Thixotropic slurry for pipe-jacking construction of offshore water-rich soft stratum and proportioning method of thixotropic slurry

Abstract

The invention relates to the field of pipe-jacking construction, and particularly discloses an offshore water-rich soft stratum pipe-jacking construction thixotropic slurry and a proportioning method thereof, and the offshore water-rich soft stratum pipe-jacking construction thixotropic slurry comprises the following components by mass: 8-10 parts of bentonite, 0.5-1 part of an alkaline stabilizer, 0.5-1 part of a thickener, 0.2-0.5 part of a water reducer, and 87.5-90.8 parts of water. The formula can effectively reduce the water loss and the bleeding rate, improve the strength and the supporting effect of the slurry, maintain good thixotropy and drag reduction characteristics, and ensure smooth construction. The water reducing agent forms a stable colloidal network in a static state, and provides high viscosity and a supporting effect; under the shearing action, the network is damaged, the slurry is easy to flow, and the friction resistance is reduced.

Description

Technical Field

[0001] The invention relates to the field of pipe jacking construction, and in particular to a thixotropic mud for pipe jacking construction in offshore water-rich soft strata and a proportioning method thereof. Background Art

[0002] As a commonly used method of trenchless construction, pipe jacking is widely used in the construction of subway stations because of its advantages such as being suitable for soft soil or water-rich soft soil layers, requiring less equipment, short construction period, low cost, high speed, and the ability to lay pipes deep underground.

[0003] During the pipeline jacking construction process, in order to reduce the friction between the soil and the pipeline, thixotropic mud is usually injected between the pipe wall and the soil through the grouting hole. After the thixotropic mud flows out of the grouting hole, it fills the over-excavation gap of the pipeline under the action of its own weight. At this time, the disturbed mud appears as a colloidal liquid, achieving the effect of reducing formation losses; when a certain penetration depth is reached, the mud no longer diffuses, and the gaps between soil particles are gradually filled with mud. Many permeable blocks are bonded together, and the slurry is still in a gel state, forming a dense and impermeable mud jacket. Under the protection of the mud jacket, the pipeline becomes floating due to the buoyancy of the mud, and the effective weight is reduced. The mud ratio will significantly affect the formation of the mud jacket, and then affect the final drag reduction effect, so the ratio of thixotropic mud is particularly important.

[0004] Different formations have different requirements for the properties of thixotropic mud. Full-section rock layers require thixotropic mud with good lubrication and fluidity. Loose formations with high water pressure require thixotropic mud with low filtration loss. Mud and gravel or sandy gravel formations require thixotropic mud with low fluidity. Offshore water-rich soft formations require thixotropic mud to have good permeability control and the ability to maintain stability for a long time.

[0005] The current thixotropic mud has poor applicability and its drag reduction effect is not ideal when applied to offshore water-rich soft formations. Summary of the invention

[0006] The purpose of the present invention is to provide a thixotropic mud for pipe jacking construction in offshore water-rich soft strata and a mixing method thereof. In order to solve the technical problems in the above-mentioned background technology and improve the permeability control and long-term stability of thixotropic mud, the technical solution adopted by the present invention is: A thixotropic mud for pipe jacking construction in offshore water-rich soft strata comprises the following components in proportion by mass: 8 to 10 parts of bentonite, 0.5 to 1 part of alkaline stabilizer, 0.5 to 1 part of thickener, 0.2 to 0.5 part of water reducer and 87.5 to 90.8 parts of water.

[0007] Preferably, the bentonite is sodium bentonite.

[0008] Preferably, the alkaline stabilizer is sodium carbonate.

[0009] Preferably, the thickener is sodium carboxymethyl cellulose (CMC).

[0010] Preferably, the water reducer is a polycarboxylate water reducer.

[0011] Preferably, the pH of the water is controlled between 6 and 8.

