Influence Of Blasting Excavation On Nearby Corroded Pipeline And Risk Assessment In Coastal Areas

Subway as a modern transportation has gradually become one of the world an important measure to solve the problem of urban traffic congestion. At present, more than20cities have subway and construction of the subway in China. Subway tunnel engineering general is in the heart of the city, the various pipelines staggered intensive in the formation. Tunnel construction is bound to adversely affect pipelines security. If inadequate control could easily cause a gas leak explosion, water pipes burst formation flooding, cable breakage caused by power failure or breakdown in communications security incidents.For the buried pipeline with a long history, due to the long buried underground, the erosion of the surrounding environment and the years of damage could result in the deterioration of mechanical properties. Especially in the coastal areas (such as Dalian, Qingdao), due to sea level rise and other natural factors cause, the underground construction facilities in this areas are long-term corrosion by seawater immersion. Coupled with relatively complex geological conditions in these areas, therefore, the main construction method of subway tunnel in the region is drilling and blasting method. When construction of the drilling and blasting method, blasting excavation produced ground motion will adversely affect neighboring already buried corrosion pipeline. These will increase the difficulty and risk of the subway construction. The present studies are focused on the non-rock area of subway tunnel constructed by shield method, without considering the adverse effects of pipeline corrosion.The studies for influence of blasting excavation on nearby corroded pipeline has not started yet.Therefore, it has important realistic and theoretical value to study the effects of the blasting construction on the corroded pipeline.This paper takes Dalian subway tunnel as background, based on the investigation of the joint type, planting age and geological conditions of the buried pipeline along the project, carry out the pipeline corrosion testing and mechanical testing. Based on the mechanism of electrochemical corrosion, the corrosion rate prediction model and residual strength prediction model of of pipeline were established. By means of in-situ test and numerical simulation method, the transmission of blasting seismic wave in rock and dynamic response of buried pipelines under blasting seismic wave were studied. The deformation of Dalian subway shallow buried pipelines was predicted by ARMA model. Combined pipeline subsidence caused economic loss model and the consideration of the pipeline residual strength security control standards, the risk of the pipeline deformation induced by tunnel construction was assessed. Finally, according to the practice of blasting excavation of Dalian subway tunnel excavation, the security control measures of buried pipelines during the construction process of blasting excavation were proposed. The main contents are as following:(1) The simulation tests were conducted on the corrosion rate of pipeline in erosion environment. The corrosion rate, corrosion regularity and characteristics of two kinds of pipeline were studied. The grey relational analysis in grey theory was used for the analysis of pipeline corrosion influence factors, and then combined with BP neural network, BP neural network prediction model based on the grey relational analysis theory was established. The corrosion rate of pipeline is predicted, and compared with the measured value; the accuracy of the predicted results of the model is high. Improved BP neural network using genetic algorithm and it is successfully applied to predict of the residual strength of corrosion pipeline.(2) Taking the drilling and blasting construction of Qianshan Road Station to Songjiang Road Station interval tunnel in Dalian Metro Line1as the engineering background, the deformation monitoring and the monitoring of blasting vibration of buried pipeline along the subway were conduct. According to the blasting monitoring data, the prediction formula for blasting seismic wave propagation characteristics of Dalian subway tunnel was established by regression analysis method. Combined with the blasting monitoring data and the prediction formula to continue to improve and adjust the blasting parameters, so as to guide the subsequent phases of drilling and blasting construction of subway tunnel.(3) Using FLAC3D software, the three-dimensional numerical model of the tunnel-the geotechnical body-corrosion pipeline was built, and the blasting construction process was simulated. Then, the results of numerical simulation and field monitoring are compared and analyzed. The comparisons show that the numerical simulation of the blasting seismic wave and the maximum vibration velocity of ground particles attenuation with distance from the explosion center in agreement with measured results. This indicates that the study of the blasting vibration effect of blasting excavation by using numerical simulation method is feasible. Based on the surface vibration velocity attenuation formula, the calculation formula for controlling maximum dose was presented. According to the peak value of vibration speed different, the relationship curves of distance from the blasting center with the single maximum charge were fitting out. Finally, the blasting vibration effect caused by blasting excavation was simulated with different buried depth of pipe, different corrosion degree of pipeline and different excavation methods. The results show that the blasting response amplitude of deep buried pipeline is greater than shallow buried pipeline. Pipeline corrosion leads to the decline of pipe stiffness, so the settlement and the maximum tensile strain of pipeline increase nonlinearly. There are three tunnel excavation ways:Full-face method, Bench excavation method and Step-by-step excavation method. The stress of surrounding rock is the largest of Full-face method.(4) Pipeline deformation is affected by many factors. It is difficult to establish the function relationship which includes all the factors for pipeline deformation changes with time. ARMA model emphasizes the "let the data speak for themselves", from the data itself to find could describe the data model, which can ensure the model fit the data better. Based on the cumulative settlement data of underground corroded pipeline in tunnel blasting construction process, ARMA model is established. Deformation of buried pipeline along Dalian subway tunnel is predicted. The model has high prediction precision, which can be used to predict the pipeline settlement.(5) The expression for pipeline settlement caused economic losses is first established. Then, the membership functions for Pipelines being damaged and destroyed are introduced. The rigid pipeline damage control standards are presented by considering the pipeline residual strength.Finally, the risk of buried pipeline along Dalian subway tunnel during tis construction was analyzed. According to the statistical data of surface subsidence value in similar projects, the maximum surface settlement probability distribution function value was fitting out. According to the function relationship between economic loss and the surface settlement, the probability distribution curve of pipeline deformation caused by the economic loss was finally obtained.(6) On the basis of blasting monitoring, numerical simulation and risk assessment, combined with the practice of blasting excavation of Dalian subway tunnel excavation, the security control measures of buried pipelines during the construction process of blasting excavation were proposed. These provide references for the security of buried pipelines during the construction of subway tunnel using drilling and blasting method.