Prestressed shield tunnel structure design method

Abstract

The invention discloses a prestressed shield tunnel structure design method. The method comprises the following steps: S1, determining basic design parameters of a prestressed shield tunnel; s2, designing a plurality of prestress schemes; s3, determining overall effective axial force distribution under various prestress schemes; s4, establishing a tunnel structure homogeneous ring model according to a new correction conventional method; s5, calculating water and soil load internal force distribution of the most unfavorable section tunnel structure by adopting a load structure method; s6, calculating the overall internal force distribution of the tunnel structure after the prestress effect is considered; s7, preferably selecting a tunnel structure reinforcement scheme and a prestress scheme by considering the cost; by means of the method, the prestressed shield tunnel structure design method which considers the prestress loss and considers the reinforcement effect of the prestress on the segment structure is creatively provided, and by representing the performance advantages of the prestressed shield tunnel structure, the use amount of reinforcing steel bars is effectively reduced, and the production cost is reduced; meanwhile, the design method is clear in concept and simple in calculation and conforms to use habits of designers.

Description

Technical Field

[0001] The present invention relates to the technical field of shield tunnel structures, and particularly to a design method for prestressed shield tunnel structures. Background Art

[0002] By applying a certain precompressive stress to concrete to form prestressed concrete, the tensile stress generated during the load-bearing of the structure can be offset or partially offset, achieving the effects of improving the mechanical properties such as crack resistance, stiffness, and bearing capacity of the structure and reducing the amount of steel bars. Introducing the prestress technology into the existing shield tunnel structure can form a prestressed shield tunnel structure.

[0003] The prestressed shield tunnel structure can provide an additional axial force for the tunnel structure by applying prestress, forming a self-stabilizing structural system. At the same time, it reduces the structural deformation and hardly increases the bending moment, and the structure is more reasonably stressed. Compared with the existing shield tunnel structure, the prestressed shield tunnel structure can achieve a stiffness close to that of cast-in-place concrete, and the mechanical properties such as structural toughness, ductility, cracking load, and ultimate bearing capacity are all greatly improved. It can effectively avoid diseases such as large deformation, water leakage, and settlement, reduce the consumption of steel bars and concrete, and extend the service life.

[0004] Therefore, in view of the above defects, the designers of the present invention, through painstaking research and design, and integrating the experience and achievements of being engaged in related industries for many years, have studied and designed a design method for prestressed shield tunnel structures that can reflect the action mechanism of prestressed shield tunnel structures, and at the same time conforms to the usage habits of designers and is simple and easy to use, so as to overcome the above defects. Summary of the Invention

[0005] The purpose of the present invention is to provide a design method for prestressed shield tunnel structures, and a design method for prestressed shield tunnel structures that considers prestress loss and takes into account the enhancement effect of prestress on the segment structure is proposed. It can characterize the performance advantages of prestressed shield tunnel structures, reduce the amount of steel bars, and reduce production costs; at the same time, the concept of the design method is clear, the calculation is simple, and it conforms to the usage habits of designers.

[0006] To achieve the above purpose, the present invention discloses a design method for prestressed shield tunnel structures, which is characterized by including the following steps: S1. Determine the basic design parameters of the prestressed shield tunnel; S2. Design multiple prestress schemes; S3. Determine the overall effective axial force distribution under multiple prestress schemes; S4. Establish a homogeneous circular ring model of the tunnel structure according to the newly revised conventional method; S5. Calculate the internal force distribution of the water and soil loads on the tunnel structure at the most unfavorable section by the load structure method; S6. Calculate the overall internal force distribution of the tunnel structure after considering the prestress effect; S7. Consider the cost and select the optimal reinforcement and prestressing schemes for the tunnel structure.

[0007] The steps include: S1. Determine the basic design parameters of prestressed shield tunnel according to tunnel type, function, ground conditions and shield parameters; S2. Design various prestressing schemes based on the bonded or non-bonded tensioning scheme and the number of single-bundle prestressing strands; S3. Calculate the long-term prestress loss of a single prestressed strand and determine the overall effective axial force distribution under various prestressing schemes; S4. Establish a homogeneous circular ring model of the tunnel structure and use the new correction method to correct the stiffness of the tunnel structure; S5. Use the load structure model to calculate the water and soil load internal force distribution of the tunnel structure at unfavorable sections along the shield tunnel, and calculate and determine the water and soil load internal force distribution of the tunnel structure at the most unfavorable section; S6. Determine the overall internal force distribution of the tunnel structure based on the water and soil load internal force distribution and the overall effective axial force distribution of the tunnel structure at the most unfavorable section; S7. Comprehensively consider the main reinforcement scheme and prestressing scheme of the prestressed shield tunnel structure, and select the scheme with the lowest cost as the reinforcement scheme of the prestressed shield tunnel structure.

[0008] Among them, the prestressed shield tunnel includes multiple prestressed blocks arranged in a ring, which are divided into prestressed anchor blocks, prestressed capping blocks, prestressed standard blocks and prestressed adjacent blocks. The prestressed standard blocks are located at the bottom of the tunnel structure, and their two ends are connected to the prestressed anchor blocks. The other end of the prestressed anchor block is connected to the prestressed adjacent block. The prestressed capping block is located at the top of the tunnel structure, and its two ends are connected to the prestressed adjacent blocks. Prestressed channels that are interconnected are pre-buried inside each prestressed block. Each prestressed block is connected in an annular direction by a longitudinal seam connector and in a longitudinal direction by an annular seam connector.

