Experimental device for observing rock mass fracture capillary action and freezing front behavior

Abstract

The invention discloses an experimental device for observing rock mass fracture capillary action and freezing front behavior. Wherein the rock mass fracture sample has two opposite ends, and the cooling system comprises a top-end Peltier element and a bottom-end Peltier element which are located at the two ends of the rock mass fracture sample. The Peltier element is used for absorbing heat of the rock mass fracture sample, so that a thermal gradient is established from the opposite end to the other end in the rock mass fracture sample and freezing is generated, and the freezing leading edge behavior is located in the rock mass fracture sample by controlling the current of the Peltier element and the Peltier element at the bottom end; and the image can be observed through the image acquisition equipment. The temperature control device has the advantages of being compact in structure, free of noise and capable of achieving accurate temperature control.

Description

Technical Field

[0001] The present invention belongs to the technical field of rock mechanics, and specifically relates to an experimental device for observing the capillary action and freezing front behavior of rock mass fractures. Background Art

[0002] When fractured rock masses in nature and engineering structures are affected by water and temperature changes, their mechanical behaviors will change significantly. Capillary action and freezing mechanisms in fractures are key factors affecting the stability and durability of these materials. Capillary action in fractures involves the adsorption, diffusion, and migration of water in rock fractures, and the freezing mechanism involves the process of water freezing in rock fractures. When the temperature drops below the freezing point, the water in the fractures begins to freeze and expand in volume, thereby exerting pressure on the fracture walls. This pressure may cause damage or deformation of the rock. These processes have a profound impact on the mechanical properties of rocks and soils. Therefore, studying the capillary action and freezing mechanism in rock mass fractures is of great significance for maintaining engineering structures.

[0003] Existing experimental devices mainly cool down by means of cold plates or liquid nitrogen to generate a certain temperature gradient to observe the freezing phenomenon. Cold plates rely on heat conduction and convection to dissipate heat and may require a liquid circulation system to enhance the cooling effect. However, cold plates are more dependent on external environmental conditions such as air flow. Liquid nitrogen can provide extremely low temperatures, so liquid nitrogen cooling has extremely high cooling capacity, but it is also accompanied by high costs, potential safety risks, and the inconvenience of requiring regular replenishment of liquid nitrogen. Therefore, the current experimental devices cannot simultaneously meet the requirements of simple structure, anti-interference, low cost, and precise control, and there is an urgent need for systematic improvement. Summary of the Invention

[0004] (1) Technical Problems to be Solved

[0005] On the one hand, the present invention aims to solve the problems that the existing experimental devices using cold plate cooling have a complex structure, are sensitive to environmental conditions, and have poor control accuracy. On the other hand, the present invention aims to solve the problems that the existing experimental devices using liquid nitrogen cooling are costly, have safety risks, and are difficult to precisely control the temperature.

[0006] (2) Technical Solutions

[0007] To solve the above technical problems, the present invention proposes an experimental device for observing the capillary action and freezing front behavior of rock mass fractures, including an observation box, a cooling system, and an image acquisition device. The observation box is used to accommodate the rock mass fracture sample; the cooling system is used to cool down the rock mass fracture sample; the image acquisition device is used to record images of the rock mass fracture sample; the rock mass fracture sample has opposite ends; the cooling system includes a top Peltier element located at the top end of the rock mass fracture sample and a bottom Peltier element located at the bottom end of the rock mass fracture sample; the top Peltier element and the bottom Peltier element are used to absorb heat from the rock mass fracture sample, so as to establish a thermal gradient and generate freezing inside the rock mass fracture sample from one end to the other; the freezing front behavior of the freezing is located inside the rock mass fracture sample and can be observed by the image acquisition device.

[0008] According to a preferred embodiment of the present invention, the powers of the Peltier elements at both ends of the rock mass fracture sample can be set separately, so that freezing starts at one end of the rock mass fracture sample, and the freezing front moves from one end to the other end.

[0009] According to a preferred embodiment of the present invention, both the Peltier elements at both ends of the rock mass fracture sample have a cold end and a hot end. The cold end faces the rock mass fracture sample and is directly connected or connected to one end of the rock mass fracture sample through a heat conduction medium, and the hot end is connected to a radiator.

