A transition structure for an orthogonal double-layer tunnel and its construction method

Abstract

The present invention provides a transition structure for an orthogonal double-layer tunnel and a construction method thereof. The transition structure includes an intersection node section where an upper tunnel and a lower tunnel are orthogonal to each other. The intersection node section includes a foundation pit A excavated in the horizontal direction, a foundation pit B excavated in a direction orthogonal to the horizontal direction at the bottom surface of the foundation pit A, and a lower tunnel floor slab, a lower tunnel side wall, and a lower tunnel roof slab of the intersection node section successively constructed upward from the bottom of the foundation pit B. An upper tunnel floor slab of the intersection node section is arranged on the foundation pit A along the direction of the upper tunnel, and the upper tunnel floor slab and the lower tunnel roof slab are integrally cast. The upper tunnel floor slab includes an intersection section where the upper tunnel floor slab and the lower tunnel roof slab intersect and two transition sections, and the two transition sections are respectively arranged at both ends of the upper tunnel floor slab. The present invention can avoid the situation of expansion joint steps, improve the smoothness and safety of driving, extend the service life of the tunnel, and effectively save costs.

Description

Technical Field

[0001] The present invention relates to a transition structure for an orthogonal double - layer tunnel and a construction method thereof, belonging to the technical field of tunnel civil engineering. Background Art

[0002] Constructing a three - dimensional underground traffic system helps improve urban traffic coverage and space utilization rate. Therefore, this kind of structure is widely used in the urban planning process.

[0003] For orthogonal tunnels, the structure of the tunnel intersection section is complex and the load distribution is uneven. When the tunnel intersection section is connected to the main tunnel section, due to the difference in the bearing capacity of the lower foundations of the two, differential settlement is likely to occur at the expansion joint of the connection. Moreover, this differential settlement will gradually accumulate over time. This situation will not only cause the road surface flatness not to meet the specification requirements, but in severe cases, the full accumulation of differential settlement will form a step at the expansion joint, which will further trigger a "bumping" phenomenon similar to that commonly seen at highway bridgeheads, thus causing high - frequency impacts on the tunnel road surface and seriously threatening the service performance and service life of the tunnel. Therefore, reasonable and effective measures must be taken to avoid such risks, so that the tunnel meets the road flatness requirements and ensures the safety of urban underground traffic, while effectively saving costs. Summary of the Invention

[0004] In view of the above problems to be solved, the present invention provides a transition structure for an orthogonal double - layer tunnel and a construction method thereof. By arranging a transition section, it can avoid the situation of expansion joint steps caused by differential settlement, improve the smoothness and safety of driving, extend the service life of the tunnel, and at the same time, effectively save costs.

[0005] To solve the above technical problems, the present invention provides a transition structure for an orthogonal double - layer tunnel. The transition structure includes: a cross - node section where the upper - layer tunnel and the lower - layer tunnel are orthogonal to each other;

[0006] The cross - node section includes a foundation pit A excavated in the horizontal direction, the depth of the foundation pit A is H1, a foundation pit B is excavated in the direction orthogonal to the horizontal at the bottom surface of the foundation pit A, the depth of the foundation pit B is H2, H2 > H1, and the lower - layer tunnel floor slab, the lower - layer tunnel side wall, and the lower - layer tunnel roof slab of the cross - node section are successively constructed upward from the bottom of the foundation pit B. The upper - layer tunnel floor slab of the cross - node section is arranged along the upper - layer tunnel direction on the foundation pit A, and the upper - layer tunnel floor slab of the cross - node section and the lower - layer tunnel roof slab of the cross - node section are integrally cast. The upper - layer tunnel side wall and the upper - layer tunnel roof slab of the cross - node section are arranged on the foundation pit A;

[0007] The upper tunnel floor slab of the cross-node section includes an intersection section where the upper tunnel floor slab of the cross-node section intersects with the lower tunnel roof slab of the cross-node section and two transition sections. The two transition sections are respectively arranged at both ends of the upper tunnel floor slab of the cross-node section. The length L of the two transition sections is determined by the following formula:

[0008] L≥3000×(d / H) (1)

[0009] Wherein, d is the maximum settlement of the transition section, with the unit of mm; H is the maximum ground clearance of the 3m ruler required for the urban road flatness, with the unit of mm.

[0010] Preferably, the upper tunnel floor slab of the cross-node section is a double-layer reinforced slab, and the increased reinforcement ratio is determined according to the maximum increase in bending moment M. The maximum increase in bending moment M is determined by the following formula:

[0011] M=N·P·L (2)

[0012] Wherein, N is the number of lanes of the upper tunnel, and P is the maximum load of a single vehicle.

