Shearing resistance load calculation method of shield tunnel circular seam joint

Abstract

The invention discloses an anti-shear bearing calculation method for a shield tunnel circular seam joint, and belongs to the technical field of shield tunnels, and the method comprises the steps: selecting a shield tunnel target circular seam joint; acquiring spatial sizes and bearing strength parameters of segments, steel bars and connecting pieces in the target circular seam joint; according to the space size in the circular seam joint, constructing a shearing resistance model of the circular seam joint in different bearing stages; and calculating the shear bearing capacity of the circular seam joint according to the shear models of the circular seam joint in different bearing stages. According to the method, the shearing resistance of the circular seam joint is calculated by constructing the shearing resistance models of the circular seam joint in different bearing stages, and the method has high theoretical guiding significance for safe construction of the shield tunnel; the method also has important guiding significance for setting parameters of the shield tunnel, including concrete strength, tensile steel bars of a concrete fracture area, duct piece thickness, connecting pieces and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of shield tunnels, and in particular relates to a shear bearing calculation method for annular joints of shield tunnels. Background Art

[0002] Shield tunneling is a fully mechanized construction method in dark excavation construction. It pushes the shield machine into the ground, and uses the shield shell and segments to support the surrounding rock to prevent collapse into the tunnel. At the same time, a cutting device is used to excavate the soil in front of the excavation face, and the soil is transported out of the cave by excavation machinery. The jack is used to pressurize and push forward at the rear, and precast concrete segments are assembled to form a mechanized construction method of tunnel structure.

[0003] During the shield tunnel construction process, the surrounding rock and soil are disturbed, which will produce huge shear forces on the segments. Therefore, the shear bearing capacity of the segment joints is very important. However, the existing technology lacks a method for calculating the shear bearing capacity of the segment joints and cannot provide theoretical support for the segment design. Summary of the invention

[0004] The purpose of the present invention is to provide a shear bearing calculation method for annular joints of shield tunnels in view of the above-mentioned deficiencies in the prior art, so as to solve the problem that the prior art lacks shear bearing calculation for segment joints.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A method for calculating the shear bearing capacity of annular joints of a shield tunnel comprises the following steps:

[0007] S1. Select the target annular joint of the shield tunnel;

[0008] S2, obtaining the spatial dimensions and bearing strength parameters of the pipe segments, steel bars, and connectors in the target annular joint;

[0009] S3, constructing the shear model of the girth joint at different load-bearing stages according to the spatial dimensions in the girth joint;

[0010] S4. Calculate the shear bearing capacity of the girth joint according to the shear model of the girth joint at different load-bearing stages.

[0011] Further, the target annular joint in S1 includes a segment joint; the segment joint includes a first segment and a second segment, a positioning tenon and a longitudinal bolt are provided between the annular joints of the first segment and the second segment; and the first segment and the second segment are connected by the positioning tenon and the longitudinal bolt;

[0012] The annular seam surface of the first pipe segment is prefabricated with a quasi-rectangular tenon groove, and the annular seam surface of the second pipe segment is prefabricated with a circular tenon hole. The tenon groove and the tenon hole are used to accommodate the positioning tenon.

[0013] Furthermore, S2 specifically includes:

[0014] The spatial dimensions of the segment include the thickness of the segment, the radial height L of the tongue and groove from the inner arc side of the first segment, and the R , the width of the upper plane of the mortise and tenon groove L D , height L from the center of the bolt hole on the joint surface to the inner arc surface r , the thickness of the segment protective layer C, the bearing strength parameters of the segment include the design value of the tensile strength of the concrete f t ;

[0015] The spatial dimensions of the steel bars include the number of steel bars i that can provide vertical tension around the locating tenon, the diameter A of the i-th steel bar, and the Si , the angle θ between the i-th steel bar and the vertical direction Si The bearing strength parameters of steel bars include the design value of the tensile strength of steel bars f y ;

[0016] The connecting parts include locating tenons and bolts; the spatial dimensions of the locating tenons include the inner diameter D of the locating tenons at the joints. Dn and outer diameter D Dw The bearing strength parameters of the locating tenon include the shear strength f D ; The space size of the bolt includes the bolt diameter D B The bearing strength parameters of the bolt include the tensile strength f B .

