A 3D printed tunnel support structure with adaptive large deformation and dynamic adjustment method

Abstract

The present invention belongs to the field of tunnel support, and specifically relates to a 3D-printed tunnel support structure with adaptive large deformation and a dynamic adjustment method. To address the problem that large deformation during current tunnel excavation increases the risk of damage to the support structure, the support structure of the present invention includes several in-situ printed concrete units, grid nodes, steel cables, jacks, and a control system. The tension of the steel cables can be adjusted by the jacks based on data collected by stress and strain sensors, so that the concrete arch deforms as the tunnel deforms. The method adjusts the tension of the steel cables based on real-time monitoring of the stress and strain sensors, causing the concrete arch to change, thereby achieving adaptive adjustment of the concrete arch, achieving stress balance in the concrete arch, reducing the possibility of damage to the concrete arch, and ensuring its structural integrity.

Description

Technical Field

[0001] The present invention belongs to the technical field of tunnel support structures, and specifically relates to a 3D printed tunnel support structure with adaptive large deformation and a dynamic adjustment method. Background Art

[0002] During tunnel excavation, the initial stress balance of the strata is disrupted, leading to stress release in the surrounding rock and deformation of the cavern. To control this deformation and ensure construction safety, primary lining (primary support) is required. This lining is installed immediately after tunnel excavation. It effectively limits deformation of the surrounding rock to a certain extent and guides the redistribution of surrounding rock stress. Secondary lining is installed after deformation of the surrounding rock and primary support has stabilized. Together with the primary support, it forms the tunnel's composite lining structure.

[0003] Currently, there are several primary lining construction technologies to address the large deformation problem during tunnel excavation: First, large deformation anchor technology; this technology uses a specifically configured anchor system to transmit and adjust stress when the tunnel structure undergoes significant deformation, ensuring the overall stability of the support structure. Second, the compressible layer design of the support structure; by introducing an energy-absorbing layer into the tunnel lining, the stress concentration caused by ground movement or structural deformation is alleviated, maintaining the overall stability of the support structure. Third, sliding support technology; this technology allows the support system to produce moderate slip when subjected to stress to adapt to ground convergence and structural deformation, thereby reducing the risk of local damage to the support structure.

[0004] Although the above technologies can to some extent deal with the large deformation problem during tunnel excavation, their main purpose is to prevent damage to the support structure, and they cannot achieve dynamic measurement of the tunnel and feedback adjustment of the support capacity of the support structure.

[0005] Therefore, it is necessary to provide an improved technical solution to the above-mentioned deficiencies in the prior art. Summary of the Invention

[0006] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a 3D printed tunnel support structure with adaptive large deformation and a dynamic adjustment method.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] A 3D-printed tunnel support structure with adaptive large deformation, comprising several concrete units, grid nodes, steel cables, jacks, and a control system; the concrete units are printed in situ on the tunnel site using 3D concrete printing equipment; some of the concrete units are embedded with stress and strain sensors;

[0009] The grid nodes are arranged in a plum blossom shape; the grid nodes include a cross-shaped node cover and a rope clamp fixed to the node cover; the concrete units are long strips, and the concrete units are connected to the node covers of adjacent grid nodes. After all the concrete units are connected to the node covers, a concrete arch with a parallelogram grid is formed;

[0010] The steel cables pass through each grid node along the longitudinal direction of the tunnel, and the grid nodes are fixedly connected to the steel cables via rope clamps; both ends of the steel cables are tensioned and fixed by jacks; all the stress and strain sensors are wirelessly connected to a control system, and the control system adjusts the tension of the steel cables via jacks based on the collected data from the stress and strain sensors, so that the concrete arch frame deforms as the tunnel deforms.

[0011] Furthermore, the node cover is closed at the top and open at the bottom, and four cover pipes are evenly arranged on the circumference, and the cover pipes cover the outer circumference of the end of the concrete unit.

[0012] Furthermore, the overlap distance between the cover pipe and the end of the concrete unit is 2 cm to 3 cm; the diameter of the cover pipe is 1 cm to 3 cm larger than the width of the end of the concrete unit.

[0013] Furthermore, the stress and strain sensor is pre-buried in the middle of the concrete unit, or pre-buried at a position of the concrete unit close to the end of the node cover.

[0014] The present invention also proposes a dynamic adjustment method for the aforementioned adaptive large deformation 3D printed tunnel support structure, comprising the following steps:

[0015] S1, Construction Phase: Grid nodes and 3D-printed concrete units are laid out along the tunnel lining, with stress and strain sensors embedded in the concrete units during printing. After the concrete arch has initially set, steel cables are passed through the grid nodes in sequence along the longitudinal direction of the tunnel. Jacks are fixed to the tunnel surrounding rock to initially tension the steel cables, which are then tightened with rope clamps.

