Small freezing sampling device and in-situ ground freezing sampling method using thereof

Abstract

To provide a small freezing sampling device that is not only economical but also easy to install, versatile, and of high quality, and an in-situ ground freezing sampling method using the device.SOLUTION: A small freezing sampling device 10 freezes the in-situ ground G to collect frozen soil B from an undisturbed area as a soil sample. It has a double-pipe structure with a bottomed section 3, including a hollow inner freezing pipe 1 for supplying a refrigerant 9, such as liquid nitrogen, and a hollow outer protective pipe 2. The inner freezing pipe 1 has a hollow enlarged diameter section 1a at its lower end. A temperature sensor 8 is installed in the axial direction and / or at a bottom of the outer protective pipe 2. The inner freezing pipe 1 is not connected to the outer protective pipe 2 and is installed directly on a top surface of the bottomed section 3. Refrigerant 9 supplied to the inner freezing pipe 1 passes through the hollow enlarged diameter section 1a and cools the bottomed section 3 located directly below it, freezing the ground directly below the bottomed section 3 and the surrounding ground G into a block B.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention belongs to the technical field of in-situ ground freezing sampling methods developed to collect undisturbed soil samples from in-situ ground in sand and gravel layers, and more specifically, relates to a technique for collecting samples with minimal disturbance in ground investigations, in particular to a small-sized freezing sampling device and an in-situ ground freezing sampling method using the same device that enables high-quality, minimally disturbed soil samples (also called ground samples or in-situ frozen samples) to be collected from undisturbed areas at low cost in order to conduct various tests such as deformation tests to determine liquefaction characteristics and cyclic shear characteristics of sandy ground, and to understand mechanical properties. [Background technology]

[0002] Conventionally, in-situ ground freezing sampling methods have been developed to collect undisturbed soil samples from in-situ sand and gravel layers, and are publicly known, as disclosed in, for example, Patent Documents 1 to 5, and have already been used in a considerable number of projects.

[0003] The existing in-situ ground freezing sampling methods described in Patent Documents 1 to 5 are known to require a large set of equipment and have high sampling costs compared to other general non-freezing sampling methods. Therefore, it is well known among those skilled in the art that their practical use in Japan is limited, and they are only used in large-scale projects.

[0004] Therefore, as shown in Patent Document 6, an invention has been disclosed that aims to significantly reduce the cost of in-situ ground freezing sampling, which has previously required enormous costs, by reviewing the process leading up to freezing the ground, the extent of freezing, and the method for collecting frozen samples (see lines 1 to 3 of paragraph

[0012] in Patent Document 6). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 3-17036 [Patent Document 2] Special Publication No. 3-80237 [Patent Document 3] Special Publication No. 4-52803 [Patent Document 4] Special Publication No. 5-54534 [Patent Document 5] Patent No. 3648641 [Patent Document 6] Patent No. 7023258 Summary of the Invention [Problem to be solved by the invention]

[0006] However, although the invention of Patent Document 6 achieves cost reduction compared to the prior art, which required enormous expenses, it is specialized for collecting soil test specimens for hollow torsional shear tests. That is, the invention of Patent Document 6 requires a step of inserting a small-diameter freezing pipe, which is a ground sample collection device, into the ground to be investigated by self-boring (see the first line of claim 1 of Patent Document 6), and therefore the collected samples are limited to hollow cylindrical shapes that do not contain gravel.

[0007] Therefore, the present invention was devised in consideration of the problems of the background art described above, and its purpose is to provide a small-sized freezing sampling device and an in-situ ground freezing sampling method using the same device, which not only achieves cost reduction with a compact structure compared to conventional technologies that required enormous expenses, but also makes it possible to collect high-quality, less disturbed soil samples to be used in various tests such as the hollow torsional shear test and deformation tests to determine cyclic shear characteristics, and which is not only economical but also easy to install, versatile, and of high quality. [Means for solving the problem]

[0008] As a means for solving the above problems, the small freezing sampling device according to the invention described in claim 1 is a small freezing sampling device that freezes the ground in situ to collect frozen soil in an undisturbed area as a soil sample, The small freezing sampling device is formed in a double-tube structure with a bottom, including a hollow inner freezing tube for supplying a refrigerant such as liquid nitrogen, and a hollow outer protective tube for protecting the inner freezing tube; the freezing inner pipe has a hollow expanded diameter portion at its lower end, the diameter of which expands toward the protective outer pipe; a temperature sensor is installed in the tube axial direction and / or at the bottom of the protective outer tube; The freezing inner pipe is not connected to the protective outer pipe and is installed directly on the upper surface of the bottomed portion, and the refrigerant supplied to the freezing inner pipe passes through the hollow expanded portion and cools the bottomed portion located directly below it, thereby freezing the ground directly below the bottomed portion and the surrounding ground in a block.

