Open-cut tunnel drainage ditch and design method thereof

Abstract

The present invention discloses a drainage ditch for an open-cut tunnel and a design method thereof. The method comprises the following steps: dividing the drainage area of ​​the tunnel into three sections based on the drainage needs and structural requirements of the tunnel, wherein the first section is a section with low drainage volume and has a length of L1; the second section is a section with high drainage volume and has a length of L2; and the third section is a transition section between the first and second sections and has a length of L3. Drainage ditches of different sizes are arranged according to the divided drainage areas. This method can solve the problem of unreasonable drainage system design during the open-cut tunnel construction design phase and adapt to the drainage needs of different sections within the tunnel.

Description

Technical Field

[0001] The present invention relates to the field of municipal engineering, in particular to an open-cut tunnel drainage ditch and a design method thereof. Background Art

[0002] Cut-and-cover tunneling, a widely used tunnel construction technique in shallow depths, plays a crucial role in various tunnel projects. Throughout the entire process of cut-and-cover tunnel construction and subsequent operation, effective management of surface rainwater from the open section and various water sources generated within the tunnel, such as flushing water, is crucial. Improper or inefficient drainage facilities can lead to water accumulation on the tunnel surface. Once the depth of accumulated water exceeds a safety threshold, the risk of traffic accidents increases significantly.

[0003] The traditional open-cut tunnel drainage system layout usually adopts drainage ditches of uniform size. This layout has the following shortcomings: it cannot adapt to the drainage needs of different sections in the tunnel. If drainage ditches of uniform size are used, the drainage needs of different sections cannot be met, affecting drainage efficiency and safety. Specifically, when the drainage ditch size is too large, it causes waste of materials and human resources. In the traditional layout method, in order to ensure the safety and reliability of the drainage system, a larger drainage ditch size is usually selected. However, this practice will lead to waste of materials and human resources and increase construction costs. When the drainage ditch size is too small, the drainage effect is affected. If the drainage ditch size is too small, the drainage capacity of the drainage ditch will not be able to meet the needs in sections with more groundwater or longer drainage distances, resulting in untimely drainage and affecting the safety of tunnel operations.

[0004] In summary, the existing technology lacks a scientific, reasonable, efficient and stable drainage system during the open-cut tunnel construction design stage. Summary of the Invention

[0005] The present invention aims to provide an open-cut tunnel drainage ditch and a design method thereof, which can adapt to the drainage requirements of different sections in the tunnel.

[0006] According to one aspect of the present invention, there is provided an open-cut tunnel drainage ditch and a design method thereof, comprising the following steps: dividing the drainage area of ​​the tunnel into three sections according to the drainage needs and structural requirements of the tunnel, wherein the first section is a section with a small drainage volume, and its length is L1; the second section is a section with a large drainage volume, and its length is L2; ​​the third section is a transition section between the first section and the second section, and its length is L3; and drainage ditches of different sizes are arranged according to the divided drainage areas.

[0007] Preferably, according to the divided drainage areas, drainage ditches of different sizes are arranged, including: arranging a small drainage ditch 2-4 in the first section, the small drainage ditch 2-4 is disc-shaped, and its longitudinal slope is i1%, and the i1% is consistent with the longitudinal slope of the tunnel; arranging a large drainage ditch 2-1 in the second section, and the longitudinal slope of the large drainage ditch 2-1 is i1%; the i1% is consistent with the longitudinal slope of the tunnel; arranging a transition type 1 drainage ditch 2-2 and a transition type 2 drainage ditch 2-3 in the third section, and the longitudinal slope of the transition type 1 drainage ditch 2-2 and the transition type 2 drainage ditch 2-3 is i2%, and i1%>i2%≥0.3%.

[0008] Preferably, arranging the transition type 1 drainage ditch 2-2 and the transition type 2 drainage ditch 2-3 in the third section includes: setting the transition type 1 drainage ditch 2-2 to connect with the large drainage ditch 2-1; setting the transition type 2 drainage ditch 2-3 to connect with the transition type 1 drainage ditch 2-2 and the small drainage ditch 2-4.

