A method for treating a rock pillar normal hole bypassing a cave in tunnel reservation

Abstract

The present application belongs to the technical field of highway and railway tunnel construction, and particularly relates to a method for treating a tunnel reserved middle rock pillar and a normal tunnel bypassing a karst cave; after tunnel excavation encounters a karst cave invading the tunnel, a middle rock pillar is reserved in the tunnel, the tunnel is expanded and excavated to bypass the karst cave section and continue subsequent tunnel construction on the side away from the karst cave; after the tunnel expansion and bypassing is completed, the reserved middle rock pillar is removed, the karst cave is treated, and the normal tunnel construction is carried out; a steel pipe column support system is used to replace the reserved middle rock pillar; the normal tunnel construction includes tunnel normal tunnel excavation, beam and raft construction, tunnel initial support, floor and filling construction, expansion and bypassing section backfilling and lining construction, and arch protection construction; the present application uses a reserved middle rock pillar and bypassing method to quickly pass through the karst cave section and ensure the construction period; a steel pipe column is used to replace the reserved middle rock pillar to support the rock mass, complete the support system conversion, remove the reserved middle rock pillar, and excavate the normal tunnel.

Description

Technical Field

[0001] This invention belongs to the field of highway and railway tunnel construction technology, specifically relating to a method for treating karst caves that bypass the main tunnel in the reserved rock pillar of a tunnel. Background Technology

[0002] Karst caves are the product of the chemical dissolution and mechanical damage to soluble rock layers caused by the continuous replenishment, runoff, infiltration, and circulation of surface and groundwater. Construction of tunnels in karst areas presents significant challenges, especially when the main tunnel encounters a karst cave. This not only increases the risk of collapse but also severely impacts the construction progress of tunnels located on critical routes.

[0003] To address the aforementioned issues, traditional construction methods include two approaches: first, directly addressing the cavities; and second, using a pilot tunnel for bypassing and small-section excavation. The former method is slow, has a long support period, and the exposed excavation face is prone to collapse due to prolonged exposure, posing a significant risk. The latter method is only suitable when the pilot tunnel and the cavities are on opposite sides; it cannot be used when the cavities and pilot tunnels are on the same side. Summary of the Invention

[0004] One object of the present invention is to solve at least the above-mentioned problems and to provide at least the advantages that will be described later.

[0005] This invention provides the following technical solution: a method for treating karst caves by reserving a central rock pillar in a tunnel and bypassing the main tunnel; after the tunnel is excavated to the point where a karst cave intrudes into the tunnel, a central rock pillar is reserved in the tunnel; the tunnel is widened and excavated away from the karst cave to bypass the karst cave section and continue the subsequent tunnel construction; after the tunnel widening and bypassing is completed, the reserved central rock pillar is removed, the karst cave is treated, and the main tunnel is constructed; a steel pipe column support system is used to replace and remove the reserved central rock pillar.

[0006] Furthermore, after the tunnel excavation reaches the point where a karst cave intrudes into the tunnel, the tunnel is widened and a step is built on the side away from the karst cave, and a central rock pillar is reserved. A steel frame arch is set in the tunnel widening bypass section, and the inner wall of the tunnel is shotcreted. The steel frame arch is connected to the locking anchor rod at the arch foot position.

[0007] Furthermore, the process of dismantling the reserved rock pillars is carried out in sections. First, the steel pipe column of one reserved rock pillar dismantling section is replaced, and then the reserved rock pillar of that section is dismantled. This process is repeated. The length of each reserved rock pillar dismantling section is controlled within 1.5m.

[0008] Two rows of steel pipe columns are installed on the side of the tunnel away from the karst cave. The first row of steel pipe columns is 50cm away from the centerline of the main tunnel. The longitudinal spacing of the steel pipe columns is as follows:

[0009] 1.5m, with a horizontal spacing of 1m, and the steel pipe columns are reinforced with channel steel in both the longitudinal and transverse directions;

[0010] The bottom of the steel pipe column is connected to the concrete foundation; at the installation location of the steel pipe column, a cast-in-place concrete foundation is constructed, and a steel plate is embedded in the top of the cast-in-place concrete foundation. The steel pipe column is welded to the embedded steel plate.

