A method for controlling deformation resistance of a small-section tunnel drill-and-blast jumbo portal system

Abstract

The application provides a deformation resistance control method for a small-section tunnel drill-and-blast jumbo portal system, and belongs to the technical field of small-section tunnel drill-and-blast jumbos.The portal structure which is integrally welded is arranged with an exciter near key nodes of the portal, dynamic excitation is applied to the exciter at a structural resonance frequency, vibration aging treatment is performed, and blind hole method is used for sampling inspection.After the jumbo is positioned, a vehicle-mounted three-dimensional laser scanner is used to collect portal measured point clouds, and an iterative nearest point algorithm is used for registration with portal building information model theoretical point clouds to output a component deformation deviation map, an audible and light warning is triggered for an out-of-limit deformation node, and in the construction process, the above point cloud collection and registration process is periodically repeated to stop work for an out-of-limit deformation node, and after pre-tightening force is supplemented, the construction is resumed, so that the technical problem that portal deformation cannot be sensed and actively controlled in real time in the operation process, and the risk of structural instability cannot be quantitatively controlled is solved.

Description

Technical Field

[0001] This invention belongs to the technical field of small-section tunnel drilling and blasting trolleys, and more specifically, relates to a method for controlling the deformation of a small-section tunnel drilling and blasting trolley gantry system. Background Technology

[0002] In drill-and-blast construction of small-section tunnels, the gantry system undertakes the load transfer task for multiple work platforms such as drilling and support. Traditional gantry systems adopt the welding and assembly method of I-beams, relying on fixed diagonal braces to provide lateral constraints and controlling the strength of nodes through welding processes. This is currently the most widely used structural form in small-section tunnel construction. Under the working conditions of slippery slopes and multiple points of vibration in the tunnel, the stability and deformation of the gantry system directly determine the level of construction safety. Existing construction specifications require static dimensional verification of the gantry before drilling and other vibration operations, and evaluation of weld quality through visual inspection and sampling inspection after welding.

[0003] However, traditional gantry systems have significant structural defects. On the one hand, the I-beam columns have extremely few lateral support points due to the limited cross-sectional clearance, resulting in excessive out-of-plane calculated lengths and a low overall critical load for lateral torsional buckling. The diagonal braces use rigid welded connections, which have initial loosening defects at the nodes. Under lateral loads, they must first undergo a lag process from relaxation to stress, resulting in a significantly delayed lateral stiffness response. On the other hand, the concentrated welding of multiple nodes causes the superposition of heat input, leading to axial bending deformation of the columns and high peak values ​​of residual tensile stress from welding, which weakens the compressive stability of the components. Traditional post-weld visual inspection and static dimensional measurement can only be completed once before the gantry is in place, making it impossible to dynamically track and quantitatively control the deformation of the gantry during construction.

[0004] In existing technologies, traditional gantry systems lack the means to continuously, comprehensively, and non-contactly monitor the deformation of each component under vibration conditions and compare it with the design model in real time. As a result, subtle deformations such as web bulging and column tilting during construction cannot be detected in a timely manner, and nodes exhibiting excessive deformation cannot be identified and addressed before jeopardizing the overall structural stability. In other words, existing technologies suffer from the technical problem of being unable to detect and actively control the deformation of I-beam gantry systems in small-section tunnels during welding and vibration operations, leading to an inability to quantify and manage the risk of structural instability. Summary of the Invention

[0005] In view of this, the present invention provides a deformation control method for a small-section tunnel drilling and blasting gantry system, which can solve the technical problem in the prior art that the deformation of the gantry system in small-section tunnels cannot be detected and actively controlled in real time during welding construction and vibration operation, resulting in the inability to quantify and manage the risk of structural instability.

[0006] This invention is implemented as follows: This invention provides a method for controlling the deformation of a small-section tunnel drilling and blasting gantry system, comprising the following steps:

[0007] Based on the clear dimensions of the small-section tunnel, three portal frames are welded from I18 I-beams. The spacing between adjacent portal frames is set to 1.9m. Horizontal tie rods and cross scissor braces are arranged in the transverse direction between adjacent portal frames to reduce the out-of-plane calculated length of the column to the spacing between the portal frames, thus obtaining the initial structure of the portal frame with lateral constraints.

[0008] At the mast column near the front of the vehicle, diagonal bracing is installed using I18 I-beams. An adjustable threaded prestressing device is installed at each end of the diagonal bracing. The design preload is applied to the adjustable threaded prestressing device using a torque wrench, so that the diagonal bracing is in a tensile working state under zero external load, forming a diagonal bracing system with initial prestress.

[0009] The initial structure of the gantry and the diagonal bracing system are welded as a whole. All nodes are triangularly welded using 306 carbon steel welding rods. The weld height is not less than 10mm. Welding is carried out simultaneously on both sides of the same cross section. Each segment is welded in sequence according to the symmetrical segmented skip welding process to obtain the gantry structure with overall welding.

