Ground improvement method and drain material assembly

Abstract

This ground improvement method offers the advantages of conventional vacuum consolidation drain methods while enabling the improvement of geological formations that were difficult to improve with conventional methods. [Solution] The ground improvement method uses a drain material assembly 1 that is driven vertically into the ground. The drain material assembly 1 comprises a first drain material 2, a second drain material 6, an airtight cap 3 provided on one end of the first drain material 6, and a drain hose 4 connected to the airtight cap 3. The second drain material 6 is connected to the other end of the first drain material 2 via a connecting part 5. The drain material assembly 1 is driven such that the upper end of the second drain material 6 is positioned in the uppermost intermediate sand layer 91a at the point where the drain material assembly 1 is driven, and the lower end of the first drain material is positioned in the improved layer 92a above the intermediate sand layer 91a.

Description

Technical Field

[0001] The present invention relates to a ground improvement method for improving soft ground and a drain material assembly used in the ground improvement method.

Background Art

[0002] The vertical drain method is widely used as a ground improvement method for improving soft ground. A typical example is the prefabricated vertical drain (PVD) method. In the PVD method, a large number of long drain materials composed of a core material and a water-permeable filter covering it are vertically driven into the ground, and then embankment is applied to the ground surface. The excess pore water pressure generated by the load of the embankment acts, and the pore water in the improved layer in the ground is discharged through the drain material, thereby promoting the consolidation of the ground.

[0003] The vacuum consolidation drain method (see Patent Document 1) is known as a type of PVD method, and is characterized in that drainage from the improved layer is promoted by applying or propagating negative pressure into the ground through the drain material. For this purpose, an airtight cap for connecting one end of the drainage hose and the drain material is provided at the upper end of the drain material, and the other end side of the drainage hose is connected to a decompression means such as a vacuum pump. According to the vacuum consolidation drain method, in addition to promoting the consolidation of the ground, the amount of embankment can be reduced or the need for embankment can be eliminated, thereby shortening the construction period.

[0004] In the vacuum consolidation drain method, if the installed drain material passes through a sand layer (intermediate sand layer) in the ground, a large amount of water is drawn up primarily from that sand layer, which can lower the groundwater level in the area surrounding the construction site and cause ground subsidence in the surrounding area. Furthermore, in such cases, negative pressure does not act on the drain material in the improved layer below the intermediate sand layer (usually a clay layer), and the improvement does not progress. For this reason, in the vacuum consolidation drain method, a waterproof seal (corresponding to the airtight portion 11d in paragraphs

[0053] and

[0054] of Patent Document 1) corresponding to the intermediate sand layer is provided on the drain material. The length of the waterproof seal is made longer than the thickness of the intermediate sand layer, and usually the waterproof seal extends about 1 meter upward from the top surface of the intermediate sand layer and about 1 meter downward from the bottom surface of the intermediate sand layer, thereby securing a negative pressure seal layer with a thickness of about 1 meter above and below the intermediate sand layer.

[0005] Furthermore, in the vacuum consolidation drain method, a negative pressure sealing layer must be secured at both the upper and lower ends of the drain material to ensure the inflow of pore water from the improved layer into the drain material. For this reason, the upper end of the drain material is usually positioned about 1 meter below the ground, and the lower end of the drain material is usually positioned about 1 meter above the unimproved layer (which is the sand or gravel layer). [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2006-241872 [Overview of the project] [Problems that the invention aims to solve]

[0007] In the vacuum consolidation drain method, if the gap between the unimproved layer and the intermediate sand layer above it is narrow, the improvement of the improved layer between them may not progress. For example, in a situation where the intermediate sand layer is located about 2.5 meters above the top surface of the unimproved layer, in addition to providing a negative pressure seal layer about 1 meter thick from the top surface of the unimproved layer, it is also necessary to provide a waterproof seal extending about 1 meter downward from the bottom surface of the intermediate sand layer as a countermeasure against the intermediate sand layer. As a result, the portion of the improved layer (2.5 meters thick) directly above the unimproved layer where the drain material is exposed (the portion into which pore water flows) will be about 0.5 meters. A similar situation can occur when the gap between intermediate sand layers flanking a certain improved layer is narrow.

[0008] Furthermore, in the vacuum consolidation drain method, in alternating layers of sand and clay, a waterproof seal is provided over all or a significant portion of the drain material passing through the alternating layers. Therefore, it is generally difficult to improve alternating layers using the vacuum consolidation drain method.

[0009] The present invention solves these problems and provides a ground improvement method that allows users to enjoy the advantages of conventional vacuum consolidation drain methods while enabling the improvement of geological formations that were difficult to improve with conventional vacuum consolidation drain methods, as well as a drain material assembly used in said ground improvement method. [Means for solving the problem]

[0010] The present invention relates to a ground improvement method using a drain material assembly, The aforementioned drain material assembly is The first drain material, An airtight cap is provided at the upper end of the first drain material, The drain hose connected to the aforementioned airtight cap, A second drain material is connected to the lower end of the first drain material via a connecting part, It is equipped with, The drain material assembly is driven into the ground in a vertical direction, Applying negative pressure to the first drain material via the aforementioned drain hose, The aforementioned ground is to be filled with soil, It includes, The drain material assembly is cast such that the upper end of the second drain material is positioned in the uppermost intermediate sand layer at the casting site of the drain material assembly, and the lower end of the first drain material is positioned in the improved layer above the intermediate sand layer. Alternatively, the drain material assembly is cast such that the upper end of the second drain material is positioned in the only intermediate sand layer present between the lower end of the second drain material and the ground surface at the casting site of the drain material assembly, and the lower end of the first drain material is positioned in the improved layer above the only intermediate sand layer.

