Internal force calculation method for circular homogeneous pipe-jacking tunnel under action of ground unbalance loading

Abstract

The invention relates to an internal force calculation method for a circular homogeneous pipe-jacking tunnel under the action of ground unbalance loading, and the method comprises the steps: firstly converting ground single-side pile load and traffic load into equivalent horizontal unbalance pressure based on a space soil arching effect and a foundation pit single-side unbalance loading model; then, a combination model is established by superposing traditional uniformly distributed loads; then, according to a 120-degree soil arc bearing angle internal force coefficient method, the bending moment and the axial force are calculated, and two kinds of load combinations of strength and deformation checking calculation are completed; and finally, circumferential reinforcement is completed according to the pure bending section and the bending section. The method fills the design blank of the unbalance loading working condition, has simplicity and engineering precision, can guarantee long-term stability of the pipe jacking tunnel under the influence of unbalance loading, and is suitable for rapid and accurate design of engineering.

Description

Technical Field

[0001] This invention relates to the field of municipal and power tunnel structural design technology, specifically to a method for calculating the internal forces of a circular homogeneous pipe jacking tunnel under ground eccentric loading. Background Technology

[0002] Pipe jacking has become the mainstream construction method for urban cable tunnels and water supply and drainage pipelines due to its minimal disruption to ground traffic and rapid construction. Current design standards (T / CECS 143-2022 "Design Standard for Buried Precast Concrete Circular Pipe Structures in Water Supply and Drainage Engineering", DL / T 5484-2024 "Design Code for Power Cable Tunnels", etc.) all adopt the "load-structure method," assuming uniform ground load distribution and neglecting the eccentric load effects commonly seen at intersections of road green belts, non-motorized vehicle lanes, and carriageways, such as single-sided soil piling and vehicles driving close to the side. This leads to the following drawbacks: the maximum bending moment and crack width of the tunnel section are underestimated; multiple engineering cases have emerged of cable tunnels cracking and leaking on the eccentric load side beneath the road; and if three-dimensional finite element analysis is directly used, the parameter values ​​are complex and the calculation cycle is long, which is not conducive to rapid engineering design.

[0003] Therefore, there is an urgent need for a method to calculate circumferential internal forces that can take into account ground eccentric loads, is easy to calculate, and has the accuracy required for engineering projects, in order to fill the gaps in the current specifications. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for calculating the internal forces of a circular homogeneous pipe jacking tunnel under ground eccentric loading to solve the aforementioned problems.

[0005] This invention provides the following technical solution: A method for calculating the internal forces of a circular homogeneous pipe jacking tunnel under eccentric ground loading includes the following steps: Step S1, Three-dimensional transformation of eccentric load: When there is an eccentric load on the surface of the pipe jacking tunnel, based on the model transformation of the spatial soil arch effect, and through the calculation method of the single-sided eccentric support structure in the foundation pit engineering, the eccentric load is transformed into an equivalent horizontal eccentric pressure acting on the circular pipe jacking tunnel structure. The formula used is: ; Where p0 is the standard value of the additional pressure on the bottom surface of the foundation, b is the width of the foundation, and a is the horizontal distance from the outer edge of the support structure to the foundation. Step S2, load model combination establishment: establish the load action model of the circular pipe jacking tunnel, including the self-weight of the pipe and equipment, vertical uniformly distributed load, the weight of the soil in the chest cavity above the pipe, lateral active earth pressure, vertical concentrated load and the equivalent horizontal deviatoric pressure in step S1. Step S3, internal force calculation: Based on the internal force coefficient method of structural mechanics, the bending moment and axial force under the four sides of the pipe structure are calculated according to the combined load in step S2. Step S4, Circumferential Reinforcement Design of Pipeline Structure: Based on the bending moment and axial force obtained in Step S3, the circumferential reinforcement scheme of the circular pipe jacking tunnel is obtained by using the reinforced concrete structure design method and calculating according to the pure bending section and the compression bending section respectively.

