Loess tunnel body shallow section subsurface construction method

Abstract

This invention relates to the field of tunnel construction technology, and more particularly to a method for the underground excavation of shallow-buried sections of loess tunnels. The invention acquires images of the steel mesh laid on the initial shotcrete surface of the tunnel from multiple perspectives. Based on the relationship between the vectors of local image regions and the captured perspective, several characteristic visible local regions are determined. Based on the tunnel excavation direction, the coordinate points of the continuously appearing steel mesh are grouped into a set of sub-domains to construct several steel mesh sub-domain planes. Based on the angle difference between the normal vectors of the steel mesh sub-domain planes, the laying qualification coefficient of the steel mesh within the characteristic visible local regions is determined to determine whether the steel mesh laying within the corresponding characteristic visible local regions is qualified. By determining the anchoring construction area, secondary anchoring construction is carried out on the steel mesh within the anchoring construction area. Furthermore, this invention overcomes the defects of inaccurate identification and missed identification of the gap between the steel mesh and the initial shotcrete surface, achieving accurate positioning and timely optimization of unqualified laying areas.

Description

Technical Field

[0001] This invention relates to the field of tunnel construction technology, and in particular to a method for the underground excavation of shallow buried sections of loess tunnels. Background Technology

[0002] In shallow-buried sections of loess tunnels, the surrounding rock structure is loose and has poor self-stability. During underground excavation, the initial support process commonly adopted is shotcrete, steel mesh laying, and shotcrete re-laying combined with anchor bolts. The fit between the steel mesh and the shotcrete surface directly affects the uniformity of stress on the initial support structure and the safety of construction. Currently, the quality of steel mesh laying is mostly judged by manual tapping or single-point inspection, which is highly subjective, has low inspection efficiency, and cannot achieve full-area quantitative judgment. Large gaps are difficult to detect and eliminate in time. After re-laying, quality defects such as voids in the shotcrete layer, uneven stress on the steel mesh, and local voids are easily formed. In severe cases, it can lead to cracking of the initial support and deformation encroachment, threatening the construction safety of shallow-buried tunnel sections.

[0003] For example, Chinese invention patent CN116717280A, published on September 8, 2023, discloses a method for installing a steel arch frame and reinforcing mesh in a tunnel, including the following steps: S1: Excavation; after excavating the tunnel according to the construction sequence, anchor bolts are installed, and then concrete is sprayed onto the tunnel wall. After the concrete has solidified to the expected hardness, the reinforcing mesh is placed side by side in sequence according to the construction direction; S2: Installation of reinforcing mesh; adjacent reinforcing mesh pieces are overlapped together using a quick-lapping assembly, and the reinforcing mesh is also connected to the anchor bolts; S3: Installation of steel arch frame; the steel arch frame is installed on the side of the reinforcing mesh away from the tunnel wall, and a protective device is placed at the lower end joint of the steel arch frame. The protective device is then backfilled with sand and gravel and sprayed with concrete again.

[0004] Existing technologies do not take into account factors such as overlapping multiple steel meshes, uneven initial sprayed surfaces, and on-site construction interference. Conventional visual inspection and point cloud acquisition methods are difficult to accurately identify the steel mesh laying status. In addition, the steel mesh wires have small cross-sections, which limits the number of effective point clouds that can be captured. This can easily lead to problems such as inaccurate identification of the gap between the steel mesh and the initial sprayed surface, and missed identification, which cannot meet the high-quality control requirements of tunnel shallow buried section excavation construction. Summary of the Invention

[0005] To address this, the present invention provides a method for the underground excavation of shallow buried sections of loess tunnels, which overcomes the limitations of existing technologies that do not consider the effects of overlapping multiple steel meshes, uneven initial sprayed surfaces, and on-site construction interference. Conventional visual inspection and point cloud acquisition methods are unable to accurately identify the steel mesh laying status. In addition, the small cross-section of the steel mesh wires limits the number of effective point clouds that can be captured, which can easily lead to inaccurate identification and missed identification of the gap between the steel mesh and the initial sprayed surface.

