Evaluation of engineering site conditions in North Gyeongsang Province, South Korea, using a large database of borehole and standard penetration test data

In this study, the distributions of seismic response parameters and engineering site classes were quantified using a large database of borehole and standard penetration test (SPT) data for the North Gyeongsang Province, Korea. Empirical shear wave velocity (VS) profiles were constructed for 17,180 boreholes by applying a series of development methodologies based on combining the SPT–N value (blow count) and the boring log. N–VS relationship for each stratum was used and representative VS values were assigned for the lower rock layer without N value. If necessary, extrapolation and estimation were additionally applied to obtain the mean VS up to a depth of 30 m (VS,30). Seismic response parameters, such as VS,30 and the mean VS of soils above the engineering bedrock (VS,Soil), were derived and analyzed based on the empirical VS profile. Engineering site classification was performed using international and Korean seismic design codes. The validity of the empirical VS acquisition methodology and the related engineering bedrock depth determination were examined by comparing the derived bedrock depth to the appearance ratio and depth of the rock layer in the boring log. The effects of limiting the maximum converted N value, which is applied to the N–VS relationship, and of defining the engineering bedrock as a stratum with VS > 760 m/s were analyzed. Finally, the spatial bias of the borehole locations was reviewed by analyzing the distribution characteristics of the borehole elevations using a digital elevation model. The results may be used as basic data to assess the adequacy of site classification systems, to derive randomized input parameters, and as reference data for international geospatial zonation verification.