ground improvement methods - Google Patents

Description

The present invention relates to an anchor member to be attached to a drainage material, and a ground improvement method using the drainage material.

The loaded embankment method using vertical drains has been known as a method for promoting consolidation settlement of soft clayey soil and increasing its strength. In the loaded embankment method, multiple drain materials are cast vertically at specified intervals into the soft clayey soil to be improved, and the upper and lower parts of the drain materials are brought into contact with the upper and lower sand layers above and below the soft clayey soil. In this state, when an embankment is constructed above the upper sand layer and loaded, the pore water in the soft clayey soil is drained through the drain materials into the upper or lower sand layer, promoting the settlement of the ground.

A vacuum consolidation method is also known as a method for promoting consolidation settlement without using embankments, in which negative pressure is applied to soft clayey soil into which multiple drainage materials have been poured to forcibly drain the soil. For example, Patent Document 1 discloses a method in which negative pressure is applied from the bottom side of the ground to be improved.

Specifically, after the ground to be improved is formed on a permeable layer, drainage material is poured in to make contact with the permeable layer, and the top surface of the ground to be improved is covered with an impermeable layer. Next, multiple collection wells equipped with suction pipes and suction pumps are placed in the ground to be improved so that they communicate with the permeable layer. After this, the collection wells are used to apply negative pressure to the ground to be improved via the permeable layer and drainage material, and moisture from the reclaimed land is collected in the collection wells.

The permeable layer used in the above-mentioned method of applying negative pressure from the bottom side of the ground to be improved is not only used when a new layer is laid, but may also be used, for example, when there is a naturally deposited sand layer that can function as a permeable layer, or when a permeable layer laid in previous construction work exists in a reusable state. Also, when the ground to be improved is an existing reclaimed land, if there is a natural sand layer or a permeable layer laid in previous construction work on the bottom side, a method of applying negative pressure from the bottom side may be used.

In all of the above construction methods, a mandrel is often used to cast the drainage material. For example, as disclosed in the prior art of Patent Document 2, this method involves inserting the drainage material into a vertically erected cylindrical mandrel, and attaching an anchor device near the end of the drainage material exposed at the bottom end of the mandrel. In this state, the mandrel is inserted into the ground to be improved.

After this, when the anchor device reaches a specified depth, the mandrel is pulled out, and the anchor device functions as a device to prevent the drain material from rising up together, so the drain material and anchor device are left in the soft ground.

JP 2001-279657 A JP 2013-124474 A

The above anchor device is made of a flat anchor plate with two parallel slit holes that are approximately longer than the width of the drain material. When attaching the drain material, the drain material is inserted into the two slit holes by moving it back and forth from the top side of the anchor plate. As a result, a direction change part of the drain material is formed on the bottom side of the anchor plate so that it follows the anchor plate.

When such an anchor device is applied to the drainage material of Patent Document 1, for example, and cast into the ground to be improved, the resistance generated during casting makes it possible to detect that the anchor device has come into contact with the permeable layer. This allows the direction-changing portion of the drainage material located on the underside of the anchor plate to come into contact with the permeable layer.

However, because the area of the direction change portion of the drain material is smaller than that of the anchor plate, if the contact with the permeable layer is not good, the pore water collected from the ground to be improved cannot be efficiently drained into the permeable layer. In order to address this, if an attempt is made to loosen the drain material on the underside of the anchor plate and increase the area of the direction change portion, this loosened direction change portion may be crushed or deformed when it comes into contact with the permeable layer, resulting in breakage. In such cases, the pore water collected by the drain material cannot be smoothly discharged into the permeable layer.

The present invention was developed in consideration of these problems, and its main purpose is to reliably connect the drainage material buried in the soil to be improved to the drainage layer located on the bottom side of the soil to be improved, and to efficiently drain the pore water in the soil to be improved.

