Foundation pit supporting method and supporting structure

Abstract

The invention relates to the technical field of foundation pit construction, and provides a foundation pit supporting method and a supporting structure.The method comprises the steps that the design length of a foundation pit and the section length of a box culvert are obtained; determining a first construction foundation pit, a second construction foundation pit... an nth construction foundation pit, a box culvert parting seam, a first interval and a second interval according to the design length of the foundation pit and the section length of the box culvert; determining a first diagonal bracing site and a second diagonal bracing site of the first construction foundation pit; a first vertical supporting part, a first supporting part and a first opposite supporting part are arranged; the first construction foundation pit is excavated to the designed bottom; arranging a first box culvert group, a second supporting part and a second diagonal bracing part; the first diagonal bracing part and the first supporting part are sequentially dismantled; arranging a second box culvert group; groove backfilling is conducted on the first construction foundation pit; and the second diagonal bracing part and the second supporting part are sequentially dismantled. According to the foundation pit supporting method and the supporting structure, the problem that in the prior art, a large-width and long-distance foundation pit is difficult to construct is solved.

Description

Technical Field

[0001] The invention relates to the technical field of foundation pit construction, and in particular to a foundation pit supporting method and a supporting structure. Background Art

[0002] Generally, linear projects have narrow structures and short lengths, so conventional support can meet construction requirements. However, for linear projects with long lengths, large structural widths, and limited surrounding environments, on the one hand, it is relatively difficult to set up support, and on the other hand, conventional support methods are difficult to meet the safety construction requirements of the project. Summary of the invention

[0003] The present invention provides a foundation pit supporting method and supporting structure, aiming to solve the problem that the construction of foundation pits with large width and long distance in traditional technologies is relatively difficult.

[0004] In view of the problems existing in the prior art, an embodiment of the present invention provides a foundation pit supporting method, comprising: Obtain the designed length of foundation pit and the length of box culvert section; Determine the first construction pit, the second construction pit, ... the nth construction pit, the box culvert joint, the first spacing, and the second spacing according to the designed length of the foundation pit and the section length of the box culvert; Determine a first pair of supporting points and a second pair of supporting points of the first construction pit respectively according to the box culvert joints, the first spacing, and the second spacing; First vertical support parts are respectively arranged on both sides of the first construction pit; Taking the bottom side of the first construction pit as a basis, a first support part is provided at each of the first pair of support points; The first pair of supporting parts are arranged based on the first vertical supporting parts and the first supporting parts on both sides; Digging the first construction pit to the designed bottom; Setting a first box culvert group in the first construction pit; Taking the upper end surface of the first box culvert group as a basis, a second support portion is provided at each of the second pair of support points; The second supporting parts are arranged based on the first vertical supporting parts and the second supporting parts on both sides; Remove the first pair of support parts and the first support parts in sequence; Arranging a second box culvert group in the first construction pit and at the inner interval of the first box culvert group; Backfilling the first construction pit with a trench; The second pair of supporting parts and the second supporting parts are removed in sequence.

[0005] According to a foundation pit supporting method provided by the present invention, the section length of the box culvert is a, the first spacing is ab, the second spacing is a+b, and the value range of b is 1≤b≤3.

[0006] According to a foundation pit supporting method provided by the present invention, determining the first pair of supporting points and the second pair of supporting points of the first construction foundation pit respectively according to the box culvert joints, the first spacing and the second spacing comprises: Determine the first pair of support points on one side of the first box culvert joint; Alternately determining the second first pair of supporting points, the third first pair of supporting points, ... the nth first pair of supporting points by using the first spacing and the second spacing; Determine the first of the second pair of support points on the other side of the first of the box culvert joints; Alternately determining the second pair of the second supporting points, the third pair of the second supporting points, ... the nth pair of the second supporting points by using the second spacing and the first spacing; The adjacent first pair of supporting points and the second pair of supporting points are respectively arranged on both sides of the corresponding box culvert joint.

