MICP layered grouting solidified calcareous sand sample preparation instrument and sample preparation method
Through the MICP layered grouting and curing calcium sand sample preparation and method, the problems of uneven curing and poor integrity of calcium sand sample in the prior art are solved, and efficient and uniform curing effect is achieved, while protecting the marine environment.
Patent Information
- Application Number
- CN202310967768.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2023-08-03
- Publication Date
- 2025-07-18
AI Technical Summary
The existing MICP cured calcium sand samples have problems such as uneven curing, poor integrity, and the inability to take into account both curing efficiency and marine environmental protection.
The MICP layered grouting cured calcium sand sample preparation and sample preparation method are used to divide calcium sand into multiple parts, and each part of the sand sample is distributed inlet through holes on the layered positioning permeable plate. The grouting area is dispersed by the layered positioning rod and permeable bottom cover to achieve multiple concentrated area solidification, ensuring that each grouting enters from above the sand sample, avoiding blockage, and injecting and discharge slurry through the water inlet through holes and drainage through holes.
It significantly improves the integrity and uniformity of the calcium sand sample, improves the curing efficiency, reduces the amount of bacterial fluid and cementitious fluid, takes into account marine environmental protection, and avoids disturbances and blockage problems caused by repeated grouting.
Smart Images
Figure CN120333936A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of microbial solidification, and specifically relates to a MICP layered grouting solidification calcareous sand sample preparation instrument and a sample preparation method. Background Art
[0002] The reefs of the South China Sea Islands in China are mainly composed of coral reefs, and their main component is calcareous sand, that is, calcareous minerals with a particle size < 2 mm. Compared with spherical quartz sand, calcareous sand has the characteristics of irregular shape, dense micropores, low strength, and easy to break. Therefore, it needs to be solidified before engineering construction. In order to protect the marine environment, a marine environment-friendly solidification technology needs to be adopted to effectively solidify the calcareous sand in the South China Sea. Microbially Induced Calcite Precipitation (MICP) is a green solidification technology that combines multiple disciplines such as biology, chemistry, engineering, and materials science. The main MICP solidification mechanisms include sulfate reduction, ferric iron reduction, denitrification, and urea hydrolysis. Among them, urea hydrolysis has been widely used due to its simple mechanism, controllable reaction process, and high mineralization efficiency. Urea hydrolysis mainly relies on Bacillus pasteurii. Urea is continuously decomposed into CO3 2- , in the presence of Ca 2+ and CO3 2- in the environment, when the concentration exceeds the solubility product (Ksp) of calcium carbonate, calcium carbonate crystals will precipitate around the bacteria, realizing microbial mineralization.
[0003] In order to promote the application of the MICP solidification calcareous sand technology in the South China Sea engineering construction, many scholars at home and abroad have conducted a large number of MICP solidification calcareous sand unit tests, in order to provide theoretical guidance for actual projects.
[0004] At present, the MICP solidification calcareous sand unit sample preparation method usually has the following three characteristics:
[0005] 1. Before MICP solidification, all the calcareous sand samples need to be loaded first. By means of oscillation, ramming, etc., the sand samples are made to reach the specified height. Whether loading the samples in batches or as a whole batch, all calcareous sand particles can move freely during the oscillation or ramming process (especially during ramming. Only when ramming into the bottom of the sample can sufficient vibration be generated to make the sand particles rearrange to reach the specified height). Due to the action of gravity, small particles are usually squeezed into the upper region, while large particles accumulate in the lower part, thus causing the particle size distribution of the calcareous sand inside the sample to be inconsistent along the height of the sample, and further leading to the non-uniformity inside the sample. In addition, in the existing method of loading sand particles in batches, the upper ends of each portion of sand particles are free segments, and it is difficult to ensure the consistency of the height of each portion of sand samples during the subsequent loading process. Only through ramming the entire height of the sample and the final compaction can the whole sample reach the specified height. The above methods will further lead to the non-uniformity of calcareous sand along the height of the sample.
[0006] 2. To prevent the rapid generation of a large amount of products due to the too-fast MICP reaction and block the grouting port, at present, the step-by-step grouting method (that is, the cementing liquid and the bacterial liquid are injected separately) is mainly used during grouting to avoid the rapid occurrence of the reaction in the grouting area and affect the subsequent grouting efficiency of the slurry. Although the step-by-step method solves the problem of product blockage at the grouting port, it will lead to the incomplete reaction of the bacterial liquid and the cementing liquid, and further seriously affect the integrity of the sample. Obvious weak surfaces will appear in the solidified sample, resulting in weak cementation and under-cementation areas, and even the situation where the sample cannot be formed. The main reasons for the above problems are as follows: ① The consistency of the cementing liquid is higher than that of the bacterial liquid. Without artificial stirring, even if the sample is filled with the bacterial liquid and the cementing liquid inside, it is difficult for the two to fully blend. For example, when a certain pore is filled with the cementing liquid, it is difficult for the bacterial liquid to fully penetrate. At the same time, solidification products will be generated in the contact area between the cementing liquid and the bacterial liquid, which will further prevent the further blending of the cementing liquid and the bacterial liquid. Therefore, it is difficult to complete an effective full-area MICP reaction inside the sample in the above way. ② When using the step-by-step grouting method for MICP solidification of calcareous sand, the products are mainly concentrated in the lower part of the sample. The reasons are as follows: (I) The bacterial liquid and the cementing liquid will accumulate in the lower part of the sample under the action of self-weight, so the MICP reaction also occurs mainly at the lower end of the sample. (II) When the cementing liquid reacts with the bacterial liquid, the initial state of the generated product is a soft floc. Even if such flocs adhere to the surface of the calcareous sand in the upper part of the sample, they are easily washed to the lower end of the sample by the slurry during the next round of grouting. Therefore, step-by-step grouting will cause significantly more products in the lower part of the sample than in the upper part, and further result in the non-uniform phenomenon of "strong at the bottom and weak at the top".
