Tunnel karst defect fine detection and scale matching construction method

Abstract

The present application relates to the technical field of tunnel karst defect detection, and discloses a tunnel karst defect fine detection and scale matching construction method, comprising the following steps: step S1, before the construction of a karst tunnel, adopting a semi-airborne transient electromagnetic exploration method and a depression analysis method to conduct geological investigation on the mountain of the proposed tunnel, regional karst water power conditions and dissolution evolution; step S2, during the construction of a karst tunnel, adopting a combination of TSP method and geological radar method to increase the prediction content of vault cave, surrounding cave and floor cave; step S3, before the exposure of a solution cavity, regulating the karst drainage channel, and taking reinforcement measures to block and control the migration of the solution cave filling; step S4, after the exposure of a solution cavity, adopting a tunnel three-dimensional space measurement technology to accurately determine the solution cavity, and establishing a solution cave-tunnel combined structure scale matching effect stress analysis model; step S5, after the treatment of a tunnel karst, establishing an automatic monitoring and measurement system, and making a safety early warning.

Description

Technical Field

[0001] This invention relates to the field of tunnel karst defect detection technology, and more specifically to a method for precise detection of tunnel karst defects and scale-matched construction. Background Technology

[0002] Complex karst tunnel projects are characterized by large investment, long construction period, complex technology, many unforeseen risk factors and high safety risks. Guangxi is a famous karst area in my country, with a karst area of ​​98,000 square kilometers, accounting for 41% of the total land area of ​​the region. The karst area has complex topography and landforms, well-developed rock strata with fractures and joints, and is subject to strong dissolution and erosion. Karst caves and underground rivers are widespread, which pose a great threat to tunnel construction.

[0003] Before designing and constructing complex karst tunnels, a detailed geological survey of the proposed tunnel site is essential. However, due to the complexity of karst geology and the limited scope of surveys, the data obtained may differ significantly from the actual conditions revealed after tunnel excavation. Insufficient understanding of the geological conditions ahead of the tunnel face leads to significant uncertainty during construction, frequently resulting in unforeseen accidents such as collapses, mudslides, and water inrushes. These accidents can range from impacting the construction schedule and increasing investment to causing casualties and posing immense challenges in post-construction management. Accurately understanding the changes in the surrounding rock structure and geological hazards ahead of the tunnel face during excavation, predicting the presence of karst caves, karst water, and other adverse geological conditions, as well as the geometry, occurrence, and size of these structures, allows for timely and rational scheduling of the excavation progress, revision of construction plans, implementation of protective measures, and prevention of potential hazards.

[0004] Therefore, there is an urgent need for a method for detecting karst defects in tunnels and for construction that coordinates scale with the target. Summary of the Invention

[0005] In order to overcome the above-mentioned defects of the prior art, the embodiments of the present invention provide a method for precise detection of karst defects in tunnels and a construction method for scale coordination, so as to solve the technical problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for precise detection and scale-coordinated construction of karst defects in tunnels, comprising the following steps:

[0007] Step S1: Before the construction of the karst tunnel, a geological survey was conducted on the karst hydrodynamic conditions and karst evolution of the proposed tunnel mountain and the surrounding area using the semi-airborne transient electromagnetic exploration method and the depression analysis method.

[0008] Step S2: During the construction of karst tunnels, a combination of the TSP method and the ground-penetrating radar method is used for forecasting, increasing the forecast content of karst caves in the arch, surrounding karst caves and bottom karst caves, and improving the accuracy of advance forecasting;

[0009] Step S3: Before the karst cavity is exposed, local sealing, drilling to reduce pressure, and treatment of karst drainage channels are carried out to prevent water inrush in the karst tunnel. Drainage consolidation and grouting reinforcement measures are also taken to seal and control the migration of karst cavity filling materials to prevent mudslide accidents.

[0010] Step S4: After the karst cavity is exposed, the karst cavity is accurately determined using tunnel three-dimensional spatial measurement technology, and a stress analysis model of the scale coordination effect of the karst cavity-tunnel combined structure is established. A support structure scheme is formulated for the size effect, and the karst cavity treatment method is improved for the scale coordination effect.

[0011] Step S5: After the karst treatment of the tunnel, establish an automated monitoring and measurement system to track the stress and deformation of the surrounding rock and support structure in real time and issue safety warnings in real time.

