A double-hole open-cut tunnel with a central drainage blind ditch and its construction method

Abstract

A double - hole open - cut tunnel with a central drainage culvert and its construction method, including the following steps: Excavate the soil by slope excavation or under the support of an upright retaining structure until the elevation of the bottom surface of the structural floor; Continue to excavate the soil in the middle of the foundation pit within the range of the central drainage ditch corresponding to the middle of the tunnel cross - section until the elevation of the bottom of the central drainage ditch below the bottom surface of the structural floor; Construct a leveling layer and a waterproof layer; Bind the steel bars of the floor structure and pour the floor concrete, simultaneously forming a cavity under the middle wall - namely the central drainage ditch; Continue to pour the reinforced concrete of the side walls, middle wall, and roof until a complete double - hole closed frame structure is formed; Simultaneously construct an open - type or a roadside catch - basin with drainage holes and a drain pipe connecting the roadside catch - basin and the central drainage ditch. The present invention can avoid the control of the vertical position of the structural floor due to the local space requirement of the depth of the drainage ditch, overall increase the elevation of the structural floor, reduce the engineering quantity, and lower the engineering risk.

Description

Technical Field

[0001] The invention belongs to the technical field of construction engineering, and particularly relates to a double-hole open-cut tunnel with a central drainage culvert and a construction method thereof, which is a drainage technical solution for a double-hole tunnel constructed by the open-cut method. Background Art

[0002] When an urban underground road or a highway tunnel is constructed by the open-cut method, a closed frame structure with a double-hole rectangular cross-section is usually adopted. On the basis of meeting the building clearance, the geometric dimensions of the inner contour section of the structure still need to leave necessary spaces for the installation and operation and maintenance of road surface structures, roadside anti-collision guardrails or curbs, drainage ditches, cable ditches, decorative surfaces, and equipment and facilities such as ventilation, lighting, fire protection, electricity, monitoring, and traffic engineering in the tunnel. And on the premise of meeting the requirements of various basic functions, the width and height of the cross-section are compressed as much as possible to reduce the project cost of the tunnel. Among them, the cross-sectional size and layout of the drainage ditch directly affect the size of the inner contour of the tunnel cross-section horizontally and vertically. To facilitate road surface drainage and ensure driving safety, a cross slope ( Figure 1 ) is set on the road surface in the tunnel. When a single-lane road adopts a one-way cross slope of 4-2, it generally slopes from the left side to the right side in the driving direction, that is, the left side is high and the right side is low in the driving direction. At the low point of the road surface cross slope, that is, on the right side, there is a drainage ditch 3. Observed from the full cross-section of two-way traffic in both directions, the center of the road surface is high and both sides are low, and drainage ditches 3 are arranged on both sides of the road. Flushing wastewater, fire protection wastewater, etc. in the tunnel are collected into the drainage ditch 3 along the road surface cross slope, and then flow longitudinally along the bottom of the ditch to the sump located at the low point of the tunnel vertically, and finally are discharged to the outside of the tunnel by a drainage pump. The roadside drainage ditch 3 generally adopts the form of a reinforced concrete culvert with a cover, and the cover is provided with drain holes to facilitate the road surface water to enter the ditch. At the same time, when the drainage ditch needs to be dredged, the cover is lifted to carry out maintenance operations such as dredging and silt cleaning.

[0003] Within the pavement width, including the carriageway width and the roadside width, the roadside width is called "marginal strip width" according to urban road specifications and "lateral width" according to highway specifications. To prevent the roadside drainage ditch and its cover slab from encroaching into the carriageway area and affecting driving safety or comfort, the drainage ditch and its cover slab should be arranged within the roadside width, that is, their width shall not exceed the roadside width. According to the specifications, the roadside width varies according to the design driving speed. The roadside drainage ditch must have a cross-sectional area that meets the drainage capacity. When the inner contour width is limited by the roadside width, it is necessary to increase the depth. The overall height of the roadside drainage ditch 3 includes: the cover slab thickness, the net height inside the drainage ditch, and the bottom slab thickness as a single component. The top surface of the cover slab is flush with the pavement 4-1, and the bottom surface of the drainage ditch is placed on the top surface of the bottom slab 6-2 of the tunnel main structure. That is to say, the overall height of the drainage ditch controls the height from the pavement 4-1 to the top surface of the bottom slab 6-2 of the tunnel main structure. Thus, the elevation of the top slab of the main structure bottom slab is controlled by the depth of the roadside drainage ditch, and the elevation of the bottom surface of the structural bottom slab determines the excavation depth 8 of the open-cut foundation pit.