[0010] According to a preferred embodiment of the present invention, the rock mass fracture sample is placed vertically, and the opposite ends are the top end and the bottom end respectively;

[0011] The power of the top Peltier element located at the top end of the rock mass fracture sample is set to be greater than the power of the bottom Peltier element located at the bottom end of the rock mass fracture sample, so that the rock mass fracture sample starts to freeze from the top end, and the freezing front moves from the top end to the bottom end.

[0012] According to a preferred embodiment of the present invention, the radiator connected to the top Peltier element is a heat sink, and the radiator connected to the bottom Peltier element is a vortex radiator.

[0013] According to a preferred embodiment of the present invention, the experimental device further includes a power supply, a relay, a top temperature sensor, and a controller. The power supply supplies power to the Peltier element at the top of the rock mass fracture sample via the relay; the top temperature sensor is used to detect the temperature of the Peltier element at the top of the rock mass fracture sample and send a temperature signal to the controller; the controller controls the on-off of the relay according to the temperature signal to control whether the Peltier element at the top of the rock mass fracture sample works, so as to control the temperature at the top of the rock mass fracture sample, so that the rock mass fracture sample starts to freeze from the top.

[0014] According to a preferred embodiment of the present invention, the power supply is connected to the Peltier element at the bottom of the rock mass fracture sample via a DC motor speed controller, and the DC motor speed controller is used to adjust the voltage output to the Peltier element at the bottom of the rock mass fracture sample.

[0015] (III) Beneficial effects

[0016] (1) The present invention has the advantages of being structurally compact (no moving parts, small size), noiseless (no fan), and capable of achieving precise temperature control.

[0017] (2) The present invention can autonomously adjust the width of the crack, which is convenient for measuring the capillary action under different crack widths, making the experiment more operable.

[0018] (3) The present invention also has the advantages of fast response and low power consumption. Description of the drawings

[0019] Figure 1 is the principle structure diagram of the Peltier element adopted by the present invention.

[0020] Figure 2 is a schematic diagram of the brief structure of the experimental device for observing the capillary action and freezing front behavior of rock mass fractures of the present invention.

[0021] Figure 3 is a perspective view of the main structure of the experimental device for observing the capillary action and freezing front behavior of rock mass fractures in an embodiment of the present invention.

[0022] Figure 4 is a detailed structure diagram of the rock mass fracture sample area of the experimental device for observing the capillary action and freezing front behavior of rock mass fractures in an embodiment of the present invention.

[0023] Figure 5 and Figure 6 is the overall structure diagram of the experimental device for observing the capillary action and freezing front behavior of rock mass fractures in an embodiment of the present invention, Figure 5 is a front perspective view, Figure 6 is a perspective view.

[0024] Figure 7 Schematic diagram of the top aluminum block structure of the experimental device for observing capillary action and freezing front behavior in rock mass fractures according to an embodiment of the present invention.

[0025] Figure 8 Schematic diagram of the bottom aluminum block structure of the experimental device for observing capillary action and freezing front behavior in rock mass fractures according to an embodiment of the present invention.

[0026] Figure 9 Schematic diagram of the power control circuit structure of the experimental device for observing capillary action and freezing front behavior in rock mass fractures according to an embodiment of the invention. Detailed implementation manners

[0027] To solve the foregoing technical problems, the present invention improves the experimental device for observing capillary action and freezing front behavior in rock mass fractures. The main improvement of the present invention lies in using a Peltier element as the heat absorption / heat release element and designing a corresponding control circuit structure for automatic adjustment and control. The advantages of the Peltier element are that it has no moving parts, no noise, a compact size, and can achieve precise temperature control, which is incomparable to other existing methods.

[0028] A Peltier element is a device that uses semiconductor materials for refrigeration and heating, and its working principle is based on the Peltier effect. The Peltier effect refers to the phenomenon that a substance exhibits a thermoelectric effect or a magnetoelectric effect under the action of an externally applied electric field or magnetic field. The Peltier element utilizes this effect to convert the energy of the electric field or magnetic field into other forms of energy to achieve signal transmission or energy conversion and regulation.

