城市地铁跨孔电阻率CT超前地质预报方法研究

STUDY ON COMPUTED TOMOGRAPHY OF CROSS-HOLE RESISTIVITY IN URBAN SUBWAY GEOLOGICAL PREDICTION

为了提高跨孔电阻率CT方法在城市地铁超前预报中的应用水平,杜绝重大地质灾害隐患,确保地铁隧道开挖施工安全,探讨基于有限元法和最小二乘法的跨孔电阻率CT正、反演数值模拟方法,构建城市地铁超前预报经常需要探测的充水溶洞、充水断层和基岩面3种地电模型,分析、总结其响应特征及规律,验证其应用于城市地铁超前预报的可行性,并指出该方法在地铁预报中的其他适用探测对象。鉴于城市地铁超前预报环境的复杂性,提出跨孔电阻率CT方法用于地铁超前预报的3种测线布置方式和一种三维切片解释方法。结合实例分析,进一步阐述该方法的实际应用特点和效果。研究结果表明,跨孔电阻率CT方法用于城市地铁超前地质预报时其精度高、准确性好、实施灵活方便、不占用隧道开挖时间,优势较为明显。

The forward and the inverse numerical simulations on the computed tomography of cross-hole resistivity was carried out based on the finite element and the least squares methods for the better geological prediction in urban subway engineering to avoid the potential geological disasters and ensure the construction safety. Three geoelectric models describing the water-filled karst cave,the water-filled fault and the bedrock surface were established respectively. The models were used to analyze the response characteristics and the behaviour and to verify the feasibility of the computed tomography of cross-hole resistivity. Meanwhile,it was pointed out that the computed tomography of cross-hole resistivity could be applied to the other type of cases in the urban subway geological prediction. Three types of layouts of the surveying lines and a 3D slice method of interpretation were presented to resolve the complexity of geological environment of the urban subway. Further case studies showed that the computed tomography of cross-hole resistivity had a high precision of detection and was flexible in implementation and did not interfere with the tunnel excavation.