Heated Expansion Grout for Settlement Control at Tunnel End Shafts and its Preparation Method

Abstract

This invention proposes a thermally expanding grout for controlling thawing settlement at tunnel end wells and its preparation method, relating to the technical field of end well construction materials. Addressing the problem of ground and surrounding environmental subsidence caused by the melting of frozen soil near tunnel end wells in existing technologies, the thermally expanding grout used in this invention comprises PNIPAM-AM copolymer thermosensitive hydrogel, lime, fine sand, fly ash, bentonite, thickener, and water-reducing agent. The PNIPAM-AM copolymer thermosensitive hydrogel includes N-isopropylacrylamide, acrylamide, N,N'-methylenebisacrylamide, an initiator, and an accelerator. The mass ratio of N-isopropylacrylamide, acrylamide, N,N'-methylenebisacrylamide, and the initiator to the accelerator is 100:12~16:0.3~0.6:0.15~0.25:0.1~0.2. The grout of this invention not only has high thermal conductivity, which can shorten the freezing time of the soil surrounding the tunnel end well joint, but also effectively controls the impact of thawing settlement at the tunnel end well.

Description

Technical Field

[0001] This invention relates to the field of materials technology for tunnel end well construction, and in particular to a heated expansion grout for controlling the melting and settling of tunnel end wells and its preparation method. Background Technology

[0002] With the development of urban underground space in my country and the widespread construction of projects such as subway tunnels, river-crossing tunnels, and underground integrated pipe corridors, the tunnel working shaft (end shaft) is a key node for the initiation and reception of shield tunneling, and its construction safety is of paramount importance.

[0003] When constructing end wells in soft strata rich in groundwater (such as silty clay and clayey soil), the industry commonly employs artificial ground freezing as an efficient temporary reinforcement and waterproofing technique to ensure safe tunnel access. However, freezing methods inevitably lead to frost heave and thaw settlement. After construction, the thawing of frozen soil near the end well will cause ground and surrounding environmental subsidence, generating additional stress on nearby buildings, underground pipelines, and existing tunnel structures, and even causing secondary disasters such as cracking and leakage. This has become one of the core bottlenecks restricting the safe application of freezing methods and urban environmental protection.

[0004] Currently, the mainstream technology for controlling thaw settlement is the grouting compensation method, which involves injecting grout into the thaw settlement-affected area during or after the thawing of frozen soil to fill soil pores and compensate for volume loss. However, existing conventional grouting materials and methods have significant limitations: traditional grouting is a passive filling method, often resulting in delayed or over-compensation, lacking proactive and synchronous compensation for thaw settlement, and easily causing adverse effects on the end well and surrounding environment.

[0005] Therefore, developing a heat-expanding grout for controlling the settling of tunnel end wells is of great theoretical value and promising engineering application prospects for ensuring the safety of surrounding buildings and underground pipelines, and improving the green, low-carbon and intelligent level of urban underground engineering construction. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a heated expansion grout for controlling the melting and settling of tunnel end wells and its preparation method. The grout of this invention not only has high thermal conductivity, which can shorten the freezing time of the soil surrounding the joint of the tunnel end well, but also can effectively control the impact of melting and settling of the tunnel end well.

[0007] This invention provides a heat-expanding grout for controlling the settling of tunnel end shafts, the heat-expanding grout comprising PNIPAM-AM copolymer thermosensitive hydrogel, lime, fine sand, fly ash, bentonite, thickener and water-reducing agent; The PNIPAM-AM copolymer thermosensitive hydrogel comprises N-isopropylacrylamide, acrylamide, N,N'-methylenebisacrylamide, an initiator, and an accelerator; the mass ratio of N-isopropylacrylamide, acrylamide, N,N'-methylenebisacrylamide, initiator, and accelerator is 100:12~16:0.3~0.6:0.15~0.25:0.1~0.2.

[0008] Furthermore, the preparation method of the PNIPAM-AM copolymer thermosensitive hydrogel includes the following steps: mixing N-isopropylacrylamide and an acrylamide solution with N,N'-methylenebisacrylamide; after the N,N'-methylenebisacrylamide is completely dissolved, adding an initiator and a promoter to obtain the PNIPAM-AM copolymer thermosensitive hydrogel.

[0009] Furthermore, by mass percentage, the heat-expanding slurry comprises 8%–10% PNIPAM-AM copolymer thermosensitive hydrogel, 2%–8% lime, 40%–50% fine sand, 15%–25% fly ash, 2%–6% bentonite, 0.05%–0.2% thickener, 0.02%–1% water-reducing agent, and the balance being water.