[0029] Figure 1 is the principle structure diagram of the Peltier element adopted by the present invention. As Figure 1 shown, a Peltier element usually consists of a Peltier thin film, electrodes, and a substrate. Among them, the Peltier thin film is the main working component and has a thermoelectric effect or a magnetoelectric effect: the electrodes are used to apply an externally applied electric field or magnetic field; the substrate plays a role in fixing and supporting. When a DC power supply provides electrical energy to the semiconductor refrigeration chip, the semiconductor refrigeration chip will generate the Peltier effect. Specifically, when an electric current passes through a thermocouple pair formed by N-type semiconductor material and P-type semiconductor material, heat transfer will occur between the two ends. Heat will transfer from one end (the hot end) to the other end (the cold end), thereby generating a temperature difference to form a hot and cold end and achieving the refrigeration effect.

[0030] Figure 2 is the brief structure diagram of the experimental device for observing capillary action and freezing front behavior in rock mass fractures according to the present invention. As Figure 2As shown in the figure, the experimental device of the present invention mainly includes an observation chamber 13, a cooling system, and an image acquisition device. The observation chamber 13 is used to accommodate the rock mass fracture sample 16. The rock mass fracture sample 16 is placed vertically and has opposite ends, namely the top end and the bottom end. The image acquisition device is used to record images of the rock mass fracture sample 16. Different from the prior art, the cooling system of the present invention includes Peltier elements respectively located at both ends of the rock mass fracture sample 16, namely the top Peltier element 15 and the bottom Peltier element 17. The Peltier elements 15 and 17 are used to cool down the rock mass fracture sample 16.

[0031] In the present invention, the Peltier elements located at the opposite ends of the rock mass fracture sample 16 are both used to absorb heat from the rock mass fracture sample 16 and dissipate heat to the outside. Moreover, the present invention proposes to control the thermal gradient from the top to the bottom so that the behavior of the freezing front is located inside the rock mass fracture sample 16, whereby the experimenter can observe through the image acquisition device.

[0032] It should be noted that, as a preferred embodiment of the present invention, the powers of the Peltier elements at both ends of the rock mass fracture sample 16 can be set separately, so that one end of the rock mass fracture sample 16 starts to freeze and the freezing front moves from one end to the other end. As a specific implementation manner, the power of the top Peltier element 15 located on the rock mass fracture sample is set to be greater than the power of the bottom Peltier element 17 located on the rock mass fracture sample, so that when the Peltier elements work, the rock mass fracture sample 16 starts to freeze from the top end and the freezing front moves from the top end to the bottom end.

[0033] Both the top Peltier element 15 and the bottom Peltier element 17 have a cold end and a hot end. The cold ends face the rock mass fracture sample 16 and are respectively connected to the rock mass fracture sample 16 through a heat-conducting medium, and the hot ends are both connected to a radiator. As a specific example of the radiator, the radiator at the top can adopt a compact heat sink, and the radiator at the bottom can adopt a vortex radiator.

[0034] In order to make the purpose, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments and the accompanying drawings.

[0035] Figure 3 is a three-dimensional view of the main structure of the experimental device for observing the capillary action and freezing front behavior of rock mass fractures in an embodiment of the present invention. As Figure 3As shown, in this embodiment, the main structure includes a heat sink 1, a top Peltier element 15, a top aluminum block 13, a rock mass fracture sample 16, a bottom aluminum block 3, a bottom Peltier element 17, and a vortex cooler 5. The top Peltier element 15 is tightly connected to the rock mass fracture sample 16 through the top aluminum block 13 as a heat conduction medium, and the bottom Peltier element 17 is tightly connected to the rock mass fracture sample 16 through the bottom aluminum block 3 as a heat conduction medium. The rock mass fracture sample 16 is formed by clamping a glass plate on one side and a granite plate on the other side to form a fracture. Thermal paste can be applied to the top and bottom of the glass or granite plate respectively to ensure good thermal connection from the top aluminum block 13 and the bottom aluminum block 3 to the rock mass fracture sample 16. To clamp the glass plate and the granite plate, fixing bolts 14 are used in this embodiment for fixation.

