Karst tunnel hole crossing CT detection system

Abstract

The utility model provides a kind of karst tunnel hole crossing CT detection system, belong to tunnel construction technical field, including the emission hole being arranged in the middle part of face and the receiving hole of edge, the emission hole is equipped with seismic wave transmitting unit, the receiving hole is equipped with seismic wave receiving unit. With the omnidirectional, high-resolution detection of the rock mass directly in front of the tunnel, the detection blind area of the core rock mass of the face and the area near the contour line of the tunnel in the traditional method is eliminated, the prediction accuracy of unfavorable geological bodies such as karst caves, corrosion fissures and water-rich zones is improved, the risks of water inrush, mud inrush and collapse can be more accurately warned, the safety and efficiency of tunnel construction are improved, and the effect of reducing the delay of construction period and the increase of cost caused by geological uncertainty is achieved.

Description

Technical Field

[0001] This utility model relates to the field of tunnel construction technology, specifically to a cross-hole CT detection system for karst tunnels. Background Technology

[0002] Cross-bore CT, short for cross-bore seismic tomography, refers to the technique of working between two or more pre-drilled boreholes. Cross-bore means working between two or more pre-drilled boreholes. CT borrows the concept from medical computed tomography (CT), where X-rays penetrate the human body from different angles and a computer reconstructs images of the internal structure. Here, seismic waves are used instead of X-rays, and the soil and rock mass is used instead of the human body, ultimately reconstructing two-dimensional or three-dimensional "slice" images of the geological structure between the boreholes.

[0003] Karst areas have extremely complex geological conditions, filled with unfavorable geological formations such as caves, dissolution fissures, water-rich zones, and faults, posing a huge threat to tunnel construction safety (such as water inrush, mudslides, and collapses). Cross-hole CT detection can predict various adverse geological conditions ahead in advance, greatly improving the safety and efficiency of tunnel construction.

[0004] Currently, cross-hole CT detection in tunnel construction typically involves drilling two or more boreholes on either side of, above, or in areas requiring focused detection along the tunnel's design axis. Seismic wave signals are emitted from one borehole and received in another. However, this lateral detection method may have blind spots or insufficient resolution in detecting the core rock mass directly in front of the tunnel face, as well as the area between the tunnel outline and the borehole. Furthermore, it lacks accurate advance prediction for the rock mass about to be excavated, resulting in relatively low detection accuracy. Utility Model Content

[0005] The purpose of this invention is to provide a cross-hole CT detection system for karst tunnels, in order to solve the problem in the existing technology where two or more boreholes are drilled on both sides, above, or in areas requiring key detection of the tunnel design axis. Seismic wave signals are emitted in one borehole and received in another. This lateral detection method may have blind spots or insufficient resolution in the detection of the core rock mass at the tunnel face directly in front of the tunnel and the area between the tunnel outline and the borehole. For the rock mass about to be excavated, there is a lack of accurate advance prediction, resulting in relatively low detection accuracy.

[0006] To achieve the above objectives, the technical solution adopted by this utility model is as follows: A cross-hole CT detection system for karst tunnels includes a transmitting hole located in the middle of the tunnel face and several receiving holes located at the edges. The transmitting hole is equipped with a seismic wave transmitting unit, and the receiving holes are equipped with a seismic wave receiving unit.

[0007] According to the above technical solution, by setting the seismic wave transmitting unit in the middle of the tunnel face and the receiving unit in multiple receiving holes at the edge of the tunnel face, a seismic wave propagation path is formed from the center to the periphery. The transmitting holes extend directly into the unexcavated rock mass, and their rays directly penetrate the traditional blind zone, effectively reducing the detection blind zone, improving the detection capability and imaging resolution of adverse geological bodies, and providing more accurate advanced geological prediction for tunnel construction. At the same time, the transmitting holes and receiving holes are constructed on the tunnel face, making construction convenient and quick.

[0008] Furthermore, along the tunnel axis, each of the receiving holes is radiating outwards.