[0009] The invention described in claim 2 is characterized in that, in the small freezing sampling device described in claim 1, a support member is provided between the outer surface of the freezing inner tube and the inner surface of the protective outer tube to allow the weight of the freezing inner tube to be borne by the protective outer tube.

[0010] The invention described in claim 3 is characterized in that, in the small freezing sampling device described in claim 1 or 2, an insulating material is provided above the hollow expanded portion of the freezing inner tube within the space formed by the outer surface of the freezing inner tube and the inner surface of the protective outer tube.

[0011] The invention described in claim 4 is characterized in that, in the small frozen sampling device described in claim 1 or 2, the bottomed portion is made of aluminum or copper, which has excellent thermal conductivity.

[0012] The invention described in claim 5 is characterized in that, in the small frozen sampling device described in claim 1 or 2, multiple studs are provided that protrude from the underside of the bottomed portion into the original ground below.

[0013] The invention described in claim 6 is characterized in that the small-sized freezing sampling device described in claim 1 or 2 has a diameter of about 165 mm.

[0014] The invention described in claim 7 is characterized in that, in the small freezing sampling device described in claim 1 or 2, the freezing inner tube and the protective outer tube are arranged concentrically.

[0015] The in-situ ground freezing sampling method according to the invention described in claim 8 is an in-situ ground freezing sampling method using the small freezing sampling device described in claim 1 or 2, Excavating the in-situ ground from above ground to a position directly above the area to be frozen using a ground excavator; positioning the compact freeze sampling device directly above the area to be frozen; a step of supplying a refrigerant such as liquid nitrogen into the freezing inner pipe of the small freezing sampling device, so that the refrigerant supplied to the freezing inner pipe passes through the hollow expanded diameter portion and cools the bottom portion located directly below it, thereby promoting freezing of the ground directly below the bottom portion and the surrounding ground; The method is characterized by comprising the steps of: freezing the ground directly below the bottom and the surrounding ground into a block; then overcoring the frozen soil to separate it from the ground; and collecting the frozen soil adhered to the bottom of the small frozen sampling device by pulling it up together with the small frozen sampling device while it is still frozen. [Effects of the Invention]

[0016] The small freezing sampling device and the in-situ ground freezing sampling method using the device according to the present invention have the following advantages. (1) By miniaturizing the freezing sampling device, the device itself can be realized at low cost. As a result, equipment such as ground excavators can also be made smaller, and the consumption of refrigerants such as liquid nitrogen can be reduced. In addition, since the freezing area can be limited to the ground directly below the bottom of the device (bottom part) and the surrounding ground, a large-scale circulating refrigerant mechanism is not required. Therefore, a small freezing sampling device with excellent economical efficiency and ease of construction can be realized, as well as an in-situ ground freezing sampling method using this device. (2) By collecting frozen soil attached to the bottom of the small freezing sampling device while it is still frozen, it is possible to collect high-quality, minimally disturbed soil samples for use in various tests, such as deformation tests to determine cyclic shear properties. This makes it possible to realize a versatile, high-quality small freezing sampling device and an in-situ ground freezing sampling method using this device. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a perspective elevational view of a compact frozen sampling device according to the present invention; FIG. [Figure 2] FIG. 2 is a bottom view of FIG. 1. [Figure 3] 2 is an explanatory diagram illustrating an example of an attachment state of a temperature sensor of the small-sized freeze sampling device in FIG. 1. FIG. [Figure 4] 1 is an elevational view showing the main part of the upper structure of the compact frozen sampling device according to the present invention. FIG. [Figure 5] FIG. 5 is an X-ray view of FIG. 4. [Figure 6] 1A to 1D are work flow charts that schematically show an in-situ ground freezing sampling method using a small freezing sampling device according to the present invention. [Figure 7] 7A is a photograph showing frozen soil (soil sample) collected by the in-situ ground freezing sampling method shown in FIG. 6, and B is a schematic diagram showing a test piece formed from the frozen soil (soil sample). [Figure 8] FIG. 7 is an explanatory diagram for confirming the quality of frozen soil (soil sample) collected by the in-situ ground freezing sampling method shown in FIG. 6. DETAILED DESCRIPTION OF THE INVENTION

