Tunnel secondary lining concrete anti-crack additive and construction and acceptance method

Abstract

The invention discloses a tunnel secondary lining concrete anti-crack additive and a construction and acceptance inspection method, and belongs to the technical field of tunnel construction. The anti-crack additive is prepared according to the time from production to delivery of concrete into a pump truck and the temperature when the concrete enters the pump truck; the negative influence that the anti-cracking functional material is ineffectively consumed too early and too fast due to long-time transportation, stirring shearing and high temperature of a stirring tank truck can be resisted, and then the anti-cracking performance of the concrete is improved; according to the construction method, region division is carried out according to the actual cracking risk of the secondary lining structure, concrete with different anti-cracking properties is poured, and the concrete cost is reduced; according to the acceptance method, a secondary lining concrete cracking risk coefficient is calculated by adopting anti-cracking key parameters obtained by inversion of actual monitoring data of temperature and deformation of solid structure concrete. The technical effects that the crack resistance of the tunnel secondary lining concrete can be improved, shrinkage cracks can be inhibited, the crack resistance effect can be accepted and accepted, and the technical scheme can be popularized can be achieved.

Description

Technical Field

[0001] The invention relates to the technical field of tunnel construction, and in particular to an anti-cracking additive for secondary lining concrete of a tunnel, and a construction and acceptance method. Background Art

[0002] Tunnels are an important part of my country's transportation power and play an important role in the modern transportation system. Among them, secondary lining tunnels are a common structural form for railways and highways to cross mountains, such as the famous Qinling Tunnel and Gaoligong Mountain Tunnel. The common secondary lining concrete strength grade is C30~C35, the structure thickness is 30cm~50cm, and the segmented casting length is 9m or 12m, which is generally smaller than the segmented casting length of 15m~30m of the weir tunnel. Although the secondary lining structure is relatively small, due to the process of first casting the invert and then casting the secondary lining, coupled with the influence of the maintenance structure, the secondary lining concrete is subject to strong constraints. At the same time, due to the requirement of demolding strength, the early strength of the secondary lining concrete is high. Under the relatively sealed space conditions in the tunnel, the temperature rise caused by the heat release of concrete hydration is also high, resulting in a large temperature shrinkage. After further superimposed on the self-shrinkage of concrete, shrinkage stress will be generated inside the secondary lining concrete structure. When the shrinkage stress exceeds the tensile strength of the concrete, cracks will appear in the secondary lining concrete, and these cracks are basically through-going cracks, which will not only cause leakage and durability problems, but also reduce the structural bearing capacity and affect the safe operation of the tunnel.

[0003] Lowering concrete temperature, reducing concrete shrinkage and reducing external constraints are common crack control measures, such as lowering concrete mold temperature, selecting low hydration heat, low shrinkage high-quality raw materials, reducing cement content in concrete mix, adding mineral admixtures, shortening the step-by-step pouring interval between the invert and secondary lining concrete, installing waterproofing rolls or isolation materials between the secondary lining and the maintenance structure, and using special maintenance trolleys. Specifically in actual tunnel construction projects, the above measures cannot be implemented well. For example, at the design level, the concrete strength design and assessment age is extended to encourage the reduction of cement content in the mix, but due to the influence of early demolding, in order to ensure the early demolding strength, the cement content of concrete is still generally high during actual construction; for example, in order to ensure structural safety, the invert and the bottom plate will be poured as soon as possible, so that the pouring interval between them and the secondary lining is generally longer. As my country's infrastructure construction is becoming increasingly complete, the current and next stage of tunnel construction environment is becoming increasingly harsh. In addition, due to the constraints of transportation distance and construction costs, high-quality raw materials are difficult to guarantee. It has become a common practice to obtain materials locally while meeting standard specifications.

[0004] When cracking cannot be solved after taking measures in terms of raw materials, mix ratio and process, the use of expansive agents to compensate for concrete shrinkage is an important means to inhibit concrete cracking. However, a large number of engineering practices and surveys have found that many concretes using expansive agents also crack, and even the number of cracks has increased. Further combined with experimental research and engineering monitoring results, it is found that the main reasons for this situation are as follows: (1) The hydration reaction of the expansive agent will also generate a large amount of hydration heat, especially calcium oxide expansive agents will increase the temperature rise of concrete, increase the risk of temperature shrinkage and cracking; (2) The expansion and shrinkage process of the expansive agent needs to match the temperature and shrinkage process of the concrete structure. For example, although calcium expansive agents have a large expansion efficiency, they mainly occur in the early temperature rise stage of the solid structure and cannot produce a compensatory shrinkage effect in the temperature drop stage where the risk of cracking is greater; (3) The length of a single highway or railway lining tunnel is generally several kilometers or tens of kilometers, and the traffic routes in the tunnel are not as open as those in ordinary outdoor projects. The transportation and waiting time of concrete from production to pumping may exceed 30 minutes, or even up to 60 minutes. At the same time, the temperature control measures that the mixing station can take are limited. When encountering hot weather construction, the temperature of the concrete leaving the machine will exceed 30°C. During the long transportation and pouring waiting process, the temperature of the concrete will reach above 35°C. Under such high temperature and long-term strong stirring in the mixing tank truck, the hydration reaction of the expansive agent will be accelerated. However, the hydration reaction of the expansive agent in the plastic stage of the concrete cannot produce expansion, so it will cause the expansive agent to be ineffectively consumed in advance, and it is difficult to play the expected compensating shrinkage role in the physical structure.

[0005] At present, the acceptance of the crack control effect of tunnels is mainly carried out by observation or measurement in the early construction period, focusing on checking whether there are cracks and water leakage. In fact, when some cracks are generated inside but not penetrated, they will not cause leakage and surface cracking for the time being, but as the concrete itself continues to shrink, cracking will occur. The results of non-destructive ultrasonic detection are easily affected by steel bars or internal defects. Under the constraints of cost, it is difficult to detect the entire surface of the secondary lining. In recent years, with the development of new crack control technologies, the risk of concrete cracking can be calculated by inputting parameters such as concrete properties and structural dimensions obtained from experimental research, and then the corresponding crack control technology solutions can be adopted. However, cement produced by the same manufacturer will adjust the cement components according to the construction season and the quality of cement clinker. In addition, the fluctuations in sand and stone mud content make the actual concrete performance and the performance during indoor mix ratio verification quite different. In addition, affected by ventilation and line length, the working parameters of different sections, such as heat dissipation coefficient, are also different. The above factors will lead to large differences in the anti-cracking effect implemented according to the plan or the anti-cracking effect is difficult to meet the requirements of the expected plan.