[0004] Combing the logical chain of the above tunnel vertical design, it can be seen that: a drainage ditch needs to be set inside the tunnel, the cross-sectional area of the drainage ditch needs to meet the drainage capacity, and the scheme of increasing the depth of the drainage ditch is adopted under the condition of limited width to reach the required cross-sectional area of the drainage ditch. The internal depth of the drainage ditch or the height of the ditch structure determines the vertical position of the main structure bottom slab, which in turn affects the excavation depth and engineering quantity of the tunnel foundation pit. Since the width of the roadside drainage ditch 3 is limited, from the perspective of the transverse width range of the full cross-section of two-way traffic in both directions, it only belongs to the local width range. However, due to the control of the depth requirement of this local width, usually, the depth within the full width of the cross-section is increased, which is uneconomical and unreasonable.

[0005] Its uneconomy is reflected in: due to the increase in the depth of the roadside drainage ditch 3, ⑴ the burial depth of the main structure bottom slab 6-2 is increased, the foundation pit depth 8 is increased, the earth excavation volume of the foundation pit is increased, and the exposed height of the retaining structure 7 is increased; ⑵ the distance between the top surface of the pavement structure layer 4-1 and the top surface of the main structure bottom slab 6-2 is enlarged, and the engineering quantity of the subgrade backfill layer 5 is increased; ⑶ the height of the side wall 6-1 of the tunnel main structure is increased, and the corresponding reinforced concrete structure engineering quantity is increased. Its unreasonableness is reflected in: ⑴ due to the increase in the foundation pit depth 8, the construction risk of the open-cut foundation pit project is increased; ⑵ due to the increase in the height of the side wall 6-1 of the tunnel main structure, the load borne by the structure is increased.

[0006] In short, being affected or even controlled by the depth requirement of this local component of the roadside drainage ditch, resulting in the vertical deepening of the full cross-section of the main structure, is uneconomical and unreasonable. Especially for tunnel projects with significant characteristics of strip-shaped structures, minor optimizations in the cross-sectional design will have significant improvement benefits after multiplying by the tunnel length. Summary of the Invention

[0007] The present invention provides a double - hole open - cut tunnel with a central drainage culvert and a construction method thereof, aiming to solve the technical problem that the vertical position of the bottom plate of the tunnel main structure is controlled by the roadside drainage ditch and to optimize the cross - section layout of the tunnel.

[0008] The technical solution of the present invention is realized as follows:

[0009] A construction method of a double - hole open - cut tunnel with a central drainage culvert, characterized by comprising the following steps:

[0010] (1) Excavate the soil by slope excavation or under the support of an upright retaining structure until the elevation of the bottom surface of the structural bottom plate 6 - 2 is reached.

[0011] (2) Continue to excavate the soil in the middle of the foundation pit within the range of the central drainage ditch corresponding to the middle of the tunnel cross - section until the elevation of the bottom of the central drainage ditch below the bottom surface of the structural bottom plate 6 - 2 is reached; construct a leveling layer and a waterproof layer.

[0012] (3) Bind the steel bars of the bottom - plate structure and pour the bottom - plate concrete 6 - 2, simultaneously forming a cavity under the middle wall 6 - 3, that is, the central drainage ditch 3 - 1; continue to pour the side - wall 6 - 1, the middle wall 6 - 3, and the roof reinforced concrete until a complete double - hole closed frame structure 1 is formed.

[0013] (4) Then construct the subgrade backfill layer 5 and the road - surface structure layer 4 - 1 of the internal structure to form a road - surface cross - slope 4 - 2; meanwhile, synchronously construct an open - ended or water - discharging - hole - equipped roadside catch - ditch 3 - 2 and a drain pipe 3 - 3 connecting the roadside catch - ditch and the central drainage ditch; the roadside catch - ditch is in the subgrade backfill layer on both sides of the middle wall 6 - 3; the drain pipe passes through the structural bottom plate 6 - 2; the roadside catch - ditch is at the lowest point of the road - surface cross - slope 4 - 2.