[0007] According to a foundation pit supporting method provided by the present invention, after first vertical supporting parts are respectively provided on both sides of the first construction foundation pit, the method further comprises: providing cap beams at the ends of each first vertical supporting part on both sides.

[0008] According to a foundation pit supporting method provided by the present invention, before and / or after sequentially removing each of the second pairs of support parts and each of the second support parts, it also includes: repeating the above steps to construct the second construction foundation pit, the third construction foundation pit...the nth construction foundation pit.

[0009] According to a foundation pit supporting method provided by the present invention, the first vertical supporting part, the first vertical supporting part, and the first supporting part include steel-cement soil mixing piles, and the second supporting part, the first pair of supporting parts, and the second pair of supporting parts include steel columns.

[0010] The present invention further provides a foundation pit support structure, using any of the foundation pit support methods described above, the foundation pit support structure comprising: The first support member includes two first vertical supporting parts, a first supporting part and a first pair of supporting parts, wherein the two first vertical supporting parts are used to be arranged on both sides of the foundation pit opposite to each other, the two ends of the first pair of supporting parts are respectively connected to the ends of the first vertical supporting parts, one end of the first supporting part is connected to the first pair of supporting parts, and the other end is used to be connected to the bottom side of the foundation pit; and The second support member is used to be arranged opposite to the first support member along the extension direction of the foundation pit, and the second support member includes a second supporting portion and a second pair of supporting portions, both ends of the second pair of supporting portions are respectively connected to the end portions of each of the first vertical supporting portions, one end of the second support portion is connected to the second pair of supporting portions, and the other end is used to be connected to the upper end surface of the box culvert.

[0011] According to a foundation pit supporting structure provided by the present invention, a first crown beam is provided at the end of each of the first vertical supporting parts, and both ends of the first pair of supporting parts and the second pair of supporting parts are respectively connected to the first crown beam.

[0012] The foundation pit support method provided by the present invention can be constructed in sections simultaneously or sequentially to meet the construction requirements of long distances by segmenting the construction. In addition, the positions of the first pair of supports and the second pair of supports are set by planning the construction parameters, and the support measures are removed sequentially during the construction of the box culvert body. On the one hand, the safety and stability of the support can be ensured, and on the other hand, the support measures have little impact on the main construction structure, which helps to significantly improve the construction efficiency and quality of the main structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0014] Figure 1 It is a schematic diagram of the process of the foundation pit supporting method provided by the present invention; Figure 2 It is a structural schematic diagram of the foundation pit supporting structure provided by the present invention; Figure 3 yes Figure 2 A schematic diagram of the cross-sectional structure of the first pair of supporting parts; Figure 4 yes Figure 2 Schematic diagram of the cross-sectional structure of the second pair of supporting parts.

[0015] Figure numerals: 100, foundation pit supporting structure; 110, first supporting member; 111, first vertical supporting portion; 112, first supporting portion; 113, first pair of supporting portions; 114, first crown beam; 120, second supporting member; 121, second supporting portion; 122, second pair of supporting portions; 200, box culvert. DETAILED DESCRIPTION

[0016] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0017] In the description of the embodiments of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "connected" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the embodiments of the present invention can be understood according to specific circumstances.

[0018] In the description of the embodiments of the present invention, it should be noted that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the embodiments of the present invention.

[0019] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0020] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0021] The disclosure below provides many different embodiments or examples to realize different structures of the present invention. In order to simplify the disclosure of the present invention, the parts and settings of specific examples are described below. Of course, they are only examples, and the purpose is not to limit the present invention. In addition, the present invention can repeat reference numbers and / or letters in different examples. This repetition is for the purpose of simplicity and clarity, and does not itself indicate the relationship between the various embodiments and / or settings discussed. In addition, the present invention provides various specific processes and examples of materials, but those of ordinary skill in the art can be aware of the applicability of other processes and / or the use of other materials.

