A new underground structure model considering the influence of initial cracks and its preparation method

Abstract

The present invention discloses an underground structure model considering the influence of initial cracks and a new preparation method, and relates to the technical field of engineering construction. The underground structure model considering the influence of initial cracks of the present invention includes a crack area and a model body, and the model adopts a brittle concrete structure at least in the crack division, so that when the model is subjected to force, cracks are generated in a predetermined crack area. The present invention uses brittle concrete materials or concrete with lower strength to cast the crack area, and uses ordinary concrete casting to form a simulated underground structure, thereby achieving the required cracks in the predetermined area, and then used for corresponding experimental research. The present invention also discloses a new preparation method for the above-mentioned model.

Description

Technical Field

[0001] The invention relates to the technical field of engineering construction, in particular to an underground structure model taking into account the influence of initial cracks and a new preparation method thereof. Background Art

[0002] After decades of rapid development, the construction of urban underground structures in my country is gradually developing from large-scale development and construction to a situation of "equal emphasis on construction and maintenance". Under the combined effects of complex hydrological and geological conditions, various diseases of underground structures in service are gradually emerging, among which structural cracks are the most common. Traditional structural calculation analysis and seismic design are based on the intact state of the structure, that is, the influence of damage such as corrosion, misalignment, and cracks on the mechanical properties and seismic performance of the structure is not considered. With the increase in the service life of underground structures, the influence of these damages on the mechanical properties and seismic performance of the structure cannot be ignored. However, how to reasonably consider these damages, especially the adverse effects of a large number of cracks, is still immature in theoretical analysis and experimental research, especially in experimental technology. Therefore, it is urgent to develop corresponding experimental technology to reasonably consider the influence of cracks on the mechanical properties and seismic performance of the structure. Summary of the invention

[0003] In view of the above shortcomings, the purpose of the present invention is to provide a concrete underground structure model that can simulate the influence of initial cracks in the underground structure. The purpose of the present invention is also to provide a new method for preparing the above-mentioned underground structure model.

[0004] To this end, the present invention provides a concrete underground structure model for simulating the impact of initial cracks, the model comprising a crack area and a model body, the model adopting a brittle concrete structure at least in crack differentiation, in such a way that when the model is subjected to stress, cracks are generated in a predetermined crack area.

[0005] Furthermore, the model body and the crack area as a whole adopt a brittle concrete structure. The model body is assembled and connected to the pile foundation, and is used to apply stress to the structural model with external loads in the laboratory. Through uneven settlement of the piles, or different lengths and types of piles, direct stress cracks and secondary cracks are generated in the areas of the structure affected by shear and tension, simulating the influence of pile settlement on cracks in the laboratory.

[0006] The crack area is cast with brittle concrete mixed with hollow capsules. The hollow capsules have brittle characteristics and break before the main body of the model when subjected to force, thereby forming the required cracks.

[0007] The present invention also includes a novel method for preparing the above-mentioned underground structure, comprising the following steps:

[0008] S1: Determine the bending and tensioning parts of the concrete underground structure, and determine the location and shape of the crack area that needs to be simulated in the underground structure;

[0009] S2: Determine the mix ratio of capsule concrete and the material properties of the capsules used;

[0010] S3: pouring concrete to form the model, wherein hollow capsule concrete is poured into the crack area.

[0011] Furthermore, the hollow capsule concrete is poured into concrete with hollow capsules added therein to form a predetermined shape, and the hollow capsule concrete is placed in a designated crack area and concrete is poured to form the model.

[0012] The model body and the crack area can also be cast synchronously using different concretes. The step S3 includes setting a main template. The casting area of ​​the model body and the crack area are separated by a wire mesh, and an auxiliary template is provided on the upper part of the wire mesh.

[0013] Furthermore, the crack area is surrounded by the casting area of ​​the model body, and the interfaces between the crack area and the casting area are separated by wire mesh. The auxiliary formwork includes a first formwork and a second formwork. The first formwork and the second formwork cooperate with each other, and both ends of the second formwork extend and are connected to the side formwork of the main formwork. The first formwork is fixed to the side formwork with tension bolts, and the tension bolts include limit plates fixed or threadedly connected to the screw rods, and the limit plates and nuts are fixed together on the first formwork and the side formwork.

