A sample preparation device for testing the specific heat capacity of a soil body and a method of using the same
By designing a combination of internal pressure mold and outer casing, and using a low-melting-point alloy column to generate channels and melt and extract the sample, the problem of probe deflection and spacing error in soil specific heat capacity testing was solved, achieving high-precision soil sample preparation and testing.
Patent Information
- Application Number
- CN202510052487.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2025-01-14
- Publication Date
- 2025-11-28
- Estimated Expiration
- 2045-01-14
AI Technical Summary
In existing technologies, soil specific heat capacity testing suffers from problems such as probe skew and large errors in the distance between the two needles, resulting in low testing accuracy. In particular, it is difficult to accurately determine the soil specific heat capacity in the two-needle thermal pulse method.
Design a sample preparation device for testing the specific heat capacity of soil. The device uses an internal pressure mold with a hole protrusion on the top of the mold body. Combined with a low melting point alloy column, a hole for probe insertion is generated during the pressing process. The alloy column is removed by melting it at low temperature to avoid damaging the hole.
It achieves high-precision soil specific heat capacity testing, reduces probe deviation and spacing errors, improves the reliability and accuracy of soil sample preparation, broadens the application range of the dual-needle thermal pulse method, simplifies the stability of the preparation process, reduces detection accuracy, improves soil sample preparation accuracy, reduces the diffusion of liquid alloy in soil sample, and ensures the integrity of the pores.
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Figure CN119804081B_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of soil thermal property detection equipment, more particularly, to a sample preparation device for testing soil specific heat capacity and a use method thereof. BACKGROUND
[0002] Specific heat capacity is one of the important thermal physical properties of soil, and its physical meaning is the heat absorbed or released by changing the temperature of unit mass of soil, which represents the heat storage capacity of soil. In engineering involving soil heat transfer and temperature field analysis, such as freezing construction, shallow geothermal energy extraction, nuclear waste disposal library heat dissipation design, specific heat capacity is an essential and important parameter.
[0003] In soil testing, the mixed calorimetry method is generally used for testing the specific heat capacity of soil. The soil is uniformly mixed with a solution (usually water) at different temperatures to reach thermal equilibrium. 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 by the heat conservation formula. In fact, the mixed calorimetry method tests the average specific heat capacity of the soil, which is more suitable for materials with constant specific heat capacity 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 applied 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 double-needle spacing fluctuation have little effect on the thermal conductivity of soil, but have a significant impact on the test accuracy of specific heat capacity. However, in recent years, some studies have explored how to use the double-needle heat pulse method to test the specific heat capacity of soil to expand the application range of the double-needle heat pulse method. For example, LIU G, LI B G, REN T S, et al. Analytical Solution of the Heat Pulse Method in a Parallelepiped Sample Space[J] . Soil Science Society of America Journal, 2008. 72(5):1208-1216, pointed out that theoretically, a 2% change in probe spacing would cause a 4% relative error in specific heat capacity, and a 1° deflection of the probe would even cause a 10% error in specific heat capacity; therefore, it is important to reduce the error in probe spacing and relative deflection when using the heat probe method to determine the specific heat capacity of soil.
[0005] Some scholars (Liu) have improved the specific heat capacity test accuracy of the double-needle heat pulse method by correcting the spacing of the embedded probe, but they still cannot solve the problem of probe deflection from the source.
[0006] As for how to reduce the error of probe deflection and double-needle spacing, there are studies on reducing the error of thermal probe method by setting a reserved hole during sample preparation. For example, a Chinese patent with application number 2023113713398 discloses a device and method for testing the thermal conductivity of granular materials, which includes a probe body, a cylinder, a lower support platform, an upper support platform, and a compaction device. The lower support platform and the upper support platform are threadedly connected with the cylinder. A reserved hole column is installed at the top center of the lower support platform. The compaction device consists of a vertical pipe, 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 large top and a small bottom is formed at the center of the pressure plate. The top end of the connecting hole is threadedly connected with the bottom end of the vertical pipe. The plug is a T-shaped column structure, the outer diameter of the horizontal part 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 the same and not larger than the inner diameter of the vertical pipe. The lower compaction hammer is sleeved on the vertical pipe. The application can effectively avoid the defects existing when the thermal conductivity of the sample is tested by drilling. By setting a reserved hole column, 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 for testing in the later stage, avoiding the defects existing when the sample is drilled for testing. However, the structure of the reserved hole column is relatively complex, and it is relatively difficult to remove the reserved hole column.
