JP2016205004A - Ground improvement method, ground improvement structure and improved ground - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ground improvement method, a ground improvement structure and an improved ground, which can improve earthquake resistance of an underground structure by restricting occurrence of liquefaction.SOLUTION: In a desaturation maintenance process #200, as shown in (A), a penetration hole that penetrates an underground structure S is formed, and an agent is injected in a liquefaction layer Lbelow the underground structure S, then a wall part 3a is constructed by curing the agent. In a desaturation treatment process #300, as shown in (B), ground water is discharged from the liquefaction layer Lbelow the underground structure S, and underground moisture in the liquefaction layer Lis removed by lowering the underground water level GWL of the liquefaction layer L. In the desaturation treatment process #300, air is supplied to the liquefaction layer Lbelow the underground structure S to force the air to be included in the soil of the liquefaction layer L, and the desaturation treatment is applied to the liquefaction layer Lbelow the underground structure S. As a result, as shown in (C), a desaturation region A is formed in the liquefaction layer Lbelow the underground structure S.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a ground improvement method for improving the ground by desaturating the liquefied layer in the ground, a ground improving structure for improving the ground to a state in which the liquefied layer in the ground is desaturated, and The present invention relates to an improved ground improved to a state in which a liquefied layer is unsaturated.

  Various construction methods have been studied and proposed for countermeasures against liquefaction of structures, but all of them are basically constructed individually as countermeasures. As a liquefaction countermeasure for desaturating the ground, methods of injecting air into the ground have been studied so far. The conventional ground improvement method is a process of forming an unsaturated region by sucking water and air in the ground open to the atmosphere, and sucking the air in the unsaturated region to make the unsaturated region negative pressure And a step of trapping air in the soil particles by sending air to the negative pressure region, and a step of restoring the groundwater level after trapping air in the soil particles. In such a conventional ground improvement method, the soil particles in the ground are dried by evacuation by opening to the atmosphere, and the air is stably trapped in the soil particles by restoring the water level, preventing liquefaction of the ground during an earthquake. It is out.

JP 2014-084559

  In the conventional ground improvement method, air is trapped in the soil particles in the unsaturated region, but the ground above the unsaturated region is open to the atmosphere. For this reason, the conventional ground improvement method has a problem that it is difficult to maintain a state where air is trapped in soil particles in an unsaturated region for a long period of time.

  The subject of this invention is providing the ground improvement construction method which can suppress generation | occurrence | production of liquefaction, and can improve the earthquake resistance of an underground structure, a ground improvement structure, and an improved ground.

The present invention solves the above-mentioned problems by the solving means described below.
In addition, although the code | symbol corresponding to embodiment of this invention is attached | subjected and demonstrated, it is not limited to this embodiment.
The invention of claim 1 is a liquefied layer in the ground (G) as shown in FIG. 2, FIG. 3, FIG. 5, FIG. 7, FIG. Is a ground improvement method to improve the ground by desaturating the groundwater level (GWL) of the liquefied layer (L ₁ ) below the underground structure (S), A ground improvement method (# 100) characterized by including a desaturation treatment step (# 300; # 500; # 700) for desaturation.

  The invention of claim 2 is the ground improvement construction method according to claim 1, as shown in FIG. 2, FIG. 3, FIG. 5, FIG. 7, FIG. It is a ground improvement construction method characterized by including the desaturation maintenance process (# 200; # 400, # 600) which maintains the liquefied layer of this in the desaturated state.

  According to a third aspect of the present invention, in the ground improvement method according to the second aspect, as shown in FIGS. 3, 5 and 12, the desaturation maintaining step extends downward or laterally from the underground structure. It is a ground improvement construction method characterized by including the process of constructing a wall (3a; 3b; 3f).

  As for invention of Claim 4, in the ground improvement construction method of Claim 2, as shown in FIG.7, FIG8 and FIG.10, the said desaturation maintenance process (# 400) is the said underground structure and earth retaining work. (7) It is a ground improvement construction method characterized by including the process of closing up the crevice between.

  According to a fifth aspect of the present invention, in the ground improvement method according to any one of the second to fourth aspects, as shown in FIGS. 7, 8, and 10, the desaturation maintaining step (# 400) Is a ground improvement method characterized by including a step of incorporating the earth retaining work to the non-liquefiable layer below the underground structure.

  As for invention of Claim 6, in the ground improvement construction method of any one of Claim 1 to Claim 5, as shown in FIG.14 and FIG.15, the said desaturation process process (# 700), Discharging the groundwater of the liquefied layer below the underground structure from the gap (Δ) between the underground structure and the earth retaining structure, and lowering the groundwater level of the liquefied layer. It is a ground improvement method.

  A seventh aspect of the present invention is the ground improvement method according to any one of the first to sixth aspects, wherein, as shown in FIGS. 2, 3, 5, 12, and 16, the unsaturation is performed. The liquefaction treatment step (# 300; # 700) includes a step of discharging the groundwater of the liquefied layer below the underground structure from the inside of the underground structure and lowering the groundwater level of the liquefied layer. It is a ground improvement method characterized by this.

  The invention of claim 8 is the ground improvement construction method according to any one of claims 1 to 7, wherein the underground structure is an urban tunnel.

In the invention of claim 9, as shown in FIGS. 1, 4, 6, 9, 11 and 13, 13 and 16, the liquefied layer in the ground (G) is in an unsaturated state. When the liquefied layer (L ₁ ) below the underground structure (S) is unsaturated, the liquefied layer is maintained in an unsaturated state. It is a ground improvement structure (2) characterized by including a desaturation maintenance part (3; 7).

  According to a tenth aspect of the present invention, in the ground improvement structure according to the ninth aspect, as shown in FIGS. 1, 4, and 11, the desaturation maintaining unit is configured so that the underground structure A ground improvement structure comprising a wall (3a; 3b; 3f) extending downward or laterally.

  As for invention of Claim 11, in the ground improvement structure of Claim 9 or Claim 10, as shown in FIG.6 and FIG.9, the said desaturation maintenance part is the said underground structure and earth retaining work (7). It is a ground improvement structure characterized by including the block part (3d; 3e) which plugs up the clearance gap between these.

  As for invention of Claim 12, in the ground improvement structure of any one of Claim 9 to Claim 11, as shown in FIGS. 13-16, the said desaturation maintenance part is the said underground structure. It is a soil improvement structure characterized in that it is a earth retaining work (7) rooted to the lower non-liquefaction layer.

