Preparation method of curing capsule based on sisal fiber and polyacrylamide

Abstract

The invention relates to the technical field of soil modification, and discloses a preparation method of a curing capsule based on sisal fiber and polyacrylamide, and the preparation method comprises the following steps: S1, preparing an inner core of the curing capsule, and mixing inner core materials for pretreatment; s2, preparing an inner membrane: forming the inner membrane of the capsule by adopting polyacrylamide gel; s3, combining the inner core and the inner membrane, and coating the inner core material in the inner membrane gel to form a semispherical preliminary capsule; s4, preparing an outer membrane, and coating the surface of the semispherical preliminary capsule with sisal fibers to form a double-layer membrane structure; and S5, drying and screening the cured capsule with the double-layer film to obtain the cured capsule with uniform particle size. Calcium chloride in the inner core absorbs moisture in soil and reacts with carbonate ions in the soil to generate calcium carbonate crystals, pores are filled, and the structural strength of a soil body is enhanced; under the combined action of the recycled aggregate and the nano silicon dioxide, the grain composition of the soil is optimized, a coherent skeleton structure is constructed, and the water absorption softening phenomenon of the collapsible loess is effectively inhibited.

Description

Technical Field

[0001] The invention relates to the technical field of soil modification, in particular to a method for preparing solidified capsules based on sisal fiber and polyacrylamide. Background Art

[0002] Collapsible loess has a certain bearing capacity in a dry state, but it is prone to structural collapse and significant settlement when exposed to water, which seriously threatens the safety and stability of foundation projects. In order to improve the performance of collapsible loess, chemical modifiers (such as lime, cement, etc.) and physical filling materials are widely used. However, these traditional methods are difficult to meet both engineering needs and environmental protection requirements. In recent years, solidified capsule technology, as an emerging soil modification method, has shown significant advantages in the slow release of modifiers and structural protection through the combination of inner core and outer membrane, providing a new research direction for the modification of collapsible loess.

[0003] In the prior art, since the core material mostly uses a single chemical modifier, it is difficult to simultaneously meet the requirements of improving soil strength and reducing collapsible water sensitivity. The reaction process of a single chemical material lacks synergy, resulting in uneven modification of the soil's internal structure and limited effect, making it difficult to meet the long-term stability requirements of complex soil environments. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention provides a method for preparing a solidified capsule based on sisal fiber and polyacrylamide, which solves the problem in the prior art that the inner core material mostly uses a single chemical modifier, making it difficult to simultaneously meet the needs of improving soil strength and reducing collapsible water sensitivity.

[0005] To achieve the above objectives, the present invention is implemented by the following technical scheme: a method for preparing a solidified capsule based on sisal fiber and polyacrylamide, comprising the following steps:

[0006] S1, preparing the inner core of the solidified capsule, mixing the inner core materials for pretreatment;

[0007] S2, preparing the inner membrane, using polyacrylamide gel to form the inner membrane of the capsule;

[0008] S3, combining the inner core and the inner membrane, and encapsulating the inner core material in the inner membrane gel to form a hemispherical preliminary capsule;

[0009] S4, preparing an outer membrane, coating the surface of the hemispherical preliminary capsule with sisal fibers to form a double-layer membrane structure;

[0010] S5. Drying and screening the solidified capsules with double-layer membranes to obtain solidified capsules with uniform particle size.

[0011] Preferably, the inner core material in S1 comprises the following components:

[0012] The particle size range of recycled aggregate is 0.2 to 2 mm;

[0013] Calcium chloride accounts for 10-30% of the total weight of the inner core;

[0014] The particle size of nano silicon dioxide ranges from 50 to 150 nm, accounting for 5 to 20% of the total weight of the inner core.

[0015] Preferably, the inner core material is uniformly mixed and then left to stand for 12 to 36 hours in an environment with a temperature of 20 to 30° C. and a humidity of 40 to 60%.

[0016] Preferably, the polyacrylamide gel in S2 is prepared by the following steps:

[0017] S201, adding polyacrylamide powder into distilled water and stirring to form a solution;

[0018] S202, controlling the molecular weight of polyacrylamide to be between 5 million and 15 million, and the degree of hydrolysis to be between 15% and 50%;

[0019] S203. Under the conditions of an ambient temperature of 20 to 40°C and a humidity of 20 to 40%, stir until the solution gels, and let stand for 0.5 to 2 hours.