[0010] Vibration aging treatment is performed on the overall welded gantry structure: exciters are arranged near the key nodes of the gantry, and dynamic excitation is applied to the key nodes of the gantry at the structural resonance frequency. After continuous treatment, the peak value of welding residual tensile stress at the key nodes of the gantry is sampled and checked using the blind hole method. It is confirmed that the peak value of welding residual tensile stress has dropped below the target value, and a gantry structure with residual stress meeting the requirements is obtained.

[0011] The gantry structure with the required residual stress is installed onto the automobile chassis. After the trolley is in place, a vehicle-mounted 3D laser scanner is used to collect point cloud data of the gantry structure to obtain the measured point cloud of the gantry. The measured point cloud of the gantry is then registered with the theoretical point cloud of the gantry building information model using an iterative nearest point algorithm. The deformation deviation map of each component is output. Nodes with deformation deviations exceeding the preset deformation threshold are triggered with audible and visual warnings and recorded as nodes with excessive deformation.

[0012] During construction, point cloud acquisition, iterative nearest point algorithm registration, and identification of nodes with excessive deformation are repeated periodically. Work is stopped for identified nodes with excessive deformation. At the same time, it is checked whether the preload of the adjustable threaded prestressing device is lower than the design preload. If it is lower than the design preload, the preload is supplemented by applying a torque wrench. After the inclined brace is restored to the tensile working state, construction continues.

[0013] The horizontal tie rod refers to a horizontal straight rod that connects two adjacent gantry columns along the transverse direction of the trolley, and is used to constrain the lateral displacement of the columns in the out-of-plane direction.

[0014] The cross scissor bracing refers to diagonal members arranged in a cross manner between two adjacent portal frames. The horizontal tie rod and the cross scissor bracing together reduce the out-of-plane calculated length of the column to the spacing between the frames.

[0015] The adjustable threaded prestressing device refers to a sleeve and screw assembly with reverse threads welded to both ends of the diagonal brace. By rotating the sleeve, the screw insertion depth can be changed to apply a quantifiable axial preload to the diagonal brace.

[0016] The principle for determining the design preload is that, under the condition of maximum lateral working load on the gantry, the axial force of the diagonal brace is always positive, i.e., under tension.

[0017] The diagonal brace is 1.6m long and is located on the mast column near the front of the vehicle.

[0018] The symmetrical segmented skip welding process refers to dividing the weld of the same component into several equal-length segments, performing welding symmetrically and synchronously on both sides of the same cross section, and completing each segment sequentially in an interval skipping order.

[0019] In the vibration aging treatment, the excitation frequency is selected in the range of 5 to 20 Hz, and the continuous treatment time is 30 min.

[0020] The target value of the peak value of the welding residual tensile stress is 150 MPa. The blind hole method refers to a detection method that drills a small-diameter blind hole at the weld near the key node of the gantry and calculates the magnitude of the welding residual tensile stress by measuring the strain release around the hole.

[0021] The vehicle-mounted 3D laser scanner takes no more than 3 minutes to collect point cloud data of the gantry structure.

[0022] The portal frame building information model theoretical point cloud refers to the standard point cloud dataset generated by virtual scanning of a three-dimensional building information model established based on portal frame structural design drawings.

[0023] The iterative nearest point registration algorithm refers to finding the optimal spatial transformation relationship between the measured point cloud of the gantry and the theoretical point cloud of the gantry building information model through repeated iterations, so that the two sets of point clouds coincide optimally in spatial position, and then calculate the deviation point by point and generate the deformation deviation map of each component.

[0024] The preset deformation threshold is determined based on the gantry structure design documents and is the upper limit of the allowable deformation of each component.

[0025] The term "over-limit deformation node" refers to a node where the deformation deviation of each component exceeds a preset deformation threshold. After triggering an audible and visual warning, the node must be manually checked and reinforced.

[0026] The key nodes of the gantry refer to the welded connection nodes at the intersections of the columns and beams, the columns and diagonal braces, the columns and horizontal tie rods, and the columns and cross scissor braces.

[0027] This invention eliminates lateral stiffness lag defects at the structural level by introducing horizontal tie rods and cross scissor braces to reduce the out-of-plane calculated length of the columns during the initial structural fabrication stage of the gantry, and by introducing an adjustable threaded prestressing device in the diagonal bracing system to apply the design preload, so that the diagonal bracing is in a tensile working state under zero external load. Furthermore, it improves the compressive stability of the components by uniformly distributing welding heat input through a symmetrical segmented skip welding process and significantly reducing the peak value of residual tensile stress during welding through vibration aging treatment. Finally, it uses a vehicle-mounted 3D laser scanner to collect the measured point cloud of the gantry and performs iterative nearest-point algorithm registration with the theoretical point cloud of the gantry's building information model, dynamically monitoring and issuing over-limit warnings for the deformation deviation of each component throughout the construction process.

[0028] Traditional gantry systems rely on static visual inspection and sampling weld measurements, which cannot cover the dynamic deformation process under vibration conditions. Joint loosening and residual stress accumulation cause substantial damage to structural stability before they are detected. This invention eliminates node hysteresis response through a prestressed active stiffness compensation mechanism and reduces the weakening effect of residual stress on the critical stability force through vibration aging treatment, making the actual stiffness of the gantry structure under disturbance conditions more consistent with the design stiffness. Furthermore, a point cloud dynamic monitoring closed loop keeps deformation deviations consistently within a preset deformation threshold, achieving quantitative control over the risk of structural instability.