[0014] The double - hole open - cut tunnel with a central drainage culvert described above includes a double - hole closed frame 1 of a tunnel constructed by the open - cut method, a drainage ditch, a road - surface structure layer 4 - 1, a subgrade backfill layer 5, and a road - surface cross - slope 4 - 2 arranged within the frame. The double - hole closed frame includes a main - structure side - wall 6 - 1, a main - structure bottom - plate 6 - 2, a main - structure middle - wall 6 - 3, and a roof; wherein,

[0015] The drainage ditch mentioned above is the central drainage ditch 3-1, which is arranged below the bottom surface of the main structure floor slab 6-2 and adjacent to the bottom of the middle wall 6-3 of the main structure; the cross slope direction 4-2 of the single-lane road surface slopes from the right side to the left side in the driving direction, that is, it is low on the left side and high on the right side in the driving direction, and it is low in the middle of the two-way driving road surface and high on both sides; an open or drain-hole-equipped roadside catch ditch 3-2 is arranged at the position of the low point of the road surface cross slope, that is, at the junction with the middle wall 6-3 of the main structure, and it is located on the top surface of the main structure floor slab 6-2; a downward drain pipe 3-3 is arranged between the roadside catch ditch and the central drainage ditch, and the drain pipe passes through the structure floor slab 6-2.

[0016] For the double-hole open-cut tunnel with a central drainage culvert described above, the tunnel structure is a double-hole closed frame with a single middle wall, and the central drainage ditch 3-1 is arranged symmetrically with double cavities on both sides of the bottom of the middle wall 6-3 of the main structure, and roadside catch ditches 3-2 and drain pipes 3-3 are respectively arranged on both sides of the middle wall 6-3 of the main structure corresponding to each cavity.

[0017] For the double-hole open-cut tunnel with a central drainage culvert described above, the tunnel structure is a three-hole closed frame with a double middle wall, the central drainage ditch 3-1 is arranged as a single cavity and is located at the bottom of the double middle wall, and roadside catch ditches 3-2 and drain pipes 3-3 are respectively arranged on both sides of the middle wall 6-3 of the main structure.

[0018] For the double-hole open-cut tunnel with a central drainage culvert described above, the central drainage ditch and the main structure floor slab 6-2 are an integrally connected structure cast in concrete; or it is an independent single component separated from the main structure floor slab 6-2, and is arranged vertically in an up-and-down overlapping manner.

[0019] For the double-hole open-cut tunnel with a central drainage culvert described above, the central drainage ditch is arranged in the center of the tunnel cross section.

[0020] For the double-hole open-cut tunnel with a central drainage culvert described above, the inner bottom wall of the central drainage ditch 3-1 is arranged with a slope from high to low longitudinally and is connected to the catch basin at the low point, and finally is discharged to the outside of the tunnel by the drainage pump station.

[0021] For the double-hole open-cut tunnel with a central drainage culvert described above, the water flow in the tunnel converges into the roadside catch ditch 3-2 along the cross slope direction 4-2 of the road surface, flows into the central drainage ditch 3-1 through the drain pipe 3-3, then flows longitudinally to the catch basin at the low point, and finally is discharged to the outside of the tunnel by the drainage pump station.

[0022] One of the features of the present invention: The tunnel drainage ditch 3-1 is placed below the bottom plate 6-2 of the main structure. This drainage ditch can be combined with the bottom plate 6-2 of the main structure to become an integral part of the stress-bearing structure, and the hollow inner cavity formed by the structure is used as a drainage ditch; it can also be used as a single component, separated from the bottom plate 6-2 of the main structure, and arranged vertically in an overlapping manner. A semi-circular and open roadside catch drain 3-2 is provided at the low point of the road surface cross slope. A vertical drain pipe 3-3 is provided to connect the roadside catch drain and the central drainage ditch.

[0023] Another feature of the present invention: The tunnel drainage ditch 3-1 is placed in the center of the tunnel cross section, that is, near the middle wall 6-3 of the double-hole closed frame constructed by the open cut method. The cross slope direction 4-2 of a single carriageway slopes from the right side to the left side in the driving direction, that is, the left side is low and the right side is high in the driving direction. At the low point of the road cross slope, that is, on the left side, a central drainage ditch 3-1 is provided. When observing the full cross section of two-way traffic in both directions, the middle of the road surface is low and both sides are high, and a central drainage ditch 3-1 is arranged in the center of the road. This drainage ditch can be designed as a single-chamber or double-chamber drainage ditch according to the structural form of the middle wall of the double-hole closed frame structure.

