A method for sealing underground rivers in karst geological formations

Abstract

This invention relates to the field of dam construction technology and discloses a method for sealing underground rivers in karst geology, comprising the following steps: Step 1: In the dam construction area, geophysical exploration and drilling techniques are used to confirm the location of underground rivers and karst cave groups that cross the curtain line; Step 2: A grouting adit is set up at the dam foundation to expose the morphology of the underground rivers and karst cavities, detect the flow velocity and flow rate of the underground river, and locate the inflow and outflow points of the underground river within the karst cavity; Step 3: A first collection well is set up to collect the water flow, with its top connected to the grouting adit; a second collection well is set up at the outflow point to collect the water flow, and a backfill grouting pipe is pre-embedded from the grouting adit to the outflow point; Step 4: A pouring hole is drilled at the top of the karst cave, and steel sleeves are installed in the pouring hole from the ground surface to the karst cavity; Step 5: Concrete is poured into the karst cavity through the pouring hole to backfill the cavity, and then the inflow point is sealed. This provides a stable, reliable, highly safe, and effective method for sealing underground rivers.

Description

Technical Field

[0001] This invention relates to the field of dam construction technology, specifically to a method for sealing underground rivers in karst geological conditions. Background Art

[0002] Constructing reservoirs in karst depressions has advantages such as minimizing the use of arable land, and the reservoir capacity can be composed of surface (karst depression) capacity and underground (karst pipelines, solution fissure systems) capacity, resulting in greater benefits and a more rational development approach. Since suitable karst depressions for reservoir construction are mainly located in river source areas, gravity-fed water supply to the receiving areas can be achieved, making it a project that promotes harmony between humans and nature.

[0003] Conventional dam construction methods for sealing underground rivers and karst cavities typically involve detecting leaks using various surface methods and then filling the cavities with grouting materials to achieve sealing and seepage prevention. This approach is particularly effective in special geological formations, such as elevated strata, karst caves, and wide fissure zones. However, under conditions of large-volume karst cavities, high-flow-rate flowing water, existing technologies often result in grouting materials that are easily diluted or washed away by the water flow, leading to significant waste. Furthermore, these methods are insufficient to completely seal underground rivers under conditions of high flow-rate, high-velocity flowing water, resulting in far from ideal performance.

[0004] The irregular dimensions of the karst cavity, through which the underground river flows, do not meet the requirements for large-scale mechanical equipment construction. Furthermore, the presence of flowing underground water within the cavity necessitates the interception and sealing of this river, making construction difficult, costly, and posing significant safety risks due to the confined space nature of the work. Therefore, a method for sealing underground rivers in karst geology is needed to ensure the safety, speed, and effectiveness of the sealing operation within the karst cavity. Summary of the Invention

[0005] The present invention aims to provide a method for sealing underground rivers in karst geological formations, providing a stable, reliable, safe, and effective method for sealing underground rivers.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a method for sealing underground rivers in karst geological formations, comprising the following steps:

[0007] Step 1: In the dam construction area, use geophysical exploration technology to confirm whether there are underground rivers, karst caves, and water channels that cross the curtain line and to confirm their locations;

[0008] The second step is to set up a grouting adit at the dam foundation to expose the morphology of the underground river and karst cavity, detect the flow velocity and flow rate of the underground river, and find the water inlet and outlet points of the underground river in the karst cavity.

[0009] Step 3: Set up the first water collection well at the water inlet to collect the water flow, and connect the top of the first water collection well to the grouting adit; set up the second water collection well at the water outlet to collect the water flow, and pre-embed the backfill grouting pipe from the grouting adit to the water outlet;

[0010] Step 4: Drill pouring holes at the top of the cave. Install steel sleeves in the pouring holes from the ground surface to the cave cavity. The ends of the steel sleeves are connected to flexible hoses.

[0011] Step 5: Pour concrete into the cavity through the pouring hole to backfill the cavity, and then seal the water inlet.

