JP2683758B2 - Ground improvement method and apparatus - Google Patents

Description

The present invention relates to a ground improvement method and apparatus, and in particular,
TECHNICAL FIELD The present invention relates to a method and an apparatus for improving a ground in which a grain-size-controlled clay suspension is allowed to naturally permeate into a formation to be improved by its head pressure.

[Conventional technology]

In general, alluvium and landfill sand grounds have a shallow groundwater level and abundant groundwater, and their strength is extremely low, which causes liquefaction, for example. Therefore, it is necessary to reduce the water permeability of the ground and increase the strength.

Conventionally, as a ground improvement means for the sand ground as described above, a pump such as a suspension of cement / clay or a chemical solution is injected under pressure by a pump through a rod or a perforated pipe temporarily buried in the sand ground. It was common to consolidate the sand ground with this improved material.

[Problems to be solved by the invention]

However, the above-mentioned conventional method has the following disadvantages.

That is, since the gel time of the above drug is usually several seconds to several tens of minutes, and at most several tens of minutes, for example, the gel time is 10 to 10
Injected at high pressure of 30kg / cm ² . Therefore, one or two sets of grout pumps are required for each injection well, and
For this purpose, the pipes and the seal around the injection well must be pressure-resistant, which complicates the equipment and increases the cost.

Also, since the drug is injected by forced pressurization,
It is difficult to uniformly inject the injected drug into the entire formation, because the injected drug is likely to concentrate in only the fragile portion of the formation or to escape into the undesired formation. Therefore, it is difficult to control the injection amount and the injection range. Further, since the drug is injected at a high pressure in this way, there is a problem that the surrounding ground is sometimes deformed.

The present invention has been made in view of the above circumstances, and it is possible to eliminate the above-mentioned drawbacks, to inject the injection agent uniformly into the target formation, and to perform injection control reliably and easily. It is an object of the present invention to provide a ground improvement method and apparatus.

[Means for solving the problem]

A method for improving a ground according to the invention of claim 1 comprises a step of preparing a particle size adjusting clay suspension by classifying clay particles contained in the suspension of clay such as bentonite, A step of storing the particle size adjusting clay suspension at a constant water level above the groundwater level while maintaining the clay so as not to change, and injecting the particle size adjusting clay suspension into a target formation A step of installing a plurality of injection pipes at a predetermined interval in the ground, and injecting the particle size adjustment clay suspension into the injection pipe, and improving the particle size adjustment clay suspension by the water head pressure generated by the water level And a step of naturally permeating the inside.

Further, the ground improvement apparatus according to the invention of claim 2 is a particle size-adjusted clay suspension obtained by classifying clay particles contained in the suspension of clay such as bentonite, It is a device for improving the ground by injecting into the formation to be improved, and an injection pipe for injecting a particle size adjusting clay suspension embedded at a predetermined interval in the ground and a particle size adjusting clay suspension. A constant water level tank for storing at a constant water level above the ground water level, a circulation tank for constantly circulating the particle size adjusting clay suspension through the constant water level tank, the constant water level tank and each of the injection pipes. An injection line for connection was provided.

[Action]

By classifying the clay suspension, for example, a clay suspension containing no coarse particles, that is, a particle size-adjusted clay suspension, can be prepared. By circulating this particle size-adjusted clay suspension, it is possible to store it for a long period of time while it is held in a constant clay.

By storing the particle size adjustment clay suspension above the groundwater head, the head pressure causes the particle size adjustment clay suspension to naturally permeate into the formation. At that time, the suspension is
Since the particle size of the contained clay particles is adjusted, a mud film or clogging does not occur in the infiltration process, and moreover, the natural infiltration allows uniform filling.

〔Example〕

Hereinafter, a first embodiment of the present invention will be described with reference to the accompanying drawings.

FIG. 1 shows an embodiment of a ground improvement device according to the present invention.
It shows an example in which the present invention is applied to a fine sand ground. The example shown in the figure shows the case where the fine sand layer is under pressure (the head of groundwater in the aquifer to be improved is higher than the upper boundary surface of the aquifer). Is.