[0017] Furthermore, S3 specifically includes:

[0018] The shear resistance model of the annular joint is used to calculate the minimum shear bearing capacity of the annular joint in the most unfavorable stress direction, that is, to calculate the extrusion load of the concrete and steel bars of the first pipe segment above the mortise and tenon groove to bear the said connecting piece;

[0019] The shear model of the annular joint includes the concrete shear model, the steel bar shear model and the connector shear model;

[0020] The concrete shear model is a quadrangular prism AEGB-CFHD, which is caused by the positioning tenon squeezing the concrete above the tenon groove of the first pipe segment. The quadrangular prism is an isosceles trapezoid AEGB on the joint surface;

[0021] The steel bar shear model is a tetrahedron O-EMNG, which is caused by the bolts squeezing the concrete above the tenon groove of the first segment. The tetrahedron is an isosceles triangle OEG on the joint surface;

[0022] The shear resistance model of the connector is composed of the shear resistance mechanics equations of the locating tenon and the bolt.

[0023] Furthermore, in the tetrahedral AEGB-CFHD, AB=L D , EG=L C , GH=C, the height of isosceles trapezoid AEGB is L R ; The height of the tetrahedral pyramid O-EMNG is L r , EM=L L ;

[0024] L L and L c Derived from experimental test statistics; in L R 116mm, L r 160mm, L D When L is 66mm, L0 The experimental test is 370mm, L c The experimental test expression is:

[0025] L C0 =494-0.1827×N

[0026] According to the geometric relationship and similarity ratio, the radial height on the inner arc side of the first segment is L R When L c The calculation formula is:

[0027]

[0028] L L The calculation formula is:

[0029]

[0030] Where N is the longitudinal axial force.

[0031] Furthermore, the quadrangular prism AEGB-CFHD is the concrete shear bearing, the rectangular AEFC and rectangular BDHG in the quadrangular prism are the concrete tensile surfaces, and the trapezoidal CFHD is the shear surface under compression;

[0032] The O-EMNG of the tetrahedron is used for the shear bearing of the steel bars, and the steel bars that pass through the tetrahedron and can provide vertical force are considered;

[0033] In the shear model of the connector, the locating tenon provides shear bearing capacity; the bolt has sufficient deformation space and is mainly subjected to tension after deformation, thus providing tensile bearing capacity.

[0034] Furthermore, according to the shear model of the annular joint in the concrete shear stage, the shear bearing capacity of the annular joint in the concrete shear stage is calculated:

[0035] Q u1 =f t C(LC -L D )+0.35f t L R (L D +L C )+μN+K(N)

[0036] Among them, Q u1 is the shear bearing capacity of concrete in the shear stage; μ is the friction coefficient between concrete joint surfaces; K (N) is the shear load increment of the trapezoidal CFHD in the prism structure caused by the longitudinal axial force;

[0037] K(N) is obtained through experimental testing, and its calculation formula is:

[0038]

[0039] Furthermore, the shear bearing capacity of the connector is:

[0040]

[0041] Among them, Q u2 is the shear resistance of the connector.

[0042] Furthermore, according to the shear model of the circumferential joint in the steel bar shear stage, the shear bearing capacity of the joint in the steel bar shear stage is calculated as:

[0043]

[0044] Among them, Q u3 It is the shear bearing capacity of the joint during the steel bar shear stage.

[0045] Furthermore, in S4, the shear bearing capacity of the circumferential joint is calculated based on the minimum shear bearing capacity of the concrete in the shear stage, the shear bearing capacity of the connector, and the shear bearing capacity of the joint in the shear stage of the steel bar:

[0046] Q u =min{max[Q u1 ;Q u3 ]; Q u2}

[0047] Among them, Q u It is the minimum shear bearing capacity of the circumferential joint in the most unfavorable stress direction.

[0048] The shear bearing calculation method of the shield tunnel annular joint provided by the present invention has the following beneficial effects:

[0049] The present invention constructs a shear model of the annular joint at different load-bearing stages to calculate the shear bearing capacity of the annular joint, which has a strong theoretical guiding significance for the safe construction of the shield tunnel; it also has important guiding significance for the parameter setting of the shield tunnel, including the specific setting of concrete strength, tensile reinforcement in the concrete rupture zone, segment thickness and connectors. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 The present invention is a flow chart of the shear bearing calculation method of the shield tunnel annular joint.

[0051] Figure 2 This is a structural diagram of the shield tunnel segment of the present invention, wherein ① is a ring joint; ② is a longitudinal bolt; ③ is a positioning tenon;

[0052] Figure 3 This is the concrete shear model of the present invention.

