WO2020114149A1

WO2020114149A1 - Sample making die for rock body structural surface shear test

Info

Publication number: WO2020114149A1
Application number: PCT/CN2019/113866
Authority: WO
Inventors: 郑博文; 祁生文; 黄晓林; 郭松峰; 邹宇
Original assignee: 中国科学院地质与地球物理研究所
Priority date: 2018-12-03
Filing date: 2019-10-29
Publication date: 2020-06-11
Also published as: AU2019392985B2; AU2019392985A1; CN109342166A; CN109342166B

Abstract

A sample making die for a rock body structural surface shear test. In order to process shear test samples of rock body structural surfaces of different sizes and shapes so as to meet the research needs of shear characteristics of the rock body structural surfaces, the sample making die comprises a die body of a semi-open space surrounded by a front vertical plate (1), a rear vertical plate (2), a left side plate (3), a right side plate (4) and a bottom plate (5). The left side plate (3) and the right side plate (4) are both L-shaped. The left side plate (3) comprises a left side vertical plate (31) and a left side bottom plate (32). The right side plate (4) comprises a right side rear vertical plate (41) and a right side vertical plate (42). The sample making die further comprises a support (6), and the support (6) is provided at a lower side of the bottom plate (5) and is used for supporting the bottom plate (5). The structural design of the sample making die for the rock body structural surface shear test may comply with the fabrication of rock body structural surface shear test samples of different sizes and shapes.

Description

Sample making mold for shear test of rock structure surface

Technical field

The invention belongs to the field experiment field of rock mass mechanics, and particularly relates to a sample preparation mold used for the shear test of rock mass structural planes.

Background technique

The rock mass structural plane is formed in the development process of rock mass geological history, has a certain extension direction and length, and the thickness is relatively small, which controls the deformation and mechanical behavior of the rock mass. This shows that accurately grasping the mechanical properties of the structural plane is the core of evaluating the stability of rock engineering. The mechanical properties of rock mass structural planes are mainly manifested in normal deformation, shear deformation and shear strength. In the low stress area, the engineering rock mass instability mainly manifests in the shear deformation and failure of the rock mass along the structural plane. Therefore, the shear strength of the structural plane is commonly used as an important index for engineering rock mass stability evaluation.

Rock mass mechanics laboratory test research is the basis for rock mass constitutive model construction and engineering design numerical simulation. The indoor direct shear test has great advantages in loading path control, normal parameter and shear parameter acquisition, and is the preferred test method for characterizing the shear behavior of structural planes. Because the shear test of the structural plane is a destructive test and cannot be repeated, and the cost of sampling, transportation and sample preparation of natural rock structural plane samples is relatively high, therefore, cement mortar, high-strength gypsum, Concrete and other rock materials are used to make artificial rock mass structural plane samples. The parallel rock samples are tested in parallel to achieve the purpose of studying the shear characteristics of natural rock mass structural planes.

Based on this, the present invention proposes a new sample-making mold to process rock structure surface shear test samples of different sizes and shapes to meet the research needs of rock structure surface shear characteristics.

Summary of the invention

In order to solve the above-mentioned problems in the prior art, that is, to process the shear test samples of different sizes and shapes of rock mass structural planes to meet the research needs of the shear characteristics of rock mass structural planes, the present invention proposes a method for rock masses A sample preparation mold for a structural plane shear test. The sample preparation mold includes a semi-open space mold body surrounded by a front vertical plate, a rear vertical plate, a left side plate, a right side plate, and a bottom plate, wherein the left side plate And the right side plate are L-shaped, the left side plate includes a left vertical plate and a left bottom plate, the right side plate includes a right rear vertical plate and a right vertical plate; the sample preparation mold further includes A bracket provided on the lower side of the bottom plate for supporting the bottom plate.

In the above preferred embodiment of the sample preparation mold used for the shear test of the rock structure surface, the connection between the left vertical plate and the left bottom plate of the L-shaped left side plate is provided along the width of the left vertical plate There is a first latch, and a lower part of the front vertical plate is provided with a long-shaped groove to the left along the opening of the front vertical plate, which matches the opening direction of the first plug, and the long-shaped groove can Pass through the first latch, and fix the left side plate and the front vertical plate by means of bolts.

