Construction method for double-track tunnel to pass through basalt with tuff in water-rich section

Abstract

The invention relates to the technical field of tunnel construction, in particular to a construction method for a double-track tunnel to pass through basalt with tuff in a water-rich section. Comprising the following steps: S1, tuff identification; s2, advanced geological forecast; s3, closing the tunnel face; s4, a forepoling system is established; S5, a tunnel body is excavated, wherein a three-step method is adopted as an excavation construction method; s6, reinforcing a steel frame lock leg support; s7, support parameters are determined; s8, arranging drainage holes; and S9, monitoring and measuring. A plurality of supporting systems are formed, the supporting effect is good, combination with the soil body is stable, the water plugging consolidation effect is obvious, and construction is safe and reliable; the supporting method and the grouting means are organically combined, the procedure connection continuity is good, safety is high, the application range is wide, the construction speed is high, and safety performance is high. The construction method is mainly applied to the construction aspect of the double-track tunnel crossing the basalt and tuff in the water-rich section.

Description

Technical Field

[0001] The present invention relates to the technical field of tunnel construction, and more specifically to a construction method for a double-line tunnel passing through a water-rich section of basalt intercalated tuff. Background Art

[0002] With the increasing maturity of tunnel construction technology and the continuous accumulation of rich construction experience brought by extensive practice, the safety performance of tunnel projects has been significantly improved, and various safety measures and emergency mechanisms have become increasingly perfect. However, when crossing those unfavorable geological sections with extremely complex geological conditions and poor stability, disasters such as tunnel collapse, roof fall, water and mud inrush are still the biggest risks that must be faced during the construction process. These risks are not only difficult to predict, but once they occur, they often have extremely serious consequences.

[0003] Over the years, there have been numerous collapse and flooding accidents caused by tunnels passing through poor geological areas around the world. These accidents not only lead to construction delays and cost overruns, but more seriously, some large-scale collapses and flooding incidents have even directly destroyed tunnel stations, severely damaging transportation infrastructure and causing great inconvenience to people's daily travel. Even more seriously, these accidents have also directly threatened the lives and safety of surrounding personnel, causing irreparable casualties and property losses.

[0004] Especially in areas with abundant groundwater resources, especially those rich in unfavorable geological structures such as tuff, the self-stabilizing ability of the surrounding rock is very fragile. Once it encounters erosion and immersion by groundwater, its self-stabilizing ability will drop sharply, further increasing the risk of tunnel construction. The geological conditions in these areas are complex and changeable, and the construction is extremely difficult, requiring extremely high technical level and construction experience. Therefore, how to effectively deal with geological disasters in these high-risk areas and ensure the safety of tunnel construction has always been an important issue that needs to be solved in the field of tunnel engineering. Summary of the invention