In the figure, reference numeral G is the ground, W is the groundwater head, 1 is a fine sand layer to be improved by the present invention, 2 is a silt layer which constitutes the lower layer of the fine sand layer 1, 3, 3, ... Intrudes into the fine sand layer 1 from the ground surface. A plurality of injection pipes (injection wells) 4 that have been subjected to particle size adjustment clay suspension A (described later) to be injected into the injection pipe 3 have a predetermined water level (head).
A constant water level tank 5 for keeping the particle size adjusting clay suspension A circulated through the predetermined water level tank 4, and 6 a particle size adjusting clay suspension A from the constant water level tank 4 Injection tube
It is a supply line for injecting into 3,3, ....

The particle size adjusting clay suspension A stored in the circulation tank 5 is
It is pumped up by the pump 7 to the constant water level tank 4 via the circulation line 8. The constant water tank 4 is provided with an overflow line 9 extending to the circulation tank 5. Thereby, the particle size adjusting clay suspension A is supplied to the circulation tank 5 and the constant water tank 4.
The water level is always maintained while circulating.

In this case, the particle size adjustment clay suspension A stored in the circulation tank 5 is prepared by, for example, the injecting clay suspension preparation device 10 shown in FIG.

In the apparatus 10, reference numeral 11 is a mixer for making water and clay such as bentonite turbid to make a clay suspension having a concentration of 5% or less, and 12 is the clay suspension made by the mixer 11 and allowed to stand for a required time. The swelling tank for sufficiently swelling the viscous particles, 13 is a storage tank for temporarily storing the clay suspension from the swelling tank 12, 14 is for separating and removing coarse particles from the clay suspension. A separating device 15 is a filtering device for further separating only fine particles of clay from the clay suspension treated by the separating device 14. Reference numerals 16 to 20 are lines connecting the above-mentioned devices and tanks. The separating device in this case
A continuous processing type centrifugal separator operated at a high G (high centrifugal force) is desirable as 14, and an automatic discharge type centrifugal separator or a high speed decanter is suitable. Further, in this case, the filtration device 15 is a filter device capable of continuously treating separation of solid matter having a particle size of up to 1 μm.

The term "clay" used here means not only bentonite,
It contains clay contained in the natural ground, or clay components separated from the locally generated soil and the like.

The injection pipe (injection well) 3 is arranged according to the extent of improvement and the condition of the formation to be improved. The injection pipe 3 is, for example, as shown in FIGS. 3 and 4, and has an opening 3a at the lower end of the pipe or the pipe wall. Further, as shown in FIG. 5, transparent resin pipes 22 communicating with the injection pipes 3 are respectively raised from the upper ends of the injection pipes 3, 3, ... The transparent resin tube
22 extends at least above the water level determined by the constant water level tank 4.

Next, the operation of the ground improvement apparatus configured as described above and the ground improvement method according to the present invention will be described.

The injection well is installed by drilling a small-diameter hole by boring or the like, and concentric with the small-diameter hole, making the injection pipe 3 slightly larger.
It is done by penetrating. However, especially when the ground is soft, the injection pipe 3 can be made to function as a so-called casing tube for a hole. These injection pipes 3 (injection wells) are approximately 2 to 8 m in view of the construction conditions and the state of the fine sand layer 1 to be improved with reference to the trial calculation result by the following formula.
Install at intervals.

Here, D: Diameter of improvement range with one injection well (m) qw: Flow rate of fresh water that can be injected from the injection well (m ³ / h) T: Duration of injection (h); Max. Ratio η: Porosity of improved ground μm / μw: Ratio of clay of injected liquid to water H: Thickness of improved ground (m) The flow rate qw of fresh water that can be injected from the injection well is the same as the actual injection in advance. It can be easily obtained by injecting fresh water, but if this is not done, it can be calculated from the hydraulic conductivity of the ground using the well formula.

On the other hand, the clay suspension preparation apparatus 10 for injection is operated in parallel with the installation of the injection pipes 3, 3, .... In this injecting clay suspension preparation apparatus 10, first, a clay suspension having a concentration of 5% or less is prepared by the mixer 11 and stored in the swelling tank 12. The clay suspension is stored in the swelling tank 12 for about 12 hours to 24 hours.
The clay particles are sufficiently swelled by allowing them to stand for a time. The clay suspension here is the same as the suspension generally used in the ordinary mud construction method and the like, and contains particles (solid matter) having a maximum particle size of 40 μm to 70 μm. The clay suspension from the swelling tank 12 is once transferred to the storage tank 13 and then applied to the separating device 14.
Since the separation device 14 performs solid-liquid separation or classification by extremely high centrifugal force as described above, large particles of the particles mixed in the clay suspension are removed by this. The clay suspension that has passed through the separating device 14 is further applied to a filtering device 15 to prepare a particle size adjusting clay suspension A whose majority has a particle size diameter of 5 μm or less. It is more preferable that most of the suspended particles have a particle size of about 1 μm. However, when the separating device 14 makes the clay particles in the suspension fine as desired, the filtering device 15 may be bypassed.