[0029] In summary, this invention solves the technical problem mentioned in the background art: the deformation of the I-beam gantry system in small-section tunnels cannot be detected and actively controlled in real time during welding construction and vibration operations, resulting in the inability to quantify and manage the risk of structural instability. Attached Figure Description

[0030] Figure 1 This is a flowchart of the method of the present invention.

[0031] Figure 2 Side view of the excavation trolley for the diversion tunnel of the lower reservoir.

[0032] Figure 3 A top view of the excavation trolley for the diversion tunnel of the lower reservoir.

[0033] Figure 4 This is a front view of the excavation trolley for the diversion tunnel of the lower reservoir. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below.

[0035] like Figure 1 The diagram shown is a flowchart of a deformation control method for a small-section tunnel drilling and blasting gantry system provided by the present invention. This method includes the following steps:

[0036] S10. Based on the clear dimensions of the small-section tunnel, three portal frames are welded from I18 I-beams. The spacing between adjacent portal frames is set to 1.9m. Horizontal tie rods and cross scissor braces are arranged in the transverse direction between the adjacent portal frames to reduce the out-of-plane calculated length of the column to the spacing between the portal frames, thereby obtaining an initial portal frame structure with lateral constraints.

[0037] S20. At the mast column near the front of the vehicle, a 1.6m long diagonal brace is set with I18 I-beams. An adjustable threaded prestressing device is installed at each end of the diagonal brace. The design preload is applied to the adjustable threaded prestressing device by a torque wrench so that the diagonal brace is in a tensile working state under zero external load, forming a diagonal brace system with initial prestress.

[0038] S30. The initial structure of the gantry described in S10 and the diagonal bracing system described in S20 are welded together. 306 carbon steel welding rods are used to perform triangular welding on all nodes. The weld height is not less than 10mm. Welding is performed simultaneously on both sides of the same cross section. Each segment is welded in sequence according to the symmetrical segmented skip welding process to obtain the gantry structure with overall welding.

[0039] S40. Vibration aging treatment is performed on the portal frame structure that has been welded as described in S30: Vibrators are arranged near the key nodes of the portal frame, and dynamic excitation is applied to the key nodes of the portal frame at the structural resonant frequency in the range of 5 to 20 Hz for 30 minutes to reduce the peak value of the welding residual tensile stress at the key nodes of the portal frame; after the vibration aging treatment is completed, the peak value of the welding residual tensile stress at the key nodes of the portal frame is sampled and checked using the blind hole method to confirm that the peak value of the welding residual tensile stress has dropped to below 150 MPa, and a portal frame structure with the required residual stress is obtained.

[0040] S50. Install the gantry structure with the residual stress meeting the requirements described in S40 onto the automobile chassis. After the trolley is in place, use an on-board 3D laser scanner to collect point cloud data of the gantry structure. The point cloud collection time shall not exceed 3 minutes to obtain the measured point cloud of the gantry. The measured point cloud of the gantry is registered with the theoretical point cloud of the gantry building information model using an iterative nearest point algorithm. Output the deformation deviation map of each component. Trigger an audible and visual warning for nodes whose deformation deviation exceeds the preset deformation threshold and record them as nodes with excessive deformation.

[0041] S60. During construction, the point cloud acquisition, iterative nearest point algorithm registration, and over-limit deformation node identification process described in S50 are repeated periodically. Work is stopped for identified over-limit deformation nodes. At the same time, it is checked whether the preload of the adjustable threaded prestressing device is lower than the design preload. If it is lower than the design preload, the preload is supplemented by applying a torque wrench. Construction can only continue after the inclined brace is restored to the tensile working state.

[0042] In S10, the horizontal tie rod refers to a horizontal straight member that connects two adjacent gantry columns laterally along the trolley, used to constrain the lateral displacement of the columns in the out-of-plane direction; the cross scissor brace refers to an oblique member arranged in a cross manner between two adjacent gantry columns, used to provide lateral stiffness in the longitudinal plane; the out-of-plane calculated length of the column refers to the equivalent length used to measure the lateral buckling risk of the column in the stability check. After being reduced to the column spacing, the out-of-plane slenderness ratio of the column can meet the stability check requirements and prevent overall lateral torsional buckling instability.

[0043] The adjustable threaded prestressing device mentioned in S20 refers to a sleeve and screw assembly with reverse threads welded to both ends of the diagonal brace. By rotating the sleeve, the screw insertion depth is changed to apply a quantifiable axial prestressing force to the diagonal brace. The principle for determining the design prestressing force is: under the condition of the gantry being subjected to the maximum lateral working load, the axial force of the diagonal brace is always positive, i.e., under tension, thereby eliminating the response lag of the node from the relaxed state to the stressed state, reducing the lateral displacement of the gantry by 40% compared to the state without prestressing, and reducing the fatigue stress amplitude at the node.