[0007] For another example, a Chinese patent with application number 2019104779972 discloses a side-inserted probe type triaxial soil sample preparation device and method, which includes a sample top cap, a sample base, a split mold, and a latex film. The latex film is sleeved on the outside of the top cap boss at the top, and sleeved on the outside of the base boss at the bottom. The split mold is installed on the outside of the latex film. The latex film has an ear hole, and the split mold has a positioning hole. An ear ring is installed in the positioning hole of the split mold, which is composed of an ear ring part and a barrel part. The ear ring part is inside the latex film, and the barrel part passes through the ear hole and the positioning hole in turn. A probe sensor is installed inside the ear ring, which 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 ear ring. The sample top cap has a water outlet channel connected with the soil sample cavity, and the sample base has a water inlet channel. The application can prepare a triaxial soil sample with a pre-implanted probe sensor, which is used to measure the characteristic parameters such as stress, temperature, moisture, acoustics, or stress wave inside the soil sample. However, the pre-implanted probe in the application may be damaged during the preparation of the soil sample. SUMMARY
[0008] In view of the problem that the soil sample preparation equipment with a reserved hole in the prior art is relatively complex, the application provides a soil sample preparation device for testing specific heat capacity of soil and a use method thereof.The scheme provides a relatively simple soil sample preparation device for testing specific heat capacity of soil, and the device can be used to prepare a soil sample with a reserved hole for testing specific heat capacity, and the soil sample is integrally formed.
[0009] To achieve the above object, the technical scheme provided by the application is as follows:
[0010] The first aspect of the application provides a soil sample preparation device for testing specific heat capacity of soil, which comprises: an inner pressure mold, the inner pressure mold comprising a cylindrical mold body, two hole protrusions corresponding to the center line of the top of the mold body and symmetrically distributed parallel to the center line, and one end of each of the two hole protrusions extending to the outer edge of the top of the mold body, the hole protrusions being used to generate a hole for placing a low-melting-point alloy column when the soil sample is pressed for the first time; a low-melting-point alloy column, the low-melting-point alloy column being used to generate a hole for inserting a probe when the soil sample is pressed for the second time; an outer sleeve, the inner diameter of the outer sleeve matching the diameter of the inner pressure mold, the outer sleeve being sleeved on the inner pressure mold, and the height of the inner pressure mold being less than the height of the outer sleeve; and a sample press, the sample press being used to press the soil material inside the outer sleeve.
[0011] Further, the hole protrusion is semicylindrical.
[0012] Further, the device further comprises a position limiter, the inner wall of the position limiter being provided with a first connecting groove and a second connecting groove which are circumferentially arranged around the position limiter, the inner diameter of the second connecting groove matching the diameter of the inner pressure mold, and the inner diameter of the first connecting groove matching the outer diameter of the outer sleeve.
[0013] Further, the sample press comprises a compaction block and a limiting part, the diameter of the compaction block matching the diameter of the inner pressure mold, the limiting part being arranged on the upper end surface of the compaction block, the diameter of the limiting part being greater than the diameter of the compaction block, and the height of the compaction block being greater than or equal to the height of the second connecting groove.
[0014] Further, the height of the first sample prepared by using the inner pressure mold is the same as the height of the mold body.
[0015] Further, the inner pressure mold is prepared by 3D printing.
[0016] The second aspect of the present application provides a method for using the sample preparation device for testing the specific heat capacity of soil, comprising: S1: calculating the required amount of soil, and placing half of the wet soil into the outer sleeve; placing the inner pressure mold hole protrusion downward in the outer sleeve, and pressing the soil in the outer sleeve with the sample press to obtain a first sample; S2: removing the first sample and the inner pressure mold from the outer sleeve; S3: placing the first sample in the outer sleeve with the hole facing upward, and placing a cylindrical low-melting alloy column in the hole of the first sample as a mold for pressing the second sample; S4: placing the remaining wet soil into the upper cavity of the outer sleeve; pressing the soil in the outer sleeve with the sample press to obtain a whole sample; and S5: removing the whole sample from the outer sleeve, adding the melting point of the alloy column, and pouring out the liquid alloy to obtain an integrally formed whole sample with a hole.