[0036] The top Peltier element 15 and the bottom Peltier element 17 connected to the top aluminum block 13 and the bottom aluminum block 3 both face the cold ends towards the aluminum blocks. The hot ends are respectively connected to the heat sink 1 and the vortex cooler 5.

[0037] In this embodiment, the heat sink 1 uses a CPU radiator. The CPU radiator can effectively control the hot end temperature within a reasonable range to meet the experimental requirements. Compared with other radiators, the CPU radiator is more compact in volume, more economical, and easier to install.

[0038] The bottom radiator uses a vortex cooler 5, which is a device that absorbs compressed air and realizes air cooling through the vortex effect. The vortex cooler 5 is used to ensure that the bottom temperature remains above freezing point to prevent the water at the bottom from freezing. Because air enters the hollow cylinder through a control valve and forms a vortex by rotating at high speed inside. Due to the centrifugal force, the heavier cold air is pushed towards the outer wall of the cylinder and discharged from the cold air outlet, while the lighter hot air is concentrated in the center and discharged through the hot air outlet. This separation process enables the vortex cooler to effectively divide the input air into cold and hot parts, thus achieving the cooling effect. Therefore, using the vortex cooler 5 can better ensure the temperature stability and reliability, ensuring that the experimental results are not affected by environmental temperature changes, and it has no moving parts or cooling liquid, with almost no wear or maintenance.

[0039] Figure 4 It is a detailed structure diagram of the rock mass fracture sample area of the experimental device for observing the capillary action and freezing front behavior of rock mass fractures in an embodiment of the present invention. As Figure 4 shown, in this embodiment, the device further includes a plurality of temperature sensors 2 and a plurality of strain sensors 6. Each sensor is fixed through an aluminum block 19. The strain sensor 6 can be pushed through the hole on the aluminum block 19 and fixedly connected. The automatic temperature and humidity regulator 18 is installed in the pocket between the top aluminum conductor and the top cover of the observation box and sealed with silicone paste.

[0040] Figure 5 And Figure 6 are the overall structure diagrams of an experimental device for observing the capillary action of rock mass fractures and the behavior of the freezing front in an embodiment of the present invention, Figure 5 is a front perspective view, Figure 6 is a three-dimensional view. As Figure 5 and Figure 6 shown, in addition to the main structure, the experimental device also includes an observation box 13, a box body support 4, an annular lamp 7, a camera 9, a camera support 10, and a camera track 11.

[0041] The observation box 13 is used to accommodate the rock mass fracture sample 16 and is suitable for experimenters to observe. In this embodiment, the observation box 13 is a transparent water bath box. The water bath box is made of polymethyl methacrylate and is designed as an open water tank for accommodating water and specimens. A temperature sensor is installed inside the water bath box to monitor the temperature change in the water bath in real time. The side walls and bottom of the water bath box are also sealed with sealing strips or silica gel to prevent water from leaking through the gaps.

[0042] The observation box 13 is placed on a box body support 4, and a cutout 8 is provided on the box body to facilitate the extension of the wires inside the box. The temperature sensor 2 and the strain sensor 6 are installed inside the observation box.

[0043] The annular lamp 7 is installed inside the water bath box, above the specimen, and the reflector is installed above the annular lamp and fixed to the inner wall of the water bath box through a support. The light emitted by the annular lamp first irradiates on the reflector and then is reflected and focused on the specimen by the reflector. This design ensures the uniform distribution and efficient utilization of light, while reducing light scattering and loss.

[0044] Before the start of the experiment, ensure the cleanliness and dryness of the sample, fix the specimen with a fixing clip, and at the same time fix the strain sensor 6 on the aluminum block attached to the front template, and then apply some thermal paste to the rear temperature sensor 2. Place the sample into the observation box 13 and clamp it with a metal clip.

[0045] In this embodiment, the camera 9, as an image acquisition device, is set on the camera track 11 of the camera support 10. During the experiment, the camera remains in a fixed position and records the dynamic changes in the specimen through the time interval shooting function. Before the start of the experiment or when the shooting angle needs to be adjusted, the camera can be manually adjusted through the support. The support can finely adjust the camera in the horizontal and vertical directions to ensure the best image effect. The annular lamp and the reflector ensure the uniform distribution of light on the surface of the specimen, reduce shadows and light spots, and improve the clarity and contrast of the image.

