Sample preparation device for testing specific heat capacity of soil body and use method of sample preparation device

Abstract

The invention discloses a sample preparation device for testing the specific heat capacity of a soil body and a use method of the sample preparation device, and belongs to the technical field of soil body thermophysical property detection equipment. The sample preparation device comprises an internal pressure mold, the internal pressure mold comprises a cylindrical mold main body, two pore channel protrusions which are parallel to a center line and are symmetrically distributed are correspondingly arranged on the two sides of the center line of the top of the mold main body, and one ends of the two pore channel protrusions extend to the outer edge of the top of the mold main body; the pore channel bulge is used for generating a pore channel for placing the low-melting-point alloy column when the soil sample is pressed for the first time; the low-melting-point alloy column is used for generating a hole channel for inserting the probe when the soil sample is pressed for the second time; the inner diameter of the outer protection barrel is matched with the diameter of the inner pressing mold, the outer protection barrel is arranged outside the inner pressing mold in a sleeving mode, and the height of the inner pressing mold is smaller than that of the outer protection barrel; and the sample pressing device is used for pressing the soil material in the outer pile casing. According to the scheme, the soil sample provided with the reserved hole channels and used for specific heat capacity testing can be prepared, and the soil sample is integrally formed.

Description

Technical Field

[0001] The invention relates to the technical field of soil thermal property detection equipment, and more specifically to a sample preparation device for testing soil specific heat capacity and a use method thereof. Background Art

[0002] Specific heat capacity is one of the important thermophysical properties of soil. Its physical meaning is the amount of heat absorbed or released by changing the unit temperature of unit mass of soil, which represents the heat storage capacity of soil. In projects involving soil heat transfer and temperature field analysis, such as freezing construction, shallow geothermal energy extraction, and heat dissipation design of nuclear waste disposal repositories, specific heat capacity is an essential and important parameter.

[0003] In geotechnical testing, the part involving the specific heat capacity of soil is generally carried out by using mixed calorimetry, which is to achieve thermal equilibrium by uniformly mixing the soil with solutions (usually water) of different temperatures. In this process, the heat released by the high-temperature object should be equal to the heat absorbed by the low-temperature object, and the specific heat capacity of the soil is calculated using the heat conservation formula. In fact, the mixed calorimetry tests the average specific heat capacity of the soil, and is more suitable for materials whose specific heat capacity does not change with temperature, but the specific heat capacity of the soil is not fixed at different temperatures.

[0004] The double-needle heat pulse method was invented in the 1990s and has been used to test the thermal properties of materials. In experimental research or engineering applications, the double-needle heat pulse method is generally used to test the thermal conductivity of soil rather than the specific heat capacity of soil. The reason is that the probe deflection and the fluctuation of the double-needle spacing have no significant effect on the thermal conductivity of the soil, but have a significant impact on the test accuracy of the specific heat capacity. However, in recent years, there have also been studies exploring how to use the double-needle heat pulse method to measure the specific heat capacity of soil in order to broaden the scope of application of the double-needle heat pulse method. For example, LIU G, LI BG, REN TS, et al. Analytical Solution of the Heat Pulse Method in a Parallel epiped Sample Space [J]. Soil Science Society of America Journal, 2008. 72 (5): 1208-1216. The study pointed out that, in theory, a 2% change in the probe spacing will cause a 4% relative error in the specific heat capacity, and a 1° deflection of the probe will even cause a 10% error in the specific heat capacity. Therefore, when using the thermal probe method to measure the specific heat capacity of soil, it is of great significance to reduce the probe spacing error and relative deflection error.

[0005] Some scholars (Liu) have improved the specific heat capacity test accuracy of the double-needle thermal pulse method to a certain extent by correcting the buried via probe spacing, but they still cannot solve the buried via probe deviation problem from the source.

[0006] Regarding how to reduce the errors of probe deflection and double-needle spacing, there is research on reducing the errors of the thermal probe method by setting reserved holes during the sample preparation process. For example, the Chinese patent application number is 2023113713398, which discloses a device and method for testing the thermal conductivity of granular materials, including a probe body, a cylinder, a lower support, an upper support and a compaction device; the lower support and the upper support are respectively threadedly connected to the cylinder; a reserved hole column is installed at the top center of the lower support; the compaction device consists of a vertical tube, a pressure plate, a plug and a lower compaction hammer; the outer diameter of the pressure plate is smaller than the inner diameter of the cylinder; a connecting hole with a thick top and a thin bottom is opened at the center of the pressure plate; the top of the connecting hole is threadedly connected to the bottom end of the vertical tube; the plug is specifically a T-shaped columnar structure, the outer diameter of the horizontal part of which is larger than the outer diameter of the reserved hole column and smaller than the inner diameter of the top end of the connecting hole; the outer diameter of the vertical part of the plug, the inner diameter of the bottom end of the connecting hole and the outer diameter of the reserved hole column are all the same and not larger than the inner diameter of the vertical tube; the lower compaction hammer is sleeved on the vertical tube; this application can effectively avoid the defects existing in the thermal conductivity test of the sample by drilling. By setting a reserved hole column, etc., a reserved hole for inserting the probe body can be effectively formed in the obtained sample, and the size of the reserved hole is consistent with the size required for inserting the probe body, so that the obtained sample does not need to be drilled later, avoiding the defects of drilling the sample. However, the structure of the reserved hole column is relatively complicated, and it is relatively difficult to remove the reserved hole column.