In order to achieve this purpose, the anchor member of the present invention is an anchor member that is buried in accumulated soil to be improved and is attached to a drainage material connected to a drainage layer provided on the bottom side of the soil to be improved, and comprises an anchor plate having an insertion portion through which the drainage material is inserted, and a drain shape-retaining member that is arranged to protrude downward from the underside of the anchor plate and that retains the shape of the lower end excess portion of the drainage material located on the lower side of the anchor plate and changes the extension direction when the drainage material is inserted into the insertion portion , and is characterized in that the drain shape-retaining member is inserted into the drainage layer together with the lower end excess portion of the drainage material with the underside of the anchor plate abutting the upper surface of the drainage layer .

The anchor member of the present invention is characterized in that the drain shape retaining member is provided with a contact portion that contacts the lower end excess portion.

The anchor member of the present invention is characterized in that a punch portion is provided at the lower end of the drain shape retaining member, which penetrates the lower end excess portion.

The anchor member of the present invention is characterized in that the drain shape retaining member is provided with a retaining portion that retains the lower end excess portion.

The anchor member of the present invention is provided with a drain shape-retaining member that protrudes downward on the underside of the anchor plate. As a result, when the drain material is inserted into the insertion portion of the anchor plate, the lower end excess portion of the drain material located on the lower side of the anchor plate is held in a shape corresponding to the drain shape-retaining member, and deformation can be suppressed even when an external force is applied.

Therefore, when connecting the drain material buried in the soil to be improved to the drainage layer provided on the bottom side of the soil to be improved, the drain material can be securely connected to the drainage layer by inserting the bottom excess part of the drain material into the drainage layer. This allows the pore water and air in the soil to be improved to be smoothly discharged from the drain material through this bottom excess part into the drainage layer, efficiently promoting the consolidation settlement of the soil to be improved.

In addition, by changing the shape of the drain shape-retaining member, the shape and size of the bottom excess part of the drain material can be easily changed. Therefore, even if it is desired to change the penetration amount or contact area of the bottom excess part in order to allow the pore water and air in the soil to be improved to flow smoothly down into the drainage layer through the drain material, it is possible to easily adjust this using the drain shape-retaining member.

The ground improvement method of the present invention is a method for improving the ground by draining pore water in soil to be improved that has accumulated on a drainage layer into the drainage layer using a drainage material to which the anchor member of the present invention is attached, and is characterized by comprising the steps of inserting the drainage material into the insertion portion of the anchor plate, attaching the anchor member to the drainage material, and providing a lower end excess portion of the drainage material below the anchor member, and casting the drainage material into the soil to be improved, and inserting the lower end excess portion of the drainage material into the drainage layer, thereby connecting the drainage layer to the drainage material.

According to the ground improvement method of the present invention, the bottom excess part of the drain material can be inserted into the drainage layer simply by pouring the drain material into the soil to be improved, and the drain material and the drainage layer can be securely connected. Therefore, it is possible to carry out high-quality ground improvement work without adding special procedures or using new equipment.

When inserting the lower end excess portion into the drainage layer, it is sufficient for the anchor plate of the anchor member to abut against the drainage layer. Therefore, the drainage layer is not disturbed by the anchor plate, making it possible to ensure a clear and sound state at the connection between the drain material and the drainage layer.

Furthermore, even when the entire anchor member is inserted into the drainage layer, the bottom excess portion of the drain material is inserted into the drainage layer before the anchor member, so the drainage layer is not significantly disturbed, at least around the bottom excess portion. Therefore, the pore water in the soil to be improved is not hindered from being discharged from the drain material into the drainage layer.

The ground improvement method of the present invention is characterized by including a step of applying negative pressure to the improvement target soil into which the drainage material has been poured, via the drainage layer and the drainage material.

The ground improvement method of the present invention utilizes a securely connected drainage material and drainage layer to apply negative pressure from below the soil to the entire height direction, making it possible to carry out high-quality ground improvement work efficiently.

According to the present invention, by providing a drain shape-retaining member on the underside of the anchor plate, a bottom excess portion can be formed in the drain material that is located below the anchor member and will not deform even when an external force is applied. This bottom excess portion can be used to reliably connect the drain material cast into the soil to be improved with the drainage layer provided on the bottom side of the soil to be improved, making it possible to efficiently drain pore water and air from the soil to be improved.