As a result of experiments, the applicant of the present invention has found that the particle size of clay particles contained in the particle size adjusting clay suspension A is 20% of the ground to be improved as a standard for classification when preparing the particle size adjusting clay suspension A. It was found that the coarse particles should be separated and removed so that the diameter becomes about 1/25 to 1/100 or less. The above numerical values vary, for example, for fine sand with a 20% particle diameter of about 0.1 mm, it is preferable that the clay particle diameter is 1/100 (= 1 μm) or less. The reason is that the clay particle size should be 1/25 or less of those. Above,
"Sand with a 20% grain size of 0.1 mm" means that if a certain sand is hung on a 0.1 mm sieve, and 20% of the total mass passes through the sieve, the sand will be a 20% grain. This is sand with a diameter of 0.1 mm.

The particle size adjusting clay suspension A prepared as described above is the first
It is supplied to the circulation tank 5 shown in FIG.

The particle size adjusting clay suspension A in the circulation tank 5 is pumped to the constant water level tank 4 via the pump 7 and the circulation line 8. In the constant water level tank 4, the particle size adjusting clay suspension A is
Due to the action of the overflow line 9, a constant water level is always maintained. The surplus from the overflow line 9 is returned to the circulation tank 5 again. Further, since the particle size adjusting clay suspension A is constantly circulated and flowing between the circulation tank 5 and the constant water level tank 4 in this way, it does not settle,
Therefore, a constant clay (concentration) can always be maintained without causing sedimentation and separation of clay particles and a change in viscosity due to thixotropy, etc., and gelation does not occur.

Now, when the constant water tank 4 filled with the particle size adjusting clay suspension A as described above and the respective injection pipes 3, 3, ... Are made to communicate with each other through the injection line 6, the particle size adjusting clay suspension A is injected respectively. The tube 3 is filled and its head pressure is applied to the particle size adjusting clay suspension A filled in the injection tube 3. Since this head pressure is higher than the pressure (water head pressure due to the groundwater level W) given to the moisture contained in the fine sand layer 1 by the groundwater, the particle size adjusting clay suspension A is contained in the fine sand layer 1 While excluding the water that is generated, it penetrates between the fine sand particles that form the fine sand layer. At this time, since the clay particles constituting the particle size adjusting clay suspension A are extremely fine as compared with the clay particles constituting the ordinary clay suspension as described above, the clay particles are also fine against fine sand. It becomes possible to penetrate without causing clogging and the like, and the entire fine sand layer 1 is surely and uniformly filled. Since the particle size adjusting clay suspension A to be injected has an extremely long gel time unlike the conventional chemical solution, such a long time natural permeation injection by hydrostatic pressure can be realized practically.

Further, when the particle size adjusting clay suspension A flows into the injection pipe 3, a pressure loss proportional to the flow velocity occurs when flowing in the branch pipe which is thinner than the main pipe. For this reason, as shown in FIG. 5, the transparent resin pipe 22 provided at the upper end of each of the injection pipes 3, 3, ... Has a level l ₂ lower than the water level l ₁ of the constant water level tank 4. The surface will be located. The difference Δh between these two levels is the pressure loss, and by reading this Δh, the injection amount Q can be obtained by the following equation, Q = K · Δh (K: conversion coefficient). Since this Δh is not so large and it is difficult to measure with high accuracy, a regular flow meter, pressure gauge, or the like may be installed if it is desired to know the flow rate exactly.

Here, the following table and FIG. 6 (a graph of the table) show the results of the experiment conducted by the applicant.

From these, it can be seen that the particle size adjusting clay suspension A according to the present invention penetrates between the fine sand layers for a long period (long time) of about 2 days or more. In the figure, an example in which fresh water is injected under the same conditions is shown for reference. Considering that the usual clay suspension used in the muddy water method and the like stops osmosis within at most half a day at the longest, how excellent the permeability of the particle size adjusting clay suspension A is? I understand.