[0012] In a preferred embodiment, during semi-airborne transient electromagnetic exploration, a grounded source is used to emit a primary pulse electromagnetic field into the ground. During the interval between the primary pulse electromagnetic fields, a coil carried by an unmanned aerial vehicle is used to observe the secondary induced eddy current field in the underground medium and calculate the medium resistivity.

[0013] In a preferred embodiment, the depression analysis method collects the surface catchment area and groundwater movement characteristics, and draws a three-dimensional visualized hydrogeological map of the tunnel site area. The hydrogeological map includes water body distribution and elevation, watershed distribution related to karst groundwater in the tunnel area, and the distribution of dissolution cover layer and dissolution funnel above the tunnel. The pore medium preferential flow theory predicts the formation and distribution of soil cavities. The depression analysis method adopts the theory of flow deviation between fractured medium and karst medium, which states that large fractures have strong water storage capacity and small fractures have weak water storage capacity, and predicts the movement law of karst water and the degree of dissolution in different areas.

[0014] In a preferred embodiment, the TSP method provides long-distance reporting from 100m to 300m. When anomalies are predicted by the TSP, ground-penetrating radar is used to obtain more detailed information on karst defects. Both the TSP method and the ground-penetrating radar method are used to predict karst caves in the arch, surrounding caves, and floor. When performing borehole prediction, drilling is conducted in front of the working face, in the arch, and in the surrounding rock. The advance prediction distance is 40m, and the prediction range for the surrounding rock and the arch is twice the cave diameter or more.

[0015] In a preferred embodiment, in step S3, the risk of water and mud inrush during tunnel excavation is predicted, and preventive and control measures are formulated. These preventive and control measures include drainage and pressure reduction, as well as reinforcement of unstable karst cave filling materials.

[0016] In a preferred embodiment, during the diversion and drainage pressure reduction, the water diversion tunnel is used to divert and drain karst water that crosses the tunnel. The water diversion tunnel starts from inside the tunnel and connects to the karst pipe that crosses the tunnel, and continues until it reaches the sinkhole. The construction of the water diversion tunnel adopts the full-section excavation construction method, and the sections with developed fissures are treated with anchor bolt shotcrete support measures.

[0017] In a preferred embodiment, during the three-dimensional spatial measurement in step S4, base points are set up inside the cavity, three-dimensional laser measurement is performed on the cavity and rock mass structure, and the coordinates of the entire cave are located using an engineering surveying total station and a satellite positioning device (GPS / RTK) and inter-interacted with the three-dimensional scanning data. The acquired cavity point cloud data is processed by noise removal, coordinate transformation and stitching, and a viewing video is generated using SCENE.

[0018] In a preferred embodiment, the noise removal is performed using a quantized noise compensation function, the formula of which is: In the formula, B is the quantization resolution. The peak value of the image signal. Sj represents the variance of the image signal sequence, and SJ represents the processed data.

[0019] In a preferred embodiment, based on the three-dimensional model of the karst cavity, a relationship diagram between karst geological defects and the tunnel is formed according to the three-dimensional intersection model, the continuous arch model, and the irregular hole model. The stress concentration around the karst cavity and the surrounding rock of the tunnel is analyzed, and the prediction of easily collapsed areas is given. Taking the stress concentration phenomenon as the main object, the size effect and scale coordination effect of karst tunnel are studied. The changes of surrounding rock pressure and the bearing capacity of various support structures with the size effect and scale coordination effect are analyzed. Support structure schemes are formulated for the size effect, and the karst cavity treatment method is improved for the scale coordination effect.

[0020] In a preferred embodiment, the automated monitoring and measurement system includes a data acquisition unit, an analysis unit, an early warning unit, and a terminal device. The data acquisition unit acquires stress data YL around karst defects, deformation data XB of the support structure, and displacement data WY of unfavorable structural surfaces, and sends the acquired data to the analysis unit. The analysis unit receives the stress data YL, deformation data XB, and displacement data WY, performs correlation processing, and generates a judgment value P. The correlation processing formula for the judgment value P is as follows: In the formula, k1 and k2 are weights, and 0≤k1≤1, 0≤k2≤1, k1+k2=1. The analysis unit sends the judgment value P to the early warning unit.