[0005] In order to overcome the deficiencies in the above-mentioned prior art, the present invention provides a construction method for a double-track tunnel crossing a water-rich section of basalt intercalated with tuff. The construction method uses comprehensive forecasting to strengthen the geological analysis ahead; counter-pressure backfilling maintains the stability of the surrounding rock itself and reduces the water and soil pressure above; multiple grouting methods are combined to reinforce the soil and enhance the self-stabilizing ability of the surrounding rock; the comprehensive support method of strengthening the locking foot improves the system support capacity and reduces the risk of tunnel collapse, roof fall, water and mud bursts. The method is novel, comprehensive and widely adaptable.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: A construction method for a double-line tunnel passing through a water-rich section of basalt intercalated with tuff comprises the following steps: S1. Tuff identification: First, identify whether a tuff section is encountered; S2. Advanced geological prediction: Based on geological survey method, advanced horizontal drilling is the main method, supplemented by elastic wave detection, and transient electromagnetic method is used to detect the development of groundwater. When the tunnel construction is about to cross the tuff geological section, pay attention to observe possible precursors, such as obvious reduction in rock strength, softening before the water-rich fault, or water seepage and gushing. Through supplementary geological survey on the surface, geological survey in the cave, and correlation analysis between surface and underground structures, it is predicted that water-rich conditions may occur; S3. Close the face: Take measures to close the face by spraying concrete. During construction, pay attention to the spraying range to fully cover the face, and the thickness of the sprayed concrete should not be less than 20cm; S4. Advance support system: Advance support adopts φ76 middle pipe shed hot-rolled seamless steel pipe plus φ42 advance small guide tube to form an advance support system; the support process includes, S41, constructing the arch and installing the guide pipe; S42 drilling rig in place; S43, installing the drill rod and casing; S44, one section of drilling is completed; S45, the drilling rig returns to its original position, the drill rod and casing are extended, and drilling continues to the designed length; S46, water is injected into the casing to clean it, the drill rod is taken out, the steel flower pipe is installed, the casing is taken out, and the next pipe shed is drilled; S47, grouting is performed after drilling is completed; S48, tunnel excavation is carried out after the grouting pressure is reached; S5. Tunnel excavation: The excavation method adopts the three-step method; S6. Strengthen the support of the steel frame lock foot: add two φ76 or φ42 lock foot anchor pipes near the original lock foot, with a single length of 6m, and inject cement slurry; drill grouting holes in the front of the lock foot anchor pipe in an alternating manner, with a hole diameter of 6-8mm and a hole spacing of 20-30cm, arranged in a plum blossom shape, and the front end is processed into a cone shape, with the tail length not less than 100cm, as a stop grouting section without drilling holes; artificially chisel out the web of the steel arch frame, and reliably connect the additional lock foot and the web of the arch frame with a 16mm thick steel plate; S7. Determination of support parameters: If the monitoring measurement data is stable and the surrounding rock self-stabilization ability is good, maintain the original design support parameters; when the displacement rate of the measuring point is >5mm / d, the supervision engineer shall organize the construction site to analyze the cause and take treatment measures; when the rate is greater than 10mm / d for 2 consecutive days, the supervision unit shall organize the construction unit to analyze the cause and formulate measures and report to the headquarters for approval before implementation; when the rate is greater than 15mm / d, the surrounding rock self-stabilization ability is revealed in combination with the actual situation, and the headquarters shall organize the design, supervision and construction units to analyze the cause and formulate measures, and the construction unit shall determine the final support parameters as required; S8. Laying out drainage holes: The tuff side has poor self-stabilization ability and many water outlets, so the face spraying concrete sealing measures are adopted. During construction, it is necessary to use a down-the-hole drill to drill drainage holes on both sides of the completed primary support section and the water outlets behind the face. The hole diameter should be no less than 76mm to reduce the water outlet of the face. The spraying range should fully cover the face, and the thickness of the sprayed concrete should be no less than 20cm; S9. Monitoring and measurement: When the tunnel passes through the tuff section, the stability of the surrounding rock and support system is monitored to provide a basis for the adjustment of the parameters of the initial support and secondary lining. The information obtained through sorting and analysis of the measured data is promptly fed back to the design and construction, and the design and construction plan is further optimized to achieve the goals of safety, economy and speed. Surrounding rock measurement is an important part of the construction management of tunnels passing through high-risk areas of tuff.

[0007] In step S1, the following situations can be preliminarily identified as tuff sections: situation 1: TSP seismic wave reflection method geological forecast indicates an increase in water volume; situation 2: during advance geological drilling, the color of rock return water changes, and breakthroughs, drill jams, and drill drops occur frequently; situation 3: the geological surface reveals basalt intercalated with thin layers of tuff, rain-like dripping water, and increased water in surrounding rock fissures.

[0008] In step S2, the number of advance geological drilling holes is increased to expand the detection range and reduce the detection blind area; transient electromagnetic geophysical exploration means are added, and when the face reveals sudden rain-like dripping and increased water in the surrounding rock fissures, transient electromagnetic geophysical exploration means are added in the geophysical exploration.

