JP2012112103A - Soft ground improvement method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a soft ground improvement method capable of effectively and surely discharging pore water and air contained in the soft ground and particularly capable of effectively expediting consolidation settlement to a deep portion of the soft ground to be improved.SOLUTION: The soft ground improvement method injects air into the ground to be improved A through air injection pipes 22 arranged between vertical drains 11, thereby increasing a pressure difference between regions where the air is injected and the regions centering around the vertical drains 11 where a pressure is reduced.

Description

  The present invention relates to an improved construction method for soft ground that can efficiently and reliably discharge pore water and air contained in the soft ground, and in particular, the softening that effectively promotes consolidation settlement to the deep part of the soft ground to be improved. It relates to the ground improvement method.

  Conventionally, as an improved construction method for soft ground, the upper surface of soft ground to be improved (hereinafter referred to as improved ground) is covered with an airtight sheet, and a vacuum pressure is applied to the improved ground. In some cases, an isolated decompression region is created, and embankment is applied to soft ground to apply a compacted load on the embankment, thereby improving the soft ground to hard ground (see Patent Document 1).

  Specifically, as shown in FIG. 6, the vertical drain material 1 is placed in the improved ground A at a predetermined interval, and then horizontally so as to contact the upper end portion 1 a of each vertical drain material 1. A drain 2 is arranged, and then, a drain pipe 3 connected to a vacuum pump 5 via a vacuum tank 4 is connected to the horizontal drain material 2, and the upper surface 1 a of the vertical drain material 1 is horizontally disposed on the improved ground A upper surface. Covering with the airtight sheet 6 together with the drain material 2 and the water collecting pipe 3. Thereafter, the vacuum pump 5 connected to the water collecting pipe 3 through the vacuum tank 4 is operated.

  As a result, the vacuum pressure from the vacuum pump 5 propagates to the improved ground A via the horizontal drain material 2 and the vertical drain material 1, and the surrounding ground around the vertical drain material 1 is in a reduced pressure region (hereinafter referred to as “the lower ground”). Referred to as a reduced pressure region).

  The vacuum pressure propagates from the ground around the vertical drain material 1 that has become the decompression region to the ground around the outside, and as a result, the ground pressure (water pressure, earth pressure) toward the vertical drain material 1 is increased. appear.

  In accordance with this ground pressurization, pore water contained in the ground around the vertical drain material 1 is sucked out toward the vertical drain material 1 and drained by using the vertical drain material 1, the horizontal drain material 2 and the water collecting pipe 3 as a drainage path, Along with this, the ground around the outside of the ground around the vertical drain material 1 also becomes a decompression region.

  Thus, the decompression region spreads around the vertical drain material 1 and the surrounding ground extends, and the entire improved ground A eventually becomes the decompression region. At the same time, the consolidation and strength increase proceed with the vertical drain material 1 as the center. The whole area is consolidated and the strength is increased.

  As described above, while the hard ground is improved, the embankment 7 is applied on the airtight sheet 6, so that the improved ground A is consolidated and dewatered by the consolidation load of the embankment 7. The consolidation subsidence of the improved ground A is promoted in cooperation with the sucking out.

  In addition, in connection with the above-mentioned application, the present inventor proposed a construction method that can realize more effective vacuum consolidation by making the propagation path of vacuum pressure and the drainage path of pore water from the improved ground independent. (See Patent Document 2). In other words, the proposed construction method provides an independent drainage path including a drainage tank that separates pore water and air from the improved ground in the improved ground, and forcibly removes the pore water in the drainage tank. It drains out.

  According to this improved construction method, pore water from the improved ground is drained out of the improved ground through the drainage route, so that more efficient ground improvement has been made.

Japanese Patent No. 3270968 (refer to claims 1 and 2 and FIG. 7) Japanese Patent No. 3704463 (see claim 1, FIG. 1)

  However, even in the improved construction method using the vacuum pressure shown in Patent Documents 1 and 2, the negative pressure does not sufficiently propagate to the location where the depth of the soft ground exceeds 8 m, and therefore, the progress of the pressure density in the deep portion is delayed. There was a problem.

  The present invention has been made in view of such technical problems, and is an improved construction method for soft ground that can efficiently and reliably discharge pore water and air contained in the soft ground, and in particular, improved. It is an object of the present invention to provide an improved construction method for soft ground that can effectively promote consolidation settlement to the deep part of the soft ground.