[0012] A method for proportioning thixotropic mud for pipe jacking construction in offshore water-rich soft strata comprises the following steps: Step S1, weighing bentonite and water in proportion, stirring evenly to form a basic mud; Step S2, adding an alkaline stabilizer and continuing stirring to fully disperse and expand the bentonite in the base mud; Step S3, adding a thickener and stirring the base mud until it is evenly dissolved; Step S4: adding a water reducing agent and continuously stirring for 20 to 30 minutes to fully mix the components in the base mud.

[0013] Preferably, the stirring time in step S1 should not be less than 5 minutes, and the basic mud obtained by stirring in step S1 is left to stand for 24 hours before proceeding to step S2.

[0014] Preferably, the thickener in step S3 is stirred and dissolved in warm water before being added into the base mud and stirred.

[0015] Compared with the prior art, the present invention has the following advantages and beneficial effects: 1. Through the dispersibility of sodium carboxymethyl cellulose (CMC), it forms a transparent colloid in water, plays a flocculation role in thixotropic mud, effectively reduces the water loss of mud, and increases the thickness and solid content of mud cake.

[0016] 2. The sodium element in CMC is conducive to the hydration reaction of bentonite.

[0017] 3. By introducing water reducing agent, the performance of thixotropic mud in terms of friction coefficient, viscosity and water separation rate can be significantly improved, making it more suitable for pipe jacking construction in water-rich soft formations.

[0018] 4. This formula can effectively reduce water loss and water separation rate, improve the strength and support effect of mud, while maintaining good thixotropy and drag reduction properties to ensure smooth construction. Water reducer forms a stable colloidal network when stationary, providing high viscosity and support; under shear, the colloidal network is destroyed, the mud becomes easy to flow, and the friction resistance is reduced. The colloidal network is a three-dimensional network structure formed by colloidal particles, which is usually formed by physical or chemical interactions between particles (such as van der Waals force, electrostatic action, hydrogen bonding or bridging). This network structure is widely used in soft matter science, materials engineering, biomedicine and other fields, and is commonly found in gels, emulsions, foams, and nanocomposites. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is the effect curve of different contents of water reducer on viscosity.

[0020] Figure 2 This is the influence curve of different contents of water reducing agent on water loss.

[0021] Figure 3 This is the influence curve of different contents of water reducer on water separation rate.

[0022] Figure 4 The curves of jacking force and jacking distance under different grouting conditions.

[0023] Figure 5 This is the influence curve of different contents of water reducer on friction coefficient. DETAILED DESCRIPTION

[0024] The technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention, so as to have a further understanding of the concept of the present invention, the technical problems solved, the technical features constituting the technical scheme and the technical effects brought about.

[0025] A thixotropic mud for pipe jacking construction in offshore water-rich soft strata comprises the following components in proportion by mass: 8 to 10 parts of bentonite, 0.5 to 1 part of alkaline stabilizer, 0.5 to 1 part of thickener, 0.2 to 0.5 part of water reducer and 87.5 to 90.8 parts of water.

[0026] Preferably, the bentonite is sodium bentonite. Compared with the same volume of calcium bentonite, sodium bentonite has more extremely thin silicate layers, making the density of sodium bentonite less than that of calcium bentonite, with more voids, and the sodium-based bentonite has stronger hydration and adsorption capacity than the calcium-based bentonite, and has better expansion performance. The expansion rate of sodium bentonite is more than 3 times that of calcium bentonite, and the fluidity, static gelation and curing properties after thixotropy are better.

[0027] Preferably, the alkaline stabilizer is sodium carbonate. The sodium ions in the soda ash exchange with the calcium ions in the bentonite to produce a hydration reaction, thereby increasing the solid-liquid bonding ability of the thixotropic mud.

