JP2016014291A - Water suction pipe system, groundwater level lowering method and saturated ground compaction method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water suction pipe system capable of effectively lowering a groundwater level even for the ground which is low in water permeability and a groundwater level lowering method and a saturated ground compaction method using the water suction pipe system.SOLUTION: A water suction pipe system 10 which can be installed in the ground for lowering a groundwater level includes: a well-point 11 disposed at the top end side; a riser pipe 12 connected to the well-point; and a drain material 13 attached to the external surface of the riser pipe for draining water toward the well-point.

Description

  The present invention relates to a water absorption pipe system that can be installed in the ground, a groundwater level lowering method using such a water absorption pipe system, and a method for compacting a saturated ground.

  Conventionally, a method is known in which a deep well is dug in the ground and pumped to lower the groundwater level, and then the ground is compacted by impact or vibration. For example, Patent Document 1 discloses a sand pile creation process that stabilizes the ground by creating a number of sand piles in the reclaimed ground, and a ground failure that causes the groundwater to be extracted by digging a pumping well in the sand pile creation ground. Proposed a ground-reinforced composite method that performs a ground compaction process in this order to obtain a high-density ground by compaction by impact or vibration, such as a dynamic compaction method or vibration compaction method, for a saturated process and an unsaturated ground. (Summary, FIG. 1).

  In addition, a well point method is known as a method for lowering the groundwater level. This method is constructed by installing a water absorption pipe (well point) below the groundwater level surface in the ground and connecting it to the water absorption pipe (riser). Pipe)) applies negative pressure from the ground to suck groundwater.

Japanese Unexamined Patent Publication No. 2000-319865

  A conventional construction example by the well point method and its problems will be described with reference to FIGS.

  As shown in FIG. 6A, the riser pipe RP provided with the well point WP on the tip side is excavated from the tip of the well point WP by jetting a jet jet from the jet pump JP, and the inside of the silt layer G1 from the ground. Insert into. As shown in FIG. 6B, the excavation proceeds while the gravel SA is inserted into the hole where the well point WP penetrates, and the tip of the well point WP is a viscous soil layer (impermeable layer) as shown in FIG. 6C. Excavation is performed until G2 is reached, and a riser pipe RP and a well point WP are installed in a hole in the silt layer G1 of the ground. The sand filter SF is formed between the well point WP and the silt layer G1 by the gravel SA in the hole.

  In the state of FIG. 6C, negative pressure is applied from the end of the riser pipe RP, and the groundwater in the silt layer G1 is sucked through the sand filter SF by the well point WP. As the suction proceeds, FIG. ), The silt ST from the silt layer G1 of the ground enters the gap between the gravel SA in the sand filter SF as a muddy water-like fine particle, and the water permeability of the sand filter SF is reduced. As a result, the water collection at the well point WP decreases, and as a result, the water absorption at the well point WP decreases, and the groundwater level cannot be effectively reduced.

  Here, it is necessary to discharge the interstitial water between the soil particles in order to compact the ground saturated with water. However, the method of compacting the ground after lowering the groundwater level in advance to desaturate the ground is a method of effectively lowering the groundwater level against a low-permeability ground such as a silt layer as described above. Because there was no, it was difficult to apply.

  In view of the above-described problems of the prior art, the present invention provides a water absorption pipe system capable of effectively lowering the groundwater level even on a low-permeability ground such as silt, and groundwater using such a water absorption pipe system. It is an object to provide a method for lowering the position and a method for compacting saturated ground.

  A water absorption pipe system for achieving the above object is a water absorption pipe system that can be installed in the ground in order to lower the groundwater level, and includes a well point provided on the tip side and a riser connected to the well point. A pipe, and a drain member attached to an outer surface of the riser pipe so as to drain water toward the well point.

  According to this water absorption pipe system, when installed in the ground, the groundwater in the ground flows toward the well point through the drain material on the outer surface of the riser pipe, thereby increasing the water collection at the well point, and the end of the riser pipe By applying a negative pressure from the side, the water can be drained efficiently, and therefore, the groundwater level can be effectively lowered even in the ground having low water permeability.