[0044] The symmetrical segmented skip welding process described in S30 refers to dividing the weld of the same component into several equal-length segments. During welding, the segments are symmetrically and synchronously performed on both sides of the same cross section, and each segment is completed in a skipping sequence rather than continuously advancing unidirectionally along the weld. This is to ensure that the heat input of each weld segment is evenly distributed on the component, avoid heat accumulation in local areas, thereby controlling the axial bending deformation of the column and reducing the peak value of residual tensile stress in welding.

[0045] Among them, the vibration aging treatment mentioned in S40 refers to applying a dynamic periodic load to the overall welded gantry structure using a vibrator. When the excitation frequency is close to the structural resonant frequency, micro-plastic deformation occurs at the key nodes of the gantry, causing the welding residual tensile stress formed during the welding process to relax, diffuse, and redistribute to the surrounding area. After the treatment, the peak value of the welding residual tensile stress is reduced from more than 350 MPa to less than 150 MPa, and the critical stability force of the gantry structure under compression conditions is correspondingly increased. The blind hole method refers to drilling a small-diameter blind hole at the weld near the key node of the gantry and calculating the magnitude of the welding residual tensile stress by measuring the strain release around the hole.

[0046] In S50, the theoretical point cloud of the portal frame building information model refers to a standard point cloud dataset generated by virtual scanning of a 3D building information model established based on the portal frame structural design drawings, used for comparison with the measured point cloud of the portal frame; the iterative nearest point algorithm registration refers to repeatedly iterating to find the optimal spatial transformation relationship between the measured point cloud of the portal frame and the theoretical point cloud of the portal frame building information model, so that the measured point cloud of the portal frame and the theoretical point cloud of the portal frame building information model coincide optimally in spatial position, and then calculating the deviation point by point and generating a deformation deviation map of each component; the preset deformation threshold refers to the upper limit of the allowable deformation of each component determined according to the portal frame structural design documents; the over-limit deformation node refers to the node where the deformation deviation of each component exceeds the preset deformation threshold.

[0047] The specific implementation method of step S10 is as follows: First, based on the clear dimensions of the tunnel excavation section, determine the control dimensions of the transverse width and height of the gantry. Use national standard I18 I-beams as the uniform cross-section specification for all components. Weld three independent gantry frames, each consisting of two columns, a horizontal beam, and a longitudinal beam, to form a frame. The spacing between adjacent gantry frames is uniformly set at 1.9m. After the three gantry frames are in place, horizontal tie rods are arranged along the transverse direction of the trolley between the corresponding columns of adjacent gantry frames. The horizontal tie rods are arranged at intervals not exceeding the spacing between frames in the column height direction to ensure the continuity of lateral constraints at each support point. Simultaneously, cross scissor bracing is arranged diagonally within the rectangular plane enclosed by adjacent gantry frames. The horizontal tie rods and cross scissor braces are all connected to the columns with fully penetrated joints, so that the out-of-plane calculated length of the columns is reduced from the total height of the gantry structure to the spacing of adjacent frames of 1.9m. This controls the out-of-plane slenderness ratio of the columns within the allowable range of stability verification, and obtains the initial gantry structure with lateral constraints.

[0048] The specific implementation of step S20 is as follows: At the location of the gantry column closest to the front of the vehicle, where lateral disturbance is greatest, the node between the column and the crossbeam is selected as the installation position for the diagonal brace. A 1.6m long diagonal brace is cut from I18 I-beams. The angle between the diagonal brace and the column is determined based on the gantry geometry, ensuring that the diagonal brace is primarily under axial tension when subjected to lateral forces. Adjustable threaded prestressing devices are welded to both ends of the diagonal brace. These devices consist of a sleeve with a left-hand thread and a screw with a right-hand thread. Rotating the sleeve simultaneously tightens the screws on both sides, applying axial prestress to the diagonal brace. The prestressing force is calculated based on the gantry's maximum lateral working load condition, requiring that the axial force of the diagonal brace not be lower than zero under the most unfavorable load combination, i.e., always maintaining a tensile state. A calibrated torque wrench is used when applying the prestressing force, controlling the amount applied based on the conversion relationship between torque and axial force. The initial torque value is recorded as a reference value for subsequent inspections, forming a diagonal brace system with initial prestress.

[0049] The specific implementation of step S30 is as follows: When welding the initial structure of the gantry and the diagonal bracing system as a whole, all nodes are welded using 306 carbon steel welding rods, with triangular welds and a weld height of not less than 10mm. The welding sequence strictly follows the symmetrical segmented skip welding process: First, each weld is divided into several equal-length segments along its length, with a segment length generally between 150 and 200mm; during welding, two welders are arranged to work simultaneously on the welds on both sides of the same cross-section to eliminate lateral bending deformation caused by welding on one side; the segments are completed in an alternating skip sequence, i.e., welding segments 1, 3, and 5 first, then welding segments 2, 4, and 6, so that the heat input is evenly distributed along the entire length of the component, avoiding the accumulation of heat in local cross-sections that could cause axial bending deformation. After each weld is completed, the slag is removed, and the welder self-inspects and confirms that there are no defects such as undercut or arc craters before moving on to the next node. After the key nodes are completed, the appearance and dimensions are checked to obtain the overall welded gantry structure.

