Modified bentonite mud for ultra-deep diaphragm wall and preparation method thereof

Abstract

The application belongs to the technical field of building materials, and particularly relates to a modified bentonite mud for super-deep underground continuous walls and a preparation method thereof, which comprises the following components in percentage by mass: modified sodium bentonite 5.86-6.46%, starch 0.1-0.16%, sodium carbonate 0.034-0.04%, carboxymethyl cellulose 0.02-0.026%, polyacrylamide 0.024-0.032%, barite powder 0.6-0.8%, and the rest is mixing water. The microstructure of the bentonite is improved by silane treatment, and the dispersion capacity of the bentonite in the mud is enhanced. The sodium bentonite is nano-modified by using a homogenizer, the synergistic effect of the nano-modified bentonite and other additives is exerted, the rheological properties of the prepared wall protection mud are more stable, the shear thinning performance is exhibited, the function of suspending and carrying out the soil residue of the mud from the ground is strengthened, a series of problems such as necking and hole collapse in the trenching process of the continuous wall construction can be effectively avoided, the wall protection effect of the mud is good, and the mud is suitable for the construction of underground continuous walls under different soil conditions.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, and in particular relates to a modified bentonite slurry for ultra-deep underground continuous walls and its preparation method. Background Technology

[0002] Diaphragm walls are constructed by excavating soil using trenching machinery with slurry backing, creating rectangular trenches of a certain depth. Underwater reinforced concrete is then poured to form individual wall units, which are connected using specific jointing methods to create a continuous underground reinforced concrete wall. Diaphragm walls are mainly divided into two categories: pile-type and wall-type. They are primarily used for foundation pit excavation and as temporary or permanent retaining structures for underground buildings. They offer advantages such as low construction vibration, low noise, high wall rigidity, good integrity, and diverse forms. Suitable for various soil types, they can be constructed using reverse construction methods and provide waterproofing, seepage prevention, and deep foundation pit support. They can also serve as foundations to withstand horizontal forces. Therefore, diaphragm walls are widely used in the construction of building basements, subway stations, tunnel shafts, and large bridge foundations.

[0003] Slurry wall construction is a crucial step in diaphragm wall construction. The slurry's role is to form an impermeable mud cake on the trench walls, effectively applying hydrostatic pressure to prevent groundwater seepage and wall spalling. It also suspends and carries away soil debris. The performance of the slurry significantly impacts the effectiveness of the wall construction; substandard slurry can easily cause trench wall collapse during construction, adversely affecting subsequent work. Generally, qualified slurry should meet requirements such as good thixotropy, low solids content, high viscosity, thin mud cake, and low water loss. Bentonite slurry is the preferred type of slurry for wall construction, and its control indicators should meet requirements for density, funnel viscosity, sand content, water loss, and pH value. In fact, the viscosity (rheological properties) of the slurry has a significant impact on its performance, and its control is more difficult than controlling the density and pH value. Viscosity affects whether the water loss and sand content meet the requirements, and also influences the stability of the slurry. However, the rheological properties (viscosity) of conventional bentonite slurry are difficult to control precisely, resulting in unstable wall-protecting effects in engineering applications. Severe separation between the slurry and water is common, especially for ultra-deep diaphragm walls. The performance of the wall-protecting slurry plays a decisive role in the success of the trenching process. If trench wall collapse occurs, the subsequent repair and reconstruction process becomes extremely complex, cumbersome, and time-consuming. Therefore, there is an urgent need for a slurry with excellent rheological properties to ensure sufficient stability. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, this invention provides a modified bentonite slurry for ultra-deep underground continuous walls and its preparation method. The microstructure of bentonite is improved by silane treatment, which enhances the dispersion ability of bentonite in the slurry. The bentonite is modified into nanoparticles by using a homogenizer. By optimizing the mix ratio, the slurry is endowed with good rheological properties, making the wall protection effect of the slurry more stable and effectively solving the problems of easy bleeding and poor wall protection effect of traditional bentonite slurry.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A modified bentonite slurry for ultra-deep underground continuous walls comprises, by mass percentage: 5.86%-6.46% modified sodium bentonite, 0.1%-0.16% starch, 0.034%-0.04% sodium carbonate, 0.02%-0.026% carboxymethyl cellulose, 0.024%-0.032% polyacrylamide, 0.6%-0.8% barite powder, with the balance being water.

