Keywords

1 Introduction

With the “Western Development” and “West-to-East Power Transmission” strategy, China has launched a large number of large-scale hydroelectric power stations, these large-scale projects are mostly arranged in the way of underground plant, and the construction of their supporting transmission projects is more difficult, and gas-insulated transmission lines (GIL) is one of the main approaches to solving this problem. The use of GIL pipe gallery in the Huangbuling 500 kV power transmission project alleviated the problem of coil out pipe gallery restriction, and improved the durability of engineering pipelines and reduced their maintenance costs. However, vehicle operation often causes undesirable vibrations in GIL, and there will be hidden dangers such as pipeline scattering and structural collapse, increasing the maintenance cost of the transmission project in later period.

Recently, scholars have conducted a large number of studies on the mechanical properties and dynamic response of integrated pipe galleries based on field tests and numerical simulations [1,2,3,4,5,6]. Yu [7] conducted numerical simulation analysis of a typical integrated pipe gallery system and nonlinear dynamic analysis of the integrated pipe gallery and its surrounding soil using finite element software.

When an integrated pipe gallery inevitably crosses traffic routes, the pipe gallery is subject to traffic loads generated by moving vehicles. In this regard, related scholars have developed a series of researches on the dynamic response of integrated pipe gallery under traffic load [8,9,10]. Jiang L et al. [11] discussed the effect of different speeds on the structure of the integrated pipe gallery under the same working condition, and analyzed the dynamic stress change rule of the integrated pipe gallery under the actual traffic load. The results show that the effect of vehicle speed on the left wall and axillary region of the longitudinal integrated pipe gallery is greater than that of the cross-section.

Moreover, relevant scholars have conducted a series of studies on GIL pipe gallery [12, 13]. Tang P et al. [14] analyzed in detail the seismic performance of the cross-river GIL integrated pipe gallery structure in terms of structural deformation, shield tunnel segment opening and structural seismic damage for the special characteristics of cross-river GIL integrated pipe gallery structure.

Based on the above, most of the current studies mainly focus on integrated pipe galleries, and some of them involve GIL pipe galleries, while there are even fewer studies on the dynamic response of GIL pipe galleries under vehicle loads.

The rest of this study is structured as follows: Sect. 2 develops a coupled numerical model of GIL considering soil-structure interaction. Section 3 carries out the analysis of the effect of soil pressure on the structural response of GIL. Section 4 proposes a simulation method for vehicle traveling loads and investigates the dynamic response law of GIL in depth by parametric analysis of traveling direction and speed. Finally, the systematic conclusions of this study are presented in Sect. 5.

2 Soil-GIL Coupling Numerical Model

2.1 Engineering Situations

The structure type of GIL pipe gallery of this project is reinforced concrete structure, the pipe gallery is made of C35 waterproof concrete, the cross-section size is 5.5 m × 5.2 m, and the top plate is 1.5 m from the ground surface. The cushion is made of 100-thick C20 concrete. Steel bars are of HPB300 and HRB400 grade. The GIL pipe gallery structure is shown in Fig. 1. The parameters of the steel bars used in the pipe gallery are shown in Table 1. According to the geotechnical engineering investigation report of this project, the soil layer around the pipe gallery mainly consists of silty clay, fully weathered volcanic breccia and strongly weathered volcanic breccia.

Fig. 1.
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Structure of GIL pipe gallery

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2.2 Basic Assumptions

The following basic assumptions are considered in the numerical modeling process: 1) the underground pipe gallery structure can be simplified as an elastic structure for analysis. The soil body will be considered as an elastic material in the numerical simulation; 2) The soil is considered to be uniformly distributed in layers without considering the internal pore ratio of the soil and the effect of groundwater; 3) the materials are all isotropic and homogeneous.

2.3 Finite Element Modeling

The finite element analysis software ABAQUS is used to establish the numerical model of GIL pipe gallery considering soil-structure interaction, as shown in Fig. 2. The width of the road above the pipe gallery is 5.5 m, the direction of the length of the pipe gallery is perpendicular to the direction of the road, and the length of the pipe gallery is taken as 5.5 m. The model size in the vertical pipe gallery length direction is taken as 40 m. The final size of the finite element model is determined to be 40 m × 5.5 m × 20 m. In the finite element model, the soil body, GIL pipe gallery and concrete cushion are simulated using solid element (C3D8R); the reinforcement is simulated using wire element (B31). After the meshing is completed, the number of model nodes is 30096 and the number of cells is 33009.