[0020] Preferably, in S3, when the inner core material is filled into the inner membrane to form a hemispherical primary capsule:

[0021] The diameter of the hemispherical groove of the mold used ranges from 5 to 15 mm;

[0022] The coated preliminary capsules are heated in an environment of 40 to 70° C. for 1 to 3 hours to perform partial gel curing.

[0023] Preferably, the outer membrane in S4 is formed by sisal fibers, specifically:

[0024] The length of sisal fibers ranges from 1 to 10 mm;

[0025] Using the incompletely cured inner membrane gel to adhere sisal fibers;

[0026] After coating, the mold is pressurized in the range of 1 to 10 kPa, and allowed to stand at a temperature of 30 to 60°C for 0.5 to 2 hours to firmly bond the outer film to the inner film.

[0027] Preferably, the drying and screening steps in S5 are:

[0028] S501, placing the double-layer film solidified capsule in a constant temperature environment of 20 to 30° C. and drying for 24 to 72 hours to remove excess moisture to form a solidified capsule;

[0029] S502, using a sieve to screen the particle size of the solidified capsules, the sieve aperture range is 5 to 15 mm, and ensure that the particle size difference after screening is controlled within the range of 0.1 to 2 mm.

[0030] Preferably, the mass proportion of the solidified capsules added into the soil sample is 5-50%.

[0031] The present invention provides a method for preparing a solidified capsule based on sisal fiber and polyacrylamide. The method has the following beneficial effects:

[0032] 1. The present invention absorbs moisture in the soil through the calcium chloride (CaCl2) in the inner core, reacts with carbonate ions in the soil to form calcium carbonate (CaCO3) crystals, fills the pores and enhances the structural strength of the soil; the recycled aggregate and nano-silicon dioxide work together to optimize the soil particle grading, construct a coherent skeleton structure, and effectively inhibit the water absorption and softening phenomenon of collapsible loess.

[0033] 2. The polyacrylamide inner membrane of the present invention has good hydrophilicity and sustained-release properties, which can gradually release the inner core material, make the chemical reaction uniform and lasting, and reduce the risk of pore collapse of collapsible loess; the toughness and strength of the sisal fiber outer membrane can further reduce the risk of the soil being affected by the external environment when the capsule decomposes, and provide additional physical support.

[0034] 3. The present invention can be adjusted according to the characteristics of collapsible loess through the double-layer membrane structure to ensure strong shear resistance under different stress combinations; the capsule particle size can be controlled within the range of 8 to 12 mm, and after screening, it can meet the modification requirements of different soil conditions.

[0035] 4. The present invention forms a tight connection in the soil pores through the mesh structure of nano-silicon dioxide, thereby improving the anti-seepage performance of the soil. Under long-term hydraulic action, the solidified capsule can maintain the high strength and low deformation characteristics of the soil, meeting the durability requirements of the foundation project. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 The present invention is a flow chart of a method for preparing a solidified capsule based on sisal fiber and polyacrylamide;

[0037] Figure 2 The technical roadmap of the method for preparing the solidified capsule based on sisal fiber and polyacrylamide of the present invention;

[0038] Figure 3 It is a stress path diagram of the penetration-consolidation shear test of the method for preparing the solidified capsule based on sisal fiber and polyacrylamide of the present invention;

[0039] Figure 4 The present invention is a schematic diagram of the capsule and double-layer membrane composition of the method for preparing solidified capsules based on sisal fiber and polyacrylamide. DETAILED DESCRIPTION

[0040] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] Please see attached Figure 1 and Figure 4 The embodiment of the present invention provides a method for preparing a solidified capsule based on sisal fiber and polyacrylamide, comprising the following steps:

[0042] S1, preparing the inner core of the solidified capsule, mixing the inner core materials for pretreatment;

[0043] S2, preparing the inner membrane, using polyacrylamide gel to form the inner membrane of the capsule;

[0044] S3, combining the inner core and the inner membrane, and encapsulating the inner core material in the inner membrane gel to form a hemispherical preliminary capsule;

[0045] S4, preparing an outer membrane, coating the surface of the hemispherical preliminary capsule with sisal fibers to form a double-layer membrane structure;

[0046] S5. Drying and screening the solidified capsules with double-layer membranes to obtain solidified capsules with uniform particle size.