[0007] 3. Since the MICP reaction occurs mainly at the lower end of the specimen, in order to improve the curing efficiency at the upper end of the specimen, it is necessary to repeatedly circulate the grouting, resulting in a relatively long curing time for the MICP-cured calcareous sand specimen at present. It takes nearly 20 days to form a single specimen. There are existing MICP improvement techniques that can effectively shorten the curing time. For example, techniques such as MICP fiber-reinforced curing, MICP combined with activated carbon curing, and MICP combined with rubber particle curing can all improve the curing efficiency of calcareous sand. However, the above MICP improvement techniques may cause non-negligible harm to the marine environment due to the presence of non-degradable materials or polluting substances in the raw materials.
[0008] Therefore, the MICP-cured calcareous sand specimens prepared by the existing technology have defects such as uneven curing and poor integrity, thus reducing the credibility of the test results of the unit body. Taking uneven curing as an example, the failure surface of the specimen mainly occurs in the weak cemented area or under-cemented area within the specimen, making it impossible to obtain the accurate mechanical mechanism of MICP-cured calcareous sand based on such test results. In addition, the existing technology cannot balance the curing efficiency and marine environmental protection, seriously hindering the large-scale popularization and application of the MICP-cured calcareous sand technology in practical engineering.
[0009] In summary, based on the rapid development of China's marine construction and the advantages of the MICP reinforcement technology, a MICP-cured calcareous sand sample preparation instrument and method that can ensure the internal uniformity, integrity and efficiency of the specimen are developed, so as to serve the construction of the South China Sea islands and reefs in China. Summary of the Invention
[0010] Aiming at the deficiencies of the existing technology, the first object of the present invention is to provide a MICP layered grouting and curing calcareous sand sample preparation instrument to solve the technical problems that the MICP-cured calcareous sand specimens prepared by the existing technology have uneven curing, poor integrity, and cannot balance the curing efficiency and marine environmental protection.
[0011] To solve the above technical problems, the present invention provides a MICP layered grouting and solidifying calcareous sand sample preparation instrument, which includes a cup body, a top cover, a permeable bottom cover, a sealed bottom cover, and a layered positioning rod. The cup body is in the shape of a hollow circular tube. A number of horizontal indentations are equidistantly arranged on the outer side wall of the cup body from bottom to top starting from the bottom end, and the distance between the indentations is less than or equal to 20 mm. The permeable bottom cover is threadedly connected to the lower end of the cup body, and the inner side wall of the permeable bottom cover is threadedly connected to the outer side wall of the cup body. The permeable bottom cover abuts against the lower end face of the cup body. The sealed bottom cover is threadedly connected to the permeable bottom cover and is located below the permeable bottom cover. The inner side wall of the sealed bottom cover is threadedly connected to the outer side wall of the permeable bottom cover. The top cover includes a cover body and a fixing mechanism. The inner side wall of the cover body is threadedly connected to the outer side wall of the upper end of the cup body. The layered positioning rod includes a support rod and a layered positioning permeable disc connected to the lower end of the support rod. The support rod is slidably connected to the cover body in the vertical direction, and the layered positioning permeable disc is slidably connected to the cup body. The fixing mechanism is used to fix the support rod. A number of vertical water inlet through holes are distributed on the layered positioning permeable disc, and a number of vertical drainage through holes are distributed on the permeable bottom cover. A grouting port is provided on the cup body and the grouting port is higher than the highest indentation.
[0012] After adopting the above structure, a MICP layered grouting and solidifying calcareous sand sample preparation instrument in the present invention has the following advantages:
[0013] 1. The calcareous sand is divided into several equal parts for sample loading. Each indentation corresponds to a portion of sand sample. After each portion of sand sample is loaded, it is directly solidified. The subsequent sample loading and solidification will not affect the previously solidified sand particles. Moreover, the ramming after each sample loading is only for one layer of sand sample, with little disturbance to the sand particles, and it only takes a short time to ram to the specified height, that is, the upper surface of the sand sample is flush with the indentation, greatly reducing the disturbance to the calcareous sand particles during subsequent sample loading, ramming, and solidification. Therefore, it can ensure that the arrangement and gradation of the calcareous sand remain consistent along the height of the sample.
[0014] 2. When using the existing one-time overall solidification method, since the MICP reaction occurs concentratedly at the lower end of the sample, in order to improve the solidification efficiency of the upper end of the sample, it is necessary to repeatedly circulate the grouting, thus prolonging the solidification time. The present invention decomposes a total sample into circular cakes with a one-time solidification height less than or equal to 20 mm, converts the one-time overall solidification into multiple concentrated area solidifications with a differential idea, and utilizes the characteristic that the area about 20 mm upward from the bottom end of the sample is the concentrated area of the MICP reaction, divides the unit sample into multiple MICP reaction concentrated areas, thereby significantly improving the integrity and uniformity of the MICP solidified calcareous sand.