[0050] The specific implementation of step S40 is as follows: Vibration aging treatment is applied to the completed gantry structure. Vibration aging treatment utilizes dynamic cyclic loading to induce micro-plastic deformation within the component, allowing the high-peak welding residual tensile stress generated during welding to relax and diffuse towards the surrounding low-stress area through micro-dislocation movement, thereby reducing the peak value of the welding residual tensile stress and making the residual stress field more uniform. During construction, exciters are placed near the key nodes of the gantry. The resonant frequencies of each order of the gantry structure are determined by frequency scanning, and the frequency with the largest response amplitude in the range of 5–20 Hz is selected as the excitation frequency. Dynamic excitation is continuously applied to the key nodes of the gantry for 30 minutes. After vibration aging treatment, the peak value of welding residual tensile stress at key nodes of the gantry was randomly checked using the blind hole method: small-diameter blind holes with a diameter of 1.5 to 2.0 mm and a depth of 2 mm were drilled near the heat-affected zone of the weld, triaxial strain rosettes were attached, and the strain release before and after drilling was measured. The value of welding residual tensile stress was calculated based on the plane stress theory of elasticity. When the sampling results confirmed that the peak value of welding residual tensile stress dropped to below 150 MPa, the gantry structure was judged to meet the requirements for residual stress.

[0051] The specific implementation of step S50 is as follows: The gantry structure with sufficient residual stress is installed and fixed onto the vehicle chassis and driven into the construction position. After the trolley is positioned and the hydraulic locking system is activated, a vehicle-mounted 3D laser scanner installed on the trolley is used to collect a full-coverage point cloud of the gantry structure. A single scan takes no more than 3 minutes, obtaining a measured point cloud of the gantry containing the spatial coordinates of each component. The measured point cloud of the gantry is imported into comparison software. Using the theoretical point cloud of the gantry's building information model as a benchmark, an iterative nearest-neighbor algorithm is used for spatial registration. The iterative nearest-neighbor algorithm repeatedly searches for the nearest neighbor pairs in the two sets of point clouds, constructs a rigid body transformation matrix, and iteratively updates it until the root mean square distance error between the two sets of point clouds converges to a preset registration accuracy threshold, typically 0.5 mm, thus achieving optimal spatial alignment. After registration, the deviation is calculated point by point, and the deformation deviation map of each component is output with color. For nodes in the deviation diagram where the deformation deviation exceeds a preset deformation threshold, the system automatically triggers an audible and visual warning. The preset deformation threshold reference value is that the lateral deformation of the column does not exceed 1 / 300 of the calculated length of the component, and the node is recorded as an over-limit deformation node.

[0052] The specific implementation of step S60 is as follows: During the entire drilling and blasting construction process, after each drilling cycle is completed or at intervals not exceeding 4 hours, the entire process of point cloud acquisition, iterative nearest point algorithm registration, and identification of nodes exceeding the limit deformation described in step S50 is repeated periodically to form a dynamic monitoring closed loop. Any identified nodes exceeding the limit deformation are immediately shut down for processing. Technicians manually verify the connection status of the horizontal tie rods, cross scissor braces, and diagonal braces of the identified nodes. Simultaneously, it is checked whether the current torque value of the adjustable threaded prestressing device is lower than the initial reference value. If it is lower than the initial reference value, it is determined that the preload has decayed. A torque wrench is used to supplement the preload to the torque value corresponding to the designed preload, restoring the diagonal braces to their tensile working state. After manual verification confirms that the gantry structure is normal and the diagonal braces have returned to their tensile working state, point cloud acquisition and registration comparison are performed again. Construction can only continue after confirming that the deformation deviation of each component does not exceed the preset deformation threshold.

[0053] It should be explained that the key technical ideas and synergistic effects of this invention are as follows.

[0054] This invention incorporates three key technical approaches. The first key approach is a column lateral stability enhancement mechanism based on spatial constraint reduction. Traditional small-section gantry systems, due to clearance limitations, rely solely on fixed diagonal braces for lateral constraint, resulting in a column out-of-plane calculated length equal to the full height of the gantry and a low overall critical load for lateral torsional buckling. This invention, by introducing horizontal tie rods and cross scissor braces between trusses, compresses the unsupported lateral length of the column to the truss spacing, significantly increasing the critical load inversely proportional to the square of the calculated length, thus fundamentally eliminating the risk of lateral instability under small-section clearance constraints.