In the above preferred embodiment of the sample preparation mold used for the shear test of the rock structure surface, the inner side of the left side vertical plate is horizontally provided with a second bolt and a third bolt, and the lower end of the bottom plate is horizontally provided with A first U-shaped fork and a second U-shaped fork with opening directions matching the second latch and the third latch, the inside of the first U-shaped fork and the inside of the second U-shaped fork It is possible to pass through the second latch and the third latch, respectively, and fix the left side plate and the bottom plate by means of bolts.

In the above preferred embodiment of the sample preparation mold used for the shear test of the rock structure surface, the rear area on the upper side of the bottom plate is horizontally provided with a fourth bolt and a fifth bolt, and the outer side of the rear vertical plate is provided horizontally There are a third U-shaped fork and a fourth U-shaped fork that are rearward in the opening direction matching the fourth plug and the fifth plug, the inner side of the third U-shaped fork and the fourth U-shaped fork The inner side can pass through the fourth plug and the fifth plug, respectively, and fix the bottom plate and the rear vertical plate by means of bolts.

In the above preferred embodiment of the sample preparation mold used for the shear test of the rock structure surface, the inner side of the rear vertical plate is horizontally provided with at least one row of through bolt holes, and the outer side of the right rear vertical plate is horizontally provided with At least one row of semi-through bolt holes matching the through bolt holes, after the outer side of the right rear vertical plate abuts against the inner side of the rear vertical plate, the bolt can pass through the through bolt holes and penetrate to The semi-through bolt holes fix the rear vertical plate and the right side plate.

In the above preferred embodiment of the sample preparation mold for the rock structure surface shear test, the through bolt holes and the semi-through bolt holes are both in two rows, and the number of semi-through bolt holes in each row is less than or equal to each row The number of through bolt holes; and/or after the rear vertical plate is fixed to the right side plate, the left end of the right rear vertical plate abuts the inner side of the left vertical plate, the right side vertical The front end of the board is in contact with the front vertical board.

In the above-mentioned preferred embodiment of the sample preparation mold for the rock mass structural plane shear test, the inner side of the right rear vertical plate is set to a straight type or a zigzag type.

In the above preferred embodiment of the sample preparation mold used for the shear test of the rock structure surface, between the elongated groove of the front vertical plate and the first plug, the first U under the bottom plate Between the second fork and the third latch, between the second U-shaped fork and the third latch, between the third U-shaped fork outside the rear riser and the fourth latch, and the The relative positions between the fourth U-shaped fork and the fifth plug can be adjusted so that the sample preparation mold can produce rock structure surface shear test samples of different sizes and different shapes.

In the above preferred embodiment of the sample preparation mold used for the shear test of the rock structure surface, the bracket includes an upper end cap, a lower end cap, and a telescopic rod located between the upper end cap and the lower end cap. The rod includes a first rod, a second rod nested in the first rod, a third rod nested in the second rod, and a fourth rod nested in the third rod Rod, the first support rod and the second support rod are connected by a first thread buckle, and the length of the second support rod extending beyond the first support rod can be adjusted by rotating the first thread buckle; The second support bar and the third support bar are connected by a second thread buckle, and the length of the third support bar extending beyond the second support bar can be adjusted by rotating the second thread buckle; the third The support rod and the fourth support rod are connected by a third thread buckle, and the length of the fourth support rod extending out of the third support rod can be adjusted by rotating the third thread buckle.

In the above preferred embodiment of the sample preparation mold used for the shear test of the rock structure surface, a first groove is provided on the lower side of the bottom plate, and a second groove is provided on the upper side of the left bottom plate. The upper end cap of the bracket is embedded in the first groove, the lower end cap of the bracket is embedded in the second groove, and thus the bracket is fixed between the bottom plate and the left side bottom plate.

The sample preparation mold provided by the present invention utilizes an L-shaped left side plate and an L-shaped right side plate to form a semi-open space with a front vertical plate, a rear vertical plate, and a bottom plate, respectively, and supports the bottom plate with a bracket. In some specific embodiments, according to the structural design of the sample preparation mold of the present invention, the bracket is a retractable bracket, between the elongated groove of the front vertical plate and the first latch, and the first U-shaped fork on the lower side of the bottom plate The relative positions between the second bolt, the second U-shaped fork and the third bolt, the third U-shaped fork and the fourth bolt outside the rear riser, and the fourth U-shaped fork and the fifth bolt It can be adjusted, and further by adjusting the retractable bracket so that the sample-making mold can produce rock structure surface shear test samples of different sizes and shapes.

