JP7044351B2 - Specimen and specimen collection method - Google Patents

Description

The present invention relates to a specimen and a method for collecting specimens.

Patent Document 1 below describes a soil sampling device that inserts a casing while excavating soil to prevent the collapse of the excavated hole wall.

Japanese Unexamined Patent Publication No. 2006-291571

When sampling soil, the core tube can be easily taken in and out by preventing the hole wall from collapsing by using a casing as in Patent Document 1. Therefore, the efficiency of sampling work is high. However, when the core tube is inserted into the soil or when the specimen is taken out from the core tube, plastic strain may occur in the specimen and the specimen may collapse. In such a case, it is difficult to obtain a specimen that can appropriately evaluate the soil constant.

In view of the above facts, an object of the present invention is to provide a specimen and a method for collecting specimens in which plastic strain is unlikely to occur.

The specimen according to claim 1 comprises soil particles and a supercooling substance that is filled and solidified between the soil particles and melts when heated to a predetermined temperature, and the supercooling material is sodium acetate 3 water . Japanese, sodium sulfate decahydrate, sodium thiosulfate pentahydrate, disodium phosphate dodecahydrate, calcium chloride hexahydrate, calcium acetate monohydrate, magnesium acetate tetrahydrate, potassium acetate , Potassium fluoride tetrahydrate, erythritol or mannitol, and has a columnar shape.

The specimen of claim 1 is filled with solidified supercooling material between soil particles instead of groundwater. Therefore, it is possible to suppress the plastic strain generated in the specimen when collecting the specimen, transporting the specimen, temporarily storing the specimen, and the like.
In one aspect of the specimen, the supercooling substance is sodium acetate trihydrate, sodium sulfate decahydrate, sodium thiosulfate pentahydrate, disodium disodium twelve hydrate, calcium chloride hexahydrate, and the like. It is any one of calcium acetate monohydrate, magnesium acetate tetrahydrate, potassium acetate, potassium fluoride tetrahydrate, erythritol and mannitol.

The method for collecting a specimen according to claim 2 is a step of injecting a supercooled solution into the ground and replacing a void portion or a groundwater portion in the ground with a supercooled solution, and solidifying the supercooled solution using a crystallization agent. It includes a step of forming a supercooled substance and a step of collecting a specimen by boring the ground on which the supercooled substance is formed.

In the method of collecting a specimen according to claim 2 , a supercooled solution is injected into the ground and solidified. After that, by boring the ground and collecting the specimen, the specimen in which the solidified supercooled substance is filled between the soil particles can be obtained. Therefore, it is possible to suppress the plastic strain generated in the specimen when collecting the specimen, transporting the specimen, temporarily supplementing the specimen, and the like.

The method for collecting a specimen according to claim 3 is a step of excavating the ground and inserting an injection pipe, and the above-mentioned to the ground in which the supercooled solution has permeated after injecting the supercooled solution from the injection pipe into the ground. A step of injecting the crystallization agent, a step of injecting the supercooled solution toward the crystallization agent after injecting the crystallization agent from the injection tube into the ground, or a step of injecting the supercooled solution from the injection tube into the ground. The step of pouring the crystallization agent into the ground in which the supercooled solution has permeated while injecting, and boring the ground in a state where the supercooled solution is solidified and the supercooled substance is formed, thereby providing the above-mentioned supply. It has a step of collecting a specimen.

In the specimen collection method according to claim 3 , after injecting the supercooled solution into the ground, the crystallization agent is added. In this case, the supercooled solution begins to solidify immediately after the crystallization agent is added.

Alternatively, after the crystallization agent is poured into the ground from the injection pipe, the supercooled solution is injected toward the crystallization agent. In this case, the supercooled solution begins to solidify immediately after injection.

Alternatively, the crystallization agent is added while injecting the supercooled solution into the ground. In this case, the supercooled solution begins to solidify immediately after the crystallization agent is added.

In this way, by using the crystallization agent, the solidification reaction of the supercooled solution starts immediately, so that the ground can be solidified without the supercooled solution being washed away even in a place where the groundwater flow is fast.

The method for collecting a specimen according to claim 4 is a method for collecting a specimen by solidifying a supercooled solution injected into the ground to form a supercooling substance and boring the ground to collect the specimen. A surfactant that lowers the freezing point is added to the cooling solution.