[0021] In a preferred embodiment, the warning unit receives a judgment value P and compares it with a threshold Y. When the judgment value P is greater than or equal to the threshold Y, the alarm unit sends an alarm to the terminal device, indicating a dangerous state. When the judgment value P is less than the threshold Y, the alarm unit is in a standby state.

[0022] The technical effects and advantages of this invention are as follows:

[0023] 1. This invention can detect hidden karst in tunnels by using semi-airborne transient electromagnetic exploration. This technology is composed of an electromagnetic transmitter and a rotary-wing UAV. It can obtain the underground apparent resistivity distribution in the tunnel site area under complex terrain conditions. Based on the three-dimensional apparent resistivity distribution map of the exploration results, the approximate distribution and direction of the tunnel karst can be known, which facilitates the construction.

[0024] 2. This invention uses depression analysis to analyze the surface catchment area, groundwater movement characteristics, and the relationship between karst groundwater and the tunnel in the tunnel site area. It then creates a three-dimensional visualized hydrogeological map, providing clear visualization of karst water characteristics and better preventing karst water inrush and mudslide accidents.

[0025] 3. This invention combines the TSP method with the ground-penetrating radar method. The TSP method has a long detection range, but its accuracy is low. Therefore, TSP is used for long-distance reporting, and ground-penetrating radar is used to acquire anomalies, thereby ensuring the accuracy of the detection. Furthermore, the detection report of this application covers the arch cave, the surrounding cave, and the bottom cave, so three-dimensional prediction can be performed. The increased number of factors considered improves the accuracy of the prediction.

[0026] 4. This invention uses three-dimensional spatial measurement of tunnels + BIM technology to determine karst cavities, establishes a stress analysis model of the scale coordination effect of karst cave-tunnel combined structure, formulates support structure schemes for size effects, and improves karst cave treatment methods for scale coordination effects, making the stress analysis of karst tunnels more comprehensive.

[0027] 5. This invention, by incorporating an automated monitoring and measurement system, uses three data points—stress data YL, deformation data XB, and displacement data WY—and performs correlation processing to accurately determine whether the treated tunnel karst is in a safe state and to issue timely warnings. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the construction method of the present invention.

[0029] Figure 2 This is a schematic diagram of the overall construction process of the present invention.

[0030] Figure 3 This is a three-dimensional visualization of hydrogeology, as presented in this invention.

[0031] Figure 4 This is a schematic diagram of the automation monitoring and measurement system of the present invention.

[0032] Figure 5 This is a schematic diagram of the working face position for the advanced drilling arrangement of the present invention. Detailed Implementation

[0033] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. In addition, the forms of the various structures described in the following embodiments are merely illustrative. The method for fine detection and scale coordination of tunnel karst defects involved in the present invention is not limited to the structures described in the following embodiments. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] Example 1, refer to Figure 1 and Figure 2 This invention provides a method for precise detection and scale-coordinated construction of karst defects in tunnels, comprising the following steps:

[0035] Step S1: Before the construction of the karst tunnel, a geological survey was conducted on the karst hydrodynamic conditions and karst evolution of the proposed tunnel mountain and the surrounding area using the semi-airborne transient electromagnetic exploration method and the depression analysis method.

[0036] Step S2: During the construction of karst tunnels, a combination of the TSP method and the ground-penetrating radar method is used for forecasting, increasing the forecast content of karst caves in the arch, surrounding karst caves and bottom karst caves, and improving the accuracy of advance forecasting;

[0037] Step S3: Before the karst cavity is exposed, local sealing, drilling to reduce pressure, and treatment of karst drainage channels are carried out to prevent water inrush in the karst tunnel. Drainage consolidation and grouting reinforcement measures are also taken to seal and control the migration of karst cavity filling materials to prevent mudslide accidents.

[0038] Step S4: After the karst cavity is exposed, the karst cavity is accurately determined using tunnel three-dimensional spatial measurement technology, and a stress analysis model of the scale coordination effect of the karst cavity-tunnel combined structure is established. A support structure scheme is formulated for the size effect, and the karst cavity treatment method is improved for the scale coordination effect.

[0039] Step S5: After the karst treatment of the tunnel, establish an automated monitoring and measurement system to track the stress and deformation of the surrounding rock and support structure in real time and issue safety warnings in real time.

