CN210946533U - A closed channel structure for open cut construction - Google Patents

Abstract

The underdrain structure used for open-cut construction includes a foundation pit and an underdrain; the foundation pit is provided with multiple sections of side slopes from the top of the pit to the bottom of the pit, and each section of the side slope is set in a stepped shape from the top of the pit to the bottom of the pit, and two adjacent sections are arranged. A side slope platform is arranged horizontally between the side slopes; each side slope is provided with a slope protection layer; the culvert is set at the bottom of the pit, and the culvert includes the top of the culvert, the left wall of the culvert, the right wall of the culvert, and the bottom of the culvert; Both the surface and the outer surface are arcs with downward openings; the inner and outer surfaces of the left wall and the right wall of the culvert are vertically arranged planes; the middle of the upper surface of the bottom of the culvert is concave to the lower surface of the bottom of the culvert in an arc shape ; The inner surfaces of the left wall and the right wall of the underdrain are connected with the inner surface of the top of the underdrain and the upper surface of the bottom of the underdrain to form a drainage channel. The cross-sectional shape of the drainage channel is a closed ring with an arc-shaped top and bottom. . The structure can facilitate the deep burial of the culvert, and at the same time, it can bear good force under the condition of deep burial.

Description

Underdrain structure for cut-and-cover construction

technical field

The utility model relates to the field of drainage channels, in particular to an underdrain structure used for open-cut construction.

Background technique

In the existing underdrain structure, the cross-sectional shapes of the drainage channel and the outer contour are rectangular; for example, in the underdrain structure disclosed in the patent application number CN201120181671.4, the outer contour of the underdrain and the cross-sectional shape of the drainage channel are both square. Problems arise when the underdrain structure is deeply buried in the ground. Since the outer contour of the underdrain and the cross-sectional shape of the drainage channel are square, the underdrain structure will not be well stressed, and a large amount of soil will be pressed on the top of the underdrain. , Due to the deep burial, the top of the culvert will be under greater pressure, which will easily lead to the collapse of the top of the culvert and reduce the service life of the entire culvert.

At the same time, in urban construction, the existing culverts are buried relatively shallow, which is better for construction. However, in projects such as airports, when the culverts are required to be buried relatively deep, there will be many construction problems, making it difficult to bury the culverts underground. deep. For example, the soil is loose, and it is not easy to excavate tunnels with underdrains; the construction of tunnels in bureaus is difficult and inefficient, requiring special tunnel excavation equipment, and high construction costs.

SUMMARY OF THE INVENTION

The purpose of this utility model is to: in view of the above-mentioned problems, provide a kind of underdrain structure for open-cut construction, this structure can facilitate the underdrain to be deeply buried underground, and at the same time, it can have good stress under the condition of deep burial, so as to ensure the underdrain. service life.

The technical scheme adopted by the utility model is as follows:

The underdrain structure used for open-cut construction includes a foundation pit and an underdrain; the foundation pit is provided with multiple sections of side slopes from the top of the pit to the bottom of the pit, and each section of the side slopes is arranged in a stepped shape from the top of the pit to the bottom of the pit, and is adjacent to each other. A side slope platform is horizontally arranged between the two sections of side slopes; each section of the side slope is provided with a slope protection layer; The left wall and the right wall of the culvert, and the bottom of the culvert with a rectangular cross-section; the inner surface and the outer surface of the top of the culvert are arcs with downward openings, and the arcs of the inner and outer surfaces have the same center; the culvert The inner surface and outer surface of the left wall and the right wall of the underdrain are vertically arranged planes; the middle part of the upper surface of the underdrain bottom is concave into an arc shape toward the lower surface of the underdrain bottom;

The inner surfaces of the left wall of the underdrain and the inner surface of the right wall of the underdrain are connected with the inner surface of the top of the underdrain and the upper surface of the bottom of the underdrain to form a drainage channel. Ring.