[0022] Combine the following Figure 1-Figure 4 The invention describes a foundation pit supporting method and a supporting structure.

[0023] In view of the fact that the traditional technology is difficult to construct a large width and long distance foundation pit, please refer to the following for the problems existing in the existing technology. Figure 1 The embodiment of the present invention provides a foundation pit supporting method, comprising: S10, obtaining the design length of the foundation pit and the section length of the box culvert; S20, determining the first construction pit, the second construction pit, ... the nth construction pit, the box culvert joint, the first spacing, and the second spacing according to the designed length of the foundation pit and the section length of the box culvert; S30, determining a first pair of supporting points and a second pair of supporting points of the first construction pit respectively according to the box culvert joints, the first spacing, and the second spacing; S40, respectively setting first vertical support parts on both sides of the first construction pit; S50, using the bottom side of the first construction pit as a basis, setting a first support part at each of the first pair of support points; S60, setting first supporting parts based on the first vertical supporting parts and the first supporting parts on both sides; S70, digging the first construction pit to the designed bottom; S80, setting a first box culvert group in the first construction pit; S90, using the upper end surface of the first box culvert group as a basis, providing a second support portion at each of the second pair of support points; S100, setting second supporting parts based on the first vertical supporting parts and the second supporting parts on both sides; S110, removing each of the first pair of supporting parts and each of the first supporting parts in sequence; S120, installing a second box culvert group in the first construction pit and at an inner interval of the first box culvert group; S130, backfilling the first construction foundation pit; S140, removing each of the second pair of supporting parts and each of the second supporting parts in sequence.

[0024] In the technical solution provided by the present invention, it is first necessary to obtain the design parameters of the foundation pit. Generally, the construction design department will determine the total length of the foundation pit and the single section length of the box culvert. According to the designed total length of the foundation pit, the length and position of each section of the construction pit can be planned in combination with the topography. The length of each section of the construction pit can be equal or unequal, and a section of the foundation pit at a continuous terrain can be used as a section of the construction pit. The specific length can be determined according to the actual situation, so that the first construction pit, the second construction pit...the nth construction pit can be planned.

[0025] Taking the first construction pit as an example, multiple box culverts will be set up in the first construction pit. According to the length of a single section of the box culvert, the position of the box culvert joints on both sides of each box culvert in the first construction pit can also be determined. This is a prior art, so the specific process will not be repeated. The first spacing and the second spacing are related to the setting position of the first support part and the second support part. The first support part and the second support part are alternately arranged. It is necessary to jointly determine the appropriate first spacing and second spacing according to the position of the box culvert joint and the length of the box culvert section. In this way, it will not affect the construction of the main structure, and can provide a stable support effect on the foundation pit. The specific implementation examples of the relevant calculation methods and setting methods will be provided later in this specification.

[0026] After the box culvert joints, the first spacing and the second spacing are determined, the first pair of support points and the second pair of support points of the first construction pit can be determined respectively. The first pair of support points are used to place the first pair of support parts, and the second pair of support points are used to place the second pair of support parts.

[0027] The above are all preparatory steps for the construction of the first construction pit. After the specific position of each support component is determined, the actual construction can be carried out.

[0028] Taking the first construction pit as an example, first, it is necessary to set the first vertical support parts on both sides of the first construction pit. The first vertical support parts are driven vertically into the ground from the ground, and the construction method is the same as the prior art. After the first vertical support parts on both sides are built, it is necessary to drive the first support parts vertically downward at the location of the first pair of support points. It should be noted that the first pair of support parts are parallel to the bottom surface of the foundation pit, and the support point of the first support part is preferably located near the midpoint of the first pair of support parts, so that the support is more stable. After the first support parts are set, the first pair of support parts can be set at the ends of each first support part, and the two ends of the first pair of support parts are respectively connected to the first vertical support parts on both sides, so that both sides of the foundation pit can be supported to ensure the stability of the main structure.

