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Yang T.-L.,Tongji University | Yang T.-L.,Shanghai Institute of Geological Survey | Gong S.-L.,Shanghai Institute of Geological Survey
Bulletin of Engineering Geology and the Environment | Year: 2010

The upper 75 m of the alluvium beneath Shanghai can be divided into three clay layers. Consolidation of the upper soft clay contributes to the average 3 mm/year land subsidence which occurs in the Shanghai region, despite mitigation measures including reduction in groundwater exploitation from the underlying aquifer and groundwater recharge. Data indicate that the soft clay is semi-dispersed, marginally stable, and susceptible to compaction. The study reports an analysis of the granulometric characteristics and aggregate components, pore-size distribution, microstructure, pore solution composition and cation exchangeability of the soft clay. The results indicate the deformation/consolidation of the soft clay is related to its microscopic physical and chemical characteristics rather than the fluctuation of the groundwater level in the underlying aquifer. © 2010 Springer-Verlag.

Cui Z.-D.,Tongji University | Cui Z.-D.,Shanghai Institute of Geological Survey | Tang Y.-Q.,Tongji University
Engineering Geology | Year: 2010

In the urban area of Shanghai, the dewatering of groundwater was controlled strictly and the engineering-environment effect of the high-rise building group became to be the main cause of land subsidence in Shanghai. Based on the high-rise building group in the soft soil area in Shanghai, the mechanism of land subsidence was studied in this paper by the centrifuge model test. The central area of the building group has larger subsidence and the subsidence superimposition effect is obvious. It can exceed the allowance and cause land subsidence hazard. The land subsidence affected by the different building distances was also studied. For smaller building distances, the subsidence superimposition effect is more obvious. The engineering characteristics of soils are controlled by the state of pore structure of soils to a great extent. The parameter of specific subsidence was put forward as a tie to analyze the relationship between land subsidence and pore structure of soils. The pore structure of each soil layer was studied by the mercury intrusion porosimetry test (MIP) and the pore distribution of each soil layer was studied by the fractal theory. There are mainly macropores in silty clay of layer no. 4, clayey soil of layer no. 8, silty sand of layer no. 7 and layer no. 9 in Shanghai. The ink-bottle effect exists in the intrusion stage in the MIP test. There are four different fractal dimensions in silty clay of layer no. 4 and clayey soil of layer no. 8 and three different fractal dimensions in silty sand of layer no. 7 and layer no. 9. © 2010 Elsevier B.V.

Chen J.-F.,Tongji University | Li H.-L.,Shanghai Institute of Geological Survey | Liu J.-X.,Tongji University | Zhou J.,Tongji University
Yantu Lixue/Rock and Soil Mechanics | Year: 2011

A large-size reinforced soil pull-out test was carried out and was simulated by particle flow code(PFC) to investigate the microscopic properties of geogrid-soil interface. The results show that the behavior of trigonometric group particles developed based on "clump" inherent in PFC is close to that of practical sand particles. The upper and lower geogrid-soil interfaces are not symmetrical such that the disturbed area of lower interface is higher than that of upper interface. Under the condition of low compactness of sand as well as low normal stress, the thickness of geogrid-soil interface decreases with increase of normal stress, exhibiting negative linear relationship.

Wang J.,Tongji University | Wu Y.,Tongji University | Zhang X.,Tongji University | Liu Y.,Tongji University | And 2 more authors.
Journal of Hydrology | Year: 2012

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=0.29498f 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. © 2012 Elsevier B.V.

Wang H.-M.,Shanghai University | Wang H.-M.,Key Laboratory of Land Subsidence Monitoring and Prevention | Wang Y.,Shanghai University | Jiao X.,Shanghai Institute of Geological Survey | Qian G.-R.,Shanghai University
Desalination and Water Treatment | Year: 2014

Land subsidence resulting from over-exploited groundwater has become a leading factor restricting the sustainable development of resources, environment, and economy in Shanghai. To design management plans to control the environment geology calamity problems arisen by land subsidence effectively, this research constructed risk index system on the basis of risk source identification of subsidence and then established risk assessment model. The risk index system is composed of hazardous conditions and vulnerability of land subsidence. Results from comprehensive consideration of the model calculations, subsidence distribution and local socio-economic trends showed that the controlling district of land subsidence in Shanghai can be divided into three subsidence-primary control zone (Zone I), second control zone (Zone II), and normal control district (Zone III), corresponding with a high, moderate, low subsidence risk, respectively. On the basis of Shanghai urban and rural planning, the control target scheme of land subsidence with each zone in the future, different groundwater, resources management schemes are put forward, which mainly refer to control groundwater exploitation, to perform artificial recharge and to strengthen construction of recharge wells. © 2013 © 2013 Balaban Desalination Publications. All rights reserved.

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