[0047] Specifically, the calcium chloride (CaCl2) in the inner core absorbs moisture in the soil and reacts with carbonate ions in the soil to form calcium carbonate (CaCO3) crystals, which fill the pores and enhance the structural strength of the soil. The recycled aggregate and nano-silica work together to optimize the soil particle grading, construct a coherent skeleton structure, and effectively inhibit the water absorption and softening phenomenon of collapsible loess.

[0048] The core material in S1 includes the following components:

[0049] The particle size range of recycled aggregate is 0.2 to 2 mm;

[0050] Calcium chloride accounts for 10-30% of the total weight of the inner core;

[0051] The particle size of nano-silicon dioxide ranges from 50 to 150 nm, accounting for 5 to 20% of the total weight of the inner core.

[0052] Specifically, the inner core is the core part of the curing capsule, and its materials include recycled aggregate, calcium chloride (CaCl2), and nano silicon dioxide (SiO2).

[0053] Recycled aggregate: The particle size range is 0.2-2mm, which is made from waste concrete after crushing. It has good particle grading and skeleton support. Recycled aggregate can improve the particle structure of soil and enhance its mechanical properties.

[0054] Calcium chloride (CaCl2): As a highly hygroscopic substance, it can concentrate on absorbing moisture in the soil, promote the formation of calcium carbonate (CaCO3) crystals when the capsule decomposes, and then solidify the surrounding soil pores and enhance the stability of the soil.

[0055] Nano-silicon dioxide (SiO2): The particle size ranges from 50 to 150 nm, and the morphology is flocculent and mesh-like, with extremely high strength and chemical stability. Its function is to form a continuous skeleton structure with recycled aggregates to inhibit the softening and large deformation of collapsible loess after absorbing water.

[0056] The inner core material is uniformly mixed and then left to stand for 12 to 36 hours in an environment with a temperature of 20 to 30° C. and a humidity of 40 to 60%.

[0057] The polyacrylamide gel in S2 was prepared by the following steps:

[0058] S201, adding polyacrylamide powder into distilled water and stirring to form a solution;

[0059] S202, controlling the molecular weight of polyacrylamide to be between 5 million and 15 million, and the degree of hydrolysis to be between 15% and 50%;

[0060] S203. Under the conditions of an ambient temperature of 20 to 40°C and a humidity of 20 to 40%, stir until the solution gels, and let stand for 0.5 to 2 hours.

[0061] Specifically, the inner membrane is made of polyacrylamide, which, as a high molecular polymer, has excellent hydrophilicity and gel-forming properties.

[0062] Polyacrylamide: The molecular weight is controlled between 5 million and 15 million, and the degree of hydrolysis is in the range of 15% to 50%. It can form a stable gel. It has good adhesion during the wrapping process of the inner core and can gradually decompose in the soil to release the inner core material.

[0063] Slowly add polyacrylamide powder into distilled water and stir with a stirrer until it is completely dissolved and forms a gel solution. Control the ambient temperature (20-40°C) and humidity (20-40%) to gel and let it stand for 0.5-2 hours to ensure the best adhesion performance.

[0064] In effect, the inner membrane not only protects the structural integrity of the core material, but also releases the core through its gradual dissolution, extending the time span of the curing process and improving soil stability.

[0065] In S3, when the inner core material is filled into the inner membrane to form a hemispherical preliminary capsule:

[0066] The diameter of the hemispherical groove of the mold used ranges from 5 to 15 mm;

[0067] The coated preliminary capsules are heated in an environment of 40 to 70° C. for 1 to 3 hours to perform partial gel curing.

[0068] Specifically, the inner core and the inner film are combined by mold forming. A hemispherical mold is selected, and the diameter of the groove is controlled within the range of 5 to 15 mm. The prepared inner core material is filled into the inner film gel, and the inner core is evenly coated in the gel through gravity and the sealing effect of the mold.

[0069] This combination process ensures the uniform distribution of the inner core material, and the inner film is initially solidified by low temperature drying (40-70°C) for 1-3 hours. The coated hemispherical capsule is stable and reliable in physical properties, and can adapt to the stress requirements of different soil environments in engineering use.

