A reinforcing steel bar cooperative 3D printing device and method for TBM lining construction

Abstract

The application discloses a reinforcing steel bar cooperative 3D printing device and method for TBM lining construction and belongs to the field of additive manufacturing. The device comprises a construction track vehicle, a laser radar, a concrete 3D printing module, a reinforcing steel bar laying module and a control module. The control module constructs a lining three-dimensional model according to tunnel topography data scanned by the laser radar, extracts a principal stress trace through finite element analysis, and generates a reinforcing steel bar arrangement path and a concrete printing track based on the principle of stress orientation. The concrete 3D printing module prints a concrete layer according to the track, the reinforcing steel bar laying module lays reinforcing steel bars along the reinforcing steel bar arrangement path, and through pushing and embedding operations, hot air heating operations and an adaptive spraying strategy based on binocular camera monitoring, the reinforcing steel bars are fixed between the concrete layers. Through the cooperative integrated construction of reinforcing steel bar in-situ laying and concrete 3D printing, high performance, full automation and adaptability to harsh environments of the lining construction are realized, and the problems of incompatibility between traditional reinforcing steel cages and 3D printing technology, poor interface bonding quality and high artificial dependence are solved.

Description

Technical Field

[0001] This invention belongs to the field of additive manufacturing, and in particular relates to a 3D printing device and method for steel bar co-printing in TBM lining construction. Background Technology

[0002] Lining is a permanent support structure constructed around the tunnel body using reinforced concrete and other materials to prevent deformation or collapse of the surrounding rock during underground construction. The structural stability and mechanical durability of the lining are prerequisites for the efficient construction of tunnels capable of withstanding long-term loads and external forces such as seismic impacts. Plain concrete, the material used for lining, is a brittle material, prone to cracking and exhibiting poor flexural strength. Currently, engineering projects typically introduce reinforcing materials such as fibers, steel cables, and steel bars to enhance the mechanical properties of concrete. Compared to fibers and steel cables, steel bars possess stronger tensile and flexural strength; therefore, reinforced concrete linings have superior mechanical properties.

[0003] Currently, reinforced concrete lining is mostly precast. Before forming the final support, the lining needs to undergo multiple processes such as production, transportation, and assembly, which still has shortcomings in terms of construction cost, construction complexity, and construction quality. To optimize the construction process, in-situ 3D printing concrete technology has been introduced into tunnel lining construction. By inverting the spatial movement trajectory of the printing module through the geometric dimensions and surface morphology data of the tunnel lining, and controlling key process parameters such as printing speed, nozzle extrusion volume, nozzle diameter, and interlayer height, high-precision and high-quality forming of the lining can be achieved directly during tunnel boring machine (TBM) excavation. This significantly shortens the time and spatial distance from lining production to installation, providing a technical possibility for the integration of TBM excavation and lining construction.

[0004] However, existing in-situ 3D printing lining technology still faces significant challenges. First, the interlayer hardening differences caused by the layer-by-layer printing process easily lead to "cold joints," resulting in insufficient strength of the in-situ 3D printed lining. Furthermore, this method is incompatible with traditional reinforced lining methods that incorporate steel cages: on the one hand, the presence of the steel cage restricts the freedom of movement of the 3D printing nozzle, and may even cause interference between the printing path of the nozzle and the steel cage; on the other hand, due to the lack of a molding vibration process, the interfacial bonding performance between the steel reinforcement and the 3D printed concrete is poor, making it prone to debonding under load, increasing the risk of premature lining failure. Simultaneously, the manufacturing of the steel cage still relies on manual labor for steel cutting, bending, welding, and assembly, resulting in high labor intensity and low automation, indicating significant potential for equipment automation upgrades. In addition, the steel cage manufacturing process currently requires auxiliary production equipment such as steel bending machines, steel binding machines, and mold production lines, which are difficult to integrate into tunnel boring equipment. In harsh environments such as high altitude, extreme cold, and complex geology, prolonged operation poses serious safety and health risks to personnel. Furthermore, the limited transportation and assembly of large equipment further restricts the implementation of traditional prefabricated steel cages and manual construction methods. Therefore, there is an urgent need to develop a highly unmanned lining construction technology and equipment designed for extreme environments, enabling integrated construction from surrounding rock identification and concrete printing to in-situ rebar laying, thereby improving the overall performance and engineering applicability of the lining structure. Summary of the Invention

[0005] To address the aforementioned issues, this invention proposes a rebar-coordinated 3D printing device and method for TBM lining construction. By scanning the geometric morphology of the tunnel cross-section using LiDAR and combining it with a mechanical model, adaptive planning of printing parameters and robotic arm movement trajectory is achieved, thereby ensuring the quality of the lining and the accuracy of the rebar placement. Simultaneously, the concrete 3D printing module and the rebar laying module work collaboratively to achieve fully unmanned construction, avoiding the safety and health risks associated with prolonged manual labor in extreme environments such as high altitude, high ground pressure, and oxygen deficiency, thus ensuring the stability, safety, and project quality of the construction process.