[0007] Preferably, the preparation process of the modified sodium bentonite includes the following steps: (1) 550g of sodium bentonite is poured into 2000ml of ethanol and stirred at high speed for 1h with a stirrer at a speed of 600-700r / min to form solution A; (2) 500g of 3-aminopropyltriethoxysilane is poured into 1000ml of ethanol and stirred with a stirrer for 1h with a speed of 300-400r / min to form solution B; (3) Solution A and solution B are then mixed and stirred at room temperature for 6h with a stirrer at a speed of 300-400r / min to form solution C. (4) Then filter the C liquid and dry it at 150°C for 48 hours. After cooling, pass the obtained sodium bentonite through a 75μm sieve. (5) Weigh the above sodium bentonite and distilled water at a mass ratio of 1:2 and add them to a homogenizer for mixing. Set the speed of the homogenizer to 5900-6100r / min and the mixing time to 2-3h. (6) After mixing, seal the sodium bentonite mixture and place it at room temperature for more than 48h. (7) Pour the sodium bentonite mixture into a container and dry it at 100°C for more than 48h. After it is completely dried, the modified sodium bentonite is obtained.

[0008] Preferably, the sodium bentonite has a particle size of 300-325 mesh.

[0009] Preferably, the carboxymethyl cellulose has a pH value of 8-9, and the barite powder has a particle size of 400 mesh.

[0010] It should be noted that the treatment of sodium bentonite with 3-aminopropyltriethoxysilane effectively improves the microstructure of bentonite, thereby improving its dispersion ability in drilling mud, enhancing the bond strength between the bentonite mud and the borehole wall, and improving the mud wall protection effect and scum removal performance. This allows the bentonite mud to be used in areas with more challenging geological conditions. Multiple shear gaps are created by the stator and rotor in the homogenizer, inducing strong turbulent shear stress and forming a turbulent jet along the stator gaps to disperse particles. Through these steps, ordinary sodium bentonite is transformed into nano-sodium bentonite. Compared to ordinary bentonite, the rheological properties (viscosity) of nano-bentonite are easier to control and more stable. By adjusting the rheological properties, the requirements for trenching and wall protection of underground continuous walls under different soil conditions can be met. Furthermore, the shear thinning behavior of nano-bentonite helps to efficiently suspend soil residue, ensuring the quality of subsequent concrete pouring.

[0011] In this invention, polyacrylamide is used as a flocculant to effectively reduce the frictional resistance of the fluid, thereby playing a role in flocculation and thickening.

[0012] This invention also provides a method for preparing modified bentonite slurry for ultra-deep underground continuous walls, comprising the following steps:

[0013] (1) Weigh each component of the mud according to the mass percentage. Each component includes: 5.86%-6.26% modified sodium bentonite, 0.1%-0.16% starch, 0.034%-0.04% sodium carbonate, 0.02%-0.026% carboxymethyl cellulose, 0.024%-0.032% polyacrylamide, 0.6%-0.8% barite powder, and the balance is water.

[0014] (2) Add water, modified sodium bentonite, starch, sodium carbonate, carboxymethyl cellulose, polyacrylamide and barite powder to a high-speed mixer in sequence, and stir the mixture thoroughly for no less than 20 minutes. The speed of the high-speed mixer is 1000±100r / min. After stirring evenly, let it stand for more than 24 hours to obtain modified bentonite wall protection mud.

[0015] Beneficial effects

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] (1) The present invention uses silane to modify the microstructure of sodium bentonite, thereby improving the dispersion ability of bentonite in mud, enhancing the bonding strength between bentonite mud and borehole wall, enhancing the mud wall protection effect and scum performance, and enabling bentonite mud to be used in areas with worse formation conditions.

[0018] (2) The present invention uses a homogenizer to nano-modify sodium bentonite. The rheological properties (viscosity) of nano-modified bentonite are easier to control and more stable, which can effectively improve the expansion performance and seepage prevention performance of the wall protection mud, and achieve a good wall protection effect.