[0011] A sand box is installed on top of the steel pipe column, and the top of the sand box is in close contact with the inner wall of the tunnel.

[0012] Furthermore, cave treatment includes:

[0013] Backfill the bottom of the karst cave up to the bottom of the upper step of the tunnel;

[0014] Remove any dangerous rocks from the top and surrounding areas of the cave;

[0015] As the demolition of the reserved rock pillars progresses, protective scaffolding is installed. During the demolition of the reserved rock pillars, multiple demolition sections of the reserved rock pillars constitute a cycle. After the demolition of the reserved rock pillars in a cycle, protective scaffolding is constructed. The protective scaffolding is set up in the karst cave space outside the concrete retaining wall.

[0016] Furthermore, after the protective scaffolding is completed, the main tunnel construction will commence;

[0017] The construction of the main tunnel includes the excavation of the main tunnel, the construction of crossbeams and raft slabs, the initial support of the tunnel, the construction of the bottom slab and filling, the backfilling and lining of the enlarged bypass section, and the construction of the arch support, carried out in sequence.

[0018] During the construction of the tunnel's main tunnel, the right-side lower bench is excavated first, followed by the left-side lower bench. The lower bench near the karst cave is defined as the right-side lower bench, and the other side is the left-side lower bench. After the right-side lower bench is excavated, supporting steel pipe columns are constructed within it, positioned 50-100cm from the centerline of the tunnel's main tunnel. Six supporting steel pipe columns form a stack, placed between adjacent crossbeams. Each stack is reinforced with channel steel enclosure after construction. After the supporting steel pipe columns have settled and stabilized, they are dismantled sequentially at intervals. After all steel pipe columns have been removed, the left-side lower bench is excavated.

[0019] A crossbeam is constructed from the bottom of the lower step on the left side to the cave wall. A raft slab is installed on the upper part of the crossbeam within the cave area. The construction of the crossbeam and raft slab includes excavation of the work area and concrete pouring. The excavation and concrete pouring are carried out in sections. After removing the backfill layer in the cave during the excavation of the work area, an opening is made on the right side of the crossbeam at the location of the cave wall. The left side of the crossbeam is constructed by using a transversely spaced groove method in the lower steps on the right and left sides. Steel frames are used for support in the openings in the cave wall. The concrete pouring includes tying reinforcing bars, using steel formwork for formwork, and conveying concrete into the formwork.

[0020] The initial support of the tunnel includes the installation of the initial support steel frame, the laying of steel mesh between the initial support steel frames to cover the inner wall of the tunnel, and the spraying of concrete on the inner wall of the tunnel.

[0021] After the initial support construction of the tunnel reaches the position of the supporting steel pipe columns, the supporting steel pipe columns are removed in sections and rows before the initial support construction of the tunnel is carried out, completing the transformation from the supporting steel pipe columns to the initial tunnel support system.

[0022] The construction of the base slab and filling is carried out after the initial support settlement of the tunnel has stabilized. The reinforced concrete base slab and invert arch filling are constructed.

[0023] The backfilling and lining of the excavated bypass section are carried out by backfilling the excavated bypass section from bottom to top through the pumping pipe reserved on the initial support of the tunnel. After the excavated bypass section is backfilled, the lining construction is carried out.

[0024] After the lining construction is completed, the arch support is constructed by entering the karst cave through a horizontal guide tube, using an arch frame with wooden formwork, and pumping backfill to form a concrete arch support.

[0025] Furthermore, the protective canopy includes I-beam arch frames and I-beam connecting rods. The spacing between the I-beam arch frames is 0.6m / frame, and the I-beam arch frames are connected longitudinally by I-beam connecting rods. The circumferential spacing of the I-beam connecting rods is 50cm. Steps are set on both sides of the cave wall, and the I-beam arch frames are anchored to the cave wall by locking foot guide pipes.