[0055] The second key technical approach is a bracing response hysteresis elimination mechanism based on prestressed active stiffness compensation. Traditional rigid welded bracing suffers from initial node loosening. When subjected to lateral disturbances, it must first complete the deformation process from relaxation to stress, and this hysteresis prevents the gantry's lateral stiffness from being fully utilized in the early stages of the disturbance. This invention pre-establishes tensile internal forces in the bracing using an adjustable threaded prestressing device, allowing the bracing's stiffness contribution to be fully utilized at the first moment of disturbance, achieving active compensation for lateral stiffness, while simultaneously reducing the fatigue stress amplitude of the nodes under alternating loads. The third key technical approach is a deformation quantification and control closed-loop mechanism based on dynamic point cloud comparison. Traditional construction relies on pre-construction static verification, which cannot cover the dynamic deformation accumulation under vibration conditions. However, the monitoring closed loop composed of a vehicle-mounted 3D laser scanner and iterative nearest-point algorithm registration transforms implicit deformation into quantifiable deviation indicators, achieving full-coverage, non-contact, and periodic dynamic control. The synergistic effect of the three technical approaches is as follows: the spatial constraint mechanism determines the upper limit of the structure's ultimate bearing capacity; the prestressed active compensation mechanism ensures that the structure's stiffness is fully utilized under actual disturbance conditions; and the dynamic monitoring closed loop continuously verifies the implementation effect of both and triggers corrective actions. Together, the three constitute a complete technical chain from the realization of design stiffness to the control of the construction process, enabling the gantry system to always maintain within the design-allowed deformation range under the superposition of vibrations in small cross-section openings.

[0056] It should be noted that this invention also solves the following technical problems: In small-section tunnel drilling and blasting construction, the peak value of residual tensile stress after welding of the gantry system is too high, weakening the critical stability force of the component under compression conditions. Traditional post-weld heat treatment processes are costly and difficult to implement under tunnel working conditions. This invention employs a vibration aging treatment method, applying dynamic excitation matching the structural resonance frequency near key nodes of the gantry using a vibrator. This utilizes a micro-plastic deformation mechanism to reduce the peak value of residual tensile stress from over 350 MPa to below 150 MPa. Furthermore, this method requires no heating equipment and can be completed directly inside the tunnel, thus solving the technical problem of insufficient applicability of post-weld residual stress treatment processes inside tunnels. This invention also solves the technical problem that the attenuation of preload at the inclined brace nodes cannot be detected in a timely manner under vibration operations combined with slippery slope conditions. By introducing a periodic inspection mechanism for the torque value of the adjustable thread prestressing device in step S60, using the initial reference torque value as the basis for judgment, and immediately applying additional preload when torque attenuation is detected, the maintenance of the preload of the diagonal brace is incorporated into the same periodic control process as the point cloud dynamic monitoring, thereby realizing the proactive perception and timely repair of preload attenuation.

[0057] Specifically, the principle of this invention is as follows: The fundamental reason why this invention can solve the above-mentioned technical problems lies in the fact that, in response to the strict constraints on the lateral dimensions of the gantry due to the clearance of small-section tunnels, the horizontal tie rods and cross scissor braces form a spatial truss mechanism between adjacent trusses, compressing the lateral support spacing of the columns from the full height to the truss spacing, so that the out-of-plane slenderness ratio meets the stability verification requirements, thus eliminating the root cause of lateral torsional buckling instability from a spatial topological perspective. The adjustable threaded prestressing device pre-establishes tensile internal forces in the diagonal braces, so that the stiffness contribution of the diagonal braces is fully utilized at the first moment when the gantry is subjected to lateral disturbance. Its principle is equivalent to eliminating geometric nonlinear initial defects through preloading in prestressed structures. The symmetrical segmented skip welding process utilizes the principle of thermo-elastic-plastic mechanics to disperse the heat source and symmetrically balance the shrinkage deformation of each weld segment, so that the overall residual stress field tends to be uniform and low. Vibration aging treatment uses dynamic cyclic loading to induce local micro-plastic deformation, relaxing the peak residual tensile stress to a level that does not affect the critical force for component stability, thereby restoring the ideal stress state assumed in the design calculation. Based on the aforementioned proactive anti-deformation measures, the dynamic monitoring closed loop formed by the vehicle-mounted 3D laser scanner and the iterative nearest point algorithm registration, through full-coverage, non-contact quantitative comparison of the measured point cloud and the theoretical point cloud of the gantry building information model in 3D space, transforms implicit deformation into quantifiable deviation indicators. This transforms deformation control from post-construction static verification to real-time dynamic control during construction, fundamentally preventing the possibility of excessive deformation accumulating to the point of endangering overall stability before it is discovered. This is precisely the inherent basis for the logical consistency of the present invention's solution and its ability to reliably solve this technical problem.

[0058] The following provides a specific embodiment 1 of the present invention, and the specific implementation of each step in this embodiment 1 is described in detail below.

[0059] To illustrate the application effects of this invention, technicians applied its method in the construction project of a diversion tunnel for the lower reservoir of a pumped storage power station. The diversion tunnel had a clear cross-sectional width of 4.6m and a clear height of 5.2m, with a maximum longitudinal slope of 3.8%. The surrounding rock was mainly weakly weathered granite, with localized fissures and water seepage. The relative humidity inside the tunnel remained above 85% for an extended period, providing a typical combination of high humidity, high vibration, and sloping unfavorable working conditions for deformation control of the gantry system.