Further, FIG. 7 is a comparison of the permeability of the particle size-adjusted clay suspension A and the untreated clay suspension in an indoor test using an API standard filtration tester. By the way, this test was conducted under the following conditions using the filtration tester 50 shown in FIG. If only the member names of each part of the filtration tester 50 are described, 51 is a frame, 52 is a holding screw,
53 is a measuring cylinder, 54 is a support, 55 is a lid, 56 is a pay valve, 57 is packing, 58 is a cylinder cell, 59 is a filter paper,
60 is a screen wire mesh, and 61 is a drain tube. The experimental conditions are as follows: △ Cylinder cell 58: Inner diameter 76.2 mm, height 63,5 mm or more, △ Pressurizing device: Normally, an air compressor or a carbon dioxide gas cylinder is operated via a pressure regulating valve.

△ Filter paper: Toyo filter paper No. 4, equivalent to 90 mm in diameter.

△ Wire mesh: Opening of 0.17 to 0.25 mm.

△ method: Place packing 57c, wire mesh 60, filter paper 59, packing 57b on the lower lid in this order, and tighten cylinder cell 58 on it. Next, 290 ml or more of the test solution is put into the cylinder cell 58. Fix the upper lid tightly, apply a pressure of 3 kgf / cm ² for 30 minutes,
Measure the amount of filtered water (ml) flowing out from the bottom of the container.

Thus, it is clear from FIG. 7 that the permeability of the particle size adjusting clay suspension A is extremely excellent.

Therefore, if the above condition is maintained for a predetermined period according to the condition of the fine sand layer 1 and the degree of improvement, the fine sand layer 1
A sufficient amount of the particle size-adjusted clay suspension A permeates the whole and is replaced with ground water, and then gradually gels due to thixotropic property. As a result, the fine sand layer 1 can be solidified, its strength can be increased, and waterproofing can be secured.

In addition, Fig. 9 is a graph showing an example of the result of the experiment for checking the water-stopping (permeability-lowering) effect after construction, showing the recovery time when 1.5m of groundwater in a well (for example, test well) is pumped. There is. Before the construction, the water level is restored to the original state in a few tens of minutes (that is, the water permeability is high = the water blocking effect is small).
It can be seen that the water level recovers only to about 40 cm even after 2 days or more after construction, and a high water-stopping effect is exhibited. By the way, the permeability of the improved ground after construction (k = 2.6 × 10
^-5 cm / s) is a value comparable to the impermeable layer.

As described above, according to the ground improvement method, since the particle size adjusting clay suspension A is used as the injecting liquid, the clay particles are surely permeated between the fine sand particles without causing clogging or the like. You will be able to. And at that time,
Since the particle size adjusting clay suspension A is injected by the head pressure in the constant water level tank 4, the injection solution is evenly and uniformly permeated into the entire fine sand layer 1 without being concentrated in a specific portion of the fine sand layer 1. be able to. In addition, if the water permeability of the fine sand layer 1 and the clay of the injecting liquid are grasped by injecting the particle size adjusting clay suspension A at a low static pressure, the particle size adjusting clay suspension can be obtained. It is possible to accurately estimate the permeation amount and permeation range of A, and the injection management becomes easy without deforming the ground G or the structure.

For example, when an upward water pressure acts on the ground G due to the injection pressure, an upward force acts on the soil particles. For this reason, when the water pressure exceeds a certain value (critical hydraulic gradient i _C ), the soil particles become fluidized and become a quick sand state, causing boiling. The critical hydraulic gradient is shown by the following equation.

Here, Gs: specific gravity of soil particles and e: void ratio of soil.

Therefore, in order to prevent ground deformation due to boiling, the hydraulic gradient should be kept below i _C.

Now, when the trial calculation for the actual example shown in FIG. 10 is performed,
It looks like this:

i <i _C (2) From the above formula (1), Also, since it is i-P / H, from equation (2), Becomes

Therefore, the injection pressure (head) P is 5.1 when P = 6m.
In the case of m and H = 10 m, if it is less than 8.5 m, boiling will not occur.

Further, according to this ground improvement method, it is not necessary to use a grout pump for injection, a pressure resistant pipe, a pressure resistant seal, etc., which have been conventionally required, and moreover, as shown in FIG.
Since it is possible to work on multiple injection wells (injection pipes 3) at the same time simply by branching, the equipment and facilities are extremely simple, and the injection material is also inexpensive clay. Construction costs can be significantly reduced, for example, the price is one-tenth the price of expensive chemicals.

