Open cut tunnel crack control structure and method based on concrete performance gradient

Abstract

The invention discloses an open cut tunnel crack control structure and method based on the concrete performance gradient, and belongs to the technical field of concrete construction. The open cut tunnel crack control method based on the concrete performance gradient comprises the steps that S1, the expansive concrete mix proportion is obtained; s2, the maximum expansion joint distance allowed by the wall is obtained; s3, expansive concrete is poured, and after the expansive concrete is poured, common concrete is poured at the two ends of the expansive concrete immediately; and S4, curing the expansive concrete and the common concrete until a stable expansive concrete wall and a stable common concrete wall are formed. Through the combination mode of the expansive concrete wall and the common concrete wall, expansive concrete is only arranged in the area with the large shrinkage stress influence, the temperature stress of the overall structure is reduced, the tensile stress is always lower than the tensile strength of concrete, and the overall stability and durability of the structure are improved; therefore, cracks in the open-cut tunnel are reduced, and materials, construction and time cost are saved.

Description

Technical Field

[0001] The invention relates to the technical field of concrete construction, and in particular to an open-cut tunnel crack control structure and method based on concrete performance gradient. Background Art

[0002] In large-volume concrete construction projects, it is difficult to avoid cracks after forming due to the shrinkage of concrete itself. Post-casting strips or expansion joints are usually set to reduce the formation of cracks, but this method has disadvantages such as complex construction process and long construction period. Due to construction conditions and cost constraints, the mainstream construction process of tunnel projects is generally layered pouring. When the middle wall part shrinks, it is strongly constrained by the lower bottom plate, resulting in tensile stress greater than its ultimate tensile strength and cracking.

[0003] At present, the technology used to reduce cracks in open-cut tunnels relies on the principle of shrinkage compensation of expansive concrete, which offsets part of the shrinkage stress of concrete through expansion stress, thereby avoiding shrinkage cracks in concrete. However, expansive concrete is usually more expensive than ordinary concrete, and when used on a large scale, the construction cost will increase significantly, thus affecting the economic efficiency of the project. Summary of the invention

[0004] The purpose of the present invention is to solve at least one of the technical problems existing in the prior art. To this end, the present invention proposes an open-cut tunnel crack control structure and method based on concrete performance gradient, which can set expansive concrete only at locations with large shrinkage stress, thereby reducing the risk of cracking while saving material, construction and time costs.

[0005] According to the first aspect of the present invention, the open-cut tunnel crack control structure based on concrete performance gradient of the embodiment comprises: an expansion joint, which is arranged in an ordinary concrete wall; an expansive concrete wall, which is arranged in the expansion joint; a closing net and a plurality of vertical reinforcing steel bars, the closing net is arranged between the expansive concrete wall and the ordinary concrete wall, the plurality of vertical reinforcing steel bars are arranged at the end of the closing net opposite to the expansive concrete wall, and the plurality of vertical reinforcing steel bars are uniformly distributed along the horizontal extension direction of the closing net; a plurality of structural main bars, each of which extends from the ordinary concrete wall at one end of the expansive concrete wall to the ordinary concrete wall at the other end of the expansive concrete wall; transverse reinforcing steel bars, the number of which is the same as the number of the structural main bars, each of which is provided with a transverse reinforcing steel bar, the plurality of transverse reinforcing steel bars are buried in the expansive concrete wall, and both ends of each transverse reinforcing steel bar extend into the ordinary concrete wall in a direction away from the expansive concrete wall.

[0006] The open-cut tunnel crack control structure based on concrete performance gradient according to the embodiment of the present invention has at least the following beneficial effects: by arranging a combination of expansive concrete walls and ordinary concrete walls, expansive concrete is only arranged in areas with greater shrinkage stress influence, which can significantly reduce the temperature stress of the overall structure, and during construction, the tensile stress is always lower than the tensile strength of the concrete, thereby improving the overall stability and durability of the structure, thereby reducing the occurrence of cracks in the open-cut tunnel, and at the same time avoiding the problem of excessive cost caused by the use of expansive concrete alone, saving material, construction and time costs, and achieving a balance between cost and benefit.