[0009] In the step S4, the φ76 middle pipe rack is spaced 40 cm apart, with an external insertion angle of 8° to 10°, and the arch is set within the range of 75° to 142 degrees. The length of a single pipe is 9 m, the overlap is 3 m, and the longitudinal spacing is 6 m. The middle pipe rack is made of hot-rolled seamless steel pipe, and grouting holes are drilled in the pipe wall with a hole diameter of 8 to 10 mm and a hole spacing of 10 to 20 cm. It is arranged in a plum blossom shape, the front end is processed into a cone, and the tail length is not less than 200 cm, serving as a grouting stop section without drilling holes; the φ42 leading small guide tubes are spaced 0.4 m in the annular direction and are interspersed with the middle pipe rack, with 40 in each ring, a longitudinal spacing of 3.2 m, and an external insertion angle of 1° to 3°.

[0010] In step S4, the small conduit is manufactured in a component processing plant, the front end is made into a pointed cone, the tail is welded with a φ8mm steel reinforcement hoop, and holes are drilled on the pipe wall at intervals of 15 cm, with the hole diameter being 6 to 8 mm.

[0011] The excavation and support construction process in step S5 is as follows: S51, under the protection of the previous cycle of advance support, the upper step is excavated by weak blasting, and the initial support around the upper step is applied, initial concrete is sprayed, steel mesh is laid, steel frame is erected, and concrete is sprayed again to the designed thickness, and the next cycle of advance support is applied; S52, the left side of the middle step is excavated by weak blasting and initial support is applied, initial concrete is sprayed, steel mesh is laid, steel frame is erected, and concrete is sprayed again to the designed thickness. The system anchor rods of the upper step and the left side of the middle step are applied in time after the spraying of concrete is completed, and a pad is set during installation, and the pad is tightly attached to the base surface; S53, the same as the middle step The left side construction process is to excavate and support the right side of the middle step. The system anchors of the upper step and the right side of the middle step are installed in time after the shotcrete is completed. A pad is set during installation, and the pad is in close contact with the base surface. S54. Weak blasting is used to excavate the left side of the lower step and perform initial support for the side wall, that is, initial shotcrete, laying of steel mesh, erection of steel frame, re-spraying of concrete to the designed thickness, and drilling of radial anchors. S55. The same construction process as the left side of the lower step is to excavate and support the right side of the lower step. S56. Weak blasting is used to excavate the bottom and perform initial support for the invert, that is, initial shotcrete, erection of steel frame, and re-spraying of concrete to the designed thickness.

[0012] In step S9, the deformation of the surrounding rock and support can be understood through monitoring and measurement, so as to adjust and correct the support parameters in time to ensure the stability of the surrounding rock and construction safety; provide a basis for judging the basic stability of the surrounding rock and support system, and determine the construction time of the secondary lining.

[0013] Compared with the prior art, the present invention has the following beneficial effects: This method optimizes the combination of traditional tunnel advance geological prediction and advance support methods, increases the number of advance horizontal drill holes, and adjusts the layout to reduce drilling blind areas; uses measures such as spraying concrete to seal the heading face, backfilling with counterpressure, and constructing temporary inverts to prevent the heading face from becoming unstable; uses a combination of φ76 medium pipe shed + φ42 small guide tube to strengthen the support strength, increase the self-stabilizing ability of the surrounding rock, form a comprehensive prediction and comprehensive advance support system, expand advantages, reduce weak links in excavation construction, and reduce the risk of collapse, roof fall, and water and mud inrush.

