Preparation method of geotechnical sample containing prefabricated hole defects

Abstract

The invention discloses a preparation method of a geotechnical sample containing prefabricated hole defects, and relates to the field of geotechnical sample preparation. Comprising the following steps: preparing ice particles to simulate hole defects, preparing sample preparation soil with optimal water content, setting a distribution mode of the hole defects, compacting and molding a geotechnical sample, demolding, and carrying out sealed room-temperature maintenance on the geotechnical sample containing prefabricated hole defects. The size and the number of the ice particles can be determined according to the specific type of the simulated hole defect, the size and the distribution precision of the hole defect and the hole defect actually formed after the ice particles are melted can be better controlled, compared with the prior art, the accuracy of simulating the hole defect is improved, and meanwhile the method is more environmentally friendly.

Description

Technical Field

[0001] This invention relates to the field of geotechnical specimen preparation, and in particular to a method for preparing geotechnical specimens with pre-fabricated void defects. Background Technology

[0002] With my country's economic and social development, the scale of completed and under-construction infrastructure projects continues to expand, including road and railway engineering, mining and tunnel engineering, underground space engineering, water conservancy and waterway engineering, slope protection engineering, and foundation engineering, among other typical civil engineering projects. These existing projects are massive in scale, and some are of high construction standards. During construction and service, various main projects and supporting facilities inevitably develop porous soil structures due to the influence of biological, climatic, hydrological, and geological factors. The presence of these porous defects severely affects the strength, deformation, permeability, and stability of the original soil structure, further impacting the safety and serviceability of geotechnical engineering. Therefore, it is necessary to conduct research on the soil mechanical properties of geotechnical samples containing porous defects to more scientifically and accurately assess the safe serviceability of porous soil structures.

[0003] Currently, the preparation of defects (cracks or pores) in geotechnical specimens mainly focuses on surface defect design, which is primarily achieved through pre-compression or cutting. However, due to the inherent limitations of these two techniques, they cannot be effectively extended to the fabrication of internal defects. Existing methods for fabricating internal pore defects mainly fall into two categories: one is "substituting the real for the virtual," which uses stable solid spherical units to simulate pore defects. A significant drawback of this method is that the solid spherical units cannot be removed from the specimen, and their parameters differ significantly from those of pores, often making accurate simulation difficult. For example, the literature "Experimental Study on Mechanical Properties of Grouted Solidified Bodies with Internal Defects" utilizes the "thermal melting effect" of paraffin wax to simulate pore defects inside grouted solidified specimens. However, this simulation method is only suitable for strength studies of grouted solidified bodies and is not feasible for permeability studies. Furthermore, because the strength difference between solid paraffin wax and geotechnical specimens is small, this method will produce significant errors in strength studies of geotechnical specimens, and it remains infeasible for permeability studies. Therefore, the application of this simulation method has significant limitations. Another approach is to "transform the real into the virtual," which involves using unstable solid spherical units and simulating pore defects after their physical phases change. For example, invention patent ZL201410113738.9 innovatively utilizes the "tin plague effect" of metallic tin to simulate pore defects inside rock samples using tin balls. It should be noted that: firstly, tin has a significant density difference from cement mortar, making it easy for stratification and sorting to occur during the vibration molding process, making it difficult to ensure a reasonable distribution of pore defects within the sample; secondly, the tin plague process increases the volume of the tin balls by approximately 20%, leading to errors in the size and shape of the originally designed pore defects; furthermore, the use of tin easily causes air, water, and soil pollution, thus the material lacks green, healthy, and environmentally friendly properties. In summary, existing technologies cannot achieve the desired results in preparing geotechnical samples with pre-fabricated pore defects, necessitating a highly operable, precise, and environmentally friendly method for preparing geotechnical samples with pre-fabricated pore defects. Summary of the Invention