In order to achieve the above object, the present invention provides a vertical drain placed at a predetermined interval in the improved ground, covers the upper surface of the improved ground with an airtight sheet, and applies a vacuum pressure under the airtight sheet. A negative pressure is applied to the improved ground through a vertical drain to create a decompression area isolated from the periphery of the improved ground, thereby draining pore water in the improved ground and improving the improved ground to a hard ground. In the improvement method of soft ground,
A soft pressure characterized in that an air injection pipe is disposed between the vertical drains to inject air into the improved ground, thereby increasing a pressure difference with a decompressed region around the vertical drain. The improved ground method was used as the gist.

  In the improved soft ground improvement method of the present invention, an air injection pipe is arranged between vertical drains so that air is injected into the improved ground. The pressure difference between the area around the vertical drain around the ground and the area around the air injection pipe into which air is injected becomes larger, and this increases the pressure on the ground toward the vertical drain. It will increase, and more effective consolidation will be realized. In addition, after the pore water is drained, the portion replaced with air is desaturated, so that an increase in strength can be expected.

The cross-sectional schematic diagram which showed the example of application of the improved construction method of this invention. The cross-sectional schematic diagram which showed another example of application of the improved construction method of this invention. The top view of FIG. 2 similarly. FIG. 4a shows a sheet having a large number of convex portions on the surface, FIG. 4b shows a sheet having irregularities, FIG. 4c shows a sheet having a large number of holes, and FIG. Showed the net. The cross-sectional schematic diagram which showed another form of the application example shown in FIG. The cross-sectional schematic diagram which showed the example of application of the conventional improved construction method.

  Hereinafter, an improved construction method for soft ground according to the present invention will be described according to an embodiment shown in the drawings. As shown in FIG. 1, the soft ground improvement method of the present invention (hereinafter referred to as the improvement method) is a method of placing a vertical drain 11 in the improved ground A at a predetermined interval and airtightly sealing the upper surface of the improved ground A. A method of creating a decompression region isolated from the improved ground peripheral part B by applying a negative pressure through the vertical drain 11 in the improved ground A by covering with the sheet 14 and applying a vacuum pressure under the airtight sheet 14 (hereinafter referred to as “reduced ground”). This is a further improvement of the vacuum consolidation method.

  In this vacuum consolidation method, the vertical drain material 11 is placed and a vertical drainage channel is created in the improved ground A, the horizontal drain material 12 is connected to the vertical drain material 11, and the horizontal drain material 12 is collected. A step of connecting the water pipe 13 and a step of covering the upper surface of the improved ground A with the airtight sheet 14 are provided.

  First, as shown in FIG. 1, the vertical drain material 11 is placed in the improved ground A at predetermined intervals. The vertical drain material 11 constitutes a vertical drainage channel, and can transmit the vacuum pressure (decompression) and function as a drainage channel even in an environment of ground pressurization, and does not clog, and is crushed by compression or decompression due to subsidence. If there is nothing, the structure, material, size, etc. are arbitrary. In the vertical drain material 11 shown in FIG. 1, a long plate-like synthetic resin wire arranged in a longitudinal direction at a constant interval is similarly provided with a long plate-like synthetic resin wire arranged at a predetermined interval in the orthogonal direction. A strip-shaped composite sheet composed of a synthetic resin net in which these synthetic resin wires are joined together at an intersection and a non-woven fabric enclosing the synthetic resin net was used. In this vertical drain material 11, even if it bends or bends, the water passage formed by the synthetic resin net and the nonwoven fabric is secured, and the entire synthetic resin net is covered with the nonwoven fabric. There is a merit that clogging is difficult to occur.

  The interval for placing the vertical drain material 11 is preferably within a range in which the vacuum pressure can be propagated by the applied vacuum pressure, and is specifically about 1 m. The vertical drain material 11 is inserted into the improved ground A in a state where it is inserted into a mandrel (not shown), and the mandrel (not shown) is pulled up while the vertical drain material 11 remains in the improved ground A. The material 11 can be placed.

  Thus, by placing the vertical drain material 11 in the improved ground A with a predetermined interval, a vertical drainage channel is created in the improved ground A with a predetermined interval. Water and air contained in the improved ground A between the roads are sucked up using the vertical drain material 11 as a drainage path.

