A construction method for expanding a small-section tunnel into a large-section tunnel in water-rich soil surrounding rock

Abstract

The application discloses a construction method for expanding a small-section tunnel into a large-section tunnel in water-rich soil surrounding rock, and belongs to the technical field of tunnel expansion construction. The small-section tunnel is constructed by using upper steps and lower steps, and the large-section tunnel is constructed by using upper steps, middle steps and lower steps, so that the upper step inclined excavation of the small-section tunnel can be connected with the upper step of the large-section tunnel, the upper step of the small-section tunnel is used as an advanced pilot hole for the inclined excavation of the large-section tunnel, the working face in the hole is increased, the reinforcement condition in the hole is formed, the construction safety is favorable, the high efficiency of the variable cross-section construction can be ensured, the vertical distance of the inclined section is separately formed into the middle steps and is separately excavated, the upper step of the small-section tunnel and the lower step of the large-section tunnel are excavated and then are cooperatively constructed, and the construction steps are clear and reasonable.

Description

Technical Field

[0001] This invention belongs to the field of tunnel expansion construction technology, and in particular relates to a construction method for expanding a small-section tunnel into a large-section tunnel in water-rich soil and surrounding rock. Background Technology

[0002] Tunnel construction inevitably involves variable cross-section tunnel construction, especially when the cross-section changes abruptly from small to large. During variable cross-section excavation, each excavation stage has a corresponding short-term tunnel shape, resulting in varied loading and unloading methods for the surrounding rock. This not only affects the stability of the surrounding rock during the widening stage but also influences the stress distribution and initial support stress condition after the tunnel is formed. In particular, the addition of unfavorable factors such as shallow burial with abundant water and weak surrounding rock leads to low construction efficiency and a high risk of construction collapse. Summary of the Invention

[0003] To address the shortcomings in the aforementioned background technology, this invention aims to provide a construction method for expanding a small-section tunnel into a large-section tunnel in water-rich soil and surrounding rock. This method solves the problem that existing variable-section tunnel construction methods involve excavating a short-term tunnel shape during construction, which can affect the stability of the surrounding rock during the expansion stage and increase the risk of construction collapse.

[0004] To achieve the above-mentioned objectives, the technical solution adopted by the present invention is as follows:

[0005] A construction method for expanding a small-section tunnel into a large-section tunnel in water-rich soil and surrounding rock is provided, comprising:

[0006] Step 1, Small cross-section tunnel construction: Excavate the upper step of the small cross-section tunnel until it connects with the junction of the small cross-section tunnel and the large cross-section tunnel, and provide initial support for the upper step of the small cross-section tunnel.

[0007] Step 2, Inclined Excavation: Using the upper step of the small-section tunnel, the inclined excavation area is excavated to the predetermined length within the large-section tunnel, and initial support is provided for the inclined excavation area;

[0008] Step 3, Excavation of large-section tunnel: The upper step of the large-section tunnel is expanded to the size of the large-section tunnel through the inclined excavation area, and the upper step of the expanded large-section tunnel is initially supported.

[0009] Step 4: Back excavation of the upper part of the inclined excavation area: The surrounding rock at the top of the inclined excavation area is back excavated to the junction of the small section tunnel and the large section tunnel to form a back excavation area. The back excavation direction of the inclined excavation area is from the upper step of the large section tunnel to the direction of the small section tunnel. The back excavation area is lined and supported.

[0010] Step 5: Excavation of the middle and lower steps of the large-section tunnel: Excavate the middle and lower steps of the large-section tunnel downwards within the upper step of the large-section tunnel. During the excavation process, the middle and lower steps of the large-section tunnel are supported by sidewalls simultaneously. The lower steps of the large-section tunnel are supported at the bottom after excavation.

[0011] Step 6: Excavation of the lower bench of the small cross-section tunnel: Excavate the lower bench of the small cross-section tunnel downward within the upper bench of the small cross-section tunnel, and provide bottom support for the lower bench of the small cross-section tunnel after excavation.