[0015] 3. By distributing water inlet through - holes on the layered positioning permeable disc to disperse the grouting area, it is equivalent to increasing the grouting positions, with high curing efficiency. It also ensures complete MICP reaction and can complete curing before blockage. Moreover, compared with the sample - making instrument in the prior art where the grouting pipe is set inside, the movable layered positioning rod and the position of the grouting port enable the mixture slurry to enter from above the sand sample each time during sample - making. Even if the grouting component is blocked, it can be cleaned in time, preventing curing failure caused by the blockage of the grouting component. The slurry and the waste liquid are respectively injected and discharged through the water inlet through - holes and the drainage through - holes. Compared with the traditional design, the increase in grouting positions directly leads to an increase in the slurry seepage channels, thereby reducing the seepage pressure and minimizing the disturbance of the slurry flow to the calcareous sand. This not only improves the curing efficiency but also improves the internal uniformity of the sample, taking into account both the curing efficiency and marine environmental protection, without repeated grouting, thus saving the usage of the bacterial solution and the cementing solution.
[0016] As an improvement, gauzes are connected to the bottom end of the layered positioning permeable disc and the top end of the permeable bottom cover; adopting this structure can prevent sand particles from leaking out.
[0017] As an improvement, the diameters of both the water inlet through - holes and the drainage through - holes are less than 1 mm; adopting this structure, if the aperture is greater than 1 mm, many small particles, including needle - shaped particles, are likely to emerge from the through - holes. Although there is a gauze, it will cause the side to be uneven. Therefore, taking the aperture less than 1 mm makes the upper and lower bottom surfaces of the sample smoother.
[0018] As an improvement, the cup body is a split - mold, the split - mold includes a first - flap mold and a second - flap mold, the first - flap mold and the second - flap mold are fixed by a pipe clamp, and the grouting port is located on the first - flap mold or the second - flap mold; adopting this structure is convenient for applying the demolding agent and removing the sample.
[0019] As an improvement, the fixing mechanism includes a connecting part and a fixing bolt. The connecting part is connected to the upper end surface of the cover body, the support rod is slidably connected to the connecting part and the cover body, and the fixing bolt is threadedly connected to the connecting part. By rotating the fixing bolt, the fixing bolt abuts against the support rod; adopting this structure has the advantages of simple structure and convenient operation.
[0020] The second object of the present invention is to provide a method for preparing a calcareous sand sample by MICP layered grouting and curing, using the above - mentioned MICP layered grouting and curing calcareous sand sample - making instrument, including the following steps:
[0021] S1. Divide the weighed calcareous sand into N parts, where N is the number of indentations;
[0022] S2. Connect the permeable bottom cover to the cup body, and connect the bottom - sealed bottom cover to the permeable bottom cover;
[0023] S3. Load one part of the calcareous sand sample, and tamp the sand sample with a tamping rod so that the top surface of the sand sample is flush with the nth indentation from bottom to top, where n is the cumulative number of sample - loading times;
[0024] S4. Connect the cover body to the cup body. The support rod passes through the cover body and the layered positioning water-permeable plate is located inside the cup body. Move the support rod so that the bottom surface of the layered positioning water-permeable plate abuts against the top surface of the sand sample, and fix the support rod using the fixing mechanism.
[0025] S5. Pour the bacteria-cement liquid mixture with a volume equal to one-fourth of the volume of the sand sample into the grouting port at a constant speed.
[0026] S6. After standing for four hours, remove the bottom sealing cover.
[0027] S7. After standing for two hours until all the slurry inside the sand sample has flowed out, install the bottom sealing cover.
[0028] S8. Repeat steps S5 to S7 four times in total, for a total of 24 hours.
[0029] S9. Remove the top cover, set the fixing mechanism to loosen the support rod from the cover body, and clean the products attached to the layered positioning water-permeable plate.
[0030] S10. Repeat steps S3 to S9 a total of N times.
[0031] S11. Put the sample preparation instrument into the oven and bake it to a constant weight, and then disassemble the sample.
[0032] After adopting the above method, a method for preparing MICP layered grouting and solidifying calcareous sand in the present invention has the following advantages: 1. Divide the calcareous sand into several equal parts for sample loading. Each indentation corresponds to a portion of the test sand sample. After loading each portion of the sand sample, it is directly solidified. The subsequent sample loading and solidification will not affect the previously solidified sand particles. Moreover, the ramming after each sample loading only targets one layer of the sand sample, with little disturbance to the sand particles, and it only takes a short time to ram to the specified height, that is, the upper surface of the sand sample is flush with the indentation, greatly reducing the disturbance to the calcareous sand particles during subsequent sample loading, ramming, and solidification. Therefore, it can ensure that the arrangement and gradation of the calcareous sand remain consistent along the height of the sample.