[0028] Preferably, the thickener is sodium carboxymethyl cellulose CMC. Sodium carboxymethyl cellulose is easily dispersible and forms a transparent colloid in water. It is often used as an industrial water-soluble colloidal thickener. It plays a flocculation role in thixotropic mud, effectively reducing the water loss of mud and increasing the thickness and solid content of mud cake. The sodium element in sodium carboxymethyl cellulose is conducive to the occurrence of bentonite hydration reaction. Sodium carboxymethyl cellulose (Na-CMC) can be regarded as a modified form of carboxymethyl cellulose (CMC), which has better solubility, stability and wide applicability, and is therefore more commonly used in industry and commerce. In actual engineering applications, CMC is generally used to refer to sodium carboxymethyl cellulose.

[0029] Preferably, the water reducing agent is a polycarboxylic acid water reducing agent. The water reducing agent can reduce the amount of water required, thereby improving the working performance and durability of the prepared thixotropic mud and improving the fluidity of the mud.

[0030] Preferably, the pH of the water is controlled between 6 and 8.

[0031] This type of thixotropic mud for pipe jacking construction is mainly used for offshore water-rich soft strata. The thixotropic mud is mainly silty clay, and also includes a small amount of coarse, gravel and sand and other geological conditions for pipe jacking construction. Traditional thixotropic mud has poor applicability under the low quality of this project, so its effect in the actual drag reduction process is not particularly ideal. Therefore, the development of a thixotropic mud suitable for offshore water-rich soft strata is of great significance in actual engineering.

[0032] The present invention proposes a method for proportioning thixotropic mud for pipe jacking construction in offshore water-rich soft strata, comprising the following steps: Step S1, weighing bentonite and water in proportion, stirring evenly to form a basic mud; Step S2, adding an alkaline stabilizer and continuing stirring to fully disperse and expand the bentonite in the base mud; Step S3, adding a thickener and stirring the base mud until it is evenly dissolved; Step S4: adding a water reducing agent and continuously stirring for 20 to 30 minutes to fully mix the components in the base mud.

[0033] Preferably, the stirring time in step S1 should not be less than 5 minutes, and the basic mud obtained by stirring in step S1 is left to stand for 24 hours before proceeding to step S2.

[0034] Preferably, the thickener in step S3 is stirred and dissolved in warm water before being added into the base mud and stirred.

[0035] Sodium carboxymethyl cellulose has dispersibility, so that sodium carboxymethyl cellulose forms a transparent colloid in water, plays a flocculation role in thixotropic mud, effectively reduces the water loss of mud, and increases the thickness and solid content of mud cake. The sodium element in sodium carboxymethyl cellulose is conducive to the occurrence of bentonite hydration reaction. By introducing a water reducer, the performance of thixotropic mud can be significantly improved, making it more suitable for pipe jacking construction in water-rich soft formations. This formula can effectively reduce water loss and water separation rate, improve the strength and support effect of mud, while maintaining good thixotropy and drag reduction properties, ensuring smooth construction. The water reducer forms a stable colloidal network when stationary, providing high viscosity and support; under shearing, the network is destroyed, the mud becomes easy to flow, and the friction resistance is reduced.

[0036] The thixotropic slurry was subjected to the following performance tests: Filtration: Filtration refers to the amount of permeability of a certain volume of mud under a constant pressure difference. It is an important indicator for measuring the quality of the mud jacket. Water loss in thixotropic mud will cause the water in the thixotropic mud to penetrate into the soil, reducing the density and structural stability of the mud jacket. In the experiment, the thixotropic mud is prepared and loaded into a container of a certain volume. A pressure difference is set at both ends of the container. Part of the water in the slurry will be pressed into the soil. This property is called filtration or water loss. During construction, it is stipulated that the filtration loss of thixotropic mud is generally not more than 25ml / 30min. Use a medium-pressure water loss meter to control the pressure of the metal mud cup through an air pump. After 15 minutes, measure the filtration loss of the thixotropic mud under pressure.