[0013] Preferably, gravel piles are arranged in the soil body under each transition section.

[0014] Preferably, a expansion joint is provided at one end of each transition section away from the intersection section.

[0015] Correspondingly, the present invention also provides a construction method for the transition structure of an orthogonal double-layer tunnel. The construction of the cross-node section includes the following steps:

[0016] S1: According to the requirements of urban road flatness, calculate the length of the transition section. The length L of each transition section is determined by the following formula:

[0017] L≥3000×(d / H) (1)

[0018] Wherein, d is the maximum settlement of the transition section, with the unit of mm; H is the maximum ground clearance of the 3m ruler required for the urban road flatness, with the unit of mm.

[0019] S2: Determine the increased reinforcement ratio of the upper tunnel floor slab of the cross-node section according to the maximum increase in bending moment M. The maximum increase in bending moment M is determined by the following formula:

[0020] M=N·P·L (2)

[0021] Wherein, N is the number of lanes of the upper tunnel, and P is the maximum load of a single vehicle.

[0022] S3: Excavate foundation pit A horizontally with a depth of H1. Then, excavate foundation pit B orthogonally to the horizontal direction at the bottom of foundation pit A, with a depth of H2, where H2 > H1. Starting from the bottom of foundation pit B, successively construct the lower tunnel floor slab of the cross-node section, the lower tunnel side wall of the cross-node section, integrally pour the lower tunnel roof slab of the cross-node section and the upper tunnel floor slab of the cross-node section. Among them, the increased reinforcement ratio of the upper tunnel floor slab of the cross-node section is determined by the above step S2, and the length of each transition section is determined by the above step S1.

[0023] S4: Set expansion joints at one end of each transition section away from the cross-section.

[0024] S5: Pour the upper tunnel side wall of the cross-node section and the upper tunnel roof slab of the cross-node section.

[0025] Preferably, in step S3, before pouring the upper tunnel floor slab of the cross-node section, gravel piles are arranged in the soil below the position where the transition section needs to be arranged.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] 1. The present invention integrally pours the lower tunnel roof slab of the cross-node section and the upper tunnel floor slab of the cross-node section, ensuring the integrity of the transition section structure, preventing it from cracking and deforming. A transition section is provided on the upper tunnel floor slab of the cross-node section, effectively avoiding differential settlement, preventing the phenomenon of "bumping" when vehicles pass through the interface between the upper tunnel and the cross-section tunnel, improving the smoothness and safety of driving, and extending the service life of the tunnel.

[0028] 2. The present invention combines the road flatness requirements and the on-site differential settlement observation values, providing a specific calculation method for the length of the transition section, saving construction costs while ensuring the avoidance of differential settlement.

[0029] 3. The foundation soil of the transition section of the present invention is filled and paved with gravel piles in layers, which strengthens the foundation, reduces the settlement of the transition section foundation, and at the same time saves construction cost.

[0030] 4. The upper tunnel floor slab of the present invention is a double-layer reinforced slab, and its increased reinforcement ratio is determined according to the maximum increase in bending moment M, effectively avoiding the additional bending moment effect caused by vehicle loads. Description of the Drawings

[0031] Figure 1 It is a schematic structural view of the transition structure of the orthogonal double-layer tunnel of the present invention.

[0032] Figure 2 It is a front view of the transition structure of the orthogonal double-layer tunnel of the present invention.

[0033] Figure 3 Cross-sectional view of the transition structure of the orthogonal double-layer tunnel.

[0034] Reference numerals: the lower tunnel floor slab 1 of the cross-node section, the lower tunnel side wall 2 of the cross-node section, the lower tunnel roof slab 3 of the cross-node section, the upper tunnel side wall 4 of the cross-node section, the upper tunnel roof slab 5 of the cross-node section, the transition section 6, the cross section 7, the expansion joint 8, the main floor slab 9 of the upper tunnel. Detailed implementation manners

[0035] The present invention will be described in detail below in combination with embodiments and the accompanying drawings. It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments may be combined with each other.