[0040] Furthermore, in semi-airborne transient electromagnetic exploration, a grounded source is used to emit a primary pulse electromagnetic field into the ground. During the interval between the primary pulse electromagnetic fields, the secondary induced eddy current field induced in the underground medium is observed by a coil carried by a UAV, and the resistivity of the medium is calculated. Semi-airborne transient electromagnetic exploration can detect the hidden karst in tunnels. This technology is composed of an electromagnetic transmitter and a rotary-wing UAV, which can obtain the underground apparent resistivity distribution in the tunnel site area under complex terrain conditions. According to the three-dimensional apparent resistivity distribution map of the exploration results, the approximate distribution and direction of the tunnel karst can be known. In addition, it should be noted that calculating the resistivity of the medium based on the secondary induced eddy current field is a conventional technical means for those skilled in the art, and this application does not limit it in detail.

[0041] Reference Figure 3 The depression analysis method collects data on surface catchment area and groundwater movement characteristics to create a three-dimensional visualized hydrogeological map of the tunnel site area. This map includes water body distribution and elevation, watershed distribution related to karst groundwater in the tunnel area, and the distribution of dissolution overburden and dissolution funnels above the tunnel. The preferential flow theory of porous media predicts the formation and distribution of soil cavities. Furthermore, the depression analysis method employs the theory of flow deviation between fractured and karst media, where large fractures have strong water storage capacity and small fractures have weak water storage capacity, predicting the movement patterns of karst water and the degree of dissolution in different areas. This method can create a three-dimensional visualized hydrogeological map of the tunnel site area, revealing the relationship between karst groundwater and the tunnel. This allows for advance knowledge of underground conditions during construction, facilitating the process. Moreover, the theory of flow deviation between fractured and karst media indicates that large fractures have strong water storage capacity and small fractures have weak water storage capacity; therefore, there is a correlation between groundwater temperature and fractures. The hydrogeological map can better reflect the underground conditions.

[0042] Furthermore, the TSP method provides long-distance reporting from 100m to 300m. When anomalies are predicted by the TSP, ground-penetrating radar is used to obtain more detailed information on karst defects. Both the TSP method and the ground-penetrating radar method are used to predict karst caves in the arch, surrounding caves, and floor caves. When drilling is used for prediction, drilling is conducted in front of the working face, in the arch, and in the surrounding rock. The advance prediction distance is 40m, and the prediction range for the surrounding rock and the arch is twice the cave diameter or more. In this embodiment, the TSP method has a longer detection distance, but its accuracy is lower. Therefore, TSP is used for long-distance reporting, and ground-penetrating radar is used to obtain information on anomalies to ensure the accuracy of the detection. Moreover, the detection report in this application covers karst caves in the arch, surrounding caves, and floor caves, so three-dimensional prediction can be performed, increasing the factors considered and thus improving the accuracy of the prediction.

[0043] Furthermore, in step S3, the risk of water inrush and mud inrush during tunnel excavation is predicted, and preventive and control measures are formulated. These measures include drainage and pressure reduction, as well as reinforcement of unstable karst cave filling materials. Drainage and pressure reduction technology is applied to dissipate karst water pressure, lower the groundwater level, and prevent water inrush accidents. Based on the relationship between the karst cave filling materials and the tunnel and their stability, the unstable karst cave filling materials are reinforced to prevent mud inrush accidents.

[0044] Furthermore, during the diversion and drainage pressure reduction process, the water diversion tunnel is used to divert and drain karst water that crosses the tunnel. The water diversion tunnel starts from inside the tunnel and connects to the karst pipe that crosses the tunnel, continuing until it reaches the sinkhole. The construction of the water diversion tunnel adopts the full-face excavation construction method. Sections with developed fissures are treated with anchor bolt shotcrete support measures. By diverting water, the karst water can smoothly cross the tunnel, at which point the pressure inside the tunnel is reduced, thereby preventing the tunnel from collapsing. Moreover, the construction of the water diversion tunnel adopts the full-face excavation construction method to ensure the smooth excavation of the tunnel.