[0009] Wherein, the S3 specifically includes: S31. Calculate the long-term prestress loss and overall effective axial force of a single prestressed strand under various prestressing schemes; S32, calculating the angle between the prestressed anchor blocks; S33. Calculate the overall effective axial force of the prestressed shield tunnel structure under various prestressing schemes based on the angles between the prestressed anchor blocks.

[0010] Wherein, the S4 specifically includes: S41. A homogeneous circular ring model of a prestressed shield tunnel is established using beam elements of equal cross-section and stiffness, and the interaction between the model and the stratum is based on a foundation spring model; S42. Set the overall stiffness of the homogeneous circular ring model according to the stiffness adjustment coefficient of the newly revised conventional method.

[0011] Among them, the specific steps of S5 are as follows: Select the most unfavorable cross-sections where the tunnel overburden is the thickest and thinnest, the groundwater level is the highest and lowest, there is overloading or bias pressure, and the tunnel passes through sudden changes in formation conditions. Use the load structure model to calculate the internal force distribution of the tunnel structure's water and soil loads for each unfavorable cross-section in turn, and determine the most unfavorable cross-section and the corresponding internal force distribution of the water and soil loads.

[0012] Among them, the specific steps of S6 are as follows: The overall bending moment of the prestressed shield tunnel structure is the bending moment of the water and soil loads after the ordinary shield tunnel structure adopts the newly revised conventional method; the overall axial force is the sum of the axial force of the water and soil loads after the ordinary shield tunnel structure adopts the newly revised conventional method and the overall effective axial force of the tunnel structure.

[0013] Among them, the specific steps of S7 are as follows: Calculate the reinforcement plans in turn according to the overall internal force distribution of the prestressed shield tunnel structure under various prestress schemes, and then calculate the total cost of steel bars and prestressed strands under various prestress schemes in turn. Select the main reinforcement plan and prestress scheme with the lowest total cost.

[0014] It can be seen from the above that the design method of the prestressed shield tunnel structure of the present invention has the following effects: 1. The newly revised conventional method proposed by the present invention takes into account the prestress loss and the strengthening effect of prestress on the segment structure on the basis of the traditional revised conventional method. The introduced stiffness adjustment coefficient can adjust the stiffness of the prestressed shield tunnel structure. The stiffness of the adjusted prestressed shield tunnel structure is between the stiffness reduction coefficient of the traditional revised conventional method and 1, which can better characterize the performance advantages of the prestressed shield tunnel structure.

[0015] 2. The present invention simplifies the calculation of the overall internal force of the prestressed shield tunnel structure, that is, the overall bending moment is the bending moment of the water and soil loads after the ordinary shield tunnel structure adopts the newly revised conventional method; the overall axial force is the sum of the axial force of the water and soil loads after the ordinary shield tunnel structure adopts the newly revised conventional method and the overall effective axial force of the tunnel structure. The concept is clear, the calculation method is simple, and it conforms to the usage habits of designers.

[0016] 3. The present invention designs various prestress schemes, and determines the main reinforcement plan and prestress scheme with the lowest total cost through calculation. Compared with the traditional shield tunnel design scheme, the amount of steel bars used is less and the production cost is lower.

[0017] The detailed content of the present invention can be obtained through the following description and the accompanying drawings. Brief Description of the Drawings

[0018] Figure 1 Shows a schematic diagram of the design method of the prestressed shield tunnel structure of the present invention.

[0019] Figure 2 Shows a schematic diagram of the prestressed shield tunnel structure of the present invention.

[0020] Figure 3 Shows a schematic diagram of the prestressed anchorage block of the prestressed shield tunnel structure of the present invention.

[0021] Figure 4 Shows a schematic diagram of the effective axial force of a single prestressed strand considering prestress losses in the present invention.

[0022] Figure 5 Shows a schematic diagram of the effective axial force of a single prestressed strand at different anchorage end positions and the overall effective axial force of the tunnel structure considering prestress losses in the present invention.

[0023] Figure 6 Shows a schematic diagram of the load-deformation curve at the elastic stage during the full-scale ring loading test of the prestressed segment structure and the ordinary segment structure of the present invention.

[0024] Figure 7 Shows a schematic diagram of the influence of the increase in the stiffness of the tunnel structure on the internal forces of the structure in the present invention.

[0025] Figure 8 Shows a schematic diagram of the new modified conventional method of the prestressed shield tunnel structure of the present invention.

[0026] Figure 9 Shows a schematic diagram of the axial force monitoring results of the full-scale ring loading test of the prestressed segment structure and the ordinary segment structure of the present invention.

[0027] Figure 10 Shows a schematic diagram of the bending moment monitoring results of the full-scale ring loading test of the prestressed segment structure and the ordinary segment structure of the present invention.

[0028] Figure 11 Shows a schematic diagram of the axial force difference between the full-scale ring loading test of the prestressed segment structure and the ordinary segment structure of the present invention and the axial force provided by the prestressed strands.

[0029] Figure 12 Shows a schematic diagram of the calculation of the prestress loss of steel bars considering reverse friction in the present invention.

[0030] Reference signs: 100: Prestressed anchorage block; 101: Prestressed crown block; 102: Prestressed standard block; 103: Prestressed duct; 104: Longitudinal joint connector; 105: Circumferential joint connector. Detailed implementation manners

[0031] See Figures 1 to 12, showing the prestressed shield tunnel structure design method of the present invention.

