A method for preparing different dissolution rate samples of a dissolvable rock body

Abstract

This invention discloses a method for pre-preparing samples of anaerobic rock masses with different dissolution rates, comprising the following steps: (1) analyzing the mechanical properties of rock masses with a dissolution rate of 0% in the target area through engineering field investigation or indoor testing, and selecting similar materials for preparing anaerobic rock masses based on their mechanical properties; (2) injecting water into an ice-making silicone mold, and obtaining multiple ice balls after freezing, cooling, and demolding; (3) stirring the selected similar materials evenly and then filling them into a cylindrical mold in layers to prepare samples, with a pre-set number of ice balls evenly embedded in each layer; (4) after the samples are prepared and pre-treated, placing them in a constant temperature curing chamber to solidify and form, and obtaining anaerobic rock masses with the target dissolution rate after demolding and curing. This invention provides a simple, mild, matrix-free, and controllable laboratory sample preparation method for anaerobic rock masses, providing direction for subsequent research on the mechanical properties of anaerobic rock masses.

Description

Technical Field

[0001] This invention relates to the field of rock-like materials technology, specifically to the preparation of samples of dissolved rock masses with different dissolution rates. Background Technology

[0002] The study of karst rock masses is widely recognized as a "challenge" in the fields of geology and geotechnical engineering. The core difficulty lies in the extreme uncertainty of the system. Karst rock masses exhibit strong spatial irregularity. Because surface water and groundwater selectively dissolve along the fissures and joints of rocks, caves and pores of varying sizes and shapes appear inside the rock mass. This results in significant differences in the physical and mechanical properties of the rock mass in different directions.

[0003] Given the importance of karst rock masses in major engineering projects, it is necessary to study the mechanical properties of rock masses with different dissolution rates. In-situ sampling is the most direct method to obtain the physical and mechanical parameters of rocks, offering both intuitiveness and in-situ accuracy. Accurate data can be obtained through experiments such as uniaxial compression and triaxial compression. However, in-situ sampling also has limitations and high risks. Due to the extremely strong heterogeneity of karst rock masses, we can only observe the surface rock mass, without knowing its internal structure. Furthermore, the structure of karst areas is uncertain, introducing unknown risks during the sampling process, thus making in-situ sampling difficult.

[0004] To overcome the limitations of on-site sampling, it is common practice to artificially create karst rock samples in the laboratory for simulation. Currently, the pore-forming materials used to create karst rock samples mainly include soluble materials such as industrial salt and paraffin. However, these materials have significant shortcomings in practical applications: First, the dissolution conditions for materials such as industrial salt and paraffin are quite demanding (e.g., requiring specific solvents, high temperatures, or prolonged immersion), making the process complex; second, these materials, or their residues, may cause chemical contamination of the rock sample matrix during dissolution, thus affecting the accuracy and reliability of subsequent mechanical test results. Summary of the Invention

[0005] Therefore, the purpose of this invention is to provide a laboratory-scale sample preparation method for karst rock masses that is simple to operate, operates under mild conditions, is free from matrix contamination, and can control the dissolution rate, thus providing direction for subsequent research on the mechanical properties of karst rock masses.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for pre-preparing samples of dissolution rock masses with different dissolution rates includes the following steps: (1) Analyze the mechanical properties of rock masses with a dissolution rate of 0% in the target area through on-site engineering investigation or indoor testing, and select similar materials for making dissolution rock masses in the target area based on their mechanical properties and geometric similarity ratio; (2) Water is poured into the ice-making silicone mold, and after freezing, cooling and molding, multiple ice balls are obtained; (3) After the selected similar materials are stirred evenly, they are filled into the cylindrical mold in layers to make the sample. Each layer is evenly filled with a pre-set number of ice balls. The number of filling layers and the number of ice balls are determined according to the preset erosion rate, which is 0%-20%. (4) After the sample is prepared and pretreated, it is placed in a constant temperature curing box to solidify and form. Then the sample is demolded and cured to obtain a dissolution-like rock mass with the target dissolution rate.

[0007] In one alternative embodiment, in step (1), the raw material composition and mass ratio of the similar materials are river sand: cement: barite powder: water = 13:4:4:3.