[0009] Preferably, setting a transition type 1 drainage ditch 2-2 so that it is connected with the large drainage ditch 2-1 includes: backfilling a ditch filling layer 3-1 at the bottom of the transition type 1 drainage ditch 2-2 for adjusting in the vertical direction to connect with the large drainage ditch 2-1; connecting the small drainage ditch 2-4 with the transition type 2 drainage ditch 2-3 includes: backfilling a ditch filling layer 3-1 at the bottom of the transition type 2 drainage ditch 2-3, and backfilling a ditch filling layer 3-1 on the side of the transition type 2 drainage ditch 2-3 adjacent to the large drainage ditch side wall 1-7, for adjusting in the vertical and horizontal directions to connect with the small drainage ditch 2-4.

[0010] Preferably, the net width of the large drainage ditch 2-1 is B1, and the net height is H1; the net width of the small drainage ditch 2-4 is b1, and the net height is h1; the net width of the transition type 1 drainage ditch 2-2 is B1, and the net height is H2, wherein H2 is a change value, and H2 is calculated according to the following formula: H2 = H1-I×(i1%-i2%), I is the horizontal distance from any position in the third section to the ditch gradient starting point 4-1, I≤L3; the net width of the transition type 2 drainage ditch 2-3 is B2, and the net height is H3, wherein B2 is a change value, and B2 is calculated according to the following formula: B2 = b1+2×(L3-I)×(B1-b1) / L3; H3 is a change value, and H3 is calculated according to the following formula: H3 = H1-I×(i1%-i2%).

[0011] Preferably, the flow cross-section A of the drainage ditch is calculated according to the following formula: A=Q / V, where Q is the drainage volume and V is the design flow velocity, and the design flow velocity V is less than or equal to 4 m / s.

[0012] Preferably, the drainage requirements include rainwater, fire drainage, and tunnel internal cleaning water; the structural requirements include the topography of the tunnel and the drainage load.

[0013] According to another aspect of the present invention, an open-cut tunnel drainage ditch is provided, comprising: a first section, which is a section of the tunnel with a small drainage volume and has a length of L1; a second section, which is a section of the tunnel with a large drainage volume and has a length of L2; and a third section, which is a transition section between the first section and the second section and has a length of L3.

[0014] Preferably, a small drainage ditch 2-4 is arranged in the first section, and the small drainage ditch 2-4 is disc-shaped, and its longitudinal slope is i1%, and the i1% is consistent with the longitudinal slope of the tunnel; a large drainage ditch 2-1 is arranged in the second section, and the longitudinal slope of the large drainage ditch 2-1 is i1%; the i1% is consistent with the longitudinal slope of the tunnel; a transition type 1 drainage ditch 2-2 and a transition type 2 drainage ditch 2-3 are arranged in the third section, and the longitudinal slope of the transition type 1 drainage ditch 2-2 and the transition type 2 drainage ditch 2-3 is i2%, and i1%>i2%≥0.3%.

[0015] Preferably, the bottom of the transition type 1 drainage ditch 2-2 is backfilled with a ditch filling layer 3-1, which is used to adjust in the vertical direction to connect with the large drainage ditch 2-1; the bottom of the transition type 2 drainage ditch 2-3 is backfilled with a ditch filling layer 3-1, and the side of the transition type 2 drainage ditch 2-3 adjacent to the large drainage ditch side wall 1-7 is backfilled with a ditch filling layer 3-1, which is used to adjust in the vertical and horizontal directions to connect with the small drainage ditch 2-4.

[0016] The present invention discloses a drainage ditch for an open-cut tunnel and a design method thereof. The method comprises the following steps: dividing the drainage area of ​​the tunnel into three sections based on the drainage needs and structural requirements of the tunnel, wherein the first section is a section with low drainage volume and has a length of L1; the second section is a section with high drainage volume and has a length of L2; and the third section is a transition section between the first and second sections and has a length of L3. Drainage ditches of different sizes are arranged according to the divided drainage areas. This method can solve the problem of unreasonable drainage system design during the open-cut tunnel construction design phase and adapt to the drainage needs of different sections within the tunnel. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0018] Figure 1 is a plan view of drainage ditch layout of an open-cut tunnel according to an embodiment of the present invention;