[0007] According to a second aspect of the present invention, an open-cut tunnel crack control method based on concrete performance gradient comprises:

[0008] S1: Obtain design documents and construction requirements, select the type of expansive agent for expansive concrete, conduct an expansive concrete mix ratio test according to the design documents, construction requirements and the type of expansive agent, and obtain the expansive concrete mix ratio according to the expansive concrete mix ratio test results;

[0009] S2: Obtain the elastic modulus of concrete within the age, the calculated value of the wall, the resistance coefficient reflecting the degree of constraint on the wall, the linear expansion coefficient of concrete, the comprehensive temperature difference and the ultimate tensile value of concrete, and obtain the maximum allowable expansion joint spacing of the wall according to the elastic modulus of concrete within the age, the calculated value of the wall, the resistance coefficient reflecting the degree of constraint on the wall, the linear expansion coefficient of concrete, the comprehensive temperature difference and the ultimate tensile value of concrete;

[0010] S3: Prepare the expansive concrete according to the mix ratio of the expansive concrete, pour the expansive concrete according to the maximum expansion joint spacing allowed by the wall, and immediately pour ordinary concrete at both ends of the expansive concrete after the pouring of the expansive concrete is completed;

[0011] S4: Curing the expansive concrete and ordinary concrete until stable expansive concrete walls and ordinary concrete walls are formed.

[0012] According to some embodiments of the present invention, in S2, the comprehensive temperature difference includes hydration heat temperature difference, air temperature difference and contraction equivalent temperature difference.

[0013] According to some embodiments of the present invention, in S2, the calculation formula for the maximum allowable expansion joint spacing of the wall is:

[0014]

[0015] Where [L] is the maximum allowable expansion joint spacing of the wall, E is the elastic modulus of the concrete at the age, H is the calculated thickness or height of the wall, and C x is the resistance coefficient reflecting the degree of constraint on the wall, α is the linear expansion coefficient of concrete, T is the comprehensive temperature difference, εp is the ultimate tensile value of concrete.

[0016] According to some embodiments of the present invention, in S3, pouring expansive concrete according to the maximum expansion joint spacing allowed by the wall includes: locating the position of the expansion joint according to the maximum expansion joint spacing allowed by the wall, and setting a closing net at both ends of the expansion joint; setting a plurality of vertical reinforcing steel bars at the end of each closing net away from the expansive concrete; evenly spreading mortar at the bottom of the pouring area of ​​the wall; forming a mortar layer after the mortar is initially set, and pouring expansive concrete in the mortar layer.

[0017] According to some embodiments of the present invention, pouring expansive concrete in the expansion joint includes: pouring the expansive concrete in layers in the expansion joint, and pouring each layer of expansive concrete in a one-time continuous pouring manner; vibrating the expansive concrete after each layer is poured until it is poured to the designed elevation.

[0018] According to some embodiments of the present invention, when pouring the expansive concrete in layers, the thickness of each layer is 1.5 m to 2 m.

[0019] According to some embodiments of the present invention, in S4, curing the expansive concrete and ordinary concrete includes: removing the formwork 12 hours after all concrete pouring is completed; covering the surface of the expansive concrete wall with a polymer curing film; covering the surface of the polymer curing film with tin foil insulation cotton; and thermally curing until the wall is cooled to the ambient temperature, during which time watering is continuously poured on the top of the wall for moisturizing curing.

[0020] According to some embodiments of the present invention, in S4, curing the expansive concrete and ordinary concrete includes: covering the formwork with tin foil insulation cotton; loosening the formwork 12 hours after all concrete pouring is completed; watering several times a day to keep the concrete moist; removing the formwork 7 days after all concrete pouring is completed; and continuously watering the top of the wall for moisturizing maintenance.

[0021] According to some embodiments of the present invention, the thickness of the tin foil thermal insulation cotton is greater than 5 mm.

[0022] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present invention is further described below in conjunction with the accompanying drawings and embodiments:

[0024] Figure 1 Schematic diagram of an open-cut tunnel crack control structure based on concrete performance gradient according to an embodiment of the first aspect of the present invention;

[0025] Figure 2 yes Figure 1 Detailed drawings of the structure in the

[0026] Figure 3 It is a schematic diagram of maintenance measures for an open-cut tunnel crack control method based on concrete performance gradient according to an embodiment of the second aspect of the present invention.