[0014] Furthermore, the side formwork is provided with tension bars, which are arranged at the upper and lower parts of the side formwork, and two vertical bars are arranged on the outer wall of the side formwork, and the tension bars are arranged between the two vertical bars. The upper side of the side formwork includes a fixed plate and a flip plate rotatably connected to the side formwork body, and a limit bar is provided on the outer side of the flip plate, and the limit bar is rotatably connected to the formwork system.

[0015] Furthermore, the tension bolts are arranged between two vertical ribs, and the limiting strip is provided with screw holes, through which the tension bolts pass.

[0016] Furthermore, the middle portion of the limit strip protrudes outward, and a groove is formed inside to accommodate the vertical ribs. The upper ends of the vertical ribs are concave inward to form an L shape, and the tensioning ribs are arranged on the inwardly concave L-shaped curved portion.

[0017] Beneficial technical effects of the present invention:

[0018] The present invention uses brittle concrete materials or concrete with lower strength to cast the crack area, and uses ordinary concrete (or concrete that is the same as the existing underground structure) to cast a simulated underground structure, or the model body and the crack area are cast as a whole with brittle concrete, and corresponding cracks are generated in the main stress-bearing area (crack area) of the model. The crack area refers to the area where cracks may occur in the existing underground structure that needs to be simulated. After the test equipment is used to apply the corresponding force to the model, the crack area of ​​the model produces cracks before other areas due to the insufficient stress-bearing capacity of the set material, thereby achieving the required cracks in the predetermined area, and then used for corresponding experimental research. In a specific embodiment of the present invention, the relatively mature capsule concrete technology is used to consider the impact of cracks in the underground structure during service on the structural performance. First, based on preliminary numerical analysis and basic mechanical principles, the parts of the structure that are bent and tensile are determined; secondly, the proportion of capsule concrete and the material properties of the capsules used are determined according to the issues that need to be considered and the stress characteristics of the structure, and the corresponding hollow capsule concrete is prepared, mainly considering the size (length and width) of the hollow capsule, which directly determines the characteristics of the cracks formed; then, when the structural model is cast, the hollow capsule concrete prepared in the previous step is poured at this location. When the structure is subjected to stress and bending deformation in the later stage, the hollow capsule will break and be destroyed due to its brittle characteristics under tension, thereby forming the required cracks, thereby preparing an underground structure model containing cracks for the corresponding experimental research.

[0019] The present invention also includes a new method for preparing the above-mentioned concrete underground structure model. In a specific embodiment, it includes first prefabricating a concrete structure in the crack area, and then pouring the prefabricated structure together with the main body of the model to form the model; in other embodiments, the separation effect of the fine-mouthed steel mesh can be used to simultaneously pour the crack area and the main body of the model.

[0020] The advantages of the present invention are that the structural model is simple to prepare and can effectively simulate the required cracks and position requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of underground structural cracks;

[0022] Figure 2 Schematic diagram of the concrete structure in the crack area with hollow capsules added;

[0023] Figure 3 This is a schematic diagram of the arrangement of the auxiliary template and the wire mesh in Example 1;

[0024] Figure 4 is a schematic top view of the template in Example 2;

[0025] Figure 5 for Figure 4 A cross-sectional schematic diagram of

[0026] Figure 6 It is a schematic diagram of the connection between the first template and the side template;

[0027] Figure 7 is a schematic diagram of Example 3;

[0028] Figure 8 is a schematic diagram of a limit bar;

[0029] Fig. 9 This is a schematic diagram of the connection between the model body and the pile foundation.