[0029] It should be noted that, in general, after the first vertical support parts on both sides are constructed, it is necessary to set a crown beam at the end of the first vertical support parts on both sides, and use the crown beam combination to connect the first vertical support parts on each side. After the crown beam is set, the two ends of the first pair of support parts are actually connected to the crown beam.

[0030] When the first supporting part, the first vertical supporting part and the first pair of supporting parts are set, the first supporting process is completed, and the first construction pit can be excavated at this time. During the excavation process, the entire first construction pit structure tends to be stable.

[0031] Furthermore, when the first construction pit is excavated to the designed bottom, the first box culvert group needs to be constructed. Figure 2-Figure 4 Taking this section as an example, the first box culvert group includes the first box culvert, the third box culvert and the fifth box culvert, that is, the box culverts are constructed at intervals. This is an existing process, so it will not be described in detail. It should be noted that the previously determined box culvert joints are located on both sides of each box culvert and exist as deformation joints of the box culvert. Since the first pair of support parts and the second pair of support parts are constructed at intervals, they will not affect the construction of the first box culvert group, and the two will not interfere with each other.

[0032] Furthermore, after the first box culvert group is set up, the second box culvert group needs to be set up. Since the setting position of the second box culvert group is different from that of the first box culvert group, the support of the second box culvert group needs to be re-set, and since the first box culvert group has been set up, the support facilities of the first box culvert group can be dismantled. Specifically, first, it is necessary to use the upper end surface of the first box culvert group as a basis, and set a second support part at the second pair of support points. The second support part is used to support the second pair of support parts. Since the first box culvert group is selected as the bottom support, the setting of the second support part is simpler and faster than the setting of the first support part. Similarly, after the second support part is set up, it is necessary to set the second pair of support parts based on the first vertical support parts and the second support parts on both sides.

[0033] Since the first vertical support, the second support and the second pair of support can effectively support the first construction pit, the first pair of support and the first support can be removed. The removal is also to avoid affecting the construction of the second box culvert group. After the removal is completed, the second box culvert group can be set up at the inner interval of the first box culvert group. Figure 2 The second box culvert, the fourth box culvert and the sixth box culvert are shown in the figure. After the first box culvert group and the second box culvert group are set, the entire first construction pit needs to be backfilled. After backfilling, the second pair of supports and the second support can be removed to complete the construction process of the first construction pit.

[0034] The foundation pit support method provided by the present invention can be constructed in sections simultaneously or sequentially to meet the construction requirements of long distances by segmenting the construction. In addition, the positions of the first pair of supports and the second pair of supports are set by planning the construction parameters, and the support measures are removed sequentially during the construction of the box culvert body. On the one hand, the safety and stability of the support can be ensured, and on the other hand, the support measures have little impact on the main construction structure, which helps to significantly improve the construction efficiency and quality of the main structure.

[0035] Specifically, the box culvert section length is a, the first spacing is ab, the second spacing is a+b, and the value range of b is 1≤b≤3. In an embodiment provided by the present invention, the value of b is 2. Figure 2 For example, the section length of the box culvert is 10m, the first spacing is 8m, and the second spacing is 12m.

[0036] Further, S30, determining a first pair of supporting points and a second pair of supporting points of the first construction pit respectively according to the box culvert joints, the first spacing, and the second spacing includes: S31, determining the first pair of support points on one side of the first box culvert joint; S32, alternately determining the second first pair of supporting points, the third first pair of supporting points, ... the nth first pair of supporting points by using the first spacing and the second spacing; S33, determining the first of the second pair of support points on the other side of the first box culvert joint; S34, alternately determining the second pair of the second supporting points, the third pair of the second supporting points, ... the nth pair of the second supporting points by using the second spacing and the first spacing; The adjacent first pair of supporting points and the second pair of supporting points are respectively arranged on both sides of the corresponding box culvert joint.

