Device and method for determining slurry injectable critical fracture opening

Abstract

The invention discloses a device and method for determining the opening degree of a critical fracture capable of being injected with slurry, the device integrates high-precision mechanical driving, fracture model customization and real-time dynamic observation functions, and precise and continuous adjustment of the fracture opening degree is achieved through continuous propulsion of a stepping motor. The device is based on a transparent fracture model structure which is narrow inside and expanded outside during deformation, the seepage resistance of slurry is reduced, and visual observation of seepage and diffusion processes of the slurry in fractures is supported; in the test, the grouting pressure and the fracture opening degree change are synchronously monitored, and when the grouting pressure is sharply increased, the corresponding opening degree is the critical fracture opening degree, so that the integrated test from fracture opening degree regulation and control, visible slurry migration to quantitative analysis of critical parameters is realized. The device is simple in structure and convenient to operate, and an effective means is provided for groutability evaluation and process optimization of geotechnical engineering grouting materials.

Description

Technical Field

[0001] This invention belongs to the field of grouting technology for fractured rock masses, specifically relating to a device and method for determining the critical fracture opening at which grout can be injected. Background Technology

[0002] The injectability of grout in fissures is a crucial basis for grouting design, especially when injecting particulate suspension grouts, such as typical cement grouts and clay grouts. These grouts are solid-liquid two-phase mixtures, with the solid phase consisting of solid particles of a specific size. When the fissure aperture is less than the critical aperture, the solid particles in the grout can clog the fissure, rendering the grout uninjectable. Determining the critical fissure aperture for injectable grout is essential; it is a vital basis for selecting grouting materials and determining the grouting process in grouting design, affecting the grouting effect and even its success or failure.

[0003] According to relevant research, the inability to inject grout into fissures is not simply due to the particle size of the grout solid phase exceeding the fissure aperture, but rather because multiple particles act as a bridge within the fissure. Existing theoretical research suggests that injection is only possible when the fissure aperture is more than three times the particle size of the grout solid phase. Previous research (Wang Kai, Wang Lianguo, Lu Yinlong, et al. Visual experimental study on the filtration effect of cement grout in micro-fissures [J]. Journal of Coal Science and Technology, 2020, 45(03): 990-997) has prepared fissures with different apertures by placing stainless steel shims of different thicknesses between two experimental plates, and obtained the critical fissure aperture for injecting different types of grout through experiments. This method cannot achieve continuous variation of the fracture aperture; the obtained aperture is only a range value. Invention patent CN104266936A uses prefabricated fractures with a rhomboid cross-section to achieve continuous variation of the fracture aperture. The critical fracture aperture for grout injection is determined by the aperture of the fractures at the periphery of the grout diffusion. In this method, grout diffusion is affected by the already grouted section; grout diffusion stopping at a certain position may not be due to reaching the critical fracture aperture. Furthermore, invention patents CN118583727A and CN111504872A can achieve continuous variation of the fracture aperture, but the formed fractures are straight. During related grouting experiments, the cessation of grout diffusion is often not due to the aperture being less than the critical injectable aperture, but rather due to the seepage resistance encountered by the grout diffusion, failing to truly reflect problems of non-injectability purely caused by changes in fracture aperture. Summary of the Invention

[0004] Technical problem solved: To address the above-mentioned technical problems, this invention provides an apparatus and method for determining the critical fracture opening for grout injection, providing an effective means for evaluating the injectability of grouting materials and optimizing the process in geotechnical engineering.