BRIEF DESCRIPTION

1 is a schematic front view of a sample preparation mold according to an embodiment of the present invention;

2 is a schematic left side view of a sample preparation mold according to an embodiment of the present invention;

3 is a schematic top view of a sample preparation mold according to an embodiment of the present invention;

4a is a schematic front view of the left side plate of the sample preparation mold of the embodiment of the present invention;

4b is a schematic plan view of the left side plate of the sample preparation mold of the embodiment of the present invention;

5 is a schematic front view of the front vertical plate of the sample preparation mold of the embodiment of the present invention;

6a is a schematic front view of a bottom plate of a sample preparation mold according to an embodiment of the present invention;

6b is a schematic left side view of the bottom plate of the sample preparation mold of the embodiment of the present invention;

7a is a schematic front view of the rear vertical plate of the sample preparation mold of the embodiment of the present invention;

7b is a schematic plan view of the rear vertical plate of the sample preparation mold of the embodiment of the present invention;

8a is a schematic front view of the right side plate of the sample preparation mold of the embodiment of the present invention;

8b is a schematic plan view of the right side plate of the sample preparation mold of the embodiment of the present invention;

9a is a schematic diagram of a bracket structure of a sample preparation mold in a shortened state according to an embodiment of the present invention;

FIG. 9b is a schematic diagram of the stent structure of the sample preparation mold in the extended state of the embodiment of the present invention.

detailed description

In order to make the embodiments, technical solutions and advantages of the present invention more obvious, the technical solutions of the present invention will be described clearly and completely in conjunction with the drawings. Obviously, the described embodiments are part of the embodiments of the present invention, but not all Examples. Those skilled in the art should understand that these embodiments are only used to explain the technical principles of the present invention, and are not intended to limit the protection scope of the present invention.

Referring first to FIGS. 1-3, FIG. 1 is a front view of a sample preparation mold of an embodiment of the invention; FIG. 2 is a left side view of a sample preparation mold of an embodiment of the invention; FIG. 3 is an embodiment of the invention View of the sample preparation mold. As shown in FIGS. 1-3, the sample preparation mold for the rock structure plane shear test of the present invention includes a front vertical plate 1, a rear vertical plate 2, a left side plate 3, a right side plate 4, a bottom plate 5 and a bracket 6 The front vertical plate 1, the rear vertical plate 2, the left side plate 3, the right side plate 4 and the bottom plate 5 form a semi-open space mold body, and the bracket 6 is provided on the lower side of the bottom plate 5 to support the bottom plate 5. Among them, the left side panel 3 and the right side panel 4 are both L-shaped. The structure of the left side panel 3 and the right side panel 4 and the left side panel 3, the right side panel 4 and the front vertical panel are respectively 1. The connection relationship between the rear vertical plate 2 and the bottom plate 5 and the bracket 6 and its connection relationship are further described.

4a and 4b, FIG. 4a is a schematic front view of the left side plate of the sample preparation mold of the embodiment of the present invention; FIG. 4b is a schematic top view of the left side plate of the sample preparation mold of the embodiment of the present invention. As shown in FIGS. 4a and 4b, the L-shaped left side plate 3 includes a left side vertical plate 31 and a left side bottom plate 32. The connection between the left side vertical plate 31 and the left side bottom plate 32 is provided along the width direction of the left side vertical plate 31 A pin 33, as shown in FIG. 4b, the first pin 33 points forward.

Referring to FIG. 5, FIG. 5 is a schematic front view of a front vertical plate of a sample preparation mold according to an embodiment of the present invention. As shown in FIG. 5, the lower portion of the front vertical plate 1 is provided with a long-shaped groove 11 to the left along the length of the front vertical plate 1 in the opening direction matching the first latch 33. Further, the long-shaped groove 11 The upper and lower sides of the left end are sharpened, and the right end of the elongated groove 11 is semicircular. When assembling the front vertical plate 1 and the left side plate 3, the elongated groove 11 can pass through the first latch 33 and fix the left side plate 3 and the front vertical plate 1 by means of bolts M. For example, after the elongated groove 11 passes through the first latch 33, the bolt M rotates on the first latch 33 to press the elongated groove 11, thereby fastening the left side plate 3 and the front vertical plate 1. Preferably, the first plug 33 is a cylindrical plug.