[0006] In summary, the existing related technologies cannot completely solve the problems of cracking of secondary lining concrete and acceptance of anti-cracking effect. Actual projects generally face the problem that the problem of cracking of secondary lining concrete can be solved from the level of theoretical calculation or a small number of test sections, but it cannot be widely promoted and applied due to cost or difficulty in matching actual construction needs. Therefore, it is very necessary to propose a technical solution that takes into account both technical effects and costs to meet the needs of crack control and anti-cracking effect acceptance of secondary lining concrete in tunnels. Summary of the invention

[0007] Technical problem to be solved: In view of the technical difficulties in shrinkage cracking of tunnel secondary lining concrete and acceptance of anti-crack effect in the background technology, the present invention provides an anti-crack additive, construction and acceptance method for tunnel secondary lining concrete. This construction method, on the basis of taking into account both technical effect and cost control, achieves the beneficial effects of improving the anti-crack performance of tunnel secondary lining concrete, suppressing shrinkage cracks, accepting anti-crack effect and promoting the technical solution.

[0008] Technical solution: The invention discloses an anti-cracking additive for secondary lining concrete of a tunnel, wherein the components of the anti-cracking additive are prepared according to the time t from when the concrete leaves the production machine to when it is transported into the pump truck and the temperature T of the concrete when it enters the pump truck; When t≥30min and T≥30°C, the anti-cracking additive is composed of 95%~98% by weight of a magnesium oxide expansion agent having an activity value of 150s~250s and 2%~5% by weight of a process control material; When t≥30min, 23℃≤T<30℃, the anti-cracking additive is composed of 95%~98% by weight of magnesium oxide expansion agent with an activity value of 80s~140s and 2%~5% by weight of process control material; When t≥30min and T<23℃, the anti-cracking additive is composed of 50%~80% by weight of magnesium oxide expansion agent with an activity value of 80s~140s, 20%~50% by weight of calcium oxide expansion agent and 0%~3% by weight of process control material; When t<30min, T≥23℃, the anti-cracking additive is composed of 50%~80% by weight of magnesium oxide expansion agent with an activity value of 80s~140s, 20%~50% by weight of calcium oxide expansion agent and 0%~3% by weight of process control material; When t<30min and T<23℃, the anti-cracking additive is composed of 50%~80% by weight of magnesium oxide expansion agent and 20%~50% by weight of calcium oxide expansion agent with an activity value of 80s~140s.

[0009] Preferably, the strength design grade of the concrete to which the anti-cracking additive is added within 60 days does not exceed C40.

[0010] Preferably, the 12h hydration heat reduction rate of the process-regulating material is ≥15%, and the 24h hydration heat reduction rate is ≤35%.

[0011] The present invention also discloses a construction method for secondary lining concrete of a tunnel, wherein the secondary lining of the tunnel is divided into a Class I area and a Class II area, and different types of concrete with anti-cracking additives are used for pouring, and the construction method comprises the following steps: Step 1: Take the tunnel cross-section with a segmented casting length of L, set the side of the secondary lining close to the inside of the tunnel as the S1 boundary curve, the side close to the maintenance structure as the S2 boundary curve, and the side of the invert close to the inside of the tunnel as the S3 boundary curve. The intersection of the S1 boundary curve and the S3 boundary curve is point P1; draw a vertical line at point P1 and intersect the S1 boundary curve at point P2, and take the vertical distance from point P1 to point P2 as H; mark the area of ​​the secondary lining below the vertical line H as Class I area, and mark the rest of the upper area as Class II area; Step 2: Prepare three types of concrete: A, B and C respectively: Among them, Class A concrete, calculated per cubic meter, includes the following components: 180kg~340kg of cement, 80kg~150kg of fly ash, 30kg~50kg of anti-cracking additive, 650kg~850kg of fine aggregate, 700kg~1100kg of coarse aggregate, 3kg~6kg of water reducer, and 140kg~170kg of mixing water; Class B concrete, calculated per cubic meter, includes the following components: 180kg~340kg of cement, 80kg~160kg of fly ash, 20kg~30kg of anti-cracking additive, 650kg~850kg of fine aggregate, 700kg~1100kg of coarse aggregate, 3kg~6kg of water reducer, and 140kg~170kg of mixing water; Class C concrete, measured per cubic meter, includes the following components: 180kg~340kg of cement, 80kg~180kg of fly ash, 650kg~850kg of fine aggregate, 700kg~1100kg of coarse aggregate, 3kg~6kg of water reducer, and 140kg~170kg of mixing water; Step 3: Select the type of concrete to be poured according to the zoning of the secondary lining and the pump inlet temperature T. Use Type A concrete in Class I area according to the pouring process conditions; when T≥30℃, use Type B concrete in Class II area according to the pouring process conditions; when T<30℃, use Type C concrete in Class II area according to the pouring process conditions.

[0012] Preferably, in step 3, the temperature difference between the concrete pump inlet temperature T and the average temperature inside the tunnel is controlled to be no greater than 15°C.

[0013] Preferably, in step 1, a waterproof roll or geotextile is provided between the secondary lining and the maintenance structure as an isolation material.

[0014] Preferably, in step 1, the thickness of the secondary lining structure is ≤1.2m and the segmented casting length is ≤21m.

[0015] The present invention also discloses a method for acceptance of secondary lining concrete of a tunnel, which uses measured data of temperature and deformation of concrete of a solid structure to inversely calculate key parameters of crack resistance, and then uses the key parameters of crack resistance obtained by inverse calculation to calculate the crack risk coefficient of the secondary lining concrete, comprising the following steps: Step 1: Select the monitoring element layout points. On any side of the Class I area at 0.5 times the L section along the longitudinal direction of the tunnel, set the center point corresponding to the 1m height layer below the height H as point P3. The surface close to the inside of the tunnel corresponding to point P3-1 and the surface close to the maintenance structure as point P3-2. In the Class II area at 0.5 times the L section along the longitudinal direction of the tunnel, set the center corresponding to the highest clearance point inside the tunnel as point P4. Step 2: Before pouring the secondary lining concrete of the tunnel, install a strain gauge at point P3 along the longitudinal and radial directions of the tunnel, a temperature gauge at point P3-1 and point P3-2, and a strain gauge at point P4 along the radial direction of the tunnel; Step 3: 21 days after the concrete pouring is completed, the monitoring results of the thermometer and strain gauge are input into the structural concrete cracking risk assessment and analysis software. When the calculated temperature and deformation curves are correlated with the temperature and deformation curves monitored by the entity, the correlation coefficient R 2 When it is ≥0.90, the iterative calculation is stopped, and the three key parameters of crack resistance, namely, adiabatic temperature rise of concrete, autogenous volume deformation of concrete under the condition of solid temperature change history, and heat dissipation coefficient of solid structure, are obtained through inverse calculation. Step 4: Input the anti-cracking parameters obtained by the above inverse calculation into the structural concrete cracking risk assessment and analysis software again to calculate the secondary lining concrete cracking risk coefficient.

[0016] Preferably, in step 2, the thermometer is an SBT-RT-1 thermocouple thermometer, the strain gauge is an SBT-15D vibrating wire strain gauge, and the data acquisition system is an SBT-CDM wireless monitoring system.

