SPATIAL AUTOCORRELATION OF PASSIVE SURFACE WAVE DATA FOR ASSESSMENT OF AN EARTH DAM IN BRASÍLIA, BRAZIL

Abstract

DraABSTRACT. Surface wave methods are commonly applied to engineering problems for S-wave velocity estimations. Conventional active Multichannel Analysis of Surface Waves (MASW) surveys for earth dam assessment suffer from limitations mainly associated to restrict depth of investigation and negative influences of near noise sources. In Brazil, the need to image around noisy sites over 30 m deep, which are non-ideal contexts for traditional active seismic data campaigns, is commonly in demand. We acquired ten minutes of ambient vibration data at the crest of a large earth dam in Brasília, Federal District. The Spatial Autocorrelation (SPAC) method was applied to develop a 2D S-wave model velocity using surface wave generated from passing vehicles on the adjacent road. A maximum depth of 42 m was achieved, and the model presented a S-wave velocity range from 274 m/s up to 713 m/s. The water level, foundation ground and possible low and high anomalous compaction zones were interpreted. Vs30 was found to vary from stiff to very dense soil along the profile, with higher values observed towards the left abutment.