A method for determining the influence of shield tunnel opening on the mechanical characteristics of the main structure

Abstract

The present invention relates to the technical field of tunnel construction engineering, and specifically to a method for determining the influence of shield tunnel opening on the mechanical characteristics of the main structure; the method comprises the following steps: S1, constructing a three-dimensional numerical calculation model of the shield tunnel; wherein the three-dimensional numerical calculation model is composed of a stratum model and a shield tunnel model arranged in the stratum model; S2, calculating the initial ground stress of the stratum model in the three-dimensional numerical calculation model; S3, calculating the deformation and stress of the shield tunnel model without opening under the action of surrounding stratum loads in the three-dimensional numerical calculation model; S4, calculating the structural mechanical characteristics of the shield tunnel model after opening in the three-dimensional numerical calculation model under the action of surrounding external loads; the present invention solves the problem that the existing method fails to clearly define the relationship between the structural analysis results of the shield tunnel opening working condition and the structural safety risk, and can more intuitively understand the safety risk of the structure after the shield tunnel opening.

Description

Technical Field

[0001] The present invention relates to the technical field of shield tunnel engineering, and in particular to a method for determining the influence of a shield tunnel opening on the mechanical characteristics of a main structure. Background Art

[0002] With the continuous development of my country's economy and the further improvement of high-speed rail, expressway, urban road, and urban rail transit networks, more and more shield tunnel projects have emerged. However, tunnel projects are long and narrow structures with closed internal environments and few entrances and exits, which makes evacuation and rescue in disaster situations more difficult. In addition, the closed and narrow tunnel structures lack connectivity with the surface transportation network and underground space infrastructure, preventing the effective utilization of underground space.

[0003] Therefore, it is necessary to drill holes in shield tunnels to connect them with other underground spaces. These drilling requirements include horizontal drilling for transverse passages, vertical drilling for municipal wells, vertical drilling for drainage pumphouses, and diagonal drilling for road ramps. Furthermore, shield tunnels are modular structures with limited structural stability. Drilling holes in shield tunnels disrupts their integrity, making their safety even more difficult to guarantee.

[0004] At present, there are some literatures that study the mechanical response of the main structure of the cross-channel constructed by shield tunnel opening. For example, Pang Kang et al. (2021) established a three-dimensional finite element model to analyze the structural stress and deformation. However, the disadvantage of this numerical model is that it simplifies the segments involved in the opening into a whole, which is inconsistent with the assembly state of the segment lining near the actual shield tunnel opening. It fails to effectively simulate the discontinuous characteristics of the lining joints near the opening, and the structural stress concentration results are different from the actual situation. In addition, it is unable to simulate the force transmission effect of the joints near the opening and the opening deformation characteristics of the joints, and cannot effectively reveal the structural safety risks. For example, Chen Rendong (2022) explored the influence of shield tunnel opening on structural stress and deformation by conducting centrifuge model tests. However, centrifuge model tests are costly and difficult. It is very expensive to conduct in-depth analysis of this issue by means of centrifuge model tests, and it is generally used as a verification of numerical analysis results.

[0005] It can be seen from this that the existing methods fail to effectively analyze the impact of shield tunnel opening on structural safety performance, cannot accurately reveal the structural safety risks that may be induced by shield tunnel opening, and thus cannot provide scientific guidance for the design of actual construction safety control measures.

[0006] Based on this, the present invention provides a method for determining the impact of shield tunnel opening on the mechanical characteristics of the main structure to solve the technical problems raised above! Summary of the Invention

[0007] The purpose of the present invention is to provide a method for determining the influence of shield tunnel opening on the mechanical characteristics of the main structure, so as to solve the problem that the existing methods fail to clearly define the relationship between the structural analysis results of the shield tunnel opening working condition and the structural safety risk.

[0008] To achieve the above object, the present invention provides the following technical solutions:

[0009] The present invention provides a method for determining the influence of shield tunnel opening on the mechanical characteristics of the main structure, comprising the following steps:

[0010] S1. Construct a three-dimensional numerical calculation model of the shield tunnel;

[0011] The three-dimensional numerical calculation model is composed of a stratum model and a shield tunnel model set in the stratum model, and the shield tunnel model is composed of ordinary segment lining, segment lining to be broken, and segment lining outside the portion to be broken;

[0012] S2. calculating the initial ground stress of the formation model in the three-dimensional numerical calculation model;

[0013] S3. Calculate the deformation and stress of the shield tunnel model without openings in the three-dimensional numerical calculation model under the action of the surrounding stratum load;

[0014] S4. Calculate the structural mechanical characteristics of the shield tunnel model after opening the hole in the three-dimensional numerical calculation model under the action of surrounding external loads.

