A method for crack control construction of secondary lining concrete for submarine tunnels

Abstract

This invention relates to the field of crack control in subsea tunnels, specifically to a method for crack control construction of secondary lining concrete in subsea tunnels. The method includes pre-construction preparation by adding a temperature-controlled crack-resistant agent to the concrete to adjust the hydration temperature peak and setting time; increasing the rigidity of the secondary lining formwork and adding vertical supports at the bottom of the formwork; controlling the positioning of reinforcing bars to improve the accuracy of bar positioning and reduce local bar protrusion or overall misalignment of the reinforcing bar skeleton; secondary lining concrete molding to ensure continuous concrete pouring, with symmetrical layer-by-layer pouring, followed by demolding 24 hours after pouring; and secondary lining concrete curing using a highly absorbent and water-retaining curing membrane or a biodegradable plastic film for covering and moisturizing, followed by sprinkling water on the lining surface after demolding. This invention enables the secondary lining concrete of subsea tunnels to have no penetrating cracks, improving the long-term durability of the concrete. Simultaneously, it avoids the need for repairs and treatment of cracks and water leakage during tunnel operation, saving operating costs.

Description

Technical Field

[0001] This invention relates to the field of submarine tunnels, and more specifically to a method for crack control construction of secondary lining concrete in submarine tunnels. Background Technology

[0002] Many underground engineering projects, such as subways and tunnels, have experienced serious structural durability issues, including concrete cracking, water leakage, and steel reinforcement corrosion, even during the initial operation or construction phases. The problems are particularly severe in undersea tunnels where reinforced concrete structures are contaminated by seawater chlorides. The secondary lining of undersea tunnels uses C45-C50 concrete, a higher strength grade than that of other highway tunnel linings. The conventional technical approach for preparing this type of concrete involves using high-efficiency water-reducing agents, a higher amount of cementitious materials, and a lower water-cement ratio. Tunnel secondary lining concrete construction faces challenges such as high requirements for concrete workability, difficulties in continuous pouring, and mismatch between vibration and concrete workability. Due to the significant loss of workability of the concrete mixture over time and the difficulty in maintaining it, non-standard practices such as blindly adding water or excessively adding water-reducing agents are common on construction sites, severely affecting concrete strength, crack resistance, and durability. In addition, improper support of the secondary lining formwork trolley, significant misalignment of the steel reinforcement cage, and inappropriate vibration regimes can all cause cracking in the secondary lining concrete, even leading to through-cracks. Once honeycomb, voids, or even through cracks appear in the secondary lining concrete, water leakage is highly likely, leading to steel reinforcement corrosion and expansion. Treating through cracks in the secondary lining of an undersea tunnel is far more difficult than in general underground engineering. Such problems weaken the structure's durability, adversely affect tunnel operational safety, and require significant subsequent maintenance and remediation costs. Summary of the Invention

[0003] The purpose of this invention is to provide a method for crack control construction of secondary lining concrete for submarine tunnels, which effectively controls the generation of cracks in the secondary lining concrete of submarine tunnels, especially through cracks, thereby improving the long-term durability of the concrete and reducing operation and maintenance costs.

[0004] To achieve the above objectives, the technical solution adopted by this invention is as follows: A method for crack control construction of secondary lining concrete in submarine tunnels, comprising, S1. Preparation of construction materials: S1.1 Preparation of crack-resistant concrete: A temperature-controlled crack-resistant agent, including an expansion component, a temperature rise regulating component, and a retarding component, is added to the concrete to adjust the hydration temperature peak and setting time of the crack-resistant concrete and reduce temperature stress. S1.2 Improve the rigidity of the formwork of the secondary lining concrete formwork trolley and add vertical support at the bottom of the secondary lining concrete formwork trolley; S2, Reinforcing bar positioning: S2.1. Use circumferential and longitudinal support rods to spatially position the reinforcing bars, and add stirrups to control the lining thickness and overall rigidity, reduce local reinforcing bar protrusion or overall deviation of the reinforcing bar skeleton, thereby improving the positioning accuracy of the reinforcing bars. S2.2 High-strength mortar spacers are installed near the reinforcing bars to improve the uniformity of the concrete cover thickness. S3. Forming, demolding, and curing of secondary lining concrete: S3.1. Starting from the bottom of both side walls, the crack-resistant concrete shall be poured symmetrically in layers from bottom to top towards the arch; and the vertical distance between the concrete outlet and the pouring surface shall not exceed 2m, the height difference between the two concrete pouring surfaces shall not exceed 1m, and the height difference between the concrete pouring surfaces on the same side shall not exceed 0.5m. S3.2 24 hours after the pouring is completed, the secondary lining concrete trolley is demolded, and the concrete is cured after demolding. S3.3 The end formwork support should begin simultaneously with the demolding of the secondary lining concrete trolley; S3.4. Use a highly absorbent and water-retaining curing film or a biodegradable plastic film to cover and moisturize the lining surface. Sprinkle water on the lining surface for curing after demolding.

