Detection Of The Shallow Velocity Structure With Artificial And Nature Source Rayleigh Wave

To obtain the near-surface S-wave velocity structure of the site is a key step in engineering survey and shallow geological survey. Since the traditional wave velocity testing of borehole technique has some limitations, such as high cost, inefficiency and so on, Rayleigh wave exploration technology has been rapid developed in the resent years and widely used to detect the shallow S-wave velocity structure because of its economy and simple operation. According to the different source type, Rayleigh wave exploration technology can be divided into two kinds, artificial and nature source method. The artificial source method is developed maturely and which provides a high precision for shallow structure, but the detection depth is low due to the limitation of the excitation energy; On the contrary, the nature source method would gives a deeper investigation depth because of the low frequency range for the passive source. However, the precision for the shallow structure is not so good as the artificial source method because at the higher frequency range the source is contaminated by the man-made noises. Therefore neither nature source nor artificial source method alone can meet the demands of many engineering. A nature solution is to combine these two methods and take respective advantages, which results a higher precision near the shallow structure and deeper investigation depth.In this paper, considering the development of the surface wave exploration and the demands of the present geotechnical engineer, we introduce the basic principle, method and theory of the joint method with artificial and nature source surface wave exploration. Based on several application examples, the data acquisition and processing are investigated in detail for the surface wave exploration with artificial source, nature source and their joint, respectively. Particularly, based on the real case of the joint exploration, equipments, observation system design, field implement and data process are discussed. A joint exploration scheme is suggested in which the same arrangement is adopted to collect the data for artificial and nature source. The dispersion curves are separately extracted and then combined to be used in the inversion.After summarizing the experience of Baijiatuan and Xiadian test site, we carry out many engineering cases in Yuxi, Jiangchuan and Tonghai basin of Yunnan, under different geological conditions. The results indicate that joint surface wave exploration is applicable and efficient. The identical dispersion curves are obtained in the overlap frequency section for the two methods and the whole frequency range is expanded notably. The detection depth is evidently deeper for the joint exploration method than the method using either active or passive source without increasing the work effort. It shows the joint exploration method will find its potential application in the field of engineering survey and shallow geological survey domain.