[0045] Furthermore, during the three-dimensional spatial measurement in step S4, base points are established inside the cavity. Three-dimensional laser measurements are performed on the cavity and rock structure. An engineering surveying total station and GPS / RTK satellite positioning equipment are used to locate the overall cave coordinates and interface with the three-dimensional scanning data. The acquired cavity point cloud data undergoes noise removal, coordinate transformation, and stitching processing. A viewing video is generated using SCENE. Noise removal employs a quantization noise compensation function, the formula of which is: In the formula, B is the quantization resolution. The peak value of the image signal. Sj represents the variance of the image signal sequence, and SJ represents the processed data.

[0046] Furthermore, based on the three-dimensional model of the karst cavity, a relationship diagram between karst geological defects and the tunnel is formed according to the three-dimensional intersection model, the continuous arch model, and the irregular hole model. The stress concentration around the karst cavity and the surrounding rock of the tunnel is analyzed, and the prediction of easily collapsed areas is given. Taking the stress concentration phenomenon as the main object, the size effect and scale coordination effect of karst tunnel are studied. The changes of surrounding rock pressure and the bearing capacity of various support structures with the size effect and scale coordination effect are analyzed. Support structure schemes are formulated for the size effect, and the karst cavity treatment methods are improved for the scale coordination effect.

[0047] In this embodiment of the application, during three-dimensional spatial measurement, after setting up base points and taking measurements, a clear image of the interior of the cavity can be generated, which is convenient for construction personnel to view. Noise is removed by a compensation function, and the transmitted data is more accurate, thereby ensuring the accuracy of the final video. In addition, it should be noted that the coordinate transformation of cloud data can be completed by JavaScript, and the stitching can be completed by Maptek I-Site Studio. This is a conventional technical means in this field, and this application does not limit it in detail.

[0048] Reference Figure 4 The automated monitoring and measurement system includes a data acquisition unit, an analysis unit, an early warning unit, and terminal equipment. The data acquisition unit collects stress data (YL) around karst defects, deformation data (XB) of the support structure, and displacement data (WY) of unfavorable structural surfaces, and sends the collected data to the analysis unit. The analysis unit receives the stress data (YL), deformation data (XB), and displacement data (WY), performs correlation processing, and generates a judgment value (P). The correlation processing formula for the judgment value (P) is as follows: In the formula, k1 and k2 are weights, and 0≤k1≤1, 0≤k2≤1, k1+k2=1. The analysis unit sends the judgment value P to the early warning unit. The early warning unit receives the judgment value P and compares it with the threshold Y. When the judgment value P is greater than or equal to the threshold Y, the alarm unit sends an alarm to the terminal device, indicating a dangerous state. When the judgment value P is less than the threshold Y, the alarm unit is in standby mode.

[0049] In this embodiment of the application, by using three data points—stress data YL, deformation data XB, and displacement data WY—and performing correlation processing, it is possible to accurately determine whether the treated tunnel karst is in a safe state. When the judgment value P is greater than or equal to the threshold Y, it indicates that the tunnel karst may be in danger, and an alarm is triggered.

[0050] Example 2: The application of this application in the Qinlan Tunnel includes the following steps:

[0051] Step A1, Semi-airborne transient electromagnetic detection. According to the "Semi-airborne transient electromagnetic detection report of Tian'e to Beihai Highway (Tian'e via Fengshan to Bama section)," the semi-airborne transient electromagnetic detection results of the first half of the Qinlan Tunnel are as follows: 4) There may be a small-scale karst development area between ZK87+540 and ZK87+580. The top of the karst development area is about 20m above the tunnel roof, and the bottom of the karst development area is about 110m below the tunnel floor; 5) There may be a small-scale karst development area between ZK89+080 and ZK89+140. The top of the karst development area is about 40m above the tunnel roof, and the bottom of the karst development area is about 25m below the tunnel floor.

[0052] Step A2, Depression Analysis of Karst Water Collection: A large-scale geological survey of karst water in the tunnel area was conducted using the depression analysis method. There were no large depressions on the surface of the tunnel area, and no water accumulation in the small depressions. The tunnel body in this section is buried at a depth of about 257-277m. The surrounding rock of the tunnel body is mainly filled karst caves, which are filled with clay and a small amount of gravel. The rock mass is relatively broken to extremely broken. Groundwater is not developed, and the excavation stability is poor. After excavation, phenomena such as rockfall, mudslide, karst cave collapse, and water seepage during the rainy season are likely to occur.