[0016] S2, Adjustment Phase: The cable tension is adjusted based on the real-time monitoring of the stress and strain sensors. When the stress exceeds the normal range, the cable is relaxed and the concrete arch enters a variable state, deforming synchronously with the tunnel to release stress. After the stress reaches the normal range, the cable is tightened to the initial tension using a jack.

[0017] Furthermore, in step S1, after printing four concrete units at an intersection, the grid nodes are aligned with the four concrete units and pressed and fixed; in step S2, the grid nodes at the position where the stress is too large are separated from the tunnel surrounding rock.

[0018] Furthermore, in steps S1 and S2, the initial tensile stress of the steel cable is 40 to 50 kN.

[0019] Furthermore, the normal stress range means that the local stress of the concrete arch is less than half of the compressive strength of the 3D printed concrete.

[0020] Furthermore, when the steel cable is relaxed, the length of the steel cable changes within a range of 20 mm to 50 mm.

[0021] Furthermore, the 3D printed concrete used in the 3D printed concrete unit has an initial setting time of less than 15 minutes and a compressive strength of C50; the steel cable uses a galvanized steel strand with a breaking strength of >150kN; and the length of the concrete unit is 0.5m to 0.8m.

[0022] The working principle of the present invention is:

[0023] The present invention dynamically analyzes the collected stress and strain data through a control system and can automatically adjust the tension of the steel cable according to the stress state of the tunnel structure.

[0024] When the concrete arch is overstressed, the control system adjusts the cables from a taut state to a moderately relaxed state, allowing the concrete arch to deform within a certain range along with the tunnel. By not completely relaxing the cables, excessive deformation is avoided. When the concrete arch stress level is within a safe range, the cables are adjusted from a relaxed state to a taut state, transforming the parallelogram structure composed of concrete units into a stable triangle composed of concrete units and cables. This ensures that deformation is within a controllable range and enables the "telescopic" adjustment of the entire structure.

[0025] The above process involves the deformation mechanism of the two:

[0026] (1) Adaptive tunnel large deformation:

[0027] The state of the steel cable changes from tensioning to relaxation and then to tensioning;

[0028] After monitoring that the concrete arch stress exceeds the normal range, the control jack releases the steel cable (note that the steel cable is not completely relaxed at this time and still has tension). The concrete unit adhered to the tunnel surrounding rock moves with the deformation of the tunnel (note that the tunnel deformation here is actually very small, with typical tunnel deformation displacement on the order of a few millimeters to a few centimeters). The concrete unit mainly moves rigidly (of course, within the strength range of the concrete material, it can undergo some plastic deformation). The node cover is weakly connected to the tunnel surrounding rock through the concrete unit enclosed within it. Therefore, if the rope clamp displacement caused by steel cable tensioning is too large, the node cover can be separated from the surrounding rock. Because the node cover is wider than the concrete unit and the concrete adhesion area between the two is small, the node cover does not affect the displacement of the concrete unit caused by tunnel surrounding rock deformation. This process is based on the variability of the parallelogram mechanism formed by the concrete unit and the node cover, which enables the grid structure unit to achieve a large degree of shape change. This parallelogram structure relies on the contraction of the concrete arch grid surface, allowing the tunnel primary lining to "contract" as a whole during the convergence process, thereby ensuring the continuity and stress balance of the overall concrete arch structure even when the tunnel is subject to large deformation.

[0029] The structure of the node cover and the four concrete units connected within it is similar to the concrete hinge in the bridge field. When the tunnel surrounding rock undergoes large deformation, the node cover detaches from some of the concrete units, allowing the concrete units to displace and rotate relative to the node cover.

[0030] (2) Tunnel deformation control:

[0031] The state of the steel cable changes from tension to tension;

[0032] When the cables are tightened, they form stable triangular configurations at the grid nodes. The stability of the triangular components ensures that local deformation is controlled, preventing structural damage caused by excessive deformation of the entire tunnel. The cables transmit external loads and adjust the relative positions of the nodes, achieving precise control of the deformation process.

[0033] The beneficial effects of the present invention are:

[0034] The support structure of the present invention has the ability to adapt to large tunnel deformations and control local tunnel deformations; the large tunnel deformation adaptation can achieve large-scale shape adjustment of the concrete arch frame serving as the primary lining based on stress monitoring data, effectively adapting to geometric changes under conditions of stratum convergence or large tunnel deformation; the local tunnel deformation control is to achieve effective control of local node deformation by forming a closed triangular stable configuration when the steel cables are in a taut state, thereby ensuring the overall stability of the structure.

