A rock freeze-thaw cycle experimental device for controlling the propagation of pre-existing fractures

Abstract

This invention relates to a rock freeze-thaw cycle experimental device for controlling the propagation of pre-existing cracks. It comprises a temperature control system, a water tank, a drainage pipe, valves, a water pump, a flow meter, a top low-temperature source, a top heat conduction device, a top low-temperature control system, a bottom low-temperature source, a bottom heat conduction device, a bottom low-temperature control system, a rock sample, pre-existing cracks, a temperature sensor, a temperature monitoring system, an upper partition, a lower partition, and an insulated chamber body. Inside the insulated chamber body, the bottom low-temperature source, the bottom heat conduction device, the rock sample, the top heat conduction device, and the top low-temperature source are arranged sequentially from bottom to top. This invention features a simple structure and convenient operation.

Description

Technical Field

[0001] This invention relates to the field of rock freeze-thaw cycle technology, specifically to a rock freeze-thaw cycle experimental device that can control the propagation of pre-existing cracks. Background Technology

[0002] During the formation of natural rock masses, complex geological processes result in numerous joints and fissures, significantly reducing the physical and mechanical properties of the rock mass. With the changing seasons, the rock mass undergoes freeze-thaw cycles. Under these cycles, water stored within the joints and fissures repeatedly freezes and thaws. The frost heave force generated by the water-ice phase change causes the joints and fissures to expand further, resulting in irreversible damage to the rock mass.

[0003] Chinese patent application CN112067636A discloses a real-time monitoring system and method for the frost heave deformation propagation of ice-bearing fissures in rocks. This system includes a CT scanning system, a rock freeze-thaw system, a fissure deformation measurement system, and a frost heave force measurement system. Through the coordination of these systems, the frost heave deformation of rock fissures can be measured, and the microscopic process of the propagation and evolution of ice-bearing fissures in rocks under freeze-thaw cycles can be observed in real time. Chinese patent application CN112834559A discloses a rock freeze-thaw cycle experimental device that can consider temperature gradients. This device can control the cooling rate of rock samples at different heights by controlling the water flow rate and temperature at different layers, thereby creating a temperature gradient inside the rock sample during the freezing process.

[0004] In real-world environments, the extent of rock fracture propagation induced by freeze-thaw cycles is influenced by numerous factors. Currently, much research focuses on freeze-thaw temperature, duration, number of fractures, and fracture size, while studies on the impact of temperature gradients on fractured rocks during freeze-thaw cycles are relatively scarce. Different temperature gradients lead to different freezing fronts, and the relative position and angle between the freezing front and the fracture affect the distribution and propagation of forces within the fracture. Therefore, it is necessary to design a freeze-thaw cycle experimental device for controlling the propagation of pre-existing fractures, thereby controlling the propagation angle of different pre-existing fractures in the rock by controlling the temperature gradient. Summary of the Invention

[0005] The purpose of this invention is to provide a rock freeze-thaw cycle experimental device for controlling the propagation of pre-existing fractures. Using this device, the propagation angle of different pre-existing fractures in the rock can be controlled by adjusting the temperature gradient during the freeze-thaw cycle. This invention features a simple structure and convenient operation.

[0006] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0007] A rock freeze-thaw cycle experimental device for controlling the propagation of pre-fabricated fissures consists of a temperature control system, a water tank, a drainage pipe, valves, a water pump, a flow meter, a top low-temperature source, a top heat conduction device, a top low-temperature control system, a bottom low-temperature source, a bottom heat conduction device, a bottom low-temperature control system, a rock sample, pre-fabricated fissures, a temperature sensor, a temperature monitoring system, an upper partition, a lower partition, and an insulated box body. The system includes drainage pipes located on the left and right sides of the main body of the insulated chamber and connected to a water tank; valves, water pumps, and flow meters are installed on the drainage pipes; inside the main body of the insulated chamber, from bottom to top, are arranged a bottom low-temperature source, a bottom heat conduction device, a rock sample, a top heat conduction device, and a top low-temperature source; pre-fabricated cracks are pre-cut on the surface of the rock sample using wire cutting; the top and bottom ends of the rock sample are in contact with the top and bottom heat conduction devices, respectively; multiple top and bottom low-temperature sources can be designed as needed; the top and bottom low-temperature sources are connected to the top and bottom low-temperature control systems, respectively; upper and lower partitions are arranged at different heights on the rock sample, forming an independent space between them; the pre-fabricated cracks on the rock sample are located inside this independent space; temperature sensors are installed within this independent space and connected to a temperature monitoring system; drainage pipes are arranged on the left and right sides of this independent space; readable temperature sensors are installed on the surface of the rock sample; and the water tank is connected to the temperature control system.