[0019] Figure 2 2. It is a elevational layout diagram of drainage ditches in an open-cut tunnel according to an embodiment of the present invention;

[0020] Figure 3 1. It is a cross-sectional view of the drainage ditch of an open-cut tunnel according to an embodiment of the present invention;

[0021] Figure 4 2. It is a cross-sectional view of the drainage ditch of an open-cut tunnel according to an embodiment of the present invention;

[0022] Figure 5 is a cross-sectional view of a drainage ditch along an open-cut tunnel according to an embodiment of the present invention; and

[0023] Figure 6 4-4 is a cross-sectional view of an open-cut tunnel drainage ditch according to an embodiment of the present invention.

[0024] In the figure: 1. Open-cut main tunnel; 1-1. Tunnel side walls; 1-2. Tunnel middle wall; 1-3. Tunnel floor; 1-4. Tunnel roof; 1-5. Tunnel pavement; 1-6. Tunnel crash barrier; 1-7: Side walls of large drainage ditch; 1-8: Side walls of small drainage ditch; 2-1. Large drainage ditch; 2-2. Transition type 1 drainage ditch; 2-3. Transition type 2 drainage ditch; 2-4. Small drainage ditch; 3-1. Ditch filling layer; 4-1: Starting point of ditch gradient; 4-2: End point of ditch gradient. DETAILED DESCRIPTION

[0025] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0026] Reference will now be made in detail to various embodiments of the present invention, examples of which are illustrated in the accompanying drawings and described below. For ease of interpretation and precise definition in the appended claims, the terms "upper," "lower," "inner," and "outer" are used to describe features of the exemplary embodiments with reference to their positions as shown in the drawings.

[0027] An embodiment of the present invention provides a method for designing a drainage ditch for an open-cut tunnel, comprising the following steps: dividing the drainage area of ​​the tunnel into three sections according to the drainage needs and structural requirements of the tunnel, wherein the first section is a section with a small drainage volume, and its length is L1; the second section is a section with a large drainage volume, and its length is L2; ​​the third section is a transition section between the first section and the second section, and its length is L3; and arranging drainage ditches of different sizes according to the divided drainage areas.

[0028] In the prior art, drainage systems typically use uniformly sized drains, which cannot adapt to the drainage needs of different sections within a tunnel. In an embodiment of the present invention, by dividing the tunnel's drainage area into a first section with low drainage volume, a second section with high drainage volume, and a transition section between the first and second sections, drainage ditches of different sizes are arranged in each section. This solves the problems of low drainage efficiency, resource waste, and lack of flexibility caused by the use of uniformly sized drains in the prior art, making the drainage system more precise, economical, and adaptable to complex tunnel environments. Furthermore, the present invention can also be divided into four or more sections based on drainage needs, structural requirements, and other requirements.

[0029] According to an embodiment of the present invention, drainage ditches of different sizes are arranged according to the divided drainage areas, including: arranging a small drainage ditch 2-4 in the first section, the small drainage ditch 2-4 is disc-shaped, and its longitudinal slope is i1%, and the i1% is consistent with the longitudinal slope of the tunnel; arranging a large drainage ditch 2-1 in the second section, and the longitudinal slope of the large drainage ditch 2-1 is i1%; the i1% is consistent with the longitudinal slope of the tunnel; arranging a transition type 1 drainage ditch 2-2 and a transition type 2 drainage ditch 2-3 in the third section, the longitudinal slope of the transition type 1 drainage ditch 2-2 and the transition type 2 drainage ditch 2-3 is i2%, and i1%>i2%≥0.3%.