[0018] Next, an embodiment of a small freezing sampling device according to the present invention and an in-situ ground freezing sampling method using the device will be described with reference to the drawings.

[0019] The small-sized freezing sampling device according to the present invention is a small-sized freezing sampling device 10 that freezes the ground in situ in order to collect frozen soil from an undisturbed area as a soil sample. As shown in Figure 1, the small freezing sampling device 10 is formed in a double-tube structure with a bottom 3, having a hollow inner freezing tube 1 for supplying a refrigerant 9 such as liquid nitrogen, and a hollow outer protective tube 2 for protecting the inner freezing tube 1. The freezing inner pipe 1 is provided at its lower end with a hollow expanded diameter portion 1a whose diameter expands toward the protective outer pipe 2. As shown in FIG. 3, a temperature sensor 8 is installed in the axial direction of the protective outer tube 2 and / or at the bottom portion 3 . Thus, the freezing inner pipe 1 is not connected to the protective outer pipe 2 and is installed directly on the upper surface of the bottomed portion 3, and the refrigerant 9 supplied to the freezing inner pipe 1 passes through the hollow expanded diameter portion 1a and cools the bottomed portion 3 located directly below it, thereby freezing the ground G directly below the bottomed portion 3 and the surrounding ground G into a mass of the required size. Here, it should be noted that the "surrounding ground G" in the "ground G directly below the bottomed portion 3 and surrounding ground G" refers to the surrounding ground G of the bottomed portion 3, and not the surrounding ground of the entire small frozen sampling device 10.

[0020] In this embodiment, liquid nitrogen is used as the coolant 9, but any coolant used in conventional freeze sampling techniques, such as a mixture of ethanol and dry ice, or brine, can be used in the same manner.

[0021] In this embodiment, the hollow inner freezing pipe 1 is made of stainless steel, and its size is merely an example. The main body has an outer diameter of approximately 90 mm and a wall thickness of approximately 5.5 mm, and its height can be modified by adding an appropriate extension depending on the distance from the ground to the area where the in-situ ground G is to be frozen. The hollow expanded diameter section 1a connected (extended) to the lower end of the main body has an outer diameter of approximately 140 mm, a wall thickness of approximately 1 to 2 mm, and a height of approximately 15 mm. It is placed directly on the upper surface of the bottomed section 3 and is shaped to abut against the inner surface of the protective outer pipe 2. In other words, the refrigerant 9 supplied inside the inner freezing pipe 1 passes through the expanded diameter section 1a and directly contacts the bottomed section 3.

[0022] In this embodiment, the hollow protective outer tube 2 is made of stainless steel, and its size is, by way of example only, approximately 165 mm in outer diameter and 5 mm in thickness, and its height is not significantly different from that of the freezing inner tube 1.

[0023] In this embodiment, the bottomed portion 3 is formed in a disk shape with two upper and lower stepped portions, and the outer periphery of the upper step is fitted (fitted inside) to the inner periphery of the protective outer pipe 2 by a joining means such as welding. The bottomed portion 3 in this embodiment is made of aluminum, which has excellent thermal conductivity, but is not limited to this and can also be made of copper. This is to efficiently and quickly freeze the ground G directly below the bottomed portion 3 and the surrounding ground G.