[0012] The beneficial effects of this plan are:

[0013] 1. This technical solution is used to seal the underground river and backfill the karst cave. By setting up a grouting adit at the dam foundation, it is possible to penetrate deep into the karst cavity, thereby accurately understanding the morphology of the underground river and the karst cavity, accurately detecting the flow velocity and flow rate of the water in the underground river, and fully grasping the characteristics of the karst cavity. Based on the above conditions, further sealing measures can be set up, and the amount of concrete to be poured in the later construction and the number of water pumps that need to be reasonably configured can be initially estimated, so as to ensure the orderly progress of subsequent construction and ensure the effective sealing of the underground river.

[0014] 2. For underground rivers and karst caves that cross the curtain line, thorough sealing is required. Otherwise, after the dam is completed, upstream water will still leak downstream through the underground rivers, causing poor dam seepage prevention. Therefore, it is necessary to focus on and fully fill the underground rivers and karst caves that cross the curtain line. In the third step, locate the water inlet (outlet of underground river water) and outlet (outflow point of underground river water) of the karst cave. Set up the first collection well at the water inlet to collect the water flow. The top of the first collection well is connected to the grouting adit. A water pump can be set up in the grouting adit to promptly pump out the water flow from the collection well, cutting off the water flow at the water inlet and creating a waterless construction environment to ensure the effectiveness of subsequent sealing. Pre-embed backfill grouting pipes to facilitate sealing the outlet point in the later stages of construction and ensure the sealing of the karst cavity.

[0015] 3. Concrete is delivered into the karst cavity via a steel casing, resulting in lower construction costs and faster pouring speed. The flexible hoses installed inside the cavity facilitate pouring at various points, taking advantage of their mobility. Since karst cavities are often irregularly shaped, the use of flexible hoses ensures thorough backfilling, guaranteeing a tight seal and stability. This backfilling process creates a robust sealing layer, effectively sealing underground rivers and karst caves.

[0016] Preferably, as an improvement, the fourth step includes the following specific steps:

[0017] 4.1: Survey and set out to determine the specific location of the material outlet at the top of the karst cave. Then, use GPS to accurately measure the specific location of the drilling and pouring hole on the ground and mark it.

[0018] 4.2: When the drilling rig is in place, use a spirit level to repeatedly check the position of the drilling rig to ensure that the borehole is vertical and the deviation is no more than 2%.

[0019] 4.3: Drilling construction, install the drilling rig, and ensure that the drilling rig is level and stable; the vertical axis of the drilling rig is consistent with the designed hole direction. When the drilling depth reaches within 1m of the top of the cavity, drilling should be carried out slowly at a low speed.

[0020] 4.4: Use steel sleeves for segmented installation, with threaded connections between adjacent sleeves.

[0021] The beneficial effects are as follows: First, a suitable outlet is found at a higher point inside the karst cave to ensure the smooth injection of subsequent concrete. Then, GPS is used to locate the corresponding drilling position on the ground to ensure the accuracy and precision of the construction, ensuring that subsequent construction can be precisely targeted at the target area. Before the drilling rig is in place, a spirit level is used to repeatedly check the position of the drilling rig to ensure the verticality of the borehole, thereby ensuring that the outlet is drilled to the set position. The installation of the steel casing can provide support and protection for the borehole wall, preventing borehole collapse and damage, while also maintaining the verticality and dimensional stability of the borehole, providing a reliable foundation for subsequent backfilling and grouting work. When the drilling depth reaches within 1m of the top of the karst cavity, drilling should be carried out slowly at a low speed. The above settings are to ensure the safety of construction as much as possible and prevent the collapse of the karst cave caused by excessive speed. A collapse of the karst cave would prolong the construction period and may also lead to rockfalls or other unstable situations. The above settings can avoid posing dangers to construction personnel.

[0022] Preferably, as an improvement, step five includes the following specific steps:

[0023] 5.1: To mix self-compacting concrete, put the weighed aggregates and cementitious materials into the mixer for dry mixing. After adding water and admixtures, continue mixing for more than 60 seconds until the workability of the self-compacting concrete meets the standards before it can be discharged from the mixer.