[0007] For another example, the Chinese patent with application number 2019104779972 discloses a side-inserted probe type three-axis soil sample preparation device and method, including a sample top cap, a sample base, a split mold and a latex film, the top of the latex film is mounted on the outside of the top cap boss, the bottom of the latex film is mounted on the outside of the base boss, the split mold is mounted on the outside of the latex film, the latex film is provided with an earring hole, the split mold is provided with a positioning hole, the positioning hole of the split mold is provided with an earring, the earring is composed of an earring part and a barrel part, the earring part is located on the inner side of the latex film, the barrel part cooperates to pass through the earring hole and the positioning hole in turn, a probe sensor is installed inside the earring, the probe sensor includes a probe and a cable, the probe is placed in the soil sample cavity of the latex film, and the cable is placed outside the earring; the sample top cap is provided with a water outlet channel connected to the soil sample cavity, and the sample base is provided with a water inlet channel. This application can complete the preparation of triaxial soil samples with pre-implanted probe sensors, which are used to measure characteristic parameters such as stress, temperature, moisture, acoustics or stress waves inside the soil sample. However, the method of pre-implanting the probe in this application may cause damage to the probe during the soil sample preparation process. Summary of the invention

[0008] In view of the relatively complicated problem of the soil sample preparation equipment with reserved channels in the prior art, the present invention provides a sample preparation device for testing the specific heat capacity of soil and a method for using the same. The solution provides a relatively simple sample preparation device for testing the specific heat capacity of soil, which can be used to prepare a soil sample with reserved channels for specific heat capacity testing, and the soil sample is integrally formed.

[0009] In order to achieve the above object, the technical solution provided by the present invention is:

[0010] The first aspect of the present invention provides a sample preparation device for testing the specific heat capacity of soil, comprising: an internal pressure mold, the internal pressure mold comprising a cylindrical mold body, the top of the mold body located on both sides of its center line correspondingly provided with two channel protrusions parallel to the center line and symmetrically distributed, and one end of the two channel protrusions extends to the top outer edge of the mold body, the channel protrusions are used to generate channels for placing low-melting point alloy columns when the soil sample is pressed for the first time; low-melting point alloy columns, the low-melting point alloy columns are used to generate channels for inserting probes when the soil sample is pressed for the second time; an outer casing, the inner diameter of the outer casing matches the diameter of the internal pressure mold, the outer casing is mounted on the internal pressure mold, the height of the internal pressure mold is less than the height of the outer casing; and a sample press, the sample press is used to press the soil material inside the outer casing.

[0011] Furthermore, the hole protrusion is semi-cylindrical.

[0012] Furthermore, it also includes a limiter, the inner wall of which is provided with a first connecting groove and a second connecting groove surrounding it along its circumference, wherein the inner diameter of the second connecting groove matches the diameter of the internal pressure mold, and the inner diameter of the first connecting groove matches the outer diameter of the outer casing.

[0013] Furthermore, the sample press includes a compacting block and a limiting portion, the diameter of the compacting block matches the diameter of the internal pressure mold, the limiting portion is arranged on the upper end surface of the compacting block, the diameter of the limiting portion is larger than the diameter of the compacting block, and the height of the compacting block is greater than or equal to the height of the second connecting groove.

[0014] Furthermore, the height of the first sample prepared by using the internal pressure mold is the same as the height of the mold body.

[0015] Furthermore, the internal pressure mold is prepared by 3D printing.

[0016] The first aspect of the present invention provides a method for using the above-mentioned sample preparation device for testing the specific heat capacity of soil, comprising: S1: calculating the amount of soil required, and placing half of the wet soil into an outer casing; placing the inner pressure mold with the pore bulge facing downward into the outer casing, and using a sample press to press the soil in the outer casing to obtain a first sample; S2: taking the first sample and the inner pressure mold out of the outer casing; S3: placing the first sample in the outer casing with the pore surface facing upward, and placing a cylindrical low-melting-point alloy column corresponding to the first sample at the pore of the first sample to serve as a mold for pressing the second sample; S4: placing the remaining wet soil into the upper cavity of the outer casing; using a sample press to press the soil in the outer casing to obtain an integral sample; S5: taking the obtained integral sample out of the outer casing, adding it to the melting point of the alloy column and pouring out the liquid alloy to obtain an integral sample with a pore.