[0017] Further, in S1, plastic film is padded on the bottom and inner wall of the outer sleeve before the inner pressure mold is placed in the outer sleeve; in S3, plastic film is padded on the bottom and inner wall of the outer sleeve before the first sample is placed in the outer sleeve; and in S3, the upper surface of the first sample is shaved after the cylindrical low-melting alloy column is placed in the hole of the first sample.
[0018] Further, in S5, the whole sample is heated in a constant temperature and humidity box.
[0019] Further, the melting point of the cylindrical low-melting alloy column is 47-70℃.
[0020] Compared with the prior art, the technical scheme provided by the present application has the following beneficial effects:
[0021] (1) The present application optimizes the design of the inner pressure mold used for preparing the soil sample, and sets two hole protrusions on the top of the mold body for generating a hole for inserting a probe when pressing the soil sample. The sample press presses the soil sample downward, and the direction of the sample press pressing the soil sample is perpendicular to the axis direction of the hole protrusion. On the one hand, a soil sample with a side-insertion reserved hole 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 the accuracy of the soil sample preparation is improved. In addition, an integrally formed sample can also be prepared.
[0022] (2) The application pre-sets a low-melting alloy column in the pressing process of the integrally formed sample, and the low-melting alloy column can be melted by low-temperature heating, and then poured out from the integrally formed sample. Compared with the traditional method of taking out the pre-set object by rotating, the method avoids damaging the inner wall of the hole, and further improves the precision of the hole. At the same time, the melting time of the low-melting alloy column is short, and the fluidity of the liquid alloy in the soil sample is small, 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 DRAWINGS
[0023] Figure 1 It is a three-dimensional structure schematic diagram of the inner pressure mold in the sample preparation device for testing the specific heat capacity of soil body.
[0024] Figure 2 It is a three-dimensional structure schematic diagram of the position limiter.
[0025] Figure 3 It is a three-dimensional structure schematic diagram of the sample press.
[0026] Figure 4 It is a split structure schematic diagram of the sample preparation device for testing the specific heat capacity of soil body in the first sample preparation state.
[0027] Figure 5 It is a split structure schematic diagram of the sample preparation device for testing the specific heat capacity of soil body in the second sample preparation state.
[0028] Figure 6 It is a perspective structure schematic diagram of the soil sample prepared by the sample preparation device for testing the specific heat capacity of soil body.
[0029] Figure 7 It is a three-dimensional structure schematic diagram of the soil sample specific heat capacity testing device.
[0030] REFERENCE NUMERALS:
[0031] 1, inner pressure mold; 101, hole protrusion; 102, mold main body;
[0032] 2, sample press;
[0033] 3, position limiter; 301, first connecting groove; 302, second connecting groove;
[0034] 4, outer protection cylinder;
[0035] 5, pad plate;
[0036] 6, screw rod;
[0037] 7, test bench;
[0038] 8. Pad block;
[0039] 9. Probe tail end. DETAILED DESCRIPTION
[0040] For further understanding of this application, reference will be made to the following detailed description and examples with accompanying drawings.
[0041] The structure, proportion, size and the like shown in the drawings of the specification are only used to cooperate with the content disclosed in the specification, to be understood and read by those skilled in the art, and are not used to limit the defined conditions that can be implemented by the application, so they do not have technical significance. Any modification of the structure, change of the proportional relationship or adjustment of the size, without affecting the effect and purpose that can be achieved by the application, should still fall within the scope of the disclosed technical content. At the same time, the terms such as "upper", "lower", "left", "right", "middle" and the like used in the specification are only for the convenience of clear description, and are not used to limit the scope of implementation. The change or adjustment of the relative relationship, without substantially changing the technical content, is also considered as the implementation scope of the application.
[0042] In the embodiment of the application, the "top of the mold body 102" refers to the "plane of the mold 102 body or in contact with the soil material during the pressing of the sample".
[0043] The application provides a sample preparation device for testing the specific heat capacity of soil, as shown in Figure 1 The application provides a sample preparation device for testing the specific heat capacity of soil, as shown in
[0044] To address the issue of the relatively complex equipment used in existing technologies for preparing soil samples with pre-reserved channels, this invention designs the aforementioned internal pressure mold. This internal pressure mold has two channel protrusions 101 on either side of its centerline at the top of the mold body. As described by the structure and position of the two channel protrusions 101, their axes are perpendicular to the axis of the internal pressure mold 1. The pre-reserved channels are positioned in the middle cross-section of the overall sample. Correspondingly, a probe is inserted into the overall sample from its outer curved surface, meaning the insertion direction of the probe is perpendicular to the axis of the overall sample, thus realizing a side-insertion dual-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. During soil sample compaction, the channel protrusion 101 creates grooves for the corresponding semi-cylindrical shapes. Specifically, the dimensions of the channel protrusion 101 are determined according to the probe size, and the center-to-center distance between two channel protrusions matches the distance between the two probes.