[0024] 5.2: Construction reserved passage: A reserved passage shall be set up between the first water collection well and the grouting adit;

[0025] 5.3: Concrete pouring: First, backfill below the bottom of the grouting adit, then construct the tunnel lining. After the tunnel lining reaches the design strength, backfill both sides in layers, with each layer being 1.5m thick. Finally, backfill the area above the arch in layers until the karst cave is backfilled and compacted.

[0026] The beneficial effects are as follows: Firstly, the self-compacting concrete is mixed in the first step. Self-compacting concrete has high fluidity, allowing it to effectively bypass obstacles in the grout cavity and fully fill any part of the cavity. It requires no tamping and can be compacted under its own weight. Secondly, it can eliminate air bubbles and voids during pouring, improving the density and uniformity of the concrete, thereby enhancing the sealing and stability of the sealing layer. A reserved passage between the first water collection well and the grouting adit facilitates material transportation and equipment access during construction, providing a convenient construction route, ensuring smooth construction, and reducing interference with the sealing area. The layered backfilling method ensures the uniformity and density of the concrete, preventing voids and uneven filling during construction.

[0027] Preferably, as an improvement, the first water collection well is a reinforced concrete structure, and a steel ladder is provided on the side wall of the first water collection well, and the first water collection well is set at an angle.

[0028] The beneficial effects are as follows: Since the water pressure at the inlet point is often high, the reinforced concrete structure, with its high strength and stability, provides a robust collection well structure capable of withstanding water pressure and external loads, ensuring the stability and safety of the first collection well for effective water collection and control. By installing steel ladders on the sidewall of the first collection well, a convenient and safe access route to and from the well is provided, facilitating monitoring, maintenance, and pump placement, ensuring the safety and smoothness of the construction process. The angled design better guides the water flow into the first collection well, reduces flow resistance, and improves flow speed and efficiency.

[0029] Preferably, as an improvement, in the third step, if the cavity is large and extends downstream, the cavity pipe opening is sealed with masonry.

[0030] The beneficial effects are: masonry has good resistance to water erosion and can remain stable in humid environments, ensuring the durability and stability of the sealing layer; at the same time, masonry construction is convenient for obtaining materials locally from the construction site, and can be shaped according to the shape of the cavity to fill the cavity and form a complete sealing layer, while saving the amount of concrete required for filling.

[0031] Preferably, as an improvement, in the fourth step, drilling is carried out using a diamond drill bit on an XY-2 type drilling rig, and deep hole drilling is carried out using a rotary drilling rig and a carbide or diamond drill bit.

[0032] The beneficial effects are as follows: The XY-2 drilling rig, when paired with diamond drill bits, can provide efficient drilling speed and results. Diamond drill bits have high hardness and wear resistance, and can handle relatively hard geological layers, including rocks and limestone. The rotary drilling rig has a large drilling depth and drilling capacity, and can meet the needs of deeper drilling. Drilling using the above-mentioned models can improve construction efficiency, meet the needs of deep hole drilling, ensure high-quality drilling results, and ensure the construction quality of the cast-in-place holes.

[0033] Preferably, as an improvement, in the fourth step, the sleeves are connected by threaded joints, and when the threaded joints are connected, the installed sleeves are fixed and securely fastened with a sleeve locker.

[0034] The beneficial effects are as follows: threaded connections enable tight connections and high sealing between sleeves, and the use of threaded connections can improve the stability and robustness of the connection between sleeves; at the same time, the use of a sleeve locking device can further increase the safety and stability of the sleeve connection, prevent the sleeves from loosening or shifting, provide additional support and protection, ensure the sleeve connection is firm and secure, and avoid the risk of accidental loosening and damage.

[0035] Preferably, as an improvement, a V-shaped funnel is welded near the surface pipe opening of the casing for unloading, and a flange is welded at the casing opening at the top of the cave, with the hose connected to the casing through the flange.

[0036] The beneficial effects are as follows: the V-shaped funnel design can guide concrete to the hose, realize a smooth unloading process, and improve construction efficiency; welding a flange at the sleeve opening at the top of the karst cave can provide a stable connection point, and the flange can ensure the sealing of the connection, ensuring a stable and reliable connection between the hose and the sleeve. This setting can prevent loosening or grout leakage and ensure the smooth progress of construction.

