Method for the hydrophobically modified illite clay based on initial water content regulation of pdms

Abstract

The application discloses a method for modifying illite soil by PDMS based on initial water content regulation. Firstly, a PDMS dosage regulation model is constructed through test analysis, then the initial moisture content of the illite soil to be treated is determined, a target drop water infiltration time is set, the target drop water infiltration time and the initial moisture content are brought into the dosage regulation model to calculate the optimal dosage of PDMS; then a hydrophobic agent solution is prepared by using PDMS; the hydrophobic agent solution is mixed into the illite soil to be treated according to the optimal dosage of PDMS, and the mixture is mixed under controlled stirring, diffused after mixing, and the organic solvent is removed by using a staged volatilization method, and the hydrophobic modified illite soil is obtained after drying, homogenizing and screening. The application takes illite soil as a modification object, takes the initial water content as a pre-variable, constructs a testable PDMS dosage regulation model in combination with drop water infiltration time-dosage-moisture content data, and converts the modification process from empirical mixing into a calculable, verifiable and reproducible regulation preparation process.

Description

Technical Field

[0001] This invention relates to the field of engineering foundation treatment technology, and in particular to a method for hydrophobic modification of illite soil using PDMS based on initial water content regulation. Background Technology

[0002] Special soil types, such as loess, mudstone, expansive soil, and saline soil, are generally subjected to continuous effects from rainfall infiltration, groundwater fluctuations, and environmental wet-dry cycles during service. Moisture migration often directly leads to decreased matric suction, weakened structural connections, accumulated collapsibility deformation, and reduced strength, ultimately causing engineering problems such as foundation settlement, slope instability, and roadbed defects. Illite, as a common and relatively abundant clay mineral in special soils, exhibits a layered structure, high specific surface area, and significant interfacial activity, making these soil types highly sensitive to changes in moisture state. Existing data indicate that illite soil has a liquid limit of approximately 41%, a plastic limit of approximately 22.8%, and a natural water content of approximately 1.07%, demonstrating a significant state dependence under the combined effects of engineering disturbance and moisture disturbance. This provides a clear target basis for conducting water-blocking modification centered on interfacial wettability control.

[0003] Hydrophobic modification technology reduces the surface free energy of soil particles by incorporating silanes, siloxanes (such as polydimethylsiloxane (PDMS)), emulsions, or organic hydrophobic components into the soil, thereby weakening the wetting effect at the soil-water interface. However, most existing modification processes assume that "the hydrophobic modifier should be uniformly incorporated," meaning that the amount of hydrophobic modifier is usually determined subjectively in advance, without considering the initial water content of the soil as a pre-controlled variable that determines film-forming efficiency, interfacial coating continuity, and the final water-blocking effect. For fine-particle, highly interfacially active systems like illite soil, the pore water distribution, capillary connectivity, and interparticle bridging states are significantly different under different initial water contents, resulting in different diffusion behaviors, coating degrees, and drip infiltration responses for the same amount of hydrophobic agent under different sample conditions. Therefore, if a uniform amount of hydrophobic modifier and a uniform preparation method are still used to modify illite soil, it is difficult to simultaneously achieve synergistic optimization of water-blocking effect, structural stability, and preparation repeatability. As a hydrophobic modifier, PDMS can achieve an apparent contact angle close to 90° at low dosages, and can stably reach 120°~123° at about 3%. Meanwhile, the drip infiltration time shows a clear unimodal distribution with the change of soil moisture content, and decays rapidly under higher moisture content. The above theories indicate that there is a nonlinear coupling relationship between "moisture content - hydrophobic agent dosage - water-blocking performance". Summary of the Invention

