Microseismic source location method considering free space diffraction for tunnel excavation process

Abstract

The application provides a microseismic source positioning method considering cavity diffraction for a tunnel excavation process, relates to a tunnel microseismic monitoring technology, and comprises the following steps: S1, a digital model of a tunnel excavated section in a monitoring area is established; S2, a spatial distance matrix of a sub-node after the tunnel wall of the tunnel excavated section is discretized is obtained according to the digital model; S3, whether a straight line section passes through a cavity of the tunnel excavated section is judged; S4, the shortest distance between a potential microseismic source and a microseismic sensor without passing through the cavity of the tunnel is calculated according to the judgment result of S3; and S5, S2-S4 are repeated until the shortest distance between the potential microseismic source and the microseismic sensor without passing through the cavity of the tunnel satisfies an adaptability function, so that the microseismic source positioning is realized. The application can quickly and accurately obtain the microseismic source in a rock mass in real time, has high practicability and accuracy, improves the monitoring effect of microseismic, and lays a foundation for realizing an intelligent early warning system.

Description

Technical Field

[0001] This invention relates to tunnel microseismic monitoring technology, and more particularly to a microseismic source location method that takes into account diffraction in the void zone, applicable to the tunnel excavation process. Background Technology

[0002] Microseismic source location is crucial for the interpretation of microseismic information. Key microseismic parameters related to microseismic source location include: the spatial coordinates of the microseismic event, the time of origin, the rupture mechanism, the spatiotemporal gradient of the microseismic parameters, and other microseismic parameters that need to be corrected based on the spatiotemporal state of the source. Furthermore, the location of microseismic events significantly impacts the prediction of the spatial location, risk level, and probability of occurrence of potential instability zones based on microseismic information. Therefore, it is necessary to improve the accuracy of microseismic source location. Among the many factors affecting the accuracy of microseismic source location, the microseismic source location algorithm has a profound impact.

[0003] Most microseismic source localization algorithms are based on the assumption that microseismic waves propagate in a straight line within the rock mass, neglecting the influence of voids on the propagation path. However, in underground rock engineering, voids gradually form within the rock mass as excavation or mining progresses, and microseismic sensors are often deployed within the surrounding rock of these voids. Therefore, some microseismic events inevitably occur, and the straight-line path from their spatial location to the sensor will traverse these voids. In this case, the actual path of the microseismic wave propagating from the source to the sensor will no longer be a straight line. Clearly, if a localization algorithm based on a straight-line propagation path is still used for microseismic source localization, significant errors will occur. During tunnel excavation, limitations such as personnel safety, installation space, and economic investment restrict the number of sensors that can be deployed. Using only sensors on the same side of the tunnel for microseismic source localization is insufficient. Furthermore, microseismic events generated during tunnel excavation are often distributed near the tunnel face, and the straight-line paths between these events and sensors located behind the tunnel face inevitably traverse tunnel voids. Therefore, for tunnel microseismic monitoring, there is an urgent need to explore a microseismic source location method that takes into account diffraction in the void. Summary of the Invention

[0004] In view of this, the purpose of this invention is to propose a microseismic source location method that considers diffraction in the tunnel excavation process, in order to solve the problem that the location algorithm based on the assumption of linear propagation of microseismic waves causes large errors in the location of microseismic sources when microseismic waves pass through the tunnel void, thereby improving the microseismic source location accuracy and thus improving the microseismic monitoring effect.

[0005] The technical means employed in this invention are as follows:

[0006] A microseismic source localization method considering diffraction in void areas, applicable to tunnel excavation processes, includes the following steps:

[0007] S1. Establish a digital model of the excavated section of the tunnel in the monitoring area;

[0008] S2. Based on the digital model, obtain the spatial distance matrix of the sub-nodes after discretization of the tunnel wall of the excavated section in the monitoring area;

[0009] S3. Determine whether the straight section crosses the empty area of ​​the already excavated section of the tunnel;

[0010] S4. Based on the judgment results of S3, calculate the shortest distance between the potential microseismic source and the microseismic sensor that does not cross the tunnel void.