Referring back to FIGS. 4a and 4b, the inside of the left side riser 31 is horizontally provided with a second latch 34 and a third latch 35. Specifically, the second latch 34 and the third latch 35 have the same structure, and are horizontally arranged side by side along the longitudinal direction of the left side vertical plate 31 (that is, in the direction from the back to the front of the left side plate) and are closely arranged inside the left side vertical plate 31 Lower area. Preferably, the second pin 34 and the third pin 35 are cylindrical pins.

6a and 6b, FIG. 6a is a schematic front view of the bottom plate of the sample preparation mold of the embodiment of the present invention; FIG. 6b is a schematic left side view of the bottom plate of the sample preparation mold of the embodiment of the present invention. As shown in FIGS. 6a and 6b, the left end of the bottom side of the bottom plate 5 is horizontally provided with a first U-shaped fork 51 and a second U-shaped fork 52 that are downward in the opening direction to match the second latch 34 and the third latch 35. When assembling the left side plate 3 and the bottom plate 5, the inside of the first U-shaped fork 51 and the inside of the second U-shaped fork 52 can pass through the second latch 34 and the third latch 35, respectively, and the left side panel is bolted M 3 is fixed with the bottom plate 5. For example, the first U-shaped fork 51 passes through the second latch 34, the second U-shaped fork 52 passes through the third latch 35, and the bolt M rotates on the second latch 34 and the third latch 35 to press the first U-shaped fork 51 and the second U-shaped fork 52 to fasten the left side plate 3 and the bottom plate 5. 6a and 6b, the rear area on the upper side of the bottom plate 5 is horizontally provided with a fourth latch 53 and a fifth latch 54.

7a and 7b, FIG. 7a is a schematic front view of the rear vertical plate of the sample preparation mold of the embodiment of the present invention; FIG. 7b is a schematic plan view of the rear vertical plate of the sample preparation mold of the embodiment of the present invention. As shown in FIGS. 7a and 7b, the outer side of the rear vertical plate 2 is horizontally provided with a third U-shaped fork 21 and a fourth U-shaped fork 22 that are rearward in the opening direction to match the fourth latch 53 and the fifth latch 54. When the rear riser 2 and the bottom plate 5 are assembled, the inside of the third U-shaped fork 21 and the inside of the fourth U-shaped fork 22 pass through the fourth latch 53 and the fifth latch 54 respectively, and the bottom plate 5 and the rear The vertical plate 2 is fixed. For example, the third U-shaped fork 21 passes through the fourth pin 53 and the fourth U-shaped fork 22 passes through the fifth pin 54, and the bolt M rotates on the fourth pin 53 and the fifth pin 54 to press the third U-shaped fork 21 and the fourth U-shaped fork 22, thereby fastening the rear riser 2 and the bottom plate 5. 7a and 7b, the inner side of the rear riser 2 is horizontally provided with at least one row of through bolt holes 23. In this embodiment, the through bolt holes 23 are in two rows, and four are provided in each row.

8a and 8b, FIG. 8a is a schematic front view of the right side plate of the sample preparation mold of the embodiment of the present invention; FIG. 8b is a schematic top view of the right side plate of the sample preparation mold of the embodiment of the present invention. As shown in FIGS. 8a and 8b, the L-shaped right side plate 4 includes a right rear vertical plate 41 and a right vertical plate 42. The outer side of the right rear vertical plate 41 is horizontally provided with at least one row matching the through bolt holes 23 Semi-through bolt hole 43. In this embodiment, the semi-through bolt holes 43 are in two rows, and four are provided in each row. When the right side plate 4 and the rear vertical plate 2 are assembled, the outer side of the right rear vertical plate 41 abuts against the inner side of the rear vertical plate 2. At this time, the semi-through bolt holes 43 and the through bolt holes 23 are aligned, and the bolt M is worn The through bolt holes 23 are penetrated and penetrated into the semi-through bolt holes 43 to fix the rear riser 2 and the right side plate 4. Further, after the rear vertical plate 2 and the right side plate 4 are fixed, the left end of the right rear vertical plate 41 abuts against the inside of the left vertical plate 31, and the front end of the right vertical plate 42 contacts the front vertical plate 1.

