High pressure jet grouting pile combined reinforcement method for soil body of sinking type mountain tunnel portal under ultra-shallow water-rich soft surrounding rock

Abstract

The present application relates to a high-pressure rotary jet grouting pile combination reinforcing method for a sinking mountain tunnel portal soil body under super-shallow buried water-rich soft surrounding rock, which uses high-pressure rotary jet grouting piles to reinforce the sinking mountain tunnel portal soil body under super-shallow buried water-rich soft surrounding rock, digs a construction platform at the portal, and forms a reinforced area by constructing high-pressure rotary jet grouting piles on the construction platform, the reinforced area including a vertical water-stop curtain and a radial fan-shaped water-stop curtain arranged in sequence along the tunnel advancing direction; in the vertical water-stop curtain area, the high-pressure rotary jet grouting piles are vertically punched, and multiple vertical high-pressure rotary jet grouting piles are arranged longitudinally in parallel with each other and transversely in a plum blossom shape; in the radial fan-shaped water-stop curtain area, the high-pressure rotary jet grouting piles are obliquely punched, and multiple high-pressure rotary jet grouting piles are arranged longitudinally in a radial fan shape and transversely in a plum blossom shape. The present application can effectively reinforce the soil body, ensure the safety and controllability of tunnel excavation, has wide application value, and belongs to the field of underground engineering geotechnical techniques.

Description

Technical Field

[0001] This invention relates to the field of geotechnical engineering for underground engineering, specifically to a high-pressure jet grouting pile combination reinforcement structure and method for the soil at the entrance of a submerged mountain tunnel in ultra-shallow, water-rich, and weak surrounding rock. Background Technology

[0002] Urban mountain tunnels are underground transportation passages built to traverse mountains or hilly areas within urban areas, combining the engineering characteristics of mountain tunnels with urban transportation service functions. They are generally located inside urban built-up areas or suburban mountains, connecting urban transportation nodes, optimizing road network structure, shortening travel distances between urban areas, alleviating surface traffic pressure, and promoting regional interconnectivity.

[0003] Shallow-buried mountain tunnels with abundant water and weak surrounding rock in urban areas are among the most geologically complex and risky types of urban tunnel construction. Their core characteristics are shallow burial depth (usually <20m), high groundwater level, low strength of surrounding rock, and softening upon contact with water.

[0004] Common reinforcement structures for the entrance of shallow, water-rich, soft rock mountain tunnels in urban areas include: grid-type arrangement, layered reinforcement, combined grouting pipes, and water-stop curtains. These reinforcement structures typically use vertical high-pressure jet grouting piles (perpendicular to the horizontal direction) and grouting to reinforce the overburden layer at the tunnel top. If the overburden thickness is large, vertical high-pressure jet grouting piles often produce many empty piles, while grouting reinforcement is often accompanied by poor reinforcement effect and environmental pollution, resulting in high project costs and a lot of waste of resources. Summary of the Invention

[0005] To address the technical problems existing in the prior art, the purpose of this invention is to provide a method for reinforcing the soil at the entrance of a submerged mountain tunnel in ultra-shallow, water-rich, and weak surrounding rock with a combination of high-pressure jet grouting piles.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A combined high-pressure jet grouting method for soil reinforcement at the entrance of a submerged mountain tunnel in ultra-shallow, water-rich, and weak surrounding rock conditions is proposed. This method utilizes high-pressure jet grouting piles to reinforce the soil at the tunnel entrance. A construction platform is excavated at the tunnel entrance, and high-pressure jet grouting piles are installed on the platform to form a reinforcement zone. This zone includes a vertical water-stop curtain and a radial fan-shaped water-stop curtain arranged sequentially along the tunnel's direction of travel. In the vertical water-stop curtain zone, high-pressure jet grouting piles are driven vertically, with multiple piles arranged parallel to each other longitudinally and in a staggered pattern laterally. In the radial fan-shaped water-stop curtain zone, high-pressure jet grouting piles are driven inclined, with multiple piles arranged radially in a fan shape longitudinally and in a staggered pattern laterally.