  Next, a horizontal drain material 12 is connected to the vertical drain material 11. The vertical drain material 11 is driven so that the upper end portion 11a protrudes from the upper surface of the improved ground A, and the horizontal drain material 12 is arranged in parallel so as to contact the upper end portion 11a. As the horizontal drain material 12, as long as it has a function as a passage through which water and air can move in the longitudinal direction (horizontal direction) of the horizontal drain 12, anything such as a linear shape, a strip shape, or a planar shape may be used. Ports, for example, holes, slits, etc., through which water and air from the improved ground A side enter the horizontal drain material 12 are blocked by sand, earth and sand in the ground, and the water and air horizontal drain material 12 inside. It is preferable to have a structure in which it is difficult for water or air to enter due to the difficulty of intrusion into the water, or due to the passage or the like being blocked by sand or earth and sand in the improved ground A. In the form shown in FIG.1 and FIG.2, what has the same structure as the said vertical drain material 11 (The strip | belt-shaped composite sheet which consists of a synthetic resin net | network and the nonwoven fabric which covers the surface) was used. In this case, water and air enter from the side of the nonwoven fabric covering the synthetic resin net and move through the gap between the synthetic resin net and the nonwoven fabric and between the constituent fibers of the nonwoven fabric.

  The form of connecting the horizontal drain material 12 to the vertical drain material 11 is not particularly limited, and the horizontal drain material 12 may simply be placed on the upper end portion 11a of the vertical drain material 11 protruding on the upper surface of the improved ground A. In the example shown in FIG. 1, a method is adopted in which the horizontal drain material 12 is folded in half along the length direction and the upper end portion 11 a of the vertical drain material 11 is sandwiched.

  Next, the water collecting pipe 13 is connected to a required portion of the horizontal drain material 12. The water collecting pipe 13 is a perforated pipe having a large number of holes on the peripheral surface of the pipe, and a vacuum pump 16 is connected to one end side of the water collecting pipe 13 via a vacuum tank 15. The vacuum pressure from the vacuum pump 16 is transmitted to the water collecting pipe 13 through the vacuum tank 15, and further, the vacuum pressure is applied to the improved ground A through the horizontal drain material 12 and the vertical drain material 11 connected to the water collecting pipe 13. Is supposed to propagate.

  It does not specifically limit as a form which connects the water collecting pipe 13 to the horizontal drain material 12, The water collecting pipe 13 should just contact the horizontal drain material 12. FIG. In the example shown in FIG. 1, the horizontal drain material 12 is wound around the water collection pipe 13 so as not to be in a non-contact state.

  Next, the upper surface of the improved ground A is covered with an airtight sheet 14 together with the upper end portion of the vertical drain material 11, the horizontal drain material 12 and the water collecting pipe 13. The airtight sheet 14 is not particularly limited as long as air can be prevented from passing therethrough. For example, a synthetic resin sheet, in particular, a fiber base material is laminated on the surface of the synthetic resin film to increase the sheet strength. It is desirable that pinholes are less likely to occur during construction. The sheet terminal of the airtight sheet 14 is embedded in the peripheral portion B of the improved ground, and the upper surface of the improved ground A is covered together with the upper end portion of the vertical drain material 11, the horizontal drain material 12 and the water collecting pipe 13. By covering the upper surface of the improved ground A with the airtight sheet 14, the vacuum pressure from the vacuum pump 16 reliably propagates into the improved ground A through the water collection pipe 13, the horizontal drain material 12 and the vertical drain material 11, More efficient vacuum consolidation can be realized.

  Next, by operating the vacuum pump 16, the vacuum pressure from the vacuum pump 16 is such that the airtight sheet 14 blocks air in and out, and the vacuum tank 15, the water collection pipe 13, the horizontal drain material 12, and the vertical drain material. 11, and the inside of the vertical drain material 11 is set to a predetermined vacuum pressure.

  The vacuum pressure in the vertical drain material 11 propagates to the ground A around the vertical drain material 11, and the ground A around the vertical drain material 11 is defined as a decompressed region (hereinafter referred to as a decompressed region). The vacuum pressure propagates from the ground A around the vertical drain material 11 in the reduced pressure region to the surrounding ground A, and then pressurizes the ground (water pressure, soil) toward the ground A around the vertical drain material 11. Pressure).