[0011] S5. Repeat S2 to S4 until the shortest distance between the potential microseismic source and the microseismic sensor that does not cross the tunnel void satisfies the fitness function, thus achieving microseismic source localization.

[0012] Furthermore, S1 includes the following steps:

[0013] S11. Select the centroid of the cross section at point 5 of the tunnel face as the origin of the coordinate system, take the forward direction of point 5 as the positive x-axis, the vertical upward direction as the positive z-axis, and determine the positive y-axis according to the right-hand screw principle.

[0014] S12. Divide the tunnel cross-section profile into equal parts and obtain the y and z coordinates of the sub-nodes on the tunnel cross-section profile.

[0015] S13. Divide the excavated section of the tunnel in the monitoring area into h equal segments, so that the length of the tunnel segment after equal division is equal to the length of the straight or curved segment after equal division of the tunnel cross-section outline, to obtain h+1 cross-sections, and calculate the x coordinates of the sub-nodes on each cross-section.

[0016] S14. Obtain a digital model of the excavated section of the tunnel in the monitoring area based on the x, y, and z coordinates of each sub-node.

[0017] Furthermore, S12 includes the following steps:

[0018] When the tunnel cross-section profile is circular, the circular tunnel cross-section profile is divided into n equal parts to obtain n child nodes on the tunnel cross-section profile and their y and z coordinates.

[0019] When the tunnel cross-section is non-circular, the intersection of the arc segment and the straight segment on the cross-section profile of the non-circular tunnel is taken as the key node. The straight segment and the curved segment between each key node are divided equally so that the lengths of the divided straight segment and the curved segment are approximately equal, thus obtaining the secondary node. The child node on the cross-section profile of the non-circular tunnel is the key node. The y and z coordinates of the child node on the cross-section profile of the non-circular tunnel are calculated by adding the key node and the secondary node.

[0020] Furthermore, the spatial distance matrix mentioned in S2 is composed of the distance between any two nodes in the discretized child nodes of the cave wall, and the method for calculating the distance between any two nodes is as follows:

[0021] When two nodes are not adjacent, the distance between the two nodes is infinite.

[0022] When two nodes are adjacent, the distance between them is the Euclidean distance in three-dimensional space, as shown in the following formula:

[0023]

[0024] In the formula: D ij The distance between child nodes i and j; (x i y i , z i (x) represents the three-dimensional spatial coordinates of child node i, and (x) represents the coordinates of child node i. j y j , z j ) represents the three-dimensional spatial coordinates of child node j.

[0025] Furthermore, S3 includes:

[0026] Project the straight line segment between any two sub-nodes of the discretized tunnel wall and the tunnel outline onto a cross section perpendicular to the tunnel axis to obtain a closed curve and a straight line segment on the projection plane. Based on the projection results, determine whether the straight line segment between the two points crosses the tunnel void.

[0027] When the number of intersections between the projection of the straight line segment between two points and the projection of the tunnel outline is two, the straight line segment between the two points passes through the tunnel void.

[0028] When the number of intersection points between the projection of the straight line segment between two points and the projection of the tunnel outline is not two, the straight line segment between the two points does not cross the tunnel void.

[0029] Furthermore, the specific steps of S4 are as follows:

[0030] If the straight line between the potential microseismic source and the microseismic sensor does not cross the excavated void of the tunnel, then the shortest distance is the three-dimensional Euclidean distance.

[0031] If the straight line segment between the potential microseismic source and the microseismic sensor passes through the excavated void of the tunnel, then the shortest distance is the shortest distance from the potential microseismic source as the root node, through the discretized sub-nodes of the tunnel wall, to the microseismic sensor as the endpoint.

[0032] Furthermore, when the straight section between the potential microseismic source and the microseismic sensor crosses an excavated area of ​​the tunnel, the shortest distance is calculated using the spatial distance matrix via Dijkstra's algorithm.

[0033] Compared with the prior art, the present invention has the following advantages:

[0034] This invention uses the spatial distance matrix of sub-nodes after discretization of the tunnel wall of the excavated section in the monitoring area to determine whether a straight line segment crosses the empty area of ​​the excavated section of the tunnel. It also calculates the shortest straight line and diffraction distance between potential microseismic sources and microseismic sensors that do not cross the empty area of ​​the tunnel. Finally, it calculates the location of microseismic sources based on the time difference positioning principle. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 This is a basic flowchart of the present invention.