[0008] As a preferred option, in a radial fan-shaped water-stop curtain, the lower ends of all high-pressure jet grouting piles are located on the same arc surface.

[0009] As a preferred embodiment, the elevation of the tunnel arch top is 13.378m, the elevation of the arch bottom is 12.678m, and the elevation of the top of the soil to be reinforced is 10.678m; the elevation of the construction platform is 8.5m, the length is 6.7m, and the width is 17m, and the construction platform is located at the waist of the newly built tunnel arch; the elevation of the tunnel invert top is 0.7m, and the elevation of the invert bottom is 0m.

[0010] As a preferred approach, a reinforcement circle with a radius of 18m is drawn with the original ground surface at the top of the tunnel 0.5m above the arch as the center, forming an arc surface along the tunnel's forward direction. The spacing between the projections of the pile bottoms on the arc surface is controlled at 0.6m. Radial high-pressure jet grouting piles are installed 1m away from the toe of the slope to be reinforced, and vertical high-pressure jet grouting piles are installed at distances of 1.6m, 2.2m, 2.8m, and 3.4m from the toe of the slope to be reinforced.

[0011] As a preferred embodiment, the number of high-pressure jet grouting piles is 231, with 35 vertical high-pressure jet grouting piles and 196 radial high-pressure jet grouting piles. The high-pressure jet grouting piles are divided into 14 columns along the transverse direction. The odd-numbered columns have 17 high-pressure jet grouting piles along the longitudinal direction, of which 3 are vertical and 14 are radial. The even-numbered columns have 16 high-pressure jet grouting piles along the longitudinal direction, of which 2 are vertical and 14 are radial. The vertical high-pressure jet grouting piles are located on one side of the arch starting point, and the radial high-pressure jet grouting piles are located on the other side of the arch starting point.

[0012] As a preferred option, vertical high-pressure jet grouting piles are driven perpendicular to the arch bottom; radial high-pressure jet grouting piles are constructed at a certain angle to the vertical: the angle between odd-numbered columns and odd-numbered rows of high-pressure jet grouting piles and the vertical ranges from 9° to 68°, the angle between odd-numbered columns and even-numbered rows of high-pressure jet grouting piles and the vertical ranges from 4° to 62°, the angle between even-numbered columns and odd-numbered rows of high-pressure jet grouting piles and the vertical ranges from 2° to 59°, and the angle between even-numbered columns and even-numbered rows of high-pressure jet grouting piles and the vertical ranges from 7° to 65°; the length of the vertical high-pressure jet grouting piles is 12.46m; in the radial high-pressure jet grouting piles, the length of the piles in the odd-numbered columns ranges from 12.66m to 15.30m, and the length of the piles in the even-numbered columns ranges from 12.62m to 15.05m.

[0013] As a preferred option, the high-pressure jet grouting piles are double-tube high-pressure jet grouting piles with a diameter of 0.6m. Any three high-pressure jet grouting piles form an equilateral triangle with a side length of 1.2m on the pile bottom plane projection. Here, the pile bottom plane projection refers to the intersection of the high-pressure jet grouting piles arranged radially at a distance of 1m from the toe of the slope M with the arc surface formed by the reinforcement circle with center O of 0.5m above the arch top (i.e., the original ground surface at the tunnel top) and the arc surface.

[0014] As a preferred option, the soil to be reinforced is naturally sloped to the construction platform with a slope ratio of 1:4, and a 10cm layer of sprayed concrete is applied to the slope surface.

[0015] As a preferred option, on the construction platform, the radial high-pressure jet grouting piles are arranged radially downwards with a horizontal line 1m away from the toe of the slope as the center line.

[0016] As a preferred method, the high-pressure jet grouting pile combination reinforcement method for the soil at the entrance of a submerged mountain tunnel in ultra-shallow, water-rich, and weak surrounding rock includes the following steps:

[0017] (1) By using geological survey data, verify the positional relationship between the soil to be reinforced and the bottom of the tunnel, and determine whether it is necessary to reinforce and improve the soil at the tunnel entrance;

[0018] (2) If reinforcement is required, the width of the soil to be reinforced in the tunnel is determined by measuring and setting out the inner contour line of the arch.