[0036] Reference Figures 1 to 3 , a transition structure of an orthogonal double-layer tunnel, the transition structure includes a cross-node section where the upper tunnel and the lower tunnel are orthogonal to each other;

[0037] The cross-node section includes a foundation pit A excavated in the horizontal direction, the depth of the foundation pit A is H1, a foundation pit B is excavated at the bottom surface of the foundation pit A in a direction orthogonal to the horizontal, the depth of the foundation pit B is H2, H2 > H1, and the lower tunnel floor slab 1 of the cross-node section, the lower tunnel side wall 2 of the cross-node section, and the lower tunnel roof slab 3 of the cross-node section are successively constructed upward from the bottom of the foundation pit B. The upper tunnel floor slab of the cross-node section is arranged along the upper tunnel direction on the foundation pit A. The height of the lower tunnel side wall of the cross-node section is all H2 - H1. The upper tunnel floor slab of the cross-node section and the lower tunnel roof slab 3 of the cross-node section are integrally cast, which ensures the integrity of the cross-node section structure and can avoid differential settlement. The upper tunnel side wall 4 of the cross-node section and the upper tunnel roof slab 5 of the cross-node section arranged on the foundation pit A;

[0038] The upper tunnel floor slab of the cross-node section includes a cross section 7 where the upper tunnel floor slab of the cross-node section intersects with the lower tunnel roof slab 3 of the cross-node section and two transition sections 6. The two transition sections 6 are respectively arranged at both ends of the upper tunnel floor slab of the cross-node section. The transition sections 6 are arranged to effectively avoid differential settlement.

[0039] According to the requirements of "Technical Specification for Highway Asphalt Pavement Maintenance (TJT073.2 - 2001)" and "Technical Specification for Highway Cement Concrete Pavement Maintenance (TJT073.2 - 2001)", the maximum ground clearance H of the 3m ruler should be standardized for urban roads.

[0040] Preferably, the lengths L of the two transition sections 6 are both calculated and determined according to the following formula:

[0041] L ≥ 3000×(d / H) (1)

[0042] Where d is the maximum settlement of the transition section 6, with the unit of mm. Preferably, d is obtained through on-site in-situ test surveys. H is the maximum ground clearance of the 3m ruler required for the urban road evenness. By accurately calculating the length of the transition section 6, differential settlement can be effectively avoided while cost can be effectively saved.

[0043] Further, the upper tunnel floor slab of the intersection node section is a double-layer reinforced slab, and the increased reinforcement ratio is determined according to the maximum increase in bending moment M. The maximum increase in bending moment M is calculated and determined by the following formula:

[0044] M = N·P·L (2)

[0045] Where N is the number of lanes of the upper tunnel, and P is the maximum load of a single vehicle.

[0046] Considering the action of vehicle loads, for the upper tunnel floor slab of the intersection node section, the vehicle loads generated during operation will exert additional bending moment on the upper tunnel floor slab. At the same time, considering the actual engineering situation, the vehicle loads are dynamic loads, and the upper tunnel floor slab with double-layer reinforced slab is used to prevent the generation of opposite-sign bending moments.

[0047] Preferably, gravel piles are arranged in the soil body at the lower part of each transition section 6. In order to ensure that the transition section with a limited length can meet the requirements of the urban road evenness specification, it is necessary to reinforce the foundation of the transition section 6 to reduce its foundation settlement. Considering the factors of construction cost and construction convenience, the method of arranging gravel piles is used to reinforce the soil body within the transition section range, improving the bearing capacity of the tunnel bed and ensuring the stable operation of the transition section.

[0048] Further, a telescopic joint 8 is provided at one end of each transition section 6 away from the intersection section 7. The telescopic joint 8 is the part with a gap between the upper tunnel main floor slab 9 and the transition section 6. The telescopic joint 8 releases the deformation of the concrete structure to prevent cracks or damage to the overall structure.

[0049] A construction method for the transition structure of an orthogonal double-layer tunnel. The construction of the intersection node section includes the following steps:

[0050] S1: According to the requirements of urban road evenness, calculate the length of the transition section 6. The length L of each transition section 6 is calculated and determined by the following formula:

[0051] L ≥ 3000×(d / H) (1)

[0052] Where d is the maximum settlement of the transition section 6, with the unit of mm, and H is the maximum ground clearance of the 3m ruler required for the urban road evenness, with the unit of mm.

[0053] S2: Determine the increased reinforcement ratio of the upper tunnel floor slab in the cross-node section according to the maximum increase in bending moment M, and the maximum increase in bending moment M is calculated and determined by the following formula:

[0054] M = N·P·L (2)

[0055] Where N is the number of lanes of the upper tunnel, and P is the maximum load of a single vehicle.

[0056] Under the condition of determining the size, concrete grade and steel bar grade of the upper tunnel floor slab in the cross-node section, calculate the increased area A of the tensile steel bars of the upper tunnel floor slab in the cross-node section through the maximum increase in bending moment M s and the increased area A s ' of the compressive steel bars of the upper tunnel floor slab in the cross-node section, and then obtain the increased reinforcement ratio of the upper tunnel floor slab in the cross-node section.