[0005] Furthermore, the crack-resistant concrete includes P×I52.5 cement, slag powder, and fly ash, wherein the slag powder accounts for ≤45% of the mass of the cementitious materials in the crack-resistant concrete, the fly ash accounts for ≤30% of the mass of the cementitious materials in the crack-resistant concrete, the maximum amount of cementitious materials in the crack-resistant concrete is 360~480kg / m3, and the water-cement ratio is ≤0.36.

[0006] Furthermore, the expanding component is a calcium sulfoaluminate-calcium oxide composite expanding agent; the temperature rise regulating component is a compound of alkyl phosphate and hydroxypropyl starch ether, and the mass ratio of alkyl phosphate to hydroxypropyl starch ether is 1:1; the retarding component is a compound of sodium gluconate and sodium pyrophosphate, and the mass ratio of sodium gluconate to sodium pyrophosphate is 2:1.

[0007] Furthermore, the circumferential support rod is mounted on the secondary lining reinforcement binding trolley via a longitudinal support rod, and the circumferential support rod is attached to the inner reinforcement; a positioning plate for controlling the spacing between adjacent reinforcement bars is provided on adjacent circumferential support rods.

[0008] Furthermore, the positioning plate is provided with a positioning groove, and a reinforcing bar is provided in the positioning groove.

[0009] Furthermore, the length of the stirrup is equal to the thickness of the secondary lining to ensure that the steel mesh does not shift.

[0010] Furthermore, 24 hours after the pouring is completed, the secondary lining concrete trolley is demolded, and the concrete is immediately cured after demolding.

[0011] Furthermore, the density of the P×I52.5 cement is not less than 3.13 g / cm3, the specific surface area is not less than 300 m2 / kg and not more than 330 m2 / kg, and the standard consistency water requirement ranges from 26.0% to 29.0%.

[0012] Furthermore, the density of the slag powder is not less than 2.85 g / cm3, and the specific surface area is in the range of 400~460 m2 / kg.

[0013] Furthermore, the fly ash has a loss on ignition of no more than 5%, a water requirement of no more than 95%, a fineness of no more than 12%, and a density of no more than 2.6 g / cm³.

[0014] Compared with the prior art, the present invention has the following advantages and beneficial effects: 1. This invention forms a complete crack control technology chain by starting with the concrete material itself, namely the temperature-controlled crack-resistant agent, combined with improving the rigidity of the formwork, accurately positioning the reinforcing bars, and refining the pouring and curing process.

[0015] 2. This invention effectively reduces the hydration heat release rate of concrete and delays the appearance time of the temperature peak by using temperature rise regulating components and retarding components in the temperature-controlled crack-resistant agent, thus significantly releasing temperature stress. Combined with the shrinkage compensation function of the expansion component, it inhibits the generation of temperature cracks and shrinkage cracks at the material level.

[0016] 3. The present invention uses high-rigidity templates, bottom supports, support rods, stirrups, and spacers to accurately position the reinforcing bars, ensuring the lining thickness, the thickness of the reinforcing bar protective layer, and the overall stability of the reinforcing bar skeleton, thus avoiding early disturbance cracks and durability problems caused by dimensional deviations and reinforcing bar displacement.

[0017] 4. This invention minimizes disturbance to the reinforcing steel and early-stage concrete during construction by controlling pouring drop and height differences and optimizing the formwork removal sequence, thus preventing the formation of early micro-cracks. Ultimately, it achieves the goal of eliminating through-cracks in the secondary lining concrete of the undersea tunnel, significantly improving the concrete's impermeability and long-term durability, avoiding high maintenance costs due to water leakage during operation, and significantly saving on total life-cycle operating costs. Attached Figure Description

[0018] Figure 1 This is a flowchart of a method for crack control construction of secondary lining concrete in submarine tunnels.