[0019] (3) Determine the depth of the soil to be reinforced by supplementing the geological columnar section and the tunnel bottom elevation;

[0020] (4) Through test piles, verify the layout, pile diameter, pile length, grout mix ratio, grouting pressure, drilling speed, lifting speed and rotation process parameters of the high-pressure jet grouting piles;

[0021] (5) Along the longitudinal excavation direction of the tunnel, the soil is reinforced and improved by the alternating pile jumping method to form a composite foundation soil reinforcement area.

[0022] (6) Monitor the settlement and stability of the arch of the tunnel.

[0023] The present invention has the following advantages:

[0024] 1. This invention employs a longitudinally radial and vertically and laterally staggered arrangement of high-pressure jet grouting piles to reinforce soil, forming a gridded cement-soil composite pile structure. Compared to the traditional technique of constructing interlocking vertical high-pressure jet grouting piles on the tunnel roof, the thickness of the overburden significantly reduces the length of individual piles and the number of interlocking piles, resulting in a smaller and more economical pile arrangement and avoiding excessive resource waste. Compared to the traditional technique of vertical small-diameter pipe grouting on the tunnel roof surface, this invention reduces the number of small-diameter pipes used and the uneven grouting effect, avoiding cement slurry waste and environmental pollution due to diffusion. It achieves precise reinforcement, controllable pile quality, and adaptability to complex geological conditions.

[0025] 2. The two types of water-stop curtain structures of the present invention can be effectively combined to produce a linkage effect, forming a radial fan-shaped water-stop curtain and a vertical water-stop curtain wall. The radial fan-shaped water-stop curtain has a large range of reinforcement and depth due to the large angle range of the piles. The adjacent piles form a thickened interlocking zone, which reduces the soil moisture content and improves the bearing capacity of the foundation at the bottom of the tunnel arch and the lateral earth pressure resistance.

[0026] 3. Vertical water-stop curtain walls can serve as a "retaining wall" at the interface between open-cut and cut-and-cover tunnels, improving the anti-sliding stability of the soil at the tunnel entrance. The tunnel arch is safe and controllable during excavation, enabling simultaneous excavation of the foundation pit for both types of tunnels and significantly shortening the construction period. Attached Figure Description

[0027] Figure 1 It is a plan view of the high-pressure jet grouting pile bottom reinforcement of the soil inside the arch of the tunnel entrance.

[0028] Figure 2 This is a longitudinal section layout diagram of the high-pressure jet grouting pile reinforcement of the soil inside the arch of the tunnel entrance.

[0029] Figure 3 This is a diagram showing the arrangement of high-pressure jet grouting piles in an equilateral triangle within the arch of a mined tunnel entrance.

[0030] Figure 4 yes Figure 1 Layout diagram of medium and high pressure jet grouting piles.

[0031] Figure 5 yes Figure 2 Enlarged view of medium- and high-pressure jet grouting piles.

[0032] Among them, 1-road edge line, 2-inner contour edge line of the arch, 3-arch start point, 4-arch end point, 5-high pressure jet grouting pile reinforcement circle, 6-construction platform, 7-radial and vertical high pressure jet grouting piles. Detailed Implementation

[0033] The present invention will now be described in further detail with reference to specific embodiments.

[0034] Example 1

[0035] In this embodiment, the sunken mountain tunnel is longitudinally connected to the lowest elevation point of the open-cut tunnel structure. High-pressure jet grouting is used to reinforce and improve the soil and foundation excavated over a large area beneath the arch of the tunnel, forming a dense and stable water-stop curtain structure. After the soil reinforcement is completed, the tunnel excavation and the excavation of the second steel support for the open-cut tunnel can be carried out simultaneously.