[0033] 2. When using the existing one-time overall solidification method, since the MICP reaction occurs concentratedly at the lower end of the sample, in order to improve the solidification efficiency at the upper end of the sample, it is necessary to repeatedly circulate the grouting, thus prolonging the solidification time. In the present invention, a total sample is decomposed into circular cakes with a one-time solidification height less than or equal to 20 mm. The one-time overall solidification is converted into multiple concentrated area solidifications with a differential idea. Utilizing the characteristic that the area about 20 mm from the bottom end of the sample is the concentrated area of the MICP reaction, the unit sample is divided into multiple MICP reaction concentrated areas, thereby significantly improving the integrity and uniformity of the MICP solidified calcareous sand.
[0034] 3. By distributing the water inlet through holes on the layered positioning permeable disc to disperse the grouting area, it is equivalent to increasing the grouting positions, with high curing efficiency, ensuring complete MICP reaction, being able to complete curing before blockage, and removing the products by taking out the layered positioning permeable disc after each round of grouting to avoid blockage; compared with the sample preparation instrument with the grouting pipe arranged inside in the prior art, the position of the movable layered positioning rod and the grouting port enables the mixture slurry to enter from above the sand sample each time when preparing the sample. Even if the grouting component is blocked, it can be cleaned in time, preventing curing failure caused by the blockage of the grouting component; the slurry and the waste liquid are respectively injected and discharged through the water inlet through holes and the drainage through holes. Compared with the traditional design, the increase in the grouting positions directly leads to an increase in the slurry seepage channels, thereby reducing the seepage pressure and minimizing the disturbance of the slurry flow to the calcareous sand, improving both the curing efficiency and the internal uniformity of the sample, taking into account the curing efficiency and marine environmental protection, without repeated grouting, thus saving the usage amount of the bacterial solution and the cementing solution.
[0035] As an improvement, before connecting the permeable bottom cover to the cup body in step S2, a demolding agent is applied to the inner wall of the cup body; in this way, it is convenient to remove the sample.
[0036] As an improvement, the oven temperature in step S11 is 60 °C.
[0037] As an improvement, the bacterial solution-cementing solution mixture in step S5 is a uniform mixture of equal volumes of the bacterial solution and the cementing solution; based on the design of the sample preparation instrument for MICP layered grouting and curing of calcareous sand, the occurrence of curing blockage has been avoided. By adopting the above method, after uniformly mixing the cementing solution and the bacterial solution and injecting them into the sand sample at a constant speed, both the curing rate is improved and the complete MICP reaction is ensured, avoiding the generation of weak cementing or under-cemented regions due to the presence of pure bacterial solution or pure cementing solution regions in certain pores.
[0038] As an improvement, the applicable object of the sample preparation scheme is calcareous sand within the full particle size range, and the present invention has a wide application range. Description of the Drawings
[0039] Figure 1 It is a schematic structural diagram of the whole sample preparation instrument in Embodiment 1 of the present invention.
[0040] Figure 2 It is a cross-sectional view of the cup body in Embodiment 1 of the present invention.
[0041] Figure 3 It is a physical diagram of the sample prepared by using the sample preparation method in Embodiment 2 of the present invention.
[0042] Figure 4 It is the unconfined compressive strength curve of the sample prepared by using the sample preparation method in Embodiment 2 of the present invention.
[0043] Figure 5SEM image (×50) of the specimen prepared by the sample preparation method in Embodiment 2 of the present invention.
[0044] Figure 6 SEM image (×60) of the specimen prepared by the sample preparation method in Embodiment 2 of the present invention.
[0045] Figure 7 SEM image (×70) of the specimen prepared by the sample preparation method in Embodiment 2 of the present invention.
[0046] Figure 8 Sample preparation result diagram of curing calcareous sand by MICP immersion method in the prior art.
[0047] Figure 9 Sample preparation result diagram of curing calcareous sand by MICP cyclic grouting method in the prior art.
[0048] Reference numerals: 1, cup body; 11, first petal mold; 12, second petal mold; 2, top cover; 21, cover body; 22, fixing mechanism; 221, connecting part; 222, fixing bolt; 3, permeable bottom cover; 30, drainage through hole; 4, bottom-sealing bottom cover; 5, layered positioning rod; 51, support rod; 52, layered positioning permeable plate; 520, water inlet through hole; 6, dent; 7, grouting port; 8, pipe hoop. Detailed implementation manners
[0049] The following will make a detailed description of a MICP layered grouting and curing calcareous sand sample preparation instrument and a sample preparation method of the present invention with reference to the accompanying drawings.
