3D geological suitability evaluation for underground space based on the AHP-cloud model

Urban development continues to reduce the amount of available ground space. The development of underground space is thus gathering increasing attention to alleviate ground congestion. However, there is currently a lack of a three-dimensional (3D) evaluation method to systematically evaluate the geological conditions of underground space and possible geological disaster risks caused by rock and soil masses. This paper presents an engineering geological suitability assessment framework based on 3D geological modeling and an analytic hierarchy process (AHP)-cloud model. As the basis for 3D evaluation, a 3D structural model of the study area is established based on the drilling data and geological profiles. Then the structural model is partitioned to obtain interpolation grids, and the ordinary Kriging interpolation method is applied to attribute interpolation. All the attributes are exported from the geological model, and the rock and soil masses are divided into four categories according to their engineering properties, namely soft soil, sandy soil, cohesive soil, and rock, upon which a targeted hierarchy structure is established based on the attributes that impact the suitability. This paper introduces the cloud model to characterize the uncertainty of these evaluation indexes, which synthesizes an AHP method, thus it is referred to as the AHP-cloud model. This new model is used to evaluate the geological suitability of underground space in the Sanlong Bay district, Foshan City, Guangdong, China. In addition, we also determine the excavation difficulty at different depths according to the lithology and weathering degree of the study area. The limitations and future directions of the proposed method are discussed, including the influencing factors and weight determination.