[0027] Reference numerals:

[0028] Expansion joint 100;

[0029] Expanded concrete wall 200, polymer curing film 210, tin foil insulation cotton 220;

[0030] Closing net 300;

[0031] Vertical reinforcement steel bars 400;

[0032] Main structural reinforcement 500;

[0033] Transverse reinforcement steel bars 600;

[0034] Geotextile 700;

[0035] Ordinary concrete wall10. DETAILED DESCRIPTION

[0036] This section will describe in detail the specific embodiments of the present invention. The preferred embodiments of the present invention are shown in the accompanying drawings. The purpose of the accompanying drawings is to supplement the description of the text part of the specification with graphics, so that people can intuitively and vividly understand each technical feature and the overall technical solution of the present invention, but it cannot be understood as a limitation on the scope of protection of the present invention.

[0037] In the description of the present invention, it should be understood that descriptions involving orientations, such as up, down, front, back, left, right, etc., and orientations or positional relationships indicated are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0038] In the description of the present invention, "several" means one or more, "more" means more than two, "greater than", "less than", "exceed" etc. are understood as not including the number itself, and "above", "below", "within" etc. are understood as including the number itself. If there is a description of "first" or "second", it is only used for the purpose of distinguishing the technical features, and cannot be understood as indicating or implying the relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0039] In the description of the present invention, unless otherwise clearly defined, terms such as setting, installing, connecting, etc. should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above terms in the present invention based on the specific content of the technical solution.

[0040] refer to Figures 1 to 3 The crack control structure and method of an open-cut tunnel based on concrete performance gradient according to an embodiment of the present invention are described.

[0041] like Figure 1 and Figure 3 As shown, the open-cut tunnel crack control structure based on concrete performance gradient according to the first embodiment of the present invention includes: an expansion joint 100, which is arranged in an ordinary concrete wall 10; an expansive concrete wall 200, which is arranged in the expansion joint 100; a closing net 300 and a plurality of vertical reinforcing steel bars 400, which are arranged between the expansive concrete wall 200 and the ordinary concrete wall 10, and the plurality of vertical reinforcing steel bars 400 are all arranged at the end of the closing net 300 opposite to the expansive concrete wall 200, and the plurality of vertical reinforcing steel bars 400 are all arranged along the horizontal extension direction of the closing net 300. Uniformly distributed; multiple structural main bars 500, each structural main bar 500 extends from the ordinary concrete wall 10 at one end of the expansive concrete wall 200 to the ordinary concrete wall 10 at the other end of the expansive concrete wall 200; transverse reinforcing steel bars 600, the number of the transverse reinforcing steel bars 600 is the same as the number of the structural main bars 500, each structural main bar 500 is provided with a transverse reinforcing steel bar 600, multiple transverse reinforcing steel bars 600 are buried in the expansive concrete wall 200, and both ends of each transverse reinforcing steel bar 600 extend to the ordinary concrete wall 10 in a direction away from the expansive concrete wall 200.

[0042] like Figure 1 and Figure 2As shown, the expansion concrete wall 200 is arranged in the expansion joint 100, and ordinary concrete walls 10 are arranged at both left and right ends of the expansion concrete wall 200, and the ordinary concrete wall 10 is connected to the expansion concrete wall 200 through a closing net 300 and a plurality of vertical reinforcing steel bars 400. Among them, the closing net 300 is arranged at the left and right ends of the expansion joint 100, and the vertical reinforcing steel bars 400 are arranged on each closing net 300 near one end of the ordinary concrete wall 10, and a plurality of vertical reinforcing steel bars 400 are arranged, and the plurality of vertical reinforcing steel bars 400 are evenly distributed along the front-back direction. A plurality of structural main bars 500 and a plurality of transverse reinforcing steel bars 600 are arranged inside the expansive concrete wall 200 and the ordinary concrete wall 10 along the left-right direction. Each structural main bar 500 is provided with a corresponding transverse reinforcing steel bar 600. The structural main bars 500 are buried in the ordinary concrete wall 10. Each structural main bar 500 extends from the ordinary concrete wall 10 toward the inside of the expansive concrete wall 200 and penetrates the expansive concrete wall 200 to extend to the ordinary concrete wall 10 at the other end. The transverse reinforcing steel bars 600 are buried in the expansive concrete wall 200. Both ends of each transverse reinforcing steel bar 600 extend into the ordinary concrete wall 10 in a direction away from the expansive concrete wall 200. Therefore, by providing a combination of an expansive concrete wall 200 and an ordinary concrete wall 10, expansive concrete is provided only in areas where shrinkage stress has a greater impact, thereby significantly reducing the temperature stress of the overall structure, ensuring that the tensile stress is always lower than the tensile strength of the concrete during construction, thereby improving the overall stability and durability of the structure, thereby reducing the occurrence of cracks in the open-cut tunnel, and avoiding the problem of excessively high costs caused by the use of all expansive concrete, saving material, construction and time costs, and achieving a balance between cost and benefit.