[0012] Furthermore, in step 1, before excavating the upper step of the small cross-section tunnel, multiple guide pipes are used to provide advance support for the arch of the small cross-section tunnel; after the upper step of the small cross-section tunnel is excavated, multiple grouting anchors are used to support the arch of the upper step of the small cross-section tunnel, a steel frame is used to support the middle of the upper step of the small cross-section tunnel, and mortar anchors and shotcrete are used to support the inner wall of the upper step of the small cross-section tunnel.

[0013] Furthermore, in step 2, before excavating the inclined excavation area, multiple guide pipes are used to provide advance support for the arch of the small-section tunnel.

[0014] The support and the excavation of the inclined excavation area are carried out simultaneously; the angle of the inclined excavation area is 30°, and the width of the inclined excavation area is consistent with the width of the upper step of the small cross-section tunnel. After the inclined excavation area is excavated to a height difference of 4.9m with the top of the upper step of the small cross-section tunnel, a 3.0m horizontal distance is reserved and excavated forward.

[0015] Furthermore, in step 3, when excavating the upper bench of the large-section tunnel, the construction is carried out in the order of first excavating the left side of the surrounding rock in the large-section tunnel, and then excavating the right side of the surrounding rock in the large-section tunnel.

[0016] Furthermore, in step 4, when back excavating the surrounding rock at the top of the inclined excavation area, the initial support at the top of the inclined excavation area is dismantled while the surrounding rock is being excavated; the excavation width of the back excavation area is consistent with the width of the large-section tunnel.

[0017] Furthermore, in step 5, the upper, middle, and lower steps of the large-section tunnel are all inverted step shapes; a leveling layer, a waterproof layer, a cement mortar protective layer, and a concrete layer are laid sequentially from bottom to top on the lower step of the large-section tunnel.

[0018] The beneficial effects of this invention are as follows:

[0019] 1. The present invention provides a construction method for expanding a small-section tunnel into a large-section tunnel in water-rich soil and surrounding rock. Compared with the existing variable-section tunnel construction method, this method uses the upper step of the small-section tunnel to diagonally excavate towards the large tunnel as a pilot tunnel, increasing the working face inside the tunnel and forming reinforcement conditions inside the tunnel. This is beneficial to construction safety and can also ensure the high efficiency of variable-section construction.

[0020] 2. The present invention provides a construction method for expanding a small-section tunnel into a large-section tunnel in water-rich soil and surrounding rock. The back excavation method is used for the construction of a small-section tunnel into a large-section tunnel with variable cross-section. Compared with direct expansion construction, it is more convenient for pipe jacking, steel frame erection, pipe grouting, etc., and the support is more efficient. At the same time, the construction safety factor is higher.

[0021] 3. The construction method of expanding a small-section tunnel into a large-section tunnel in water-rich soil rock according to the present invention provides support after the surrounding rock is excavated, which can effectively prevent tunnel collapse and improve safety.

[0022] 4. The present invention provides a construction method for expanding a small-section tunnel into a large-section tunnel in water-rich soil and surrounding rock. The small-section tunnel is constructed using upper and lower steps, while the large-section tunnel is constructed using upper, middle, and lower steps. This allows the inclined excavation of the upper step of the small-section tunnel to connect with the upper step of the large-section tunnel. Furthermore, the vertical distance of the inclined section is separately excavated as a middle step. Finally, the excavation of the upper step of the small-section tunnel and the lower step of the large-section tunnel are carried out in a coordinated manner, making the construction sequence clearer and more reasonable. Attached Figure Description

[0023] Figure 1 This is a flowchart of a construction method for expanding a small-section tunnel into a large-section tunnel in water-rich soil and surrounding rock.

[0024] Figure 2 This is a schematic diagram of the inclined excavation construction of a small-section tunnel leading to a large-section tunnel.

[0025] Figure 3 This is a schematic diagram of the upper steps and inclined excavation area support of a small-section tunnel.

[0026] Figure 4 This is a schematic diagram of the construction of a large-section tunnel expansion project.

[0027] Figure 5 This is a schematic diagram of the back excavation construction above the inclined excavation area.

[0028] Figure 6 A schematic diagram of lining support for the excavated area.