[0026] Furthermore, the removal of dangerous rocks at the top and around the cave includes using scaffolding to build a working platform and combining manual drilling with controlled blasting and anchor bolt fixation to deal with the dangerous rocks at the top and around the cave.

[0027] Manual drilling controls the blasting location. After the detonation point is set, the scaffolding is dismantled. After the blasting is completed, the scaffolding is re-erected. Exposed rock surfaces are protected with wet shotcrete and reinforced with anchor bolts. The next construction process is carried out after the shotcrete reaches the design strength.

[0028] Furthermore, the initial support steel frame is installed at a spacing of 0.6m, and no more than two initial support steel frames are constructed per cycle; adjacent initial support steel frames are longitudinally connected by steel tie rods, with a circumferential spacing of 1m between the steel tie rods; locking anchor rods are installed at the joints of the initial support steel frames, and the sleeves of the locking anchor rods are welded to the initial support steel frames by transverse connecting bars.

[0029] Furthermore, during the backfilling process of the expanded bypass section, concrete is backfilled from bottom to top, and the slump of the backfilled concrete is controlled within 200mm. The flow of concrete is observed through the observation holes reserved on the initial support of the tunnel, and a vibrator is used for compaction. At the same time, the backfilling height is controlled below 3m each time. Surrounding rock monitoring and measurement points and clearance convergence points are set on the initial support of the tunnel.

[0030] Furthermore, the thickness of the protective arch is 2m. After the construction of the protective arch is completed, tires are filled between the protective arch and the cave wall.

[0031] Compared with the prior art, the advantages of the present invention are:

[0032] This invention utilizes a method of pre-reserving a central rock pillar to bypass the karst cave section when the main tunnel encounters it, thus ensuring the construction period is met.

[0033] This invention uses steel pipe columns to replace the reserved intermediate rock support rock mass, completes the support system conversion, removes the reserved intermediate rock columns and excavates the main tunnel, and completes the tunnel excavation of the karst cave section.

[0034] The base karst caves are treated using a combination of backfilling, crossbeams, and raft slabs to ensure the safety of construction in the karst cave section of the tunnel. Attached Figure Description

[0035] Figure 1 This is a plan view of the cave section;

[0036] Figure 2 A diagram illustrating the process of removing dangerous rocks from the top and surrounding area of ​​a cave.

[0037] Figure 3 This is a schematic diagram of the steel pipe column installation.

[0038] Figure 4 A schematic diagram of the protective canopy installation;

[0039] Figure 5 This is a schematic diagram of the excavation of the upper step on the right side and the installation of the supporting steel pipe columns;

[0040] Figure 6 This is a schematic diagram of the steel pipe column demolition and the excavation of the upper step on the left side;

[0041] Figure 7 This is a schematic diagram of the crossbeams, raft slab, and bottom slab;

[0042] Figure 8 A schematic diagram of the arch support;

[0043] Figure 9 This is a schematic diagram of the initial support steel frame;

[0044] Figure 10 This is a schematic diagram of the connections between the initial support steel frames.

[0045] In the diagram: 1-Tunnel; 2-Expanded bypass section; 3-Keloid cave; 4-Crossbeam; 5-Locked rock; 6-Backfill layer; 7-Left lower bench; 8-Right lower bench; 9-Reserved central rock column; 10-Steel pipe column; 11-Protective canopy; 12-Supporting steel pipe column; 13-Bottom slab; 14-Crossbeam; 15-Raft slab; 16-Initial support steel frame; 17-Liner; 18-Arch protection; 19-Anchor bolt group; 20-Reinforcing steel tie rod; y-Centerline of the main tunnel. Detailed Implementation

[0046] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0047] like Figure 1 As shown: A method for treating a karst cave by reserving a central rock pillar in the tunnel and bypassing the main tunnel. After tunnel 1 is excavated to the point where it encounters a karst cave 3 that intrudes into tunnel 1, a central rock pillar is reserved in tunnel 1. Tunnel 1 is then widened and excavated away from the karst cave to bypass the karst cave section and continue the subsequent tunnel construction. After the tunnel widening and bypassing is completed, the reserved central rock pillar 9 is removed, the karst cave is treated, and the main tunnel is constructed.