[0043] It should be noted that tunnel projects are affected by factors such as geological conditions and temperature changes, and are prone to cracks. By setting an expansive concrete wall 200 in the expansion joint 100 and combining it with an ordinary concrete wall 10, a closing net 300 and a plurality of vertical reinforcing steel bars 400, it will not cause major changes to the original construction process, and can effectively control the occurrence of cracks to adapt to the complex environment of tunnel projects.

[0044] According to a second aspect of the present invention, an open-cut tunnel crack control method based on concrete performance gradient comprises:

[0045] S1: Obtain design documents and construction requirements, select the type of expansive agent for expansive concrete, conduct an expansive concrete mix ratio test based on the design documents, construction requirements and expansive agent type, and obtain the expansive concrete mix ratio based on the expansive concrete mix ratio test results.

[0046] Preferably, the expansion agent is an M-type magnesium oxide expansion agent having medium- and long-term shrinkage compensation performance.

[0047] S2: Obtain the elastic modulus of concrete within the age, the calculated value of the wall, the resistance coefficient reflecting the degree of constraint on the wall, the linear expansion coefficient of concrete, the comprehensive temperature difference and the ultimate tensile value of concrete, and obtain the maximum allowable expansion joint spacing of the wall according to the elastic modulus of concrete within the age, the calculated value of the wall, the resistance coefficient reflecting the degree of constraint on the wall, the linear expansion coefficient of concrete, the comprehensive temperature difference and the ultimate tensile value of concrete. Among them, the comprehensive temperature difference includes the hydration heat temperature difference, the air temperature difference and the shrinkage equivalent temperature difference.

[0048] Furthermore, the calculation formula for the maximum allowable expansion joint spacing of the wall is:

[0049]

[0050] Where [L] is the maximum allowable expansion joint spacing of the wall, E is the elastic modulus of the concrete at the age, H is the calculated thickness or height of the wall, and C x is the resistance coefficient reflecting the degree of constraint on the wall, α is the linear expansion coefficient of concrete, T is the comprehensive temperature difference, ε p is the ultimate tensile value of concrete.

[0051] S3: Prepare the expansive concrete according to its mix ratio, pour the expansive concrete according to the maximum expansion joint spacing allowed by the wall, and immediately pour ordinary concrete at both ends of the expansive concrete after the pouring of the expansive concrete is completed.

[0052] Among them, pouring expansive concrete according to the maximum expansion joint spacing allowed by the wall includes: locating the position of the expansion joint 100 according to the maximum expansion joint spacing allowed by the wall, respectively setting a closing net 300 at the opposite ends of the expansion joint 100, and setting a plurality of vertical reinforcing steel bars 400 at the end of each closing net 300 away from the expansive concrete. Before pouring the wall concrete, first evenly spread a layer of mortar at the bottom of the pouring area of ​​the wall, and after the mortar is initially set, a mortar layer is formed, and expansive concrete is poured in the mortar layer.

[0053] Specifically, the expansive concrete is poured in layers in the expansion joint 100, each layer having a thickness of 1.5 m to 2 m, and each layer of the expansive concrete is poured in a one-time continuous pouring manner. After each layer is poured, the expansive concrete is vibrated until it is poured to the designed elevation.

