A kind of anti-cracking additive for secondary lining concrete of tunnel, construction and acceptance method

Abstract

The present invention discloses an anti-cracking additive for secondary lining concrete of tunnels, a construction method and an acceptance method, belonging to the technical field of tunnel construction. The anti-cracking additive is formulated according to the time elapsed from the production of the concrete out of the machine to its conveyance into the pump truck and the temperature when it enters the pump truck, and can resist the negative impacts caused by the long-time transportation, stirring shear and high temperature of the mixer truck, which result in the premature and excessive ineffective consumption of the anti-cracking functional materials, thereby improving the anti-cracking performance of the concrete. The construction method divides the area according to the actual cracking risk of the secondary lining structure and pours concrete with different anti-cracking performances, reducing the concrete cost. The acceptance method calculates the cracking risk coefficient of the secondary lining concrete by using the key anti-cracking parameters inversed from the actual monitoring data of the temperature and deformation of the concrete of the entity structure. The present invention can achieve the technical effects of improving the anti-cracking performance of the secondary lining concrete of tunnels, suppressing shrinkage cracks, accepting the anti-cracking effect, and popularizing the technical solution.

Description

Technical Field

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

[0002] Tunnels are an important part of transportation and play an important role in the modern transportation system. Among them, secondary lining tunnels are common structural forms for railways and highways to pass through mountains, such as the famous Qinling Tunnel and Gaoligongshan Tunnel. The common strength grade of secondary lining concrete is C30 - C35, the structural thickness is 30 cm - 50 cm, and the segmented pouring length is 9 m or 12 m, which is generally less than the segmented pouring length of 15 m - 30 m for cast-in-place tunnels. Although the structural dimensions of the secondary lining are relatively small, due to the process of first pouring the inverted arch and then pouring the secondary lining, and the influence of the maintenance structure, the restraint on the secondary lining concrete is relatively strong. At the same time, due to the requirement of the stripping 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 hydration heat of the concrete is also relatively high, resulting in a large temperature shrinkage. After further superimposing the autogenous shrinkage of the 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 cracks, which will not only cause leakage and durability problems, but also reduce the structural bearing capacity and affect the operation safety of the tunnel.

[0003] Reducing the concrete temperature, reducing the concrete shrinkage and reducing the external restraint are common crack control measures. For example, reducing the concrete pouring temperature, selecting high-quality raw materials with low heat of hydration and low shrinkage, reducing the cement dosage in the concrete mix ratio, adding mineral admixtures, shortening the interval age of the staged pouring between the inverted arch and the secondary lining concrete, setting waterproof coiled materials or isolation materials between the secondary lining and the maintenance structure, and using special curing trolleys and other measures. Specifically in actual tunnel construction projects, the above measures cannot be well implemented. For example, at the design level, the design and evaluation age of the concrete strength is extended to encourage reducing the cement dosage in the mix ratio. However, affected by early stripping, in order to ensure the early stripping strength, the cement dosage of the concrete is still generally high during actual construction; another example is that in order to ensure the structural safety, the inverted arch and the floor will be poured as soon as possible, resulting in a generally long pouring interval age between them and the secondary lining. With the increasing improvement of China's infrastructure construction, the construction environment of current and next-stage tunnel projects is becoming increasingly harsh. Coupled with the constraints of transportation distance and construction cost, it is difficult to ensure high-quality raw materials. It has become a common situation to obtain materials locally and nearby on the basis of meeting the standard specifications.

[0004] When measures taken in terms of raw materials, mix proportion and technology still cannot solve the problem of cracking, using an expansive agent to compensate for concrete shrinkage is an important means to inhibit concrete cracking. However, a large number of engineering practices and investigations have found that many concretes with expansive agents have also cracked, and even the number of cracks has increased. Further combining 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-based expansive agents will increase the temperature rise value of concrete, increasing the temperature shrinkage and cracking risk; (2) The process of the expansive agent generating expansion to compensate for shrinkage needs to match the temperature and shrinkage process of the concrete in the solid structure. For example, although calcium-based expansive agents have high expansion efficiency, they mainly occur in the early temperature rise stage of the solid structure and cannot produce compensatory shrinkage in the temperature drop stage with a greater cracking risk; (3) The length of a single highway or railway lining tunnel is generally several kilometers or dozens of kilometers or more, and the traffic lines in the tunnel are not as open as those of 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 can be taken by the mixing plant are limited. When constructing in hot weather, the temperature of the concrete out of the machine will exceed 30°C. During the long transportation and pouring waiting process, the temperature of the concrete will be as high as above 35°C. Under such high temperatures and the strong agitation of the mixing truck for a long time, the hydration reaction of the expansive agent will be accelerated. However, the hydration reaction of the expansive agent in the plastic stage of concrete cannot produce expansion, so the expansive agent will be consumed ineffectively in advance and it is difficult to play the expected compensatory shrinkage role in the solid structure.

[0005] At present, for the acceptance of the tunnel crack control effect, it is mainly through observation or measurement methods during the early construction period, focusing on checking for cracks and water leakage. In fact, when some cracks occur internally but do not penetrate, it will not cause leakage and surface cracking temporarily. However, with the continuous shrinkage of the concrete itself, cracking will still occur. The test results of the non-destructive ultrasonic method are easily affected by steel bars or internal defects, and it is difficult to detect the entire surface of the secondary lining under the restriction of cost. In recent years, with the development of new crack control technologies, the cracking risk of concrete can be calculated by inputting parameters such as concrete performance and structural dimensions obtained from experimental research, and then corresponding crack control technical solutions can be adopted. However, the cement produced by the same manufacturer will adjust the cement components according to the construction season and the quality of the cement clinker. Coupled with the fluctuations in the mud content of sand and gravel, there are significant differences between the actual concrete performance and the performance during indoor mix proportion verification. In addition, affected by ventilation and line length, etc., the working condition parameters such as the heat dissipation coefficient in different sections are not the same. The above factors will lead to great differences in the crack resistance effect implemented according to the plan or the crack resistance effect is difficult to meet the requirements of the expected plan.

[0006] In summary, the existing related technologies cannot fully solve the problems of the cracking of the secondary lining concrete in tunnels and the acceptance of the crack resistance effect. In actual projects, although the problem of the cracking of the secondary lining concrete can be solved theoretically or at the level of a small number of test sections, it is difficult to be widely applied on a large scale due to cost or difficulty in matching the actual construction requirements. Therefore, it is very necessary to propose a technical solution that takes into account both technical effects and costs to meet the requirements of crack control of the secondary lining concrete in tunnels and the acceptance of the crack resistance effect. Summary of the Invention

[0007] Technical problems to be solved: Aiming at the technical problems of the shrinkage cracking of the secondary lining concrete in tunnels and the acceptance of the crack resistance effect in the background technology, the present invention provides an anti-cracking additive, construction and acceptance method for the secondary lining concrete in tunnels. Based on taking into account both technical effects and cost control, the construction method realizes the beneficial effects of improving the anti-cracking performance of the secondary lining concrete in tunnels, suppressing shrinkage cracks, being able to accept the crack resistance effect, and the technical solution being able to be promoted.