[0046] Figure 7 And Figure 8They are respectively the schematic structural diagrams of the top aluminum block and the bottom aluminum block of the experimental device for observing the capillary action and freezing front behavior of rock mass fractures in an embodiment of the present invention.

[0047] For the above embodiment, the cables of each sensor and regulator are pulled out through the cut 8, and a small focal plane is installed on the plane where the two plates meet to ensure that the camera can accurately focus on the crack area in the specimen.

[0048] The signals of the temperature sensor 2 and the strain sensor 6, as well as the images acquired by the camera 9, are all transmitted to a data acquisition system (not shown in the figure). During the experiment, the top and back of the observation box are covered, and all gaps around the insulation are sealed with tape, and then the data acquisition system is turned on for data acquisition. Specifically, the strain sensor 6 is connected to an interface that can be directly inserted into the Ethernet port of the computer of the data acquisition system. The acquisition process of the data acquisition system can be monitored in real time on the screen. The data acquisition of the temperature sensor 2 can be connected to the computer of the data acquisition system through a USB cable, and the data can be directly imported into MATLAB in real time, and a graph is created in real time. At the same time, the data is automatically saved to the computer.

[0049] Figure 9 It is the schematic structural diagram of the power control circuit of the experimental device for observing the capillary action and freezing front behavior of rock mass fractures in an embodiment of the invention. As Figure 9 shown, in this embodiment, the experimental device further includes a power supply 20, a controller 21, and a relay 22. And, the multiple temperature sensors 2 located in the observation box described above include a top temperature sensor 2a at the cold end of the Peltier element at the top of the rock mass fracture sample.

[0050] The power supply 20 supplies power to the top Peltier element 15 at the top of the rock mass fracture sample 16 via the relay 22. The top temperature sensor 2a at the cold end of the top Peltier element 15 is used to detect the temperature at the cold end of the top Peltier element at the top of the rock mass fracture sample 16, and send the temperature signal to the controller 21. The controller controls the on / off of the relay 22 according to the temperature signal to control whether the top Peltier element 15 works, so as to control the temperature at the top of the rock mass fracture sample 16, so that the rock mass fracture sample 16 starts to freeze from the top.

[0051] In addition, the power supply 20 is connected to the bottom Peltier element 17 at the bottom of the rock mass fracture sample 16 via a DC motor speed controller 23, and the DC motor speed controller 23 can adjust the voltage output to the bottom Peltier element at the bottom of the rock mass fracture sample.

[0052] The power supply 20 can be a power transformer (ZDM 30A 360W DC 12V to AC110 - 220V iron power supply), which converts 230 volts into 12 volts and can manage a current of up to 30 amperes. To control the cooling cycle at the bottom end of the rock mass fracture sample 16, a DC motor speed controller (DC 6 - 90V) with a potentiometer is used. For the cooling control at the top end of the rock mass fracture sample 16, the controller 21 adopts an automatic temperature and humidity controller (XY - WTH1), and the top - end temperature sensor 2a is correspondingly a temperature and humidity sensor (XSHT20). The wires of the temperature and humidity sensors are connected using D - sub9 connectors. This controller 21 provides a 12 - volt power supply and can also control higher voltages because it only turns on and off a relay to cut off or connect the direct connection from the power supply 20 to the top - end Peltier element 15.

[0053] The power of the Peltier elements at both ends of the rock mass fracture sample 16 can be set separately so that one end of the rock mass fracture sample starts to freeze and the freezing front moves from one end to the other. Specifically, when conducting experiments through the above experimental device, through the automatic control of the controller and adjusting the speed controller to an appropriate position, after the temperature of the specimen reaches stability, the injected water is first cooled in the water bath, which is filled with ice generated by the freezer. After a period of time, the bottom turns back to prevent capillary water from rising to the full height. Strain is measured throughout the experiment to observe whether capillary rise or freezing will exert any force on the crack.