[0060] During the initial structural fabrication phase of the gantry, technicians selected standard I18 I-beams to weld three gantry frames based on the clearance dimensions. The spacing between adjacent gantry frames was set at 1.9m. Horizontal tie rods and cross scissor braces were arranged between the columns of every two adjacent gantry frames, reducing the out-of-plane calculated length of the columns from the total gantry height of 5.2m to 1.9m. The out-of-plane slenderness ratio of the columns was reduced from exceeding the specification limit to meeting the stability verification requirements. At the gantry column near the front of the train, a 1.6m long diagonal brace was cut from I18 I-beams. An adjustable threaded prestressing device was installed at each end of the diagonal brace. The design preload was applied using a calibrated torque wrench, and the initial reference torque values ​​are recorded in Table 1.

[0061] Table 1. Initial Preload Torque Recording Table for Adjustable Threaded Prestressing Device for Diagonal Braces

[0062]

[0063] During the overall welding stage, all nodes were welded using a symmetrical segmented skip welding process. Each weld was divided into 150mm equal-length segments, and two welders were assigned to simultaneously weld both sides of the same cross-section. The weld height was controlled between 10 and 12mm, and 306 carbon steel welding rods were used. After welding, vibrators were placed near the critical nodes of the gantry. The first-order resonant frequency of the gantry structure was determined to be 11.3Hz through frequency scanning. Dynamic excitation was continuously applied to the critical nodes of the gantry at 11.3Hz for 30 minutes to complete the vibration aging treatment. The peak value of the welding residual tensile stress at the eight critical nodes of the gantry was randomly inspected using the blind hole method. The inspection results are shown in Table 2.

[0064] Table 2. Spot check results of peak residual tensile stress in welding of key nodes of the gantry before and after vibration aging treatment.

[0065]

[0066] As shown in Table 2, the peak residual tensile stress of all eight key nodes of the gantry decreased to below 150 MPa after vibration aging treatment, meeting the requirements. Therefore, the gantry structure was determined to be a gantry structure with satisfactory residual stress. After the trolley was installed and positioned in its workstation, the hydraulic locking system was activated, and the vehicle-mounted 3D laser scanner was used to perform the first point cloud acquisition of the gantry structure. A single scan took 2.4 minutes, obtaining the measured point cloud of the gantry. The measured point cloud of the gantry was then registered with the theoretical point cloud of the gantry building information model established based on the design drawings using an iterative nearest-point algorithm. The registration accuracy converged to 0.5 mm, and the deformation deviation diagram of each component was output, as shown below. Figure 4 As shown, the initial scan results indicate that the deformation deviation of each component did not exceed the preset deformation threshold (the lateral deformation of the column does not exceed 1 / 300 of the calculated length, i.e., 6.3mm), and all components are in normal condition.

[0067] During subsequent construction, point cloud acquisition and iterative nearest-point algorithm registration were repeated after each drilling cycle, for a total of 18 construction cycles. In the point cloud comparison after the 7th construction cycle, the system identified a deformation deviation of 6.8mm at the midpoint of the left column, exceeding the preset deformation threshold of 6.3mm, triggering an audible and visual warning, recording it as an over-limit deformation node, and halting work. Technicians manually verified the node and checked the torque value of diagonal brace 1, measuring a current torque of 172 N·m, lower than the initial reference torque value of 185 N·m, indicating a decrease in preload. The preload was then supplemented to 186 N·m using a torque wrench, restoring the diagonal brace to its tensile working state. After supplementing the preload, point cloud acquisition and registration were repeated, confirming that the deformation deviation at this node had recovered to 4.1mm, below the preset deformation threshold, and construction continued. The audible and visual warning was triggered twice during the 18 construction cycles, both times returning to normal after work stoppage. No overall lateral instability occurred in the gantry structure throughout the entire construction period. The overall shape of the trolley moving and positioning inside the tunnel is as follows Figure 2 As shown, the top view arrangement of the trolleys is as follows: Figure 3 As shown, by Figure 2 and Figure 3 As can be seen, the horizontal tie rods and cross scissor braces are evenly arranged between the frames, forming a complete spatial constraint network together with the diagonal bracing system, which provides sufficient guarantee for the lateral stability of the portal frame structure.

[0068] The advancements of this invention compared to traditional methods are as follows: Traditional methods rely on manual static measurement, the accuracy of which is limited by personnel skills and the timing of measurement. They cannot detect deformation in real time during vibration operations, and manual measurement only targets a limited number of preset measurement points, failing to achieve full coverage of all component nodes. This invention, through a point cloud dynamic monitoring closed loop constructed using three-dimensional laser scanning and iterative nearest-point algorithm registration, transforms latent deformation into a quantifiable spatial deviation field. This upgrades deformation control from post-event verification of discrete measurement points to real-time dynamic tracking of all components, fundamentally eliminating the possibility of excessive deformation accumulating to the point of endangering the overall structural stability before it is detected. The introduction of a prestressed active stiffness compensation mechanism and vibration aging treatment eliminates the inherent defects of node hysteresis response and high residual stress in traditional gantry systems at both the structural and material levels, making the actual load-bearing capacity of the gantry structure under disturbed conditions more consistent with its design load-bearing capacity.

