Dynamic Response and Parameter Analysis of Buried Pipeline Induced by Blasting Seismic Wave Wang Haitao School of Civil and Safety Engineering, Dalian Jiaotong University Dalian Liaoning 116028, China e-mail：[email protected] Jin Hui School of Civil and Safety Engineering, Dalian Jiaotong University Dalian Liaoning 116028, China Wu Yuedong School of Civil and Safety Engineering, Dalian Jiaotong University Dalian Liaoning 116028, China Wang Kai State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian Liaoning 116024，China) ABSTRACT In order to study the adverse effect of the drilling and blasting excavation of subway tunnel on the adjacent buried pipeline, the field blasting vibration test and numerical simulation was carried out based on the drilling and blasting construction of Dalian metro tunnel, and the attenuation law of blasting seismic wave and the blasting vibration response of buried pipeline was studied. A Sa Rodolfo J Ki prediction formula of particles vibration velocity to reflect the propagation characteristics of the blasting seismic wave caused by drilling and blasting excavation was established by using regression analysis method. The maximum explosive charge control equation was established based on the vibration velocity attenuation formula. By considering the influence factors of pipeline buried depth, pipeline corrosion degree and tunnel excavation method, the blasting vibration effect of buried pipeline caused by drilling and blasting excavation was revealed using numerical simulation method. The results show that the blasting response of deep buried pipeline is more intense than shallow buried pipeline; The maximum tensile strain of pipeline is increased nonlinearly due to the decrease of pipe stiffness caused by pipeline corrosion; The stress of surrounding rock caused by the full face excavation is larger than by the benching stepping method KEYWORDS: drilling and blasting excavation; buried pipeline; field blasting test; numerical simulation; - 10625 - Vol. 21 [2016], Bund. 27 10626 INTRODUCTION The blasting seismic effect has been one of hot topics in the study of geotechnical field since the 1920s.The dynamic interaction between the underground structure and surrounding rock mass caused by explosive loading is the key issue in this field[1-8].At present, the main research methods are theoretical analysis, experimental research and numerical simulation. By using the principle of rock mass blasting mechanics, the theory of blasting shock wave propagation, the movement of rock mass and the deformation and failure of rock mass were systematically studied by Chen Shihai, Ozer and others[9,10];The blasting cavity-rock-underground structure dynamic interaction model was established by using LS-DYNA software based on the actual project , and then, the dynamic response of underground structure induced by blasting seismic load was analyzed by Du Yixin, Luo Kunsheng and others[11,12].Centrifugal model tests of underground structures such as pipelines, tunnels and other underground structures were carried out by Anirban and Zimmie[13]. Li youlv, Yao Anlin and others[14]using LS-DYNA software, based on a variety of working conditions of numerical simulation analysis, studied the dynamic response of buried pipeline. The relationship between the particle velocity and dynamic stress peak value, the explosive charge and the explosion center distance of the pipeline was analyzed. Liang Xiangqian and Xie Mingli[15] took the middle route of the South to North Water Diversion Project-Beijing Shijiazhuang section as an example, the propagation attenuation law of blasting seismic wave and the influence of blasting vibration on the safety of water supply pipeline was studied in combination with on-site blasting vibration test and construction monitoring. It can be seen from the above research that the research on the influence of tunnel blasting excavation on adjacent buried pipelines is still relatively few, and it is mainly aimed at field test and numerical simulation research of certain engineering conditions. The construction of tunnel between Qianshan Road Station and Songjiang Road Station in Dalian Subway Line 1 is excavated by drilling and blasting method. There are a lot of buildings and buried pipelines in this area. Therefore, in the early stage of the project construction, reasonable vibration safety control standards must be formulated, and optimized control blasting technology and effective safety monitoring methods should be adopted to ensure the smooth construction of the tunnel project and the safe operation of the pipeline around the tunnel. DYNAMIC RESPONSE ANALYSIS OF BURIED PIPELINES INDUCED BY BLASTING SEISMIC WAVES The tunnel project starts at the Shandong Road and