[0014] Comprehensive forecasts are used to strengthen the geological analysis ahead; counter-pressure backfilling maintains the stability of the surrounding rock itself and reduces the water and soil pressure above; multiple grouting methods are combined to strengthen the soil and enhance the self-stabilizing ability of the surrounding rock; the comprehensive support method of strengthening the locking foot improves the support capacity of the system and reduces the risk of tunnel collapse, roof caving, water and mud inrush. The method is novel, comprehensive and adaptable; a multi-channel support system is formed with good support effect, stable combination with the soil, obvious water blocking and consolidation effect, and safe and reliable construction; the support method is organically combined with the grouting method, the process connection is continuous and the safety is high. This construction method has a wide range of applications, fast construction speed and high safety performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a construction flow chart of the advanced middle pipe shed in the present invention; Figure 2 This is a schematic diagram of the processing of the advanced small catheter in the present invention; Figure 3 It is a cross-sectional schematic diagram of the three-step construction in the present invention; Figure 4 It is a schematic diagram of the horizontal and vertical sections of the three-step construction in the present invention. DETAILED DESCRIPTION

[0016] In order to more clearly understand the above-mentioned purpose, features and advantages of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

[0017] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from the description. Therefore, the protection scope of the present invention is not limited to the specific embodiments disclosed below.

[0018] like Figures 1 to 4 As shown, a construction method for a double-line tunnel passing through a water-rich section of basalt intercalated with tuff comprises the following steps: S1. Tuff identification: First, identify whether you have encountered a tuff section; from the perspective of geological lithology, tuff is very similar to fully weathered basalt, both of which are yellow and brown in color, easily softened when exposed to water, with extremely developed joints and fissures, and in the form of fragments and breccias. However, if the construction is organized according to the strongly weathered basalt, it is easy to form risks such as face instability, local collapse, and water and mud inrush after excavation. S2. Advanced geological prediction: Based on geological survey method, advanced horizontal drilling is the main method, supplemented by elastic wave detection, and transient electromagnetic method is used to detect the development of groundwater. When the tunnel construction is about to cross the tuff geological section, pay attention to observe possible precursors, such as obvious reduction in rock strength, softening before the water-rich fault, or water seepage and gushing. Through supplementary geological survey on the surface, geological survey in the cave, and correlation analysis between surface and underground structures, it is predicted that water-rich conditions may occur; S3. Close the face: Take measures to close the face by spraying concrete. During construction, pay attention to the spraying range to fully cover the face, and the thickness of the sprayed concrete should not be less than 20cm; S4. Advance support system: Advance support adopts φ76 middle pipe shed hot-rolled seamless steel pipe plus φ42 advance small guide tube to form an advance support system; the support process includes, S41, constructing the arch and installing the guide pipe; S42 drilling rig in place; S43, installing the drill rod and casing; S44, one section of drilling is completed; S45, the drilling rig returns to its original position, the drill rod and casing are extended, and drilling continues to the designed length; S46, water is injected into the casing to clean it, the drill rod is taken out, the steel flower pipe is installed, the casing is taken out, and the next pipe shed is drilled; S47, grouting is performed after drilling is completed; S48, tunnel excavation is carried out after the grouting pressure is reached; S5. Tunnel excavation: The excavation method adopts the three-step method; S6. Strengthen the support of the steel frame lock foot: add two φ76 or φ42 lock foot anchor pipes near the original lock foot, with a single length of 6m, and inject cement slurry; drill grouting holes in the front of the lock foot anchor pipe in an alternating manner, with a hole diameter of 6-8mm and a hole spacing of 20-30cm, arranged in a plum blossom shape, and the front end is processed into a cone shape, with the tail length not less than 100cm, as a stop grouting section without drilling holes; artificially chisel out the web of the steel arch frame, and reliably connect the additional lock foot and the web of the arch frame with a 16mm thick steel plate; S7. Determination of support parameters: If the monitoring measurement data is stable and the surrounding rock self-stabilization ability is good, maintain the original design support parameters; when the displacement rate of the measuring point is >5mm / d, the supervision engineer shall organize the construction site to analyze the cause and take treatment measures; when the rate is greater than 10mm / d for 2 consecutive days, the supervision unit shall organize the construction unit to analyze the cause and formulate measures and report to the headquarters for approval before implementation; when the rate is greater than 15mm / d, the surrounding rock self-stabilization ability is revealed in combination with the actual situation, and the headquarters shall organize the design, supervision and construction units to analyze the cause and formulate measures, and the construction unit shall determine the final support parameters as required; S8. Laying out drainage holes: The tuff side has poor self-stabilization ability and many water outlets, so the face spraying concrete sealing measures are adopted. During construction, it is necessary to use a down-the-hole drill to drill drainage holes on both sides of the completed primary support section and the water outlets behind the face. The hole diameter should be no less than 76mm to reduce the water outlet of the face. The spraying range should fully cover the face, and the thickness of the sprayed concrete should be no less than 20cm; S9. Monitoring and measurement: When the tunnel passes through the tuff section, the stability of the surrounding rock and support system is monitored to provide a basis for the adjustment of the parameters of the initial support and secondary lining. The information obtained through sorting and analysis of the measured data is promptly fed back to the design and construction, and the design and construction plan is further optimized to achieve the goals of safety, economy and speed. Surrounding rock measurement is an important part of the construction management of tunnels passing through high-risk areas of tuff.