[0053] Figure 4 This is the steel bar shear model of the present invention.

[0054] Figure 5 is the inclination angle of the steel bars in the steel bar shear resistance model of the present invention.

[0055] Figure 6 Q under different longitudinal axial forces of the present invention u1 , Q u2 , Q u3 and Q u The change curve. DETAILED DESCRIPTION

[0056] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0057] Example

[0058] This embodiment provides a method for calculating the shear bearing capacity of the annular joint of a shield tunnel. Figure 1 , which specifically includes the following steps:

[0059] Step S1, selecting the target annular joint of the shield tunnel, which specifically includes the following contents:

[0060] refer to Figure 2In this embodiment, the outer diameter of the shield tunnel is 8.3m, the inner diameter is 7.5m; the thickness of the segment is 0.4m, the width is 1.8m, and one ring of segments is divided into 1+2+4 blocks. The segments are connected by 19 evenly distributed longitudinal bolts. In order to control the number of variables studied, this embodiment selects Figure 2 The segment joint connected by one longitudinal bolt in the middle red line area is taken as the target object.

[0061] The pipe segment joint includes a first pipe segment and a second pipe segment. Specifically, a positioning tenon and a longitudinal bolt are provided between the annular seam of the first pipe segment and the second pipe segment. The first pipe segment and the second pipe segment are connected by the positioning tenon and the longitudinal bolt. Figure 2 The second segment is Figure 2 Segment 2 in the tube.

[0062] The annular seam surface of the first pipe segment is prefabricated with a quasi-rectangular tenon groove, and the annular seam surface of the second pipe segment is prefabricated with a circular tenon hole. The tenon groove and the tenon hole are used to accommodate the positioning tenon, so that the tenon holes and the tenon holes are at the same height, the tenon groove and the positioning tenon are in line-to-line contact, and the tenon hole and the positioning tenon are in surface-to-surface contact.

[0063] As a preferred embodiment of the present embodiment, in order to facilitate the assembly of the locating tenons, the locating tenons are larger in the middle and smaller on both sides, with a total length of 91 mm, a minimum inner diameter of 51.8 mm, and outer diameters of 86.8 mm at the center and 75.8 mm at the edge, respectively. The locating tenons are placed in prefabricated mortises and mortises; the mortise and tenon grooves are quasi-rectangular, located on the annular seam surface of the first segment, and form a line contact with the locating tenons; the mortise and tenon holes are circular, located on the annular seam surface of the second segment, and form a surface contact with the locating tenons. The longitudinal bolts are grade 8.8 and have a diameter of 30 mm. For the convenience of research, this embodiment stipulates that the coordinate axes X, Y, and Z are the circumferential, radial, and longitudinal directions of the segment, respectively, and the origin of the coordinate axes is shown at Figure 2 .

[0064] Step S2, obtaining the spatial dimensions and bearing strength parameters of the pipe segments, steel bars, and connectors in the target annular joint, which specifically includes the following contents:

[0065] refer to Figure 2 The spatial dimensions of the segment include the thickness of the segment, the radial height L of the tongue and groove from the inner arc side of the first segment, and the R , the width of the upper plane of the mortise and tenon groove L D , height L from the center of the bolt hole on the joint surface to the inner arc surface r , the thickness of the segment protective layer C, the bearing strength parameters of the segment include the design value of the tensile strength of the concrete f t .

[0066] The spatial dimensions of the steel bars include the number of steel bars i that can provide vertical tension around the locating tenon, the diameter A of the i-th steel bar, and the Si, the angle θ between the i-th steel bar and the vertical direction Si The bearing strength parameters of the steel bars include the design value of the tensile strength of the steel bars f y .

[0067] The connecting parts include locating tenons and bolts; the spatial dimensions of the locating tenons include the inner diameter D of the locating tenons at the joints. Dn and outer diameter D Dw The bearing strength parameters of the positioning tenon include the shear strength f D ; The space size of the bolt includes the bolt diameter D B The bearing strength parameters of the bolt include the tensile strength f B .

[0068] In this embodiment, the net distance between the mortise and tenon and the inner arc surface of the segment is 116 mm, and the net distance between the mortise and tenon hole and the outer arc surface is 196 mm. The inner arc side of the segment is the weakest part of the segment annular seam shear resistance. In addition, the mortise and tenon groove has a wider slot width than the tenon hole, and the inner arc side of the mortise and tenon groove of the first segment is the weakest part of the annular seam shear resistance. When the shear force borne by the segment is less than the shear bearing capacity of the inner arc side of the mortise and tenon groove of the first segment, the force on the segment is in an absolutely safe range.