  In the above-described water absorption pipe system, it is preferable that the drain material includes a water passage through which water flows and a filter that transmits water flowing into the water passage. Since the filter does not allow fine particles to permeate, the water that has flowed into the water passage efficiently flows toward the well point.

  Moreover, it is preferable that the said drain material is comprised from the core material which consists of plastics, and filters, such as a nonwoven fabric provided around the said core material.

  Moreover, it is preferable that the said drain material is comprised from the porous tube which formed many holes in the outer peripheral surface, and filters, such as a nonwoven fabric wound around the outer peripheral surface of the said porous tube.

  In addition, the said drain material is comprised by flat form, and it can comprise so that a pair of said flat drain material may be attached so that the said riser pipe may be pinched | interposed. The drain material may be configured to be attached so as to be wound around the outer peripheral surface of the riser pipe.

  Moreover, it is preferable that the said drain material is at least 1 m shorter in the upper part than the installation depth of the said riser pipe. Thereby, when the water absorption pipe system is installed in the ground, the ground surface layer having a thickness of at least 1 m from the upper end of the drain material in the ground to the ground surface can be used as an airtight layer, so that the negative pressure effect can be enhanced. Water absorption at the well point can be increased.

  The groundwater level lowering method for achieving the above purpose is a groundwater level lowering method for lowering the groundwater level in the ground, and the well point is located below the groundwater level in the ground. The groundwater is sucked by applying a negative pressure from the upper end side of the riser pipe.

  According to this groundwater level lowering method, the water absorption pipe system is installed in the ground, and the groundwater in the ground flows toward the well point through the drain material on the outer surface of the riser pipe. By applying a negative pressure from the end side of the pipe, the water can be efficiently drained, and therefore, the groundwater level can be effectively lowered even in the ground having low water permeability.

  Another groundwater level lowering method for achieving the above object is a groundwater level lowering method for lowering the groundwater level in the ground, and is provided with a drain material that is at least 1 m shorter than the above-described riser pipe installation depth. A water absorption pipe system is installed in the ground such that the well point is located below the groundwater level in the ground, the upper end of the drain material is located at least 1 m deeper than the ground surface, and from the upper end side of the riser pipe A negative pressure is applied to suck groundwater.

  According to this groundwater level lowering method, the water absorption pipe system is installed in the ground, and the groundwater in the ground flows toward the well point through the drain material on the outer surface of the riser pipe. It is possible to drain efficiently by applying negative pressure from the end side of the pipe, and therefore, even in the ground with low water permeability, the groundwater level can be effectively lowered, and the underground Since the ground surface layer having a thickness of at least 1 m from the upper end of the drain material to the ground surface can be used as an airtight layer, the negative pressure effect can be enhanced and the water absorption at the well point can be enhanced.

  In the groundwater level lowering construction method, it is preferable to insert the water absorption pipe system into the ground while jetting jet water from the tip of the well point in order to install the water absorption pipe system in the ground.

  In addition, after the suction of the groundwater is completed, it is preferable that the water suction pipe system is pulled up from the ground while jet water is jetted from the tip of the well point. Thereby, after construction, the water absorption pipe system can be efficiently recovered, and the water absorption pipe system does not remain in the ground, so that it does not become an obstacle to performing the subsequent steps.

  Moreover, since the ground targeted for lowering the groundwater level is silty ground, the groundwater level in the silty ground having low water permeability can be efficiently lowered.

  In order to achieve the above object, the saturated ground compaction method is to install the above-mentioned water absorption pipe system in the ground to lower the groundwater level in the ground, or the groundwater in the ground by the groundwater lowering method described above. The ground is lowered, and then the ground is compacted.

  According to this saturated ground compaction method, when the water absorption pipe system is installed in the ground, the groundwater in the ground flows toward the well point through the drain material on the outer surface of the riser pipe. It is possible to efficiently drain water by applying a negative pressure from the end side of the riser pipe. For this reason, the groundwater level can be effectively lowered even in the ground having low water permeability. Therefore, after that, the saturated ground can be efficiently compacted by compacting the ground.

  In the above-mentioned saturated ground compaction method, the ground compaction can be performed by press-fitting, vibration or impact of a material to the ground.

  According to the present invention, it is possible to provide a water absorption pipe system capable of effectively lowering a groundwater level even on a low-permeability ground, a groundwater level lowering method using such a water absorption pipe system, and a method for compacting a saturated ground. Can do.