[0005] Technical Solution: In a first aspect, the present invention provides a device for determining the critical fracture aperture for grout injection, comprising a test model frame, wherein the test model frame includes a first support and a second support arranged vertically, the first support being provided with a stepper motor, the second support being provided with a platform, and a prefabricated fracture model being provided on the platform, the prefabricated fracture model being an integrated transparent disk. The prefabricated fracture model includes an upper fracture plate and a lower fracture plate. Several supporting feet are fixedly installed on the upper surface of the lower fracture plate. The upper fracture plate is placed on the supporting feet, forming a fracture between the upper and lower fracture plates. A grout buffer chamber is formed at the center of the fracture, and the grout buffer chamber communicates with the fracture. The end of the fracture communicates with a grout discharge joint. A grouting inlet is provided at the center of the lower fracture plate. One end of the grouting inlet communicates with the grout buffer chamber, and the other end is connected to a grouting pipe via a grouting interface. The end of the push rod of the stepper motor abuts against the upper surface of the fracture plate. A fixed guide sleeve is fitted around the push rod. A displacement meter mounting bracket is provided on the second bracket. A displacement meter is provided on the displacement meter mounting bracket. The probe head of the displacement meter is vertically set on the upper surface of the fracture plate and corresponds to the position of the fracture entrance.

[0006] Preferably, the upper plate of the crack has controllable micro-deformation capability.

[0007] Preferably, a gasket is provided between the push rod and the upper plate of the slit.

[0008] Furthermore, the support foot is a retractable foot.

[0009] In a second aspect, the present invention provides a method for determining the critical fracture aperture for grout injection based on the apparatus described in the first aspect, comprising the following steps: S1, Device assembly; S2. Determine the correspondence between the propulsion amount and the opening degree; S3. Construct the grouting system; S4. Grouting and opening adjustment; S5. Determine the critical opening degree of the slurry to be tested.

[0010] Preferably, the specific process of step S1 is as follows: the upper crack plate is covered on the lower crack plate to ensure that the upper crack plate is completely attached to the upper surface of the support pad of the lower crack plate; Install the stepper motor on the first support of the test model frame, install the support platform on the second support of the test model frame, and fix the prefabricated fracture model on the support platform; make the end of the stepper motor's push rod abut against the pad at the center of the fracture upper plate; install the displacement gauge on the displacement gauge mounting bracket, so that the probe head of the displacement gauge is in perpendicular contact with the upper surface of the fracture upper plate and corresponds to the position of the fracture entrance in the vertical direction; finally connect the stepper motor power cable and the displacement gauge power cable.

[0011] Preferably, the specific process of step S2 is as follows: based on the initial crack opening corresponding to the height of the initial support pad, combined with the advance amount of the stepper motor, the correspondence between the two is calibrated, and the reference value of the critical crack opening that the grout can be injected is estimated.

[0012] Preferably, the grouting system includes a grouting pump, a grouting pipe, and a grouting pressure monitoring system. The grouting system is used to inject grout into the grout buffer chamber in the precast fracture model and monitor the grouting pressure at the same time.

[0013] Furthermore, the specific process of step S4 is as follows: start the grouting pump to inject grout into the fissure, and monitor the grouting pressure throughout the process; at the same time, control the stepper motor to advance slowly and uniformly, and press the center of the upper plate of the fissure by the push rod, so that the upper edge of the fissure entrance gradually approaches the lower edge of the fissure entrance, thereby realizing the continuous and smooth reduction of the fissure entrance opening.

[0014] Furthermore, the specific process of step S5 is as follows: real-time monitoring of grouting pressure data. When the grouting pressure rises sharply, it indicates that the grout is blocked at the fracture entrance. At this time, the vertical distance between the plane containing the upper and lower edges of the fracture entrance is the critical fracture opening that the grout to be tested can be injected into the corresponding fracture.

