JP6188081B2 - Fluidized sand and ground improvement method using it - Google Patents

Description

  The present invention relates to a fluidized sand in which a sanding material used for ground improvement is mixed with a fluidizing agent so that it can be pumped, and a ground improvement method such as press-fitting sand pile formation and sand filling using the sand.

  Among the ground improvements, for example, the sand compaction pile method (SCP method) increases the density of the ground by creating a compacted sand pile in the ground, and is a common liquefaction countermeasure method. Since a large construction machine is used, it is often not applicable due to constraints in securing construction space. As alternative construction methods, the application of chemical injection systems using small construction machines and methods of press-fitting cement mortar are increasing, but in addition to increasing costs, it is possible to use sand materials that can reduce environmental impact A construction method was desired. From such a background, as disclosed in Patent Documents 1 to 3, the present applicants put the sand material into a fluidized state that can be pumped by pumping, and press-fitting into the ground to reduce cost and environmental burden. A press-in sand pile construction method that enables reduction has been developed and put into practical use. This construction method is called sand press-in type static compaction method (SAVE-SP method (registered trademark): equivalent to the press-in type sand pile construction method of the present invention). Furthermore, since it can also be used for oblique construction, it can also cope with improvements directly under existing structures.

  Patent Document 1 discloses the basics of the press-fit sand pile construction method. That is, in this construction method, a sand pile material fluidized material (hereinafter referred to as fluidized sand) containing a fluidizing agent and a slow-acting plasticizing agent in the sand material used for ground improvement is maintained in the ground while maintaining the fluidized state. Press fit into the ground and plasticize in the ground. The details are as follows. After the hollow tube 24 has penetrated into the ground to the design depth, fluidized sand containing a slow-acting plasticizer is pressed through the hollow tube 24 from the ground surface to the ground, and the flow into the ground. The sand pile 25 having a predetermined length is formed by leaving the fossil sand and press-fitting the fluidized sand for the next step on this, and repeating this. As shown in FIG. 4, the apparatus includes a fluidized sand production plant 10 containing a slow-acting plasticizer, a hollow pipe 23 for sand pile formation, and fluidized sand produced in the production plant 10. A pressure feed pump 4 that feeds the empty pipe 23 through a pipe 34 is provided. Reference numeral 1 denotes fluidized sand supply means, 2 denotes sand material supply means, 3 denotes fluidizing agent supply means, and 5 denotes a slow-acting plasticizer supply apparatus.

  Patent Document 2 discloses a fluidized sand production plant. In this production plant, a fluidizing sand is produced by mixing a fluidizing agent with a sand material. The fluidizing sand is mixed with water, a fluidizing agent, and a slow-acting plasticizer in this order. Preferably, the fluidized sand measures the weight of the sand material, and based on the weight, water, a fluidizing agent, and a slow-acting plasticizer are automatically calculated and mixed.

  Drawing 5 is a mimetic diagram showing the state change of the material at the time of construction using the above fluidized sand. The same (a) shows fluidized sand before press-fitting. Until the fluidized sand is pressed into the ground from the hollow tube, the fluidizing agent (for example, an anionic polymer material) increases the viscosity of the pore water between the sand particles and eliminates the friction between the particles. Suppresses separation from water and maintains high fluidity. The same (b) shows fluidized sand during press-fitting. During the press-fitting, the fluidized sand is dehydrated and compacted into a dense state. The fluidizer remains reticulated. (C) shows the plasticized end state. In this state, the slow-acting plasticizing agent electrically neutralizes the fluidizing agent and disappears the network structure of the fluidizing agent, and the friction between particles is completely recovered. In addition, Patent Document 3 discloses a sand filling method for stabilizing the ground by filling the underground cavity with fluidized sand as an example of the use of the fluidized sand other than those described in Patent Documents 1 and 2. ing.

Japanese Patent No. 5188894 Japanese Patent No. 5189951 JP2012-12878A

  When applying the press-fit sand pile construction method using fluidized sand, the characteristics of the target ground are ascertained through preliminary surveys, and sand material selection and blending specifications are determined accordingly. In the actual construction method, a hollow pipe having a diameter of about 100 to 200 mm is generally used, and a sand pile having a diameter of about 500 to 700 mm is often formed by injecting fluidized sand into the ground. Here, since the sand material is pumped in a state where the fluidity is enhanced, the sand material needs to have a property of having both good water retention that does not block in the piping and good drainage that dehydrates during press-fitting. The pressability of fluidized sand is also affected by the drainage of the original ground. For example, compared to sandy ground with a fine grain content Fc = about 10 to 20%, the fine sand content is less like gravel ground. On the other hand, in the ground having good water permeability, even when a sand material having the same particle diameter is used, the pressure generated when fluidized sand is injected into the ground tends to increase.