[0009] According to the above technical solution, the receiving holes are arranged in a divergent pattern along the tunnel axis, so that the ray paths of seismic waves from the central emission point to each edge receiving point form a ray network with large intersection angles and spatial three-dimensional coverage. Compared with the traditional parallel hole ray paths, this arrangement optimizes the mathematical inversion conditions of tomographic imaging, and can more accurately distinguish and locate the spatial position and morphology of adverse geological bodies such as karst caves and fissures in the rock mass in front of the tunnel face, thereby improving the resolution and reliability of imaging.

[0010] Furthermore, the tunnel is a stepped excavation tunnel, and the starting ends of both the transmitting hole and the receiving hole are located on the upper step cross-section.

[0011] According to the above technical solution, the tunnel is excavated in a stepped manner, and the starting ends of both the transmitting and receiving holes are set on the upper step cross-section. This facilitates the operation of construction personnel and the installation of equipment, while ensuring that the detection covers the upper step area and avoiding detection omissions caused by the step excavation sequence, thereby improving the applicability and practicality of the detection system.

[0012] Furthermore, along the tunnel axis, the launching hole extends obliquely downwards, and the end point of the launching hole is located below the preset excavation path of the tunnel.

[0013] According to the above technical solution, the launching hole extends downward at an angle, and the end point is located below the preset excavation path of the tunnel. This can effectively detect the rock mass condition below the tunnel floor, which helps to discover karst caves, water-rich zones or weak layers below in advance, prevent accidents such as water inrush and collapse during construction, and enhance the early warning capability for geological risks at the bottom of the tunnel.

[0014] Furthermore, the angle between the transmitting hole and the tunnel axis is 10°-30°, and the angle between the receiving hole and the tunnel axis is 10°-30°.

[0015] According to the above technical solution, by controlling the angle between the transmitting hole and the receiving hole and the tunnel axis within the range of 10°-30°, the incident and receiving angles of seismic waves are optimized, ensuring that the beam effectively covers the key areas in front of and around the tunnel.

[0016] Furthermore, the emission hole is provided with several seismic wave emission nodes at equal intervals along the axial direction.

[0017] According to the above technical solution, multiple seismic wave transmission nodes are set at equal intervals along the axial direction in the emission hole, realizing multi-point and multi-angle seismic wave transmission, increasing the density and diversity of data acquisition, which helps to improve the accuracy of tomographic imaging, reconstruct the geological structure through more signal paths, reduce imaging errors, and enhance the ability to identify small adverse geological bodies.

[0018] Furthermore, a seismic wave receiving node is provided along the axial direction of each seismic wave transmitting node within the receiving hole.

[0019] The above technical solution ensures the synchronization and correspondence between the transmitted and received signals, reduces data loss and interference, improves the integrity of signal reception and processing efficiency, thereby enhancing the accuracy and reliability of imaging.

[0020] Furthermore, the seismic wave transmitting unit includes a transmitting rod that can move within the transmitting hole, and at least one transmitting probe is fixedly mounted on the transmitting rod.

[0021] According to the above technical solution, the seismic wave transmitting unit adopts a movable transmitting rod and a fixed transmitting probe design, which allows for flexible adjustment of the transmitting position to adapt to different detection needs, improves the flexibility of detection, and facilitates targeted detection in complex karst environments.

[0022] Furthermore, the seismic wave receiving unit includes a receiving rod, which is fixed inside the receiving hole. A series probe is fixedly mounted on the receiving rod. The series probe includes several receiving probes arranged at equal intervals along the axial direction of the receiving rod and wires that connect each receiving probe in sequence. Each receiving probe corresponds to a seismic wave receiving node.

[0023] Based on the above technical solution, synchronous, multi-channel data acquisition is achieved, simplifying the installation and operation process, ensuring accurate location of receiving nodes, improving data acquisition speed and consistency, thereby optimizing imaging processing efficiency and image quality.

