Construction method for underground excavation channel below dewatering well

Abstract

The invention discloses a construction method for an underground excavation channel below a dewatering well, belongs to the technical field of construction, and improves the accuracy of the excavation position of a transverse channel door opening through survey setting-out construction. Through hole blocking breaking construction, the error of an excavation contour line is accurately ensured, and the accuracy of positioning and breaking of the hole portal is improved; through hole reinforcing construction, the stability of the hole can be improved through an internal reinforcing mesh, sprayed concrete and a grating steel frame; channel excavation supporting construction is conducted, a soil layer is detected and reinforced before a transverse channel is excavated, the situation that the soil layer collapses is effectively reduced, and the safety of transverse channel excavation is guaranteed; channel supporting construction is conducted, supporting and protecting operation on a transverse channel is enhanced, the supporting force of foreign matter on a soil layer is reduced when the foreign matter is cut and taken out, and the foreign matter treatment safety is improved; and through channel backfilling construction and secondary pouring operation, the compactness of a backfilling area is confirmed, and it is ensured that the pressure is kept stable in the shield tunneling process.

Description

Technical Field

[0001] This invention belongs to the field of construction technology, specifically relating to a method for constructing a tunnel beneath a dewatering well. Background Technology

[0002] During tunnel boring machine (TBM) construction, when a cross-shaped impact cone-shaped foreign object appears in front of the TBM and obstructs its progress, it is necessary to excavate a cross passage to remove the object. However, when the object is located under a bridge or river channel, it will be affected by river water, directly impacting the safety of the cross passage excavation. To meet the needs of cross passage construction, it is necessary to coordinate with dewatering wells. The cross passage is excavated from the bottom side of the dewatering well towards the location of the foreign object in front of the TBM to clear it. However, traditional methods of creating a portal at the bottom of the dewatering well result in low demolition precision, large dimensional deviations, and poor process coordination, which not only affects the efficiency of foreign object removal but also the stability of the cross passage excavation. Therefore, we propose a cross passage construction method below the dewatering well to solve the problems existing in the current technology. Summary of the Invention

[0003] The purpose of this invention is to provide a method for constructing a tunnel beneath a dewatering well, in order to solve the problems mentioned in the background art.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A method for constructing a tunnel beneath a dewatering well includes surveying and setting out: surveying and setting out on one side of the bottom of the dewatering working well, and determining the position of the tunnel entrance based on the elevation of the entrance, and drawing the excavation outline.

[0006] Segmented Demolition of the Tunnel Portal: The tunnel portal is divided into sections, and the demolition work is divided into eight sections. The sections are then demolished sequentially, and the demolished materials are hoisted to the slag hopper for transfer and cleaning.

[0007] Reinforcement of the opening: After the opening is broken, it is necessary to reinforce it in time with steel mesh + shotcrete + grid steel frame to prevent the opening from collapsing. The grid steel frame needs to be trial assembled and tested outside the opening in advance so as to measure the size and prevent excessive deviation from the opening.

[0008] Excavation and support of the passage: Before excavation, the stability of the soil layer is tested to determine whether soil reinforcement is needed. The passage is excavated using the bench method, and a grid steel frame is laid. The upper bench is excavated and the initial support of the upper bench is constructed. The lower bench is excavated and the initial support of the lower bench is constructed.

[0009] The passageway support is achieved by erecting I-beams inside the passageway for reinforcement, allowing for stability testing after foreign objects have been cut and cleared, and facilitating the subsequent removal of the I-beams.

[0010] Backfilling of the working shaft passage: A backfill retaining wall is poured at the tunnel entrance, and the inside of the tunnel is also poured. The pouring inside the tunnel is carried out in two stages to confirm the compaction of the backfill area and ensure that the pressure remains stable during the tunnel boring process.

[0011] Preferably, in the surveying and setting out construction, the surveying team measures and sets out the position of the tunnel entrance based on the elevation of the tunnel entrance, then sets out the center line position, and then returns the coordinate points to both sides to draw the excavation outline.

[0012] Preferably, during the segmented demolition of the opening, the opening needs to be demolished in segments from the top left to the bottom right to control the size error of each segment and ensure the continuity of the hoisting and reinforcement processes after demolition.

[0013] Preferably, during the reinforcement of the opening, after the opening is broken, a glass fiber reinforced steel mesh is immediately used, arranged in a single layer across the entire cross section, and shotcrete is applied, with a grid steel frame installed inside the concrete.