[0037] Preferably, as an improvement, the free fall height of the concrete in the karst cave in the fifth step should not exceed 2m. If it exceeds 2m, a slow descent measure should be adopted for pouring.

[0038] The beneficial effects are as follows: the above-mentioned settings can prevent aggregate separation during the free fall of concrete slurry, and avoid causing concrete stratification and voids, which would affect the density and uniformity of the sealing layer. By adopting slow-fall measures, the concrete can be uniformly filled into the karst cave, reducing the occurrence of stratification and voids.

[0039] Preferably, as an improvement, step 5 also includes step 5.4: embedding a backfill grouting pipe on the top arch of the grouting adit, the backfill grouting pipe penetrating more than 10cm into the bedrock, and then grouting the backfill grouting pipe.

[0040] The beneficial effects are as follows: by burying backfill grouting pipes at the top arch of the grouting adit and penetrating more than 10cm into the bedrock, the connection and bonding force between the grouting adit and the bedrock can be increased, forming a firm bond and improving the stability and reliability of the grouting adit position. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the cave morphology in an embodiment of the present invention;

[0042] Figure 2 This is a cross-sectional view of the grouting adit in an embodiment of the present invention;

[0043] Figure 3 A cross-sectional view of the reserved channel in an embodiment of the present invention;

[0044] Figure 4 This is a cross-sectional view of the second water collection well according to an embodiment of the present invention;

[0045] Figure 5 This is a cross-sectional view of the first water collection well according to an embodiment of the present invention;

[0046] Figure 6 This is a schematic diagram of the structure of the infusion cavity in an embodiment of the present invention. Detailed Implementation

[0047] The following detailed description illustrates the specific implementation method:

[0048] The reference numerals in the accompanying drawings include: 1. Curtain line; 2. Grouting adit; 3. Solution cavity; 4. Water inlet point; 5. Water outlet point; 6. First water collection well; 7. Steel ladder; 8. Second water collection well; 9. Backfill grouting pipe; 10. Masonry wall; 11. Bedrock; 12. Drainage pipe; 13. Reserved passage; 14. Flange; 15. V-shaped funnel; 16. Sleeve; 17. Flexible hose.

[0049] Example

[0050] A method for sealing underground rivers in karst geological formations includes the following steps:

[0051] Step 1: In the dam construction area, geophysical exploration and drilling techniques are used to confirm the location of any underground rivers, karst caves, or water channels that cross Curtain Line 1, obtaining the following results: Figure 1 The diagram shown;

[0052] Step 2: Set up a grouting adit 2 at the dam foundation to expose the morphology of the underground river and the karst cavity 3, detect the flow velocity and flow rate of the underground river, and find the water inlet 4 and water outlet 5 of the underground river in the karst cavity 3.

[0053] By setting up a grouting adit 2 at the dam foundation, it is possible to penetrate deep into the karst cavity 3, thereby accurately understanding the morphology of the underground river and the karst cavity 3, accurately detecting the flow velocity and flow rate of the water in the underground river, fully grasping the characteristics of the karst cavity 3, and then further setting up sealing measures based on the above conditions, preliminarily estimating the amount of concrete to be poured in the later construction and the number of water pumps that need to be reasonably configured, so as to ensure the orderly progress of subsequent construction and ensure the effective sealing of the underground river.

[0054] Step 3: As Figure 2 As shown, the first collection well 6 is set up at water inlet point 4 to collect the water flow, such as... Figure 5 The top of the first collection well 6 is connected to the grouting adit 2. Water from upstream rises to the elevation of the first collection well 6 and is then drained into the grouting adit 2. A drainage pipe 12 is installed in the first collection well 6, or a water pump can be used to extract water from it. The first collection well 6 is a C25 reinforced concrete structure. Since the water pressure at the water inlet 4 is often high, the reinforced concrete structure provides high strength and stability, ensuring a robust collection well structure capable of withstanding water pressure and external loads. A steel ladder 7 is installed on the side wall of the first collection well 6, with a step spacing of 30cm. The first collection well 6 is angled with a slope ratio of 1:0.5.