[0024] To ensure the straightness and continuous stress of the middle wall 6-3 and enable the structural load passing through the middle wall to be reliably transmitted to the foundation, when the tunnel structure adopts a double-hole closed frame with a single middle wall ( Figure 2 ), the drainage ditch can be set as a double chamber, located on both sides of the single middle wall, respectively collecting the road surface wastewater from the left and right chambers; when the tunnel structure adopts a three-hole closed frame with a double middle wall ( Figure 3 ), the drainage ditches can be combined into a single chamber and located between the double middle walls.

[0025] The flushing wastewater and fire-fighting wastewater in the tunnel are collected along the cross slope direction 4-2 of the road surface into the roadside catch drain 3-2, and then flow into the central drainage ditch 3-1 through the drain pipe 3-3, and then flow longitudinally to the sump located at the low point, and finally are discharged outside the tunnel by the drainage pump station.

[0026] Technical features of the present invention:

[0027] In the prior art solution, the drainage ditch 3 is placed above the top surface of the bottom plate 6-2 of the main structure, and the depth of the drainage ditch affects and controls the vertical position of the bottom plate 6-2 of the main structure, that is, a "strong correlation" relationship is formed between the drainage ditch and the structural bottom plate.

[0028] In the technical solution of the present invention, the central drainage ditch 3-1 is placed below the bottom surface of the main structure floor slab 6-2, which releases the "strong association" relationship formed between the central drainage ditch 3-1 and the structural floor slab 6-2, and avoids the drawback that the drainage ditch, as a local component, affects and controls the vertical position of the entire cross-section. The required excavation depth of the drainage ditch below the floor slab is further excavated in the foundation pit of the main structure, so that the required excavation depth of the local component is also locally excavated in the cross-section of the foundation pit, rather than deepened within the entire width of the cross-section.

[0029] The central drainage ditch 3-1 is placed below the bottom surface of the main structure floor slab 6-2. Whether it is part of the main stress-bearing structure or a single component, it is separated from the road surface structure layer 4-1 by the main structure floor slab 6-2. Therefore, its width is no longer restricted by the roadside width. Even when the drainage ditch is below the width range of the driving lane, it will not affect driving safety or comfort. The width of the drainage ditch can be determined according to the width of the central isolation belt and the layout requirements of the drain pipes and inspection wells, so it is easier to meet the effective drainage cross-sectional area of the drainage ditch.

[0030] If the drainage ditch set below the structural floor slab is still in the same position as the prior art solution and is arranged on both sides of the cross-section of the two-way road, although it can also achieve the effect of locally deepening the position where the drainage ditch is provided and overall raising the elevation of the structural floor slab, the earthwork volume of the foundation pit excavation can be reduced. However, since the locally deepened position is on both sides of the transverse width of the foundation pit excavation and is adjacent to the retaining structure, it is difficult to effectively play the role of reducing the excavation depth of the foundation pit. At the same time, since the range of this local deepening coincides with the passive earth pressure zone that provides lateral resistance for the retaining structure, that is, the original soil body in the passive earth pressure zone of the retaining structure is excavated due to local deepening, the exposed height of the retaining structure is increased, making the force of the retaining structure less reasonable.

[0031] Therefore, the present invention proposes to change the direction of the road surface cross slope 4-2 usually adopted in the prior art solution, that is, to change the distribution position of the low points of the road surface in the cross-section, and change the roadside drainage ditches set on both sides in the prior art solution to the central drainage ditch near the middle wall, so that the necessary local deepening due to the drainage ditch set below the floor slab is far away from the retaining structure, and the original soil near the passive earth pressure zone of the retaining structure is retained as much as possible, reducing the exposed height of the retaining structure, which is beneficial to improving the force condition of the retaining structure and reducing the engineering quantity of the retaining structure.

[0032] Advantages of the present invention

[0033] The drainage ditch proposed by the present invention is arranged below the bottom surface of the structural floor slab, changing the direction of the road cross slope and adjusting the position of the low point of the road surface, so that the drainage ditches arranged on both sides in the prior art solution are changed to a technical solution in which they are concentrated and arranged below the middle wall of the double-hole structure. This can avoid the control of the vertical position of the structural floor slab due to the local space requirement of the depth of the drainage ditch, improve the elevation of the structural floor slab as a whole, thereby reducing the engineering quantity and lowering the engineering risk. Due to the overall elevation of the vertical elevation of the tunnel structural floor slab, the excavation depth of the foundation pit can be reduced, the earthwork volume of the foundation pit excavation can be reduced, and the stress condition of the retaining structure can be improved; the height of the side wall of the main structure can be reduced; the backfill engineering quantity of the road surface base layer can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 FIG. is a schematic diagram of the overall structure of the closed frame structure and the drainage ditch of the double-hole rectangular cross-section in the prior art.