Due to the above structure, the method of excavating foundation pits solves the problem of digging tunnels deep underground to build culverts, and the construction efficiency is higher, avoiding the occurrence of tunnel collapse due to loose soil. At the same time, in the foundation pit structure of the utility model, the slope surface is stepped, so that the foundation pit can be excavated deeper, and each slope surface is provided with a slope protection layer to prevent the foundation pit from collapsing during the excavation and construction process. The underdrain of the utility model is arranged at the bottom of the pit. After the underdrain is constructed at the bottom of the pit, backfill soil is filled in the foundation pit to deeply bury the underdrain underground. At the same time, the top of the outer contour of the underdrain of the present invention is arc-shaped, and when the soil is pressed on the top of the arch, the arc can disperse the force well, reduce the force on the top of the underdrain, and prevent the top of the underdrain from being crushed; At the same time, the top and bottom of the drainage channel are also arc-shaped, which can also ensure that the top and bottom of the drainage channel are better stressed.

Further, a layer of concrete cushion is provided at the bottom of the pit, and the bottom of the underdrain is arranged on the concrete cushion, wherein the area of the concrete cushion is larger than the area of the lower surface of the bottom of the underdrain.

Because some soils are loose and unstable, if the bottom of the culvert is built directly on the soil, the bottom of the culvert will be unstable. A cushion should be built to support the bottom of the culvert to ensure the stability of the culvert structure.

Further, inner film layers are provided on the inner surface of the top of the underdrain, the inner surface of the left wall of the underdrain, the inner surface of the right wall of the underdrain, and the upper surface of the bottom of the underdrain; the outer surface of the top of the underdrain, the outer surface of the left wall of the underdrain, The outer surface of the right wall and the left and right outer surfaces of the bottom of the underdrain are provided with an outer film layer; the surfaces of the inner film layer and the outer mold layer are both flat surfaces; on the inner film layer on the upper surface of the underdrain bottom, there are also arranged There is a layer of wear-resistant layer; the surface of the wear-resistant layer is a flat surface; the inner film layer, the outer mold layer and the wear-resistant layer are all made of concrete, and a steel mesh is arranged inside the wear-resistant layer.

Due to the above structure, the surfaces of the inner film layer and the outer mold layer are flat and can be uniformly stressed, and the outer contour of the underdrain and the inner wall of the drainage channel can be well protected. In the drainage channel, water mainly flows in the lower part of the drainage channel, so the lower part is most easily eroded by water. Therefore, a wear-resistant layer is added to improve the bottom strength of the drainage channel, to prevent the lower part of the drainage channel from being eroded by water, and to improve the service life.

Further, the top of the underdrain, the left wall of the underdrain, the right wall of the underdrain and the bottom of the underdrain are all made of concrete, and the underdrain top, the left wall of the underdrain, the right wall of the underdrain, and the bottom of the underdrain are provided with underdrain steel skeletons;

On the cross section of the underdrain, the steel skeleton at the top of the underdrain includes the underdrain top inner steel bar matching the arc of the underdrain top inner surface and the underdrain top outer steel bar matching the underdrain top outer surface arc; the underdrain top inner steel bar and The outer reinforcement bars at the top of the underdrain are connected by a number of reinforcement bars at the top of the underdrain arranged between them;

On the cross section of the culvert, the steel skeleton of the left wall of the culvert includes vertically arranged steel bars in the left wall of the culvert and vertically arranged outer steel bars on the left wall of the culvert; A number of culverts between them are connected by reinforcing steel bars on the left wall of the culvert;

On the cross section of the culvert, the steel skeleton of the right wall of the culvert includes the steel bars in the right wall of the culvert and the outer steel bars on the right wall of the culvert. The reinforcement bars on the right wall of several culverts between them are connected;

On the cross section of the culvert, the steel skeleton at the bottom of the culvert includes the lower steel bars at the bottom of the culvert arranged horizontally and the upper steel bars at the bottom of the culvert matching the arc shape of the upper surface of the bottom of the culvert; They are connected by reinforcing steel bars at the bottom of several culverts.

Due to the above structure, each part of the culvert reinforcement skeleton of the culvert includes two main rebars and reinforced rebars connecting the two main rebars. The main rebars ensure the contour forming of each part, and the reinforced rebars ensure the stability of the entire rebar skeleton.