[0030] Explanation of the accompanying drawings: 1. hollow capsule concrete; 2. hollow capsule; 3. crack area; 4. wire mesh; 5. profile; 6. auxiliary formwork; 601. first formwork; 602. second formwork; 7. tension bolts; 701. limiting plates; 8. side formwork; 801. fixing plate; 802. flip plate; 9. tension reinforcement; 10. vertical reinforcement; 11. limiting strips; 12. pile foundation. DETAILED DESCRIPTION

[0031] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the specific implementation mode, structure, characteristics and effects of the present invention are described in detail below in combination with the accompanying drawings and preferred embodiments.

[0032] Reference Figures 2 to 9 As shown, a concrete underground structure model for simulating the impact of initial cracks of the present invention, the first embodiment, referring to Figure 1 , Figure 2 and 8 As shown, both the main body of the model and the crack area adopt brittle concrete structure. In the laboratory, the structure is subjected to external loads, and the external loads can be loaded by a pressure loading device, such as a common electronic universal testing machine. Direct stress cracks and secondary cracks are generated in the area where the structure is affected by shear force and tension. Further, assembly holes can be set in a predetermined area of ​​the main body of the model for assembly connection with the pile foundation 12. By connecting different pile diameters, lengths, and different soil bodies, the generation of cracks during the uniform or uneven settlement of the piles is simulated. In this embodiment, the crack area can be regarded as the entire main body of the model. In a second embodiment, it includes a crack area 3 and a main body of the model, wherein the crack area 3 adopts a brittle concrete structure or the concrete strength of the crack area 3 is lower than the strength of the concrete of the main body of the model, so that when the model is subjected to force, cracks are first generated in the crack area 3. Figure 1 The figure shows the locations where cracks are likely to occur in the existing underground structure. The model of the present invention simulates the existing underground structure (or part of the structure), especially the locations of cracks, to analyze the possible impacts. Figure 2As shown, the crack area 3 uses hollow capsule concrete 1. Capsule concrete is a prior art. Existing capsule concrete often uses conventional micro-concrete mixed with capsules. The capsules are filled with substances for repairing cracks in advance. When cracks appear in the structure, the capsules will also break to release the internal substances for self-healing of concrete cracks. The hollow capsule concrete 1 of this embodiment is basically the same as the prior art and also uses conventional micro-concrete. The difference is that the hollow capsule 2 is not filled with substances. Since the hollow capsule 2 has brittle characteristics, it is easy to break when subjected to force, so as to achieve the desired cracks at the predetermined position. The corresponding crack characteristics are formed by setting the size of the hollow capsule 2. Of course, the above-mentioned hollow capsule 2 can also be replaced with a low-grade concrete material so that cracks appear earlier than the main structure of the model when subjected to force.

[0033] The present invention also includes a novel method for preparing the above-mentioned concrete underground structure model, comprising the following steps:

[0034] S1: Determine the bending and tensioning parts of the concrete underground structure, and determine the location and shape of the crack area that needs to be simulated in the underground structure;

[0035] S2: Determine the mix ratio of capsule concrete and the material properties of the capsules used;

[0036] S3: pouring concrete to form a model, wherein the crack area 3 is poured with hollow capsule concrete.

[0037] In the above-mentioned new preparation method, in step S3, a hollow capsule concrete 1 of a predetermined shape can be cast by concrete mixed with hollow capsules 2 as a prefabricated part, and the hollow capsule concrete 1 (i.e., the prefabricated part) is placed in a designated crack area 3 (i.e., the area where cracks need to be formed) and ordinary concrete (or concrete of the same grade as the simulated underground structure) is cast to form the model.