[0053] Step A3: Advanced geological prediction and detection. Based on the intermediate report No. 009 of the "Advanced Geological Prediction (Ground Radar) Report for the First Half (Left Exit Line) of Qinlan Tunnel in Contract Section NO.5 of Tianba Road" (predicted mileage: ZK87+920~ZK87+890), the advanced geological prediction (ground radar) detection results for the left tunnel exit of the first half of Qinlan Tunnel are as follows: The surrounding rock of the predicted section from ZK87+920 to ZK87+890 is mainly moderately weathered limestone. The overall surrounding rock is relatively broken. It is inferred that the surrounding rock is broken or has developed filling karst caves within the range of 0~20m in front of the tunnel face (corresponding mileage: ZK87+920~ZK87+900). It is recommended to carry out advanced drilling.

[0054] Step A4, refer to Figure 5 Advanced drilling was carried out at the ZK87+909 face, based on the layout of the advanced drilling at the left tunnel exit of the first half of the Qinlan tunnel, the tunnel construction conditions, and the site conditions.

[0055] Step A5: The surrounding rock is moderately weathered limestone, with a thick to very thick layered structure. The rock is relatively hard and intact, with some localized dissolution fissures. The surrounding rock grade is Class III. During this geological advance drilling, the working face of the left tunnel exit of the first half of the Qinlan tunnel was at mileage ZK87+909. The lithology revealed at the working face was mainly filled karst caves, filled with clay and a small amount of gravel. The karst caves were continuously distributed, and occasional seepage from bedrock fissures was observed in dripping form.

[0056] Step A6, Karst Treatment Plan: Due to the small horizontal clearance between the right tunnel and the left tunnel, blasting and excavation of the left tunnel would affect the right tunnel and could potentially cause further deformation. Therefore, it was decided on-site that construction of the karst treatment area in the right tunnel would only proceed after the left tunnel's invert arch reaches this position and closes into a ring.

[0057] (1) After the karst is exposed, the ZK87+909 section is backfilled with cavitary material. The cavitary material should fill the entire working face to exert counter-pressure on the section.

[0058] (2) I22b type I-beams were used to construct the guide wall inside the tunnel. Three I22b type I-beams were erected in parallel and welded into a whole. Φ108 steel pipes were fixed at the arch frame as guide steel pipes. Geotextile was used to seal both sides of the guide steel pipes, and C25 concrete was sprayed. The thickness of the sprayed concrete was 70cm and the width was 50cm. After the strength of the sprayed concrete reached the design value, the construction of the middle pipe shed inside the tunnel began. Φ89 perforated steel pipes were used for the middle pipe shed. Drilling should be carried out as far as possible towards the tunnel face. The root pipe method was used to send the pipe during the drilling process. Grouting was carried out after the pipe was sent. After the pipe shed was constructed, the root pipe method was used to drill exploratory holes in the karst area above the arch crown and arch waist to find out the location of the cavity. A pumping pipe was welded at the head of the Ø108 steel pipe. 7 meters of C30 fine stone concrete was backfilled into the cavity to make the 7-meter area above the arch crown densely filled.

[0059] (3) The double-sided wall pilot tunnel method is used to excavate the working face. Priority is given to excavating the karst side. After advancing 5 meters, the probe hole is continued to be made on the other side to find out the location of the cavity and backfill with fine stone concrete.

[0060] In this embodiment, a precise detection and scale-coordinated construction method for karst defects in tunnels is introduced. This method ensures accurate karst defect detection, safe and efficient tunnel construction, timely early warning of surrounding rock structures, and reasonable and economical project investment. It successfully solves the problems of inaccurate detection of geological conditions ahead of the tunnel face, untimely early warning of surrounding rock structures, and lack of targeted construction plans in complex karst tunnels, thereby accelerating the project progress and reducing project investment.

[0061] Example 3: This application is applied to Tunnel No. 3 in Jiazhuan Town, part of the Tian'e to Beihai Highway (Tian'e via Fengshan to Bama section). Tunnel No. 3 in Jiazhuan Town is located in Fengshan County, Hechi City, Guangxi Zhuang Autonomous Region. The tunnel entrance is situated in a low mountain, hilly, and ravine area, making transportation relatively inconvenient, with only a construction access road connecting it to the outside world. The tunnel is 1696m long. The surrounding rock of the designed entrance section is moderately weathered, fractured limestone with well-developed solution fissures.