FIG. 6 shows the particle size distribution of the sand material used in the construction work so far, that is, the applicable sand. The applicable sand material is basically sand having an average particle diameter D ₅₀ = about 0.5 mm and a fine particle content Fc = about 5% or less. When sand having a coarse particle size composition is used as fluidized sand, the material cannot be sufficiently pumped into the ground because it is drained during pumping or immediately after ground injection. Such a problem is not improved even if the mixing ratio of the fluidizing agent and the slow-acting plasticizing agent is changed. The pressurization amount does not reach the target value due to the increase in the amount of fluidized sand or the dehydration of fluidized sand. In addition, applicable sand materials are often more expensive than sand materials that can be used for the SCP method because the selection range is limited, which is a limiting factor in further expanding the application of the press-in sand pile construction method. It has become.

  Therefore, the object of the present invention is to reduce the constraints from the soil properties of the ground when applying the press-fitting sand pile construction method (SAVE-SP method) or the sand filling method, even for rough sand that is difficult to apply as a sand material. The purpose is to expand the opportunity for further application of the method by allowing a sufficient amount to be pumped into the ground. Other objects will be clarified in the following description.

  In order to achieve the above object, the invention of claim 1 is a fluidization process in which a fluidizing agent is added to a sand material used for ground improvement such as press-fitting type sand pile formation and sand filling, and processed so as to be transportable through a pipe by a pressure pump. In the sand, among the water-absorbent resins, the water-absorbing resin has a high water-absorbing power and does not have thickening and cohesiveness or a very low water-absorbing resin together with the fluidizing agent, and the amount of the superabsorbent resin added is increased or decreased. This is characterized by adjusting the fluidization maintenance time in which the fluidization state is maintained.

  The present invention as described above is more preferably embodied as follows. That is, the invention of claim 2 has a configuration in which the sand material is mixed with the fluidizing agent, the superabsorbent resin, water content adjustment water, and a slow-acting plasticizing agent. The invention of claim 3 is the structure according to claim 2, wherein the bleeding rate after 3 hours of filling the bag with fluidized sand is 0.5% or less. From Tables 1 and 2, this bleeding rate value is a configuration in which the superabsorbent resin contains 0.5 g or more per 1,000 g of sand material (dry sand).

In order to achieve the above object, the invention according to claim 4 is a ground improvement method such as press-fitting sand pile formation or sand filling, wherein the fluidized sand according to claim 2 or 3 is penetrated into the ground through a pipe by a pump. It is characterized by being pumped to a hollow tube to be pulled out and pressed into the ground from the tip side of the hollow tube and plasticized in the ground.

  Further, the invention of claim 5 is the fluidized sand according to claim 4, wherein the fluidized sand is contained in the fluidized sand at a location where the earth covering pressure is small (for example, a location where the depth approaches the ground surface side). By injecting a forced drainage agent that enables forced drainage of water and rapidly plasticizing the fluidized sand, the sand material of the fluidized sand that has been pressed into the ground rises to the surface side and is discharged. It is a configuration to prevent.

The inventions of claims 1 and 4 contain a superabsorbent resin having a high water absorbing power and no thickening and cohesiveness as compared with conventional fluidized sand together with a fluidizing agent. The following advantages can be obtained when using it for ground improvement methods such as press-fitting sand pile creation and sand filling because it is possible to adjust the fluidization maintenance time to keep the fluidized state by increasing and decreasing the amount of addition. Is obtained.
(A) The fluidized sand of the present invention is difficult to drain even with sand having a coarse particle size composition, which has been considered to be unusable until now, due to the load received when injecting into the ground in addition to the pumping process. Coarse sand material that has been impossible in the past can be used, and the range of usable sand material can be expanded.
(B) At the same time, even if the soil soil properties are changed from medium sand to coarse sand, and further from coarse sand to gravel, the amount of water that is immediately dehydrated after being injected into the ground is suppressed, maintaining water retention and thus maintaining fluidity. Therefore, the necessary amount of press-fitting can be injected, and as a result, restrictions from the soil properties of the ground can be relaxed.