[0019] In the step S1, the following situations can be preliminarily identified as tuff sections. Situation 1: TSP seismic wave reflection method geological forecast indicates an increase in water volume; the integrity of the surrounding rock is basically consistent with the face, the rock mass is relatively broken, joints and fissures are developed, and fissure water is developed, which manifests as seepage. The joints and fissures are extremely developed or weak interlayers are developed, and the water output increases, which manifests as rain-like water output. When the advanced geological forecast TSP seismic wave reflection method indicates an increase in water volume, attention should be paid to the possibility of encountering tuff interlayers. Situation 2: During advanced geological exploration, the color of the rock stratum return water changes, and breakthroughs, drill jams, and drill drops occur frequently; the tuff rock properties are mainly characterized by soft rock, broken to extremely broken, and obvious mud characteristics. When the geological drill rig drills in the basalt and tuff strata, breakthroughs, drill jams, and drill drops are prone to occur. During drilling, the water returned from basalt is mostly blue-brown, blue-gray, and yellow, and the water returned from tuff is mostly yellow and tawny. When the water returned from the rock layer changes repeatedly between yellow, tawny, blue-brown, and blue-gray, it should be noted that the surrounding rock ahead is likely to be a basalt-tuff stratum. Situation 3: The geological surface reveals a thin layer of basalt-tuff, with rain-like dripping water and increased water in the surrounding rock fissures.

[0020] In step S2, the number of advance geological drilling holes is increased to expand the detection range and reduce the detection blind area; transient electromagnetic geophysical exploration means are added, and when the face reveals sudden rain-like dripping and increased water in the surrounding rock fissures, transient electromagnetic geophysical exploration means are added in the geophysical exploration.

[0021] In the step S4, the φ76 middle pipe rack is spaced 40 cm apart, with an external insertion angle of 8° to 10°, and the arch is set within the range of 75° to 142 degrees. The length of a single pipe is 9 m, the overlap is 3 m, and the longitudinal spacing is 6 m. The middle pipe rack is made of hot-rolled seamless steel pipe, and grouting holes are drilled in the pipe wall with a hole diameter of 8 to 10 mm and a hole spacing of 10 to 20 cm. It is arranged in a plum blossom shape, the front end is processed into a cone, and the tail length is not less than 200 cm, serving as a grouting stop section without drilling holes; the φ42 leading small guide tubes are spaced 0.4 m in the annular direction and are interspersed with the middle pipe rack, with 40 in each ring, a longitudinal spacing of 3.2 m, and an external insertion angle of 1° to 3°.