[0004] Given the common problems in existing illite soil hydrophobic modification technologies: the initial water content of the soil is not explicitly incorporated into the preparation design, leading to significant differences in the diffusion, spreading, and fixation behavior of hydrophobic agents under different initial states; the dosage of hydrophobic agents is mostly selected empirically, lacking quantitative calculation basis coupled with the water content; and under high water content, a uniform dosage is difficult to simultaneously achieve multiple engineering objectives such as prolonged drip infiltration time, increased apparent contact angle, and reduced saturated permeability coefficient. Therefore, this invention proposes a method for hydrophobic modification of illite soil based on the control of initial water content. By establishing a PDMS dosage control model, the synergistic optimization of PDMS dosage and preparation path is achieved.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A method for hydrophobically modified illite soil using PDMS based on initial water content regulation mainly includes the following steps: S1. A PDMS doping control model is constructed through experimental analysis. The PDMS doping control model is as follows: ; in, , A dimensionless parameter characterizing the initial water content of soil, The initial water content of the illite soil. The liquid limit water content of illite soil; The target drip infiltration time; In the initial water-bearing state The following is a time limit for drip infiltration. The optimal PDMS doping level; As the baseline infiltration time, The peak response amplitude induced by PDMS. These are the peak water state parameters. The peak distribution width, The critical parameter for high water content decay, To reduce the steepness factor, This is the doping sensitivity coefficient; S2. Determine the initial moisture content of the illite soil to be treated; S3. Set the target drip infiltration time for the modified illite soil, and calculate the optimal PDMS dosage based on the target drip infiltration time and the initial moisture content using the PDMS dosage control model. S4. Dissolve PDMS in an organic solvent to prepare a hydrophobic agent solution; S5. Based on the calculated optimal dosage of PDMS, slowly add the hydrophobic agent solution into the illite soil to be treated in proportion, and mix under controlled stirring conditions to ensure that the PDMS is in full contact with the soil particles. S6. Mix and allow to diffuse at rest; S7. Organic solvents are removed by a staged volatilization method, so that PDMS is gradually fixed on the surface of soil particles. S8. After drying, homogenization and sieving are carried out to obtain hydrophobic modified illite soil.

[0006] Further, in step S1, the method for constructing the PDMS dosage control model through experimental analysis is as follows: modified illite soil with different PDMS dosages is selected, and drip infiltration time is tested under different soil moisture content conditions to obtain experimental data. Based on the experimental data, a drip infiltration time response model is constructed through regression analysis. The drip infiltration time response model is used to characterize the coupling relationship between drip infiltration time and PDMS dosage and soil moisture content. Then, the PDMS dosage control model is obtained by back-calculation based on the drip infiltration time response model.

[0007] Furthermore, the drip infiltration time response model is as follows: ; in, This indicates that the PDMS doping content is The water state parameters are The infiltration time of water dripping into the soil under certain conditions.

[0008] Compared with the prior art, the present invention has the following advantages: (1) Realize the transformation from empirical dosage to calculated dosage: This invention takes illite soil as the direct modification object, raises the initial water content state to the preparation pre-variable, and constructs a verifiable PDMS dosage control model by combining drip infiltration time-dosage-water content data, so that the modification process is transformed from empirical mixing into a calculable, verifiable and reproducible controlled preparation process. (2) Taking into account both interface and seepage indicators: This invention combines the variation law of apparent contact angle and saturated permeability coefficient to form a synergistic optimization of contact angle, infiltration time and permeability coefficient, thereby achieving dual support for interface wettability and macroscopic water-blocking performance. (3) Strong engineering operability: The process conditions used in this invention are all within the controllable range of conventional experiments and engineering, the parameter window is clear, the preparation process is stable, and it is easy to promote and apply in soils with high illite content. Attached Figure Description

[0009] Figure 1 This is a flowchart of the method for hydrophobic modification of illite soil by PDMS based on the initial water content control of the present invention; Figure 2 Discrete test data of drip infiltration time obtained by modifying illite soil with different PDMS content under different soil moisture conditions, and fitting curve of drip infiltration time response model constructed; Figure 3 Comparison of apparent contact angles of illite soil modified with different hydrophobic agents; Figure 4 The figure shows the effect of PDMS dosage on the saturated permeability coefficient of hydrophobically modified illite soil.