  The invention of claim 2 specifies an ideal composition of fluidized sand. The action of the fluidized sand will be described with reference to FIG. First, the slow-acting plasticizer acts to electrically neutralize the fluidizing agent from the state (a) to the state (c) and separates the water retained in the fluidized sand little by little. . The superabsorbent resin reinforces the water holding power of the fluidized sand and suppresses the degree of shrinkage of the fluidizing agent that binds the particles generated by the load that the fluidized sand receives before and during the press-fitting, The fluidizing agent makes it difficult to touch the slow-acting plasticizing agent. As a result, in this configuration, the time for the fluidized sand to change from the state (a) to the state (b), that is, the fluidization maintaining time for maintaining the fluidized state by delaying the drainage can be adjusted to be longer than before. Become.

  The invention of claim 3 is based on whether or not the fluidized sand contains a superabsorbent resin, the bleeding rate, that is, the ratio of the separated water to the total fluidized sand when 3 hours have passed after the bag is filled with the fluidized sand. Is based on the physical property test results (see Tables 1 and 2) that are significantly reduced, and is important as an evaluation index when the fluidized sand of the present invention is produced.

  In the invention of claim 5, the fluidized sand (sand material) can be achieved as designed without the amount of press-fitting of sand (sand material) being insufficient or conversely excessive. That is, when the fluidized sand according to claims 1 to 3 is used in an improved construction method such as press-fitting sand pile formation or sand filling disclosed in claim 4 or patent documents 1 to 3, a place where the earth pressure is small (for example, In areas where the depth approaches the ground surface, where the hydraulic conductivity is small), a part of the fluidized sand that has been pressed into the ground from the lower end of the hollow pipe rises through a gap formed around the hollow pipe. It becomes easy to be discharged to the front side. As a countermeasure, the present invention, as shown in FIG. 2, injects a forced drainage agent into fluidized sand that is press-fitted into the ground, and rapidly plasticizes the fluidized sand. Only the drained and separated water is raised to the ground surface and discharged.

It is a schematic diagram for description which showed the apparatus structure in the case of implementing the press-fit type sand pile construction method and sand filling construction method of this invention. It is the principal part enlarged view to which the A section of FIG. 1 was expanded. (A) is a graph showing bleeding test results among physical property test results for fluidized sand blends (Tables 1 and 2), (b) is a dehydration test result for superabsorbent resin blends (Tables 3 and 4), It is a graph about the relationship between dehydration time and dehydration amount. It is explanatory drawing which shows the sand pile production apparatus currently disclosed by patent document 1. FIG. (A)-(c) is explanatory drawing which shows the state change of the fluidization sand at the time of construction. It is the actual product figure which described the particle size distribution of the sand material used by the press-fit type sand pile construction method.

  Embodiments to which the present invention is applied will be described below with reference to the drawings. In this explanation, after clarifying the construction machine used for the press-in sand pile construction method and the sand filling method, the manufacturing plant for producing fluidized sand, and the press-in sand pile construction method, a superabsorbent resin is used as Example 1. A physical property test of the contained fluidized sand and a dehydration test using a superabsorbent resin as Example 2 will be described.

(Construction machine) The construction machines used in the construction method of claim 4 or 5 can be roughly classified into a crawler type (inclination angle is vertical, that is, 0 degrees) in which a hollow tube is vertically inserted or pulled out along a leader, Boring machine type (tilt angle is about 0-20 degrees) that penetrates and pulls out the empty pipe suspended from the auxiliary crane, and rotary percussion drill type that tilts the hollow pipe at an arbitrary angle (tilt angle is About 0-60 degrees), and is selected according to the target ground and construction depth.

  FIG. 1 schematically shows a small crawler type construction machine 1 and a fluidized sand production plant 2 among the above three types. The construction machine 1 includes an elevating mechanism 4 that moves the hollow tube 3 up and down, a rotating mechanism 5 that is held by the elevating mechanism 4 and rotates the hollow tube 3, and a swivel provided at the upper end 3a of the hollow tube. 15, a pump P for pumping the fluidized sand produced in the production plant 2, a pipe 16 connecting the outlet of the pump P and the swivel 15, and a pump 16 provided in the middle of the pipe 16. A pressure gauge 6 for detecting the pressure of fluidized sand is provided.