[0011] In the present invention, the drain material assembly may be cast such that the lower end of the second drain material is placed in a supporting layer which is a sand layer or a gravel layer.

[0012] In the present invention, the connecting portion includes one or more flexible strip-shaped or plate-shaped members, one end of the one or more strip-shaped or plate-shaped members may be fixed directly to the first drain material or via an intermediate member, and the other end of the strip-shaped or plate-shaped member may be fixed directly to the second drain material or via an intermediate member.

[0013] In the present invention, the connecting portion includes one or more ropes, one end of the one or more ropes is fixed directly to the first drain material or via an intermediate member, and the other end of the strip-shaped or plate-shaped member is fixed directly to the second drain material or via an intermediate member.

[0014] In the present invention, the first drain material may comprise a core material and a water-permeable filter attached to the core material.

[0015] In this invention, the lower end of the first drain material may be closed or sealed.

[0016] In the present invention, the second drain material may comprise a core material and a water-permeable filter attached to the core material.

[0017] The drain material assembly of the present invention is a drain material assembly used in the above-described ground improvement method, and the connecting portion is configured not to guide the water flowing upward into the second drain material to the first drain material.

[0018] The drain material assembly of the present invention is a drain material assembly used in the above-described ground improvement method, and the connecting portion does not define a closed space connecting the water channel in the second drain material to the water channel in the first drain material.

Advantages of the Invention

[0019] According to the present invention, while enjoying the advantages of the conventional vacuum consolidation drain method, it becomes possible to improve the ground layer that was difficult to improve with the conventional vacuum consolidation drain method.

Brief Description of the Drawings

[0020] [Figure 1] FIG. 1 is a front view showing an overview of a drain material assembly according to an embodiment of the present invention. [Figure 2] FIG. 2 is an explanatory view showing an overview of a drain material included in a drain material assembly according to an embodiment of the present invention. [Figure 3] FIG. 3 is an explanatory view showing a first example in which a first drain material and a second drain material are connected via a connecting portion in a drain material assembly according to an embodiment of the present invention. [Figure 4] FIG. 4 is an explanatory view showing a second example in which a first drain material and a second drain material are connected via a connecting portion in a drain material assembly according to an embodiment of the present invention. [Figure 5] FIG. 5 is an explanatory view showing a third example in which a first drain material and a second drain material are connected via a connecting portion in a drain material assembly according to an embodiment of the present invention. [Figure 6]Figure 6 is an explanatory diagram showing a fourth example in which a first drain material and a second drain material are connected via a connecting portion in a drain material assembly, which is an embodiment of the present invention. [Figure 7] Figure 7 shows an assembly roll, which is composed of a drain material assembly according to an embodiment of the present invention, in an unfolded state. [Figure 8] Figures 8(a) to 8(d) are explanatory diagrams illustrating the outline of the process of installing the drain material assembly of the present invention into the ground in the ground improvement method of the present invention. [Figure 9] Figure 9 is an explanatory diagram showing an overview of the ground improvement method of the present invention. [Figure 10] Figure 10 is an explanatory diagram showing the first case of ground improvement using the conventional vacuum consolidation drain method. [Figure 11] Figure 11 is an explanatory diagram showing a first case of ground improvement using the ground improvement method of the present invention. [Figure 12] Figure 12 is an explanatory diagram showing a second case of ground improvement using the conventional vacuum consolidation drain method. [Figure 13] Figure 13 is an explanatory diagram showing a second case of ground improvement using the ground improvement method of the present invention. [Modes for carrying out the invention]

[0021] Embodiments of the present invention will be described below with reference to the figures. Figure 1 is a front view showing an overview of a drain material assembly 1 according to an embodiment of the present invention. The drain material assembly 1 comprises a first drain material 2, a drain hose 4 connected to one end or upper end of the first drain material 2 via an airtight cap 3, and a second drain material 6 connected to the other end or lower end of the first drain material 2 via a connecting part 5. In the following description, unless otherwise specified, the description of the operation of the drain material assembly 1 assumes that the drain material assembly 1 is driven vertically into the ground and ground improvement is carried out.

[0022] Figure 2 is an explanatory diagram showing an overview of the first drain material 2. The first drain material 2 is commonly used in PVD construction and comprises a long, plate-shaped plastic core material 21 and a pair of strip-shaped water-permeable filters 23 fixed to sandwich the core material 21. On both sides of the core material 21, shallow grooves 25 and deep grooves 27 are formed along its length and are arranged alternately in the width direction of the core material 21.

[0023] The core material 21 is formed from, for example, a polyolefin-based synthetic resin such as polyethylene resin or polypropylene resin, or a synthetic resin such as polyvinyl chloride. The permeable filter 23 uses a fabric made of synthetic fibers such as polyester synthetic fibers or polypropylene synthetic fibers. For example, the width of the first drain material 2 is about 10 to 15 cm, and the thickness of the first drain material 2 is about 3 to 8 mm. The core material 21 may be formed from a biodegradable resin such as polylactic acid resin, and the permeable filter 23 may use a fabric made of biodegradable fibers such as polylactic acid fibers.

[0024] In the first drain material 2 shown in Figure 2, a pair of strip-shaped water-permeable filters 23 are attached to each main surface side of the core material 21. However, a single water-permeable filter may be attached to the core material 21 by wrapping around it, or multiple water-permeable filters may be attached to the main surface of the core material 21.

[0025] The second drain material 6 may be constructed in the same manner as the first drain material 2. However, in the present invention, the first drain material 2 and the second drain material 6 do not need to be the same, and the shape and material of the core material 21, the configuration and material of the water permeable filter 23, etc., may differ between the first drain material 2 and the second drain material 6.