[0019] (3) By adding nano-modified bentonite to the wall protection mud, the viscosity value of the nano-bentonite mud under low shear conditions is higher than that of ordinary bentonite mud of the same concentration. The mud under the same viscosity target only needs to consume a small amount of nano-bentonite, which can save the amount of bentonite used. It also enhances the function of mud suspending soil residue and carrying soil residue out of the ground, ensuring the quality of subsequent concrete pouring.

[0020] (4) The wall-protecting mud proposed in this invention exhibits shear thinning behavior under high shear conditions, which can enhance the separation ability of circulating mud and soil sediment in the subsequent mud tank, and is conducive to the reuse or rapid discharge of circulating mud.

[0021] (5) This invention can meet the requirements of trenching and wall protection of underground continuous walls under various soil conditions by adjusting the rheological properties. It is especially suitable for the construction of ultra-deep underground continuous walls in soft soil geological conditions such as silty clay, silty clay and silty sand.

[0022] (6) Through the optimized design of the mud mix ratio, the nano-modified bentonite, under the synergistic effect of other additives, makes it easy for the mud to meet the specifications. The rheological properties of the mud are stable and the mud will not separate from the water over a long period of time. This effectively avoids a series of problems such as necking or hole collapse during the trenching process of continuous wall construction. It is suitable for the construction of underground continuous walls under various soil conditions. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0024] The range endpoint values ​​and any values ​​given in this invention are not limited to these precise ranges or values; such ranges or values ​​should be values ​​close to these ranges or values.

[0025] All materials used in the embodiments of this invention are commercially available. Among them, the pH value of sodium bentonite is 8-10.5 and the particle size is 300-325 mesh; the pH value of carboxymethyl cellulose is 8-9; and the barite powder is a white powder with a particle size of 400 mesh.

[0026] Example 1

[0027] This embodiment of a modified bentonite slurry for ultra-deep underground continuous walls comprises the following components by mass percentage: 5.86% modified sodium bentonite, 0.1% starch, 0.034% sodium carbonate, 0.02% carboxymethyl cellulose, 0.024% polyacrylamide, 0.6% barite powder, and the balance being mixing water.

[0028] Modified sodium bentonite is obtained by modifying ordinary sodium bentonite. The preparation process of modified sodium bentonite includes the following steps: (1) Pour 550g of the received sodium bentonite into 2000ml of ethanol and stir at high speed for 1h with a stirrer set to 600-700r / min to form solution A; (2) Pour 500g of 3-aminopropyltriethoxysilane into 1000ml of ethanol and stir with a stirrer for 1h with a stirrer set to 300-400r / min to form solution B; (3) Then mix solution A and solution B and stir with a stirrer at room temperature for 6h with a stirrer set to 300-400r / min to form solution C. (4) Then filter the C liquid and dry it at 150°C for 48 hours. After cooling, pass the sodium bentonite through a 75μm sieve. (5) Weigh the sodium bentonite and distilled water at a mass ratio of 1:2. Add the sodium bentonite and distilled water to a homogenizer. Set the homogenizer speed to 5900-6100r / min and the mixing time to 2-3h. (6) After mixing, seal the sodium bentonite mixture and place it at room temperature for more than 48h. (7) Pour the sodium bentonite mixture into a container and dry it at 100°C for more than 48h. After it is completely dried, the modified sodium bentonite is obtained.

[0029] This embodiment describes a method for preparing modified bentonite slurry for ultra-deep underground continuous walls, comprising the following steps:

[0030] (1) Weigh each raw material component according to the mass percentage of the mud, including: 5.86% modified sodium bentonite, 0.1% starch, 0.034% sodium carbonate, 0.02% carboxymethyl cellulose, 0.024% polyacrylamide, 0.6% barite powder, and the remainder is mixing water.

[0031] (2) Add water, modified sodium bentonite, sodium carbonate, carboxymethyl cellulose, polyacrylamide and barite powder to a high-speed mixer in sequence, stir the mixture thoroughly for 20 minutes, and let it stand for 24 hours after stirring evenly to obtain modified bentonite wall protection mud.

