A ground pre-grouting structure

Abstract

This application relates to a ground pre-grouting structure. This application is applicable to the field of underground laboratory and mine roadway water inrush control technology. The technical problem to be solved by this application is: to provide a ground pre-grouting structure. The technical solution adopted in this application is: a ground pre-grouting structure for water inrush control in an experimental tunnel next to an inclined shaft, comprising: a group of grouting holes drilled above the pre-excavated tunnel and above the connection between the pre-excavated tunnel and the inclined shaft, extending vertically or at a predetermined angle to the top and periphery of the pre-excavated tunnel; the group of grouting holes is symmetrically arranged with the axis of the pre-excavated tunnel as the center line, and the spatial distribution range of the grouting hole group covers the tunnel projection area and the surrounding seepage path; a shell-shaped grouting curtain, formed by grouting and solidification within the grouting hole group, to form a three-dimensional enveloping shell-shaped structure around the pre-excavated tunnel.

Description

Technical Field

[0001] This utility model relates to the field of underground laboratory and mine tunnel water inflow control technology, and in particular to a ground pre-grouting structure. Background Technology

[0002] When expanding experimental tunnels in inclined shafts of mines, the existing roadway surrounding rock is affected by historical mining activities, resulting in the development of fractures. The excavation of new tunnels can easily activate the pore water in the aquifer, causing continuous water inrush.

[0003] Currently, most methods employed are in-tunnel drainage or localized grouting, but these have significant limitations: the narrow space of the inclined shaft and the interference between in-tunnel grouting and tunneling not only slow down construction progress but also pose significant safety hazards such as high-altitude operations and equipment collisions; localized grouting is insufficient to seal the three-dimensional seepage network in inclined rock strata, and high-pressure groundwater easily seeps around the joints of the rock strata, leading to sealing failure; traditional methods cannot block the recharge source of deep aquifers, and the gushing water repeatedly erodes concrete, corrodes equipment, and may even induce surrounding rock instability, resulting in insufficient long-term stability. Especially for inclined shaft-type inclined tunnels with a burial depth of less than 100m, the aquifer coverage is wide and the hydraulic connections are complex, making conventional in-tunnel water control technologies costly and with limited effectiveness. More importantly, for experimental tunnels expanded next to inclined shafts, the water inflow mainly originates from the surrounding sandstone aquifers, and the groundwater is strictly controlled by the highly inclined rock strata joints and mining-induced fractures, generating "inclined seepage" along the dominant direction and "seeping around" into the tunnel chamber. Traditional vertical ground curtain systems, due to their drilling direction being approximately parallel to the main seepage channels, struggle to achieve effective orthogonal penetration and three-dimensional sealing, resulting in poor treatment outcomes.

[0004] Therefore, there is an urgent need for a water inrush control structure and method that can block water sources in advance before cavern excavation, ensure safe and efficient construction, and form a long-term anti-seepage system. Summary of the Invention

[0005] The technical problem to be solved by this utility model is to provide a ground pre-grouting structure to address the above-mentioned problems.

[0006] The technical solution adopted in this utility model is: a ground pre-grouting structure for water inrush control in an experimental tunnel next to an inclined shaft, comprising: Grouting hole groups are drilled above the pre-excavated experimental tunnel and above the connection between the pre-excavated experimental tunnel and the inclined shaft. They extend vertically or at a predetermined angle to the top and perimeter of the experimental tunnel. The grouting hole groups are symmetrically arranged with the axis of the experimental tunnel as the center line. The spatial distribution range of the grouting hole groups covers the tunnel projection area and the surrounding seepage path. The shell-shaped grouting curtain is formed by grouting and solidification within the grouting hole group, creating a three-dimensional enveloping shell structure around the experimental tunnel.

[0007] Using the above-mentioned technical means, grouting hole groups are drilled above the experimental tunnel and above the connection between the experimental tunnel and the inclined shaft. Grout is injected into the grouting hole groups so that the grout between adjacent holes can overlap to form a continuous shell-shaped grouting curtain, thereby blocking the seepage path above the experimental tunnel and improving long-term sealing.