[0035] The concrete arch frame of the present invention realizes the rapid prototyping of the complex structure of the tunnel primary lining, reduces the construction period and labor costs, meets the requirements of green construction and energy conservation, and improves the overall economic benefits of the project; the dynamic adjustment method of the present invention automatically adjusts the tightness of the steel cable according to the monitored stress changes of the concrete arch frame to achieve adaptive adjustment of the concrete arch frame, realize stress balance, reduce the possibility of damage to the concrete arch frame, and ensure the structural integrity of the concrete arch frame. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The drawings and the accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. Among them:

[0037] Figure 1 Schematic diagram of an application of an embodiment of the present invention.

[0038] Figure 2 Schematic diagram of the top structure of an embodiment of the present invention.

[0039] Figure 3 This is a schematic diagram of the state of the jack pulling the steel cable according to an embodiment of the present invention.

[0040] Figure 4 for Figure 3 A partial enlarged view of the jack position in the figure.

[0041] Figure 5 Schematic diagram of the connection between the node cover and the steel cable according to an embodiment of the present invention.

[0042] Figure 6 Schematic diagram of the connection between the node cover and the concrete unit according to an embodiment of the present invention.

[0043] Figure 7 Schematic diagram of the structure of the node cover according to an embodiment of the present invention.

[0044] Figure 8 Schematic diagram of deformation of a parallelogram grid according to an embodiment of the present invention.

[0045] Figure 9 This is a simulation result diagram of the concrete arch frame in the initial state of an embodiment of the present invention.

[0046] Figure 10 This is a simulation result diagram of a concrete arch in a relaxed state according to an embodiment of the present invention.

[0047] In the figure: 1-concrete unit, 2-node cover, 3-rope clamp, 4-steel cable, 5-jack, 100-tunnel surrounding rock. DETAILED DESCRIPTION

[0048] The technical solutions in the embodiments of the present invention will be described clearly and completely below. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field are within the scope of protection of the present invention.

[0049] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments. It should be noted that, in the absence of conflict, the embodiments and features of the embodiments of the present invention can be combined with each other.

[0050] like Figures 1 to 7 As shown, an adaptive large deformation 3D printed tunnel support structure includes several concrete units 1, grid nodes, steel cables 4, jacks 5 and a control system; the concrete units 1 are printed in situ at the tunnel site by 3D printing concrete equipment; some of the concrete units 1 are embedded with stress and strain sensors;

[0051] The grid nodes are arranged in a plum blossom shape; the grid nodes include a cross-shaped node cover 2 and a rope clamp 3 fixed to the node cover 2; the concrete unit 1 is a long strip block, and the concrete unit 1 is connected to the node cover 2 of the adjacent grid nodes. After all the concrete units 1 and the node cover 2 are connected, a concrete arch with a parallelogram grid is formed;

[0052] The steel cables 4 pass through each grid node along the longitudinal direction of the tunnel, and the grid nodes are fixedly connected to the steel cables 4 via rope clamps 3; both ends of the steel cables 4 are tensioned and fixed by jacks 5; all the stress and strain sensors are wirelessly connected to the control system, and the control system adjusts the tension of the steel cables 4 via the jacks 5 based on the collected data of the stress and strain sensors, so that the concrete arch frame deforms as the tunnel deforms.

[0053] Concrete unit 1 is the smallest unit of the concrete arch. It is printed closely against the tunnel surrounding rock 100 and adheres to it after solidification. The 3D-printed concrete used in concrete unit 1 has an initial setting time of less than 15 minutes and a compressive strength of C50. Each concrete unit 1 is 0.5 to 0.8 meters long and has a 10 cm x 5 cm rectangular cross-section (5 cm thick perpendicular to the surrounding rock). Each unit is printed in two layers, each measuring 10 cm x 2.5 cm (width x thickness). After the first layer is printed, sensors are embedded at selected locations, followed by the second layer. The steel cable 4 utilizes galvanized steel strands with a breaking strength of >150 kN.

[0054] like Figures 5 to 7As shown, the node cover 2 is closed at the top and open at the bottom. Four cover tubes are evenly spaced around the circumference of the ends of the concrete units 1. A rope clamp 3 is mounted on the top of the node cover 2. The inlet and outlet of the rope clamp 3 can be rotated, allowing the angle of the rope clamp 3 to be adjusted according to the direction of the steel cable 4. The node cover 2 is a prefabricated steel node, shaped like a pipe cross split in the middle. The overlap between the cover tubes and the ends of the concrete units 1 is 2 to 3 cm. The diameter of the cover tube is 1 to 3 cm larger than the width of the ends of the concrete units 1, ensuring that the concrete units 1 do not fill the entire semicircular cross section of the cover tube after insertion. This overlap distance and width ensure the initial securement of the node cover 2. Compared to a node cover 2 completely filled with concrete, the connection area with the concrete units 1 is smaller. This allows the concrete units 1 to detach from the node cover 2 (i.e., the connection between the node cover 2 and the concrete units 1 can be broken) as the tunnel surrounding rock 100 deforms and moves, which is a prerequisite for the concrete units 1 to move relative to the node cover 2. At the same time, the node covers 2 are used to reinforce the joints of the concrete arch, ensuring stable and reliable stress transmission at each node throughout the deformation process, while achieving an organic combination of large deformation and local stability. This also reduces the possibility of damage to the node covers 2 during the deformation of the concrete arch. The node covers 2 adhere to the tunnel surrounding rock 100 through the concrete at the joints with the concrete units 1, maintaining a weak connection with the tunnel surrounding rock 100. During tunnel deformation, the node covers 2 will be pulled away from the tunnel surrounding rock 100 by the pull of the steel cables 4.