[0032] Example 2

[0033] This embodiment of a modified bentonite slurry for ultra-deep underground continuous walls comprises the following components by mass percentage: 6.06% modified sodium bentonite, 0.13% starch, 0.037% sodium carbonate, 0.023% carboxymethyl cellulose, 0.028% polyacrylamide, 0.7% barite powder, and the balance being mixing water.

[0034] The preparation process of the modified sodium bentonite and the preparation method of the modified bentonite slurry are the same as in Example 1.

[0035] Example 3

[0036] This embodiment of a modified bentonite slurry for ultra-deep underground continuous walls comprises, by mass percentage: 6.46% modified sodium bentonite, 0.16% starch, 0.04% sodium carbonate, 0.026% carboxymethyl cellulose, 0.032% polyacrylamide, 0.8% barite powder, and the balance being mixing water. The preparation process of the modified sodium bentonite and the preparation method of the modified bentonite slurry are the same as in Example 1.

[0037] Comparative Example 1

[0038] Compared to Example 1, this comparative example did not modify the sodium bentonite.

[0039] This comparative example describes a modified bentonite slurry for ultra-deep underground continuous walls, comprising the following components by mass percentage: 5.86% ordinary sodium bentonite, 0.1% starch, 0.034% sodium carbonate, 0.02% carboxymethyl cellulose, 0.024% polyacrylamide, 0.6% barite powder, and the balance being mixing water.

[0040] The preparation method of the bentonite slurry is the same as that in Example 1.

[0041] Comparative Example 2

[0042] Compared to Example 3, this comparative example did not modify the sodium bentonite.

[0043] This comparative example describes a modified bentonite slurry for ultra-deep underground continuous walls, comprising the following components by mass percentage: 6.46% ordinary sodium bentonite, 0.16% starch, 0.04% sodium carbonate, 0.026% carboxymethyl cellulose, 0.032% polyacrylamide, 0.8% barite powder, and the balance being mixing water.

[0044] The preparation method of the bentonite slurry is the same as that in Example 1.

[0045] Comparative Example 3

[0046] Compared to Example 2, this comparative example reduces the amount of modified sodium bentonite used.

[0047] This comparative example of a modified bentonite slurry for ultra-deep underground continuous walls comprises, by mass percentage: 4.06% modified sodium bentonite, 0.13% starch, 0.037% sodium carbonate, 0.023% carboxymethyl cellulose, 0.028% polyacrylamide, 0.7% barite powder, and the balance being mixing water.

[0048] The preparation process of the modified sodium bentonite and the preparation method of the modified bentonite slurry are the same as in Example 1.

[0049] According to the standard DB / T 29-103-2018 "Technical Specification for Construction of Reinforced Concrete Underground Continuous Walls in Tianjin", the relative density, funnel viscosity, sand content, water loss, colloid ratio, pH value and mud cake thickness of the modified bentonite wall protection mud in Examples 1-3 and Comparative Examples 1-3 were tested. The test results are shown in Table 1.

[0050] Table 1. Performance of modified bentonite wall-protecting slurry in Examples 1-3 and Comparative Examples 1-3

[0051]

[0052]

[0053] According to the standard DB / T 29-103-2018 "Technical Specification for Construction of Reinforced Concrete Diaphragm Walls in Tianjin", the relative density, funnel viscosity, sand content, and water loss of bentonite slurry are all important indicators for controlling slurry performance. Newly prepared bentonite slurry should meet the following performance requirements: relative density between 1.04 and 1.15, funnel viscosity between 20 and 30 seconds, sand content less than 3%, water loss less than 20 ml / 30 min, and pH value between 8 and 10.5. If the prepared bentonite slurry does not meet the specifications, it will be difficult to achieve a good wall-protecting effect, and it will also adversely affect the performance of the concrete during pouring and after hardening.