[0015] Beneficial Effects: This invention provides a device and method for determining the critical fracture aperture for grout injection. The device integrates high-precision mechanical drive, a customized fracture model, and real-time dynamic observation capabilities. Precise and continuous adjustment of the fracture aperture is achieved through continuous advancement by a stepper motor. Based on a transparent fracture model structure that deforms with an "inner narrowing and outer expansion" shape, the device reduces grout seepage resistance and supports visual observation of the grout's seepage and diffusion process within the fracture. During testing, changes in grouting pressure and fracture aperture are monitored simultaneously. The aperture corresponding to a sharp increase in grouting pressure is the critical fracture aperture, thus achieving integrated testing from fracture aperture control and grout migration visualization to quantitative analysis of critical parameters. The device has a simple structure and is easy to operate, providing an effective means for evaluating the injectability of grouting materials and optimizing the process in geotechnical engineering. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the device for determining the critical fracture opening for grout injection according to the present invention. Figure 2 This is a schematic diagram of the structure of the lower fracture plate in the device for determining the critical fracture opening degree for grout injection according to the present invention. Figure 3 This is a cross-sectional view of a prefabricated fracture model in a device for determining the critical fracture aperture for grout injection according to the present invention. Figure 4 This is a diagram showing the results of a grouting experiment conducted using the device of this invention; The numbers in the diagram are as follows: 1. Stepper motor, 2. Stepper motor power cord, 3. Motor slide, 4. Motor drive shaft, 5. Fixed guide sleeve, 6. Test model frame, 7. Push rod, 8. Shim, 9. Support platform, 10. Precast crack model, 11. Grouting pipe, 12. Displacement gauge fixing frame, 13. Displacement gauge, 14. Displacement gauge power cord, 15. Grout buffer chamber, 16. Lower crack plate, 17. Support pad, 18. Grouting inlet, 19. Crack inlet, 20. Grout discharge joint, 21. Precast crack, 22. Upper edge of crack inlet, 23. Lower edge of crack inlet, 24. Grouting interface, 25. Upper crack plate. Detailed Implementation

[0017] The present invention will be described in detail below with reference to specific embodiments: Example 1

[0018] like Figures 1-3 As shown, the present invention provides a device for determining the critical fracture opening for grout injection, comprising a test model frame 6, the test model frame 6 including a first support and a second support arranged vertically, the first support being equipped with a stepper motor 1, the second support being equipped with a platform 9, the platform 9 being equipped with a prefabricated fracture model 10, the prefabricated fracture model 10 being an integrated transparent disc, the prefabricated fracture model 10 including a fracture upper plate 25 and a fracture lower plate 16, the upper surface of the fracture lower plate 16 being fixedly provided with a plurality of support pads 17, the fracture upper plate 25 being disposed on the support pads 17, the fracture 21 being formed between the fracture upper plate 25 and the fracture lower plate 16, and a grout buffer chamber 15 being formed at the center, the grout buffer chamber 15 and the fracture... The crack 21 is connected, and the end of the crack 21 is connected to the grout discharge joint 20. A grouting inlet 18 is provided at the center of the crack lower plate 16. One end of the grouting inlet 18 is connected to the grout buffer chamber 15, and the other end is connected to the grouting pipe 11 through the grouting interface 24. The end of the push rod 7 of the stepper motor 1 abuts against the upper surface of the crack upper plate 25. A fixed guide sleeve 5 is sleeved on the outside of the push rod 7. The stepper motor 1 drives the motor slide 3 to move through the motor drive shaft 4, thereby driving the push rod 7 to apply a load. A displacement gauge fixing frame 12 is provided on the second bracket. A displacement gauge 13 is provided on the displacement gauge fixing frame 12. The probe head of the displacement gauge 13 is vertically set on the upper surface of the crack upper plate 25 and corresponds to the position of the crack inlet 19.

[0019] The aforementioned crack upper plate 25 has controllable micro-deformation capability, such as by using acrylic (PMMA) or flexible photosensitive resin to make the crack upper plate 25.

[0020] A gasket 8 is provided between the push rod 7 and the upper plate 25 of the fissure, so that a buffer layer is formed between the push rod 7 and the upper plate 25 of the fissure, so that the concentrated point load is evenly distributed and diffused, and the uneven force causes the upper and lower edges of the fissure entrance to close asynchronously.