[0008] In the above-mentioned device, the main body of the insulated box, the upper partition, and the lower partition are all made of low-temperature resistant materials.

[0009] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0010] By placing multiple top cryogenic sources at the top of the rock sample and multiple bottom cryogenic sources at the bottom, along with a top heat conduction device, a top cryogenic control system, a bottom heat conduction device, and a bottom cryogenic control system, and arranging them as described above, a temperature gradient can be formed inside the rock sample during the freezing process. By placing readable temperature sensors on the surface of the pre-fabricated fractured rock sample, the temperature values ​​and temperature gradient distribution of the rock sample can be obtained, thereby forming freezing fronts at different angles within the rock sample. For different pre-fabricated fracture angles, by adjusting the temperature values ​​of the multiple top and bottom cryogenic sources, the spatial relationship between the freezing front and the pre-fabricated fracture can be adjusted. When the freezing front and the pre-fabricated fracture are parallel, deformation of the rock sample can be caused by moisture migration and freezing, leading to a change in the stress state inside the pre-fabricated fracture, thus controlling the expansion of the pre-fabricated fracture. Furthermore, through the coordination of the temperature control system, water tank, drainage pipe, valves, water pump, and flow meter, water can be replenished to the rock sample, ensuring sufficient moisture inside the pre-fabricated fracture. Attached Figure Description

[0011] Figure 1 This is a schematic diagram of the experimental device for controlling the propagation of pre-fabricated cracks in rocks under freeze-thaw cycles according to the present invention.

[0012] Figure 2 This is a schematic diagram of the freezing process of a rock sample when the pre-fabricated fracture angle is 0°.

[0013] Figure 3 This is a schematic diagram of the freezing process of a rock sample with a pre-fabricated fracture angle of 30°.

[0014] The labels in the diagram are as follows: 1-Temperature control system, 2-Water tank, 3-Drainage pipe, 4-Valve, 5-Water pump, 6-Flow meter, 7-Top low temperature source, 8-Top heat conduction device, 9-Top low temperature control system, 10-Bottom low temperature source, 11-Bottom heat conduction device, 12-Bottom low temperature control system, 13-Rock sample, 14-Pre-fabricated fracture, 15-Temperature sensor, 16-Temperature monitoring system, 17-Upper partition, 18-Upper partition, 19-Insulation box body, 20-Freezing front. Detailed Implementation

[0015] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of the present invention.

[0016] Example:

[0017] like Figure 1It is a rock freeze-thaw cycle experimental device that can control the propagation of pre-fabricated cracks. It consists of a temperature control system 1, a water tank 2, a drainage pipe 3, a valve 4, a water pump 5, a flow meter 6, a top low temperature source 7, a top heat conduction device 8, a top low temperature control system 9, a bottom low temperature source 10, a bottom heat conduction device 11, a bottom low temperature control system 12, a rock sample 13, a pre-fabricated crack 14, a temperature sensor 15, a temperature monitoring system 16, an upper partition 17, a lower partition 18, and an insulated box body 19. The drainage pipes 3 are arranged on the left and right sides of the main body 19 of the insulation box and connected to the water tank 2. A valve 4, a water pump 5, and a flow meter 6 are arranged on the drainage pipes 3. Inside the main body 19 of the insulation box, from bottom to top, a bottom low-temperature source 10, a bottom heat conduction device 11, a rock sample 13, a top heat conduction device 8, and a top low-temperature source 7 are arranged sequentially. Pre-fabricated cracks 14 are pre-cut on the surface of the rock sample 13 using wire cutting. The top and bottom of the rock sample 13 are in contact with the top heat conduction device 8 and the bottom heat conduction device 11, respectively. Four top low-temperature sources 7 and four bottom low-temperature sources 7 are respectively provided. Source 10; Top low temperature source 7 and bottom low temperature source 10 are respectively connected to top low temperature control system 9 and bottom low temperature control system 12; upper partition 17 and lower partition 18 are respectively arranged at different heights of rock sample 13 and form an independent space between the partitions, the pre-made crack 14 on rock sample 13 is located inside the independent space, temperature sensor 15 is installed in the independent space, temperature sensor 15 is connected to temperature monitoring system 16, drainage pipe 3 is arranged on the left and right sides of the independent space; readable temperature sensor 15 is arranged on the surface of rock sample 13; water tank 2 is connected to temperature control system 16.