It is a front view showing roughly the whole water absorption pipe system by this embodiment. It is sectional drawing (a) (b) which cut | disconnected the riser pipe and drain material of the water absorption pipe system of FIG. 1 in the II-II line direction. It is a flowchart for demonstrating process S01-S07 of the groundwater level fall construction method and the compaction construction method by this embodiment. It is the schematic which shows the main processes (a)-(c) of installation process S01 of the water absorption pipe system of FIG. It is the schematic which shows the water absorption process S03 by the water absorption pipe system of FIG. It is the schematic (a)-(d) for demonstrating the example of the conventional construction by a well point construction method. It is the schematic for demonstrating the water absorption process by the conventional well point construction method of FIG. Schematic (a) for demonstrating the groundwater level fall construction method by the water absorption pipe system of this embodiment, Sectional drawing (b) of the water absorption pipe system corresponding to FIG. 2 (a), and another corresponding to FIG. 2 (b) It is sectional drawing (c) of the water absorption pipe | tube system using the drain material of, and the schematic diagram (d) for demonstrating the vacuum consolidation method by the conventional plastic board drain with a cap, and sectional drawing (e) of a drain. It is the schematic (a) which shows the state of the soil particle before compacting the ground in this embodiment, and the schematic (b) which shows the state of the soil particle after compacting. It is a front view which shows roughly the whole another water absorption pipe system by this embodiment.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

<Water absorption pipe system>
FIG. 1 is a front view schematically showing the entire water absorption pipe system according to the present embodiment. 2 is a cross-sectional view (a) and (b) of the riser pipe and drain material of the water absorption pipe system of FIG.

  As shown in FIG. 1, the water absorption pipe system 10 includes a well point 11 provided on the distal end side, a riser pipe 12 connected to the well point 11, and a drain material 13 attached to the outer surface of the riser pipe 12. Can be installed in the ground with the well point 11 as the tip (lower end).

  The drain material 13 has a lower end 13 a positioned at a connection portion between the well point 11 and the riser pipe 12, and a length to the upper end 13 b is shorter than the riser pipe 12. That is, as shown in FIG. 1, when the water absorption pipe system 10 is installed in the ground, the drain material 13 with respect to the installation depth D of the riser pipe 12 positioned below the ground surface S (underground side). Is configured to be shorter by the distance d from the ground surface S to the upper end 13b. The distance d is set to at least 1 m.

  As shown in FIG. 2A, the drain material 13 is composed of a pair of flat plate drain materials 13 c and 13 d attached so as to sandwich the riser pipe 12. The flat drain materials 13c and 13d are configured by adhering filters 15 made of non-woven fabric on both surfaces of a plastic board 14 on which a large number of water passages p are formed.

  Moreover, the drain material 13 may be comprised from the circular drain material 13e attached so that it might wind around the outer peripheral surface of the riser pipe 12 like FIG.2 (b). The circular drain member 13e can be formed by winding a plastic board 14 having a large number of water passages p around the outer peripheral surface of the riser pipe 12 for one turn, and attaching a filter 15 made of nonwoven fabric to the outer peripheral surface.

  The drain material 13 is configured such that the nonwoven fabric of the filter 15 transmits water and does not transmit fine particles, and the transmitted water flows into the water passage p in the plastic board 14.

  The flat drain materials 13c and 13d and the circular drain material 13e can be attached to the outer surface of the riser pipe 12 using an adhesive, a fastening band, or the like. Moreover, the drain material 13c-the drain material 13e can be comprised from the plastic board drain used for the soft ground improvement construction method by vacuum consolidation.

  Moreover, the well point 11 of FIG. 1 has the water absorption part 11a provided in the outer peripheral surface, and the nozzle 11b provided in the front-end | tip. The water absorption part 11a is composed of a known structure that sucks the surrounding groundwater through a filter made of a wire mesh or the like when absorbing water, and the nozzle 11b is composed of a known structure that ejects a jet jet, and the nozzle 11b is automatically operated when sucking in the water absorption part 11a. It is designed to close.