[0048] like Figure 2 As shown: After tunnel 1 is excavated to the point where it encounters karst cave 3 which intrudes into the tunnel, the tunnel is widened and a step is built on the side away from the karst cave, with a reserved central rock pillar 9. The width of the reserved central rock pillar 9 is 3m. The width of the tunnel widening bypass section 2 is 11m to meet the passage conditions of tunnel boring machinery. A steel frame arch is set in the tunnel widening bypass section 2. The steel frame arch adopts I18 type steel frame arch with an installation spacing of 0.6m. The inner wall of the tunnel is shotcreted with a thickness of 25cm. Locking foot anchors are connected at the arch foot position of the steel frame arch, with 2 anchors at each location and each anchor being 3m long. During construction, the angle and direction of the locking foot anchors are determined based on the dip angle and strike of the rock strata and the direction of joint development.

[0049] After the tunnel 1 widening and detour is completed, the reserved rock pillar 9 will be removed and the karst cave will be treated.

[0050] like Figure 3 As shown: To ensure that the top surrounding rock does not collapse due to stress release during the removal of the reserved intermediate rock column 9, a steel pipe column support system is used to replace and remove the reserved intermediate rock column 9. The removal of the reserved intermediate rock column is carried out in sections. First, the steel pipe column 10 for the removal section of the reserved intermediate rock column is replaced, and then the removal of the reserved intermediate rock column 9 in that section is carried out, and so on. The length of each reserved intermediate rock column removal section is controlled within 1.5m.

[0051] Two rows of steel pipe columns 10 are set on the side of the tunnel away from the karst cave. The first row of steel pipe columns is 50cm away from the centerline of the main tunnel. The longitudinal spacing of the steel pipe columns 10 is 1.5m and the transverse spacing is 1m. The steel pipe columns 10 are reinforced with channel steel in the longitudinal and transverse directions to enhance their stability.

[0052] The bottom of the steel pipe column is connected to the concrete foundation; at the installation location of the steel pipe column, a cast-in-place concrete foundation is constructed using C30 concrete, and a 2cm thick steel plate is pre-embedded on the top of the cast-in-place concrete foundation, and the steel pipe column is welded to the pre-embedded steel plate.

[0053] An 80cm*80cm sand box is installed on the top of the steel pipe column, and the top of the sand box is in close contact with the inner wall of the tunnel.

[0054] like Figure 2 , Figure 4 As shown: Cave treatment includes:

[0055] Large stones and cave debris were used to backfill the bottom of cave 3 up to the bottom of the upper step of the tunnel.

[0056] To ensure construction safety during the subsequent construction of the main structure, dangerous rocks at the top and around the cave were removed. Since the dangerous rocks at the top of the cave are relatively high from the backfill layer 6, about 19 to 27 meters vertically, it is inconvenient to use a hoist for drilling. Therefore, scaffolding was used to set up a working platform, and manual drilling and controlled blasting were combined with anchor bolts to deal with the dangerous rocks at the top and around the cave.

[0057] Manual drilling is used to control the blasting location. A manual pneumatic drill is used to set the detonation point. No more than 3 people are allowed on the work platform during each operation. After the detonation point is set, the scaffolding is dismantled. After the blasting is completed, the scaffolding is re-erected. Exposed rock surfaces are protected with wet shotcrete with a thickness of 10cm. Anchor bolts are installed for reinforcement. The next construction process is carried out after the shotcrete reaches the design strength. If there are still dangerous rocks, the dangerous rocks should be repeatedly removed until they are completely removed.