FIG. 1 is a diagram showing an outline of ground improvement work using a drain material equipped with an anchor member according to an embodiment of the present invention. FIG. 2 is a diagram showing an outline of a drainage material according to an embodiment of the present invention. FIG. 2 is a diagram showing an outline of a mandrel used when pouring drainage material in an embodiment of the present invention. FIG. 1 is a diagram showing an anchor member equipped with a contact-type drain shape-retaining member in an embodiment of the present invention (part 1). FIG. 2 is a diagram showing an anchor member equipped with a contact-type drain shape-retaining member in an embodiment of the present invention (part 2). FIG. 1 is a diagram showing an anchor member equipped with a penetrating type drain shape-retaining member in an embodiment of the present invention (part 1). FIG. 2 is a diagram showing an anchor member equipped with a penetrating type drain shape-retaining member in an embodiment of the present invention (part 2). FIG. 1 is a diagram showing an anchor member provided with a retaining type drain shape retaining member in an embodiment of the present invention (part 1). FIG. 2 is a diagram showing an anchor member provided with a retaining type drain shape retaining member in an embodiment of the present invention (part 2). FIG. 2 is a diagram showing the procedure of a ground improvement method using a drain material provided with an anchor member in an embodiment of the present invention. FIG. 11 is a diagram showing another example of a ground improvement method according to an embodiment of the present invention.

The present invention is an anchor member to be attached to a drainage material, and a ground improvement method using the drainage material, which are suitable for ground improvement work that uses vacuum pressure or embankment to drain pore water from the ground to be improved, causing consolidation settlement in the ground to be improved, thereby increasing the strength of the ground.

Below, we will explain the details of a method for promoting consolidation by applying negative pressure to the bottom of the soil to be improved in landfill work carried out in marine areas, as an example, with reference to Figures 1 to 11. First, we will provide an overview of the consolidation promotion method, which applies negative pressure to the bottom of the ground to be improved.

<Consolidation promotion method using negative pressure>
As shown in FIG. 1, in a reclaimed land area 10 separated by a concrete embankment E, improvement target soil D is piled up to form a reclaimed land base, and pore water and air are forcibly discharged through a soil drainage device 1.

The soil drainage device 1 is equipped with a water collection facility 2 that collects pore water in the soil D to be improved, and a negative pressure application facility 3 that applies negative pressure to the soil D to be improved via the water collection facility 2. As shown in FIG. 1, the water collection facility 2 is composed of a drainage layer 21 with blocking portions 211a, 211b on the periphery and bottom surface, a horizontal drain 22 embedded in the drainage layer 21, and a vertical drain 23 connected to the drainage layer 21.

The vertical drains 23 are arranged upright in the soil D to be improved that is piled up on the top surface of the drainage layer 21, and when the drainage layer 21 is viewed in a plan view, multiple drains are distributed across the entire surface. Any strip-shaped drainage material that is permeable to moisture and air but can prevent the inflow of soil and sand may be used, and in this embodiment, a deformable strip-shaped board drain is used.

As shown in Figure 2, the board drain is composed of a long core material 23a with multiple grooves formed in the longitudinal direction and a filter material 23b that covers the core material 23a. The filter material 23b is made of a nonwoven fabric or the like that has high water permeability but does not allow granular materials to pass through.

As shown in Figure 1, the vertical drain 23 configured in this way is buried in the soil D to be improved so that it is not exposed to the air, with an airtight cap 233 installed near the upper end. In addition, an anchor member 4 (described later) is attached to the lower end at a height position corresponding to the surface of the drainage layer 21, and the lower end excess portion 231 located below the anchor member 4 is inserted into the drainage layer 21.

The drainage layer 21 is a sand mat made of high-quality sand and has high water permeability. It is laid on the seabed of the landfill area 10 with a certain distance between it and the revetment embankment E. A horizontal drain 22, which is a board drain similar to the vertical drain 23, is buried within the drainage layer 21 so that it is not exposed.

Any material may be used for the drainage layer 21, so long as it has high water permeability, can be laid flat on the upper surface of the ground, and is made of a material into which the lower end excess portion 231 provided near the lower end of the vertical drain 23 can be inserted.