[0046] In one specific embodiment, an SH-3 probe is used with a KD2-Pro thermal property analyzer manufactured by Meter Corporation, USA. The probe has a diameter of 1.3 mm and the distance between the two probes is 6 mm. The internal pressure mold 1 is specifically a cylinder with a diameter of 61.8 mm and a height of 20 mm. The two channel protrusions 101 on the top of the mold body 102 are specifically semi-cylindrical with a length of 30 mm and a diameter of 1.3 mm, and the distance between the two channel protrusions 101 is 6 mm.
[0047] Further reference Figure 2 As shown, it also includes a limiter 3. The inner wall of the limiter 3 is provided with a first connecting groove 301 and a second connecting groove 302 that surround it circumferentially. The inner diameter of the second connecting groove 302 matches the diameter of the inner pressure mold 1, and the inner diameter of the first connecting groove 301 matches the outer diameter of the outer casing 4. When pressing the soil sample, the limiter 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] Furthermore, refer to Figure 3As shown, the compactor 2 comprises a compaction block 201 and a limiting part 202. The diameter of the compaction block 201 matches the diameter of the inner compression mold 1, and thus the inner diameter of the second connecting groove 302 matches the diameter of the compaction block 201 in the compactor 2, so that the second connecting groove 302 guides the downward direction of the compactor 2. The limiting part 202 is arranged at the upper end surface of the compaction block 201, and the diameter of the limiting part 202 is greater than the diameter of the compaction block 201. The height of the compaction block 201 is greater than or equal to the height of the second connecting groove 302, so that the compaction block 201 can descend to the inside of the outer casing 4 or at least be flush with the upper end surface thereof. It should be understood that, because the diameter of the limiting part 202 is greater than the diameter of the compaction block 201, as the compaction block 201 descends to compact the soil in the inside of the outer casing 4, when the lower end surface of the limiting part 202 contacts the upper end surface of the limiter 3, the limiter 3 limits the compaction block 201 from continuing to descend, so as to ensure consistent compaction height and prevent the compaction force from exceeding the preset load.
[0049] In one specific embodiment described above, the height of the compaction block is 20 mm, and the height of the second connecting groove 302 is 20 mm. When the compactor 2 is in use, the lowest position of the compaction block 201 descending is flush with the upper end surface of the outer casing 4.
[0050] Preferably, the height of the first sample prepared by using the inner compression mold 1 is the same as the height of the mold body 102. That is, when the compaction block 201 descends to the lowest position in the compaction process, the distance from the lower end surface of the compaction block 201 to the bottom of the outer casing 4 is equal to twice the height of the mold body 102.
[0051] In one specific embodiment described above, the height of the outer casing 4 is 40 mm, and the height of the first sample prepared by using 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 process of preparing the soil sample, for the side-inserted double-probe detection, the reserved hole is generally arranged at the middle of the height of the soil sample, and for the traditional split-type sample preparation and then spliced sample, the soil is generally divided into two parts for compaction. Through the optimized design of the relationship between the height of the inner compression mold 1 and the first sample prepared by using the same, the height of the first sample and the second sample prepared by using the same is the same, so as to accurately ensure that the reserved hole is arranged at the middle of the height of the soil sample.
[0053] In order to improve the accuracy of the inner compression mold 1, the inner compression mold 1 is prepared by 3D printing.
[0054] Reference Figure 4 , Figure 5 , Figure 6 As shown, the use method of the sample preparation device for testing the specific heat capacity of the soil body according to any one of the above embodiments comprises:
[0055] S1: Calculate the amount of soil required, and place half of the wet soil into the outer sleeve 4; then place the channel protrusion 101 of the inner pressure mold 1 into the outer sleeve 4 with the channel protrusion 101 facing downward, and use the static pressure method of the compactor 2 to compact the soil in the outer sleeve 4 to obtain the first sample;
[0056] S2: Remove the first sample and the inner pressure mold 1 from the outer sleeve 4;
[0057] S3: Place the first sample into the outer sleeve 4 with the channel facing upward, and place a cylindrical low-melting alloy column that is compatible with the channel of the first sample into the channel of the first sample as a mold for compacting the second sample;
[0058] S4: Place the soil into the upper cavity of the outer sleeve 4, and use the compactor 2 to compact the soil in the outer sleeve 4 to obtain the overall sample;
[0059] S5: Remove the overall sample from the outer sleeve 4, heat the overall sample to the melting point of the alloy column, and pour out the liquid alloy to obtain the integrally formed overall sample with the channel.