[0058] As the demolition of the reserved rock pillars progresses, the protective canopy 11 is installed. During the demolition of the reserved rock pillars 9, multiple demolition sections of the reserved rock pillars constitute a cycle. After the demolition of the reserved rock pillars in a cycle, the protective canopy 11 is installed. The protective canopy 11 is set in the karst cave space outside the concrete retaining wall.

[0059] The protective canopy consists of I-beam arch frames and I-beam connecting rods. The spacing between the I-beam arch frames is 0.6m / frame. The I-beam arch frames are connected longitudinally by I-beam connecting rods, and the circumferential spacing of the I-beam connecting rods is 50cm. Steps are set on both sides of the cave wall, and the I-beam arch frames are anchored to the cave wall by locking foot small guide pipes.

[0060] like Figure 4 , Figure 5 , Figure 6 As shown: After the protective canopy 11 is completed, the main tunnel construction will proceed;

[0061] The construction of the main tunnel includes the excavation of the main tunnel, the construction of the crossbeam 14 and raft slab 15, the initial support of the tunnel, the construction of the bottom slab 13 and filling, the backfilling and lining of the enlarged bypass section 2, and the construction of the arch support 18, all carried out in sequence.

[0062] During the construction of the main tunnel, the right lower bench 8 is excavated first, followed by the left lower bench 7. The lower bench of Tunnel 1 near the karst cave 3 is defined as the right lower bench 8, and the other side is defined as the left lower bench 7. After the excavation of the right lower bench 8 is completed, the supporting steel pipe columns 12 are constructed within the right lower bench 8. The supporting steel pipe columns 12 are set at a position 50-100cm away from the centerline of the main tunnel. The supporting steel pipe columns 12 are arranged in clusters of 6, between two adjacent crossbeams 14. After the construction of each cluster of supporting steel pipe columns 12 is completed, it is reinforced with channel steel enclosure. After the settlement of the supporting steel pipe columns 12 is completed and stabilized, the steel pipe columns 10 are removed in sequence at intervals. After all the steel pipe columns 10 are removed, the left lower bench 7 is excavated.

[0063] The excavation cycle advance of the right-side lower step 8 and the left-side lower step 7 is controlled below 1.5m, with an excavation depth of approximately 5.7m.

[0064] like Figure 7 As shown: A crossbeam 14 is constructed from the bottom of the left lower step 7 to the cave wall. A raft slab 15 is installed on the upper part of the crossbeam 14 within the cave area. The construction of the crossbeam 14 and the raft slab 15 includes the excavation of the work area and the pouring of concrete. The excavation of the work area and the pouring of concrete are carried out in sections. When the backfill layer 6 in the cave is removed during the excavation of the work area, a hole is opened on the right side of the crossbeam 14 at the location of the cave wall. The left side of the crossbeam 14 is constructed in the lower step 8 on the right and the lower step 7 on the left using a transversely spaced groove method as the crossbeam construction work area. The opening in the cave wall is supported by I18 type steel frames with a longitudinal spacing of 0.8m. The concrete pouring includes tying steel bars, using steel formwork for formwork, and conveying concrete into the formwork. The steel bars are processed in the processing plant and tied on site.

[0065] When delivering concrete into the formwork, reduce the concrete temperature upon entry (below 28℃). Concrete should be poured in horizontal layers, with each layer not exceeding 30cm in thickness. When the free fall height of the concrete exceeds 2m, use a tremie pipe to prevent concrete segregation.

[0066] like Figure 9 , Figure 10 As shown: The initial support of the tunnel includes the installation of the initial support steel frame 16, the laying of steel mesh between the initial support steel frames 16 to cover the inner wall of the tunnel, the spraying of concrete on the inner wall of the tunnel with a thickness of 30cm, the allowable deviation of the flatness of the concrete surface is 100mm, and the wet spraying process is adopted.

[0067] The shotcrete on the inner wall of the tunnel is carried out in two stages. The first shotcrete is 4cm thick. After the first shotcrete has solidified, the initial support steel frame 16 and steel mesh are installed, and then the shotcrete is sprayed again to the designed thickness.