[0057] According to the calculation principle of the increased area of the compressive steel bars in the concrete slab reinforcement:[[]]

[0058]

[0059] Where α1 is the ratio of the stress value of the rectangular stress diagram of the concrete in the compression zone to the design value of the axial compressive strength of the concrete, and α1 is obtained by looking up the table according to the concrete grade. β1 is the ratio of the height x of the compression zone of the rectangular stress diagram to the height x c of the neutral axis, and β1 is obtained by looking up the table according to the concrete grade. f c is the axial compressive strength of the concrete, f y ' is the compressive strength of the longitudinal compressive steel bars, b is the width of the flexural section of the concrete slab, h is the height of the flexural section of the concrete slab, h0 is the effective height of the flexural section, a s ' is the thickness of the compression zone protection layer, x is the height of the compression zone, let the tensile strength f y of the longitudinal compressive steel bars be equal to the compressive strength f y ' of the longitudinal compressive steel bars, and according to formula (3), we get:[[]]

[0060]

[0061] According to formula (3) and formula (4), we get:[[]]

[0062]

[0063] Under the condition of knowing the size and material strength of the upper tunnel floor slab in the cross-node section, introduce the minimum value of (A s +A s ') as the preferred value, take the derivative of formula (5) with respect to x, and let

[0064]

[0065] To meet the applicable conditions, the relative boundary compression zone height ξ is determined according to the strength grades of concrete and steel bars. b , where ξ is the relative compression zone height. When ξ > ξ b , ξ = ξ b should be taken; when ξ < ξ b , ξ is directly taken.

[0066] When ξ > ξ b is taken, let x = x b , and the following is obtained:

[0067]

[0068] x b is the boundary compression zone height. When f y ' = f y , the following is obtained:

[0069]

[0070] When ξ < ξ b is taken, the following is obtained:

[0071]

[0072] x is the compression zone height. When f y ' = f y , the following is obtained:

[0073]

[0074] The increased area of the tension steel bars of the upper tunnel floor slab in the cross-node section, A s , is determined by Equation (7) or Equation (9), and the increased area of the compression steel bars of the upper tunnel floor slab in the cross-node section, A s ', is determined by Equation (8) or Equation (10). The increased amount of the reinforcement ratio of the upper tunnel floor slab in the cross-node section is obtained by dividing A s and A s ' by the cross-sectional area of the corresponding steel bars used.

[0075] On the basis of the original reinforcement, considering the bending moment at the joint increased due to the vehicle load, the reinforcement ratio of the upper tunnel floor slab in the cross-node section needs to be increased. To prevent the phenomenon of "over-reinforced slab", the cross-sectional size of the upper tunnel floor slab in the cross-node section can be increased to make the upper tunnel floor slab in the cross-node section a "properly reinforced slab".

[0076] S3: Excavate foundation pit A horizontally with a depth of H1. Then, excavate foundation pit B in a direction orthogonal to the horizontal at the bottom of foundation pit A, with a depth of H2, where H2 > H1. Starting from the bottom of foundation pit B, successively construct the lower tunnel floor slab 1 of the cross-node section, the lower tunnel side walls 2 on both sides of the cross-node section, with the height of both side walls being H2 - H1. Integrally pour the lower tunnel roof slab 3 of the cross-node section and the upper tunnel floor slab of the cross-node section, where the increased reinforcement ratio of the upper tunnel floor slab of the cross-node section is determined through the above step S2, and the length of each transition section 6 is determined through the above step S1.

[0077] S4: At one end of each transition section 6 away from the cross-section 7, set expansion joints 8 to release the deformation of the concrete structure through the expansion joints 8 and prevent cracks or damage to the overall structure.

[0078] S5: Pour the upper tunnel side walls 4 of the cross-node section and the upper tunnel roof slab 5 of the cross-node section.

[0079] Preferably, in the step S3, before pouring the upper tunnel floor slab of the cross-node section, arrange gravel piles in the soil below the position where the transition section 6 needs to be arranged. In order to ensure that the use of a transition section 6 with a limited length can meet the requirements of the urban road flatness specification, it is necessary to reinforce the foundation of the transition section 6 to reduce its foundation settlement. Considering the factors of construction cost and construction convenience, the method of using gravel piles is adopted to arrange gravel piles in the soil within the range of the transition section 6 for reinforcement, improve the bearing capacity of the tunnel bed, and ensure the stable operation of the transition section 6.