[0037] Funnel viscosity: Funnel viscosity can also be called viscosity. Viscosity reflects the fluidity of thixotropic mud. During construction, the viscosity of thixotropic mud is required to be ≥30 s (s is in seconds, representing the funnel viscosity). The test equipment uses MLN-2 conical Marsh funnel viscometer. Pour the thixotropic mud vertically into the Marsh funnel and record the time it takes to flow out. The larger the funnel seconds, the longer the outflow time, and the greater the apparent viscosity of the mud.

[0038] Steps to use the Marsh funnel: Preparation: ① Check the cleanliness of the Martens funnel to ensure that the funnel is not blocked. ② Calibrate the stopwatch and measuring cylinder; Sample preparation: Experiment starts: ① Pour the sample into the Marsh funnel and make sure the liquid level reaches the standard scale line of the funnel. ② Block the outlet at the bottom of the funnel with your finger or a baffle to prevent the liquid from flowing out; Measuring time: ① Remove the baffle to allow the liquid to start flowing. ② Simultaneously start a stopwatch and record the time required for a certain volume of liquid to flow out (usually 50mL or 100mL, 750mL in this test); Repeat the experiment: To ensure data accuracy, measure 3 times and take the average value.

[0039] Water separation rate: After the thixotropic mud is prepared, place it in a measuring cylinder for 24 hours. The ratio of the volume of water separated from the original thixotropic mud liquid to the volume of the original thixotropic mud is called the water separation rate. This indicator reflects the stability of the thixotropic mud. Place 1000ml of the stirred experimental mud in a stoppered measuring cylinder covered with a glass stopper and place it in a constant temperature room for 24 hours. Read the amount of water separated and convert it into the water separation rate. The smaller the water separation rate of the thixotropic mud, the better the stability of the thixotropic mud.

[0040] Table 1 is the physical and mechanical performance index requirements of thixotropic mud .

[0041] The requirements of offshore water-rich soft formations for thixotropic mud are: good permeability control and the ability to maintain stability for a long time. The present invention normalizes the three indicators of friction coefficient, viscosity and water loss as follows: (1) Friction coefficient. Considering that a low friction coefficient can reduce the friction resistance of pipe jacking, the normalized formula is: ; (2) Viscosity. In water-rich soft formations, appropriate viscosity is conducive to the fluidity of the mud and provides sufficient anti-permeability. The maximum viscosity in the test was 300 s and the minimum was 55 s. The normalized formula is: ; (3) Water loss. The anti-water loss performance of mud is one of the key indicators of water-rich soft formations. Lower water loss means that the mud can maintain its lubrication and support performance during long-term construction. The normalized formula is: ; Considering the requirements of water-rich soft formations on mud performance, the weighted average method is selected to weight each index in combination with the formation characteristics. The weights of friction coefficient, viscosity and water loss are set to 0.4, 0.3 and 0.2 respectively. The calculation formula of the total score is: ; Table 2 is the thixotropic mud ratio table for different working conditions .

[0042] Table 3 shows the normalized index and score table under different working conditions .

[0043] From the data in Table 1 and Table 2, it can be seen that the score of working condition 11 is the highest, reaching 0.78. Figure 1 , Figure 2 , Figure 3The curves of the influence of different contents of water reducing agent on viscosity, water loss and water separation rate respectively show that the ratio of working condition 11 has the best comprehensive performance in terms of friction coefficient, viscosity and water loss, and is suitable for pipe jacking construction in offshore water-rich soft formations. The thixotropic mud ratio of working condition 11 is: 10% bentonite, 0.1% CMC, 0.2% soda ash, 0.5% water reducing agent, and water. This thixotropic mud ratio is the optimal ratio. This ratio has good fluidity and water loss resistance under the condition of low friction coefficient, and can effectively cope with the challenges of pipe jacking construction in offshore water-rich soft formations. Among them, Table 2 is the data table obtained after the data of Table 4 is sorted, and Table 4 is the initial table of thixotropic mud ratios for different working conditions.

[0044] Table 4 shows the initial proportion of thixotropic mud under different working conditions .

[0045] Table 5 is the corresponding table of X friction coefficient under different working conditions .