[0035] Figure 2 FIG. is a schematic diagram of the overall structure of the central drainage ditch of the single middle wall structure in Embodiment 1 of the present invention.

[0036] Figure 3 FIG. is a schematic diagram of the overall structure of the central drainage ditch of the double middle wall structure in Embodiment 2 of the present invention.

[0037] Figure 4 FIG. is a schematic diagram for comparing the excavation depth of the foundation pit between the prior art solution and the present invention.

[0038] DESCRIPTION OF THE REFERENCE NUMBERS IN THE DRAWINGS:

[0039] Double-hole closed frame structure 1, roadside cable trench and its cover 2, roadside drainage ditch 3, central drainage ditch 3-1, roadside catchment ditch 3-2, drain pipe 3-3 (connecting the roadside catchment ditch and the central drainage ditch), road surface structural layer 4-1, road surface cross slope (direction) 4-2, subgrade backfill layer 5, side wall 6-1 (of the main structure), structural floor slab 6-2 (of the main body), middle wall 6-3 (of the main structure), retaining structure 7, foundation pit depth 8 (excavation depth of the foundation pit), local excavation depth of the foundation pit 8-1, excavation line of the bottom of the foundation pit in the prior art solution 9, excavation line of the bottom of the foundation pit in Solution (B) or Solution (C) 10-1 DETAILED DESCRIPTION OF THE INVENTION

[0040] In order to more clearly understand the technical solution of the present invention, the following specifically describes the embodiments of the present invention in detail with reference to the drawings.

[0041] A construction method for a double-hole open-cut tunnel provided with a central drainage culvert according to the present invention includes the following steps:

[0042] (1) Excavate the soil by slope excavation or under the support of the vertical retaining structure 7 until the elevation of the bottom surface of the structural floor slab 6-2 is reached; see Figure 2-3 as shown

[0043] (2) Continue to excavate the soil in the middle of the foundation pit corresponding to the range of the central drainage ditch set in the middle of the tunnel cross-section until the bottom elevation of the central drainage ditch below the bottom surface of the structural floor slab 6-2; construct the leveling layer and waterproof layer;

[0044] (3) Tie the steel bars of the floor slab structure and pour the floor slab concrete 6-2, simultaneously forming a cavity - namely the central drainage ditch 3-1 - under the middle wall 6-3 and below the bottom surface of the structural floor slab 6-2; continue to pour the side wall 6-1, middle wall 6-3, and roof reinforced concrete until a complete double-hole closed frame structure 1 is formed;

[0045] (4) Then construct the subgrade backfill layer 5 and pavement structure layer 4-1 of the internal structure, form the pavement cross slope 4-2 and make the middle of the pavement horizontal low and the two sides high; simultaneously construct the roadside catchment ditch 3-2 with an open mouth or drainage holes and the drain pipe 3-3 connecting the roadside catchment ditch and the central drainage ditch during this period; the roadside catchment ditch is in the subgrade backfill layer on both sides of the middle wall 6-3; the drain pipe passes through the structural floor slab 6-2; the roadside catchment ditch is the lowest point of the pavement cross slope 4-2.

[0046] See Figure 2-3 As shown, a double-hole open-cut tunnel with a central drainage culvert of the present invention includes a double-hole closed frame 1 of the open-cut tunnel, a drainage ditch, a pavement structure layer 4-1, a subgrade backfill layer 5, and a pavement cross slope 4-2 arranged inside the frame. The double-hole closed frame includes a main structure side wall 6-1, a main structure floor slab 6-2, a main structure middle wall 6-3, and a roof; among them,

[0047] The drainage ditch is the central drainage ditch 3-1, which is arranged below the bottom surface of the main structure floor slab 6-2 and adjacent to the bottom of the main structure middle wall 6-3; the pavement cross slope direction 4-2 of a single carriageway slopes from the right side to the left side in the driving direction, that is, it is low on the left side and high on the right side in the driving direction, and it is low in the middle and high on both sides for two-way driving; an open or drain-hole-equipped roadside catchment ditch 3-2 is arranged at the position of the low point of the pavement cross slope, that is, at the junction with the main structure middle wall 6-3, and is located on the top surface of the main structure floor slab 6-2; a downward drain pipe 3-3 is arranged between the roadside catchment ditch and the central drainage ditch for connection, and the drain pipe passes through the structural floor slab 6-2 to connect the central drainage ditch.