[0055] like Figure 4 As shown, a second water collection well 8 is set up at water elimination point 5 to collect the water flow. A backfill grouting pipe 9 is pre-embedded from the grouting adit 2 to water elimination point 5. The second water collection well 8 is made of masonry. After the cavity 3 is backfilled to the elevation of the grouting adit 2, grouting is carried out through the backfill grouting pipe 9 to seal the water elimination point 5. Cement mortar is poured first, followed by cement grout.

[0056] If the karst cavity 3 is large and extends downstream, the pipe opening of the karst cavity 3 shall be sealed with masonry to form a masonry wall 10. The thickness of the masonry wall 10 shall be at least 50cm to prevent concrete from flowing outward along the karst pipe during backfilling and to ensure that the karst cavity 3 is backfilled densely and fully.

[0057] Therefore, it is necessary to focus on and fully fill the underground river and karst cave that pass through the curtain line 1. In the third step, find the water inlet 4 (the water outlet of the underground river) and the water outlet 5 (the water outflow point of the underground river) of the karst cave. Set up the first water collection well 6 at the water inlet 4 to collect the water flow. The top of the first water collection well 6 is connected to the grouting adit 2. A water pump can be set up in the grouting adit 2 to extract the water flow in the first water collection well 6 in time, cut off the water flow at the water inlet 4, and form a waterless construction environment to ensure the effectiveness of the subsequent sealing. The backfill grouting pipe 9 is pre-embedded to facilitate the sealing of the water outlet 5 in the later stage of construction and ensure the sealing of the karst cavity 3.

[0058] The fourth step includes the following steps:

[0059] 4.1: Surveying and setting out to determine the specific location of the outlet at the top of the karst cave. Further, using GPS, accurately measure and mark the exact location of the drilling and pouring holes on the ground. First, find a suitable outlet at a higher point inside the karst cave to ensure smooth subsequent concrete injection. Then, use GPS to find the corresponding drilling location on the ground to ensure the accuracy and precision of the construction. Drill a 200mm hole at the marked location, and install a 194mm steel sleeve 16 inside the hole. The steel sleeve 16 extends from the ground surface to the top of the karst cave. Figure 6 As shown, a V-shaped funnel 15 is welded to the surface pipe opening for unloading. A flange 14 is welded to the steel pipe opening at the top of the cave, and then a 194mm flexible hose 17 is connected. The flexible hose 17 is connected to the sleeve 16 through the flange 14. The mobility of the flexible hose 17 is used to pour concrete into various parts of the cave cavity 3.

[0060] 4.2: Position the drilling rig and use a spirit level to repeatedly check the position of the drilling rig to ensure that the drill hole is vertical, thereby ensuring that the position of the discharge port is hit at the set position, with a deviation of no more than 2%.

[0061] 4.3: Drilling Construction. Install the drilling rig, ensuring it is level and stable. Use an XY-2 type drilling rig with a diamond drill bit for rotary drilling. For deep hole drilling, use a rotary drilling rig with carbide or diamond drill bits. Using the above-mentioned models can improve construction efficiency, meet the requirements of deep hole drilling, ensure high-quality drilling results, and ensure the construction quality of the casting holes. The vertical axis of the drilling rig and the direction of the hollow pipe should be consistent with the designed hole direction. Longer, larger diameter drill bits should be used for drilling, and the drilling pressure should be appropriately controlled. When the drilling depth reaches within 1m of the top of cavity 3, drilling should be slow and low-speed. The above settings are to ensure construction safety as much as possible and prevent the collapse of the cavity due to excessive speed. A collapse of the cavity will prolong the construction period and may also lead to rockfalls or other unstable situations. The above settings can avoid danger to construction personnel.

[0062] 4.4: After drilling is completed, install 194mm steel casing in sections. Each section of casing 16 is 2m long. The casing 16 is connected by threads. The threaded connection ensures a tight connection and high sealing between the casing 16. When connecting the threaded connection, the installed casing 16 is fixed firmly with a pipe locking device. The pipe locking device can further increase the safety and stability of the casing 16 connection and prevent the casing 16 from loosening or shifting.