[0006] The technical solution adopted in this invention is as follows:

[0007] In a first aspect, the present invention proposes a 3D printing device for steel reinforcement collaboration in TBM lining construction, comprising:

[0008] The construction railcar moves along the tunnel axis via a construction rail inside the tunnel, and is equipped with a lidar for scanning the tunnel shape.

[0009] The concrete 3D printing module is mounted on a construction railcar via an independent robotic arm and is used to print concrete layers along the concrete printing trajectory.

[0010] The rebar laying module is mounted on a construction track vehicle via an independent robotic arm. It consists of a binocular camera integrated on the base, a rebar clamping and pressing unit, and a rebar auxiliary laying unit. The rebar clamping and pressing unit is used to push and press the rebar into the newly printed concrete layers along the rebar layout path. The rebar auxiliary laying unit accelerates the curing of the rebar-concrete interface through hot air heating and selective spraying. The binocular camera is used to monitor the morphology of the rebar-concrete interface.

[0011] The control module is used to construct a 3D model of the lining based on the tunnel topography data scanned by lidar, extract the principal stress trajectories through finite element analysis, and generate the steel reinforcement layout path and concrete printing trajectory based on the stress-oriented principle; and to control the collaborative printing work of the concrete 3D printing module and the steel reinforcement laying module.

[0012] Preferably, the concrete 3D printing module includes a stepper motor, a hopper, and a spiral extruder. The stepper motor drives the spiral extruder to rotate inside the hopper via a rigid coupling. A feeding interface is provided on the side wall of the hopper, and a nozzle is connected to the bottom of the hopper. A wall scraper is welded onto the spiral extruder to scrape off the concrete adhering to the hopper wall during rotation.

[0013] Preferably, the rebar clamping and pushing unit in the rebar laying module includes a flexible clamping head, a pushing head, a pushing cylinder, and a clamping cylinder. The flexible clamping head is installed on the base via a transverse sliding groove structure. The output end of the clamping cylinder is connected to the flexible clamping head via a pneumatic interface to drive the flexible clamping head to clamp the rebar. The pushing head is installed on the base via a vertical sliding groove structure and is located between the flexible clamping heads. The output end of the pushing cylinder is connected to the pushing head via a piston rod to drive the pushing head to apply pushing force to the rebar clamped between the flexible clamping heads, so that it is embedded in the concrete layer.

[0014] Preferably, the auxiliary rebar laying unit in the rebar laying module includes a gas and concrete spraying port, a compressed air inlet, a hot air inlet, and a concrete feed inlet. The gas and concrete spraying port is connected to the compressed air inlet, the hot air inlet, and the concrete feed inlet through pipes, respectively, to achieve gas compaction, hot air heating, or concrete supplementary spraying.

[0015] Secondly, this invention proposes a printing method for a steel reinforcement co-printing device for TBM lining construction, comprising the following steps:

[0016] Step 1: The construction track vehicle moves along the construction track inside the tunnel, driving the lidar fixed on it to scan the tunnel cross section, obtain morphological data and construct a three-dimensional model of the lining.

[0017] Step 2: The control module performs finite element mechanical analysis based on the lining 3D model, calculates the direction of the maximum principal stress in each finite element after meshing, sets a stress threshold to screen high stress seed points, uses a clustering algorithm to generate continuous streamlines, and generates a steel reinforcement layout path and concrete printing trajectory based on the streamlines and stress-oriented principle; based on the path and trajectory, the lining 3D model is decomposed into several printing layers using a slicing algorithm, and the printing sequence of each layer is planned.

[0018] Step 3: Following the printing sequence, the concrete 3D printing module prints concrete layers along the concrete printing trajectory using its robotic arm. Then, the rebar laying module lays rebar along the rebar placement path using its robotic arm. Through pushing and embedding operations, hot air heating operations, and an adaptive spraying strategy based on binocular camera monitoring, the rebar is fixed between the concrete layers, achieving collaborative molding.

[0019] Furthermore, in the finite element mechanical analysis, an equivalent surrounding rock load, calibrated by geological survey data, is applied to the outside of the lining three-dimensional model.

[0020] Furthermore, methods for generating continuous streamlines include:

[0021] Mechanical simulation analysis was performed on the meshed 3D model of the lining to extract the maximum principal stress value and the corresponding direction of each finite element.

[0022] Set a principal stress threshold and select high-stress region elements as candidate seed points;

[0023] The KMeans clustering algorithm was used to group the candidate seed points and select representative seed points.

[0024] Starting from the selected seed point, streamline tracing is performed along the principal stress direction of the unit. During the tracing process, the principal stress directions of adjacent units are processed by distance weighted averaging to smooth abrupt changes in the principal stress direction, generating streamlines that reflect the continuous transmission path of the principal stress inside the lining.

[0025] Furthermore, in step 2, generating the reinforcement layout path based on the stress-directed principle includes:

[0026] Based on the continuous streamlines, the main reinforcement path is arranged along the main streamline direction so that the reinforcement direction coincides with the direction of the maximum principal stress.