[0014] Shotcrete was used for filling to enhance its adhesion to the surrounding rock mass, thus ensuring the stability of the tunnel entrance structure after the tunnel portal was breached.

[0015] Preferably, during the shotcrete process, the shotcrete operation should be carried out in sections and segments, with each section not exceeding 6m in length, and the shotcrete should be carried out in the order of first the wall and then the arch, from bottom to top.

[0016] The spraying angle and distance need to be controlled to ensure that the concrete is evenly and densely covered on the steel mesh and grating frame. After the shotcrete has set, it should be sprayed with water for curing to ensure the strength development and durability of the concrete.

[0017] Preferably, during the installation of the grating steel frame, it is necessary to complete the grating trial assembly on site, assemble each unit on the ground according to the design drawings, inspect it after assembly, and then put it into the well for final assembly after passing the inspection;

[0018] The grid frame is closely attached to the surrounding rock, and the arch foot is set on the original stratum. When the bottom surface is soft or over-excavation occurs, concrete pads must be placed, and anchor pipes for locking feet must be installed at the arch foot.

[0019] Preferably, during the excavation of the tunnel, horizontal boreholes are drilled at the tunnel entrance to extract core samples;

[0020] If the soil within the passageway is well-reinforced and the strata are relatively stable, then no reinforcement is required.

[0021] If the soil has poor self-stability and high water content, then grouting should be added to reinforce the soil.

[0022] Preferably, during the excavation of the upper step, before the excavation of the upper step, a layer of advanced grouting small pipes is set in the arch to reinforce the surrounding strata. The excavation cycle of the upper step is controlled at half a meter, and manual excavation is carried out using pneumatic picks and shovels.

[0023] The upper step support includes initial shotcrete, hanging fiberglass mesh, installing fiberglass positioning anchors, fiberglass grid frame, and wrapping with shotcrete. The construction procedures and methods for the lower step support are the same as those for the upper step.

[0024] Preferably, during the construction of the channel support, the channel base is cleaned to ensure that the base is flat, firm, and free of debris and water. A pad is laid at the base of the I-beam. The pad should be flat and tightly attached to the base. After the I-beam is in place, the steel bar ends are spot-welded to the surrounding area to prevent displacement or overturning during subsequent construction. The spot welding positions should be evenly distributed to ensure the overall stability of the I-beam.

[0025] After the foreign objects in the passage have been cut and cleared, when dismantling the I-beams in the transverse passage, monitoring data should be used to analyze the deformation of the surrounding rock after excavation, including convergence, settlement, and the stress on the support structure, such as the stress of the steel frame and the cracks in the shotcrete. Only after confirming that the data is stable and the surrounding rock has reached a stable state can the dismantling operation be carried out. During dismantling, the principle of "top to bottom, inside to outside" should be followed, prioritizing the dismantling of the arch I-beams, and then gradually dismantling the side wall I-beams downwards to avoid concentrated dismantling that could lead to instability of the surrounding rock.

[0026] Preferably, during the backfilling construction of the working shaft passage, the concrete backfilling operation is carried out through the unloading port of the working shaft; the outer retaining wall is poured first, and after it has initially set, the inner concrete is poured; the backfilling construction inside the tunnel is carried out in two stages.

[0027] Technical effects and advantages of the present invention: The method for constructing a tunnel beneath a dewatering well proposed in this invention has the following advantages compared with the prior art:

[0028] This invention improves the accuracy of the cross passage excavation location through surveying and setting out construction; it ensures the accuracy of the excavation outline by using segmented demolition at the opening, improving the accuracy of the opening positioning and demolition, while also facilitating subsequent hoisting and handling after demolition; the opening reinforcement construction, using internal steel mesh, shotcrete, and grating steel frame, enhances the stability of the opening, and the grating steel frame assembly structure is pre-assembled at the factory and on-site, improving installation efficiency and further ensuring dimensional accuracy; the passage excavation and support construction, by testing and reinforcing the soil layer before the cross passage excavation, effectively reduces the occurrence of soil layer collapse, and the use of the bench method excavation combined with bench support ensures the safety of the cross passage excavation; the passage support construction strengthens the support and protection of the cross passage, reducing the stress on the soil layer support layer when cutting and removing foreign objects, and improving the safety of foreign object handling; the passage backfilling construction, through secondary pouring, confirms the compaction of the backfill area, ensuring stable pressure during shield tunneling. Attached Figure Description

[0029] Figure 1 This is a flowchart illustrating the channel construction process of the present invention;

[0030] Figure 2 This is a flowchart illustrating the construction process of the grating steel frame of the present invention.