[0024] Furthermore, both the launching hole and the receiving hole are filled with well fluid.

[0025] According to the above technical solution, by filling the borehole with well fluid, the acoustic coupling efficiency is improved, which directly brings three major advantages: stronger signal, lower noise, and more stable data. Ultimately, this will translate into higher resolution, more accurate interpretation, and more reliable prediction of cross-hole CT detection images.

[0026] The beneficial effects of this utility model are: 1. This application, by setting up a transmitting hole in the middle of the tunnel face and multiple receiving holes at the edges, changes the traditional lateral detection method, achieving all-round, high-resolution detection of the rock mass directly in front of the tunnel. This arrangement effectively eliminates the detection blind spots in the core rock mass of the tunnel face and the area near the tunnel outline in traditional methods, improving the prediction accuracy of adverse geological bodies such as karst caves, dissolution fissures, and water-rich zones. Therefore, it can more accurately predict risks such as water inrush, mudslides, and collapses, improving the safety and efficiency of tunnel construction, while reducing delays and cost increases caused by geological uncertainties.

[0027] 2. This application uses downward-facing emission holes and side-forward-facing receiving holes to create a three-dimensional cone-shaped coverage area from below the tunnel floor to outside the tunnel outline. In particular, the downward-sloping emission holes allow the rays to directly penetrate the traditional core blind zone, achieving full-section detection without blind spots.

[0028] 3. The starting ends of the transmitting hole and receiving hole in this application are both drilled on the tunnel face, which facilitates the drilling operation and also facilitates the installation of the transmitting rod and receiving rod. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the longitudinal section of a tunnel in a karst tunnel cross-hole CT detection system according to the present invention; Figure 2 This is a schematic diagram of the cross-section of a tunnel in a karst tunnel cross-hole CT detection system according to the present invention. Figure 3 This is a schematic diagram of the receiving unit in the receiving hole of a karst tunnel cross-hole CT detection system according to the present invention.

[0030] Among them, there are receiving hole 1, transmitting hole 2, tunnel 3, seismic wave receiving node 4, upper bench section 5, seismic wave transmitting node 6, well fluid 7, receiving probe 8, wire 9, receiving rod 10, and sealing structure 11. Detailed Implementation

[0031] The embodiments of this utility model will be described below with reference to the accompanying drawings and preferred embodiments. Those skilled in the art can easily understand other advantages and effects of this utility model from the content disclosed in this specification. This utility model can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this utility model. It should be understood that the preferred embodiments are only for illustrating this utility model and not for limiting the scope of protection of this utility model.

[0032] It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show the components related to the present invention and are not drawn according to the number, shape and size of the components in actual implementation. In actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0033] This embodiment proposes a cross-hole CT detection system for karst tunnels, such as... Figures 1 to 3 As shown, the tunnel includes a transmitting hole 2 located in the middle of the tunnel face and several receiving holes 1 at the edge. The transmitting hole 2 contains a seismic wave transmitting unit, and the receiving hole 1 contains a seismic wave receiving unit. In this embodiment, the transmitting hole 2 and the receiving hole 1 are formed at the tunnel face of tunnel 3, which is convenient for construction. The transmitting hole 2 is located in the middle of the tunnel face of tunnel 3, and the receiving hole 1 is located at the edge of the tunnel face of tunnel 3. The seismic waves emitted from the transmitting hole 2 have a short path and low signal attenuation when they are transmitted to the receiving hole 1. At the same time, the transmitting hole 2 extends directly into the unexcavated rock mass, and its rays directly penetrate the traditional blind zone, effectively reducing the detection blind zone and improving the detection capability and imaging resolution of adverse geological bodies.

[0034] Along the axis of tunnel 3, each receiving hole 1 is radiating outwards.

[0035] Tunnel 3 is a stepped excavation tunnel 3, and the starting ends of both the launching hole 2 and the receiving hole 1 are located on the upper step section 5.