[0060] The inventor has tried to prepare a split soil sample and then splice the sample into an overall sample when preparing a soil sample required for testing the specific heat capacity of the soil, but the precision of the soil sample is relatively low when the soil sample is used to test the specific heat capacity of the soil because of the gap between the spliced surfaces. The inventor has also tried to prepare an integrally formed soil sample, but it is relatively difficult to remove the cylindrical object inserted into the corresponding position of the reserved channel during the compaction process, and the integrity of the channel in the soil sample is extremely easy to be damaged. In order to ensure the precision of the pre-embedded channel in the soil sample, the inventor has creatively designed the specific structure of the inner pressure mold 1, and has innovated the preparation method of the soil sample based on the inner pressure mold 1, and has ingeniously used the first sample with the low-melting alloy column placed therein as a mold for compacting the second sample to obtain the integrally formed soil sample.
[0061] It needs to be particularly pointed out that, in the design of the specific structure of the internal pressure mold 1, 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 is also considered. During the second pressing of the soil sample, the contact surface of the first soil sample and the upper layer of 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 used for side-inserted double-probe detection; on the other hand, and most importantly, if the soil sample is designed to have a vertical channel, the low-melting-point alloy column is vertically placed in the outer sleeve, at which time the support condition of the low-melting-point alloy column is poor, and during the process of adding new soil and pressing the compactor, the soil will laterally extrude the low-melting-point alloy column, and the low-melting-point alloy column is prone to tilting. However, by horizontally arranging the channel into which the probe is inserted, the support condition of the low-melting-point alloy column is improved, and during the process of adding new soil and pressing the compactor, the stress condition of the low-melting-point alloy column is improved, and the low-melting-point alloy column is not prone to tilting, thereby improving the accuracy of the prepared channel. Furthermore, the low-melting-point alloy column is cleverly used to melt into a liquid state at a relatively low temperature, thereby facilitating the removal of the low-melting-point alloy column. Compared with the traditional method of removing the pre-placed object by rotating, this method avoids damaging the inner wall of the channel and improves the integrity of the channel. At the same time, the low-melting-point alloy column requires a relatively short melting time, and the fluidity of the liquid alloy in the soil sample is relatively small, 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, pretreatment of the soil sample: dry soil particles are dried at 105°C for 24 hours, the dry soil is humidified by spraying, and the wet soil material with a predetermined water content is obtained by indoor stewing for more than one week. The actual water content of the wet soil material is tested, and the required wet soil material under the fixed dry density is calculated.
[0063] Preferably, in step S1, in order to more accurately control the water content of the soil material, a plastic film is laid in the bottom and inner wall of the internal pressure mold 1 before half of the soil material is placed into the outer sleeve 4. At the same time, the plastic film can also prevent soil from leaking from the bottom of the outer sleeve 4. In addition, by laying a plastic film in the outer sleeve 4, it is also considered how to more conveniently remove the first test sample from the outer sleeve 4. The plastic film can reduce the friction between the outer sleeve 4 and the internal pressure mold 1 and the soil material, thereby facilitating the removal of the first test sample from the outer sleeve 4. Specifically, during the removal of the test sample, if the soil material is cohesive soil, it will stick to the inner wall of the outer sleeve 4 and be difficult to remove; however, the plastic film plays a role in reducing friction and prevents the soil material from sticking to the inner wall of the outer sleeve 4, thereby facilitating removal. If the soil material is non-cohesive soil, such as sand, the soil body has weak cohesiveness, and the plastic film can also play a protective role during the sampling process.
[0064] The process of taking out the first sample is as follows: first, take out the sample press 2, and directly take out the inner compression mold 1 from the outer sleeve 4. If the inner compression mold 1 cannot be directly taken out from the outer sleeve 4, that is, the first sample and the top of the inner compression mold 1 have a larger viscosity, the outer sleeve 4 is inverted, the inner compression mold 1 is adjusted to be below, placed on a cylinder with a diameter slightly smaller than the inner diameter of the outer sleeve 4 and a height equal to or greater than the height of the outer sleeve 4, and the outer sleeve 4 is held by hand and gently pressed to push the first sample out of the outer sleeve 4.