[0026] Referring again to Figure 1, the first drain material 2, airtight cap 3, and drain hose 4 constitute a so-called capped drain material used in conventional vacuum consolidation drainage methods. The airtight cap 3 is made of synthetic resin such as polyvinyl chloride, polyethylene, or polypropylene, and the drain hose 4 is made of synthetic resin such as polyvinyl chloride. The airtight cap 3 has a rectangular cylindrical part into which the end of the first drain material 2 is fitted and a cylindrical part into which one end of the drain hose 4 is fitted, and the internal spaces of the rectangular cylindrical part and the cylindrical part are connected (see, for example, the airtight cap 12 in Figure 3 of Patent Document 1). One end of the first drain material 2 is inserted into the rectangular cylindrical part of the airtight cap 3, and one end of the drain hose 4 is inserted into the cylindrical part of the airtight cap 3. The first drain material 2 and the drain hose 4 are airtightly fixed to the airtight cap 3 using, for example, adhesive tape or adhesive.

[0027] A key feature of the drain material assembly 1 of the present invention is that the connecting portion 5 does not guide the flow of water from the second drain material 6 to the first drain material 2, nor is it configured to do so. Alternatively, in the drain material assembly 1 of the present invention, the connecting portion 5 does not define a closed space connecting the water channel in the second drain material 6 to the water channel in the first drain material 2. Therefore, pore water that enters the second drain material 6 from underground does not flow from the second drain material 6 through the connecting portion 5 to the first drain material 2. In the drain material assembly 1 of the present invention, similar to general PVD methods, pore water that flows into the second drain material 6 from underground flows through the water channel in the second drain material 6 and is then discharged from the second drain material 6 into the underground drainage layer.

[0028] In other words, in the drain material assembly 1 of the present invention, the connecting portion 5 is a component provided for the purpose of connecting one end of the first drain material 2 and one end of the second drain material 6 while the two ends are separated by a predetermined distance. For example, the connecting portion 5 includes one or more flexible strip-shaped or plate-shaped members, one end of which is fixed to the first drain material 2 directly or via an intermediate member, and the other end of which is fixed to the second drain material 6 directly or via an intermediate member. Alternatively, the connecting portion 5 includes one or more ropes, one end of which is fixed to the first drain material 2 directly or via an intermediate member, and the other end of which is fixed to the second drain material 6 directly or via an intermediate member.

[0029] Figure 3 is an explanatory diagram showing an example in which the first drain material 2 and the second drain material 6 are connected via a connecting portion 5. The first drain material 2 and the second drain material 6 are configured similarly as shown in Figure 2. In this example, the connecting portion 5 is made of a rectangular thin plate 51, one end of which is fixed to the main surface of the first drain material 2, and the other end of which is fixed to the main surface of the second drain material 6. The first drain material 2 and the second drain material 6 are fixed to the same main surface of the thin plate 51, and for example, in Figure 3, the first drain material 2 is not fixed to the upper surface of the thin plate 51 and the second drain material 6 is not fixed to the lower surface of the thin plate 51.

[0030] The thin plate 51 is fixed directly (i.e., without an intermediate member) to the first drain material 2 or the second drain material 6 using, for example, staples or adhesive. The width of the thin plate 51 is made to be approximately the same as the width of the first drain material 2 and the second drain material 6, and the first drain material 2, the second drain material 6, and the connecting part 5 are arranged so that their centerlines are aligned. To avoid obstructing the pouring of the drain material assembly 1, it is desirable to make the thin plate 51 as thin as possible and to minimize the step difference between it and the first drain material 2 and the second drain material 6. In addition, if necessary, both ends of the thin plate 51 may be chamfered to form a slope leading to the first drain material 2 or the second drain material 6.

[0031] To prevent mud and sand from entering the first drain material 2 and clogging the flow path, the lower end of the first drain material 2, i.e., the end on the connecting portion 5 side, is closed or sealed. In the example shown in Figure 3, at the lower end of the first drain material 2, the water channel within the first drain material 2, defined by the core material 21 and the permeable filter 23, is sealed with a sealing material 29. For example, a silicone-based sealing material is used as the sealing material 29, but other types of sealing materials may also be used.

[0032] For reasons to be described later, it is desirable that the main body portion of the connecting portion 5 of the drain material assembly 1 of the present invention, in this example the thin plate 51, be flexible. The material forming the connecting portion 5 is a synthetic resin such as polyethylene resin or polypropylene resin, but the material forming the connecting portion 5 is not limited as long as the effects of the present invention are obtained, and may be natural rubber, nonwoven fabric, woven fabric, paper, etc. In addition, the connecting portion 5 may be made of a flexible metal sheet such as aluminum.

[0033] Figure 4 is an explanatory diagram showing another example in which the first drain material 2 and the second drain material 6 are connected via a connecting portion 5. In the example shown in Figure 4, the thin plate 51 is provided with a first ramp portion 53 that provides an inclined surface connecting one main surface of the first drain material 2 and one main surface of the connecting portion 5, and a second ramp portion 55 that provides an inclined surface connecting the main surface of the connecting portion 5 and one main surface of the second drain material 6. The first ramp portion 53 and the second ramp portion 55 are formed on the main surface of the connecting portion 5 by, for example, solidifying a filler such as putty or an adhesive such as hot melt. Alternatively, pre-formed triangular prism-shaped resin members as the first ramp portion 53 and the second ramp portion 55 may be bonded to the connecting portion 5 with adhesive or double-sided tape.