Further, since the particle size adjusting clay suspension A is injected with the injection pipe 3 installed in the ground, the hole wall is protected, and the collapse of the hole wall during the construction is surely prevented. Further, in the present embodiment, since the flow rate measuring means (transparent resin pipe 22) is installed in each of the injection pipes 3, 3, ..., By this, the permeation state of each injection pipe 3, 3 ,. It is possible to grasp the relative difference in the injection amount between the injection tubes 3 and the like. And the first
As shown in FIG. 5 and FIG. 5, only a specific injection pipe 3 (for example, an injection pipe 3 having a particularly slow permeation rate) is provided by providing a valve 21 for limiting the injection amount corresponding to each injection pipe 3. It is also possible to supply the particle size adjusting clay suspension A to the above.

FIG. 11 shows a case where the fine sand layer 1 to be improved is an unconfined aquifer in the first embodiment.

Even in this case, the construction method is the same as that of the above example. In this case, as the injection pipe 3, the fine sand layer 1 to be improved
What has the opening 3a (screen) on the tube wall of the portion corresponding to (for example, the one shown in FIG. 4) may be used. Also in this example, the same effect as that of the above-described example can be obtained.

By the way, this time, the present applicant has developed a device and a method as shown in FIG. 12 as a method (apparatus) for confirming the improvement effect after construction, simultaneously with the method for improving the ground. As a method of confirming the construction effect (permeability) on the ground with low permeability after soil improvement, the i-pumping method (variable water level method = recovery method), ii) water injection method ( Water level method),
iii) The constant water level injection method is implemented. The pumping method is
As shown in Fig. 13 midline diagram a, once the water in the test well is discharged to a level below the natural groundwater level and lowered, then the rise (recovery) level of the water level in the test well is detected, and the variable water level injection The method is to inject water into the test well to raise the water level, and then detect the degree of decrease (line b in the figure). The constant water level injection method ensures that the water level in the test well always remains at a constant level. The water permeability is calculated by calculating the water permeability by the amount of water injected at that time (line c in the figure). No. 12 provided this time
Referring to the figure, reference numeral 30 in the figure is a test well, and this test well 30 uses one (or a plurality) of the injection pipes (injection wells) 3, 3 ,. It may be provided separately or may be provided separately. The test well 30 is a pumping pump 32 for pumping the water in the test well 30 through a pipe 31.
Electrodes provided at an arbitrary level L ₁ below the initial water level L ₀
E ₁ , an electrode provided at a level L ₂ lower than the level L ₁
E ₂ , an electrode E ₀ provided further below the electrode E ₂ , a level switch 33 for performing ON / OFF control of the pumping pump 32 by the signals of these electrodes E ₀ , E ₁ , and E ₂ , in the test well 30 It is configured to include a water level meter 34 for detecting the water level (depth), a computer 35 for recording a signal from the water level meter 34, and the like.
Further, in the figure, reference numeral 36 is a mountain sand, 37 is a water blocking mortar, and 38 is a filter made of silica sand. The confirmation method using this test well 30 is the constant level pumping method and the variable level pumping method (recovery method).
It is a type of the test well 30 and the water level in the test well 30 is repeated within a certain range by drainage (pumping) recovery. It is to confirm the effect. That is,
When the water level in the test well 30 reaches the electrode E ₁ (level L ₁ ) at a high level, the level switch 33 operates to activate the pumping pump 32 to discharge water, and the discharge causes the electrode E at a low level. When the water level drops to ₂ (level L ₂ ), the pumping pump 32 is automatically stopped and the water level in the test well 30 rises again. That is, according to this test method, a diagram as shown by the symbol d in FIG. 13 can be obtained.
In the conventional test method, the storage coefficient cannot be obtained in the pumping method of i), and the permeability calculation method is limited in the water injection method of ii) and iii), and the pore wall is clogged. There were some drawbacks, such as lower values than they actually are,
According to this test method, both the hydraulic conductivity and the storage coefficient can be obtained, and since they can be calculated by multiple methods, highly reliable calculation results can be obtained.

