地基施工对天水深井地电阻率观测的干扰

Quantitative analysis of the disturbance on borehole geoelectric resistivity observation at Tianshui station caused by foundation excavation

2018年7月,天水地电台NW向地电阻率出现高频突跳,经现场核实,发现测区附近正在修建综合大楼。利用有限元方法建立三维水平层状结构物理模型,分析地基施工对天水NW向地电阻率观测的影响。结果表明:地基开挖区域可视为电阻率无穷大的空气介质,测区17号、19号电极间形成一个高阻体,对观测造成一定高频扰动影响;将施工中钢架混凝土结构地基简化为地基中铺设的相互串联的金属导线,则测区局部形成一个高阻体,有限元模型计算结果显示,简单的4条钢架串联时会引起地电阻率上升,变化值与观测值基本吻合。从数值分析角度确定,金属结构框架会对该台NW向地电阻率观测产生干扰。

The NW component of the geoelectric resistivity observation data in the Tianshui station showed a high-frequency sudden jump in July 2018.Field investigation suggested that it was related to the ongoing foundation excavation in the survey area.The finite element method is used to establish a three-dimensional physical model of the horizontal layered structure and analyze the infuence of foundation construction on NW component resistivity observation at Tianshui station.The results show that the ground excavation area can be regarded as an infinite air medium so that a high resistivity body is formed between the electrodes of A17 and C19 in the survey area,which will cause certain high-frequency disturbances compared with the original soil media.The foundation-formed reinforced concrete structure can be simplified as metal wires laid in series in the foundation,which makes part of the survey area a high resistance body.The calculation of the fnite element model shows that a simple four steel string in series can cause the rising of the ground resistivity,and the change values agreed with the observed value.The numerical analysis suggests that the existence of metal structure may lead to the interference of resistivity observation at the station.