[0010] Figure 5 This is a comparison chart of drip infiltration time in illite soil modified with different dosages and with uniform dosages using the PDMS dosage control model of this invention. Detailed Implementation

[0011] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0012] Example 1: A method for hydrophobic modification of illite soil using PDMS based on initial water content control, referring to... Figure 1 Specifically, it includes the following steps: Step S1: Construct a PDMS doping control model Modified illite soils with PDMS content of 1%, 2%, 3%, 4%, and 5% were selected, and drip infiltration time tests were conducted under different soil moisture contents. The results are as follows: Figure 2 As shown, the drip infiltration time under different PDMS dosages first increases and then decreases with increasing water content, exhibiting a unimodal distribution. The peak value generally appears in the medium water content region, while it rapidly decays to a lower level under higher water content conditions. With the PDMS dosage increasing from 1% to 3%–5%, the peak value significantly increases, indicating that increasing the PDMS content enhances the water-blocking response, but this enhancement does not continue indefinitely in the high water content decay region. Then, a drip infiltration time response model is constructed based on regression analysis of the experimental data: ; in, This indicates that the PDMS doping content is The water state parameters are The drip infiltration time of soil under certain conditions; A dimensionless parameter characterizing the initial water content of soil, , The initial water content of the illite soil. The liquid limit water content of illite soil; As the baseline infiltration time, The peak response amplitude induced by PDMS. These are the peak water state parameters. The peak distribution width, The critical parameter for high water content decay, To reduce the steepness coefficient, This is the doping sensitivity coefficient.

[0013] In the drip infiltration time response model constructed above, " The item reflects the enhanced water-blocking effect brought about by the increased PDMS dosage; "This represents the Gaussian peak term, characterizing the dominant response window in the medium-water-aquifer region;" The term "" represents the Logistic decay term, which characterizes the rapid decay of drip infiltration time after the formation of a continuous aqueous phase under high water content conditions. Therefore, this model can not only quantitatively characterize the coupling relationship between "dosage concentration - water content - drip infiltration time", but also provide a basis for solving the minimum effective dosage of PDMS under different initial water content conditions.

[0014] The PDMS dosage control model can be obtained by back-calculation based on the constructed drip infiltration time response model: ; in, The target drip infiltration time; In the initial water-bearing state The following is a time limit for drip infiltration. The optimal PDMS doping level.

[0015] Step S2: The initial moisture content of the illite soil to be treated was determined by the drying method, and its normalized characterization was performed. .

[0016] Step S3: Set the target drip infiltration time for the modified illite soil, and input the target drip infiltration time and initial moisture content into the constructed PDMS dosage control model to calculate the optimal PDMS dosage.

[0017] Step S4: Weigh PDMS with a viscosity of approximately 2000 mPa·s at 1.0% of the dry soil mass and prepare a homogeneous solution with a PDMS:butyl acetate mass ratio of 1:10.

[0018] Step S5: Based on the optimal dosage of PDMS, slowly add the prepared solution to illite soil according to the ratio, and mechanically stir at 40 r / min for 15 min at room temperature to ensure that PDMS is in full contact with soil particles.

[0019] Step S6: After mixing, let stand for 1 hour to promote the diffusion and directional spreading of PDMS on the particle surface.

[0020] Step S7: Remove organic solvents by a staged evaporation method, including pre-evaporating the sample at 70°C for 1 hour, then heating it to 105°C until the mass is constant, so that PDMS is gradually fixed on the surface of soil particles.

[0021] Step S8: After drying, the soil is sieved through a 0.75mm sieve and sealed for 24 hours to obtain hydrophobic modified illite soil.

[0022] Test Example 1: Comparison and Verification of Apparent Contact Angles of Illite Soil Modified with Different Hydrophobic Agents To compare the ability of different hydrophobic agents to regulate the interfacial wettability of illite soil, illite soil was modified with PDMS, silane coupling agents, and vegetable oil-based hydrophobic agents, respectively. The apparent contact angle was measured using the seat drop method. The results are as follows: Figure 3 As shown in the figure. The results show that, under the same dosage conditions, the apparent contact angle of PDMS-modified illite soil is significantly higher than that of other hydrophobic agents; among them, when the PDMS dosage is 0.25% to 0.5%, the apparent contact angle is close to 90°; when the dosage is increased to 1.0% to 3.0%, the apparent contact angle is further improved and stabilized in the range of 120° to 123°.