[0065] Further preferably, before the inner compression mold 1 is placed in the outer sleeve 4, a plastic film is placed between the surface of the soil and the outer sleeve 4, which can further prevent the soil from sticking to the inner compression mold 1, facilitate the removal of the inner compression mold 1 from the outer sleeve 4, and will not affect the formation of the hole.
[0066] And in step S3, before the surface of the hole of the first sample is placed upward in the outer sleeve 4, a plastic film is placed on the bottom and inner wall of the outer sleeve 4.
[0067] Further preferably, in step S1 and step S3, the plastic film is preferably an entire plastic film.
[0068] In order to further improve the bonding force of the first sample and the secondly added soil, in step S3, after the cylindrical low-melting-point alloy column is placed at the hole of the first sample, the upper surface of the first sample is subjected to a scraping treatment. Through the scraping treatment, the upper surface of the first sample becomes uneven. When the second sample is pressed, the mechanical interlocking force between the upper surface of the first sample and the newly added soil above is improved, so that the two samples are more integrated.
[0069] Further, in step S4, after the pressing is completed, the plastic film on the upper edge of the outer sleeve 4 is removed, and thus a compacted soil sample with a predetermined water content and dry density is obtained, and the soil sample is tightly covered by the plastic film except for the upper surface, and is well sealed.
[0070] In step S5, after the entire sample is taken out of the outer sleeve 4, the outer surface thereof is sealed, and then heated.
[0071] Specifically, the above operation is performed on the cushion plate 5.
[0072] In other embodiments, the outer sleeve 4 is preferably a penetration ring knife. Further, during the sample pressing, the edge of the penetration ring knife is downward, preventing the film placed in S1 from being cut off. In addition, the other end of the penetration ring knife can better fit the first connecting groove 301 in the stopper 3, improving the contact area between the two.
[0073] Preferably, in step S5, the overall sample is heated in a constant temperature and humidity chamber. Specifically, the temperature of the constant temperature and humidity chamber is adjusted, the overall sample with the plastic film is moved into the constant temperature and humidity chamber (temperature control accuracy ±0.1℃), and the temperature is adjusted to the melting point of the alloy column. After the alloy column made of low-melting-point alloy melts, the sample is taken out of the constant temperature and humidity chamber, the plastic film is removed, and the liquid alloy is poured out, so as to obtain a sample with parallel and symmetrical holes. Then the outer surface of the sample is resealed with the plastic film.
[0074] In the above operation process, the overall sample with the plastic film is moved into the constant temperature and humidity chamber. If the outside of the overall sample is not covered with the plastic film when the temperature is above the melting point of the low-melting-point alloy column, the evaporation of moisture inside the overall sample will be accelerated, and the plastic film can effectively prevent the evaporation of moisture. Because the specific heat capacity of water is generally about five times that of soil, the water content of soil has a great influence on the measured specific heat capacity.
[0075] In order to further improve the accuracy of the sample, the mass of the overall sample before and after the low-melting-point alloy melts can be measured to determine whether there is residual low-melting-point alloy liquid in the sample and whether the water content changes.
[0076] Regarding the further optimization of the low-melting-point alloy column, the melting point of the cylindrical low-melting-point alloy column is 47-70℃. It should be understood that the type of low-melting-point alloy column used in the present application is not specifically limited, and generally low-melting-point alloys can be used, such as tin-bismuth alloy, Wood's metal, and indium-tin-bismuth alloy. Low-melting-point alloys below 60℃ are relatively rare and expensive, while those above 60℃ are relatively common and inexpensive, but temperatures above 70℃ are difficult to operate and are relatively dangerous. At the same time, it has been found that the evaporation of water in soil is obvious above 60℃, and part of the water will evaporate during the melting process of the low-melting-point alloy, which will affect the results. Therefore, in the above specific embodiment, the cylindrical low-melting-point alloy column is preferably 60℃. Correspondingly, the temperature of the constant temperature and humidity chamber is adjusted to 60 degrees, and after the low-melting-point alloy column melts and the liquid alloy is poured out of the soil sample, it is re-poured into a mold for forming a cylinder, and a new alloy column is obtained by solidification for repeated use.