[0018] For ease of description, the four top low-temperature sources 7 are named from left to right as Left Top Low-Temperature Source 7, Left Second Top Low-Temperature Source 7, Right First Top Low-Temperature Source 7, and Right Second Top Low-Temperature Source 7; the four bottom low-temperature sources 10 are named from left to right as Left Bottom Low-Temperature Source 10, Left Second Bottom Low-Temperature Source 10, Right First Bottom Low-Temperature Source 10, and Right Second Bottom Low-Temperature Source 10; the drainage pipe 3 located on the left side of the insulation box body 19 is named the water inlet pipe, and the drainage pipe 3 located on the right side of the insulation box body 19 is named the water outlet pipe.

[0019] The main body 19, upper partition 17, and lower partition 18 of the insulated box are all made of low-temperature resistant materials.

[0020] Analysis suggests that the force driving the expansion of the precast crack 14 comes from two sources: first, the frost heave force generated when the water inside the precast crack 14 freezes; and second, the tensile force generated inside the precast crack 14 due to the deformation of the rock sample 13.

[0021] The freeze-thaw cycle test procedure is as follows:

[0022] First step, according to Figure 1 The rock sample 13 and the freeze-thaw cycle experimental apparatus were arranged in a specific manner.

[0023] The second step is to fill water tank 2 with water and use temperature control system 1 to adjust the water temperature. After the required water temperature is reached, close valve 4 on the outlet pipe and open valve 4 on the inlet pipe. Use the corresponding water pump 5 to flow the water in water tank 2 through the diversion pipe 3 to the independent space between the upper partition 17 and the lower partition 18 inside the insulation box body 19, and then close valve 4 on the inlet pipe.

[0024] The third step is to turn on all the top low temperature sources 7 and bottom low temperature sources 10 after the pre-fabricated crack 14 is filled with water. The temperature of each top low temperature source 7 and each bottom low temperature source 10 is adjusted using the top low temperature control system 9 and the bottom low temperature control system 12. The temperature field distribution of the rock sample 13 is obtained by using the temperature sensor 15 that can be read on the surface of the rock sample 13, so that different freezing fronts 20 are formed during freezing.

[0025] Here, the angle between the pre-fabricated fissure 14 and the rock sample 13 in the transverse direction is defined as the angle of the pre-fabricated fissure 14, and the angle between the freezing front 20 and the rock sample 13 in the horizontal direction is defined as the angle of the freezing front 20. The angle of the freezing front 20 is adjusted according to the angle of the pre-fabricated fissure 14. When the angle of the freezing front 20 is parallel to the angle of the pre-fabricated fissure 14, due to the effect of water migration, the water in the rock sample 13 will migrate to the freezing front 20 and eventually form an ice band parallel to the freezing front 20, causing the rock sample 13 to deform. The longitudinal deformation will cause tensile stress to be generated in the pre-fabricated fissure 14, thereby promoting the expansion of the pre-fabricated fissure 14.