  Further, the well point 11 of the water absorption pipe system 10 of FIG. 1 has, for example, an inner diameter of 50 mm and a length of 0.7 to 1.0 m, a riser pipe 12 has an inner diameter of 40 mm, and the flat drain materials 13c and 13d have a width of 100 mm and a thickness. The circular drain material 13e can be 3 mm in thickness, but these dimensions are merely examples and can be changed as appropriate.

<Groundwater level lowering method and compaction method for saturated ground>
Next, a groundwater level lowering method and a compacting method for saturated ground using the water absorption pipe system shown in FIGS. 1 and 2 will be described with reference to FIGS. FIG. 3 is a flowchart for explaining steps S01 to S07 of the groundwater level lowering method / consolidation method according to this embodiment. FIG. 4 is a schematic diagram showing main steps (a) to (c) of the installation step S01 of the water absorption pipe system of FIG. FIG. 5 is a schematic view showing a water absorption step S03 by the water absorption pipe system of FIG.

  As shown in FIGS. 3 and 4 (a) to 4 (c), the groundwater level in the silt ground G1 is determined in the ground G composed of the silt ground G1 saturated with water and the viscous soil layer (impermeable layer) G2 below the water. In order to reduce, the water absorption pipe system 10 of FIG. 1, FIG. 2 is installed in the silt ground G1 (S01).

  First, as shown in FIG. 4 (a), a jet jet is jetted from the nozzle 11b of the well point 11 of the water absorption pipe system 10 through the hose HS and the riser pipe 12 from the jet pump JP, so that the silt ground from the ground surface S. G1 is cut to start excavation of the silt ground G1, and the water absorption pipe system 10 is inserted in the downward direction a from the nozzle 11b into the silt ground G1. With this excavation, excavated soil overflows the ground surface S.

  As shown in FIG. 4B, the water suction pipe system 10 is continuously inserted into the silt ground G1 while jet jets are ejected. During this time, sand is not thrown into the excavation hole as in the prior art.

  Next, as shown in FIG. 4 (c), when the nozzle 11b at the tip of the well point 11 of the water suction pipe system 10 reaches the viscous soil layer (impermeable layer) G2, the jet pump JP is stopped and the jet jet is ejected. And the insertion of the water absorption pipe system 10 into the silt ground G1 is stopped. Thus, the water absorption pipe system 10 is installed in the silt ground G1. At this time, as shown in FIG.4 (c), the distance d from the ground surface S to the upper end 13b of the drain material 13 is at least 1 m.

  When the installation of the water suction pipe system 10 to the silt ground G1 is completed as described above, next, the end portion 12a on the ground side of the riser pipe 12 is connected via the swing joint 17 as shown in FIGS. Connect to the header pipe 18 (S02). The header pipe 18 is connected to a riser pipe of another water absorption pipe system similarly installed at other positions via a swing joint, and is connected to a negative pressure source (not shown) such as a vacuum pump. ing.

  Next, a negative pressure source (not shown) is operated to start water absorption from the water absorption part 11a of the well point 11 of the water absorption pipe system 10, and the groundwater is sucked and discharged to the outside (S03). Thereby, as shown in FIG. 5, the groundwater level H in the silt ground G <b> 1 decreases from the natural groundwater level H <b> 0 and decreases to the water level H <b> 1 in the well by the well point 11. The infiltration line gradually approaches the natural groundwater level H0 as the distance from the water suction pipe system 10 increases.

  The water absorption step S03 is continued until the groundwater level H in the silt ground G1 falls to a predetermined water level (S04). Thereby, the saturated silt ground G1 can be desaturated.

  Next, when the groundwater level H falls to a predetermined water level, the target work such as excavation or compaction by dry work is performed (S05).

  That is, a granular material such as sand is pressed into the unsaturated ground G1, and the ground is compacted. The press-fitting of the granular material is performed by a back compaction method of the SCP method in which a casing pipe having a diameter of about 40 to 50 cm is driven into the ground while being vibrated using a known sand compaction pile (SCP) construction machine. be able to. In addition, excavation work is performed as necessary.

  Next, when the target work process S05 is completed, the negative pressure source is stopped (S06). In this way, the water absorption step S03 is continuously performed until the completion of the target work step S05.

