A method for reinforcing a coral sand body by micp-bionic structure sandwich

Abstract

The present application relates to the field of building technology, especially to a MICP-bionic structure sandwich reinforcement method for coral sand soil body, which comprises the following steps: S1, grading the undisturbed coral sand, using fine particles as sandwich material and using medium and coarse particles as main filling material; S2, laying 3D printed bionic geosynthetic material in the fine particles, sequentially injecting Paenibacillus pasteuria bacterial liquid and urea-calcium chloride cementing liquid, and alternately grouting multiple times after standing; S3, layering and stacking and compacting the composite sandwich and the main sand layer to build a layered composite structure; S4, repeating steps S1-S3. The present application combines ecological reinforcement technology with reinforcement technology to build a collaborative system of "layered construction-sandwich construction-whole reinforcement", which effectively improves the reinforcement effect and efficiency.

Description

Technical Field

[0001] This invention relates to the field of building technology, and in particular to a MICP-bionic structure sandwich reinforcement method for coral sand. Background Technology

[0002] Coral sand, a typical carbonate granular soil, suffers from high porosity, irregular particle shape, and fragility, resulting in weak natural foundation bearing capacity and often leading to uneven settlement. During layered construction, the difference in specific gravity and hydrodynamics naturally creates a layered structure with alternating layers of fine-grained interlayers and medium-to-coarse-grained layers. However, the fine-grained interlayers generally suffer from low strength and slow dissipation of pore water pressure, making them a contributing factor to settlement and weak surfaces.

[0003] Traditional foundation reinforcement measures suffer from drawbacks such as high carbon emissions, environmental pollution, and poor construction adaptability. While patent CN202510892512.1 proposes a multi-dimensional ecological low-carbon reinforcement method for coral sand, its use of enzyme-induced calcium carbonate precipitation (EICP) to pretreat individual coral sand particles requires multiple spraying and settling operations with urease solution and urea-calcium chloride cementitious solution. This cumbersome process prolongs the construction cycle and increases energy consumption. Furthermore, urease extraction relies on specialized equipment, significantly increasing construction complexity and cost. More importantly, this method does not address the natural layering characteristics of coral sand with a targeted reinforcement scheme. The spraying method easily results in a "hard top, soft bottom" phenomenon where the surface reinforcement is better than the deeper layers, making it difficult to solve the stability problem of fine-grained interlayers and posing risks of fine-grain loss and uneven settlement. Meanwhile, the traditional bidirectional grid used in this method only has a simple longitudinal and transverse structure, resulting in a single stress path and making it prone to stress concentration under dynamic loads. Furthermore, compared to the biomimetic spiderweb structure, this grid structure lacks a multi-directional, dense embedding structure, failing to effectively embed fine particles. This leads to the easy loss of fine particles under load, making it difficult to solve the fundamental problem of poor stability in coral sand fine-grained interlayers. Therefore, a MIP-biomimetic structural interlayer reinforcement method for coral sand is urgently needed. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the existing technology and to provide a method for reinforcing coral sand with a MIP-biomimetic structure sandwich layer, which addresses problems such as insufficient bearing capacity, uneven settlement, uneven distribution of MIP solidification, and limited effect of single reinforcing materials.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] The technical solution of this invention is to provide a MICP-biomimetic structural interlayer reinforcement method for coral sand, comprising the following steps:

[0007] S1. Grade the original coral sand, using the fine particles obtained by screening or sedimentation as interlayer material and the medium and coarse particles as main filling material.

[0008] S2. Lay 3D printed biomimetic geosynthetic material in the fine particulate material obtained in step S1, and inject Pasteurella multocida bacterial solution and urea-calcium chloride cementitious solution in sequence. After standing, alternate grouting multiple times to form a composite interlayer. The 3D printed biomimetic geosynthetic material is made of polylactic acid or high-density polyethylene material and is printed as a biomimetic spider web structure grid.

[0009] S3. The composite interlayer formed in step S2 is piled up and compacted in layers with the main sand layer, so that the interlayer and the main layer are combined to form a layered composite structure.

[0010] S4. Repeat steps S1 to S3 to form a multi-layered “MICP-biomimetic structure” sandwich system.