[0026] Two typical perspectives are as follows:

[0027] like Figure 2 As shown, when the angle of the pre-fabricated crack 14 is 0°, the low temperature sources 7 at the top left, the second top left, the top right, and the second top right are set to the same negative temperature, and the low temperature sources 10 at the bottom left, the second bottom left, the first bottom right, and the second bottom right are set to the same negative temperature. This allows the freezing front 20 formed by the rock sample 13 during freezing to have an angle of 0°, thereby causing the rock sample 13 to undergo vertical deformation, that is, deformation perpendicular to the pre-fabricated crack 14. This will generate tensile stress inside the pre-fabricated crack 14, thereby controlling the pre-fabricated crack 14 to expand in the horizontal direction.

[0028] like Figure 3As shown, when the angle of the pre-fabricated crack 14 is 30°, the temperatures of the left top low temperature source 7, the left second top low temperature source 7, the right top low temperature source 7, and the right second top low temperature source 7 are increased sequentially, while the temperatures of the left bottom low temperature source 10, the left second bottom low temperature source 10, the right first bottom low temperature source 10, and the right second bottom low temperature source 10 are decreased sequentially. Through temperature adjustment, the freezing front 20 formed by the rock sample 13 during freezing is ultimately made to have an angle of 30°, thereby causing the rock sample 13 to deform perpendicular to the angle of the pre-fabricated crack 14. This will cause tensile stress to be generated inside the pre-fabricated crack 14, thereby controlling the pre-fabricated crack 14 to expand in the 30° direction.

[0029] Fourth step: After freezing is complete, maintain the temperature of the top low temperature source 7 and the bottom low temperature source 10;

[0030] Fifth step: After the set freezing time is reached, close the top low temperature control system 9 and the bottom low temperature control system 12, open the valve 4 and water pump 5 on the water outlet and water inlet pipes, and use the temperature control system 1 to adjust the water temperature so that the rock sample 13 gradually melts. After the required melting time is reached, one freeze-thaw cycle is completed.

Claims

1. A rock freeze-thaw cycle test method for controlling the propagation of pre-fabricated cracks, comprising a rock freeze-thaw cycle test device for controlling the propagation of pre-fabricated cracks, wherein the drain pipe (3) is arranged on the left and right sides of the main body (19) of the insulated box and connected to the water tank (2); a valve (4), a water pump (5) and a flow meter (6) are arranged on the drain pipe (3); a bottom low temperature source (10), a bottom heat conduction device (11), a rock sample (13), a top heat conduction device (8) and a top low temperature source (7) are arranged sequentially from bottom to top inside the main body (19); pre-fabricated cracks (14) are pre-set on the surface of the rock sample (13) by wire cutting; the top and bottom of the rock sample (13) are respectively connected to the top heat conduction device (8) and the bottom heat conduction device (11). Contact; multiple top low temperature sources (7) and bottom low temperature sources (10) can be designed as needed; the top low temperature source (7) and bottom low temperature source (10) are respectively connected to the top low temperature control system (9) and the bottom low temperature control system (12); the upper partition (17) and the lower partition (18) are respectively arranged at different heights of the rock sample (13) and form an independent space between the partitions, the prefabricated crack (14) on the rock sample (13) is located inside the independent space, the temperature sensor (15) is set in the independent space, the temperature sensor (15) is connected to the temperature monitoring system (16), the drainage pipe (3) is arranged on the left and right sides of the independent space; the surface of the rock sample (13) is arranged with a readable temperature sensor (15); the water tank (2) is connected to the temperature control system (1), this method Includes the following steps: First, arrange the rock sample (13) and the freeze-thaw cycle test device. Second, fill the water tank (2) with water and use the temperature control system (1) to adjust the water temperature. After the required water temperature is reached, close the valve (4) on the outlet pipe and open the valve (4) on the inlet pipe. Use the corresponding water pump (5) to flow the water in the water tank (2) through the drainage pipe (3) to the independent space between the upper partition (17) and the lower partition (18) inside the main body of the insulation box (19). Then close the valve (4) on the inlet pipe. Third, after the prefabricated crack (14) is filled with water, adjust the temperature values ​​of the top low temperature source (7) and the bottom low temperature source (10) for different prefabricated crack (14) angles to adjust the spatial position relationship between the freezing front (20) and the prefabricated crack (14) and achieve the purpose of controlling the expansion of the prefabricated crack (14).

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