[0029] Figure 7 This diagram illustrates the excavation construction of the lower bench in a large-section tunnel and the lower bench in a small-section tunnel.

[0030] Figure 8 A schematic diagram of the support structure for all areas.

[0031] Among them, 1. Small cross-section tunnel; 2. Upper step of small cross-section tunnel; 3. Large cross-section tunnel; 4. Junction; 5. Inclined excavation area; 6. Upper step of large cross-section tunnel; 7. Backfilling area; 8. Middle step of large cross-section tunnel; 9. Lower step of large cross-section tunnel; 10. Lower step of small cross-section tunnel. Detailed Implementation

[0032] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0033] like Figure 1 As shown, this scheme provides a construction method for widening a small-section tunnel into a large-section tunnel in water-rich soil and surrounding rock, which includes:

[0034] Step 1, Construction of Small-Section Tunnel 1: (e.g.) Figure 2 As shown, the upper step 2 of the small cross-section tunnel is excavated in the small cross-section tunnel 1 until it connects with the junction 4 of the small cross-section tunnel 1 and the large cross-section tunnel 3, and the upper step 2 of the small cross-section tunnel is initially supported.

[0035] like Figure 3 As shown, in step 1, before excavating the upper step 2 of the small cross-section tunnel, multiple guide pipes are used to provide advance support for the arch of the small cross-section tunnel 1. Specifically, the guide pipes are 3.5m long, 42mm in diameter, with a circumferential longitudinal spacing of 0.4m × 1.5m, arranged in a quincunx pattern, and with an overlap distance of 1m.

[0036] After the excavation of the upper step 2 of the small-section tunnel is completed, multiple grouting anchors are used to support the arch of the upper step 2. The grouting anchors are 3m long, 25mm in diameter, and arranged in a staggered pattern with a circumferential spacing of 1×1m. A steel frame is used to support the middle of the upper step 2 of the small-section tunnel; mortar anchors and shotcrete are used to support the inner wall of the upper step 2 of the small-section tunnel.

[0037] The mortar anchor bolts are 3.5m long, 18mm in diameter, and 1×1m in circumferential spacing, arranged in a quincunx pattern; the concrete used is C25 shotcrete with a thickness of 200mm.

[0038] Step 2, Inclined Excavation: (e.g.) Figure 2As shown, the inclined excavation area 5 is excavated to a predetermined length through the upper step 2 of the small cross-section tunnel within the large cross-section tunnel 3, and initial support is provided for the inclined excavation area 5.

[0039] Specifically, in step 2, before excavating the inclined excavation area 5, multiple guide pipes are used to provide advance support for the arch of the small cross-section tunnel 1. Based on the horizontal direction of the arch top of the small cross-section tunnel 1, Φ42mm guide pipes are erected at an angle of 30° upwards. The length of the guide pipes is 3.5m, the circumferential longitudinal spacing of the multiple guide pipes is 0.4m×1.5m, the multiple guide pipes are arranged in a quincunx pattern, the overlap distance is 1m, and the overlap width is consistent with that of the small cross-section tunnel 1. When reaching the top of the large cross-section tunnel 3, the overlap form is based on the shape of the arch of the large cross-section tunnel 3, and the overlap width is consistent with the width of the inclined surface. Then, the guide pipes are erected horizontally forward for another 3.0m.

[0040] The support and the excavation of the inclined excavation area 5 are carried out simultaneously. The angle of the inclined excavation area 5 is 30°. The width of the inclined excavation area 5 is consistent with the width of the upper step 2 of the small cross section tunnel. After the inclined excavation area 5 is excavated to a height difference of 4.9m with the top of the upper step 2 of the small cross section tunnel, it is then excavated horizontally forward to leave a 3.0m horizontal distance.

[0041] like Figure 3 As shown, the initial support for the inclined excavation area 5 is specifically as follows: Multiple hollow grouting anchor bolts with a diameter of 25mm, a length of 3.5m, and a circumferential spacing of 1×1m, arranged in a staggered pattern, are installed in the arch of the inclined excavation area 5. A 240mm thick layer of concrete is sprayed onto the inner wall of the arch of the inclined excavation area 5. Multiple mortar anchor bolts with a diameter of 18mm, a length of 3.5m, and a circumferential spacing of 1×1m, arranged in a staggered pattern are installed on the sidewalls of the inclined excavation area 5; a 200mm thick layer of concrete is sprayed onto the sidewalls of the inclined excavation area 5.