[0036] A combined high-pressure jet grouting method for soil reinforcement at the entrance of a submerged mountain tunnel in ultra-shallow, water-rich, and weak surrounding rock conditions is proposed. This method utilizes high-pressure jet grouting piles to reinforce the soil at the tunnel entrance. A construction platform is excavated at the tunnel entrance, and high-pressure jet grouting piles are installed on the platform to form a reinforcement zone. This zone includes a vertical water-stop curtain and a radial fan-shaped water-stop curtain arranged sequentially along the tunnel's direction of travel. In the vertical water-stop curtain zone, high-pressure jet grouting piles are driven vertically, with multiple piles arranged parallel to each other longitudinally and in a staggered pattern laterally. In the radial fan-shaped water-stop curtain zone, high-pressure jet grouting piles are driven inclined, with multiple piles arranged radially in a fan shape longitudinally and in a staggered pattern laterally.

[0037] In this embodiment, the longitudinal length of the reinforced area is 20m (based on the horizontal projection of the pile end) and the transverse width is 15.4m (based on the horizontal projection of the pile end).

[0038] In the radial fan-shaped water-stop curtain, the lower ends of all high-pressure jet grouting piles are located on the same arc surface.

[0039] The elevation of the tunnel arch top is 13.378m, the elevation of the arch bottom is 12.678m, and the elevation of the top of the soil to be reinforced is 10.678m; the construction platform has an elevation of 8.5m, a length of 6.7m, and a width of 17m, and is located at the waist of the new tunnel arch; the elevation of the tunnel invert top is 0.7m, and the elevation of the invert bottom is 0m.

[0040] Using the original ground level at the top of the tunnel, 0.5m above the arch, as the center, and a radius of 18m, a reinforcement circle is drawn, forming an arc surface along the tunnel's direction of travel. The spacing between the projected bottoms of each pile on the arc surface is controlled at 0.6m. Radial high-pressure jet grouting piles are installed 1m away from the toe of the slope to be reinforced, and vertical high-pressure jet grouting piles are installed at distances of 1.6m, 2.2m, 2.8m, and 3.4m from the toe of the slope to be reinforced.

[0041] In this embodiment, based on the geological survey columnar section, the reinforcement depth should extend at least 2m into the clay layer at the bottom of the tunnel invert, thus determining the center O and radius R. The toe M of the slope to be reinforced is shown below. Figure 5 .

[0042] There are 231 high-pressure jet grouting piles, including 35 vertical high-pressure jet grouting piles and 196 radial high-pressure jet grouting piles. The high-pressure jet grouting piles are divided into 14 rows along the transverse direction. The odd-numbered rows have 17 high-pressure jet grouting piles along the longitudinal direction, including 3 vertical high-pressure jet grouting piles and 14 radial high-pressure jet grouting piles. The even-numbered rows have 16 high-pressure jet grouting piles along the longitudinal direction, including 2 vertical high-pressure jet grouting piles and 14 radial high-pressure jet grouting piles. The vertical high-pressure jet grouting piles are located on one side of the arch starting point, and the radial high-pressure jet grouting piles are located on the other side of the arch starting point.

[0043] In this embodiment, there are a total of 14 columns in odd and even columns, 7 columns in odd columns and 7 columns in even columns; there are a total of 33 rows in odd columns and even columns, 17 rows in odd columns and even columns, and 16 rows in even columns and even columns, with 9 rows in odd columns and 8 rows in even columns; and 8 rows in even columns and 8 rows in even columns.

[0044] Vertical high-pressure jet grouting piles are arranged in odd-numbered columns and rows, totaling 7 columns and 2 rows, numbered as 1-1 to 1-3, 3-1 to 3-3...13-1 to 13-3; vertical high-pressure jet grouting piles are arranged in odd-numbered columns and even-numbered rows, totaling 7 columns and 1 row, numbered as 1-2, 3-2...13-2; vertical high-pressure jet grouting piles are arranged in even-numbered columns and even-numbered rows, totaling 7 columns and 1 row, numbered as 2-1, 4-1...14-1; vertical high-pressure jet grouting piles are arranged in even-numbered columns and even-numbered rows, totaling 7 columns and 1 row, numbered as 2-2, 4-2...14-2; radial high-pressure jet grouting piles are arranged in odd-numbered columns and even-numbered rows. The odd-numbered rows of the sequence total 7 columns and 7 rows, numbered as 1-5, 1-7...13-5, 13-17; the radial high-pressure jet grouting piles have odd-numbered columns and even-numbered rows totaling 7 columns and 7 rows, numbered as 1-4, 1-6...13-14, 13-16; the radial high-pressure jet grouting piles have even-numbered columns and odd-numbered rows totaling 7 columns and 7 rows, numbered as 2-3, 2-5...14-13, 14-15; the radial high-pressure jet grouting piles have even-numbered columns and even-numbered rows totaling 7 columns and 7 rows, numbered as 2-4, 2-6...14-14, 14-16.