[0030] In this embodiment of the present invention, by arranging drainage ditches of corresponding sizes and shapes within different drainage areas, the problem of the existing technology of single drainage ditch design that cannot fully adapt to the drainage needs of various tunnel sections is solved. Specifically, a small dish-shaped drainage ditch is arranged in the first section with a smaller drainage volume, aligned with the longitudinal slope of the tunnel to ensure smooth drainage; a large drainage ditch is arranged in the second section with a larger drainage volume to meet high drainage needs; and a transitional drainage ditch is arranged in the third section, with an adaptive longitudinal slope to ensure continuous and smooth drainage in each section. The design of small drainage ditch 2-4 with the same slope as the large drainage ditch 2-1 helps maintain the continuity of water flow and avoid backflow or scouring caused by slope differences, thereby simplifying construction, reducing maintenance difficulties, and improving the efficiency and stability of the entire drainage system. The slope design of i1%>i2%≥0.3% can effectively control the water flow velocity and reduce scouring force by reducing the slope of the drainage ditch in the transition section, thereby avoiding damage to the drainage ditch structure. In addition, ensuring that i2% is not less than 0.3% can also ensure the smooth discharge of water, prevent water accumulation and silt deposition, and improve the overall stability and efficiency of the drainage system.

[0031] According to an embodiment of the present invention, arranging the transition type 1 drainage ditch 2-2 and the transition type 2 drainage ditch 2-3 in the third section includes: setting the transition type 1 drainage ditch 2-2 to connect with the large drainage ditch 2-1; setting the transition type 2 drainage ditch 2-3 to connect with the transition type 1 drainage ditch 2-2 and the small drainage ditch 2-4.

[0032] According to an embodiment of the present invention, setting a transition type 1 drainage ditch 2-2 so that it is connected with the large drainage ditch 2-1 includes: backfilling a ditch filling layer 3-1 at the bottom of the transition type 1 drainage ditch 2-2 for adjusting in the vertical direction to connect with the large drainage ditch 2-1; connecting the small drainage ditch 2-4 with the transition type 2 drainage ditch 2-3 includes: backfilling a ditch filling layer 3-1 at the bottom of the transition type 2 drainage ditch 2-3, and backfilling a ditch filling layer 3-1 on the side of the transition type 2 drainage ditch 2-3 adjacent to the large drainage ditch side wall 1-7, for adjusting in the vertical and horizontal directions to connect with the small drainage ditch 2-4.

[0033] In this embodiment of the present invention, by providing a ditch filling layer at the bottom or sides of the transition type 1 and transition type 2 drains, the height difference and discontinuity issues encountered in the prior art when connecting drains of different sizes are resolved. Specifically, by backfilling the ditch filling layer at the bottom of the transition type 1 drain, it smoothly connects vertically with the large drain. Simultaneously, by backfilling the ditch filling layer at the bottom and sides of the transition type 2 drain, it ensures a smooth transition both vertically and horizontally with the small drain. This ensures the continuity and stability of the entire drainage system, and improves the drainage efficiency and reliability of the tunnel drainage system.

[0034] According to an embodiment of the present invention, the net width of the large drainage ditch 2-1 is B1, and the net height is H1; the net width of the small drainage ditch 2-4 is b1, and the net height is h1; the net width of the transition type 1 drainage ditch 2-2 is B1, and the net height is H2, wherein H2 is a change value, and H2 is calculated according to the following formula: H2 = H1-I×(i1%-i2%), I is the horizontal distance from any position in the third section to the ditch gradient starting point 4-1, I≤L3; the net width of the transition type 2 drainage ditch 2-3 is B2, and the net height is H3, wherein B2 is a change value, and B2 is calculated according to the following formula: B2 = b1+2×(L3-I)×(B1-b1) / L3; H3 is a change value, and H3 is calculated according to the following formula: H3 = H1-I×(i1%-i2%).

[0035] In this embodiment of the present invention, by precisely calculating and setting the clear widths and heights of large, small, and transitional drains, the existing problem of poor drainage and discontinuous connection caused by mismatched drain sizes is addressed. Specifically, the calculation formulas for the clear heights H2 of the transitional type 1 drain 2-2 and H3 of the transitional type 2 drain 2-3 gradually decrease with increasing horizontal distance I, taking into account the slope differences (i1%-i2%) at different locations in the tunnel. This design ensures a smooth transition in drain height between different slopes, avoiding water flow shock or structural instability caused by sudden changes in drain height, thereby ensuring the stability and efficiency of the drainage system. The calculation formula for the clear width B2 of the transitional type 2 drain 2-3 gradually transitions from the width b1 of the small drain to the width B1 of the large drain, based on the length L3 of the transition section and the horizontal distance I from the starting point of the drain gradient. This gradual design allows for a natural transition in drain width, avoiding flow disturbances or structural stress concentrations caused by sudden width changes, thereby ensuring the stability and fluidity of the drainage system.