The negative pressure application equipment 3 includes a connecting pipe 31, one end of which is connected to the horizontal drain 22, and a water tank 32, which is connected to the other end of the connecting pipe 31. It also includes a pressure reducing device 33 including a vacuum pump that reduces the pressure inside the water tank 32, and a drainage device 34 including a pump that discharges the interstitial water stored in the water tank 32.

When the pressure inside the water tank 32 is reduced by operating the pressure reducing device 33 and the drainage device 34 in the soil drainage device 1 configured as described above, negative pressure is applied to the entire soil D to be improved from the connecting pipe 31 via the horizontal drain 22, the drainage layer 21, and the vertical drain 23. This allows the interstitial water and air in the soil D to be improved to be efficiently discharged.

To reliably obtain such a ground improvement effect, it is necessary to reliably insert and connect the bottom excess portion 231 of the vertical drain 23 located below the anchor member 4 into the drainage layer 21. Therefore, the anchor member 4 attached to the vertical drain 23 is provided with a drain shape retaining member 6 that maintains the shape of the bottom excess portion 231. Details of the anchor member 4 are described below.

<Anchor parts>
As shown in Figure 3, the anchor member 4 comprises an anchor plate 5 of a size that can be contacted by the tip of a mandrel 7 used when casting the vertical drain 23 into the soil D to be improved, and a drain shape-retaining member 6 provided on the underside of the anchor plate 5.

As shown in FIG. 4(a), the anchor plate 5 is made of a flat plate material such as a steel plate, and in the middle of it, a pair of slits 51a, 51b are formed parallel to each other with a gap between them, through which the vertical drain 23 can be inserted. The drain shape-retaining member 6 is provided between the pair of slits 51a, 51b so as to protrude downward from the bottom surface of the anchor plate 5.

When attaching an anchor member 4 of this shape to the vertical drain 23, the vertical drain 23 is inserted into one of the slits 51a from the top side of the anchor plate 5. Then, the side of the vertical drain 23 comes into contact with the drain shape retaining member 6, and the extension direction of the vertical drain 23 is changed using this drain shape retaining member 6.

Then, the redirected vertical drain 23 is inserted into the other slit 51b from the underside of the anchor plate 5. In this way, the vertical drain 23 is attached to the anchor member 4 by moving it back and forth across the anchor plate 5 using the pair of slits 51a, 51b. In addition, the bottom end excess portion 231 of the vertical drain 23 located below the anchor member 4 is kept in an approximately U-shape by the drain shape retaining member 6.

In this way, the lower end excess portion 231 of the vertical drain 23 is maintained in a shape corresponding to the drain shape-retaining member 6, and deformation is suppressed even when an external force is applied. Therefore, to connect the drainage layer 21 and the vertical drain 23, as shown in Figure 4 (b), the lower end of the mandrel 7 is abutted against the upper surface of the anchor plate 5 and a pressing force is applied, so that the vertical drain 23 is cast into the improvement target ground D1.

Then, the casting work is stopped when the anchor plate 5 abuts against the drainage layer 21. Then, the lower end excess portion 231 of the vertical drain 23 located below the anchor plate 5 is securely inserted into the drainage layer 21 while its shape is maintained by the drain shape retaining member 6, and a connection structure is formed between the vertical drain 23 and the drainage layer 21.

In this way, the bottom excess portion 231 of the vertical drain 23 is securely inserted into the drainage layer 21, making the connection between the two clear. This allows the interstitial water and air in the improvement target soil D to be smoothly discharged from the vertical drain 23 through this bottom excess portion 231 into the drainage layer 21. This makes it possible to efficiently proceed with the consolidation drainage of the improvement target soil D.

The shape and size of the bottom excess portion 231 of the vertical drain 23 can be easily changed by changing the shape of the drain shape retaining member 6. Therefore, it is possible to appropriately adjust the penetration amount and contact area of the bottom excess portion 231 with respect to the drainage layer 21 using the drain shape retaining member 6 so that the pore water and air in the soil D to be improved can smoothly flow down through the vertical drain 23 into the drainage layer 21.