[0004] To address the above technical problems, this invention provides a method for preparing geotechnical specimens with pre-fabricated void defects.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing a geotechnical specimen with pre-fabricated void defects includes the following steps: a. Preparation of ice particles to simulate pore defects: ice particles are prepared by placing cotton fibers in an ice mold, filling it with distilled water, and then freezing it at a constant temperature in a refrigerator. b. Prepare soil for the optimal moisture content: Weigh the dried soil sample required for the preparation of the geotechnical sample, calculate the required amount of distilled water, add the required amount of distilled water evenly to the dried soil sample, stir and mix thoroughly to ensure uniform moisture distribution, seal and let stand for 24 hours, and then sieve. c. Define the distribution pattern of the hole defects: This includes the size and spatial location of the hole defects. Specific distribution patterns include: Once the location of the hole defect is determined, compact the soil for sample preparation to the target height inside the sample preparation mold, and position the ice particles at the target height surface; When the location of the pores and defects is random, the ice particles are mixed with the soil used for sample preparation, and then the mixture is placed into the sample preparation mold and compacted. d. The geotechnical specimen is compacted, molded, and then demolded; e. Seal and cure geotechnical samples containing pre-fabricated void defects at room temperature.

[0006] More preferably, the ice mold is made of low-temperature resistant silicone rubber material, with a low temperature tolerance value not exceeding -50℃. The shape of the ice mold includes, but is not limited to, a standard sphere, cube, tetrahedron, ellipsoid, and / or a shape customized according to the test requirements. The length of the cotton fiber does not exceed the diameter of a single ice ball. The size and number of the ice particles are determined according to the specific type of hole defect being simulated. Before use, the ice particles are placed in a constant temperature chamber at -5℃ to -2℃ for constant temperature static setting.

[0007] More preferably, the required amount of distilled water is calculated according to the following formula: required amount of distilled water = weight of dried soil sample × optimal moisture content; the sieving process includes: sieving using a sieve with a mesh size of 2 mm.

[0008] More preferably, the soil used for sample preparation is pre-cooled in a test chamber at -1℃ to 0℃ before use to ensure that the temperature difference between the ice particles and the soil used for sample preparation does not exceed 4℃.

[0009] More preferably, the process of compacting the soil to the target height, the process of mixing ice particles with the soil, and the process of compacting and demolding the geotechnical sample are all completed in a constant temperature test chamber, with the temperature of the test chamber being higher than -1℃ and lower than 0℃.

[0010] In a further preferred embodiment, step c, which involves compacting the soil for sample preparation to the target height and positioning the ice particles on the target height surface, includes: determining the mass of soil for sample preparation for different geotechnical sample sections based on the controlled dry density of the geotechnical sample required by the specific engineering project; compacting to the target height; positioning the ice particles on the target height surface; and roughening the remaining positions on the target height surface to ensure that the integrity of the ice particles is not damaged; repeating this layered compaction process until a complete geotechnical sample is obtained.

[0011] In a further preferred embodiment, the mixing of ice particles with soil for sample preparation in step c, and the loading and compaction of the mixture into a sample preparation mold, includes: determining the required mass of soil for complete geotechnical sample preparation based on the controlled dry density of the geotechnical sample according to the specific requirements of the project; thoroughly mixing the ice particles with the soil for sample preparation until homogeneous; compacting the mixture in layers to the target height; roughening the remaining areas within the target height surface to ensure that the integrity of the ice particles is not damaged; and repeating the layered compaction process until a complete geotechnical sample is obtained.

[0012] In a further preferred embodiment, in step e, the geotechnical sample containing pre-fabricated hole defects is sealed and cured at room temperature for a period of not less than 48 hours, and the curing temperature is 20℃~25℃.

[0013] The technological advancements achieved by this invention compared to existing technologies are as follows: This invention can determine the distribution location, size, and number of ice particles based on the specific type, size, and number of the hole defects to be simulated. It can better simulate the size, number, and distribution accuracy of hole defects. The hole defects actually formed after the ice particles melt are improved in accuracy compared with the prior art. This invention uses ice particles to simulate pore defects. After the ice particles melt, they are mainly water, which does not pollute the environment and is more environmentally friendly. This invention strengthens ice particles by reinforcing them with cotton fibers, making the ice particles less prone to breakage during sample preparation and ensuring the effective inheritance of the geometric dimensions of the pre-fabricated pore defects from those of the ice particles. Furthermore, the cotton fibers within the pore defects do not provide fiber reinforcement or skeletal support to the geotechnical sample, thus enhancing the fidelity of the pore defects. Attached Figure Description

[0014] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof.

[0015] In the attached diagram: Figure 1 This is a flowchart of the method for preparing geotechnical specimens with pre-fabricated void defects according to the present invention.