[0008] Technical solution: An anti-cracking additive for the secondary lining concrete in tunnels according to the present invention, wherein the components of the anti-cracking additive are prepared according to the time t experienced by the concrete from being produced out of the machine to being transported into the pump truck and the temperature T of the concrete when it enters the pump truck;

[0009] When t≥30min and T≥30℃, the anti-cracking additive is composed of 95% - 98% by weight of magnesium oxide expansive agent with an activity value of 150s - 250s and 2% - 5% by weight of process control material;

[0010] When t≥30min and 23℃≤T<30℃, the anti-cracking additive is composed of 95% - 98% by weight of magnesium oxide expansive agent with an activity value of 80s - 140s and 2% - 5% by weight of process control material;

[0011] When t≥30min and T<23℃, the anti-cracking additive is composed of 50% - 80% by weight of magnesium oxide expansive agent with an activity value of 80s - 140s, 20% - 50% by weight of calcium oxide expansive agent, and 0% - 3% by weight of process control material;

[0012] When t<30min and T≥23℃, the anti-cracking additive is composed of 50% - 80% by weight of magnesium oxide expansive agent with an activity value of 80s - 140s, 20% - 50% by weight of calcium oxide expansive agent, and 0% - 3% by weight of process control material;

[0013] When t<30min and T<23℃, the anti-cracking additive is composed of 50% - 80% by weight of magnesium oxide expansive agent with an activity value of 80s - 140s and 20% - 50% by weight of calcium oxide expansive agent.

[0014] Preferably, the strength design grade of the concrete with the crack-resistant additive within 60 days of age does not exceed C40.

[0015] Preferably, the 12h heat of hydration reduction rate of the process regulation material is ≥15% and the 24h heat of hydration reduction rate is ≤35%.

[0016] The present invention also discloses a construction method for the secondary lining concrete of a tunnel. The secondary lining of the tunnel is divided into Class I area and Class II area, and different types of concrete with crack-resistant additives are used for pouring. The construction method includes the following steps:

[0017] Step 1: Take the cross-sectional view of the tunnel with a segmented pouring length of L. Set the side close to the inside of the tunnel of the secondary lining as the S1 boundary curve, the side close to the maintenance structure as the S2 boundary curve, and the side close to the inside of the tunnel of the invert as the S3 boundary curve. The intersection point of the S1 boundary curve and the S3 boundary curve is the P1 point; draw a perpendicular line at the P1 point to intersect with the S1 boundary curve at the P2 point, and take the vertical distance from the P1 point to the P2 point as H; mark the area within the range of the H perpendicular line and below of the secondary lining as the Class I area, and the remaining upper area as the Class II area;

[0018] Step 2: Prepare three types of concrete, namely Type A, Type B, and Type C, respectively:

[0019] Among them, for Type A concrete per cubic meter, it includes the following components: 180 kg - 340 kg of cement, 80 kg - 150 kg of fly ash, 30 kg - 50 kg of crack-resistant additive, 650 kg - 850 kg of fine aggregate, 700 kg - 1100 kg of coarse aggregate, 3 kg - 6 kg of water reducer, and 140 kg - 170 kg of mixing water;

[0020] For Type B concrete per cubic meter, it includes the following components: 180 kg - 340 kg of cement, 80 kg - 160 kg of fly ash, 20 kg - 30 kg of crack-resistant additive, 650 kg - 850 kg of fine aggregate, 700 kg - 1100 kg of coarse aggregate, 3 kg - 6 kg of water reducer, and 140 kg - 170 kg of mixing water;

[0021] For Type C concrete per cubic meter, it includes the following components: 180 kg - 340 kg of cement, 80 kg - 180 kg of fly ash, 650 kg - 850 kg of fine aggregate, 700 kg - 1100 kg of coarse aggregate, 3 kg - 6 kg of water reducer, and 140 kg - 170 kg of mixing water;

[0022] Step 3: Select the type of concrete for pouring according to the zoning of the secondary lining and the pump-in temperature T. For Class I areas, use Class A concrete for pouring according to the pouring process conditions; when T ≥ 30°C, for Class II areas, use Class B concrete for pouring according to the pouring process conditions; when T < 30°C, for Class II areas, use Class C concrete for pouring according to the pouring process conditions.

[0023] Preferably, in Step 3, the temperature difference between the pump-in temperature T of the concrete and the average air temperature inside the tunnel is controlled to be no more than 15°C.

[0024] Preferably, in Step 1, a waterproof coiled material or geotextile is provided between the secondary lining and the maintenance structure as an isolation material.

[0025] Preferably, in Step 1, the thickness of the secondary lining structure ≤ 1.2 m and the segmented pouring length ≤ 21 m.

[0026] The present invention also discloses an acceptance method for the concrete of the tunnel secondary lining. The key anti-cracking parameters are obtained by inverse calculation using the measured data of the temperature and deformation of the solid structure concrete, and then the cracking risk coefficient of the secondary lining concrete is calculated using the key anti-cracking parameters obtained by the inverse calculation, including the following steps:

[0027] Step 1: Select the layout points of the monitoring elements. Along either side of the Class I area of the 0.5-fold L section in the longitudinal direction of the tunnel, the center points corresponding to the 1 m height layer below the set distance height H are respectively set as Point P3. The surface on the side close to the inside of the tunnel corresponding to Point P3 is Point P3-1, and the surface on the side close to the maintenance structure is Point P3-2; in the Class II area of the 0.5-fold L section in the longitudinal direction of the tunnel, the center corresponding to the highest point of the internal clearance of the tunnel is set as Point P4.

[0028] Step 2: Before pouring the concrete of the tunnel secondary lining, install a strain gauge along the longitudinal and radial directions of the tunnel at Point P3, install a thermometer at each of Point P3-1 and Point P3-2, and install a strain gauge along the radial direction of the tunnel at Point P4.

[0029] Step 3: When 21 days have passed since the concrete pouring is completed, input the monitoring results of the thermometer and strain gauge into the structural concrete cracking risk assessment and analysis software. When the correlation coefficient R of the calculated temperature and deformation curves and the temperature and deformation curves monitored in the entity 2 ≥ 0.90, stop the iterative calculation, and inversely calculate three key anti-cracking parameters: the adiabatic temperature rise of the concrete, the autogenous volume deformation of the concrete under the condition of the actual temperature change process, and the heat dissipation coefficient of the solid structure.

[0030] 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 cracking risk coefficient of the secondary lining concrete.

[0031] Preferably, in step 2, an SBT-RT-1 thermocouple thermometer is used, an SBT-15D vibrating wire strain gauge is used, and an SBT-CDM wireless monitoring system is used for the data acquisition system.