Therefore, for the drain shape-retaining member 6, examples of the shape and the connection with the vertical drain 23 are classified into three types: a contact type that contacts the lower end excess portion 231, a penetration type that partially penetrates the lower end excess portion 231, and a retention type that retains the lower end excess portion 231, and are explained below.

<Drain shape retaining material: Contact type>
4(a) and 4(b), a box is used as the drain shape-retaining member 6 and is fixed to the underside of the anchor plate 5. In this case, the outer peripheral edge of the drain shape-retaining member 6 becomes the contact portion 61 with the bottom end excess portion 231. Therefore, by preparing a plurality of boxes of different sizes and shapes in advance and replacing them as appropriate, it is possible to change the shape of the bottom end excess portion 231 and appropriately adjust the penetration amount and contact area of the bottom end excess portion 231 with the drainage layer 21.

The box functioning as the drain shape-retaining member 6 may be formed by processing a steel plate, or a reinforcing bar cage may be used. Furthermore, the shape is not limited to a rectangular parallelepiped, and it may be formed into a three-dimensional shape such as a square column or pyramid, or a thin plate-like member may be used.

In addition, if you want to reduce the resistance to penetration when the lower end excess portion 231 of the vertical drain 23 penetrates into the drainage layer 21, it is advisable to form the lower end shape of the drain shape retaining member 6 into a curved surface, for example, as shown in Figures 5 (a) and (b).

In FIG. 5(a), multiple cylindrical bodies in a recumbent position are bundled together to form the drain shape-retaining member 6. In this way, the lower end portion that forms the contact portion 61 with the lower end excess portion 231 is curved, which reduces the resistance when inserted into the drainage layer 21.

The cylinder can be made of PVC pipes, steel pipes, or the like that are commonly available on the market. This makes it economical and also makes it possible to reduce weight. Furthermore, since the cut length and the number of pieces to be bundled can be changed as needed, the length and shape of the lower end excess portion 231 can be freely changed, and the penetration amount and contact area of the lower end excess portion 231 with respect to the drainage layer 21 can be easily adjusted.

In FIG. 5(b), the anchor plate 5 itself is bent so that the lower end portion, which is the contact portion 61 with the lower end excess portion 231, forms a gentle convex portion to form the drain shape-retaining member 6. This makes it possible to omit the cumbersome task of separately preparing the drain shape-retaining member 6 and fixing it to the anchor plate 5.

Furthermore, as shown in FIG. 5(c), multiple bolts may be used as the drain shape-retaining member 6. In this case, a bolt may be attached to each of the multiple through holes provided in the anchor plate 5, and a channel steel may be provided at the tip of the bolt to form the contact portion 61 with the lower end excess portion 231. In this way, the amount of sagging of the bolt relative to the anchor plate 5 can be appropriately changed at the construction site, and the amount of penetration and contact area of the lower end excess portion 231 relative to the drainage layer 21 can be adjusted.

<Drain shape retaining member: through type>
6(a), a triangular prism in a recumbent position is used as the drain shape-retaining member 6, and this is fixed to the lower surface of the anchor plate 5. In this case, the lower end portion of the drain shape-retaining member 6 (the side wall corner portion of the triangular prism) functions as a punch portion 62 that penetrates the lower end excess portion 231.

In other words, as shown in FIG. 6(b), when the vertical drain 23 is cast into the soil D to be improved, the lower end excess portion 231 before being inserted into the drainage layer 21 only comes into contact with the drain shape retaining member 6 and forms an approximately U-shape. However, when the anchor plate 5 is cast until it abuts against the drainage layer 21, the resistance of the drain shape retaining member 6 and the lower end excess portion 231 when inserted into the drainage layer 21 causes the punch portion 62 to penetrate the middle of the vertical drain 23 in the width direction.

As a result, part of the bottom excess portion 231 is damaged, but its shape is maintained. The damaged portion 232 in the bottom excess portion 231 functions as a water path that allows the interstitial water of the improvement target soil D collected by the vertical drain 23 to flow down to the drainage layer 21. The punch portion 62 provided in the drain shape retaining member 6 should be formed to be shorter than the width of the vertical drain 23. This is to prevent the bottom excess portion 231 from being cut by the punch portion 62.