[0037] Figure 2 This is a schematic diagram of the spatial relationship between the TSP point seismic source and the microseismic sensor array of the present invention.

[0038] Figure 3 This is a schematic diagram of the digital model of the excavated section of the railway tunnel monitoring area according to the present invention.

[0039] Figure 4 This invention provides a three-dimensional image for determining whether a straight line segment between two points crosses a tunnel void using projection.

[0040] Figure 5 This invention provides a projection diagram for determining whether a straight line segment between two points crosses a tunnel void using projection.

[0041] Figure 6 is a schematic diagram of the positional relationship between two coplanar non-coincident line segments of the present invention, wherein (a) is a normal intersection, (b) is a first special intersection, (c) is a second special intersection, (d) is neither intersecting nor parallel, and (e) is parallel.

[0042] Figure 7 This is a three-dimensional display of the TSP point source location result obtained by the microseismic source location algorithm that considers void diffraction in this invention.

[0043] In the figure: 1. Microseismic sensor; 2. Excavation direction; 3. TSP point source; 4. Excavated void; 5. Working face; 6. Unexcavated tunnel section; 7. Projected plane; 8. Tunnel void; 9. Tunnel outline projection; 10. Separation status; 11. Tangency status; 12. Intersection status; 13. Positioning result. Detailed Implementation

[0044] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0045] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0046] Example

[0047] A microseismic source localization method considering diffraction in void areas, applicable to tunnel excavation, includes the following steps:

[0048] Step 1: When tunnel face 5 of a railway tunnel was excavated to chainage K196+204, a tunnel advance geological prediction (TSP) was conducted. Twenty-four point source excitation boreholes were arranged on the south sidewall of the section from chainage K196+147 to K196+182 behind tunnel face 5. The borehole spacing was approximately 1.5m, the borehole opening was approximately 1.0m above the tunnel floor, the borehole depth was approximately 1.5m, and the boreholes were inclined downwards at 10°–20°. Eight microseismic sensors were arranged in the section from chainage K196+021 to K196+059 behind tunnel face 5. The spatial relationship between the TSP point sources and the microseismic sensor array is shown in [the diagram]. Figure 2 Excavation proceeds from direction 2, and the unexcavated area is designated as unexcavated tunnel section 6. The tunnel walls of the monitored area from K196+054 to K196+254 are discretized into sub-nodes in three-dimensional space, and a digital model is established, such as... Figure 3 As shown.

[0049] Step 2: Obtain the spatial distance matrix of the child nodes after discretizing the tunnel wall of the excavated section in the monitoring area. The spatial distance matrix consists of the distance between any two points in the discretized child nodes of the tunnel wall, and its structure is shown in Table 1. Calculate the spatial distance matrix of the child nodes in the digital model obtained in Step 1. The method for calculating the distance between any two child nodes in the digital model is as follows:

[0050] (a) If two nodes are not adjacent, then their distance is infinite;

[0051] (b) If two nodes are adjacent, their distance is the Euclidean distance in three-dimensional space, calculated by the following formula:

[0052]

[0053] In the formula: D ij Let m be the distance between child nodes i and j; (x i y i , z i ) and (x j y j , z j ) are the three-dimensional spatial coordinates of child nodes i and j, respectively.

[0054] Table 1. Schematic diagram of the spatial distance matrix

[0055]

[0056]

[0057] Step 3: Determine whether the straight section crosses an empty area of ​​the already excavated section of the tunnel:

[0058] (a) Project the straight line segment between the two points and the tunnel outline 9 onto a cross-section perpendicular to the tunnel axis, i.e., projection plane 7. On this projection plane, a closed curve (the projection of the tunnel outline) and a straight line segment are obtained. Based on this projection result, determine whether the straight line segment between the two points crosses the tunnel void 8. There are three possible projection results: disjoint (case 10), tangent (case 11), and intersecting (case 12). That is, when the projection of the straight line segment between the two points intersects the projection of the tunnel outline at two points (case 12), the straight line segment crosses the tunnel void 8; otherwise, it does not. A schematic diagram illustrating how to determine whether the straight line segment between the two points crosses the tunnel void 8 using projection is shown below. Figure 4 and Figure 5 .