[0008] In one alternative embodiment, in step (2), the diameter of the ice ball is 1 cm.

[0009] In one alternative implementation, in step (2), the mold is filled during the water injection process.

[0010] In an optional embodiment, in step (3), the spacing between adjacent ice balls in the upper and lower layers of the sample is 0.8 to 1.5 cm, and the spacing between adjacent ice balls in the same layer is 0.4 to 0.55 cm.

[0011] In one alternative embodiment, in step (3), the cylindrical mold has a size of 50mm*100mm.

[0012] Compared with the prior art, the technical solution of the present invention has the following advantages: (1) This invention determines the number and layers of ice balls in each layer by pre-setting the dissolution rate, and pre-embeds a fixed number of ice balls with a fixed diameter (1 cm), which can form a regular and controllable dissolution pore structure inside the sample. Compared with the unpredictability of on-site sampling and the difficulty in accurately controlling the degree of dissolution with pore-forming materials such as industrial salt and paraffin, this invention significantly improves the preparation accuracy and experimental repeatability of dissolution rock mass samples.

[0013] (2) This invention uses ice balls as the pore-forming material. The ice balls melt naturally at room temperature or under curing conditions to form pores without the need for any chemical solvents or high-temperature treatment. The dissolution conditions are mild and the operation is simple. At the same time, the ice melts and only produces water, which will not cause any chemical pollution or residual interference to the mineral composition, cementation structure and physical and mechanical properties of the rock sample matrix. This ensures the authenticity and reliability of the subsequent mechanical test results such as uniaxial compression and triaxial compression, and overcomes the defect that industrial salt, paraffin and other materials are prone to contaminating the matrix.

[0014] (3) By using layered filling and uniformly pre-embedded ice balls in each layer, and by reasonably controlling the spacing between adjacent ice balls in the upper and lower layers and the spacing between adjacent ice balls in the same layer, this invention can effectively avoid the interconnection or excessive sparseness between dissolution pores, resulting in a uniform distribution and controllable anisotropy of dissolution pores inside the sample. In addition, by uniformly setting the diameter of the ice balls to 1 cm, the size of the resulting dissolution pores is consistent, which facilitates the quantitative study of the mechanical response law of rock mass under different dissolution rates.

[0015] (4) The method used in this invention does not require complex dissolution equipment or expensive reagents. The ice ball is made by freezing with a silicone mold, and the sample preparation uses a conventional cylindrical mold and a constant temperature curing chamber. The process is simple, short, and low-cost. At the same time, it avoids the unknown geological risks in field sampling, and the laboratory operation is safe and controllable. It is suitable for large-scale application in the study of karst rock masses in the fields of geotechnical engineering and geomechanics. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the ice hockey puck arrangement in Embodiment 1 of the present invention.

[0017] Figure 2 for Figure 1 A schematic diagram of the cross-section of the sample ice ball arrangement.

[0018] Figure 3 for Figure 1 A schematic diagram of the cave formed after the ice ball of the sample melted.

[0019] Figure 4 for Figure 3 A schematic diagram of the cross-section of the sample cavity.

[0020] Figure 5 This is a graph showing the relationship between the erosion rate and uniaxial compressive strength of the present invention.

[0021] Figure 6 This is a graph showing the relationship between the erosion rate and the elastic modulus of the present invention. Detailed Implementation

[0022] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present application.

[0023] Example 1 The following steps were taken to prepare a sample of a dissolution-like rock mass with a dissolution rate of 15%: (1) By analyzing the mechanical properties of the rock mass with a dissolution rate of 0% in the target area (the Huayingshan Tunnel area of ​​Xiyu High-speed Railway in Dazhu County, Dazhou City, Sichuan Province) through on-site engineering investigation or indoor testing, a geometric similarity ratio of 5 was selected.

[0024] (2) Prepare similar materials for making karst rock bodies, 50mm*100mm cylindrical molds made of ABS material, ice-making silicone molds (all with a diameter of 1cm), electronic scales, mixers, release oil, spatulas and other experimental tools.

