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Shanghai has the largest newly reclaimed area in China's coastal regions, and dredger fills are universally distributed in reclaimed lands there. Multi-scale geotechnical properties of dredger fills in region-scale (>1 km2), site-scale (1 m2–1 km2), mesoscale (1 cm2–1 m2), and microscale (1 µm2–1 cm2) were studied mainly through cone penetration investigation, borehole investigation, and microscopic inspections. Dredger impact craters, soil structures, and soil textures were investigated qualitatively and quantitatively to identify the dredger fills. Ultimate land subsidence since 1 July 2018 and land subsidence velocity characterized by the land subsidence from 1 July 2018 to 1 January 2019 were evaluated in Shanghai's typical reclaimed regions. Afterwards, Bayesian network including sixteen variables was proposed for land subsidence risk assessment. Surface subsidence, land subsidence velocity, and comprehensive land subsidence were the most sensitive to data point location and average initial void ratio of underlying strata. These three risk variables were also highly correlated to the thickness of the dredger fill layer and the reclamation time. This finding indicates that variances of the four independent variables (i.e., data point location, average initial void of underlying strata, land reclamation time, and thickness of dredger fill layer) significantly decide variances of the three risk levels. [ABSTRACT FROM AUTHOR]

Summary: Shanghai is one of the cities suffering from land subsidence in China. Land subsidence has caused serious financial losses. Thus, artificial recharge measures have been adopted to compensate the drawdown in shallow, confined aquifers and thereby control land subsidence. In this study, a multi-cycle recharge–recovery field experiment was performed to investigate the response of a shallow, confined aquifer to artificial recharge through a well. In the experiment, a series of recharge–recovery cycles with different recharge volumes and durations, with and without artificial pressure, were performed. The water levels monitored in the recharge and observation wells indicated the response of the aquifer to the multi-cycle recharge–recovery process. Meanwhile, a finite-difference method (FDM) numerical model was established, and its parameters were obtained via a reversed numerical analysis on the experimental data. The responses of the shallow, confined aquifer to the multi-cycle recharge–recovery process were simulated in detail using the model. The calculation results showed that the water level dropped significantly when the recharge ended. Moreover, the efficiency of a multi-cycle recharge was found to be higher than that of a concentrated one under the same recharge volume and time. The relationship between recharge frequency and efficiency, expressed as H =0.29498 f 0.40163 and R 2 =0.97264, respectively, was obtained through the FDM numerical simulation. In the recharge intervals, the optimal recharge efficiency was achieved when the water level rose to 40% of the peak. [ABSTRACT FROM AUTHOR]