[0008] In some embodiments, the spatial extent of the shell-shaped grouting curtain is determined by the axis, burial depth, sandstone aquifer distribution, and mining-induced fracture development range of the experimental tunnel.

[0009] In some embodiments, the spatial range includes a planar range, a vertical range, and the minimum thickness of the shell-shaped grouting curtain. The planar range extends symmetrically outward by 10 to 15 meters to both sides, centered on the tunnel axis of the experimental tunnel. The vertical range extends upward from the designed top elevation of the inclined shaft to the top boundary of the aquifer, and downward through the aquifer and embedded 1 to 2 meters into the underlying stable water-resistant rock layer. The effective thickness of any cross-section of the shell-shaped grouting curtain shall not be less than 5 meters.

[0010] In some embodiments, the drilling network of the grouting hole group adopts a quincunx pattern, with both the hole spacing and row spacing being 10m.

[0011] In some embodiments, the construction parameters for the borehole network layout include the opening diameter, the final diameter, the depth, and the drilling direction. The opening diameter is not less than 130 mm, the final diameter is not less than 91 mm, the depth penetrates the target aquifer and enters the impermeable layer by 1-2 m, and the maximum deviation angle of the borehole in the drilling direction does not exceed 15°.

[0012] In some embodiments, the shell-shaped grouting curtain uses grout that is graded and selected based on the development characteristics of the underlying cracks. The graded selection includes: for micro-crack areas with a crack width of <2mm, ordinary cement grout is used with a water-cement ratio of 0.8:1 to 1:1 to achieve permeable filling. For medium to large cracks or areas with strong water inflow with a crack width ≥ 2 mm, a cement-water glass dual-liquid grout is used. The cement-water glass dual-liquid grout has a mixing ratio of cement:water glass = 1:0.5 to achieve rapid gelling and sealing. For the fine fracture network region, ultrafine cement slurry is used with a water-cement ratio of 1.2:1 to 1.5:1 to enhance the penetration and bonding ability.

[0013] In some embodiments, the shell-shaped grouting curtain adopts a refined segmented skip-hole grouting construction method, including a downward segmented grouting process, with the length of each grouting segment controlled at 3 to 5 meters, and the grouting pressure controlled in a stepped pressurization manner. The construction adopts the method of first constructing the outer perimeter boreholes to build a closed water-stop boundary, and then constructing the inner ring filling holes in the form of skip-hole grouting.

[0014] In some embodiments, the grouting pressure is controlled by a stepped pressurization, which includes gradually increasing the grouting pressure from an initial 0.5 MPa to a final pressure of 2.0 MPa.

[0015] In some embodiments, the termination criteria for single-hole grouting in the refined segmented skip-hole grouting construction include the grouting pressure reaching the preset final pressure and being maintained stably for more than 10 minutes, or the cumulative grouting volume of a single hole reaching 1.5 times the design estimate.

[0016] The beneficial effects of this utility model are: 1. The ground pre-grouting structure in this application constructs a three-dimensional shell-shaped grouting curtain that coordinates with the axis of the inclined shaft and the attitude of the rock strata before the excavation of the experimental tunnel through ground drilling and grouting, thereby achieving aquifer source sealing and directional interception of inclined seepage. At the same time, personnel and equipment operate entirely on the surface, which can, to a certain extent, avoid the risk of cross-operation within the inclined shaft and tunnel, and ensure the safety of construction in the confined space of the inclined shaft.

[0017] 2. The three-dimensional enveloping curtain structure formed in this application differs from traditional vertical curtains or hole-laying schemes that only target the area directly above the tunnel. By drilling a group of grouting holes symmetrically arranged around the axis of the pre-excavated tunnel on the ground, a "shell-like" grouting curtain is constructed, embedding downwards into the aquifer, covering upwards the aquifer, and wrapping around the entire cavern and the connection of the inclined shaft. This fully enclosed three-dimensional structure can block seepage paths from any direction without any blind spots, and in particular, effectively solves the problem of "around-seepage" of high-pressure groundwater along inclined dominant joints.