[0032] Preferably, the acceptance criteria for evaluating the anti-cracking effect are that the maximum crack width on the surface of the secondary lining within the concrete strength evaluation age period is ≤ 0.05 mm, and the maximum cracking risk coefficient obtained by back-calculation is ≤ 0.70.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] 1. Aiming at the specific working conditions of the secondary lining concrete of the tunnel, based on the quantitative evaluation of the multi-factor coupling action mechanism, experimental research and a large number of engineering practices, the present invention proposes a closed-loop crack control technical solution from three aspects: anti-cracking additives, construction methods, and acceptance. To ensure the improvement effect of the anti-cracking functional materials on the concrete performance, the present invention designs a special anti-cracking additive according to the on-site working condition parameters. To balance the technical effect and cost control, the present invention divides the secondary lining construction into sectional pouring and uses different types of concrete respectively. Under the condition of no surface cracks, to further realize the quantitative evaluation of the anti-cracking implementation effect, an acceptance scheme for back-calculating the cracking risk coefficient by using the entity monitoring results is adopted. Through the above 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 popularizing the technical solution are finally achieved;

[0035] 2. The anti-cracking additive can resist the negative impacts caused by the long-time transportation, mixing of the concrete mixer truck and the temperature, which lead to the premature and excessive ineffective consumption of the expansion performance of the expansive agent, and can match the temperature and shrinkage history of the secondary lining concrete, thereby greatly improving the anti-cracking performance of the concrete;

[0036] 3. The construction method 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 different types of anti-cracking performance concrete with anti-cracking additives for pouring, thereby avoiding waste of resources and not increasing or even reducing the concrete cost;

[0037] 4. This acceptance method monitors the temperature and deformation of concrete at multiple key feature points of the secondary lining structure, and inputs the obtained temperature and deformation results into the software for iterative calculation of the early cracking risk assessment and analysis of structural concrete. When the correlation coefficient between the monitored temperature and deformation curves and the calculation is not less than 0.90, the adiabatic temperature rise, autogenous volume deformation and other performance parameters of the concrete used in the entity structure and the heat dissipation coefficient of the formwork under actual working conditions can be obtained. Then, input the concrete performance of the entity structure and the boundary conditions and parameters under actual working conditions into the software for calculation of the early cracking risk assessment and analysis of structural concrete, and the cracking risk coefficient of the secondary lining concrete of the entity structure can be obtained. Description of the Drawings

[0038] Figure 1 It is the construction and acceptance process flow chart of the tunnel secondary lining concrete of the present invention;

[0039] Figure 2 It is the schematic diagram of the tunnel secondary lining section structure of Embodiment 1 of the present invention;

[0040] Figure 3 It is the temperature monitoring curve and calculation curve diagram of point P3 in Embodiment 1 of the present invention;

[0041] Figure 4 It is the temperature monitoring curve and calculation curve diagram of point P3-1 in Embodiment 1 of the present invention;

[0042] Figure 5 It is the temperature monitoring curve and calculation curve diagram of point P3-2 in Embodiment 1 of the present invention;

[0043] Figure 6 It is the temperature monitoring curve and calculation curve diagram of point P4 in Embodiment 1 of the present invention;

[0044] Figure 7 It is the deformation monitoring curve and calculation curve diagram of point P3 along the longitudinal direction of the tunnel in Embodiment 1 of the present invention;

[0045] Figure 8 It is the deformation monitoring curve and calculation curve diagram of point P3 along the radial direction of the tunnel in Embodiment 1 of the present invention;

[0046] Figure 9 It is the deformation monitoring curve and calculation curve diagram of point P4 along the radial direction of the tunnel in Embodiment 1 of the present invention;

[0047] Figure 10 It is the adiabatic temperature rise curve diagram of concrete obtained by inverse calculation in Embodiment 1 of the present invention;

[0048] Figure 11 It is the autogenous volume deformation curve diagram of concrete under the condition of variable temperature history of the entity structure obtained by inverse calculation in Embodiment 1 of the present invention;

[0049] Figure 12 is the diagram of the cracking risk coefficient of the entity structure obtained by inversion calculation in Embodiment 1 of the present invention;

[0050] Figure 13 is the schematic diagram of the cross-sectional structure of the secondary lining of the tunnel in Embodiment 2 of the present invention;

[0051] Figure 14 is the curve diagram of the adiabatic temperature rise process of concrete obtained by inversion calculation in Embodiment 2 of the present invention;

[0052] Figure 15 is the curve diagram of the autogenous volume deformation of concrete under the condition of the variable temperature process of the entity structure obtained by inversion calculation in Embodiment 2 of the present invention;

[0053] Figure 16 is the diagram of the cracking risk coefficient of the entity structure obtained by inversion calculation in Embodiment 2 of the present invention;

[0054] Figure 17 is the schematic diagram of the cross-sectional structure of the secondary lining of the tunnel in Embodiment 3 of the present invention;

[0055] Figure 18 is the diagram of the cracking risk coefficient of the entity structure obtained by inversion calculation in Embodiment 3 of the present invention;

[0056] Figure 19 is the diagram of the cracking risk coefficient of the entity structure obtained by inversion calculation in Embodiment 4 of the present invention;

[0057] Figure 20 is the schematic diagram of the cross-sectional structure of the secondary lining of the tunnel in Embodiment 5 of the present invention;

[0058] Figure 21 is the diagram of the cracking risk coefficient of the entity structure obtained by inversion calculation in Embodiment 5 of the present invention.

[0059] Reference numerals: 1, invert; 2, Class I area; 3, Class II area; 4, S1 boundary curve; 5, S2 boundary curve; 6, S3 boundary curve; 7, Point P1; 8, vertical line H; 9, Point P2; 10, Point P3; 11, Point P4; 12, Point P3-1; 13, Point P3-2. Detailed implementation manners

[0060] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the following will combine the attached Figures 1 - 21 to clearly and completely describe the technical solutions of the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the described embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art belong to the scope of protection of the present invention.

[0061] In view of the specific working conditions of the secondary lining concrete of tunnels, based on the quantitative evaluation of the coupling action mechanism of multiple factors, experimental research, and a large number of engineering practices, a closed-loop crack control technical solution is proposed from three aspects: anti-cracking additives, construction methods, and acceptance. To ensure the improvement effect of anti-cracking functional materials on the performance of concrete, the present invention designs a special anti-cracking additive according to the on-site working condition parameters. To balance the technical effect and cost control, the present invention divides the secondary lining construction into sectional pouring and uses different types of concrete respectively. In the case of achieving no surface cracks, to further realize the quantitative evaluation of the anti-cracking implementation effect, an acceptance scheme for inverting and calculating the cracking risk coefficient by using the results of in-situ monitoring is adopted. Through the above-mentioned closed-loop technical solution, the beneficial effects of effectively improving the anti-cracking performance of the secondary lining concrete of tunnels, suppressing shrinkage cracks, accepting the anti-cracking effect, and popularizing the technical solution are finally achieved.