  Here, the elevating mechanism 4 is moved up and down via a rack and pinion mechanism or the like along one side of the columnar leader 12 erected so as to be movable by the traveling base machine 10. The rotating mechanism 5 is moved up and down along the leader 12 by the elevating mechanism 4 and forwardly and reversely rotates the hollow tube 3 via a motor and a reduction gear mechanism. The base machine 10 positions and holds the lower end side of the leader 12 in front of the cab 11, and a hydraulic device, an electric motor, and the like not shown are mounted on the rear side of the cab 11. In the cab 11, various construction operation units and control units are arranged. The leader 12 is supported by an expansion / contraction rod 13 or the like, and is attached to the lower side to restrain the swinging of the hollow tube 3, and the guide tool 17 is attached to the upper side and supports the upper side of the pipe line 16. Etc. The upper end of the pipe line 16 is connected to the upper end 3 a of the hollow pipe 3 through the swivel 15.

  As for the pump P, a pumping structure using a hydraulic piston is selected as a pump P that does not cause particularly high suction force, confidentiality, and air suction, and can keep the change in fluidized sand property low. The pump drive is automatically controlled via a control unit arranged in the cab 11. The pressure gauge 6 detects the pressure of the fluidized sand being pumped by the pump P and press-fits into the ground side region (location where the density is lowered by drawing the hollow tube and its surroundings) from the lower end opening of the hollow tube 3. Allows the pressure of the fluid to be measured when measured. Moreover, the pressure gauge 6 detects the pressure at the time of pumping of fluidized sand at the time of construction, and transmits the detection signal to the control part of the cab 11. In the control unit, a drive stop signal is transmitted to the pump P when the set press-fit pressure is reached as the press-fit pressure of the fluid based on the detection signal. In addition, if the pressure flow meter which detects a flow volume with a pressure is used as the pressure gauge 6, the filling amount of the fluidized sand according to drawing of 1 pitch mentioned later can also be known immediately.

(Fluidized sand production plant) This production plant 2 is mainly composed of a production apparatus 20 having a mixing chamber 21 and an agitator chamber 22 and the like, and sand supply means 23 such as a backhoe for feeding sand material 7 into the mixing chamber 21. Fluidizing agent supplying means 24 for supplying a fluidizing agent, water supplying means 25 for supplying water for adjusting the water content, plasticizing agent supplying means 26 for supplying a plasticizing agent, water absorbing property for supplying a highly water-absorbing resin Resin supply means 27 is provided. Further, in this example, as a part of the manufacturing plant 2, forced drainage agent supply means 28 for injecting the forced drainage agent into the fluidized sand press-fitted from the hollow pipe 3 is provided. Although this forced drainage agent supply means 28 is shown in a location away from the production plant 2 in the drawing, it can also be provided near the production plant 2. Moreover, although the above manufacturing plant 2 is illustrated for convenience in the place which approached the construction area, since the fluidized sand and forced drainage agent which are manufactured are pumped by the dedicated pump means P, 100 mm or more from the construction area. It can also be provided at a remote location.

  When applying the press-fit sand pile construction method using fluidized sand, selection of sand materials and blending specifications are determined according to the characteristics of the target ground through a preliminary survey. In the production plant 2, the intended fluidized sand is usually produced for each batch (sand pile 9) in the mixing chamber 21. Sand material 7 supplied by the sand supply means 23, fluidizer supplied by the fluidizer supply means 24, water supplied by the water supply means, plasticizer supplied by the plasticizer supply means 26, water absorption With respect to the highly water-absorbent resin supplied by the functional resin supply means 27, the selection criteria and functions will be made clear below.

(1) Since the sand material is pumped in a state where the fluidity is once enhanced, the sand material preferably has the property of having both good water retention that does not block in the piping and good drainage that dehydrates during press-fitting. However, in the present invention, coarser sand and gravel than the particle size composition that can be applied in the conventional SAVE-SP method shown in FIG.

(2) A fluidizing agent is an additive that increases the viscosity of pore water between sand particles and suppresses separation of sand and water in a saturated state to improve pumpability. Preferably, it is an anionic polymer flocculant that increases the viscosity and suppresses the settling and separation of sand particles, and may also be a nonionic polymer flocculant or a cationic polymer flocculant. These are excellent in the performance of retaining moisture inside the polymer hydrophilic groups and the polymer network, and also have high quality long-term stability. As anionic polymer flocculants, homopolymers such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, acrylamide 2-methylpropane sulfonic acid, vinyl sulfonic acid, styrene sulfonic acid, and copolymers with acrylamide Is mentioned.

