In view of the research status and main problems of artificial island construction in the underwater tunnel engineering, this study collects typical engineering cases of artificial island in the underwater tunnel projects, and summarizes key construction technologies of foundation treatment, cofferdam construction and fill reinforcement of artificial islands. Two main problems in the construction process of underwater tunnel artificial islands were proposed: firstly, the combination of schemes and process optimization for the soft foundation treatment and the soil filling reinforcement; secondly, the utilization rate of dredged soil in the construction of artificial islands in China was relatively low. Based on the existing construction technology of artificial islands, the future development direction of artificial island construction is to achieve the green and rapid island building through prefabricated artificial island components.

This paper sorted out the current situation of the variation of shield tunnel distance and introduced four typical long-distance shield-tunneling engineering examples. Combined with the typical engineering, five problems in the long-distance excavation, such as the cutter wear, shield tail sealing failure, pipeline wear, opening chamber in complex stratum and underground junction of shield, were systematically analyzed. The principle, technical process, application scope, advantages and disadvantages of main technologies in the long-distance excavation were summarized. The development of intelligent and rapid construction technology has also been prospected. It can provide some references for the formation of a systematic and standardized long-distance shield construction technology in the future.

The water volume and total phosphorus data of Taihu Lake from 2000 to 2020 were collected and sorted out. The the Taihu Lake Basin flood in 2020 and the change trend of total phosphorus pollution in Taihu Lake thereafter were analyzed and compared with the flood in 2016. The characteristics of flood, phosphorus flux in and out of the lake, phosphorus concentration in rivers around the lake, phosphorus stock and composition of Taihu Lake were studied, and the impact of the flood in 2020 on total phosphorus pollution in Taihu Lake was clarified. The results show that the flood in 2020 did not cause the rebound of total phosphorus pollution in Taihu Lake, and the total phosphorus pollution in Taihu Lake improved significantly after 2020. Unlike the flood in 2016, the flood in 2020 did not cause an increase in lake-inlet phosphorus flux. The total phosphorus mass concentration entering the lake in 2020 has decreased by 21.5% compared to the average value since 2007, which is the main reason why the phosphorus flux into the lake has not increased.

In order to clarifying the impact of temperature reduction on the decline and sedimentation of Microcystis, the decline process of Microcystis bloom in Gonghu Lake was monitored and low temperature culture experiments were conducted. The results show that the laboratory simulation results are basically consistent with the phenomenon in the field in autumn and winter. Microcystis generally declines at temperature below 15℃ and sinks in large numbers below 12.5℃. The temperature reduction leads to a significant decrease in the size of the Microcystis colonies, which is related to the number of dead algal cells within the colony. When the mortality rate reaches 25%~45%, the large colonies will generally begin to disintegrate and disperse into small colonies. Gravity density of Microcystis continues to increase at low temperatures, and it eventually loses its ability to autonomously float to the surface. The initial decline in sedimentation of Microcystis in autumn and winter is mainly caused by colonies miniaturization and loosening, and the increase of gravity density is likely to be the main cause of Microcystis sedimentation in the later stages of temperature reduction.