[0069] Based on this, reference Figure 3 In this embodiment, a shear test is performed on the selected target annular joint to verify the accuracy of the calculation method of the present invention. Among them, the inner arc side, outer arc side and the free annular joint surface on the left side of the first segment are constrained by the reaction beam of the loading platform, limiting their displacement in the vertical and horizontal directions. Two vertical jacks and two horizontal jacks are installed on the outer arc side and the free annular joint surface of the second segment, respectively, for applying shear load and longitudinal axial force. Under this loading scheme, the inner arc side of the tenon groove of the first segment will bear the shear load.

[0070] Step S3, constructing a shear model of the annular joint at different load-bearing stages, which specifically includes the following contents:

[0071] The shear model of the annular joint is used to calculate the minimum shear bearing capacity of the annular joint in the most unfavorable stress direction, that is, the concrete and steel bars of the first segment above the mortise and tenon bearing the extrusion load of the connector.

[0072] The shear model of the annular joint includes the concrete shear model, the steel bar shear model and the connector shear model;

[0073] The construction of the concrete shear model is as follows:

[0074] refer to Figure 3According to the failure characteristics of the pipe segment, the concrete crack body is simplified into a prism structure, that is, the concrete shear model is a quadrangular prism AEGB-CFHD, which is caused by the positioning tenon squeezing the concrete above the tenon groove of the first pipe segment; the quadrangular prism is an isosceles trapezoid AEGB on the joint surface;

[0075] The quadrangular prism AEGB-CFHD is the concrete shear bearing, the rectangular AEFC and rectangular BDHG in the quadrangular prism are the concrete tensile surfaces, and the trapezoidal CFHD is the shear surface under compression;

[0076] In the tetrahedral AEGB-CFHD, AB=L D , EG=L C , GH=C, the height of trapezoid AEGB is L R The height of the tetrahedral pyramid O-EMNG is L r , EM=L L .

[0077] L L and the L c Derived from experimental test statistics; in L R 116mm, L r 160mm, L D When L is 66mm, L0 The experimental test is 370mm, L c The experimental test expression is:

[0078] L C0 =494-0.1827×N (1)

[0079] Where N is the longitudinal axial force, unit is kN, L c0 The unit is mm. According to the geometric relationship and similarity ratio, the radial height on the inner arc side of the segment 1 is L R Time c The calculation formula is:

[0080]

[0081] L L The calculation formula is:

[0082]

[0083] Specifically, refer to Figure 3 The bottom and top surfaces of the prism are both trapezoidal, and the width of the concrete crack at the mortise and tenon is L D , the length in the circumferential direction of the inner arc surface is L C , which is the width of the main fracture zone. The length of the concrete fracture body in the longitudinal direction of the segment is C, and the height in the radial direction of the joint surface is L RThe concrete crack body mainly has three shear surfaces, among which the ACEF rectangular surface and the BDGH rectangular surface are tensile surfaces, and the CDFH trapezoidal surface is the shear surface under compression;

[0084] According to the force relationship in the vertical direction of the joint surface, the shear resistance of the circumferential joint must meet the following requirements:

[0085] Q u1 -F f =F D1 ×cosθ D1 +F D2 ×cosθ D2 +F D3 (4)

[0086] Where:

[0087] Q u1 is the minimum shear bearing capacity of concrete in the shear stage, and its calculation formula is:

[0088] Q u1 =QG (5)

[0089] Q is the shear load during loading; F f is the friction between the joint surfaces, and the calculation formula is:

[0090] F f =μ×N (6)

[0091] Where: μ is the friction coefficient between the concrete joint surfaces; N is the longitudinal axial force; G is the deadweight of segment 2; F D1 is the maximum tension of the rectangular AEFC; θ D1 F D1 Angle with vertical direction; F D2 is the maximum tension of the rectangular BDHG; θ D2 F D2 Angle with vertical direction; F D3 is the shear capacity of the trapezoidal CFHD.