[0045] Vertical high-pressure jet grouting piles are driven perpendicular to the arch bottom; radial high-pressure jet grouting piles are constructed at a certain angle to the vertical: the angle between odd-numbered columns and odd-numbered rows of high-pressure jet grouting piles and the vertical is 9°–68°, the angle between odd-numbered columns and even-numbered rows of high-pressure jet grouting piles and the vertical is 4°–62°, the angle between even-numbered columns and odd-numbered rows of high-pressure jet grouting piles and the vertical is 2°–59°, and the angle between even-numbered columns and even-numbered rows of high-pressure jet grouting piles and the vertical is 7°–65°; the length of vertical high-pressure jet grouting piles is 12.46m; in radial high-pressure jet grouting piles, the length of odd-numbered columns ranges from 12.66m to 15.30m, and the length of even-numbered columns ranges from 12.62m to 15.05m.

[0046] In this embodiment, the angle between the radial high-pressure jet grouting piles in odd-numbered columns and rows and the vertical direction is 9° to 68°, such as the angle of the 5th row of the 1st column being 9° and the angle of the 17th row of the 1st column being 68°. The angle between the radial high-pressure jet grouting piles in odd-numbered columns and even-numbered rows and the vertical direction is 4° to 62°, such as the angle of the 4th row of the 1st column being 4° and the angle of the 16th row of the 1st column being 62°. The angle between the radial high-pressure jet grouting piles in even-numbered columns and odd-numbered rows and the vertical direction is 2° to 59°, such as the angle of the 3rd row of the 2nd column being 2° and the angle of the 15th row of the 2nd column being 59°. The angle between the radial high-pressure jet grouting piles in even-numbered columns and even-numbered rows and the vertical direction is 7° to 65°, such as the angle of the 4th row of the 2nd column being 7° and the angle of the 16th row of the 2nd column being 65°.

[0047] In this embodiment, in the radial high-pressure jet grouting piles, the pile length of odd-numbered columns ranges from 12.66m to 15.30m, such as the pile length of the 4th row of the 1st column being 12.66m and the pile length of the 17th row of the 1st column being 15.30m. The pile length of even-numbered columns ranges from 12.62m to 15.05m, such as the pile length of the 4th row of the 2nd column being 12.62m and the pile length of the 16th row of the 2nd column being 15.05m.

[0048] The high-pressure jet grouting piles use a double-tube high-pressure jet grouting pile design with a diameter of 0.6m. Any three high-pressure jet grouting piles are installed in... Figure 1 The pile bottom forms an equilateral triangle with a side length of 1.2m on the plane projection.

[0049] In this embodiment, the high-pressure jet grouting pile has a water-cement ratio of 1:1, a pressure of 20-40 MPa, a drilling speed of 30-40 cm / min, a lifting speed of 20-25 cm / min, a rotation speed of 20-25 rpm, and an unconfined compressive strength of not less than 1.2 MPa at 28 days of age.

[0050] The soil to be reinforced is naturally sloped to the construction platform with a slope ratio of 1:4, and a 10cm layer of sprayed concrete is applied to the slope surface.

[0051] On the construction platform, radial high-pressure jet grouting piles are arranged diagonally downwards with a horizontal line 1m away from the toe of the slope as the center line.