[0036] In the above embodiment, the tunnel face 3 is horseshoe-shaped. The stepped excavation of tunnel 3 includes an upper step and a lower step, usually divided at the 1 / 2 position of the tunnel height. During excavation, the upper step is excavated first, followed by the lower step. In this embodiment, the work is carried out after the upper step is excavated and before the lower step is excavated, which increases the working face, reduces interference between the front and rear, and is conducive to mechanized operation. At this time, the cross-section 5 of the upper step is approximately semi-circular. The starting end of the launching hole 2 is located at the center of the cross-section 5 of the upper step, which is also the center of the tunnel face 3. There are several receiving holes 1 evenly distributed on the edge of the cross-section 5 of the upper step. The number of receiving holes 1 can be adjusted according to the actual construction situation on site. For example, there are three receiving holes 1, one of which is located directly above the launching hole 2, and the other two are located on the left and right sides of the launching hole 2.

[0037] Along the axis of tunnel 3, the launching hole 2 extends downward at an angle, and the end point of the launching hole 2 is located below the preset excavation path of tunnel 3.

[0038] The angle between the launching hole 2 and the axis of tunnel 3 is 10°-30°, and the angle between the receiving hole 1 and the axis of tunnel 3 is 10°-30°.

[0039] In the above embodiment, the receiving holes 1 located on both sides of the emitter hole 2 seat can be horizontally tilted to the left / right, or they can be horizontally tilted while simultaneously tilting downwards. Normally, the preferred angle for the emitter hole 2 and the receiving hole 1 is rotated by 15°, which is a very balanced and universally applicable angle, significantly superior to traditional parallel hole layouts in most cases. Depending on the on-site construction conditions, different angle adjustments can be made, specifically: The geological conditions are relatively simple, and the main focus is on probing directly in front: a 10°-15° angle can be used.

[0040] Due to the complex geological conditions, special attention needs to be paid to the front and side: a 20°-25° angle can be used.

[0041] Extreme cases (such as when it is necessary to detect large structures on the three sides of the tunnel): 25°-30° can be considered, but its cost and construction feasibility need to be evaluated.

[0042] In summary, the downward-sloping emission port 2 and the outward-radiating receiving port 1 together form a three-dimensional detection network extending from below the bottom plate of tunnel 3 to the front and then to the side front. This network is highly compatible with the actual spatial range that tunnel 3 needs to control (the area in front of the tunnel face and the surrounding area of ​​tunnel 3), making it more targeted.

[0043] Several seismic wave emission nodes 6 are provided at equal intervals along the axial direction inside the emission hole 2.

[0044] Seismic wave receiving nodes 4 are provided along the axial direction of each seismic wave transmitting node 6 inside receiving hole 1.

[0045] In the above embodiments, seismic wave transmitting nodes 6 and seismic wave receiving nodes 4 are set at intervals of 0.5m, 1m, 1.5m, or other intervals according to the site conditions. This pre-planned and preset method simplifies the operation process and increases the density and diversity of data acquisition, which helps to improve the accuracy of tomographic imaging. It also allows for the reconstruction of geological structures through more signal paths, reduces imaging errors, and enhances the ability to identify small, aberrant geological bodies.

[0046] The seismic wave transmitting unit includes a transmitting rod that can move within the transmitting hole 2. The outer diameter of the transmitting rod is smaller than the inner diameter of the transmitting hole 2. At least one transmitting probe is fixedly mounted on the transmitting rod. In this embodiment, the transmitting probe can excite seismic waves. The transmitting probe can be a spark source, a hammer source, or similar device. The seismic wave receiving unit includes a receiving rod 10, which is fixed inside a receiving hole 1. A series of probes are fixedly mounted on the receiving rod 10. The series of probes includes several receiving probes 8 arranged at equal intervals along the axial direction of the receiving rod 10, and wires 9 connecting each receiving probe 8 sequentially. Each receiving probe 8 corresponds one-to-one with a seismic wave receiving node 4. In this embodiment, the outer diameter of the receiving rod 10 is also smaller than the inner diameter of the receiving hole 1. The receiving rod 10 can be fixed inside the receiving hole 1 by means of clamps, bolts, etc. The receiving probes 8 are seismic detectors. Multiple seismic detectors are strung together and fixed on the receiving rod 10, allowing for synchronous reception of seismic wave signals from the transmitting end.