[0048] For the double-hole open-cut tunnel with a central drainage culvert, the tunnel structure is a double-hole closed frame with a single middle wall. The central drainage ditch 3-1 is arranged in a double-chamber symmetrically on both sides of the bottom of the main structure middle wall 6-3, and roadside catchment ditches 3-2 and the drain pipes 3-3 are respectively arranged on both sides of the main structure middle wall 6-3 corresponding to each chamber for connection.

[0049] The described double - hole open - cut tunnel with a central drainage culvert, wherein the tunnel structure is a three - hole closed frame with a double middle wall, the central drainage ditch 3 - 1 is set as a single chamber, located at the bottom of the double middle wall, and roadside catch basins 3 - 2 and drain pipes 3 - 3 are respectively arranged on both sides of the middle wall 6 - 3 of the main structure and are connected.

[0050] The described double - hole open - cut tunnel with a central drainage culvert, wherein the central drainage ditch and the bottom slab 6 - 2 of the main structure are integrally connected by concrete casting; or it is an independent single member separated from the bottom slab 6 - 2 of the main structure and adopts a vertical arrangement with upper and lower staggering.

[0051] The described double - hole open - cut tunnel with a central drainage culvert, preferably, the central drainage ditch is arranged in the center of the tunnel cross - section.

[0052] The described double - hole open - cut tunnel with a central drainage culvert, wherein the inner bottom wall of the central drainage ditch 3 - 1 is arranged as a slope from high to low longitudinally and is connected to the catch basin at the low point, and finally is discharged outside the tunnel by a drainage pump station.

[0053] The described double - hole open - cut tunnel with a central drainage culvert, wherein the water flow in the tunnel converges into the roadside catch basin 3 - 2 along the cross - slope direction 4 - 2 of the road surface, then flows into the central drainage ditch 3 - 1 through the drain pipe 3 - 3, and then flows longitudinally to the catch basin at the low point, and finally is discharged outside the tunnel by a drainage pump station. The drainage ditch of the technical solution of the present invention is placed below the bottom surface of the structural floor slab and when arranged in the center, the excavation line of the foundation pit bottom includes local deepening.

[0054] See Figure 4 As shown, through the comparison of the existing technical solution (A), one of the possible solutions (B) and the technical solution of the present invention (C), it is intended to illustrate the implementation effect of the technical solution of the present invention.

[0055] Solution (A) is the existing technical solution, that is, the case where the roadside drainage ditch is located above the top surface of the structural floor slab, where 8 is the foundation pit depth and 9 is the excavation line of the foundation pit bottom of the existing technical solution;

[0056] Solution (B) is one of the possible solutions, that is, the roadside drainage ditch is located below the bottom surface of the structural floor slab, but this drainage ditch is located on both sides of the cross - section of the foundation pit, where 8 is the foundation pit depth, 8 - 1 is the local deepening of the foundation pit, 9 is the excavation line of the foundation pit bottom of the existing technical solution, 10 - 1 is the excavation line of the foundation pit bottom of this solution (B), and 4 - 2 is the cross - slope direction of the road surface, and at this time the slope is towards both sides;

[0057] Scheme (C) is the solution of the present invention, that is, the roadside drainage ditch is located below the bottom surface of the structural floor, and this drainage ditch is located in the center of the cross-section of the foundation pit. Among them, 8 is the depth of the foundation pit, 9 is the excavation line at the bottom of the foundation pit in the prior art solution, 10-1 is the excavation line at the bottom of the foundation pit in the solution of the present invention, 8-1 is the local deepening, and 4-2 is the direction of the road surface cross slope. At this time, the slope is towards the center.

[0058] For Scheme (B) and Scheme (C), the elevation of the excavation line at the bottom of the foundation pit (10-1) adopting the technical solution of the present invention is higher than that of the excavation line at the bottom of the foundation pit (9) in the prior art, and the excavation depth of the foundation pit (8) including the local deepening (8-1) is smaller than that of the excavation depth of the foundation pit (8) in the prior art. The comparison between Scheme (B) and Scheme (C) illustrates the intention and necessity of adjusting the cross slope direction in the solution of the present invention and setting it to be high on both sides and low in the middle.