[0034] By providing the first ramp section 53 and the second ramp section 55, the step difference caused by the end of the first drain material 2 and the end of the second drain material 6 is eliminated. This allows the drain material assembly 1 to be poured smoothly. In addition, by providing the first ramp section 53, the lower end of the first drain material 2, i.e., the end on the connecting section 5 side, is closed, preventing mud and sand from entering the first drain material 2 and clogging the flow path.

[0035] In the examples shown in Figures 3 and 4, the connecting portion 5 includes one thin plate 51, but the connecting portion 5 may also consist of multiple thin plates arranged in parallel (narrower in width than the thin plate 51). Alternatively, a strip-shaped member made of fabric or the like may be used instead of each of these thin plates or the thin plate 51. Furthermore, the plate-shaped member such as the thin plate 51 that constitutes the main body of the connecting portion 5, or a strip-shaped member that replaces it, may be fixed to the first drain material 2 or the second drain material 6 via an intermediate member. Such an intermediate member may be, for example, a gripping member into which the ends of the first drain material 2 or the second drain material 6 fit, and provided at both ends of the thin plate 51.

[0036] Figure 5 is an explanatory diagram showing how the first drain material 2 and the second drain material 6 are connected using a connecting part 5 which has a core material 57 of the drain material as its main body. For example, the core material 57 may be made of the same material as the core material 21 of the first drain material 2 and the second drain material 6. This reduces costs. However, the core material 57 used in the connecting part 5 may have a different cross-sectional shape from the core material 21, and its width, thickness, etc. may differ from those of the core material 21.

[0037] The first joint 59 and the second joint 61 are, for example, rectangular tubes made of synthetic resin or sleeves made of fabric. One end of the first drain material 2 is inserted and fixed to one end of the first joint 59, and one end of the core material 57 is inserted and fixed to the other end of the first joint 59. Similarly, one end of the second drain material 6 is inserted and fixed to one end of the second joint 61, and the other end of the core material 57 is inserted and fixed to the other end of the second joint 61. The core material 57 or the first drain material 2 is fixed to the first joint 59, and the core material 57 or the second drain material 6 is fixed to the second joint 61, for example, using staples or adhesive. As in the example shown in Figure 3, the lower end of the first drain material 2 is sealed with sealant 29.

[0038] Figure 6 is an explanatory diagram showing how the first drain material 2 and the second drain material 6 are connected using a single rope 63 as a connecting part 5. The end of the rope 63 is fixed to the first drain material 2 or the second drain material 6, for example, using staples. Multiple ropes arranged in parallel may be used instead of the rope 63. Similar to the example shown in Figure 3, the lower end of the first drain material 2 is sealed with a sealing material 29. The rope 63 is made of synthetic fibers such as nylon (registered trademark) or polyester, for example, but the material of the rope 63 is not limited in this invention. In addition, the rope 63 or multiple ropes that replace it may be fixed to the first drain material 2 or the second drain material 6, for example, via an intermediate member to which their ends are tied.

[0039] In the examples shown in Figures 3 to 6, the thin plate 51, the first joint 59, the second joint 61, or the rope 63 constituting the connecting portion 5 were joined to the first drain material 2 or the second drain material 6 by overlapping. However, the joining of the members constituting the connecting portion 5 to the first drain material 2 or the second drain material 6 may be done by butt joint. For example, a member constituting the connecting portion 5, having a similar thickness and width to the first drain material 2 and the second drain material 6, may be joined to the ends of the first drain material 2 and the second drain material 6 by butt joint.

[0040] Figures 3 to 6 show examples of the connecting portion 5, but it will be easy to understand that various forms of the connecting portion 5 are possible in the present invention, and that the examples shown in Figures 3 to 6 are only a part of the connecting portion 5 that can be adopted in the present invention.

[0041] Similar to the capped drain materials used in conventional vacuum consolidation drain construction methods, the drain material assembly 1 of the present invention is manufactured with multiple drain material assemblies 1 connected in series, and then transported to the site in a rolled state and attached to the concrete pouring device. In this specification, the roll in which multiple drain material assemblies 1 are connected in series is referred to as an assembly roll.

[0042] Figure 7 is an explanatory diagram showing the unfolded state of an assembly roll 7 containing the drain material assembly 1 shown in Figure 2. The assembly roll 7 illustrated in Figure 7 contains nine drain material assemblies 1, which are connected via connection regions S of the assembly roll 7. The assembly roll 7 is formed, for example, by individually manufacturing the drain material assemblies 1 contained therein and connecting these manufactured drain material assemblies 1 using connecting means. In this process, each drain material assembly 1 is manufactured to include the portion constituting the connection region S as a margin. As will be described later, each connection region S is removed during the pouring process of the drain material assembly 1.

[0043] In the assembly roll 7 shown in Figure 7, the drain material assemblies 1 are connected using connecting caps 33 as connecting means. One end of the drain hose 4 of a drain material assembly 1 (except for the drain material assembly 1 that is the last to be installed) is connected via the connecting cap 33 to the end of the second drain material 6 of the next drain material assembly 1 to be installed. The connecting cap 33 may be the same as the airtight cap 3 that makes up the drain material assembly 1. The upper end of the drain hose 4 of a drain material assembly 1 (except for the drain material assembly 1 that is the last to be installed) is inserted into and fixed to the cylindrical part of the connecting cap 33, and the lower end of the second drain material 6 of a drain material assembly 1 (except for the drain material assembly 1 that is the first to be installed) is inserted into and fixed to the rectangular cylindrical part of the connecting cap 33.

[0044] In the present invention, the connection method between drain material assemblies 1 is not limited thereto. For example, the connection between drain material assemblies 1 may be made by butting one end of the drain hose 4 of one drain material assembly 1 against the end of the second drain material 6 of another drain material assembly 1 and fixing them together using adhesive or adhesive tape.