[0092] F D1 The calculation formula is:

[0093] F D1 =f t ×A D1 (7)

[0094] Where: f t A is the design value of tensile strength of concrete; D1 is the area of ​​the rectangular AEFC;

[0095] F D2 The calculation formula is:

[0096] FD2 =f t ×A D2 (8)

[0097] Where: A D2 is the area of ​​rectangle BDHG;

[0098] According to the geometric relationship, A D1 and θ D1 The calculation formulas are:

[0099]

[0100] Where: C is the thickness of the protective layer on the joint surface of segment 1; L R is the height of the rupture body in the radial direction of the joint surface; L C L is the length of the rupture body in the circumferential direction of the inner arc surface; D is the width of the rupture body at the mortise and tenon;

[0101] According to the geometric characteristics of the rupture body, there are:

[0102] A D2 =A D1 (11)

[0103] θ D2 =θ D1 (12)

[0104] So we have:

[0105] F D2 =F D1 (13)

[0106] Because F D3 is the shear load of the trapezoidal CFHD under compression. Its shear strength is significantly different from pure shear, because the shear strength of the structure is positively correlated with the axial force. Unlike the friction between the joint surfaces, the increase in the longitudinal axial force not only increases the pressure between the joint surfaces, but also the concrete is bidirectionally stressed under compression-shear load, which is more conducive to improving the shear strength of the concrete. Therefore, F D3 can be expressed as:

[0107] F D3 =V0+K(N) (14)

[0108] Where: V0 is the pure shear load of the trapezoidal CFHD; K (N) is the shear load increment of the trapezoidal CFHD caused by the longitudinal axial force; V0 is calculated according to the "Concrete Structure Design Code", that is:

[0109] V0=0.7×β h ×f t ×A D3(15)

[0110] Where: β h A is the cross-section height influence coefficient, which is taken as 1.0; D3 is the area of ​​the trapezoidal CFHD, which is calculated as:

[0111]

[0112] Substituting equations (7) to (16) into equation (4), we can obtain the shear bearing capacity of the concrete shear model:

[0113] Q u1 =f t ×C×(L C -L D )+0.35×β h ×f t ×L R ×(L D +L C )+μ×N+K(N) (17)

[0114] There is an unknown function K(N) in this expression, which must satisfy that when N=0, K(N)=0; K(N) can be obtained through shear tests on concrete under compression.

[0115] This embodiment provides a method for calculating K(N):

[0116] When there is only one set of compression-shear test data of annular joints, the function K(N) can be set as:

[0117] K(N)=k×N (18)

[0118] In the formula, k is a constant coefficient.

[0119] When there are multiple sets of test data, the function K(N) can be:

[0120] K(N)=k(N)×N (19)

[0121] Where k(N) is a function of the longitudinal axial force N, which can be obtained through mathematical statistics. Obviously, the more test data there are, the more accurate the value of the function K(N) will be.

[0122] K(N) is obtained through experimental testing, and its calculation formula is:

[0123]

[0124] The shear model of the connector is constructed; the shear model of the connector is composed of the shear mechanics equations of the locating tenon and the bolt. In the shear model of the connector, the locating tenon provides shear bearing capacity; the bolt has sufficient deformation space and is mainly tensile after deformation, providing tensile bearing capacity;

[0125] Therefore, the bearing capacity of the force transmission component, that is, the shear bearing capacity of the locating tenon and bolt is calculated as:

[0126] Q u2 =F D +F B +F f (twenty one)

[0127] In the formula, Q u2 is the shear bearing capacity of the force transmission component, and its calculation formula is:

[0128] Q u2 =QG (22)

[0129] In the formula, F D F is the shear bearing capacity of the locating tenon; B is the shear capacity of the bolt.

[0130] Finally, the shear bearing capacity of the connector is:

[0131]

[0132] Among them, Q u2 is the shear resistance of the connector.

[0133] For the construction of steel bar shear model;

[0134] refer to Figure 4 The steel bar shear model is a tetrahedron O-EMNG, which is caused by the bolts squeezing the concrete above the tenon groove of the first pipe segment. The tetrahedron is an isosceles triangle OEG on the joint surface; the tetrahedron O-EMNG is the steel bar shear bearing, and the steel bars that pass through the tetrahedron and can provide vertical force are considered;

[0135] The steel bar shear stage occurs after the concrete shear stage, and the shear load is mainly borne by the steel bars in the rupture area. According to the mechanical equilibrium equation, the steel bars that can provide vertical tension are mainly considered in the steel bar shear stage. Figure 4 As shown in the figure, the tearing of the concrete inside the segment is mainly caused by the longitudinal bolts, so the concrete rupture body is simplified into a pyramid structure, namely a tetrahedron OEMNG, to construct the shear model of the annular joint in the steel bar shear stage;

[0136] That is, the shear load is borne by the steel bars passing through the tetrahedron OEMNG, such as Figure 4 The red line in.