  The invention of claim 13 is the ground improvement structure according to any one of claims 9 to 12, wherein the underground structure is an urban tunnel.

The invention of claim 14 is improved to a state in which the liquefied layer in the ground (G) is unsaturated as shown in FIGS. 1, 4, 6, 9, 11, 13, and 16. Improved ground, characterized in that this liquefied layer is desaturated by lowering the groundwater level (GWL) of the liquefied layer (L ₁ ) below the underground structure (S) The improved ground (1).

  The invention of claim 15 is the improved ground according to claim 14, characterized in that the liquefied layer below the underground structure is maintained in an unsaturated state.

The invention of claim 16 is the improved ground according to claim 14 or claim 15,
The underground structure is an improved ground characterized in that it is an urban tunnel.

  According to this invention, generation | occurrence | production of liquefaction can be suppressed and the earthquake resistance of an underground structure can be improved.

It is sectional drawing which shows typically the improved ground improved by the ground improvement construction method which concerns on 1st Embodiment of this invention. It is process drawing of the ground improvement construction method which concerns on 1st Embodiment of this invention. It is sectional drawing for demonstrating the ground improvement construction method which concerns on 1st Embodiment of this invention, (A) is sectional drawing for demonstrating a desaturation maintenance process, (B) is a desaturation process process. (C) is sectional drawing of the improved ground after a desaturation process. It is sectional drawing which shows typically the improved ground improved by the ground improvement construction method which concerns on 2nd Embodiment of this invention. It is sectional drawing for demonstrating the ground improvement construction method which concerns on 2nd Embodiment of this invention, (A) is sectional drawing for demonstrating a desaturation maintenance process, (B) is a desaturation process process. (C) is sectional drawing of the improved ground after a desaturation process. It is sectional drawing which shows typically the improved ground improved by the ground improvement construction method which concerns on 3rd Embodiment of this invention. It is process drawing of the ground improvement construction method which concerns on 3rd Embodiment of this invention. It is sectional drawing for demonstrating the ground improvement construction method which concerns on 3rd Embodiment of this invention, (A) is sectional drawing for demonstrating a desaturation maintenance process and a desaturation process, (B) Is a cross-sectional view for explaining the desaturation maintaining step, and (C) is a cross-sectional view of the improved ground after the desaturation maintaining step. It is sectional drawing which shows typically the improved ground improved by the ground improvement construction method which concerns on 4th Embodiment of this invention. It is sectional drawing for demonstrating the ground improvement construction method which concerns on 4th Embodiment of this invention, (A) is sectional drawing for demonstrating a desaturation maintenance process and a desaturation process, (B) Is a cross-sectional view for explaining the desaturation maintaining step, and (C) is a cross-sectional view of the improved ground after the desaturation maintaining step. It is sectional drawing which shows typically the improved ground improved by the ground improvement construction method which concerns on 5th Embodiment of this invention. It is sectional drawing for demonstrating the ground improvement construction method which concerns on 5th Embodiment of this invention, (A) is sectional drawing for demonstrating a desaturation maintenance process, (B) is a desaturation process process. (C) is sectional drawing of the improved ground after a desaturation process. It is sectional drawing which shows typically the improved ground improved by the ground improvement construction method which concerns on 6th Embodiment of this invention. It is process drawing of the ground improvement construction method which concerns on 6th Embodiment of this invention. It is sectional drawing for demonstrating the ground improvement construction method which concerns on 6th Embodiment of this invention, (A) (B) is sectional drawing for demonstrating a desaturation process, (C) is unsaturated. It is sectional drawing of the improved ground after a chemical conversion treatment process. It is sectional drawing for demonstrating the ground improvement construction method which concerns on 7th Embodiment of this invention, (A) (B) is sectional drawing for demonstrating an desaturation process process.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described in detail with reference to the drawings.
The ground G shown in FIG. 1 is the ground that supports the foundation of the structure. The groundwater level GWL is the depth at which groundwater is distributed. The groundwater level GWL is a surface in which the water pressure on the surface of the water that exists by filling a gap or a crack in the ground is equal to the atmospheric pressure, and is a depth from the reference surface of the groundwater surface. The liquefied layer L ₁ is a layer in which earth and sand containing a lot of moisture is deposited. The liquefied layer L ₁ is, for example, a saturated loose sandy ground below the groundwater level GWL. The non-liquefaction layer L ₂ is a layer that is determined not to cause liquefaction. The non-liquefied layer L ₂ is, for example, a viscous soil layer, a dense sandy soil layer, or a dense gravel layer. The unsaturated region A is a region where gas remains in the gap between the soil particles. The unsaturated zone A is formed by desaturating the liquefied layer L ₁ below the underground structure S.

The underground structure S is a structure constructed under the ground surface. The underground structure S is, for example, an urban tunnel constructed in a soft ground G in an urban area. The underground structure S is a box culvert that is a reinforced concrete box-type ramen structure that resists earth pressure, and an internal space is used as a subway track or a subway station building. The underground structure S constitutes an upper floor board S ₁ constituting the roof part of the underground structure S, a lower floor board S ₂ constituting the bottom part of the underground structure S, and a side wall part of the underground structure S. A side plate S ₃ and a middle column S ₄ connecting the upper floor plate S ₁ and the lower floor plate S ₂ are provided.

The improved ground 1 is a ground improved to a state in which the liquefied layer L ₁ in the ground G is unsaturated. In the improved ground 1, the liquefied layer L ₁ is desaturated by lowering the groundwater level GWL of the liquefied layer L ₁ below the underground structure S. In the improved ground 1, the liquefied layer L ₁ is desaturated for the purpose of improving the properties of the liquefied layer L ₁ in order to increase the strength of the ground G and suppress the settlement of the underground structure S. The improved ground 1 is maintained in a state in which the liquefied layer L ₁ below the underground structure S is unsaturated.

The ground improvement structure 2 is a structure for improving the ground G to a state where the liquefied layer L ₁ in the ground G is desaturated. The ground improvement structure 2 maintains the liquefied layer L ₁ below the underground structure S in an unsaturated state, maintains the strength of the ground G, and suppresses the settlement of the underground structure S. The ground improvement structure 2 includes an desaturation maintaining unit 3 and the like.