  In accordance with this ground pressurization, pore water contained in the ground A around the vertical drain material 11 is sucked out toward the vertical drain material 11, and accordingly, the outside of the ground A around the vertical drain material 11 also becomes a decompression region. . Thus, the decompression region spreads around the vertical drain material 11 to the surrounding ground A, and the entire improved ground A eventually becomes the decompression region. At the same time, the consolidation and strength increase proceed with the vertical drain material 11 as the center. The consolidation and strength increase of the entire area A is performed.

  Further, in the vacuum consolidation method shown in FIG. 1, in addition to the vacuum consolidation by the above method, the following method is adopted. That is, the pore water sucked out from the improved ground A through the vertical drain 11 is drained through a drainage path independent of the vacuum pressure propagation path. In the example shown in FIGS. 1 and 2, a drain tank 18 is disposed in the improved ground A below the water collecting pipe 13 via a separator 17 and sucked through the vertical drain material 11 and the horizontal drain material 12 and once collected. While the pore water from the improved ground A that has entered the water pipe 13 is separated from the air by the separator 17, it flows into the drain tank 18 below the water collection pipe 13 according to gravity and is stored here.

  A drainage pump 19 is built in the drainage tank 18, and the gap water stored in the drainage tank 18 is outside the improved ground A through a drainage pipe 21 connected to the drainage tank 18 via a connecting pipe 20 ( The water is forcibly drained into the vacuum tank 15).

  As described above, in the vacuum consolidation method shown in FIG. 1, an independent drainage path including a drainage tank for separating pore water and air is provided in the improved ground, and the gap water in the drainage tank is forcibly removed from the improved ground. The ground can be improved more efficiently because it is drained.

  Moreover, in the aspect shown in FIG. 1, the air injection pipe | tube 22 is arrange | positioned between the vertical drains 11 set | placed in the improved ground A by the predetermined space | interval. The air injection pipe 22 is a perforated pipe such as a plastic pipe having many holes or an iron pipe, and is arranged in the improved ground A in parallel with the vertical drain 11. Air is injected into the improved ground by the air injection pipe 22.

  When the above-described vacuum consolidation method is applied to the improved ground A, a reduced pressure area is formed around the vertical drain 11 in the improved ground A, and the ground pressure (water pressure, soil) toward the vertical drain 11 is formed. The pore water contained in the ground A around the vertical drain material 11 is sucked out toward the vertical drain material 11 according to the pressure), and the improved ground A is passed through the air injection pipe 22 disposed between the vertical drain materials 11. When air is injected into the inside, the action of atmospheric pressure accompanying the air injection works, and between the area around the vertical drain 1 and the area around the air injection pipe 22 into which the air is injected. The pressure difference increases. As a result, the ground pressurization toward the vertical drain 1 is increased, the drainage speed of the interstitial water in the ground is increased, the drainage amount is increased, and more effective consolidation is realized.

  In the example shown in FIG. 1, a blower 24 is connected to the upper end portion of the air injection pipe 22 via an on-off valve 23. In other words, in the embodiment shown in FIG. 1, air is injected from the air injection pipe 22 between a region where the pressure is reduced around the vertical drain 1 and a region around the air injection pipe 22 where the air is injected. When it is considered that a sufficient pressure difference is generated, the on-off valve 23 is opened so that the air can be adjusted to be injected into the improved ground A from the air injection pipe 22.

  In the example shown in FIG. 1, since the blower 24 is connected to the upper end portion of the air injection pipe 22 via the on-off valve 23, the air injection from the air injection pipe 22 may be forced injection. it can.