[0019] Figure 2 This is a comparison chart of the peak temperature and retarding time of ordinary concrete and crack-resistant concrete.

[0020] Figure 3A schematic diagram showing the addition of vertical supports to the secondary lining concrete formwork trolley.

[0021] Figure 4 This is a schematic diagram showing the positions of the inner reinforcing bars, circumferential support rods, and longitudinal support rods.

[0022] Figure 5 This is a schematic diagram of the inner reinforcing bars.

[0023] Figure 6 This is a schematic diagram showing the positions of the ring support rod, longitudinal support rod, and secondary lining reinforcement binding trolley.

[0024] Figure 7 This is a schematic diagram of the positioning plate. Detailed Implementation

[0025] like Figure 1 and Figure 2 As shown, a method for crack control construction of secondary lining concrete in submarine tunnels includes, S1. Preparation of construction materials: S1.1 Preparation of Crack-Resistant Concrete: C50 crack-resistant concrete is used in this project. The total amount of cementitious materials in the crack-resistant concrete is 480 kg / m³, and the water-cement ratio is 0.35. The specific mix proportions are as follows: P×I52.5 cement (density 3.15 g / cm³, specific surface area 320 m² / kg) 240 kg, slag powder (density 2.9 g / cm³, specific surface area 430 m² / kg) 82 kg, fly ash (loss on ignition 4.5%, water requirement ratio 92%) 129 kg, other raw materials: crushed stone 977 kg, sand 737 kg, admixture 8.2 kg, and rust inhibitor 14.4 kg.

[0026] in: The density of the P×I52.5 cement is not less than 3.13 g / cm³. 3 Specific surface area not less than 300m² 2 / kg and not exceeding 330m 2 / kg, the standard consistency water requirement ranges from 26.0% to 29.0%.

[0027] The density of the slag powder is not less than 2.85 g / cm³. 3 The specific surface area ranges from 400 to 460 m². 2 / kg.

[0028] The fly ash has a loss on ignition of no more than 5%, a water requirement of no more than 95%, a fineness of no more than 12%, and a density of no more than 2.6 g / cm³.

[0029] Then, 29 kg of a temperature-controlled crack-resistant agent, including an expansion component, a temperature rise regulating component, and a retarding component, was added to the concrete. The amount of the temperature-controlled crack-resistant agent was 6% of the gel material in the crack-resistant concrete. This ratio can inhibit the early hydration of C3A through the temperature rise regulating component and delay the hydration of C3S through the retarding component, so that the hydration exothermic curve tends to be flat and the temperature peak is delayed until after 24 hours. At the same time, the expansion component generates moderate volume expansion to compensate for the later shrinkage, thereby adjusting the hydration temperature peak and setting time of the crack-resistant concrete and reducing temperature stress. in: The expansion component consists of: calcium sulfoaluminate-calcium oxide composite expansion agent; The composition and dosage of the temperature rise regulating component are: a compound of alkyl phosphate and hydroxypropyl starch ether in a mass ratio of 1:1; The retarding component consists of a compound of sodium gluconate and sodium pyrophosphate in a mass ratio of 2:1.

[0030] S1.2, Improve the rigidity of the secondary lining concrete formwork trolley and add vertical supports of 10 mm at the bottom of the formwork; such as Figure 3 As shown, the panel thickness and back rib density are increased to ensure the overall rigidity of the formwork. Simultaneously, adjustable threaded rod vertical supports are added between the bottom of the formwork and the invert arch filling surface. Before pouring, pre-tightening force is applied to all vertical supports to ensure they are securely fixed without loosening, resisting the enormous upward buoyancy generated during concrete pouring and preventing vertical displacement of the trolley and formwork.

[0031] S2, Reinforcing bar positioning: S2.1, Use circumferential and longitudinal support rods to spatially position the reinforcing cage; such as Figures 4 to 7 As shown, the circumferential support rod 1 is mounted on the secondary lining reinforcement binding trolley 3 via the longitudinal support rod 2, and the circumferential support rod 1 is attached to the inner reinforcement 6; positioning plates 4 for controlling the spacing between adjacent reinforcement bars are provided on adjacent circumferential support rods 1. The positioning plates 4 are provided with positioning grooves 5, which are used to hold the circumferential reinforcement bars to achieve precise three-dimensional positioning of the reinforcement bars. All stirrups are fully hooked and hung according to design requirements, and each intersection node is firmly tied with tie wire in a figure-eight shape to prevent the reinforcement mesh from loosening or shifting during concrete pouring. This reduces local reinforcement bar protrusion or overall reinforcement skeleton misalignment, thereby improving the positioning accuracy of the reinforcement bars.