[0011] In some specific embodiments, in step S1, the coral sand grading can be performed using multi-layer standard sieves or sedimentation grading methods, with a sieving time of 10 to 20 minutes to ensure uniform particle distribution. More preferably, in step S1, the sieving time is 15 minutes. The fine particle size range can be 0.075 to 0.6 mm, and the medium to coarse particle size range can be 0.6 to 4 mm.

[0012] In some specific embodiments, in step S2, the OD600 value of the *Bacillus pasteurellii* bacterial solution is 1.2 ± 0.1, and the injection volume is 1 to 3 times the pore volume of the coral sand. The volume ratio of the bacterial solution to the cementing solution is 1:(1~3). More preferably, in step S2, the injection volume of the bacterial solution is twice the pore volume of the sample. The volume ratio of the bacterial solution to the cementing solution can be 1:1, 1:1.5, 1:2, 1:2.5, or 1:3.

[0013] In some specific embodiments, in step S2, the concentration of the urea-calcium chloride cementing solution is 0.25~2.0 mol / L. More preferably, in step S2, the urea and calcium chloride solutions are prepared at equal concentrations, with a concentration of 0.5 mol / L, and then the two are mixed after preparation.

[0014] In some specific embodiments, in step S2, the grouting adopts a bidirectional grouting method. That is, in the first grouting cycle, the bacterial solution is injected once at the top of the interlayer, followed by the cementing solution 3-6 times; in the second grouting cycle, the bacterial solution is injected once at the bottom of the interlayer, followed by the cementing solution 3-6 times, and so on, alternating between the two. The grouting rate is controlled at 1-4 mL / min. More preferably, in step S2, one grouting cycle consists of injecting the bacterial solution once, followed by injecting the cementing solution 3 times, with a grouting rate of 2 mL / min, for a total of 4-6 grouting cycles, to ensure uniform diffusion and reaction of the solution in the sand pores.

[0015] In some specific embodiments, the rib width of the biomimetic spider web structure grid is 0.5~1.5mm, the rib thickness is 1.5~2.5mm, the spacing between each rib is 1~3mm, the tensile modulus is 2400~2700MPa, the tensile strength is 40~70MPa, the elongation at break is 8~15%, the flexural modulus is 2500~2900MPa, the impact strength is 20~40J / m, and the deformation temperature is 50~70℃.

[0016] In some specific embodiments, in step S2, after each grouting cycle is completed, the sample is left to stand in an environment of 20~35℃ for 12 h to promote the deposition of calcium carbonate crystals and structural stabilization.

[0017] In some specific embodiments, in step S3, the interlayer thickness is 20~40 mm, and the layers are arranged at equal intervals.

[0018] In some specific implementations, in step S3, compaction is performed using light vibration or low-energy compaction to ensure that the interlayer and the main layer are tightly bonded without damaging the cemented structure formed by the MICP.

[0019] Even better, the thickness and spacing of the interlayers can be flexibly designed according to the geological conditions. Where local weak layers are detected in the foundation, composite interlayers can be strategically arranged to enhance the structural stability and deformation coordination of the weak layers. Through the superposition and construction of a multi-layer "MICP-biomimetic structure" interlayer system, it can be implemented simultaneously in the layered construction process without changing the original procedures, achieving synergistic control of structural layering and overall reinforcement, and significantly improving the bearing capacity, uniformity and long-term stability of the coral sand foundation.

[0020] This invention discloses a MICP-biomimetic structural interlayer reinforcement method for coral sand soil. By constructing a layered composite interlayer system of "microbial induced mineralization (MICP) + biomimetic geosynthetic materials," it achieves efficient reinforcement of coral sand foundations. Figure 2 As shown, the structure consists of a coarse-grained soil layer in coral sand (as the main filling material) and a fine-grained soil layer in the middle treated with MICP-bionic structure. Inside the fine-grained soil layer, a 3D-printed bionic spider web synthetic material structure is embedded. The two work synergistically with the MICP mineralization products to enhance the mechanical properties of the interlayer.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) During construction, coral sand naturally forms a layered structure with alternating fine-grained interlayers and medium-coarse-grained layers due to differences in specific gravity and hydrodynamics. This invention innovatively utilizes this natural characteristic and uses multi-layer standard sieves or sedimentation grading methods to grade the original coral sand. The fine-grained part is used as the interlayer material and the medium-coarse-grained part is used as the main filling material. This grading method matches the natural layered characteristics of coral sand and implements directional reinforcement of the fine-grained interlayer with weak mechanical properties, which significantly improves the overall foundation stability.