Next, FIGS. 14 and 15 explain a second embodiment of the present invention. In the above-mentioned first embodiment, the case where the stratum into which the particle size adjusting clay suspension A is injected, that is, the stratum to be improved is the fine sand layer is described, but the second embodiment is intended for the coarse sand layer or the medium sand layer. It was done.

FIG. 14 shows an apparatus 10 'for preparing a clay suspension for injection in the second embodiment. Second first
The same components as those of the injecting clay suspension preparation apparatus 10 shown in the figure are designated by the same reference numerals, and the description thereof will be omitted. Reference numeral 39 in the figure
Is a settling tank and 40 is a hydrocyclone. A line 41 extends from the overflow side of the hydrocyclone 40 to the circulation tank 5 '. This circulation tank 5'has the same structure as that of the first embodiment, and has a constant water level tank 4 ', a pump 7',
A circulation line 8 ', an overflow line 9', etc. are arranged. Although not shown here, one end of the injection line 6'is connected to the constant water tank 4 ', which is not shown here. On the other hand, a storage tank 13 is provided on the underflow side of the liquid cyclone 40. A line 42 extends from the storage tank 13 to a circulation tank 5 ″ different from the above. The circulation tank 5 ″ also has a constant water level tank 4 ″,
The pump 7 ″, the circulation line 8 ″, the overflow line 9 ″, the injection line 6 ″ and the like are similarly configured.

According to the above-mentioned clay suspension preparation apparatus for injection 10 ', the clay suspension prepared by the mixer 11 is once stored in the settling tank 39, and the clay particles contained therein have a particle size of about 40 μm or more. The coarse particles are separated by settling. Thereafter, the clay suspension from which the coarse particles have been removed is transferred to the liquid cyclone.
40 times. In this liquid cyclone 40, among the clay particles contained in the clay suspension from the settling tank 39, those smaller than a predetermined particle size (for example, particle size 10 μm) are on the overflow side, and those larger than that are on the underflow side. Is separated into And the overflow amount is line 41
The underflow portion is temporarily stored in the storage tank 13 via one line and then stored in the other circulation tank 5 ″ via the line 42. The subsequent operation is the same as that of the above embodiment. The particle size adjusting clay suspensions A ', A "stored in the respective circulation tanks 5', 5" are circulated through the constant water level tanks 4 ', 4 ", so that the clay is always a constant clay. The concentration is kept.

On the other hand, FIG. 15 shows an injection well portion in the present embodiment. In the figure, reference numeral 45 is a medium sand layer (grain size 0.2 mm to 0.6 mm), and 46 is a coarse sand layer below the medium sand layer 45 (grain size 0.6 mm to 0.6 mm). 2.0 mm). Injecting pipes 3 ', 3 "are buried from the surface corresponding to the respective layers 45, 46, and these injecting pipes 3', 3" are as shown in the figure.
Each of them has a configuration having an opening 3a in a portion to be injected. An injection line 6'from the constant water level tank 4'is provided in one injection pipe 3 ', and an injection line 6 "from the constant water level tank 4" is provided in the other injection pipe 3 ".
Is connected.

In the above configuration, the particle size adjusting clay suspension A'from one of the constant water level tanks 4'is applied to the intermediate sand layer 45 via the injection pipe 3 ', and
The particle size adjusting clay suspension A ″ from the other constant water level layer 4 ″ is statically pressure injected into the coarse sand layer 46 through the injection pipe 3 ″.

Here, since the particle size adjusting clay suspension A'stored in the constant water level layer 4'includes clay particles having a diameter of 10 μm or less, the medium sand layer having a particle size of 0.2 mm to 2.0 mm is The natural permeation injection by the water head pressure of the constant water level tank 4'is possible, and the injection is smoothly performed without causing clogging. Moreover, since the clay particle diameter contained in the particle size adjusting clay suspension A ′ is not too fine with respect to the particle diameter of the layer, proper packing properties are not caused, and there is no water leakage and excessive (infinite) penetration. Moreover, there is no possibility that the injected clay suspension for controlling particle size is easily discharged (that is, due to the viscosity being too low) due to groundwater flow. This also applies to the coarse sand layer 46.

That is, since the particle size-adjusted clay suspension A ″ stored in the constant water level tank 4 ″ has a clay particle diameter of 10 μm to 40 μm, the coarse sand layer 46 having a particle diameter of 0.6 mm to 2.0 mm is It becomes possible to inject by the water head pressure of the water level tank 4 ", and it is possible to inject smoothly by static pressure without causing significant clogging, etc. Also, the particle size adjusting clay suspension relative to the particle size of the layer Since the diameter of the clay particles contained in A ″ is not too small, efficient injection can be carried out.