[0062] In order to avoid the ineffective consumption of the expansive agent, an anti-cracking functional material, caused by factors such as the agitation and shear of the mixer truck during long-distance transportation and high temperature, and the current situation that the in-mold temperature is usually difficult to measure, under the general working conditions where the design strength grade of concrete within 60 days of age does not exceed C40, the present invention proposes to design an additive for improving the anti-cracking property of concrete according to the time t experienced by the concrete from being produced and exiting the mixer to being transported into the concrete pump truck and the in-pump temperature T of the concrete when it enters the pump truck. The time t and the in-pump temperature T can be determined by the concrete of the invert part poured first or process tests. The composition of the anti-cracking additive in the embodiments of the present invention is shown in Table 1:

[0063] Table 1 Composition of anti-cracking additive (unit: %):

[0064] 。

[0065] The anti-cracking additive of the present invention can resist the negative impacts of the long-time transportation, agitation, and temperature of the concrete mixer truck on the premature and excessive ineffective consumption of the expansive performance of the expansive agent, and can match the temperature and shrinkage history of the secondary lining concrete, thereby greatly improving the anti-cracking performance of the concrete.

[0066] The hydration process control material used in the anti-cracking additive of the present invention is a starch-based hydration process control material, which is a commercially available product, such as SBT ® -TRI concrete hydration temperature rise inhibitor; the hydration process control material will play a regulatory role in both the hydration process of the expansive agent and cement. To ensure the regulatory effect on the early hydration process of the expansive agent and not overly regulate the cement hydration process to avoid reducing the early strength of the concrete, the 12-hour hydration heat reduction rate of the hydration process control material ≥ 15% and the 24-hour hydration heat reduction rate ≤ 35%.

[0067] The magnesium oxide expansive agent, calcium oxide expansive 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 measuring the activity reaction time of magnesium oxide in Appendix A of the Technical Specification for the Use of Magnesium Oxide in Hydraulic Concrete (DL / T 5296). The calcium oxide expansive agent meets the type II technical requirements in the Concrete Expansive Agent (GB / T 23439), and the process control material uses SBT ® -TRI concrete hydration temperature rise inhibitor.

[0068] The present invention also discloses a construction method for the secondary lining concrete of a tunnel. According to the actual cracking risk of the secondary lining concrete, the secondary lining of the tunnel is divided into Class I areas and Class II areas, and concrete with different anti-cracking performances added with anti-cracking additives is used for pouring, thereby avoiding waste of resources and not increasing or even reducing the concrete cost.

[0069] The construction method of the present invention specifically includes the following steps:

[0070] Step 1: As Figure 2 shown, take a tunnel cross-section diagram with a segmented pouring length of L. Set the side of the secondary lining close to the inside of the tunnel as the S1 boundary curve 4, the side close to the maintenance structure as the S2 boundary curve 5, and the side of the inverted arch close to the inside of the tunnel as the S3 boundary curve 6. The intersection point of the S1 boundary curve 4 and the S3 boundary curve 6 is the P1 point 7; draw a perpendicular line at the P1 point 7 to intersect with the S1 boundary curve 4 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 below and including the H perpendicular line 8 of the secondary lining as the Class I area 2, and the remaining upper area as the Class II area 3.

[0071] The cracking risks of different parts of the secondary lining structure are different. The cracking risk of the arch wall in the middle and lower parts is high, and the cracking risks of the arch shoulders and the arch top in the middle and upper parts are relatively low. On the premise that there are isolation materials such as waterproof coiled materials or geotextiles and maintenance is carried out according to the specifications between the secondary lining and the maintenance structure, cracks can be avoided in the parts with low cracking risks such as the arch shoulders and the arch top by optimizing the mix ratio and appropriately controlling the concrete pouring temperature. However, for the arch wall in the middle and lower parts with high cracking risks, further measures such as controlling the pouring temperature and using anti-cracking functional materials are required. If the crack control scheme for the arch wall part is adopted for the entire secondary lining concrete, it will inevitably increase costs and cause waste of resources.

[0072] Step 2: Considering that the cracking risk of concrete increases with the increase of the pumping temperature, although the cracking risks of the arch shoulders and the arch top in the middle and upper parts of the secondary lining are relatively small compared with the arch wall in the middle and lower parts, there is still a cracking risk when the pumping temperature is relatively high. The present invention prepares three types of concrete, namely Type A, Type B, and Type C. The main difference lies in the dosage of the anti-cracking additive. The component ratios of the three types of concrete are shown in Table 2.

[0073] Table 2 Composition of three types of concrete, namely Type A, Type B and Type C (unit: kg / m 3 ):

[0074] .

[0075] Step 3: Select the type of concrete for pouring according to the zoning of the secondary lining and the pumping temperature T, and control the temperature difference between the pumping temperature T of the concrete and the average temperature inside the tunnel to be no more than 15°C; in Area I-2, use Type A concrete for pouring according to the pouring process conditions; when T≥30°C, in Area II-3, use Type B concrete for pouring according to the pouring process conditions; when T<30°C, in Area II-3, use Type C concrete for pouring according to the pouring process conditions.

[0076] For the technological parameters of the selection of raw materials, production, pouring, vibration and maintenance of the secondary lining concrete, etc., they should meet the national and relevant industry standard specifications. As for the selection of raw materials, major raw materials including cement, fly ash, fine aggregate, coarse aggregate, water reducer and mixing water should, on the basis of meeting the requirements of relevant national and industry standard specifications, also meet the specification requirements of the engineering field. For example, when it is the secondary lining of a railway tunnel, it should also comply with the provisions of "Railway Concrete" TB / T 3275; when it is the secondary lining of a highway tunnel, it should also comply with the provisions of "Technical Specification for Construction of Highway Bridges and Culverts" JTG / T 3650. To ensure the effect of concrete crack control and achieve crack-free concrete, the present invention also makes limitations on the pumping temperature of the concrete, the thickness of the secondary lining structure and the length of segmented pouring, specifically including controlling the pumping temperature not to be higher than the average temperature inside the tunnel by 15°C. The scheme is applicable to the secondary lining with a structural thickness ≤1.2m, and controls the length of segmented pouring ≤21m. The production, pouring, vibration and maintenance of the secondary lining concrete, etc., only need to meet the requirements of national and relevant industry standard specifications, such as the heat and moisture preservation and maintenance time including the formwork time is not less than 14d, etc.

[0077] As Figure 1 shown, the present invention also discloses an acceptance method for the secondary lining concrete of a tunnel. This acceptance method monitors the temperature and deformation of the 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 the software registration number of 1470077 for iterative calculation. When the correlation coefficient between the monitored temperature and deformation curves and the calculation is not less than 0.90, the adiabatic temperature rise, autogenous volume deformation and other performance parameters of the concrete used in the entity structure and the heat dissipation coefficient of the actual working condition formwork can be obtained. Then, input the concrete performance of the entity structure and the boundary conditions and parameters of the actual working condition into the "Structural Concrete Early Cracking Risk Assessment and Analysis Software" with the software registration number of 1470077 for calculation, and the cracking risk coefficient of the secondary lining concrete of the entity structure can be obtained.