[0023] (2) This invention directly uses MICP technology to reinforce fine particle interlayers, omitting the cumbersome single-particle pretreatment, urease solution extraction, multiple spraying, and settling steps of EICP technology; the latter not only relies on specialized equipment and increases energy consumption, but also significantly prolongs the construction period and raises costs. In contrast, this method only requires the preparation of Bacillus pasteurellus bacterial solution and urea-calcium chloride cementing solution, greatly simplifying the process flow. It requires no special equipment, significantly reducing construction complexity, cost, and time, while still achieving a uniform, stable reinforcement effect comparable to that of EICP pretreated single particles, significantly improving efficiency and on-site adaptability.

[0024] (3) The biomimetic spiderweb structure used in this invention provides a richer interface for microbial attachment, thereby promoting the microbial mineralization reaction. Ordinary bidirectional grids only have simple longitudinal and transverse force-bearing structures, with no clear distinction between load-bearing and buffering functions, and a single force transmission path, which easily leads to local stress concentration under dynamic loads. In contrast, the biomimetic spiderweb structure of this invention, through optimized design, makes the force more uniform and significantly improves the overall mechanical properties of the interlayer. In addition, the spiderweb structure has a multi-directional, dense rib network that can effectively embed fine particles and effectively prevent the loss of fine sand under flowing water or load.

[0025] (4) Compared with the spraying method, which is prone to uneven reinforcement due to gravity causing the solution to accumulate on the surface and form a "hard on top and soft on the bottom", the present invention adopts a two-way grouting method, which allows the bacterial solution and the cementing solution to penetrate and mix in opposite directions in the fine-grained interlayer, significantly improving the uniformity of the reaction solution distribution; at the same time, through multiple rounds of grouting and standing, calcium carbonate is continuously and densely deposited throughout the thickness of the interlayer, effectively eliminating local weak areas and achieving a reinforcement effect with stronger overall integrity and more complete structure. Attached Figure Description

[0026] Figure 1 A process flow diagram for the MICP-biomimetic structural interlayer reinforcement method for coral sand.

[0027] Figure 2 A schematic diagram of the MICP-biomimetic interlayer reinforcement method for coral sand.

[0028] Figure 3The graph shows the effect data of Example 1 and Comparative Examples 1-4. Detailed Implementation

[0029] like Figure 1 The flowchart shown is a MICP-biomimetic structure sandwich reinforcement method for coral sand provided by the present invention, which includes the following steps: S1, the original coral sand is graded, and the fine particles obtained by sieving or sedimentation are used as sandwich material, and the medium and coarse particles are used as main filling material.

[0030] The specific method for grading is as follows: Coral sand is graded using multi-layer standard sieves or sedimentation grading methods to distinguish different particle size components. The sieving time is generally 10-20 minutes, preferably 15 minutes, to ensure uniform particle distribution and sufficient grading. The fine particles obtained from sieving are used as interlayer filler, with a particle size range of 0.075-0.6 mm; the medium-coarse particles are used as the main filling material, with a particle size range of 0.6-4.0 mm.

[0031] S2. Lay 3D printed biomimetic geosynthetic material in the fine particulate material obtained in step S1, and inject Bacillus pasteurellus bacterial solution and urea-calcium chloride cement solution in sequence. After standing, grouting is alternately injected multiple times to form a composite interlayer.

[0032] In the fine-particle material obtained in step S1, 3D-printed biomimetic geosynthetic material is first uniformly laid in the middle position according to the designed interlayer thickness. The biomimetic material can be made of polylactic acid (PLA) or high-density polyethylene (HDPE), and the printed structure is spider web-like, which is used to provide the spatial skeleton of the interlayer and the interface for microbial attachment, thereby enhancing the structural embedding of mineralized products.