[0045] Before the series of drain material assemblies 1 included in the assembly roll 7 are manufactured, a ground investigation is conducted on the ground where these drain material assemblies 1 will be installed. As a result of the ground investigation, information such as the depth and thickness of the improved layer, intermediate sand layer, and bearing layer at the site where each drain material assembly 1 will be installed is obtained. Based on this information, the length of the first drain material 2, the length of the second drain material 6, the distance between the first drain material 2 and the second drain material 6, the length of the connecting part 5 or its main body, the length of the drain hose 4, etc., are determined for each drain material assembly 1. At this time, the lengths of the second drain material 6 and the drain hose 4 are determined so as to include the portion constituting the connection area S as a margin (excluding the second drain material 6 and drain hose 4 that do not include the portion constituting the connection area S). In Figure 7, for simplification, the length of the first drain material 2, the length of the second drain material 6, the distance between the first drain material 2 and the second drain material 6, etc., are the same for each drain material assembly 1.

[0046] For each drain material assembly 1 included in the assembly roll 7, a first drain material 2, a second drain material 6, a connecting part 5, and a drain hose 4 having the lengths determined as described above are manufactured. Then, the first drain material 2, the second drain material 6, and the connecting part 5 are connected so as to have the spacing between the first drain material 2 and the second drain material 6 determined as described above, and the drain hose 4 is further connected via an airtight cap 3. After a series of drain material assemblies 1 are manufactured individually in this way, they are connected as described above according to the installation order of the drain material assemblies 1 to form the assembly roll 7 shown in Figure 7. Note that this procedure for manufacturing the assembly roll 7 is just one example, and for example, the assembly roll 7 may be formed by combining the components such as the first drain material 2 and the second drain material 6 in order so that a series of drain material assemblies 1 are constructed in order from the first drain material assembly 1 to the last drain material assembly 1 in the installation order.

[0047] Figures 8(a) to 8(d) are explanatory diagrams showing an overview of the process of vertically driving the drain material assembly 1 of the present invention into the ground 9 in the ground improvement method of the present invention. The driving device 8 used for driving the drain material assembly 1 comprises a mobile carriage 81 having a means of movement such as a crawler and a control means for controlling various mechanisms and means included in the driving device 8, a long casing 83 supported by a leader 82 provided on the mobile carriage 81, a group of friction rollers 84 which are driving means for driving the casing 83 up and down, a reel 85 around which the assembly roll 7 is wound, a guide mechanism 86 which guides the assembly roll 7 or drain material assembly 1 pulled out from the reel 85, and an anchor 87 which is attached to the end of the second drain material 6 of the drain material assembly 1 pulled out from the lower end of the casing 83.

[0048] The installation of the drain material assembly 1 into the ground 9 by the installation device 8 is carried out as follows. First, as shown in Figure 8(a), the installation device 8 is positioned at the desired location where the drain material assembly 1 will be installed, and the end of the drain material assembly 1 of the assembly roll 7 inserted into the casing 83 is pulled out from the lower end of the casing 83 and the anchor 87 is attached. Next, as shown in Figure 8(b), the friction roller group 84 is driven to drive the casing 83 into the ground 9 to the desired depth. After that, as shown in Figure 8(c), the friction roller group 84 is driven in the reverse direction to pull the casing 83 out of the ground 9. At this time, the casing 83 is pulled out while the drain material assembly 1 and anchor 87 remain in the ground. As shown in Figure 8(d), after the casing 83 has been completely pulled out, the assembly roll 7 is cut by removing the connection area S (see Figure 7) connected to the installed drain material assembly 1, and the installed drain material assembly 1 is separated. The process described above is repeated until all the drain material assemblies 1 included in the assembly roll 7 are driven into the ground 9, and after all the drain material assemblies 1 included in the assembly roll 7 have been driven, a new assembly roll 7 is attached to the driving device 8.

[0049] The guide mechanism 86 of the concrete casting device 8 includes a plurality of guide members (not shown) that restrict the movement of the portion of the assembly roll 7 that is pulled out from the reel 85. If the step difference in the assembly roll 7 or each drain material assembly 1 that constitutes it is large, the assembly roll 7 may get caught on the guide members during the above process. Therefore, in the present invention, it is preferable that the connecting portion 5 of the drain material assembly 1 is configured so as to not create a step difference as described above.

[0050] Figure 9 is an explanatory diagram illustrating the outline of the ground improvement method of the present invention, showing the pattern and related mechanisms after a predetermined number of drain material assemblies 1 required for ground improvement have been driven into the ground 9. In the example shown in Figure 9, there are two intermediate sand layers 91a and 91b in the ground. Between the ground surface and the upper intermediate sand layer 91a, there is a clay layer 92a, which is an improved layer. Between the upper intermediate sand layer 91a and the lower intermediate sand layer 91b, there is a clay layer 92b, which is an improved layer. Between the lower intermediate sand layer 91b and the unimproved support layer 93, there is a clay layer 92c, which is an improved layer. The support layer 93 is, for example, a sand layer or a gravel layer. The lower end of each drain material assembly 1 is positioned to reach the support layer 93 (anchors 87 are not shown in Figures 9 to 14). In Figure 9, the depth of the lower end of each drain material assembly 1 is the same, but as mentioned above, the depth of the lower end is determined for each drain material assembly 1 based on the ground investigation.

[0051] The upper end of the first drain material 2 of each drain material assembly 1 is located approximately 1 meter underground from the upper end of the improved layer, thereby ensuring an upper sealing layer 94 for the first drain material 2. The drainage hose 4 of each drain material assembly 1 extends to the ground through the upper sealing layer 94.