[0077] In the present example, in order to tightly fit the sample with the probe, the sample is placed between two pads 8, and then the whole is moved into the test bench 7. The screw rod 6 is slowly rotated to tightly fit the upper end surface of the pad 8, and then the SH-3 probe is smoothly inserted into the sample hole, and the screw rod 6 is slowly tightened.
[0078] To prevent the air convection from affecting the thermal equilibrium of the sample, a plastic box is used to cover the sample and the test bench, and the plastic box is provided with a through hole for the probe external wire to pass through; only the SH-3 probe external wire coated with thermal conductive silicone grease is connected to the KD-2pro thermal physical property analyzer to control the test process and ensure that the probe tail end 9 plastic sealing block is tightly attached to the plastic film, and then the whole is moved into the constant temperature and humidity box (temperature control accuracy ±0.1℃), and the test result is counted after the predetermined temperature point is kept constant for 24h before each thermal conductivity test.
[0079] In order to further improve the precision of the test, the whole sample wrapped with the plastic film can also be placed in an annular sleeve, the inner diameter of the annular sleeve matches the outer diameter of the whole sample, and the through hole of the annular sleeve matches the size of the probe tail end 9 plastic sealing block, thereby further enhancing the sealing of the sample and protecting the whole sample. In addition, the through hole of the annular sleeve matches the size of the probe tail end 9 plastic sealing block, which can make the probe better inserted into the sample and not easily fall off from the sample.
[0080] The above-mentioned sample preparation device for testing the specific heat capacity of soil and the use method are used to prepare the soil sample, and the use method is recorded as the split group hole method. After the soil sample is prepared and the hole for inserting the probe is processed, the use method is recorded as the limiting drilling method. MX80 bentonite is used as the soil material to prepare the compacted soil sample with a moisture content of 21.8%, and dry densities of 1.2 g cm -3 , 1.3 g cm -3 , 1.4 g cm -3 , 1.5 g cm -3 , respectively. The specific heat capacity test is carried out by using the double probe pulse method (DPHP), and three parallel groups are set under each dry density. Each group of samples is tested three times with an interval of 15 minutes, and the average value of three measurements of the sample is taken as the specific heat capacity reference value. The test results are shown in Table 1.
[0081] Table 1 Specific heat capacity of soil samples obtained by split group hole method and limiting drilling method under different dry densities
[0082]
[0083] As shown in Table 1, under different dry densities, the specific heat capacity data of the three parallel groups measured based on the split group hole method has smaller fluctuation and is more stable, and the maximum error is only 0.097 MJ m -3 K -1The results of the specific heat capacity of soil measured by the original limited drilling method are relatively unstable, and the maximum error can reach 0.28867 MJ m -3 K -1 It can be seen that, compared with the original limited drilling method, the specific heat capacity of soil measured by the split pressure group hole method is more stable, and effectively solves the problem of large fluctuation of results in the determination of the specific heat capacity of soil based on the double-needle heat pulse method.
[0084] In addition, as a three-phase porous medium, the specific heat capacity of soil is a comprehensive representation of the specific heat capacities of its internal components, and its theoretical calculation model is the weighted average formula of the specific heat capacities of the solid, liquid, and gas components of the soil:
[0085] (1)
[0086] 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 ), respectively, and m s , m l , and m g are the mass percentages of the solid, liquid, and gas phases in the soil (%).
[0087] In fact, the influence of the specific heat capacity of the gas phase in the soil can be ignored, and a more simplified prediction model is obtained as follows:
[0088] (2)
[0089] 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 solid particles (kJ kg -3 K -1 ), and C w is the specific heat capacity of water (kJ kg -3 K -1 ). At room temperature, the specific heat capacity of dry soil C d = 0.75 kJ kg-1 K -1 , water specific heat capacity C w =4.18 kJ kg -1 K -1 .
[0090] Taking MX80 bentonite as an example, the water content is set to 11.1%, 15.8%, 21.8%, 25.8% and 29%, 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 is tested by using DPHP and DSC respectively, and compared with the theoretical value, and the test results are shown in Table 2.
[0091] Table 2 Specific heat capacity of soil sample prepared by the present application by double-needle heat pulse method, other methods and theoretical calculation
[0092]
[0093] From Table 2, the specific heat capacity of the soil measured by the two methods is very consistent with the theoretical value, and there is a small amplitude fluctuation within the range of ±5% of the theoretical value. The DSC method is a standard method for testing the specific heat capacity of soil, and the DPHP method is used to test the specific heat capacity of the soil sample, and the results are close to the results measured by the DSC method, indicating that the soil sample prepared based on the differential pressure group hole method is used for the DPHP method, and the measured specific heat capacity of the soil is accurate and reliable, and can be used for testing the specific heat capacity of soil in soil test.