[0033] The method for preparing *Bacillus pasteurellii* bacterial suspension is as follows: First, dissolve each component in deionized water according to the ratio of ammonium chloride 10 g / L, yeast extract 20 g / L, manganese sulfate monohydrate 10 mg / L, and nickel chloride hexahydrate 24 mg / L, and bring the volume to 1000 mL to prepare a culture medium for activation and expansion. Inoculate *Bacillus pasteurellii* into the activation medium and culture in a constant temperature shaking incubator at (28–32) ℃ and 120 r / min for 36 h to obtain the first-generation activated bacterial suspension. Subsequently, expand the culture by mixing the activated bacterial suspension with the expansion medium at a volume ratio of 1:100, and culture with shaking at (25–37) ℃ and 120 r / min for 24–36 h to obtain a bacterial suspension suitable for the MIP reaction. The OD of the obtained bacterial suspension... 600 The value is 1.2±0.1. When using it, inject it into the sand body at a ratio of 1 to 3 times the pore volume of the coral sand.

[0034] The preparation method of urea-calcium chloride cementing solution is as follows: urea solution and calcium chloride solution are prepared at equal concentrations (0.5~2.0 mol / L), fully dissolved, and then mixed and stirred until no visible precipitate is observed. The volume ratio of bacterial solution to cementing solution is 1:(1~3).

[0035] The specific grouting method is as follows: a two-way grouting approach is adopted. In the first grouting cycle, bacterial solution is injected once at the top of the interlayer, followed by cementing solution 3-6 times; in the second grouting cycle, bacterial solution is injected once at the bottom of the interlayer, followed by cementing solution 3-6 times. These two processes are alternated, for a total of 4-6 cycles. The grouting rate is controlled at 1-4 mL / min to ensure uniform diffusion and reaction of the solution in the sand pores. After each grouting cycle, the mixture is allowed to stand at (25-35)℃ for 8-12 hours to promote sufficient deposition of calcium carbonate crystals and structural stabilization.

[0036] This step forms a uniform and continuous calcium carbonate cementitious body within the interlayer, significantly enhancing the bonding and load-bearing capacity of the fine-grained sand. 3D-printed biomimetic geomaterials form a stable supporting framework within this structure, allowing biomineralization products to be deposited directionally along its surface and pore interfaces. This achieves a synergistic enhancement effect of "microbial mineralization – biomimetic support," constructing a MICP composite interlayer structure with excellent compressive, shear, and durability properties.

[0037] S3. The composite interlayer formed in step S2 is piled up and compacted in layers with the main sand layer, so that the interlayer and the main layer are combined to form a layered composite structure.

[0038] Figure 2 As shown in the schematic diagram of the reinforcement method, after the composite interlayer is formed in step S2, it is layered and stacked with the medium-coarse particle main layer material. During the layering process, the thickness of the interlayer can be 20~40 mm, preferably 30 mm, and they are arranged at equal intervals. The compaction method adopts light vibration compaction or low-energy compaction to ensure that the interlayer and the main layer are tightly bonded without destroying the calcium carbonate cement structure formed by MICP.

[0039] S4. Repeat steps S1 to S3 to form a multi-layered “MICP-biomimetic structure” sandwich system.

[0040] After completing step S3, the layered filling and interlayer preparation are continued, repeating steps S1 to S3 to construct a multi-layered "MICP-biomimetic structure" interlayer system. The thickness and spacing of the interlayers can be flexibly designed according to geological conditions and engineering requirements. Interlayers can be directionally placed at locations where local weak layers or fine-grained enrichment zones are detected in the foundation to form localized reinforcement areas, thereby improving the overall uniformity and deformation resistance of the foundation.

[0041] Depending on the actual needs, steps 1 to 3 can be repeated multiple times.

[0042] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0043] This embodiment is implemented based on the technical solution of the present invention, and provides detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiment.

[0044] Unless otherwise specified, the raw materials or processing techniques used in the following examples are conventional commercially available raw materials or conventional processing techniques in the art.