[0010] Furthermore, by mass percentage, the heat-expanding slurry comprises 9%–10% PNIPAM-AM copolymer thermosensitive hydrogel, 4%–6% lime, 45%–50% fine sand, 20%–25% fly ash, 2%–4% bentonite, 0.1%–0.2% thickener, 0.5%–1% water-reducing agent, and the balance being water.

[0011] Furthermore, the initiator is ammonium persulfate; the accelerator is N,N,N',N'-tetramethylethylenediamine.

[0012] Furthermore, the thickener is one or more of carboxymethyl cellulose, gum arabic, polyvinyl alcohol, and polyvinylpyrrolidone; the water-reducing agent is an FDN-C type naphthalene-based water-reducing agent.

[0013] Furthermore, the N-isopropylacrylamide has a molecular weight ≥ 1 million.

[0014] Furthermore, the calcium content in the lime is ≥95%.

[0015] Furthermore, the fineness modulus of the fine sand is 1.6-2.2.

[0016] Furthermore, the fly ash has a particle size of 2800-3200 mesh; the bentonite has a particle size of 1400-1600 mesh, and the bentonite is sodium-based bentonite.

[0017] The present invention also provides a method for preparing the thermally expanding slurry described in the above technical solution, comprising the following steps: The PNIPAM-AM copolymer thermosensitive hydrogel, lime, fine sand, fly ash, bentonite, thickener, water-reducing agent and water are mixed evenly to obtain a heat-expanding slurry.

[0018] The present invention also provides the application of the heated expansion grout described above in the control of thawing settlement at the tunnel end well. The heated expansion grout is injected into the thawing settlement affected zone of the frozen area of ​​the end well, and the expansion is carried out in response to temperature to fill the formation loss.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: Firstly, the slurry obtained by this invention has a high thermal conductivity, allowing it to fill and solidify rapidly when pumped to the designated location, thus reducing the time required for the soil to freeze. Secondly, the slurry obtained by this invention can absorb impact and vibration energy, reducing noise and minimizing its impact on the surrounding environment. Finally, the slurry obtained by this invention has a high coefficient of thermal expansion, which can reduce settlement caused by soil melting near the end well.

[0020] Secondly, this invention achieves intelligent and adaptive compensation for freeze-thaw cycles by precisely controlling the lowest critical dissolution temperature (LCST) of the PNIPAM-AM copolymer thermosensitive hydrogel to 0℃±2℃ and utilizing its reverse volume change compared to the natural water-ice phase transition process: When the temperature > LCST (approximately 0℃), the hydrogen bonds between the gel polymer chains and water molecules are strengthened, resulting in water absorption and swelling, which compensates for the volume shrinkage that occurs when ice transforms into water, preventing ground subsidence; when the temperature < 0℃ (water freezes into ice): the hydrophobicity of the gel polymer chains is enhanced, resulting in dehydration and shrinkage, which accommodates the volume expansion that occurs when water freezes into ice, alleviating the pressure of frost heave on the surrounding soil; this process is based on the physical change of polymer chain conformation, without the participation of chemical reactions. As the ambient temperature fluctuates around 0℃, the gel can cyclically achieve a completely reversible transformation of "heating up swelling - cooling down shrinkage," exhibiting excellent cycle stability (performance remains essentially unchanged after hundreds of cycles), enabling long-term, multiple responses to temperature fluctuations that may occur during operation, achieving long-term effective control.

[0021] Thirdly, in the grout system described in this invention, the components, through scientific proportioning and synergistic effects, jointly achieve excellent thaw settlement control and engineering performance. The PNIPAM-AM copolymer thermosensitive hydrogel has a high linear thermal expansion coefficient, which significantly enhances the thermal expansion capacity of the grout after solidification, thereby actively compensating for volume shrinkage during the thawing stage of frozen soil and effectively suppressing thaw settlement. This material also possesses excellent energy absorption and damping characteristics, effectively dissipating impact and vibration energy during construction and operation, significantly reducing noise propagation, and thus mitigating disturbance to the surrounding environment. Lime and fly ash undergo hydration reactions, producing new hydration products—gelatinous, filamentous, fibrous, and needle-like hydrated calcium silicate. These hydration products can fill the pores of the thermally conductive network structure, increasing the density and impermeability of the grout after solidification, and also improving the viscosity and fluidity of the grout, thus facilitating rapid and sufficient filling and preparing for rapid grout solidification. The synergistic effect of thickeners and water-reducing agents reduces the water absorption capacity of the slurry and increases its viscosity, thereby reducing solid-liquid separation and improving its stability, resulting in a more uniform strength after solidification. Fine sand can further fill the pores that form a thermally conductive network structure, which is beneficial for improving the strength of the solidified slurry. Bentonite contains silicates and aluminates, which can react with silicate ions in lime to form a gel, thus increasing the strength of the slurry after molding.