[0078] Under the condition that the cracking risk coefficient ≤ 1.0, the concrete does not necessarily crack. However, in order to improve the guarantee rate of the concrete not cracking, the cracking risk coefficient ≤ 0.70 should be regarded as the qualified acceptance of the anti-cracking effect. At this time, the corresponding non-cracking guarantee rate ≥ 95%. Considering that it is difficult to avoid the tiny shrinkage cracks on the concrete surface due to water loss, and such tiny 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 on the surface of the secondary lining within the concrete strength assessment age ≤ 0.05 mm.

[0079] The acceptance method of the present invention includes the following steps:

[0080] Step 1: Select the layout points of the monitoring elements. Along either side of the Class I area 2 of the 0.5-fold L section in the longitudinal direction of the tunnel, the center points corresponding to the 1 m height plane below the set distance height H are respectively Point P3-10, the surface on the side close to the inside of the tunnel corresponding to Point P3-10 is Point P3-112, and the surface on the side close to the maintenance structure is Point P3-113; in the Class II area 3 of the 0.5-fold L section in the longitudinal direction of the tunnel, the center corresponding to the highest point of the internal clearance of the tunnel is Point P4-11.

[0081] Step 2: Before the concrete pouring of the tunnel secondary lining, install a strain gauge along the longitudinal and radial directions of the tunnel at Point P3-10, install a thermometer at each of Point P3-112 and Point P3-113, and install a strain gauge along the radial direction of the tunnel at Point P4-11. The in-situ monitoring data is an important support for the acceptance of the anti-cracking effect. The accuracy and survival rate of the monitoring elements are crucial. For this reason, 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.

[0082] Step 3: When 21 days have passed since the concrete pouring is completed, input the monitoring results of the thermometer and the strain gauge into the structural concrete cracking risk assessment and analysis software. When the correlation coefficient R 2 ≥ 0.90, stop the iterative calculation, and inversely calculate three key anti-cracking parameters: the adiabatic temperature rise of the concrete, the autogenous volume deformation of the concrete under the condition of the in-situ temperature change process, and the heat dissipation coefficient of the in-situ structure.

[0083] Step 4: Input the anti-cracking parameters obtained from the above inverse calculation into the structural concrete cracking risk assessment and analysis software again to calculate the cracking risk coefficient of the secondary lining concrete.

[0084] The following uses specific construction cases and experimental data to illustrate the above-mentioned tunnel secondary lining concrete anti-cracking additives, construction and acceptance methods provided by the present invention.

[0085] Example 1: The secondary lining concrete additive, construction and acceptance method provided by the present invention are applied to a tunnel project. The secondary lining of this tunnel is constructed by the open cut method, with a secondary lining thickness of 1.2 m and a segmented pouring length of 9 m. The design and evaluation age of the concrete strength is 60 d, and the strength grade is C40.

[0086] (I) Preparation of crack-resistant additive:

[0087] The secondary lining concrete of this tunnel is mainly constructed from May to August, with an average temperature of 28 °C. The time t from the production of the concrete to its transportation into the pump truck is about 20 - 30 min. During night construction, the temperature T of the concrete entering the pump is in the range of 31 °C - 33 °C. Based on this, the crack-resistant additive is designed to be composed of 60% by weight of magnesium oxide expansive agent with an activity value of 120 s, 38% by weight of calcium oxide expansive agent, and 2% by weight of process control material, all provided by the applicant.

[0088] (II) Construction of secondary lining concrete:

[0089] The secondary lining of the tunnel is divided into Class I area and Class II area as shown in Figure 2 . The height H of the Class I area is 5.2 m. Then, concrete preparation is carried out, and concrete raw materials that meet the requirements are selected, including P•O 42.5 cement, Class F Grade I fly ash, medium sand in Zone 2, continuously graded gravel with a size of 5 mm - 25 mm, mixing water, PCA-I polycarboxylate water reducer, and crack-resistant additive. Concrete of Class A and Class B is prepared by mixing according to the mixing ratio shown in Table 3. The Class I area below a height of 3.7 m of the secondary lining is poured with Class A concrete, and the remaining parts are poured with Class B concrete. The formwork is removed 4 d after the concrete is poured, and then a maintenance trolley is used for heat and moisture preservation maintenance until 14 d.

[0090] Table 3 Mix ratio of Class A and Class B concrete (unit: kg / m 3 )

[0091] .

[0092] (III) Acceptance of the crack resistance effect of secondary lining concrete:

[0093] Before the casting of the secondary lining concrete, one SBT-15D vibrating wire strain gauge was installed at point P3-10 along the longitudinal and radial directions of the tunnel, one SBT-RT-1 thermocouple thermometer was installed at each of point P3-1-12 and point P3-2-13, and one SBT-15D vibrating wire strain gauge was installed at point P4-11 along the radial direction of the tunnel. The data acquisition frequency was once every 2 hours. On the 21st day after the completion of the concrete casting, the temperature and deformation data were exported and input into the software "Structural Concrete Early Cracking Risk Assessment and Analysis Software" with the software registration number of 1470077 for iterative calculation until the correlation coefficient R 2 ≥ 0.90, and the temperature calculation results and monitoring results of point P3-10, point P3-1-12, point P3-2-13, and point P4-11 were as follows Figures 3 - 6 shown. The deformation calculation results and monitoring results of point P3-10 along the longitudinal and radial directions of the tunnel were as follows Figures 7 - 8 shown. The deformation calculation results and monitoring results of point P4-11 along the radial direction of the tunnel were as follows Figure 9 shown. At this time, the adiabatic temperature rises of Class A and Class B concretes were inversely calculated as follows Figure 10 shown. The autogenous volume deformations of Class A and Class B concretes under the condition of the temperature change process of the solid structure were as follows Figure 11 shown. The heat dissipation coefficient of the steel formwork under the actual working conditions was inversely calculated to be 30 kJ / m 2 •h•K. It should be noted that the empirical parameter of the heat dissipation coefficient of the steel formwork was 60 kJ / m 2 •h•K. It can be seen that there is a large gap between the empirical parameter and the parameter under the actual working conditions. The parameters such as the adiabatic temperature rise, autogenous volume deformation, and heat dissipation coefficient of the concrete inversely calculated were input into the software "Structural Concrete Early Cracking Risk Assessment and Analysis Software" with the software registration number of 1470077 again, and the maximum cracking risk coefficients of the concretes in Area I-2 and Area II-3 were calculated as follows Figure 12 shown. The results showed that the maximum cracking risk coefficient of the concrete in Area I-2 was 0.55, and the maximum cracking risk coefficient of the concrete in Area II-3 was 0.64. There were no cracks on the surface of the secondary lining of the solid structure during the 2-month observation after the casting. Based on the monitoring results of the solid structure, the inversely calculated maximum cracking risk coefficient ≤ 0.70, and finally, it was evaluated that the crack resistance effect of the secondary lining concrete passed the acceptance.