  The blending ratio of the fluidizing agent is 0.01 to 2.0% by weight, preferably 0.1 to 1.0% by weight, based on the sand material. If the blending ratio is too small, the sand material will not be fluidized and will not be pumped due to separation or clogging in the piping, and if it is too large, the fluidization effect will not change and the cost will be increased. It will be. Here, the fluidity that can be pumped by the pump P means a material having a stable shear strength of less than 0.3 kg in the “vane shear test” defined by the Japanese Industrial Standard.

(3) The slow-acting plasticizer is an additive that has the effect of separating sand and water over time and returning them to the original sand. For example, when the fluidizing agent is an anionic polymer agent, a cationic polymer agent having a molecular weight of 10 ⁴ to 10 ⁷ is used. When the fluidizing agent is a cationic polymer agent, an anion having a molecular weight of 10 ⁴ to 10 ⁷ is used. Based on high molecular weight polymer. This electrically neutralizes the fluidizing agent, separates it from water and returns it to the original sand. That is, the interstitial water between the sand particles returns to normal water having no viscosity, and the friction of the sand particles is restored.

  The amount of the slow-acting plasticizing agent used is a blending amount capable of plasticizing the fluidized sand, and is 0.001 to 2% by weight, preferably 0.001 to 2% by weight, based on the sand material in the fluidized sand to be produced. 0.01 to 1.0% by weight. If this amount is too small, the fluidized material will not be plasticized, and it will not be possible to create a sand pile as designed.If too much is added, plasticization will occur quickly, hindering pump pumping, and high cost. Become.

(4) Water is used for adjusting the water content ratio, and it is preferable to use neutral tap water, avoiding industrial water and seawater containing various components that affect the fluidizing agent and the like. The amount of water used is usually calculated so that the water content of the fluidized sand produced is 30% to 40%.

(5) The superabsorbent resin is a cross-linked product of hydrophilic linear or molecular polymer, and the fluidized sand maintains the fluidized state of the fluidized sand by increasing or decreasing the content of the resin. It is possible to adjust the fluidization maintenance time at the time of formation to be long, and a water absorption power is high, and there is no or extremely low viscosity, agglomeration and dispersibility. In addition, the superabsorbent resin generally has a water absorption capacity (amount) of 10 times or more of its own weight in water. However, in order to effectively adjust the fluidization maintenance time of fluidized sand, It is preferable to use a force (amount) that is 100 times higher than its own weight in water. This is because if the water absorption is less than 100 times its own weight, the amount of use increases, handling becomes worse and cost increases.

  By the way, among the water-absorbing resins, synthetic polymer-based high water-absorbing resins include polyacrylates, polysulfonates, maleic anhydrides, polyacrylamides, and polyethylene oxides. Depending on the application, the ability to absorb water can be changed by changing the type of the hydrophilic resin chain serving as a trunk, and the strength of the gel swollen by absorbing water can be changed by changing the crosslinking density. Therefore, for example, some polyacrylate water-absorbing polymers have dispersibility and water absorption is less than 10 times their own weight. In the present invention, such a water-absorbing polymer having a small water-absorbing power is excluded, and a water-absorbing resin having a water-absorbing power of 10 times or more, preferably 100 times or more of its own weight in water, such as a polyacrylate-based high water-absorbing resin. Etc. are used. As a commercial item, "Himosub 300" of the polyacrylic acid bridge | crosslinking type made from Hymo Co., Ltd. used in the Example is mentioned, for example. This was a white powder and the water absorption (amount) was about 300 to 600 times in water. The amount of the superabsorbent resin used is 0.01 to 1.0% by weight, preferably 0.05 to 0.2% by weight, based on the sand material in the fluidized sand to be produced. . This is 0.01% by weight or less in the sand material used in this test (comparative example and example) in adjusting the fluidization maintenance time to be long as inferred from FIGS. 3 (a) and 3 (b). On the contrary, if it is 0.25% by weight or more, the effect becomes excessive or the cost becomes high.

  As an example of the polyacrylate-based superabsorbent resin, a sodium polyacrylate-based superabsorbent resin (SAP) is synthesized by partially neutralizing acrylic acid and copolymerizing it with a crosslinkable monomer. The synthesized poly (sodium acrylate) SAP is shown as a unit molecular arrangement having the following constitution, and has a crosslinked three-dimensional network structure. When the carboxyl group in some places contains water, sodium ions are contained in the gel. Dissociate. High water absorption (100 to 1000 times its own weight) is said to be in the balance of the three forces of affinity, osmotic pressure, and crosslinking density of this resin.