[0021] The aforementioned support foot 17 is a retractable foot. Example 2

[0022] The method for determining the critical fracture aperture for grout injection based on the apparatus described in Example 1 includes the following steps: S1. Assembly of the device: The specific process is as follows: Cover the upper crack plate 25 onto the lower crack plate 16, ensuring that the upper crack plate 25 is completely attached to the upper surface of the support pad 17 of the lower crack plate 16. Install the stepper motor 1 on the first support of the test model frame 6, install the platform 9 on the second support of the test model frame 6, and fix the prefabricated fracture model 10 on the platform 9; make the end of the push rod 7 of the stepper motor 1 abut against the pad 8 at the center of the fracture upper plate 25; install the displacement meter 13 on the displacement meter fixing bracket 12, so that the probe head of the displacement meter 13 is in vertical contact with the upper surface of the fracture upper plate 25 and corresponds to the position of the fracture entrance 19 in the vertical direction; finally connect the stepper motor power cable 2 and the displacement meter power cable 14.

[0023] S2. Determine the correspondence between the advance amount and the opening. The specific process is as follows: Based on the initial crack opening corresponding to the height of the initial support pad 17, combined with the advance amount of the stepper motor 1, calibrate the correspondence between the two, and estimate the reference value of the critical crack opening that the grout can be injected.

[0024] S3. Construct a grouting system, which includes a grouting pump, a grouting pipe 11, and a grouting pressure monitoring system. The grouting system is used to inject grout into the grout buffer chamber 15 in the precast crack model 10, while monitoring the grouting pressure.

[0025] S4. Grouting and opening adjustment: The specific process is as follows: Start the grouting pump to grout into the crack 21 and monitor the grouting pressure throughout the process; at the same time, control the stepper motor 1 to advance slowly and uniformly, and press the center of the crack upper plate 25 through the push rod 7, so that the upper edge 22 of the crack entrance gradually approaches the lower edge 23 of the crack entrance, so that the opening of the crack entrance 19 is continuously and smoothly reduced.

[0026] S5. Determine the critical opening of the grout to be tested. The specific process is as follows: monitor the grouting pressure data in real time. When the grouting pressure rises sharply, it indicates that the grout is blocked at the crack inlet 19. At this time, the vertical distance between the planes where the upper edge 22 and the lower edge 23 of the crack inlet are located is the critical (minimum) crack opening that the grout to be tested can be injected into the corresponding crack. Example 3

[0027] In this embodiment, ordinary silicate cement grout was selected as the grouting material. The experiment used the hydration time of the cement grout as a variable, and an independent grouting experiment was conducted for grouts with different hydration times. By monitoring changes in grouting pressure and the flow state of the grout, the aperture corresponding to complete blockage within the fracture model was determined, and this aperture value was recorded as the critical fracture aperture that the grout could be injected under the corresponding hydration time conditions. The results are as follows: Figure 4 As shown, the critical fracture aperture of ordinary silicate cement grout exhibits a "V"-shaped trend with hydration time, initially decreasing rapidly and then slowly increasing. In the initial stage (0-200 minutes), as the hydration reaction proceeds, the grout fluidity decreases, and the critical aperture decreases rapidly. However, in the later stage (200-500 minutes), due to the formation of flocculated structures within the grout, it is more prone to overall blockage during flow, leading to a gradual increase in the critical aperture. This pattern reveals that the injectability of cement grout does not decrease monotonically with time; there is an optimal injectable time window at approximately 200 minutes, at which the injectable fracture aperture is minimized. This finding has significant guiding implications for grout preparation timing, fracture matching, and process window selection in grouting projects, emphasizing the need for time control or admixture adjustment to ensure that the grouting operation is performed at the stage of optimal grout performance.