[0018] 3. This application employs a spatially adapted borehole layout for inclined seepage. Instead of using a single vertical borehole for inclined seepage in the surrounding rock mass of the inclined shaft tunnel, this application allows for adaptive adjustments to the borehole inclination angle based on the dominant fracture orientation revealed on-site (maximum deviation angle not exceeding 15°). This borehole layout strategy ensures that the borehole trajectory achieves maximum orthogonal intersection with high-angle fractures, significantly improving the sealing efficiency of the grout on the main water inflow channels.

[0019] 4. The technical solution of this application is a systematic solution for a specific scenario. From the three-dimensional boundary design of the curtain wall and the quincunx-shaped hole layout to the graded grouting and skip-hole construction, all are designed to address the water inrush control needs in the specific and complex environment of the "inclined shaft-experimental tunnel". It not only achieves long-term water control in terms of technology, but also enables all-surface operation at the construction level, completely avoiding the safety risks and process interference in the narrow space of the inclined shaft, forming a safe, efficient and economical systematic solution. Attached Figure Description

[0020] Figure 1 This is a structural schematic diagram of the inclined shaft and experimental tunnel in this application.

[0021] Figure 2 This is a top view of the grouting hole arrangement in this application.

[0022] Figure 3 yes Figure 2 Cross-sectional view along the middle AA.

[0023] Explanation of reference numerals in the attached figures: 1. Inclined shaft; 2. Experimental tunnel; 3. Grouting hole group.

[0024] This specification includes references to "one embodiment" or "implementation". The use of the phrase "in one embodiment" or "in an embodiment" does not necessarily refer to the same embodiment. Specific features, structures, or characteristics may be combined in any suitable manner consistent with this disclosure.

[0025] The term "comprising" is open-ended. As used in the appended claims, it does not exclude additional structures or steps.

[0026] "First," "second," etc. As used in this article, these terms serve as labels for the nouns preceding them and do not imply any type of ordering (e.g., spatial, temporal, logical, etc.).

[0027] The term "based on," as used herein, describes one or more factors that influence the determination. This term does not exclude additional factors influencing the determination. That is, the determination may be based solely on these factors or at least partially on them. Consider the phrase "A is determined based on B." In this case, B is the factor influencing the determination of A, and such phrases do not exclude the possibility that the determination of A may also be based on C. In other instances, A may be determined solely on B. Detailed Implementation

[0028] To enable those skilled in the art to better understand the present invention, the technical solution of the present invention will be further described below with reference to specific embodiments.

[0029] Example 1: Combination Figures 1 to 3 As shown, this embodiment is a ground pre-grouting structure used for water inrush control in the experimental tunnel 2 next to the inclined shaft 1. It includes a grouting hole group 3 and a shell-shaped grouting curtain. The grouting hole group 3 is drilled on the ground surface above the pre-excavated experimental tunnel 2 and above the connection between the pre-excavated experimental tunnel 2 and the inclined shaft 1. The grouting hole group 3 extends vertically or at a predetermined angle to the top and perimeter of the experimental tunnel 2, and is symmetrically arranged with the axis of the experimental tunnel 2 as the center line. By injecting grout into the grouting hole group 3, the grout between adjacent holes overlaps, forming a three-dimensional encapsulating shell-shaped grouting curtain around the perimeter of the experimental tunnel 2 that can block water infiltration.

[0030] Before tunnel excavation, a three-dimensional grouting curtain is constructed using surface drilling, coordinating with the axis of inclined shaft 1 and the rock strata's orientation. This achieves "aquifer source sealing and directional interception of inclined seepage." Traditional "in-tunnel drainage / local grouting" only treats exposed water points and cannot block regional recharge. This solution constructs an underground waterproof shell before excavation, transforming passive leak sealing into active source interception. Its core value lies in completely avoiding high-risk operations inside the tunnel and ensuring the safety of construction within the confined space of inclined shaft 1.

[0031] In some implementation schemes, the spatial extent of the shell-shaped grouting curtain is determined by the axis, burial depth, sandstone aquifer distribution, and mining-induced fracture development range of the experimental tunnel 2.