[0016] Figure 2 This is a schematic diagram of fiber-reinforced ice particles used to simulate pore defects according to the present invention.

[0017] Figure 3 This is a schematic diagram of a geotechnical sample containing pre-fabricated void defects according to the present invention. Detailed Implementation

[0018] The embodiments of the present invention will now be described with reference to the accompanying drawings.

[0019] like Figures 1 to 3 As shown, the specific process of preparing a geotechnical specimen with pre-fabricated void defects according to the present invention is as follows: Step 1: Prepare ice particles to simulate pore defects. The specific method is as follows: After placing cotton fibers inside the ice mold, fill it with distilled water and place the ice mold in a freezer to freeze at a constant temperature. The size and quantity of ice particles (selection of ice mold) are determined according to the specific type of hole defect being simulated. Before use, the ice particles should be placed in a constant temperature chamber at -5℃ to -2℃. The ice mold is made of low-temperature resistant silicone rubber, with a low temperature tolerance not exceeding -50℃. The shape of the ice mold includes, but is not limited to, standard spheres, cubes, tetrahedrons, ellipsoids, and / or customized shapes according to experimental requirements. Depending on the experimental requirements, a single ice mold can be used, or different shapes of ice molds can be mixed and used in combination. Alternatively, ice molds of the required shape can be customized according to experimental requirements. The length of the cotton fibers should not exceed the diameter of a single ice ball.

[0020] Step 2: Prepare soil samples with the optimal moisture content. The specific method is as follows: Weigh the dried soil sample required for preparing the geotechnical sample, calculate the required amount of distilled water, and mix the distilled water and soil sample thoroughly at the optimal moisture content. After standing at room temperature for 24 hours in a sealed container, break up the lumps in the soil sample and sieve them (sieve mesh size 2 mm) for later use. Before use, the soil used for sample preparation should be pre-cooled in a test chamber at -1℃ to 0℃ to ensure that the temperature difference between the ice particles and the soil used for sample preparation does not exceed 4℃.

[0021] The required amount of distilled water is calculated using the following formula: Required amount of distilled water = Weight of dried soil sample × Optimal moisture content. The optimal moisture content varies depending on the soil type and must be determined based on the specific project conditions.

[0022] Step 3: Define the distribution pattern of the hole defects. The specific method is as follows: Based on the characteristics of the research question, the distribution pattern of pores and defects inside the geotechnical sample is defined, including but not limited to the distribution of pore and defect size or spatial location.

[0023] If the location of the hole defect is determined, compact the soil used for sample preparation to the target height inside the mold, and locate the ice particles at the target height surface. The specific method is as follows: Geotechnical samples were prepared in a constant-temperature test chamber, with the chamber temperature controlled between -1℃ and 0℃. The mass of different soil sample segments was determined based on the controlled dry density of the geotechnical samples. After compaction to the target height, ice particles were positioned within the target height plane. Following current geotechnical testing procedures, the remaining areas within the target height plane were roughened. This layered compaction process was repeated until a complete geotechnical sample was obtained. The mass of each soil sample segment = volume of each soil sample segment × controlled dry density.

[0024] If the location of the pores and defects is random, the ice particles are mixed with the test soil, and the ice-soil mixture is filled into the sample preparation mold and compacted. The specific method is as follows: Geotechnical specimens were prepared in a constant-temperature test chamber, with the chamber temperature controlled between -1°C and 0°C. The required mass of soil sample for a complete geotechnical specimen was determined based on the controlled dry density of the specimen. The volumetric parameters of the soil mass needed correction using the formula: Soil volume = Apparent volume of geotechnical specimen - Defect volume of geotechnical specimen. The ice particles were thoroughly mixed with the soil sample until homogeneous. Following current geotechnical testing procedures, the mixture was compacted in layers to the target height, followed by roughening. It is important to note that this roughening process should not damage the integrity of the ice particles. This process was repeated until the geotechnical specimen was fully compacted.

[0025] Step 4: Compact and demold the geotechnical sample. The specific method is as follows: After the geotechnical specimens were prepared, they were demolded using a demolding machine. The demolding process was completed in a constant temperature test chamber, where the temperature was controlled between -1℃ and 0℃.

[0026] Step 5: Obtain geotechnical samples with pre-fabricated hole defects by sealing and curing at room temperature.