[0006] To achieve the above objectives, the present invention provides a method for the underground excavation of shallow-buried sections of loess tunnels, comprising: Acquire images of the steel mesh laid on the initial sprayed surface of the tunnel from different perspectives, and determine several characteristic explicit local regions based on the relationship between the vector direction of each local surface region in the laying images and the capture perspective. Identify the body coordinates of the steel mesh in each feature-explicit local area, and form a set of subdomains based on the tunnel excavation direction by continuously appearing body coordinates. Construct several steel mesh subdomain planes based on the points in each subdomain set. Obtain the normal vector of each steel mesh sub-domain plane, and determine the laying qualification coefficient of the steel mesh in the characteristic explicit local area based on the angle difference between the normal vectors of the steel mesh sub-domain planes, so as to determine whether the laying of the steel mesh in the corresponding characteristic explicit local area is qualified. In response to the judgment result of unqualified steel mesh laying, the anchoring construction area is determined according to the analysis result of the normal vector pointing of the steel mesh sub-domain plane, and secondary anchoring construction is carried out on the steel mesh in the anchoring construction area.

[0007] Furthermore, the process of identifying several dominant local regions includes: Each frame of the steel mesh laying image is divided into grids to obtain several local surface regions; Determine the normal vector of each local surface region and the capture line of sight of the corresponding frame of the steel mesh laying image; Calculate the angle between the normal vector of each local surface region and the capture line of sight of the corresponding frame's steel mesh laying image, and determine the local surface region corresponding to the minimum angle as the feature explicit local region.

[0008] Furthermore, the process of identifying the body coordinates of the steel mesh within each characteristic explicit local region includes: In a global coordinate system established parallel to the explicit local regions of features, the normal dimension perpendicular to the explicit local regions of features is used as the recognition dimension. Extract the three-dimensional spatial coordinates of all identification points within the feature-explicit local region, and compare the coordinate values ​​of each identification point in the identification dimension; Identification points whose coordinate values ​​are outside the coordinate recognition range are identified as the body coordinate points of the steel mesh.

[0009] Furthermore, the coordinate recognition range is determined based on the maximum and minimum coordinate values ​​of points in the characteristic visible local area on the initial sprayed surface before steel mesh laying in the recognition dimension.

[0010] Furthermore, the process of forming a set of subdomains includes: Using the tunnel excavation direction as the vertical axis as the sorting benchmark, all steel mesh body coordinate points identified in the same characteristic explicit local area are sorted in ascending order of their coordinate values ​​on the vertical axis; Three consecutive body coordinate points are grouped together as a point group along the positive direction of the vertical axis, and the point groups are selected sequentially in a sliding progressive manner. Define the three body coordinate points within each point group as a subdomain set; In this case, two adjacent point groups share a single body coordinate point.

[0011] Furthermore, the process of constructing several steel mesh subdomain planes is as follows: the plane of the triangle fitted with three body coordinate points in each subdomain set as vertices is taken as the steel mesh subdomain plane.

[0012] Furthermore, the process of determining the laying qualification factor of the steel mesh in the characteristic explicit local area includes: Calculate the angle between the plane normal vectors of any two steel mesh subdomains within the same dominant local region and obtain several angle values; Calculate the standard deviation of several included angle values ​​and use it as the qualification coefficient for steel mesh laying in this area.

[0013] Furthermore, the process of determining whether the steel mesh laying in the corresponding characteristic visible local area is qualified includes: The laying qualification coefficient is compared with the preset qualification coefficient threshold. If the laying qualification coefficient is greater than the preset qualification coefficient threshold, the steel mesh laying in the corresponding characteristic visible local area is determined to be unqualified. If the laying qualification coefficient is less than or equal to the qualification coefficient threshold, the steel mesh laying in the corresponding characteristic visible local area is deemed qualified.

[0014] Furthermore, the process of determining the anchorage construction area includes: The angle between the normal vector of the plane of all steel mesh sub-domains in the non-compliant area and the capture line of sight of the steel mesh laying image in the corresponding frame; The spatial range corresponding to the steel mesh sub-domain plane with an included angle greater than the preset included angle reference value or the maximum included angle is selected as the anchoring construction area.

[0015] Furthermore, the process of carrying out secondary anchoring construction on the steel mesh within the anchoring construction area includes adding a steel frame to the anchoring construction area; The anchoring direction of the steel frame is parallel to the extension of the direction of the normal vector of the steel mesh sub-domain plane.