The “Embedded” in “Constraints” is used between the concrete and the steel reinforcement cage inside the pipe gallery; “Surface-to-surface contact” is used between the pipe gallery, the concrete cushion and the silty clay, and the tangential behavior in the “Contact Properties” defines the friction coefficient μ = 0.194, and the normal behavior is defined as “Hard Contact”; Only the normal behavior between the fully weathered volcanic breccia and the strongly weathered volcanic breccia is defined as “Hard Contact”; The pipe gallery and the concrete cushion are poured as a single entity, with “Tie” in “Constraints” between the two. The soil surrounding the pipe gallery has a large proportion of volcanic breccia, which are in rigid contact with each other, so the soil body boundary conditions can be defined as fixed constraints. The material parameters of the soil are shown in Table 1 and the material parameters of the GIL structure are detailed in Table 2.

Fig. 2.
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GIL pipe gallery-soil body finite element model. (a) Overall finite element model; (b) GIL model; (c) Reinforcement cage model

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Table 1. Soil material parameters.
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Table 2. GIL structure material parameters.
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3 Static Analysis of Soil Pressure in GIL Pipe Gallery

3.1 Soil Pressure Analysis

After geo-stress balance, a static general analysis step is created to analyze the effect of soil pressure on the pipe gallery. The stress and displacement clouds of the concrete and the reinforcement cage of the pipe gallery are shown in Fig. 3. It can be seen that overlying soil body gravity and pipe gallery’s own gravity, region of high structural stress in the pipe gallery appears in the pipe gallery side wall root, the maximum value of stress is located in the pipe gallery right side wall root (1.814 MPa) under the effect of lateral soil pressure. The concrete strength used in the pipe gallery is C35 and the design value of strength is 16.7 MPa, which is much larger than 1.814 MPa, the pipe gallery concrete strength meets the requirements. Region of high stress in the reinforcement cage appears in the cage side root and the middle of the bottom surface, the maximum value of stress is located in the cage right side root (17.94 MPa). The longitudinal bars strength used in the cage are of HRB400 grade and the design value of tensile and compressive strength is 360 MPa, which is much larger than 17.94 MPa, the cage strength meets the requirements. From the displacement cloud map, it can be seen that overlying soil body gravity and pipe gallery’s own gravity, the maximum displacement response of the concrete and the maximum displacement of the steel reinforcement cage appear in the middle of the top plate and are both 6.556 cm under the effect of lateral soil pressure.

Fig. 3.
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The stress and displacement clouds of the concrete and the reinforcement cage of the pipe gallery. (a) Concrete stress cloud; (b) Concrete displacement cloud map; (c) Reinforcement cage stress cloud map; (d) Reinforcement cage displacement cloud map

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4 Dynamic Response Analysis of GIL Under Vehicle Traveling Loads

4.1 Vehicle Traveling Load Simulation

In order to simulate the vehicle load in a more standardized way, the vehicle load passing through the road with buried GIL pipe gallery is now expressed according to the standard vehicle load on bridges in the Technical Specification of Urban Road Engineering (GB51286–2018), which is the Urban-Class B vehicle load, as shown in Table 3. Figure 4 shows a distribution diagram of the vehicle traveling load.

Table 3. Urban-Class B vehicle load
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Fig. 4.
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Distribution diagram of the vehicle traveling load. (a) Elevation distribution diagram; (b) Plane distribution diagram.

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In this study, the application of vehicle traveling loads is achieved by using the continuous step loading method, and the spacing between the vehicle loads applied by two adjacent steps is set to 3 m. In the model, the length of the soil body in the vertical pipe gallery length direction is 40 m, and the length of the selected standard heavy vehicle is 12.8 m, after calculation, a total of ten steps are required to move the vehicle from one side of the soil to the other in the direction of the vertical GIL to simulate the whole process of vehicle passing through the GIL.

4.2 Dynamic Response Analysis

Four speeds, 10 km/h, 20 km/h, 30 km/h and 40 km/h, are selected to analyze the dynamic response of the pipe gallery. The vehicle load conditions are shown in Table 4.