The desaturation maintaining portion 3, when the lower layer of the liquid layer L ₁ is desaturated than underground structures S, which is a portion for maintaining the liquid layer L ₁ in the state in which desaturate. The desaturation maintaining unit 3 includes a wall 3a extending from the underground structure S to the lower side of the underground structure. The wall 3a extends vertically downward from both lower edges of the underground structure S, and is constructed without a gap continuously in the length direction of the underground structure S. For example, the wall 3a is formed by injecting a mixture of a water glass-based chemical, a curing agent, and an auxiliary agent vertically from the inside of the underground structure S to the lower side of the underground structure S by a permanent chemical injection method. Built. Wall 3a is, for example, embedment at a predetermined depth in the lower end non-liquefied layer L ₂ of the wall portion 3a.

Next, the operation of the improved ground improved by the ground improvement method according to the first embodiment of the present invention will be described.
As shown in FIG. 1, when the liquefied layer L ₁ below the underground structure S is desaturated and an unsaturated region A is formed in the liquefied layer L ₁ , Gas remains in the gap between the soil particles. Or repositioned underground water level GWL after once lowering the groundwater level GWL to desaturate liquefaction layer L _1, even or groundwater level GWL is increased during an earthquake, the gas in the liquid layer L ₁ It becomes difficult state to enter groundwater in the liquid layer L ₁ because it is enclosed, floating of underground structures S is suppressed. In addition, the wall 3a of the desaturation maintaining unit 3 causes the gas remaining in the gap between the soil particles in the unsaturated region A to rise in the ground G from both edges of the underground structure S toward the ground surface. And the liquefied layer L ₁ is maintained in an unsaturated state. Furthermore, rainwater wall 3a of the desaturation maintaining unit 3 to penetrate from the ground G in the liquid layer L ₁ is prevented, the liquid layer L ₁ is maintained in a state of being desaturated.

Next, the ground improvement method according to the first embodiment of the present invention will be described.
The ground improvement method # 100 shown in FIGS. 2 and 3 is a method for improving the ground G by desaturating the liquefied layer L ₁ in the ground G. The ground improvement method # 100 is a countermeasure against liquefaction by desaturating the ground G. By desaturating the liquefied layer L ₁ below the underground structure S, the occurrence of liquefaction is suppressed. To improve the earthquake resistance of the underground structure S. The ground improvement method # 100 is an improvement method of the ground G performed for the existing underground structure S. As shown in FIG. 2, the desaturation maintaining step # 200 and the desaturation treatment step # 300 are performed. Including.

The injection device 4 shown in FIG. 3A is a device for injecting a medicine that strengthens the ground G. The injection device 4 injects water glass-based chemicals with additives such as hardeners and auxiliaries into the ground G in order to reduce the water permeability of the ground G and increase the strength of the ground G. Device. Injection device 4 includes an injection pipe 4a, which is a pipe vertically into the liquid layer L ₁ through the underground construction S, the injected agent in the lower layer of the liquid layer L ₁ than underground structures S A delivery pump 4b for feeding through the tube 4a is provided. As shown in FIG. 3A, the injection device 4 injects a drug below the underground structure S, thereby constructing a wall 3 a below the underground structure S.

The drainage device 5 shown in FIG. 3 (B) is a device that discharges groundwater from the liquefied layer L ₁ below the underground structure S. Drainage device 5 comprises a riser pipe 5a, which is piping vertically into the liquid layer L ₁ through the underground construction S, the pumping groundwater of the lower liquid layer L ₁ than underground structures S A pump 5b for discharging through the pipe 5a is provided. Drainage device 5, underground structures S, the right and left wall portions 3a and by discharging the groundwater from the liquid layer L ₁ that is surrounded by a non-liquefied layer L _2, the groundwater level of the liquid layer L ₁ GWL Reduce.

The supply device 6 shown in FIG. 3 (B) is a device that supplies gas to the liquefied layer L ₁ below the underground structure S. Feeder 6 includes a supply pipe 6a that is plumbed to penetrate the underground construction S liquefied layer L _1, the gas through the feed pipe 6a into the lower layer of the liquid layer L ₁ than underground structures S The compressor 6b to supply is provided. Feeder 6 injects air, a gas such as air bubbles or micro bubbles (microbubbles) to the liquid layer L _1. The supply device 6 desaturates the liquefied layer L ₁ by supplying gas to the liquefied layer L ₁ surrounded by the underground structure S, the left and right walls 3a and the non-liquefied layer L ₂ . An unsaturated region A is formed in the liquefied layer L ₁ .

The desaturation maintaining step # 200 shown in FIGS. 2 and 3A is a step of maintaining the liquefied layer L ₁ below the underground structure S in an unsaturated state. The desaturation maintaining step # 200 includes a step of constructing the wall 3a extending downward from the underground structure S. In the desaturation maintaining process # 200, as shown in FIG. 3A, a through-hole penetrating the underground structure S is formed, and the liquefied layer L ₁ below the underground structure S is supplied from the injection device 4 to the liquefied layer L _1. A chemical | drug | medicine is inject | poured, this chemical | medical agent is hardened, and the wall part 3a is constructed under the underground structure S. FIG.

The desaturation process # 300 shown in FIG. 2 and FIG. 3 (B) lowers the groundwater level GWL of the liquefied layer L ₁ below the underground structure S, and desaturates the liquefied layer L ₁ . It is a process to make. In desaturation step # 300, as shown in FIG. 3 (B), the drainage device 5 from the liquid layer L ₁ of the lower layer than the underground structures S to drain groundwater, groundwater liquid layer L ₁ The position GWL is lowered to remove moisture from the soil of the liquefied layer L ₁ . Further, the desaturation process # 300, state by supplying a gas by a supply device 6 in the liquid layer L ₁ of the lower layer than the underground structures S, the gas is sealed in the soil of the liquid layer L ₁ Then, the liquefied layer L ₁ below the underground structure S is desaturated. For this reason, as shown in FIG. 3C, an unsaturated zone A is formed in the liquefied layer L ₁ below the underground structure S. As a result, since gas remains in the gaps between the soil particles, it becomes difficult for the groundwater to enter the liquefied layer L ₁ even if the groundwater level GWL is restored, and the liquefied layer L ₁ becomes unsaturated and the ground G Will be strengthened. In addition, since the gas (bubbles) present in the liquefied layer L ₁ acts as a cushion to suppress the increase in pore water pressure that occurs during an earthquake, the strength against liquefaction increases.

The ground improvement method, the ground improvement structure, and the improved ground according to the first embodiment of the present invention have the following effects.
(1) In the first embodiment, in the desaturation treatment step # 300, the groundwater level GWL of the liquefied layer L ₁ below the underground structure S is lowered, and the liquefied layer L ₁ is desaturated. Let For this reason, the unsaturated liquefied layer L ₁ below the underground structure S can be covered with the underground structure S, and the gas escapes from the unsaturated liquefied layer L _1. It can be prevented by the underground structure S. As a result, the occurrence of liquefaction can be suppressed and the earthquake resistance of the underground structure S can be improved.