[0016] The beneficial effects of the technical solution presented in this application include: acquiring laying images of the steel mesh on the initial shotcrete surface of the tunnel from multiple perspectives; determining several characteristic visible local regions based on the relationship between the local region vectors of the images and the captured perspective; forming a set of subdomains from the body coordinates of the continuously appearing steel mesh based on the tunnel excavation direction to construct several steel mesh subdomain planes; determining the laying qualification coefficient of the steel mesh within the characteristic visible local regions based on the angle difference between the normal vectors between the steel mesh subdomain planes to determine whether the steel mesh laying within the corresponding characteristic visible local regions is qualified; and implementing secondary anchoring construction on the steel mesh within the anchoring construction area by determining the anchoring construction area. Furthermore, this overcomes the defects of inaccurate identification and missed identification of the gap between the steel mesh and the initial shotcrete surface, achieving accurate positioning and timely optimization of unqualified laying areas.

[0017] Furthermore, this invention calculates the angle between the normal vector of each local surface region and the corresponding captured line of sight, and determines the local surface region corresponding to the minimum angle as the feature explicit local region, thereby obtaining the local surface region with the least perspective distortion and the most accurate and reliable recognition of the steel mesh outline and coordinate information, thus avoiding recognition interference caused by the overlap of multiple steel meshes.

[0018] Furthermore, this invention utilizes the geometric principle of determining a unique plane using three points to provide a stable and reliable foundation for the construction of each subdomain set. Through continuous sliding and point sharing, the subsequently generated steel mesh subdomain planes can be seamlessly connected and continuously covered along the tunnel excavation direction, avoiding detection blind spots and ensuring full-domain identification of steel mesh laying flatness, bulging, and offset defects, thereby improving the integrity and reliability of steel mesh laying status determination.

[0019] Furthermore, the present invention uses a triangular plane as the sub-domain plane of the steel mesh, which can avoid the plane fitting distortion problem caused by local deformation of the steel mesh, sparse points or coordinate fluctuations, and ensure that the plane shape is highly consistent with the actual direction of the local steel mesh. In addition, the posture difference between adjacent steel mesh sub-domain planes can accurately characterize whether there are uneven laying defects such as bulging, depression, and offset of the steel mesh.

[0020] Furthermore, by calculating the laying qualification coefficient, this invention can objectively and accurately reflect the overall smoothness and posture consistency of the steel mesh laying. When the laying qualification coefficient is greater than the preset qualification coefficient threshold, it indicates that the local posture of the steel mesh in the area changes significantly and the spatial orientation is disordered. Correspondingly, there are problems such as excessive laying gaps, poor fit, and local suspension. It is impossible to guarantee the compactness of the subsequent sprayed concrete and the uniformity of the initial support structure. Therefore, it is judged as unqualified laying and secondary anchoring rectification is required.

[0021] Furthermore, by screening the anchoring construction area, this invention can accurately locate the part with the most serious defects in the steel mesh laying, and achieve targeted locking of the anchoring area. By accurately locating and timely optimizing the unqualified areas, the initial support structure is ensured to be dense and reliable.

[0022] Furthermore, this invention ensures that the anchoring direction of the steel frame is parallel to the extension of the normal vector of the steel mesh sub-domain plane. This allows for a full fit with the local spatial laying posture of the steel mesh. Anchoring along this direction maximizes the gap between the steel mesh and the initial sprayed surface, avoiding problems such as localized lifting or inadequate clamping of the steel mesh caused by arbitrary anchoring. It effectively eliminates defects such as bulging, suspension, and poor fit of the steel mesh, enabling precise positioning and timely optimization of substandard laying areas, and improving the density and structural stability of the initial support in the shallow buried section of the loess tunnel. Attached Figure Description

[0023] Figure 1 This is a step diagram illustrating the method for underground excavation of shallow-buried sections of loess tunnels according to an embodiment of the present invention. Figure 2 A flowchart illustrating the steps for determining a dominant local region of a feature in an embodiment of the present invention; Figure 3 This is a step diagram illustrating the process of identifying the body coordinates of the steel mesh according to an embodiment of the present invention; Figure 4 This is a flowchart illustrating the logic for determining whether the steel mesh installation is qualified according to an embodiment of the present invention. Detailed Implementation

[0024] To make the objectives and advantages of the present invention clearer, the present invention will be further described below with reference to embodiments; it should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention.

