深埋长隧道洞线岩性CSAMT法分析研究

ANALYTICAL STUDY ON ROCK PROPERTY OF LONG-DEEP TUNNEL WITH CSAMT METHOD

深埋长隧道的地球物理勘查工作主要是探测洞线高程附近的隐伏不良地质体的赋存情况。深埋长隧道的不良地质体主要为断层和破碎带,可控源音频大地电磁(CSAMT)法对于勘查这些不良地质体则是比较有效的一种方法。对西南一改建铁路进行CSAMT法勘查隧道洞线不良地质体的研究。结合CSAMT法对于本区的原始数据的质量要求,以及后期数据处理,特别对正常地层和存在断层、破碎带等不良地质体的典型视电阻率–频率曲线进行分析,了解这些特征构造的电性响应;对经过圆滑处理后数据进行反演,反演后的数据与原始数据进行拟合比对,判释反演的合理性。结合研究区钻孔所获得的地质信息,对CSAMT结果进行地质解释和验证。研究结果表明,CSAMT法在勘查深埋长隧道岩性分析方面具有可行性,对于隧道施工有一定的指导意义。

In geophysical exploration work for deep-long tunnel,the issue is mainly concentrated on bearing conditions of potential unfavourable geologic body near the area of tunnel line. As for deep-long tunnel,the unfavourable geologic bodies mainly include fault and fractures,and because of distinct electric differences between unfavourable geologic body and surrounding medium ,the controlled source audio frequency magnetotelluric(CSAMT) method is used to detect such unfavourable geologic bodies. CSAMT method has been adopted for the study on rock property of tunnel line about rebuilt railway in southwestern area. Based on related standard or literatures on CSAMT method,the data are firstly introduced. With the effective data,indoors data processing can be done. The much attention is paid on the analysis of typical apparent resistivity frequency curves,especially on unfavourable geologic body. The electric response of these unfavourable geologic bodies can be known and the differences between normal stratum and those containing unfavourable geologic bodies can be determined. Smoothing process can be done on original data and then processed data can be inverted. With the comparison between inverted data and original data,the fitness curves can be obtained. It is the fitness information that can help us determine the effect of inversion results. If the fitness data are too large to get correct inverted data,processing flow would return to smooth processing and should change parameters to invert again till getting correct result. Combined with geologic information of relative boreholes,the geologic interpretation can be carried out,and inverted results can also be verified. The study results show that CSAMT method is effective in exploring unfavourable geologic bodies and it is applicable for the analysis of rock property of tunnel line. Therefore,CSAMT method is an instructive guide for tunnel construction.