As the drain shape-retaining member 6 provided with the punch portion 62, for example, as shown in FIG. 7(a), a number of bolts may be used that are screwed into bolt holes provided in the anchor plate 5, and the tips of these bolts may function as the punch portion 62 to create a damaged portion 232 in the lower end excess portion 231. Alternatively, as shown in FIG. 7(b), when the anchor plate 5 itself is bent to form the drain shape-retaining member 6, the lower end may be formed into an acute-angled protrusion that functions as the punch portion 62. The punch portion 62 may then create a damaged portion 232 in the lower end excess portion 231.

<Drain shape retention material: retention type>
In Fig. 8(a), a box having a hole through which the vertical drain 23 can pass is used as the drain shape-retaining member 6, and is fixed to the underside of the anchor plate 5. In this case, the hole through which the vertical drain 23 can pass functions as a retaining portion 63 for the vertical drain 23. In Fig. 8(b), a plurality of cylindrical bodies in a recumbent position are bundled together to form the drain shape-retaining member 6, and gaps through which the vertical drain 23 can pass are provided between the cylindrical bodies, and these function as retaining portions 63.

In this way, as shown in Figures 8(a) and (b), the vertical drain 23 penetrates the pair of slits 51a, 51b and the retaining portion 63, thereby maintaining the shape of the bottom excess portion 231. Then, in this state, as shown in Figure 8(c), when the vertical drain 23 is cast into the soil D to be improved until the anchor plate 5 also abuts the drainage layer 21, the bottom end of the drain shape retaining member 6 is inserted first into the drainage layer 21, making it possible to protect the bottom excess portion 231 of the vertical drain 23.

In addition, in any of the above contact type, penetration type, and retention type drain shape retaining members 6, the drain shape retaining members 6 can be installed on the anchor plate 5 via hinge members 64, as shown in FIG. 9(a). FIG. 9(a) shows an example of a drain shape retaining member 6 provided with a retention portion 63.

In this case, as shown in FIG. 9(b), when the vertical drain 23 is cast, the anchor plate 5 is cast in an inclined state in the soil D to be improved. This reduces the casting resistance compared to casting with the anchor plate 5 held horizontally, making the casting work of the vertical drain 23 easier.

When a pressing force is applied through the mandrel 7 in this state, the drain shape retaining member 6 of the anchor member 4 is inserted into the drainage layer 21 first, and then a part of the anchor plate 5 reaches the surface of the drainage layer 21. The inclined anchor plate 5 rotates through the hinge member 64 due to the resistance of the drainage layer 21, and becomes horizontal on the drainage layer 21.

<Ground improvement method>
The procedure for carrying out ground improvement work using the vertical drain 23 equipped with the above-mentioned anchor member 4 will be described below with reference to Figures 3, 4 and 10, along with a method for casting the vertical drain 23.

As shown in FIG. 10(a), a drainage layer 21 with a horizontal drain 22 buried therein is laid in a reclaimed area 10 having a closed portion 211b made of seabed ground, and a water tank 32 is installed along the inner wall surface of the revetment embankment E, and the horizontal drain 22 and the water tank 32 are connected via a connecting pipe 31. Before or after this, or at the same time, a pressure reducing device 33 and a drainage device 34 are installed in the water tank 32, and a soil drainage device 1 is constructed. After this, the soil D to be improved is dropped on the top surface of the drainage layer 21 to cover the entire surface of the drainage layer 21, and the negative pressure application equipment 3 is operated. In this way, the pressure inside the water tank 32 is reduced and the drainage device 34 is operated to pump up the interstitial water drained into the water tank 32.

The work of piling such improvement target soil D on the drainage layer 21 and the work of forcibly sucking and draining the pore water of the piled improvement target soil D are started almost simultaneously, and thereafter, both work is carried out in parallel. When the piled improvement target soil D reaches a predetermined height, the work of piling the improvement target soil D is temporarily stopped, and a vertical drain 23 is installed at a predetermined position in the improvement target soil D.

