大亚湾中微子试验隧道工程不同物探方法探测结果综合分析

Comprehensive analysis of geophysical results via different exploration methods in granites of Daya Bay Neutrino tunnel

对不同埋深花岗岩采用重力法、电法和电磁法、地震法等地球物理勘探方法的结果差异性如何?本文以广东大亚湾花岗岩为例,先后开展了重力法、高密度电法、地震折射法、可控源音频大地电磁法(CSAMT)等4种不同方法,探测中微子场地断层破碎带、花岗岩与沉积岩接触带、风化壳厚度、地下水埋深等与隧道工程设计方案和围岩稳定性密切相关的地质条件.地球物理勘探以岩层物性(电阻率、波速和密度等)为基础,这些特征与岩性及地下水状态相关.同时相同物性特征对应不同岩层和含水状态,因而物探结果具有多解性.在工作中采用多种物探方法进行了相互补充验证.勘探结果比较后发现,对浅表50 m以内风化壳厚度,以人工重锤为激发震源的地震折射法效果较好,对风化壳分带和厚度达100多米的风化囊,高密度电法探测效果较好,而对于深大断裂或密闭断裂,重力法和电磁法效果较好.这四种不同物探方法结果的综合分析,对全面深入认识花岗岩地质条件提供了依据,其结果得到了钻探和隧道工程施工开挖揭露的验证.

In order to explore the difference of the exploration results for the geological conditions of the granites with depth by applying different geophysics exploration methods including gravitational method, electrical method, electromagnetic method and seismic method, the granites of Daya Bay in Guangdong Province was taken as an example in this study. A combination of gravity method,high density resistivity method,seismic reflection method and Controlled Source Audio Magnetic Telluric method（ CSAMT） were used in the exploration of the neutrino site,leading to the conclusions that for the weathering crust buried in less than about 50 meters the seismic refraction method which takes manual hammar as the seismic source is much more reliable and effective;for the weathered troughs whose depth is more than 100 meters the high density resistivity method is relatively more reliable and effective; while for the discordogenic fault and closed fault the gravity method and electromagnetic method are more suitable.According to the comprehensive analysis of the four geophysics exploration methods,we can have an overall and deep perception on the geological conditions of the granites. Moreover the geophysical results were also proved by both the drilling results and the appeared geological conditions during excavation.