[0006] Furthermore, the diffusion angle of the eccentric load is θ, and the vertical distance from the top surface of the support structure to the calculation point of the additional vertical stress in the soil is... z a Where, when calculating the depth of the point z a < a / tan θ or z a >(3a+b) / tan θ At that time, take =0.

[0007] Furthermore, the load combination coefficient for calculating the internal force of the equivalent horizontal eccentric pressure in step S1 is determined based on the lateral active earth pressure coefficient.

[0008] Furthermore, the off-center load includes ground-side surcharge and traffic load.

[0009] Furthermore, the internal force coefficient method described in step S3 involves calculating the internal force coefficient by referring to the corresponding internal force coefficient table based on the soil arc support angle at the bottom of the pipeline foundation being 120°.

[0010] Furthermore, two sets of load combinations are applied to the obtained bending moment and axial force: a basic combination consisting of permanent load, eccentric load, and construction load is used for strength verification; a quasi-permanent combination consisting of permanent load and eccentric load is used for deformation verification; the permanent load includes self-weight and earth pressure.

[0011] The present invention has the following beneficial technical effects: This invention introduces for the first time a method for calculating the load on the pipe sidewall caused by ground eccentric load, and systematically proposes a design method that considers the internal forces of the pipe structure caused by eccentric load. The method for calculating the soil lateral pressure on the pipe sidewall caused by eccentric load is widely used in foundation pit engineering, with reliable results. After its introduction, the calculation is convenient and applicable to engineering results.

[0012] This invention considers the impact of unilateral eccentric load on the circumferential stress of cable tunnels, and proposes a response load action model, load calculation method, and circumferential reinforcement design for tunnels. It fills the gap in existing design regarding the calculation of longitudinal internal forces and deformations in tunnels, and ensures the long-term stability and safety of cable tunnel structures affected by traffic on one side. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of a typical pipe jacking structure in existing technology; Figure 2 This is a typical load structure form and its simplified calculation diagram for existing circular pipe jacking technology; Figure 3 This is a calculation diagram of the rigid pipe assumption for pipe jacking; Figures 4-6 This is a schematic diagram of the internal force coefficient table for rigid pipes; Figure 7 This is a schematic diagram of the eccentric load acting on the tunnel when a vehicle is traveling on one side. Figure 8 This is a schematic diagram of the strip or rectangular additional load on the ground of the support structure for unilateral eccentric loading in the foundation pit engineering of the present invention. Figure 9 This is a schematic diagram of the force model of the load caused by the eccentric loading of the present invention on the pipeline structure; Figure 10 This is a schematic diagram of the internal force calculation method for a circular homogeneous pipe jacking tunnel under ground eccentric loading according to the present invention. Detailed Implementation

[0014] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0015] Example I. Existing technical calculation methods for non-eccentric load conditions If this project is designed using existing technologies (such as T / CECS 143-2022 and DL / T 5484-2024 standards), the process is as follows: Structural and load model establishment Referring to Figure 1 (Schematic diagram of a typical pipe jacking structure in the prior art) and Figure 2 (Load structure form and calculation diagram of a typical circular pipe jacking in the prior art), the pipe jacking is simplified as a rigid pipe. The calculation model is established using the "load-structure method". Only the uniformly distributed load is considered, including the self-weight of the pipe and internal equipment, the vertical uniformly distributed soil load on the top of the pipe, the weight of the soil in the chest cavity above the pipe, the lateral active earth pressure, and the vertical concentrated load (such as the pipe test load). The unilateral eccentric load on the carriageway side is completely ignored.

[0016] Internal force calculation Based on Figure 3 (a schematic diagram of the calculation of the rigid pipe assumption of the pipe jacking), the soil arc support angle at the bottom of the pipe foundation is set to 120°. Then, by referring to the internal force coefficient table in Figures 4-6 (a schematic diagram of the internal force coefficient table of the rigid pipe of the present invention), the bending moment coefficient and axial force coefficient corresponding to each uniformly distributed load are obtained. The circumferential bending moment and axial force of the pipe under each load are calculated respectively. Finally, the load combination is performed to obtain the structural control internal force.