[0015] The present invention is further configured such that: in step S1, each of the segment linings is an elastic unit.

[0016] The present invention is further configured as follows: the elastic unit is a mechanical characteristic unit used to simulate the interaction between the segments and their joints, soil layers and structures in the shield tunnel model.

[0017] The present invention is further configured as follows: in step S1, shear-resistant, tensile-resistant and elastic joints are provided between the segment linings, and the joints are spring units.

[0018] The present invention is further configured as follows: the spring unit is a three-dimensional numerical calculation model unit for simulating the mechanical behavior of the joint when it is subjected to force.

[0019] The present invention is further configured as follows: in step S1, a binding constraint is set between the segment lining to be broken and the segment lining outside the portion to be broken.

[0020] The present invention is further configured as follows: in the step S1, it also includes reasonably cutting the segment lining to be broken and the segment lining outside the portion to be broken, and dividing the segment lining to be broken and the segment lining outside the portion to be broken into hexahedrons.

[0021] The present invention is further configured as follows: in step S1, the boundary conditions of the three-dimensional numerical calculation model are:

[0022] The sides of the formation model are normal constraints;

[0023] The bottom of the stratum model is a fixed constraint;

[0024] The top of the stratigraphic model is the free surface;

[0025] The normal preload is set in the longitudinal direction of the segment lining.

[0026] The present invention is further configured as follows: the formula for selecting the normal preload force is:

[0027] Where p is the normal preload, F is the resultant water and soil pressure in front of the shield tunnel excavation face, S is the shield lining annular joint contact area, and α is the lining annular joint stress relaxation coefficient.

[0028] The present invention is further configured as follows: in step S3, the opening shape of the shield tunnel model is square or circular.

[0029] The present invention is further configured as follows: in step S4, the calculation formula for the number of longitudinal lining rings at the opening of the shield tunnel model is:

[0030] N = n + 2 × (m + 2), where N is the number of longitudinal rings of the shield tunnel model, n is the number of lining rings involved in the opening, and m is the range of the non-affected area on both sides of the opening, and m ≥ 5.

[0031] The present invention is further configured as follows: in step S4, when the state of the segment lining to be broken changes under the action of the surrounding external load, the states of all contact and spring units related thereto are updated, the contact between the segment lining to be broken and the adjacent segment lining to be broken is set to an inactive state, the outer surface of the segment lining having a contact relationship with the formation model is updated so that it is only included in the active state in the current analysis step, and the spring units having a connection relationship with the segment lining to be broken are killed.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] The present invention provides a numerical modeling scheme for conveniently and effectively calculating the impact of shield tunnel openings on structural safety. In the numerical model, both the stratum model and the shield tunnel model are solid units. By providing a method for setting contact and spring units in key analysis steps, the accuracy and convergence of the numerical calculation are improved. The provided method for determining the impact of shield tunnel openings on the mechanical characteristics of the main structure, and the obtained numerical calculation results can be used to judge whether the stress safety of the shield tunnel model, the stress safety of the joints, the waterproof safety of the joints, and the structural deformation meet the requirements of the specifications, thereby providing a basis for the formulation of safety measures. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The numerical calculation model of the shield tunnel opening with a rectangular opening in Example 1;

[0035] Figure 2 The numerical calculation model of the shield tunnel opening for the rectangular opening in which the segment lining to be removed is killed in Example 1;

[0036] Figure 3 Schematic diagram of applying equal ground stress to the formation model in Example 1;

[0037] Figure 4 This is a schematic diagram of local stress concentration after the shield tunnel model is opened in Example 1;

[0038] Figure 5 Schematic diagram of the joint state of the shield tunnel model after opening in Example 1;

[0039] Figure 6 Schematic diagram of the stress conditions of the joints after the shield tunnel is opened in Example 1. In the figure, "×" indicates the location of the bolt joints, and the numbers are the tensile forces (kN) on the bolts.

[0040] Figure 7 The numerical model of the shield tunnel opening with a circular opening in Example 1;

[0041] Figure 8 This is an analysis diagram of Example 2 in which the rectangular opening is located on the upper layer;

[0042] Figure 9 This is an analysis diagram of Example 2 where the rectangular opening is located at the lower layer;

[0043] Figure 10 This is an analysis diagram of Example 2 in which the circular opening is located on the upper layer;

[0044] Figure 11 This is an analysis diagram of Example 2 in which the circular opening is located in the lower layer.