[0017] Furthermore, in S1, before the internal pressure mold is placed on the outer casing, a plastic film is padded at the bottom and inner wall of the outer casing; in S3, before the first sample is placed on the outer casing, a plastic film is padded at the bottom and inner wall of the outer casing; and in S3, after a cylindrical low-melting-point alloy column corresponding to the first sample is placed at the channel of the first sample, the surface of the first sample is scraped.

[0018] Furthermore, in S5, the entire sample is heated in a constant temperature and humidity chamber.

[0019] Furthermore, the melting point of the cylindrical low-melting-point alloy column is 47-70°C.

[0020] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects:

[0021] (1) The present invention optimizes the design of the internal pressure mold used for soil sample preparation, and sets two channel protrusions on the top of the mold body for generating channels for probe insertion when pressing the soil sample. The sample press presses the soil sample downward, and the direction in which the sample press presses the soil is perpendicular to the axial direction of the channel protrusion. On the one hand, a soil sample with a side-inserted reserved channel is prepared; on the other hand, when the first sample is used as a mold for pressing the second sample, the design of the pressing path is more conducive to the preparation of the sample and improves the accuracy of soil sample preparation. In addition, an integrally formed sample can also be prepared.

[0022] (2) The present invention pre-sets low-melting-point alloy columns during the pressing process of the one-piece molded sample, and the low-melting-point alloy columns can be melted by low-temperature heating, and then poured out from the one-piece molded sample. Compared with the traditional method of removing the pre-set object by rotation, this method of removing the pre-set object avoids damaging the inner wall of the channel and further improves the precision of the channel. At the same time, the melting time of the low-melting-point alloy column is shorter, and the fluidity of the liquid alloy in the soil sample is smaller, thereby reducing the diffusion of the liquid alloy in the soil sample and further reducing the adverse effects on the soil sample. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the three-dimensional structure of the internal pressure mold in the sample preparation device for testing the specific heat capacity of soil according to an embodiment of the present invention.

[0024] Figure 2 Schematic diagram of the three-dimensional structure of the limiter in the embodiment of the present invention.

[0025] Figure 3 It is a schematic diagram of the three-dimensional structure of the sample press in an embodiment of the present invention.

[0026] Figure 4 The present invention is an embodiment of the present invention and shows a disassembled structure for preparing a first sample for use in testing the specific heat capacity of soil using a sample preparation device.

[0027] Figure 5 This is a schematic diagram of the disassembled structure of the sample preparation device for testing the specific heat capacity of soil according to an embodiment of the present invention, in use for preparing a second sample.

[0028] Figure 6 This is a perspective structural schematic diagram of a soil sample prepared by a sample preparation device for testing the specific heat capacity of soil according to an embodiment of the present invention.

[0029] Figure 7 It is a schematic diagram of the three-dimensional structure of a soil sample specific heat capacity testing device in an embodiment of the present invention.

[0030] Description of labels:

[0031] 1. Internal pressure mold; 101. Hole protrusion; 102. Mold body;

[0032] 2. Sample press;

[0033] 3. Stopper; 301. First connecting groove; 302. Second connecting groove;

[0034] 4. Outer casing;

[0035] 5. Pad;

[0036] 6. Screw;

[0037] 7. Test bench;

[0038] 8. Pads;

[0039] 9. Probe tail end. DETAILED DESCRIPTION

[0040] In order to further understand the content of the present invention, the present invention is described in detail in conjunction with the accompanying drawings and embodiments.

[0041] The structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the contents disclosed in the specification for people familiar with this technology to understand and read, and are not used to limit the limiting conditions for the implementation of the present invention, so they have no substantial technical significance. Any modification of the structure, change of the proportion relationship or adjustment of the size, without affecting the effects and purposes that can be achieved by the present invention, should still fall within the scope of the technical content disclosed by the present invention. At the same time, the terms such as "upper", "lower", "left", "right", "middle" and so on quoted in this specification are only for the convenience of description, and are not used to limit the scope of implementation. The change or adjustment of their relative relationship should also be regarded as the scope of implementation of the present invention without substantially changing the technical content.

[0042] In the embodiment of the present invention, the “top of the mold body 102 ” refers to “the plane of the mold body 102 or the contact with the soil material during the pressing process of the sample”.

[0043] The present invention provides a sample preparation device for testing the specific heat capacity of soil, referring to Figure 1 As shown, it includes an internal pressure mold 1, which includes a cylindrical mold body 102, and the top of the mold body 102 is located on both sides of its center line, and two channel protrusions 101 are correspondingly provided which are parallel to the center line and symmetrically distributed, and one end of the two channel protrusions 101 extends to the top outer edge of the mold body 102, and the channel protrusions 101 are used to generate a channel for inserting a probe when the soil sample is pressed for the first time; the low-melting point alloy column is cylindrical, and the low-melting point alloy column is used to generate a channel for inserting a probe when the soil sample is pressed for the second time; an outer casing 4, the inner diameter of the outer casing 4 matches the diameter of the internal pressure mold 1, and it is mounted on the outside of the internal pressure mold 1, and the height of the internal pressure mold 1 is less than the height of the outer casing 4; and a sample press 2, the sample press 2 is used to press the soil material inside the outer casing 4.