  Next, an example in which the improved construction method of the present invention is applied to the above-described vacuum consolidation method and applied to a construction method that promotes consolidation settlement of the improved ground using reaction force will be described. Soft soil is dried by injecting air. Drying increases the strength of soft soil. However, the gaps between the soil particles are reduced by the self-weight consolidation accompanying the vacuum pressure and water level drop, but the voids remain. For this reason, a load is required to reduce the air interposed between the soil particles. The following FIGS. 2 to 5 show examples in which the ground is pressurized by a reaction force or a load due to embankment in order to reduce the air interposed between the soil particles. As shown in FIGS. 2 to 4, the upper end portion of the vertical drain material 11, the horizontal drain material 12, the water collection pipe 13 and the air injection pipe 22 are disposed in the improved ground A, and a large number of belt-like tension materials 31 are placed. Then, one or a plurality of inflatable bag-like objects 32 are arranged on the upper surface of the improved ground A, and the support member 33 made of a non-stretchable material connected to the upper end of the belt-like tension material 31 is attached to the one or more bags. It arrange | positions so that it may straddle the upper surface of the strip | belt-shaped object 32, and the tension | tensile_strength tension material 31 connected with the said support member 33 is tensioned by expanding the one or several bag-shaped object 32 after that, The ground between this belt-shaped tension material 31 Thus, the consolidation settlement is promoted by applying an actual load with atmospheric pressure as a reaction force to the deep part of the improved ground. In this case, the belt-like tension member 31, the bag-like object 32, and the support member 33 are disposed under the airtight sheet 16 that covers the upper surface of the improved ground A together with the upper end portion of the vertical drain member 11, the horizontal drain member 12, and the water collecting pipe 13. Is done. In addition, since the arrangement | positioning form of the upper end part of the vertical drain material 11, the horizontal drain material 12, the water collection pipe 13, and the air injection pipe 22 is the same as what is shown in FIG. 1, description here is omitted.

  First, as shown in FIGS. 2 and 3, a large number of belt-like tendons 31 are placed in the improved ground A at predetermined intervals. The belt-like tendon 31 is tensioned by the expansion of one or a plurality of bag-like objects 32, and acts to tighten the improved ground A between the belt-like tendons 32. The belt-like tendon 31 is driven by a frictional force generated between the improved ground A against the tensile force (pull-out force toward the upper surface of the improved ground A) due to the expansion of one or more bag-like objects 32. A material having a material and a structure having a large frictional resistance with the improved ground A so as to remain in position is preferable. Specifically, as shown in FIG. 4, a long strip-shaped resin plate or metal plate (FIG. 4a) having a large number of projections, a long strip-shaped resin plate or metal plate having a large number of projections and depressions (FIG. 4). 4b), a long strip-shaped resin plate or metal plate having a large number of holes (FIG. 4c), a long strip-shaped resin net or wire mesh (FIG. 3d), a non-stretchable or hardly stretchable long strip shape One of the fiber sheets or one made of a composite material thereof can be mentioned.

  The belt-like tendon 31 is placed by penetrating the improved ground A with the belt-like tendon 31 inserted in a mandrel (not shown) and leaving the belt-like tendon 31 in the improved ground A (illustrated). Not) can be done. At this time, the belt-like tendon 31 is driven so that the upper end portion 11 a protrudes from the upper surface of the improved ground A so that the upper end portion 31 a can be fixed to the support member 33. In the example of FIGS. 2 and 3, a long belt-like resin plate having a large number of irregularities is adopted as the belt-like tension member 31, and the mandrel is used as a predetermined interval in the improved ground A in the same manner as the vertical drain material 11. Was placed in parallel with the vertical drain material 11.

  In addition, the belt-like tension material 31 includes a belt-like tension drain that ensures a function as a drainage path and a function of preventing clogging by enclosing a resin net provided in a long belt shape with a fiber sheet such as a nonwoven fabric or a woven fabric. It can also be adopted. In this case, the belt-like tension drain has the two functions of the belt-like tension member 31 and the vertical drain member 11, and it is not necessary to drive the belt-like tension member 31 and the vertical drain member 11 separately. It is very efficient because the vertical drainage can be created and the belt-like tendon that tightens the improved ground A can be installed.

  Next, one or a plurality of bag-like objects 32 are arranged on the upper surface of the improved ground A depending on the scale of the improved ground A. As shown in FIGS. 2 and 3, the bag-like object 32 is arranged between the belt-like tendons 31 corresponding to the positions of the adjacent belt-like tendons 31 placed in the improved ground A. This bag-like object 32 is a balloon that is inflated using a liquid such as water or a gas such as air as a pressure source, and has a strength that does not easily rupture due to pressure applied during inflation or loading under vacuum pressure. If it is a thing, the material and structure will not be specifically limited. Preferable specific examples of the bag-like product 32 include a synthetic resin sheet, a composite sheet in which a tensile resistance material such as a wire net, a net, and a wire is integrated with the synthetic resin sheet to increase the strength, and a canvas is coated with a resin. A material obtained by laminating a resin film and imparting airtightness is preferably used as a raw material, which is formed into a spherical shape, a disc shape, a cigar shape, or a plate shape when expanded.