[0137] According to the mechanical balance of the segment annular joint in the vertical direction, the shear resistance of the joint in the steel bar shear resistance stage needs to meet the following requirements:

[0138]

[0139] In the formula, Q u3 is the joint shear bearing capacity in the steel bar shear stage, and its calculation formula is:

[0140] Q u3 =QG (25)

[0141] F Si is the tension of the i-th steel bar passing through the tetrahedron OEMNG; θ Si is the angle between the i-th steel bar and the vertical direction;

[0142] F Si The calculation formula is:

[0143] F Si =f y ×A Si (26)

[0144] f y A is the design value of steel bar tensile strength; Si is the cross-sectional area of ​​the i-th steel bar.

[0145] Step S4, calculating the shear bearing capacity of the annular joint according to the shear resistance model of the annular joint at different load-bearing stages, which is specifically:

[0146] From the above formula, we can know that the parameters corresponding to the shear bearing of the annular joint are obtained from three sources, namely, the Code for Design of Concrete Structures, segment design, and experimental statistics. Table 1 Parameters involved in the calculation formula. Among them, the segment is C50 concrete, and its density is 24.2kN / m 3 The volume of the second segment is based on Figure 2 The size calculation of the structural reinforcement (θ S1 to θ S4 )like Figure 5 The width L of the prism fracture body in the longitudinal direction of the ring L Taking the average value of Table 1, the circumferential width L of the prism fracture body is C Calculated by formula (2).

[0147] Table 1 Parameters involved in equations (1) to (26)

[0148]

[0149]

[0150] In addition, there are three parameters related to the experiment that need to be explained in detail. The friction coefficient between the annular joints is obtained according to the experiment, that is, the ratio of the maximum static friction force of the joint to the longitudinal axial force. The maximum static friction force is the shear force corresponding to the significant increase in the misalignment of the annular joint, as shown in Table 3. Finally, the friction coefficient takes the average value of the experimental value, that is, μ = 0.2. K (N) is calculated by formula (20), that is:

[0151]

[0152] Table 3 Load statistics at each stage of the test

[0153]

[0154] Since the mortise and tenon provide displacement space for the longitudinal bolts, the maximum tensile strength of the longitudinal bolts is 800MPa. The shear bearing capacity of the locating tenon is measured according to the specification "Insulation products for building use - Determination of shear properties" (GB / T 32382-2015). The maximum shear loads of the three locating tenon components are 198kN, 184kN and 183kN, respectively, with an average value of 188.3kN, that is, the maximum shear strengths of the three locating tenon components are 51.969MPa, 48.294MPa and 48.032MPa, respectively, with an average value of 49.432MPa. Based on the above parameters, Q u1 , Q u2 and Q u31 The expressions are:

[0155]

[0156] Q u2 =753.8+0.2N (29)

[0157] Q u3 =168.16+0.2N (30)

[0158] That is, according to the minimum shear bearing capacity of concrete in the shear stage, the shear bearing capacity of the force transmission component and the shear bearing capacity of the joint in the shear stage of the steel bar, the shear bearing capacity of the circumferential joint is calculated as:

[0159] Q u =min{max[Q u1 ;Q u3 ]; Q u2} (31)

[0160] According to formula (31), the shear bearing calculation formula of the circumferential joint is:

[0161]

[0162] Among them, Q u is the shear bearing capacity of the circumferential joint.

[0163] The theoretical value of the shear bearing capacity of the annular joint can be calculated by formula (32). The theoretical value and experimental value of the shear bearing capacity of the annular joint are shown in Table 4. By comparison, it is found that the theoretical calculation value and the experimental value are very consistent, and the error between the two does not exceed 1.1%. This shows that the shear bearing calculation method of the annular joint proposed in the present invention is reasonable and accurate, as shown in Table 4;

[0164] Table 4 Shear model verification

[0165]