<How to pour drainage material>
When the vertical drain 23 is cast, as shown in Fig. 3, the vertical drain 23 is inserted into the upright mandrel 7 while being unwound from the reel 71. Then, the anchor member 4 described above is attached to the vertical drain 23 near the lower end of the mandrel 7. As a result, a lower end excess portion 231 of the vertical drain 23, whose shape is maintained by the drain shape-retaining member 6, is provided below the anchor member 4.

After this, as shown in FIG. 4(b), for example, a pressing force is applied via the mandrel 7 that abuts against the upper surface of the anchor plate 5, and the vertical drain 23 is cast into the soil D to be improved. When the anchor plate 5 comes into contact with at least the upper surface of the drainage layer 21, the casting operation is terminated, and the mandrel 7 is pulled out while leaving the vertical drain 23 and anchor member 4 in place. In addition, an airtight cap 233 is provided at the upper end of the vertical drain 23.

As a result, as shown in FIG. 10(b), the lower end excess portion 231 of the vertical drain 23 located below the anchor member 4 is inserted into the drainage layer 21 while its shape is maintained by the drain shape retaining member 6. In addition, the drainage layer 21 is not disturbed by the anchor member 4. Therefore, it is possible to ensure a clear and sound state at the connection between the vertical drain 23 and the drainage layer 21.

Even when the entire anchor member 4 is inserted into the drainage layer 21, the lower end excess portion 231 of the vertical drain 23 is inserted into the drainage layer 21 first, so the drainage layer 21 is not significantly disturbed, at least around the lower end excess portion 231. Therefore, the behavior of the pore water and air in the improvement target soil D being discharged from the vertical drain 23 into the drainage layer 21 is not hindered.

The above procedure is repeated to cast the vertical drains 23. After all the planned vertical drains 23 have been cast, dumping of the improvement target soil D is resumed. Alternatively, dumping of the improvement target soil D is resumed in parallel with the casting work. In this way, the improvement target soil D is piled up until the top ends of the vertical drains 23 are completely buried, as shown in Figure 1.

The dumping operation is terminated when the soil D to be improved reaches the desired height, but the pressure reducing device 33 and drainage device 34 of the negative pressure application equipment 3 are operated until the settlement of the soil D to be improved is stopped or the amount of settlement falls below a predetermined value.

As described above, according to the ground improvement method using the vertical drain 23 equipped with the anchor member 4, by casting the vertical drain 23 into the soil D to be improved, the lower end excess portion 231 of the vertical drain 23 can be inserted into the drainage layer 21, and the vertical drain 23 and the drainage layer 21 can be securely connected. Therefore, it is possible to carry out high-quality ground improvement work without adding special procedures or using new equipment.

The anchor member 4 and ground improvement method of the present invention are not limited to the above embodiment, and various modifications are possible without departing from the spirit of the present invention.

In this embodiment, the example is given of a case where the method is used for new landfill work carried out in marine areas, but the present invention is not limited to this, and the method can also be used for existing reclaimed land or ground improvement work carried out on land. Therefore, the soil D to be improved can be any of dredged soil generated during dredging work, soil and sand generated during underground excavation, construction waste soil generated during construction work, muddy materials such as construction sludge and sludge, soil and sand mixtures containing soil and sand, etc.

The drainage layer 21 is not limited to being newly laid, and may be used, for example, if there is a naturally deposited sand layer that can function as a drainage layer, or if a drainage layer laid in a previous construction project exists in a reusable state.

In addition, in this embodiment, the pair of slits 51a, 51b provided in the anchor plate 5 are used as the insertion portion for the vertical drain 23, but this is not limited to this. Any number of slits is acceptable as long as the vertical drain 23 can be inserted, and the shape is not limited to a groove hole, but may be formed by cutting out the anchor plate 5.

In addition, in this embodiment, a case where negative pressure is applied to the soil D to be improved is given as an example of a ground improvement method, but this is not necessarily limited to this. For example, it can also be adopted as a ground improvement method for promoting consolidation settlement by loading an embankment, as shown in Figure 11, to strengthen the ground.