It should be noted here that the length of the right rear vertical plate 41 can be flexibly selected for different sizes. According to different sizes and shapes of the right rear vertical plate 41, different numbers of halves are provided on the right rear vertical plate 41 Through the bolt hole 43. For example, based on the length of the right rear riser 41 shown in FIGS. 8a and 8b, when the length of the right rear riser 41 is reduced by half, the number of semi-through bolt holes 43 in each row can be reduced by two No, these do not deviate from the protection scope of the present invention. In addition, the inner side of the right rear vertical plate 41 may be set to a straight type or a zigzag type, or may be set to other forms according to actual needs by those skilled in the art.

9a and 9b, FIG. 9a is a schematic diagram of the stent structure of the sample preparation mold in the shortened state of the embodiment of the present invention; FIG. 9b is a schematic diagram of the stent structure of the sample preparation mold in the extended state of the embodiment of the present invention. As shown in FIGS. 9a and 9b, the bracket 6 includes an upper end cap 61, a lower end cap 62, and a telescopic rod 63 located between the upper end cap 61 and the lower end cap 62. The telescopic rod 63 includes a first support rod 631, nested in the first support The second rod 632 of the rod 631, the third rod 633 nested in the second rod 632, and the fourth rod 634 nested in the third rod 633. The first rod 631 and the second rod 632 are connected by a first thread buckle 64, and the length of the second rod 632 extending out of the first rod 631 can be adjusted by rotating the first thread buckle 64; the second rod 632 and the second rod 632 The three supporting rods 633 are connected by the second threaded buckle 65, and the length of the third supporting rod 633 extending beyond the second supporting rod 632 can be adjusted by rotating the second threaded latch 65; the third supporting rod 633 and the fourth supporting rod 634 pass through the third The screw buckle 66 is connected. By rotating the third screw buckle 66, the length of the fourth supporting rod 634 extending beyond the third supporting rod 633 can be adjusted. In other words, the bracket 6 has a four-section telescopic range, and the height of the bottom plate 5 can be adjusted by adjusting the height of the bracket 6. Specifically, referring back to FIGS. 4a, 4b and FIGS. 6a and 6b, the bottom side of the bottom plate 5 is provided with a first groove 50, the upper side of the left side bottom plate 32 is provided with a second groove 30, and the upper end cap 61 of the bracket 6 is inserted into In the first groove 50, the lower end cap 62 of the bracket 6 is embedded in the second groove 30, and thus the bracket is fixed between the bottom plate 5 and the left bottom plate 32.

As described above, those skilled in the art can understand that between the elongated groove 11 of the front riser 1 and the first latch 33, and between the first U-shaped fork 51 and the second latch 34 under the bottom plate 5 , Between the second U-shaped fork 52 and the third bolt 35, the third U-shaped fork 21 and the fourth bolt 53 outside the rear riser 2 and the fourth U-shaped fork 22 and the fifth bolt 54 The positions can be adjusted, and the bracket 6 is further adjusted to enable the sample-making mold to manufacture rock structure surface shear test samples of different sizes and shapes.

For example, on the basis of the assembly of the above sample preparation mold, when processing a sawtooth rock sample, the size of the sample body is adjusted to adjust the space size of the mold body, while adjusting the height of the bracket, and using two saw teeth The right rear plate 41 of the model forms two sample-making molds, and the slurry material is poured into the two sample-making molds respectively, and the rock mass sample is finally formed after curing and curing, and then the rock bodies in the two sample-making molds are taken out For the specimen, rotate the two rock specimens clockwise and counterclockwise along the length of the rock specimen and merge the sawtooth surfaces. Install the combined rock specimens in the shear tester to perform the shear test .

So far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the accompanying drawings, but it is easily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent changes or replacements to the related technical features, and the technical solutions after these changes or replacements will fall within the protection scope of the present invention.