(2) In the first embodiment, in the desaturation maintaining step # 200, the liquefied layer L ₁ below the underground structure S is maintained in an unsaturated state. Further, in the first embodiment, when the liquefied layer L ₁ below the underground structure S is desaturated, the desaturation maintaining unit is brought into a state where the liquefied layer L ₁ is desaturated. 3 to maintain. Furthermore, in the first embodiment, the liquefied layer L ₁ below the underground structure S is maintained in an unsaturated state. For this reason, generation | occurrence | production of liquefaction can be suppressed over a long period of time, and the earthquake resistance of the underground structure S can be improved.

(3) In the first embodiment, in the desaturation maintaining step # 200, the wall 3a extending from the underground structure S to the lower side of the underground structure S is constructed. In the first embodiment, the wall portion 3a extends from the underground structure S to the lower side of the underground structure S. Therefore, penetration it is possible to gas than underground structures S remaining in the gap of the underlying soil particles is prevented by the wall portion 3a from being released from the ground surface, the liquid layer L ₁ rainwater from ground G This can be prevented by the wall portion 3a of the desaturation maintaining unit 3. As a result, the liquefied layer L ₁ below the underground structure S can be maintained in an unsaturated state for a long time. Moreover, compared with the case where a chemical | drug | medicine is inject | poured extensively from the lower surface of the underground structure S to the predetermined depth like the conventional ground improvement construction method, the injection amount of a chemical | medical agent can be reduced significantly and the ground G is low-cost. Can be strengthened.

(4) In the first embodiment, the liquefied layer L ₁ is desaturated by lowering the groundwater level GWL of the liquefied layer L ₁ below the underground structure S. For this reason, the earthquake resistance of the underground structure S can be easily improved only by forcibly lowering the groundwater level GWL of the liquefied layer L ₁ below the underground structure S.

(Second Embodiment)
In the following, the same parts as those shown in FIGS. 1 and 3 are denoted by the same reference numerals and detailed description thereof is omitted.
Unlike the desaturation maintaining unit 3 illustrated in FIG. 1, the desaturation maintaining unit 3 illustrated in FIG. 4 includes wall portions 3 b extending from both edges of the underground structure S to the side of the underground structure. Yes. The wall 3b extends horizontally outward from both lower edges of the underground structure S and is constructed continuously in the length direction of the underground structure S. For example, the wall 3b is formed by horizontally mixing a mixture of a water glass-based chemical, a curing agent, and an auxiliary agent from the inside of the underground structure S to the outside by a permanent chemical injection method. Built by injecting into.

Injection device 4 shown in FIG. 5, through the injection pipe 4a, which is a pipe in the horizontal direction within the liquid layer L ₁ through the underground construction S, delivering drug from the delivery pump 4b in the liquid layer L ₁ . The ground improvement method # 100 shown in FIG. 3 is an improvement method of the ground G performed on the existing underground structure S. In the desaturation maintaining process # 200, as shown in FIG. 5 (A), a through-hole penetrating the underground structure S is formed, and the liquefied layer L ₁ on the side of the underground structure S is supplied to the liquefied layer L _{1 from} the injection device 4. A chemical | drug | medicine is inject | poured, this chemical | medical agent is hardened, and a wall part is built in the side of the underground structure S. FIG. In desaturation step # 300, as shown in FIG. 5 (B), the processing desaturation liquid layer L ₁ by lowering the lower groundwater level GWL liquid layer L ₁ than underground structures S . As a result, an unsaturated region A is formed in the liquefied layer L ₁ as shown in FIG.

In addition to the effects of the first embodiment, the ground improvement method and the ground improvement structure according to the second embodiment of the present invention have the effects described below.
In the second embodiment, in the desaturation maintaining step # 200, the wall portion 3b extending from the underground structure S to the side of the underground structure S is constructed. In the second embodiment, the wall portion 3b extends from the underground structure S to the side of the underground structure S. For this reason, it can suppress by the wall part 3b that the gas which remained in the clearance gap between the soil particles below the underground structure S is discharge | released from the ground surface. Further, the penetration of rainwater from the ground G into the liquefied layer L ₁ can be suppressed by the wall 3 b of the desaturation maintaining unit 3. Furthermore, compared with the case where a medicine is injected over a wide range from the lower surface of the underground structure S to a predetermined depth as in the conventional ground improvement method, the amount of medicine injected can be greatly reduced, and the ground G can be reduced in cost. Can be strengthened.

(Third embodiment)
The underground structure S shown in FIG. 6 is an urban tunnel such as an excavation tunnel constructed by an excavation method. The desaturation maintaining unit 3 includes blocking portions 3c and 3d that block the gap Δ between the underground structure S and the earth retaining work 7. The closing portion 3 c is filled between the outer side surface of the underground structure S and the inner side surface of the earth retaining work 7, and is filled with no gap in the length direction of the underground structure S. The clogging portion 3c, for example, pumps backfill material such as fluidized soil in which water and cement are mixed into construction residual soil between the both side surfaces of the underground structure S and the side surfaces of the earth retaining work 7 by using a pump. Built with filling in between. The closing portion 3d is laid from the inner side surface of one earth retaining work 7 to the inner side surface of the other earth retaining structure 7 through the bottom surface of the underground structure S, and is continuous along the length direction of the underground structure S. And laid. The closing portion 3d is made of, for example, a waterproof material such as a butyl rubber-based or vinyl chloride-based rubber sheet laid on the lower surface of the underground structure S, and bends both edges of the waterproof material substantially vertically upwardly. It is bonded to the side with an adhesive.

The earth retaining work 7 is a structure for preventing the ground G from collapsing. The earth retaining work 7 is constructed to ensure the stability of the surrounding ground G when excavating the ground G to construct the underground structure S. The earth retaining work 7 is, for example, a steel sheet pile (sheet pile) driven into the ground G by a steel sheet pile method. The earth retaining work 7 is constructed without a gap along the length direction of the underground structure S with a predetermined gap Δ between the underground structure S and the outer side surface of the underground structure S. For example, the lower end portion of the earth retaining work 7 is embedded in the non-liquefied layer L ₂ at a predetermined depth. The earth retaining work 7 also functions as a part for maintaining the liquefied layer L ₁ in an unsaturated state when the liquefied layer L ₁ below the underground structure S is unsaturated.