[0017] Preferably, the acceptance criteria for evaluating the anti-cracking effect are based on the maximum crack width on the secondary lining surface within the concrete strength assessment age being ≤0.05mm, and the maximum cracking risk coefficient calculated by inversion being ≤0.70.

[0018] Compared with the prior art, the present invention has the following beneficial effects: 1. Aiming at the specific working conditions of the secondary lining concrete of the tunnel, the present invention proposes a closed-loop crack control technical solution from three aspects: anti-cracking additives, construction methods and acceptance, based on the quantitative evaluation of the multi-factor coupling mechanism, experimental research and a large number of engineering practices. In order to ensure the performance improvement effect of the anti-cracking functional materials on the concrete, the present invention designs a special anti-cracking additive according to the on-site working condition parameters. In order to take into account both the technical effect and cost control, the present invention performs partitioned pouring of the secondary lining construction and adopts different types of concrete respectively. In order to further realize the quantitative evaluation of the anti-cracking implementation effect under the condition of achieving no cracks on the surface, the acceptance scheme of the cracking risk coefficient is adopted by inverting the physical monitoring results. Through the above-mentioned closed-loop technical solution, the beneficial effects of effectively improving the anti-cracking performance of the secondary lining concrete of the tunnel, suppressing shrinkage cracks, accepting the anti-cracking effect and promoting the technical solution are finally achieved; 2. The anti-cracking additive can resist the negative impact of the premature and rapid ineffective consumption of the expansion agent caused by long-term transportation, mixing and temperature of the concrete mixing tank truck, and can match the temperature and shrinkage history of the secondary lining concrete, thereby greatly improving the anti-cracking performance of the concrete; 3. This construction method divides the secondary lining of the tunnel into Class I and Class II areas according to the actual cracking risk of the secondary lining concrete, and uses concrete with different types of crack resistance and anti-cracking additives for pouring, thereby avoiding waste of resources and not increasing or even reducing concrete costs; 4. This acceptance method monitors the temperature and deformation of concrete at multiple key characteristic points of the secondary lining structure, and inputs the obtained temperature and deformation results into the structural concrete early cracking risk assessment and analysis software for iterative calculation. When the monitored temperature and deformation curves have a correlation coefficient with the calculation of not less than 0.90, the performance parameters such as the adiabatic temperature rise and autogenous volume deformation of the concrete used in the solid structure and the heat dissipation coefficient of the actual working condition template can be obtained. The concrete performance of the solid structure and the actual working condition boundary conditions and parameters are input into the structural concrete early cracking risk assessment and analysis software for calculation to obtain the cracking risk coefficient of the secondary lining concrete of the solid structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The present invention is a flow chart of the construction and acceptance process of the tunnel secondary lining concrete; Figure 2 This is a schematic diagram of the cross-sectional structure of the secondary lining of a tunnel according to Embodiment 1 of the present invention; Figure 3 The temperature monitoring curve and calculation curve of point P3 of Example 1 of the present invention are shown; Figure 4 The temperature monitoring curve and calculation curve of point P3-1 of Example 1 of the present invention; Figure 5The temperature monitoring curve and calculation curve of point P3-2 in Example 1 of the present invention; Figure 6 It is the temperature monitoring curve and calculation curve diagram of point P4 in Example 1 of the present invention; Figure 7 It is a deformation monitoring curve and a calculation curve diagram of point P3 along the longitudinal direction of the tunnel in Example 1 of the present invention; Figure 8 is a deformation monitoring curve and a calculation curve diagram of point P3 along the radial direction of the tunnel in Example 1 of the present invention; Fig. 9 is a deformation monitoring curve and a calculation curve diagram of point P4 along the radial direction of the tunnel in Example 1 of the present invention; Fig.10 is a concrete adiabatic temperature rise curve obtained by inversion calculation in Example 1 of the present invention; Fig.11 is a graph of the autogenous volume deformation of concrete under the condition of temperature change of the solid structure obtained by inversion calculation in Example 1 of the present invention; Fig.12 is a solid structure cracking risk coefficient diagram obtained by inversion calculation in Example 1 of the present invention; Fig.13 This is a schematic diagram of the cross-sectional structure of the secondary lining of a tunnel according to Embodiment 2 of the present invention; Fig.14 is a graph of the adiabatic temperature rise history of concrete obtained by inversion calculation in Example 2 of the present invention; Fig.15 is a graph of the autogenous volume deformation of concrete under the condition of temperature change of the solid structure obtained by inversion calculation in Example 2 of the present invention; Fig.16 is a solid structure cracking risk coefficient diagram obtained by inversion calculation in Example 2 of the present invention; Fig.17 This is a schematic diagram of the cross-sectional structure of the secondary lining of a tunnel according to Embodiment 3 of the present invention; Fig.18 is a solid structure cracking risk coefficient diagram obtained by inversion calculation in Example 3 of the present invention; Fig.19 is a solid structure cracking risk coefficient diagram obtained by inversion calculation in Example 4 of the present invention; Fig. 20 This is a schematic diagram of the cross-sectional structure of the secondary lining of a tunnel according to Embodiment 5 of the present invention; Fig.21 It is a diagram of the risk factor of cracking of a solid structure obtained by inversion calculation in Example 5 of the present invention.

[0020] Figure numerals: 1. inverted arch; 2. Class I area; 3. Class II area; 4. S1 boundary curve; 5. S2 boundary curve; 6. S3 boundary curve; 7. P1 point; 8. H vertical line; 9. P2 point; 10. P3 point; 11. P4 point; 12. P3-1 point; 13. P3-2 point. DETAILED DESCRIPTION

[0021] To make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the following will be combined with the attached Figures 1 to 21 The technical solutions of the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the described embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field belong to the scope of protection of the present invention.

[0022] Aiming at the specific working conditions of tunnel secondary lining concrete, the present invention proposes a closed-loop crack control technical scheme from three aspects: anti-cracking additives, construction methods and acceptance, based on quantitative evaluation of multi-factor coupling mechanism, experimental research and a large number of engineering practices. In order to ensure the performance improvement effect of anti-cracking functional materials on concrete, the present invention designs a special anti-cracking additive according to the on-site working conditions parameters. In order to take into account both technical effects and cost control, the present invention carries out zoned casting of the secondary lining construction and adopts different types of concrete respectively. Under the condition of achieving a surface without cracks, in order to further realize the quantitative evaluation of the anti-cracking effect, an acceptance scheme of the cracking risk coefficient is adopted by inverting the physical monitoring results. Through the above-mentioned closed-loop technical scheme, the beneficial effects of effectively improving the anti-cracking performance of tunnel secondary lining concrete, suppressing shrinkage cracks, accepting the anti-cracking effect and promoting the technical scheme are finally achieved.