Claims

A sample-making mold for a rock mass structural plane shear test, characterized in that the sample-making mold includes a semi-open space surrounded by a front vertical plate, a rear vertical plate, a left side plate, a right side plate and a bottom plate Mold body,

Wherein, the left side plate and the right side plate are both L-shaped, the left side plate includes a left vertical plate and a left bottom plate, and the right side plate includes a right rear vertical plate and a right vertical plate;

The sample preparation mold further includes a bracket, which is disposed on the lower side of the bottom plate and is used to support the bottom plate.
The sample preparation mold for shear test of rock structure surface according to claim 1, characterized in that the connection between the left vertical plate and the left bottom plate of the L-shaped left side plate is along the left vertical plate A first plug is provided in the width direction of the front door, and a lower strip of the front vertical plate is provided with a long-shaped groove to the left along the opening of the front vertical plate to match the opening direction of the first plug,

The elongated groove can pass through the first latch and fix the left side plate and the front vertical plate by means of bolts.
The sample preparation mold for the shear test of a rock mass structural plane according to claim 2, wherein the inner side of the left vertical plate is provided with a second bolt and a third bolt horizontally, and the lower side of the bottom plate The left end is horizontally provided with a first U-shaped fork and a second U-shaped fork that are downward in the opening direction matching the second plug and the third plug,

The inside of the first U-shaped fork and the inside of the second U-shaped fork can pass through the second latch and the third latch, respectively, and fix the left side plate and the bottom plate by means of bolts.
The sample-making mold for the shear test of a rock structure surface according to claim 3, wherein the rear area on the upper side of the bottom plate is horizontally provided with a fourth bolt and a fifth bolt, and the rear vertical plate A horizontal U-shaped fork and a fourth U-shaped fork that are rearward in the opening direction matching the fourth plug and the fifth plug are provided horizontally on the outside of the,

The inner side of the third U-shaped fork and the inner side of the fourth U-shaped fork can pass through the fourth latch and the fifth latch, respectively, and fix the bottom plate and the rear riser by means of bolts.
The sample preparation mold for the shear test of a rock mass structural surface according to claim 4, wherein at least one row of through bolt holes is horizontally arranged on the inner side of the rear vertical plate, and the The outside is horizontally provided with at least one row of semi-through bolt holes matching the through bolt holes,

After the outer side of the right rear vertical plate abuts the inner side of the rear vertical plate, the bolt can pass through the through bolt hole and penetrate into the semi-through bolt hole to connect the rear vertical plate with the The right side plate is fixed.
The sample preparation mold for shear test of a rock structure surface according to claim 5, wherein the through bolt holes and the semi-through bolt holes are in two rows, and the number of semi-through bolt holes in each row Less than or equal to the number of through bolt holes in each row; and/or

After the rear vertical plate and the right side plate are fixed, the left end of the right rear vertical plate abuts against the inner side of the left vertical plate, and the front end of the right vertical plate and the front vertical plate contact.
The sample preparation mold for shear test of a rock mass structural surface according to claim 6, wherein the inner side of the right rear vertical plate is set to a straight type or a zigzag type.
The sample preparation mold for rock structure structural surface shear test according to claim 7, characterized in that between the elongated groove of the front vertical plate and the first plug, the bottom side of the bottom plate Between the first U-shaped fork and the second bolt, between the second U-shaped fork and the third bolt, outside the third vertical U-shaped fork and the fourth bolt The relative position between the fourth U-shaped fork and the fifth plug can be adjusted so that the sample preparation mold can produce rock structure surface shear test samples of different sizes and different shapes.
The sample preparation mold for shear test of rock mass structural plane according to any one of claims 1 to 8, wherein the bracket includes an upper end cap, a lower end cap, and the upper end cap and the lower end Telescopic rod between caps,

The telescopic rod includes a first strut, a second strut nested in the first strut, a third strut nested in the second strut, and a third strut nested in the third strut The fourth pole,

The first strut and the second strut are connected by a first threaded buckle, and the length of the second strut extending beyond the first strut can be adjusted by rotating the first threaded buckle; the first The second support bar and the third support bar are connected by a second threaded buckle, and the length of the third support bar extending beyond the second support bar can be adjusted by rotating the second threaded buckle; the third support bar It is connected with the fourth supporting rod through a third threaded buckle, and the length of the fourth supporting rod extending out of the third supporting rod can be adjusted by rotating the third threaded buckle.
The sample-making mold for the shear test of a rock structure surface according to claim 9, wherein a first groove is provided on the lower side of the bottom plate, and a second concave is provided on the upper side of the left bottom plate groove,

The upper end cap of the bracket is embedded in the first groove, the lower end cap of the bracket is embedded in the second groove, and thus the bracket is fixed to the bottom plate and the left side plate between.