Further, on the same cross section of the culvert, the steel bars in the left wall of the underdrain, the steel bars in the right wall of the underdrain, the steel bars outside the left wall of the underdrain and the outside steel bars of the right wall of the underdrain, the steel bars at the top of the underdrain, the outside steel bars at the top of the underdrain, the steel bars on the bottom of the underdrain, and The steel bars at the bottom of the culvert together form the steel skeleton of the cross-section of the culvert; the upper ends of the steel bars in the left wall of the underdrain and the upper ends of the steel bars in the right wall of the underdrain are respectively connected to the two ends of the steel bars at the top of the underdrain, and the steel bars in the left wall of the underdrain and the lower ends of the steel bars in the right wall of the underdrain are connected The two ends of the steel bars on the bottom of the culvert, the upper ends of the outer steel bars on the left wall of the culvert and the upper ends of the outer steel bars on the right wall of the culvert are respectively connected to the two ends of the outer steel bars at the top of the culvert, and the lower ends of the steel bars on the left wall of the culvert and the outer steel bars on the right wall of the culvert are connected at the bottom of the culvert. Both ends of the lower rebar.

Further, along the extension direction of the underdrain, the underdrain includes a plurality of underdrain cross-section steel skeletons, and each adjacent underdrain cross-section steel skeleton is connected by a plurality of longitudinal steel bars.

Further, the slope protective layer includes a cement protective layer 1, a steel mesh layer and a cement protective layer 2; the reinforced mesh layer is sandwiched between the cement protective layer 1 and the cement protective layer 2, and the cement protective layer 1 is provided. On the slope surface; and between each side slope and each slope surface protective layer is also provided with inserted reinforcement, one end of the inserted reinforcement is inserted into the side slope, and the other end penetrates the cement protection layer and is connected to the steel mesh layer.

Due to the above structure, the foundation pit can be effectively prevented from collapsing through the three-layer support of the cement protection layer 1, the steel mesh layer and the cement protection layer 2, and the reinforcement mesh layer in the slope protection layer can further ensure the protection of the entire slope. layer strength. The slope protective layer is fixed on the slope surface by inserting the reinforcement, so that the slope protective layer can better protect the slope surface and improve the support strength.

Further, the inserting ribs are inserted into the slope surface in an array arrangement, and the spacing distance between the two adjacent inserting ribs in the horizontal direction of the slope surface is equal to the spacing distance between the two adjacent inserting ribs in the slope surface inclination direction; and then Ensure that the entire slope is evenly stressed and supported. The depth of inserting the rib into the slope surface is greater than the depth of inserting the protective layer of the slope surface.

Further, the reinforcing steel mesh layer includes a reinforcing steel mesh and a reinforcing steel skeleton arranged on the surface of the reinforcing steel mesh, and the reinforcing steel skeleton includes a number of horizontal reinforcing steel skeletons arranged in parallel and at equal intervals and a number of vertical reinforcing steel bars arranged in parallel and at equal intervals. Frame, the vertical reinforcing steel frame is parallel to the slope surface, the horizontal reinforcing steel frame and the vertical reinforcing steel frame are staggered together, and the distance between two adjacent horizontal reinforcing steel frames is the same as the adjacent two vertical reinforcing steel frames. The interval distance between the reinforcing bar frames is equal; the inserting bars are inserted into the slope protection layer and connected to the reinforcing steel bar frame; the connection point between the inserting bars and the reinforcing steel bar frame is located at the cross-connection point of the horizontal reinforcing bar frame and the vertical reinforcing bar frame .

Due to the above structure, the insert bars are directly connected with the reinforcing steel skeleton, so that the connection between the steel mesh layer and the insert bars is more reliable.

Further, a slope protective layer is also provided on the top of the pit, and a rib is also arranged between the pit top and the slope protective layer. One end of the rib is inserted into the pit top, and the other end penetrates the cement protective layer and the steel mesh layer connected.

To sum up, due to the adoption of the above-mentioned technical solutions, the beneficial effects of the present utility model are:

The utility model solves the problem of digging tunnels deep underground to build culverts by digging foundation pits, improves construction efficiency, avoids tunnel collapse due to loose soil, and ensures construction safety. At the same time, the outer contour of the top of the underdrain of the utility model is arc-shaped, which can well disperse the force on the top and avoid the top from being crushed. At the same time, the top and bottom of the drainage channel are also arc-shaped, so that the force of the entire drainage channel is better. , which further ensures the good force of the culvert. At the same time, a wear-resistant layer is also provided at the bottom of the drainage channel, and the wear-resistant layer can prevent the bottom of the drainage channel from being eroded by water and improve the service life of the drainage channel.