[0023] In order to avoid the ineffective consumption of anti-cracking functional material expansion agent caused by factors such as tank truck mixing shear and high temperature during long-term transportation, and the current situation that the temperature entering the mold is usually difficult to test, facing the general working conditions that the concrete strength design grade does not exceed C40 within 60d, the present invention proposes to design additives for improving the crack resistance of concrete based on the time t experienced from the concrete production machine entering the mixing tank truck to the transportation entering the concrete pump truck and the pump inlet temperature T when the concrete enters the pump truck. The time t and the pump inlet temperature T can be determined by the concrete of the first cast arch part or process test. The components of the anti-cracking additives in the embodiment of the present invention are shown in Table 1:

[0024] Table 1 Composition of anti-cracking additives (unit: %): .

[0025] The anti-cracking additive of the present invention can resist the negative influence of premature and rapid ineffective consumption of the expansion performance of the expansion agent caused by long-term transportation, mixing and temperature of the concrete mixing tank truck, and can match the temperature and shrinkage history of the secondary lining concrete, thereby greatly improving the anti-cracking performance of the concrete.

[0026] The process regulating material used in the anti-cracking additive of the present invention is a starch-based hydration process regulating material, which is a commercially available product, such as SBT ® -TRI concrete hydration temperature rise inhibitor; process control materials will play a regulatory role in the hydration process of both expansive agents and cement. In order to ensure the regulatory effect of the early hydration process of the expansive agent, while not over-regulating the cement hydration process to avoid reducing the early strength of concrete, the 12h hydration heat reduction rate of the process control material is ≥15%, and the 24h hydration heat reduction rate is ≤35%.

[0027] The magnesium oxide expansion agent, calcium oxide expansion agent and process control material used in the present invention are all commercially available products. The activity value of magnesium oxide is tested according to the method for determining the active reaction time of magnesium oxide in Appendix A of the Technical Specification for Magnesium Oxide for Hydraulic Concrete DL / T 5296. The calcium oxide expansion agent meets the Type II technical requirements in the Concrete Expansion Agent GB / T 23439. The process control material adopts SBT ® -TRI concrete hydration temperature rise inhibitor.

[0028] The present invention also discloses a construction method for secondary lining concrete of a tunnel, which divides the secondary lining of the tunnel into Class I area and Class II area according to the actual cracking risk of the secondary lining concrete, and uses concrete with different types of anti-cracking properties with anti-cracking additives for pouring, thereby avoiding waste of resources and not increasing or even reducing concrete costs.

[0029] The construction method of the present invention specifically comprises the following steps: Step 1: If Figure 2 As shown, take the tunnel cross-section diagram with a segmented casting length of L, set the side of the secondary lining close to the inside of the tunnel as S1 boundary curve 4, the side close to the maintenance structure as S2 boundary curve 5, the side of the invert close to the inside of the tunnel as S3 boundary curve 6, and the intersection of S1 boundary curve 4 and S3 boundary curve 6 as P1 point 7; draw a vertical line at P1 point 7 and intersect S1 boundary curve 4 at P2 point 9, and take the vertical distance from P1 point 7 to P2 point 9 as H; mark the range of the secondary lining within the H vertical line 8 and below as Class I area 2, and the rest of the upper area as Class II area 3.

[0030] Different parts of the secondary lining structure have different cracking risks. The arch wall in the middle and lower parts has a high cracking risk, while the spandrels and vaults in the middle and upper parts have a lower cracking risk. Under the premise that waterproof membranes or geotextiles and other isolation materials are installed between the secondary lining and the maintenance structure and maintained in accordance with the specifications, the spandrels and vaults and other parts with low cracking risks can be made crack-free by optimizing the mix ratio and properly controlling the concrete injection temperature. However, for the middle and lower arch walls with high cracking risks, further measures are needed to control the injection temperature and use anti-cracking functional materials. If the entire secondary lining concrete adopts the crack control plan for the arch wall, it will inevitably increase costs and cause waste of resources.

[0031] Step 2: Considering that the risk of concrete cracking increases with the increase of the pump inlet temperature, although the risk of cracking of the spandrel and the vault in the middle and upper part of the secondary lining is smaller than that of the arch wall in the middle and lower part, there is still a risk of cracking when the pump inlet temperature is high. The present invention prepares three types of concrete, namely, Class A, Class B and Class C, respectively. The main difference between them is the amount of anti-cracking additives. The composition ratios of the three types of concrete are shown in Table 2.

[0032] Table 2 Composition of three types of concrete: A, B and C (unit: kg / m 3 ): .

[0033] Step 3: Select the type of concrete to be poured according to the zoning of the secondary lining and the pump inlet temperature T, and control the temperature difference between the concrete pump inlet temperature T and the average temperature inside the tunnel to be no more than 15°C; Class I area 2 uses Class A concrete for pouring according to the pouring process conditions; when T≥30°C, Class II area 3 uses Class B concrete for pouring according to the pouring process conditions; when T<30°C, Class II area 3 uses Class C concrete for pouring according to the pouring process conditions.

[0034] The process parameters of secondary lining concrete pouring, such as raw material selection, production, pouring, vibration and maintenance, should meet the national and relevant industry standards and specifications. As for the selection of raw materials, bulk raw materials including cement, fly ash, fine aggregate, coarse aggregate, water reducer and mixing water should not only meet the requirements of relevant national and industry standards and specifications, but also meet the specifications of the engineering field. For example, when used as the secondary lining of railway tunnels, it should also meet the provisions of "Railway Concrete" TB / T 3275. When used as the secondary lining of highway tunnels, it should also meet the provisions of "Highway Bridge and Culvert Construction Technical Specifications" JTG / T 3650. In order to ensure the effect of concrete crack control and achieve concrete without cracks, the present invention also limits the concrete pump inlet temperature, the secondary lining structure thickness and the segmented pouring length, specifically including controlling the pump inlet temperature not higher than the average temperature inside the tunnel by 15°C. The scheme is applicable to secondary linings with a structural thickness of ≤1.2m, and the segmented pouring length is controlled to be ≤21m. The production, pouring, vibration and maintenance of secondary lining concrete only needs to meet the requirements of national and relevant industry standards and specifications, such as the thermal insulation and moisture retention maintenance time including the formwork time being no less than 14 days.

[0035] like Figure 1 As shown, the present invention also discloses an acceptance method for secondary lining concrete of a tunnel. The acceptance method monitors the temperature and deformation of concrete at multiple key characteristic points of the secondary lining structure, and inputs the obtained temperature and deformation results into the "Structural Concrete Early Cracking Risk Assessment and Analysis Software" with Software Registration No. 1470077 for iterative calculation. When the monitored temperature and deformation curves have a correlation coefficient with the calculation of not less than 0.90, the performance parameters such as the adiabatic temperature rise and autogenous volume deformation of the concrete used in the physical structure and the heat dissipation coefficient of the actual working condition template can be obtained. The concrete performance of the physical structure and the actual working condition boundary conditions and parameters are input into the "Structural Concrete Early Cracking Risk Assessment and Analysis Software" with Software Registration No. 1470077 for calculation, and the cracking risk coefficient of the secondary lining concrete of the physical structure can be obtained.

