Geotextile filters have gained extensive applications in geotechnical and geoenvironmental drainage systems. Despite of the abundant research about geotextiles filtering coarse-grained soils, there is little experimental study on the performance of geotextiles filtering fine-grained soils. Since clogging and blinding of geotextiles are more likely to occur in clayey soils, a complex filtration performance of the filters is expected, posing great challenges to the long-term durability of the filtration system. In this research, long-term permeability tests were conducted on silty clay filtrated by three types of nonwoven needle-punched geotextiles. Comprehensive results regarding the permeability evolution, soil retention and clogging behavior were obtained. Interior clogging behavior of the geotextile was checked after the tests by means of scanning electron microscopy. Significant reduction around two orders of magnitude from 10⁻⁸ m/s to 10⁻¹⁰ m/s was observed in the permeability coefficient of the silty clay-geotextile system after 90 days of seepage flow. The influence of filtration opening size of the geotextile was obviously noticed in the initial permeation process, while the thickness played an increasingly important role at the later stage. Geotextile with the larger thickness and smaller filtration opening size had more soil retention and poorer filtration performance. In addition, a theoretical equation relating permeability coefficient and filtration opening size of nonwoven geotextile under clogged condition was proposed.

With the rapid advancement of urbanization, the development and utilization of urban underground space resource (UUSR) has become one of the dominant features. However, in certain areas, the development of UUSR may cause disasters and accidents, such as ground collapse, settlements, and tunnel water gushing. Geological environmental factors (GEFs) are recognized as the fundamental constraining factor of UUSR development. In this paper, quality based on GEFs is defined to assess the development difficulty degree of UUSR. A 3D assessment framework is proposed based on 3D geological modelling and the interval continuous mathematical model (ICMM). The subjective and objective joint weight method of analytic hierarchy process and entropy weight method (AHP–EWM) is utilized to determine the weight of each indicator. The quality index (QI) of each spatial node of the 3D geological model is calculated by the ICMM mathematical model. A case study conducted in the Jiangbei New District of Nanjing, China, serves as a demonstration of the UUSR assessment. The results clearly illustrate the 3D distribution characteristics of the quality in the study area, offering valuable insights for future 3D urban underground space planning.

Urban underground space resource (UUSR) constitutes a critical natural resource and a vital component of the natural environment, whose rational utilization is essential for the sustainable development of cities. Mathematical models are indispensable for the multi-object evaluation of UUSR. However, in previous research based on traditional mathematical models, neither the continuous expression of evaluation results has been considered, nor has the comparability been addressed. In this paper, the interval continuous mathematical model (ICMM) is presented at the theoretical level for UUSR multi-object evaluation. By achieving the continuous distribution of quantitative values of evaluation indicators, removing the step-like output features of evaluation results, and eliminating predefined grade boundaries, the ICMM achieves continuous expression of the results and improves their comparability across different areas. The correlation analysis conducted on the UUSR evaluation indicators demonstrates a significant monotonic relationship between the indicator value and the evaluation result, regardless of the increasing trend or the decreasing trend. Finally, a numerical experiment clearly demonstrates that the ICMM is valid for evaluating different UUSR objects.