[0094] Example 2: The tunnel secondary lining concrete additive, construction, and acceptance method provided by the present invention were applied to a certain tunnel project. The total length of the tunnel was 20 km, the thickness of the secondary lining was 0.6 m, the segmented casting length was 9 m, the design and evaluation age of the concrete strength was 28 d, and the strength grade was C35.

[0095] (1) Preparation of crack resistance additive:

[0096] The cross-section of the secondary lining of the tunnel in this embodiment is as shown in 13. The average annual temperature in the tunnel is 23-28 °C. Taking winter construction as an example, the average temperature in the tunnel is about 23 °C. The time t from the production of concrete to its transportation into the pump truck is about 40-50 min. During winter construction, the temperature T of the concrete entering the pump is in the range of 18 °C - 22 °C. Based on this, the designed crack-resistant additive is composed of 55% by weight of magnesium oxide expansive agent with an activity value of 100 s, 43% by weight of calcium oxide expansive agent, and 2% by weight of process control material, all provided by the applicant.

[0097] (2) Construction of secondary lining concrete:

[0098] The secondary lining of the tunnel is divided into Class I area and Class II area as shown in Figure 13 . The height H of the Class I area is 4.5 m. Then, concrete preparation is carried out. The concrete raw materials that meet the requirements are selected, including P•O 42.5 cement, F-class grade I fly ash, medium sand in Zone 2, continuously graded gravel with a size of 5 mm - 25 mm, mixing water, PCA-I polycarboxylate water reducer, and crack-resistant additive. Class A and Class C concrete are prepared by mixing according to the mixing ratio shown in Table 4. Class A concrete is used for pouring in the Class I area below 2.3 m of the secondary lining height, and Class C concrete is used for pouring in the remaining parts. The formwork is removed 3 d after the concrete is poured, and then a maintenance trolley is used for heat and moisture preservation maintenance until 18 d.

[0099] Table 4 Mix ratio of Class A and Class C concrete (unit: kg / m 3 )

[0100] .

[0101] (3) Acceptance of crack resistance effect of secondary lining concrete:

[0102] Before the pouring of the secondary lining concrete, one SBT-15D vibrating wire strain gauge is installed at point P3-10 along the longitudinal and radial directions of the tunnel, one SBT-RT-1 thermocouple thermometer is installed at each of points P3-1-12 and P3-2-13, and one SBT-15D vibrating wire strain gauge is installed at point P4-11 along the radial direction of the tunnel. The data acquisition frequency is once every 2 hours. On the 21st day after the concrete is poured, the temperature and deformation data are exported and input into the software "Structural Concrete Early Cracking Risk Assessment and Analysis Software" with software copyright registration number 1470077 for iterative calculation until the correlation coefficient R of the calculation result and the monitoring result curve 2 ≥0.90, and parameters such as the adiabatic temperature rise, autogenous volume deformation, and formwork heat dissipation coefficient of the concrete are inversely calculated as shown in Figures 14 - 15 . Then, the maximum cracking risk coefficients of the concrete in the Class I area 2 and the Class II area 3 are calculated again as shown in Figure 16As shown in the figure, 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. There are no cracks on the surface of the secondary lining of the solid structure during the 1-month observation after pouring. Based on the back-calculation of the monitoring results of the solid structure, the maximum cracking risk coefficient ≤ 0.70. Finally, it is evaluated that the anti-cracking effect of the secondary lining concrete passes the acceptance.

[0103] Example 3: Apply the tunnel secondary lining concrete additive, construction and acceptance method provided by the present invention to a certain tunnel project. The total length of the tunnel is 10 km, the thickness of the secondary lining is 0.5 m, the segmented pouring length is 9 m, the designed and evaluated age of concrete strength is 28 d, and the strength grade is C35.

[0104] (I) Preparation of anti-cracking additive:

[0105] The cross-section of the tunnel secondary lining in this example is as Figure 17 shown. The average annual temperature in the tunnel is 25 - 30 °C, and the time t from concrete production to being pumped into the pump truck is about 35 - 55 min. During summer construction, the concrete pumping temperature T is in the range of 35 °C - 38 °C. Based on this, it is designed that the anti-cracking additive is composed of 50% by weight of magnesium oxide expansive agent with an activity value of 150 s, 46.5% by weight of magnesium oxide expansive agent with an activity value of 250 s, and 3.5% by weight of process control material, all provided by the applicant.

[0106] (II) Construction of secondary lining concrete:

[0107] Divide the tunnel secondary lining into Class I area and Class II area as Figure 17 shown. The height H of Class I area is 3.9 m. Then prepare the concrete. Select concrete raw materials that meet the requirements, including P•O 42.5 cement, F-class II fly ash, medium sand in Zone 2, 5 mm - 25 mm continuously graded gravel, mixing water, PCA-I polycarboxylate water reducer, and anti-cracking additive. Mix and prepare Class A and Class B concrete according to the mixing ratio shown in Table 5. Use Class A concrete for pouring in Class I area below the height of 3.9 m of the secondary lining, and use Class B concrete for pouring in the remaining parts. Remove the formwork 3 d after concrete pouring, and then use a maintenance trolley for heat and moisture preservation maintenance until 15 d.

[0108] Table 5 Mix ratio of Class A and Class B concrete (unit: kg / m 3 )

[0109] .

[0110] (III) Acceptance of anti-cracking effect of secondary lining concrete:

[0111] Before the casting of the secondary lining concrete, one SBT-15D vibrating wire strain gauge was installed at point P3-10 in the longitudinal and radial directions of the tunnel, one SBT-RT-1 thermocouple thermometer was installed at each of point P3-1 (at 12) and point P3-2 (at 13), and one SBT-15D vibrating wire strain gauge was installed at point P4-11 in the radial direction of the tunnel. The data acquisition frequency was once every 2 hours. On the 21st day after the concrete casting was completed, the temperature and deformation data were exported and input into the software "Structural Concrete Early Cracking Risk Assessment and Analysis Software" with the software registration number of 1470077 for iterative calculation until the correlation coefficient R 2 ≥0.90 between the calculated result and the monitoring result curve, and then parameters such as the adiabatic temperature rise, autogenous volume deformation, and formwork heat dissipation coefficient of the concrete were obtained by inversion. The maximum cracking risk coefficients of the concrete in Class I area 2 and Class II area 3 were calculated again as Figure 18 shown. The results show that the maximum cracking risk coefficient of the concrete in Class I area 2 is 0.56, and the maximum cracking risk coefficient of the concrete in Class II area 3 is 0.64. There are no cracks on the surface of the secondary lining of the solid structure during the one-month observation after the casting is completed. Based on the inversion calculation of the monitoring results of the solid structure, the maximum cracking risk coefficient ≤0.70, and finally it is evaluated that the crack resistance effect of the secondary lining concrete passes the acceptance.