[0032] like Figure 4 As shown in Figure S2.2, lining thickness control: Stirrups are arranged in a staggered pattern at 1.0m x 1.0m intervals between the upper and lower reinforcing meshes. These stirrups are made of bent steel bars of the same diameter as the main reinforcing bars, and their length is precisely equal to the design thickness of the secondary lining structure. This ensures accurate spacing between the two layers of reinforcing mesh, thereby guaranteeing the lining thickness and overall rigidity.

[0033] like Figure 5 As shown in Figure S2.3, protective layer control: High-strength mortar spacers are installed at 0.8m x 0.8m intervals on the upper reinforcing mesh near the formwork (inner ring). The contact surfaces between the spacers and the formwork should be point contact or line contact. It is strictly forbidden for the spacers to be pressed tightly against the formwork or squeezed too tightly, so as to prevent the spacers from breaking when the secondary lining concrete trolley vibrates or shifts, disturbing the newly poured concrete around them and forming early micro-cracks.

[0034] S3. Forming, demolding, and curing of secondary lining concrete: S3.1 Secondary Lining Concrete Forming: S3.1.1 Layered symmetrical pouring: The concrete pump pipe is connected to the diversion channel on the top of the secondary lining pouring trolley, and the concrete is introduced into the working windows of both side walls through the chute. The principle of "pouring from bottom to top, layered symmetrically" is adopted. First, concrete is poured from the bottommost side wall window, and after the lower layer of concrete is fully vibrated, the upper layer window is opened.

[0035] S3.1.2, Control of pouring parameters: Strictly control the free fall of concrete, and always keep the vertical distance between the concrete pump pipe outlet and the current pouring surface within 2m. Monitor the height of the concrete surface on both sides in real time during the pouring process to ensure that the height difference between the two sides does not exceed 1m. The thickness of the layered pouring on the same side is controlled at about 40cm, and the height difference does not exceed 0.5m to prevent the trolley from deviating due to uneven lateral pressure.

[0036] S3.1.3, Anti-disturbance measures: A flexible hose must be connected to the end of the concrete pump pipe. Direct contact between the iron pipe portion of the concrete pump pipe and the reinforcing steel mesh is strictly prohibited to prevent the pumping impact force from being transmitted to the reinforcing steel mesh. A combination of "attached vibrator and immersion vibrator" should be used for compaction, that is, a combination of external and internal vibration of the formwork. When vibrating internally, the vibrator should be inserted quickly and withdrawn slowly to avoid touching the formwork and reinforcing steel.

[0037] S3.1.4 Continuous pouring: By rearranging the positions of the chutes and windows, multiple windows can be operated simultaneously or in cycles, reducing the frequency of disconnecting and reconnecting pump pipes, ensuring a continuous supply of concrete, and avoiding cold joints.

[0038] S3.2 Formwork Removal and Demolding of Secondary Lining Concrete: Formwork removal begins 24 hours after concrete pouring. The removal sequence is as follows: first remove the end formwork, then loosen the lateral supports, and finally loosen the top supports. The removal of supports in all directions of the secondary lining reinforcement binding trolley 3 should be carried out simultaneously and slowly to avoid the secondary lining reinforcement binding trolley 3 suddenly falling and impacting the concrete or tilting to the side.

[0039] S3.3 Moisture curing of secondary lining concrete: Immediately after demolding, spray water onto the surface of the lining concrete, then cover it with a highly absorbent and water-retaining curing membrane. The curing membrane should overlap tightly to ensure that the inside of the membrane remains moist at all times.

[0040] Using the above construction methods, the secondary lining concrete of the undersea tunnel has a dense and smooth appearance after molding. Non-destructive testing and on-site observation revealed no cracks wider than 0.2mm, and in particular, no through cracks were found, effectively ensuring the structural safety and long-term durability of the tunnel.

[0041] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A method for crack control construction of secondary lining concrete in submarine tunnels, characterized in that, include, S1. Preparation of construction materials: S1.1 Preparation of crack-resistant concrete: A temperature-controlled crack-resistant agent, including an expansion component, a temperature rise regulating component, and a retarding component, is added to the concrete to adjust the hydration temperature peak and setting time of the crack-resistant concrete and reduce temperature stress. S1.2 Improve the rigidity of the formwork of the secondary lining concrete formwork trolley and add vertical support at the bottom of the secondary lining concrete formwork trolley; S2, Reinforcing bar positioning: S2.