[0027] In areas of high stress concentration, the number of rebar paths can be increased or the spacing between paths can be reduced, depending on the density of the streamline distribution.

[0028] In areas with high streamline curvature, adjust the bending angle of the rebar path or add auxiliary rebar paths to match the rebar distribution with the changes in streamline curvature.

[0029] Furthermore, in step 2, the process of generating the concrete printing trajectory includes:

[0030] Based on the geometric contour of the lining 3D model, a continuous printing path matching the tunnel surface is generated, and the concrete printing trajectory and the steel reinforcement layout path are spatially coordinated to ensure that the steel reinforcement can form a tight bond within the printed concrete layer.

[0031] Furthermore, in step 3, the adaptive injection strategy includes:

[0032] The surface condition of the concrete in the area where the reinforcing bars are embedded is monitored using a binocular camera.

[0033] If the surface is uniformly moistened and completely covered, curing can be accelerated by hot air heating only;

[0034] If there are interface voids or edge collapses, compact them first by injecting compressed gas, and then heat them with hot air.

[0035] If there are areas lacking material, hot air is used to heat the concrete after it is sprayed in place.

[0036] Furthermore, the pressing and embedding operation and the hot air heating operation include:

[0037] The steel bar clamping and pressing unit is equipped with a drivable pressing head. By driving the pressing head, a controlled pressing force is applied to the steel bar, so that the steel bar is locally pressed into the incompletely hardened concrete layer to a predetermined depth.

[0038] The steel reinforcement auxiliary laying unit is equipped with a hot air inlet. Hot air is introduced through the hot air inlet to locally heat the area where the steel reinforcement is embedded, thereby accelerating the hydration reaction of the concrete and inhibiting the rebound or floating of the steel reinforcement.

[0039] The beneficial effects of this invention are:

[0040] (1) This invention integrates the principal stress traces obtained from finite element mechanics inversion into the 3D printing slicing algorithm. By constructing a three-dimensional finite element model of the lining that conforms to actual working conditions and conducting stress analysis, the distribution characteristics of the principal stress inside the lining are obtained. Through stress-guided path planning, the reinforcement is arranged along the main stress direction, no longer relying on a pre-set regular mesh reinforcement scheme. This method not only significantly improves the overall bearing capacity and crack resistance of the lining, but also reduces unnecessary reinforcement usage, achieving the dual goals of optimizing material utilization and maximizing structural performance.

[0041] (2) This invention transforms the lining forming process from traditional formwork casting to a collaborative process involving a concrete 3D printing module and a rebar laying module. Addressing the challenges of effectively introducing rebar reinforcement and unstable interface quality between rebar and the printed layer in existing concrete 3D printing lining technologies, this invention introduces a rebar laying module that is highly integrated with the 3D printing process. This module embeds the rebar into the interlayer along a preset path before the concrete printed layer has fully hardened. Combined with a multi-logic rebar laying auxiliary unit, it adaptively executes different control strategies such as heating and curing, gas compaction, or localized spraying based on observable conditions such as concrete surface wettability, morphological continuity, and stability. This achieves high-quality collaborative forming of the rebar and concrete. While adapting to different construction conditions and material states, it also ensures stable improvement in laying efficiency and interface quality. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of the overall structure of a steel reinforcement collaborative 3D printing device used for TBM lining construction.

[0043] Figure 2 This is a schematic diagram of the tunnel construction environment;

[0044] Figure 3 This is a schematic diagram showing the assembly relationship between the concrete 3D printing module and the concrete 3D printing robotic arm.

[0045] Figure 4 This is a schematic diagram of a concrete 3D printing module structure;

[0046] Figure 5 This is a schematic diagram showing the assembly relationship between the rebar laying module and the rebar laying robotic arm;

[0047] Figure 6 This is a schematic diagram of the steel reinforcement module structure;

[0048] Figure 7 This is a finite element analysis cloud diagram of the lining load;

[0049] Figure 8 This is a principal stress streamline diagram of the lining load finite element analysis;

[0050] In the diagram, 1-Construction track, 2-Construction track vehicle, 3-LiDAR, 4-Rebar laying robotic arm, 5-Rebar laying module, 6-Concrete 3D printing module, 7-Concrete 3D printing robotic arm, 8-Tunnel ring, 501-Binocular camera, 502-Connecting plate, 503-Flexible clamping head, 504-Pushing head, 505-Pushing cylinder, 506-Gas and concrete injection nozzle, 507-Compressed air inlet, 508-Hot air inlet, 509-Concrete feed inlet, 510-Clamping cylinder, 601-Stepper motor, 602-Motor support, 603-Rigid coupling, 604-Hopper, 605-Nozzle, 606-Spiral extrusion rod, 607-Cylinder wall scraper, 608-Feeding interface, 609-Fixed mounting plate. Detailed Implementation

[0051] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0052] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" 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 also refer to the internal connection of two components. "A plurality of" or "several" means two or more. Those skilled in the art can understand the specific meaning of the above terms in this invention in light of the specific circumstances.