[0032] like Figure 1 As shown, the present invention discloses a prestressed shield tunnel structure design method, which may include the following steps: S1. The basic design parameters of prestressed shield tunnels can be determined according to tunnel type, function, ground conditions, shield parameters, etc. S2. Design various prestressing schemes based on the bonded or non-bonded tensioning scheme, the number of single-bundle prestressing strands, etc.; S3. Calculate the long-term prestress loss of a single prestressed strand and determine the overall effective axial force distribution under various prestressing schemes; S4. Establish a homogeneous circular ring model of the tunnel structure and use the new correction method to correct the stiffness of the tunnel structure; S5. Use the load structure model to calculate the water and soil load internal force distribution of the tunnel structure at unfavorable sections along the shield tunnel, and calculate and determine the water and soil load internal force distribution of the tunnel structure at the most unfavorable section; S6. Determine the overall internal force distribution of the tunnel structure based on the water and soil load internal force distribution and the overall effective axial force distribution of the tunnel structure at the most unfavorable section; S7. Comprehensively consider the main reinforcement scheme and prestressing scheme of the prestressed shield tunnel structure, and select the scheme with the lowest cost as the reinforcement scheme of the prestressed shield tunnel structure.

[0033] Figures 2 to 3 The schematic diagram of the prestressed shield tunnel structure design is shown. Figure 2 In the present invention, the prestressed shield tunnel includes a plurality of prestressed blocks arranged in a ring, which can be divided into a prestressed anchor block 100, a prestressed capping block 101, a prestressed standard block 102 and a prestressed adjacent block. The prestressed standard block 102 is located at the bottom of the tunnel structure, and its two ends are connected to the prestressed anchor block 100. The other end of the prestressed anchor block 100 is connected to the prestressed adjacent block. The prestressed capping block 101 is located at the top of the tunnel structure, and its two ends are connected to the prestressed adjacent block. Prestressed channels 103 interconnected with each other are embedded in each prestressed block, such as Figure 3 Each prestressed block is connected in the annular direction by a longitudinal seam connector 104 and in the longitudinal direction by an annular seam connector 105.

[0034] The design method of the prestressed shield tunnel structure of the present invention is carried out according to the following principles: First, the outer diameter, ring width, erection plan of the erector, etc. of the prestressed shield tunnel structure should meet the performance requirements of the shield machine equipment; the prestressed anchorage block 100 should be arranged near the pedestrian passage of the shield machine and symmetrically arranged on both sides of the tunnel structure to ensure that the prestress tensioning can utilize the pedestrian passage of the shield machine and ensure that the circumferential prestress distribution of the entire tunnel is more uniform; the segmental plan of the prestressed shield tunnel structure can adopt a prestressed crown block 101 with a larger central angle according to the erection ability of the erector to improve the top stiffness of the tunnel structure and reduce the damage of the prestressed crown block 101; the prestressed shield tunnel structure preferably adopts a continuous joint erection plan to ensure the position of the prestressed anchorage block 100 remains unchanged and can reduce the cost of the pre-embedded system; the prestressed shield tunnel structure should be provided with at least two prestressed ducts 103, and each prestressed duct 103 should ensure that the tunnel structure is covered circumferentially by 360°; it is recommended to cancel the bolts as the longitudinal joint connectors 104 and circumferential joint connectors 105 for the prestressed shield tunnel structure. The longitudinal joint connectors 104 are preferably connected by positioning rods, male and female tenons or flat joints, and the circumferential joint connectors 105 are preferably connected by socket joints.

[0035] Among them, preferably in the present invention, the design of multiple prestress schemes in step S2 may include the following steps: S21. The prestressed strands can be selected with a bonded tensioning scheme or an unbonded tensioning scheme. When the bonded tensioning scheme is adopted, prestressed strands are selected. However, after the strands are tensioned, grouting needs to be carried out in the prestressed duct 103. The advantage is to ensure the bonding performance between the prestressed strands and the tunnel structure. Even if the tensioning anchor fails, the structural safety can still be ensured. However, this scheme has a large prestress loss and poor uniformity of circumferential prestress distribution; when the unbonded tensioning scheme is adopted, PE sheath steel strands need to be selected (a type of prestressed strand specifically used for the unbonded tensioning scheme, that is, a layer of PE material jacket is wrapped outside the prestressed strand, and the jacket is filled with grease). Grease is filled between this prestressed strand and the PE. The advantages are small prestress loss, greater increase in the circumferential axial force of the tunnel structure, and more uniform stress, but the cost is higher and the reliability requirements for the anchorage system are also higher.