[0044] In view of the relatively complex equipment used for preparing soil samples with reserved channels in the prior art, the present invention designs the above-mentioned internal pressure mold. The internal pressure mold is provided with two channel protrusions 101 corresponding to the two sides of the center line of the top of the mold body; it can be seen from the structure and position description of the two channel protrusions 101 that the axes of the two channel protrusions 101 are perpendicular to the axis of the internal pressure mold 1, and the reserved channel is set in the middle cross section of the whole sample. Correspondingly, the probe is inserted into the whole sample from the outer curved surface of the whole sample, that is, the insertion direction of the probe is perpendicular to the axis of the whole sample, realizing a side-insertion double-probe soil specific heat capacity detection method.

[0045] In some embodiments, the channel protrusion 101 is semi-cylindrical, and the rectangular side of the channel protrusion 101 coincides with the top of the mold body 102. When pressing the soil sample, the channel protrusion 101 generates a groove for the corresponding semi-cylindrical shape. Specifically, the specific size of the channel protrusion 101 is determined according to the size of the probe, and the center distance between the two channel protrusions matches the distance between the two probes.

[0046] In one specific embodiment, the SH-3 probe of the KD2-Pro thermal characteristic analyzer produced by Meter Company of the United States is used, the diameter of the probe is 1.3mm, and the distance between the two probes is 6mm. The shape of the internal pressure mold 1 used is specifically a cylinder with a diameter of 61.8mm and a height of 20mm, and the shape of the two channel protrusions 101 on the top of the mold body 102 is specifically a semi-cylindrical shape with a length of 30mm and a diameter of 1.3mm, and the distance between the two channel protrusions 101 is 6mm.

[0047] For further reference, Figure 2 As shown, it also includes a stopper 3, the inner wall of the stopper 3 is provided with a first connection groove 301 and a second connection groove 302 surrounding the inner wall, wherein the inner diameter of the second connection groove 302 matches the diameter of the inner pressure mold 1, and the inner diameter of the first connection groove 301 matches the outer diameter of the outer casing 4. When pressing the soil sample, the stopper 3 is sleeved on the outside of the upper end of the outer casing 4, and the inner pressure mold 1 is placed inside the outer casing 4, limiting the relative position of the inner pressure mold 1 and the outer casing 4.

[0048] Further, refer to Figure 3As shown, the sample press 2 includes a compacting block 201 and a limiting portion 202. The diameter of the compacting block 201 matches the diameter of the internal pressure mold 1, so the inner diameter of the second connecting groove 302 matches the diameter of the compacting block 201 in the sample press 2, so that the second connecting groove 302 guides the downward pressing direction of the sample press 2. The limiting portion 202 is arranged on the upper end surface of the compacting block 201, and the diameter of the limiting portion 202 is greater than the diameter of the compacting block 201. The height of the compacting block 201 is greater than or equal to the height of the second connecting groove 302, so that the compacting block 201 can go down to the inside of the outer casing 4 or at least be flush with its upper end surface. It should be understood that because the diameter of the limiting portion 202 is greater than the diameter of the compacting block 201, as the compacting block 201 moves downward, it presses the soil inside the outer casing 4. When the lower end surface of the limiting portion 202 contacts the upper end surface of the limiter 3, the limiter 3 limits the compacting block 201 from continuing to move downward, thereby ensuring consistent pressing height and preventing the pressing force from exceeding the preset load.

[0049] In the above specific embodiment, the height of the compacting block is 20 mm, and the height of the second connecting groove 302 is 20 mm. When the sample press 2 is in compression, the lowest position of the compacting block 201 is flush with the upper end surface of the outer casing 4.

[0050] Preferably, the height of the first sample prepared by the internal pressure mold 1 is the same as the height of the mold body 102. That is, during the pressing process, when the compacting block 201 descends to the lowest position, the distance from the lower end surface of the compacting block 201 to the bottom of the outer casing 4 is equal to twice the height of the mold body 102.

[0051] In the above-mentioned specific embodiment, the height of the outer casing 4 is 40 mm, and the height of the first sample obtained by pressing the outer casing 4 is 20 mm, which is equal to the height of the mold body 102 .

[0052] It should be understood that in the soil sample preparation process, for the side-insertion dual-probe detection, the reserved hole is generally opened in the middle of the soil sample height, and for the traditional split preparation and then assembled soil sample, because the soil material is generally divided into two parts for pressing. By optimizing the height relationship between the internal pressure mold 1 and the first sample obtained by pressing, the heights of the first sample and the second sample obtained are the same, thereby accurately ensuring that the reserved channel is opened in the middle of the soil sample height.

[0053] In order to improve the manufacturing accuracy of the internal pressure mold 1, the internal pressure mold 1 is prepared by 3D printing.