[0028] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A device for determining the critical fracture aperture at which grout can be injected, characterized in that: The test model includes a test model frame (6), which includes a first support and a second support arranged vertically. A stepper motor (1) is provided on the first support, and a support platform (9) is provided on the second support. A prefabricated crack model (10) is provided on the support platform (9). The prefabricated crack model (10) is an integrated transparent disc. The prefabricated fracture model (10) includes a fracture upper plate (25) and a fracture lower plate (16). Several support pads (17) are fixedly installed on the upper surface of the fracture lower plate (16). The fracture upper plate (25) is installed on the support pads (17). A fracture (21) is formed between the fracture upper plate (25) and the fracture lower plate (16), and a grout buffer chamber (15) is formed at the center. The grout buffer chamber (15) is connected to the fracture (21). The end of the fracture (21) is connected to the grout discharge joint (20). A grouting inlet (18) is opened at the center of the fracture lower plate (16). One end of the grouting inlet (18) is connected to the grout buffer chamber (15), and the other end is connected to the grouting pipe (11) through the grouting interface (24). The end of the push rod (7) of the stepper motor (1) abuts against the upper surface of the fracture plate (25). The push rod (7) is fitted with a fixed guide sleeve (5). The second bracket is provided with a displacement meter fixing frame (12). The displacement meter fixing frame (12) is provided with a displacement meter (13). The probe head of the displacement meter (13) is vertically set on the upper surface of the fracture plate (25) and corresponds to the position of the fracture entrance (19).

2. The device for determining the critical fracture aperture for grout injection according to claim 1, characterized in that: The upper plate (25) with cracks has controllable micro-deformation capability.

3. The device for determining the critical fracture aperture for grout injection according to claim 1, characterized in that: A gasket (8) is provided between the push rod (7) and the upper plate of the crack (25).

4. The device for determining the critical fracture aperture for grout injection according to claim 3, characterized in that: The support foot (17) is a retractable foot.

5. A method for determining the critical fracture aperture for grout injection based on the apparatus of claim 4, characterized in that, Includes the following steps: S1, Device assembly; S2. Determine the correspondence between the propulsion amount and the opening degree; S3. Construct the grouting system; S4. Grouting and opening adjustment; S5. Determine the critical opening degree of the slurry to be tested.

6. The method according to claim 5, characterized in that, The specific process of step S1 is as follows: cover the upper crack plate (25) onto the lower crack plate (16) to ensure that the upper crack plate (25) is completely attached to the upper surface of the support pad (17) of the lower crack plate (16); The stepper motor (1) is installed on the first support of the test model frame (6), the support platform (9) is installed on the second support of the test model frame (6), and the prefabricated crack model (10) is fixedly set on the support platform (9); Make the end of the push rod (7) of the stepper motor (1) abut against the pad (8) at the center of the upper plate (25) of the crack; install the displacement meter (13) on the displacement meter holder (12) so that the probe head of the displacement meter (13) is in vertical contact with the upper surface of the upper plate (25) of the crack and corresponds to the position of the crack entrance (19) in the vertical direction; finally connect the power line (2) of the stepper motor and the power line (14) of the displacement meter.

7. The method according to claim 5, characterized in that, The specific process of step S2 is as follows: based on the initial crack opening corresponding to the height of the initial support pad (17), combined with the propulsion amount of the stepper motor (1), the correspondence between the two is calibrated, and the reference value of the critical crack opening that the grout can be injected is estimated.

8. The method according to claim 5, characterized in that, The grouting system includes a grouting pump, a grouting pipe (11), and a grouting pressure monitoring system. The grouting system is used to inject grout into the grout buffer chamber (15) in the precast crack model (10) while monitoring the grouting pressure.

9. The method according to claim 8, characterized in that, The specific process of step S4 is as follows: start the grouting pump to inject grout into the crack (21) and monitor the grouting pressure throughout the process; at the same time, control the stepper motor (1) to advance slowly and uniformly, and press the center of the crack upper plate (25) through the push rod (7) so that the upper edge (22) of the crack entrance gradually approaches the lower edge (23) of the crack entrance, so that the opening of the crack entrance (19) decreases continuously and smoothly.

10. The method according to claim 9, characterized in that, The specific process of step S5 is as follows: real-time monitoring of grouting pressure data. When the grouting pressure rises sharply, it indicates that the grout is blocked at the crack inlet (19). At this time, the vertical distance between the planes where the upper edge (22) and lower edge (23) of the crack inlet are located is the critical crack opening that the grout to be tested can be injected into the corresponding crack.

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