[0055] The stress and strain sensor is embedded in the middle of the concrete unit 1. The stress and strain sensor transmits the monitored data to the control system in real time using wireless transmission. No sensor is required in the node cover 2.

[0056] The present invention also proposes a dynamic adjustment method for a 3D printed tunnel support structure with adaptive large deformation, comprising the following steps:

[0057] S1, construction phase: grid nodes and 3D printed concrete units 1 are laid out along the tunnel lining, wherein the grid nodes are weakly connected to the tunnel surrounding rock 100 through the concrete units 1; stress and strain sensors are embedded in the concrete units 1 while printing; data from the stress and strain sensors is transmitted to the control system in real time;

[0058] After the concrete arch initially sets, the steel cables 4 are sequentially passed through the grid nodes along the longitudinal direction of the tunnel. The jacks 5 are fixed to the tunnel surrounding rock 100 and used to initially tension the steel cables 4. The rope clamps 3 are then used to clamp the steel cables 4 and secure the node covers 2 on the steel cables 4. The initial tension stress of the steel cables 4 is 40-50 kN, preferably 45 kN.

[0059] S2, Adjustment Phase: The tension of the steel cables 4 is adjusted based on real-time monitoring by the stress and strain sensors. When the monitored stress exceeds the normal range, the cables 4 are relaxed, and the concrete arch enters a variable state, releasing stress in sync with the tunnel deformation until the stress reaches the normal range. Jacks 5 then tighten the cables 4 to the initial tension stress. When the stress exceeds the normal range, the concrete arch deforms at certain locations, meaning that the concrete units 1 at the relevant locations shift. Relaxing the cables 4 removes the constraints on the grid nodes, equalizing the stress at the deformed locations of the concrete arch and preventing structural damage. The node caps 2 are weakly connected to the tunnel surrounding rock 100 and fixedly connected to the cables 4. Therefore, the movement of the cables 4 may cause the concrete units 1 to separate from the node caps 2 (separation here refers to the concrete connecting the concrete units 1 and the node caps 2 being disconnected from the node caps 2, while the ends of the concrete units 1 remain within the internal space of the cap tube). This allows for deformation adjustment of the concrete arch with the cables 4 relaxed. When the steel cable 4 is tightened, the steel cable 4, the node cover 2 and the concrete unit 1 form a stable triangular configuration, which can achieve "telescopic" adjustment of the overall structure of the concrete arch within a certain deformation range of the concrete arch.

[0060] During the adjustment process, mesh nodes at locations with excessive stress can be separated from the tunnel surrounding rock 100. The normal stress range means that the local stress of the concrete arch is less than half the compressive strength of the 3D-printed concrete. For example, in one embodiment, the 3D-printed concrete is C50. When the local stress at the node approaches or exceeds 25 MPa, the control system issues a command to loosen the steel cable 4.

[0061] When the steel cable 4 is relaxed, the length of the steel cable 4 changes within 20 mm to 50 mm. The concrete arch serves as the primary lining and is arranged before the secondary lining. The general length is 2 to 3 meters. It can be seen that for the parallelogram grid composed of each concrete unit 1, the displacement caused by deformation is smaller.

[0062] The concrete arch of the present invention serves as the primary tunnel lining. The arch is rapidly constructed using 3D concrete printing technology. Stress and strain sensors are embedded during the concrete printing process for monitoring. Multiple steel cables are threaded through each grid node along the tunnel's longitudinal axis, with both ends secured by jacks. A control system dynamically analyzes collected data and automatically adjusts the adjustable cables arranged along the tunnel's longitudinal axis based on the stress state of the tunnel structure. When data indicates excessive stress in the tunnel's primary lining (concrete arch), the control system automatically lengthens the cables (using either the jacks near the tunneling end or the jacks farther from the tunneling end, depending on their location). The cables are adjusted from a taut state to a relaxed state, allowing the concrete arch structure to deform within a certain range as the tunnel progresses. Simultaneously, the jacks near the tunneling end are limited in displacement, and the jack pistons extend to the opposite side, relaxing the cables and preventing excessive deformation of the concrete arch. When data indicates that the stress level of the primary tunnel lining (concrete arch) is within a safe range, the cables are adjusted from a relaxed state to a taut state, transforming the parallelogram structure into a stable triangular configuration and ensuring that deformation remains within a controllable range.