[0036] According to an embodiment of the present invention, the flow cross-section A of the drainage ditch is calculated according to the following formula: A=Q / V, where Q is the drainage volume and V is the design flow velocity, and the design flow velocity V is less than or equal to 4m / s.

[0037] In this embodiment, a formula for calculating the flow cross-section is introduced to address the mismatch between flow velocity and drainage volume in existing drainage ditch designs. Specifically, the flow cross-section of the drainage ditch is calculated using the formula A = Q / V, where the design flow velocity V is strictly controlled to no more than 4 m / s. This ensures efficient drainage while preventing scouring and structural damage caused by excessive flow velocity, thereby improving the stability and service life of the tunnel drainage system.

[0038] According to an embodiment of the present invention, the drainage requirements include rainwater, fire drainage, and tunnel internal cleaning water; the structural requirements include the topography of the tunnel and the drainage load.

[0039] According to another embodiment of the present invention, an open-cut tunnel drainage ditch is provided, comprising: a first section, which is a section of the tunnel with a small drainage volume and has a length of L1; a second section, which is a section of the tunnel with a large drainage volume and has a length of L2; and a third section, which is a transition section between the first section and the second section and has a length of L3.

[0040] In the prior art, drainage systems typically use uniformly sized drains, which cannot adapt to the drainage needs of different sections within a tunnel. In an embodiment of the present invention, by dividing the tunnel's drainage area into a first section with low drainage volume, a second section with high drainage volume, and a transition section between the first and second sections, drainage ditches of different sizes are arranged in each section. This solves the problems of low drainage efficiency, resource waste, and lack of flexibility caused by the use of uniformly sized drains in the prior art, making the drainage system more precise, economical, and adaptable to complex tunnel environments. Furthermore, the present invention can also be divided into four or more sections based on drainage needs, structural requirements, and other requirements.

[0041] According to an embodiment of the present invention, a small drainage ditch 2-4 is arranged in the first section, and the small drainage ditch 2-4 is disc-shaped, and its longitudinal slope is i1%, and the i1% is consistent with the longitudinal slope of the tunnel; a large drainage ditch 2-1 is arranged in the second section, and the longitudinal slope of the large drainage ditch 2-1 is i1%, and the i1% is consistent with the longitudinal slope of the tunnel; a transition type 1 drainage ditch 2-2 and a transition type 2 drainage ditch 2-3 are arranged in the third section, and the longitudinal slope of the transition type 1 drainage ditch 2-2 and the transition type 2 drainage ditch 2-3 is i2%, and i1%>i2%≥0.3%.

[0042] According to an embodiment of the present invention, the bottom of the transition type 1 drainage ditch 2-2 is backfilled with a ditch filling layer 3-1, which is used for adjusting in the vertical direction to connect with the large drainage ditch 2-1; the bottom of the transition type 2 drainage ditch 2-3 is backfilled with a ditch filling layer 3-1, and the side of the transition type 2 drainage ditch 2-3 adjacent to the large drainage ditch side wall 1-7 is backfilled with a ditch filling layer 3-1, which is used for adjusting in the vertical and horizontal directions to connect with the small drainage ditch 2-4.

[0043] The method of the present invention is further described in detail below with reference to specific embodiments and accompanying drawings.

[0044] The design method and steps of the open-cut tunnel drainage ditch are as follows:

[0045] (1) Drainage area division: During the design phase of an open-cut tunnel, the tunnel is first divided into several drainage areas based on the drainage requirements of different sections within the tunnel. The division of each drainage area should take into account factors such as rainwater, fire drainage, and tunnel internal cleaning water.