Description of drawings

Fig. 1 is the structure diagram that the underdrain is arranged in the foundation pit;

Figure 2 is a schematic diagram of the cross-sectional structure of the underdrain;

Figure 3 is a schematic diagram of the cross-sectional steel structure of the underdrain;

Fig. 4 is a schematic diagram of a foundation pit structure;

Figure 5 is a structural diagram of a slope protective layer arranged on a side slope;

Figure 6 is a structural diagram of a slope protection layer;

FIG. 7 is a structural diagram of a reinforcing mesh layer.

Detailed ways

The present utility model will be described in detail below in conjunction with the accompanying drawings.

In order to make the purpose, technical solutions and advantages of the present utility model more clearly understood, the present utility model will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, and are not intended to limit the present invention.

The utility model discloses an underdrain structure for open-cut construction, which includes a foundation pit and an underdrain; the foundation pit is provided with a plurality of sections of side slopes 103 from the pit top 101 to the pit bottom 102, and each section of the side slopes 103 starts from the pit top. 101 to the pit bottom 102 are arranged in a stepped shape, and a side slope platform 104 is horizontally arranged between two adjacent side slopes 103; each side slope 103 is provided with a slope protection layer 106; the underdrain is arranged at the pit bottom 102 As shown in Figure 2, the underdrain comprises an underdrain top 1 with an arched cross-section, an underdrain left wall and an underdrain right wall 2 with a rectangular cross-section, and an underdrain bottom 3 with a rectangular cross-section to form the overall structure of the underdrain; The inner and outer surfaces of the top 1 of the underdrain are arcs with downward openings, and the arc centers of the inner and outer surfaces are the same; the inner and outer surfaces of the left wall of the underdrain and the right wall 2 of the underdrain are both. Vertically arranged plane; the middle of the upper surface of the underdrain bottom 3 is concave into an arc to the lower surface of the underdrain bottom 3;

The inner surfaces of the left wall of the underdrain and the right wall 2 of the underdrain are connected with the inner surface of the top 1 of the underdrain and the upper surface of the bottom 3 of the underdrain to form a drainage channel. The cross-sectional shape of the drainage channel is a top surface and an arc bottom surface. shaped closed ring.

As shown in FIG. 4 , the foundation pit has three sections of side slopes 103 and two side slope platforms 104. From the pit top 101 to the pit bottom 102, the slope ratio of the next-level slope 103 is greater than or equal to the previous level. In Fig. 4, the slope of the first section of side slope 103 is 1:0.75, and its depth is 5m; the slope of the second section of side slope 103 is 1:0.4, and its depth is 6m; the slope of the third section of side slope 103 is 1 : 0.4, and its depth is 5m. The width of the two slope platforms 104 is 2m. In this embodiment, slope=height of the side slope 103 : the horizontal projection of the hypotenuse of the side slope 103 , which can be understood as the ratio of the height to the base of a right triangle for the convenience of understanding. Meanwhile, in this embodiment, the height from the outer surface of the top 1 of the underdrain to the lower surface of the bottom 3 of the underdrain is 10.7m, and the distance from the highest point of the top of the drainage channel to the lowest point of the bottom of the drainage channel is 7.1m.

The pit bottom 102 is provided with a layer of concrete cushion 4 , and the underdrain bottom 3 is disposed on the concrete cushion 4 , wherein the area of the concrete cushion is larger than the area of the lower surface of the underdrain bottom 3 .

The inner surface of the top 1 of the underdrain, the inner surface of the left wall of the underdrain, the inner surface of the right wall 2 of the underdrain, and the upper surface of the bottom 3 of the underdrain are all provided with an inner film layer 6; The outer surface, the outer surface of the underdrain right wall 2 and the left and right outer surfaces of the underdrain bottom 3 are all provided with an outer film layer; the surfaces of the inner film layer 6 and the outer mold layer 7 are flat surfaces; on the underdrain bottom 3 On the inner film layer 6 of the surface, there is also a layer of wear-resistant layer 5; the surface of the wear-resistant layer 5 is a flat surface; the inner film layer 6, the outer mold layer 7 and the wear-resistant layer 5 are all made of concrete , wherein a steel mesh is arranged inside the wear-resistant layer 5 . The diameter of the steel mesh reinforcement is HRB400 steel mesh with a diameter of 12 mm, and the size of the spacing mesh is 10×10 cm; the thickness of the wear-resistant layer 55 is 3 cm.