[0054] In this embodiment, the Peltier elements at both ends of the rock mass fracture sample 16 have different powers, thus achieving an asymmetric heat absorption / heat release capacity. The top - end Peltier element 15 adopts TEC1 - 12710 (10 amperes), and the bottom - end Peltier element 17 adopts TEC1 - 12706 (6 amperes). The power and refrigeration capacity of the top - end Peltier element 15 are both stronger than those of the bottom - end Peltier element 17. By adjusting the current, the top - end Peltier element 15 can absorb heat from the rock mass fracture sample 16 more effectively, thus rapidly cooling the top of the rock mass fracture sample 16 and promoting the freezing of capillary water; while the bottom - end Peltier element 17 can release heat relatively slowly to maintain the temperature at the bottom and keep the water at the bottom in a liquid state.

[0055] In this embodiment, software can be used to track objects. To conduct the tracking, first, a size reference mark is added to the sample, and coordinate systems are set at three positions on the left, middle, and right of the sample. The center lines of the coordinate systems on the left and right are located 1 centimeter from the left and right edges of the sample respectively, while the middle coordinate system is located at the center of the sample. Next, a data set is created by clicking on the positions of the water / ice front frame by frame. This process simultaneously generates a table and a chart, and the data can be imported into an Excel file for further analysis.

[0056] The specific embodiments described above further elaborate on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. An experimental device for observing the capillary action of rock mass fractures and the freezing front behavior, comprising an observation box, a cooling system and an image acquisition device, wherein: The observation box is used to accommodate rock mass fracture samples; The cooling system is used to cool the rock mass fracture sample; The image acquisition device is used to record images of the rock mass fracture samples; Features: The rock mass fracture sample has two opposite ends; The cooling system includes a top Peltier element located at the top of the rock mass fracture sample and a bottom Peltier element located at the bottom of the rock mass fracture sample; The top Peltier element and the bottom Peltier element are used to absorb heat from the rock fracture sample so as to establish a thermal gradient from one opposite end to the other end inside the rock fracture sample and produce freezing; The frozen freeze front behavior is located inside the rock fracture sample and can be observed by the image acquisition device.

2. The experimental device for observing the capillary action of rock mass fissures and the freezing front behavior according to claim 1, characterized in that: The powers of the Peltier elements at both ends of the rock fracture sample can be set respectively so that one end of the rock fracture sample starts to freeze and the freezing front moves from one end to the other end.

3. The experimental device for observing rock mass fissure capillary action and freezing front behavior according to claim 2, characterized in that: The Peltier elements at both ends of the rock fracture sample have a cold end and a hot end, the cold end faces the rock fracture sample and is connected to one end of the rock fracture sample directly or through a heat conducting medium, and the hot end is connected to a radiator.

4. The experimental device for observing the capillary action of rock mass fissures and the freezing front behavior according to claim 3, characterized in that: The rock mass fracture sample is placed vertically, and the two opposite ends are respectively the top end and the bottom end; The power of the top Peltier element located at the top of the rock fracture sample is set to be greater than the power of the bottom Peltier element located at the bottom of the rock fracture sample, so that the rock fracture sample starts to freeze from the top and the freezing front moves from the top to the bottom.

5. The experimental device for observing the capillary action of rock mass fissures and the freezing front behavior according to claim 4, characterized in that: The heat sink connected to the top Peltier element is a heat sink, and the heat sink connected to the bottom Peltier element is a vortex heat sink.

6. The experimental device for observing the capillary action of rock mass fissures and the freezing front behavior according to claim 5, characterized in that: The experimental device also includes a power supply, a relay, a top temperature sensor and a controller; The power supply supplies power to the Peltier element at the top of the rock fracture sample via the relay; The top temperature sensor is used to detect the temperature of the Peltier element at the top of the rock fracture sample and send a temperature signal to the controller; The controller controls the on and off of the relay according to the temperature signal to control whether the Peltier element at the top of the rock fracture sample is working, thereby controlling the temperature of the top of the rock fracture sample so that the rock fracture sample starts to freeze from the top.

7. The experimental device for observing the capillary action of rock mass fissures and the freezing front behavior according to claim 6, characterized in that: The power supply is connected to the Peltier element at the bottom end of the rock fracture sample via a DC motor speed regulator, and the DC motor speed regulator is used to adjust the voltage output to the Peltier element at the bottom end of the rock fracture sample.

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