[0054] It should be noted that in the conventional concrete pouring method, the construction workers directly pour all the ordinary concrete of the wall on the bottom slab concrete, and pour it in layers until it reaches the designed elevation. Compared with the conventional method, first spreading a layer of mortar on the bottom can reduce the restraining effect of the old concrete on the new concrete, so that the expansion effect of the expansive concrete can be maximized. At the same time, the closing nets 300 are set at both ends of the expansive concrete to separate the ordinary concrete wall 10 and the expansive concrete wall 200, which can prevent the two concretes from mixing with each other.

[0055] S4: Curing the expansive concrete and the ordinary concrete until a stable expansive concrete wall 200 and an ordinary concrete wall 10 are formed.

[0056] It should be noted that in conventional concrete curing methods, the formwork is removed 24 to 48 hours after pouring, and after the formwork is removed, the wall surface is covered with geotextile 700, and watering is performed irregularly for curing. In open-cut tunnel projects, steel membranes are usually used for the walls, which have poor thermal insulation effects, causing the wall concrete temperature to drop quickly, resulting in large temperature shrinkage. In addition, due to the on-site workers' untimely watering and the weak water retention capacity of geotextile 700, the wall surface cannot be kept moist, resulting in cracks caused by water loss and shrinkage of the concrete under dry conditions.

[0057] In some specific embodiments of the present invention, curing the expansive concrete and ordinary concrete includes: removing the mold 12 hours after all concrete pouring is completed, covering the surface of the expansive concrete wall 200 with a polymer curing film 210, covering the surface of the polymer curing film 210 with tin foil insulation cotton 220, and performing thermal curing until the wall is cooled to the ambient temperature, during which time the top of the wall is continuously watered for moisturizing curing. Compared with conventional methods, moisturizing curing is performed by using the polymer curing film 210, and the polymer curing film 210 has a good water retention and water locking ability. It only needs to be replenished once every 7 days to keep the wall surface moist, thereby avoiding the occurrence of untimely watering and curing by construction workers.

[0058] In some other specific embodiments of the present invention, the curing of the expansive concrete and the ordinary concrete includes: covering the formwork with tin foil insulation cotton 220, loosening the formwork 12 hours after all concrete pouring is completed, watering the concrete several times a day to keep the concrete moist, removing the formwork 7 days after all concrete pouring is completed, and continuously watering the top of the wall for moisturizing and curing. Since the steel film also has good impermeability, delaying the demoulding time to 7 days, loosening the formwork in time and watering the gap between the concrete and the formwork can also achieve a good moisturizing and curing effect.

[0059] It should be noted that during the concrete pouring process, the pre-prepared concrete needs to be poured into the formwork or supporting structure. Specifically, according to the design requirements and construction drawings, the formwork needs to be installed to ensure that the position of the formwork is accurate and stable, and the height and level of the formwork need to be adjusted to ensure the structural size and flatness after the concrete is poured.

[0060] It should be noted that in the two curing schemes for concrete of the present invention, tin foil insulation cotton 220 is used for insulation to reduce the cooling rate of the wall concrete, thereby further reducing the risk of cracking. Specifically, the thickness of the tin foil insulation cotton 220 is greater than 5 mm.

[0061] The present open-cut tunnel crack control method based on concrete performance gradient is described below with a specific embodiment.

[0062] For a side wall of an open-cut tunnel, the length is 30m, the width is 1.1m, the height is 5.15m, and the strength grade is C40.

[0063] S1: According to the design documents and construction requirements, the expansive concrete mix ratio is optimized, and the M-type magnesium oxide expansive agent is selected to conduct an expansive concrete mix ratio test. According to the expansive concrete mix ratio test results, the dosage of the M-type magnesium oxide expansive agent is determined to be 8%, among which, the concrete mix ratio and limited expansion rate test results are shown in the table below.

[0064]

[0065] S2: The elastic modulus E of C40 concrete is 3.25×104N / mm 2 , the calculated height of the wall is H is 5.15m, C x Take 1.0N / mm 3 , the linear expansion coefficient of concrete is 1×10 -5 / ℃, the comprehensive temperature difference T is 11℃, the ultimate tensile value of concrete ε p is 0.0001.