In order to ensure the strength of the culvert, the top 1 of the culvert, the left wall of the culvert, the right wall 2 of the culvert and the bottom 3 of the culvert are all made of concrete. There is a culvert steel frame;

On the cross section of the underdrain, the steel skeleton of the underdrain top 1 includes the underdrain top inner steel bars 1-2 that match the arc of the inner surface of the underdrain top 1 and the underdrain top outer steel bars 1-2 that match the arc of the underdrain top 1 outer surface. 1; the inner reinforcement bars 1-2 at the top of the underdrain and the outer reinforcement bars 1-1 at the top of the underdrain are connected by a plurality of reinforcement reinforcement bars 1-3 at the top of the underdrain arranged between them;

On the cross section of the culvert, the steel skeleton of the left wall of the culvert includes vertically arranged steel bars in the left wall of the culvert and vertically arranged outer steel bars on the left wall of the culvert; A number of culverts between them are connected by reinforcing steel bars on the left wall of the culvert;

On the cross-section of the underdrain, the steel skeleton of the right wall 2 of the underdrain includes a vertically arranged inner steel bar 2-2 on the right wall of the underdrain and a vertically arranged outer steel bar 2-1 on the right wall of the underdrain; the inner steel bar 2-1 of the underdrain right wall 2 and the outer steel bars 2-1 of the right wall of the underdrain are connected by a number of reinforcing steel bars 2-3 of the right wall of the underdrain arranged between them;

On the cross section of the culvert, the steel skeleton of the bottom 3 of the culvert includes the lower reinforced bars 3-1 at the bottom of the culvert and the upper reinforced bars 3-2 at the bottom of the culvert matching the arc shape of the upper surface of the bottom 3 of the culvert; 3-2 and the bottom lower reinforcement bars 3-1 of the culvert are connected by a plurality of reinforcement bars 3-3 at the bottom of the culvert provided between them.

On the same cross section of the underdrain, the steel bars in the left wall of the underdrain, the steel bars in the right wall of the underdrain 2-2, the steel bars outside the left wall of the underdrain and the outside bars of the right wall of the underdrain 2-1, the steel bars in the top of the underdrain 1-2, the steel bars outside the underdrain top 1-1. The upper steel bar 3-2 at the bottom of the underdrain and the lower steel bar 3-1 at the bottom of the underdrain together constitute the cross-section steel skeleton of the underdrain; the upper ends of the steel bars in the left wall of the underdrain and the steel bars 2-2 in the right wall of the underdrain are respectively connected to the steel bars in the top of the underdrain. Both ends of 1-2, the lower end of the steel bars in the left wall of the underdrain and the lower ends of the steel bars 2-2 in the right wall of the underdrain are connected to the two ends of the steel bars 3-2 on the bottom of the underdrain, the steel bars outside the left wall of the underdrain and the steel bars 2-1 outside the right wall of the underdrain The upper ends of the culvert are respectively connected to the two ends of the outer steel bars 1-1 at the top of the underdrain, and the lower ends of the outer steel bars of the left wall of the underdrain and the outer steel bars of the right wall of the underdrain 2-1 are connected to the two ends of the lower steel bars 3-1 at the bottom of the underdrain.

The number of reinforcing bars on the left wall = the number of reinforcing bars on the left wall; the number of reinforcing bars on the bottom ≥ the number of reinforcing bars on the left wall and the number of reinforcing bars on the left wall ≥ the number of reinforcing bars on the top.

Since the bottom 3 of the underdrain is the foundation of the entire underdrain, its instability will lead to the instability of the entire underdrain structure, and the force will be large, especially for large-section underdrains, the stability of the bottom 3 of the underdrain is very important for the stability of the entire underdrain structure; The intensity of bottom 3 should be set higher.

Further, the diameter of the top inner steel bar and the top outer steel bar > the diameter of the top reinforcing steel bar;

The diameter of the inner steel bar on the left wall and the outer steel bar on the left wall > the diameter of the reinforcing steel bar on the left wall;

The diameter of the inner steel bar on the right wall and the outer steel bar on the right wall > the diameter of the reinforcing steel bar on the right wall;

The diameter of the upper and lower reinforcement bars at the bottom > the diameter of the reinforcement reinforcement at the bottom.