  Next, the swing joint 17 shown in FIGS. 1 and 5 is removed from the end 12a on the ground side of the riser pipe 12, and the hose HS of the jet pump JP is attached, and then the jet jet is drawn from the jet pump JP to the well of the water absorption pipe system 10. The water suction pipe system 10 is pulled upward and removed while the ground is loosened by ejecting from the nozzle 11b at the point 11 (S07).

  As described above, according to the water absorption pipe system 10 of the present embodiment, the drain material 13 constitutes the drainage channel, and the groundwater in the silt ground G1 faces the water passage p (FIG. 2) in the drain material 13 downward. Since it flows in the vicinity of the water absorption part 11a of the well point 11, drainage can be performed efficiently, and the groundwater level can be effectively reduced even in a low water-permeable ground such as a silt layer. it can. Further, as shown in FIG. 5, the distance d from the upper end 13b of the underground drain material 13 to the ground surface S is at least 1 m, and this silt layer having a thickness of at least 1 m can be used as the airtight layer SL. The negative pressure effect can be increased, and the water absorption at the well point can be increased.

  As described above, according to the water absorption pipe system 10, by providing the drain material 13 around the riser pipe 12, a reliable drainage path to the well point 11 is constructed and airtightness of the ground surface is ensured and negative pressure action is achieved. By increasing the effect of, groundwater can be discharged more efficiently and the groundwater level can be lowered efficiently.

  FIG. 7 shows a schematic diagram for explaining the water absorption process by the conventional well point method of FIG. 6, but according to the conventional water absorption process of FIGS. 6 (a) to (c), as shown in FIG. Although the water level H2 in the well filled with sand falls to the vicinity of the upper end of the well point WP, the surrounding groundwater is only discharged only by the lowering of the water level in the well. Moreover, since the upper end surface S1 of the sand filter SF made of sand in the well is open to the atmosphere, the negative pressure generated by the negative pressure source for discharging the groundwater does not efficiently apply to the silt layer and lowers the groundwater level. Low suction force for On the other hand, according to this embodiment, in addition to lowering the water level in the well, a silt layer having a thickness of at least 1 m can be used as the airtight layer SL as shown in FIG. 5, and negative pressure acts on the entire silt ground G1. Therefore, groundwater can be discharged more efficiently.

  In addition, according to the conventional well point method shown in FIGS. 6A to 6C, the sand filter SF by the gravel in the well constructs a drainage layer, and converts the groundwater from the surrounding silt layer to the well point WP. However, as the drainage proceeds, the silt from the silt layer enters the sand filter SF as a mud-like fine granule (FIG. 6 (d)), and the water permeability of the sand filter SF decreases. The sand filter SF has a reduced function as a drainage layer. On the other hand, according to this embodiment, groundwater can be efficiently flowed to the well point 11 through a large number of water channels p (FIG. 2) in the drain material 13, and the drain material 13 is reliably used as a drainage layer. In addition to functioning, in the drain material 13, the filter 15 does not pass through fine particles such as silt. Therefore, even if drainage proceeds, clogging is unlikely to occur, and the function of the drainage layer can be efficiently maintained.

  5 and 7, the infiltration line representing the groundwater level H indicated by a broken line is lower in the present embodiment in FIG. 5 than in the conventional example in FIG. 7, but this causes clogging. This is probably due to the use of difficult drain materials and the presence of the airtight layer SL.

  Here, the difference between the groundwater level lowering method by the water absorption pipe system 10 of this embodiment and the vacuum consolidation method by the conventional plastic board drain with a cap is demonstrated with reference to Fig.8 (a)-(e). FIG. 8 is a schematic diagram (a) for explaining the groundwater level lowering method by the water absorption pipe system of the present embodiment, a cross-sectional view of the water absorption pipe system corresponding to FIG. 2 (a), and FIG. 2 (b). Sectional view (c) of a water absorption pipe system using another drain material corresponding to, a schematic diagram (d) for explaining a vacuum consolidation method using a conventional plastic board drain with a cap, and a sectional view (e) of the drain is there.