[0032] In some implementation schemes, the spatial range includes the planar range, the vertical range, and the minimum thickness of the shell-shaped grouting curtain. The planar range extends symmetrically outward by 10 to 15 meters to both sides, centered on the tunnel axis of the experimental tunnel 2. The vertical range extends upward from the designed top elevation of the inclined shaft 1 to the top boundary of the aquifer, and downward through the aquifer and embedded 1 to 2 meters into the underlying stable water-resistant rock layer. The effective thickness of any cross-section of the shell-shaped grouting curtain shall not be less than 5 meters.

[0033] In some implementation schemes, the drilling network of grouting hole group 3 adopts a quincunx pattern, with both hole spacing and row spacing being 10m.

[0034] In some implementation schemes, the construction parameters for the borehole network layout include the opening diameter, the final diameter, the depth, and the drilling direction. The opening diameter is not less than 130 mm, the final diameter is not less than 91 mm, the depth penetrates the target aquifer and enters the impermeable layer by 1 to 2 m, and the maximum deviation angle of the borehole in the drilling direction does not exceed 15°.

[0035] In some implementation schemes, the grout used in the shell-shaped grouting curtain is graded and selected based on the development characteristics of the underlying cracks. The graded selection includes: for micro-crack areas with crack width <2mm, ordinary cement grout is used with a water-cement ratio of 0.8:1 to 1:1 to achieve permeable filling; For medium to large cracks or areas with strong water inflow with a crack width ≥ 2 mm, a cement-water glass dual-liquid grout is used. The cement-water glass dual-liquid grout has a mixing ratio of cement:water glass = 1:0.5 to achieve rapid gelling and sealing. For the fine fracture network region, ultrafine cement slurry is used with a water-cement ratio of 1.2:1 to 1.5:1 to enhance the penetration and bonding ability.

[0036] In some implementation schemes, the shell-shaped grouting curtain adopts a refined segmented skip-hole grouting construction method, including the use of a downward segmented grouting process, with the length of each grouting segment controlled at 3 to 5 meters, and the grouting pressure controlled in a stepped pressurization manner. The construction adopts the method of prioritizing the construction of the outer perimeter boreholes to build a closed water-stop boundary, and then constructing the inner ring filling holes in the form of skip-hole grouting.

[0037] In some implementation schemes, the grouting pressure is controlled in a stepped manner, including gradually increasing the grouting pressure from an initial 0.5 MPa to a final pressure of 2.0 MPa.

[0038] In some implementation schemes, the termination criteria for single-hole grouting in refined segmented skip-hole grouting construction include the grouting pressure reaching the preset final pressure and maintaining it stably for more than 10 minutes, or the cumulative grouting volume of a single hole reaching 1.5 times the design estimate.

[0039] Example 2: This embodiment describes a construction method for a pre-grouted ground structure, applied to the pre-grouted ground structure described in Embodiment 1, and includes the following steps: S1. Based on the axis, burial depth, sandstone aquifer distribution and mining-induced fracture development range of experimental tunnel 2, design the spatial range of the grouting curtain and determine the three-dimensional control boundary of the curtain. S2. Drilling network layout and hole construction are carried out according to drilling construction parameters; S3. Based on the development characteristics of the underlying fissures, select grouting materials in stages; S4. Refined segmented skip-hole grouting construction.

[0040] The construction method described in this application combines multiple parameters to design a three-dimensional control boundary for the curtain, ensuring that the curtain caps upwards, embeds itself into the impermeable layer downwards, and wraps around the cavern and its connections laterally. This spatially cuts through all seepage channels from the aquifer to the cavern, reducing water inflow at its source and significantly decreasing the cavern's water inflow, providing a dry construction environment for the experimental tunnel. Graded grout selection based on fracture development characteristics not only matches fracture scale, improving bonding efficiency and durability, but also solves the problem that a single grout cannot simultaneously address permeability and erosion resistance, thereby enhancing the overall integrity of the surrounding rock and reducing later convergence deformation. Segmented skip-hole grouting improves the overlap quality and ensures the grout fully fills the fractures, enhancing the self-stabilizing capacity of the surrounding rock. Simultaneously, it enhances the overall impermeability of the surrounding rock, providing a reliable guarantee for the stable operation of the cavern throughout its entire life cycle.