[0050] Embodiment 1:
[0051] As Figures 1 to 2As shown in the figure, in this embodiment, a MICP layered grouting and solidifying calcareous sand sample preparation instrument is provided, which includes a cup body 1, a top cover 2, a permeable bottom cover 3, a sealed bottom cover 4 and a layered positioning rod 5. The cup body 1 is in a hollow circular tube shape. A number of horizontal indentations 6 are equidistantly arranged on the side wall of the cup body 1 from bottom to top starting from the bottom end. That is, not only the distance between each indentation 6 is the same, but also the distance between the lowermost indentation 6 and the bottom end of the cup body 1 is the same as the distance between the indentations 6. The distance between the indentations 6 is less than or equal to 20 mm. The permeable bottom cover 3 is threadedly connected to the lower end of the cup body 1, and the inner side wall of the permeable bottom cover 3 is threadedly connected to the outer side wall of the cup body 1. The permeable bottom cover 3 abuts against the lower end face of the cup body 1. The sealed bottom cover 4 is threadedly connected to the permeable bottom cover 3 and is located below the permeable bottom cover 3. The inner side wall of the sealed bottom cover 4 is threadedly connected to the outer side wall of the permeable bottom cover 3. The top cover 2 includes a cover body 21 and a fixing mechanism 22. The cover body 21 is threadedly connected to the upper end of the cup body 1, and the inner side wall of the cover body 21 is threadedly connected to the outer side wall of the upper end of the cup body 1. The layered positioning rod 5 includes a support rod 51 and a layered positioning permeable disc 52 connected to the lower end of the support rod 51. The support rod 51 is slidably connected to the cover body 21 in the vertical direction. The layered positioning permeable disc 52 is slidably connected to the cup body 1. The fixing mechanism 22 is used to fix the support rod 51. A number of vertical water inlet through holes 520 are distributed on the layered positioning permeable disc 52. A number of vertical drainage through holes 30 are distributed on the permeable bottom cover 3. A grouting port 7 is provided on the cup body 1, and the grouting port 7 is higher than the highest indentation 6. A gauze (not shown in the figure) is connected to the bottom end of the layered positioning permeable disc 52 and the top end of the permeable bottom cover 3, and the diameters of the water inlet through holes 520 and the drainage through holes 30 are both less than 1 mm.
[0052] As Figure 2 shown, the cup body 1 is a split mold, and the split mold includes a first half mold 11 and a second half mold 12. The first half mold 11 and the second half mold 12 are symmetric semi-circular ring structures. The first half mold 11 and the second half mold 12 are fixed by a pipe clamp 8. As Figure 1 shown, a total of two upper and lower pipe clamps 8 are provided. The grouting port 7 is located on the first half mold 11 or the second half mold 12. In this embodiment, the grouting port 7 is located on the first half mold 11.
[0053] As Figure 1 shown, the fixing mechanism 22 includes a connecting part 221 and a fixing bolt 222. The connecting part 221 is connected to the upper end face of the cover body 21. The support rod 51 is slidably connected to the connecting part 221 and the cover body 21. The fixing bolt 222 is threadedly connected to the connecting part 221, and the fixing bolt 222 is made to abut against the support rod 51 by rotating the fixing bolt 222.
[0054] Divide the calcareous sand into several equal parts for sample loading. Each indentation 6 corresponds to one sand sample. After loading each sand sample, it is directly solidified. The subsequent sample loading and solidification will not affect the previously solidified sand particles. Moreover, the ramming after each sample loading only targets one layer of sand sample, with little disturbance to the sand particles, and it only takes a short time to ram to the specified height, that is, the upper surface of the sand sample is flush with the indentation 6, greatly reducing the disturbance to the calcareous sand particles during subsequent sample loading, ramming, and solidification. Therefore, it can ensure that the arrangement and gradation of the calcareous sand remain consistent along the height of the specimen.
[0055] When using the existing one-time overall solidification method, since the MICP reaction occurs intensively at the lower end of the specimen, in order to improve the solidification efficiency at the upper end of the specimen, it is necessary to repeatedly circulate the grouting, thus prolonging the solidification time. In the present invention, a total specimen is decomposed into round cakes with a one-time solidification height less than or equal to 20 mm. The one-time overall solidification is converted into multiple centralized area solidifications with a differential idea. Utilizing the characteristic that the area about 20 mm upward from the bottom end of the specimen is the concentrated area of the MICP reaction, the unit specimen is divided into multiple MICP reaction concentrated areas, thereby significantly improving the integrity and uniformity of the MICP-solidified calcareous sand.
[0056] By distributing the water inlet through holes 520 on the layered positioning permeable disk 52, the grouting area is dispersed, which is equivalent to increasing the grouting positions. The solidification efficiency is high, and it also ensures the completion of the MICP reaction and can complete the solidification before clogging. Moreover, compared with the sample preparation instrument with the grouting pipe arranged inside in the prior art, the positions of the movable layered positioning rod 5 and the grouting port 7 enable the mixture slurry to enter from above the sand sample every time sample preparation is carried out. Even if the grouting component is clogged, it can be cleaned in time, preventing the solidification failure caused by the clogging of the grouting component; the slurry and the waste liquid are respectively injected and discharged through the water inlet through holes 520 and the drain through holes 30. Compared with the traditional design, the increase in the grouting positions directly leads to an increase in the slurry seepage channels, thereby reducing the seepage pressure and minimizing the disturbance of the slurry flow to the calcareous sand, improving both the solidification efficiency and the internal uniformity of the specimen, taking into account both the solidification efficiency and the marine environmental protection, without the need for repeated grouting, thus also saving the usage amount of the bacterial solution and the cementing solution.