[0036] Under the condition that the cracking risk coefficient is ≤1.0, concrete will not necessarily crack, but in order to improve the guarantee rate of concrete not cracking, the cracking risk coefficient ≤0.70 should be regarded as the acceptance of crack resistance, and the corresponding non-cracking guarantee rate is ≥95%. Considering that it is difficult to avoid the shrinkage micro cracks on the concrete surface due to water loss, and such micro cracks do not affect the structural bearing capacity and will not cause water leakage, the present invention also proposes the requirement that the maximum crack width of the secondary lining surface within the concrete strength assessment age is ≤0.05 mm.

[0037] The acceptance method of the present invention comprises the following steps: Step 1: Select the monitoring element layout points. On any side of the Class I area 2 at 0.5 times the L section along the longitudinal direction of the tunnel, set the center point corresponding to the 1m height layer below the height H as P3 point 10, the surface close to the inside of the tunnel corresponding to P3 point 10 is P3-1 point 12, and the surface close to the maintenance structure is P3-2 point 13; in the Class II area 3 at 0.5 times the L section along the longitudinal direction of the tunnel, set the center corresponding to the highest clearance inside the tunnel as P4 point 11.

[0038] Step 2: Before pouring the secondary lining concrete of the tunnel, install a strain gauge at P3 point 10 along the longitudinal and radial directions of the tunnel, a thermometer at P3-1 point 12 and P3-2 point 13, and a strain gauge at P4 point 11 along the radial direction of the tunnel. Physical monitoring data is an important support for the acceptance of anti-cracking effects. The accuracy and survival rate of monitoring elements are crucial. For this purpose, the thermometer uses the SBT-RT-1 thermocouple thermometer, the strain gauge uses the SBT-15D vibrating wire strain gauge, and the data acquisition system uses the SBT-CDM wireless monitoring system.

[0039] Step 3: 21 days after the concrete pouring is completed, the monitoring results of the thermometer and strain gauge are input into the structural concrete cracking risk assessment and analysis software. When the calculated temperature and deformation curves are correlated with the temperature and deformation curves monitored by the entity, the correlation coefficient R 2 When ≥0.90, the iterative calculation is stopped, and the inverse calculation is used to obtain three key parameters of crack resistance: concrete adiabatic temperature rise, concrete autogenous volume deformation under the conditions of solid temperature change history, and solid structure heat dissipation coefficient.

[0040] Step 4: Input the anti-cracking parameters obtained by the above inverse calculation into the structural concrete cracking risk assessment and analysis software again to calculate the secondary lining concrete cracking risk coefficient.

[0041] The following describes the anti-cracking additive, construction and acceptance method of the tunnel secondary lining concrete provided by the present invention through specific construction cases and experimental data.

[0042] Example 1: The tunnel secondary lining concrete additive, construction and acceptance method provided by the present invention are applied to a certain tunnel project. The tunnel secondary lining is constructed by open excavation method, the secondary lining thickness is 1.2m, the segmented casting length is 9m, the concrete strength design and assessment age is 60d, and the strength grade is C40.

[0043] (I) Preparation of anti-cracking additives: The secondary lining concrete of the tunnel was constructed from May to August, with an average temperature of 28°C. The time t from concrete production to transportation into the pump truck was about 20 to 30 min. During nighttime construction, the concrete pump temperature T was in the range of 31°C to 33°C. Based on this, the anti-cracking additive was designed to consist of 60% by weight of magnesium oxide expansion agent with an activity value of 120s, 38% by weight of calcium oxide expansion agent and 2% by weight of process control material, all of which were provided by the applicant.

[0044] (II) Secondary lining concrete construction: The secondary lining of the tunnel is divided into Figure 2 The Class I and Class II areas shown in the figure, where the height H of the Class I area is 5.2m, and then concrete is prepared. The concrete raw materials that meet the quality requirements include P•O 42.5 cement, Class I fly ash of Class F, medium sand in Zone 2, 5mm~25mm continuously graded crushed stone, mixing water, PCA-I polycarboxylate water reducer and anti-cracking additives. Class A and Class B concrete are prepared by mixing according to the proportions and quantities shown in Table 3. Class I areas with a secondary lining height of less than 3.7m are poured with Class A concrete, and the rest of the parts are poured with Class B concrete. The formwork is removed 4 days after the concrete is poured, and then a curing trolley is used for heat preservation and moisture retention curing for 14 days.

[0045] Table 3 A and B concrete mix ratio (unit: kg / m 3 ): .

[0046] (III) Acceptance of crack resistance of secondary lining concrete: Before pouring the secondary lining concrete, an SBT-15D vibrating wire strain gauge was installed at point 10 of P3 along the longitudinal and radial directions of the tunnel, an SBT-RT-1 thermocouple thermometer was installed at point 12 of P3-1 and point 13 of P3-2, and an SBT-15D vibrating wire strain gauge was installed at point 11 of P4 along the radial direction of the tunnel. The data acquisition frequency was once every 2 hours. On the 21st day after the concrete pouring was completed, the temperature and deformation data were exported and input into the "Structural Concrete Early Cracking Risk Assessment and Analysis Software" with the registration number of 1470077 for iterative calculation until the correlation coefficient R between the calculation result and the monitoring result curve was 2 When ≥0.90, the temperature calculation results and monitoring results of P3 point 10, P3-1 point 12, P3-2 point 13, and P4 point 11 are as follows: Figures 3~6 As shown in the figure, the deformation calculation results and monitoring results of point P3 10 along the longitudinal and radial directions of the tunnel are shown in Figure 7-8 As shown in the figure, the deformation calculation results and monitoring results of point P4 11 along the radial direction of the tunnel are as follows: Fig. 9 As shown. At this time, the inversion results show that the adiabatic temperature rise of type A and type B concrete is as follows Fig.10 As shown in the figure, the autogenous volume deformation of type A and type B concrete under the condition of temperature change of solid structure is as follows: Fig.11 As shown in the figure, the heat dissipation coefficient of the steel formwork under actual working conditions is 30kJ / m 2 •h•K, it should be pointed out that the empirical parameter of the heat dissipation coefficient of the steel formwork is 60kJ / m 2 •h•K, it can be seen that there is a large gap between the empirical parameters and the parameters under actual working conditions. The parameters such as the adiabatic temperature rise, autogenous volume deformation and heat dissipation coefficient of concrete obtained by inversion are input again into the "Structural Concrete Early Cracking Risk Assessment and Analysis Software" with the registration number of 1470077, and the maximum cracking risk coefficient of concrete in Class I area 2 and Class II area 3 is calculated as follows Fig.12 As shown, the results show that the maximum cracking risk coefficient of concrete in Class I area 2 is 0.55, and the maximum cracking risk coefficient of concrete in Class II area 3 is 0.64. There is no crack on the surface of the secondary lining of the solid structure when it is observed 2 months after pouring. The maximum cracking risk coefficient calculated by inversion based on the monitoring results of the solid structure is ≤0.70. Finally, the crack resistance effect of the secondary lining concrete has passed the acceptance.