[0024] As an example, the temperature sensors 8 are provided in a pair (two at positions corresponding to both ends of the axis of symmetry) at a height of about 160 mm from the bottom end of the protective outer pipe 2, and then in pairs (one pair at a height of about 80 mm upward) at left and right sides, for a total of five pairs (ten sensors). Furthermore, at a height of about 20 mm from the bottom end of the protective outer pipe 2, the temperature sensors are provided in a straight line passing through the hollow portion of the enlarged diameter portion 1a and penetrating the protective outer pipe 2 in the horizontal direction. Furthermore, in this embodiment, a temperature sensor 8 is also provided in the vertical temperature sensor installation hole 3a provided in the center of the bottom portion 3. Incidentally, the symbol 2a in the figure indicates a horizontal temperature sensor installation hole drilled in the protective outer tube 2 to support both ends of the temperature center 8, the symbol 81 indicates a temperature data logger, and the symbol 82 indicates a cable. The installation form (installation location, quantity) of the temperature sensors 8 is not limited to the example shown in the figure, and can be modified as appropriate on the condition that an operator (a person skilled in the art) can predict and judge, based on experience, insight, track record, etc., from the values, etc. of the temperature data logger 81, that the ground G directly below the bottomed portion 3 and the surrounding ground G are formed into the required lumpy frozen soil. For example, the temperature sensors 8 in this embodiment are installed in the axial direction of the protective outer pipe 2 and in the bottomed portion 3, but are not limited to this, and may be installed only in the axial direction of the protective outer pipe 2 or only in the bottomed portion 3, as long as the above-mentioned conditions are met.

[0025] In this embodiment, a support member 4 is provided between the outer peripheral surface of the freezing inner pipe 1 and the inner surface of the protective outer pipe 2 to allow the weight of the freezing inner pipe 1 to be shared by the protective outer pipe 2. The support member 4 is made of metal, and is formed from aluminum to prioritize thermal conductivity. As a result, the support member 4 prevents the weight of the freezing inner pipe 1 from concentrating on the bottomed portion 3, where strength and rigidity are concerns, and also serves as a spacing member to more reliably arrange the freezing inner pipe 1 and the protective outer pipe 2 concentrically. The support member 4 in this embodiment is formed into a horizontal tire shape by joining an upper surface portion 41, a lower surface portion 42, and an outer peripheral surface 43 by means of welding or other joining means, and the upper surface portion 41 and the lower surface portion 42 are integrally formed on the outer peripheral surface of the freezing inner pipe 1, and the outer peripheral surface 43 is configured to rest on the inward protruding portion (jaw portion) 2b of the protective outer pipe 2. The form of the support member 4 is not limited to the example shown in the drawing, and can be implemented in various forms as long as it is configured to allow part of the weight of the inner freezing pipe 1 to be borne by the outer protective pipe 2. However, the support member 4 does not need to be provided as long as the bottomed portion 3 is made of a material (e.g., stainless steel, iron, etc.) that has sufficient strength and rigidity to bear the entire weight of the inner freezing pipe 1.

[0026] Furthermore, a heat insulating material 5 is provided above the hollow expanded diameter portion 1a of the freezing inner pipe 1 in the space formed by the outer peripheral surface of the freezing inner pipe 1 and the inner surface of the protective outer pipe 2. In this embodiment, the heat insulating material 5 is filled inside the support member 4, i.e., the hollow portion formed by the upper surface portion 41, the lower surface portion 42, and the outer peripheral surface 43. In this way, in this embodiment, by filling (confining) the heat insulating material 5 in the hollow portion, a rational design is achieved, such as effective use of the hollow portion (space) and the restraining effect of the heat insulating material 5. The insulating material 5 is made of, for example, glass wool, rock wool, expanded polystyrene, etc., and is provided directly above the expanded diameter portion 1a to block as much as possible the movement (diffusion) of the cold air of the refrigerant 9 that directly cools the bottomed portion 3, and to efficiently freeze the ground G directly below the bottomed portion 3 and the surrounding ground G.

[0027] Furthermore, in this embodiment, a plurality of studs 6 are provided on the bottomed portion 3 using a caulking agent, protruding from its underside into the in-situ ground (ground directly below) G below. The studs 6 are made of metal and are provided to embed themselves in the frozen soil that forms chunks of the ground G directly below the bottomed portion 3 and the surrounding ground G, thereby increasing adhesion strength and ensuring the collection of the frozen soil. The studs 6 in this embodiment have a protruding dimension of 30 mm, and twelve of them are provided evenly across the entire surface of the bottomed portion 3, but the protruding dimension and number can be appropriately modified in design as long as it facilitates the collection of frozen soil.