In the sample collection method of claim 4 , the freezing point of the supercooled solution is lowered by the surfactant. The closer the temperature of the supercooled solution to the freezing point, the more unstable the supercooled state becomes, and the more easily the supercooled solution solidifies by stimulation without giving a crystallization agent. That is, it becomes easy to solidify at an unintended timing. By lowering the freezing point of the supercooled solution with a surfactant, the supercooled state can be stabilized even in a low temperature state.

According to the present invention, it is possible to provide a specimen and a method for collecting specimens in which plastic strain is unlikely to occur.

It is a graph which shows the relationship between the cooling time at the time of cooling the supercooled solution used in the specimen collection method which concerns on 1st to 3rd Embodiment of this invention, and the temperature of a supercooled solution. Plot diagram showing uniaxial compression strength according to the mixing ratio of water to anhydrous sodium acetate when sodium acetate trihydrate is used as a supercooling solution in the specimens according to the first to third embodiments of the present invention. Is. Relationship between strain and compressive stress according to the mixing ratio of water to anhydrous sodium acetate when sodium acetate trihydrate is used as a supercooling solution in the specimens according to the first to third embodiments of the present invention. It is a graph which shows. (A) is a graph showing the relationship between temperature and volume in a solid supercooled substance and the relationship between temperature and volume in a liquid supercooled solution, and (B) is a graph showing the relationship between temperature and volume in a solid state of water. It is a graph which showed the relationship with, and the relationship between temperature and volume in a liquid state. (A) is a cross-sectional view showing a state in which a supercooled solution is injected into the ground in the specimen collecting method according to the first embodiment of the present invention, and (B) is a permeation in which the supercooled solution permeates the ground. It is a cross-sectional view which shows the state which the crystallization agent is put into a body, (C) is the cross-sectional view which shows the state which the solidification reaction propagates from the part where the crystallization agent and a penetrant are in contact, and (D) is. It is a cross-sectional view which shows the state which solidified the supercooled solution in the ground, and the solidified body was formed, and (E) is the cross-sectional view which shows the state which the specimen is taken from the solidified body. It is a side view which showed the triaxial compression tester which investigates the soil quality of the specimen which concerns on 1st to 3rd Embodiment of this invention. (A) is a cross-sectional view showing a state in which a crystallization agent is charged into the ground in the specimen collecting method according to the second embodiment of the present invention, and (B) is a cross-sectional view showing a state in which a supercooled solution is injected toward the crystallization agent. It is a cross-sectional view showing the state in which the supercooled solution is injected, and (C) is a state in which the supercooled solution is injected toward the solidified body formed by propagating the solidification reaction from the portion where the crystallization agent and the supercooled solution are in contact with each other. (D) is a cross-sectional view showing a state in which a solidified body is formed up to the ground surface, and (E) is a cross-sectional view showing a state in which a specimen is collected from the solidified body. (A) is a cross-sectional view showing a state in which a supercooled solution is injected into the ground in the specimen collecting method according to the third embodiment of the present invention, and (B) is a sectional view showing a state in which a supercooled solution is injected toward the supercooled solution. It is a cross-sectional view which shows the state which has been charged, (C) is the sectional view which shows the state which the crystallization agent is charged intermittently at intervals, and (D) is the solidified body formed to the ground surface. It is a cross-sectional view which shows the state which was in the state, and (E) is the cross-sectional view which shows the state which the specimen is collected from the solidified body.

[First Embodiment]
(Test piece)
The specimen according to the embodiment of the present invention comprises soil particles and sodium acetate trihydrate (CH ₃ COONa · 3H ₂ O) as a supercooling substance filled between the soil particles in a solidified state. It is a test sample and is used, for example, in a triaxial compression test. Further, the specimen collecting method according to the embodiment of the present invention is a sampling method for collecting the above-mentioned specimen from the ground.

(Supercooled solution)
As shown in FIG. 1, the supercooled solution retains a liquid state in a temperature range higher than the melting point, like liquids other than the supercooled solution (A to B). The supercooled solution does not solidify even when cooled to a temperature range below the melting point and maintains a liquid state (BC). This phenomenon is called "supercooling", and this state is called "supercooling state". The supercooled solution in the liquid state (A to C) can be permeated into the ground by press-fitting it into the permeable layer or the impermeable layer in the ground.