[0052] The method for reinforcing the soil at the entrance of an ultra-shallow, water-rich, soft, and submerged mountain tunnel using a combination of high-pressure jet grouting piles includes the following steps:

[0053] (1) By using geological survey data, verify the positional relationship between the soil to be reinforced and the bottom of the tunnel, and determine whether it is necessary to reinforce and improve the soil at the tunnel entrance;

[0054] (2) If reinforcement is required, the width of the soil to be reinforced in the tunnel is determined by measuring and setting out the inner contour line of the arch.

[0055] (3) Determine the depth of the soil to be reinforced by supplementing the geological columnar section and the tunnel bottom elevation;

[0056] (4) Through test piles, verify the layout, pile diameter, pile length, grout mix ratio, grouting pressure, drilling speed, lifting speed and rotation process parameters of the high-pressure jet grouting piles;

[0057] (5) Along the longitudinal direction of the tunnel, the soil is reinforced and improved by the alternating pile jumping method to form a composite foundation soil reinforcement area.

[0058] (6) Monitor the settlement and stability of the arch of the tunnel.

[0059] This invention employs a novel combined arrangement of high-pressure jet grouting piles. The longitudinal piles utilize a combination of fan-shaped radial and vertical arrangements, while the transverse piles are arranged at the center of the distance between two longitudinal piles, forming a staggered pattern. The radial high-pressure jet grouting piles are fully distributed without interlocking joints, forming a fan-shaped water-stop curtain structure. Compared to a surface arrangement with all vertical jet grouting piles interlocking, this reduces the amount of pile work and saves on construction costs. The vertical high-pressure jet grouting piles form a 3m thick vertical water-stop curtain wall, providing both support and waterproofing, ensuring... Simultaneous excavation of earthwork in both open-cut and cut-and-cover tunnels effectively improves the stability of the tunnel arch and core soil at the tunnel entrance, as well as the surface settlement of the tunnel roof during the excavation process. The quincunx arrangement of transverse piles connects the longitudinal fan-shaped and vertical water-stop curtain reinforcement structures into a whole, improving the overall stability of the soil at the tunnel entrance. This invention, through the implementation of a combination of radial, vertical, and quincunx-shaped reinforced soil piles, can effectively reinforce mountain soils with water-rich and weak soil layers, ensuring safe and controllable tunnel excavation, and has broad application value.

[0060] Comparative Example 1

[0061] This comparative example uses a vertical high-pressure jet grouting pile water-stop curtain constructed above the surface soil at the tunnel entrance. The high-pressure jet grouting piles are spaced 0.4m apart, have an interlocking overlap of 0.2m, and are 21m long, totaling 1295 piles. Other construction process parameters are the same as in Example 1.

[0062] Comparative Example 2

[0063] This comparative example uses small-diameter pipes to reinforce the soil above the surface soil at the tunnel entrance. The pipes have a diameter of D = 50 mm, a spacing of 0.6 m, and are arranged in a quincunx pattern. The pipes are 5 m long and there are a total of 863 pipes.

[0064] Comparison of different reinforcement schemes:

[0065] Table 1 Comparison of Different Reinforcement Schemes

[0066]

[0067]

[0068] As can be seen from the table above, in terms of pile length: the average length of the vertical piles in Example 1 is 12.46m, and the average length of the radial piles is 13.91m. The pile lengths of Comparative Examples 1 and 2 are 21m and 5m respectively, which are 37.14% and 163.70% less and 163.70% more than Comparative Examples 1 and 2 respectively. The pile length of Example 1 is of medium length among the three schemes.

[0069] Regarding the number of piles: Example 1 has 231 piles, while Comparative Examples 1 and 2 have 1295 and 863 piles respectively, which are 82.16% and 73.23% less than Comparative Examples 1 and 2 respectively. The number of piles in Example 1 is the fewest among the three schemes.

[0070] Regarding cement usage: Example 1 used 885.5t, while Comparative Examples 1 and 2 used 7614.6t and 2406.2t respectively, which is a reduction of 88.37% and 63.20% compared to Comparative Examples 1 and 2. The cement usage in Example 1 is the lowest among the three schemes.