[0025] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0026] It should be noted that in the description of this invention, the terms "upper," "lower," "inner," "outer," etc., which indicate the direction or positional relationship, are based on the direction or positional relationship shown in the drawings. This is only for the convenience of description and is not intended to indicate or imply that the device or element must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of this invention.

[0027] It should be understood that although the terms "first," "second," etc., may be used in this invention to describe various types of information, these information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another. For example, without departing from the scope of this invention, first information may also be referred to as second information, and similarly, second information may also be referred to as first information.

[0028] Furthermore, it should be noted that, in the description of this invention, unless otherwise explicitly specified and limited, the terms "installation" and "connection" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0029] Please see Figure 1 The diagram illustrates the steps of a method for underground excavation of shallow-buried sections of loess tunnels according to an embodiment of the present invention. The method includes: Step S100: Obtain images of the steel mesh laid on the initial sprayed surface of the tunnel from different perspectives, and determine several characteristic explicit local regions based on the relationship between the vector direction of each local surface region in the laying image and the capture perspective. In this invention, a binocular camera mounted on the end of the mechanical arm of the tunnel wet spraying trolley can be used as the acquisition device. After the initial setting of the tunnel initial sprayed concrete and the initial anchoring of the steel mesh are completed, and before the re-spraying concrete is constructed, a scan is performed. At least 5 frames of laying images are acquired with the same steel mesh laying area as the target. During the acquisition process, the capture line of sight corresponding to each frame of image is recorded simultaneously.

[0030] Step S200: Identify the body coordinate points of the steel mesh in each feature explicit local area, and form a subdomain set based on the tunnel excavation direction by continuously appearing body coordinate points, and construct several steel mesh subdomain planes based on the points in each subdomain set. Step S300: Obtain the normal vector of each steel mesh sub-domain plane, and determine the laying qualification coefficient of the steel mesh in the characteristic explicit local area based on the angle difference between the normal vectors of the steel mesh sub-domain planes, so as to determine whether the laying of the steel mesh in the corresponding characteristic explicit local area is qualified. In step S400, in response to the judgment result of unqualified steel mesh laying, the anchoring construction area is determined according to the analysis result of the normal vector pointing of the steel mesh sub-domain plane, and secondary anchoring construction is carried out on the steel mesh in the anchoring construction area.

[0031] Specifically, please refer to Figure 2The diagram illustrates the steps for determining dominant local regions of features according to an embodiment of the present invention. The process for determining several dominant local regions of features includes: Step S101: Divide each frame of steel mesh laying image into a grid to obtain several local surface regions; In this invention, when dividing each frame of steel mesh laying image into grids, the entire frame image is divided into several local surface regions of the same size. The length direction of the local surface region is the tunnel excavation direction, the length of the local surface region is the length of the steel mesh laying image, the width direction is perpendicular to the tunnel excavation direction, and the width of the local surface region is 1 / m of the width of the steel mesh laying image. Optionally, the value of m is 10.

[0032] Step S102: Determine the normal vector of each local surface region and the capture line of view of the steel mesh laying image of the corresponding frame; In this invention, the normal vector of a local surface region can be obtained by fitting the spatial plane of the region using the least squares method through the three-dimensional spatial coordinates of all pixels in the local surface region. The unit normal vector of the spatial plane is then used as the normal vector of the local surface region. Fitting the spatial plane of the region using the least squares method is a prior art technique and will not be elaborated here.

[0033] In this invention, the line of sight for capturing the image of the steel mesh laying is the central axis of the camera lens when the image frame is acquired.

[0034] Step S103: Calculate the angle between the normal vector of each local surface region and the capture line of sight of the steel mesh laying image of the corresponding frame, and determine the local surface region corresponding to the minimum angle as the feature explicit local region.

[0035] In this invention, the angle between the normal vector and the captured line of sight is the spatial angle between the two vectors.

[0036] It is understandable that when the normal vector of a local surface region is parallel to the image capture line of sight, the local surface region appears to be in an approximately frontal state in the image, with minimal perspective distortion and the most accurate and reliable recognition of the steel mesh outline and coordinate information. Therefore, by calculating the angle between the normal vector of each local surface region and the corresponding capture line of sight, and determining the local surface region corresponding to the minimum angle as the feature-explicit local region, the recognition interference caused by the overlap of multiple steel meshes can be avoided.

