JP6432776B2 - Triaxial frost heaving test apparatus and measuring method of three-dimensional freezing expansion characteristics - Google Patents

Description

  The present invention relates to a triaxial freezing test apparatus and a method for measuring the three-dimensional freezing and expansion characteristics of soil.

  The ground freezing method is widely used for the purpose of improving the strength and water imperviousness of the ground, but the effect of freezing expansion and the stress (frosting pressure) generated by this on existing structures may become a problem. For evaluation and countermeasures, a frost heaving test is conducted for the purpose of measuring the freezing and expansion characteristics of soil.

  In frost heave tests, in general, the amount of frost heaving in the direction of freezing (freezing direction) on the ground near the ground surface is often targeted, and the amount of expansion in the freezing direction is measured under unconstrained pressure or low constrained pressure. Thus, the freezing and expansion characteristics of the soil are captured (for example, see Non-Patent Document 1).

  On the other hand, when the ground freezing method is used for deep underground structures such as urban tunnels, it is necessary to evaluate not only the freezing direction but also the freezing up pressure in the direction orthogonal to the freezing direction, as the ground pressure acts in three dimensions. is there. For this reason, in recent years, a triaxial freezing test for measuring the three-dimensional freezing-expansion characteristic of soil has been proposed and implemented (for example, see Patent Document 1 and Non-Patent Document 2).

  In this triaxial freezing test, the antifreeze, which is a refrigerant whose temperature is controlled, is circulated and supplied to the pedestal in the triaxial cell that has the same loading means as the triaxial compression test, and the test specimen (test specimen) is one-dimensional. And the amount of displacement in the freezing direction (axial direction of the test specimen) and the freezing orthogonal direction (radial direction of the test specimen) under each restraining pressure is measured.

Japanese Patent No. 2746413

Geotechnical Society Standard, JGS0172: “Soil frost heaving test method for frost heaving test”, 2009 Hideo Yamamoto, Yoji Ueda, Hisao Izuda, “Experimental Study on Triaxial Freezing and Expansion of Saturation”, Journal of the Japanese Society of Snow and Ice, Japanese Society of Snow and Ice, December 1994, Volume 56, No. 4, p. 325-333

  However, in the above conventional triaxial freezing test method, the amount of displacement in the direction perpendicular to freezing is obtained as the average value of the measured diameter of the test specimen after completion of freezing. Distribution etc. are not measured. For this reason, it is impossible to grasp how the expansion in the orthogonal direction occurs as the freezing progresses.

  Further, only the displacement amount is measured in both the freezing direction and the freezing orthogonal direction, and the stress, that is, the frost heave pressure cannot be captured. For this reason, it is possible to measure what amount of freezing and expansion will eventually occur for the target soil, but to examine the mechanism of frost heave pressure generation during the freezing process and the effect of changes in freezing speed and restraint pressure on the frost heave pressure. There was a problem that sufficient data could not be obtained.

  In view of the above circumstances, the present invention provides a triaxial freezing test apparatus and a method for measuring the three-dimensional freezing and expansion characteristics of soil, which can measure the temporal change and spatial distribution of the freezing pressure in the freezing and freezing directions in the freezing process. The purpose is to do.

  In order to achieve the above object, the present invention provides the following means.

  A triaxial frost heaving test apparatus according to the present invention is a triaxial frost heaving test apparatus for measuring a frost heaving pressure and a displacement amount in a freezing direction along the axial direction of a soil specimen and a freezing orthogonal direction perpendicular to the freezing direction. An upper pedestal and a lower pedestal disposed so as to sandwich the test body between upper and lower ends of the test body, and a refrigerant supply means for circulating a coolant to the upper pedestal and / or the lower pedestal, A plurality of elastically deformable resin rings that cover and hold the test body by mounting the test body inside, and the resin rings adjacent to the top and bottom of the plurality of resin rings that are stacked on the same axis. An elastic adhesive layer that connects the upper and lower resin rings so as to be relatively displaceable, a displacement measuring means that measures the displacement of each resin ring, and / or the test that is attached to each resin ring. Characterized in that it comprises a pressure measuring means for measuring a pressure.

  The soil three-dimensional freezing and expansion characteristic measuring method of the present invention uses the above-described three-axis frost heaving test apparatus and circulates and supplies a coolant to the upper pedestal and / or the lower pedestal to freeze the specimen in the axial direction. And measuring the displacement of the test specimen in the axial direction and the displacement of the resin ring and / or the pressure of the specimen over time by the displacement measuring means and / or the pressure measuring means. It is characterized by that.

  In the triaxial frost heaving test apparatus and the method for measuring the three-dimensional freezing expansion characteristics of the soil according to the present invention, in the triaxial frost heaving test of soil, the temporal change and spatial distribution of the frost heave pressure in the freezing direction and the freezing orthogonal direction in the freezing process. Can be measured.