[0112] Example 4: Example 4 and Example 3 are for the same tunnel project, the difference being that the construction season is autumn.

[0113] (1) Preparation of crack resistance additive:

[0114] In this example, the time t from the production of the concrete to its delivery into the pump truck is about 40 - 55 minutes. During the autumn construction, the concrete inlet temperature T is in the range of 30℃ - 32℃. Based on this, the designed crack resistance additive is composed of 98% by weight of magnesium oxide expansive agent with an activity value of 150s and 2% by weight of process control material, both provided by the applicant.

[0115] (2) Construction of secondary lining concrete:

[0116] The secondary lining of the tunnel is divided into Class I area and Class II area as Figure 17 shown, where the height H of Class I area is 3.9m. Then, the concrete is prepared, and the concrete raw materials that meet the requirements are selected, including P•O 42.5 cement, F-class II fly ash, medium sand in Zone 2, 5mm - 25mm continuously graded gravel, mixing water, PCA-I polycarboxylate water reducer, and crack resistance additive. The A-class and B-class concretes are prepared by mixing according to the proportioning amounts shown in Table 6. The Class I area below the height of 3.9m of the secondary lining is cast with A-class concrete, and the remaining parts are cast with B-class concrete. The formwork is removed 3 days after the concrete casting, and then the curing trolley is used for heat and moisture preservation curing until 14 days.

[0117] Table 6 Mix Proportions of Class A and Class B Concrete Unit: kg / m 3 :

[0118] 。

[0119] (III) Acceptance of the Crack Resistance Effect of Secondary Lining Concrete:

[0120] Before the casting of the secondary lining concrete, install one SBT-15D vibrating wire strain gauge each along the longitudinal and radial directions of the tunnel at point P3 at 10, install one SBT-RT-1 thermocouple thermometer each at points P3-1 at 12 and P3-2 at 13, and install one SBT-15D vibrating wire strain gauge along the radial direction of the tunnel at point P4 at 11. The data acquisition frequency is once every 2 hours. When it is the 21st day after the concrete casting is completed, export the temperature and deformation data and input it into the "Structural Concrete Early Cracking Risk Assessment and Analysis Software" with the software registration number of 1470077 for iterative calculation until the correlation coefficient R of the calculation result and the monitoring result curve 2 ≥0.90, and then invert parameters such as the adiabatic temperature rise, autogenous volume deformation, and formwork heat dissipation coefficient of the concrete. Calculate the maximum cracking risk coefficients of the concrete in Region I at 2 and Region II at 3 again as Figure 19 shown. The results show that the maximum cracking risk coefficient of the concrete in Region I at 2 is 0.54, and the maximum cracking risk coefficient of the concrete in Region II at 3 is 0.58. There are no cracks on the surface of the secondary lining of the solid structure during the 1-month observation after the casting is completed. Based on the inversion calculation of the monitoring results of the solid structure, the maximum cracking risk coefficient ≤0.70. Finally, it is evaluated that the crack resistance effect of the secondary lining concrete passes the acceptance.

[0121] Example 5: Apply the tunnel secondary lining concrete additive, construction, and acceptance method provided by the present invention to a certain tunnel project. The total length of the tunnel is 5 km, the thickness of the secondary lining is 1.0 m, the segmented casting length is 9 m, the design and evaluation age of the concrete strength is 60 d, and the strength grade is C40.

[0122] (I) Preparation of the Crack Resistance Additive:

[0123] The cross-section of the tunnel secondary lining in this example is as shown in 20. The annual average temperature in the tunnel is 28~30 °C, and the time t from the production of the concrete to its transportation into the pump truck is about 45~60 min. During the summer construction, the concrete inlet pump temperature T is in the range of 38 °C~40 °C. Based on this, it is designed that the crack resistance additive is composed of 95% by weight of magnesium oxide expansion agent with an activity value of 250 s and 5% by weight of the process control material, both provided by the applicant.

[0124] (II) Construction of the Secondary Lining Concrete:

[0125] Divide the tunnel secondary lining into as Figure 20The Class I area and Class II area shown, where the height H of the Class I area is 4.8 m. Then, concrete preparation is carried out, and concrete raw materials that meet the requirements are selected, including P•O 42.5 cement, Class I F fly ash, medium sand in Zone 2, continuously graded gravel with a size of 5 mm - 25 mm, mixing water, PCA-I polycarboxylate water reducer, and crack-resistant additives. According to the mixing ratio shown in Table 7, Class A and Class B concretes are prepared by mixing. The Class I area below the height of 3.9 m of the secondary lining is poured with Class A concrete, and the remaining parts are poured with Class B concrete. The formwork is removed 3 days after the concrete pouring, and then a curing trolley is used for heat and moisture preservation curing until 15 days.

[0126] Table 7 Mix Ratio of Class A and Class B Concretes Unit: kg / m 3 :

[0127] 。

[0128] (3) Acceptance of the crack resistance effect of the secondary lining concrete:

[0129] Before the pouring of the secondary lining concrete, one SBT-15D vibrating wire strain gauge is installed at point P3-10 along the longitudinal and radial directions of the tunnel, one SBT-RT-1 thermocouple thermometer is installed at point P3-11 and point P3-12 respectively, and one SBT-15D vibrating wire strain gauge is installed at point P4-11 along the radial direction of the tunnel. The data acquisition frequency is once every 2 hours. On the 21st day after the concrete pouring is completed, the temperature and deformation data are exported and input into the "Structural Concrete Early Cracking Risk Assessment and Analysis Software" with the software registration number of 1470077 for iterative calculation until the correlation coefficient R 2 ≥0.90, and parameters such as the adiabatic temperature rise, autogenous volume deformation, and formwork heat dissipation coefficient of the concrete are inversely derived. Then, the maximum cracking risk coefficients of the concrete in the Class I area 2 and Class II area 3 are calculated again as Figure 21 shown. The results show that the maximum cracking risk coefficient of the concrete in the Class I area 2 is 0.66, and the maximum cracking risk coefficient of the concrete in the Class II area 3 is 0.63. When observing the surface of the solid structure secondary lining 1 month after the pouring is completed, there are no cracks. Based on the monitoring results of the solid structure, the inversely calculated maximum cracking risk coefficient ≤0.70. Finally, it is evaluated that the crack resistance effect of the secondary lining concrete passes the acceptance.

[0130] In summary, the tunnel secondary lining concrete additive, construction, and acceptance method provided by the present invention are improved and innovated in terms of crack-resistant functional materials, construction technology, and crack resistance effect acceptance, which can effectively solve the problems of cracking and leakage caused by the shrinkage of the secondary lining concrete. At the same time, the crack resistance implementation effect can be quantitatively evaluated, realizing the closed-loop of construction and acceptance for the crack control of the tunnel secondary lining concrete.

