Method for designing and constructing tunnel lining structure with variable cross-section based on jet 3D printing

Abstract

The application discloses a tunnel variable cross-section lining structure design and construction method based on jet 3D printing. Firstly, in the design stage, the cross-section direction is divided into stress zones, an optimization function with double targets of "minimum amount of material + structure safety coefficient homogenization" is established to optimize the cross-section shape, and the maximum and minimum safety coefficient ratio of different parts of the lining is ensured to be not greater than 1.2; the longitudinal direction is dynamically adjusted according to the surrounding rock pressure, hydrogeology and stress data of different sections of the tunnel, and the thickness of the lining is dynamically adjusted to form a whole design scheme with gradually changing thickness. In the construction stage, the printing path planning is generated according to the design scheme, and the jet 3D printing technology is used for layer-by-layer additive manufacturing. The application fundamentally changes the material redundancy and safety coefficient dispersion problem caused by the traditional equal-thickness lining, ensures the safety and stress continuity of the structure, and significantly saves the material, improves the construction automation degree and efficiency.

Description

Technical Field

[0001] This invention relates to the field of tunnel engineering technology, specifically to a design and construction method for a tunnel variable cross-section lining structure based on jet 3D printing. Background Technology

[0002] Tunnel lining is the core load-bearing structure of tunnel engineering. Its function is to withstand the pressure of the surrounding rock, prevent the deformation of the surrounding rock, and isolate groundwater intrusion. Traditional tunnel lining often adopts a uniform cross-section design and is constructed by splicing cast slabs. This method has significant drawbacks, such as serious material waste, low construction efficiency, and poor adaptability. Furthermore, during the construction process using a formwork casting trolley, all sections of the secondary lining are of uniform thickness, resulting in a large dispersion of the safety factor along different radial angles. The minimum and maximum safety factor values ​​generally differ by no less than 5 times, causing serious safety redundancy and material waste.

[0003] In recent years, 3D printing technology, with its advantages of "on-demand molding, no templates required, and high degree of automation," has begun to be applied to tunnel lining construction. Among existing technologies, jet printing has become the mainstream technology for tunnel lining construction due to its fast printing speed and adaptability to large-size structures. However, current jet printing tunnel linings are still mainly based on constant cross-section structures, failing to fully incorporate changes in tunnel geological conditions to optimize structural design and failing to solve the material waste problem of traditional constant cross-section designs. At the same time, existing printing path planning often uses fixed parameters, making it difficult to achieve a continuous and smooth transition of variable cross-sections, which can easily lead to the cross-section not meeting stress requirements and affecting structural safety.

[0004] Therefore, there is a need for a jet 3D printing method that can dynamically optimize the lining section design based on tunnel geological conditions and achieve automated, high-precision construction of variable cross sections, in order to solve the problems of material waste, low efficiency, and poor adaptability in traditional lining construction. Summary of the Invention

[0005] The purpose of this invention is to provide a design and construction method for tunnel variable cross-section lining structures based on jet 3D printing. This optimizes existing tunnel variable cross-section lining technology, improving material utilization while ensuring the tunnel variable cross-section lining meets the requirements of jet 3D printing.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: In a first aspect, the present invention provides a method for designing tunnel variable cross-section lining structures based on jet 3D printing, including the following: Determine the basic parameters for tunnel construction, including: design alignment, outer contour, and minimum internal clearance requirements; Based on the tunnel shape, topography, and hydrogeological conditions, longitudinal sections are divided along the tunnel length to obtain data on surrounding rock pressure, hydrogeological conditions, and structural stress in different longitudinal sections. In each longitudinal section, several stress zones are divided along the circumferential direction of the lining. For each stress zone, an optimization function is established with the goal of "minimum material usage + uniform structural safety factor" to perform bi-objective optimization, thereby obtaining the wall thickness distribution of the cross section of each longitudinal section. After obtaining the wall thickness distribution of the cross section of each longitudinal section, linear interpolation of adjacent sections is used to achieve a continuous and smooth gradual change in thickness, forming a variable cross section lining structure design scheme with gradually changing longitudinal section thickness. Combining the design scheme of the variable cross-section lining structure with gradually changing longitudinal section thickness and the wall thickness distribution of the cross section of each longitudinal section, the inner and outer contour lines of the three-dimensional variable thickness lining of each section are fitted and generated, thus completing the design of the tunnel variable cross-section lining structure based on jet 3D printing.