[0046] Figure 4 The curves of jacking force and jacking distance under different grouting conditions are shown in Figure 2. Figure 5 The figure shows the influence curve of different contents of water reducer on the friction coefficient. It is obvious from the figure that the friction coefficient is significantly reduced after grouting, and the mud sleeve can transform solid-solid friction into solid-liquid friction. In summary, after adding water reducer to thixotropic mud, the mud sleeve can obtain better drag reduction performance by adjusting the ratio.

[0047] Water reducer can promote the gelation of thixotropic mud, form a dense gel structure, increase the viscosity of thixotropic mud, reduce water loss and water separation rate, enhance the anti-water loss performance of mud, and significantly improve the physical properties of mud. The friction coefficient of the new thixotropic mud is reduced by 77.1% compared with that of the un-grouted mud; the data of working condition 8 and working condition 11 in the normalized index and score table under different working conditions (Table 3) are compared. The normalized friction coefficient of working condition 8 is 0.62, and the normalized friction coefficient of working condition 11 is 1.00. The relationship between the normalized friction coefficient M and the friction coefficient X shows that the friction coefficient of working condition 11 is reduced by 38.5% relative to the friction coefficient of working condition 8, which means that the friction coefficient of thixotropic mud with 0.5% water reducer is reduced by 38.5% compared with the traditional mud without water reducer, which significantly improves the jacking efficiency. Through normalized analysis, the optimal ratio was selected as 10% bentonite, 0.1% CMC, 0.2% soda ash and 0.5% water reducer. This ratio of mud has good fluidity, resistance to water loss and drag reduction effect, and is suitable for offshore water-rich soft formations.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments can still be modified, or some or all of the technical features therein can be replaced by equivalents. However, these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A thixotropic mud for pipe jacking construction in offshore water-rich soft strata, characterized by: The invention comprises the following components in the following mass proportions: bentonite: 8-10 parts, alkaline stabilizer: 0.5-1 parts, thickener: 0.5-1 parts, water reducer: 0.2-0.5 parts, and water: 87.5-90.8 parts.

2. The thixotropic mud for pipe jacking construction in offshore water-rich soft strata according to claim 1 is characterized by: The bentonite is sodium bentonite.

3. The thixotropic mud for pipe jacking construction in offshore water-rich soft strata according to claim 1 is characterized by: The alkaline stabilizer is sodium carbonate.

4. The thixotropic mud for pipe jacking construction in offshore water-rich soft strata according to claim 1 is characterized by: The thickener is sodium carboxymethyl cellulose (CMC).

5. The thixotropic mud for pipe jacking construction in offshore water-rich soft strata according to claim 1 is characterized by: The water reducer is a polycarboxylate water reducer.

6. The thixotropic mud for pipe jacking construction in offshore water-rich soft strata according to claim 1 is characterized by: The pH of the water is controlled between 6 and 8.

7. A method for proportioning thixotropic mud for pipe jacking construction in offshore water-rich soft strata applicable to claims 1-6, characterized in that: The following steps are involved: Step S1, weighing bentonite and water in proportion, stirring evenly to form a basic mud; Step S2, adding an alkaline stabilizer and continuing stirring to fully disperse and expand the bentonite in the base mud; Step S3, adding a thickener and stirring the base mud until it is evenly dissolved; Step S4: adding a water reducing agent and continuously stirring for 20 to 30 minutes to fully mix the components in the base mud.

8. The method for proportioning thixotropic mud for pipe jacking construction in offshore water-rich soft strata according to claim 7 is characterized in that: The stirring time in step S1 should not be less than 5 minutes, and the basic mud obtained by stirring in step S1 should be left to stand for 24 hours before proceeding to step S2.

9. The method for proportioning thixotropic mud for pipe jacking construction in offshore water-rich soft strata according to claim 7, characterized in that: The thickener in step S3 is stirred and dissolved in warm water in advance and then added into the base mud for stirring.

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