[0054] refer to Figure 4 , Figure 5 , Figure 6 As shown, a method for using a sample preparation device for testing specific heat capacity of soil using any of the above embodiments comprises:

[0055] S1: Calculate the amount of soil required, and place half of the wet soil into the upper cavity of the outer casing 4; then place the inner pressure mold 1 with the protrusion 101 of the channel facing downward into the outer casing 4, and use the static pressure method to press the soil in the outer casing 4 to obtain the first sample;

[0056] S2: taking out the first sample and the internal pressure mold 1 from the outer casing 4;

[0057] S3: The first sample is placed in the outer casing 4 with the hole facing upward, and a cylindrical low-melting-point alloy column adapted to the hole of the first sample is placed at the hole of the first sample to serve as a mold for pressing the second sample;

[0058] S4: placing soil material into the upper cavity of the outer casing 4; the sample pressing device 2 presses the soil material in the outer casing 4 to obtain an integral sample;

[0059] S5: The prepared integral sample is taken out from the outer casing 4, heated to the melting point of the alloy column and the liquid alloy is poured out to obtain an integrally formed integral sample with a pore.

[0060] When preparing the soil samples required for the soil specific heat capacity test, the inventors tried to prepare split soil samples and then piece them together into a whole sample. However, due to the gaps on the pieced surfaces, the accuracy was relatively low when the soil samples were used for the soil specific heat capacity test. They also tried to prepare one-piece soil samples, but during the pressing process, it was relatively difficult to remove the cylindrical objects inserted into the corresponding positions of the reserved channels, and it was extremely easy to destroy the integrity of the channels in the soil samples. In order to ensure the accuracy of the preset channels in the soil samples, the inventors creatively designed the specific structure of the internal pressure mold 1, and innovated the soil sample preparation method based on the internal pressure mold 1, cleverly using the first sample with a low-melting-point alloy column as a mold for pressing the second sample to obtain an one-piece soil sample.

[0061] It should be noted that the design of the specific structure of the internal pressure mold 1 also considers the influence of the pressing direction of the sample press on the accuracy of the soil sample channel during the second pressing of the soil sample. During the second pressing of the soil sample, the contact surface between the first soil sample and its upper soil material is perpendicular to the pressing direction. This pressing method, on the one hand, prepares a soil sample with a side-inserted reserved channel, which can be detected by a side-inserted double probe; on the other hand, and most importantly, if the soil sample is designed as a soil sample with a vertical channel, the low-melting-point alloy column is placed vertically in the outer casing. At this time, the support of the low-melting-point alloy column is poor. The newly added soil material and the process of the compactor pressing down will cause the soil material to squeeze the low-melting-point alloy column laterally, and the low-melting-point alloy column is prone to tilt. The present invention improves the support of the low-melting-point alloy column by setting the channel into which the probe is inserted horizontally, and the stress of the low-melting-point alloy column is improved during the process of the newly added soil material and the compactor pressing down, and the low-melting-point alloy column is not easy to tilt, thereby improving the accuracy of the prepared channel. Furthermore, the low-melting-point alloy column is cleverly used to melt into liquid at a lower temperature, thereby facilitating the removal of the low-melting-point alloy column. Compared with the traditional method of removing the preset object by rotation, this method avoids damage to the inner wall of the channel and improves the integrity of the channel. At the same time, the melting time of the low-melting-point alloy column is shorter, and the fluidity of the liquid alloy in the soil sample is smaller, thereby reducing the diffusion of the liquid alloy in the soil sample and further reducing the adverse effects on the soil sample.

[0062] Before sample preparation, soil samples were pretreated: air-dried soil particles were dried at 105°C for 24 hours, the dry soil was humidified by spraying, and the material was stewed indoors for more than one week to obtain wet soil with a predetermined moisture content for use. The actual moisture content of the wet soil was tested by sampling, and the wet soil required at a fixed dry density was calculated.

[0063] Preferably, in step S1, in order to more accurately measure the moisture content of the soil material, before placing half of the soil material into the outer casing 4, a plastic film is padded at the bottom and inner wall of the internal pressure mold 1. At the same time, the plastic film can also prevent the soil from leaking from under the outer casing 4. In addition, by padding the plastic film in the outer casing 4, full consideration is given to how to more conveniently remove the first sample from the outer casing 4. The plastic film can reduce the friction between the outer casing 4 and the internal pressure mold 1 and the soil material, thereby facilitating the removal of the first sample from the outer casing 4. Specifically, during the sample removal process, if the soil material is cohesive soil, it will stick to the inner wall of the outer casing 4, making it difficult to remove; and the plastic film plays a role in reducing friction, preventing the soil material from sticking to the inner wall of the outer casing 4, thereby facilitating removal. If the soil material is non-cohesive soil, such as sandy soil; the soil body has weak viscosity, and the plastic film can also play a protective role during the sampling process.