[0037] See also Figure 2 In a certain embodiment, the first first pair of supporting points is located on the right side of the first box culvert joint, the distance between the second first pair of supporting points and the first first pair of supporting points is the first distance (8m in the figure); the distance between the third first pair of supporting points and the second first pair of supporting points is the second distance (12m in the figure); the distance between the fourth first pair of supporting points and the third first pair of supporting points is the first distance (8m in the figure), and the distance between the fifth first pair of supporting points and the fourth first pair of supporting points is the second distance (12m in the figure). By alternating in this way, all the first pairs of supporting points can be determined.

[0038] Approximately, the first second pair of supporting points is located on the left side of the first box culvert joint, the distance between the second second pair of supporting points and the first second pair of supporting points is the second distance (12m in the figure); the distance between the third second pair of supporting points and the second second pair of supporting points is the first distance (8m in the figure); the distance between the fourth second pair of supporting points and the third second pair of supporting points is the second distance (12m in the figure), and the distance between the fifth second pair of supporting points and the fourth second pair of supporting points is the first distance (8m in the figure). By alternating in this way, all the second pairs of supporting points can be determined.

[0039] It should be noted that the adjacent first pair of supporting points and the second pair of supporting points are respectively arranged on both sides of the corresponding box culvert joint, so that when the first box culvert group is set up, the first supporting part and the first pair of supporting parts on the first pair of supporting points are staggered with the positions of the first box culvert group, which will not affect the construction of the first box culvert group; when the second box culvert group is set up, the second supporting part and the second pair of supporting parts on the second pair of supporting points are staggered with the positions of the second box culvert group, which will not affect the construction of the second box culvert group.

[0040] Finally, before and / or after sequentially removing each of the second pairs of support parts and each of the second support parts, the method further includes: repeating the above steps to construct the second construction pit, the third construction pit...the nth construction pit. That is, the construction method of the second construction pit, the third construction pit...the nth construction pit is the same as that of the first construction pit, and the construction sequence of several construction pits can be carried out sequentially or simultaneously, which is not limited by the present invention. It should be noted that since the single section length of the box culvert in a construction project should be the same, the box culvert joints, the first spacing and the second spacing can use the parameters of the first construction pit.

[0041] Furthermore, the first vertical supporting part, the first vertical supporting part, and the first supporting part include steel-cement-soil mixing piles, which can also be concrete piles; the second supporting part, the first pair of supporting parts, and the second pair of supporting parts include steel columns, which can also be precast concrete columns.

[0042] On the basis of the above-mentioned support method, the present invention also provides a foundation pit support structure 100, comprising: a first support member 110, comprising two first vertical support parts 111, a first support part 112 and a first pair of support parts 113, the two first vertical support parts 111 are used to be relatively arranged on both sides of the foundation pit, the two ends of the first pair of support parts 113 are respectively connected to the end parts of each first vertical support part 111, one end of the first support part 112 is connected to the first pair of support parts 113, and the other end is used to be connected to the bottom side of the foundation pit; and, a second support member 120, which is used to be arranged opposite to the first support member 110 along the extension direction of the foundation pit, the second support member 120 comprises a second support part 121 and a second pair of support parts 122, the two ends of the second pair of support parts 122 are respectively connected to the end parts of each first vertical support part 111, one end of the second support part 121 is connected to the second pair of support parts 122, and the other end is used to be connected to the upper end surface of the box culvert 200. Furthermore, each first vertical support portion 111 has a first crown beam 114 at its end, and both ends of the first pair of support portions 113 and the second pair of support portions 122 are respectively connected to the first crown beam 114. The detailed application of the foundation pit support structure 100 can refer to the support method, and the present invention will not repeat it.