[0063] Step 5: Backfill cavity 3 by pouring concrete into cavity 3 through the pouring hole, as shown below. Figure 6 As shown.

[0064] 5.1: Mixing C15 self-compacting concrete, put the weighed aggregates and cementitious materials into the mixer for dry mixing. After adding water and admixtures, continue mixing for more than 60 seconds until the workability of the self-compacting concrete meets the standards before it can be discharged from the machine. Self-compacting concrete has the characteristics of high fluidity. It can effectively bypass obstacles in the cavity 3 and fully fill any position in the cavity 3. At the same time, it does not require tamping operation and can be compacted under its own gravity.

[0065] 5.2: For example Figure 3 As shown, a reserved passage 13 is constructed between the first water collection well 6 and the grouting adit 2. The reserved passage 13 is lined with 30cm thick C25 reinforced concrete, and is a gate-shaped passage with dimensions of 1.0m × 1.0m (width × height). The formwork is installed and reinforced on-site using 50mm*50mm square timber and bamboo plywood. Joints in the formwork are sealed with adhesive strips to prevent grout leakage during concrete pouring. Before each layer of concrete backfill, the reserved passage 13 is constructed, with a construction height not less than the concrete backfill height. The reserved passage 13 rises with the height of the backfill concrete, extending until it is level with the tunnel floor. The reserved passage 13 facilitates material transportation and equipment access during construction, providing a convenient construction route, ensuring smooth construction progress, and minimizing interference with the sealing area.

[0066] 5.3: Concrete pouring. First, backfill the area below the bottom of the grouting adit 2, then construct the tunnel lining. After the tunnel lining reaches 100% of its design strength, backfill both sides in layers, with each layer being 1.5m thick. Finally, backfill the area above the arch in layers, also in layers, with each layer being 1.5m thick, until the karst cave is compacted. The free fall height of concrete within the karst cave should not exceed 2m. If it exceeds 2m, use slow-fall measures for pouring, such as using chutes, inclined troughs, or pipes, to prevent aggregate segregation during free fall and to avoid concrete stratification and voids, which would affect the compactness and uniformity of the sealing layer.

[0067] 5.4: Two backfill grouting pipes 9 are symmetrically embedded on the top arch of the grouting adit 2, penetrating at least 10cm into the bedrock. The backfill grouting pipes 9 are spaced 3m apart. Grouting is then performed on the backfill grouting pipes 9 to increase the connection and adhesion between the grouting adit 2 and the bedrock 11, forming a strong bond and improving the stability and reliability of the grouting adit 2's position. The backfill grouting pipes 9 should extend to a distant location upstream and downstream of the grouting adit 2 to ensure that the gap between the sealing concrete and the wall of the cavity 3 is backfilled densely.

[0068] Step 6: Use geotextile bags to seal the reserved channel 13 and then seal the water inlet point 4. Geotextile bags are selected as the material, which has good adaptability to the cross-section of the reserved channel 13 and is easy to construct. When using geotextile bags for sealing, since the geotextile bags have a certain degree of permeability and do not leak cement, after concrete or cement mortar is poured in, excess water is squeezed out through the gaps in the fabric, which can quickly reduce the water-cement ratio and accelerate the setting speed of concrete. It has advantages for sealing large or high-speed water flows and is suitable for sealing underground rivers.

[0069] Step six includes the following specific steps:

[0070] 6.1 Weld multiple layers of steel fences into the reserved channel 13 to limit the mold bag;

[0071] 6.2 Make a film bag of appropriate size and lay the film bag in the reserved channel 13;

[0072] 6.3 Grout the formwork bag, and the overall thickness of the grouting should exceed 1m.

[0073] 6.4 Seal the reserved passage completely. After the membrane bag is grouted to stop the water, pump out the water in the water collection well at the water inlet and quickly backfill with self-compacting concrete with an appropriate amount of quick-setting agent to ensure that the reserved passage is sealed quickly.