[0080] The above content is a further detailed description of the present invention in combination with specific preferred embodiments. It cannot be determined that the specific implementation of the present invention is only limited to these descriptions. For those of ordinary skill in the technical field to which the present invention belongs, without departing from the concept of the present invention, several simple deductions and substitutions can still be made, which should all be regarded as belonging to the protection scope of the present invention.

Claims

1. A transition structure for an orthogonal double-layer tunnel, characterized in that The transition structure includes a cross-node section where the upper tunnel and the lower tunnel are orthogonal to each other; The cross-node section includes a foundation pit A excavated in the horizontal direction, with a depth of H1. At the bottom of foundation pit A, a foundation pit B is excavated in a direction orthogonal to the horizontal, with a depth of H2, where H2 > H1. From the bottom of foundation pit B upwards, the lower tunnel floor slab (1) of the cross-node section, the lower tunnel side wall (2) of the cross-node section, and the lower tunnel roof slab (3) of the cross-node section are successively constructed. On foundation pit A, the upper tunnel floor slab of the cross-node section is arranged along the upper tunnel direction. The upper tunnel floor slab of the cross-node section and the lower tunnel roof slab (3) of the cross-node section are integrally cast. On foundation pit A, the upper tunnel side wall (4) and the upper tunnel roof slab (5) of the cross-node section are arranged; The upper tunnel floor slab of the cross-node section includes an intersection section (7) where the upper tunnel floor slab of the cross-node section intersects with the lower tunnel roof slab (3) of the cross-node section and two transition sections (6). The two transition sections (6) are respectively arranged at both ends of the upper tunnel floor slab of the cross-node section. The length L of the two transition sections (6) is determined by the following formula: L≥3000×(d / H) (1) Where d is the maximum settlement of the transition section (6), in mm, and H is the maximum ground clearance of a 3m ruler required for the urban road flatness, in mm.

2. The transition structure of the orthogonal double-layer tunnel according to claim 1, characterized in that The upper tunnel floor slab of the cross-node section is a double-layer reinforced slab, and the increased reinforcement ratio is determined according to the maximum increase in bending moment M. The maximum increase in bending moment M is determined by the following formula: M=N·P·L (2) Where N is the number of lanes of the upper tunnel, and P is the maximum load of a single vehicle.

3. The transition structure of the orthogonal double-layer tunnel according to claim 2, characterized in that, Stone columns are arranged in the soil body under each transition section (6).

4. The transition structure of the orthogonal double-layer tunnel according to claim 3, characterized in that Expansion joints (8) are provided at one end of each transition section (6) away from the intersection section.

5. A construction method for a transition structure of an orthogonal double-layer tunnel as described in claim 4, characterized in that, Constructing the cross-node section includes the following steps: S1: According to the requirements of urban road flatness, calculate the length of the transition section (6). The length L of each transition section (6) is determined by the following formula: L≥3000×(d / H) (1) Where d is the maximum settlement of the transition section (6), in mm, and H is the maximum ground clearance of a 3m ruler required for the urban road flatness, in mm; S2: Determine the increased reinforcement ratio of the upper tunnel floor slab of the cross-node section according to the maximum increase in bending moment M. The maximum increase in bending moment M is determined by the following formula: M=N·P·L (2) Where N is the number of lanes of the upper tunnel, and P is the maximum load of a single vehicle; S3: Excavate foundation pit A in the horizontal direction, with a foundation pit depth of H1. At the bottom of foundation pit A, excavate foundation pit B in a direction orthogonal to the horizontal, with a foundation pit depth of H2, where H2 > H1. From the bottom of foundation pit B upwards, successively construct the lower tunnel floor slab (1) of the cross-node section, the lower tunnel side wall (2) of the cross-node section, integrally cast the lower tunnel roof slab (3) of the cross-node section and the upper tunnel floor slab of the cross-node section. The increased reinforcement ratio of the upper tunnel floor slab of the cross-node section is determined through the above step S2, and the length of each transition section (6) is determined through the above step S1; S4: Expansion joints (8) are provided at one end of each transition section (6) away from the intersection section (7). S5: Pour the upper tunnel side wall (4) of the intersection node section and the upper tunnel roof slab (5) of the intersection node section.

6. The construction method of the transition structure of the orthogonal double-layer tunnel according to claim 5, characterized in that, In the step S3, before pouring the upper tunnel floor slab of the intersection node section, gravel piles are arranged in the soil body below the position where the transition section (6) needs to be arranged.

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