[0037] Specifically, please refer to Figure 3 The diagram illustrates the steps for identifying the body coordinates of a steel mesh according to an embodiment of the present invention. The process of identifying the body coordinates of the steel mesh within each prominent local region includes: Step S201: In the global coordinate system established parallel to the local region of the tunnel feature, the normal dimension perpendicular to the local region of the tunnel feature is used as the recognition dimension. Step S202: Extract the three-dimensional spatial coordinates of all identification points within the feature-explicit local region and compare the coordinate values ​​of each identification point in the identification dimension. Step S203: Identify the identification points whose coordinate values ​​are not within the coordinate identification range as the body coordinate points of the steel mesh.

[0038] For example, the global coordinate system is a right-handed rectangular coordinate system with the lower left corner vertex of the feature-expanded local region as the origin, the tunnel excavation direction as the positive Y-axis, the direction perpendicular to the tunnel excavation direction as the positive X-axis, and the direction perpendicular to the feature-expanded local region as the positive Z-axis. The normal dimension perpendicular to the feature-expanded local region is the identification dimension, and the coordinate value of this dimension directly represents the vertical distance between the identification point and the initial spray surface.

[0039] In this invention, the normal dimension perpendicular to the prominent local region is used as the recognition dimension because this dimension can best distinguish the spatial positional differences between the initial sprayed surface and the steel mesh. It is understood that the coordinate values ​​of points on the initial sprayed surface are within a preset coordinate recognition range in the recognition dimension, while the steel mesh itself, being laid above the initial sprayed surface, will have coordinate values ​​significantly exceeding this range. Based on this, the three-dimensional spatial coordinates of all recognition points within the prominent local region are extracted and compared with their coordinate values ​​in the recognition dimension. Recognition points whose coordinate values ​​are outside the coordinate recognition range are identified as the steel mesh's body coordinate points. This allows for accurate and efficient extraction of the steel mesh's body coordinate points without interference from points on the initial sprayed surface, avoiding recognition errors caused by overlapping multiple steel mesh layers and sparse point clouds.

[0040] Specifically, the coordinate recognition range is determined based on the maximum and minimum coordinate values ​​of points in the characteristic visible local area on the initial sprayed surface before steel mesh laying in the recognition dimension.

[0041] The coordinate recognition range is determined in advance before steel mesh laying. Before steel mesh laying, the same equipment and station used for subsequent image acquisition are used to collect three-dimensional point cloud data of the initial sprayed surface in the corresponding visible local area. The coordinate values ​​of all points in the recognition dimension are extracted to obtain the minimum coordinate value Z. min With the maximum coordinate Z max .

[0042] Specifically, the process of forming a set of subdomains includes: Using the tunnel excavation direction as the vertical axis as the sorting benchmark, all steel mesh body coordinate points identified in the same characteristic explicit local area are sorted in ascending order of their coordinate values ​​on the vertical axis; Three consecutive body coordinate points are grouped together as a point group along the positive direction of the vertical axis, and the point groups are selected sequentially in a sliding progressive manner. Define the three body coordinate points within each point group as a subdomain set; In this case, two adjacent point groups share a single body coordinate point.

[0043] For example, using the tunnel excavation direction as the sorting criterion, the steel mesh body coordinate points identified within the same characteristic explicit local area are sorted and grouped. All valid steel mesh body coordinate points within the same characteristic explicit local area are extracted and sorted in ascending order of their Y-axis coordinate values, forming an ordered point sequence: P1, P2, P3, P4, P5, P6...P n ; Sort along the vertical axis in the positive direction, and select three consecutive body coordinate points in a sliding progressive manner as a point group. Each point group is defined as a subdomain set, where adjacent point groups share a single body coordinate point; the specific grouping is as follows: The first subdomain set is formed by points P1, P2, and P3; The second subdomain set is formed by points P3, P4, and P5; The third subdomain set is formed by points P5, P6, and P7; By analogy, the division of all subdomain sets is completed in sequence, so that adjacent subdomain sets share a common body coordinate point, ensuring continuous coverage of the steel mesh detection area along the tunnel excavation direction.