[0166] In this example, Q u1 , Q u2 , Q u3 and Q u At the same time, it stated Figure 6 In. By Figure 6 It can be seen that the shear bearing curve of the annular joint consists of three curves, and the shear bearing capacity of the annular joint increases with the increase of the longitudinal axial force. Among them, in the lower longitudinal axial force section (0≤N<277.1kN), Q u2 The lowest, at this time, after the segment concrete breaks, the steel bars continue to resist shear, which is similar to the tensile failure mode of the "properly reinforced beam" of the concrete component, and belongs to plastic failure. In the medium longitudinal axial force section (277.1kN≤N<928.3kN), Q u1 The lowest, at this stage, the shear bearing capacity of the annular joint is controlled by the segment concrete, and the concrete failure will mark the shear failure of the annular joint. At this time, the shear failure of the segment joint is unpredictable, similar to the tensile failure mode of the "less-reinforced beam" of the concrete component, which is a brittle failure. In the larger longitudinal axial force section (N ≥ 928.3kN), the connecting components, including bolts and locating tenons, will become the weak points of the annular joint (Q u3 ), at this stage, the shear bearing capacity of the girth joint is controlled by the connecting member. In summary, the failure mode of the girth joint is different with different longitudinal axial forces. With the increase of longitudinal axial force, the girth joint can be divided into three control stages, namely, the steel bar control stage, the concrete control stage and the connector control stage.

[0167] From the above analysis, it can be seen that strengthening the concrete strength, the tensile reinforcement in the concrete rupture zone, the thickness of the pipe segment and the connectors can all increase the shear bearing capacity of the girth joint. It is worth noting that the longitudinal axial force between the girth joints is closely related to the geology. In the low longitudinal axial force section, strengthening the tensile reinforcement in the concrete rupture zone has the most obvious effect on the shear resistance of the girth joint. In the medium longitudinal axial force section, strengthening the tensile reinforcement in the concrete rupture zone will compress the length of the concrete control section, while strengthening the connector will extend the length of the high shear stage, and increasing the thickness of the pipe segment will improve the shear bearing capacity of the girth joint as a whole. Therefore, these three methods can all improve the shear resistance of the girth joint in the medium longitudinal axial force section. For geological sections with large longitudinal axial force and shear load, strengthening the connector is the most effective way to improve the shear strength of the girth joint. In addition to the above measures, other strengthening measures may not have a significant effect on enhancing the shear resistance of the girth joint.

[0168] Although the specific implementation of the invention is described in detail in conjunction with the drawings, it should not be understood as limiting the scope of protection of this patent. Within the scope described in the claims, various modifications and variations that can be made by those skilled in the art without creative work still fall within the scope of protection of this patent.

Claims

1. A method for calculating the shear bearing capacity of annular joints in a shield tunnel, characterized in that: The following steps are involved: S1. Select the target annular joint of the shield tunnel; S2, obtaining the spatial dimensions and bearing strength parameters of the pipe segments, steel bars, and connectors in the target annular joint; S3, constructing the shear model of the girth joint at different load-bearing stages according to the spatial dimensions in the girth joint; S4. Calculate the shear bearing capacity of the girth joint according to the shear model of the girth joint at different load-bearing stages.

2. The shear bearing calculation method of the shield tunnel annular joint according to claim 1 is characterized by: The target annular joint in S1 includes a segment joint; the segment joint includes a first segment and a second segment, a positioning tenon and a longitudinal bolt are provided between the annular joints of the first segment and the second segment; and the first segment and the second segment are connected by the positioning tenon and the longitudinal bolt; The annular seam surface of the first pipe segment is prefabricated with a quasi-rectangular tenon groove, and the annular seam surface of the second pipe segment is prefabricated with a circular tenon hole, and the tenon groove and the tenon hole are used to accommodate the positioning tenon.

3. The shear bearing calculation method of the shield tunnel annular joint according to claim 1 is characterized in that: The S2 specifically includes: The spatial dimensions of the segment include the thickness of the segment, the radial height L of the tongue and groove from the inner arc side of the first segment, and the R , the width of the upper plane of the mortise and tenon groove L D , height L from the center of the bolt hole on the joint surface to the inner arc surface r , the thickness of the segment protective layer C, the bearing strength parameters of the segment include the design value of the tensile strength of the concrete f t ; The spatial dimensions of the steel bars include the number of steel bars i that can provide vertical tension around the positioning tenon, the diameter A of the i-th steel bar, and the Si , the angle θ between the i-th steel bar and the vertical direction Si The bearing strength parameters of the steel bars include the design value of the tensile strength of the steel bars f y ; The connecting piece includes a positioning tenon and a bolt; the spatial dimensions of the positioning tenon include the inner diameter D of the positioning tenon at the joint Dn and outer diameter D Dw The bearing strength parameters of the positioning tenon include the shear strength f D The space size of the bolt includes the diameter D of the bolt B The bearing strength parameters of the bolt include the tensile strength f B .