In this embodiment, steel bars 1-2 in the top of the underdrain, steel bars 1-1 outside the top of the underdrain, steel bars inside the left wall of the underdrain, steel bars outside the left wall of the underdrain, steel bars 2-2 inside the right wall of the underdrain, and steel bars 2-1 outside the right wall of the underdrain , The diameter of the steel bar 3-2 at the bottom of the culvert and the steel bar 3-1 at the bottom of the culvert can be 22mm or 28mm;

The diameters of reinforcing bars 1-3 at the top of the underdrain, reinforcing bars on the left wall of the underdrain, reinforcing bars 2-3 on the right wall of the underdrain, and reinforcing bars 3-3 at the bottom of the underdrain can be 12mm.

Along the extension direction of the culvert, the culvert includes a plurality of underdrain cross-section steel skeletons, and each adjacent underdrain cross-section steel skeleton is connected by a number of longitudinal steel bars.

Each section of side slope 103 is provided with a slope protection layer 106, the slope protection layer 106 includes a cement protection layer 1061, a steel mesh layer 1062 and a cement protection layer 2 1063; the steel mesh layer 1062 is sandwiched between the cement protection layer 1061. Between the first layer 1061 and the second cement protective layer 1063, the cement protective layer 1 1061 is arranged on the slope; and between each side slope 103 and each slope protective layer 106 is also provided with inserted reinforcement 107, the inserted reinforcement 107 One end is inserted into the side slope 103, and the other end is connected to the steel mesh layer 1062 through the cement protective layer 1061.

The inserting ribs 107 are inserted into the slope surface in an array arrangement, and the spacing distance between the two adjacent inserting ribs 107 in the horizontal direction of the slope surface is equal to the spacing distance between the two adjacent inserting ribs 107 in the slope surface inclined direction; The spacing distance between two adjacent inserting ribs 107 in the horizontal direction of the slope is 1.5m; the spacing distance between two adjacent inserting ribs 107 in the slope direction is 1.5m.

The depth of inserting the rib 107 into the slope is greater than the depth of inserting the protective layer 106 on the slope. The insertion rib 107 is 3m long, the depth of insertion into the side slope 103 is 2.9m, and the diameter of the insertion rib 107 is 2.5cm.

The reinforcing steel mesh layer 1062 includes a reinforcing steel mesh 108 and a reinforcing steel skeleton 109 arranged on the surface of the reinforcing steel mesh 108. The reinforcing steel skeleton 109 includes a plurality of horizontal reinforcing steel skeletons 109 arranged in parallel and at equal intervals and a plurality of vertical reinforcing steel frames 109 arranged in parallel and at equal intervals. To the reinforcing steel bar frame 109, the vertical reinforcing steel bar frame 109 is parallel to the slope, the horizontal reinforcing steel bar frame 109 and the vertical reinforcing steel bar frame 109 are staggered together, and the interval between two adjacent horizontal reinforcing steel bar frames 109 The distance is equal to the distance between the adjacent two vertical reinforcing steel skeletons 109; the inserting bars 107 are inserted into the slope protection layer 106 and are connected to the reinforcing steel skeleton 109; The cross-connection point of the horizontal reinforcing steel frame 109 and the vertical reinforcing steel frame 109 .

The diameter of the reinforcing bar frame 109 is larger than that of the reinforcing bar mesh. The diameter of the steel bars of the horizontal steel frame and the vertical steel frame is 1.6cm; the diameter of the steel bars of the steel mesh is 0.8cm

As shown in FIG. 5 , a slope protection layer 106 is also provided on the pit roof 101, and an insertion rib 107 is also arranged between the pit roof 101 and the slope protection layer 106. One end of the insertion rib 107 is inserted into the pit roof 101, and the other One end runs through the cement protective layer 1061 and is connected to the steel mesh layer 1062. The pit roof 101 is also provided with a drainage ditch 105 and a guardrail.

The above are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention shall be included in the present invention. within the scope of protection of the utility model.