In this case, the lower drainage layer 11 is laid, and then the soil D to be improved is dropped and piled up so as to cover it. When the soil D to be improved reaches a predetermined height, the vertical drain 23 to which the anchor member 4 is attached is cast into the soil D to be improved using the mandrel 7 described above. When the anchor plate 5 abuts against the upper surface of the drainage layer 21, the casting operation is terminated, and the mandrel 7 is pulled out, leaving the vertical drain 23 and anchor member 4 in place. As a result, the lower end excess portion 231 of the vertical drain 23 is inserted into the lower drainage layer 11, and the vertical drain 23 and the lower drainage layer 11 are securely connected.

Then, the upper drainage layer 12 is laid so as to cover the top surface of the improvement target soil D, and the vicinity of the upper end of the vertical drain 23 exposed above the improvement target soil D is bent and buried in the upper drainage layer 12 together with the horizontal drain 22. As a result, the upper part of the vertical drain 23 is connected to the upper drainage layer 12, and the lower part is securely connected to the lower drainage layer 11 via the lower end excess part 231.

In this state, embankment 13 is constructed on the upper drainage layer 12 and loaded onto the improvement target soil D. Then, the interstitial water in the improvement target soil D is collected in the vertical drain 23, and then efficiently drained via the upper drainage layer 12 and the lower drainage layer 11. This makes it possible to increase the strength of the ground made of the improvement target soil D efficiently and with high quality, compared to conventional ground improvement work using embankment loading.

1 Soil drainage device 2 Water collection equipment 21 Drainage layer 211a Blocking portion 211b Blocking portion 22 Horizontal drain 221 Core material 23 Vertical drain (drain material)
23a Core material 23b Filter material 231 Lower end excess portion 232 Broken portion 233 Airtight cap 3 Negative pressure application device 31 Connecting pipe 32 Water tank 33 Pressure reducing device 34 Drainage device 4 Anchor member 5 Anchor plate 51a Slit (insertion portion)
51b Slit (insertion part)
6 Drain shape retaining member 61 Contact portion 62 Punch portion 63 Holding portion 7 Mandrel 71 Reel

10 Reclaimed area 11 Lower drainage layer 12 Upper drainage layer 13 Embankment D Improvement target soil E Revetment embankment

Claims (6)

An anchor member that is buried in accumulated soil to be improved and attached to a drainage material connected to a drainage layer provided on the bottom side of the soil to be improved,
An anchor plate having an insertion portion through which the drain material is inserted;
The anchor plate is provided so as to protrude downward from a lower surface side of the anchor plate,
A drain shape retaining member that retains the shape of the lower end excess portion of the drain material located below the anchor plate and changes the extending direction when the drain material is inserted into the insertion portion,
An anchor member characterized in that the drain shape-retaining member is inserted into the drainage layer together with the lower end excess portion of the drainage material with the lower surface of the anchor plate abutting the upper surface of the drainage layer . The anchor member according to claim 1,
An anchor member, characterized in that the drain shape-retaining member is provided with a contact portion that contacts the lower end excess portion. The anchor member according to claim 1,
An anchor member, characterized in that a punch portion is provided at the lower end of the drain shape-retaining member, the punch portion penetrating the lower end excess portion. The anchor member according to claim 1,
An anchor member, characterized in that the drain shape-retaining member is provided with a retaining portion for retaining the lower end excess portion. A ground improvement method for performing ground improvement by draining interstitial water of soil to be improved deposited on a drainage layer into the drainage layer using a drainage material equipped with the anchor member according to any one of claims 1 to 4,
a step of inserting the drain material through the insertion portion of the anchor plate, attaching the anchor member to the drain material, and providing a lower end excess portion of the drain material below the anchor member;
A step of pouring the drainage material into the soil to be improved and inserting a lower end excess portion of the drainage material into the drainage layer to connect the drainage layer and the drainage material;
A ground improvement method comprising: The ground improvement method according to claim 5,
A ground improvement method comprising the step of applying negative pressure to the improvement target soil into which the drainage material has been poured, via the drainage layer and the drainage material.

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