[0071] Regarding the construction period: Example 1 took 25 days, while Comparative Examples 1 and 2 took 35 days and 40 days respectively, which is 28.57% and 37.5% shorter than Comparative Examples 1 and 2 respectively. The construction period of Example 1 is the shortest among the three schemes.

[0072] Regarding the settlement of the arch fitting: Example 1 has a settlement of 5 mm, while Comparative Examples 1 and 2 have settlements of 15 mm and 60 mm respectively, which are 66.67% and 91.67% lower than Comparative Examples 1 and 2 respectively. The settlement of the arch fitting in Example 1 is the smallest among the three schemes.

[0073] Regarding the grouting effect: Example 1 is good, Comparative Examples 1 and 2 are good and poor respectively. The grouting effect of Example 1 and Comparative Example 1 is the best among the three schemes.

[0074] In summary, among the three comparative schemes, considering overall benefits, Example 1 > Comparative Example 1 > Comparative Example 2. In Example 1, the two types of water-stop curtain structures can be effectively combined to produce a synergistic effect, forming a radial fan-shaped water-stop curtain and a vertical water-stop curtain wall. The radial fan-shaped water-stop curtain, due to the large angle range of the piles, has a wide reinforcement range and depth. Adjacent piles form a thickened interlocking zone, reducing soil moisture content and improving the bearing capacity and lateral earth pressure resistance of the foundation at the bottom of the tunnel arch. The vertical water-stop curtain wall can serve as a "retaining wall" at the interface between open-cut and cut-and-cover tunnels, improving the anti-sliding stability of the soil at the tunnel entrance. The tunnel arch is safe and controllable during excavation, enabling simultaneous excavation of the foundation pit for both types of tunnels, significantly shortening the construction period.

[0075] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for reinforcing the soil at the entrance of a sunken mountain tunnel in ultra-shallow, water-rich, and weak surrounding rock, using a combination of high-pressure jet grouting piles. The method is characterized by: A construction platform is excavated at the tunnel entrance, and high-pressure jet grouting piles are installed on the platform to form a reinforced area. The reinforced area includes a vertical water-stop curtain and a radial fan-shaped water-stop curtain arranged sequentially along the tunnel's direction of travel. In the vertical water-stop curtain area, high-pressure jet grouting piles are driven vertically, with multiple vertical high-pressure jet grouting piles arranged parallel to each other longitudinally and in a staggered pattern laterally. In the radial fan-shaped water-stop curtain area, high-pressure jet grouting piles are driven inclined, with multiple high-pressure jet grouting piles arranged radially in a fan shape longitudinally and in a staggered pattern laterally. The construction platform is located at the arch waist of the newly constructed tunnel.

2. The method for reinforcing the soil at the entrance of a submerged mountain tunnel in shallow, water-rich, soft rock as described in claim 1, is characterized by: In the radial fan-shaped water-stop curtain, the lower ends of all high-pressure jet grouting piles are located on the same arc surface.

3. The method for reinforcing the soil at the entrance of a shallow, water-rich, soft, and weak mountain tunnel using a combination of high-pressure jet grouting piles, as described in claim 2, is characterized by: The elevation of the tunnel arch top is 13.378m, the elevation of the arch bottom is 12.678m, and the elevation of the top of the soil to be reinforced is 10.678m; the elevation of the construction platform is 8.5m, the length is 6.7m, and the width is 17m; the elevation of the tunnel invert top is 0.7m, and the elevation of the invert bottom is 0m.

4. The method for reinforcing the soil at the entrance of a shallow, water-rich, soft, and weak mountain tunnel using a combination of high-pressure jet grouting piles, as described in claim 3, is characterized in that: Using the original ground level at the top of the tunnel, 0.5m above the arch, as the center, and a radius of 18m, a reinforcement circle is drawn, forming an arc surface along the tunnel's direction of travel. The spacing between the projected bottoms of each pile on the arc surface is controlled at 0.6m. Radial high-pressure jet grouting piles are installed 1m away from the toe of the slope to be reinforced, and vertical high-pressure jet grouting piles are installed at distances of 1.6m, 2.2m, 2.8m, and 3.4m from the toe of the slope to be reinforced.