[0045] Example 1

[0046] This embodiment takes triaxial specimen preparation and reinforcement testing as an example to provide a MICP-biomimetic structure sandwich reinforcement method for coral sand, including the following steps:

[0047] Step 1: Coral Sand Grading and Main Layer Preparation. First, the undisturbed coral sand is graded using multi-layer standard sieves or sedimentation grading methods. The sieving time is controlled to 10-20 min, with 15 min being a more preferred method. The fine particles (0.075-0.6 mm in diameter) obtained from sieving are collected as interlayer material, while the medium-coarse particles (0.6-4.0 mm in diameter) are used as the main filling material. The medium-coarse particles are layered into the triaxial mold according to the mold requirements and lightly compacted to achieve an overall relative density of approximately 60%, leaving a predetermined thickness for subsequent interlayer laying (in this embodiment, the interlayer thickness is 30 mm).

[0048] Step 2: Laying of 3D-printed biomimetic geosynthetic material and preparation of bacterial solution and cementing solution. According to the designed interlayer thickness, 3D-printed biomimetic geosynthetic material is evenly laid in the middle of the sample. The preferred material is polylactic acid (PLA), and it is printed as a biomimetic spiderweb structure to provide a spatial framework and attachment interface.

[0049] The basic physical parameters of the biomimetic spider web structure grid are: rib width 1mm, rib thickness 2mm, and spacing between ribs 2mm; the corresponding physical and mechanical properties are: tensile modulus 2598MPa, tensile strength 58MPa, elongation at break 11%, flexural modulus 2755MPa, impact strength 30J / m, and deformation temperature 65℃.

[0050] The specific method for preparing *Bacillus pasteurellii* bacterial suspension is as follows: Prepare the activation / expansion medium. First, dissolve each component in deionized water according to the ratio of ammonium chloride 10 g / L, yeast extract 20 g / L, manganese sulfate monohydrate 10 mg / L, and nickel chloride hexahydrate 24 mg / L, and bring the volume to 1000 mL to obtain the medium for activation and expansion. Inoculate *Bacillus pasteurellii* into the activation medium and incubate at 30℃ and 120 r / min for 36 h to obtain the activated bacterial suspension. Subsequently, expand the culture by mixing the activated bacterial suspension and expansion medium at a volume ratio of 1:100, and incubate at 30℃ and 120 r / min for 36 h with shaking to obtain the bacterial suspension suitable for the MICP reaction. The OD of the obtained bacterial suspension... 600 The value is 1.2±0.1. When using it, inject it into the sand body at twice the pore volume of the coral sand.

[0051] The preparation method of urea-calcium chloride cementing solution is as follows: urea solution and calcium chloride solution are prepared at equal concentrations (0.5 mol / L), fully dissolved, and then mixed and stirred until no visible precipitate is observed. The volume ratio of bacterial solution to cementing solution is 1:1.5.

[0052] Step 3: Constructing the MICP composite interlayer using bidirectional alternating grouting. Grouting employed a bidirectional, alternating grouting cycle: each cycle consisted of injecting bacterial solution once at the top of the interlayer, followed by four injections of cementing liquid, then injecting bacterial solution once at the bottom of the interlayer in the same sequence, followed by four injections of cementing liquid. This process was repeated between the top and bottom, for a total of six grouting cycles. The injection volume was based on the pore volume of the sand mass, with the bacterial solution injection volume being twice the pore volume of the sand mass, and the bacterial solution to cementing liquid volume ratio being 1:1.5. The grouting rate was controlled at 2 mL / min. After each grouting cycle, the sample was placed in a 30 ℃ environment for 8 h to promote calcium carbonate crystal deposition and structural stabilization. Through the above alternating grouting and settling process, a uniform and continuous calcium carbonate cementitious body was formed within the interlayer, creating an embedded effect with the biomimetic material.

[0053] Step 4: Layered Filling, Compaction, and Multi-Layer Construction. After the interlayer is formed, the composite interlayer and the upper and lower medium-coarse particle main layers are continued to be layered and moderately compacted. The compaction method adopts light vibration compaction or low-energy compaction to avoid damaging the cemented structure formed by the MICP.