[0063] Example

[0064] The following is a specific application step of the dynamic adjustment method for adaptive large deformation 3D printed tunnel support structure based on process conditions and material parameters:

[0065] 1. Materials and equipment preparation:

[0066] (1) 3D printed concrete: initial setting time is within 15 minutes, final setting time is 40 to 60 minutes; design compressive strength: C50; the cross-section of the concrete unit is a 10 cm × 5 cm rectangle, and the shape is a square rod;

[0067] (2) Steel cable: Made of high-strength galvanized steel strand, diameter φ12mm, breaking strength >150kN;

[0068] (3) Grid nodes:

[0069] Composition: The node cover is a prefabricated steel structure, formed in one piece, with a length and width of 12 cm. The cover tube is semi-circular in shape, with a length of 3.5 cm, a height of 6 cm, and a wall thickness of 5 mm. The length of the concrete unit in the cover tube is 2 to 3 cm. The rope clamp uses a single wire rope clamp (such as Figure 5 ), its structure includes a screw nut, a clamp body and a clip. The screw is welded to the center of the outer surface of the node cover, and the clamp body and the clip can be rotated on the screw to adjust the angle.

[0070] (4) Sensor: Embedded stress strain gauge, supports wireless transmission, accuracy ±1% FS;

[0071] (5) Jack: A through-type hydraulic jack with a single thrust of ≥300kN and a mechanical locking function is used for cable tensioning, limiting and locking operations. The dedicated base of the jack is directly bonded to the tunnel concrete wall.

[0072] 2. Process and construction steps:

[0073] 2.1 Concrete arch construction stage:

[0074] A track-mounted 3D printing system is installed 2 to 3 meters behind the tunnel boring. It prints concrete units layer by layer in a parallelogram-shaped grid, following the tunnel contour. For example, if the track-mounted 3D printing system is installed 3 meters behind the tunnel boring, the final printed concrete arch will be approximately 2.8 meters long (allowing for jack mounting). The standard grid unit dimensions are 0.5 meters on each side and 1 meter diagonally, but these dimensions can be adjusted based on site conditions. During the concrete unit printing process, wireless stress and strain sensors are embedded in the center of each short, rod-shaped unit and wirelessly connected to the control system. The front end of the finished concrete arch is 15 to 20 cm away from the tunnel secondary lining and another 15 to 20 cm away from the tunnel face. These two spacings are where the jacks at each end of the steel cable are fixed, preventing them from interfering with construction at the tunnel face (excavation end). The jacks are mounted on a dedicated base, which is then fixed to the tunnel surrounding rock using anchors and / or concrete.

[0075] During the first layer of printing, a node cover is simultaneously pressed and fixed at the intersection of four concrete units at each grid node. Since the cross-section of the node cover is larger than that of the concrete unit, part of the inner surface of the node cover adheres to the concrete unit. This forms a weak connection between the node, the concrete unit, and the tunnel surrounding rock (the weak connection is a local point contact and does not require a large-area connection), ensuring that subsequent node cover nodes can be adjusted with the sliding of the steel cable, and that the concrete unit is not restricted by the node cover during the displacement with the surrounding rock.

[0076] After the 3D-printed concrete has finally set, steel cables are threaded longitudinally through the tunnel, passing through rope clamps at each grid node along the longitudinal rows. At the tunnel end away from the tunneling end (the rear end, i.e., the end near the secondary lining), the cables are tensioned to the predetermined initial tension (approximately 45kN) using hydraulic jacks and mechanically locked. Near the tunneling end (2-3 meters ahead) (the front end, i.e., the end near the tunnel face), the cables are also tensioned to the same initial tension using hydraulic jacks, ensuring the overall structure of the concrete arch is initially secured. The cables are then clamped with rope clamps. Once secure, they are gently tugged to ensure they do not move relative to the clamps.

[0077] 2.2 Adjustment stage:

[0078] When it is monitored that the local stress at the node is close to or exceeds half of the concrete compressive strength (about 25MPa), the central system issues a release command.

[0079] The steel cables away from the tunneling end remain tensioned and fixed, serving as stable anchors. The through-hole jacks near the tunneling end (face) are operated to release the tension locks and appropriately loosen the cables. Cable displacement is controlled within 20mm to 50mm, but still maintained within a restricted displacement to prevent complete loss of control. This loosening operation causes the grid nodes near the tunneling end (face) to undergo axial slippage, driven by the cables. This gradually drives the nodes in the intermediate area to follow suit, causing the entire grid surface to contract longitudinally, relieving surrounding rock pressure and reducing stress levels within the support structure. Once the surrounding rock pressure has returned to normal, the through-hole jacks near the tunneling end (face) are operated to pull the cables to the predetermined initial tension (approximately 45kN) and then mechanically lock them.