  Next, the support member 33 is disposed so as to straddle the upper surface of the one or more bag-like objects 32, and the upper end of the belt-like tension material 31 adjacent to the edge of the support member 33 is fixed. Thereby, the adjacent belt-like tension members 31 are connected via the support member 33 arranged on the upper surface of the bag-like object 32, and the adjacent belt-like tension members 31 and the support member 33 are formed in an inverted U shape so as to surround the bag-like object 32. Will be arranged.

  The support member 33 is not particularly limited in its material and structure as long as it has a non-stretch property that does not easily break even by a tensile force due to the expansion of the bag-like object 32. Preferable specific examples of the support member 33 include a non-extensible or hardly extensible fiber sheet, a resin net, a metal net, a resin plate, a metal plate, or a composite material thereof. In the example shown in FIGS. 2 and 3, a resin net is used as the support member 33.

  In the form shown in FIG. 4, for example, first, one end 40 a (a portion acting as a belt-like tension material) of the belt-like resin plate 40 in which the support member and the belt-like tension material are integrated is placed in the improved ground A. Next, the bag-like object 32 is arranged along the resin plate 40 protruding on the upper surface of the improved ground A, and then the central part 40b (the part acting as a support member) of the resin plate 40 is straddled across the bag-like object 32. Then, the other end 40c of the resin plate 40 (portion that acts as a belt-like tension material) can be formed by placing it in the improved ground A so as to have an inverted U shape.

  In addition, it can also be set as the form by which the supporting member 33 and the strip | belt-shaped tension | tensile_strength material 31 were integrally provided, for example, strip | belt-shaped tension | tensile_strength etc., such as a elongate strip-shaped composite sheet | seat which consists of a synthetic resin net | network and this As the material 31 and the support member 33, a material that also functions as a drain can be employed.

  Next, the one or more bag-like objects 32 are inflated. Thereby, the support member 33 arranged so that the expanded bag-like object 32 straddles the upper surface of the bag-like object 32 is pushed up, and the belt-like tension material 31 is connected to the belt-like tension material 31 connected thereto. The pulling-up force acts on the belt-like tension material 31 and the belt-like tension material 31 is tensioned, and the ground is tightened between the belt-like tension materials 31. As a result, the actual load with the reaction force of atmospheric pressure is applied to the deep part of the improved ground A (the depth position where the belt-like tendon 31 is placed), further promoting the consolidation settlement by the above-mentioned vacuum consolidation method, It is possible to increase the strength. In the case of this example, the effect of the vacuum consolidation method and the reaction force can be expected on the action of atmospheric pressure accompanying air injection, and more effective ground improvement can be performed.

  In addition, by applying the example shown in the figure, when improving the ground, such as a river embankment, where there is a restriction on embankment even though the support capacity of the ground is required, Since it can be used as a countermeasure for residual settlement instead of embankment for increasing the bearing capacity of the ground, it is possible to increase the strength of the improved ground in a short period without embankment.

  FIG. 5 shows an example in which the improved construction method of the present invention is applied to a construction method in which a reaction force is applied to the vacuum consolidation method and further embankment is applied. In addition, in this example, since it is the same as that shown in FIGS. 1-4 other than embankment, description here is omitted. As shown in FIG. 5, the embankment 34 is applied on the airtight sheet 16. In this case, as long as the strength of the material used allows, a reaction force caused by the embankment load can also be transmitted to the improved ground A as the tension force of the belt-like tension material 31, so that it is usually indicated by a thin arrow in FIG. As shown by the thick arrows in FIG. 5, the stress dispersion can be suppressed against the stress dispersion in the case of the embankment, and as a result, the reaction force due to the embankment load can be deepened through the belt-like tendon 31 ( It is possible to add up to the depth position where the tendon 31 is placed, and in combination with the action of the atmospheric pressure by the air injection, a higher consolidation strength can be increased.

  2 to 5 show examples in which the load of vacuum pressure and the load of loading pressure due to the expansion of the bag-like material are performed simultaneously, the present invention is not limited to this, and the load of vacuum pressure and the bag-like material are shown. It is also possible to alternately perform loading pressure loading due to the expansion.