[0045] Legend: 1. Stratum model; 2. Shield tunnel model; 21. Ordinary segmental lining; 22. Segmental lining to be broken; 23. Segmental lining outside the area to be broken. DETAILED DESCRIPTION

[0046] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0047] Example 1:

[0048] like Figure 1-Figure 7 As shown, this embodiment provides a method for determining the influence of shield tunnel opening on the mechanical characteristics of the main structure, comprising the following steps:

[0049] S1. Construct a three-dimensional numerical calculation model of the shield tunnel.

[0050] The three-dimensional numerical calculation model is composed of a stratum model and a shield tunnel model 2 set in the stratum model 1. The shield tunnel model 2 is composed of an ordinary segment lining 21, a segment lining 22 to be broken, and a segment lining 23 outside the portion to be broken.

[0051] In addition, shear-resistant, tensile-resistant and elastic joints should be set between the linings of each segment, and the joints are spring units.

[0052] The spring unit is a three-dimensional numerical calculation model used to simulate the mechanical behavior of the joint when it is subjected to force.

[0053] A binding constraint is set between the segment lining 22 to be broken and the segment lining 23 outside the portion to be broken.

[0054] At the same time, it also includes reasonable cutting of the segment lining 22 to be broken and the segment lining 23 outside the portion to be broken, and dividing the segment lining 22 to be broken and the segment lining 23 outside the portion to be broken into hexahedrons.

[0055] Among them, the boundary conditions of the three-dimensional numerical calculation model are:

[0056] The side of the formation model 1 is normal constrained;

[0057] The bottom of the formation model 1 is a fixed constraint;

[0058] The top of the formation model 1 is the free surface;

[0059] The normal preload is set in the longitudinal direction of the segment lining.

[0060] Furthermore, the formula for selecting the normal preload is:

[0061] Where p is the normal preload, F is the resultant water and soil pressure in front of the shield tunnel excavation face, S is the shield lining annular joint contact area, and α is the lining annular joint stress relaxation coefficient.

[0062] In this embodiment, it should be noted that the stratum model 1 and the shield tunnel model 2 are both solid unit models (three-dimensional finite element units), and hard contact is adopted between the stratum model 1 and the shield tunnel model 2. Since the ordinary segment lining 21, the segment lining 22 to be broken, and the segment lining 23 outside the to-be-broken portion in the shield tunnel model 2 all adopt elastic units, the difficulty of model convergence can be reduced; at the same time, the segment lining 22 to be broken and the segment lining 23 outside the to-be-broken portion are combined and reasonably cut so that they can be divided into hexahedral units, thereby improving the accuracy of the calculation.

[0063] In addition, it should be noted that hard contact is adopted for the adjacent parts of the longitudinal seams and circumferential seams between all the segment linings in the shield tunnel model 2, which can simulate the opening and dislocation deformation trend of the segment lining at the joints. The segment lining 22 to be broken is set as an independent component, where an independent component means that the part is set separately, which includes but is not limited to the following types: fixed constraints, contact constraints, hinge constraints, and elastic constraints, thereby more accurately simulating the interaction between the segment lining 22 to be broken and the surrounding structure under actual working conditions. Through the transmission effect of the binding constraint, the true distribution of stress and deformation during the demolition process can be reflected; binding constraints are set between the segment lining 22 to be broken and the segment lining 23 outside the to-be-broken part, and shear and tensile joints are set between the segment linings of the shield tunnel model 2, and the joints use spring units; by setting different degrees of freedom and different stiffness curves of the joints, shear and tensile stiffness are simulated, and the stiffness curve can be set to nonlinear.

[0064] S2. Calculate the initial geostress of the formation model 1 in the three-dimensional numerical calculation model.

[0065] In this embodiment, it should be noted that this analysis step only activates the stratum model 1 and does not activate the shield tunnel model 2, that is, only the stratum model 1 is used and the shield tunnel model 2 is not used.

[0066] S3. Calculate the deformation and stress of the shield tunnel model 2 without openings in the three-dimensional numerical calculation model under the action of the surrounding stratum load.

[0067] Among them, the opening shape of the shield tunnel model 2 is square or circular.

[0068] In this embodiment, it should be noted that in this step, the stratum units within the outer contour of the shield tunnel model 2 will be killed (hidden or deleted), and the shield tunnel model 2 will be activated at the same time, and then the deformation and stress of the shield tunnel model 2 without a hole in the three-dimensional numerical calculation model under the action of the surrounding stratum load will be calculated.

[0069] S4. Calculate the structural mechanical characteristics of the shield tunnel model 2 after the hole is opened in the three-dimensional numerical calculation model under the action of the surrounding external load.