Next, the operation of the improved ground improved by the ground improvement method according to the third embodiment of the present invention will be described.
As shown in FIG. 6, when the liquefied layer L ₁ below the underground structure S is desaturated and the unsaturated region A is formed in the liquefied layer L ₁ , Gas remains in the gap between the soil particles. Or repositioned underground water level GWL after once lowering the groundwater level GWL to desaturate liquefaction layer L _1, even or groundwater level GWL is increased during an earthquake, the gas in the liquid layer L ₁ It becomes difficult state to enter groundwater in the liquid layer L ₁ because it is enclosed, floating of underground structures S is suppressed. In addition, the gas remaining in the gap between the soil particles in the unsaturated region A rises in the ground G from both edges of the underground structure S toward the ground surface, and the blocking portion 3c of the desaturation maintaining portion 3 3d and the earth retaining work 7 are blocked, and the liquefied layer L ₁ is maintained in an unsaturated state. Furthermore, stopping portions 3c of the desaturation maintaining portion 3 of rain water to penetrate the soil G to the liquid layer L _1, 3d and earth retaining Engineering 7 is prevented, a state where the liquid layer L ₁ is desaturated Maintained.

Next, a ground improvement method according to a third embodiment of the present invention will be described.
The ground improvement method # 100 shown in FIGS. 7 and 8 is an improvement method of the ground G performed on the newly installed underground structure S. The desaturation maintaining step # 400 and the desaturation treatment step # 500. And desaturation maintaining step # 600. 7 and desaturation maintaining step # 400 shown in FIG. 8 (A) is a step of maintaining the state of the liquid layer L ₁ of the lower layer was desaturation than underground construction S. The desaturation maintaining step # 400 includes a step of incorporating the earth retaining work 7 to the non-liquefied layer L ₂ below the underground structure S. In the desaturation maintaining step # 200, as shown in FIG. 8 (A), the earth retaining work 7 is driven into the ground G, and the lower end of the earth retaining work 7 is rooted in the non-liquefied layer L ₂ , and then is predetermined from the ground surface. The ground G is excavated to a depth of. The excavation surface R is the final excavation surface when excavating the ground G in order to construct the underground structure S. The excavation surface R functions as a support ground that supports the underground structure S.

The desaturation process # 500 shown in FIGS. 7 and 8A lowers the groundwater level GWL of the liquefied layer L ₁ below the underground structure S, and desaturates the liquefied layer L ₁ . It is a process to make. In desaturation step # 500, as shown in FIG. 8 (A), to drain groundwater by drainage device 5 from the lower liquid layer L ₁ than excavating surface R, the groundwater level of the liquid layer L ₁ The water is removed from the soil of the liquefied layer L ₁ by lowering the GWL. Further, the desaturation process # 500, by supplying the gas by a supply device 6 in the liquid layer L ₁ of the lower layer than the excavating surface R, in a state in which the gas is sealed soil liquefaction layer L ₁ The liquefied layer L ₁ below the excavation surface R is desaturated.

7 and desaturation maintaining step # 600 shown in FIG. 8 (B) is a step of maintaining the state of the liquid layer L ₁ of the lower layer was desaturation than underground construction S. The desaturation maintaining step # 600 includes a step of closing the gap Δ between the underground structure S and the earth retaining work 7. In the desaturation maintaining step # 600, as shown in FIG. 8 (B), a closing portion 3d is laid on the excavation surface R, and both edges of the closing portion 3d are bent upward to form an inner side surface of the earth retaining work 7. In the bonded state, the underground structure S is constructed on the upper surface of the closing portion 3d. Next, in the desaturation maintaining step # 600, between the outer side surface of the underground structure S and the inner side surface of the earth retaining work 7, between the outer side surface of the underground structure S and the surface of the closing portion 3d, and the closing portion. The clogging portion 3c is constructed by filling the fluidized soil on the upper surface of 3d. For this reason, as shown in FIG. 8C, an unsaturated region A is formed in the liquefied layer L ₁ below the excavation surface R. As a result, since gas remains in the gaps between the soil particles, it becomes difficult for the groundwater to enter the liquefied layer L ₁ even if the groundwater level GWL is restored, and the liquefied layer L ₁ becomes unsaturated and the ground G Will be strengthened. In addition, since the gas (bubbles) present in the liquefied layer L ₁ acts as a cushion to suppress the increase in pore water pressure that occurs during an earthquake, the strength against liquefaction increases.

In addition to the effects of the first embodiment, the ground improvement method and the ground improvement structure according to the third embodiment of the present invention have the following effects.
(1) In the third embodiment, in the desaturation treatment step # 500, the groundwater level GWL of the liquefied layer L ₁ below the underground structure S is lowered, and the liquefied layer L ₁ is unsaturated. Make it. For this reason, the fall of the groundwater level GWL implemented as a part of construction when newly installing the underground structure S can be used as a countermeasure for liquefaction. As a result, the construction period can be shortened, the cost can be reduced, and the construction can be performed at a lower cost than the existing liquefaction countermeasure construction method.

(2) In the third embodiment, in the desaturation maintaining step # 600, the gap between the underground structure S and the earth retaining work 7 is closed. Further, in the third embodiment, the desaturation maintaining step # 600, to put roots earth retaining Engineering 7 to the non-liquefied layer L ₂ of the lower layer than the underground construction S. Further, in the third embodiment, the gaps 3c, 3d block the gap Δ between the underground structure S and the earth retaining work 7. Further, in the third embodiment, the earth retaining work 7 is embedded up to the non-liquefaction layer L ₂ below the underground structure S. For this reason, the gas remaining in the gap between the soil particles below the underground structure S is discharged from between the underground structure S and the earth retaining work 7, or the gas from below the underground structure S to the outside of the earth retaining work 7. Can be prevented from being released. In addition, rainwater can be prevented from penetrating from the ground G into the liquefied layer L ₁ , and rainwater and the like can be prevented from entering the underground structure S from the outside of the earth retaining work 7. As a result, it is possible to maintain the liquefied layer L ₁ below the underground structure S in an unsaturated state for a long time.