From the above, the first
The above-mentioned various effects obtained in the examples, that is, uniform penetration of the injecting liquid into the entire target layer, cost reduction, prevention of adverse effects on the surrounding ground, and the like can be similarly obtained.

In addition, a clay suspension preparation apparatus for injection according to the second embodiment
10 'requires a device having a lower processing accuracy than that of the device 10 shown in the first embodiment, and has a simple structure, and can be constructed at a lower cost. Further, when the injecting clay suspension preparation apparatus 10 'is configured as in this embodiment, the particle size adjusting clay suspension A'for injecting the medium sand layer and the particle size adjusting clay for injecting the coarse sand layer are used as described above. The simultaneous production with the suspension A ″ is performed, and it is efficient. By constructing the injection pipe 3 as the above-mentioned injection pipes 3 ′, 3 ″, the medium sand layer 45 and the coarse sand layer 46 are also formed. Simultaneous injection is possible,
You can expect extremely efficient construction.

FIG. 16 is a development of the second embodiment,
The fine sand layer 1 shown in the first embodiment can be improved. In the figure, the same components as those described above are designated by the same reference numerals, and description thereof will be omitted.

This example is the same as the one shown in FIG. 14 above. A second liquid cyclone 47 is provided between the line 41 described from the liquid cyclone 40 and the circulation tank 5 ′, and the circulation tank is provided on the underflow side thereof. 5'is arranged and the same circulation tank 5 as shown in the first embodiment is provided on the overflow side in the line 43.
It is arranged through. The second liquid cyclone
47 has a higher classification ability than the liquid cyclone 40 and can classify particles having a particle size of 5 μm or less, preferably 1 μm or less.

That is, if the clay suspension preparing apparatus for injection 10 ″ is configured in this way, the circulation tank 5 (constant water level tank 4) has a particle size of 5 μm.
A particle size-adjusted clay suspension A containing only the following clay particles was added to the circulation tank 5 '(constant water level tank 4'), and a particle size-adjusted clay suspension A'containing clay particles having a particle size of about 5 μm to 10 μm was used. Circulation tank 5 "
In the (constant water level tank 4 ″), a particle size adjusting clay suspension A ″ containing clay particles having a particle size of about 10 μm to 40 μm is circulated and stored. Therefore, in the same manner as in Fig. 15, the injection pipes 3 (3 ', 3 ") are installed corresponding to the fine sand layer 1, the medium sand layer 45, and the coarse sand layer 46 of the ground, respectively, and the constant water level is set for each. Tier 4, 4 ′,
If you inject the particle size adjustment clay suspension A, A ′, A ″ from 4 ″,
It is also possible to carry out all the improvements of the fine sand layer 1, the medium sand layer 45 and the coarse sand layer 45 in parallel and simultaneously.

In the present invention, the water level of the particle size adjusting clay suspension A is changed by changing the installation height of the constant water level tank 4, etc., and the total injection pressure is slightly changed according to the ground condition etc. It is also possible to let. Further, in the embodiment, only the example in which the injection pipes 3, 3, ... Are vertically installed on the ground G is shown, but they may be installed in the horizontal direction or the inclined direction, for example, from a slope or a face.

〔The invention's effect〕

As described above, according to the ground improvement method of the first aspect of the present invention, since the particle size adjusting clay suspension is used as the injection liquid, clogging or the like is caused in the ground (geosphere) to be improved with clay particles. Can be spread without fail. Moreover, since the particle size-adjusted clay suspension is injected at a low installation pressure in a constant water level tank, a layer to be improved without concentrating the injected solution on a specific part and without affecting other formations. It can be evenly dispersed throughout the entire interior. Further, by injecting the particle size adjusting clay suspension at a static pressure, the certainty in estimating the permeation amount and permeation range of the injecting liquid is increased, and the injection control can be performed accurately and easily. In addition, there is no need to use high-pressure injection pumps, pressure-resistant pipes, pressure-resistant seals, etc., and multiple simultaneous constructions can be easily realized, so equipment and facilities are extremely simple, and construction costs are high. Can be significantly reduced. Furthermore, since the injection of the particle size adjusting clay suspension is performed while the injection pipe is installed in the ground, the hole wall is protected, and it is possible to reliably prevent the collapse of the hole wall during construction. .