(6) Forced drainage agent is a fluid that is press-fitted in order to prevent some of the fluidized sand that is press-fitted from the hollow pipe from rising up the gap formed around the hollow pipe and being discharged to the surface side. By injecting into the sand and rapidly plasticizing the fluidized sand, only the water drained from the fluidized sand (suppressing the rise of the sand material) is raised to the surface side and discharged. This action is due to the ionization of sodium ions when the sodium polyacrylate-based superabsorbent resin absorbs water as a superabsorbent resin. Since the concentration is high outside and thin inside, we apply the phenomenon that water goes out from inside by osmotic pressure. As the forced drainage agent, calcium chloride, magnesium chloride, aluminum chloride, etc. may be used in addition to sodium chloride. Further, as illustrated in FIG. 2, the forced drainage agent is preferably injected into the fluidized sand 7 ′ immediately after being pressed into the ground as an aqueous solution through the liquid injection pipe 8 from the surface side. However, it is also effective to inject an appropriate amount of the forced drainage agent into the mixing chamber 21 or the agitator chamber 22 on the manufacturing apparatus side as a powder or an aqueous solution at an appropriate time in the latter half of one batch without using the injection pipe 8.

(Manufacturing procedure of fluidized sand) In the production plant 2, in order to exhibit the water absorption performance of the superabsorbent resin satisfactorily, for example, the superabsorbent resin and the water content adjustment water were added while stirring the sand material 7. Thereafter, a fluidizing sand is prepared by adding a fluidizing agent and a slow-acting plasticizing agent. The rule of thumb is that, after preparing fluidized sand, which is a mixture of water content adjustment water, fluidizing agent, and slow-acting plasticity, after adding a superabsorbent resin, The water absorption performance of the resin cannot be fully exhibited or it takes a lot of time for water absorption. Further, when the water-absorbing resin is added after adding water content adjustment water to the sand material, the water content adjustment water is absorbed and gelled, so that stirring takes time. This is to avoid these.

  Based on the above explanation, the blending specification of the fluidized sand determines the selection of sand materials, the fluidizing agent, the plasticizing agent, the water content adjustment water, and the superabsorbent resin by the blending test. The standard is the maximum particle size and fine particle content set in advance as the particle size characteristics for sand materials, and the flow rate, texture test, and bleeding test are performed for fluidized sand to determine the optimal blend ratio and blend amount. . For superabsorbent resins, see Examples 1 and 2 below. It has been found that fluidized sand containing a highly water-absorbent resin can reduce the amount of fluidizing agent to be less than before.

(Press-fit type sand pile construction method) This construction method is as follows when the characteristic points are exemplified in the example using the construction machine 1 of FIG. First, the operation procedure is such that the hollow tube 3 is penetrated to the design depth in the ground via the lifting mechanism 4 and then pulled out by a predetermined pitch, and the density that can be formed below the hollow tube 3 in the pulling step. The improved sand pile 9 having a predetermined length is formed by repeatedly performing the feeding process of press-fitting fluidized sand around the low area and the surrounding area. The construction management is carried out in the control section of the cab 11 with the maximum penetration depth of the hollow tube 3 (lower end depth), the drawing length L for one pitch, the total number of pitches ((lower end depth−upper end depth) / L), Values such as the set press-fit (discharge) pressure are input to the program. The produced fluidized sand is prepared in the agitator section 22.

  At the time of construction, after the construction machine 1 is moved and positioned at the construction site, the hollow tube 3 is inserted into the ground while being rotated through the lifting mechanism 4 and the rotating mechanism 5. This penetration is determined by a signal from a depth meter (not shown) whether or not the lower end of the hollow tube 3 has reached the design depth (lower end depth). The penetration is stopped.

  Next, the control unit controls to start drawing the hollow tube 3 by one pitch (for example, 20 cm) through the lifting mechanism 4, and at the same time, the pump P is operated and the fluidized sand is pumped. It controls so that it may press-fit in the area | region formed under the hollow tube 3, and its periphery with drawing | extracting. That is, the control unit determines whether or not the drawing has reached one pitch, and when it is determined that the drawing has reached one pitch, controls the lifting mechanism 4 to be stopped or in an idling state. Further, the control unit determines whether or not the press-fitting pressure of the fluidized sand discharged to the above-described region has reached a set value as the press-fitted state of the fluidized sand based on the detection signal sent from the pressure gauge 6. When it is determined that the press-fitting pressure has reached the set pressure, the pump P stops or switches an open / close valve (not shown) to a closed state.