[0068] The initial support steel frame 16 is installed at a spacing of 0.6m, and no more than two initial support steel frames 16 are constructed per cycle. Adjacent initial support steel frames 16 are longitudinally connected by steel tie rods 20, and the circumferential spacing of the steel tie rods 20 is 1m. The initial support steel frame 16 includes several steel frame segments. Locking anchor bolt groups 19 are installed at the arch foot position of the initial support steel frame 16 outside the karst cave area and at the joint position of two steel frame segments. The sleeves of the locking anchor bolts in the locking anchor bolt group 19 are fixedly connected to the initial support steel frame 16. The locking anchor bolt group 19 includes a horizontal first locking anchor bolt, a downwardly inclined second locking anchor bolt, and a third locking anchor bolt.

[0069] After the initial tunnel support construction reaches the location of the supporting steel pipe columns, the supporting steel pipe columns 12 are removed in sections and rows before the initial tunnel support construction is carried out, completing the transformation from the supporting steel pipe columns 12 to the initial tunnel support system.

[0070] The construction of the bottom slab 13 and the filling is carried out after the initial support settlement of the tunnel has stabilized. The reinforced concrete bottom slab and the invert arch filling are then constructed.

[0071] like Figure 8 As shown: the backfilling and lining 17 construction of the expanded bypass section 2 is carried out by backfilling the expanded bypass section 2 from bottom to top through the pumping pipe reserved on the initial support of the tunnel. After the expanded bypass section 2 is backfilled, the lining 17 construction is carried out.

[0072] During the backfilling process of the extended bypass section 2, concrete is backfilled from bottom to top, and the slump of the backfilled concrete is controlled within 200mm. The flow of concrete is observed through the observation holes reserved on the initial support of the tunnel, and vibration is carried out using vibrators. At the same time, the backfilling height is controlled below 3m each time to prevent excessive lateral pressure of concrete from causing deformation and encroachment on the initial support of the tunnel. Surrounding rock monitoring and measurement points and clearance convergence points are set on the initial support of the tunnel.

[0073] After the construction of the arch support 18 is completed, the arch support 17 will be constructed and then enter the karst cave 3 through the horizontal guide tube. The arch support 18 will be constructed by pumping back the wooden formwork to form the concrete arch support 18. The thickness of the arch support 18 is 2m. After the construction of the arch support 18 is completed, tires will be filled between the arch support 18 and the cave wall.

[0074] Construction Examples

[0075] A new railway tunnel connecting City A and City B is 9647m long. 5937m of the tunnel lies within the seasonal variation zone of karst water, and 2450m lies within the horizontal circulation zone of karst water. The karst water is abundant, with a maximum flow rate of 76,900 cubic meters per day. The tunnel passes through soluble rock strata dominated by limestone and dolomite, with a soluble rock section of 8387m in length. The karst caves are moderately to strongly developed, making construction extremely difficult.

[0076] Since the tunnel construction reached DK260+464 on March 13, 2022, where a large karst cave intruding into the main tunnel was discovered, China Railway 12th Bureau Group Co., Ltd., through careful geological survey and combined with the actual conditions of the tunnel construction site, adopted the "tunnel pre-reserved central rock pillar bypass karst cave treatment method" and focused on the technology of clearing and reinforcing dangerous rocks on the karst cave wall and the technology of pre-reserved central rock pillar bypass control for the main tunnel. On March 25, 2022, the tunnel successfully passed through the karst cave, saving 45 days of construction time. Key technologies such as steel pipe column support system and "raft slab + crossbeam + backfill" control were implemented. At the same time, strict on-site construction management was carried out. The tunnel karst cave treatment started on August 10, 2022 and was completed on November 10, 2022. During this period, each process strictly followed the rapid construction method of pre-reserved central rock pillar bypass for karst cave tunnels, and the quality, safety and progress were effectively guaranteed.

