Assessing quality of urban underground spaces by coupling 3D geological models: The case study of Foshan city, South China

Urban underground spaces (UUS), especially those containing natural resources that have not yet been utilized, have been recognized as important for future sustainable development in large cities. One of the key steps in city planning is to estimate the quality of urban underground space resources, since they are major determinants of suitable land use. Yet geological constraints are rarely taken into consideration in urban planning, nor are the uncertainties in the quality of the available assessments. Based on Fuzzy Set theory and the analytic hierarchy process, a 3D stepwise process for the quality assessment of geotechnical properties of natural resources in UUS is presented. The process includes an index system for construction factors; area partitioning; the extraction of geological attributes; the creation of a relative membership grade matrix; the evaluation of subject and destination layers; and indeterminacy analysis. A 3D geological model of the study area was introduced into the process that extracted geological attributes as constraints. This 3D geological model was coupled with borehole data for Foshan City, Guangdong province, South China, and the indeterminacies caused by the cell size and the geological strata constraints were analyzed. The results of the case study show that (1) a relatively correct result can be obtained if the cell size is near to the average sampling distance of the boreholes; (2) the constraints of the 3D geological model have a major role in establishing the UUS quality level and distribution, especially at the boundaries of the geological bodies; and (3) the assessment result is impacted by an interaction between the cell resolution and the geological model used.