[0053] The overall diagram of the steel reinforcement co-printing 3D printing device for TBM lining construction proposed in this invention is as follows: Figure 1As shown, the system mainly includes a construction railcar 2, a lidar 3, a rebar laying robotic arm 4, a rebar laying module 5, a concrete 3D printing module 6, and a concrete 3D printing robotic arm 7. The construction railcar 2 operates on the construction rail 1 at the bottom of the tunnel. Its bottom-mounted walking mechanism forms a support platform that can move along the tunnel axis. The construction rail 1 provides precise guidance and stable support for the construction railcar 2. The lidar 3 is placed on a tripod, which is fixed to the railcar. It can follow the railcar to scan the tunnel printing surface and generate point cloud data of the actual tunnel cross-section. The bases of the concrete 3D printing robotic arm 7 and the rebar laying robotic arm 4 are firmly installed on the platform surface of the construction railcar 2. The ends of the two robotic arms are respectively equipped with the concrete 3D printing module 6 and the rebar laying module 5. Due to the narrow and complex tunnel construction environment, continuous operation is achieved through railcar movement, avoiding frequent equipment adjustments. The separate design of the robotic arm and module improves flexibility and maintainability. Figure 2 This is a schematic diagram of a tunnel construction environment, illustrating the operation of the steel reinforcement co-printing 3D printing device for TBM lining construction described in this invention inside a tunnel, where steel reinforcement and concrete are co-printed onto the inner wall of tunnel ring 8. During lining construction on the inner wall of tunnel ring 8, the concrete 3D printing module 6 is responsible for depositing concrete material along a planned trajectory, while the steel reinforcement laying module 5 embeds the steel reinforcement between the newly printed concrete layers, achieving integrated molding of reinforced concrete. The confined tunnel construction environment requires equipment with high integration and mobility. This device, through the collaborative operation of two robotic arms, avoids the problem of frequent adjustments to multiple devices in traditional construction.

[0054] like Figure 3 As shown, the concrete 3D printing module 6 is detachably connected via a circumferential threaded hole on the end flange of the concrete 3D printing robotic arm 7. Figure 4As shown, the concrete 3D printing module 6 mainly includes a stepper motor 601, a motor support 602, a rigid coupling 603, a hopper 604, a nozzle 605, a spiral extrusion rod 606, a cylinder wall scraper 607, a feeding interface 608, and a fixed mounting plate 609. Stepper motor 601 is threaded onto motor support 602, which is bolted to mounting plate 609. The output shaft of stepper motor 601 passes vertically through mounting plate 609 and is connected to spiral extrusion rod 606 via rigid coupling 603. Hopper 604 is bolted to mounting plate 609. A side opening in hopper 604 serves as feed inlet 608 for connecting to an external concrete conveying pipeline for continuous material supply. Nozzle 605 is threaded onto outlet of hopper 604. Spiral extrusion rod 606 is vertically installed in hopper 604, and a wall scraper 607 is welded to spiral extrusion rod 606 to thoroughly mix concrete accumulated on the hopper wall during 3D printing. The combination of spiral extrusion rod and wall scraper prevents concrete segregation or clogging, ensuring uniform extrusion. The rigid coupling ensures stable torque transmission, preventing printing interruptions. The nozzle can be replaced according to actual needs and adapted to the construction and forming requirements of different lining conditions. Its special curved surface design ensures smooth and stable extrusion of concrete filaments, improving printing accuracy and efficiency.

[0055] When the concrete 3D printing module 6 is working, freshly mixed concrete is continuously fed into the hopper 604 through the feed interface 608. Under the rotation of the spiral extrusion rod 606 driven by the stepper motor 601, the concrete is evenly conveyed downwards to the nozzle 605. The control system adjusts the speed of the stepper motor 601 according to the real-time printing speed, thereby precisely controlling the amount of concrete extruded and ensuring the uniformity and continuity of the printed filament. As the end of the concrete 3D printing robotic arm 7 moves along the planned trajectory, concrete is extruded from the nozzle 605 and deposited onto the surface of the tunnel ring 8, forming high-precision printed filaments, which are stacked layer by layer to form the lining structure.

[0056] like Figure 5 As shown, the rebar laying module 5 is detachably connected via a circumferential threaded hole on the end flange of the rebar laying robotic arm 4. Figure 6 As shown, this module consists of a binocular camera 501, a connecting plate 502, and two sub-units: a rebar clamping and pushing unit and a rebar auxiliary laying unit. The binocular camera 501, the rebar auxiliary laying unit, and the rebar clamping and pushing unit are all threadedly connected to the connecting plate 502, forming a compact, integrated module. This module can work collaboratively with the concrete 3D printing module 6 according to different cross-sectional dimensions, surrounding rock grades, and construction segment requirements, adapting to different printing rhythms and construction conditions, and achieving coordinated execution of the rebar laying and concrete printing processes.

