해안매립지 형상 파악을 위한 극천부 S파 반사법 탐사

Abstract

In this study, high-resolution S-wave reflection surveying has been successfully conducted on a landfill area, the Busan North Port redevelopment site, using a variable offset multi-coverage data acquisition method with a 48-channel reflection system. This paper demonstrates the feasibility of using ultra-shallow S-wave, high-resolution surveys to characterize stratigraphy of near-surface layers of the landfill site for civil engineering purposes. Delineation of the near-surface structure and estimation of the geological properties of surface layers are important in site characterization. To identify the near-surface landfill soil conditions, conventional drilling is inadequate to detect such local anomalies as abrupt changes in soil layer thickness, or the difference of geological compositions. P-wave reflection surveys do not have enough resolution to image local near-surface layers less than 20 m because of the ground roll (surface-wave energy) that travels along or near the surface of the ground. Ground roll is usually characterized by relatively low velocity, low frequency, and high amplitude. It tends to mask desired reflection signals of the ultra-shallow layers. By contrast, S-wave surveys possess sufficient resolution to reveal local anomalies and the detailed structure in surface layers. The advantage of using S waves is increased resolution because of their lower velocities and consequent shorter wavelengths compared with P waves in soft sediments. In addition, an S-wave reflection survey provides S-wave velocity structure, which is fundamental information that can be used directly to estimate the strong motion response of a survey site. A series of super-resolution S-wave reflection surveys on landfill areas can delineate detailed structures of near-surface layers shallower than 50 m, and prove the wide applicability of the tool to civil engineering, environmental applications, and estimation of the geotechnical properties. The S-wave, high-resolution section obtained from the landfill site clearly reveals seaside landfill sediment and a good consistency with drilling results in the survey area.