[0038] In the above embodiment, since the structure of the crack area 3 is cast first, during the stress process, cracks may also occur at the interface between the crack area 3 and the model body concrete, thereby affecting the cracks that need to be generated. In another embodiment, the model body and the crack area 3 are cast simultaneously using different concretes. Step S3 includes setting a main formwork, and the casting area of ​​the model body and the crack area 3 are separated by a wire mesh 4. The wire mesh 4 is a dense mesh. The wire mesh 4 is fixed in the groove of the profile 5, and the profile 5 is fixed to the formwork such as bolts. An auxiliary formwork 6 is provided on the upper part of the wire mesh 4, and the auxiliary formwork 6 can be fixed to the profile 5. Figure 3The specific embodiment 1 is shown, and a steel mesh 4 is set perpendicular to the length direction of the model. When pouring, the hollow capsule concrete 1 is first injected into the crack area 3, and then ordinary concrete is injected into the main area of ​​the model at both ends of the crack area 3. Since the height of the concrete will drop after vibration, when a sufficient amount of concrete is poured into the corresponding area, the initial height of the concrete will be higher than the height of the structure after molding, and the concrete in different areas will flow to other areas. The auxiliary formwork 6 is used to separate and prevent this situation. In addition, in order to increase the contact area between the steel mesh 4 and the concrete, the steel mesh 4 can be set at a 45° angle.

[0039] In the above-mentioned embodiment 1, the model is usually used to form transverse cracks. When it is necessary to form cracks in the longitudinal direction, the crack area 3 is set in the middle of the model body as an example. In embodiment 2, referring to Figure 4 , Figure 5 and Figure 6 As shown, the crack area 3 is surrounded by the casting area of ​​the main body of the model, and the interface between the crack area 3 and the casting area is separated by a wire mesh 4. The auxiliary formwork 6 includes a first formwork 601 and a second formwork 602. The first formwork 601 and the second formwork 602 cooperate with each other, and the two ends of the second formwork 602 extend and are connected to the side formwork 8 of the main formwork. In this embodiment, the first formwork 601 is parallel to the side formwork 8 of the main formwork, and the second formwork 602 is perpendicular to the first formwork 601. The two ends of the second formwork 602 are fixed to the side formwork 8, and the two ends of the first formwork 601 are connected to the second formwork 602, such as by common bolt connection. In order to prevent the first formwork 601 from expanding during the concrete injection process, the first formwork 601 and the side formwork 8 are fixed by tension bolts 7. The tension bolts 7 include a limit plate 701 fixed or threaded on the screw rod, and the limit plate 701 and the nut are fixed to the first formwork 601 and the side formwork 8 together. The upper surface of the first template 601 can also be connected to the upper surface of the side template 8 by a connecting strip. After the model is cast, the surface of the crack area 3 can be directly polished. After the tie rods 9 between the first template 601 and the side template 8 are removed, the surface of the concrete in the main area of ​​the model on both sides of the crack area 3 can be polished.

[0040] Reference Figure 7 and Figure 8As shown, in order to avoid mold expansion during model casting, tension bars 9 can be provided on the upper and lower parts of the side formwork 8 on both sides, and two vertical bars 10 are provided on the outer wall of the side formwork 8. The tension bars 9 are provided between the two vertical bars 10, and the tension nuts are fixed in cooperation with the two vertical bars 10. The upper side of the side formwork 8 includes a fixed plate 801 and a flip plate 802 rotatably connected to the main body of the side formwork 8. The position of the fixed plate 801 corresponds to the position of the vertical bars 10. The flip plate 802 is provided between adjacent fixed plates 801. The flip plate 802 can be flipped by hinges. A limit strip 11 is provided on the outer side of the flip plate 802, and the limit strip 11 is rotatably connected to the formwork system. In this embodiment, the tension bolt 7 is provided between the two vertical bars 10, and the limit strip 11 is provided with a screw hole. The tension bolt 7 passes through the screw hole on the limit strip 11, and the tension nut fixes the limit strip 11 to the tension bolt 7. The shape of the limit strip 11 refers to Figure 8 As shown, the middle part thereof protrudes outwards on the inner side of the limiting strip 11 to form a groove to accommodate the vertical rib 10 and cooperate with the vertical rib 10. At the same time, the inner surfaces on both sides of the limiting strip 11 contact the flip plate 802 and prevent outward expansion during the concrete pouring process. In this embodiment, by setting the limiting strip 11, the number of the tension bolts 7 can be reduced, so the surface calendering can be performed even if the tension bolts 7 are not removed. Further, the limiting strip 11 can be rotated so that the limiting strip 11 no longer restricts the flip plate 802, and the flip plate 802 is flipped and then the surface calendering is performed. In this embodiment, when the height of the flip plate 802 (or the auxiliary formwork 6) is high, the surface treatment can be performed more conveniently. In order to reduce the workload of removing the tension nut, the upper end of the vertical rib 10 can be concave inward (bent toward the crack area 3) to form an L shape, and the tension rib 9 is set on the inwardly concave L-shaped curved portion, so that the limiting strip 11 is rotated to the vertical direction without being hindered and restricted by the tension rib 9.

