Engineering Geology: Fundamental Input or Random Variable?

Geologists and engineers view the world in complementary but different ways. Science seeks to explain all observed details, whereas engineering seeks to design with specific objectives and multiple constraints. National guidance in the United States calls for geotechnical site investigations to be performed by geotechnical engineers and engineering geologists. Site characterization should start with geologic models, which form the basis for ground models (geologic models with engineering parameters) and geotechnical models (ground models with predicted performance based on design parameters). If the geologic model is wrong, then neither the ground model nor the geotechnical model can be correct. Fundamental geologic variability makes some details unforeseeable. Insufficient geotechnical investigations, faulty interpretations, or failure to portray results understandably contribute to inappropriate designs or failures. If the geologist does not interpret the geology and explain it clearly, then the engineer will be forced to interpret it or ignore it. Incomplete or inaccurate geotechnical site characterization can lead to selection of incorrect models, geotechnical properties, and design values. Furthermore, project managers responsible only for design and construction may view geologic site characterization as extra cost if benefits result in improved life-cycle reliability or reduced maintenance costs but do not improve design or construction.