[0070] The outer membrane in S4 is formed by sisal fibers, specifically:

[0071] The length of sisal fibers ranges from 1 to 10 mm;

[0072] Using the incompletely cured inner membrane gel to adhere sisal fibers;

[0073] After coating, the mold is pressurized in the range of 1 to 10 kPa, and allowed to stand at a temperature of 30 to 60°C for 0.5 to 2 hours to firmly bond the outer film to the inner film.

[0074] Specifically, the outer membrane is made of sisal fiber, and its length ranges from 1 to 10 mm. Sisal fiber has high toughness and excellent durability, and is an important material for constructing double-layer membranes. Through the protection of the outer membrane, the inner core and inner membrane can be effectively prevented from external damage during transportation and construction.

[0075] When the hemispherical preliminary capsule is coated with the outer membrane, the outer membrane coating is completed by rolling and attaching the sisal fibers with the help of the incomplete solidification characteristics of the inner membrane gel. The pressure treatment (pressure range 110kPa) ensures that the sisal fibers are tightly attached to the surface, and the outer membrane structure is stabilized by heating at low temperature (30-60°C) and standing for 0.5-2 hours.

[0076] The formed double-layer membrane capsule has internal and external protection, can better adapt to the complex environment of collapsible loess, and significantly improve the curing efficiency and durability of the capsule.

[0077] The drying and screening steps in S5 are:

[0078] S501, placing the double-layer film solidified capsule in a constant temperature environment of 20 to 30° C. and drying for 24 to 72 hours to remove excess moisture to form a solidified capsule;

[0079] S502, using a sieve to screen the particle size of the solidified capsules, the sieve aperture range is 5 to 15 mm, and ensure that the particle size difference after screening is controlled within the range of 0.1 to 2 mm.

[0080] Specifically, the coated capsules need to be dried and placed in a constant temperature (20-30°C) environment for 24-72 hours to remove excess moisture. The capsules are then screened using a sieve with a sieve aperture of 5-15mm to ensure that the particle size difference after screening is less than 1mm and the overall mass ratio is uniform.

[0081] After screening, the capsules are uniform in size, suitable for engineering needs of different soil particle gradations, while ensuring the consistency of curing performance.

[0082] The mass proportion of the solidified capsules added into the soil sample is 5 to 50%.

[0083] Specifically, it can be used for modifying collapsible loess, and the water sensitivity of the soil can be significantly reduced by adjusting the admixture ratio (5 to 50%).

[0084] The following is an introduction in conjunction with specific embodiments:

[0085] This project is planned to be carried out by combining experimental research with theoretical analysis. The technical route to be adopted is as follows: Figure 2 As shown. Typical collapsible loess was selected, and solidified soil samples with various proportions and dosages were configured, and indoor tests that were closer to the actual state were designed. Under different stress combinations and dissolution and filtration, characteristic data of strength characteristics, permeability and microstructural changes of solidified loess were obtained from the test; finally, a set of solidified capsule preparation technology from configuration, engineering property evaluation to macro-micro mechanism analysis was established.

[0086] (1) Preparation of capsules

[0087] 1) Inner core preparation

[0088] Adding recycled aggregate to soil can improve the particle size distribution of soil and support the soil skeleton. At the same time, the cement hydrate Ca(OH)2 contained in the aggregate can react with CO3 2- 、HCO3 - The plasma reacts to produce CaCO3 and other substances, further solidifying the soil.

[0089] The curing agent CaCl2 has strong water absorption, which can help the water in the soil to concentrate in the curing capsule during the soil infiltration process, and prevent the collapse of the pores of collapsible loess at the physical and chemical level. At the same time, CaCl2 can also react with CO3 in the soil2- 、HCO3 - The reaction generates CaCO3 and then solidifies the surrounding soil. 100nm SiO2 particles are selected. Its particle microstructure is spherical, with flocculent and mesh quasi-particle structure. Since nano-SiO2 has strong physical and chemical stability and high strength, it is added to the soil to assist the recycled aggregate to form a coherent skeleton system, inhibiting the structural weakening and large deformation of collapsible loess after absorbing water.