Table 4. Vehicle load conditions
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In order to comprehensively analyze the effect of heavy vehicle passing through on various parts of the GIL pipe gallery, a total of five locations in the pipe gallery cross-section are selected for analysis: a) midpoint at the top of the pipe gallery, b) upper-left corner of the pipe gallery, c) midpoint of the pipe gallery side wall, d) lower-left corner of the pipe gallery, and e) midpoint at the bottom of the pipe gallery, as shown in Fig. 2(b). By extracting the dynamic response time travel curves of heavy vehicle traveling vertically in the direction of the pipe gallery in the above mentioned parts under different working conditions, the dynamic response of different locations of the pipe gallery to the heavy vehicle load transmitted from the soil body above is analyzed, and at the same time, the location of the pipe gallery structure most affected by the heavy vehicle load is summarized.

A comparison of the peak vertical and horizontal acceleration, velocity, displacement response and stress response of each part of the GIL pipe gallery when the vehicle speed is 10 km/h is shown in Fig. 5. It can be seen that the vertical acceleration, velocity and displacement responses of the midpoint at the top of the pipe gallery are the largest, and subsequently only the midpoint at the top of the pipe gallery is extracted as a characteristic point for vertical acceleration, velocity and displacement response analysis; the lower-left corner of the pipe gallery has the largest stress response, and subsequently only the lower-left corner of the pipe gallery is extracted as a characteristic point for stress response analysis.

Fig. 5.
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Peak response of each measurement point in the GIL pipe gallery at a vehicle speed of 10 km/h. (a) Acceleration; (b) Velocity; (c) Displacement; (d) Stress

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Figure 6(a) shows the acceleration response of the GIL pipe gallery under each working condition, and it can be seen that when heavy vehicle passes over the pipe gallery at different speeds, the peak acceleration of the pipe gallery tends to increase with the increase of the vehicle speed, and the peak acceleration reaches a maximum of 18.99 m/s2 when the vehicle speed reaches 40 km/h. The analysis results of velocity response are illustrated in Fig. 6(b), it can be seen that when heavy vehicle passes over the pipe gallery at different speeds, the peak velocity of the pipe gallery tends to increase with the increase of the vehicle speed, and the peak velocity reaches a maximum of 50 mm/s when the vehicle speed reaches 40 km/h. Figure 6(c) shows that when heavy vehicle passes over the pipe gallery at different speeds, the peak stress of the pipe gallery tends to increase with the increase of the vehicle speed, and the peak stress reaches a maximum of 2.484 MPa when the vehicle speed reaches 40 km/h. For Fig. 6(d), when heavy vehicle passes over the pipe gallery at different speeds, the peak displacement of the pipe gallery does not change significantly and fluctuates within a small range as the speed increases, and the peak displacement reaches a maximum of 6.806 cm when the vehicle speed reaches 30 km/h.

Figure 7 illustrates the dynamic response cloud map of the GIL in vertical direction for the condition where the peak response is the largest, the maximum acceleration and velocity values occur at the GIL’s top midpoint, the maximum stress value occurs at the GIL’s lower-left corner, and the maximum displacement value occurs at the GIL’s right top, and the dynamic response of the other parts is small.

Fig. 6.
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Peak dynamic response of GIL in vertical direction under each working condition. (a) Acceleration; (b) Velocity; (c) Displacement; (d) Stress

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Fig. 7.
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Dynamic response cloud map of GIL in vertical direction for working conditions with maximum peak response. (a) Acceleration (Condition 4); (b) Velocity (Condition 4); (c) Displacement (Condition 4); (d) Stress (Condition 3)

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5 Conclusions

This study relies on the Huangbuling 500 kV transmission project to investigate the dynamic response law of GIL pipe gallery under vehicle traveling loads. A numerical model of GIL pipe gallery considering soil-structure interaction is developed using finite element software ABAQUS, and the effect of soil pressure on GIL is studied through static analysis. A continuous step loading method for simulating vehicle traveling loads is proposed, and parametric analyses of different traveling directions and speeds are carried out to reveal the GIL’s dynamic response law in depth. The following conclusions are mainly obtained:

  1. (1)

    Based on soil pressure analysis, the Max. Stress value of pipe gallery is located in the root of the right-side wall (1.814 MPa), which is much smaller than the concrete strength design value. The Max. Stress value of the reinforcement cage is located in the root of the right-side face (17.94 MPa), much smaller than the tensile and compressive strength design value. The Max. Value of displacement occurs in the middle position of the top plate (6.556 cm).

  2. (2)

    The vertical acceleration, velocity and displacement responses are largest at the midpoint of the top of the pipe gallery and the stress response is largest at the lower-left corner under vehicle load. When heavy vehicle passes over the pipe gallery at different speeds, the peak acceleration, velocity and stress of the pipe gallery tends to increase with the increase of vehicle speed, while the peak displacement does not change significantly.