[0044] It is understandable that establishing a sorting benchmark with the tunnel excavation direction as the vertical axis can ensure that the arrangement of the coordinate points of the steel mesh body is consistent with the actual construction direction of the tunnel. By utilizing the geometric principle of three points determining a unique plane, a stable and reliable plane construction foundation is provided for each subdomain set. Through continuous sliding and point sharing, the planes of the subsequently generated steel mesh subdomains can be seamlessly connected and continuously covered along the tunnel excavation direction, avoiding detection blind spots and ensuring full-domain identification of steel mesh laying flatness, bulging and offset defects, thereby improving the integrity and reliability of steel mesh laying status judgment.

[0045] Specifically, the process of constructing several steel mesh subdomain planes is as follows: the plane of the triangle fitted with three body coordinate points in each subdomain set as vertices is taken as the steel mesh subdomain plane.

[0046] In the implementation of this invention, when constructing the steel mesh subdomain plane, the three body coordinate points in each subdomain set are used as the three vertices of a triangle. Based on the geometric principle that three points determine a unique plane, a unique triangular plane is determined. If the three body coordinate points are collinear, the fitted plane is invalid, the subdomain set is discarded, and the next subdomain set is selected to fit the plane.

[0047] It is understandable that using a triangular plane as the sub-domain plane of the steel mesh can avoid the plane fitting distortion caused by local deformation of the steel mesh, sparse points, or coordinate fluctuations, and ensure that the plane shape is highly consistent with the actual direction of the local steel mesh. In addition, the posture difference between adjacent steel mesh sub-domain planes can accurately characterize whether there are uneven laying defects such as bulging, depression, or offset of the steel mesh.

[0048] Specifically, the process of determining the laying qualification factor of the steel mesh in the characteristic explicit local area includes: Calculate the angle between the plane normal vectors of any two steel mesh subdomains within the same dominant local region and obtain several angle values; Calculate the standard deviation of several included angle values ​​and use it as the qualification coefficient for steel mesh laying in this area.

[0049] Those skilled in the art will understand that, under qualified laying conditions, the steel mesh should be smooth and continuous in posture, with minimal spatial posture differences between adjacent local areas, and the included angle of the normal vectors of the corresponding steel mesh sub-domain planes should be generally consistent. If the steel mesh has defects such as bulging, depressions, misalignment, or poor adhesion, its local spatial posture will change abruptly, causing significant fluctuations in the included angle of the normal vectors of adjacent steel mesh sub-domain planes. By calculating the included angle between the normal vectors of any two steel mesh sub-domain planes within the same characteristic explicit local area, the posture differences of the steel mesh in each local interval can be comprehensively quantified. Then, using the standard deviation of all included angle values ​​as the laying qualification coefficient, the overall smoothness and posture consistency of the steel mesh laying can be objectively and accurately reflected: the smaller the standard deviation, the more uniform the posture between the steel mesh sub-domain planes and the smoother the laying; the larger the standard deviation, the more significant the posture differences and the more prominent the laying defects, thus achieving a comprehensive judgment of the steel mesh laying quality.

[0050] Specifically, please refer to Figure 4 As shown, this is a flowchart illustrating the logic of determining whether the steel mesh laying is qualified according to an embodiment of the present invention. The process of determining whether the steel mesh laying is qualified in the corresponding characteristic explicit local area includes: The laying qualification coefficient is compared with the preset qualification coefficient threshold. If the laying qualification coefficient is greater than the preset qualification coefficient threshold, the steel mesh laying in the corresponding characteristic visible local area is determined to be unqualified. If the laying qualification coefficient is less than or equal to the qualification coefficient threshold, the steel mesh laying in the corresponding characteristic visible local area is deemed qualified.

[0051] Optionally, the preset pass coefficient threshold is determined through a preliminary test: select standard samples of the same tunnel project, steel mesh of the same specification, and which have passed manual inspection and laying, and conduct no less than 5 sets of repeated tests, calculate the laying pass coefficient of each set of samples, and take 1.2 times the average value of all test results as the preset pass coefficient threshold; in this embodiment, the pass coefficient threshold is preset to 5°.