[0090] According to the above material properties, three materials, namely recycled aggregate, CaCl2 and nano-SiO2, are selected as the inner core of the curing capsule. Among them, the recycled aggregate is crushed by a crusher to crush concrete, and is prepared into three kinds of materials with particle sizes of 0.25mm, 0.5mm and 2mm, and then mixed evenly for use. CaCl2 and nano-SiO2 are both powdery materials. Since the three materials, recycled aggregate, CaCl2 and nano-SiO2, have good physical and chemical stability at room temperature (-10 to 40°C) and common humidity (30 to 65%), no special treatment is required.

[0091] The three materials of recycled aggregate, CaCl2 and nano-SiO2 were sequentially prepared into 3×3×3=27 kinds of capsule cores according to the proportions shown in Table 1. The core materials with different proportions were directly fed into the feeding screw machine for mixing for 0.5 hours until the three materials were evenly mixed. Then the mixed core fillings were placed in a constant temperature (25°C) and constant humidity (humidity 45%) box for 1 day.

[0092] Table 1 Curing capsule ratio scheme

[0093] Mix ratio Recycled Aggregates <![CDATA[CaCl2]]> <![CDATA[Nanometer SiO2]]> Quality Ratio 1 5 2 1.5 Quality Ratio 2 3 1 1 Quality Ratio 3 1 0.5 0.5

[0094] 2) Inner membrane preparation

[0095] Polyacrylamide is not easy to dissolve with water in the air at 25-40°C and humidity at 25%-35%. Therefore, this ambient temperature and humidity range is selected to prepare the inner membrane. Weigh 0.3-2g of polyacrylamide powder sample with a weighing bottle. Measure 100mL of distilled water and pour it into a conical flask; use an electromagnetic stirrer to stir the distilled water to form a vortex with a depth of about 1cm; then slowly pour the weighed polyacrylamide into the conical flask and continue stirring for 1 hour until the solution becomes a gel. Standard hydrolysis tests were carried out on polyacrylamide gels of different concentrations. Determine the concentration of polyacrylamide gel with a hydrolysis degree in the range of 20-50%. Select the polyacrylamide gel solution with no flocculent precipitation or obvious agglomeration, a molecular weight between 5-15 million, and the lowest concentration within this range as the optimal concentration for preparing the capsule inner membrane.

[0096] Make rows of hemispherical molds with diameters of 8 mm, 10 mm, and 12 mm, with 30 hemispherical grooves in each row, and 20 rows in total, that is, the mold has a total of 600 hemispherical grooves. After the polyacrylamide gel is prepared, pour it into the grooves of the hemispherical mold.

[0097] 3) Preparation of outer membrane + capsule

[0098] Using special sieves with diameters of 10mm, 12mm and 14mm, the stirred capsule cores are slowly poured into the 8mm, 10mm and 12mm hemispherical mold grooves covered with polyacrylamide. Relying on the gravity of the core, part of the polyacrylamide gel is squeezed out of the groove, and this process also allows the capsule core to be fully wrapped by the gel.

[0099] Place the mold in an electric heating box, adjust the temperature to 60°C, and bake at low temperature for 2 hours. Take out the double-number mold. At this time, the gel in the hemispherical groove shows plastic properties due to water loss. Squeeze the two rows of molds together, one positive and one negative, and press them statically with a heavy object for 1 hour. Then take out the spherical single-layer membrane solidified capsule, place it on a slide covered with sisal fiber, and slide down by the capsule's own gravity. At this time, because the gel is not completely dry, it can rely on its own adhesion to wrap around the surface to form the outer membrane of the solidified capsule.

[0100] The prepared solidified capsules were placed in a dry thermostatic box at 25°C for 2 days until excess water was absorbed and the outer membrane of the capsule became hard.

[0101] Use special sieves of 8mm, 10mm and 12mm to screen and sort solidified capsules of different particle sizes, so as to ensure that the particle size difference of the sieved capsules is between 0.05mm and 1mm, and the mass proportion of the overall particle size difference is controlled within 20%.

[0102] (2) Soil sample selection and specimen preparation

[0103] The collapsible loess foundation in the area from Wulongkou to Huanggang Temple in Zhengzhou City is planned to be the research object. Combining the engineering investigation and test data before and after filling and excavation, the compacted loess near the representative new buildings is selected as the sampling target.