[0080] 3. Construction precautions

[0081] (1) The cable tensioning force should be controlled accurately, with an error not exceeding ±5%.

[0082] (2) The cable relaxation process needs to be strictly limited to avoid excessive slippage that may cause overall structural instability.

[0083] (3) The concrete printing temperature is controlled at 10-30°C to ensure printing quality.

[0084] (4) Sensors and control systems must be online throughout the entire process, and monitoring interruptions are strictly prohibited.

[0085] (5) Every time a section of the tunnel is excavated, a corresponding section of the concrete arch frame of the present invention is made on the surrounding rock, and the steel cables of each section of the concrete arch frame are independent.

[0086] As the rock mass around the tunnel converges towards the tunnel interior, the radial stress at the tunnel boundary gradually changes. This paper provides a derivation process for the relationship between surrounding rock stress and tunnel convergence to illustrate the working process of the present invention. The derivation process is as follows:

[0087] For a deep tunnel, assuming that earthquake and tectonic stress are not considered, the initial ground stress can be considered as isotropic hydrostatic pressure: ;

[0088] The bulk density γ is taken as 20kN / m 3 , H is taken as 100m, the initial ground stress can be obtained σ 0 is 2MPa.

[0089] After tunnel excavation, part of the surrounding rock is unloaded, the stress is redistributed, and the pressure originally borne by the boundary (tunnel surface) is reduced, thus causing the tunnel to converge and deform.

[0090] ①Assume that the initial ground stress is isotropic hydrostatic pressure σ 0. After tunnel excavation, a pressure pi (actual value) is applied at the tunnel boundary radius, causing elastic strain in the surrounding rock.

[0091] ② In the elastic region, the displacement satisfies the basic relationship of elasticity (assuming small deformation and linear elasticity), then:

[0092] The radial strain is:

[0093] ;

[0094] The hoop strain is:

[0095] ;

[0096] According to the elastic constitutive relation under plane strain conditions:

[0097] ;

[0098] ;

[0099] In the above four formulas, u r is the radial convergence of the tunnel, r is the distance from the center of the tunnel to a certain point, σ r Radial stress, σ θ Hoop stress, E elastic modulus, ν Poisson's ratio.

[0100] The stress boundary conditions at the boundary are:

[0101] At r=R, radial stress σ r (R)=p i ; R = outer radius of the concrete arch = tunnel radius;

[0102] When r→∞, tunnel excavation does not affect the initial ground stress, so σ r (∞)=σ0; then:

[0103] ;

[0104] ;

[0105] Substituting the above stress into the strain formula, we get:

[0106] ;

[0107] Expand and sort out, get;

[0108] ;

[0109] By integration, we can deduce that the displacement at the boundary (at r=R) is:

[0110] ;

[0111] Support pressure P i It is about the surrounding rock convergence u r A linear function of

[0112] ;

[0113] In this formula, Poisson's ratio ν is 0.35, the initial ground stress σ0 is 2 MPa, the elastic modulus E is 10 GPa, and the tunnel radius R is 5 m.

[0114] When the surrounding rock convergence amount u r When it is 0, the support pressure P i =4.15MPa, when the surrounding rock convergence amount u r When it is 0.005m, the support pressure P i =1.07MPa; This indicates that after the concrete arch frame converges and deforms, the support pressure P will be reduced. i Reduce and release stress.

[0115] Figure 8 The diamond in the figure represents a parallelogram grid composed of four concrete units and node covers, and the solid diamond is the shape of the dotted diamond after tension deformation. When the steel cable is controlled by the jack, and then the axial displacement of the grid node is controlled, the radial direction of the grid node will also change accordingly, and this change will lead to a decrease in the stress of the surrounding rock, thereby reducing the stress of the temporary support structure, and realizing the deformation of the support structure as the tunnel converges, thereby releasing stress. In order to verify the effect of force changes in the adaptive large deformation 3D printed tunnel structure during the dynamic adjustment process, this embodiment established a simulation model on the ABAQUS finite element platform to perform structural response simulation analysis. The simulation analysis process is as follows:

[0116] (1) Simulation model settings:

[0117] After establishing the geometric model, set the corresponding material parameters and perform working condition settings at the same time.

[0118] Geometric model: A concrete arch model was constructed to actual scale. The grid consisted of square rod-shaped concrete units. Specifically, the cross-section of each concrete unit was a 10cm x 5cm rectangle, and each rod-shaped concrete unit was 30cm long. The radius of the concrete arch was 5m.

[0119] Material parameters: concrete elastic modulus: 20GPa; Poisson's ratio: 0.2; density: 2000kg / m³.

[0120] Working conditions: Hydrostatic pressure was applied to the surrounding rock to simulate the original stress state of the formation. Two working conditions were simulated: 1. Initial tension state: 4.15 MPa surrounding rock pressure was applied without releasing the tunnel end cables. 2. Relaxed displacement state: 1.07 MPa surrounding rock pressure was applied after a 1 cm axial relaxation (5 mm radial displacement) was applied to the jack near the tunnel end (the tunnel face).