When a stimulus such as vibration is given to the supercooled solution in the supercooled state, crystallization starts from the place where the stimulus is given and solidifies while generating heat of solidification (C to D). In addition, in order to solidify the supercooled solution in the supercooled state, in addition to the method of giving a stimulus, a method of adding a crystallization agent (a crystallized solid state supercooled substance) into the supercooled solution in the supercooled state is used. , A method of injecting a supercooled solution in a supercooled state toward a crystallization agent, a method of cooling to a freezing point, and the like.

The supercooled solution in the supercooled state is maintained in the liquid state when it is continuously cooled without giving any irritation and without contacting with the crystalline agent. When cooling is continued while maintaining the liquid state, it eventually reaches the freezing point and solidifies to form a supercooled substance. The difference between this melting point and the freezing point is called the degree of supercooling. The smaller the degree of supercooling, the more unstable the supercooled state becomes, and the weaker the stimulus is, the more unstable the supercooled state becomes. That is, when there are two types of supercooled solutions in a supercooled state, the supercooled solution having a high freezing point is in an unstable state than the supercooled solution having a low freezing point, and it is highly probable that the supercooled solution will solidify by an unintended stimulus.

Once solidified, the supercooled substance retains its solid state unless it is heated to its melting point (DE). The specimen according to the embodiment of the present invention is obtained by collecting a solid supercooled substance permeated between soil particles together with soil particles.

The "melting point" in the present embodiment is the temperature at which the supercooled substance in the solidified state melts, and the "freezing point" is the temperature at which the supercooled solution in the liquefied state solidifies. ..

The supercooled solution in the embodiment of the present invention contains sodium acetate trihydrate produced by mixing water at a ratio of 100:66 (molecular weight ratio) to anhydrous sodium acetate and heating and melting. The supercooled solution containing sodium acetate trihydrate is a substance that maintains a supercooled state at an underground temperature (10 to 20 ° C.), and has a melting point of about 58.0 ° C. The freezing point is 0 ° C. or lower. This freezing point is adjusted by a surfactant described later. As a result, the supercooled solution is maintained in a supercooled state in the ground where the temperature is lower than the melting point and the temperature is higher than the freezing point, and the supercooled solution can be solidified by stimulation or addition of a crystallization agent. Further, the solidified supercooled material does not melt unless the ground is heated to 58.0 ° C. or higher.

FIG. 4A shows the relationship between the temperature T (K) and the density ρ (kg / cm ³ ) in the supercooled substance in the solid state by solid lines and black dots, and in the supercooled solution in the liquid state. The relationship between the temperature T (K) and the density ρ (g / cm ³ ) is shown by solid lines, white dots, and the like. As shown here, in the range of T = 260 to 310 (K) (-13 to 37 (° C.)), the densities of the supercooled substance in the solid state and the supercooled solution in the liquid state are almost equal. Therefore, even if the supercooled solution in the liquid state is solidified, the volume change is small. (Exhibition in Fig. 4 (A): "JSME Proceedings (Vol. B) Vol. 58, No. 553, Paper No. 92-2002, Fig. 10, 1992")

On the other hand, as shown in the relationship between T (K) and the density ρ (g / cm ³ ) in water (H ₂ O) shown in FIG. 4 (B), water in a solid state, that is, The densities of ice (solid line) and water in liquid state (broken line) are different. Specifically, solid water has a lower density than liquid water. Therefore, when water is frozen, its volume expands.

(Surfactant)
In addition to sodium acetate trihydrate, oxycarboxylate-based Floric (registered trademark) T is added to the supercooled solution as a surfactant. As a result, the freezing point of the supercooled solution is adjusted to an arbitrary temperature (0 ° C. or lower in this embodiment).

By using this surfactant, for example, the freezing point of the supercooled solution can be lowered. The lower the freezing point of the supercooled solution, the higher the stability in the supercooled state, so it is possible to suppress solidification due to unintended stimuli (vibration of vehicles running on the road surface, minute seismic motion, etc.).