[0066] Substitute the above values ​​into the calculation formula for the maximum allowable expansion joint spacing of the wall:

[0067]

[0068] The maximum allowable expansion joint spacing of the wall, that is, the expansion concrete spacing [L] = 15m, is calculated.

[0069] S3: Figure 2 As shown, the front-to-back direction is the direction of the wall thickness. When tying the bottom plate reinforcement, a steel bar with a length the same as the wall height and a diameter of 10mm to 14mm is welded every 10cm along the wall thickness at both ends of the expansion joint 100 as a vertical reinforcement steel bar 400, and then the bottom plate is poured.

[0070] After the bottom slab is poured, when tying the wall reinforcement, the vertical reinforcement steel bars 400 are fixed to the frame bars by tying or welding, and the quick-closing net 300 is installed inside the vertical reinforcement steel bars 400. The transverse reinforcement steel bars 600 are arranged in parallel with the main structural bars 500, and the length of the transverse reinforcement steel bars 600 extending from the left and right ends of the middle expansion joint 100 is 1m to 1.5m.

[0071] Before pouring the wall concrete, evenly spread a 5cm thick mortar layer at the bottom, and then pour the wall concrete after the mortar layer is initially set. Pour the expansive concrete in layers, with each layer pouring 1.5 to 2m. After each layer is poured, vibrate it until it reaches the designed elevation. After the expansive concrete is poured, pour the ordinary concrete on both sides of the expansive concrete immediately. The mix ratio of the ordinary concrete is the same as the mix ratio of the expansive concrete after removing the stones.

[0072] S4: After the side wall is poured, the mold is removed 12 hours later, the surface of the ordinary concrete wall 10 is covered with geotextile 700, and water is poured three times a day in the morning, noon and evening to keep the wall moist. The surface of the expanded concrete wall 200 is covered with a polymer curing film 210, and then covered with tin foil insulation cotton 220 with a thickness of more than 5 mm for thermal insulation and curing until the wall is cooled to the ambient temperature, and water is continuously poured on the top of the wall during this period. It should be noted that the moisturizing curing is at least 14 days, and preferably, the moisturizing curing time reaches 28 days.

[0073] The embodiments of the present invention are described in detail above with reference to the accompanying drawings, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge scope of ordinary technicians in the technical field without departing from the purpose of the present invention.

Claims

1. An open-cut tunnel crack control structure based on concrete performance gradient, arranged in an ordinary concrete wall (10), characterized in that: include: An expansion joint (100), wherein the expansion joint (100) is provided in an ordinary concrete wall (10); An expansion concrete wall (200), wherein the expansion concrete wall (200) is arranged in the expansion joint (100); A closing net (300) and a plurality of vertical reinforcing steel bars (400), wherein the closing net (300) is arranged between the expansive concrete wall (200) and the ordinary concrete wall (10), the plurality of vertical reinforcing steel bars (400) are arranged at an end of the closing net (300) opposite to the expansive concrete wall (200), and the plurality of vertical reinforcing steel bars (400) are evenly distributed along the horizontal extension direction of the closing net (300); A plurality of structural main reinforcements (500), each of the structural main reinforcements (500) extending from the ordinary concrete wall (10) at one end of the expansive concrete wall (200) to the ordinary concrete wall (10) at the other end of the expansive concrete wall (200); Transverse reinforcing steel bars (600), the number of the transverse reinforcing steel bars (600) is the same as the number of the structural main bars (500), each of the structural main bars (500) is provided with one transverse reinforcing steel bar (600), a plurality of the transverse reinforcing steel bars (600) are embedded in the expansive concrete wall (200), and both ends of each transverse reinforcing steel bar (600) extend into the ordinary concrete wall (10) in a direction away from the expansive concrete wall (200).