[0031] Figure 3 This is a flow chart of the sprayed concrete construction process of the present invention;

[0032] Figure 4 This is a construction status diagram of the underground excavation of the cross passage for the dewatering well according to the present invention;

[0033] Figure 5 This is a construction sequence diagram of the segmented demolition of the portal in this invention;

[0034] Figure 6 This is a construction drawing of the reinforced state after the portal opening is broken according to the present invention;

[0035] Figure 7 This is a schematic diagram of the cross-channel bench excavation method of the present invention:

[0036] Figure 8 This is a schematic diagram of the transverse channel grid frame support of the present invention.

[0037] Figure 9 This is a schematic diagram of the cross passage backfilling construction of the present invention. Detailed Implementation

[0038] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The specific embodiments described herein are merely used to explain the present invention and are not intended to limit the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] This invention provides, for example Figure 1-9 The method for constructing a tunnel beneath a dewatering well includes surveying and setting out: surveying and setting out on one side of the bottom of the dewatering working well, and setting out the position of the tunnel entrance according to the elevation of the entrance, and drawing the excavation outline.

[0040] Segmented Demolition of the Tunnel Portal: The tunnel portal is divided into sections, and the demolition work is divided into eight sections. The sections are then demolished sequentially, and the demolished materials are hoisted to the slag hopper for transfer and cleaning.

[0041] Reinforcement of the opening: After the opening is broken, it is necessary to reinforce it in time with steel mesh + shotcrete + grid steel frame to prevent the opening from collapsing. The grid steel frame needs to be trial assembled and tested outside the opening in advance so as to measure the size and prevent excessive deviation from the opening.

[0042] Excavation and support of the passage: Before excavation, the stability of the soil layer is tested to determine whether soil reinforcement is needed. The passage is excavated using the bench method, and a grid steel frame is laid. The upper bench is excavated and the initial support of the upper bench is constructed. The lower bench is excavated and the initial support of the lower bench is constructed.

[0043] The passageway support is achieved by erecting I-beams inside the passageway for reinforcement, allowing for stability testing after foreign objects have been cut and cleared, and facilitating the subsequent removal of the I-beams.

[0044] Backfilling of the working shaft passage: A backfill retaining wall is poured at the tunnel entrance, and the inside of the tunnel is also poured. The pouring inside the tunnel is carried out in two stages to confirm the compaction of the backfill area and ensure that the pressure remains stable during the tunnel boring process.

[0045] During the surveying and setting-out construction, the surveying team determined the position of the tunnel entrance based on its elevation, then marked the center line, and finally traced the coordinates to both sides to draw the excavation outline. During the segmented demolition of the tunnel entrance, the opening was dismantled in sections, proceeding from top left to bottom right, with each section's dimensional error controlled to ≤5mm to ensure seamless connection between the subsequent hoisting and reinforcement processes.

[0046] During the tunnel portal demolition, a water drill can be used to break down the tunnel body, dividing the demolition work into eight sections. The first and second sections are 800mm high, 1327mm long, and 500mm thick; the third to eighth sections are 800mm high, 1450mm long, and 500mm thick. The demolished material is then hoisted to a slag hopper using a gantry crane and transferred to the ground. Sectional demolition: Strictly follow the sequence of "first to second section (1327mm long) → third to eighth section (1450mm long)," controlling the dimensional error of each section to ≤5mm to ensure seamless connection between the subsequent hoisting and reinforcement processes.

[0047] After demolition, the hoisting calculations for the materials also need to be performed.

[0048] 1. Dimensions and volume calculations

[0049] (1) It is known that the height of each piece is h=800mm=0.8m, the length is L=1450 mm=1.45m, and the thickness is d=500mm=0.5m.

[0050] (2) According to the formula for the volume of a cuboid, V=L×d×h, the volume of each piece is V=1.45×0.5×0.8=0.58m3.

[0051] 2. Weight Calculation

[0052] The density of C30 concrete is generally taken as ρ=2400kg / m3.