[0064] The specific process of taking out the first sample is as follows: first take out the sample press 2, and directly take out the internal pressure mold 1 from the outer casing 4. If the internal pressure mold 1 cannot be directly taken out from the outer casing 4, that is, when the first sample and the top of the internal pressure mold 1 are highly viscous, turn the outer casing 4 upside down, adjust the internal pressure mold 1 to be at the bottom, and place it on a cylinder with a diameter slightly smaller than the inner diameter of the outer casing 4 and a height equal to or greater than the height of the outer casing 4, hold the outer casing 4, and gently press down to push the first sample out of the outer casing 4.

[0065] Further preferably, before the internal pressure mold 1 is placed into the outer casing 4, a plastic film is placed on the surface of the soil material and between the outer casing 4, so as to further prevent the soil material from sticking to the internal pressure mold 1, facilitate the removal of the internal pressure mold 1 from the outer casing 4, and will not affect the formation of the channel.

[0066] And in step S3, before the first sample is placed in the outer casing 4 with the hole facing upward, a plastic film is inserted into the bottom and inner wall of the outer casing 4.

[0067] More preferably, the plastic film in step S1 and step S3 is preferably a whole plastic film.

[0068] In order to further improve the bonding strength between the first sample and the soil material added for the second time, in step S3, after placing a cylindrical low-melting-point alloy column adapted to the first sample at the hole of the first sample, the upper surface of the first sample is shaved. The shaved surface of the first sample becomes uneven. When pressing the second sample, the mechanical bite force between the upper surface of the first sample and the newly added soil material above it is increased, so that the two samples are more completely integrated.

[0069] Furthermore, in step S4, after the pressing is completed, the excess plastic film on the upper edge of the outer casing 4 is removed, thereby obtaining a compacted soil sample with a predetermined moisture content and dry density, and the soil sample except the upper surface is tightly covered by the plastic film and well sealed.

[0070] In step S5, after the prepared integral sample is taken out from the outer casing 4, its outer surface is sealed and then heated.

[0071] Specifically, the above operations are performed on the pad 5 .

[0072] In other embodiments, the outer casing 4 is preferably a permeable ring cutter. Furthermore, when pressing the sample, the edge of the permeable ring cutter faces downward to prevent the film placed in S1 from being cut off. In addition, the other end of the permeable ring cutter can better fit with the first connecting groove 301 in the stopper 3, thereby increasing the contact area between the two.

[0073] Preferably, in step S5, the whole sample is heated in a constant temperature and humidity chamber. Specifically, the temperature of the constant temperature and humidity chamber is adjusted, the whole sample with the plastic film is moved into the constant temperature and humidity chamber (temperature control accuracy ±0.1°C), and the temperature is adjusted to the melting point of the alloy column. After the alloy column made of the low melting point alloy is melted, the sample is taken out of the constant temperature and humidity chamber, the plastic film is removed, and the liquid alloy is poured out, thereby obtaining a sample with parallel symmetrical channels, and then the outer surface of the sample is resealed with the plastic film.

[0074] In the above operation, the whole sample with plastic film is moved into the constant temperature and humidity chamber. When the melting point of the low melting point alloy column is above the melting point, if the whole sample is not covered with plastic film, the water inside evaporates faster. The plastic film can effectively prevent the evaporation of water. Because the specific heat capacity of water is generally about five times that of soil, the moisture content of soil has a greater impact on the measured specific heat capacity.

[0075] In order to further improve the sample accuracy, the overall sample mass of the low-melting-point alloy before and after melting can be measured to determine whether there is any residual melting point metal liquid in the sample and the change in moisture content.

[0076] Regarding the further optimization of the low-melting alloy column, the melting point of the cylindrical low-melting alloy column is 47-70°C. It should be understood that the low-melting alloy column used in the present invention has no specific restrictions on the type of alloy, and general low-melting alloys can be used, such as tin-bismuth alloy, Wood's alloy, and indium-tin-bismuth alloy. Low-melting alloys below 60°C are relatively rare and expensive, and those above 60°C are more common and cheap, but the temperature exceeds 70°C, which is not easy to operate and more dangerous. At the same time, studies have found that the evaporation of water in the soil above 60°C is obvious, and part of the water will evaporate during the melting process of the low-melting alloy, affecting the results. Therefore, in the above specific embodiments, the cylindrical low-melting alloy column is preferably 60°C. Accordingly, the temperature of the constant temperature and humidity chamber is adjusted to 60 degrees, and after the low-melting alloy column is melted and the liquid alloy is poured out of the soil sample, it is poured back into the mold made into a cylinder, solidified to obtain a new alloy column, and reused.

[0077] In this example, in order to make the sample fit tightly with the probe, the sample is placed between two pads 8, and then the whole sample is translated into the test bench 7, the screw 6 is slowly unscrewed so that it fits tightly with the upper end surface of the pad 8, and then the SH-3 probe is smoothly inserted into the sample hole, and then the screw 6 is slowly tightened.