  As shown in FIG. 8 (d), the vacuum consolidation method using a plastic board drain with a cap is connected to the upper end of a plastic board drain (drain material) PBD placed in the ground G through an impermeable cap portion CP. By applying a negative pressure to the drainage pipe DP, the atmospheric pressure resulting from the negative pressure is applied to the ground, and the ground is improved by discharging water from the ground. A specific example of such a plastic board drain with a cap is described in, for example, JP-A-2006-241872. As shown in FIG. 8 (e), the drain material PBD has a cross-sectional area of typically about 100 mm width × 3 mm thickness, and the inner diameter of the riser pipe 12 of the water absorption pipe system 10 shown in FIG. b) If it is set to 40 mm as in (c), it is about 1/4 of the riser pipe 12, the water passing ability is small, and the water passage resistance is large. In the case of silt ground having a larger hydraulic conductivity than clay, energy loss becomes a problem when the amount of water absorption increases. In addition, since silt has less water retention capacity than clay, the groundwater level decreases while water is absorbed and the ground becomes unsaturated. When the ground is desaturated from the top, air flows into the drain that is in contact. For this reason, the upper air and the water sucked from the lower part interfere with each other in the drain water passage, resulting in a water passage resistance, resulting in a decrease in pumping capacity.

  On the other hand, a well point with a drain material such as the water absorption pipe system 10 of FIGS. 8A to 8C has sufficient pumping capacity because water collected at the lower part is pumped by the riser pipe 12 (for example, inner diameter 40 mm). Can be secured. Even if the amount of water absorption increases on a highly permeable ground such as a sand layer, there is little energy loss. Groundwater collected in the drain material 13 is drained through the riser pipe 12 from the water absorption part 11 a of the well point 11. Since the water is pumped at the bottom by the well point 11, the pumping capacity does not decrease even if the upper portion of the drain material 13 becomes unsaturated.

  As described above, the compacting method according to the present embodiment is a method of compacting after effectively lowering the groundwater level for low-permeability silty ground saturated with water. This will be described with reference to FIG. FIG. 9: is the schematic (a) which shows the state of the soil particle before compacting the ground, and the schematic (b) which shows the state of the soil particle after compacting.

  That is, as shown in FIG. 9A, when the gap P between the soil particles D and D in the ground is large and the ground is loose, and the ground P is saturated with pore water due to the saturated ground, Even if tightened, pore water cannot be quickly discharged from the gap P, so the gap P between the soil particles D and D cannot be reduced, and it is difficult to compact the ground. On the other hand, according to the saturated ground compaction method of the present embodiment, the groundwater level of the saturated ground is lowered and desaturated before the ground is tightened, so that the gap P is changed from the gap P in FIG. After draining the water and then tightening the ground by press-fitting the granular material, even if the ground has many fine particles such as silt and low water permeability as shown in FIG. , D can be effectively reduced and the ground can be efficiently compacted.

  In addition, in the water absorption pipe system installation step S01 and the removal step S07 in FIG. 3, the water absorption pipe system 10 is installed and then withdrawn and removed, but since both steps are carried out while jetting a jet, installation / removal is performed. It can be done easily and quickly, improving the efficiency of construction.

  In addition, in the vacuum consolidation method in which the plastic board drain PBD is driven by the drain driving machine as shown in FIG. 8D, it is considerably difficult to remove the drain. Removal of 10 can be done easily and quickly.

  Further, in the present embodiment, the target ground for lowering and compacting the groundwater level is preferably a silty ground having a particle size of silt to fine sand, and such a silty ground is generally low in water permeability, but compared to clay. The ground is highly permeable.

  As described above, the modes for carrying out the present invention have been described. However, the present invention is not limited to these, and various modifications can be made within the scope of the technical idea of the present invention. For example, as the drain material to be attached to the riser pipe, a plastic board drain is used in the present embodiment, but the present invention is not limited to this, for example, the drain material is a perforated tube having a large number of holes formed on the outer peripheral surface, You may comprise from the filter which consists of a nonwoven fabric etc. which were wound around the outer peripheral surface of a porous tube so that water might permeate | transmit and a fine particle part may not be permeate | transmitted. Such a drain material can be arranged on the outer peripheral surface of the riser pipe to form a double pipe structure water absorption pipe system.