[0052] In the ground improvement method of the present invention, each drain material assembly 1 is positioned such that the upper end of its second drain material 6 is located within the uppermost intermediate sand layer at the installation site. The uppermost intermediate sand layer refers to the intermediate sand layer with the lowest depth among the intermediate sand layers located between the ground surface and the supporting layer at the installation site. In the example shown in Figure 9, this corresponds to the upper intermediate sand layer 91a for each drain material assembly 1. If there is only one intermediate sand layer located between the ground surface and the lower end of the second drain material or the supporting layer 93 at the installation site, that intermediate sand layer becomes the uppermost intermediate sand layer.

[0053] Furthermore, in the ground improvement method of the present invention, each drain material assembly 1 is installed such that the connecting portion 5 passes over the upper surface of the uppermost intermediate sand layer, and the lower end of the first drain material 2 is located within the improved layer, away from the uppermost intermediate sand layer at the installation site. The lower end of the first drain material 2 of the drain material assembly 1 is positioned away from the uppermost intermediate sand layer to such an extent that a lower seal layer 95 is secured for the first drain material 2 (for example, about 1 meter). In the example shown in Figure 9, the lower end of the first drain material 2 of each drain material assembly 1 is positioned within the clay layer 92a, about 1 meter above the upper intermediate sand layer 91a.

[0054] After all the drain material assemblies 1 have been placed, an embankment 100 is constructed on the ground. The drainage hoses 4 of each drain material assembly 1 are extended as needed and run through the embankment 100 to a water collection pipe 201 located on the embankment 100. The water collection pipe 201 is connected to a header pipe 205 that is in fluid communication with a depressurization means, in this embodiment, a vacuum pump 203. In the example shown in Figure 9, in addition to the seven drain material assemblies 1 shown, there are multiple or many other drain material assemblies 1 that are not shown. These drain material assemblies 1 are also connected to their respective water collection pipes 201, and these water collection pipes 201 are also connected to the header pipe 205.

[0055] The load applied to the ground 9 by the embankment 100 generates excess pore water pressure in the ground. Furthermore, when the vacuum pump 203 is activated, negative pressure acts on the first drain material 2 of each drain material assembly 1 via the header pipe 205, the water collection pipe 201, and the drainage hose 4, reducing the pressure inside the first drain material 2. Due to this negative pressure propagating to the clay layer 92a and the excess pore water pressure caused by the embankment 100, pore water flows from the clay layer 92a through the permeable filter 23 into the first drain material 2, causing consolidation of the clay layer 92a. The pore water that has flowed into the first drain material 2 of each drain material assembly 1 is sucked up via the drainage hose 4 and sent to the vacuum pump 203 via the water collection pipe 201 and the header pipe 205, and then discharged into a drainage tank or drainage channel (neither of which are shown). In Figure 9, the flow of water in the ground and inside the drain material assembly 1 is indicated by arrows for several drain material assemblies 1.

[0056] Similar to conventional vacuum consolidation drain methods, it is preferable that the airtight caps 3 of each drain material assembly 1 are positioned below the groundwater level 96. This reduces the amount of air flowing from the ground into the first drain material 2 when the vacuum pump 203 is operating, thereby ensuring the negative pressure necessary to promote consolidation.

[0057] As described above, and as explained with reference to Figure 3, the lower end of the first drain material 2 of each drain material assembly 1 is closed or blocked, so that the mud and sand of the improved clay layer 92a do not enter the first drain material 2 and clog the flow path of the first drain material 2.

[0058] Furthermore, in the ground improvement method of the present invention, due to the excess pore water pressure caused by the embankment, pore water flows into the second drain material 6 of each drain material assembly 1 from the improved layer in which the second drain material 6 is embedded, causing consolidation of the improved layer. As described above, the connecting portion 5 of each drain material assembly 1 is not configured to guide the water that flows into the second drain material 6 and through it to the first drain material 2. Therefore, the pore water that flows into the second drain material 6 of each drain material assembly 1 from the improved layer flows through the water channel of the second drain material 6 according to the pressure distribution within the second drain material 6, and is then discharged into the underground drainage layer through the permeable filter 23 of the second drain material 6 (or from the upper end of the second drain material). The drainage layer is a sand layer or gravel layer, and since the excess pore water pressure in the drainage layer is lower than the excess pore water pressure in the improved layer, which is a clay layer, this water flow occurs.

[0059] In the example shown in Figure 9, pore water flows into the second drain material 6 of each drain material assembly 1 from clay layers 92b and 92c, causing consolidation of clay layers 92b and 92c. Intermediate sand layers 91a and 91b both function as drainage layers, and the water flowing into the second drain material 6 from clay layer 92b flows to the uppermost intermediate sand layer 91a or the intermediate sand layer 91b below it according to the water pressure distribution within the second drain material 6, where it is discharged.

[0060] In the example shown in Figure 9, as the clay layers 92a to 92c are consolidated, the ground 9 gradually settles. The first drain material 2 and the second drain material 6 of the drain material assembly 1 are flexible, similar to conventional drain materials, and deform to follow this ground settlement. As described above, it is preferable that the connecting part 5 or its main body is also flexible and deforms to follow the ground settlement. This ensures that even as ground settlement progresses, the upper end of the second drain material 6 is positioned within the intermediate sand layer 91, and the lower end of the first drain material 2 is positioned above the intermediate sand layer 91 within the clay layer 92a above the uppermost intermediate sand layer 91a, thus more reliably maintaining the function of the drain material assembly 1 described above.

[0061] In the example shown in Figure 9, by using the ground improvement method of the present invention, the upper clay layer 92a is modified in the same way as the conventional vacuum consolidation drain method. As a result, the amount of embankment 100 is reduced and the construction period is shortened compared to when the conventional PVD method is applied.