[0047] In the above embodiments, the number of transmitting probes can vary as follows: During detection, a transmitting rod is placed into a transmitting hole 2, and seismic waves are generated at each seismic wave transmitting node 6. A receiving probe 8 in a receiving hole 1 synchronously receives the seismic wave signals from the transmitting end. By systematically moving the position of the transmitting point, travel time data for hundreds to thousands of different ray paths traversing the target area can be obtained. The travel time of the seismic wave along each ray path is measured. Seismic waves propagate quickly in intact, hard rock masses, but slowly in fractured, weak, or mud-filled karst caves. The computer discretizes the area between boreholes into thousands of small grid cells and uses an inversion algorithm similar to medical CT to calculate the wave velocity value of each grid cell based on massive amounts of ray travel time data. Finally, a color or grayscale image is generated, clearly and intuitively displaying the wave velocity distribution of the rock mass between boreholes using different colors, thus revealing its internal structure. Multiple (e.g., 2 or 3) but less than the total number of seismic wave transmitting nodes 6 are considered as a transmitting group and moved in the same way within the transmitting hole 2. Each movement distance can be multiple seismic wave transmitting nodes 6, and each movement distance can be longer. Multiple probes are deployed, each corresponding to a seismic wave transmitting node 6, allowing for a single-step detection without the need for frequent movement of the transmitting rod.

[0048] In the above embodiments, since both the transmitting hole 2 and the receiving hole 1 are inclined, in order to facilitate the insertion of the transmitting rod and the receiving rod 10 into the corresponding holes, the transmitting rod and the receiving rod 10 can adopt a segmented structure, and the adjacent two segments can be relatively fixed.

[0049] In the above embodiments, the depth of the transmitting hole 2 and the depth of the receiving hole 1 can be adjusted according to the actual construction situation. However, it is preferred that the depths of the transmitting hole 2 and the receiving hole 1 are the same, and preferably 20-40m.

[0050] In the above embodiments, when a detection is completed and excavation is successful, during the second CT detection, the upper step section 5 can fall into the area at the end of the previous detection borehole, so that there is a certain overlap between the two adjacent detections, further reducing the detection blind zone.

[0051] Both the launching hole 2 and the receiving hole 1 are filled with well fluid 7. In this embodiment, the well fluid 7 can be water, which is pumped by a pumping device. The pumping system is existing technology and will not be described in detail here. It should be noted that the receiving hole 1, located above the launching hole 2, is inclined and the orifice is located at the lower end. Therefore, it is necessary to take sealing measures at the orifice to prevent the well fluid 7 from flowing out. There are many sealing methods, such as expansion airbags, grouting sealing, or the use of fast sealing materials (such as polymer sealant). After the receiving rod 10 is fixed in the hole, the outer end of the receiving rod 10 needs to extend out of the hole. The sealing structure 11 covers the surface of the receiving rod 10 and seals the gap between the receiving rod 10 and the receiving hole 1. A water conveying channel is opened in the middle of the receiving rod 10 so that the pumping system can pump the well fluid 7 into the hole. Without well fluid 7, an air gap exists between the transmitting / receiving probe 8 and the borehole wall. Due to the significant difference between the acoustic impedance of air (the product of density and wave velocity) and that of rock, seismic wave energy undergoes strong reflection when passing through this interface, resulting in the energy being unable to effectively enter the rock mass (for the transmitting end) or be effectively received by the probe (for the receiving end). After filling with well fluid 7 (water), the acoustic impedance of water falls between that of air and rock, acting as an "impedance matching" medium. As a highly efficient conductive medium, it allows seismic wave energy to be efficiently transmitted from the transmitting probe to the surrounding rock mass through well fluid 7. Similarly, signals within the rock mass can also be efficiently transmitted to the receiving probe 8 through well fluid 7, greatly reducing energy loss at the contact surface.