[0027] The demolded geotechnical specimens were sealed with plastic wrap and placed in sealed bags. After labeling the geotechnical specimens with their parameters, they were placed at room temperature for at least 48 hours. The curing temperature was 20℃~25℃.

[0028] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a geotechnical specimen containing pre-fabricated void defects, characterized in that, Includes the following steps: a. Preparation of ice particles to simulate pore defects: ice particles are prepared by placing cotton fibers in an ice mold, filling it with distilled water, and then freezing it at a constant temperature in a refrigerator. b. Prepare soil for the optimal moisture content: Weigh the dried soil sample required for the preparation of the geotechnical sample, calculate the required amount of distilled water, add the required amount of distilled water evenly to the dried soil sample, stir and mix thoroughly to ensure uniform moisture distribution, seal and let stand for 24 hours, and then sieve. c. Define the distribution pattern of the hole defects: This includes the size and spatial location of the hole defects. Specific distribution patterns include: Once the location of the hole defect is determined, compact the soil for sample preparation to the target height inside the sample preparation mold, and position the ice particles at the target height surface; When the location of the pores and defects is random, the ice particles are mixed with the soil used for sample preparation, and then the mixture is placed into the sample preparation mold and compacted. d. The geotechnical specimen is compacted, molded, and then demolded; e. Seal and cure geotechnical samples containing pre-fabricated void defects at room temperature.

2. The method for preparing a geotechnical specimen with pre-fabricated void defects according to claim 1, characterized in that, In step a, the ice mold is made of low-temperature resistant silicone rubber, with a low temperature tolerance of no more than -50℃. The shape of the ice mold includes, but is not limited to, a standard sphere, cube, tetrahedron, ellipsoid, and / or a shape customized according to the test requirements. The length of the cotton fiber does not exceed the diameter of a single ice ball. The size and number of ice particles are determined according to the specific type of hole defect being simulated. Before use, the ice particles are placed in a constant temperature chamber at -5℃ to -2℃ for constant temperature static setting.

3. The method for preparing a geotechnical specimen with pre-fabricated void defects according to claim 1, characterized in that, The required amount of distilled water in step b is calculated using the following formula: Required amount of distilled water = weight of dried soil sample × optimum moisture content; The sieving process includes sieving using a sieve with a mesh size of 2 mm.

4. The method for preparing a geotechnical specimen with pre-fabricated void defects according to claim 1, characterized in that, Before using the soil for sample preparation in step b, it should be pre-cooled in a test chamber at -1℃ to 0℃ to ensure that the temperature difference between the ice particles and the soil for sample preparation does not exceed 4℃.

5. The method for preparing a geotechnical specimen with pre-fabricated void defects according to claim 1, characterized in that, The process of compacting the soil to the target height, mixing ice particles with the soil, and compacting and demolding the geotechnical sample are all completed in a constant temperature test chamber, where the temperature is above -1℃ and below 0℃.

6. The method for preparing a geotechnical specimen with pre-fabricated void defects according to claim 5, characterized in that, Step c, which involves compacting the soil for sample preparation to the target height and positioning the ice particles at the target height, includes: determining the mass of soil for different geotechnical sample sections based on the controlled dry density of the geotechnical sample required by the specific engineering project; compacting to the target height; positioning the ice particles at the target height; and roughening the remaining areas at the target height to ensure that the integrity of the ice particles is not damaged. This layered compaction process is repeated until a complete geotechnical sample is obtained.

7. The method for preparing a geotechnical specimen with pre-fabricated void defects according to claim 1, characterized in that, The mixing of ice particles with soil for sample preparation in step c, and the loading and compaction of the mixture into the sample preparation mold, includes: determining the required mass of soil for complete geotechnical sample preparation based on the control dry density of the geotechnical sample according to the specific requirements of the project; thoroughly mixing the ice particles with the soil for sample preparation until uniform; compacting the mixture in layers to the target height; roughening the remaining areas within the target height surface to ensure that the integrity of the ice particles is not damaged; and repeating the layered compaction process until a complete geotechnical sample is obtained.

8. The method for preparing a geotechnical specimen with pre-fabricated void defects according to claim 1, characterized in that, In step e, the geotechnical sample containing precast void defects is sealed and cured at room temperature for no less than 48 hours, and the curing temperature is 20℃~25℃.

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