The extreme precipitation events caused by climate change and the rapid development of urbanization have brought hidden flood risks to the cities. This paper comprehensively considered two major factors of vulnerability of urban flood-bearing and disaster prevention and mitigation (DPAM) capacity and built a comprehensive evaluation index system for urban flood-bearing risks. Secondly, a combined model consisted of composite fuzzy matter-element and entropy weight model was constructed to calculate the comprehensive risk indicator. Finally, the Zhengzhou City was taken as an example, the comprehensive indices of urban flood-bearing risk from 2006 to 2015 were evaluated. The results showed that the comprehensive risk of Zhengzhou City was generally on a slow upward trend, from II level (moderate-risk) in 2006 to III level (secondary high-risk) in 2015, which was mainly due to the mismatch between the rapid development of urbanization and the slow improvement of DPAM capabilities. This paper is expected to provide scientific reference and technical support for urban flood disaster prevention and sponge city construction.
In this paper, a model is proposed to simulate frost jacking performances of a pile foundation within an axisymmetric pile–soil system through a coupling strategy. We consider three diversified stages for frost heave of adjacent foundation soil below freezing point, where mathematical expressions for the volumetric strain are given in terms of volumetric ice content, negative temperature and porosity. A modified strain-softening model characterizing frozen soil–pile interactions is established based on experimental results, taking into account the effects of normal pressure, negative temperature and moisture content. The proposed computational approach is then illuminated and validated via the numerical example of a simplified bridge pile foundation under natural permafrost condition. Variation of temperature regime, volumetric ice content, displacement and stress over time is analyzed. This model can be further applied to evaluating effects of different countermeasures that mitigate frost jacking hazard of single pile subjected to cold climate.