[0121] In this model, the node covers are not modeled. The following are the reasons:

[0122] From the perspective of simplification in simulation modeling, minor components that have little impact on the overall stress behavior can be simplified and omitted to reduce model complexity without sacrificing accuracy. This principle of simplification is widely recognized. Small components that do not directly bear loads and have a negligible impact on the overall stress situation are often deleted from the model. This deletion does not change the overall stress path and response of the structure.

[0123] From a structural connection perspective, the joint caps and concrete elements utilize a weak, overlapping connection, resulting in negligible mechanical interaction. The cap tubes on the joint caps simply fit over the ends of the concrete elements, with an overlap of only approximately 2 to 3 centimeters. The cap tube diameter is 1 to 3 centimeters wider than the ends of the concrete elements. This connection is essentially a localized overlap, not a rigid fixation. The contact area is minimal, lacking effective bonding. As previously noted, "since only a small area of ​​the inner surface of the joint caps adheres to the concrete ends, forming a weak connection (localized point contact, without requiring a large-area bond)," the joint caps do not participate in the primary load transmission. When the concrete arch is subjected to stress or deformation, the joint caps do not constrain the movement of the concrete elements and cannot bear or transmit significant loads. This weak connection design ensures that the joint caps can slide and adjust with the prestressed cables as the concrete arch deforms, allowing the concrete elements to deform freely without being hindered by the joint caps. In other words, the joint caps function more as auxiliary positioning or protective components, and do not form an effective load-bearing and load-transmission path with the primary structure (concrete elements, cables, and surrounding rock). Therefore, omitting the node cover from the simulation model does not have a substantial impact on the overall stress analysis results: the main load is still transmitted through the concrete arch and steel cables, and the node cover does not bear the structural load due to its weak connection nature. After omission, the simulation results are still reliable and consistent with the actual mechanical behavior.

[0124] These two aspects together demonstrate that omitting the node caps in finite element simulations of concrete arches is reasonable and feasible: model simplification does not compromise accuracy, as the node caps contribute minimally to global stiffness and strength; and their connection method means they do not participate in the primary loads, thus not affecting stress transfer paths or structural response. This approach aligns with conventional simplification principles in finite element modeling and practical engineering experience, and is consistent with the patent's stated inability to effectively transfer loads due to overlapping node caps.

[0125] In the actual structure, the four concrete elements are indirectly connected through the node cover instead of being directly integrated. Figure 9 、 Figure 10 The simulation model simulates the indirect stress relationship transmitted by the node cover, rather than a physical rigid connection. Therefore, the diagram shows the four concrete power supply connections forming an "X" shape. This simplified representation of the four concrete elements at the node cover as a "connected state" is reasonable, conforming to the finite element modeling principle of simplification while effectively reflecting the core laws of structural stress, consistent with the invention's technical principles and simulation objectives.

[0126] (2) Simulation analysis process:

[0127] Initial state: A uniform hydrostatic pressure of 4.15 MPa is applied; all cables are in tension and locked state, and the grid nodes are fixed; the axial stress distribution in the S22 direction in the concrete arch is recorded.

[0128] Relaxed state at the tunneling end: The steel cables near the tunneling end are relaxed by 1 cm and controlled by limited displacement; the steel cables away from the tunneling end continue to be tensioned and fixed; a surrounding rock pressure of 1.07 MPa is applied to simulate the secondary stress field after the surrounding rock is unloaded; the axial stress distribution in the S22 direction at the same location is recorded.

[0129] (3) Simulation results:

[0130] The simulation results in the initial state are as follows Figure 9 As shown in the figure, the axial stress in the concrete arch is concentrated, the axial compressive stress of the concrete is about 90 MPa, and the compressive stress at the node is about 130 MPa.

[0131] The simulation results of the tunneling end in the relaxed state are as follows Figure 10 As shown in the figure: the overall axial stress of the concrete arch is significantly reduced, the axial compressive stress of the concrete is about 25MPa, and the compressive stress at the node is about 50MPa.

[0132] The simulation results show that when no adjustment is made, the axial compressive stress of the concrete is 90MPa, which is much greater than the compressive strength of 3D printed concrete. After displacement adjustment control, the axial compressive stress is reduced to 25MPa, which can achieve structural stability. This shows that by controlling the relaxation of the steel cables at the excavation end, the primary lining of the tunnel can be effectively induced to produce axial shrinkage deformation, thereby reducing the stress inside the concrete structure. In the actual structure, the node cover allows the relative displacement of the concrete unit, but the concrete unit is the main load-bearing component, and its stress distribution is mainly determined by the steel cable tension and the surrounding rock pressure. The simplified drawing method of the concrete unit at the intersection node in the simulation does not change the core logic of "steel cable tensioning → arch frame constraint → stress concentration" and "steel cable relaxation → arch frame deformation → stress release". Therefore, the simulation results can prove the feasibility and effectiveness of the dynamic adjustment mechanism proposed in this invention.

