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Significance Prof. Chongxi Chen has long been engaged in teaching courses, personnel training and scientific research in the field of hydrogeology, working diligently and innovatively, and has achieved fruitful academic research results. Progress This article makes a systematic review of Prof. Chongxi Chen's academic contributions in the field of hydrogeology, mainly including three aspects: ① Carrying out innovative and theoretical researchon groundwater hydraulics. He corrected the historical model error of "steady-state well flow within the influence radius", developed a series of analytical models for special hydrogeological problems, and improved and extended classical well flow models. ② Continuously exploring hydrogeological simulation methods. He proposed a number of techniques and methods to improve the emulational level of groundwater simulation, such as the equivalent submarine discharge boundary of coastal groundwater, the coupling seepage-pipe flow model, the linear-nonlinear flow model in triple Karst media of cave-fracture-porous and the groundwater withdrawal-land subsidence model, etc. He also developed a unique and advantageous software for groundwater flow simulation, PGMS. ③ Proposing a theory of recharge-discharge changes for the evaluation of the sustainable groundwater extraction. He completed groundwater modelling in several typical regions in China, which played a demonstration role for the scientific assessment of groundwater resources. Conclusions and Prospects Prof. Chongxi Chen's innovative research has played an important role in promoting the development of hydrogeology in China.

Internal erosion is one of the main causes of dike failures. Their failure mechanism is related to the physical characteristics (distribution of particle size, permeability characteristics, clay content, etc.), stress state, and hydraulic conditions of the soil around the dikes. In this study, a series of erosion tests under different rising rates of the water head were conducted to study the internal erosion mechanism of a dike foundation under varying hydraulic conditions. It was found that different water head rising rates resulted in different internal erosion failure modes; furthermore, two critical values of water head rising rate were observed that decided whether erosion or piping occurred, and influenced the failure destructiveness of the internal erosion. Under the action of a continuous water head, the continuous failure through internal erosion occurred primarily in four stages. Moreover, under different water head rising rates, the change rules of the water head, seepage flow, and Jx–Q (average horizontal hydraulic gradient–seepage flow) curve were different. The mechanism of internal erosion and the critical hydraulic gradient could be determined based on the Jx–Q change characteristics. The backward erosion piping, based on the well flow model, suggested that the water head changing rate influenced the piping process. [ABSTRACT FROM AUTHOR]

Underground coal mining destroys overlying strata, and phreatic aquifer above the panel is destabilized, causing phreatic water level (PWL) variation. On-site monitoring of the PWL variation throughout the mining period is of great significance to the management and conservation of groundwater resources in arid and semiarid mining areas. The research on the decline of the PWL when phreatic aquifer leakage is concentrated, but there is little research on the fluctuation characteristics of PWL under the condition of phreatic aquifer without leakage. Therefore, using the #108 coalface in the Jinjitan colliery of the Yushenfu mining area as a case study to carry out the research on PWL fluctuation induced by underground coal mining. First, phreatic water without leakage throughout the coal mining period in the #108 coalface was determined. Second, considering surface subsidence induced by mining activities and PWL in fluviograph comprehensively, true PWL fluctuation characteristics were analyzed throughout the whole coal seam mining period. It is concluded that the buried depth of PWL presented a trend of "decreasing sharply—increasing sharply—decreasing slowly—increasing slowly—becoming stable" in the monitoring period of 1 year. Furthermore, a well flow model was established to simulate the PWL variation process before and after coal mining and to predict the PWL recovery time after coal mining. On these bases, the error analysis of the measured and predicted PWL recovery time, the relationship between the PWL fluctuation and the residual aquiclude thickness, the impact of rainfall on PWL recovery, the response of surface vegetation eco-environment, and phreatic water resources management and conservation were discussed. These research results are important for achieving a win–win situation strategy that balances the exploitation of coal resources and the conservation of phreatic water resources, promoting the sustainable development of coal mining. [ABSTRACT FROM AUTHOR]