[0057] The rebar clamping and pressing unit includes a flexible clamping head 503, a pressing head 504, a pressing cylinder 505, and a clamping cylinder 510. The flexible clamping head 503 consists of multiple independently movable sliding columns, capable of accommodating rebars of different diameters and shapes. The clamping cylinder 510 is connected to the flexible clamping head 503 via a pneumatic pipeline. Under the action of an external air pump, it drives the clamping head to extend and retract along a transverse sliding groove, completing the stable clamping of the rebar. After clamping, the rebar moves along the trajectory of the robotic arm's end effector, preparing for subsequent embedding operations. The pressing cylinder 505 is rigidly connected to the pressing head 504 via a piston rod, allowing for reciprocating extension and retraction to apply controllable pushing force to the clamped rebar. After the rebar is positioned, to accommodate multi-angle, high-degree-of-freedom rebar placement, the pressing cylinder 505 drives the pressing head 504 to reciprocate, applying controlled small-amplitude pushing force to the clamped rebar. The pushing force can be adjusted in real time according to the concrete state, allowing the reinforcing bars to be locally pressed and embedded into the pre-hardened concrete layer to a predetermined depth. The embedding depth is adaptively adjusted based on the variability of the concrete, ensuring that the reinforcing bars are anchored between layers without excessively disturbing the printed structure. After pushing and embedding, the reinforcing bars initially bond with the concrete, but the interface stability needs further reinforcement through heating and spraying processes. This invention, by using a flexible reinforcing bar clamping head, achieves in-situ laying of reinforcing bars between 3D printed lining layers, allowing the reinforcing bars to be rationally arranged along the main force direction, significantly enhancing the lining's bending, tensile, and overall load-bearing capacity. It effectively solves the incompatibility problem between in-situ 3D printed lining methods and traditional reinforcing cage reinforcement methods, as well as the problem of easy detachment between reinforcing bars and printed layers in traditional methods, laying the foundation for the overall structural stress.

[0058] The rebar auxiliary laying unit includes a gas and concrete injection port 506, a compressed air inlet 507, a hot air inlet 508, and a concrete inlet 509. The injection port 506 serves as an integrated output terminal, connected to the compressed air inlet 507, hot air inlet 508, and concrete inlet 509 via pressure-resistant hoses or metal pipes. The pipe interfaces can be threaded or quick-connect designs for easy maintenance. Each inlet is equipped with an independent valve and sensor. The compressed air inlet 507 is used to input high-pressure compressed air, directly connected to the injection port 506 via a pipe. Its function is to compact the rebar embedding area with gas when needed, improving the density of the concrete. The hot air inlet 508 is used to input hot air, connected to the injection port 506 via an independent pipe. In this embodiment, the hot air is generated by an external heating system, designed to accelerate the hydration reaction and initial curing of the concrete. The concrete inlet 509 is used to replenish a small amount of freshly mixed concrete. It is connected to the spray nozzle 506 via a conveying pipe, and its function is to provide supplementary spraying when there is a localized shortage of material. The concrete inlet 509 is connected to an external silo, and the amount of supplementary spraying is controlled by a precision pump. The gas and concrete spray nozzle 506 serves as a multi-functional output end. Its internal flow channel design integrates the media from three inlets into a single outlet, enabling multi-functional spraying operations. After the reinforcing bars are embedded, the reinforcing bar auxiliary laying unit immediately initiates heating and selective spraying operations. Its core is the real-time monitoring and multi-logic control of the binocular camera 501, achieving stable in-situ laying and rapid fixation of the reinforcing bars between the 3D printed concrete layers.

[0059] In one specific embodiment of the present invention, a vision-based adaptive control strategy is adopted. After the steel reinforcement is initially embedded, the system monitors the state of the steel reinforcement-concrete interface in real time through a binocular camera 501, and executes corresponding adaptive control strategies according to different surface morphology characteristics:

[0060] Heating-only curing: When the surface of the area where the reinforcing bar is embedded exhibits a uniform, moist gloss, and the outline of the reinforcing bar is continuously covered by concrete with a stable surface morphology, it indicates that the concrete has good plasticity and has already encapsulated the reinforcing bar. The system only inputs hot air through the hot air inlet 508, and locally heats the embedded area through the spray nozzle 506. The heating temperature and time are adjustable, aiming to accelerate the hydration reaction and initial curing of the concrete, and inhibit the rebound or floating of the reinforcing bar. In this embodiment, the hot air temperature is generally 50-70°C, and the embedded area is continuously heated for 10-20 seconds at a wind speed of 5-8 m / s.

[0061] Gas compaction followed by heating: If there are tiny openings or discontinuous textures at the interface, and the concrete experiences edge collapse, it indicates that the concrete and steel reinforcement have initially bonded but there are local interface voids. The system first activates the compressed air inlet 507, and high-pressure gas impacts and compacts the embedded area through the injection port 506, eliminating voids and improving the density of the concrete around the steel reinforcement. Subsequently, the compressed air is shut off, and the hot air inlet 508 is activated for heating and curing. In this embodiment, the pressure of the high-pressure gas is generally 0.4-0.6 MPa, and the gas injection lasts for several seconds.