[0104] Soil samples were prepared according to the standard of mixing and curing capsules accounting for 0%, 10%, 20%, 30%, and 40% of the total soil sample mass. The specific control variables are shown in Table 2. Standard compaction tests were carried out on the soil samples to determine the optimal moisture content and maximum dry density of soil samples mixed with different proportions of curing capsules. According to the optimal moisture content and maximum dry density, the soil samples were cut into triaxial specimens with a diameter of 39.1 mm and a height of 80 mm using a sample preparation device. Physical and chemical indicators such as dry density, moisture content, specific gravity of soil particles, liquid and plastic limits, particle grading curves, and initial soluble salt content were measured, and samples with similar above indicators were selected as samples for this project. Therefore, this project needs to prepare 3×3=9 groups of cured loess samples with different capsule diameters and dosages.

[0105] Table 2 Control variables for preparing samples

[0106]

[0107] (2) Permeability and consolidation test of solidified loess under combined stress

[0108] The solidified loess samples with different blending ratios were placed in a stress-controlled triaxial apparatus, and consolidation and permeability tests were carried out after applying a certain confining pressure and constant shear stress. The test process and control conditions are as follows:

[0109] 1) Test process

[0110] The process of the filtration test is as follows: isostatic consolidation; normal shear stage of loading to the first stress level (defined in the next paragraph); infiltration stage (after the infiltration deformation is stable, the next stress level is loaded until it is stable and then water is infiltrated again, until the last stress level or the sample undergoes infiltration failure under constant shear stress); drainage and shearing until the sample is destroyed. During the test, the changes in the permeability coefficient and axial force of the sample are monitored in real time. As well as the decomposition rate of the double-layer membrane of the solidified capsule, the decomposition rate analysis is carried out using a control group test. The maximum diameter of the damaged holes in the double-layer membrane in the sample and the proportion of the hole area are measured to verify the curing efficiency of the solidified capsule. The stress path of the filtration test is shown in Figure 3 .

[0111] 2) Control conditions

[0112] It is proposed to set the net confining pressure σ3 into 4 groups, namely 50kPa, 100kPa, 150kPa, and 200kPa, to represent the compacted loess at different depths. The stress level s is set to 4 levels, representing the additional stress transmitted by the building above the foundation. The definition of the stress level is s = p i / p fd . Where pi is a certain level of deviatoric stress applied before penetration; p fdis the failure bias pressure of the non-permeable sample during normal shear. Previous research results show that when the s value under each confining pressure is close to 0.75, the sample is prone to dissolution shear failure. Therefore, it is planned to select the last level s value as 0.75; because it is divided into 4 levels of loading, s is taken as 0, 0.375, 0.5625, and 0.75 respectively. Different confining pressures and stress levels can form a group of stress combinations, so this test has a total of 16 groups of stress combinations S rc There are 9 groups of sample control variables in Table 2. Therefore, this project is expected to carry out 16×9=144 groups of triaxial tests.

[0113] (3) Study on the mechanism of capsule solidification of collapsible loess

[0114] 1) Analysis of mechanical properties of solidified loess

[0115] ① Macro analysis

[0116] The consolidation-permeability-shear test was carried out on the solidified loess with different particle sizes and masses. The collapsibility coefficient δ in the partial pressure consolidation-permeability stage was calculated by comparison. s (Non-self-weight collapsibility coefficient), as follows

[0117] δ s =(h z2 -h z1 ) / h0

[0118] Where h0 is the initial height of the sample, mm; h z1 h is the height of the sample after consolidation stabilization under the previous level of eccentric load, mm; z2 is the height of the specimen after consolidation stabilization under the current bias load, mm.

[0119] According to formula (1), the variation law of the collapsibility coefficient and the critical variation range with a value less than or equal to 0.015 under various levels of loading and different stress combinations are calculated.

[0120] Compare and analyze the axial and volume strains and the development law of permeability coefficient of the solidified soil in the consolidation-permeability stage under different stress combinations and different capsule mixing particle sizes and mixing amounts; at the same time, explore the evolution characteristics of the solidified soil strength in the shear stage. Thus, a comprehensive analysis method and evaluation standard for the deformation, permeability and durability (strength under long-term hydraulic action) of the solidified soil under the combined action of water and force is formed. That is, a quantitative standard of small consolidation deformation, good permeability and high shear strength.