[0057] Example 2:
[0058] In this example, a method for preparing a sample of MICP layered grouting solidified calcareous sand is given. Using a MICP layered grouting solidified calcareous sand sample preparation instrument in Example 1, it includes the following steps:
[0059] S1. Divide the weighed calcareous sand into N parts, where N is the number of indentations 6;
[0060] S2. Connect the permeable bottom cover 3 to the cup body 1, and connect the sealed bottom cover 4 to the permeable bottom cover 3;
[0061] S3. Load a sample of calcareous sand, and tamp the sand sample with a tamping rod until the top surface of the sand sample is flush with the nth indentation 6 from bottom to top, where n is the cumulative number of times of sample loading;
[0062] S4. Connect the cover body 21 to the cup body 1. The support rod 51 passes through the cover body 21 and the layered positioning permeable disc 52 is located inside the cup body 1. Move the support rod 51 so that the bottom surface of the layered positioning permeable disc 52 abuts against the sand sample, and fix the support rod 51 by using the fixing mechanism 22;
[0063] S5. Pour the mixture of bacteria solution and cementing solution with a volume equal to one-fourth of the volume of the sand sample into the grouting port 7 at a constant speed;
[0064] S6. Remove the bottom sealing cover 4 after standing for four hours;
[0065] S7. Install the bottom sealing cover 4 after standing for two hours until all the slurry inside the sand sample has flowed out;
[0066] S8. Repeat steps S5 to S7 four times in total, for a total of 24 hours;
[0067] S9. Remove the top cover 2, set the fixing mechanism 22 to loosen the support rod 51 from the cover body 21, and clean the products attached to the layered positioning permeable disc 52;
[0068] S10. Repeat steps S3 to S9 N times in total;
[0069] S11. Put the sample preparation instrument into the oven and dry it to a constant weight, and then disassemble the sample.
[0070] In addition, before connecting the permeable bottom cover 3 to the cup body 1 in step S2, apply a demolding agent to the inner wall of the cup body 1. The temperature of the oven in step S11 is 60°C. The mixture of bacteria solution and cementing solution in step S5 is a uniform mixture of equal volumes of bacteria solution and cementing solution. And the object applicable to this sample preparation method is calcareous sand within the full particle size range, that is, calcareous minerals with a particle size < 2 mm.
[0071] Divide the calcareous sand into several equal parts for sample loading. Each indentation 6 corresponds to a sand sample. After each sand sample is loaded, it is directly cured. The subsequent sample loading and curing will not affect the previously cured sand particles. Moreover, the tamping after each sample loading only targets one layer of sand sample, with little disturbance to the sand particles, and it only takes a short time to tamp to the specified height, that is, the upper surface of the sand sample is flush with the indentation 6, greatly reducing the disturbance to the calcareous sand particles during subsequent sample loading, tamping, and curing. Therefore, it can ensure that the arrangement and gradation of calcareous sand remain consistent along the height of the sample.
[0072] When the existing one-time overall solidification method is adopted, since the MICP reaction occurs intensively at the lower end of the specimen, in order to improve the solidification efficiency of the upper end of the specimen, it is necessary to repeatedly circulate grouting, which prolongs the solidification time. In the present invention, a total specimen is decomposed into round cakes with a one-time solidification height less than or equal to 20 mm, and the one-time overall solidification is converted into multiple centralized area solidifications with a differential idea. By utilizing the characteristic that the area about 20 mm upward from the bottom end of the specimen is the MICP reaction concentrated area, the unit specimen is divided into multiple MICP reaction concentrated areas, thus significantly improving the integrity and uniformity of the MICP-solidified calcareous sand.
[0073] After uniformly mixing the cementation liquid and the bacterial liquid, it is injected into the sand sample at a constant speed, which not only improves the solidification rate but also ensures the complete MICP reaction, avoiding the generation of weak cementation or under-cementation areas due to the presence of pure bacterial liquid or pure cementation liquid areas in certain pores; by distributing the water inlet through holes 520 on the layered positioning water permeable plate 52, the grouting area is dispersed, which is equivalent to increasing the grouting positions, with high solidification efficiency and ensuring the complete MICP reaction, and can complete the solidification before blockage. Moreover, after each round of grouting, the layered positioning water permeable plate 52 is taken out to remove the products, avoiding the blockage situation; compared with the sample preparation instrument with the grouting pipe arranged inside in the prior art, the positions of the movable layered positioning rod 5 and the grouting port 7 enable the mixture slurry to enter from above the sand sample every time the sample is prepared. Even if the grouting component is blocked, it can be cleaned in time, preventing the solidification failure caused by the blockage of the grouting component; the slurry and the waste liquid are respectively injected and discharged through the water inlet through holes 520 and the drainage through holes 30. Compared with the traditional design, the increase in the grouting positions directly leads to an increase in the slurry seepage channels, thereby reducing the seepage pressure and minimizing the disturbance of the slurry flow to the calcareous sand, improving both the solidification efficiency and the internal uniformity of the specimen, taking into account both the solidification efficiency and the marine environmental protection, without the need for repeated grouting, and thus saving the usage amount of the bacterial liquid and the cementation liquid.