[0007] Furthermore, the safety factor is the bending safety factor of the lining section calculated based on the finite element method or the load-structure method.

[0008] Furthermore, the bi-objective optimization employs the bi-objective WESO topology optimization algorithm.

[0009] Furthermore, the constraints of the optimization function include: the ratio of the maximum safety factor to the minimum safety factor of different parts of the lining structure is ≤1.2; the overall strength of the lining structure meets the requirements of the tunnel engineering design specifications; the deviation of the inner clearance dimension is ≤±50mm; and the thickness of each zone gradually transitions without abrupt changes.

[0010] Secondly, the present invention also provides a method for constructing a tunnel variable cross-section lining structure based on jet 3D printing, which uses jet 3D printing technology for layer-by-layer additive construction, including the following steps: Step C1: Generate a path planning file for jet 3D printing based on the inner and outer contours of the three-dimensional variable thickness lining of the target section determined by the design method. Step C2: Debug the jetting 3D printing construction platform. Based on the wall thickness distribution data of the cross section of each longitudinal section, debug the concrete jetting flow rate, moving speed and jetting angle parameters of the 3D printing equipment in each section and zone. Based on the design scheme of the variable cross section lining structure with gradually changing longitudinal section thickness, debug the concrete jetting flow rate, moving speed and jetting angle parameters of the 3D printing equipment in the longitudinal transition section. Step C3: The lining material is sprayed layer by layer using 3D printing equipment, and the construction is carried out in a cyclical manner from bottom to top. The lining thickness and forming accuracy are monitored in real time during the construction process. The longitudinal section is constructed in segments along the tunnel extension direction to achieve a continuous transition and smooth gradient of the longitudinal section thickness, thus completing the construction of the overall variable cross-section lining structure.

[0011] Furthermore, the lining material is fiber-reinforced concrete, geopolymer, or special printing mortar, and the material needs to be pretreated before spraying to ensure that its workability meets the requirements of layer-by-layer spraying molding.

[0012] Furthermore, a laser rangefinder and a 3D scanning device are used to monitor the lining thickness and forming accuracy in real time. When the monitoring data exceeds the allowable deviation, the jetting parameters of the 3D printing equipment are adjusted immediately.

[0013] Furthermore, the segment length in the longitudinal direction is 5-10m, and the transition slope of the lining thickness between adjacent sections is ≤1:50 to ensure the continuity of structural stress.

[0014] Compared with the prior art, the beneficial effects of the present invention include: 1. The jet 3D printing tunnel variable cross-section lining structure design method of the present invention, in the transverse direction, establishes an optimization function based on the division of stress zones, with the objectives of "minimum material usage + uniform structural safety factor" for dual-objective optimization, thereby determining the wall thickness distribution of the transverse section in each longitudinal section. In the longitudinal direction, the tunnel lining can dynamically adjust the lining section thickness of the corresponding section according to the surrounding rock pressure, hydrogeological conditions and structural stress data of different sections, forming a variable cross-section lining structure design scheme with gradually changing longitudinal section thickness, avoiding the material waste of traditional constant cross-section design and significantly reducing engineering costs.

[0015] 2. The construction method of this invention generates a path planning file for jet 3D printing based on the optimal variable thickness lining outline of the section. Lining material is then jetted layer by layer using 3D printing equipment, with construction proceeding from bottom to top in a cyclical manner. The lining thickness and forming accuracy are monitored in real time during construction. This method can achieve tunnel linings with arbitrary cross-sectional shapes and variations. Utilizing jet 3D printing technology eliminates the need for slab installation, significantly improving construction efficiency compared to traditional molding methods and greatly shortening tunnel construction time. It is particularly suitable for tunnels with complex geological conditions. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the tunnel cross-section of the present invention.

[0017] Figure 2 This is a schematic longitudinal section of the tunnel variable cross-section lining of the present invention. Detailed Implementation

[0018] The present invention will be further explained below with reference to the embodiments and accompanying drawings, but this is not intended to limit the scope of protection of this application.