[0062] On August 23, 2021, when the right-line tunnel face of the No. 3 tunnel entrance in Jiazhuan Town reached K83+385, a hall-like karst cave was exposed in front of the tunnel face. The cave's dimensions were approximately 22m long, 55m wide, and 25m high. The cave extended from the left side to the left and traversed the entire tunnel face. The surrounding rock of the cave wall was relatively stable. The bottom of the cave was filled with a large amount of silt. There were multiple drainage holes at the top of the cave and a water-reducing hole on the right side of the cave. Water was dripping out of the cave.

[0063] On September 10, 2021, when the left tunnel face reached ZK83+374, a corridor-like karst cave was exposed in front of the tunnel face. The cave was about 20m long, 84m wide, and 9-60m high. The cave was oblique to the tunnel at about 45° and connected to the right tunnel cave. The surrounding rock of the cave wall was relatively stable, and the bottom of the cave was filled with a large amount of silt.

[0064] The detection and treatment of large karst caves here incorporates a construction method that combines precise detection and dimensional coordination of karst defects in tunnels. The detection of karst defects follows the same procedures as described above, and the treatment methods are as follows:

[0065] (1) First, remove the loose debris and silt layer from the bottom of the cave and remove the dangerous rocks; then, conduct a cavity and bearing layer detection on the bottom of the cave and investigate the direction of water flow and the drainage cave in the cave.

[0066] (2) The water system of the left and right karst caves is connected by a 2m diameter corrugated steel pipe with a longitudinal slope of 1%. The inside of the pipe must be rust-proofed and the outside of the pipe is wrapped with 2m thick C15 concrete.

[0067] (3) The lining structure type of the left line ZK83+365.5~ZK83+396.5 section and the right line K83+373.5~K83+415.5 section adopts the S5-P type.

[0068] (4) C20 concrete arches with a thickness of not less than 3m are constructed on both sides of the tunnel lining in the karst section; the right arch of the right line lining adopts stepped formwork backfilling with a step size of 200*50cm.

[0069] In this embodiment, the stress analysis model of the scale coordination effect of the karst cave-tunnel combined structure is used to optimize the design and construction scheme of karst cave support and reinforcement and tunnel support and lining, so as to make the surrounding rock and support structure of the tunnel safe and stable. By analyzing the flow rate and drainage capacity requirements of karst conduit flow, the karst water passage in the tunnel is optimized, thereby accelerating the project progress and reducing the project investment.

[0070] In the several embodiments provided in this application, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between apparatuses or units may be electrical, mechanical, or other forms.

[0071] In addition, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit.

[0072] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

[0073] In conclusion, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. 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 precise detection and dimensional coordination of karst defects in tunnels, characterized in that, Includes the following steps: Step S1: Before the construction of the karst tunnel, a geological survey was conducted on the karst hydrodynamic conditions and karst evolution of the proposed tunnel mountain and the surrounding area using the semi-airborne transient electromagnetic exploration method and the depression analysis method. Step S2: During the construction of karst tunnels, a combination of the TSP method and the ground-penetrating radar method is used for forecasting, and the forecasting content of karst caves in the arch, surrounding karst caves and floor karst caves is added; Step S3: Before the karst cavity is exposed, local sealing, drilling for decompression, and treatment of karst drainage channels are carried out. Drainage consolidation and grouting reinforcement measures are also taken to seal and control the migration of karst cavity filling materials. Step S4: After the karst cavity is exposed, the karst cavity is accurately determined using tunnel three-dimensional spatial measurement technology, and a stress analysis model of the scale coordination effect of the karst cavity-tunnel combined structure is established. A support structure scheme is formulated for the size effect, and the karst cavity treatment method is improved for the scale coordination effect. Step S5: After the karst treatment of the tunnel, establish an automated monitoring and measurement system to track the stress and deformation of the surrounding rock and support structure in real time and issue safety warnings in real time. In step S4, during the three-dimensional spatial measurement, base points are established inside the cavity. Three-dimensional laser measurements are performed on the cavity and rock structure. An engineering surveying total station and GPS / RTK satellite positioning equipment are used to locate the overall cave coordinates and interface with the three-dimensional scanning data. The acquired cavity point cloud data undergoes noise removal, coordinate transformation, and stitching processing. A viewing video is then generated using SCENE. The noise removal employs a quantized noise compensation function, the formula of which is: In the formula, B is the quantization resolution. The peak value of the image signal. Sj represents the variance of the image signal sequence, and SJ represents the processed data. Based on the three-dimensional model of the karst cavity, a relationship diagram between karst geological defects and the tunnel is formed according to the three-dimensional intersection model, the continuous arch model, and the irregular hole model. The stress concentration around the karst cavity and the surrounding rock of the tunnel is analyzed, and the prediction of easily collapsed areas is given. Taking the stress concentration phenomenon as the main object, the size effect and scale coordination effect of karst tunnel are studied. The changes of surrounding rock pressure and bearing capacity of various support structures with size effect and scale coordination effect are analyzed. Support structure schemes are formulated for size effect, and karst cavity treatment methods are improved for scale coordination effect.