[0041] In some implementation schemes, in step S1, the spatial range of the grouting curtain includes the planar range, the vertical range, and the minimum thickness of the curtain body. The planar range is centered on the tunnel axis of the experimental tunnel 2, extending symmetrically outward by 10 to 15 meters to both sides, covering the tunnel projection area and the main seepage path around it. The vertical range extends upward from the designed top elevation of the inclined shaft 1 to the top boundary of the aquifer, penetrates the aquifer downward and embeds itself into the underlying stable water-resistant rock layer by 1 to 2 meters, forming a three-dimensional curtain structure with a completely closed top. The effective thickness of any section of the grouting curtain body is not less than 5 meters to ensure the continuity of anti-seepage.

[0042] In some implementations, in step S2, such as Figure 2 As shown, the borehole network is laid out in a quincunx pattern, with both the hole spacing and row spacing being 10m.

[0043] By rationally setting the hole spacing based on the slurry diffusion radius, and coordinating with the precise quincunx-shaped hole arrangement, the slurry veins of adjacent holes are ensured to overlap, achieving fusion and forming a continuous body.

[0044] In some implementation schemes, in step S2, the construction parameters include the opening diameter, the final diameter, the hole depth, and the drilling direction. The opening diameter is not less than 130 mm, the final diameter is not less than 91 mm, and the hole depth must ensure that it penetrates the target aquifer and enters the impermeable layer by 1-2 m. The drilling direction is mainly vertical, and the drilling inclination angle can be adjusted locally according to the dominant fracture orientation revealed on site, but the maximum deviation angle shall not exceed 15° to ensure that the borehole intersects with the main fracture system efficiently.

[0045] Traditional vertical perforated curtain walls are ineffective against groundwater flowing along bedding planes / fractures. This solution, through angle adaptation, overlap control, and densification in key areas, forms a truly three-dimensional enclosed structure.

[0046] In some implementation schemes, in step S3, grouting materials are selected and matched according to the development characteristics of the underlying fissures, including: for micro-fissure areas with fissure width < 2 mm, ordinary cement grout is used with a water-cement ratio of 0.8:1 to 1:1 to achieve permeable filling; for medium and large fissures or areas with strong water inflow with fissure width ≥ 2 mm, cement-water glass dual-liquid grout is used with a cement:water glass ratio of 1:0.5 to achieve efficient sealing by utilizing rapid cementing characteristics; for fine fissure network areas, ultrafine cement grout is used with a water-cement ratio of 1.2:1 to 1.5:1 to enhance permeability and bonding ability.

[0047] By establishing a grouting material system adapted to the characteristics of fractures, it is tailored to rock fractures of different scales as needed. Thin grout is used for penetration into micro-fractures, while thick / rapid-setting grout is used to seal large fractures, improving grout permeability and bonding efficiency. A cement-water glass dual-liquid grout is used for rapid sealing under flowing water conditions to prevent the grout from being washed away. Ultrafine cement grout is used to strengthen the bonding of the fine fracture network, improving overall integrity.

[0048] In some implementation schemes, step S4 involves refined segmented skip-hole grouting construction, including the use of a downward segmented grouting process, with each grouting segment controlled to a length of 3 to 5 meters, and the grouting pressure controlled in a stepped manner. The construction prioritizes drilling the outer perimeter holes to construct a closed water-stop boundary, and then constructs the inner ring filling holes in a skip-hole grouting manner.

[0049] By utilizing gravity and pressure in a downward grouting process, the grout preferentially fills the lower fissures, reducing the risk of grout seepage to the surface. In this embodiment, the construction follows the principle of "boundary first, then filling, skip-hole construction": outer boreholes are drilled first to form a closed water-stop boundary, followed by inner filling holes constructed using a "skip-hole grouting" method, ensuring uniform grout diffusion. By constructing a closed boundary, the grout is guided to diffuse towards the tunnel, allowing for initial grouting of the outer holes to form a grout-stopping shell. During inner grouting, the grout is confined and concentrated towards the tunnel perimeter, increasing the saturation of the target area. Skip-hole grouting promotes overlap; grouting every 1-2 holes allows for lateral diffusion of the grout, facilitating grout cross-linking and forcing the formation of a continuous body.