[0054] Figure 2This is a schematic diagram of a MICP-biomimetic interlayer reinforcement method for coral sand. This embodiment uses standard triaxial specimen dimensions: a diameter of 39.1 mm and a height of 80 mm. Based on the specimen dimensions, the interlayer thickness is designed to be 30 mm. Coral sand naturally forms a layered structure with alternating fine-grained interlayers and medium-to-coarse-grained layers due to differences in specific gravity and hydrodynamics. To address this characteristic, the undisturbed coral sand is first graded: using multi-layer standard sieves or sedimentation grading methods (sieving time controlled at 10-20 min, preferably 15 min), the particles are separated into fine particles (0.075-0.6 mm) and medium-to-coarse particles (0.6-4.0 mm). Fine particles serve as the interlayer material, and medium-to-coarse particles serve as the main filling material. Specimens are constructed with a relative density of 60% to simulate a loosely compacted state, and the compaction method employs light vibration compaction or low-energy compaction. A 3D-printed biomimetic spiderweb structure is laid at the target location of the fine-particle interlayer. The "hard top, soft bottom" problem caused by the spraying method is solved by bidirectional grouting (alternating injection of *Bacillus pasteurellii* bacterial solution and urea-calcium chloride cementing solution from the top and bottom), thus forming a stable MICP-biomimetic composite interlayer. The final layered structure is: a medium-coarse particle layer at the bottom, a pretreated composite interlayer in the middle, and a medium-coarse particle layer on top, forming a three-layer structure of "medium-coarse particles - composite interlayer - medium-coarse particles". This method effectively improves the strength of the fine-particle interlayer through the synergistic effect of the biomimetic spiderweb skeleton support and MICP mineralization, solving problems such as fine particle loss and uneven foundation settlement, and optimizing the mechanical properties of the layered structure.

[0055] Comparative Example 1

[0056] The comparative example is a fine-grained interlayer without any treatment.

[0057] Comparative Example 2

[0058] This comparative example prepared a MICP-treated fine-grained sandwich without using any grid, and the remaining conditions were the same as in Example 1.

[0059] Comparative Example 3

[0060] This comparative example prepared a MICP-bidirectional grid-treated fine-grained sandwich, which replaced the biomimetic spider web structure grid in Example 1 with a bidirectional grid, and the other conditions were the same as in Example 1.

[0061] Comparative Example 4

[0062] This comparative example prepared EICP pretreated single particles followed by MICP-bionic spider web treatment fine particle interlayers, using the method in Example 1 of CN202510892512.1.

[0063] Figure 3The figures show the stress-strain curves of the triaxial tests in Example 1 and Comparative Examples 1-4. Under a confining pressure of 200 kPa, the deviatoric stress-strain curves of each sample showed significant differences: the untreated fine-grained interlayer had a peak deviatoric stress of 988.5 kPa, the lowest strength, and a flat curve, indicating its weakest mechanical properties; after MIP treatment alone, the peak deviatoric stress increased to 2700 kPa, a strength increase of 173% compared to the untreated state, confirming that microbial-induced calcium carbonate precipitation technology can effectively improve the cementing characteristics and bearing capacity of fine-grained coral sand; the MIP-bidirectional grid treatment further increased the peak deviatoric stress to 3115.44 kPa, a strength increase of 215%, demonstrating the auxiliary enhancement effect of the reinforcement structure on the cementing effect of MIP; the MIP-biomimetic spider web structure synergistic reinforcement method proposed in this invention achieved a peak deviatoric stress of 3535.384 kPa, an increase of 257% compared to the untreated fine-grained interlayer, and an additional increase of 30.9% compared to the simple MIP treatment, demonstrating the best strengthening effect; the peak deviatoric stress of the EICP pretreated single-particle layer combined with the MIP-biomimetic spider web treatment was 3518.89 kPa. The strength improvement (256%) was similar to that of the MIP-biomimetic spiderweb treatment, further validating the synergistic effect mechanism of biomimetic structure and microbial mineralization. It is worth noting that although the EICP pretreatment single-particle layer + MIP biomimetic spiderweb combination technology exhibits excellent strength performance, it relies on a single-particle pretreatment step, specialized equipment, and a complex process. In contrast, this method only requires the preparation of Bacillus pasteurellii bacterial solution and urea-calcium chloride cementing solution, significantly simplifying the process and eliminating the need for special equipment. While significantly reducing construction complexity and cost, it still achieves uniform, stable reinforcement effects comparable to EICP pretreatment single particles, significantly improving efficiency and on-site adaptability. This synergistic mechanism of "microbial mineralization + biomimetic structure" not only avoids the dependence on chemical additives or complex equipment in traditional reinforcement technologies but also optimizes the spatial distribution and interfacial bonding performance of the cement through bio-inspired structural design, providing an efficient, low-carbon, and easily scalable technical path for coral sand foundation reinforcement.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. The basic principles and main features of the present invention have been described above with specific implementation schemes. Based on the present invention, some modifications or substitutions can be made, but these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of protection claimed by the present invention.