[0041] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technical personnel in this field can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. An underground structure model considering the influence of initial cracks, characterized in that: The model comprises a crack region, a model body and cracks, and the model adopts a brittle concrete structure at least in the crack region in such a way that after applying a corresponding force, the cracks are generated in the predetermined crack region; The model body and the crack area are made of brittle concrete structure as a whole. The model body is connected to the pile foundation in an assembled manner, and is used to apply stress to the structural model by external load in the laboratory. Through the uneven settlement of the piles, or the different lengths and types of the piles, direct stress cracks and secondary cracks are generated in the area of ​​the structure affected by shear force and tension, simulating the influence of the settlement of the piles on the cracks in the laboratory; or The crack area is cast with brittle concrete mixed with hollow capsules. The hollow capsules have brittle characteristics and break when subjected to force, thereby forming the required cracks.

2. A new method for preparing an underground structure model taking into account the influence of initial cracks as claimed in claim 1, characterized in that: The following steps are involved: S1: Determine the bending and tensioning parts of the concrete underground structure, and determine the location and shape of the crack area that needs to be simulated in the underground structure; S2: Determine the mix ratio of capsule concrete and the material properties of the capsules used; S3: pouring concrete to form the model, wherein hollow capsule concrete is poured into the crack area.

3. The new method for preparing an underground structure model taking into account the influence of initial cracks according to claim 2 is characterized in that: The hollow capsule concrete with a predetermined shape is cast by pouring concrete mixed with the hollow capsule, and the hollow capsule concrete is placed in a designated crack area and concrete is poured to form the model.

4. The novel method for preparing an underground structure model taking into account the influence of initial cracks according to claim 2 is characterized in that: The model body and the crack area are cast synchronously using different concretes, and the step S3 includes setting a main template, and the casting area of ​​the model body and the crack area are separated by a wire mesh, and an auxiliary template is provided on the upper part of the wire mesh.

5. The new method for preparing an underground structure model taking into account the influence of initial cracks according to claim 4 is characterized in that: The crack area is surrounded by the casting area of ​​the model body, and the interfaces between the crack area and the casting area are separated by wire mesh. The auxiliary formwork includes a first formwork and a second formwork. The first formwork and the second formwork cooperate with each other, and both ends of the second formwork extend and are connected to the side formwork of the main formwork. The first formwork is fixed to the side formwork with tension bolts, and the tension bolts include limit plates fixed or threadedly connected to the screw rod, and the limit plates and nuts are fixed together on the first formwork and the side formwork.

6. The new method for preparing an underground structure model taking into account the influence of initial cracks according to claim 5, characterized in that: The side formwork is provided with tension bars, which are arranged at the upper and lower parts of the side formwork. Two vertical bars are arranged on the outer wall of the side formwork, and the tension bars are arranged between the two vertical bars. The upper side of the side formwork includes a fixed plate and a flip plate rotatably connected to the side formwork body. A limit bar is provided on the outer side of the flip plate, and the limit bar is rotatably connected to the formwork system.

7. A new method for preparing an underground structure model taking into account the influence of initial cracks according to claim 6, characterized in that: The tension bolts are arranged between two vertical ribs, and the limit strips are provided with screw holes, through which the tension bolts pass.

8. The new method for preparing an underground structure model taking into account the influence of initial cracks according to claim 7, characterized in that: The middle part of the limit strip protrudes outwards, and a groove is formed inside to accommodate the vertical ribs. The upper end of the vertical ribs is concave inwards to form an L shape, and the tensioning ribs are arranged on the inwardly concave L-shaped curved part.

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