[0054] As shown in Table 1, the modified bentonite prepared in Examples 1-3 met all the specifications and had good wall-protecting effects. The mud funnel viscosity, sand content, and water loss in Comparative Examples 1 and 2 were not within the specified ranges, and the colloid content was low, resulting in poor wall-protecting effects and hole collapse. This was mainly because neither Comparative Examples 1 nor 2 modified the bentonite; the insufficient amount of ordinary bentonite led to low mud viscosity and high water loss, failing to effectively suspend soil residue and protect the wall. This indirectly reflects that modifying bentonite not only improves mud performance but also saves on bentonite usage. Comparative Example 3 used modified bentonite, but in significantly smaller quantities. The mud in Comparative Example 3 exhibited similar performance to Comparative Example 2, indicating that mud containing a small amount of modified bentonite can achieve the same wall-protecting effect as mud containing a larger amount of ordinary bentonite.

[0055] Overall, the performance of the wall-protecting mud in Examples 1-3 is significantly better than that in Comparative Examples 1-3. Furthermore, the mud prepared in Examples 1-3 has a lower sand content, a more stable funnel viscosity, a higher colloid ratio, and less water loss, thereby producing a better wall-protecting effect and effectively avoiding a series of problems such as necking or hole collapse during the trenching process of continuous wall construction.

[0056] The foregoing detailed examples of the present invention are merely preferred embodiments and should not be construed as limiting the scope of the invention. All equivalent variations and modifications made within the scope of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A modified bentonite mud for use in ultra deep diaphragm walls, characterized in that, By mass percentage, it comprises the following components: 5.86%-6.46% modified sodium bentonite, 0.1%-0.16% starch, 0.034%-0.04% sodium carbonate, 0.02%-0.026% carboxymethyl cellulose, 0.024%-0.032% polyacrylamide, 0.6%-0.8% barite powder, with the balance being water; The preparation process of the modified sodium bentonite includes the following steps: (1) 550g of sodium bentonite is poured into 2000ml of ethanol and stirred at high speed for 1h with a stirrer at a speed of 600-700 r / min to form solution A; (2) 500g of 3-aminopropyltriethoxysilane is poured into 1000ml of ethanol and stirred with a stirrer for 1h with a speed of 300-400 r / min to form solution B; (3) Solution A and solution B are then mixed and stirred at room temperature for 6h with a stirrer at a speed of 300-400 r / min. (4) Then filter the C liquid and dry it at 150°C for 48 hours. After cooling, pass the obtained sodium bentonite through a 75µm sieve. (5) Weigh the above sodium bentonite and distilled water at a mass ratio of 1:2 and add them to a homogenizer for mixing. Set the speed of the homogenizer to 5900-6100 r / min and the mixing time to 2-3 h. (6) After mixing, seal the sodium bentonite mixture and place it at room temperature for more than 48 h. (7) Pour the sodium bentonite mixture into a container and dry it at 100°C for more than 48 h. After it is completely dried, the modified sodium bentonite is obtained.

2. The modified bentonite slurry for ultra-deep underground continuous walls according to claim 1, characterized in that, The particle size of the sodium bentonite is 300-325 mesh.

3. The modified bentonite slurry for ultra-deep underground continuous walls according to claim 1, characterized in that, The carboxymethyl cellulose has a pH of 8-9, and the barite powder has a particle size of 400 mesh.

4. A method for preparing modified bentonite slurry for ultra-deep underground continuous walls according to any one of claims 1-3, characterized in that, Includes the following steps: (1) Weigh each raw material of the mud according to the mass percentage. The components of each raw material include: 5.86%-6.26% modified sodium bentonite, 0.1%-0.16% starch, 0.034%-0.04% sodium carbonate, 0.02%-0.026% carboxymethyl cellulose, 0.024%-0.032% polyacrylamide, 0.6%-0.8% barite powder, and the balance is water; (2) Add water, modified sodium bentonite, starch, sodium carbonate, carboxymethyl cellulose, polyacrylamide and barite powder to a high-speed mixer in sequence, stir the mixture thoroughly for no less than 20 minutes, and let it stand for more than 24 hours after stirring evenly to obtain modified bentonite wall protection mud.

5. The method for preparing modified bentonite slurry for ultra-deep underground continuous walls according to claim 4, characterized in that, The high-speed mixer has a rotation speed of 1000±100 r / min.

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