Claims

1. A method for reinforcing coral sandstone with a MICP-biomimetic structural interlayer, characterized in that, The process includes the following steps: S1. Grading the original coral sand, using the fine particles obtained by sieving or sedimentation as interlayer material and the medium and coarse particles as the main filling material. The particle size range of the fine particles is 0.075~0.6mm, and the particle size range of the medium and coarse particles is 0.6~4.0mm. S2. A 3D-printed biomimetic geosynthetic material is laid in the fine-particle material obtained in step S1, and *Bacillus pasteurellii* bacterial solution and urea-calcium chloride cementitious solution are sequentially injected. After standing, the mixture is alternately injected multiple times to form a composite interlayer. The 3D-printed biomimetic geosynthetic material is made of polylactic acid or high-density polyethylene and is printed as a biomimetic spiderweb-like structure grid. The rib width of the biomimetic spiderweb-like structure grid is 0.5~1.5mm, the rib thickness is 1.5~2.5mm, and the spacing between each rib is 1~3mm. The tensile modulus is 2400~2700MPa, tensile strength is 40~70MPa, elongation at break is 8~15%, flexural modulus is 2500~2900MPa, impact strength is 20~40J / m, and deformation temperature is 50~70℃. A two-way grouting method is adopted, namely: the first grouting cycle injects bacterial solution once and cementing liquid 3~6 times at the top of the interlayer; the second grouting cycle injects bacterial solution once and cementing liquid 3~6 times at the bottom of the interlayer; and so on, for a total of 4~6 grouting cycles. S3. The composite interlayer formed in step S2 is piled up and compacted in layers with the main sand layer, so that the interlayer and the main layer are combined to form a layered composite structure. S4. Repeat steps S1 to S3 to form a multi-layer "MICP-biomimetic structure" sandwich system.

2. The MICP-biomimetic structural interlayer reinforcement method for coral sandstone as described in claim 1, characterized in that, In step S1, the coral sand is graded using multi-layer standard sieves or sedimentation grading methods, with a sieving time of 10-20 minutes to ensure uniform particle distribution.

3. The MICP-biomimetic structural interlayer reinforcement method for coral sandstone as described in claim 1, characterized in that, In step S2, the OD of the *Bacillus pasteurellii* bacterial culture was... 600 The value is 1.2±0.1, the injection volume is 1 to 3 times the pore volume of coral sand, and the volume ratio of bacterial solution to cementing solution is 1:(1 to 3).

4. The MICP-biomimetic structural interlayer reinforcement method for coral sandstone as described in claim 1, characterized in that, In step S2, the concentration of the urea-calcium chloride cementing solution is 0.5~2.0 mol / L.

5. The MICP-biomimetic structural interlayer reinforcement method for coral sandstone according to claim 1, characterized in that, In step S2, after each grouting cycle is completed, the sample is left to stand for 12 hours in an environment of 20~35℃ to promote the deposition of calcium carbonate crystals and structural stabilization.

6. The MICP-biomimetic structural interlayer reinforcement method for coral sandstone according to claim 5, characterized in that, In step S2, the grouting rate is controlled at 1~4 mL / min to ensure uniform diffusion and reaction of the solution in the sand pores.

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