[0046] Figure 1 is a plan view of a drainage ditch according to an embodiment of the present invention, Figure 2 This is a elevational layout diagram of a drainage ditch according to an embodiment of the present invention, as shown in FIG. Figure 1 、 Figure 2As shown, the connecting section between the large drainage ditch and the small drainage ditch is divided into three sections. Section 1 is L1 long and is the small drainage ditch section. Section 2 is L2 long and is the large drainage ditch section. Section 3 is L3 long and is the transition section, which is divided into transition section 1 and transition section 2. Transition section 1 is a vertical transition section, and transition section 2 is a horizontal and vertical transition section.

[0047] (2) Determination of drainage ditch dimensions: For each drainage area, designers need to calculate the required drainage ditch dimensions based on parameters such as drainage volume, drainage distance, and drainage time, using hydraulic principles and drainage system design experience. These dimensions include the width, depth, and slope of the drainage ditch to ensure that the drainage ditch can effectively collect and transport groundwater within the area.

[0048] The large drainage ditch 2-1 is used in the section with larger drainage volume. Its longitudinal slope is i1%, which is consistent with the longitudinal slope of the tunnel. Its net width is B1 and its net height is H1.

[0049] Small drainage ditches 2-4 are used in smaller sections of the drainage ditch. The small drainage ditch 2-4 is dish-shaped with a longitudinal slope of i1%, which is consistent with the longitudinal slope of the tunnel, a net width of b1, and a net height of h1.

[0050] The vertical transition section adopts transition type 1 drainage ditch 2-2 with a longitudinal slope of i2%, and i1%>i2%≥0.3%, a net width of B1, and a net height of H2, where H2 is a change value and is calculated according to the following formula: H2=H1-I×(i1%-i2%), I is the horizontal distance from any position in the third section to the starting point 4-1 of the ditch gradient, and I≤L3.

[0051] The horizontal and vertical transition sections use transition type 2 drainage ditches 2-3 with a longitudinal slope of i2%, and i1%>i2%≥0.3%. The net width is B2 and the net height is H3, where B2 is a variable value and is calculated according to the following formula: B2=b1+2×(L3-I)×(B1-b1) / L3; H3 is a variable value and is calculated according to the following formula: H3=H1-I×(i1%-i2%).

[0052] The flow section A can be calculated using the following formula: A=Q / V, where A is the ditch area, Q is the drainage volume, and V is the design flow velocity. The maximum design flow velocity shall not exceed 4m / s.

[0053] (3) Drainage ditch setting: Based on the determined drainage ditch size, drainage ditches are set in each drainage area using prefabricated or cast-in-place methods.

[0054] Arrange small drainage ditches 2-4 in the first section;

[0055] Arrange a large drainage ditch 2-1 in the second section;

[0056] Arrange transition type 1 drainage ditch 2-2 and transition type 2 drainage ditch 2-3 in the third section;

[0057] Backfill the bottom of the transition type 1 drainage ditch 2-2 with a ditch filling layer 3-1 for adjusting it in the vertical direction to connect with the large drainage ditch 2-1;

[0058] The ditch filling layer 3-1 is backfilled at the bottom of the transition type 2 drainage ditch 2-3, and the ditch filling layer 3-1 is backfilled on the side of the transition type 2 drainage ditch 2-3 adjacent to the large drainage ditch side wall 1-7 for adjustment in the vertical and horizontal directions to connect with the small drainage ditch 2-4.

[0059] Through the implementation of the above technical solution, the present invention can reasonably set the size and layout of the drainage ditch according to the specific conditions of different sections in the tunnel, thereby improving the overall performance and efficiency of the drainage system, ensuring the safety of tunnel operation, and maximizing the project investment benefits.