  Further, in the region indicated by the symbol a in FIG. 1 which is relatively close to the ground surface where the earth pressure is small, the forced drainage agent (for example, sodium chloride) is supplied to the fluidized sand that is press-fitted from the hollow pipe 3. Aqueous solution) is injected through the pipe 29 and the liquid injection pipe 8. For this reason, in this control part, the alarm sound etc. which notify when the hollow pipe 3 enters the range of the symbol a and press-fits the fluidized sand and when the fluidized sand is pressed into the range of the symbol a are generated. An operator pulls out the middle liquid pipe 8 based on the alarm sound or the like, or fluidizes the forced drainage agent being injected or injected from the forced drainage agent supply means 28 through the pipe 29 and the liquid injection pipe 8. Inject into the sand. In this example, the liquid injection pipe 8 is manually penetrated to the lower side of the region a, and is manually pulled out stepwise as the hollow pipe 3 is drawn. However, the hollow pipe 3 is mechanically penetrated. Or may be pulled out.

  The above-mentioned forced drainage agent supply means 28 is, for example, a part of fluidized sand that is pressed into the ground from the lower end of the hollow tube 3 at a place near the ground surface side of the ground as a place where the earth pressure is small. As a measure for preventing the gas from rising through the gap formed around the empty pipe and being discharged to the surface side, a forced drainage agent can be injected into the fluidized sand during or as shown in FIG. Thereby, in this structure, since the pressurized fluidized sand is rapidly plasticized, only the water separated from the fluidized sand rises to the ground surface side and is discharged.

In the above control unit, it is determined whether or not the total number of pitches or all pitches have been drawn, and the drawing and press-fitting of fluidized sand are repeated until the total number of pitches is reached. When the total number of pitches is reached, one sand pile 9 is finished. Then, after the ground improvement apparatus 1 is moved to the next construction location and positioned, the above operation is performed again.
After being positioned, the above operation is performed again.

(Example 1) In this example, a physical property test was conducted on fluidized sand containing a superabsorbent resin (SAP). Comparative Example 1 and Examples 1-4 are fluidized sand produced by the same mixing method with the compositions and blending amounts shown in Table 1. Comparative Example 1 is a conventional fluidized sand that does not contain a superabsorbent resin, and Example 1-4 is a fluidized sand according to the present invention that includes SAP (“Himo Sub 300” manufactured by Hymo Co., Ltd.). The sand material, water content adjustment water, fluidizing agent, and slow-acting plasticizing agent used are the same in both the comparative examples and the examples.

  During the physical property tests in Table 2, the table flow test was conducted in accordance with a cement physical property test method (JIS R5201-1997). From this test result, the table flow value is, for example, 17 mm smaller on average than the comparison between Comparative Example 1 and Example 1 even when 0.5 g of SAP is contained per 1,000 g of dry sand. 4 shows that it becomes smaller in proportion to the SAP content.

In the texture test, fluidized sand (sample) is filled in a predetermined container and set in a commercially available texture test device (a table-type physical property measuring instrument manufactured by Yamaden Co., Ltd.). From 20 mm to 20 mm. The penetration stress (unit: Pa) is a value obtained by converting the maximum load ha at the time of penetration into stress. Adhesive force (J / m ³ ) is a value corresponding to the drawing resistance energy at the time of drawing. The weight (g) is the initial weight of the sample filled in the container. Also from this test result, the penetration stress is, for example, 122 Pa larger on average than the comparison between Comparative Example 1 and Example 1, even if 0.5 g of SAP is contained per 1,000 g of dry sand, and Example 1-4. It can be seen that the value increases steeply in proportion to the SAP content. It can be seen that this point has the same tendency although the adhesive force varies somewhat.

  The bleeding test was conducted in accordance with the Japan Society of Civil Engineers standard "Testing method for bleeding rate and expansion rate of pre-packed concrete injection mortar (polyethylene bag method)" and a method for testing physical properties of cement (JSCE F522-2007). The polyethylene bag used has a diameter of 50 mm and a length of 500 mm or more with fluidized sand (sample) put therein. The sample is filled into the bag to a height of about 20 cm. The separation rate of the fluidized sand was evaluated by setting the ratio of separated water to the total sample after 3 hours from filling as the bleeding rate (%). In this test result, as can be seen from FIG. 3A, the bleeding value is 3 in Comparative Example 1 even when 0.5 g of SAP is contained per 1,000 g of dry sand as compared with Comparative Example 1 and Example 1. It can be seen that it drops rapidly from 2% to 0.5%.