(Fourth embodiment)
The underground structure S shown in FIG. 9 is an urban tunnel based on the non-cutting method, unlike the urban tunnel based on the cutting method shown in FIGS. 6 and 8. In such a non-cutting method, for example, a track such as the HEP & JES method (High Speed Element Pull method and Jointed Element Structure method (steel element joint method)) that builds an underground structure S without cutting. The underground structure S is constructed by the lower crossing method (under the line crossing method). Here, the under-track crossing method is a box-type ramen type that is inserted into the roadbed and the roadbed under the road while pulling the steel element having the excavator by the towing device installed on the arrival side, and is uncut under the roadbed surface. This is a construction method for constructing the underground structure S.

  The desaturation maintaining unit 3 includes a closing portion 3e that closes the gap Δ between the underground structure S and the earth retaining work 7. The closing portion 3e is filled between the outer side surface of the underground structure S and the inner side surface of the earth retaining work 7, and is filled without a gap in the length direction of the underground structure S. The closing part 3e is, for example, pumping high water-stopping concrete obtained by mixing water into water-stopping cement between the both side surfaces of the underground structure S and the side surfaces of the earth retaining works 7 and filling between them. Built.

Next, the effect | action of the improved ground improved by the ground improvement construction method which concerns on 4th Embodiment of this invention is demonstrated.
As shown in FIG. 9, when the liquefied layer L ₁ below the underground structure S is desaturated and the unsaturated region A is formed in the liquefied layer L ₁ , Gas remains in the gap between the soil particles. Or repositioned underground water level GWL after once lowering the groundwater level GWL to desaturate liquefaction layer L _1, even or groundwater level GWL is increased during an earthquake, the gas in the liquid layer L ₁ It becomes difficult state to enter groundwater in the liquid layer L ₁ because it is enclosed, floating of underground structures S is suppressed. In addition, the gas remaining in the gap between the soil particles in the unsaturated region A rises in the ground G from both edges of the underground structure S toward the ground surface, and the blocking portion 3e of the desaturation maintaining portion 3 and The earth retaining work 7 is blocked and the liquefied layer L ₁ is maintained in an unsaturated state. Furthermore, rainwater stopping portions 3e and earth retaining Engineering 7 of desaturation maintaining unit 3 to penetrate the liquid layer L ₁ is prevented from ground G, the liquid layer L ₁ is maintained in a state of being desaturated The

Next, a ground improvement method according to a fourth embodiment of the present invention will be described.
The ground improvement method # 100 shown in FIG. 10 is an improvement method of the ground G implemented for the newly installed underground structure S, and includes the desaturation maintaining step # 400, the desaturation treatment step # 500, Saturation maintenance process # 600 etc. are included. The desaturation maintaining process # 400 shown in FIG. 10A is the same process as the desaturation maintaining process # 400 shown in FIG. 8A, and the desaturation treatment process # 500 is shown in FIG. This is the same process as the desaturation process # 500 shown in FIG. Desaturation maintaining step # 600 shown in FIG. 10B is a step of maintaining the liquefied layer L ₁ below the underground structure S in an unsaturated state. The desaturation maintaining step # 600 includes a step of closing the gap Δ between the underground structure S and the earth retaining work 7. In the desaturation maintenance process # 600, after the underground structure S is constructed on the excavation surface R, concrete having a high water-stopping capacity is filled between the outer side surface of the underground structure S and the inner side surface of the earth retaining work 7. The closing part 3e is constructed. For this reason, as shown in FIG. 10C, an unsaturated region A is formed in the liquefied layer L ₁ below the excavation surface R. As a result, since gas remains in the gaps between the soil particles, it becomes difficult for the groundwater to enter the liquefied layer L ₁ even if the groundwater level GWL is restored, and the liquefied layer L ₁ becomes unsaturated and the ground G Will be strengthened. In addition, since the gas (bubbles) present in the liquefied layer L ₁ acts as a cushion to suppress the increase in pore water pressure that occurs during an earthquake, the strength against liquefaction increases. The fourth embodiment of the present invention has the same effect as the third embodiment.

(Fifth embodiment)
The desaturation maintaining unit 3 shown in FIG. 11 includes a wall 3f extending downward from the underground structure S. The wall 3f extends vertically downward from both lower edges of the underground structure S, and is constructed without a gap continuously in the length direction of the underground structure S. Walls 3f, for example, and a slurry-like cured material of cement or cement-based solidifying material together with water, was sprayed while rotating about a vertical axis toward the underground structures S in the liquid layer L _1, the injection material It is a solidification improvement body which was built perpendicularly toward the lower part of the underground structure S by the stirring and mixing method for forcibly stirring and mixing. Walls 3f, for example, the lower end of the desaturation maintaining portion 3 is embedment in a predetermined depth in the non-liquefied layer L _2.

Next, a ground improvement method according to a fifth embodiment of the present invention will be described.
The ground improvement method # 100 shown in FIG. 12 is an improvement method of the ground G performed on the existing underground structure S, and includes the desaturation maintaining step # 200, the desaturation treatment step # 300, and the like. The stirring and mixing device 8 is a device that stirs and mixes the ground G while injecting a hardener onto the ground G. The stirring and mixing device 8 penetrates the underground structure S and advances while rotating around the vertical axis in the liquefied layer L ₁ , and the liquefaction below the underground structure S. and a like delivery pump 8b for delivering curable material through the injection pipe 8a into the layer L _1.

In the desaturation maintaining step # 200 shown in FIG. 12 (A), a through-hole penetrating the underground structure S is formed, and the hardening material is supplied from the stirring and mixing device 8 to the liquefied layer L ₁ below the underground structure S. The liquefied layer L ₁ is agitated and mixed while injecting, and the hardener is cured to construct the wall 3 f below the underground structure S. The desaturation process # 300 shown in FIG. 12B is the same process as the desaturation process # 300 shown in FIG. Therefore, as shown in FIG. 12 (C), unsaturated region A is formed in the liquid layer L ₁ of the lower layer than the underground construction S. As a result, since gas remains in the gaps between the soil particles, it becomes difficult for the groundwater to enter the liquefied layer L ₁ even if the groundwater level GWL is restored, and the liquefied layer L ₁ becomes unsaturated and the ground G Will be strengthened. In addition, since the gas (bubbles) present in the liquefied layer L ₁ acts as a cushion to suppress the increase in pore water pressure that occurs during an earthquake, the strength against liquefaction increases. The fifth embodiment has the same effect as the first embodiment.

(Sixth embodiment)
An underground structure S shown in FIG. 13 is an urban tunnel such as an excavation tunnel constructed by an excavation method. The earth retaining work 7 is, for example, an existing steel sheet pile remaining in the ground G when the underground structure S is constructed by the open-cut method, and the lower end portion of the earth retaining work 7 becomes the non-liquefied layer L ₂ . Rooted at a predetermined depth.