(Method of collecting specimens)
In the specimen collecting method according to the embodiment of the present invention, as shown in FIG. 5A, first, the ground G is excavated (boring) using the rod 22 attached to the ground excavation device 20. An excavation bit (not shown) is attached to the tip (lower end) of the rod 22, and by rotating the rod 22, the excavation bit excavates the ground G and the rod 22 is inserted into the ground G.

After excavating the ground G to a predetermined depth H1 using the excavation bit, the rod 22 was formed at the tip end portion of the rod 22 closer to the rear end (upper end portion) than the excavation bit while being pulled out while rotating. A supercooled solution in a supercooled state (15 ° C.) is injected sideways from an injection nozzle (not shown) toward the ground G. As a result, the void portion or the groundwater portion in the ground G is replaced with the supercooled solution, and the supercooled solution permeates the ground G.

The temperature of the ground G is generally 10 to 20 ° C., which is lower than the melting point (about 58.0 ° C.) of the supercooled solution and higher than the freezing point (0 ° C. or lower). The cooling solution is maintained in a supercooled state.

The rod 22 is an example of an injection tube in the present invention. Further, although the excavation bit and the injection (injection) nozzle are provided on the same rod 22 in the present embodiment, they may be provided on different rods.

When the supercooled solution permeates the ground G, the penetrant 30 is formed around the rod 22 and the excavation hole 22A excavated by the rod 22.

As shown in FIG. 5B, after the penetrant 30 is formed up to the ground surface GL, the crystallization agent 32 is charged into the excavation hole 22A. When the crystallizer 32 and the supercooled solution in a liquid state forming the penetrant 30 come into contact with each other, the supercooled solution solidifies. Further, when the solidified supercooled substance comes into contact with the supercooled solution in the liquid state, the supercooled solution in the liquid state solidifies. Therefore, as shown in FIG. 5C, the solidification reaction gradually propagates to form the solidified body 34. Then, as shown in FIG. 5 (D), the solidified body 34 is formed.

In the present embodiment, the solidified body 34 is formed up to the ground surface GL, but the embodiment of the present invention is not limited to this, and the solidified body 34 may be formed in a portion where the specimen P needs to be collected. ..

Next, as shown in FIG. 5 (E), the rod 24 is used to excavate a portion where the solidified body 34 is formed and a portion different from the excavation hole 22A.

The rod 24 is composed of a double pipe, and the ground G is rotationally cut by a bit formed at the tip of the outer pipe, and the non-rotating inner pipe (core tube) is pushed into the ground G to form a columnar specimen P (Fig.). 6) is collected.

The test piece P can be used as a test piece for a triaxial compression test. In the triaxial compression test, as shown in the triaxial compression tester 40 shown in FIG. 6, the specimen P coated with the impermeable membrane S (for example, a rubber membrane) is placed in the triaxial chamber 42. .. Then, the triaxial chamber 42 is filled with water W, a pressure C1 is applied to the specimen P from the side, and the pressure C1 is further compressed in the axial direction (pressure C2) to obtain the strength-deformation characteristics of the specimen P. Further, the triaxial compression tester 40 has a structure in which water is passed from top to bottom along the axial direction of the specimen P by using the water supply channel WS and the drainage channel WW, and the structure is such that water is passed between the soil particles of the specimen P. It can replace the interstitial water. The specimen P is formed of a supercooled solution in which the pore water between the soil particles is solidified, and the solidified supercooled substance is dissolved in water at room temperature.

By substituting the melted supercooled solution with water, the specimen P returns to the normal state (the state before the groundwater is replaced with the supercooled solution) in the ground G. This makes it possible to investigate the soil quality of the ground G.

(Action / effect)
In the specimen collection method according to the first embodiment, as shown in FIGS. 5A to 5D, a supercooled solution is injected into the ground G to form a penetrant 30 and solidified using a crystallization agent 32. Let me. As a result, the solidified body 34 is formed. By collecting the solidified body 34 by boring, a test piece P in which the solidified supercooled solution is filled between soil particles can be obtained.

This makes it possible to use the specimen as a specimen when inserting the core tube into the ground or when removing the specimen from the core tube, as compared with the conventional technique of collecting the specimen filled with liquid groundwater between soil particles. Disturbance is unlikely to occur (plastic strain is unlikely to occur). In addition, it is possible to prevent soil particles from being consolidated and changing in strength when the specimen is transported or temporarily stored.