[0022] In step S4, the small conduit is manufactured in a component processing plant, the front end is made into a pointed cone, the tail is welded with a φ8mm steel reinforcement hoop, and holes are drilled on the pipe wall at intervals of 15 cm, with the hole diameter being 6 to 8 mm.

[0023] After the construction of the pipe shed and small conduit, secondary spraying and sealing is required before grouting to ensure the sealing of the grouting, and the pipe mouth should be protected before spraying and sealing; after the construction of the medium pipe shed grouting pre-support is completed, the excavation process should strengthen monitoring and measurement, among which the vault sinking and clearance changes are mandatory items. Take appropriate measures in a timely manner according to the monitoring feedback information to ensure construction safety and quality.

[0024] The excavation and support construction process in step S5 is as follows: S51, under the protection of the previous cycle of advance support, the upper step is excavated by weak blasting, and the initial support around the upper step is applied, initial concrete is sprayed, steel mesh is laid, steel frame is erected, and concrete is sprayed again to the designed thickness, and the next cycle of advance support is applied; S52, the left side of the middle step is excavated by weak blasting and initial support is applied, initial concrete is sprayed, steel mesh is laid, steel frame is erected, and concrete is sprayed again to the designed thickness. The system anchor rods of the upper step and the left side of the middle step are applied in time after the spraying of concrete is completed, and a pad is set during installation, and the pad is tightly attached to the base surface; S53, the same as the middle step The left side construction process is to excavate and support the right side of the middle step. The system anchor bolts of the upper step and the right side of the middle step are installed in time after the shotcrete is completed. A pad is set during installation, and the pad is in close contact with the base surface. S54. Weak blasting is used to excavate the left side of the lower step and implement the initial support of the side wall, that is, initial shotcrete, laying steel mesh, erecting steel frame, re-spraying concrete to the designed thickness, and drilling radial anchor bolts. S55. The same construction process as the left side of the lower step is to excavate and support the right side of the lower step. S56. Weak blasting is used to excavate the bottom and implement the initial support of the invert, that is, initial shotcrete, erecting steel frame, and re-spraying concrete to the designed thickness. Pour the V part invert and the side wall foundation. After the initial setting of the invert concrete, pour the VI part invert filling part to the designed height.

[0025] In step S9, the deformation of the surrounding rock and support can be understood through monitoring and measurement, so as to adjust and correct the support parameters in time to ensure the stability of the surrounding rock and construction safety; provide a basis for judging the basic stability of the surrounding rock and support system, and determine the construction time of the secondary lining.

[0026] Special situation treatment plan: According to the summary of on-site construction, when the tunnel face shows the surrounding rock conditions shown in the figure above: the surrounding rock lithology reveals that it is all tuff, with yellow and yellow-brown colors, loose structure of gravel breccia, poor self-stabilization ability, and sliding in the cave in front of the arch. The outflow is sandy tuff weathering products, and the groundwater is rain-like to strand-like water, and the sliding is accompanied by small strands of water. The following measures are mainly taken: In order to avoid the continuous instability of the face, continuous sliding into the tunnel, causing roof collapse, support deformation, and the formation of large cavities, when the face has poor self-stabilization ability and the front of the arch is sliding into the tunnel, counter-pressure backfilling measures should be taken immediately. After the above counter-pressure backfilling measures are taken to effectively stop the surrounding rock from sliding into the tunnel, the face spraying concrete sealing measures should be taken in time. During construction, pay attention to the spraying range to fully cover the face, and the thickness of the sprayed concrete should not be less than 20cm.

[0027] Only the preferred embodiments of the present invention are described in detail above, but the present invention is not limited to the above embodiments. Various changes can be made within the knowledge scope of ordinary technicians in this field without departing from the purpose of the present invention, and various changes should be included in the protection scope of the present invention.

