Abstract
Abstract Continuous seismic velocity measurements use a special automated wave source and advanced post-processing analyses to provide fast, detailed, and reliable profiles of shear wave velocity (Vs) with depth. Conventional geophysical techniques such as crosshole tests (CHTs) and downhole tests (DHTs) in boreholes are slow because they have several required steps: (1) rotary drilling, (2) installation of casing and grouting, (3) inclinometer measurements (for CHTs), and (4) deployment of geophones for seismic readings. Direct-push technologies include the use of seismic cones and seismic dilatometers that offer DHT-type Vs data at intervals of 1 m or less without the need for drilling, casing, grouting, or separate field events. The recent development of a new portable autoseis source allows the generation of reliable and consistent shear waves either intermittently or as frequently as every 1 to 10 s. Continuous shear wave measurements can provide improved detailing of the small-strain stiffness (G0) at frequent depth intervals and fast field production times. Appreciable sensitivity errors in Vs calculations can be experienced because of the extremely small time shifts between adjacent shear wave records, as well as significant signal noise due to vibration, external sources, and refracted waves. This paper details continuous-interval seismic piezocone testing and explains how to handle signal post-processing in both the time domain and the spectral frequency domain in order to obtain a reliable in situ Vs profile.
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