[0025] (3) Before the experiment, use a syringe to inject water into the ice-making silicone mold. After completion, put it in the refrigerator (note that each mold should be filled during the water injection process to prevent air bubbles from appearing inside the mold). After it cools and solidifies, demold it and select ice balls with full shape and no gaps to put in the storage box for later use. The purpose of making ice balls with molds of the same size is to ensure that each ice ball is the same size.

[0026] (4) Calculate the required number of ice balls: Calculate the required ice ball volume percentage based on the preset dissolution rate (the percentage of ice ball volume to the total sample volume). Then, determine the total number of ice balls required for each sample block by calculating the volume of a single ice ball, as shown in the following formula:

[0027] Where n is the required number of ice balls, C is the dissolution rate, and V... 总 For a cylindrical specimen measuring 50mm x 100mm, V 球 The volume of a single ice puck is 1cm in diameter. Determine the number of material layers and the number of ice pucks to be embedded in each layer. Each layer needs to embed the same number of ice pucks. The number of layers and the number of ice pucks in each layer are determined based on the total number of ice pucks.

[0028] Based on the formula above, a dissolution rate of 15% requires 56 ice balls to be pre-embedded in the eroded rock mass. The design specifies a spacing of 1 cm between adjacent layers of ice balls, meaning 9 layers are arranged, with 6 ice balls evenly distributed in each layer, for a total of 54 ice balls (removing 2 has little impact). The spacing between two adjacent ice balls in the same layer is approximately 0.5 cm.

[0029] The number of layers and the arrangement of the ice hockey pucks are as follows: Figure 1 and Figure 2 As shown, A represents a type of karst rock mass; B represents an ice ball. The internal structure of the sample after the ice ball melts is shown below. Figure 3 and Figure 4 As shown.

[0030] It should be noted that when arranging the ice balls, the distance between adjacent layers of ice balls should not exceed twice the distance between two adjacent ice balls in the same layer. This will ensure that the ice balls are evenly distributed in the sample.

[0031] (5) Select similar materials for making the karst rock mass. Based on the mechanical properties and geometric similarity ratio of the karst rock mass in step (1), determine the ingredients and mass ratio of the similar materials as river sand: cement: barite powder: water = 13:4:4:3. Use an electronic scale to accurately measure the weight of each material. Then put all the materials into a mixer and stir for 3-5 minutes until the color is uniform.

[0032] The process for determining the proportions and mass ratios of similar materials is as follows: Based on previous experience in preparing similar materials, river sand, barite powder, cement, and water were used to prepare the similar materials. An orthogonal design scheme was employed, with four factors and four levels, resulting in 16 schemes, as shown in Table 1. Uniaxial compression tests were conducted on the similar material specimens to obtain the stress-strain curves and model mechanical parameters. Based on the principle of geometric similarity and the mechanical parameters of the original rock and the rock mass under ideal conditions, the final mass ratio of the similar materials was determined to be river sand:cement:barite powder:water = 13:4:4:3.

[0033] Table 1

[0034] (6) Apply a layer of oil to the inner wall and bottom of the cylindrical experimental mold to facilitate demolding after the sample solidifies.

[0035] (7) Fill the cylindrical mold with the mixed similar material in layers, each time with the same mass of similar material. Place an ice ball on each layer of material, and arrange the ice balls in a five-pointed star shape on each layer of similar material, with another one placed in the center to ensure uniform distribution. When filling the sixth layer of material, compact it. After compaction, roughen the surface with the tip of a trowel (the purpose is to ensure full contact between the upper and lower layers of similar material to prevent the test block from being cut directly along the horizontal layer line during the uniaxial compression test, which would cause the test to fail). The roughening depth is about 1-2 mm.

[0036] (8) After the sample is filled, scrape off the excess material on the surface with a spatula and smooth the surface. Finally, wrap the sample surface with plastic wrap and place it in a constant temperature curing box to wait for the sample to solidify.

[0037] (9) After 24 hours, the sample was demolded and then placed in a constant temperature curing chamber and cured under standard curing conditions for 28 days to obtain a dissolved rock mass with a dissolution rate of 15%.