The drainage device 5 shown in FIG. 15 (A) has an underground structure through a pumping pipe 5a that is vertically routed from the surface of the ground G through the gap Δ between the underground structure S and the earth retaining work 7. Groundwater is discharged from the liquefied layer L ₁ below S by the pumping pump 5b. The drainage device 5 lowers the groundwater level GWL of the liquefied layer L ₁ by discharging the groundwater from the liquefied layer L ₁ surrounded by the underground structure S, the earth retaining work 7 and the non-liquefied layer L ₂ . Let

The supply device 6 shown in FIG. 15 (B) passes through the gap Δ between the underground structure S and the earth retaining work 7 from the surface of the ground G, and supplies the underground structure through the supply pipe 6a that is vertically connected. Gas is supplied into the liquefied layer L ₁ below S by the compressor 6b. The supply device 6 desaturates the liquefied layer L ₁ by supplying gas to the liquefied layer L ₁ surrounded by the underground structure S, the earth retaining work 7 and the non-liquefied layer L ₂ . An unsaturated region A is formed in the chemical layer L ₁ . The supply device 6 is arranged at a distance from the drainage device 5 along the length direction of the underground structure S.

The ground improvement method # 100 shown in FIGS. 14 and 15 is an improvement method of the ground G performed on the existing underground structure S, and includes the desaturation treatment step # 700 and the like. 14 and desaturation step # 700 shown in FIG. 15 (A) (B), rather than underground construction S reduces the underlying water table GWL liquid layer L _1, the liquid layer L ₁ This is a step of desaturation. Desaturation step # 700, and discharges the underlying ground water liquid layer L ₁ from the gap Δ from the underground structures S between the underground structures S and earth retaining Engineering 7, of the liquid layer Including a step of lowering the groundwater level GWL. In the desaturation process # 700, as shown in FIG. 15A, the groundwater is discharged from the gap Δ between the both side surfaces of the underground structure S and the side surface of the earth retaining work 7 by the drainage device 5, and the groundwater The position GWL is lowered to remove moisture from the soil of the liquefied layer L ₁ . Further, in the desaturation treatment step # 700, as shown in FIG. 15B, gas is supplied by the supply device 6 from the gap Δ between the both side surfaces of the underground structure S and the side surface of the earth retaining work 7. , the soil liquefaction layer L ₁ in a state in which the gas is filled, the liquid layer L ₁ of the lower layer is processed desaturated than underground construction S. For this reason, as shown in FIG. 15C, an unsaturated zone A is formed in the liquefied layer L ₁ below the underground structure S. As a result, since gas remains in the gaps between the soil particles, it becomes difficult for the groundwater to enter the liquefied layer L ₁ even if the groundwater level GWL is restored, and the liquefied layer L ₁ becomes unsaturated and the ground G Will be strengthened. In addition, since the gas (bubbles) present in the liquefied layer L ₁ acts as a cushion to suppress the increase in pore water pressure that occurs during an earthquake, the strength against liquefaction increases.

The ground improvement method according to the sixth embodiment of the present invention has the following effects in addition to the effects of the third and fourth embodiments.
In the sixth embodiment, the desaturation process # 700, the groundwater underlying liquid layer L ₁ is discharged than the underground construction S through the gap Δ between the underground structures S and earth retaining Engineering 7 Thus, the groundwater level GWL of the liquefied layer L ₁ is lowered. For this reason, it is possible to easily reduce the groundwater level GWL below the existing underground structure S and to take measures against liquefaction in a short time at a low cost.

(Seventh embodiment)
The underground structure S shown in FIG. 16 is an urban tunnel such as an excavation tunnel constructed by the excavation method, like the underground structure S shown in FIGS. 13 and 15. The earth retaining work 7 shown in FIG. 16 is an existing steel sheet pile or the like that is left in the ground G when the underground structure S is constructed by the open-cut method, similarly to the earth retaining work 7 shown in FIGS. 13 and 15. . Desaturation process step # 300 shown in FIGS. 16A and 16B is the same process as desaturation process step # 300 shown in FIG. In desaturation step # 300, as shown in FIG. 16 (A), the underlying ground water liquid layer L ₁ than underground structures S is discharged by the drainage device 5 from the interior of the underground structures S The groundwater level GWL is lowered to remove moisture from the soil of the liquefied layer L ₁ . Further, in the desaturation treatment step # 300, as shown in FIG. 16B, gas is supplied from the inside of the underground structure S to the liquefied layer L ₁ below the underground structure S by the supply device 6. to, the soil liquefaction layer L ₁ in a state in which the gas is filled, the liquid layer L ₁ of the lower layer is processed desaturated than underground construction S. Therefore, as shown in FIG. 16 (B), the unsaturated zone A is formed in the liquid layer L ₁ of the lower layer than the underground construction S. As a result, since gas remains in the gaps between the soil particles, it becomes difficult for the groundwater to enter the liquefied layer L ₁ even if the groundwater level GWL is restored, and the liquefied layer L ₁ becomes unsaturated and the ground G Will be strengthened. In addition, since the gas (bubbles) present in the liquefied layer L ₁ acts as a cushion to suppress the increase in pore water pressure that occurs during an earthquake, the strength against liquefaction increases.

The ground improvement method according to the seventh embodiment of the present invention has the following effects in addition to the effects of the third and fourth embodiments.
In the seventh embodiment, in the desaturation process step # 300, the underground water of the liquefied layer L ₁ below the underground structure S is discharged from the inside of the underground structure S, and this liquefied layer L ₁ is discharged. Reduce the groundwater level. For this reason, it is possible to easily lower the groundwater level GWL below the existing underground structure S, and the pipe lengths of the pumping pipe 5a and the supply pipe 6a are shortened as compared with the sixth embodiment. Cost reduction and shortening of construction period can be achieved.

(Other embodiments)
The present invention is not limited to the embodiment described above, and various modifications or changes can be made as described below, and these are also within the scope of the present invention.
(1) In this embodiment, the case where the underground structure S is an urban tunnel has been described as an example. However, underground structures such as a gutter, a pipeline, an underground tank, a public underground commercial facility, a sewage treatment facility, or an underground power plant The present invention can also be applied to structures. In this embodiment, the case where the underground structure S is an urban tunnel constructed by the open-cut method is described as an example. However, the present invention is also applied to an urban tunnel constructed by a shield method or an urban NATM. can do. Furthermore, in this embodiment, the case where air is supplied by the supply device 6 has been described as an example, but a gas other than air can also be supplied.