Qianshan Road interchange, along the Shandong Road, ends at Shandong Road and Songjiang road intersection. Interval mileage number is AK8+017.365 ~ AK8+902.360, 884.995 meters long[16]. The topography of the interval is moraine hills, the north and south sides are low, the middle is high, and the ground elevation is 37.70 ~ 48.65m. There are a lot of buildings and buried pipelines in this area. The buried depth of the tunnel is shallow, and the depth is about 8.0~15.0m, the seismic effect caused by blasting is easy to have adverse effect on the adjacent buried pipeline. Therefore, in order to minimize the Vol. 21 [2016], Bund. 27 10627 damage of buried pipeline induced by blasting vibration to the minimum, corresponding damping measures must be taken to strictly control the parameters of blasting seismic effect ,combined with the field blasting vibration monitoring and data analysis Monitoring scheme of blasting vibration The blasting monitoring mainly includes the vibration frequency, vibration velocity and duration of blasting. TC-4850 blasting vibration meter as monitoring equipment shown in Figure 1.The gas pipeline with the depth of 1.5m was selected as the monitoring pipeline, and the sensor was arranged in the surface soil (monitoring point) above the gas pipeline axis To analyze the decay law of ground vibration velocity, it is required to collect the vibration velocity of each particle in different blasting center in the same blasting. Ensure the same explosive charge and blasting methods, the blasting distance and ground vibration velocity are analyzed. Monitoring scheme shown in Figure 2.Where H is the distance from the explosion center to the ground (m), and L is the horizontal distance between the measuring point and the explosive center (m), and R is the distance from the explosion center(m). Figure 1: TC-4850 Blasting vibration monitoring meter Figure 2: Schematic of blasting vibration monitoring Vol. 21 [2016], Bund. 27 10628 Establishment of Numerical Analysis Model (1)Material parameters The geological data provided by the Dalian Metro Line 1and combined with relevant engineering experience, the mechanical parameters of each soil layer are determined as shown in Table 1. According to the buried time and initial mechanical parameters of the buried pipeline, the mechanical parameters of the pipeline are determined in Table 2. The model of the overlying soil and surrounding rock uses the Mohr-coulomb ideal elastic plastic model. and analysis using FLAC3D[17]. (2) Calculation model and load The length of the model is 36m in the X direction, 20m in the Y direction, 42.3m in the Z direction, The model is shown in Fig. 3.A total of 6280 hexahedral solid elements and 7392 nodes. The load produced by blasting is reduced to the form of triangular load wave. Load to peak time is 100μs, the unloading time is 600μs, and load in the form shown in Figure 4. Table1: Mechanical parameters of rock soil body Parameter Bulk modulus Shear modulus Cohesion Internal friction angle Density（ Material (MPa) (MPa) (MPa) (°) kg/m³） Overburden 1900 4 2.5 0.037 18 Surrounding rock 2200 6.5 2.7 0.08 30 Table 2: Mechanical parameters of pipelines Parameter Bulk density Elastic modulus Tangent modulus Yield stress Poisson's ratio Material ( kN /m3) （GPa） (GPa) （MPa） Buried steel pipe 7800 0.3 195 12.5 420 Figure 3: Excavation model of pipeline buried under 1.5m Vol. 21 [2016], Bund. 27 10629 Figure 4: Blasting load curve (3) Selection of Dynamic Boundary Conditions and Related Parameters In FLAC3D analysis software, the free-field boundary conditions can be simulated by generating a one-dimensional and two-dimensional grid around the model. The free-field grids are coupled with the dampers to achieve the side boundaries of the main grid and the unbalanced force of the free field grid is applied to the grid boundary. The free field boundary provides the same effect as the infinite field causes the upward surface wave is not distorted in the boundary mainly. Free field boundary is used to simulate the dynamic calculation. Mechanical damping must be considered in dynamic calculation in order to simulate the damping of natural systems under dynamic loads. The damping is mainly caused by the sliding and friction of the internal contact surface of the material. Rayleigh damping method is used in this calculation. The natural frequencies of the model can be obtained by calculating the natural vibration without damping in the FLAC3D software. By comparing the different frequency values, it can be concluded that the natural frequency of the model is 6.11Hz. Comparison and analysis of the results of field monitoring and numerical simulation (1) Analysis of velocity of ground particle In the numerical results, it is important