[0121] ②Microscopic analysis

[0122] The electron microscope scanning test was carried out on the solidified loess after shear failure to obtain the microstructure image SEM map. The microstructure characteristic parameters were quantitatively obtained, including the particle and pore size and distribution curve, the connection coefficient curve, etc. The microscopic parameters were used to analyze the evolution law of the microstructure during consolidation-permeability and shear, and the impact was compared with the non-solidified samples. Finally, an analysis and evaluation system was formed with equivalent diameters of particles and pores, fractal index of particle and pore distribution, and connection coefficient.

[0123] Using nonlinear principal component analysis, two parameters that can comprehensively characterize the microstructural geometry and strength characteristics during dissolution and filtration were obtained, and the microscopic mechanism of the structural evolution of solidified loess was explored. Using nonlinear correlation analysis, the correlation between the two parameters and the macroscopic permeability coefficient and strength parameters was explored, and the change mechanism of the shear strength parameters and permeability coefficient of solidified loess under different stress combinations and permeability was deeply revealed.

[0124] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a solidified capsule based on sisal fiber and polyacrylamide, characterized in that: The following steps are involved: S1, preparing the inner core of the solidified capsule, mixing the inner core materials for pretreatment; S2, preparing the inner membrane, using polyacrylamide gel to form the inner membrane of the capsule; S3, combining the inner core and the inner membrane, and encapsulating the inner core material in the inner membrane gel to form a hemispherical preliminary capsule; S4, preparing an outer membrane, coating the surface of the hemispherical preliminary capsule with sisal fibers to form a double-layer membrane structure; S5. Drying and screening the solidified capsules with double-layer membranes to obtain solidified capsules with uniform particle size.

2. The method for preparing a solidified capsule based on sisal fiber and polyacrylamide according to claim 1, characterized in that: The inner core material in S1 includes the following components: The particle size range of recycled aggregate is 0.2 to 2 mm; Calcium chloride accounts for 10-30% of the total weight of the inner core; The particle size of nano silicon dioxide ranges from 50 to 150 nm, accounting for 5 to 20% of the total weight of the inner core.

3. The method for preparing a solidified capsule based on sisal fiber and polyacrylamide according to claim 2, characterized in that: The inner core material is uniformly mixed and then left to stand for 12 to 36 hours in an environment with a temperature of 20 to 30° C. and a humidity of 40 to 60%.

4. The method for preparing a solidified capsule based on sisal fiber and polyacrylamide according to claim 1, characterized in that: The polyacrylamide gel in S2 is prepared by the following steps: S201, adding polyacrylamide powder into distilled water and stirring to form a solution; S202, controlling the molecular weight of polyacrylamide to be between 5 million and 15 million, and the degree of hydrolysis to be between 15% and 50%; S203. Under the conditions of an ambient temperature of 20 to 40°C and a humidity of 20 to 40%, stir until the solution gels, and let stand for 0.5 to 2 hours.

5. The method for preparing a solidified capsule based on sisal fiber and polyacrylamide according to claim 1, characterized in that: In said S3, when the inner core material is filled into the inner membrane to form a hemispherical preliminary capsule: The diameter of the hemispherical groove of the mold used ranges from 5 to 15 mm; The coated preliminary capsules are heated in an environment of 40 to 70° C. for 1 to 3 hours to perform partial gel curing.

6. The method for preparing a solidified capsule based on sisal fiber and polyacrylamide according to claim 1, characterized in that: The outer membrane in S4 is formed by sisal fibers, specifically: The length of sisal fibers ranges from 1 to 10 mm; Using the incompletely cured inner membrane gel to adhere sisal fibers; After coating, the mold is pressurized in the range of 1 to 10 kPa, and allowed to stand at a temperature of 30 to 60°C for 0.5 to 2 hours to firmly bond the outer film to the inner film.

7. The method for preparing a solidified capsule based on sisal fiber and polyacrylamide according to claim 1, characterized in that: The drying and screening steps in S5 are: S501, placing the double-layer film solidified capsule in a constant temperature environment of 20 to 30° C. and drying for 24 to 72 hours to remove excess moisture to form a solidified capsule; S502, using a sieve to screen the particle size of the solidified capsules, the sieve aperture range is 5 to 15 mm, and ensure that the particle size difference after screening is controlled within the range of 0.1 to 2 mm.

8. The method for preparing a solidified capsule based on sisal fiber and polyacrylamide according to claim 1, characterized in that: The solidified capsule is added into the soil sample at a mass ratio of 5 to 50%.

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