[0050] Furthermore, the grouting pressure is controlled in a stepped manner, including gradually increasing the grouting pressure from an initial 0.5 MPa to a final pressure of 2.0 MPa.

[0051] An initial pressure of 0.5 MPa allows the grout to gently penetrate into micro-fractures, while a final pressure of 2.0 MPa compacts the rock mass, improving density and strength. In shallow burial conditions (<100m), stepped pressurization can, to some extent, prevent the rock strata from being split or the ground from heaving due to a single application of high pressure.

[0052] In some implementations, in step S4, the termination criteria for single-hole grouting include the grouting pressure reaching the preset final pressure and remaining stable for more than 10 minutes, or the cumulative grouting volume of a single hole reaching 1.5 times the design estimate.

[0053] The implementation principle of the construction method for a ground pre-grouting structure in this embodiment is as follows: The "inclined seepage" in the background technology refers to groundwater flow within rock and soil masses that is not solely driven by gravity but moves vertically, primarily along advantageous structural surfaces such as high-angle joints, fissures, or inclined bedding planes. This seepage direction is determined by geological structures and often intersects or even runs parallel to the extension direction of traditional vertical grouting boreholes at large angles. This makes it difficult for conventional grouting methods to effectively seal the seepage, and is the main cause of "circumferential seepage" and repeated water inrush.

[0054] Traditional solutions often involve creating one or more roughly vertical curtain walls through vertical drilling to achieve horizontal interception in a linear or planar manner. In this case, a three-dimensional continuous low-permeability shell is artificially constructed from the ground surface using a pre-grouting structure before excavation, enclosing the proposed tunnel in a dry and stable environment. Regarding encapsulation, the structure extends outwards from the axis of the experimental tunnel 2, reaching the top of the aquifer and embedding an impermeable layer downwards, forming a three-dimensional curtain structure. The top of the curtain extends to the top of the aquifer, blocking the vertical infiltration path of atmospheric precipitation / surface water; the sides of the curtain enclose the tunnel and its connections, intercepting groundwater flowing along bedding planes / fissures; and the bottom of the curtain embeds an impermeable layer to prevent cross-flow recharge and bottom-level seepage. Utilizing the extremely low permeability of the grout-formed rock mass, a hydraulic barrier is constructed around the tunnel. Compared to traditional solutions, this upgrade from a two-dimensional cutoff wall to a three-dimensional waterproof shell effectively encloses the entire tunnel and its connections.

[0055] In terms of morphological adaptability, drilling primarily employs vertical boreholes, with local adjustments to the borehole inclination based on the dominant fracture orientation. This matches the rock strata joints and mining-induced fracture orientation, allowing the grout to actively embed into the advantageous seepage channels. Specifically, denser boreholes are placed above the connection between the tunnel and inclined shaft 1 to seal abrupt structural changes and stress concentration zones, preventing water inrush. The grout penetrates into the mining-induced fracture network, solidifying to form a rock-grout composite, improving the overall integrity of the rock mass. By sealing the aquifer fracture network across the entire cross-section, water inflow is reduced at its source, significantly decreasing the cavern's water inflow and providing a dry construction environment for the experimental tunnel. Simultaneously, the overall impermeability of the surrounding rock is enhanced, providing a reliable guarantee for the stable operation of the cavern throughout its entire life cycle.