[0023] The results show that PDMS has a high interfacial hydrophobic induction efficiency in illite soil systems, and can achieve a significant transformation from hydrophilic to hydrophobic at low dosages, providing experimental basis for the present invention to achieve effective modification with low or medium dosages.

[0024] Test Example 2: Verification of the effect of PDMS doping on saturated permeability coefficient To evaluate the effect of PDMS dosage on the macroscopic seepage blocking capacity of soil, saturated permeability tests were conducted under different PDMS dosage conditions. The results are as follows: Figure 4 As shown, the saturated permeability coefficient of modified illite soil continued to decrease with increasing PDMS content; the decrease was most significant when the PDMS content increased from 0% to 1.0%; when the content further increased to 3.0%–5.0%, the permeability coefficient continued to decrease, but the rate of decrease slowed down.

[0025] The above results indicate that PDMS modification can effectively weaken the continuous seepage channels inside the soil and achieve significant water-blocking effects even under medium and low dosage conditions.

[0026] Test Example 3: Comparison of PDMS Dosage Control Model with Unified Dosage Modification of Illite Soil Illite soil samples with initial moisture contents of 2%, 6%, and 9% were selected, representing low, medium, and high moisture contents, respectively. The PDMS dosage was determined using the PDMS dosage control model of this invention, and a uniform 2% dosage method was used for modification. The drip infiltration time results are shown below. Figure 5As shown in the figure. The results show that, for low water content samples, although a uniform 2% dosage can achieve high hydrophobicity, there is material redundancy; for medium water content samples, the dosage control method of this invention can keep the drip infiltration time in the advantageous range; for high water content samples, the drip infiltration time decreases significantly under a uniform 2% dosage, while the dosage control method based on the initial water content can significantly improve its water-blocking and retention capabilities.

[0027] Therefore, the strategy based on initial water content control proposed in this invention can reduce the blindness of dosage, improve the consistency of modification effect, and enhance water-blocking stability under high water content conditions.

[0028] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for hydrophobically modified illite soil using PDMS based on initial water content regulation, characterized in that, Includes the following steps: S1. A PDMS doping control model is constructed through experimental analysis. The PDMS doping control model is as follows: ； in, , A dimensionless parameter characterizing the initial water content of soil, The initial water content of the illite soil. The liquid limit water content of illite soil; The target drip infiltration time; In the initial water-bearing state The following is a time limit for drip infiltration. The optimal PDMS doping level; As the baseline infiltration time, The peak response amplitude induced by PDMS. These are the peak water state parameters. The peak distribution width, The critical parameter for high water content decay, To reduce the steepness factor, This is the doping sensitivity coefficient; S2. Determine the initial moisture content of the illite soil to be treated; S3. Set the target drip infiltration time for the modified illite soil, and calculate the optimal PDMS dosage based on the target drip infiltration time and the initial moisture content using the PDMS dosage control model. S4. Dissolve PDMS in an organic solvent to prepare a hydrophobic agent solution; S5. Based on the calculated optimal dosage of PDMS, slowly add the hydrophobic agent solution into the illite soil to be treated in proportion, and mix under controlled stirring conditions to ensure that the PDMS is in full contact with the soil particles. S6. Mix and allow to diffuse at rest; S7. Organic solvents are removed by a staged volatilization method, so that PDMS is gradually fixed on the surface of soil particles. S8. After drying, homogenization and sieving are carried out to obtain hydrophobic modified illite soil.

2. The method for hydrophobically modified illite soil with PDMS according to claim 1, characterized in that, In step S1, the method for constructing the PDMS dosage control model through experimental analysis is as follows: modified illite soil with different PDMS dosages is selected, and drip infiltration time is tested under different soil moisture content conditions to obtain experimental data. Based on the experimental data, a drip infiltration time response model is constructed through regression analysis. The drip infiltration time response model is used to characterize the coupling relationship between drip infiltration time and PDMS dosage and soil moisture content. Then, the PDMS dosage control model is obtained by back-calculation based on the drip infiltration time response model.

3. The method for hydrophobically modified illite soil with PDMS according to claim 2, characterized in that, The drip infiltration time response model is as follows: ； in, This indicates that the PDMS doping content is The water state parameters are The infiltration time of water dripping into the soil under certain conditions.

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