1. Use circumferential and longitudinal support rods to spatially position the reinforcing bars, and add stirrups to control the lining thickness and overall rigidity, reduce local reinforcing bar protrusion or overall deviation of the reinforcing bar skeleton, thereby improving the positioning accuracy of the reinforcing bars. S2.2 High-strength mortar spacers are installed near the reinforcing bars to improve the uniformity of the concrete cover thickness. S3. Forming, demolding, and curing of secondary lining concrete: S3.

1. Starting from the bottom of both side walls, the crack-resistant concrete shall be poured symmetrically in layers from bottom to top towards the arch; and the vertical distance between the concrete outlet and the pouring surface shall not exceed 2m, the height difference between the two concrete pouring surfaces shall not exceed 1m, and the height difference between the concrete pouring surfaces on the same side shall not exceed 0.5m. S3.2 24 hours after the pouring is completed, the secondary lining concrete trolley is demolded, and the concrete is cured after demolding. S3.3 The end formwork support should begin simultaneously with the demolding of the secondary lining concrete trolley; S3.

4. Use a highly absorbent and water-retaining curing film or a biodegradable plastic film to cover and moisturize the lining surface. Sprinkle water on the lining surface for curing after demolding.

2. The method for crack control construction of secondary lining concrete for submarine tunnels according to claim 1, characterized in that, The crack-resistant concrete comprises P×I52.5 cement, slag powder, and fly ash, wherein slag powder accounts for ≤45% of the mass of the cementitious materials in the crack-resistant concrete, fly ash accounts for ≤30% of the mass of the cementitious materials in the crack-resistant concrete, and the maximum amount of cementitious materials in the crack-resistant concrete is 360~480 kg / m³. 3 The water-to-binder ratio is ≤0.

36.

3. The method for crack control construction of secondary lining concrete for submarine tunnels according to claim 1, characterized in that, The expanding component is a calcium sulfoaluminate-calcium oxide composite expanding agent; the temperature rise regulating component is a compound of alkyl phosphate and hydroxypropyl starch ether, and the mass ratio of alkyl phosphate to hydroxypropyl starch ether is 1:1; the retarding component is a compound of sodium gluconate and sodium pyrophosphate, and the mass ratio of sodium gluconate to sodium pyrophosphate is 2:

1.

4. The method for crack control construction of secondary lining concrete for submarine tunnels according to claim 1, characterized in that, The circumferential support rod is mounted on the secondary lining reinforcement binding trolley via a longitudinal support rod, and the circumferential support rod is attached to the inner reinforcement; a positioning plate for controlling the spacing between adjacent reinforcement bars is provided on adjacent circumferential support rods.

5. A method for crack control construction of secondary lining concrete for submarine tunnels according to claim 4, characterized in that, The positioning plate is provided with a positioning groove, and a reinforcing bar is provided in the positioning groove.

6. The method for crack control construction of secondary lining concrete for submarine tunnels according to claim 1, characterized in that, The length of the stirrup reinforcement is equal to the thickness of the secondary lining to ensure that the steel mesh does not shift.

7. The method for crack control construction of secondary lining concrete for submarine tunnels according to claim 1, characterized in that, Twenty-four hours after the pouring is completed, the secondary lining concrete trolley is used for demolding, and the concrete is immediately cured after demolding.

8. A method for crack control construction of secondary lining concrete for submarine tunnels according to claim 2, characterized in that, The density of the P×I52.5 cement is not less than 3.13 g / cm³. 3 Specific surface area not less than 300m² 2 / kg and not exceeding 330m 2 / kg, the standard consistency water requirement ranges from 26.0% to 29.0%.

9. A construction method for crack control in the secondary lining concrete of a submarine tunnel according to claim 2, characterized in that, The density of the slag powder is not less than 2.85 g / cm³. 3 The specific surface area ranges from 400 to 460 m². 2 / kg.

10. A construction method for crack control in the secondary lining concrete of a submarine tunnel according to claim 2, characterized in that, The fly ash has a loss on ignition of no more than 5%, a water requirement of no more than 95%, a fineness of no more than 12%, and a density of no more than 2.6 g / cm³.

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