[0036] S22. The tensile control stress of a single prestressed strand is generally 0.75 of the ultimate tensile strength. After considering the prestress loss, the effective axial force on the prestressed shield tunnel structure is basically fixed. By increasing the number of strands in a single bundle of prestressed strands, the effective axial force on the prestressed shield tunnel structure can be effectively increased. During the subsequent reinforcement process, the main reinforcement ratio can be reduced. However, there is a requirement for the minimum main reinforcement ratio of 0.2%, and the cost of prestressed strands is higher than that of ordinary steel bars. That is, there is an optimal value between the number of strands in a single bundle of prestressed strands and the main reinforcement ratio. Due to the large differences in tunnel structure design parameters, stratum conditions, etc. in different projects, the number of strands in a single bundle of prestressed strands cannot be determined. Therefore, it is necessary to design multiple prestress schemes. For the convenience of designers to design the number of strands in a single bundle of prestressed strands, the effective axial force can be estimated and the number of strands in a single bundle of prestressed strands can be selected according to the following cases. For example, the tensile control stress of a single prestressed strand with a diameter of 15.2 mm is 1320 MPa, and the area is about 140 mm 2 , and the prestress loss is calculated at 45%. Then the effective axial force of a single prestressed strand is about 1320 MPa * 140 mm 2 * (1 - 45%) = 101.64 kN. Generally speaking, for a prestressed shield tunnel structure with an outer diameter of 6 m, when 2 prestress ducts 103 are tensioned, the recommended number of strands in a single bundle of prestressed strands is 4, and the effective axial force that can be provided at this time is about 813.12 kN; for a prestressed shield tunnel structure with an outer diameter of 10 m, when 2 prestress ducts 103 are tensioned, the recommended number of strands in a single bundle of prestressed strands is 6, and the effective axial force that can be provided at this time is about 1219.68 kN. However, as the number of strands in a single bundle of prestressed strands increases, the inner diameter of the prestress duct 103 also needs to be increased accordingly. Thus, those skilled in the art can know that the number of strands in a single bundle of prestressed strands is related to tunnel structure design parameters, stratum conditions, etc., and the prestress scheme can be designed based on the above number of strands and the corresponding axial force values.

[0037] Among them, preferably in the present invention, the calculation method for the long-term prestress loss of a single bundle of prestressed strands and the overall effective axial force distribution of the prestressed shield tunnel structure in step S3 is as follows: S31. Refer to Section 6.2 of the current industry standard "Code for Design of Highway Reinforced Concrete and Prestressed Concrete Bridges and Culverts" JTG 3362 to calculate the long-term prestress loss of a single bundle of prestressed strands. The main influencing factors of the prestress loss include: : The friction between the prestressed strand and the prestress duct wall; : The deformation of the anchor at the tensioning end and the retraction of the prestressed strand; : The temperature difference between the prestressed strand and the pedestal (not applicable to the post-tensioning method); :Elastic compression of concrete; :Stress relaxation of prestressed strands; :Shrinkage and creep of concrete.

[0038] Among them to are short-term prestress losses, and are long-term prestress loss terms. The post-tensioning method is used for the construction of the prestressed shield tunnel structure, and the design service life of the tunnel structure exceeds 100 years. Long-term prestress losses need to be considered. That is, the calculation of prestress losses needs to consider 、 、 、 、 、 .

[0039] Among them, each parameter that needs to be considered in the above calculation of prestress losses can be determined according to the current national standards. Specifically, the calculation method of prestress losses for prestressed shield tunnels is as follows: The calculation method of is as shown in Equation 1: In the formula —— Tensile control stress value of prestressed strands; —— Friction coefficient between prestressed strands and the wall of prestressed ducts; —— Sum of the angles of the tangent lines of the curved duct part from the tensioning end to the calculated section; —— Influence coefficient of local deviation per meter of prestressed duct on friction; —— Duct length from the tensioning end to the calculated section.

[0040] The prestressed shield tunnel structure is symmetrically tensioned at both ends. Since the prestress losses are symmetric, The value range can be half of the total length of the prestressed duct 103.

[0041] The calculation method of The prestressed shield tunnel has a curved prestressed strand. It is usually assumed that the reverse friction coefficient caused by anchor deformation, retraction, etc. is the same as the forward friction coefficient, and the direction of prestress loss is opposite. As Figure 12 shown, among which The reverse friction influence length of (2) (3) Wherein — The prestress loss caused by pipeline friction per unit length; — The prestress loss caused by pipeline friction; — The deformation of the anchor at the tensioning end and the retraction value of the prestressed strand; — The distance between the tensioning end and the anchoring end; — The elastic modulus of the prestressed strand.

[0042] The prestressed shield tunnel structure is symmetrically tensioned at both ends. Therefore, When, the prestress loss of the prestressed strand at the position away from the tensioning end Considering the reverse friction can be calculated according to the following formulas (4) and (5): (4) (5) The calculation method of is as formula (6): (6) Wherein — The normal stress of concrete generated by the later tensioned prestressed strands at the centroid of the prestressed strands completed in tensioning at the calculated section; — The ratio of the elastic modulus of the prestressed strand to the elastic modulus of concrete.

[0043] In the prestressed shield tunnel structure, considering that the influence range of the prestressed strand on other surrounding prestressed strands is limited, it is assumed that each prestressed strand is only affected by half of the prestressed strands on both sides, and since the circumferential prestressed strands are located on the neutral plane, the item of the increase in the normal positive pressure caused by eccentricity is not considered. Then the above formula becomes: (7) Wherein — The area of a single prestressed strand; — The thickness of the segment; — The spacing of the prestressed ducts; — The effective stress value after deducting the first two prestress losses.

[0044] The calculation method of is as formula (8): (8) Wherein — Standard value of the tensile strength of the prestressed stranded wire.

[0045] The prestressed shield tunnel structure adopts low-relaxation prestressed stranded wires. After deducting the anchorage friction loss, the tension control stress does not exceed 0.7 .

[0046] The calculation methods are as shown in Equations 9 and 10: (9) (10) Wherein — Normal compressive stress of concrete generated by the prestressed stranded wire and self-weight (vertical prestressed stranded wire needs to be considered). During calculation, the corresponding stage prestress loss is deducted; — Elastic modulus of the prestressed stranded wire; — Reinforcement ratio of the main reinforcement and prestressed stranded wire; — Net cross-sectional area, that is, the area after deducting the duct and steel bars; — Area of a single bundle of prestressed stranded wire; — Number of bundles of prestressed stranded wire; — Area of the main reinforcement, taking 0.002A n ; — Ultimate value of the shrinkage strain; — Ultimate value of the creep coefficient.