[0062] The advantages and effects of the vacuum consolidation drain method using the drain material assembly 1 of the present invention, compared to the conventional vacuum consolidation drain method, will be explained below with reference to the exemplary cases shown in Figures 10 to 13. In Figures 10 to 13, only one capped drain material 10 used in the conventional vacuum consolidation drain method, or one drain material assembly 1 based on the present invention, is shown, but it goes without saying that many of these are installed in the ground to be improved.

[0063] Figure 10 is an explanatory diagram showing the first case of ground improvement using the conventional vacuum consolidation drain method. The capped drain material 10 used in the conventional vacuum consolidation drain method consists of a drain material 2', a drain hose 4', and an airtight cap 3' connecting them. The drain hose 4' is connected to a vacuum pump (not shown), which is a means of reducing pressure. In Figure 10, the same reference numerals as in Figure 9 are used for the parts described in Figure 9, and the flow of water is indicated by arrows. The same applies to Figures 11 to 13, which will be referenced below.

[0064] In the case shown in Figure 10, there is an intermediate sand layer 91 in the area of ​​the ground 9 to be improved, and above and below the intermediate sand layer 91 are clay layers 92d and 92e, which are the improved layers. The distance between the lower clay layer 92e and the unmodified layer 93 (supporting layer in the case shown in Figure 11), which is a sand or gravel layer below it, is about 2.5 meters. The lower end of the capped drain material 10 is positioned about 1 meter above the unmodified layer 93 in order to secure the lower seal layer 95.

[0065] Since the drain material 2' passes through the intermediate sand layer 91, a waterproof seal 13 corresponding to the intermediate sand layer 91 is provided on the drain material 2' to prevent a large amount of water from flowing in from the intermediate sand layer 91 when negative pressure is applied. The waterproof seal 13 covers not only the portion of the drain material 2' in the intermediate sand layer 91, but also the portion of the drain material 2' about 1 meter above and below the intermediate sand layer 91 in order to secure the seal layers 97 and 98 above and below the intermediate sand layer 91. For this reason, in the case shown in Figure 10, the area of ​​the drain material 2' not covered by the waterproof seal 13 in the clay layer 92e below the intermediate sand layer 91 is about 0.5 meters. Therefore, in the case shown in Figure 10, although the clay layer 92d above the intermediate sand layer 91 is improved using the conventional vacuum consolidation drain method, the improvement of the clay layer 92e below the intermediate sand layer 91 does not progress easily.

[0066] Figure 11 is an explanatory diagram showing how the vacuum consolidation drain method using the drain material assembly 1 of the present invention is applied in place of the conventional vacuum consolidation drain method in the case shown in Figure 10. The lower end of the second drain material 6 of the drain material assembly 1 is positioned to reach the lower unmodified layer, i.e., the support layer 93, and the upper end of the second drain material 6 is positioned in the intermediate sand layer 91. The lower end of the first drain material 2 is positioned about 1 meter above the intermediate sand layer 91 in order to secure the lower seal layer 95 for the intermediate sand layer 91. The upper end of the first drain material 2 is positioned about 1 meter below the ground surface in order to secure the upper seal layer 94.

[0067] Due to the excess pore water pressure caused by the load from the embankment 100, pore water from the clay layer 92e flows into the second drain material 6 of the drain material assembly 1. The water flows through the channels of the second drain material 6 according to the pressure distribution within the second drain material 6 and is discharged to the drainage layer, which is the intermediate sand layer 91 or the bearing layer 93. Since pore water flows thoroughly into the second drain material 6 of the drain material assembly 1 throughout the depth direction of the clay layer 92e, consolidation of the clay layer 92e proceeds in the same way as when using a typical conventional PVD method. On the other hand, when a vacuum pump (not shown) is driven, negative pressure acts on the first drain material 2 of the drain material assembly 1. Due to the propagation of negative pressure and the excess pore water pressure, pore water from the clay layer 92d flows into the first drain material 2 and is discharged from the ground 9 via the drainage hose 4. Consolidation of the clay layer 92d proceeds in the same way as in the conventional vacuum consolidation drain method.

[0068] As described above, by applying the ground improvement method of the present invention to the case shown in Figure 10, it is possible to improve the clay layer 92e, which was difficult or impossible to improve when using the conventional vacuum consolidation drain method. On the other hand, the clay layer 92d is improved in the same way as the conventional vacuum consolidation drain method, resulting in a shorter construction period and a reduction in the amount of embankment 100 compared to the conventional typical PVD method.

[0069] Figure 12 is an explanatory diagram showing a second case of ground improvement using the conventional vacuum consolidation drain method. In the second case shown in Figure 12, the area below the intermediate sand layer 91 is a layered structure in which sand layers 99a and clay layers 99b are alternately stacked. Because of the presence of the intermediate sand layer 91, a waterproof seal 13 is provided on the drain material 2' of the capped drain material 10. The waterproof seal 13 extends to about 1 meter above the intermediate sand layer 91 in order to secure the seal layer 97. Since the drain material 2' also needs to be waterproofed from the alternating sand layers 99a, the waterproof seal 13 is provided so as to cover the drain material 2' from the intermediate sand layer 91 beyond the lowest sand layer 99a in the alternating layers. In the alternating layers below the intermediate sand layer 91, the area where the drain material 2' is not waterproofed is small relative to the range of the alternating layers, and in the case shown in Figure 12, it is difficult to improve the clay layer 99b of the alternating layers using the conventional vacuum consolidation drain method.