  From the above test results, referring to FIG. 5, when the fluidized sand contains SAP, the load that the fluidized sand receives before and during press-fitting is reinforced by the water retention capacity of the fluidized sand. The degree of shrinkage of the fluidizing agent bonding between the particles produced by the above is suppressed, and the fluidizing agent makes it difficult to touch the slow-acting plasticizing agent. Accordingly, in the fluidized sand containing SAP, the time for changing from (a) to (b), that is, the fluidization maintaining time for maintaining the fluidized state by delaying the drainage does not include SAP. It turns out that it can adjust so that it may become long compared with fluidization sand. In addition, among the above test results, in particular, the value of the bleeding rate is determined by whether or not the fluidized sand contains SAP and only 0.5 g of SAP per 1000 g of dry sand contains all of the separated water. Since the ratio with respect to the fluidized sand is significantly reduced, it is important as an evaluation index when the fluidized sand of the present invention is manufactured.

(Example 2) In this example, as the fluidized sand containing SAP, the influence of the blending amount of SAP on the amount of dewatering and the rate of dewatering was examined. Comparative Example 2 and Examples 5-8 are fluidized sand produced by the same mixing method with the compositions and blending amounts shown in Table 3. Comparative Example 2 is a conventional fluidized sand containing no SAP, and Examples 5-8 are fluidized sands of the present invention containing SAP “Himo Sub 300”. The sand material, water content adjustment water, fluidizing agent, and slow-acting plasticizing agent used are the same in both the comparative examples and the examples.

 In this dehydration test, fluidized sand (sample) is filled into a storage container, and then pressurized with 0.3 MP from the top of the sample, and the amount of dehydration from the sample is measured every elapsed time shown in Table 4. The dehydration rate and water content ratio in Table 4 are calculated based on the value of the dehydration amount. In this test result, as for the amount of dehydration, in Example 5-8 containing SAP, both decrease after 0.1 minutes after pressurization compared to Comparative Example 2 which is fluidized sand not containing SAP. (Note that the values of 0.03 minutes and 0.06 minutes after pressurization are considered to contain measurement errors.) As is apparent from FIG. 3B, the amount of dehydration is proportional to the amount of SAP added. Can also be seen.

  In addition, the above form example and Example do not restrict | limit this invention at all. The present invention only needs to include technical elements specified in the claims, and the details can be variously changed as necessary. Moreover, about "the ground improvement, such as press-fitting type sand pile creation and sand filling", the construction methods described in Patent Documents 1 to 3 and the construction method easily considered from the contents are included.

DESCRIPTION OF SYMBOLS 1 ... Construction machine 2 ... Fluidized sand manufacturing plant 3 ... Hollow pipe 4 ... Elevating mechanism 5 ... Rotating hand mechanism 6 ... Pressure gauge 7 ... Sand material 8 ... Injection pipe 9 ... Sand pile P ... Pump 15 ... Swivel 16 ... Pipeline

Claims (5)

In fluidized sand that has been processed so that it can be transferred through a pipe by a pressure pump by adding a fluidizing agent to the sand material used for ground improvement such as press-fitting sand pile creation and sand filling,
Among the water-absorbing resins, the water-absorbing resin has a high water-absorbing power and does not have thickening and cohesiveness or contains a very low water-absorbing resin. Fluidized sand characterized by adjusting the fluidization maintenance time.   The fluidized sand according to claim 1, wherein the fluidizing agent, the superabsorbent resin, water content adjustment water, and a slow-acting plasticizer are mixed in the sand material.   The fluidized sand according to claim 2, wherein the bleeding rate after 3 hours of filling the bag with fluidized sand is 0.5% or less. In ground improvement construction methods such as press-fitting sand pile formation and sand filling , the fluidized sand according to claim 2 or 3 is pumped to a hollow pipe that is inserted into or pulled out of the ground through a pipe by a pump. A ground improvement method characterized by press-fitting into the ground from the end of the pipe and making it plastic in the ground.   By injecting into the fluidized sand a forced drainage agent that enables the forced drainage of water contained in the fluidized sand, and rapidly plasticizing the fluidized sand The ground improvement construction method according to claim 4, wherein the sand material of the fluidized sand press-fitted into the ground is prevented from rising to the ground surface and being discharged.

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