(2) In this embodiment, the case where gas is supplied by the supply device 6 while the groundwater in the liquefied layer L ₁ below the underground structure S is discharged by the drainage device 5 has been described as an example. However, the present invention is not limited to the case where the discharge operation and the gas supply operation are simultaneously performed. Vacuum example, and supplies the gas by a supply device 6 after discharging the groundwater by drainage device 5, from the liquid layer L ₁ after discharging the underground water from the liquid layer L ₁ by discharging air liquefaction layer L ₁ After that, gas can be supplied to the liquefied layer L ₁ . In the first embodiment, the second embodiment, the fifth embodiment, and the seventh embodiment, the case where air is supplied to the liquefied layer L ₁ by the supply device 6 has been described as an example. Can be omitted. In this case, a through hole is formed in the bottom of the underground structures S, when discharging the groundwater by drainage device 5, air may also be a natural flow into the liquid layer L ₁ from the underground structures S.

(3) In the first embodiment, the second embodiment, and the fifth to seventh embodiments, the case where the present invention is applied to the existing underground structure S has been described as an example. The present invention can also be applied to the structure S. Further, in the first embodiment and the fifth embodiment, the wall portion 3a, has been described as an example a case of putting roots 3f to non liquefaction layer L _2, was placed root to the non-liquefied layer L ₂ Instead, it can also be embedded in the liquefied layer L ₁ to a predetermined depth. Moreover, in this 3rd Embodiment and 4th Embodiment, the case where this invention was applied to the newly installed underground structure S was mentioned as an example, However, This invention is applied also to the existing underground structure S Can do. Furthermore, in this 3rd Embodiment, although the case where the fluidized soil was poured only between the outer side surface of the underground structure S and the inner side surface of the earth retaining work 7 was described as an example, the upper surface of the underground structure S It is also possible to pour fluidized soil between the ground and the ground surface and backfill the ground G dug down to the original state with the fluidized soil.

(4) In the third embodiment, the fourth embodiment, the sixth embodiment, and the seventh embodiment, the case where the earth retaining work 7 is rooted up to the non-liquefaction layer L ₂ has been described as an example. The liquefied layer L ₁ may be rooted to a predetermined depth without being rooted to the liquefied layer L ₂ . Moreover, in this 4th Embodiment, although the case where the underground structure S was constructed | assembled by non-opening was mentioned as an example, this invention is applicable also to the case where the underground structure S is constructed by open cutting. Furthermore, in this 5th Embodiment, although the case where the wall part 3f was constructed | assembled below from both edge parts of the underground structure S was mentioned as an example, it has been demonstrated below from both edges and center parts of the underground structure S. The wall 3f can also be constructed.

DESCRIPTION OF SYMBOLS 1 Improved ground 2 Ground improvement structure 3 Desaturation maintenance part 3a, 3b Wall part 3c-3e Blocking part 3f Wall part 4 Injection | pouring apparatus 4a Injection pipe 4b Delivery pump 5 Drainage apparatus 5a Drain pipe 5b Pumping pump 6 Supply apparatus 6a Supply pipe 6b Compressor 7 Earth retaining (unsaturation maintenance section)
8 Stir and Mixer 8a Injection Pipe 8b Delivery Pump G Ground
GWL Groundwater level L ₁ Liquefied layer L ₂ Non-liquefied layer A Unsaturated zone S Underground structure S ₁ Upper floor plate S ₂ Lower floor plate S ₃ Side S ₄ Middle column Δ Gap R Drilling surface

Claims (16)

A ground improvement method that improves the ground by desaturating the liquefied layer in the ground,
Including a desaturation treatment step of lowering the groundwater level of the liquefied layer below the underground structure to desaturate the liquefied layer;
A ground improvement method characterized by In the ground improvement construction method according to claim 1,
Including an unsaturation maintaining step of maintaining a liquefied layer below the underground structure in an unsaturated state;
A ground improvement method characterized by In the ground improvement construction method according to claim 2,
The desaturation maintaining step includes a step of constructing a wall portion extending downward or laterally from the underground structure;
A ground improvement method characterized by In the ground improvement construction method according to claim 2,
The desaturation maintaining step includes a step of closing a gap between the underground structure and the earth retaining work;
A ground improvement method characterized by In the ground improvement construction method according to any one of claims 2 to 4,
The desaturation maintaining step includes a step of incorporating a soil retaining work into a non-liquefiable layer below the underground structure;
A ground improvement method characterized by In the ground improvement construction method according to any one of claims 1 to 5,
The desaturation treatment step is a step of lowering the groundwater level of the liquefied layer by discharging the groundwater of the liquefied layer below the underground structure from the gap between the underground structure and the earth retaining work. Including
A ground improvement method characterized by In the ground improvement construction method according to any one of claims 1 to 6,
The desaturation treatment step includes a step of discharging the groundwater of the liquefied layer below the underground structure from the inside of the underground structure to lower the groundwater level of the liquefied layer,
A ground improvement method characterized by In the ground improvement construction method according to any one of claims 1 to 7,
The underground structure is an urban tunnel;
A ground improvement method characterized by A ground improvement structure that improves this ground to a state where the liquefied layer in the ground is desaturated,
When the liquefied layer below the underground structure is desaturated, a desaturation maintaining unit that maintains the liquefied layer in an unsaturated state is provided.
Ground improvement structure characterized by In the ground improvement structure according to claim 9,
The desaturation maintaining part includes a wall part extending from the underground structure to a lower side or a side of the underground structure;
Ground improvement structure characterized by In the ground improvement structure according to claim 9 or 10,
The desaturation maintaining unit includes a blocking unit that blocks a gap between the underground structure and the earth retaining work;
Ground improvement structure characterized by In the ground improvement structure according to any one of claims 9 to 11,
The desaturation maintaining part is a soil retaining work rooted in a non-liquefiable layer below the underground structure;
Ground improvement structure characterized by In the ground improvement structure according to any one of claims 9 to 12,
The underground structure is an urban tunnel;
Ground improvement structure characterized by An improved ground improved to a state in which the liquefied layer in the ground is unsaturated,
The liquefied layer is desaturated by lowering the groundwater level of the liquefied layer below the underground structure,
Improved ground characterized by The improved ground according to claim 14,
The liquefied layer below the underground structure is maintained in an unsaturated state,
Improved ground characterized by The improved ground according to claim 14 or 15,
The underground structure is an urban tunnel;
Improved ground characterized by

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