[0133] The foregoing description is merely a preferred embodiment of the present application and is not intended to limit the present application. Persons skilled in the art will readily appreciate that various modifications and variations are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. A 3D printed tunnel support structure with adaptive large deformation, characterized by: The invention comprises a plurality of concrete units (1), grid nodes, steel cables (4), jacks (5) and a control system; the concrete units (1) are printed in situ at a tunnel site by 3D printing concrete equipment; some of the concrete units (1) are embedded with stress and strain sensors; The grid nodes are arranged in a plum blossom shape; the grid nodes include a cross-shaped node cover (2) and a rope clamp (3) fixed to the node cover (2); the concrete unit (1) is a long strip block, and the concrete unit (1) is connected to the node cover (2) of adjacent grid nodes, and all the concrete units (1) are connected to the node cover (2) to form a concrete arch with a parallelogram grid; The steel cables (4) pass through each grid node in the longitudinal direction of the tunnel, and the grid nodes are fixedly connected to the steel cables (4) via rope clamps (3); both ends of the steel cables (4) are tensioned and fixed by jacks (5); all the stress and strain sensors are wirelessly connected to a control system, and the control system adjusts the tension of the steel cables (4) via the jacks (5) based on the collected data of the stress and strain sensors, so that the concrete arch frame deforms as the tunnel deforms.

2. The self-adaptive large-deformation 3D-printed tunnel support structure according to claim 1, characterized in that: The node cover (2) has a closed top and an open bottom, and four cover pipes are evenly arranged on the circumference, the cover pipes covering the outer circumference of the end of the concrete unit (1).

3. The self-adaptive large-deformation 3D-printed tunnel support structure according to claim 2, characterized in that: The overlap distance between the cover pipe and the end of the concrete unit (1) is 2 cm to 3 cm; the diameter of the cover pipe is 1 cm to 3 cm larger than the width of the end of the concrete unit (1).

4. The adaptive large deformation 3D printing tunnel support structure according to claim 1, characterized in that: The stress and strain sensor is pre-buried in the middle of the concrete unit (1), or pre-buried at a position of the concrete unit (1) close to the end of the node cover (2).

5. A dynamic adjustment method for a 3D printed tunnel support structure with adaptive large deformation according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1, construction phase: grid nodes and 3D printed concrete units (1) are laid out along the tunnel lining, and stress and strain sensors are embedded in the concrete units (1) during printing; after the concrete arch frame is initially set, the steel cables (4) are sequentially passed through the grid nodes along the longitudinal direction of the tunnel; the jacks (5) are fixed to the tunnel surrounding rock (100), and the steel cables (4) are initially tensioned with the jacks, and then the steel cables (4) are clamped with the rope clamps (3); S2, adjustment stage: the tension of the steel cable (4) is adjusted according to the real-time monitoring of the stress and strain sensor; when the stress exceeds the normal range, the steel cable (4) is relaxed, and the concrete arch enters a variable state, which releases stress synchronously with the deformation of the tunnel until the stress reaches the normal range, and the steel cable (4) is tightened to the initial tension stress by the jack (5).

6. The dynamic adjustment method of the adaptive large deformation 3D printed tunnel support structure according to claim 5, characterized in that: In step S1, after printing four concrete units (1) at an intersection, the grid nodes are aligned with the four concrete units (1) and pressed to fix them; in step S2, the grid nodes at the excessive stress position are separated from the tunnel surrounding rock (100).

7. The dynamic adjustment method of the adaptive large deformation 3D printed tunnel support structure according to claim 5, characterized in that: In steps S1 and S2, the initial tensile stress of the steel cable (4) is 40 to 50 kN.

8. The dynamic adjustment method of the adaptive large deformation 3D printed tunnel support structure according to claim 5, characterized in that: The normal stress range means that the local stress of the concrete arch is less than half of the compressive strength of the 3D printed concrete.

9. The dynamic adjustment method of the adaptive large deformation 3D printed tunnel support structure according to claim 5, characterized in that: When the steel cable (4) is loosened, the length of the steel cable (4) changes within a range of 20 mm to 50 mm.

10. The dynamic adjustment method of the adaptive large deformation 3D printed tunnel support structure according to claim 5, characterized in that: The 3D printed concrete used in the 3D printed concrete unit (1) has an initial setting time of less than 15 minutes and a compressive strength of C50; the steel cable (4) uses a galvanized steel strand with a breaking strength greater than 150 kN; and the length of the concrete unit (1) is 0.5 m to 0.8 m.

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