[0053] The mass formula is m=ρV. The mass of each piece is m=2400×0.58=1392kg, which is converted to weight G=mg (g is taken as 9.8N / kg). G=1392×9.8=13641.6N≈13.64kN, about 1.392t.

[0054] 3. Select steel rope and shackles

[0055] Given that the gantry crane has a lifting capacity of 10t and the heaviest block weighs approximately 1.392t, the 10t gantry crane meets the lifting requirements. For the selection of steel ropes, a safety factor must be considered; generally, a safety factor of K=6 is used for lifting. The force on a single steel rope (n=4 steel ropes lifting one block) is F= 13641.6 / 4=3410.4N. Considering the safety factor, the tension Fs =K×F=6×3410.4=20462.4N. According to the allowable tension table for steel ropes, a 6×19-12.5 steel wire rope is selected (its breaking strength is greater than the calculated tension). The selection of shackles also requires consideration of the safety factor, generally K=6. The rated load of the shackle should be greater than Fs =20462.4N≈2.05t; a shackle with a rated load of 3t is selected.

[0056] During the reinforcement of the tunnel entrance, after the tunnel entrance was broken, a glass fiber reinforced steel mesh was immediately used, arranged in a single layer across the entire cross section with a spacing of 150×150mm, and 250mm thick C25 early-strength concrete was sprayed, with a grid steel frame inside the concrete. Shotcrete was used to fill the gap to enhance its bonding with the surrounding rock mass, so as to ensure the stability of the tunnel entrance structure after the tunnel entrance was broken.

[0057] During the shotcrete process, the shotcrete operation should be carried out in sections and segments, with each section not exceeding 6m in length. The shotcrete should be carried out in the order of first the wall and then the arch, from bottom to top. The spraying angle and distance need to be controlled to ensure that the concrete is evenly and densely covered on the steel mesh and grating frame. Two hours after the shotcrete has set, water curing should be carried out to ensure the strength development and durability of the concrete.

[0058] Shotcrete is transported by material truck to the reserved opening platform of the Pihe working shaft, and then conveyed to the bottom of the working shaft through the unloading pipe. A wet shotcrete process is adopted, using a concrete shotcrete machine for construction. The height of each layer on the sidewalls is controlled at 3-4cm, and on the arch at 2.5-3cm. Each subsequent layer should be shotcrete after the previous layer has fully set. When shotcreting is done 1 hour after final setting, the surface of the shotcrete layer should be cleaned with air and water first. The time between the final setting of the concrete and the next cycle should not be less than 3 hours. The rebound rate of shotcrete should not exceed 25% for the arch and 15% for the sidewalls. The nozzle should be perpendicular to the sprayed surface, with a spacing of 0.6-1.0m. The nozzle should move continuously and slowly in a transverse circular motion, and the thickness of the shotcrete layer should be uniform.

[0059] During the installation of the grid steel frame, it is necessary to complete the grid trial assembly on site. Each unit is assembled on the ground according to the design drawings. After the assembly is completed, it is inspected. After passing the inspection, it is then lowered into the well for final assembly. The grid frame is close to the surrounding rock, and the arch foot is set on the original stratum. When the bottom surface is soft or over-excavation occurs, concrete pads must be placed, and two anchor pipes are installed at the arch foot.

[0060] The steel frame for the fiberglass grid arrived on site and completed the trial assembly of the first fiberglass grid. On the ground, each unit was assembled according to the design drawings. After assembly, an inspection was conducted. Once the inspection was passed, the grid was lowered into the well to improve the accurate positioning of the grid.

[0061] During tunnel excavation, horizontal boreholes are drilled at the tunnel entrance to extract core samples. If the soil within the tunnel area is well-reinforced and the strata are relatively stable, no further reinforcement is required. If the soil has poor self-stability and high water content, grouting reinforcement is performed. During grouting reinforcement, when the well is excavated to approximately 2m above the tunnel, four layers of Φ25 small guide pipes are used to reinforce the bottom layer within a 120° radius. Sleeve valve pipes are used for grouting reinforcement within the shield tunnel's passage area to ensure soil stability above the transverse passage. Small guide pipes are applied circumferentially at 0.25m intervals in four layers, with a length L=3.0m.