[0019] The present invention provides a method for designing a tunnel variable cross-section lining structure using jet 3D printing, comprising the following steps: Before designing the tunnel, S1 clarifies the basic parameters for tunnel construction, including the design alignment, specifying the tunnel's route, starting point, and turning points; the outer contour line, specifying the tunnel's external dimensions and outline; and the minimum internal clearance requirements, ensuring that the tunnel's internal space meets traffic requirements.

[0020] S2 divides the tunnel into longitudinal sections along its length based on its shape, topography, and hydrogeological conditions, and obtains data on surrounding rock pressure, hydrogeological conditions, and structural stress in different longitudinal sections.

[0021] S3 divides each longitudinal section into several stress zones along the circumferential direction of the lining. These stress zones include the arch crown zone, arch waist zone, arch foot zone, and invert arch zone. Based on the vertical and lateral surrounding rock pressure, groundwater hydrostatic pressure, topographic bias coefficient, and surrounding rock grade of each longitudinal section, the minimum required thickness for each section is calculated. This serves as the initial thickness range for subsequent bi-objective optimization. Then, based on the stress zones, an optimization function is established with the objective of "minimum material usage + uniform structural safety factor" to perform bi-objective optimization, obtaining the wall thickness distribution of the cross-section of each longitudinal section. The safety factor is the bending safety factor of the lining section calculated using the finite element method or the load-structure method.

[0022] After obtaining the wall thickness distribution of the cross section of each longitudinal section, S4 uses linear interpolation between adjacent sections to achieve a continuous and smooth gradual change in thickness, with a transition slope ≤1:50, forming a variable cross section lining structure design scheme with a gradual change in longitudinal section thickness, that is, obtaining the longitudinal section thickness gradual change curve of each longitudinal section.

[0023] The ratio of the maximum safety factor to the minimum safety factor in different parts of the lining structure is ≤1.2; the overall strength of the lining structure meets the requirements of the tunnel engineering design specifications; the deviation of the inner clearance dimension is ≤±50mm; there is no abrupt change in the thickness transition between each stress zone in the cross section, and the slope of the lining thickness transition between adjacent longitudinal sections is ≤1:50, with a gradual transition without abrupt changes.

[0024] The bi-objective optimization employs the bi-objective WESO (Weighted Evolutionary Structural Optimization) topology optimization algorithm. The algorithm's input parameters include: the tunnel's outer contour geometry, the minimum internal clearance boundary, the surrounding rock pressure distribution values ​​for each stress zone, the lining material strength parameters (compressive and flexural strength), and the initial thickness range. The output results are the optimal thickness values ​​for each stress zone and their corresponding flexural safety factors.

[0025] The algorithm process is as follows: (1) In the finite element analysis software, the cross section is discretized into a number of mesh elements with the element density of each stress zone of the lining as the design variable. (2) Constructing a dual objective function: Objective 1 is to minimize the total weight of the structure (i.e., the minimum amount of material used), and Objective 2 is to minimize the variance of the safety factor of each zone (i.e., to homogenize the safety factor). The dual objective is transformed into a single objective by using the linear weighted sum method, and the initial weight coefficients are all set to 0.5. (3) Perform finite element analysis to obtain the stress and safety factor of each zone under the current thickness distribution; (4) Calculate the sensitivity of each element (i.e. the degree of influence of the element thickness change on the objective function), introduce a sensitivity filtering mechanism to filter out local extreme values ​​and avoid optimization oscillations; (5) Sort by sensitivity from smallest to largest, delete several units with lower sensitivity (the deletion rate is initially set to 2%, and decreases to 0.5% as the number of iterations increases), and adjust the thickness value of the corresponding partitions simultaneously. (6) Check the constraints after each iteration: If the safety factor ratio is greater than 1.2, then forcibly restore the part of the deleted unit located in the weak partition (partition with a smaller safety factor), increase the lower limit of the partition thickness, and re-enter the next iteration; (7) Repeat steps (3) to (6) until the rate of change of the objective function between two adjacent iterations is less than 1%, and output the current thickness value of each partition as the optimal solution.