[0078] In order to prevent air convection from affecting the thermal balance of the sample, a plastic box is used to cover the sample and the test bench. The plastic box cover is provided with a through hole for the external wiring of the probe to pass through. The test process is controlled only by connecting the external wiring of the SH-3 probe coated with thermal conductive silicone grease to the KD-2pro thermal physical property analyzer and ensuring that the plastic sealing block 9 at the tail end of the probe is in close contact with the plastic film. The whole is then moved into a constant temperature and humidity chamber (temperature control accuracy of ±0.1°C). Before each thermal conductivity test, the test result is calculated after it is kept at a predetermined temperature point for 24 hours.

[0079] In order to further improve the precision of the test, the whole sample wrapped in the plastic film can also be placed in an annular sleeve, the inner diameter of which matches the outer diameter of the whole sample, and a through hole matching the size of the plastic seal block at the probe tail end 9 is provided at the annular sleeve directly opposite the hole, thereby further strengthening the sealing of the sample and protecting the whole sample. In addition, the through hole of the annular sleeve matches the size of the plastic seal block at the probe tail end 9, so that the probe can be better inserted into the sample and is not easy to fall off the sample.

[0080] The soil sample was prepared by the sample preparation device and method for testing the specific heat capacity of soil, and the method was recorded as the pressure group hole method. After preparing the soil sample and processing the hole for the probe to be inserted, the method was recorded as the limited drilling method. MX80 bentonite was used as the soil material, and the moisture content was 21.8%, and the dry density was 1.2 g·cm -3 , 1.3 g·cm -3 , 1.4 g·cm -3 , 1.5 g·cm -3 The compacted soil samples were tested for specific heat capacity using the double probe pulse method (DPHP), and three groups of parallel samples were set at each dry density. Each group of samples was tested three times with an interval of 15 minutes. The average value of the three measurements of the sample was taken as the specific heat capacity benchmark value. The test results are shown in Table 1.

[0081] Table 1 Specific heat capacity of soil samples obtained by pressure group drilling method and limited drilling method at different dry densities

[0082]

[0083]

[0084] It can be seen from Table 1 that at different dry densities, the fluctuation of the soil specific heat capacity data of the three parallel groups measured by the partial pressure group hole method is small and relatively stable, with the maximum error being only 0.097 MJ·m -3 ·K -1 However, the soil specific heat capacity test results of the three parallel groups measured by the original limited drilling method at the corresponding dry density were relatively unstable, with the maximum error reaching 0.28867 MJ·m -3 ·K -1It can be seen that compared with the original limited drilling method, the soil specific heat capacity value measured by the pressure group drilling method is more stable before and after, which effectively solves the problem of large fluctuations in results when measuring the soil specific heat capacity based on the double-needle thermal pulse method.

[0085] In addition, as a three-phase porous medium, the specific heat capacity of soil is a comprehensive reflection of the specific heat capacity of its internal components. Its theoretical calculation model is the weighted average formula of the specific heat capacity of the solid, liquid and gas phase components of the soil:

[0086] C m =C s m s +C l m l +C g m g (1)

[0087] In the above formula, Cm is the mass specific heat capacity of soil (kJ·kg -3 ·K -1 ); Cs, C l and Cg are the specific heat capacities of the solid, liquid and gas phases in the soil (kJ·kg -3 ·K -1 ), m s 、m l 、m g are the mass percentage (%) of solid, liquid and gas phase in the soil respectively.

[0088] In fact, the influence of the relative heat capacity of the gas in the soil can be ignored, and a more simplified prediction model can be obtained as follows:

[0089]

[0090] In the above formula, C m is the specific heat capacity of soil (kJ·kg -3 ·K -1 ), C d is the specific heat capacity of the solid particles (kJ·kg -3 ·K -1 ), C w is the specific heat capacity of water (kJ·kg -3 ·K -1 ). At room temperature, the specific heat capacity of dry soil is C d =0.75 kJ kg -1 ·K -1 , specific heat of water C w =4.18 kJ kg -1 ·K -1 .

[0091] Taking MX80 bentonite as an example, the moisture content is set to 11.1%, 15.8%, 21.8%, 25.8% and 29%, and the dry density is 1.2 g cm -3 , the theoretical value of the specific heat capacity of bentonite is calculated based on formula (1). The specific heat capacity of MX80 bentonite was tested using DPHP and DSC respectively and compared with the theoretical value. The test results are shown in Table 2.

[0092] Table 2 Specific heat capacities obtained by using the double-needle heat pulse method, other methods and theoretical calculation of soil samples prepared by the present invention

[0093]

[0094]

[0095] As can be seen from Table 2, the soil specific heat capacity measured by the two methods is very consistent with the theoretical value, and is basically within the range of ±5% of the theoretical value with a small fluctuation. The DSC method is a standard method for testing the specific heat capacity of soil. The specific heat capacity of the soil sample was tested using the DPHP method, and the results were close to those measured by the DSC method, indicating that the soil specific heat capacity results measured by the DPHP method using the soil sample prepared by the partial pressure group pore method are accurate and reliable, and can be used for soil specific heat capacity testing in geotechnical tests.