[0094] The above experimental results show that the soil sample prepared by the present application has good practicability and reliability in testing the specific heat capacity of soil. By preparing an integrally formed whole 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 widening the application range of the double-needle heat pulse method.
[0095] The above describes the present application and its embodiments in a schematic manner, which is not restrictive, and the drawings shown are only one of the embodiments of the present application, and the actual structure is not limited thereto. Therefore, if a person skilled in the art is inspired thereby, without departing from the purpose of the present application, similar structural modes and embodiments can be designed without creativity, which shall belong to the protection scope of the present application.
Claims
1. A method for using a sample preparation device for testing the specific heat capacity of soil, characterized in that, The device includes: An internal pressure mold (1) includes a cylindrical mold body (102). The top of the mold body (102) is provided with two channel protrusions (101) that are parallel to and symmetrically distributed on both sides of the center line. One end of each channel protrusion (101) extends to the outer edge of the top of the mold body (102). The channel protrusions (101) are used to generate channels for probe insertion during the first pressing of the soil sample. A low-melting-point alloy column, which is used to generate channels for probe insertion during the second compaction of the soil sample; An outer casing (4) has an inner diameter that matches the diameter of the inner pressure mold (1) and is fitted onto the outside of the inner pressure mold (1). The height of the inner pressure mold (1) is less than the height of the outer casing (4). A sampler (2) is used to press the soil material inside the outer casing (4); The usage method includes: S1: Calculate the required amount of soil, place half of the soil into the outer casing (4); then place the hole protrusion (101) in the inner pressure mold (1) with the hole facing down into the outer casing (4), and press the soil in the outer casing (4) with the sample press (2) to obtain the first sample; S2: Remove the first sample and the inner pressure mold (1) from the outer casing (4); S3: Place the first sample in the outer casing (4) with the surface of its hole facing upward, and place a cylindrical low-melting-point alloy column that is compatible with it in the hole of the first sample as a mold for pressing the second sample. S4: Place the remaining wet soil material into the upper cavity of the outer casing (4); the sample press (2) presses the soil material inside the outer casing (4) to obtain an integral sample; S5: Take the obtained integral sample out of the outer casing (4), heat it to the melting point of the alloy column and pour out the liquid alloy to obtain an integral sample with channels.
2. The method of using 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 method of using the sample preparation device for testing the specific heat capacity of soil according to claim 1, characterized in that, The device also includes a limiter (3), the inner wall of which is provided with a first connecting groove (301) and a second connecting groove (302) that surround it in the circumference, wherein the inner diameter of the second connecting groove (302) matches the diameter of the inner pressure mold (1), and the inner diameter of the first connecting groove (301) matches the outer diameter of the outer protective cylinder (4).
4. The method of using the sample preparation device for testing the specific heat capacity of soil according to claim 3, characterized in that, The sample press (2) includes a compaction block (201) and a limiting part (202). The diameter of the compaction block (201) matches the diameter of the inner pressure mold (1). The limiting part (202) is located on the upper end face of the compaction block (201). The diameter of the limiting part (202) is greater than the diameter of the compaction block (201). The height of the compaction block (201) is greater than or equal to the height of the second connecting groove (302).
5. The method of using 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 method of using the sample preparation device for testing the specific heat capacity of soil according to any one of claims 1-5, characterized in that, The internal pressure mold (1) is prepared by 3D printing.
7. The method of using the sample preparation device for testing the specific heat capacity of soil according to claim 1, characterized in that, In S1, before placing half of the soil material into the outer casing (4), a plastic film is placed at the bottom and inside the outer casing (4); In S3, before the first sample is placed in the outer protective tube (4), a plastic film is inserted into the bottom and inner wall of the outer protective tube (4); In step S3, after placing a cylindrical low-melting-point alloy column suitable for the first sample at the pore, the upper surface of the first sample is roughened.
8. The method of using the sample preparation device for testing the specific heat capacity of soil according to claim 1, characterized in that, In step S5, the entire sample is heated in a constant temperature and humidity chamber.
9. The method of using the sample preparation device for testing the specific heat capacity of soil according to claim 1, characterized in that, The cylindrical low-melting-point alloy column has a melting point of 47~70℃.