In the prior art, in order to suppress the disturbance of the specimen, a cooling pipe in which liquid nitrogen is circulated may be buried in the ground and the groundwater may be frozen and collected. However, as shown in FIG. 4B, the volume of water expands when it is frozen, so that the porosity of the soil particles of the specimen increases. Further, when the frozen groundwater is thawed after the specimen is collected, the volume of the specimen becomes smaller. Alternatively, it absorbs water and maintains a large porosity. As described above, when the groundwater is frozen and the specimen is collected, it is difficult to reproduce the normal state in the ground G. In addition, the scale of the equipment becomes large, and it takes time from the installation of the equipment to the collection of the specimen.

On the other hand, as shown in FIG. 4A, the volume of the supercooled solution used in the specimen P collected by the specimen collection method according to the first embodiment expands even when solidified. hard. As a result, the porosity of the soil particles of the specimen P is unlikely to change. Further, even if the solidified supercooled solution is dissolved by the triaxial compression tester 40, the volume of the specimen P does not change easily.

[Second Embodiment]
In the specimen collecting method according to the first embodiment, the supercooling solution was injected into the ground G, and then the crystallization agent 32 was charged into the ground G. However, in the specimen collecting method according to the second embodiment, FIG. 7 (A). ), First, the crystallization agent 32 is added to the ground G. Then, as shown in FIG. 7B, the supercooled solution is injected toward the crystallization agent 32. As a result, the solidified body 34 is formed around the crystallizer 32.

Further, as shown in FIG. 7 (C), the supercooled solution is continuously injected toward the solidified body 34 while pulling out the rod 22. As a result, solidification reactions occur in sequence, and a columnar solidified body 34 is formed as shown in FIG. 7 (D). Then, as shown in FIG. 7 (E), the specimen P is collected using the rod 24.

In the specimen collection method according to the second embodiment, the supercooled solution is injected toward the crystallization agent 32, so that the supercooled solution is immediately solidified after being injected into the ground G. Therefore, even when the flow of groundwater in the ground G is fast, the supercooled solution is unlikely to be washed away and the solidified body 34 is easily formed.

[Third Embodiment]
In the specimen collection method according to the third embodiment, as shown in FIG. 8 (A), first, the supercooled solution is injected into the ground G as in the first embodiment, but as shown in FIG. 8 (B). 32 is charged into the ground (penetrator 30) in which the supercooled solution has permeated while injecting the supercooled solution. The crystallization agent 32 can accelerate the solidification reaction by adding the crystallization agent 32 at intervals as shown in FIG. 8C. As a result, as shown in FIG. 8D, a columnar solidified body 34 is formed. Then, as shown in FIG. 8 (E), the specimen P is collected using the rod 24.

In the sample collection method according to the third embodiment, the crystallizer 32 is charged into the ground (penetrator 30) in which the supercooled solution has permeated while injecting the supercooled solution, so that the supercooled solution is sequentially solidified. Therefore, as in the specimen collection method according to the second embodiment, the solidified body 34 is likely to be formed even when the groundwater flow in the ground G is fast.

(Modification example)
The sodium acetate trihydrate used in the supercooled solution in the above-described embodiment is produced by mixing water at a ratio of 100:66 to anhydrous sodium acetate and heating and melting the mixture. The embodiment is not limited to this.

For example, the mixing ratio of sodium acetate anhydrous and water may be changed. Increasing the mixing ratio of water increases the stability of the supercooled solution in the supercooled state.

As specific examples of the supercooled solution in which the mixing ratio of sodium acetate anhydrous and water is changed, FIGS. 2 and 3 show sodium acetate 3 in which the molecular weight ratio of water to sodium acetate anhydrous is 100: 66, 75, 80, 90. Data on hydrates are shown.

The data shown in FIG. 2 shows the molecular weight ratio of water to sodium acetate anhydrous in a columnar body (test piece) filled with silica sand No. 5 (glass sand having a particle size of about 5 mm) at a gap ratio of 35% at 100: 66. , 75, 80, 90 is the uniaxial compression strength of the test piece impregnated with sodium acetate trihydrate and solidified. Further, the data shown in FIG. 3 is the relationship between the compressive stress and the strain generated when pressure is applied to each test piece in the uniaxial compressive strength test.