[0077] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for treating karst caves that bypass the main tunnel in the presence of rock pillars during tunnel construction, characterized in that: After the tunnel excavation reaches the point where a karst cave intrudes into the tunnel, a central rock pillar is reserved inside the tunnel. The tunnel is then widened and excavated away from the karst cave to bypass the karst cave section and continue the subsequent tunnel construction. After the tunnel widening and bypassing is completed, the reserved central rock pillar is removed, the karst cave is treated, and the main tunnel is constructed. A steel pipe column support system is used to replace and remove the reserved central rock pillar.

2. The method for treating karst caves bypassing rock pillars in tunnel pre-reserved sections according to claim 1, characterized in that: After the tunnel excavation reached the point where a karst cave invaded the tunnel, the tunnel was widened and a step was built on the side away from the karst cave, and a central rock pillar was reserved. A steel frame arch was set in the tunnel widening bypass section, and the inner wall of the tunnel was shotcreted. The steel frame arch was connected to the locking anchor rod at the arch foot position.

3. The method for treating karst caves bypassing the main tunnel in the reserved rock pillar of a tunnel according to claim 2, characterized in that: The process of dismantling the reserved rock pillars is carried out in sections. First, the steel pipe column of one reserved rock pillar dismantling section is replaced, and then the reserved rock pillar of that section is dismantled. This process is repeated. The length of each reserved rock pillar dismantling section is controlled within 1.5m. Two rows of steel pipe columns are installed on the side of the tunnel away from the karst cave. The first row of steel pipe columns is 50cm away from the centerline of the main tunnel. The longitudinal spacing of the steel pipe columns is 1.5m and the transverse spacing is 1m. The steel pipe columns are reinforced with channel steel in both the longitudinal and transverse directions. The bottom of the steel pipe column is connected to the concrete foundation; at the installation location of the steel pipe column, a cast-in-place concrete foundation is constructed, and a steel plate is embedded in the top of the cast-in-place concrete foundation. The steel pipe column is welded to the embedded steel plate. A sand box is installed on top of the steel pipe column, and the top of the sand box is in close contact with the inner wall of the tunnel.

4. The method for treating karst caves bypassing the main tunnel in the reserved rock pillar of a tunnel according to claim 3, characterized in that, Cave treatment includes: Backfill the bottom of the karst cave up to the bottom of the upper step of the tunnel; Remove any dangerous rocks from the top and surrounding areas of the cave; As the demolition of the reserved rock pillars progresses, protective scaffolding is installed. During the demolition of the reserved rock pillars, multiple demolition sections of the reserved rock pillars constitute a cycle. After the demolition of the reserved rock pillars in a cycle, protective scaffolding is constructed. The protective scaffolding is set up in the karst cave space outside the concrete retaining wall.