  For example, as shown in FIG. 10, the water absorption pipe system 10 </ b> A includes a porous tube 19 having a large number of holes 19 a on the outer peripheral surface, and a filter 20 made of a non-woven fabric wound around the outer peripheral surface of the porous tube 19 (broken line in FIG. 10). And a perforated tube 19 is inserted into a riser pipe 12 having a well point 11 on the tip side and partially fixed. When the water absorption pipe system 10A is installed in the ground, the drain material porous pipe 19 is at least 1 m shorter than the installation depth D of the riser pipe 12, and the distance from the upper end 13b of the porous pipe 19 to the ground surface S d is at least 1 m.

  When the gap formed between the inner surface of the porous tube 19 and the outer surface of the riser pipe 12 becomes a water passage p, and the water absorption pipe system 10A is installed in the ground, the water passage p constructs a drainage passage. The water is drained to the well point 11 through the drainage channel.

  According to the water absorption pipe system 10A of FIG. 10, a drainage material by the porous pipe 19 is provided so as to cover the riser pipe 12, thereby constructing a reliable drainage path to the well point 11 and shortening the porous pipe 19 at the upper end. By ensuring the airtightness of the ground surface and enhancing the effect of negative pressure action, groundwater can be discharged more efficiently and the groundwater level can be lowered efficiently.

  Further, the material press-fitting step in the target operation step S05 of FIG. 3 may be replaced with a step of applying vibration or impact to the ground, and the same ground compaction effect can be obtained.

  According to the present invention, since the groundwater level can be effectively lowered even for a low-permeability ground such as silt, the saturated ground can be efficiently compacted by compaction after the groundwater level is lowered. Can do.

10, 10A Water absorption pipe system 11 Well point 11a Water absorption part 11b Nozzle 12 Riser pipe 13 Drain material 13b Upper end 14 Plastic board 15 Filter 19 Porous pipe 20 Filter G Ground G1 Silt ground H Groundwater level JP Jet pump SL Airtight layer d Distance p Waterway

Claims (12)

A water absorption pipe system that can be installed in the ground to lower the groundwater level,
A well point provided on the tip side;
A riser pipe connected to the well point;
And a drain member attached to an outer surface of the riser pipe so as to drain water toward the well point.   The said drain material is a water absorption pipe system of Claim 1 provided with the water flow path through which water flows, and the filter which permeate | transmits the water which flows into the said water flow path.   3. The water absorption pipe system according to claim 1, wherein the drain material includes a core material made of plastic and a filter provided around the core material.   3. The water absorption pipe system according to claim 1, wherein the drain material includes a porous tube having a large number of holes formed on an outer peripheral surface thereof, and a filter wound around the outer peripheral surface of the porous tube.   5. The water absorption pipe system according to claim 1, wherein the drain material is at least 1 m shorter at an upper portion than an installation depth of the riser pipe. A groundwater level lowering method that lowers the groundwater level in the ground,
The water absorption pipe system according to any one of claims 1 to 4 is installed in the ground such that the well point is located below the groundwater level in the ground,
A groundwater level lowering method in which a negative pressure is applied from the upper end side of the riser pipe to suck groundwater. A groundwater level lowering method that lowers the groundwater level in the ground,
The water absorption pipe system according to claim 5 is installed in the ground so that the well point is located below the groundwater level in the ground, and the upper end of the drain material is located at least 1 m deep from the ground surface,
A groundwater level lowering method in which a negative pressure is applied from the upper end side of the riser pipe to suck groundwater.   The groundwater level lowering method according to claim 6 or 7, wherein the water absorption pipe system is inserted into the ground while jet water is sprayed from a tip of the well point for installation of the water absorption pipe system in the ground.   The groundwater level lowering method according to any one of claims 6 to 8, wherein after the suction of the groundwater is completed, the water suction pipe system is pulled up from the ground while jet water is sprayed from a tip of the well point.   The groundwater level lowering method according to any one of claims 6 to 9, wherein the target ground for lowering the groundwater level is silty ground. A method for compacting saturated ground,
The water absorption pipe system according to any one of claims 1 to 5 is installed in the ground to lower the groundwater level in the ground, or by the groundwater lowering method according to any one of claims 6 to 10. A saturated ground compaction method that lowers the groundwater level in the ground and then compacts the ground.   The method for compacting a saturated ground according to claim 11, wherein the compacting of the ground is performed by press-fitting, vibration, or impact of a material on the ground.

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