[0038] Example 2 A pre-prepared sample of a 5% dissolution-like rock mass was prepared using the same process as in Example 1, except for the number of ice balls and their layered arrangement. Based on the calculation formula in Example 1, a total of 18 ice balls were required, arranged in 6 layers, with 3 ice balls in each layer. The spacing between ice balls in adjacent layers was approximately 1.4 cm, and the spacing between adjacent ice balls within the same layer was approximately 0.52 cm, resulting in a 5% dissolution-like rock mass.

[0039] It should be noted that when arranging ice pucks, if the distance between ice pucks in adjacent layers is much greater than twice the distance between two adjacent ice pucks in the same layer, 2-3 ice pucks should be reduced per layer (relative to the number of ice pucks arranged per layer in Example 1) to increase the number of layers and achieve a uniform arrangement.

[0040] Example 3 A pre-prepared sample of a 20% dissolution rate was constructed using the same process as in Example 1, except for the number of ice balls and their layered arrangement. Based on the calculation formula in Example 1, a total of 75 ice balls were required, arranged in 11 layers, with 7 ice balls per layer (adding 2 more had little impact). The spacing between ice balls in adjacent layers was approximately 0.8 cm, and the spacing between adjacent ice balls within the same layer was approximately 0.43 cm, resulting in a 20% dissolution rate anaerobic rock mass.

[0041] It should be noted that when arranging the ice balls, if the distance between ice balls in adjacent layers is less than twice the distance between adjacent ice balls in the same layer, 1-2 more ice balls should be added to each layer (relative to the number of ice balls arranged in each layer in Example 1) to reduce layering and achieve uniform arrangement. Once the maximum porosity exceeds 20%, the specimen cannot be formed due to the close spacing between the ice balls (less than 1 cm), therefore the maximum is limited to 20%.

[0042] Example 4 A pre-prepared sample of a 10% dissolution rate was prepared using the same process as in Example 1, except for the number of ice balls and their layered arrangement. Based on the calculation formula in Example 1, a total of 37 ice balls were required, arranged in 9 layers, with 4 ice balls in each layer. The spacing between ice balls in adjacent layers was approximately 1.1 cm, and the spacing between adjacent ice balls in the same layer was approximately 0.51 cm, resulting in a 10% dissolution rate anaerobic rock mass.

[0043] It should be noted that when arranging ice pucks, if the distance between ice pucks in adjacent layers is slightly greater than twice the distance between two adjacent ice pucks in the same layer, 1-2 ice pucks should be reduced per layer (relative to the number of ice pucks arranged per layer in Example 1) to increase the number of layers and achieve a uniform arrangement.

[0044] Test case The two ends of the samples prepared in Examples 1-4 above were polished. The prepared dissolved rock mass specimens (three specimens for each dissolution rate of 5%, 10%, 15%, and 20%) were subjected to uniaxial compression tests. A dissolved rock mass with a dissolution rate of 0% was used as a control. Acoustic emission events were monitored during loading to obtain the strength parameters of the dissolved rock mass at different dissolution rates and its deformation and failure mechanism. The uniaxial compression test process is as follows: (1) Place the polished test block on the servo press and use transparent tape to fix the four acoustic emission probes at 1 / 3 and 2 / 3 of the height of the side and back of the test block, respectively. Then connect the probes to the acoustic emission instrument. Ensure that the probes are properly fixed to prevent the lack of data during the test.

[0045] (2) Turn on the acoustic emission instrument, set the data import folder and probe position parameters, and ensure that the instrument measurement system is working properly. Start the servo press computer and enter the instrument control interface to set the relevant parameters for this test.

[0046] (3) Start the test run. Before running, clear the load to zero and use an acoustic emission instrument to monitor the deformation and failure of the test block.

[0047] (4) Observe the computer of the servo press. When the sample is compressed, the load change will be displayed on the computer interface. The load curve will reach a peak and begin to decline. At this time, observe the acoustic emission signal displayed on the acoustic emission instrument. When the acoustic emission signal suddenly increases explosively, stop running immediately and record the data.

[0048] (5) Repeat steps (1)-(4) to complete the measurement of the remaining test blocks. After completion, turn off the test instrument and analyze the test data.