[0042] Step 3, Excavation and widening of the large-section tunnel 3: (e.g.) Figure 4 As shown, the upper step 6 of the large-section tunnel is expanded within the large-section tunnel 3 through the inclined excavation area 5 to the size of the large-section tunnel 3, and initial support is provided for the expanded upper step 6 of the large-section tunnel; in step 3, when expanding the upper step 6 of the large-section tunnel, the construction is carried out in the order of first excavating the left side of the surrounding rock in the large-section tunnel 3, and then excavating the right side of the surrounding rock in the tunnel.

[0043] Step 4, Excavation of the upper part of the inclined excavation area 5: (e.g.) Figure 5 and Figure 6As shown, the surrounding rock at the top of the inclined excavation area 5 is back excavated to the junction 4 of the small-section tunnel 1 and the large-section tunnel 3 to form the back excavation area 7. The back excavation direction of the inclined excavation area 5 is from the upper step of the large-section tunnel 3 towards the small-section tunnel 1. The back excavation area 7 is lined and supported. In step 4, when back excavating the surrounding rock at the top of the inclined excavation area 5, the initial support at the top of the inclined excavation area 5 is dismantled while the surrounding rock is being excavated. The excavation width of the back excavation area 7 is consistent with the width of the large-section tunnel 3.

[0044] Step 5: Excavation and construction of the lower bench of the large-section tunnel 3: (e.g.) Figure 7 and Figure 8 As shown, the middle step 8 and the lower step 9 of the large cross-section tunnel are excavated downward within the upper step 6 of the large cross-section tunnel. During the excavation process, the middle step 8 and the lower step of the large cross-section tunnel are supported by sidewalls simultaneously, and the lower step 9 of the large cross-section tunnel is supported at the bottom after the excavation is completed.

[0045] In step 5, the upper, middle, and lower steps of the large-section tunnel are all inverted step shapes. On the lower step 9 of the large-section tunnel, a leveling layer, a waterproofing layer, a cement mortar protective layer, and a concrete layer are laid sequentially from bottom to top. The leveling layer is a 100mm thick fine aggregate concrete layer, the waterproofing layer is a 1.5mm thick HDPE self-adhesive waterproof membrane, the cement mortar protective layer is 20mm thick, and the concrete layer is 500mm thick and graded C40.

[0046] Step 6: Excavation of the lower step 10 of the small cross-section tunnel: Excavate the lower step 10 of the small cross-section tunnel downward within the upper step 2 of the small cross-section tunnel, and provide bottom support for the lower step 10 of the small cross-section tunnel after excavation.

[0047] In summary, the construction method for expanding a small-section tunnel 1 into a large-section tunnel in water-rich soil rock, as described in this invention, compared to existing variable-section tunnel construction methods, utilizes the upper step 2 of the small-section tunnel to diagonally excavate towards the large-section tunnel as a pilot tunnel, increasing the working face within the tunnel and creating reinforcement conditions, which is beneficial for construction safety while ensuring high efficiency in variable-section construction. The backfilling method used for the variable-section construction from the small-section tunnel 1 to the large-section tunnel 3 is more convenient than direct expansion excavation in terms of duct splicing, steel frame erection, and duct grouting, resulting in more efficient support. It is highly efficient and has a higher construction safety factor. Support is provided after the surrounding rock is excavated, which can effectively prevent tunnel collapse and improve safety. The small cross-section tunnel 1 adopts upper and lower bench construction, while the large cross-section tunnel 3 adopts upper, middle and lower bench construction. This allows the inclined excavation of the upper bench 2 of the small cross-section tunnel to connect with the upper bench 6 of the large cross-section tunnel. The vertical distance of the inclined section is separately excavated as a middle bench. Finally, the excavation of the upper bench 2 of the small cross-section tunnel and the lower bench 9 of the large cross-section tunnel are carried out in a coordinated manner, making the construction sequence clearer and more reasonable.