[0022] Fourth, the method for obtaining the slurry in this invention is simple and easy to implement, which is conducive to industrial production; moreover, the heat-expanding slurry provided by this invention has low initial viscosity and good fluidity, making it easy to inject into the formation through grouting equipment. Its LCST precisely matches the freezing point of water and can intelligently sense changes in formation temperature. It can automatically activate the compensation mechanism without external triggering, making it particularly suitable for complex environments such as tunnel end shafts that have undergone artificial freezing construction. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below. 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 specific embodiments of the present invention will be described below.

[0025] Example 1 Prepare 100 parts of N-isopropylacrylamide (PNIPAM), 15 parts of acrylamide (AM), 0.5 parts of N,N'-methylenebisacrylamide (MBA) crosslinking agent, 0.2 parts of ammonium persulfate (APS), and 0.1 parts of N,N,N',N'-tetramethylethylenediamine (TEMED) accelerator for later use.

[0026] PNIPAM and AM were dissolved in water and stirred until completely dissolved; then MBA crosslinking agent was added, and after dissolution, APS and TEMED were added to obtain PNIPAM-AM copolymer thermosensitive hydrogel.

[0027] A heated expansion slurry is prepared by uniformly mixing PNIPAM-AM copolymer thermosensitive hydrogel, lime with a calcium content of not less than 95%, fine sand with a fineness modulus of 1.6-2.2, fly ash with a particle size of 2800-3200 mesh, sodium bentonite with a particle size of 1400-1600 mesh, thickener (carboxymethyl cellulose), FDN-C type naphthalene-based water-reducing agent, and water. The mass fractions of each substance in the heated expansion slurry are as follows: PNIPAM-AM copolymer thermosensitive hydrogel 10%, lime 6%, fine sand 45%, fly ash 20%, sodium bentonite 4%, thickener 0.15%, and water-reducing agent 0.5%.

[0028] Example 2 PNIPAM-AM copolymer thermosensitive hydrogel was prepared according to the method described in Example 1.

[0029] The PNIPAM-AM copolymer thermosensitive hydrogel, lime with a calcium content of not less than 95%, fine sand with a fineness modulus of 1.6-2.2, fly ash with a particle size of 2800-3200 mesh, sodium bentonite with a particle size of 1400-1600 mesh, thickener (carboxymethyl cellulose), FDN-C type naphthalene-based water-reducing agent, and water are mixed evenly to obtain a heat-expanding slurry. The mass fractions of each substance in the heat-expanding slurry are as follows: PNIPAM-AM copolymer thermosensitive hydrogel 10%, lime 2%, fine sand 40%, fly ash 25%, sodium bentonite 2%, thickener 0.05%, and water-reducing agent 1%.

[0030] Example 3 PNIPAM-AM copolymer thermosensitive hydrogel was prepared according to the method described in Example 1.

[0031] A heated expansion slurry is prepared by uniformly mixing PNIPAM-AM copolymer thermosensitive hydrogel, lime with a calcium content of not less than 95%, fine sand with a fineness modulus of 1.6-2.2, fly ash with a particle size of 2800-3200 mesh, sodium bentonite with a particle size of 1400-1600 mesh, thickener (carboxymethyl cellulose), FDN-C type naphthalene-based water-reducing agent, and water. The mass fractions of each substance in the heated expansion slurry are as follows: PNIPAM-AM copolymer thermosensitive hydrogel 8%, lime 8%, fine sand 50%, fly ash 15%, sodium bentonite 6%, thickener 0.2%, and water-reducing agent 0.02%.

[0032] Comparative Example 1 Take lime with a calcium content of not less than 95%, fine sand with a fineness modulus of 1.6-2.2, fly ash with a particle size of 2800-3200 mesh, sodium bentonite with a particle size of 1400-1600 mesh, thickener (carboxymethyl cellulose), FDN-C type naphthalene-based water-reducing agent and water, mix them evenly to obtain a control slurry.

[0033] No temperature-sensitive hydrogel components are added.

[0034] The mass fractions of each substance in the comparative slurry were as follows: lime 7%, fine sand 50%, fly ash 22%, sodium bentonite 5%, thickener 0.15%, water-reducing agent 0.5%, and water 15.35%.