[0056] Engineering practice shows that after adopting this structure, the water inflow in the cavern can be significantly reduced from over 35.8 cubic meters per hour before treatment to below 2 cubic meters per hour, demonstrating a good water control effect. All grouting operations are completed on the surface, completely avoiding the high-risk environment of construction inside the cavern and eliminating interference with cavern excavation processes. This shortens the construction period by more than 30%, and compared to emergency grouting inside the cavern, the overall treatment cost of this solution is significantly reduced. The rapid bonding characteristics of cement-water glass dual-liquid grout combined with the later strength growth of ordinary cement grout form a high-strength, highly impermeable permanent solidified body in the rock mass fissures, effectively ensuring the permeability stability and structural safety of the cavern throughout its service life. Through a quincunx-shaped perforation pattern, a multi-material compatibility system, and pressure segmentation control technology, this structure can precisely seal multiple sets of dominant joints, effectively addressing complex hydrogeological conditions and multi-scale fissure development characteristics, demonstrating strong applicability.

[0057] The above are all preferred embodiments of this utility model, and are not intended to limit the scope of protection of this utility model. Therefore, all equivalent changes made to the structure, shape and principle of this utility model should be covered within the scope of protection of this utility model.

Claims

1. A ground pre-grouting structure, characterized in that, Water inrush control for the experimental tunnel (2) next to the inclined shaft (1) includes: Grouting hole group (3) is drilled above the pre-excavated experimental tunnel (2) and above the connection between the pre-excavated experimental tunnel (2) and the inclined shaft (1). It extends vertically or at a predetermined angle to the top and periphery of the experimental tunnel (2). The grouting hole group (3) is symmetrically arranged with the axis of the experimental tunnel (2) as the center line. The spatial distribution range of the grouting hole group (3) covers the tunnel projection area and the surrounding seepage path. The shell-shaped grouting curtain is formed by grouting and solidification within the grouting hole group (3) to create a three-dimensional enveloping shell structure around the experimental tunnel (2).

2. The ground pre-grouting structure according to claim 1, characterized in that: The spatial range of the shell-shaped grouting curtain is determined by the axis, burial depth, sandstone aquifer distribution, and mining-induced fracture development range of the experimental tunnel (2).

3. A ground pre-grouting structure according to claim 2, characterized in that: The spatial range includes the planar range, the vertical range and the minimum thickness of the shell-shaped grouting curtain. The planar range is centered on the tunnel axis of the experimental tunnel (2) and extends symmetrically outward by 10 to 15 meters to both sides. The vertical range extends upward from the designed top elevation of the inclined shaft (1) to the top boundary of the aquifer, and downward through the aquifer and embedded into the underlying stable water-resistant rock layer for 1 to 2 meters. The effective thickness of any cross-section of the shell-shaped grouting curtain shall not be less than 5 meters.

4. The ground pre-grouting structure according to claim 1, characterized in that: The drilling network of the grouting hole group (3) adopts a plum blossom pattern, with a hole spacing and row spacing of 10m.

5. A ground pre-grouting structure according to claim 4, characterized in that: The construction parameters for the borehole network layout include the opening diameter, the final diameter, the depth, and the drilling direction. The opening diameter is not less than 130 mm, the final diameter is not less than 91 mm, the depth penetrates the target aquifer and enters the impermeable layer by 1-2 m, and the maximum deviation angle of the borehole in the drilling direction does not exceed 15°.

6. A ground pre-grouting structure according to claim 1, characterized in that: The shell-shaped grouting curtain adopts a refined segmented skip-hole grouting construction method, including the use of a downward segmented grouting process, with the length of each grouting segment controlled at 3 to 5 meters, and the grouting pressure controlled in a stepped pressurization manner. The construction adopts the method of prioritizing the construction of the outer perimeter boreholes to build a closed water-stop boundary, and then constructing the inner ring filling holes in the form of skip-hole grouting.

7. A ground pre-grouting structure according to claim 6, characterized in that: The grouting pressure is controlled by a stepped pressurization method, which involves gradually increasing the grouting pressure from an initial 0.5 MPa to a final pressure of 2.0 MPa.

8. A ground pre-grouting structure according to claim 6, characterized in that: The termination criteria for single-hole grouting in the refined segmented skip-hole grouting construction include the grouting pressure reaching the preset final pressure and maintaining it stably for more than 10 minutes, or the cumulative grouting volume of a single hole reaching 1.5 times the design estimate.

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