[0028] Next, we will explain the in-situ ground freezing sampling method using the above-configured small freezing sampling device 10. It should be noted that the procedures etc. explained below are merely an example.

[0029] First, as shown in Fig. 6A, a ground excavator (not shown) is used to excavate the in-situ ground G from the ground to a position directly above the area to be frozen, forming a borehole H. Then, as shown in Fig. 6B, the small freezing sampling device 10 is positioned directly above the area to be frozen. In this embodiment, the borehole H is drilled using the small freezing sampling device 10, so it can be drilled with a small diameter hole. This allows equipment such as a ground excavator to be made smaller. For example, in this embodiment, the outer diameter of the small freezing sampling device 10 (protective outer tube 2) is about 165 mm, so it is sufficient to drill a hole with a diameter (φ) of about 215 mm. The excavation depth of the borehole H varies depending on the test purpose, etc., but is generally not more than 20 m. Even when the small freezing sampling device 10 is lengthened by appropriately extending the freezing inner pipe 1 and the protective outer pipe 2, as shown in Figures 4 and 5, by providing a plurality of centralizers (spacers) 7 at appropriate intervals in the axial direction of the freezing inner pipe 1, the freezing inner pipe 1 and the protective outer pipe 2 can be arranged concentrically, or other measures can be taken as appropriate.

[0030] Next, as shown in Fig. 6C, a refrigerant 9 such as liquid nitrogen is supplied into the freezing inner tube 1 of the positioned small freezing sampling device 10 using an input tube 11 (or directly). Reference numeral 12 in the figure denotes a liquid nitrogen container. The refrigerant 9 supplied into the freezing inner pipe 1 passes through the hollow expanded diameter portion 1a formed at the lower end of the freezing inner pipe 1 and directly cools the bottomed portion 3 located directly below it. Because the refrigerant 9 cools through the expanded diameter portion 1a, which is as wide as the bottomed portion 3, it can cool the bottomed portion 3 more efficiently and quickly than a freezing inner pipe 1 without an expanded diameter portion 1a. In addition, a heat insulating material 5 is provided above the expanded diameter portion of the expanded diameter portion 1a, so it can cool the bottomed portion 3 more efficiently and quickly. Note that control such as keeping the filling amount of the refrigerant 9 approximately constant is smoothly performed on the ground. Thus, the refrigerant 9 supplied to the freezing inner pipe 1 passes through the hollow expanded diameter portion 1a and directly cools the bottomed portion 3 located directly below it, thereby promoting the freezing of the ground G directly below the bottomed portion 3 and the surrounding ground G, thereby making it possible to freeze the ground G directly below the bottomed portion 3 and the surrounding ground G into chunks of a required size. The size of the chunks and the state of freezing are predicted and determined by an operator (person skilled in the art) based on experience, insight, track record, etc., from the values ​​of the temperature sensor logger that accumulates the values ​​of the temperature sensor 8.

[0031] Next, after determining that the ground G directly below the bottom portion 3 and the surrounding ground G have been frozen into a block of the required size, as shown in Figure 6D, a casing 13 larger than the outer diameter of the small frozen sampling device 10 is used to perform overcoring to separate the frozen soil B from the ground G using waterless excavation that does not disturb the soil sample, and the frozen soil B fixed to the bottom portion 3 of the small frozen sampling device 10 is collected by pulling up the small frozen sampling device 10 while still frozen (see Figure 7A). The collected frozen soil (soil sample) B according to Figure 7A is formed into test pieces (four in the illustrated example) for various tests such as liquefaction tests, as shown in Figure 7B. In addition, in order to maintain the frozen state of the frozen soil B during the overcoring, appropriate measures may be taken, such as supplying a cooling material such as dry ice from the freezing inner tube 1 to the top surface of the bottomed portion 3, which is the bottom of the hole of the small freezing sampling device 10.