[0047] Example 2: The tunnel secondary lining concrete additive, construction and acceptance method provided by the present invention are applied to a tunnel project. The total length of the tunnel is 20 km, the secondary lining thickness is 0.6 m, the segmented casting length is 9 m, the concrete strength design and assessment age is 28 d, and the strength grade is C35.

[0048] (I) Preparation of anti-cracking additives: The secondary lining section of the tunnel in this embodiment is shown in 13. The average temperature in the tunnel is 23~28℃ throughout the year. Taking winter construction as an example, the average temperature in the tunnel is about 23℃. The time t from concrete production to transportation into the pump truck is about 40~50 min. During winter construction, the concrete pump temperature T is in the range of 18℃~22℃. Based on this, the anti-cracking additive is designed to consist of 55% by weight of magnesium oxide expansion agent with an activity value of 100s, 43% by weight of calcium oxide expansion agent and 2% by weight of process control material, all of which are provided by the applicant.

[0049] (II) Secondary lining concrete construction: The secondary lining of the tunnel is divided into Fig.13The Class I and Class II areas shown in the figure, where the height H of the Class I area is 4.5m, and then concrete is prepared. The concrete raw materials that meet the quality requirements include P•O 42.5 cement, Class I fly ash of Class F, medium sand in Zone 2, 5mm~25mm continuously graded crushed stone, mixing water, PCA-I polycarboxylate water reducer and anti-cracking additives. Class A and Class C concrete are prepared by mixing according to the proportions and quantities shown in Table 4. Class I areas with a secondary lining height of less than 2.3m are poured with Class A concrete, and the rest are poured with Class C concrete. The formwork is removed 3 days after the concrete is poured, and then a curing trolley is used for heat preservation and moisture retention curing for 18 days.

[0050] Table 4 Class A and Class C concrete mix ratio (unit: kg / m 3 ): .

[0051] (III) Acceptance of crack resistance of secondary lining concrete: Before pouring the secondary lining concrete, an SBT-15D vibrating wire strain gauge was installed at point 10 of P3 along the longitudinal and radial directions of the tunnel, an SBT-RT-1 thermocouple thermometer was installed at point 12 of P3-1 and point 13 of P3-2, and an SBT-15D vibrating wire strain gauge was installed at point 11 of P4 along the radial direction of the tunnel. The data acquisition frequency was once every 2 hours. On the 21st day after the concrete pouring was completed, the temperature and deformation data were exported and input into the "Structural Concrete Early Cracking Risk Assessment and Analysis Software" with the registration number of 1470077 for iterative calculation until the correlation coefficient R between the calculation result and the monitoring result curve was 2 When ≥0.90, the inversion results show that the adiabatic temperature rise of concrete, the autogenous volume deformation and the heat dissipation coefficient of the formwork are as follows: Figures 14 and 15 As shown, the maximum cracking risk factor of concrete in Class I Zone 2 and Class II Zone 3 is calculated again as follows Fig.16 As shown, the results show that the maximum cracking risk coefficient of concrete in Class I area 2 is 0.54, and the maximum cracking risk coefficient of concrete in Class II area 3 is 0.65. The secondary lining of the solid structure has no cracks on the surface when observed one month after pouring. The maximum cracking risk coefficient calculated by inversion based on the monitoring results of the solid structure is ≤0.70. Finally, the crack resistance effect of the secondary lining concrete has passed the acceptance.

[0052] Example 3: The tunnel secondary lining concrete additive, construction and acceptance method provided by the present invention are applied to a tunnel project. The total length of the tunnel is 10 km, the secondary lining thickness is 0.5 m, the segmented casting length is 9 m, the concrete strength design and assessment age is 28 days, and the strength grade is C35.

[0053] (I) Preparation of anti-cracking additives: The secondary lining section of the tunnel in this embodiment is as follows Fig.17 As shown, the average temperature in the tunnel is 25-30℃ throughout the year, the time t from concrete production to transportation into the pump truck is about 35-55 min, and during summer construction, the concrete pumping temperature T is in the range of 35-38℃. Based on this, the anti-cracking additive is designed to consist of 50% by weight of magnesium oxide expansion agent with an activity value of 150s, 46.5% by weight of magnesium oxide expansion agent with an activity value of 250s and 3.5% by weight of process control material, all of which are provided by the applicant.

[0054] (II) Secondary lining concrete construction: The secondary lining of the tunnel is divided into Fig.17 The Class I and Class II areas shown in the figure, where the height H of the Class I area is 3.9m, and then concrete is prepared. The concrete raw materials that meet the quality requirements include P•O 42.5 cement, Class F Class II fly ash, Zone 2 medium sand, 5mm~25mm continuous graded crushed stone, mixing water, PCA-I polycarboxylate water reducer and anti-cracking additives. Class A and Class B concrete are prepared by mixing according to the proportions and quantities shown in Table 5. Class I areas with a secondary lining height of less than 3.9m are poured with Class A concrete, and the rest are poured with Class B concrete. The formwork is removed 3 days after the concrete is poured, and then a curing trolley is used for heat preservation and moisture retention curing for 15 days.

[0055] Table 5 A and B concrete mix ratio (unit: kg / m 3 ): .

[0056] (III) Acceptance of crack resistance of secondary lining concrete: Before pouring the secondary lining concrete, an SBT-15D vibrating wire strain gauge was installed at point 10 of P3 along the longitudinal and radial directions of the tunnel, an SBT-RT-1 thermocouple thermometer was installed at point 12 of P3-1 and point 13 of P3-2, and an SBT-15D vibrating wire strain gauge was installed at point 11 of P4 along the radial direction of the tunnel. The data acquisition frequency was once every 2 hours. On the 21st day after the concrete pouring was completed, the temperature and deformation data were exported and input into the "Structural Concrete Early Cracking Risk Assessment and Analysis Software" with the registration number of 1470077 for iterative calculation until the correlation coefficient R between the calculation result and the monitoring result curve was 2 When the value is ≥0.90, the inversion results in the parameters such as the adiabatic temperature rise of concrete, the autogenous volume deformation and the heat dissipation coefficient of the formwork. The maximum cracking risk coefficient of concrete in Category I zone 2 and Category II zone 3 is calculated again. Fig.18As shown, the results show that the maximum cracking risk coefficient of concrete in Class I area 2 is 0.56, and the maximum cracking risk coefficient of concrete in Class II area 3 is 0.64. The secondary lining of the solid structure has no cracks on the surface when observed one month after pouring. The maximum cracking risk coefficient calculated by inversion based on the monitoring results of the solid structure is ≤0.70. Finally, the crack resistance effect of the secondary lining concrete has passed the acceptance.