[0074] In this embodiment, taking a unit specimen with a solidification diameter of 39.1 mm and a height of 80 mm as an example, the cup body 1 has a height of 120 mm, an inner diameter of 39.1 mm, and a thickness of 2 mm. Four horizontal indentations 6 are arranged at intervals of 20 mm from bottom to top, for a total of four. According to the designed relative density, calcareous sand is weighed and divided into four equal parts. A demolding agent is applied to the inner wall of the split mold for subsequent specimen removal. The sample preparation instrument is assembled, and the split mold is fixed using the pipe clamp 8. The permeable bottom cover 3 and the bottom sealing cover 4 are connected in sequence; the first portion of sand sample is slowly loaded, and the sand sample is gently tamped with a tamping rod to adjust the height so that the top surface of the sand sample is flush with the first indentation 6 from bottom to top; the top cover 2 is connected, and the bottom surface of the layered positioning permeable disc 52 is made to closely adhere to the top surface of the sand sample, and the fixing bolt 222 is rotated to fix the support rod 51; an equal volume of bacterial liquid and cementing liquid are mixed and stirred evenly, and a bacterial liquid-cementing liquid mixture with a volume of one-fourth of the specimen is uniformly poured from the grouting port 7; after four hours, the bottom sealing cover 4 is removed, and it is left standing for two hours. After all the slurry in the sand sample has flowed out, the bottom sealing cover 4 is installed; then the operations of grouting and standing are repeated three times, that is, a total of four groutings are performed in one specimen preparation, for a total of 24 hours; the top cover 2 is removed and the products on the layered positioning permeable disc 52 are cleaned, and the second portion of sand sample is loaded, and the above steps are repeated. A total of four sand samples are solidified, for a total of 96 hours; after solidification is completed, it is placed in an oven at 60 °C together with the sample preparation instrument and dried to a constant weight before specimen removal. The solidified specimen is as shown in Figure 3 shown, and the unconfined compressive strength test is carried out on the specimen, and the curve as shown in Figure 4 is obtained. It can be seen that the unconfined compressive strength of this specimen is 818.695 kPa, and the residual strength is 465.74 kPa. This represents that the solidification of the specimen is not limited to the surface of the specimen. The MICP layered grouting method realizes the overall effective solidification of calcareous sand in the South China Sea, and when the main crack appears in the specimen and the strength decreases, the residual blocks still have a relatively high strength.
[0075] As shown in Figures 5 to 7 the SEM image, it can be seen that the MICP solidification products are mainly attached to the contact points between calcareous sand particles. Through the attachment of the products, the point-point contact and point-plane contact between the particles are both transformed into plane-plane contact, thus realizing the effective solidification of calcareous sand in the full particle size range; there are also certain product attachments on the surface of calcareous sand particles except for the particle contact areas, but the main function of this type of attachment form is to fill pores, rather than to cement calcareous sand particles; and it can be seen from the figure that the pores that can be effectively filled by the MICP solidification products mainly include: the pores generated by the arrangement of calcareous sand particles and the open holes on the surface of calcareous sand particles; the products generated by this MICP solidification reaction are relatively dense, and the surface roughness is significantly higher than that of calcareous sand surface. The generated products are mainly in the form of massive blocks with strong integrity, and there are fewer fragile sheet-like or strip-like products. Therefore, the MICP layered grouting method can significantly improve the integrity of the specimen.
[0076] In addition, apart from the split mold dimensions in the above embodiments, split molds with a height of 140 mm and an inner diameter of 100 mm can also be set up to produce unit bodies with a height of 100 mm and a diameter of 100 mm; split molds with a height of 120 mm and an inner diameter of 38 mm can be used to produce unit bodies with a height of 80 mm and a diameter of 38 mm; split molds with a height of 90 mm and an inner diameter of 50 mm can be used to produce unit bodies with a height of 50 mm and a diameter of 50 mm. Among them, the arrangement of the indentations 6 of the split mold with a height of 120 mm and an inner diameter of 38 mm is the same as that of the split mold with a height of 120 mm and an inner diameter of 39.1 mm; the split mold with a height of 90 mm and an inner diameter of 50 mm has a total of 5 indentations 6, and the indentations 6 are spaced 10 mm apart; the split mold with a height of 140 mm and an inner diameter of 100 mm has a total of 5 indentations 6, and the indentations 6 are spaced 20 mm apart.
[0077] Comparative Example 1:
[0078] To compare with the specimens prepared by the sample preparation method in Embodiment 2 of the present invention, the activity of the bacterial solution, the concentration of the cementing solution, and the curing time are now controlled to be unchanged, and the traditional soaking method is used for MICP curing of calcareous sand for sample preparation. The sample preparation results after 96 hours are as Figure 8 shown. The products of the calcareous sand cured by the soaking method cannot be observed with the naked eye, and there is no cementation phenomenon between the sand particles, and the MICP curing fails.
[0079] Comparative Example 2:
[0080] To compare with the specimens prepared by the sample preparation method in Embodiment 2 of the present invention, the activity of the bacterial solution, the concentration of the cementing solution, and the curing time are now controlled to be unchanged, and the traditional cyclic grouting method is used for MICP curing of calcareous sand for sample preparation. The sample preparation results after 96 hours are as Figure 9 shown. Although some calcareous sand is cemented into blocks, the whole does not take shape, and the MICP curing of calcareous sand is not successful either.
[0081] The embodiments of the present invention have been described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the above two embodiments. All other embodiments obtained by those skilled in the art without creative efforts fall within the scope of protection of the present invention.