[0062] The process includes: 1) Before grouting, spray a 5cm thick layer of concrete to seal the working face to prevent grout leakage. 2) Grouting should proceed from bottom to top, with the grout mixed using a mixer. 3) Tighten the grouting valves to the threads at the end of each small guide pipe, and connect the other end of the grouting valve to a high-pressure hose (with a threaded tip). 4) Grouting uses cement grout injected into the grouting pipes. 5) Welding the threads: Weld threads to the end of each small guide pipe requiring grouting to connect the grouting valve. 6) The grouting pressure is generally 0.5–1.0 MPa, depending on the actual situation. 7) Grouting can be terminated when the final grouting pressure reaches the design final pressure, the grouting volume reaches 95% of the design grouting volume, or even if the design final pressure has not been reached, the grouting volume has reached the design grouting volume, or grout leakage occurs at the ground surface or working face.

[0063] During the excavation of the upper bench, before the excavation of the upper bench, a layer of four layers of pre-grouting pipes with a circumferential spacing of 0.25m and a row spacing of 0.5m are installed in the arch, with the external insertion angle controlled at 25°, to reinforce the surrounding strata. The excavation cycle of the upper bench is controlled at 0.5m, and excavation is carried out manually with pneumatic picks and shovels. The upper bench support includes initial shotcrete, hanging fiberglass steel mesh, installing fiberglass positioning anchors, fiberglass grid frame, and wrapping with shotcrete. The construction procedures and methods for the lower bench support are the same as those for the upper bench.

[0064] The fiberglass anchor bolts are installed at the arch foot of each step, using Φ28 mortar anchor bolts with a horizontal inclination angle of 60° and a length of 3m. Two bolts are installed at the bottom of the arch crown and arch foot on each side of each arch. A fiberglass reinforced mesh is then attached: the mesh uses φ8mm steel bars in both the longitudinal and circumferential directions, with a mesh size of 150mm×150mm. The steel bars are pre-processed and transported into the tunnel. The mesh panels are securely overlapped with each other and with the already shotcreted mesh panels, with an overlap length of not less than 200mm. The mesh panels must be free from damage and deformation during stacking and transportation, and any rust should be removed before installation.

[0065] During the construction of the passage support, the passage base should be cleaned to ensure that the base is flat, firm, and free of debris and water. A pad should be laid at the base of the I-beam. The pad should be flat and tightly attached to the base. After the I-beam is in place, the steel bar ends should be spot welded to the surrounding area to prevent displacement or overturning during subsequent construction. The spot welding positions should be evenly distributed to ensure the overall stability of the I-beam.

[0066] During I-beam installation, the center line and elevation of the I-beam are measured and marked with red paint; a plumb line is used to determine verticality and ensure installation accuracy; the base is cleaned to ensure it is flat, firm, and free of debris and water; a base plate is laid at the base, ensuring it is flat and tightly fitted to the base. Erection process: The I12 I-beam is manually installed into position; its position is adjusted according to the measured center line, elevation, and verticality markings to ensure accurate placement. Erection and re-measurement: Verticality and elevation are re-measured using a plumb line and steel tape measure; any deviations are promptly adjusted. Longitudinal connection: Tie bars are installed at the designed spacing (e.g., φ22@500) and securely welded together. Fixing measures: After the I-beam is in place, it is spot-welded to the surrounding area using rebar ends to prevent displacement or overturning during subsequent construction. The spot welds should be evenly distributed to ensure the overall stability of the I-beam. Safety Inspection: After erection, a comprehensive inspection of the I-beam connections, fixation, and overall verticality should be conducted, with a focus on checking for any incomplete or missing welds in the welded areas to ensure compliance with safety regulations. After foreign objects are removed, the dismantling of the I-beams in the cross passage should be based on monitoring data. Once monitoring data indicates stable deformation, the I-beams can be dismantled and backfilling operations can commence in an orderly manner to ensure the stability of the surrounding rock and construction safety.

[0067] After the foreign objects in the passage are cut and cleared, when dismantling the I-beams in the transverse passage, the monitoring data should be analyzed to determine the deformation of the surrounding rock after excavation (including convergence and settlement) and the stress on the support structure (such as steel frame stress and shotcrete cracks). Only after confirming that the data is stable and the surrounding rock has reached a stable state can the dismantling operation be carried out. During dismantling, the principle of "top to bottom, inside to outside" should be followed. The I-beams at the top of the arch should be dismantled first, and then the I-beams on the side walls should be dismantled gradually downwards to avoid concentrated dismantling that could lead to instability of the surrounding rock.