[0043] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A foundation pit support method, characterized in that: include: Obtain the designed length of foundation pit and the length of box culvert section; Determine the first construction pit, the second construction pit, ... the nth construction pit, the box culvert joint, the first spacing, and the second spacing according to the designed length of the foundation pit and the section length of the box culvert; Determine a first pair of supporting points and a second pair of supporting points of the first construction pit respectively according to the box culvert joints, the first spacing, and the second spacing; First vertical support parts are respectively arranged on both sides of the first construction pit; Taking the bottom side of the first construction pit as a basis, a first support part is provided at each of the first pair of support points; The first pair of supporting parts are arranged based on the first vertical supporting parts and the first supporting parts on both sides; Digging the first construction pit to the designed bottom; Setting a first box culvert group in the first construction pit; Taking the upper end surface of the first box culvert group as a basis, a second support portion is provided at each of the second pair of support points; The second supporting parts are arranged based on the first vertical supporting parts and the second supporting parts on both sides; Remove the first pair of support parts and the first support parts in sequence; Arranging a second box culvert group in the first construction pit and at the inner interval of the first box culvert group; Backfilling the first construction pit with a trench; The second pair of supporting parts and the second supporting parts are removed in sequence.

2. The foundation pit supporting method according to claim 1, characterized in that: The section length of the box culvert is a, the first spacing is ab, the second spacing is a+b, and the value range of b is 1≤b≤3.

3. The foundation pit supporting method according to claim 2, characterized in that: Determining the first pair of supporting points and the second pair of supporting points of the first construction pit according to the box culvert joints, the first spacing, and the second spacing comprises: Determine the first pair of support points on one side of the first box culvert joint; Alternately determining the second first pair of supporting points, the third first pair of supporting points, ... the nth first pair of supporting points by using the first spacing and the second spacing; Determine the first of the second pair of support points on the other side of the first of the box culvert joints; Alternately determining the second pair of the second supporting points, the third pair of the second supporting points, ... the nth pair of the second supporting points by using the second spacing and the first spacing; The adjacent first pair of supporting points and the second pair of supporting points are respectively arranged on both sides of the corresponding box culvert joint.

4. The foundation pit supporting method according to claim 1, characterized in that: After first vertical supporting parts are respectively provided on both sides of the first construction pit, the method further includes: providing cap beams at the ends of each first vertical supporting part on both sides.

5. The foundation pit supporting method according to claim 1, characterized in that: Before and / or after sequentially removing each of the second pairs of support parts and each of the second support parts, the method further includes: repeating the above steps to construct the second construction pit, the third construction pit, ... the nth construction pit.

6. The foundation pit supporting method according to claim 1, characterized in that: The first vertical supporting part, the first vertical supporting part, and the first supporting part include steel-cement-soil mixing piles, and the second supporting part, the first pair of supporting parts, and the second pair of supporting parts include steel columns.

7. A foundation pit support structure, characterized in that: The foundation pit supporting method according to any one of claims 1 to 6 is applied, wherein the foundation pit supporting structure comprises: The first support member includes two first vertical supporting parts, a first supporting part and a first pair of supporting parts, wherein the two first vertical supporting parts are used to be arranged on both sides of the foundation pit opposite to each other, the two ends of the first pair of supporting parts are respectively connected to the ends of the first vertical supporting parts, one end of the first supporting part is connected to the first pair of supporting parts, and the other end is used to be connected to the bottom side of the foundation pit; and The second support member is used to be arranged opposite to the first support member along the extension direction of the foundation pit, and the second support member includes a second supporting portion and a second pair of supporting portions, both ends of the second pair of supporting portions are respectively connected to the end portions of each of the first vertical supporting portions, one end of the second support portion is connected to the second pair of supporting portions, and the other end is used to be connected to the upper end surface of the box culvert.

8. The foundation pit supporting structure according to claim 6, characterized in that: A first crown beam is disposed at the end of each of the first vertical supporting parts, and both ends of the first pair of supporting parts and the second pair of supporting parts are respectively connected to the first crown beam.

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