Claims

1. A construction method for a double-line tunnel passing through a water-rich section of basalt intercalated with tuff, characterized in that: The following steps are involved: S1. Tuff identification: First, identify whether a tuff section is encountered; S2. Advanced geological prediction: Based on geological survey method, advanced horizontal drilling is the main method, supplemented by elastic wave detection, and transient electromagnetic method is used to detect the development of groundwater. When the tunnel construction is about to cross the tuff geological section, pay attention to observe possible precursors, such as obvious reduction in rock strength, softening before the water-rich fault, or water seepage and gushing. Through supplementary geological survey on the surface, geological survey in the cave, and correlation analysis between surface and underground structures, it is predicted that water-rich conditions may occur; S3. Close the face: Take measures to close the face by spraying concrete. During construction, pay attention to the spraying range to fully cover the face, and the thickness of the sprayed concrete should not be less than 20cm; S4. Advance support system: Advance support adopts φ76 middle pipe shed hot-rolled seamless steel pipe plus φ42 advance small guide tube to form an advance support system; the support process includes, S41, constructing the arch and installing the guide pipe; S42 drilling rig in place; S43, installing the drill rod and casing; S44, one section of drilling is completed; S45, the drilling rig returns to its original position, the drill rod and casing are extended, and drilling continues to the designed length; S46, water is injected into the casing to clean it, the drill rod is taken out, the steel flower pipe is installed, the casing is taken out, and the next pipe shed is drilled; S47, grouting is performed after drilling is completed; S48, tunnel excavation is carried out after the grouting pressure is reached; S5. Tunnel excavation: The excavation method adopts the three-step method; S6. Strengthen the support of the steel frame lock foot: add two φ76 or φ42 lock foot anchor pipes near the original lock foot, with a single length of 6m, and inject cement slurry; drill grouting holes in the front of the lock foot anchor pipe in an alternating manner, with a hole diameter of 6-8mm and a hole spacing of 20-30cm, arranged in a plum blossom shape, and the front end is processed into a cone shape, with the tail length not less than 100cm, as a stop grouting section without drilling holes; artificially chisel out the web of the steel arch frame, and reliably connect the additional lock foot and the web of the arch frame with a 16mm thick steel plate; S7. Determination of support parameters: If the monitoring measurement data is stable and the surrounding rock self-stabilization ability is good, maintain the original design support parameters; when the displacement rate of the measuring point is >5mm / d, the supervision engineer shall organize the construction site to analyze the cause and take treatment measures; when the rate is greater than 10mm / d for 2 consecutive days, the supervision unit shall organize the construction unit to analyze the cause and formulate measures and report to the headquarters for approval before implementation; when the rate is greater than 15mm / d, the surrounding rock self-stabilization ability is revealed in combination with the actual situation, and the headquarters shall organize the design, supervision and construction units to analyze the cause and formulate measures, and the construction unit shall determine the final support parameters as required; S8. Laying out drainage holes: The tuff side has poor self-stabilization ability and many water outlets, so the face spraying concrete sealing measures are adopted. During construction, it is necessary to use a down-the-hole drill to drill drainage holes on both sides of the completed primary support section and the water outlets behind the face. The hole diameter should be no less than 76mm to reduce the water outlet of the face. The spraying range should fully cover the face, and the thickness of the sprayed concrete should be no less than 20cm; S9. Monitoring and measurement: When the tunnel passes through the tuff section, the stability of the surrounding rock and support system is monitored to provide a basis for the adjustment of the parameters of the initial support and secondary lining. The information obtained through sorting and analysis of the measured data is promptly fed back to the design and construction, and the design and construction plan is further optimized to achieve the goals of safety, economy and speed. Surrounding rock measurement is an important part of the construction management of tunnels passing through high-risk areas of tuff.

2. The construction method of a double-track tunnel passing through a water-rich section of basalt intercalated with tuff according to claim 1, characterized in that: In step S1, the following situations can be preliminarily identified as tuff sections: situation 1: TSP seismic wave reflection method geological forecast indicates an increase in water volume; situation 2: during advance geological drilling, the color of rock return water changes, and breakthroughs, drill jams, and drill drops occur frequently; situation 3: the geological surface reveals basalt intercalated with thin layers of tuff, rain-like dripping water, and increased water in surrounding rock fissures.