[0070] The calculation formula for the number of longitudinal lining rings at the opening of shield tunnel model 2 is:

[0071] N = n + 2 × (m + 2), where N is the number of longitudinal rings of the shield tunnel model, n is the number of lining rings involved in the opening, and m is the range of the non-affected area on both sides of the opening, and m ≥ 5.

[0072] In addition, when the state of the segment lining 22 to be broken changes under the action of the surrounding external load, the states of all the contact and spring units related to it must be updated, the contact between the segment lining 22 to be broken and the adjacent segment lining 22 to be broken is set to an inactive state, the outer surface of the segment lining that has a contact relationship with the formation model 1 is updated so that it is only included in the active state in the current analysis step, and the spring unit that has a connection relationship with the segment lining 22 to be broken is killed.

[0073] In this embodiment, it should be noted that by killing the segmental lining 22 to be removed and applying equal ground stress to the stratum model 1 outside the segmental lining 22 to be removed, the stability of the stratum model 1 is maintained. The structural mechanical characteristics of the shield tunnel model 2 after the opening in the three-dimensional numerical calculation model are then calculated under the action of surrounding external loads. By setting up under the action of surrounding external loads, it is possible to avoid structural calculation non-convergence caused by factors such as the lack of contact between multiple ordinary segmental linings 21, the segmental lining 22 to be removed, and the segmental lining 23 outside the area to be removed, as well as distortion of the shield tunnel model 2 due to unconstrained springs.

[0074] Example 2:

[0075] The three-dimensional numerical calculation model of this embodiment can open holes of different shapes, positions, and angles in the simulated shield tunnel. The method is universal, and the structural responses under different opening conditions can be compared and analyzed.

[0076] As an implementation method of this embodiment, Figures 8-11As shown in the figure, the distribution curve of the lateral displacement of the arch haunch on the opening side along the tunnel axis is roughly "M" shaped, that is, the center of the opening moves horizontally toward the inside of the tunnel, and the positions on both sides of the opening move horizontally toward the outside of the tunnel. For assembled linings, the bending of the structure may cause the joints in the tensioned parts to open. In addition, it can be found that the circular opening ( Figure 10 and Figure 11 ) compared to the rectangular opening ( Figure 8 and Figure 9 ), the range of variation of the main tunnel structure displacement and the degree of curve bending are also larger.

[0077] As for the lateral displacement of the arch waist on the opposite side of the opening, the three working conditions of the circular opening are generally smaller than the three working conditions of the rectangular opening. This may be because the open ring in the middle of the circular opening has no direct effect of the external soil load on the opening side, so the displacement of the lining ring toward the opposite side of the opening is relatively small. In addition, for the same working conditions of circular or rectangular openings, the opening is located on the upper layer. Figure 8 and Figure 10 The outward horizontal displacement of the arch waist on the opposite side of the opening is greater. This is because the stiffness of the upper half of the lining structure is greatly weakened. Under the direct action of the overlying load, the lining structure has a more obvious "flattening" deformation trend, which leads to an increase in the horizontal displacement of the arch waist on the opposite side of the lining ring where the opening is located toward the outside of the tunnel.

[0078] Since the circular opening size is larger than the rectangular opening size, the overall vertical settlement of the vault in the circular opening working condition is greater than that in the rectangular opening working condition. The distribution curve of the vertical displacement of the lining vault along the tunnel axis for different rectangular opening working conditions is roughly "U"-shaped, and the vertical settlement of the lining ring vault at the opening is the largest. The distribution curve of the vertical displacement of the lining ring vault along the tunnel axis for different circular opening working conditions is roughly "V"-shaped, and the vertical settlement of the lining ring vault at the opening is the largest. This is because the circular opening size is larger and the middle is an unclosed ring, so the sudden change trend of the vertical deformation of the middle ring is greater. In the three working conditions of rectangular openings, under the combined influence of the weakening of structural stiffness and the disappearance of external loads on the lining at the opening, the vault settlement of the working condition where the opening is located in the upper layer is the largest, followed by the working condition where it is located at the bottom of the arch. In the two working conditions of circular openings, the middle part of the opening is an unclosed ring with low stiffness, which is the main influencing factor of the deformation of the lining ring. The opening is located in the upper layer. Figure 10 The vault settlement is the largest.

[0079] The influence of the opening position on the structural convergence deformation is relatively complex. On the one hand, the opening will cause the structural stiffness to weaken, and the degree of weakening of the structural stiffness varies with the shape of the opening. On the other hand, the initial load on the lining ring at the opening disappears, and the stress state of the structure changes. In addition, the assembly point of the lining ring may also affect the structural deformation. At different assembly points, the position of the joints and seams between the pipe rings near the opening may be different. Therefore, the influence of the opening position on the convergence deformation of the lining structure is complex, but for the same size opening working conditions, the overall difference in the vertical convergence rate of the main tunnel is small: the difference in deformation rate of different working conditions for rectangular openings is less than 0.67%, and the difference in deformation rate of different working conditions for circular openings is less than 1.15%.