[0057] Example 4: Example 4 and Example 3 are the same tunnel project, the difference is that the construction season is autumn.

[0058] (I) Preparation of anti-cracking additives: In this embodiment, the time t from the production of concrete to its delivery into the pump truck is about 40 to 55 minutes. During autumn construction, the temperature T of concrete entering the pump is in the range of 30°C to 32°C. Based on this, the anti-cracking additive is designed to consist of 98% by weight of a magnesium oxide expansion agent with an activity value of 150s and 2% by weight of a process control material, both of which are provided by the applicant.

[0059] (II) Secondary lining concrete construction: The secondary lining of the tunnel is divided into Fig.17 The Class I and Class II areas shown in the figure, where the height H of the Class I area is 3.9m, and then concrete is prepared. The concrete raw materials that meet the quality requirements include P•O 42.5 cement, Class F Class II fly ash, Zone 2 medium sand, 5mm~25mm continuous graded crushed stone, mixing water, PCA-I polycarboxylate water reducer and anti-cracking additives. Class A and Class B concrete are prepared by mixing according to the proportions and quantities shown in Table 6. Class I areas with a secondary lining height of less than 3.9m are poured with Class A concrete, and the rest are poured with Class B concrete. The formwork is removed 3 days after the concrete is poured, and then a curing trolley is used for heat preservation and moisture retention curing for 14 days.

[0060] Table 6 Class A and Class B concrete mix ratio Unit: kg / m 3 : .

[0061] (III) Acceptance of crack resistance of secondary lining concrete: Before pouring the secondary lining concrete, an SBT-15D vibrating wire strain gauge was installed at point 10 of P3 along the longitudinal and radial directions of the tunnel, an SBT-RT-1 thermocouple thermometer was installed at point 12 of P3-1 and point 13 of P3-2, and an SBT-15D vibrating wire strain gauge was installed at point 11 of P4 along the radial direction of the tunnel. The data acquisition frequency was once every 2 hours. On the 21st day after the concrete pouring was completed, the temperature and deformation data were exported and input into the "Structural Concrete Early Cracking Risk Assessment and Analysis Software" with the registration number of 1470077 for iterative calculation until the correlation coefficient R between the calculation result and the monitoring result curve was 2 When the value is ≥0.90, the inversion results in the parameters such as the adiabatic temperature rise of concrete, the autogenous volume deformation and the heat dissipation coefficient of the formwork. The maximum cracking risk coefficient of concrete in Category I zone 2 and Category II zone 3 is calculated again. Fig.19 As shown, the results show that the maximum cracking risk coefficient of concrete in Class I area 2 is 0.54, and the maximum cracking risk coefficient of concrete in Class II area 3 is 0.58. The secondary lining of the solid structure has no cracks on the surface when observed one month after pouring. The maximum cracking risk coefficient calculated by inversion based on the monitoring results of the solid structure is ≤0.70. Finally, the crack resistance effect of the secondary lining concrete has passed the acceptance.

[0062] Example 5: The tunnel secondary lining concrete additive, construction and acceptance method provided by the present invention are applied to a tunnel project. The total length of the tunnel is 5 km, the secondary lining thickness is 1.0 m, the segmented casting length is 9 m, the concrete strength design and assessment age is 60 d, and the strength grade is C40.

[0063] (I) Preparation of anti-cracking additives: The secondary lining section of the tunnel in this embodiment is shown in 20. The average temperature in the tunnel throughout the year is 28-30°C. The time t from the production of concrete to its delivery into the pump truck is about 45-60 min. During summer construction, the concrete entering the pump temperature T is in the range of 38°C-40°C. Based on this, the anti-cracking additive is designed to consist of 95% by weight of a magnesium oxide expansion agent with an activity value of 250s and 5% by weight of a process control material, both of which are provided by the applicant.

[0064] (II) Secondary lining concrete construction: The secondary lining of the tunnel is divided into Fig. 20The Class I and Class II areas shown in the figure, where the height H of the Class I area is 4.8m, and then concrete is prepared. The concrete raw materials that meet the quality requirements include P•O 42.5 cement, Class I fly ash of Class F, medium sand in Zone 2, 5mm~25mm continuously graded crushed stone, mixing water, PCA-I polycarboxylate water reducer and anti-cracking additives. Class A and Class B concrete are prepared by mixing according to the proportions and quantities shown in Table 7. Class I areas with a secondary lining height of less than 3.9m are poured with Class A concrete, and the rest are poured with Class B concrete. The formwork is removed 3 days after the concrete is poured, and then a curing trolley is used for heat preservation and moisture retention curing for 15 days.

[0065] Table 7 Class A and Class B concrete mix ratio Unit: kg / m 3 : .

[0066] (III) Acceptance of crack resistance of secondary lining concrete: Before pouring the secondary lining concrete, an SBT-15D vibrating wire strain gauge was installed at point 10 of P3 along the longitudinal and radial directions of the tunnel, an SBT-RT-1 thermocouple thermometer was installed at point 12 of P3-1 and point 13 of P3-2, and an SBT-15D vibrating wire strain gauge was installed at point 11 of P4 along the radial direction of the tunnel. The data acquisition frequency was once every 2 hours. On the 21st day after the concrete pouring was completed, the temperature and deformation data were exported and input into the "Structural Concrete Early Cracking Risk Assessment and Analysis Software" with the registration number of 1470077 for iterative calculation until the correlation coefficient R between the calculation result and the monitoring result curve was 2 When the value is ≥0.90, the inversion results in the parameters such as the adiabatic temperature rise of concrete, the autogenous volume deformation and the heat dissipation coefficient of the formwork. The maximum cracking risk coefficient of concrete in Category I zone 2 and Category II zone 3 is calculated again. Fig.21 As shown, the results show that the maximum cracking risk coefficient of concrete in Class I area 2 is 0.66, and the maximum cracking risk coefficient of concrete in Class II area 3 is 0.63. The secondary lining of the solid structure has no cracks on the surface when observed one month after pouring. The maximum cracking risk coefficient calculated by inversion based on the monitoring results of the solid structure is ≤0.70. Finally, the crack resistance effect of the secondary lining concrete has passed the acceptance.

[0067] In summary, the tunnel secondary lining concrete additive, construction and acceptance method provided by the present invention have improved and innovated in terms of anti-crack functional materials, construction technology and anti-crack effect acceptance, which can effectively solve the cracking and leakage problems caused by shrinkage of secondary lining concrete. At the same time, it can quantitatively evaluate the anti-cracking implementation effect and realize the construction and acceptance closed loop of tunnel secondary lining concrete crack control.

