为查明隧道穿湖段软硬不均地层变化情况及不良地质体分布,提出了一套地震共振频率成像法探测陆域段,高密度电法探测水陆过渡段,地震反射波法探测水域段,并结合地质钻探的综合勘察技术,部分区段选用两种方法进行探测,有效克服了单一物探方法多解性问题。结果表明:(1)地震共振频率成像法辅以少量地质钻孔,适用于圈定构造破碎带及划分岩土层;(2)高密度电法能有效查明埋深30 m以内基岩面起伏形态及暗渠等地球物理异常的分布,有效衔接水域段和陆域段物探成果;(3)经多次波衰减后,水上地震反射波法剖面信噪比有很大的提高,水土界面和土岩界面反射波同相轴清晰可见,结合地质钻探成果的校正,对水下地层结构划分取得了较好的效果。
A set of prospecting technologies is proposed to determine the variation of hard-soft heterogeneous strata and the distribution of unfavorable geological bodies, such as fault fracture zones, along the lake-crossing shield tunnel. These include the seismic resonant frequency imaging method for land-based areas, the high-density resistivity method for water-land transition zones, the seismic reflection method for water areas, and geological drilling for validation. Two geophysical prospecting techniques are selected for comprehensive geophysical exploration in some sections, and effectively overcoming the problem of multiplicity of a single geophysical prospecting method. The results show that: (1) The seismic resonant frequency imaging method supplemented by a few geological drilling holes, can delineate the structural fracture zone and classify the rock and soil stratum. (2) The high-density resistivity method can effectively link up the geophysical prospecting results of land-based area and water area, and identify the undulation patterns of bedrock surfaces, as well as the distribution of geophysical anomaly like closed conduits with the burial depth within 30 m. (3) The signal-to-noise ratio of seismic reflection section is improved significantly, and the reflection events of soil-water interface and soil-rock interface are clearly visible after multiple attenuation. A satisfactory result of underwater stratum structure classification is obtained by the seismic reflection method with the correction of drilling results. The integrated prospecting technologies, combining geophysical methods with geological drilling, effectively enhance the quality of survey results and provide a reliable engineering geological basis for design and construction.
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