[0080] The main results of the calculation and analysis output of the present invention include deformation, stress, and contact status. By analyzing the deformation of the lining, it can be determined whether the opening of a hole in the shield tunnel may cause excessive structural deformation, exceeding the limits of the specification; by analyzing the stress of the lining, it can be determined whether the local stress concentration of the structure caused by the opening of the hole in the shield tunnel model exceeds the bearing capacity limit of the material; by analyzing the stress of the joint, the safety status of the joint can be determined in combination with the tensile or shear bearing capacity of the joint; by analyzing the contact state of the segment lining joint, including the amount of opening and slippage, combined with the requirements of the joint waterproofing specification, the safety of the segment joint waterproofing can be determined. Then, according to the different adverse response characteristics of the shield tunnel model, a targeted structural safety assurance strategy can be formulated.

[0081] Throughout this specification, references to terms such as "one embodiment," "example," or "specific example" indicate that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0082] The preferred embodiments of the present invention disclosed above are intended only to help illustrate the present invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the present invention to the specific embodiments described. Obviously, many modifications and variations are possible based on the content of this specification. These embodiments are selected and described in detail in this specification to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to better understand and utilize the present invention. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for determining the influence of shield tunnel opening on the mechanical characteristics of the main structure, characterized in that: The following steps are involved: S1. Construct a three-dimensional numerical calculation model of the shield tunnel; The three-dimensional numerical calculation model is composed of a stratum model and a shield tunnel model set in the stratum model, and the shield tunnel model is composed of ordinary segment lining, segment lining to be broken, and segment lining outside the portion to be broken; S2. calculating the initial ground stress of the formation model in the three-dimensional numerical calculation model; S3. Calculate the deformation and stress of the shield tunnel model without openings in the three-dimensional numerical calculation model under the action of the surrounding stratum load; S4. Calculate the structural mechanical characteristics of the shield tunnel model after opening in the three-dimensional numerical calculation model under the action of surrounding external loads; In step S1, the boundary conditions of the three-dimensional numerical calculation model are: The sides of the formation model are normal constraints; The bottom of the stratum model is a fixed constraint; The top of the stratigraphic model is the free surface; The normal preload is set in the longitudinal direction of the segment lining; The selection formula of the normal preload force is: , where p is the normal preload, F is the resultant water and soil pressure in front of the shield tunnel excavation face, S is the shield lining annular joint contact area, and α is the lining annular joint stress relaxation coefficient; In step S4, when the state of the segment lining to be broken changes under the action of the surrounding external load, the states of all the contact and spring units related to it are updated, the contact between the segment lining to be broken and the adjacent segment lining to be broken is set to an inactive state, the outer surface of the segment lining that has a contact relationship with the formation model is updated so that it is only included in the active state in the current analysis step, and the spring unit that has a connection relationship with the segment lining to be broken is killed.

2. The method for determining the influence of shield tunnel opening on the mechanical characteristics of the main structure according to claim 1 is characterized in that: In step S1, each segment lining is an elastic unit.

3. The method for determining the influence of shield tunnel opening on the mechanical characteristics of the main structure according to claim 1 is characterized in that: In step S1, shear-resistant, tensile-resistant and elastic joints are provided between the segment linings, and the joints are spring units.

4. The method for determining the influence of shield tunnel opening on the mechanical characteristics of the main structure according to claim 1 is characterized in that: In step S1, a binding constraint is set between the segment lining to be broken and the segment lining outside the portion to be broken.

5. The method for determining the influence of shield tunnel opening on the mechanical characteristics of the main structure according to claim 1 is characterized in that: In the step S1, the segment lining to be broken and the segment lining outside the portion to be broken are also included in a reasonable cutting process, whereby the segment lining to be broken and the segment lining outside the portion to be broken are divided into hexahedrons.

6. The method for determining the influence of shield tunnel opening on the mechanical characteristics of the main structure according to claim 1 is characterized in that: In step S3, the opening shape of the shield tunnel model is square or circular.

7. The method for determining the influence of shield tunnel opening on the mechanical characteristics of the main structure according to claim 1 is characterized in that: In step S4, the calculation formula for the number of longitudinal lining rings at the opening of the shield tunnel model is: , where N is the number of longitudinal rings of the shield tunnel model, n is the number of lining rings involved in the opening, m is the range of the non-affected area on both sides of the opening, and m≥5.

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