  This provides basic data for accurately predicting frost heave pressure and freezing expansion due to freezing and expansion under earth pressure, and underground structures such as ground freezing methods and LNG underground tanks constructed and operated at low temperatures. It is possible to rationalize countermeasures for frost heave pressure.

It is a figure which shows the triaxial freezing test apparatus which concerns on one Embodiment of this invention. It is the figure which expanded the test body holding part of the triaxial freezing test apparatus which concerns on one Embodiment of this invention.

  Hereinafter, with reference to FIG.1 and FIG.2, the measuring method of the three-dimensional freezing expansion test apparatus and soil three-dimensional freezing expansion characteristic which concern on one Embodiment of this invention is demonstrated.

  The method for measuring the three-dimensional freezing and expansion characteristics of the soil according to the present embodiment is based on the frost heave pressure in the freezing direction (the specimen axis direction) and the freezing orthogonal direction (the specimen circumferential direction) in the freezing process in the soil triaxial freezing test. This is a method for measuring a temporal change and a spatial distribution, and uses a triaxial freezing test apparatus A shown in FIG.

  The triaxial frost heaving test apparatus A according to this embodiment includes a pressure vessel (mold) 1 and upper and lower sides of a specimen (frozen sample / specimen) 2 provided in the pressure vessel 1 and collected, for example, by in situ ground excavation. An upper pedestal (top cap) 3 and a lower pedestal 4 disposed so as to sandwich the test body 2 on the end side, a loading piston 6 of loading means for applying a load from above via the load cell 5, the upper pedestal 3 and / or Alternatively, a coolant supply means 7 for circulating and supplying coolant to the lower pedestal 4 and a pore water supply / discharge means 8 for supplying and discharging pore water to and from the test body are provided.

  The pressure vessel 1 includes an acrylic transparent cylindrical body 1a, and an upper board 1b and a lower board 1c that are disposed so as to close and sandwich the upper and lower openings of the transparent cylindrical body 1a. And it is comprised so that a desired side pressure can be added to the test body 2 hold | maintained in the pressure vessel 1 by atmospheric pressure or liquid pressure. The upper pedestal 3 and the lower pedestal 4 are indirectly and directly supported by the upper board 1b and the lower board 1c, respectively, and are disposed on the central axis of the transparent cylindrical body 1a. Furthermore, a displacement meter (freezing direction displacement measuring means) 10 for measuring an axial displacement that is a freezing direction of the upper pedestal 3 (and / or the lower pedestal 4) and the test body 2 is provided.

  On the other hand, in the triaxial freezing test apparatus A of the present embodiment, as shown in FIGS. 1 and 2, the test body 2 is not covered with a rubber sleeve, but an elastically deformable resin ring 11 made of acrylic or the like is used. Use to hold the coating.

  Specifically, in this embodiment, a plurality of acrylic resin rings 11 of the same shape and the same size having an inner diameter substantially equal to the outer diameter of the cylindrical test body 2 are stacked on the same axis, and the test body is placed inside the same. Wear 2 In addition, the upper and lower resin rings 11 are bonded to each other by using an interposed material having elasticity and adhesiveness such as a silicon caulking material. That is, the elastic adhesive layer 12 is provided between the resin rings 11 adjacent to each other in the vertical direction.

  For example, the test body 2 is formed with a diameter of 60 mm and a height of 90 mm. In contrast, each resin ring 11 has an inner diameter d1 of 60.1 mm and an outer diameter d2 of 90 mm (thickness d3 of 15 mm). The uppermost resin ring 11 attached to the outer periphery of the upper pedestal 3 has a height t1 of 25 mm, and the lowermost resin ring 11 attached to the outer periphery of the lower pedestal 4 has a height t2 of 40 mm. The plurality of resin rings 11 provided at the intermediate portion between the pedestal 3 and the lower pedestal 4 and attached to the test body 2 are formed with a height t3 of 10 mm. The thickness t4 of the elastic adhesive layer 12 is 1 mm.

  Further, a strain gauge (strain measuring means) 13 is attached to the outer peripheral surface of each resin ring 11 attached to the test body 2. Each resin ring 11 attached to the test body 2 is provided with a through hole penetrating from the outer surface to the inner surface, and a pressure gauge (pressure measuring means) 14 is disposed in the through hole.

  In the triaxial freezing test apparatus A of the present embodiment configured as described above, the side of the test body 2 is restrained by each resin ring 11, and each resin ring 11 is elastic when the test body 2 freezes and expands. Deform. Further, due to the elastic deformation of the elastic adhesive layer 12, the laminated resin rings 11 can be freely displaced following the expansion of the test body 2 individually.

  When the frost heaving test is performed using the triaxial frost heaving test apparatus A of the present embodiment having the above-described configuration, the pore water pressure of the test body 2 is adjusted to a desired pore water pressure by the pore water supply / discharge means 8 and loaded. A predetermined upper pressure is applied to the test body 2 by means 6.