[0062] Concrete repair spraying followed by heating: When there is a significant material shortage area or a continuous exposed section at the interface, and the surface morphology changes greatly (generally manifested as a stable shadow area), the system activates the concrete repair spraying function. That is, the concrete inlet 509 is activated first, and a small amount of freshly mixed concrete is sprayed into the material shortage area through the spray nozzle 506 to repair and fill the embedded area, achieving filling and wrapping; then the concrete conveying is turned off, and the hot air inlet 508 is activated to heat and solidify.

[0063] This multi-logic control mechanism based on visual feedback integrates the outputs of different logics into a single output port, the gas and concrete spray port 506. Gas is input through compressed air inlet 507 and hot air inlet 508, while concrete is input through concrete feed port 508. Through the aforementioned method of coordinated clamping, pressing, heating, and selective spraying in the reinforcement laying process, stable embedding and reliable fixing of the reinforcement within the printed concrete layers are achieved, effectively ensuring the bonding quality of the reinforcement-concrete interface and suppressing reinforcement springback and floating phenomena. In this embodiment, the binocular camera 501 continuously acquires RGB channel images of the printed strip, and combines image processing algorithms to quantitatively analyze the surface state. The wettability gradient distribution is calculated using the clustering intensity of high-brightness pixels in the image, and the coverage continuity index and edge collapse area ratio are obtained through an edge detection algorithm. This part can be implemented based on existing technologies in the field and will not be elaborated further.

[0064] This invention achieves intelligent path planning guided by principal stress through finite element analysis. Before construction begins, the construction track vehicle 2 moves along the construction track 1 to the work area. A high-precision scan of the tunnel excavation face and the area to be constructed is performed using lidar to acquire real construction topography data, which is automatically converted into a three-dimensional solid model and imported into finite element analysis software to construct a three-dimensional model of the lining. Numerical simulation analysis of the structural stress state is performed within the finite element analysis software, adaptively planning printing process parameters (including nozzle speed, extrusion volume, rebar layout path and density, etc.). The rebar layout path and density are generated by extracting the principal stress traces of the lining. Subsequently, after obtaining the rebar layout path and the three-dimensional model of the lining to be printed, a slicing algorithm is used to decompose the entire lining into several printing layers, generating digital slices with adaptive rebar direction. This forms a slice model for the collaborative printing of rebar and concrete. Subsequent layer-by-layer path planning can be performed based on this slice, thereby generating the concrete printing trajectory and the rebar additive trajectory, ensuring that the concrete material uniformly covers the rebar. Figure 7 As shown, this invention establishes a three-dimensional finite element model of the lining based on ABAQUS software, with structural dimensions strictly determined according to the actual working conditions of a TBM tunnel. To realistically simulate the interaction between the surrounding rock and the lining structure, an equivalent surrounding rock load calibrated by geological survey data is applied outside the model, and boundary conditions conforming to actual constraints are set. The concrete material adopts a concrete damage-plastic (CDP) constitutive model to accurately characterize the nonlinear mechanical behavior of concrete under alternating tension and compression. This invention identifies key stress zones in the lining by performing a three-dimensional scan of the actual construction surface and combining it with finite element analysis, thereby planning the reinforcement layout path and density to achieve structural optimization of the reinforcement arrangement. This strategy can reduce redundant reinforcement usage, improve stress efficiency, improve interface bonding quality, and significantly enhance the overall safety and reliability of the lining structure.

[0065] After completing the finite element analysis, the system first extracts the maximum principal stress value and corresponding principal stress direction for each element, using the centroid position of high principal stress elements as seeds. Then, by setting a principal stress threshold (e.g., selecting the top 15%–30% of high principal stress elements), high-stress regions are screened as candidate streamline seeds, intelligently identifying key stress areas of the structure. To ensure that streamlines cover key stress areas, this invention uses the KMeans clustering algorithm to group candidate seeds based on spatial location and principal stress measurement, selecting several representative seed points to generate continuous streamlines. During streamline generation, to ensure streamline continuity and conformity to actual structural stress, a principal stress direction smoothing algorithm is introduced. This involves using a distance-weighted average of the principal stress directions of neighboring elements to effectively reduce abrupt changes in direction. Simultaneously, streamline points are located within structural elements, ensuring that streamlines accurately reflect the stress transmission direction within the lining, providing a reliable basis for reinforcement arrangement.