[0059] (b) Since the tunnel wall of the excavated section has been discretized into sub-nodes, the projection of the tunnel outline becomes a series of line segments connected end to end. Therefore, finding the number of intersections between the projection of the straight line segment between two points and the tunnel outline projection 9 is transformed into finding the total number of intersections between the projection of the straight line segment and the series of line segments that make up the tunnel outline projection 9.

[0060] Furthermore, calculating the total number of intersection points between the projection of the straight line segment and the series of line segments constituting the tunnel outline projection 9 is transformed into determining whether the projection of the straight line segment intersects with each line segment constituting the tunnel outline projection 9. The initial value of the total number of intersection points is set to 0. The series of line segments constituting the tunnel outline projection 9 is traversed. If the projection of the straight line segment intersects with a certain line segment, the total number of intersection points increases by 1. When there are 10 disjoint cases, the total number of intersection points remains unchanged. When the total number of intersection points equals 2, it indicates that the projection of the straight line segment intersects with the tunnel outline projection 9, meaning that the straight line segment between the two points crosses the tunnel void 8.

[0061] Furthermore, we can use vector-based cross products and dot products to determine whether two line segments intersect. For example... Figures 6a-6e As shown, when line segment MN does not coincide with line segment PQ and simultaneously satisfies formulas (2) and (3), then line segment MN intersects with line segment PQ.

[0062]

[0063] Step 4: Calculate the shortest distance between the potential microseismic source (any point in the monitoring area) and the 8 microseismic sensors 1 that does not cross the tunnel void 8:

[0064] (a) If the straight line between the potential microseismic source and the 8 microseismic sensors 1 does not cross the excavated void 4 of the tunnel, then the shortest distance is the three-dimensional Euclidean distance, calculated by equation (1).

[0065] (b) If the straight segment from the potential microseismic source to the eight microseismic sensors 1 crosses the excavated section 4 of the tunnel, then the shortest distance is the shortest distance from the potential microseismic source as the root node, through the discretized child nodes of the tunnel wall, to the microseismic sensor 1 as the endpoint. This shortest distance is calculated using the spatial distance matrix of the nodes after discretization of the tunnel wall of the excavated section of the monitoring area obtained in step 2, and using the Dijkstra algorithm.

[0066] Step 5: After implementing TSP, all 8 sensors clearly captured the seismic waves generated by the blast at the 24 point seismic sources. Microseismic data analysis yielded 192 arrival times for the 24 seismic waves at the 8 sensors. Based on these 192 arrival times, steps 2-4 were repeated. In the step-by-step localization algorithm based on the time difference positioning principle, the length of the non-tunnel gap 8 between the potential microseismic source and each sensor was used to replace the straight-line length between any point and each sensor. The fitness function was solved using the particle swarm optimization algorithm, and the microseismic wave velocity, microseismic source coordinates, and seismic origin time were solved step-by-step to achieve microseismic source localization calculation considering gap diffraction. The basic calculation process is as follows: Figure 1 As shown.

[0067] The microsource localization algorithm considering void diffraction described above was used to locate 24 point seismic sources. The calculation results are shown in Table 2 and... Figure 7 As shown.

[0068] Table 2 shows the source location results of the TSP point obtained using the microsource localization algorithm that considers diffraction in the void.

[0069]

[0070]

[0071] Note: Absolute error D is the Euclidean distance between the actual spatial location of the point source and its location.

[0072] Depend on Figure 7 It can be seen that the location result 13 of the TSP point source 3 obtained by the micro-source location algorithm that takes into account the diffraction of the empty area is basically near the actual spatial location of the point source, and the location effect is good.