Claims (10)

1. The underdrain structure used for open-cut construction is characterized in that: it comprises a foundation pit and an underdrain; the foundation pit is provided with a plurality of sections of side slopes (103) from the top of the pit (101) to the bottom of the pit (102), and the sides of each section are The slope (103) is arranged in a stepped shape from the pit top (101) to the pit bottom (102), and a side slope platform (104) is horizontally arranged between two adjacent side slopes (103); Both are provided with a slope protection layer (106); the underdrain is arranged at the bottom of the pit (102), and the underdrain includes an underdrain top (1) with an arched cross-section, a left wall of the underdrain and a right underdrain (1) with a rectangular cross-section. 2), the bottom of the underdrain (3) with a rectangular cross section; the inner surface and the outer surface of the top of the underdrain (1) are arcs with downward openings, and the centers of the arcs on the inner and outer surfaces are the same; the described The inner and outer surfaces of the left wall of the underdrain and the right wall of the underdrain (2) are vertically arranged planes; the middle of the upper surface of the underdrain bottom (3) is concave to the lower surface of the underdrain bottom (3) in an arc shape; The inner surfaces of the left wall of the underdrain and the right wall (2) of the underdrain are connected with the inner surface of the underdrain top (1) and the upper surface of the underdrain bottom (3) to form a drainage channel, and the cross-sectional shape of the drainage channel is a top surface. and the bottom surface are arc-shaped closed ring. 2. The underdrain structure for open-cut construction according to claim 1, characterized in that: the bottom of the pit (102) is provided with a layer of concrete cushion (4), and the bottom of the underdrain (3) is arranged on the concrete cushion (4). 4), wherein the area of the concrete cushion is larger than the lower surface area of the bottom of the underdrain (3). 3. the underdrain structure for open-cut construction according to claim 2, is characterized in that: the inner surface of underdrain top (1), the inner surface of underdrain left wall, the inner surface of underdrain right wall (2) and underdrain bottom The upper surface of (3) is provided with inner film layer (6); Both outer surfaces are provided with an outer film layer; the surfaces of the inner film layer (6) and the outer mold layer (7) are flat surfaces; on the inner film layer (6) on the upper surface of the underdrain bottom (3), A layer of wear-resistant layer (5) is also provided; the surface of the wear-resistant layer (5) is a flat surface; the inner film layer (6), the outer mold layer (7) and the wear-resistant layer (5) are all made of concrete The steel mesh is arranged inside the wear-resistant layer (5). 4. The underdrain structure for open-cut construction according to claim 1, wherein the underdrain top (1), underdrain left wall, underdrain right wall (2) and underdrain bottom (3) are all made of concrete The underdrain top (1), the underdrain left wall, the underdrain right wall (2) and the underdrain bottom (3) are provided with underdrain steel skeletons; On the cross section of the underdrain, the steel skeleton of the underdrain top (1) includes the underdrain top inner steel bars (1-2) that match the inner surface arc of the underdrain top (1) and the underdrain top (1) that matches the outer surface arc of the underdrain top (1). Matching outer reinforcement bars (1-1) at the top of the underdrain; the inner reinforcement bars (1-2) at the top of the underdrain and the outer reinforcement bars (1-1) at the top of the underdrain are provided by a plurality of reinforcement bars (1-3) at the top of the underdrain. connected; The reinforced skeleton of the left wall of the culvert includes vertically arranged steel bars in the left wall of the culvert and vertically arranged outer steel bars of the left wall of the culvert; Wall reinforcement bars are connected; The steel skeleton of the right wall (2) of the underdrain includes vertically arranged inner steel bars (2-2) on the right wall of the underdrain and vertically arranged outer steel bars (2-1) on the right wall of the underdrain; the inner steel bars (2-1) of the underdrain right wall 2) Connect with the outer steel bars (2-1) of the right wall of the underdrain through a plurality of reinforcing steel bars (2-3) on the right wall of the underdrain arranged between them; The reinforced skeleton at the bottom of the underdrain (3) includes a lower steel bar (3-1) at the bottom of the underdrain arranged horizontally and an upper steel bar (3-2) at the bottom of the underdrain matching the arc shape of the upper surface of the underdrain bottom (3); The reinforcing bars (3-2) and the lower reinforcing bars (3-1) at the bottom of the culvert are connected by a plurality of reinforcing bars (3-3) at the bottom of the culvert arranged between them. 5. The underdrain structure for open-cut construction