2. The method for precise detection and dimensional coordination of tunnel karst defects according to claim 1, characterized in that: During semi-airborne transient electromagnetic exploration, a grounded source is used to emit a primary pulse electromagnetic field into the ground. During the interval between the primary pulse electromagnetic fields, the secondary induced eddy current field in the underground medium is observed by a coil carried by an unmanned aerial vehicle, and the resistivity of the medium is calculated.

3. The method for precise detection and dimensional coordination of tunnel karst defects according to claim 1, characterized in that: The depression analysis method collects data on surface catchment area and groundwater movement characteristics, and draws a three-dimensional visualized hydrogeological map of the tunnel site area. The hydrogeological map includes water body distribution and elevation, watershed distribution related to karst groundwater in the tunnel area, and the distribution of dissolution cover layer and dissolution funnel above the tunnel. The preferential flow theory of porous media predicts the formation and distribution of soil cavities. The depression analysis method adopts the theory of flow deviation between fractured media and karst media, which states that large fractures have strong water storage capacity and small fractures have weak water storage capacity, and predicts the movement law of karst water and the degree of dissolution in different areas.

4. The method for precise detection and dimensional coordination of tunnel karst defects according to claim 1, characterized in that: The TSP method is used for long-distance reporting from 100m to 300m. When anomalies are predicted by the TSP, the ground-penetrating radar method is used to obtain more detailed information on karst defects. Both the TSP method and the ground-penetrating radar method are used to predict karst caves in the arch, surrounding caves and bottom slab. When drilling is used for prediction, drilling is carried out in front of the working face, the arch and the surrounding rock. The advance prediction distance is 40m. The prediction range of the surrounding rock and the arch is twice the diameter of the cave or more.

5. The method for precise detection and dimensional coordination of tunnel karst defects according to claim 1, characterized in that: In step S3, the risk of water and mud inrush during tunnel excavation is predicted, and prevention and control measures are formulated. These measures include drainage and pressure reduction, as well as reinforcement of unstable karst cave filling materials.

6. The method for precise detection and dimensional coordination of tunnel karst defects according to claim 5, characterized in that: During water diversion and drainage pressure reduction, the water diversion tunnel is used to divert and drain karst water that crosses the tunnel. The water diversion tunnel starts from inside the tunnel and connects to the karst pipe that crosses the tunnel, and continues until it reaches the sinkhole. The construction of the water diversion tunnel adopts the full-section excavation construction method, and the sections with developed fissures are treated with anchor bolt shotcrete support measures.

7. The method for precise detection and dimensional coordination of karst defects in tunnels according to claim 1, characterized in that: The automated monitoring and measurement system includes a data acquisition unit, an analysis unit, an early warning unit, and terminal equipment. The data acquisition unit collects stress data YL around karst defects, deformation data XB of the support structure, and displacement data WY of unfavorable structural surfaces, and sends the collected data to the analysis unit. The analysis unit receives the stress data YL, deformation data XB, and displacement data WY, performs correlation processing, and generates a judgment value P. The correlation processing formula for the judgment value P is as follows: In the formula, k1 and k2 are weights, and 0≤k1≤1, 0≤k2≤1, k1+k2=1. The analysis unit sends the judgment value P to the early warning unit. The early warning unit receives the judgment value P and compares it with the threshold Y. When the judgment value P is greater than or equal to the threshold Y, the alarm unit sends an alarm to the terminal device, indicating a dangerous state. When the judgment value P is less than the threshold Y, the alarm unit is in standby mode.

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