[0047] Then the effective prestress of a single prestressed stranded wire at each section considering the long-term prestress loss is shown in Equation 11: (11) Wherein — Effective prestress; — Tension control stress value of the prestressed stranded wire.

[0048] The effective axial force of the prestressed shield tunnel structure at each section is shown in Equation 12: (12) Wherein — Effective axial force; —— Area of single - bundle prestressed strand; —— Number of prestressed strand bundles.

[0049] Example 1: Calculation of the effective axial force of a single - bundle prestressed strand and the overall effective axial force of the tunnel structure: The outer diameter of the prestressed segment structure is 6000 mm, the thickness is 300 mm, the ring width is 1200, the concrete is C50, 2 prestressed ducts are set, the spacing of the prestressed ducts is 600 mm, each bundle of prestressed strands uses 4 steel strands with a diameter of 15.2 mm, the cross - sectional area of a single - bundle prestressed strand is 560 mm 2 , the tension control stress is 1320 MPa, and the bonded tensioning scheme is adopted. The friction coefficient between the prestressed steel bars and the wall of the prestressed duct is 0.2, the influence coefficient of local deviation per meter of the prestressed duct on friction is 0.0015, the deformation of the anchor at the tensioning end and the retraction value of the prestressed tendon is 6 mm, the elastic modulus of the prestressed strand is 195 GPa. The ultimate value of the shrinkage strain is 0.000277, and the ultimate value of the creep coefficient is 1.73.

[0050] Substituting the relevant data of the prestressed segment structure in Example 1 into Equations (1) - (12), the effective axial force of each cross - section of a single - bundle prestressed strand within 360° in the circumferential direction can be calculated. As Figure 4 shown, the top of the prestressed segment structure is 0°, the rotation angle increases clockwise, and 180° is the anchoring end.

[0051] From Figure 4 it can be seen that due to the different distances of each cross - section of the prestressed segment structure from the anchoring end, the prestress losses of each cross - section are different, so the effective axial force shows a non - uniform distribution characteristic along the 360° circumferential range. Among them, the bottom is the anchoring end and the anchor retraction needs to be considered. The top is the farthest from the anchoring end, so the effective axial forces at the bottom and the top are smaller. The maximum and minimum values of the effective axial force are 478 kN and 298 kN respectively, and the difference is 195 kN, and the difference is 39.5% of the maximum value.

[0052] S32. From Figure 4 it can be seen that the difference in the effective axial force of a single - bundle prestressed strand within 360° in the circumferential direction is obvious. For the prestressed shield tunnel structure, if the anchoring positions of multiple bundles of prestressed strands are different, it will cause different overall effective axial force effects of the tunnel structure, that is, the position of the prestressed anchoring block 100 and the included angle between them have a greater impact on the overall effective axial force. Generally speaking, the anchoring end of the prestressed strand is located in the middle of the prestressed anchoring block 100, and there is na prestressed standard block 102, if the central angle of the prestressed anchorage block 100 is α 1, and the central angle of the prestressed standard block 102 is α 2, the included angle between the prestressed anchorage blocks 100 is α ( Figure 1 ) is: α=α 1 + nα 2.

[0053] Figure 5 shows the effective axial force of a single prestressed strand and the overall effective axial force of the tunnel structure at different anchorage end positions considering prestress losses. Among them, the anchorage ends of the two prestressed ducts are respectively located on both sides of the tunnel structure. The central angle of the prestressed anchorage block 100 is 67.5°, the central angle of the prestressed standard block 102 is 67.5°, and the included angle between the prestressed anchorage blocks 100 is 135°. The overall effective axial force of the tunnel structure is Figure 4 obtained by superimposing the data after clockwise selection of 67.5° and counterclockwise rotation of 67.5° of the effective axial force curve of a single prestressed strand in Figure 4 . Since the anchorage end of the effective axial force curve of a single prestressed strand in Figure 4 is at 180°, that is, at the bottom of the tunnel structure, the data of clockwise rotation of 67.5° is the effective axial force of the prestressed duct 103 corresponding to the left prestressed anchorage block 100, and the counterclockwise rotation of 67.5° is the effective axial force of the prestressed duct 103 corresponding to the right prestressed anchorage block 100. The distribution of the overall effective axial force is more uniform than that of the effective axial force of a single prestressed strand. The maximum and minimum values of the effective axial force are 928 kN and 753 kN respectively, and the difference is 175 kN, and the difference is 18.9% of the minimum value.

[0054] Among them, preferably in the present invention, the process of establishing the homogeneous circular ring model of the prestressed shield tunnel structure in step S4 is as follows: S41. Establish a homogeneous circular ring model of the prestressed shield tunnel using beam elements with equal cross-sections and stiffness, and adopt the foundation spring model for the interaction between the model and the stratum; Preferably, the beam element, equal cross-section, equal stiffness, and homogeneous circular ring model can refer to Article 7.2.2 of the current national standard "Design Standard for Shield Tunnel Engineering" GB / T 51438; the foundation spring model can refer to Article 7.2.7 of the current national standard "Design Standard for Shield Tunnel Engineering" GB / T 51438.