5. The method for reinforcing the soil at the entrance of a submerged mountain tunnel in shallow, water-rich, soft rock as described in claim 4, is characterized in that: The number of high-pressure jet grouting piles is 231, of which 35 are vertical and 196 are radial. The high-pressure jet grouting piles are divided into 14 rows along the transverse direction. The odd-numbered rows have 17 high-pressure jet grouting piles along the longitudinal direction, of which 3 are vertical high-pressure jet grouting piles and 14 are radial high-pressure jet grouting piles. The even-numbered rows have 16 high-pressure jet grouting piles along the longitudinal direction, of which 2 are vertical high-pressure jet grouting piles and 14 are radial high-pressure jet grouting piles. Vertical high-pressure jet grouting piles are located on one side of the arch starting point, while radial high-pressure jet grouting piles are located on the other side of the arch starting point.

6. The method for reinforcing the soil at the entrance of a shallow, water-rich, soft, and weak mountain tunnel using a combination of high-pressure jet grouting piles, as described in claim 5, is characterized in that: Vertical high-pressure jet grouting piles are installed perpendicular to the bottom of the arch; Radial high-pressure jet grouting piles are constructed at a certain angle to the vertical: the angle between the odd-numbered columns and odd-numbered rows of high-pressure jet grouting piles and the vertical is 9°~68°, the angle between the odd-numbered columns and even-numbered rows of high-pressure jet grouting piles and the vertical is 4°~62°, the angle between the even-numbered columns and odd-numbered rows of high-pressure jet grouting piles and the vertical is 2°~59°, and the angle between the even-numbered columns and even-numbered rows of high-pressure jet grouting piles and the vertical is 7°~65°. The vertical high-pressure jet grouting pile has a length of 12.46m; In radial high-pressure jet grouting piles, the length of odd-numbered rows of piles ranges from 12.66m to 15.30m, while the length of even-numbered rows ranges from 12.62m to 15.05m.

7. The method for reinforcing the soil at the entrance of a shallow, water-rich, soft, and weak mountain tunnel using a combination of high-pressure jet grouting piles, as described in claim 2, is characterized in that: The high-pressure jet grouting pile adopts a double-pipe high-pressure jet grouting pile with a diameter of 0.6m. Any three high-pressure jet grouting piles can form an equilateral triangle with a side length of 1.2m on the bottom plane projection.

8. The method for reinforcing the soil at the entrance of a shallow, water-rich, soft, and weak mountain tunnel using a combination of high-pressure jet grouting piles, as described in claim 3, is characterized in that: The soil to be reinforced is naturally sloped to the construction platform with a slope ratio of 1:4, and a 10cm layer of sprayed concrete is applied to the slope surface.

9. The method for reinforcing the soil at the entrance of a submerged mountain tunnel in shallow, water-rich, soft rock as described in claim 4, is characterized in that: On the construction platform, radial high-pressure jet grouting piles are arranged diagonally downwards with a horizontal line 1m away from the toe of the slope as the center line.

10. The method for reinforcing the soil at the entrance of a submerged mountain tunnel in shallow, water-rich, soft rock as described in claim 1, is characterized in that... Includes the following steps: (1) By checking the positional relationship between the soil to be reinforced and the bottom of the tunnel through geological supplementary survey data, it is determined whether the soil at the tunnel entrance needs to be reinforced and improved. (2) If reinforcement is required, the width of the soil to be reinforced in the tunnel is determined by measuring and setting out the inner contour line of the arch. (3) Determine the depth of the soil to be reinforced by supplementing the geological columnar section and the bottom elevation of the tunnel; (4) Through test piles, verify the layout, pile diameter, pile length, grout mix ratio, grouting pressure, drilling speed, lifting speed and rotation process parameters of the high-pressure jet grouting piles; (5) Along the longitudinal direction of the tunnel excavation, the soil is reinforced and improved using the alternating pile skipping method to form a composite foundation soil reinforcement area; (6) Monitor the settlement and stability of the arch of the tunnel.

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