[0017] II. Specific Implementation Process of the Method of the Invention To overcome the limitations of existing technologies, the method for calculating the internal forces of a circular homogeneous pipe jacking tunnel under ground eccentric loading, as described in this invention, involves the following steps: Step S1: Three-dimensional transformation of eccentric load. This project has a unilateral eccentric load on the carriageway side. Referring to Figure 7 (Schematic diagram of eccentric load acting on the tunnel during unilateral traffic in this invention), the eccentric load distribution pattern is clarified. Then, referring to Figure 8 (Schematic diagram of strip or rectangular additional load acting on the ground by the support structure of the foundation pit project under unilateral eccentric load in this invention), the unilateral eccentric load support calculation model is used to complete the three-dimensional transformation of the eccentric load based on the spatial soil arching effect. First, the eccentric load diffusion angle is determined. θ (45° is used in this project) Calculate the vertical distance from the top surface of the support structure to the calculation point of the additional vertical stress in the soil. Za The effective range, when Za In a / tan θ With (3) a + b ) / tan θ During this period, the unilateral eccentric load on the ground is converted into an equivalent horizontal eccentric pressure acting on the circular pipe jacking tunnel structure, using the formula: ; in p 0 is the standard value of additional pressure on the base surface. b Based on the width, a The horizontal distance from the outer edge of the support structure to the foundation; if Za If the load exceeds the above range, it is determined that the eccentric load has no effect on the tunnel, and the equivalent horizontal eccentric pressure is taken as 0. At the same time, the load combination coefficient for calculating the internal force of the equivalent horizontal eccentric pressure is taken as the value of the lateral active earth pressure coefficient.

[0018] Step S2: The load model is established by combining the loads. Referring to Figure 9 (a schematic diagram of the force model of the load caused by the eccentric load of the present invention acting on the pipeline structure), on the basis of the existing uniformly distributed load model, the equivalent horizontal eccentric pressure obtained in step S1 is superimposed to form a complete load model. This model includes six types of loads: the self-weight of the pipeline and equipment, the vertical uniformly distributed load, the weight of the soil in the chest cavity above the pipe, the lateral active earth pressure, the vertical concentrated load, and the equivalent horizontal eccentric pressure, so as to achieve accurate matching of the actual stress conditions of the project.

[0019] Step S3: Internal force calculation. Based on the 120° soil arc support angle set in Appendix 3, and using the internal force coefficient tables in Appendix 4-6, the structural mechanics internal force coefficient method is employed to calculate the bending moment and axial force around the pipeline structure under various loads (including equivalent horizontal eccentric pressure). After completing the single-load internal force calculation, two load combinations are executed: one is a basic combination consisting of permanent loads (self-weight, earth pressure), eccentric loads, and construction loads, used for structural strength verification; the other is a quasi-permanent combination consisting of permanent loads and eccentric loads, used for structural deformation verification. Finally, the structural control internal forces considering the eccentric load condition are obtained.

[0020] Step S4: Circumferential reinforcement design of the pipeline structure. Based on the bending moment and axial force obtained in Step S3, the reinforcement calculation is performed using reinforced concrete structure design methods, considering both pure bending and compression-bending sections. Addressing the characteristic of "maximum bending moment of the pipeline deviating from the horizontal / vertical direction" caused by eccentric loading, the reinforcement configuration on the side facing the eccentric load is locally strengthened, ultimately forming a circumferential reinforcement scheme for a circular pipe jacking tunnel that balances strength and deformation requirements.