  1 to 5, the clogging promoting material can be injected into the improved ground A through the air injection pipe 22. Examples of the clogging promoting material include bentonite, wood powder, and water glass. The clogging promoting material is sent into the improved ground A together with the air injected through the air injection pipe 22. As described above, soft soil is dried by applying the improved construction method of the present invention and injecting air into the improved ground. Drying increases the strength of soft soil. However, the gaps between the soil particles are reduced by the self-weight consolidation accompanying the vacuum pressure and water level drop, but the voids remain. The clogging promoting material sent into the improved ground A through the air injection pipe 22 enters the space between the soil particles and fills the gap. The clogging promoting material in contact with water swells, and the voids are clogged, and the air flow path in the improved ground A is changed, so that expansion of the flow path can be expected.

  With the expansion of the air flow path in the improved ground A, the expansion of the clogging region and the expansion of the unsaturated region occur continuously, and as a result, the improved region is expanded. In addition, drying shrinkage may occur in the air injection path, and an increase in strength can be expected.

  The present invention is not limited to the above example. For example, when the vertical drain material, the horizontal drain material, the airtight sheet, the belt-like tension material, the support member and the bag-like material are buried after being improved in the ground. It can be carried out by freely changing within the scope described in the claims, such as being composed of a biodegradable material such as a biodegradable resin that decomposes naturally.

DESCRIPTION OF SYMBOLS 11 ... Vertical drain material 12 ... Horizontal drain material 13 ... Water collecting pipe 14 ... Vacuum tank 15 ... Vacuum pump 16 ... Airtight sheet 22 ... Air injection pipe 31 ... Band shape Tension material 32 ... bag-like material 33 ... support member 34 ... embankment 40 ... resin plate A ... improved ground B ... peripheral ground

Claims (12)

A vertical drain is placed at a predetermined interval in soft ground to be improved (hereinafter referred to as improved ground), the upper surface of the improved ground is covered with an airtight sheet, and a vacuum pressure is applied under the airtight sheet to improve the above. A soft ground in which a negative pressure is applied through the vertical drain in the ground to create a decompression area isolated from the periphery of the improved ground, thereby draining pore water in the improved ground and improving the improved ground into a hard ground In the improved construction method,
A soft pressure characterized in that an air injection pipe is disposed between the vertical drains to inject air into the improved ground, thereby increasing a pressure difference with a decompressed region around the vertical drain. Ground improvement method.   2. The air injection pipe according to claim 1, wherein an opening / closing valve is provided at an upper end portion of the air injection pipe, and the opening / closing valve is opened / closed according to a decompression state in the improved ground to inject air from the air injection pipe. An improved construction method for soft ground.   The soft ground improvement method according to claim 1 or 2, wherein a blower is connected to an upper end portion of the air injection pipe so that air is forcibly injected into the improved ground.   A number of belt-like tendons are placed in the improved ground, and then one or a plurality of inflatable bags are disposed on the upper surface of the improved ground, and the non-stretchable material is connected to the upper end of the belt-like tendons. The support member is disposed so as to straddle the upper surface of the one or more bag-like objects, and then the belt-like tension material connected to the support member is tensioned by inflating the one or more bag-like objects. The improvement method of the soft ground according to any one of claims 1 to 3, wherein the ground is tightened between materials.   The belt-like tension material is made of a resin plate or a metal plate having a large number of irregularities or holes, a non-extensible or hardly extensible fiber sheet, a resin net, a wire mesh, or a composite material thereof. Item 5. An improved construction method for soft ground according to Item 4.   The method for improving soft ground according to claim 4 or 5, wherein the belt-like tendon is a belt-like tendon drain that also functions as a vertical drain member.   The soft ground improvement method according to any one of claims 4 to 6, wherein the bag-like material is made of a non-breathable sheet that expands using liquid or gas as a pressure source.   The support member is made of any one of a non-extensible or hardly extensible fiber sheet, a resin net, a metal net, a resin plate, a metal plate, or a composite material thereof. Improvement method of soft ground described.   The improvement method for soft ground according to claim 4, wherein the belt-like tendon material and the support member are integrally provided.   The improvement method of the soft ground according to any one of claims 4 to 9, wherein a load of a vacuum pressure and a load of a loading pressure due to expansion of one or a plurality of bag-like objects are performed simultaneously or alternately.   The improvement method for soft ground according to any one of claims 1 to 10, wherein embankment is performed on an airtight sheet.   The improvement method for soft ground according to any one of claims 1 to 3, wherein a clogging promoting material is injected into the improved ground through an air injection pipe.

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