为了研究在地下车站结构顶板上方设置人工接地网的合理性和可行性,首先对地下车站的接地结构进行了叙述,采用CDEGS软件建立了地下车站的接地网模型,对比接地网在车站结构底板下方和车站结构顶板上方的工频接地电阻值区别,两者的电阻值相差60%~70%,并由此展开了车站结构顶板上方的土壤电阻率、结构顶板上方覆土土壤厚度和接地网网格尺寸、导体直径的细化研究,结果表明土壤电阻率和土壤厚度对接地电阻值起重要作用,接地网的网格尺寸和导体直径对电阻值的影响甚微。如果以1Ω作为地下车站接地网电阻值的衡量指标,在大部分情况下,接地网设置在车站结构顶板上方能够较好的将工频接地电阻值限值在1Ω以内,接地电阻值的计算结果整体在0.7Ω~0.8Ω范围内。最后对接地网上方地表的接触电压和跨步电压等安全性指标进行了研究,结果表明：当发生严重的短路接地故障时,在车站结构顶板上方设置接地网并不会引起地表上方的接触电压、跨步电压超标,具有较高的安全系数,证明在地下车站结构顶板上方设置人工接地网是可行的,是合理的。研究结果具有较高的工程实践参考意义,具有较强的应用价值。

In order to study the rationality and feasibility of setting artificial grounding grid above the top plate of underground station structure, firstly, the grounding structure of underground station is described, the grounding grid model of underground station is established by using CDEGS software, and the difference of power frequency grounding resistance between the grounding grid below the bottom plate of station structure and above the top plate of station structure is compared. The difference of resistance between them is 60% ~ 70%, The results show that the soil resistivity and soil thickness play an important role in the grounding resistance, and the grid size and conductor diameter of the grounding grid have little effect on the resistance. If 1 Ω is taken as the measurement index of grounding grid resistance value of underground station, in most cases, the grounding grid is set above the top plate of station structure, which can better limit the power frequency grounding resistance value within 1 Ω, and the calculation result of grounding resistance value is in the range of 0.7 Ω ~ 0.8 Ω as a whole. Finally, the safety indexes such as contact voltage and step voltage on the square surface of the grounding grid are studied. The results show that when a serious short-circuit grounding fault occurs, setting the grounding grid above the top plate of the station structure will not cause the contact voltage and step voltage above the surface to exceed the standard, and has a high safety factor, It is proved that it is feasible and reasonable to set up artificial grounding grid above the roof of underground station structure. The research results have high engineering practice reference significance and strong application value.

TM862

广州地铁设计研究院股份有限公司科技项目(20210305001)