[0096] The above experimental results show that the soil sample prepared by the present invention has good practicality and reliability in testing the specific heat capacity of soil. By preparing an integrally formed integral sample with high-precision pores, the accuracy of the double-needle heat pulse method in measuring the specific heat capacity of soil is improved, thereby broadening the application scope of the double-needle heat pulse method.

[0097] The present invention and its embodiments are described schematically above, and the description is not restrictive. The drawings show only one embodiment of the present invention, and the actual structure is not limited thereto. Therefore, if a person skilled in the art is inspired by it and designs a structural method and an embodiment similar to the technical solution without creativity without departing from the purpose of the invention, they shall all fall within the protection scope of the present invention.

Claims

1. A sample preparation device for testing the specific heat capacity of soil, characterized in that: include: An internal pressure mold (1), the internal pressure mold (1) comprising a cylindrical mold body (102), the top of the mold body (102) being located on both sides of its center line and correspondingly provided with two channel protrusions (101) parallel to the center line and symmetrically distributed, and one end of the two channel protrusions (101) both extending to the top outer edge of the mold body (102), the channel protrusions (101) being used to generate a channel for inserting a probe when the soil sample is pressed for the first time; A low melting point alloy column, wherein the low melting point alloy column is used to generate a channel for inserting a probe when the soil sample is pressed for the second time; An outer casing (4), the inner diameter of which matches the diameter of the internal pressure mold (1), and which is sleeved on the outside of the internal pressure mold (1), wherein the height of the internal pressure mold (1) is smaller than the height of the outer casing (4); as well as A sample press (2) is used to press the soil material inside the outer casing (3).

2. The sample preparation device for testing the specific heat capacity of soil according to claim 1, characterized in that: The channel protrusion (101) is semi-cylindrical.

3. The sample preparation device for testing the specific heat capacity of soil according to claim 1, characterized in that: It also comprises a stopper (3), wherein the inner wall of the stopper (3) is provided with a first connecting groove (301) and a second connecting groove (302) surrounding the inner wall along the circumference thereof, wherein the inner diameter of the second connecting groove (302) matches the diameter of the internal pressure mold (1), and the inner diameter of the first connecting groove (301) matches the outer diameter of the outer casing (3).

4. The sample preparation device for testing the specific heat capacity of soil according to claim 3, characterized in that: The sample press (2) comprises a compacting block (201) and a limiting portion (202); the diameter of the compacting block (201) matches the diameter of the internal pressure mold (1); the limiting portion (202) is arranged on the upper end surface of the compacting block (201); the diameter of the limiting portion (202) is greater than the diameter of the compacting block (201); and the height of the compacting block (201) is greater than or equal to the height of the second connecting groove (302).

5. The sample preparation device for testing the specific heat capacity of soil according to claim 4, characterized in that: The height of the first sample prepared using the internal pressure mold (1) is the same as the height of the mold body (102).

6. The sample preparation device for testing the specific heat capacity of soil according to any one of claims 1 to 5, characterized in that: The internal pressure mold (1) is prepared by 3D printing.

7. A method for using the sample preparation device for testing the specific heat capacity of soil as claimed in any one of claims 1 to 6, characterized in that: include: S1: Calculate the required amount of soil material and place half of the soil material into the outer casing (4); Then, the inner pressure mold (1) is placed in the outer casing (4) with the hole protrusion (101) facing downward, and the sample pressing device (2) presses the soil material in the outer casing (4) to obtain the first sample; S2: taking out the first sample and the internal pressure mold (1) from the outer casing (4); S3: placing the first sample in the outer casing (4) with the hole facing upward, and placing a cylindrical low-melting-point alloy column adapted to the hole of the first sample to serve as a mold for pressing the second sample; S4: placing the remaining wet soil material into the upper cavity of the outer casing (4); the sample pressing device (2) presses the soil material in the outer casing (4) to obtain an integral sample; S5: taking the obtained integral sample out of the outer casing (4), heating it to the melting point of the alloy column and pouring out the liquid alloy to obtain an integrally formed integral sample with a pore.

8. The method for using the sample preparation device for testing the specific heat capacity of soil according to claim 7, characterized in that: In S1, before placing half of the soil material into the outer casing (4), a plastic film is placed on the bottom and inner wall of the outer casing (4); In S3, before the first sample is placed on the outer casing (4), a plastic film is placed on the bottom and inner wall of the inner and outer casings (4); And in said S3, after placing a cylindrical low-melting-point alloy column adapted to the hole of the first sample, the surface of the first sample is scraped.

9. The method for using the sample preparation device for testing the specific heat capacity of soil according to claim 7, characterized in that: In the above-mentioned S5, the entire sample is heated in a constant temperature and humidity chamber.

10. The method for using the sample preparation device for testing the specific heat capacity of soil according to claim 7, characterized in that: The melting point of the cylindrical low-melting-point alloy column is 47-70°C.

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