  In this state, the refrigerant is circulated and supplied to the upper pedestal 3 and / or the lower pedestal 4. When a negative temperature refrigerant is circulated and supplied to the upper pedestal 3, the specimen 2 can be frozen from the upper side toward the lower side, and when a negative temperature refrigerant is circulated and supplied to the lower pedestal 4. The test body 2 can be frozen from the lower side toward the upper side.

  Thereby, the frost heaving test can be performed while controlling the progress of the freezing region. Then, the amount of frost heave in the specimen axis direction, which is the freezing direction, is measured by a displacement meter (freezing direction displacement measuring means 10) connected to the upper pedestal 3 (or lower pedestal 4) as in the normal uniaxial frost heaving test.

On the other hand, the frost heave pressure in the test body radial direction, which is the direction perpendicular to freezing, is measured by one of the following first method, second method, or in combination.
In the first method, the displacement amount of the outer periphery of each resin ring 11 is measured by a strain gauge 13 installed on the outer periphery of each of the laminated resin rings 11, and the thick cylinder theory is calculated from the deformation coefficient and shape of each resin ring 11. Based on the above, the internal pressure generated in the specimen 2 is calculated.
In the second method, the pressure is measured by the pressure gauge 14 installed in the through hole formed in each resin ring 11 so that the pressure receiving surface is in contact with the side surface of the test body 2.
Thereby, the internal pressure change of each site | part of the test body 2 according to progress of the freezing area | region of the test body 2 is calculated | required, The freezing-up pressure of a freezing orthogonal direction can be estimated from this value.

  Therefore, in the three-axis frost heaving test apparatus A and the method for measuring the three-dimensional freezing expansion characteristics of the soil according to the present embodiment, it is possible to obtain a change with time in the freezing process, a distribution in the direction of the specimen axis, and the like. Accordingly, it is possible to grasp how the expansion in the orthogonal direction occurs.

  Further, the pressure generated in both the freezing direction and the freezing orthogonal direction can be captured. This will not only determine the amount of freezing and expansion that will eventually occur for the target soil, but also examine the mechanism of frost heave pressure generation during the freezing process and the effects of changes in freezing speed and restraint pressure on the frost heave pressure. Sufficient data can be obtained.

  Therefore, according to the three-axis frost heaving test apparatus A and the method for measuring the three-dimensional freezing and expansion characteristics of the soil according to the present embodiment, the basis for accurately predicting the frost heaving pressure and the amount of freezing expansion due to freezing and expansion under earth pressure action. Data can be obtained. For this reason, it becomes possible to rationalize measures for frost heaving pressure in underground structures such as the ground freezing method and LNG underground tanks constructed and operated at low temperatures.

  As mentioned above, although one embodiment of the triaxial freezing test apparatus and the method for measuring the three-dimensional freezing and expansion characteristics of soil according to the present invention has been described, the present invention is not limited to the above one embodiment, Changes can be made as appropriate without departing from the scope.

1 Pressure vessel (mold)
1a Transparent cylindrical body 1b Upper panel 1c Lower panel 2 Specimen (frozen sample / specimen)
3 Upper pedestal (top cap)
4 Lower pedestal 5 Load cell 6 Loading piston (loading means)
7 Refrigerant supply means 8 Pore water supply / discharge means 9 Liquid supply / discharge means 10 Displacement meter (displacement measurement means)
11 Resin ring 12 Elastic adhesive layer 13 Strain meter (strain measuring means)
14 Pressure gauge (pressure measuring means)
A Triaxial freezing test equipment

Claims (2)

A three-axis frost heaving test apparatus for measuring a frost heave pressure and a displacement amount in a freezing direction perpendicular to the freezing direction and the freezing direction along the axial direction of the soil specimen,
An upper pedestal and a lower pedestal disposed so as to sandwich the test body between upper and lower ends of the test body;
A refrigerant supply means for circulating and supplying a refrigerant to the upper pedestal and / or the lower pedestal,
A plurality of elastically deformable resin rings that hold the test body inside and cover and hold the test body;
An elastic adhesive layer that is interposed between the resin rings adjacent to the upper and lower sides of the plurality of resin rings that are stacked on the same axis and that couples the upper and lower resin rings so as to be capable of relative displacement;
Displacement measuring means for measuring the displacement of each resin ring and / or pressure measuring means for measuring the pressure of the test body attached to each resin ring. . Using the triaxial freezing test apparatus according to claim 1,
The coolant is circulated and supplied to the upper pedestal and / or the lower pedestal to freeze the test body in the axial direction, and the axial displacement of the test body, the displacement measuring means, and / or the pressure measurement. A method for measuring the three-dimensional freezing-expansion characteristics of soil, characterized in that the displacement amount of the resin ring and / or the pressure of the specimen is measured over time by means.

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