Research On Integrated Grounding Technology Of Excavated Pile Foundation For Land-Saving Green Construction

In recent years,the demand for long-distance,large-capacity and high-voltage transmission lines in urban construction and development has been increasing.The actual operation and maintenance experience shows that good grounding of lines is the most effective way to reduce lightning damage.However,in the construction process of transmission line,social problems such as land expropriation compensation are often faced.Therefore,the effective grounding of tower pile foundation under limited construction area has become the top priority of transmission line design.Based on this,this paper analyzes the construction process of transmission line pile foundation,refines modeling with actual excavated pile foundation,studies its grounding resistance and dispersion characteristics and proposes integrated grounding methods for excavated pile foundation oriented to land-saving green construction.At the same time,the refined simulation calculation is carried out on the excavated four-pile foundation with practical application of the integrated grounding methods,and the traditional grounding methods is compared to study the amount of artificial grounding electrode and the land saving area.The specific work are as follows:(1)After analyzing the research results of grounding dispersion,resistance reduction methods and grounding materials for transmission line towers at home and abroad,two kinds of concrete pile foundation construction process and application range commonly used for transmission lines are studied.The simulation software is used to model the excavated pile foundation of SZK-DZ1416,and the grounding resistance calculated by the simulation is compared with the grounding resistance calculated by the grounding formula to verify the accuracy of the model.(2)The natural grounding characteristics of single excavated pile foundation with or without electrical connection between anchor bolt and reinforcement cage are compared and studied,and the natural grounding characteristics of four-pile foundation with traditional grounding girds in two cases are analyzed.It can be seen from the research results that when the anchor bolt is connected with the steel cage,the steel cage can provide a downward flow channel for the lightning current,but there are many safety hazards.When the two are not connected,although there are fewer dispersion channels leading to higher grounding resistance,the artificial grounding body is highly utilized,and the percentage of lightning current in its artificial grounding body is as high as 88.16%.Considering various factors such as operation safety and construction operation,the excavated pile foundation without electrical connection between the anchor bolt and the steel cage is selected for simulation calculation.(3)Using flexible graphite composite grounding material as artificial grounding body,two integrated grounding methods of vertical external grounding application and cage external grounding application are proposed.The various external grounding applications in the two integrated grounding methods are studied respectively,and the grounding characteristics and the optimal structure of the external application are simulated and analyzed.The calculation results show that the integrated grounding methods can effectively reduce the grounding resistance of transmission line tower,and the resistance reduction efficiencies are all above 88%.Among them,the effect of the graphite grounding fabric,combined graphite electrode,4-turn 3-bar cage electrode and 4-turn 4-bar cage electrode are the best.(4)Based on the natural grounding of four-pile foundation,the integrated grounding methods of excavated pile foundation for land-saving green construction is applied.Comparing with three kinds of traditional grounding grids connected to the four-pile foundation,the equivalent extension and land using area of the grounding methods are calculated.From the results of the study,it can be seen that the grounding resistance of transmission line tower that using integrated grounding methods can meet the requirements of safe operation,and it covers an area of only 330.04m~2,which can save a lot of land using area.The land saving area of the integrated grounding methods is about 3～6 times than its using area,while a maximum of 2,225.51 m~2 of land area can be saved compared to the foundation with 45°square-ray grounding grid.