[0068] Monitoring data verification: After analyzing the monitoring data on the deformation of the surrounding rock (including convergence and settlement) and the stress on the support structure (such as steel frame stress and shotcrete cracks) after excavation, and confirming that the data is stable and the surrounding rock has reached a stable state, demolition operations can be carried out; underwater cutting guns are used to cut the welds at the joints of the I-beams, and it is strictly forbidden to cut the I-beams directly (to prevent sudden instability of the structure).

[0069] During the backfilling construction of the working shaft passage, the concrete backfilling operation is carried out through the unloading port of the working shaft; first, the outer 500mm retaining wall is poured, and after it has initially set, the inner concrete is poured; the backfilling construction inside the tunnel is carried out in two stages, with the first pouring height being 2050mm and the last pouring height being 150mm.

[0070] The backfill material is a mixture of gravel and cement. During the installation of the backfill formwork, one side of the formwork is erected first according to the edge line, supported with temporary supports, and the verticality of the formwork is checked with a plumb bob. Tie bolts are then installed, and Φ48 steel pipe vertical supports and horizontal timber crossbars are installed. Simultaneously, φ20 steel bars (200mm each) are inserted into the initial supports at both ends of the tunnel, exposing 200mm of the secondary lining. Then, the other side of the formwork is installed, aligned, and the through-wall bolts are tightened. The tie bolts are Φ14 with a spacing of 500mm x 500mm. Note that the tie bolt holes should be straight and aligned to ensure the through-wall bolts are perpendicular to the wall formwork; the through-wall bolts must not be pulled at an angle or forced into the formwork. Finally, the formwork butterfly clips and bolts are checked for tightness.

[0071] The gravel particle size should be 20-50mm, with a mud content ≤3%. PO 42.5 grade cement should be used, with a strict admixture dosage of 6% by weight. The moisture content of the mixture should be controlled within ±2%, judged on-site by the criterion of "forming a clump when squeezed in hand, but crumbling when dropped." Each layer should have a loose thickness ≤300mm, compacted 4-6 times with a tamping machine, achieving a compaction degree ≥93%. After each backfill layer, one set of ring samplers should be taken per 1000㎡ to test dry density and compaction degree. The 7-day unconfined compressive strength of the cement-soil mixture should be ≥0.8MPa, with a curing period ≥7 days and kept moist. Close attention must be paid to weather changes during backfilling, avoiding backfilling operations in rainy weather. In case of sudden rainfall, the backfilled area should be immediately covered with plastic sheeting to prevent the cement-soil mixture from being washed away and altering the mix proportions. A forced mixer should be used during mixing to ensure thorough mixing of cement and gravel soil, with a mixing time of no less than 90 seconds, strictly prohibiting cement lumps.

[0072] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for constructing a tunnel beneath a dewatering well, characterized in that, Includes the following steps: S1 Surveying and Setting Out: Conduct surveying and setting out on one side of the bottom of the dewatering working well, and according to the elevation of the tunnel portal, measure and set out the position of the tunnel portal and draw the excavation outline; S2 Tunnel Portal Segment Demolition: The tunnel portal is divided into segments, and the demolition work is divided into eight segments. The segments are then demolished sequentially, and the demolished materials are hoisted to the slag hopper for transfer and cleaning. S3 opening reinforcement: After the opening is broken, it is necessary to reinforce it in time with steel mesh + shotcrete + grid steel frame to prevent the opening from collapsing. The grid steel frame needs to be trial assembled and tested outside the opening in advance so as to measure the size and prevent excessive deviation from the opening. S4 Channel Excavation and Support: Before excavation, the stability of the soil layer is tested to determine whether soil reinforcement is needed. The inside of the channel is excavated using the bench method, and a grid steel frame is laid. The upper bench is excavated and the initial support of the upper bench is constructed. The lower bench is excavated and the initial support of the lower bench is constructed. S5 passage support: I-beams are erected inside the passage for support, which facilitates the reinforcement of the passage, the testing of the passage stability after cutting and cleaning foreign objects, and the subsequent removal of the I-beams; S6 working shaft passage backfilling: A backfill retaining wall is poured at the tunnel entrance, and the inside of the tunnel is poured. The pouring inside the tunnel is carried out in two stages to confirm the compaction of the backfill area and ensure that the pressure remains stable during the tunnel boring process.