[0049] Table 2 shows the uniaxial compressive strength and elastic modulus of karst-like rock masses under different dissolution rates. The fitting relationship between dissolution rate and uniaxial compressive strength is as follows: Figure 5 As shown, the fitting relationship between the dissolution rate and the elastic modulus is as follows: Figure 6 As shown in the figure. Based on the curve fitting formula and similarity ratio, the relationship between the uniaxial strength and elastic modulus of the karst rock mass and the dissolution rate can be obtained as shown in the following formula, which can be used to estimate the mechanical parameters of the karst rock mass.

[0050]

[0051] In the formula: E represents the uniaxial compressive strength of the dissolved rock mass, in MPa. k is the dissolution rate. m The elastic modulus of the dissolved rock mass. The geometric similarity ratio is 5.

[0052] Table 2 Uniaxial compressive strength and elastic modulus of karst-like rock masses under different dissolution rates

[0053] Three groups of intact original rocks with dissolution rates of 0, 5, 10, 15, and 20, collected from different sampling points in the same area of ​​Dazhu County, Dazhou City, Sichuan Province, were randomly selected for uniaxial compression tests. The uniaxial compression test process was the same as above. The results were compared with the uniaxial compressive strength and elastic modulus of similar dissolution rock masses with different dissolution rates prepared in this invention (calculated by the relationship between the uniaxial strength and elastic modulus of the above-mentioned similar dissolution rock masses and the dissolution rate). The results are shown in Table 3 (the model represents the sample (similar dissolution rock mass) prepared in this invention, and the dissolution rate is directly substituted into the formula for calculation).

[0054] Table 3 Uniaxial compressive strength and elastic modulus of dissolved and quasi-dissolved rock masses under different dissolution rates

[0055] As shown in Table 3, the maximum error between the model results and the experimental results is 10.00%, indicating relatively high reliability and credibility. The model results are highly similar to the original rock, indicating that the similar model test prepared by the preparation method of this application can qualitatively and quantitatively reflect the stress characteristics of natural rock masses, which has important guiding significance for analyzing actual geotechnical engineering problems related to the construction process.

[0056] Although the present invention has been described using the above preferred embodiments, it is not intended to limit the scope of protection of the present invention. Any changes and modifications made by those skilled in the art to the above embodiments without departing from the spirit and scope of the present invention shall still fall within the scope of protection of the present invention.

Claims

1. A method for pre-preparing samples of dissolution-type rock masses with different dissolution rates, characterized in that, Includes the following steps: (1) Analyze the mechanical properties of rock masses with a dissolution rate of 0% in the target area through on-site engineering investigation or indoor testing, and select similar materials for making dissolution rock masses in the target area based on their mechanical properties and geometric similarity ratio; (2) Water is poured into the ice-making silicone mold, and after freezing, cooling and molding, multiple ice balls are obtained; (3) After the selected similar materials are stirred evenly, they are filled into the cylindrical mold in layers to make the sample. Each layer is evenly filled with a pre-set number of ice balls. The number of filling layers and the number of ice balls are determined according to the preset erosion rate, which is 0%-20%. (4) After the sample is prepared and pretreated, it is placed in a constant temperature curing box to solidify and form. Then the sample is demolded and cured to obtain a dissolution-like rock mass with the target dissolution rate.

2. The method for pre-preparing samples of dissolution rock masses with different dissolution rates according to claim 1, characterized in that, In step (1), the raw material composition and mass ratio of the similar materials are river sand: cement: barite powder: water = 13:4:4:

3.

3. The method for pre-preparing samples of dissolution rock masses with different dissolution rates according to claim 1, characterized in that, In step (2), the diameter of the ice ball is 1 cm.

4. The method for pre-preparing samples of dissolution rock masses with different dissolution rates according to claim 1, characterized in that, In step (2), the mold is filled during the water injection process.

5. The method for pre-preparing samples of dissolution rock masses with different dissolution rates according to claim 1, characterized in that, In step (3), the distance between adjacent ice balls in the upper and lower layers of the sample is 0.8 to 1.5 cm, and the distance between adjacent ice balls in the same layer is 0.4 to 0.55 cm.

6. The method for pre-preparing samples of dissolution rock masses with different dissolution rates according to claim 1, characterized in that, In step (3), the cylindrical mold has a size of 50mm*100mm.

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