5. A method for treating karst caves bypassing the main tunnel in the presence of rock pillars as described in claim 4, characterized in that, After the protective scaffolding is completed, the main tunnel construction will begin. The construction of the main tunnel includes the excavation of the main tunnel, the construction of crossbeams and raft slabs, the initial support of the tunnel, the construction of the bottom slab and filling, the backfilling and lining of the enlarged bypass section, and the construction of the arch protection, carried out in sequence. During the construction of the tunnel's main tunnel, the right-side lower bench is excavated first, followed by the left-side lower bench. The lower bench near the karst cave is defined as the right-side lower bench, and the other side is designated as the left-side lower bench. After the right-side lower bench is excavated, supporting steel pipe columns are constructed within it, positioned 50-100cm from the centerline of the tunnel's main tunnel. Six supporting steel pipe columns form a stack, placed between adjacent crossbeams. Each stack is reinforced with channel steel enclosure after construction. After the supporting steel pipe columns have been completed and the settlement has stabilized, they are dismantled sequentially at intervals. After all steel pipe columns have been removed, the left-side lower bench is excavated. A crossbeam is constructed from the bottom of the lower step on the left side to the cave wall. A raft slab is installed on the upper part of the crossbeam within the cave area. The construction of the crossbeam and raft slab includes excavation of the work area and concrete pouring. The excavation and concrete pouring are carried out in sections. After removing the backfill layer in the cave during the excavation of the work area, an opening is made on the right side of the crossbeam at the location of the cave wall. The left side of the crossbeam is constructed by using a transversely spaced groove method in the lower steps on the right and left sides. Steel frames are used for support in the openings in the cave wall. The concrete pouring includes tying reinforcing bars, using steel formwork for formwork, and conveying concrete into the formwork. The initial support of the tunnel includes the installation of the initial support steel frame, the laying of steel mesh between the initial support steel frames to cover the inner wall of the tunnel, and the spraying of concrete on the inner wall of the tunnel. After the initial support construction of the tunnel reaches the position of the supporting steel pipe columns, the supporting steel pipe columns are removed in sections and rows before the initial support construction of the tunnel is carried out, completing the transformation from the supporting steel pipe columns to the initial tunnel support system. The construction of the base slab and filling is carried out after the initial support settlement of the tunnel has stabilized. The reinforced concrete base slab and invert arch filling are constructed. The backfilling and lining of the excavated bypass section are carried out by backfilling the excavated bypass section from bottom to top through the pumping pipe reserved on the initial support of the tunnel. After the excavated bypass section is backfilled, the lining construction is carried out. After the lining construction is completed, the arch support is constructed by entering the karst cave through a horizontal guide tube, using an arch frame with wooden formwork, and pumping backfill to form a concrete arch support.

6. The method for treating karst caves bypassing the main tunnel in the reserved rock pillar of a tunnel according to claim 4, characterized in that: The protective canopy consists of I-beam arch frames and I-beam connecting rods. The spacing between the I-beam arch frames is 0.6m / frame. The I-beam arch frames are connected longitudinally by I-beam connecting rods, and the circumferential spacing of the I-beam connecting rods is 50cm. Steps are set on both sides of the cave wall, and the I-beam arch frames are anchored to the cave wall by locking foot small guide pipes.

7. A method for treating karst caves bypassing rock pillars in tunnel pre-reserved sections, as described in claim 4, characterized in that: The removal of dangerous rocks from the top and surrounding areas of the cave includes using scaffolding to build a working platform and combining manual drilling with controlled blasting and anchor bolt fixation to deal with the dangerous rocks from the top and surrounding areas of the cave. Manual drilling controls the blasting location. After the detonation point is set, the scaffolding is dismantled. After the blasting is completed, the scaffolding is re-erected. Exposed rock surfaces are protected with wet shotcrete and reinforced with anchor bolts. The next construction process is carried out after the shotcrete reaches the design strength.

8. A method for treating karst caves bypassing the main tunnel in the presence of rock pillars as described in claim 5, characterized in that: The initial support steel frame is installed at a spacing of 0.6m, and no more than two initial support steel frames are constructed per cycle. Adjacent initial support steel frames are longitudinally connected by steel tie rods with a circumferential spacing of 1m. Locking anchor rods are installed at the joints of the initial support steel frames, and the sleeves of the locking anchor rods are welded to the initial support steel frames with transverse connecting bars.

9. A method for treating karst caves bypassing the main tunnel in the presence of rock pillars as described in claim 5, characterized in that, During the backfilling process of the excavation and bypass section, concrete is backfilled from bottom to top, and the slump of the backfilled concrete is controlled within 200mm. The flow of concrete is observed through the observation holes reserved on the initial support of the tunnel, and vibration is carried out using vibrators. At the same time, the backfilling height is controlled below 3m each time. Surrounding rock monitoring and measurement points and clearance convergence points are set on the initial support of the tunnel.

10. A method for treating karst caves bypassing the main tunnel in the presence of rock pillars as described in claim 5, characterized in that, The arch is 2m thick. After the arch construction is completed, tires are filled between the arch and the cave wall.

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