[0035] Comparative Example 2 Prepare 100 parts of acrylamide (AM), 0.5 parts of N,N'-methylenebisacrylamide (MBA) crosslinking agent, 0.2 parts of ammonium persulfate (APS), and 0.1 parts of N,N,N',N'-tetramethylethylenediamine (TEMED) accelerator.

[0036] AM was dissolved in water and stirred until completely dissolved; then MBA crosslinking agent was added, and after dissolution, APS and TEMED were added to obtain ordinary polyacrylamide (PAM) hydrogel.

[0037] The above-mentioned PAM hydrogel, lime with a calcium content of not less than 95%, fine sand with a fineness modulus of 1.6-2.2, fly ash with a particle size of 2800-3200 mesh, sodium bentonite with a particle size of 1400-1600 mesh, thickener (carboxymethyl cellulose), FDN-C type naphthalene-based water-reducing agent, and water were mixed evenly to obtain a control slurry. The mass fractions of each substance in the control slurry were as follows: PAM hydrogel 10%, lime 6%, fine sand 45%, fly ash 20%, sodium bentonite 4%, thickener 0.15%, and water-reducing agent 0.5%.

[0038] Comparative Example 3 Prepare 100 parts of N-isopropylacrylamide (low molecular weight PNIPAM) with a number average molecular weight of 500,000, 15 parts of acrylamide (AM), 0.5 parts of N,N'-methylenebisacrylamide (MBA) crosslinking agent, 0.2 parts of ammonium persulfate (APS), and 0.1 parts of N,N,N',N'-tetramethylethylenediamine (TEMED) accelerator for later use.

[0039] Low molecular weight PNIPAM and AM were dissolved in water and stirred until completely dissolved; then MBA crosslinking agent was added, and after dissolution, APS and TEMED were added to obtain low molecular weight PNIPAM-AM copolymer thermosensitive hydrogel.

[0040] The aforementioned low molecular weight hydrogel, lime with a calcium content of not less than 95%, fine sand with a fineness modulus of 1.6-2.2, fly ash with a particle size of 2800-3200 mesh, sodium bentonite with a particle size of 1400-1600 mesh, thickener (carboxymethyl cellulose), FDN-C type naphthalene-based water-reducing agent, and water were mixed evenly to obtain a control slurry. The mass fractions of each substance in the control slurry were as follows: 10% low molecular weight PNIPAM-AM copolymer thermosensitive hydrogel, 6% lime, 45% fine sand, 20% fly ash, 4% sodium bentonite, 0.15% thickener, and 0.5% water-reducing agent.

[0041] Comparative Example 4 A conventional two-component grout was prepared according to the formula of commonly used passive filling grouting materials in engineering. Specifically, PO 42.5 ordinary Portland cement, water glass with a modulus of 2.4, fine sand with a fineness modulus of 1.6-2.2, and water were mixed evenly to obtain a control grout (conventional two-component grout). The mass fractions of each substance in the control grout were as follows: cement 35%, water glass 15%, fine sand 45%, and water 5%.

[0042] Test Example 1 Using the thermally expanding slurries prepared in Examples 1-3 and the control slurries prepared in Comparative Examples 1-4 as sample slurries, the equivalent thermal conductivity and the freezing time required for the center temperature to drop to -5℃ of each specimen were determined according to the methods described in Chapter 31 "Test of Thermal Conductivity of Frozen Soil" and Chapter 32 "Determination of Freezing Characteristic Curve" of GB / T 50123-2019 "Standard for Geotechnical Testing Methods". The frost heave rate, thaw settlement rate, and cumulative deformation of each specimen during the freeze-thaw cycle were determined according to the methods described in Chapter 28 "Frost Heave Rate Test" and Chapter 29 "Thaw Settlement Coefficient Test" of GB / T 50123-2019 (with modifications based on TB 10115-2014 "Specifications for Frozen Soil Testing in Railway Engineering"). The results are shown in Table 1.