2. The method for constructing a tunnel beneath a dewatering well according to claim 1, characterized in that: During the surveying and setting out construction, the surveying team measures and sets out the position of the tunnel entrance based on its elevation, then sets out the center line position, and then returns the coordinate points to both sides to draw the excavation outline.

3. The method for constructing a tunnel beneath a dewatering well according to claim 2, characterized in that: During the segmented demolition of the tunnel entrance, the opening needs to be dismantled in segments from top left to bottom right, controlling the dimensional error of each segment to ensure the continuity of the hoisting and reinforcement processes after demolition.

4. The method for constructing a tunnel beneath a dewatering well according to claim 1, characterized in that: During the reinforcement of the opening, after the opening is broken, a single layer of glass fiber reinforced steel mesh is immediately used across the entire cross section, and shotcrete is applied. The concrete contains a grating steel frame. Shotcrete was used for filling to enhance its adhesion to the surrounding rock mass, ensuring the stability of the tunnel entrance structure after the tunnel portal was breached.

5. The method for constructing a tunnel beneath a dewatering well according to claim 4, characterized in that: During the shotcrete process, the shotcrete operation should be carried out in sections and segments in sequence, with each section not exceeding 6m in length, and the shotcrete should be carried out in the order of first the wall and then the arch, from bottom to top. The spraying angle and distance need to be controlled to ensure that the concrete is evenly and densely covered on the steel mesh and grating frame. After the shotcrete has set, it should be sprayed with water for curing to ensure the strength growth and durability of the concrete.

6. The method for constructing a tunnel beneath a dewatering well according to claim 5, characterized in that: During the installation of the grating steel frame, it is necessary to complete the trial assembly of the grating on site. Each unit is assembled on the ground according to the design drawings. After the assembly is completed, it is inspected. After passing the inspection, it is then put into the well for final assembly. The grid frame is closely attached to the surrounding rock, and the arch foot is set on the original stratum. When the bottom surface is soft or over-excavation occurs, concrete pads must be placed, and two anchor pipes are installed at the arch foot.

7. The method for constructing a tunnel beneath a dewatering well according to claim 1, characterized in that: During the excavation of the tunnel, horizontal boreholes were drilled at the opening to extract core samples; If the soil within the passageway is well-reinforced and the strata are relatively stable, then no reinforcement is required. If the soil has poor self-stability and high water content, then grouting should be added to reinforce the soil.

8. The method for constructing a tunnel beneath a dewatering well according to claim 1, characterized in that: During the excavation of the upper step, before the upper step is excavated, a layer of advanced grouting pipes is set in the arch to reinforce the surrounding strata. The excavation of the upper step is controlled by cyclic advance and is carried out manually with pneumatic picks and shovels. The upper step support includes initial shotcrete, hanging fiberglass mesh, installing fiberglass positioning anchors, fiberglass grid frame, and wrapping with shotcrete. The construction procedures and methods for the lower step support are the same as those for the upper step.

9. The method for constructing a tunnel beneath a dewatering well according to claim 1, characterized in that: During the construction of the channel support, the channel base should be cleaned to ensure that the base is flat, firm, and free of debris and water. A pad should be laid at the base of the I-beam. The pad should be flat and tightly attached to the base. After the I-beam is in place, the steel bar ends should be spot welded to the surrounding area to prevent displacement or overturning during subsequent construction. The spot welding positions should be evenly distributed to ensure the overall stability of the I-beam. After the foreign objects in the passage have been cut and cleared, when dismantling the I-beams in the transverse passage, monitoring data should be used to analyze the deformation of the surrounding rock after excavation, including convergence, settlement, and the stress on the support structure, such as the stress of the steel frame and the cracks in the shotcrete. Only after confirming that the data is stable and the surrounding rock has reached a stable state can the dismantling operation be carried out. During dismantling, the principle of "top to bottom, inside to outside" should be followed. Priority should be given to dismantling the I-beams at the top of the arch, and then the I-beams on the side walls should be dismantled gradually downwards to avoid concentrated dismantling that could lead to instability of the surrounding rock.

10. The method for constructing a tunnel beneath a dewatering well according to claim 1, characterized in that: During the backfilling construction of the working shaft passage, the concrete backfilling operation is carried out through the unloading port of the working shaft; the outer retaining wall is poured first, and after it has initially set, the inner concrete is poured; the backfilling construction inside the tunnel is carried out in two stages.

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