[0021] The complete implementation process of this invention can be found in Figure 10 (a schematic diagram of the internal force calculation method for a circular homogeneous pipe jacking tunnel under ground eccentric load according to this invention). First, a typical tunnel section and geological conditions are selected, and the live load is determined in combination with the ground traffic conditions. Then, the geometric dimensions of the pipe jacking are simplified. First, the internal force of the uniformly distributed load without eccentric load is calculated. Then, the internal force of the horizontal load on the pipe side generated by the eccentric load on the ground surface is calculated. Finally, the total internal force is obtained by integrating the internal force coefficient method and the reinforcement is completed. If necessary, other sections can be switched and the above process can be repeated to achieve accurate design of the entire tunnel section.

[0022] By adopting the method of this invention, the influence of unilateral eccentric load on the circumferential force of the tunnel can be accurately captured, avoiding the underestimation of the internal forces of the structure by the existing technology. At the same time, the method has clear calculation logic and simple process, taking into account both design accuracy and engineering efficiency, and ensuring the long-term stability and safety of the cable tunnel structure affected by traffic on one side in this project.

[0023] The embodiments described above are merely illustrative of specific implementations of the present invention, and while the descriptions are detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for calculating the internal forces of a circular homogeneous pipe jacking tunnel under eccentric ground loading, characterized in that, Includes the following steps: Step S1, Three-dimensional transformation of eccentric load: When there is an eccentric load on the surface of the pipe jacking tunnel, based on the model transformation of the spatial soil arch effect, and through the calculation method of the single-sided eccentric support structure in the foundation pit engineering, the eccentric load is transformed into an equivalent horizontal eccentric pressure acting on the circular pipe jacking tunnel structure. The formula used is: ； Where p0 is the standard value of the additional pressure on the bottom surface of the foundation, b is the width of the foundation, and a is the horizontal distance from the outer edge of the support structure to the foundation. Step S2, load model combination establishment: establish the load action model of the circular pipe jacking tunnel, including the self-weight of the pipe and equipment, vertical uniformly distributed load, the weight of the soil in the chest cavity above the pipe, lateral active earth pressure, vertical concentrated load and the equivalent horizontal deviatoric pressure in step S1. Step S3, internal force calculation: Based on the internal force coefficient method of structural mechanics, the bending moment and axial force under the four sides of the pipe structure are calculated according to the combined load in step S2. Step S4, Circumferential Reinforcement Design of Pipeline Structure: Based on the bending moment and axial force obtained in Step S3, the circumferential reinforcement scheme of the circular pipe jacking tunnel is obtained by using the reinforced concrete structure design method and calculating according to the pure bending section and the compression bending section respectively.

2. The method for calculating the internal forces of a circular homogeneous pipe jacking tunnel under eccentric ground loading as described in claim 1, characterized in that, The diffusion angle of the eccentric load is θ, and the vertical distance from the top surface of the support structure to the calculation point of the additional vertical stress in the soil is... z a Where, when calculating the depth of the point z a < a / tan θ or z a > (3a+b) / tan θ At that time, take =0.

3. The method for calculating the internal forces of a circular homogeneous pipe jacking tunnel under eccentric ground loading as described in claim 1, characterized in that, The load combination coefficient for calculating the internal force of the equivalent horizontal eccentric pressure in step S1 is determined based on the lateral active earth pressure coefficient.

4. The method for calculating the internal forces of a circular homogeneous pipe jacking tunnel under eccentric ground loading as described in claim 1, characterized in that, The eccentric load includes ground-side surcharge and traffic load.

5. The method for calculating the internal forces of a circular homogeneous pipe jacking tunnel under eccentric ground loading as described in claim 1, characterized in that, The internal force coefficient method described in step S3 involves calculating the internal force coefficients by referring to the corresponding table based on the soil arc support angle at the bottom of the pipeline foundation being 120°.

6. The method for calculating the internal forces of a circular homogeneous pipe jacking tunnel under eccentric ground loading as described in claim 1, characterized in that, Two sets of load combinations are applied to the obtained bending moment and axial force: a basic combination consisting of permanent load, eccentric load and construction load is used for strength verification; a quasi-permanent combination consisting of permanent load and eccentric load is used for deformation verification; the permanent load includes self-weight and earth pressure.

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