According to the ground improvement device of the invention of claim 2,
The above method can be reliably realized, and the viscosity of the particle size adjusting clay suspension to be injected can be maintained at a constant low viscosity at all times, and the injection effect obtained by the above method can be further promoted.

[Brief description of the drawings]

FIG. 1 is an overall side sectional view showing an embodiment of a ground improvement device according to the first embodiment of the present invention, and FIG. 2 is a schematic configuration diagram showing an injection clay suspension preparation device according to the same embodiment, 3 and 4 are elevation sectional views showing the injection pipe together with the ground G, FIG. 5 is an elevation view showing the superstructure of the injection pipe in one embodiment, and FIGS. 6 and 7 are experimental results. 6th in an example
Fig. 7 is a graph showing the relationship between the elapsed time and the cumulative injection amount,
Fig. 8 is a graph showing elapsed time and cumulative permeation amount, Fig. 8 is a perspective view showing a filtration tester, Fig. 9 is a graph showing the relationship between elapsed time and water level drop, and Fig. 10 is an injection pipe installed. A longitudinal cross-sectional view showing a part of the ground, FIG. 11 is an overall side cross-sectional view showing another configuration example of the improved device, FIG. 12 is a side cross-sectional view showing a test well together with an observation device, and FIG. 13 is a view after construction. The graph which shows the relationship between the elapsed time and the water level drop in the field permeability test, FIG. 14 is a schematic block diagram which shows the clay suspension preparation apparatus for injection | pouring by the 2nd Example of this invention, FIG. 15 is the same Example. FIG. 16 is a vertical cross-sectional view showing the injection pipe together with the ground G, and FIG. 16 is a schematic configuration diagram showing another configuration example of the clay suspension preparation device for injection. A, A ′, A ″ …… Grain size controlled clay suspension, G …… Soil, W …… Groundwater head, 1 …… Narrow sand layer, 3,3 ′, 3 ″ …… Injection pipe, 4,4 ′, 4 ″ …… constant water level tank, 5,5 ′, 5 ″ …… circulation tank, 6 …… injection line, 8,8 ′, 8 ″ …… circulation line, 9,9 ′, 9 ″ …… overflow line, 10,10 ′, 10 ″ …… Injection clay suspension preparation device, 45 …… Medium sand layer, 46 …… Coarse sand layer.

Front Page Continuation (72) Inventor Yonosuke Hosaka 2-16-1, Kyobashi, Chuo-ku, Tokyo Shimizu Construction Co., Ltd. (72) Inventor Satoshi Takahashi 2-16-1, Kyobashi, Chuo-ku, Tokyo Shimizu Construction Co., Ltd. (72) Inventor Ken Amano 2-16-1 Kyobashi, Chuo-ku, Tokyo Shimizu Construction Co., Ltd. (72) Inventor Fumiaki Hirano 2-16-1 Kyobashi, Chuo-ku, Tokyo Shimizu Construction Co., Ltd. (56) Reference Reference JP-A-61-207713 (JP, A) JP-A-61-207714 (JP, A)

Claims (2)

(57) [Claims] 1. From a suspension of clay such as bentonite, clay particles contained in the suspension are classified,
Creating a particle size adjusting clay suspension; storing the particle size adjusting clay suspension at a constant water level above the groundwater level while maintaining a viscosity change; A step of installing a plurality of injection pipes for injecting the suspension into the target formation at a predetermined interval in the ground, and injecting the particle size adjustment clay suspension into the injection pipe, the particle size adjustment clay suspension And a step of allowing the liquid to naturally permeate into the formation to be improved by the water head pressure generated by the water level, the method for improving the ground. 2. A particle size adjusting clay suspension obtained by classifying clay particles contained in a suspension of clay such as bentonite into the formation to be improved. A device for improving the ground by means of a plurality of embedded in the ground at a predetermined interval, the injection pipe for injecting the particle size adjusting clay suspension into the intended formation, the particle size adjusting clay suspension A constant water level tank for storing at a constant water level above the ground water level, a circulation tank for constantly circulating the particle size adjusting clay suspension through the constant water level tank, the constant water level tank and the respective injection pipes A ground improvement device, which is equipped with an injection line that connects the