[0060] The above embodiments are merely examples for the purpose of clearly illustrating the present invention and are not intended to limit the embodiments of the present invention. Those skilled in the art will appreciate that other variations or modifications may be made based on the following description. These variations, modifications, substitutions, and variations arising from the principles and spirit of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for designing drainage ditches in open-cut tunnels, characterized in that: The following steps are involved: According to the drainage needs and structural requirements of the tunnel, the drainage area of ​​the tunnel is divided into three sections, among which: The first section is the section with small displacement, and its length is L1; The second section is the section with large displacement, and its length is L2; The third section is a transition section between the first section and the second section, and has a length of L3; According to the divided drainage areas, drainage ditches of different sizes are arranged, including: Arranging a small drainage ditch (2-4) in the first section, wherein the small drainage ditch (2-4) is dish-shaped and has a longitudinal slope of i1%, wherein the i1% is consistent with the longitudinal slope of the tunnel; A large drainage ditch (2-1) is arranged in the second section, wherein the longitudinal slope of the large drainage ditch (2-1) is i1%, and the i1% is consistent with the longitudinal slope of the tunnel; In the third section, a transition type 1 drainage ditch (2-2) is provided to connect with the large drainage ditch (2-1), and a transition type 2 drainage ditch (2-3) is provided to connect with the transition type 1 drainage ditch (2-2) and the small drainage ditch (2-4). The longitudinal slope of the transition type 1 drainage ditch (2-2) and the transition type 2 drainage ditch (2-3) is i2%, and i1%>i2%≥0.3%; The bottom of the transition type 1 drainage ditch (2-2) is backfilled with a ditch filling layer (3-1) for adjusting in the vertical direction to connect with the large drainage ditch (2-1); the bottom of the transition type 2 drainage ditch (2-3) is backfilled with a ditch filling layer (3-1); the side of the transition type 2 drainage ditch (2-3) adjacent to the large drainage ditch sidewall (1-7) is backfilled with a ditch filling layer (3-1) for adjusting in the vertical and horizontal directions to connect with the small drainage ditch (2-4); The large drainage ditch (2-1) has a net width of B1 and a net height of H1; The net width of the small drainage ditch (2-4) is b1, and the net height is h1; The net width of the transition type 1 drainage ditch (2-2) is B1, and the net height is H2, wherein: H2 is the change value, and H2 is calculated according to the following formula: H2 = H1-I×(i1%-i2%), I is the horizontal distance from any position in the third section to the starting point (4-1) of the ditch gradient, I≤L3; The net width of the transition type 2 drainage ditch (2-3) is B2, and the net height is H3, wherein: B2 is the change value, which is calculated according to the following formula: B2 = b1 + 2 × (L3 - I) × (B1 - b1) / L3; H3 is the change value, which is calculated according to the following formula: H3 = H1 - I × (i1% - i2%); Calculate the flow cross section A of the drainage ditch according to the following formula: A=Q / V, where Q is the discharge volume and V is the design flow velocity, and the design flow velocity V is less than or equal to 4 m / s.

2. The design method according to claim 1, characterized in that: The drainage requirements include rainwater, fire drainage, and tunnel internal cleaning water; The structural requirements include the topography and drainage load of the tunnel.

3. An open-cut tunnel drainage ditch, characterized in that: include: The first section is a section of the tunnel with a small drainage volume and has a length of L1, wherein a small drainage ditch (2-4) is arranged in the first section. The small drainage ditch (2-4) is dish-shaped and has a longitudinal slope of i1%, which is consistent with the longitudinal slope of the tunnel; The second section is a section of the tunnel with a large drainage volume and a length of L2, wherein a large drainage ditch (2-1) is arranged in the second section, and the longitudinal slope of the large drainage ditch (2-1) is i1%, and the i1% is consistent with the longitudinal slope of the tunnel; The third section is a transition section between the first section and the second section, with a length of L3, wherein a transition type 1 drainage ditch (2-2) and a transition type 2 drainage ditch (2-3) are arranged in the third section, and the longitudinal slope of the transition type 1 drainage ditch (2-2) and the transition type 2 drainage ditch (2-3) is i2%, and i1%>i2%≥0.3%, wherein the bottom of the transition type 1 drainage ditch (2-2) is backfilled with a ditch filling layer (3-1) for adjusting in the vertical direction to connect with the large drainage ditch (2-1), the bottom of the transition type 2 drainage ditch (2-3) is backfilled with a ditch filling layer (3-1), and the side of the transition type 2 drainage ditch (2-3) adjacent to the side wall (1-7) of the large drainage ditch is backfilled with a ditch filling layer (3-1) for adjusting in the vertical and horizontal directions to connect with the small drainage ditch (2-4).

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