[0131] The above are the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A construction method for the secondary lining concrete of a tunnel, characterized in that, The components of the crack-resistant additive are formulated according to the time t that the concrete experiences from being produced out of the machine to being transported into the pump truck and the temperature T of the concrete when it enters the pump truck. When t≥30 min and T≥30 °C, the crack-resistant additive consists of 95% - 98% by weight of magnesium oxide expansive agent with an activity value of 150 s - 250 s and 2% - 5% by weight of process control material. When t≥30 min and 23 °C≤T<30 °C, the crack-resistant additive consists of 95% - 98% by weight of magnesium oxide expansive agent with an activity value of 80 s - 140 s and 2% - 5% by weight of process control material. When t≥30 min and T<23 °C, the crack-resistant additive consists of 50% - 80% by weight of magnesium oxide expansive agent with an activity value of 80 s - 140 s, 20% - 50% by weight of calcium oxide expansive agent, and 0% - 3% by weight of process control material. When t<30 min and T≥23 °C, the crack-resistant additive consists of 50% - 80% by weight of magnesium oxide expansive agent with an activity value of 80 s - 140 s, 20% - 50% by weight of calcium oxide expansive agent, and 0% - 3% by weight of process control material. When t<30 min and T<23 °C, the crack-resistant additive consists of 50% - 80% by weight of magnesium oxide expansive agent with an activity value of 80 s - 140 s and 20% - 50% by weight of calcium oxide expansive agent. The secondary lining of the tunnel is divided into Class I area and Class II area, and different types of concrete added with the above crack-resistant additive are used for pouring. The construction method includes the following steps: Step 1: Take a cross-sectional view of the tunnel with a segmented pouring length of L. Set the side close to the inside of the tunnel of the secondary lining as the S1 boundary curve (4), the side close to the maintenance structure as the S2 boundary curve (5), and the side close to the inside of the tunnel of the invert as the S3 boundary curve (6). The intersection point of the S1 boundary curve (4) and the S3 boundary curve (6) is the P1 point (7). Make a perpendicular line at the P1 point (7) to intersect with the S1 boundary curve (4) at the P2 point (9). Take the vertical distance from the P1 point (7) to the P2 point (9) as H. Mark the area below the H perpendicular line (8) of the secondary lining as the Class I area (2), and the remaining upper area as the Class II area (3). Step 2: Prepare three types of concrete, namely Type A, Type B, and Type C, respectively: Among them, for Type A concrete per cubic meter, it includes the following components: 180 kg - 340 kg of cement, 80 kg - 150 kg of fly ash, 30 kg - 50 kg of crack-resistant additive, 650 kg - 850 kg of fine aggregate, 700 kg - 1100 kg of coarse aggregate, 3 kg - 6 kg of water reducer, and 140 kg - 170 kg of mixing water. For Type B concrete per cubic meter, it includes the following components: 180 kg - 340 kg of cement, 80 kg - 160 kg of fly ash, 20 kg - 30 kg of crack-resistant additive, 650 kg - 850 kg of fine aggregate, 700 kg - 1100 kg of coarse aggregate, 3 kg - 6 kg of water reducer, and 140 kg - 170 kg of mixing water. Class C concrete, per cubic meter, includes the following components: 180 kg - 340 kg of cement, 80 kg - 180 kg of fly ash, 650 kg - 850 kg of fine aggregate, 700 kg - 1100 kg of coarse aggregate, 3 kg - 6 kg of water reducing agent, and 140 kg - 170 kg of mixing water; Step 3: Select the type of concrete to be poured according to the zoning of the secondary lining and the pumping temperature T. In area I (2), Class A concrete is used for pouring according to the pouring process conditions; when T ≥ 30°C, in area II (3), Class B concrete is used for pouring according to the pouring process conditions; when T < 30°C, in area II (3), Class C concrete is used for pouring according to the pouring process conditions.

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

3. The construction method of the secondary lining concrete of the tunnel according to claim 1, characterized in that, The 12-hour heat of hydration reduction rate of the process control material ≥ 15% and the 24-hour heat of hydration reduction rate ≤ 35%.

4. The construction method of the secondary lining concrete of the tunnel according to claim 1, characterized in that, In Step 3, the temperature difference between the pumping temperature T of the concrete and the average temperature inside the tunnel is controlled not to be greater than 15°C.

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

6. The construction method of the secondary lining concrete of the tunnel according to claim 1, characterized in that, In Step 1, the thickness of the secondary lining structure ≤ 1.2 m and the segmented pouring length ≤ 21 m.

7. An acceptance method for the secondary lining concrete of a tunnel, characterized in that, For the acceptance of the concrete for Claim 1, the key anti-cracking parameters are obtained by inverse calculation using the measured data of the temperature and deformation of the solid structure concrete, and then the cracking risk coefficient of the secondary lining concrete is calculated using the anti-cracking key parameters obtained by inverse calculation, including the following steps: Step 1: Select the layout points of the monitoring elements. Along either side of the 0.5-fold L section in area I (2) of the tunnel longitudinal direction, the center points corresponding to the 1 m height layer below the set distance height H are respectively point P3(10). The surface on the side close to the inside of the tunnel corresponding to point P3(10) is point P3-1(12), and the surface on the side close to the maintenance structure is point P3-2(13); In the 0.5-fold L section in area II (3) of the tunnel longitudinal direction, the center corresponding to the highest point of the internal clearance of the tunnel is point P4(11); Step 2: Before the pouring of the tunnel secondary lining concrete, install a strain gauge along the longitudinal and radial directions of the tunnel at point P3(10), install a thermometer at each of point P3-1(12) and point P3-2(13), and install a strain gauge along the radial direction of the tunnel at point P4(11); Step 3: When it has been 21 days since the concrete pouring was completed, input the monitoring results of the thermometer and strain gauge into the structural concrete cracking risk assessment and analysis software. When the correlation coefficient R of the calculated temperature and deformation curves and the temperature and deformation curves monitored in the entity 2 ≥ 0.90, stop the iterative calculation, and inversely calculate three key anti-cracking parameters: the adiabatic temperature rise of the concrete, the autogenous volume deformation of the concrete under the condition of the actual temperature change process, and the heat dissipation coefficient of the actual structure. Step 4: Input the anti-cracking parameters obtained from the above inverse calculation into the structural concrete cracking risk assessment and analysis software again to calculate the cracking risk coefficient of the secondary lining concrete.

8. The acceptance method of the secondary lining concrete of the tunnel according to claim 7, characterized in that, In Step 2, the thermometer uses an SBT-RT-1 thermocouple thermometer, the strain gauge uses an SBT-15D vibrating wire strain gauge, and the data acquisition system uses an SBT-CDM wireless monitoring system.

9. The acceptance method of the secondary lining concrete of the tunnel according to claim 7, characterized in that The basis for the acceptance standard for evaluating the anti-cracking effect is that the maximum crack width on the surface of the secondary lining within the age of concrete strength evaluation ≤ 0.05 mm, and the maximum cracking risk coefficient obtained by inverse calculation ≤ 0.70.

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