微动勘探技术及其在土木工程中的应用

ARRAY MICROTREMOR SURVEY AND ITS APPLICATION TO CIVIL ENGINEERING

介绍阵列微动勘探这一新的勘探方法,并结合现场试验数据探讨该方法在土木工程地质调查领域中的应用。在土木工程、地震防灾等领域,地下的横波速度分布是一个重要物性参数,通常是通过钻孔,利用P-S波测井取得。这一方法虽然能获得较精确的速度值,但由于需要钻孔,成本高,费时长,而且对环境有一定的破坏作用。近年来在日本开发了一种新的勘探方法——阵列微动勘探(array microtremor survey),该方法通过布置于一定范围内的数台地震仪同步地记录微动信号,然后以平稳随机过程为理论依据,从微动信号中提取瑞雷面波的频散特性,最后通过对频散曲线反演来推测地下的横波速度分布。通过现场试验数据分析,探讨该方法在土木工程领域的应用可能性。试验结果表明,由微动勘探获得的地下横波速度模型与传统的P-S波测井结果整体上具有很好的一致性,虽然阵列微动勘探的分辨率差一些,但对于较厚的地层,求得的横波速度及界面深度有较高的精度。该方法与传统的利用钻孔的P-S波测井方法相比,施工简单、成本低、费时短、对环境无任何影响,特别适用于人口密集、交通繁忙的市区。如果该方法与钻孔相结合,可以通过少量钻孔快速、准确地把握地下的三维横波速度模型。

The Array Microtremor Survey(AMS) is briefly presented and its application is discussed to geotechnical investigation for civil engineering based on field experiment data. For this method, first, microtremors are observed simultaneously by a number of seismometers deployed in an area on the ground surface, then, phase velocity of surface wave is calculated from the observed microtremors using stationary stochastic process theory, finally, the subsurface shear wave velocity structure is estimated by phase velocity inversion. To study the application of this method to shallow geotechnical investigation for civil engineering, a series of field experiments and theoretical analyses are made. The result of the study shows that shear wave velocity structure given by AMS agrees well with the result of the conventional P-S log method in general. Though the AMS is slightly inferior to the PS log in resolution, it gives good accuracy for thick layers. Unlike the P-S log method, the AMS does not need to drill a borehole, thus it can save both money and time and be gentle to the environment. Furthermore, since the traffic vibration is no more a noise, but it provides a source for high frequency signal, the AMS method can be considered as an inexpensive, fast and gentle method for geotechnical investigation in urban area.