Problems Encountered with Field Measurements for Site-Specific Seismic Response

Abstract eng:
This paper discusses problems encountered with field measurements made for development of seismic microzonation maps that contouring the site specific seismic response for a seismically active area. This Area is located in the far northwestern region of the Kingdom of Saudi Arabia. The field measurements included: (a) Conventional soil exploration borings with Standard Penetration Test (SPT), Cross-Hole (CH) and or DownHole (DH) measurements of shear wave velocity (SWV) profiles, and Non-invasive measurements of SWV. Comparisons and correlations of the results depicted the factors that probably affected the measurements related to different site conditions. Some of the major difficulties encountered with the field measurements were attributed to: a) drilling and casing of the boreholes, and non-uniform backfill between the borehole and its casing, b) Drilling of boreholes at increasing depths due to the unstable saturated sand conditions, c) existence of coral formations, d) influence of the water on the SWV where the water level is near the surface. In general, the SWV results of the different methods used in the study correlate well for most sites investigated where only minor problems occurred with the field measurements. Notwithstanding that, the experience gained from this study confirms that the field determination of soil profile class of individual site as per the current NEHRP provisions is very difficult or even prohibitive in some cases. It would therefore be significant evolution that more practical and economical solutions for the site–soil characterization are adopted in the future versions of the major international seismic codes.

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