[0055] 1. According to the design parameters of the prestressed shield tunnel structure, including the outer diameter, inner diameter, ring width, thickness, concrete strength grade, etc. of the segment, establish a homogeneous circular ring model without considering the joint surface using beam elements. The cross-sectional dimensions of the circular ring model are equal (equal cross-section) and the elastic modulus of each cross-section is EI (equal stiffness); 2. The surrounding rock will impose loads on the prestressed shield tunnel. The surrounding rock can be equivalent to a foundation spring that only bears pressure in the normal direction and does not bear tension. The stiffness calculation formula of the foundation spring is as follows: (13) (14) In the formula —— normal spring stiffness of foundation (kN / m); —— Normal bed coefficient of the formation (kN / m 3 ); —— Calculation unit width (m); —— Average length of adjacent calculation units (m); —— Average bed coefficient of the stratum (kN / m 3 ); —— Average vertical bed coefficient of the stratum (kN / m 3 ); ——The angle between the center line of action of the spring and the horizontal line.

[0056] S42. Since the shield tunnel structure is a non-integral structure, the segments are connected by bolts and other connectors. Since the strength of bolts and other connectors is low and the preload provided is small, the stiffness of the segment joints is smaller than that of the segment body, making the overall stiffness of the shield tunnel structure lower than that of the homogeneous ring model. The traditional correction method uses the stiffness reduction factor η The stiffness of the homogeneous circular ring model is reduced, and the stiffness of the homogeneous circular ring model after reduction is ηEI However, after the prestress is applied to the prestressed shield tunnel structure, the prestressed strands can provide a joint load far greater than that of bolts and other connectors, greatly improving the stiffness of the segment joints and the tunnel structure. η , which will cause the numerical simulation stiffness of the prestressed shield tunnel structure to be lower than the actual stiffness, thereby causing an increase in structural deformation.

[0057] Example 2: Analysis of the stiffness difference between the full-scale full-ring loading test of the prestressed segment structure and the ordinary segment structure: Figure 6It is the load-deformation curve of the elastic stage during the full-scale full ring loading test of the prestressed segment structure and the ordinary segment structure. The dimensions of the prestressed segment structure and the ordinary segment structure are the same, with an outer diameter of 6000mm, a thickness of 300mm, and a ring width of 1200mm. The prestressed shield tunnel structure is equipped with two prestressed channels. Each prestressed strand uses 4 15.2mm steel strands with an area of ​​560mm. 2 The tension control stress is 1320MPa, and a bonded tensioning scheme is adopted. The loads applied to the tunnel structure are exactly the same. Through calculation, the stiffness of the ordinary segment structure and the prestressed segment structure in the elastic stage are 11.6kN / mm and 20.1kN / mm respectively, and the stiffness of the prestressed segment structure is increased by 73%.

[0058] Figure 7 The effect of tunnel structural stiffness improvement on structural internal force is shown. The percentage increase of structural stiffness is 0.8. EI As a benchmark, the internal force increase rate is 0.8 EI As shown in the figure, the increase in structural stiffness has little effect on the axial force, but has a certain effect on the maximum bending moment and the minimum bending moment, that is, when the stiffness increases by 10%, the maximum positive bending moment and the maximum negative bending moment increase by about 5.2% and 3.7% respectively.

[0059] Based on the test results of the full-scale ring test, the stiffness of the prestressed shield tunnel structure is about 1.73 ηEI , the stiffness reduction factor of the traditional modified method η Generally, the value is 0.7 or 0.8, then the stiffness of the prestressed shield tunnel structure will be greater than EI Considering that a certain amount of safety reserve should be reserved in actual design work, the parameter values ​​should be appropriately conservative. At the same time, the stiffness increase of the prestressed shield tunnel structure is not easy to accurately define during the design process. Taking all factors into consideration, the stiffness is increased based on the traditional modified method, but the increase should not exceed the cross-sectional stiffness of the homogeneous ring model. EI , forming a new modified practice applicable to prestressed shield tunnels, the stiffness of the ordinary segment structure is ηEI , Formula (15) takes into account the stiffness of the section after the prestressing force enhances the stiffness of the prestressed segment structure, and Formula (16) constrains the maximum stiffness of the prestressed segment structure, that is, k p ≤EI.

[0060] k p = ληEI (15) λη ≤1 (16) Where: k p—— The stiffness of the prestressed segment structure after cross-section adjustment; λ —— stiffness adjustment coefficient; η —— Stiffness reduction coefficient of traditional modified method; EI —— The section stiffness of the ordinary segment structure before the stiffness is reduced.

[0061] The new revised practice for prestressed shield tunnel structures is given in Figure 8 The new modified conventional method is used to calculate the internal forces of the tunnel structure. Due to the increase in stiffness, the axial force of the tunnel structure remains unchanged, but the bending moment increases slightly.

[0062] Preferably, in step S5, the stratum conditions, tunnel burial depth, groundwater level, surrounding environment, etc. along the shield tunnel are constantly changing, resulting in large differences in the water and soil loads of the shield tunnel structure at various sections along the tunnel, resulting in different distributions of its water and soil load internal forces. When analyzing the water and soil loads of the shield tunnel structure, unfavorable locations such as the thickest and thinnest tunnel cover, the highest and lowest groundwater levels, the presence of overload or bias, and the sudden change of the stratum conditions through which the tunnel passes should be selected to calculate the distribution of the water and soil load internal forces of the tunnel structure in sequence. Then, the most unfavorable sections in each calculated section are selected in sequence for reinforcement calculation, and then the most unfavorable section in the most unfavorable section along the entire tunnel is determined. Generally speaking, in the distribution of water and soil load internal forces in different sections, the top, bottom and both sides of the tunnel structure are unfavorable sections, and their bending moments are large and the axial forces are small.