[0052] In summary, the cross-hole CT detection system for karst tunnel 3 in this embodiment can accurately delineate the location, shape, size, and spatial distribution of karst caves between boreholes, distinguishing between cavitary caves (high-velocity or low-velocity anomalies, depending on the difference between the filling material and the surrounding rock) and filled caves (usually significant low-velocity anomalies). It can clearly identify fault fracture zones, karst fissure development zones, and weak interlayers, which typically exhibit obvious low-velocity anomaly zones. Water-filled fissures or caves cause a significant reduction in seismic wave velocity; therefore, low-velocity anomaly zones often indicate that the area may be rich in groundwater, providing crucial evidence for assessing the risk of water inrush in tunnel 3. Cross-hole CT detection ahead of the tunnel face of tunnel 3 allows for early prediction of adverse geological conditions. Based on the CT results, it is possible to determine whether grouting reinforcement, adjustments to excavation methods, and strengthened support measures are needed, as well as the specific scope and parameters of these measures. This improves the safety and efficiency of tunnel 3 construction, avoiding catastrophic accidents and economic losses that may result from blind construction. Compared to ground-based geophysical methods, it avoids the influence of low-velocity layers and interference on the surface, has higher resolution, more accurate results, and displays geological anomalies in image form, making it easy for non-professionals to understand.

[0053] The above embodiments are merely preferred embodiments provided to fully illustrate the present utility model, and the protection scope of the present utility model is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present utility model are all within the protection scope of the present utility model.

Claims

1. A cross-hole CT detection system for karst tunnels, characterized in that: It includes a transmitting hole located in the middle of the working face and several receiving holes at the edges. The transmitting hole is equipped with a seismic wave transmitting unit, and the receiving hole is equipped with a seismic wave receiving unit.

2. The karst tunnel cross-hole CT detection system according to claim 1, characterized in that: Along the tunnel axis, each of the receiving holes is radiating outwards.

3. The karst tunnel cross-hole CT detection system according to claim 1 or 2, characterized in that: The tunnel is a stepped excavation tunnel, and the starting ends of both the transmitting hole and the receiving hole are located on the upper step cross-section.

4. The karst tunnel cross-hole CT detection system according to claim 3, characterized in that: Along the tunnel axis, the launching hole extends downward at an angle, and the end point of the launching hole is located below the preset excavation path of the tunnel.

5. The karst tunnel cross-hole CT detection system according to claim 4, characterized in that: The angle between the transmitting hole and the tunnel axis is 10°-30°, and the angle between the receiving hole and the tunnel axis is 10°-30°.

6. The karst tunnel cross-hole CT detection system according to claim 1, characterized in that: The emission hole is provided with several seismic wave emission nodes at equal intervals along the axial direction.

7. The karst tunnel cross-hole CT detection system according to claim 6, characterized in that: Each seismic wave receiving node is provided along the axial direction within the receiving aperture, corresponding to each seismic wave transmitting node.

8. The karst tunnel cross-hole CT detection system according to claim 6, characterized in that: The seismic wave transmitting unit includes a transmitting rod that can move within a transmitting hole, and at least one transmitting probe is fixedly mounted on the transmitting rod.

9. The karst tunnel cross-hole CT detection system according to claim 7, characterized in that: The seismic wave receiving unit includes a receiving rod, which is fixed inside the receiving hole. A series probe is fixed on the receiving rod. The series probe includes several receiving probes arranged at equal intervals along the axial direction of the receiving rod and wires that connect the receiving probes in sequence. Each receiving probe corresponds to a seismic wave receiving node.

10. The karst tunnel cross-hole CT detection system according to claim 1, characterized in that: Both the launching hole and the receiving hole are filled with well fluid.

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