[0066] like Figure 8As shown, the final generated principal stress streamlines clearly demonstrate the force flow distribution characteristics within the structure. Based on this streamline map, the arrangement of the foundation reinforcement is optimized: First, the main reinforcement bars are arranged along the main streamline direction, ensuring that the direction of the reinforcement bars matches the direction of the maximum principal stress, thereby guaranteeing that the reinforcement bars can effectively bear tensile stress. In areas of high stress concentration, the number of reinforcement bars is increased or the spacing is reduced according to the density of streamlines to achieve localized reinforcement; in areas with large streamline curvature, the bending angle of the reinforcement bars is adjusted or auxiliary reinforcement bars are added to match the reinforcement bar path with the streamline curvature, ensuring continuous and uniform force transmission. Similarly, in low-stress areas, the number of reinforcement bars can be reduced or the spacing can be extended. Through the above strategies, the reinforcement arrangement not only closely matches the actual stress direction of the structure but also balances material utilization efficiency and the overall load-bearing capacity of the structure, significantly improving the load-bearing efficiency and construction feasibility of the lining structure.

[0067] The concrete 3D printing module 6 first prints concrete layers, responsible for stably extruding printable concrete material along a planned path to achieve high-precision layer stacking. Concrete is continuously supplied by the feed interface 508 of the concrete 3D printing module 5, and is stably conveyed under the action of a spiral extrusion rod 606 driven by a stepper motor 601. The speed of the stepper motor 601 is adjusted by a control system, allowing real-time adjustment of the extrusion speed according to the printing speed to ensure the uniformity of the printed filament. Freshly mixed concrete is extruded through the nozzle 605 and deposited onto the surface of the tunnel ring 8. As the end of the concrete 3D printing robotic arm 7 moves along the planned trajectory, it forms high-precision printed filaments. In this embodiment, the nozzle 605 can adopt a special curved surface design, allowing the extruded concrete filaments to perfectly conform to the tunnel contour.

[0068] After the single-layer concrete printing is completed, the rebar laying module begins operation. Clamping cylinder 510 drives flexible clamping head 503 to clamp the precast rebar, which is then positioned on the printed concrete layer following the trajectory of the rebar laying robotic arm 4. Pushing cylinder 505 drives pushing head 504 to apply controlled pushing force to the rebar, locally pressing it into the not-yet-fully-hardened concrete layer to a predetermined depth. Throughout the process, the control system adaptively adjusts the pushing force, hot air intensity, and spraying strategy based on real-time monitoring data from binocular camera 501 to ensure the quality of the rebar-concrete interface bonding. Through multiple cycles of printing-laying operations, the high-quality manufacturing of the rebar-reinforced 3D-printed lining is finally completed.

[0069] This invention uses finite element analysis and layable constraints such as curvature and accessibility to obtain layable principal stress flow lines as the basis for rebar placement, balancing material utilization and structural load-bearing capacity. Simultaneously, this lining device achieves integrated rapid prototyping of lining 3D printing and in-situ rebar placement, solving the incompatibility problem between traditional lining reinforcement cage placement methods and in-situ 3D printing. The device can adaptively adjust the printing trajectory, extrusion speed, and rebar placement path based on tunnel cross-sectional geometry and the morphology of the printed layer, achieving highly adaptable lining printing under different construction environments. The robotic arm and flexible rebar clamping elements enable in-situ placement and quick disassembly / replacement, supporting unmanned construction. In summary, this invention highly integrates the concept of principal stress-guided steel reinforcement with the printing process, achieving continuous, efficient, and operable steel reinforcement path planning. It provides a complete, highly adaptable, and mechanically superior integrated construction solution for lining structures under TBM tunneling. This laying method is highly compatible with existing concrete 3D printing lining technology, requiring no changes to the material system or construction conditions. It has significant application value in terms of highly adaptable construction in harsh environments, optimization of structural stability, and reduction of reliance on manual labor.