As the molecular weight ratio of water to sodium acetate anhydrous increases, the uniaxial compressive strength decreases, as shown in FIG. On the other hand, as shown in FIG. 3, the strain with respect to the compressive stress becomes large. That is, when the mixing ratio of water in the sodium acetate trihydrate increases, the compressive strength of the specimen decreases, but the malleability becomes high and brittle fracture becomes difficult.

In this way, by changing the mixing ratio of sodium acetate anhydrous and water, it is possible to form a specimen having performance suitable for the method of transportation and storage, the test content, and the like. The uniaxial compressive strength required to collect a specimen with less turbulence is approximately 0.05 N / mm ² . Therefore, no matter which of the molecular weight ratios of 100: 66, 75, 80, and 90 is adopted as the molecular weight ratio of water to sodium acetate anhydrous, a specimen with less disturbance can be collected.

In the first to third embodiments, sodium acetate trihydrate was used as the supercooled solution, but the embodiment of the present invention is not limited to this. For example, sodium sulfate decahydrate (Na ₂ SO _{4.10H 2} O, melting point 32.0-38.0 ° C.), sodium thiosulfate pentahydrate (Na ₂ S ₂ O _{3.5H 2} O, melting point 48. 3 ° C), disodium phosphate dodecahydrate (Na ₂ HPO _{4.12H 2} O, melting point 35.0 ° C), calcium chloride hexahydrate (CaCl _{2.6H 2 O} , melting point 30.0 ° C), Calcium acetate monohydrate (C ₄ H ₆ CaO ₄ · H ₂ O, melting point 100-150 ° C), magnesium acetate tetrahydrate (C ₄ H ₆ MgO _4.4 H ₂ O, melting point 79.0 ° C), Potassium acetate (C ₂ H ₃ KO ₂ , melting point 292 ° C), potassium fluoride tetrahydrate (KF · 4H ₂ O, melting point 18.5 ° C), erythritol (C ₅ H ₁₂ O ₄ , melting point 119 ° C), Various substances having a melting point higher than the temperature of the ground G, such as mannitol (C ₆ H ₁₄ O ₆ , melting point 167 ° C.), can be used.

These supercooled solutions can adjust the freezing point to an arbitrary temperature by adding a surfactant, and can maintain a stable supercooled state in the ground. It is not always necessary to add a surfactant to the supercooled solution, and the presence or absence of application can be selected according to the ground temperature, the need to keep the supercooled state stable, and the like.

22 Rod (injection tube)
32 Crystallizer P Specimen G Ground

Claims (4)

With soil particles
A supercooled substance that is filled between the soil particles and solidified, and melts when heated to a predetermined temperature.
Equipped with
The supercooled substances are sodium acetate trihydrate, sodium sulfate decahydrate, sodium thiosulfate pentahydrate, disodium disodium twelve hydrate, calcium chloride hexahydrate, calcium acetate monohydrate, and the like. A columnar specimen that is any one of magnesium acetate tetrahydrate, potassium acetate, potassium fluoride tetrahydrate, erythritol and mannitol . A step of injecting a supercooled solution into the ground and replacing a void portion or a groundwater portion in the ground with a supercooled solution.
A step of solidifying the supercooled solution using a crystallization agent to form a supercooled substance, and
A method for collecting a specimen, comprising a step of collecting the specimen by boring the ground on which the supercooled substance is formed. The process of excavating the ground and inserting an injection pipe,
The step of injecting the supercooled solution from the injection tube into the ground and then injecting the crystallization agent into the ground in which the supercooled solution has permeated, or after injecting the crystallization agent from the injection tube into the ground. A step of injecting a supercooled solution toward the crystallization agent, or a step of injecting the crystallization agent into the ground in which the supercooled solution has permeated while injecting the supercooled solution from the injection tube into the ground.
A step of collecting the specimen by boring the ground in a state where the supercooled solution is solidified and the supercooled substance is formed.
The specimen collection method according to claim 2 . A specimen collection method in which a supercooled solution injected into the ground is solidified to form a supercooling substance, and the specimen is collected by boring the ground.
A method for collecting specimens, wherein a surfactant that lowers the freezing point is added to the supercooled solution.

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