[0068] The above are preferred embodiments of the present invention. It should be pointed out that, for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. An anti-cracking additive for secondary lining concrete of a tunnel, characterized in that: The components of the anti-cracking additive are formulated based on the time t that the concrete takes to pass from the production machine to the delivery into the pump truck and the temperature T of the concrete when it enters the pump truck; When t≥30min and T≥30°C, the anti-cracking additive is composed of 95%~98% by weight of a magnesium oxide expansion agent having an activity value of 150s~250s and 2%~5% by weight of a process control material; When t≥30min, 23℃≤T<30℃, the anti-cracking additive is composed of 95%~98% by weight of magnesium oxide expansion agent with an activity value of 80s~140s and 2%~5% by weight of process control material; When t≥30min and T<23℃, the anti-cracking additive is composed of 50%~80% by weight of magnesium oxide expansion agent with an activity value of 80s~140s, 20%~50% by weight of calcium oxide expansion agent and 0%~3% by weight of process control material; When t<30min, T≥23℃, the anti-cracking additive is composed of 50%~80% by weight of magnesium oxide expansion agent with an activity value of 80s~140s, 20%~50% by weight of calcium oxide expansion agent and 0%~3% by weight of process control material; When t<30min and T<23℃, the anti-cracking additive is composed of 50%~80% by weight of magnesium oxide expansion agent and 20%~50% by weight of calcium oxide expansion agent with an activity value of 80s~140s.

2. The anti-cracking additive for secondary lining concrete of tunnel according to claim 1, characterized in that: The strength design grade of the concrete to which the anti-cracking additive is added within 60 days does not exceed C40.

3. The anti-cracking additive for secondary lining concrete of tunnel according to claim 1, characterized in that: The 12h hydration heat reduction rate of the process-regulated material is ≥15%, and the 24h hydration heat reduction rate is ≤35%.

4. A method for constructing secondary tunnel lining concrete, characterized in that: The secondary lining of the tunnel is divided into a Class I area and a Class II area, and different types of concrete with the anti-cracking additive as claimed in any one of claims 1 to 3 are used for pouring. The construction method comprises the following steps: Step 1: Take a tunnel cross-section with a segmented casting length of L, set the side of the secondary lining close to the tunnel interior as the S1 boundary curve (4), the side close to the maintenance structure as the S2 boundary curve (5), the side of the invert close to the tunnel interior as the S3 boundary curve (6), and the intersection of the S1 boundary curve (4) and the S3 boundary curve (6) as the P1 point (7); draw a vertical line at the P1 point (7) and the S1 boundary curve (4) intersecting at the P2 point (9), and take the vertical distance from the P1 point (7) to the P2 point (9) as H; mark the area of ​​the secondary lining below the H vertical line (8) as the Class I area (2), and mark the rest of the upper area as the Class II area (3); Step 2: Prepare three types of concrete: A, B and C respectively: Among them, Class A concrete, calculated per cubic meter, includes the following components: 180kg~340kg of cement, 80kg~150kg of fly ash, 30kg~50kg of anti-cracking additive, 650kg~850kg of fine aggregate, 700kg~1100kg of coarse aggregate, 3kg~6kg of water reducer, and 140kg~170kg of mixing water; Class B concrete, calculated per cubic meter, includes the following components: 180kg~340kg of cement, 80kg~160kg of fly ash, 20kg~30kg of anti-cracking additive, 650kg~850kg of fine aggregate, 700kg~1100kg of coarse aggregate, 3kg~6kg of water reducer, and 140kg~170kg of mixing water; Class C concrete, measured per cubic meter, includes the following components: 180kg~340kg of cement, 80kg~180kg of fly ash, 650kg~850kg of fine aggregate, 700kg~1100kg of coarse aggregate, 3kg~6kg of water reducer, and 140kg~170kg of mixing water; Step 3: Select the type of concrete to be poured according to the secondary lining zoning and pump inlet temperature T. For Class I area (2), use Class A concrete for pouring according to the pouring process conditions. When T ≥ 30 °C, use Class B concrete for pouring according to the pouring process conditions in Class II area (3). When T < 30 °C, use Class C concrete for pouring according to the pouring process conditions in Class II area (3).

5. The construction method of tunnel secondary lining concrete according to claim 4, characterized in that: In step 3, the temperature difference between the concrete pump temperature T and the average temperature inside the tunnel is controlled to be no greater than 15°C.

6. The construction method of tunnel secondary lining concrete according to claim 4, characterized in that: In step 1, a waterproof membrane or geotextile is provided as an isolation material between the secondary lining and the maintenance structure.

7. The construction method of tunnel secondary lining concrete according to claim 4, characterized in that: In step 1, the thickness of the secondary lining structure is ≤1.2m and the segmented casting length is ≤21m.

8. A method for acceptance of secondary lining concrete of a tunnel, characterized in that: For acceptance of the concrete applied in claim 4, the key parameters of crack resistance are obtained by inverse calculation using the measured data of temperature and deformation of the concrete of the solid structure, and then the crack risk coefficient of the secondary lining concrete is calculated using the key parameters of crack resistance obtained by inverse calculation, including the following steps: Step 1: Select the monitoring element layout points. On any side of the Class I area (2) at 0.5 times the L section along the longitudinal direction of the tunnel, set the center point corresponding to the 1 m height layer below the height H as point P3 (10). The surface of the side close to the inside of the tunnel corresponding to point P3 (10) is point P3-1 (12), and the surface of the side close to the maintenance structure is point P3-2 (13). In the Class II area (3) at 0.5 times the L section along the longitudinal direction of the tunnel, set the center corresponding to the highest clearance point inside the tunnel as point P4 (11). Step 2: Before pouring the secondary lining concrete of the tunnel, install a strain gauge at point P3 (10) along the longitudinal and radial directions of the tunnel, install a temperature gauge at point P3-1 (12) and point P3-2 (13), and install a strain gauge at point P4 (11) along the radial direction of the tunnel; Step 3: 21 days after the concrete pouring is completed, the monitoring results of the thermometer and strain gauge are input into the structural concrete cracking risk assessment and analysis software. When the calculated temperature and deformation curves are correlated with the temperature and deformation curves monitored by the entity, the correlation coefficient R 2 When it is ≥0.90, the iterative calculation is stopped, and the three key parameters of crack resistance, namely, adiabatic temperature rise of concrete, autogenous volume deformation of concrete under the condition of solid temperature change history, and heat dissipation coefficient of solid structure, are obtained through inverse calculation. Step 4: Input the anti-cracking parameters obtained by the above inverse calculation into the structural concrete cracking risk assessment and analysis software again to calculate the secondary lining concrete cracking risk coefficient.

9. The acceptance method for secondary tunnel lining concrete according to claim 8, characterized in that: In step 2, the thermometer uses the SBT-RT-1 thermocouple thermometer, the strain gauge uses the SBT-15D vibrating wire strain gauge, and the data acquisition system uses the SBT-CDM wireless monitoring system.

10. The acceptance method for secondary tunnel lining concrete according to claim 8, characterized in that: The acceptance criteria for evaluating the anti-cracking effect are based on the maximum crack width on the secondary lining surface within the concrete strength assessment age of ≤0.05mm, and the maximum cracking risk coefficient calculated by inverse calculation is ≤0.70.

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