2. A method for crack control in open-cut tunnels based on concrete performance gradient, characterized in that: The open-cut tunnel crack control structure based on concrete performance gradient according to claim 1 comprises: S1: Obtain design documents and construction requirements, select the type of expansive agent for expansive concrete, conduct an expansive concrete mix ratio test according to the design documents, construction requirements and the type of expansive agent, and obtain the expansive concrete mix ratio according to the expansive concrete mix ratio test results; S2: Obtain the elastic modulus of concrete within the age, the calculated value of the wall, the resistance coefficient reflecting the degree of constraint on the wall, the linear expansion coefficient of concrete, the comprehensive temperature difference and the ultimate tensile value of concrete, and obtain the maximum allowable expansion joint spacing of the wall according to the elastic modulus of concrete within the age, the calculated value of the wall, the resistance coefficient reflecting the degree of constraint on the wall, the linear expansion coefficient of concrete, the comprehensive temperature difference and the ultimate tensile value of concrete; S3: Prepare the expansive concrete according to the mix ratio of the expansive concrete, pour the expansive concrete according to the maximum expansion joint spacing allowed by the wall, and immediately pour ordinary concrete at both ends of the expansive concrete after the pouring of the expansive concrete is completed; S4: Curing the expansive concrete and the ordinary concrete until the stable expansive concrete wall (200) and the ordinary concrete wall (10) are formed.

3. The open-cut tunnel crack control method based on concrete performance gradient according to claim 2 is characterized in that: In S2, the comprehensive temperature difference includes hydration heat temperature difference, air temperature difference and contraction equivalent temperature difference.

4. The open-cut tunnel crack control method based on concrete performance gradient according to claim 2 is characterized in that: In S2, the calculation formula for the maximum allowable expansion joint spacing of the wall is: Where [L] is the maximum allowable expansion joint spacing of the wall, E is the elastic modulus of the concrete at the age, H is the calculated thickness or height of the wall, and C x is the resistance coefficient reflecting the degree of constraint on the wall, α is the linear expansion coefficient of concrete, T is the comprehensive temperature difference, ε p is the ultimate tensile value of concrete.

5. The open-cut tunnel crack control method based on concrete performance gradient according to claim 2 is characterized in that: In S3, pouring expansive concrete according to the maximum allowable expansion joint spacing of the wall includes: The expansion joint (100) is positioned according to the maximum expansion joint spacing allowed by the wall, and the closing nets (300) are respectively arranged at both ends of the expansion joint (100); A plurality of the vertical reinforcing steel bars (400) are arranged at one end of each of the closing nets (300) away from the expansive concrete; Evenly spread mortar at the bottom of the wall pouring area; After the mortar is initially set, a mortar layer is formed, and expansive concrete is poured in the mortar layer.

6. The open-cut tunnel crack control method based on concrete performance gradient according to claim 5 is characterized in that: The pouring of expansive concrete in the expansion joint (100) comprises: pouring expansive concrete in the expansion joint (100) in layers, and pouring each layer of expansive concrete in a one-time continuous pouring manner; After each layer is poured, the expansive concrete is vibrated until it is poured to the designed elevation.

7. The open-cut tunnel crack control method based on concrete performance gradient according to claim 6 is characterized in that: When pouring expansive concrete in layers, the thickness of each layer is 1.5m to 2m.

8. The open-cut tunnel crack control method based on concrete performance gradient according to claim 2 is characterized in that: In S4, the curing of the expansive concrete and the ordinary concrete includes: The formwork will be removed 12 hours after all concrete pouring is completed; Covering the surface of the expanded concrete wall (200) with a polymer curing film (210); Covering the surface of the polymer curing film (210) with tin foil heat-insulating cotton (220); Insulation maintenance is carried out until the wall is cooled down to the ambient temperature. During this period, water is continuously poured on the top of the wall for moisturizing maintenance.

9. The open-cut tunnel crack control method based on concrete performance gradient according to claim 2, characterized in that: In S4, the curing of the expansive concrete and the ordinary concrete includes: Covering the template with tin foil insulation cotton (220); The formwork will be loosened 12 hours after all concrete pouring is completed; Water several times a day to keep the concrete moist; All concrete pouring is completed 7 days after the formwork is removed; Continue to water the top of the wall to maintain moisture retention.

10. The open-cut tunnel crack control method based on concrete performance gradient according to claim 8 or 9, characterized in that: The thickness of the tin foil heat-insulating cotton (220) is greater than 5 mm.

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