according to claim 4, characterized in that: on the same cross section of the underdrain, the steel bars in the left wall of the underdrain, the steel bars (2-2) in the right wall of the underdrain, and the left wall of the underdrain Outer reinforcement and outer reinforcement of the right wall of the culvert (2-1), inner reinforcement at the top of the underdrain (1-2), outer reinforcement at the top of the underdrain (1-1), upper reinforcement at the bottom of the underdrain (3-2), and lower reinforcement at the bottom of the underdrain (3 -1) Together, they form the reinforced skeleton of the cross-section of the culvert; the steel bars in the left wall of the culvert and the upper ends of the steel bars (2-2) in the right wall of the culvert are respectively connected to the two ends of the steel bars (1-2) in the top of the culvert, and the steel bars in the left wall of the culvert are respectively connected The lower end of the steel bar (2-2) in the right wall of the underdrain is connected to the two ends of the steel bar (3-2) on the bottom of the underdrain, and the upper end of the steel bar (2-1) outside the left wall of the underdrain and the outer steel bar (2-1) of the right wall of the underdrain are respectively connected to the underdrain. The two ends of the top outer steel bar (1-1), the lower ends of the outer steel bar on the left wall of the underdrain and the lower end of the outer steel bar on the right wall of the underdrain (2-1) are connected to the two ends of the lower steel bar (3-1) at the bottom of the underdrain. 6. The underdrain structure for open-cut construction according to claim 5, characterized in that: along the extension direction of the underdrain, the underdrain comprises a plurality of underdrain cross-section steel skeletons, and each adjacent underdrain cross-section steel skeleton is connected by a number of longitudinal steel bars . 7. The underdrain structure for open-cut construction according to any one of claims 1-6, wherein the slope protective layer (106) comprises a cement protective layer (1061), a steel mesh layer (1062) and the second cement protection layer (1063); the steel mesh layer (1062) is sandwiched between the cement protection layer one (1061) and the cement protection layer two (1063), and the cement protection layer one (1061) is arranged on the slope surface and each side slope (103) and each slope protective layer (106) are also provided with inserting ribs (107), one end of the inserting ribs (107) is inserted into the side slope (103), and the other end penetrates the cement protective layer One (1061) is connected to the reinforcing mesh layer (1062). 8. The underdrain structure for cut-and-cover construction according to claim 7, characterized in that: the inserting ribs (107) are inserted into the slope surface in an array arrangement, and two adjacent inserting ribs (107) are inserted into the slope surface. The spacing distance in the horizontal direction of the surface is equal to the spacing distance between the two adjacent insert bars (107) in the slope direction of the slope; The insertion depth of the insertion rib (107) into the slope surface is greater than the depth of insertion into the slope protection layer (106). 9. The underdrain structure for open-cut construction according to claim 7, characterized in that: the steel mesh layer (1062) comprises a steel mesh (108) and a reinforcing steel skeleton provided on the surface of the steel mesh (108) (109), the reinforcing steel bar frame (109) includes a plurality of horizontal reinforcing steel bar frames (109) arranged in parallel and at equal intervals and a plurality of vertical reinforcing steel bar frames (109) arranged in parallel and at equal intervals. The vertical reinforcing steel bar frame (109) 109) is parallel to the slope, the horizontal reinforcing steel frame (109) and the vertical reinforcing steel frame (109) are staggered together, and the distance between two adjacent horizontal reinforcing steel frames (109) is the same as that between the two adjacent vertical reinforcing steel frames (109). The distances between the reinforcing steel bar frames (109) are equal; the inserting bars (107) are inserted into the slope protection layer (106) and are connected to the reinforcing steel bar frames (109); the inserting bars (107) are connected to the reinforcing steel bar frames (109). The connection point of 109) is located at the cross-connection point of the horizontal reinforcing steel frame (109) and the vertical reinforcing steel frame (109). 10. The underdrain structure for open-cut construction according to claim 8, wherein the pit roof (101) is also provided with a slope protection layer (106), and the pit roof (101) and the slope protection layer are also provided Insertion bars (107) are also arranged between (106), one end of the insertion bars (107) is inserted into the pit roof (101), and the other end penetrates the cement protection layer one (1061) and is connected to the steel mesh layer (1062).

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