Development of 3-D geotechnical database and its application to the evaluation of nonlinear site response and seismic zonation

Past earthquakes have shown that the distribution of damage is often directly related to the geotechnical and geological conditions of the deposits underlaying the civil engineering structures. To advance the understanding of the effects of local geologic and soil conditions on the intensity and characteristics of ground shaking and related damages on a regional level, and to improve methods for dealing with these effects, a new approach is developed based on modern computing technologies. This new approach contains two components and it was applied and tested for the area of Los Angeles. The two components are: (1) computer based 3-dimensional (3-D) geotechnical database describing the variation of local soil conditions and geology spatially (horizontally and with depth) for the area of Los Angeles, and (2) a unique geographic information system (GIS) for the calculation of ground motions and related effects for an area of interest obtained by the integration of the geotechnical database and a nonlinear site response model. The database and the GIS are generated by the software called "Techbase".; The geotechnical database is developed by digitizing relevant information from more than 1000 geotechnical boring logs. Such database can be used to generate automatically the maps of average soil properties for selected area and vertical soil profiles between any two selected points. The maps and profiles can be then compared to past earthquake damages or other types of information, and in this way used readily by geotechnical and earthquake engineering professions for the expeditious assessment of the sites of civil engineering structures.; The nonlinear site response model integrated into the GIS is a modified version of the computer model DESRA-2, which is named DESRAMOD-2. The nonlinear site effects can be delineated by such a GIS in the form of various maps, such as the map of maximum ground surface accelerations, maps of spectral accelerations for selected oscillation periods, map of maximum seismic pore water pressures for the entire area regardless of the depth at which the pressures were generated or for a specific depth interval, and maps of accelerations, velocities, displacements, stresses and strains for any given depth interval. The comparisons of such GIS maps show the anticipated correlations between different data and nonlinear site response phenomena. The consistency of such correlations and other data presented in the study indicate that the developed geotechnical database and GIS have a great potential for advancing the state of practice in seismic microzoning, and thus in the fields of earthquake damage evaluation and prediction, earthquake hazard mitigation and earthquake emergency response.