[0032] <Considerations regarding the test results of the collected soil samples (specimens)> FIG. 8 is a graph showing the "liquefaction strength ratio" on the vertical axis and the "corrected N value" on the horizontal axis for the collected soil samples (specimens). As shown in Figure 8, the liquefaction strength ratio (see ● in the graph) of the specimen obtained by the in-situ ground freezing sampling method using the compact freezing sampling device 10 of the present invention is high, corresponding to the relationship of the Architectural Institute of Japan's Building Foundation Design Guidelines (see the solid line in Figure 8), which is estimated partially using conventional in-situ ground freezing sampling methods. Furthermore, the results are significantly superior to those of specimens obtained by a general tube sampling method that does not involve ground freezing, which is subject to loosening or compaction due to sampling (see the dashed line and ■ in Figure 8). In other words, as can be seen from the graph in Figure 8, the specimen obtained by the in-situ ground freezing sampling method of the present invention has the advantage of being a high-quality soil sample with minimal disturbance, and is of very high quality.

[0033] Although the embodiments have been described above based on the drawings, it should be noted that the present invention is not limited to the illustrated examples and includes the range of design modifications and application variations that would normally be made by a person skilled in the art, provided that they do not deviate from the technical concept of the present invention. [Explanation of symbols]

[0034] 1 Inner tube for freezing 1a Expanded diameter part 2 Protective outer tube 2a Temperature sensor installation hole 2b Projection (jaw) 3 Bottomed part 3a Temperature sensor installation hole 4 Support member 5. Insulation 6 studs 7 Centralizer 8 Temperature Sensor 81 Temperature Data Logger 82 Cable 9 Refrigerant (liquid nitrogen) 10. Small frozen sampling device 11 Input pipe 12 Liquid nitrogen container 13 Waterless drilling casing 14 Cooling material (refrigerant) B. Frozen soil (soil sample) G. Ground directly below and surrounding areas H borehole

Claims

1. A small freezing sampling device that freezes the ground in situ to collect frozen soil in an undisturbed area as a soil sample, The small freezing sampling device is formed in a double-tube structure with a bottom, including a hollow inner freezing tube for supplying a refrigerant such as liquid nitrogen, and a hollow outer protective tube for protecting the inner freezing tube; the freezing inner pipe has a hollow expanded diameter portion at its lower end, the diameter of which expands toward the protective outer pipe; a temperature sensor is installed in the tube axial direction and / or at the bottom of the protective outer tube; The freezing inner pipe is not connected to the protective outer pipe and is installed directly on the top surface of the bottomed portion, and the refrigerant supplied to the freezing inner pipe passes through the hollow expanded portion and cools the bottomed portion located directly below it, thereby freezing the ground directly below the bottomed portion and the surrounding ground in a block.This is a small freezing sampling device.

2. 2. The small freezing sampling device according to claim 1, wherein a support member is provided between the outer surface of the freezing inner tube and the inner surface of the protective outer tube to allow the weight of the freezing inner tube to be borne by the protective outer tube.

3. 3. A small freezing sampling device as described in claim 1 or 2, characterized in that an insulating material is provided above the hollow, expanded portion of the freezing inner tube within the space formed by the outer surface of the freezing inner tube and the inner surface of the protective outer tube.

4. 3. The small-sized frozen sampling device according to claim 1, wherein the bottomed portion is made of aluminum or copper, which has excellent thermal conductivity.

5. 3. The small-sized freezing sampling device according to claim 1, further comprising a plurality of studs projecting from the underside of said bottomed portion toward the underlying ground.

6. 3. A small-sized freezing sampling device according to claim 1 or 2, characterized in that the diameter is about 165 mm.

7. 3. The small-sized freezing sampling device according to claim 1, wherein the inner freezing tube and the outer protective tube are concentrically arranged.

8. An in-situ ground freezing sampling method using the small freezing sampling device according to claim 1 or 2, Excavating the in-situ ground from above ground to a position directly above the area to be frozen using a ground excavator; positioning the compact freeze sampling device directly above the area to be frozen; a step of supplying a refrigerant such as liquid nitrogen into the freezing inner pipe of the small freezing sampling device, so that the refrigerant supplied to the freezing inner pipe passes through the hollow expanded diameter portion and cools the bottom portion located directly below it, thereby promoting freezing of the ground directly below the bottom portion and the surrounding ground; a step of freezing the ground directly below the bottom and the surrounding ground into a mass, then overcoring the frozen soil to separate it from the ground, and collecting the frozen soil fixed to the bottom of the small frozen sampling device by lifting it up together with the small frozen sampling device while it is still frozen; An in-situ ground freezing sampling method comprising:

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