Claims

1. A construction method for expanding a small-section tunnel into a large-section tunnel in water-rich soil and surrounding rock, characterized in that, include: Step 1, Small cross-section tunnel construction: Excavate the upper step of the small cross-section tunnel until it connects with the junction of the small cross-section tunnel and the large cross-section tunnel, and provide initial support for the upper step of the small cross-section tunnel. Step 2, Inclined Excavation: Using the upper step of the small-section tunnel, the inclined excavation area is excavated to the predetermined length within the large-section tunnel, and initial support is provided for the inclined excavation area; Step 3, Excavation of large-section tunnel: The upper step of the large-section tunnel is expanded to the size of the large-section tunnel through the inclined excavation area, and the upper step of the expanded large-section tunnel is initially supported. Step 4: Back excavation of the upper part of the inclined excavation area: The surrounding rock at the top of the inclined excavation area is back excavated to the junction of the small section tunnel and the large section tunnel to form a back excavation area. The back excavation direction of the inclined excavation area is from the upper step of the large section tunnel to the direction of the small section tunnel. The back excavation area is lined and supported. Step 5: Excavation of the middle and lower steps of the large-section tunnel: Excavate the middle and lower steps of the large-section tunnel downwards within the upper step of the large-section tunnel. During the excavation process, the middle and lower steps of the large-section tunnel are supported by sidewalls simultaneously. The lower steps of the large-section tunnel are supported at the bottom after excavation. Step 6: Excavation of the lower bench of the small cross-section tunnel: Excavate the lower bench of the small cross-section tunnel downward within the upper bench of the small cross-section tunnel, and provide bottom support for the lower bench of the small cross-section tunnel after excavation.

2. The construction method for expanding a small-section tunnel into a large-section tunnel in water-rich soil and surrounding rock according to claim 1, characterized in that, In step 1, before excavating the upper step of the small-section tunnel, multiple guide pipes are used to provide advance support for the arch of the small-section tunnel; after the upper step of the small-section tunnel is excavated, multiple grouting anchors are used to support the arch of the upper step of the small-section tunnel, a steel frame is used to support the middle of the upper step of the small-section tunnel, and mortar anchors and shotcrete are used to support the inner wall of the upper step of the small-section tunnel.

3. The construction method for expanding a small-section tunnel into a large-section tunnel in water-rich soil and surrounding rock according to claim 1, characterized in that, In step 2, before excavating the inclined excavation area, multiple guide pipes are used to provide advance support for the arch of the small-section tunnel. The support and the excavation of the inclined excavation area are carried out simultaneously; the angle of the inclined excavation area is 30°, and the width of the inclined excavation area is consistent with the width of the upper step of the small cross-section tunnel. After the inclined excavation area is excavated to a height difference of 4.9m with the top of the upper step of the small cross-section tunnel, a 3.0m horizontal distance is reserved and excavated forward.

4. The construction method for expanding a small-section tunnel into a large-section tunnel in water-rich soil and surrounding rock according to claim 1, characterized in that, In step 3, when excavating the upper bench of the large-section tunnel, the construction is carried out in the order of first excavating the left side of the surrounding rock in the large-section tunnel, and then excavating the right side of the surrounding rock in the large-section tunnel.

5. The construction method for expanding a small-section tunnel into a large-section tunnel in water-rich soil and surrounding rock according to claim 1, characterized in that, In step 4, when back excavating the surrounding rock at the top of the inclined excavation area, the initial support at the top of the inclined excavation area is dismantled while the surrounding rock is being excavated; the excavation width of the back excavation area is consistent with the width of the large-section tunnel.

6. The construction method for expanding a small-section tunnel into a large-section tunnel in water-rich soil and surrounding rock according to claim 1, characterized in that, In step 5, the upper, middle and lower steps of the large-section tunnel are all inverted step shape; on the lower step of the large-section tunnel, a leveling layer, a waterproof layer, a cement mortar protective layer and a concrete layer are laid from bottom to top.

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