[0052] Specifically, the process of determining the anchoring construction area includes: The angle between the normal vector of the plane of all steel mesh sub-domains in the non-compliant area and the capture line of sight of the steel mesh laying image of the corresponding frame; The spatial range corresponding to the steel mesh sub-domain plane with an included angle greater than the preset included angle reference value or the maximum included angle is selected as the anchoring construction area.

[0053] In this invention, the angle between the normal vector of the steel mesh sub-domain plane in the unqualified area and the line of sight captured by the corresponding frame image is the spatial angle between the two vectors, and the spatial angle ranges from [0°, 90°].

[0054] For example, in the implementation of the present invention, the preset included angle reference value is 8°; steel mesh sub-domain planes with included angles greater than 8° are selected, and the continuous spatial regions corresponding to the steel mesh sub-domain planes that meet the conditions are integrated to obtain the anchoring construction area; or, when there is no included angle greater than the preset included angle reference value, the steel mesh sub-domain plane corresponding to the maximum included angle is selected as the anchoring construction area.

[0055] Understandably, in areas with substandard steel mesh installation, the angle between the normal vector of the steel mesh sub-domain plane and the line of sight captured by the corresponding frame image can directly reflect the severity of the defects in the local steel mesh: the larger the angle, the larger the gap between the steel mesh and the initial sprayed surface in the steel mesh sub-domain plane, and the more prominent the bonding defects. By screening the anchoring construction area, the part with the most serious steel mesh installation defects can be accurately located, achieving targeted locking of the anchoring area and ensuring that the initial support structure is dense and reliable.

[0056] In this invention, when performing secondary anchoring of the steel mesh in the anchoring construction area, I-beam steel frames are used for reinforcement anchoring. After the secondary anchoring construction is completed, the laying images of the corresponding area are re-acquired, and the steel mesh laying qualification coefficient is checked. Only when the check result is determined to be qualified can subsequent sprayed concrete construction be carried out.

[0057] Specifically, the process of carrying out secondary anchoring construction on the steel mesh in the anchoring construction area includes adding a steel frame to the anchoring construction area; The anchoring direction of the steel frame is parallel to the extension of the direction of the normal vector of the steel mesh sub-domain plane.

[0058] In this invention, the anchoring direction of the steel frame is the direction in which the steel frame applies force to press the steel frame and the steel mesh tightly against the initial sprayed surface.

[0059] In this invention, when performing secondary anchoring of the steel mesh within the anchoring construction area, a steel frame is added so that the anchoring direction of the steel frame is parallel to the extension of the normal vector of the steel mesh sub-domain plane. This allows for full conformity to the local spatial laying posture of the steel mesh. The normal vector direction of the steel mesh sub-domain plane represents the true spatial normal of the steel mesh in that area. Anchoring construction along this direction maximizes the gap between the steel mesh and the initial sprayed surface, avoiding problems such as localized lifting or inadequate compression of the steel mesh caused by arbitrary anchoring. This effectively eliminates defects such as steel mesh bulging, suspension, and poor fit, and counteracts the radial separation force and tangential shear force of the surrounding rock on the steel mesh, thereby improving the density and structural stability of the initial support in the shallow buried section of the loess tunnel during excavation.

[0060] This embodiment also provides a computer-readable storage medium storing computer program code. When the computer program code is run on a computer, the computer executes the above-mentioned method steps to implement the underground excavation method for shallow buried sections of loess tunnels provided in the above embodiment.

[0061] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the scope of protection of the present invention.

[0062] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for underground excavation of shallow-buried sections of loess tunnels, characterized in that, include: Acquire images of the steel mesh laid on the initial sprayed surface of the tunnel from different perspectives, and determine several characteristic explicit local regions based on the relationship between the vector direction of each local surface region in the laying images and the capture perspective. Identify the body coordinates of the steel mesh in each feature-explicit local area, and form a set of subdomains based on the tunnel excavation direction by continuously appearing body coordinates. Construct several steel mesh subdomain planes based on the points in each subdomain set. Obtain the normal vector of each steel mesh sub-domain plane, and determine the laying qualification coefficient of the steel mesh in the characteristic explicit local area based on the angle difference between the normal vectors of the steel mesh sub-domain planes, so as to determine whether the laying of the steel mesh in the corresponding characteristic explicit local area is qualified. In response to the judgment result of unqualified steel mesh laying, the anchoring construction area is determined according to the analysis result of the normal vector pointing of the steel mesh sub-domain plane, and secondary anchoring construction is carried out on the steel mesh in the anchoring construction area.