[0070] The above-described embodiments are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention. Those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A printing method for a steel bar collaborative 3D printing device for TBM lining construction, characterized in that the device Comprise: Construction track vehicle (2), through the tunnel construction track (1) along the tunnel axial movement, which is provided with a laser radar (3) for scanning tunnel topography; Concrete 3D printing module (6), through a separate mechanical arm installed on the construction track vehicle (2), for printing concrete layer along the concrete printing track; Steel laying module (5), through a separate mechanical arm installed on the construction track vehicle (2), composed of binocular camera (501) integrated on the base, steel clamping and pushing unit and steel auxiliary laying unit, the steel clamping and pushing unit is used for embedding the steel into the newly printed concrete layer along the steel arrangement path, the steel auxiliary laying unit accelerates the steel-concrete interface solidification by hot air heating and selective injection, the binocular camera (501) is used for monitoring the steel-concrete interface topography; The steel clamping and pushing unit in the steel laying module (5) includes flexible clamping head (503), pushing head (504), pushing cylinder (505) and clamping cylinder (510); the flexible clamping head (503) is installed on the base through the transverse sliding slot structure, the output end of the clamping cylinder (510) is connected with the flexible clamping head (503) through the pneumatic interface, which is used to drive the flexible clamping head (503) to clamp the steel; the pushing head (504) is installed on the base through the vertical sliding slot structure and is located between the flexible clamping head (503), the output end of the pushing cylinder (505) is connected with the pushing head (504) through the piston rod, which is used to drive the pushing head (504) to apply pushing force to the steel clamped between the flexible clamping head (503), so as to embed it into the concrete layer; Control module, for constructing lining three-dimensional model according to tunnel topography data scanned by laser radar (3), and extracting principal stress trace by finite element analysis, generating steel arrangement path and concrete printing track based on stress orientation principle; And, for controlling the cooperation of concrete 3D printing module (6) and steel laying module (5) in printing work; The printing method comprises the following steps: Step 1, the construction track vehicle (2) moves along the construction track (1) in the tunnel, driving the laser radar (3) fixed thereon to scan the tunnel section, obtain topography data and construct a lining three-dimensional model; Step 2, the control module performs finite element mechanics analysis based on the lining three-dimensional model, applies equivalent surrounding rock load calibrated by geological survey data on the outside of the lining three-dimensional model, calculates the maximum principal stress direction in each finite element after grid division, sets stress threshold to screen high stress seed points, generates continuous streamline by clustering algorithm, and generates steel arrangement path and concrete printing track based on the streamline, including: arranging main steel path along the main streamline direction based on the continuous streamline, so that the steel trend is consistent with the maximum principal stress direction; in the high stress concentration area, the number of steel paths or the distance between the paths is increased or reduced according to the density of streamline distribution; in the area with large streamline curvature, the bending angle of steel path is adjusted or auxiliary steel path is added, so that the steel distribution matches the change of streamline curvature. Based on path and trajectory, a slicing algorithm is used to decompose the lining 3D model into several printing layers, and the printing sequence of each layer is planned. Step 3: According to the printing order, the concrete 3D printing module (6) prints concrete layers along the concrete printing trajectory through its robotic arm. Then, the rebar laying module (5) lays rebar along the rebar arrangement path through its robotic arm. The rebar is fixed between the concrete layers by the push-embedding operation, hot air heating operation and adaptive spraying strategy based on binocular camera (501) monitoring, so as to achieve collaborative molding. The adaptive spraying strategy includes: monitoring the concrete surface condition of the reinforcing bar embedded area using a binocular camera (501); if the surface is uniformly moist and completely covered, then curing is accelerated by hot air heating only; if there are interface voids or edge collapses, then compaction is carried out by compressed gas spraying first, followed by hot air heating; if there are areas with material shortage, then hot air heating is carried out after concrete replenishment spraying.

2. The printing method of the steel bar collaborative 3D printing device for TBM lining construction according to claim 1, characterized in that, Methods for generating continuous streamlines include: Mechanical simulation analysis was performed on the meshed 3D model of the lining to extract the maximum principal stress value and the corresponding direction of each finite element. Set a principal stress threshold and select high-stress region elements as candidate seed points; The KMeans clustering algorithm was used to group the candidate seed points and select representative seed points. Starting from the selected seed point, streamline tracing is performed along the principal stress direction of the unit. During the tracing process, the principal stress directions of adjacent units are processed by distance weighted averaging to smooth abrupt changes in the principal stress direction, generating streamlines that reflect the continuous transmission path of the principal stress inside the lining.

3. The printing method of the steel bar collaborative 3D printing device for TBM lining construction according to claim 1, characterized in that, The push-fit operation and hot air heating operation include: The steel bar clamping and pressing unit is equipped with a drivable pressing head. By driving the pressing head, a controlled pressing force is applied to the steel bar, so that the steel bar is locally pressed into the incompletely hardened concrete layer to a predetermined depth. The steel reinforcement auxiliary laying unit is equipped with a hot air inlet. Hot air is introduced through the hot air inlet to locally heat the area where the steel reinforcement is embedded, thereby accelerating the hydration reaction of the concrete and inhibiting the rebound or floating of the steel reinforcement.

4. The printing method of the steel bar collaborative 3D printing device for TBM lining construction according to claim 1, characterized in that, The concrete 3D printing module (6) includes a stepper motor (601), a hopper (604), and a spiral extrusion rod (606). The stepper motor (601) drives the spiral extrusion rod (606) to rotate inside the hopper (604) through a rigid coupling (603). The side wall of the hopper (604) is provided with a feeding interface (608), and the bottom of the hopper (604) is connected to a nozzle (605). A cylinder wall scraper (607) is welded on the spiral extrusion rod (606) for scraping off the concrete adhering to the hopper wall during rotation.

5. The printing method of the steel bar coordinated 3D printing device for TBM lining construction according to claim 1, characterized in that, The steel reinforcement laying module (5) includes a steel reinforcement auxiliary laying unit comprising a gas and concrete injection port (506), a compressed air inlet (507), a hot air inlet (508), and a concrete feed inlet (509). The gas and concrete injection port (506) is connected to the compressed air inlet (507), the hot air inlet (508), and the concrete feed inlet (509) respectively through pipes, for the purpose of achieving gas compaction, hot air heating, or concrete supplementary spraying.

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