[0069] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for controlling the deformation of a small-section tunnel drilling and blasting gantry system, characterized in that, Includes the following steps: Based on the clear dimensions of the small-section tunnel, three portal frames are welded from I18 I-beams. The spacing between adjacent portal frames is set to 1.9m. Horizontal tie rods and cross scissor braces are arranged in the transverse direction between adjacent portal frames to reduce the out-of-plane calculated length of the column to the spacing between the portal frames, thus obtaining the initial structure of the portal frame with lateral constraints. At the mast column near the front of the vehicle, diagonal bracing is installed using I18 I-beams. An adjustable threaded prestressing device is installed at each end of the diagonal bracing. The design preload is applied to the adjustable threaded prestressing device using a torque wrench, so that the diagonal bracing is in a tensile working state under zero external load, forming a diagonal bracing system with initial prestress. The initial structure of the gantry and the diagonal bracing system are welded as a whole. All nodes are triangularly welded using 306 carbon steel welding rods. The weld height is not less than 10mm. Welding is carried out simultaneously on both sides of the same cross section. Each segment is welded in sequence according to the symmetrical segmented skip welding process to obtain the gantry structure with overall welding. Vibration aging treatment is performed on the overall welded gantry structure: exciters are arranged near the key nodes of the gantry, and dynamic excitation is applied to the key nodes of the gantry at the structural resonance frequency. After continuous treatment, the peak value of welding residual tensile stress at the key nodes of the gantry is sampled and checked using the blind hole method. It is confirmed that the peak value of welding residual tensile stress has dropped below the target value, and a gantry structure with residual stress meeting the requirements is obtained. The gantry structure with the required residual stress is installed onto the automobile chassis. After the trolley is in place, a vehicle-mounted 3D laser scanner is used to collect point cloud data of the gantry structure to obtain the measured point cloud of the gantry. The measured point cloud of the gantry is then registered with the theoretical point cloud of the gantry building information model using an iterative nearest point algorithm. The deformation deviation map of each component is output. Nodes with deformation deviations exceeding the preset deformation threshold are triggered with audible and visual warnings and recorded as nodes with excessive deformation. During the construction process, the point cloud collection, iterative nearest point algorithm registration, and over-limit deformation node identification process are repeated periodically. Work is stopped at any identified nodes that exceed the deformation limit. At the same time, it is checked whether the preload of the adjustable threaded prestressing device is lower than the design preload. If it is lower than the design preload, the preload is supplemented by applying a torque wrench. After the diagonal brace is restored to its tensile working state, construction can continue.

2. The deformation control method for the small-section tunnel drilling and blasting gantry system according to claim 1, characterized in that, The horizontal tie rod refers to a horizontal straight rod that connects two adjacent gantry columns laterally along the trolley, used to constrain the lateral displacement of the columns in the out-of-plane direction.

3. The deformation control method for the small-section tunnel drilling and blasting gantry system according to claim 2, characterized in that, The cross scissor bracing refers to diagonal members arranged in a cross manner between two adjacent portal frames. The horizontal tie rod and the cross scissor bracing together reduce the out-of-plane calculated length of the column to the spacing between the frames.

4. The deformation control method for the small-section tunnel drilling and blasting gantry system according to claim 3, characterized in that, The adjustable threaded prestressing device refers to a sleeve and screw assembly with reverse threads welded to both ends of the diagonal brace. By rotating the sleeve, the screw insertion depth can be changed to apply a quantifiable axial preload to the diagonal brace.

5. The deformation control method for the small-section tunnel drilling and blasting gantry system according to claim 4, characterized in that, The principle for determining the design preload is: under the condition that the gantry is subjected to the maximum lateral working load, the axial force of the diagonal brace is always positive, i.e., under tension.

6. The deformation control method for the small-section tunnel drilling and blasting gantry system according to claim 5, characterized in that, The diagonal brace is 1.6m long and is located on the mast column near the front of the vehicle.

7. The deformation control method for the small-section tunnel drilling and blasting gantry system according to claim 6, characterized in that, The symmetrical segmented skip welding process refers to dividing the weld of the same component into several equal-length segments, performing welding symmetrically and synchronously on both sides of the same cross section, and completing each segment sequentially in an alternating skip order.

8. The method for controlling deformation of a small-section tunnel drilling and blasting gantry system according to claim 7, characterized in that, In the vibration aging treatment, the excitation frequency is selected in the range of 5 to 20 Hz, and the continuous treatment time is 30 min.

9. The deformation control method for the small-section tunnel drilling and blasting gantry system according to claim 8, characterized in that, The target value of the peak value of the welding residual tensile stress is 150 MPa. The blind hole method refers to a detection method that drills a small-diameter blind hole at the weld near the critical node of the gantry and calculates the magnitude of the welding residual tensile stress by measuring the strain release around the hole.

10. The deformation control method for a small-section tunnel drilling and blasting gantry system according to claim 9, characterized in that, The vehicle-mounted 3D laser scanner takes no more than 3 minutes to collect point cloud data of the gantry structure.

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