[0074] The above descriptions are merely embodiments of the present invention, and common knowledge such as specific technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A method for sealing underground rivers in karst geological formations, characterized in that: The following steps are involved: Step 1: In the dam construction area, use geophysical exploration technology to confirm whether there are underground rivers, karst caves, and water channels that cross the curtain line and to confirm their locations; The second step is to set up a grouting adit at the dam foundation to expose the morphology of the underground river and karst cavity, detect the flow velocity and flow rate of the underground river, and find the water inlet and outlet points of the underground river in the karst cavity. Step 3: Set up the first water collection well at the water inlet to collect the water flow, and connect the top of the first water collection well to the grouting adit; set up the second water collection well at the water outlet to collect the water flow, and pre-embed the backfill grouting pipe from the grouting adit to the water outlet; Step 4: Drill pouring holes at the top of the cave. Install steel sleeves in the pouring holes from the ground surface to the cave cavity. The ends of the steel sleeves are connected to flexible hoses. Step 5: Pour concrete into the cavity through the pouring hole to backfill the cavity, and then seal the water inlet. Step 5 includes the following specific steps: 5.1: To mix self-compacting concrete, put the weighed aggregates and cementitious materials into the mixer for dry mixing. After adding water and admixtures, continue mixing for more than 60 seconds until the workability of the self-compacting concrete meets the standards before it can be discharged from the mixer. 5.2: Construction reserved passage: A reserved passage shall be set up between the first water collection well and the grouting adit; 5.3: Concrete pouring: First, backfill below the bottom of the grouting adit, then construct the tunnel lining. After the tunnel lining reaches the design strength, backfill both sides in layers, with each layer being 1.5m thick. Finally, backfill the area above the arch in layers until the karst cave is backfilled and compacted. Step 6: Use the grouting method with geotextile bags to seal the reserved channel and thus block the water inlet.

2. The method for sealing underground rivers in karst geological formations according to claim 1, characterized in that: The fourth step includes the following specific steps: 4.1: Survey and set out to determine the specific location of the material outlet at the top of the karst cave. Then, use GPS to accurately measure the specific location of the drilling and pouring hole on the ground and mark it. 4.2: Once the drilling rig is in place, use a spirit level to repeatedly check its position to ensure the borehole is vertical, with a deviation of no more than 2%. 4.3: Drilling construction, install the drilling rig, and ensure that the drilling rig is level and stable; the vertical axis of the drilling rig is consistent with the designed hole direction. When the drilling depth reaches within 1m of the top of the cavity, drilling should be carried out slowly at a low speed. 4.4: Use steel sleeves for segmented installation, with threaded connections between adjacent steel sleeves.

3. The method for sealing underground rivers in karst geological formations according to claim 2, characterized in that: The first water collection well is a reinforced concrete structure, and a steel ladder is installed on the side wall of the first water collection well. The first water collection well is set at an angle.

4. The method for sealing underground rivers in karst geological formations according to claim 3, characterized in that: In the third step, if the cavity is large and extends downstream, the cavity pipe opening is sealed with masonry.

5. A method for sealing underground rivers in karst geological formations according to claim 4, characterized in that: In the fourth step, the steel sleeves are connected by thread. When connecting the threaded sleeves, the installed steel sleeves are fixed and secured with a pipe locking device.

6. A method for sealing underground rivers in karst geological formations according to claim 5, characterized in that: A V-shaped funnel is welded near the surface of the steel casing for unloading. A flange is welded at the top of the casing at the top of the cave, and the hose is connected to the steel casing through the flange.

7. A method for sealing underground rivers in karst geological formations according to claim 6, characterized in that: In the fifth step, the free fall height of concrete inside the karst cave should not exceed 2m. If it exceeds 2m, a slow descent measure should be adopted for pouring.

8. A method for sealing underground rivers in karst geological formations according to claim 7, characterized in that: The fifth step also includes step 5.4: embed backfill grouting pipes on the top arch of the grouting adit, with the backfill grouting pipes penetrating more than 10cm into the bedrock, and then grouting is performed on the backfill grouting pipes.

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