[0026] To address the challenge of conventional algorithms struggling to find the optimal solution due to dual-objective conflict and multiple constraint coupling, this embodiment employs the dual-objective WESO (Window-based Progressive Structure Topology Optimization) topology optimization algorithm. By dynamically adjusting the weights to approximate the optimal solution, the ratio of the maximum / minimum safety factor of each section of the cross-section is reduced from over 5.0 in traditional equal-section design to ≤1.2, resulting in a material saving of 15%~25%.

[0027] This invention relates to a method for constructing a tunnel variable cross-section lining structure using jet 3D printing. The method employs jet 3D printing technology for layer-by-layer additive manufacturing. The specific process is as follows: Before construction, S1 first carried out construction preparation. High-pressure water guns were used to clean the surface of the surrounding rock after the tunnel excavation to remove slag, dust and loose rock blocks. For the depressions in the plane, C25 shotcrete was used to level them. After leveling, it was tested again to ensure that the surface flatness error was ≤ ±5mm to avoid affecting the accuracy of the lining thickness. Based on the wall thickness distribution and thickness gradient curve of each longitudinal section obtained during the design phase, S2 fits and generates the inner and outer contour lines of the three-dimensional variable thickness lining for each section. Using this as a basis, a path planning file for jet 3D printing is generated. This path planning file is then imported, and the concrete jetting flow rate, moving speed, and jetting angle parameters of the 3D printing equipment are adjusted to ensure stable operation during the printing process. Based on the wall thickness distribution data of each longitudinal section's cross-section, the concrete jetting flow rate, moving speed, and jetting angle parameters of the 3D printing equipment for each zone of different sections are adjusted. Based on the design scheme of the variable cross-section lining structure with gradually changing longitudinal thickness, the concrete jetting flow rate, moving speed, and jetting angle parameters of the 3D printing equipment for the longitudinal transition section are also adjusted. The S3 lining material is fiber-reinforced concrete, geopolymer, or special printing mortar, and the material must be pretreated before spraying to ensure that its workability meets the requirements of layer-by-layer spraying. The S4 is equipped with a laser rangefinder and 3D scanning equipment to monitor the lining thickness and forming accuracy in real time.

[0028] After completing the preparation work, S5 began construction. Following the path planning document, the lining material was sprayed layer by layer using 3D printing equipment, starting from the lowest point and working upwards in a cyclical manner. During the construction process, a laser rangefinder and a 3D scanning device were used to monitor the lining thickness and forming accuracy in real time. When the monitoring data exceeded the allowable deviation, the spraying parameters of the 3D printing equipment were adjusted immediately to ensure printing accuracy.

[0029] After each layer of spraying is completed, S6 checks the lining thickness to ensure it meets the optimized thickness requirements in the design scheme. Adjustments are made for any areas exceeding the allowable deviation.

[0030] Construction along the S7 longitudinal section of the tunnel is carried out in segments, each segment being 5-10 meters long, ensuring controllable construction quality and progress for each segment. For each longitudinal segment along the tunnel's longitudinal section, different optimized lining thicknesses are assigned based on surrounding rock pressure, hydrogeological data, and structural stress data. The spraying parameters and construction speed of the spraying equipment are dynamically adjusted according to the path planning to achieve a continuous and smooth transition in longitudinal section thickness, completing the construction of the overall variable cross-section lining structure. The transition slope of the lining thickness between adjacent segments is ≤1:50 to ensure structural stress continuity.

[0031] During this construction process, the concrete spraying flow rate, printing speed and spraying angle are precisely controlled, and construction is carried out in a bottom-up cycle. Laser ranging and three-dimensional scanning are used to monitor the forming accuracy in real time, so as to achieve precise forming with variable thickness in the cross section and continuous smooth gradient in the longitudinal section.

[0032] Any aspects not covered in this invention are applicable to existing technologies.