[0070] Figure 13 is an explanatory diagram showing the application of the vacuum consolidation drain method using the drain material assembly 1 of the present invention to the case shown in Figure 12. The lower end of the second drain material 6 of the drain material assembly 1 reaches the support layer 93, and the upper end of the second drain material 6 is positioned within the intermediate sand layer 91. The lower end of the first drain material 2 is positioned approximately 1 meter above the intermediate sand layer 91 in order to secure a lower seal layer 95 for the intermediate sand layer 91.

[0071] Due to the excess pore water pressure caused by the load from the embankment 100, pore water from the interlayered clay layer 99b flows into the second drain material 6 of the drain material assembly 1. The water flows through the water channel of the second drain material 6 according to the pressure distribution within the second drain material 6 and is discharged into the drainage layer, which consists of the intermediate sand layer 91, the supporting layer 93, or the interlayered sand layer 99a. In this way, by using the drain material assembly 1 of the present invention, the interlayered clay layer 99b below the intermediate sand layer 91, which was difficult to improve with conventional vacuum consolidation drain methods, can be improved. On the other hand, the clay layer 92d above the intermediate sand layer 91 can be improved in the same way as with conventional vacuum consolidation drain methods.

[0072] As explained with reference to Figures 10 to 13, the ground improvement method using the drain material assembly 1 of the present invention makes it possible to improve ground areas that could not be improved by conventional vacuum consolidation drain methods. On the other hand, the ground improvement method of the present invention also enjoys the advantages of conventional vacuum consolidation drain methods, such as a reduction in embankment 100 and a shortened construction period compared to a typical conventional PVD method.

[0073] In the example described above, the lower end of the second drain material 6 of the drain material assembly 1 is cast so that it settles on a hard support layer 93 which is a sand or gravel layer. However, in the present invention, it is possible to cast the lower end of the second drain material 6 of the drain material assembly 1 so that it settles on a soft improved layer (for example, the clay layer 92c in Figure 9). However, when settling on a soft layer, the anchor 87 is likely to rise together with the casing 83 when it is pulled out during casting, so it is preferable to cast the drain material assembly 1 so that it settles on a hard support layer 93.

[0074] The drain material assembly 1 shown in Figures 1, 7, 9, 11, and 13, which are referenced to illustrate the present invention, is for illustrative purposes only and does not reflect the dimensions, geometric ratios, etc., of the individual components of the drain material assembly 1 that may actually occur when the present invention is implemented.

[0075] The ground improvement method of the present invention does not exclude the use of conventional capped drain materials used in vacuum consolidation drain methods, such as the capped drain material 10 shown in Figure 10. Conventional capped drain materials may be used together with the drain material assembly 1. For example, if the results of a ground investigation determine that using conventional capped drain materials is more effective or efficient than using the drain material assembly of the present invention at some installation sites, then conventional capped drain materials may be installed at those installation sites.

[0076] The above description is for the purpose of explaining the present invention and should not be interpreted as limiting or narrowing the scope of the invention described in the claims. Furthermore, the configuration of each part of the present invention is not limited to the above embodiments, and various modifications are possible within the technical scope described in the claims. [Explanation of Symbols]

[0077] 1. Drain material assembly 2. First drain material 3. Drain hose 4. Airtight cap 5 Connecting part 6. Second drain material 21 Core material 23 Permeable filter 9 Ground 91 Intermediate sand layer 91a~b Intermediate sand layer 92a~e Clay layer 93 Supporter layer 100 Embankment

Claims

1. A ground improvement method using a drain material assembly, The aforementioned drain material assembly is The first drain material, An airtight cap is provided at the upper end of the first drain material, The drain hose connected to the aforementioned airtight cap, A second drain material is connected to the lower end of the first drain material via a connecting part, It is equipped with, The drain material assembly is driven into the ground in a vertical direction, Applying negative pressure to the first drain material via the aforementioned drain hose, The aforementioned ground is to be filled with soil, It includes, The drain material assembly is cast such that the upper end of the second drain material is positioned in the uppermost intermediate sand layer at the casting point of the drain material assembly, and the lower end of the first drain material is positioned in the improved layer above the intermediate sand layer. Alternatively, the drain material assembly is installed such that the upper end of the second drain material is positioned in the only intermediate sand layer present between the lower end of the second drain material and the ground surface at the installation site of the drain material assembly, and the lower end of the first drain material is positioned in the improved layer above the only intermediate sand layer.

2. The ground improvement method according to claim 1, wherein the drain material assembly is driven in such a way that the lower end of the second drain material is placed in a supporting layer which is a sand layer or a gravel layer.

3. The ground improvement method according to claim 1, wherein the connecting portion includes one or more flexible strip-shaped or plate-shaped members, one end of the one or more strip-shaped or plate-shaped members is fixed directly to the first drain material or via an intermediate member, and the other end of the strip-shaped or plate-shaped members is fixed directly to the second drain material or via an intermediate member.

4. The ground improvement method according to claim 1, wherein the connecting portion includes one or more ropes, one end of the one or more ropes is fixed directly to the first drain material or via an intermediate member, and the other end of the strip-shaped or plate-shaped member is fixed directly to the second drain material or via an intermediate member.

5. The ground improvement method according to claim 1, wherein the first drain material comprises a core material and a permeable filter attached to the core material.

6. The ground improvement method according to claim 5, wherein the lower end of the first drain material is closed or sealed.

7. The ground improvement method according to claim 1, wherein the second drain material comprises a core material and a permeable filter attached to the core material.

8. A drain material assembly used in a ground improvement method according to any one of claims 1 to 7, wherein the connecting portion is configured not to guide water that enters the second drain material and flows upward to the first drain material.

9. A drain material assembly used in a ground improvement method according to any one of claims 1 to 7, wherein the connecting portion does not define a closed space connecting the water channel in the second drain material to the water channel in the first drain material.

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