[0063] Optionally, the internal force calculation can refer to Chapter 7 of the current national standard "Shield Tunnel Engineering Design Standard" GB / T 51438, and the reinforcement calculation can refer to Section 6.2 of the current national standard "Concrete Structure Design Standard" GB / T50010-2010 (2024 Edition).

[0064] Example 3: The difference in internal force distribution between the prestressed segment structure and the ordinary segment structure. A full-scale full-ring loading comparison test of the prestressed segment structure and the ordinary segment structure under the same conditions was carried out. The loading conditions included construction, operation, earthquake, overload, unloading, close construction, eccentric load, damage and other conditions. The test parameters are as follows: The dimensions of the prestressed segment structure and the ordinary segment structure are both 6000mm in outer diameter, 300mm in thickness, and 1200mm in ring width. The prestressed segment structure is equipped with 2 prestressed channels. Each bundle of prestressed strands uses 4 15.2mm steel strands with an area of ​​560mm 2 The anchoring ends of the two prestressed channels are located on both sides of the tunnel structure, the central angle of the prestressed anchor block 100 is 67.5°, the central angle of the prestressed standard block 102 is 67.5°, and the angle between the prestressed anchor blocks 100 is 135°. Under various loading conditions, the internal force difference between the prestressed segment structure and the ordinary segment structure shows the same trend.

[0065] Taking the operating conditions of a tunnel with a depth of 34m and a water level of -14.6m as an example, the difference in internal force distribution between the prestressed segment structure and the ordinary segment structure is explained. The bending moment and axial force are calculated from the strain gauge monitoring data during the test. Figure 9 and Figure 10 The bending moment difference between the prestressed segment structure and the ordinary segment structure is small, the maximum bending moment is 107kN·m and 101kN·m respectively, with a difference of 6kN·m; the axial force difference is large, the maximum axial force is 2606kN and 1830kN respectively, with a difference of 776kN.

[0066] Figure 11 The relationship between the difference in axial force between the two types of segment structures and the axial force provided by the prestressed strands is given by: Figure 5 The overall effective axial force of the tunnel structure, area 560mm 2 . Figure 10 The changing trends of the two curves are basically consistent and the values ​​are close, indicating that the difference in axial force between the prestressed segment structure and the ordinary segment structure is caused by the annular prestress applied by the prestressed segment structure.

[0067] Based on the above analysis, the bending moment of the prestressed segment structure is slightly greater than that of the ordinary segment structure under the same working condition. Considering that in the design process, when the new modified conventional method is used to calculate the internal force of the prestressed shield tunnel structure, the bending moment will increase slightly due to the use of higher stiffness. The result after the increase in bending moment is basically the same as the bending moment of the ordinary shield tunnel structure after the new modified conventional method is used. The axial force of the prestressed segment structure is approximately equal to the sum of the axial force of the ordinary segment structure under the same working condition and the axial force provided by the prestressed strand. Since the increase in stiffness has no effect on the axial force, the axial force of the ordinary segment structure is basically the same as the axial force of the ordinary segment structure using the new modified conventional method.

[0068] Therefore, in step S6, the overall bending moment distribution of the prestressed shield tunnel structure can be characterized by the bending moment distribution of the water and soil loads of the ordinary shield tunnel structure after the new modified conventional method is adopted, and the overall axial force distribution of the prestressed shield tunnel structure can be characterized by the sum of the axial force distribution of the water and soil loads of the ordinary shield tunnel structure after the new modified conventional method is adopted and the overall effective axial force distribution of the tunnel structure.

[0069] In step S7, under various prestressing schemes, due to the different numbers of single-bundle prestressing strands, for the prestressed shield tunnel structure, the overall axial force increases and the bending moment remains unchanged. According to the current national standard "Concrete Structure Design Code" GB50010, the axial force-bending moment combination under various prestressing schemes is reinforced, and the main reinforcement area and reinforcement amount of the segment section can be determined. The total cost of steel bars under different prestressing schemes is formula 17: C = W mr · C 1 + W hr · C 1 + W ps · C 2 + W pp · C 1 (17) Wherein: C — Total cost of steel bars for the prestressed shield tunnel structure; Wmr — Weight of main bars, related to the prestressing scheme. Generally, as the number of single - strand prestressing tendons increases, the amount of main - bar reinforcement decreases, and the weight reduces, but it cannot be lower than the minimum reinforcement ratio; C1 — Price of steel bars; Whr — Weight of stirrups, independent of the prestressing scheme; Wps — Weight of prestressing tendons, proportional to the number of single - strand prestressing tendons; C2 — Price of prestressing tendons; Wpp — Weight of prestressed protective steel bars.

[0070] Since the weights of stirrups and prestressed protective steel bars remain unchanged under different schemes. That is W hr · C 1 = 0, W pp · C 1 = 0. Then the total cost of steel bars can be simplified as: C = W mr · C 1 + W ps · C 2 (18) W mr = A s *π D ( D-H c / 2) (19) W ps = A p *π( D-H c / 2) (20) Where As —— Area of main reinforcement; A p —— Area of single - bundle prestressed stranded wire; n —— Number of prestressed stranded - wire bundles; D —— Outer diameter of segment; H c —— Thickness of segment.

[0071] By calculating the C values under different prestressed design schemes, select C the scheme with the minimum value.