Claims

1. A design method for tunnel variable cross-section lining structures based on jet 3D printing, characterized in that, Includes the following: Determine the basic parameters for tunnel construction, including: design alignment, outer contour, and minimum internal clearance requirements; Based on the tunnel shape, topography, and hydrogeological conditions, longitudinal sections are divided along the tunnel length to obtain data on surrounding rock pressure, hydrogeological conditions, and structural stress in different longitudinal sections. In each longitudinal section, several stress zones are divided along the circumferential direction of the lining. For each stress zone, an optimization function is established with the goal of "minimum material usage + uniform structural safety factor" to perform bi-objective optimization, thereby obtaining the wall thickness distribution of the cross section of each longitudinal section. After obtaining the wall thickness distribution of the cross section of each longitudinal section, linear interpolation of adjacent sections is used to achieve a continuous and smooth gradual change in thickness, forming a variable cross section lining structure design scheme with gradually changing longitudinal section thickness. Combining the design scheme of the variable cross-section lining structure with gradually changing longitudinal section thickness and the wall thickness distribution of the cross section of each longitudinal section, the inner and outer contour lines of the three-dimensional variable thickness lining of each section are fitted and generated, thus completing the design of the tunnel variable cross-section lining structure based on jet 3D printing.

2. The design method according to claim 1, characterized in that, The safety factor is the bending safety factor of the lining section calculated based on the finite element method or the load-structure method.

3. The design method according to claim 1, characterized in that, The dual-objective optimization adopts the dual-objective WESO topology optimization algorithm, and the constraints include: the ratio of the maximum safety factor to the minimum safety factor of different parts of the lining structure is ≤1.2; the overall strength of the lining structure meets the requirements of the tunnel engineering design specifications; the deviation of the inner clearance dimension is ≤±50mm; and the thickness of each stress zone gradually transitions without abrupt changes.

4. The design method according to claim 1, characterized in that, The input parameters of the bi-objective WESO topology optimization algorithm include: the geometric dimensions of the tunnel outer contour, the minimum inner clearance boundary, the distribution value of the surrounding rock pressure in each stress zone, the strength parameters of the lining material and the initial thickness range. The output results are the optimal thickness value of each stress zone and its corresponding bending safety factor.

5. The design method according to claim 4, characterized in that, When deleting the units with the lowest deletion sensitivity, the deletion rate is initially set to 2%, and then decreases to 0.5% as the number of iterations increases.

6. A method for constructing a tunnel variable cross-section lining structure based on jet 3D printing, characterized in that, Layer-by-layer additive construction using jet 3D printing technology includes the following steps: Step C1: Generate a path planning file for jet 3D printing based on the inner and outer contours of the three-dimensional variable thickness lining of the target section determined by the design method described in claims 1-5; Step C2: Debug the jetting 3D printing construction platform. Based on the wall thickness distribution data of the cross section of each longitudinal section, debug the concrete jetting flow rate, moving speed and jetting angle parameters of the 3D printing equipment in each section and zone. Based on the design scheme of the variable cross section lining structure with gradually changing longitudinal section thickness, debug the concrete jetting flow rate, moving speed and jetting angle parameters of the 3D printing equipment in the longitudinal transition section. Step C3: The lining material is sprayed layer by layer using 3D printing equipment, and the construction is carried out in a cyclical manner from bottom to top. The lining thickness and forming accuracy are monitored in real time during the construction process. The longitudinal section is constructed in segments along the tunnel extension direction to achieve a continuous transition and smooth gradient of the longitudinal section thickness, thus completing the construction of the overall variable cross-section lining structure.

7. The construction method according to claim 6, characterized in that, The lining material mentioned in step C3 is fiber-reinforced concrete, geopolymer, or special printing mortar. Before spraying the material, the surface of the surrounding rock after tunnel excavation needs to be pretreated to ensure that its workability meets the requirements of layer-by-layer spraying.

8. The construction method according to claim 6, characterized in that, In step C3, a laser rangefinder and a 3D scanning device are used to monitor the lining thickness and forming accuracy in real time. When the monitoring data exceeds the allowable deviation, the jetting parameters of the 3D printing equipment are adjusted immediately.

9. The construction method according to claim 6, characterized in that, The segment length in the longitudinal direction is 5-10m, and the transition slope of the lining thickness between adjacent sections is ≤1:50 to ensure the continuity of structural stress.

10. A tunnel variable cross-section lining structure obtained by the construction method described in claims 6-9, characterized in that, The structure is designed with unequal cross-sections.

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