[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A microseismic source location method considering diffraction in void areas, applicable to tunnel excavation processes, characterized in that, Includes the following steps: S1. Establish a digital model of the excavated section of the tunnel in the monitoring area; S2. Based on the digital model, obtain the spatial distance matrix of the sub-nodes after discretization of the tunnel wall of the excavated section in the monitoring area; The spatial distance matrix described in S2 is composed of the distance between any two nodes in the discretized child nodes of the cave wall. The method for calculating the distance between any two nodes is as follows: When two nodes are not adjacent, the distance between the two nodes is infinite. When two nodes are adjacent, the distance between them is the Euclidean distance in three-dimensional space, as shown in the following formula: In the formula: D ij child node i and j The distance between them; x i ，y i ，z i ) is a child node i The three-dimensional spatial coordinates, x j ，y j ，z j ) is a child node j Three-dimensional spatial coordinates; S3. Determine whether the straight section crosses an empty area of ​​the already excavated section of the tunnel, which includes the following steps: Project the straight line segment between any two sub-nodes of the discretized tunnel wall and the tunnel outline onto a cross section perpendicular to the tunnel axis to obtain a closed curve and a straight line segment on the projection plane. Based on the projection results, determine whether the straight line segment between the two points crosses the tunnel void. When the number of intersections between the projection of the straight line segment between two points and the projection of the tunnel outline is two, the straight line segment between the two points passes through the tunnel void. When the number of intersection points between the projection of the straight line segment between two points and the projection of the tunnel outline is not two, the straight line segment between the two points does not cross the tunnel void. S4. Based on the judgment results of S3, calculate the shortest distance between the potential microseismic source and the microseismic sensor that does not cross the tunnel void, specifically including the following steps: If the straight line between the potential microseismic source and the microseismic sensor does not cross the excavated void of the tunnel, then the shortest distance is the three-dimensional Euclidean distance. If the straight line segment between the potential microseismic source and the microseismic sensor passes through the excavated void of the tunnel, then the shortest distance is the shortest distance from the potential microseismic source as the root node, through the discretized sub-nodes of the tunnel wall, to the microseismic sensor as the endpoint. S5. Repeat S2~S4 until the shortest distance between the potential microseismic source and the microseismic sensor that does not cross the tunnel void satisfies the fitness function, and then the microseismic source is located.

2. The microseismic source positioning method considering diffraction in the tunnel excavation process according to claim 1, characterized in that, S1 includes the following steps: S11. Select the centroid of the cross section at point 5 of the tunnel face as the origin of the coordinate system, take the forward direction of point 5 as the positive x-axis, the vertical upward direction as the positive z-axis, and determine the positive y-axis according to the right-hand screw principle. S12. Divide the tunnel cross-section profile into equal parts and obtain the y and z coordinates of the sub-nodes on the tunnel cross-section profile. S13. Divide the excavated section of the tunnel in the monitoring area into h equal segments, so that the length of the tunnel segment after equal division is equal to the length of the straight or curved segment after equal division of the tunnel cross-section outline, to obtain h+1 cross-sections, and calculate the x coordinates of the sub-nodes on each cross-section. S14. Obtain a digital model of the excavated section of the tunnel in the monitoring area based on the x, y, and z coordinates of each sub-node.

3. The microseismic source positioning method considering diffraction in the tunnel excavation process according to claim 2, characterized in that, S12 includes the following steps: When the tunnel cross-section profile is circular, the circular tunnel cross-section profile is divided into n equal parts to obtain n child nodes on the tunnel cross-section profile and their y and z coordinates. When the tunnel cross-section is non-circular, the intersection of the arc segment and the straight segment on the cross-section profile of the non-circular tunnel is taken as the key node. The straight segment and the curved segment between each key node are divided equally so that the lengths of the divided straight segment and the curved segment are approximately equal, thus obtaining the secondary node. The child node on the cross-section profile of the non-circular tunnel is the key node. The y and z coordinates of the child node on the cross-section profile of the non-circular tunnel are calculated by adding the key node and the secondary node.

4. The microseismic source positioning method considering diffraction in the tunnel excavation process according to claim 1, characterized in that, When the straight section between the potential microseismic source and the microseismic sensor crosses the excavated void area of ​​the tunnel, the shortest distance is calculated using the spatial distance matrix and the Dijkstra algorithm.

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