2. The method for underground excavation of shallow-buried sections of loess tunnels according to claim 1, characterized in that, The process of determining several dominant local regions includes: Each frame of the steel mesh laying image is divided into grids to obtain several local surface regions; Determine the normal vector of each local surface region and the capture line of sight of the corresponding frame of the steel mesh laying image; Calculate the angle between the normal vector of each local surface region and the capture line of sight of the corresponding frame's steel mesh laying image, and determine the local surface region corresponding to the minimum angle as the feature explicit local region.

3. The method for underground excavation of shallow-buried sections of loess tunnels according to claim 2, characterized in that, The process of identifying the body coordinates of the steel mesh within each prominent local region includes: In a global coordinate system established parallel to the explicit local regions of features, the normal dimension perpendicular to the explicit local regions of features is used as the recognition dimension. Extract the three-dimensional spatial coordinates of all identification points within the feature-explicit local region, and compare the coordinate values ​​of each identification point in the identification dimension; Identification points whose coordinate values ​​are outside the coordinate recognition range are identified as the body coordinate points of the steel mesh.

4. The method for underground excavation of shallow-buried sections of loess tunnels according to claim 3, characterized in that, The coordinate recognition range is determined based on the maximum and minimum coordinate values ​​of points in the characteristic visible local area on the initial sprayed surface before steel mesh laying in the recognition dimension.

5. The method for underground excavation of shallow-buried sections of loess tunnels according to claim 1, characterized in that, The process of forming a set of subdomains includes: Using the tunnel excavation direction as the vertical axis as the sorting benchmark, all steel mesh body coordinate points identified in the same characteristic explicit local area are sorted in ascending order of their coordinate values ​​on the vertical axis; Three consecutive body coordinate points are grouped together as a point group along the positive direction of the vertical axis, and the point groups are selected sequentially in a sliding progressive manner. Define the three body coordinate points within each point group as a subdomain set; In this case, two adjacent point groups share a single body coordinate point.

6. The method for underground excavation of shallow-buried sections of loess tunnels according to claim 5, characterized in that, The process of constructing several steel mesh subdomain planes is as follows: the plane of the triangle fitted with three body coordinate points in each subdomain set as vertices is the steel mesh subdomain plane.

7. The method for underground excavation of shallow-buried sections of loess tunnels according to claim 6, characterized in that, The process of determining the laying qualification factor of steel mesh in characteristic explicit local areas includes: Calculate the angle between the plane normal vectors of any two steel mesh subdomains within the same dominant local region and obtain several angle values; Calculate the standard deviation of several included angle values ​​and use it as the qualification coefficient for steel mesh laying in this area.

8. The method for underground excavation of shallow-buried sections of loess tunnels according to claim 7, characterized in that, The process of determining whether the steel mesh laying in the corresponding characteristic visible local area is qualified includes: The laying qualification coefficient is compared with the preset qualification coefficient threshold. If the laying qualification coefficient is greater than the preset qualification coefficient threshold, the steel mesh laying in the corresponding characteristic visible local area is determined to be unqualified. If the laying qualification coefficient is less than or equal to the qualification coefficient threshold, the steel mesh laying in the corresponding characteristic visible local area is deemed qualified.

9. The method for underground excavation of shallow-buried sections of loess tunnels according to claim 8, characterized in that, The process of determining the anchorage construction area includes: The angle between the normal vector of the plane of all steel mesh sub-domains in the non-compliant area and the capture line of sight of the steel mesh laying image in the corresponding frame; The spatial range corresponding to the steel mesh sub-domain plane with an included angle greater than the preset included angle reference value or the maximum included angle is selected as the anchoring construction area.

10. The method for underground excavation of shallow-buried sections of loess tunnels according to claim 9, characterized in that, The process of carrying out secondary anchoring construction on the steel mesh within the anchoring construction area includes adding a steel frame to the anchoring construction area; The anchoring direction of the steel frame is parallel to the extension of the direction of the normal vector of the steel mesh sub-domain plane.

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