Claims
1. A MICP layered grouting and solidifying calcareous sand sample preparation instrument, characterized in that, It includes a cup body (1), a top cover (2), a permeable bottom cover (3), a sealed bottom cover (4) and a layered positioning rod (5). The cup body (1) is in the shape of a hollow circular tube. A number of horizontal indentations (6) are equidistantly arranged on the outer side wall of the cup body (1) from the bottom end upwards. The spacing of the indentations (6) is less than or equal to 20 mm. The permeable bottom cover (3) is threadedly connected to the lower end of the cup body (1), and the inner side wall of the permeable bottom cover (3) is threadedly connected to the outer side wall of the cup body (1). The permeable bottom cover (3) abuts against the lower end surface of the cup body (1). The sealed bottom cover (4) is threadedly connected to the permeable bottom cover (3) and is located below the permeable bottom cover (3). The inner side wall of the sealed bottom cover (4) is threadedly connected to the outer side wall of the permeable bottom cover (3). The top cover (2) includes a cover body (21) and a fixing mechanism (22). The inner side wall of the cover body (21) is threadedly connected to the outer side wall of the upper end of the cup body (1). The layered positioning rod (5) includes a support rod (51) and a layered positioning permeable disc (52) connected to the lower end of the support rod (51). The support rod (51) is slidably connected to the cover body (21) in the vertical direction. The layered positioning permeable disc (52) is slidably connected to the inside of the cup body (1). The fixing mechanism (22) is used to fix the support rod (51). A number of vertical water inlet through holes (520) are distributed on the layered positioning permeable disc (52). A number of vertical drainage through holes (30) are distributed on the permeable bottom cover (3). A grouting port (7) is provided on the cup body (1), and the grouting port (7) is higher than the highest indentation (6).
2. The MICP layered grouting and solidifying calcareous sand sample preparation instrument according to claim 1, wherein A gauze is connected to both the bottom end of the layered positioning permeable disc (52) and the top end of the permeable bottom cover (3).
3. A MICP layered grouting and solidifying calcareous sand sample preparation instrument according to claim 2, characterized in that, The pore diameters of the water inlet through holes (520) and the drainage through holes (30) are both less than 1 mm.
4. A MICP layered grouting and solidifying calcareous sand sample preparation instrument according to claim 1, characterized in that, The cup body (1) is a split mold. The split mold includes a first split mold (11) and a second split mold (12). The first split mold (11) and the second split mold (12) are fixed by a pipe clamp (8). The grouting port (7) is located on the first split mold (11) or the second split mold (12).
5. The MICP layered grouting and solidifying calcareous sand sample preparation instrument according to claim 1, wherein, The fixing mechanism (22) includes a connecting part (221) and a fixing bolt (222). The connecting part (221) is connected to the upper end surface of the cover body (21). The support rod (51) is slidably connected to the connecting part (221) and the cover body (21). The fixing bolt (222) is threadedly connected to the connecting part (221), and by rotating the fixing bolt (222), the fixing bolt (222) abuts against the support rod (51).
6. A method for preparing a calcium sand sample by MICP layered grouting and solidification, characterized in that, Using a MICP layered grouting and solidifying calcareous sand sample preparation instrument according to any one of claims 1 to 5, the following steps are included: S1. Divide the weighed calcareous sand into N parts, where N is the number of the indentations (6); S2. Connect the permeable bottom cover (3) to the cup body (1), and connect the sealed bottom cover (4) to the permeable bottom cover (3); S3. Load a sample of calcareous sand, and tamp the sand sample with a tamping rod so that the top surface of the sand sample is flush with the nth indentation (6) from bottom to top, where n is the cumulative number of times of loading the sample; S4. Connect the cover body (21) to the cup body (1), pass the support rod (51) through the cover body (21), and place the layered positioning permeable disk (52) inside the cup body (1). Move the support rod (51) so that the bottom surface of the layered positioning permeable disk (52) abuts against the top surface of the sand sample, and fix the support rod (51) using the fixing mechanism (22); S5. Slowly pour in a mixture of bacterial solution and cementing solution with a volume equal to one-fourth of the volume of the sand sample from the grouting port (7); S6. Remove the bottom sealing cover (4) after standing for four hours; S7. Install the bottom sealing cover (4) after standing for two hours until all the slurry inside the sand sample has flowed out; S8. Repeat steps S5 to S7 four times in total, for a total of 24 hours; S9. Remove the top cover (2), set the fixing mechanism (22) to loosen the support rod (51) from the cover body (21), and clean the products attached to the layered positioning permeable disk (52); S10. Repeat steps S3 to S9 a total of N times; S11. Put the sample preparation instrument into an oven and dry it to a constant weight, and then disassemble the sample.
7. A method for preparing a calcareous sand sample by MICP layered grouting and curing according to claim 6, characterized in that Before connecting the permeable bottom cover (3) to the cup body (1) in step S2, apply a demoulding agent to the inner wall of the cup body (1).
8. A method for preparing a calcareous sand sample by MICP layered grouting and curing according to claim 6, wherein, The temperature of the oven in step S11 is 60 °C.
9. A method for preparing a calcium sand sample by MICP layered grouting and curing according to claim 6, characterized in that, The mixture of bacterial solution and cementing solution in step S5 is a uniform mixture of equal volumes of bacterial solution and cementing solution.
10. A method for preparing a calcareous sand sample by MICP layered grouting and curing according to claim 6, characterized in that, The object applicable to the sample preparation method is calcareous sand within the full particle size range.