4. The shear bearing calculation method of the shield tunnel annular joint according to claim 3 is characterized in that: The S3 specifically includes: The shear resistance model of the annular joint is used to calculate the minimum shear bearing capacity of the annular joint in the most unfavorable stress direction, that is, to calculate the extrusion load of the concrete and steel bars of the first pipe segment above the mortise and tenon groove to bear the said connecting piece; The shear model of the annular joint includes a concrete shear model, a steel bar shear model and a connector shear model; The concrete shear model is a quadrangular prism AEGB-CFHD, which is caused by the positioning tenon squeezing the concrete above the tenon groove of the first pipe segment, and the quadrangular prism is an isosceles trapezoid AEGB on the joint surface; The steel bar shear model is a tetrahedral pyramid O-EMNG, which is caused by the bolts squeezing the concrete above the tenon groove of the first pipe segment, and the tetrahedral pyramid is an isosceles triangle OEG on the joint surface; The shear resistance model of the connector is composed of shear resistance mechanics equations of the locating tenon and the bolt.

5. The shear bearing calculation method of the shield tunnel annular joint according to claim 4 is characterized in that: In the tetrahedral AEGB-CFHD, AB=L D , EG=L C , GH=C, the height of isosceles trapezoid AEGB is L R ; The height of the tetrahedral pyramid O-EMNG is L r , EM=L L ; L L and L c Derived from experimental test statistics; In L R 116mm, L r 160mm, L D When L is 66mm, L0 The experimental test is 370mm, L c The experimental test expression is: L C0 =494-0.1827×N According to the geometric relationship and similarity ratio, the radial height on the inner arc side of the first segment is L R When L c The calculation formula is: L L The calculation formula is: Where N is the longitudinal axial force.

6. The shear bearing calculation method of the shield tunnel annular joint according to claim 4 or 5 is characterized in that: The quadrangular prism AEGB-CFHD is the concrete shear bearing, the rectangular AEFC and the rectangular BDHG in the quadrangular prism are the concrete tensile surfaces, and the trapezoidal CFHD is the shear surface under compression; The tetrahedral pyramid O-EMNG is a steel bar shear bearing, and steel bars that pass through the tetrahedral pyramid and can provide vertical force are considered; In the shear resistance model of the connector, the positioning tenon provides shear resistance; the bolt has sufficient deformation space and is mainly subjected to tension after deformation, thus providing tensile resistance.

7. The shear bearing calculation method of the shield tunnel annular joint according to claim 6 is characterized in that: According to the shear model of the annular joint in the concrete shear stage, the shear bearing capacity of the annular joint in the concrete shear stage is calculated: Q u1 =f t C(L C -L D )+0.35f t L R (L D +L C )+μN+K(N) Among them, Q u1 is the shear bearing capacity of concrete in the shear stage; μ is the friction coefficient between concrete joint surfaces; K (N) is the shear load increment of the trapezoidal CFHD in the prism structure caused by the longitudinal axial force; K(N) is obtained through experimental testing, and its calculation formula is:

8. The shear bearing calculation method of the shield tunnel annular joint according to claim 7 is characterized in that: The shear bearing capacity of the connector is: Among them, Q u2 is the shear resistance of the connector.

9. The shear bearing calculation method of the shield tunnel annular joint according to claim 8 is characterized in that: According to the shear model of the circumferential joint in the steel bar shear stage, the shear bearing capacity of the joint in the steel bar shear stage is calculated as: Among them, Q u3 It is the shear bearing capacity of the joint during the steel bar shear stage.

10. The shear bearing calculation method of the shield tunnel annular joint according to claim 9 is characterized in that: In S4, the shear bearing capacity of the annular joint is calculated based on the minimum shear bearing capacity of the concrete in the shear stage, the shear bearing capacity of the connector and the shear bearing capacity of the joint in the shear stage of the steel bar: Q u =min{max[Q u1 ;Q u3 ];Q u2 } Among them, Q u It is the minimum shear bearing capacity of the circumferential joint in the most unfavorable stress direction.

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