Claims

1. A construction method for a double - hole open - cut tunnel with a central drainage culvert, characterized in that, The double-Kongming excavation method tunnel includes a double-hole closed frame for the cut-and-cover tunnel construction, a central drainage ditch (3-1), a pavement structure layer (4-1), a subgrade backfill layer (5), and a pavement cross slope (4-2) arranged inside the frame. The double-hole closed frame includes a main structure side wall (6-1), a main structure bottom slab (6-2), a main structure middle wall (6-3), and a top slab. The central drainage ditch (3-1) is arranged below the bottom surface of the main structure bottom slab (6-2) and adjacent to the bottom of the main structure middle wall (6-3). The direction of the pavement cross slope (4-2) of a single carriageway slopes from the right side to the left side in the driving direction, that is, it is lower on the left side and higher on the right side in the direction of driving. In the case of a two-way driving pavement, it is lower in the middle and higher on both sides. An open or drain-hole-equipped roadside catchment ditch (3-2) is arranged at the position of the low point of the pavement cross slope, that is, at the junction with the main structure middle wall (6-3), and is located on the top surface of the main structure bottom slab (6-2). A downward drain pipe (3-3) is arranged to connect the roadside catchment ditch and the central drainage ditch. The drain pipe passes through the main structure bottom slab (6-2). Among them, the tunnel structure is a double-hole closed frame with a single middle wall. The central drainage ditch (3-1) is arranged in a double-chamber symmetrical manner on both sides of the bottom of the main structure middle wall (6-3). Corresponding to each chamber, roadside catchment ditches (3-2) are respectively arranged on both sides of the main structure middle wall (6-3), and the drain pipes (3-3) are connected. This construction method includes the following steps: (1) Excavate the soil by slope excavation or under the support of an upright retaining structure until the elevation of the bottom surface of the main structure bottom slab (6-2) is reached. (2) Continue to excavate the soil in the middle of the foundation pit corresponding to the range of the central drainage ditch arranged in the middle of the tunnel cross-section until the elevation of the bottom of the central drainage ditch below the bottom surface of the main structure bottom slab (6-2) is reached. Construct a leveling layer and a waterproof layer. (3) Bind the steel bars of the bottom slab structure and pour the concrete of the main structure bottom slab (6-2), simultaneously forming a cavity under the middle wall (6-3), that is, the central drainage ditch (3-1). Continue to pour the reinforced concrete of the main structure side wall (6-1), the main structure middle wall (6-3), and the top slab until a complete double-hole closed frame structure is formed. (4) Then construct the subgrade backfill layer (5) and the pavement structure layer (4-1) of the internal structure to form a pavement cross slope (4-2). Meanwhile, construct an open or drain-hole-equipped roadside catchment ditch (3-2) and a drain pipe (3-3) connecting the roadside catchment ditch and the central drainage ditch synchronously. The roadside catchment ditch is in the subgrade backfill layer on both sides of the middle wall (6-3). The drain pipe passes through the main structure bottom slab (6-2). The roadside catchment ditch is at the lowest point of the pavement cross slope (4-2).

2. The construction method of a double - hole open - cut tunnel with a central drainage blind ditch as described in claim 1, characterized in that, The central drainage ditch and the main structure bottom slab (6-2) are an integrally connected structure formed by concrete pouring; or they are independent single components separated from the main structure bottom slab (6-2), and are arranged vertically in an up-and-down stacked manner.

3. The construction method of a double-hole open-cut tunnel with a central drainage blind ditch as claimed in claim 1, characterized in that, The central drainage ditch is arranged in the center of the tunnel cross-section.

4. The construction method of a double - hole open - cut tunnel with a central drainage blind ditch as described in claim 1, characterized in that, The inner bottom wall of the central drainage ditch (3-1) is arranged with a longitudinal slope from high to low and is connected to a sump at the low point, and finally is discharged to the outside of the tunnel by a drainage pump station.

5. The construction method of a double - hole open - cut tunnel with a central drainage blind ditch as described in claim 1, characterized in that, The water flow in the tunnel converges along the cross slope (4-2) of the road surface into the roadside catch drain (3-2), and then flows into the central drain (3-1) through the drain pipe (3-3), and then flows longitudinally to the catch basin at the low point, and finally is discharged outside the tunnel by the drainage pump station.

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