珊瑚岛礁工程地球物理方法初探

Discussion on geophysical methods applied to investigation of coral island and reef

梳理了国内珊瑚岛礁岩土工程物探调查的现状,结合钻孔原位测试,采用成熟的物探方法对珊瑚岛礁进行综合地球物理勘探,说明了各种物探方法的场地适应性和效果。主动源面波探测效果好,面波视速度剖面很好地反映了珊瑚碎屑层与礁灰岩的地层层序;水域地震反射波对外礁坪、向海坡、外海的沉积层界面反映清晰,发现某岛礁的西南、东北端的水底形态不对称,沉积层差异大,可能与珊瑚礁成长的海洋水动力环境有关。孔内电阻率原位测试数据表明,松散珊瑚碎屑层与礁灰岩的电阻率差异很小,在同一数量级,总体上无法采用电法类勘探方法进行地质分层。

The thesis summaries China's recent situations of geophysical prospecting in coral island and reef. Combined with the In-situ borehole test, three regular geophysical methods are adopted in the investigation of a coral island; their applicabilities and results are specified. It is shown that the active surface wave(ASW) and marine seismic reflection(MSR) can achieve satisfactory results; but the resistivity method is not suitable for coral island and reef. Apparent velocity profiling of ASW method figures out the geological stratigraphic sequence of coral clastic deposit and underlying reef limestone. MSR does well in the distinguishing the deposit interface of outer reef flat, seaward slope, offshore and discovers the unsymmetrical structure of sea bottom, deposit between the northeast and southwest survey line, which is probably related with the marine hydrodynamics in the coral growth and development. In-situ borehole test showes that the loose coral clastic sediments has little difference in electric resistivity with the reef limestone; therefore the resistivity method is overall not suitable for the geotechnical profiling for the reason of the same order of magnitude in electrical resistivity.