[0072] It is obvious that the above description and record are only examples and not intended to limit the disclosure, application or use of the present invention. Although it has been described in the embodiments and illustrated in the drawings, the present invention is not limited to the specific examples shown in the drawings and described in the embodiments as the currently considered best mode for implementing the teachings of the present invention. The scope of the present invention will include any embodiments falling within the foregoing specification and the appended claims. The specification of the present invention contains multiple inventive concepts. Expressions such as "preferably" or "according to a preferred embodiment" indicate that the corresponding paragraphs disclose an independent inventive concept. The applicant reserves the right to file divisional applications according to each inventive concept. Throughout the text, the features guided by "preferably" are only optional and should not be construed as must - be - set. Therefore, the applicant reserves the right to waive or delete the relevant preferred features at any time.

Claims

1. A design method for a prestressed shield tunnel structure, characterized in that The following steps are involved: S1. Determine the basic design parameters of prestressed shield tunnel; S2. Design various prestressing schemes; S3. Determine the overall effective axial force distribution under various prestressing schemes; S4. Establish a homogeneous circular ring model of the tunnel structure according to the new modified conventional method; S5. Use the load structure method to calculate the internal force distribution of water and soil loads in the most unfavorable section of the tunnel structure; S6. Calculate the overall internal force distribution of the tunnel structure after taking into account the effect of prestressing; S7. Consider the cost and select the optimal reinforcement and prestressing schemes for the tunnel structure.

2. The design method for a prestressed shield tunnel structure according to claim 1, characterized in that The following steps are included: S1. Determine the basic design parameters of prestressed shield tunnel according to tunnel type, function, ground conditions and shield parameters; S2. Design various prestressing schemes based on the bonded or non-bonded tensioning scheme and the number of single-bundle prestressing strands; S3. Calculate the long-term prestress loss of a single prestressed strand and determine the overall effective axial force distribution under various prestressing schemes; S4. Establish a homogeneous circular ring model of the tunnel structure and use the new correction method to correct the stiffness of the tunnel structure; S5. Use the load structure model to calculate the water and soil load internal force distribution of the tunnel structure at unfavorable sections along the shield tunnel, and calculate and determine the water and soil load internal force distribution of the tunnel structure at the most unfavorable section; S6. Determine the overall internal force distribution of the tunnel structure based on the water and soil load internal force distribution and the overall effective axial force distribution of the tunnel structure at the most unfavorable section; S7. Comprehensively consider the main reinforcement scheme and prestressing scheme of the prestressed shield tunnel structure, and select the scheme with the lowest cost as the reinforcement scheme of the prestressed shield tunnel structure.

3. The design method for a prestressed shield tunnel structure according to claim 1 or 2, characterized in that: The prestressed shield tunnel comprises a plurality of prestressed blocks arranged in an annular manner, which are divided into prestressed anchor blocks, prestressed capping blocks, prestressed standard blocks and prestressed adjacent blocks. The prestressed standard blocks are located at the bottom of the tunnel structure, and both ends of the prestressed anchor blocks are connected. The other end of the prestressed anchor blocks is connected to the prestressed adjacent blocks. The prestressed capping blocks are located at the top of the tunnel structure, and both ends of the prestressed anchor blocks are connected to the prestressed adjacent blocks. Prestressed channels interconnected with each other are embedded in each prestressed block. Each prestressed block is connected in an annular direction by a longitudinal seam connector and in a longitudinal direction by an annular seam connector.

4. The design method for a prestressed shield tunnel structure according to claim 1 or 2, characterized in that The S3 specifically includes: S31. Calculate the long-term prestress loss and overall effective axial force of a single prestressed strand under various prestressing schemes; S32, calculating the angle between the prestressed anchor blocks; S33. Calculate the overall effective axial force distribution of the prestressed shield tunnel structure under various prestressing schemes based on the angles between the prestressed anchor blocks.

5. The design method for a prestressed shield tunnel structure according to claim 1 or 2, characterized in that The S4 specifically includes: S41. A homogeneous circular ring model of a prestressed shield tunnel is established using beam elements of equal cross-section and stiffness, and the interaction between the model and the stratum is based on a foundation spring model; S42. Set the overall stiffness of the homogeneous circular ring model according to the stiffness adjustment coefficient of the new modified convention.

6. The design method for a prestressed shield tunnel structure according to claim 1 or 2, characterized in that The S5 specifically includes: selecting unfavorable sections such as the thickest and thinnest tunnel cover, the highest and lowest groundwater levels, the presence of overload or bias, and the tunnel passing through a sudden change in stratum conditions, and using the load structure model to calculate the water and soil load internal force distribution of the tunnel structure at each unfavorable section in turn, and determining the most unfavorable section and the corresponding water and soil load internal force distribution.

7. The design method for a prestressed shield tunnel structure according to claim 1 or 2, characterized in that The S6 specifically includes: the overall bending moment of the prestressed shield tunnel structure is the bending moment of the water and soil loads after the new modified conventional method is adopted for the ordinary shield tunnel structure; the overall axial force is the sum of the axial force of the water and soil loads after the new modified conventional method is adopted for the ordinary shield tunnel structure and the overall effective axial force of the tunnel structure.

8. The design method for a prestressed shield tunnel structure according to claim 1 or 2, characterized in that The S7 specifically includes: calculating the reinforcement schemes in sequence according to the overall internal force distribution of the prestressed shield tunnel structure under various prestress schemes, then calculating the total costs of the steel bars and prestressed strands under various prestress schemes in sequence, and selecting the main reinforcement scheme and prestress scheme with the lowest total cost.

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