[0043] Table 1 Comparison of freezing efficiency and thaw settlement control performance of grout-filled soil samples As shown in Table 1, the equivalent thermal conductivity of the slurry in Examples 1-3 is significantly higher than that in Comparative Examples 1-4, and the freezing time of the Example groups is only 17.5-18.2 hours, which is about 30% shorter than that of the traditional cement slurry in Comparative Example 4 and about 26% shorter than that of the anhydrous gel group in Comparative Example 1. This proves that the slurry of the present invention can effectively accelerate the transfer of cold energy, significantly shorten the freezing period of the tunnel end well, and reduce energy consumption. In addition, Comparative Examples 1, 2, and 4 all showed significant volume shrinkage (melt-settlement rate of 1.75%~2.45%) during the melting stage, resulting in ground subsidence; while the melt-settlement rate of Example 1 was -0.05% (melt-settlement rate is the change in volume relative to the pre-freezing volume, and a negative value indicates slight expansion after melting), and Examples 2 and 3 were also close to zero. This indicates that the PNIPAM-AM gel in the slurry of the present invention accurately filled the pores left by the melting of ice into water by absorbing water and swelling when the temperature rises above 0°C, achieving a control effect of zero settlement or even slight heave.

[0044] After freeze-thaw cycles, the cumulative settlement of the comparative group was as high as 2.35%-6.80%, and the specimens showed varying degrees of cracking, indicating that traditional materials cannot withstand repeated freeze-thaw stress. In contrast, the cumulative settlement of the example group was controlled within 0.21%, and the appearance remained intact. This verifies that the intelligent response of the slurry based on physical conformational changes in this invention has excellent reversibility and durability, and can adapt to temperature fluctuations during long-term operation.

[0045] In summary, the thermally expanding slurry prepared by this invention can not only shorten the freezing time through high thermal conductivity, but also completely eliminate the risk of melting and settling by utilizing its temperature-sensitive properties. Its overall performance is significantly better than that of existing technologies and comparative solutions.

[0046] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the technical solutions of the embodiments of the present invention.

Claims

1. A heated expansion grout for controlling settlement at tunnel end shafts, characterized in that, The heat-expanding slurry includes PNIPAM-AM copolymer thermosensitive hydrogel, lime, fine sand, fly ash, bentonite, thickener and water-reducing agent; The PNIPAM-AM copolymer thermosensitive hydrogel comprises N-isopropylacrylamide, acrylamide, N,N'-methylenebisacrylamide, an initiator, and an accelerator; the mass ratio of N-isopropylacrylamide, acrylamide, N,N'-methylenebisacrylamide, initiator, and accelerator is 100:12~16:0.3~0.6:0.15~0.25:0.1~0.

2.

2. The heat-expanding slurry as described in claim 1, characterized in that, The preparation method of the PNIPAM-AM copolymer thermosensitive hydrogel includes the following steps: mixing N-isopropylacrylamide and acrylamide solution with N,N'-methylenebisacrylamide; after the N,N'-methylenebisacrylamide is completely dissolved, adding an initiator and a promoter to obtain the PNIPAM-AM copolymer thermosensitive hydrogel.

3. The heat-expanding slurry as described in claim 1, characterized in that, By mass percentage, the heat-expanding slurry comprises 8%–10% PNIPAM-AM copolymer thermosensitive hydrogel, 2%–8% lime, 40%–50% fine sand, 15%–25% fly ash, 2%–6% bentonite, 0.05%–0.2% thickener, 0.02%–1% water-reducing agent, and the balance being water.

4. The heat-expanding slurry as described in claim 1, characterized in that, The initiator is ammonium persulfate; the accelerator is N,N,N',N'-tetramethylethylenediamine.

5. The heat-expanding slurry as described in claim 1, characterized in that, The thickener is one or more of carboxymethyl cellulose, gum arabic, polyvinyl alcohol, and polyvinylpyrrolidone; the water-reducing agent is an FDN-C type naphthalene-based water-reducing agent.

6. The heat-expanding slurry as described in claim 1, characterized in that, The N-isopropylacrylamide has a molecular weight ≥ 1 million.

7. The heat-expanding slurry as described in claim 1, characterized in that, The lime contains ≥95% calcium; the fine sand has a fineness modulus of 1.6-2.

2.

8. The heat-expanding slurry as described in claim 1, characterized in that, The fly ash has a particle size of 2800-3200 mesh; the bentonite has a particle size of 1400-1600 mesh, and the bentonite is sodium-based bentonite.

9. A method for preparing the thermally expanding slurry according to any one of claims 1 to 8, characterized in that, The method includes the following steps: The PNIPAM-AM copolymer thermosensitive hydrogel, lime, fine sand, fly ash, bentonite, thickener, water-reducing agent and water are mixed evenly to obtain a heat-expanding slurry.

10. The application of the heated expansion grout according to any one of claims 1 to 8 or the heated expansion grout prepared by the method of claim 9 in the control of settling at the tunnel end shaft, characterized in that, The heated expansion slurry is injected into the melting and settling zone of the frozen area at the end of the well, and expands in response to temperature to fill the formation loss.

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