3. The construction method of a double-track tunnel passing through a water-rich section of basalt intercalated with tuff according to claim 1, characterized in that: In step S2, the number of advance geological drilling holes is increased to expand the detection range and reduce the detection blind area; transient electromagnetic geophysical exploration means are added, and when the face reveals sudden rain-like dripping and increased water in the surrounding rock fissures, transient electromagnetic geophysical exploration means are added in the geophysical exploration.

4. The construction method of a double-track tunnel passing through a water-rich section of basalt intercalated with tuff according to claim 1, characterized in that: In the step S4, the φ76 middle pipe rack is spaced 40 cm apart, with an external insertion angle of 8° to 10°, and the arch is set within the range of 75° to 142 degrees. The length of a single pipe is 9 m, the overlap is 3 m, and the longitudinal spacing is 6 m. The middle pipe rack is made of hot-rolled seamless steel pipe, and grouting holes are drilled in the pipe wall with a hole diameter of 8 to 10 mm and a hole spacing of 10 to 20 cm. It is arranged in a plum blossom shape, the front end is processed into a cone, and the tail length is not less than 200 cm, serving as a grouting stop section without drilling holes; the φ42 leading small guide tubes are spaced 0.4 m in the annular direction and are interspersed with the middle pipe rack, with 40 in each ring, a longitudinal spacing of 3.2 m, and an external insertion angle of 1° to 3°.

5. The construction method of a double-track tunnel passing through a water-rich section of basalt intercalated with tuff according to claim 1, characterized in that: In step S4, the small conduit is manufactured in a component processing plant, the front end is made into a pointed cone, the tail is welded with a φ8mm steel reinforcement hoop, and holes are drilled on the pipe wall at intervals of 15 cm, with the hole diameter being 6 to 8 mm.

6. The construction method of a double-track tunnel passing through a water-rich section of basalt intercalated with tuff according to claim 1, characterized in that: The excavation and support construction process in step S5 is as follows: S51, under the protection of the previous cycle of advance support, the upper step is excavated by weak blasting, and the initial support around the upper step is applied, initial concrete is sprayed, steel mesh is laid, steel frame is erected, and concrete is sprayed again to the designed thickness, and the next cycle of advance support is applied; S52, the left side of the middle step is excavated by weak blasting and initial support is applied, initial concrete is sprayed, steel mesh is laid, steel frame is erected, and concrete is sprayed again to the designed thickness. The system anchor rods of the upper step and the left side of the middle step are applied in time after the spraying of concrete is completed, and a pad is set during installation, and the pad is tightly attached to the base surface; S53, the same as the middle step The left side construction process is to excavate and support the right side of the middle step. The system anchors of the upper step and the right side of the middle step are installed in time after the shotcrete is completed. A pad is set during installation, and the pad is in close contact with the base surface. S54. Weak blasting is used to excavate the left side of the lower step and perform initial support for the side wall, that is, initial shotcrete, laying of steel mesh, erection of steel frame, re-spraying of concrete to the designed thickness, and drilling of radial anchors. S55. The same construction process as the left side of the lower step is to excavate and support the right side of the lower step. S56. Weak blasting is used to excavate the bottom and perform initial support for the invert, that is, initial shotcrete, erection of steel frame, and re-spraying of concrete to the designed thickness.

7. The construction method of a double-track tunnel passing through a water-rich section of basalt intercalated with tuff according to claim 1, characterized in that: In step S9, the deformation of the surrounding rock and support can be understood through monitoring and measurement, so as to adjust and correct the support parameters in time to ensure the stability of the surrounding rock and construction safety; provide a basis for judging the basic stability of the surrounding rock and support system, and determine the construction time of the secondary lining.

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