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To study the collapse characteristics of high-density silt under complex loads, three series of hollow-cylinder tests were conducted on high-density saturated silt samples taken from the sea entrance of the Yangtze River. In the first series of tests, samples with high density were isotropically consolidated and then sheared under undrained triaxial loads. In subsequent tests, samples with low and high densities were isotropically consolidated and then cyclically sheared by principal stress rotation of 0-180°. Collapse and liquefaction were clearly observed in all the samples tested under cyclic principal stress rotation when the pore water pressure was equal to the initial effective confining pressure. Two critical points, the graded phase transformation point and the cataclysmic phase transformation point (collapse point), were observed for the high-density samples before liquefaction; these divided the buildup of the pore water pressure into three or two stages depending the shear stress level. At low shear stresses, the characteristics of the transformation points were hardly influenced by load frequency. The isotropic consolidated high-density silt and low-density silt expressed similar behaviors. However, in the high-density silt, the strain development could be divided into two stages by the collapse point, which corresponds to the cataclysmic phase transformation point of the pore water pressure representing the state of structure collapse. The deviator strains were limited within a narrow range of 0.2-0.4% at the collapse state. The stress state of collapse can be normalized by the quasi-unstable line in the p'-q space. Finally, we introduce the modified Seed model to successfully estimate the development of pore water pressure in high-density silt. [ABSTRACT FROM AUTHOR]

Based on analyzing water and sediment condition and deposition characteristics in Chongqing reach of the Three Gorges Reservoir(TGR). the influence on the deposition and the navigation in Chongqing reach caused by the reservoirs built in the upper stream of the Yangtze River is researched, by using two-dimensional flow and sediment mathematical model. The results indicates that along with river regime adjustment in the early operation stage of TGR and extends upward the backwater end of level 155m. Chongqing reach is the main impeding navigation area in the fluctuating backwater area; Under the combined effects of upstream reservoirs in the stem stream. Chongqing reach will be obviously scoured, making the quantities and thickness of deposition significantly reduced at the original deposition location and even appearing scour, the navigation condition at the stem stream of Chongqing reach has improved a lot. Jinshaqi reach at the junction of the Jia-Ling River is less affected by the construction of upstream reservoir, which making the impeding navigation condition same as that in no upstream reservoir. [ABSTRACT FROM AUTHOR]

The reservoirs built in the upper stream of the Yangtze River intercept the sediment from upstream, this will decrease the sediment into the Three Gorges Reservoir (TGR) in downstream and slow down the deposition development of TGR. moreover, this also affect navigation condition for a long-term operation. In this paper, calculations are made about the influence of the deposition and navigation of TGR caused by the reservoirs built in the upper stream of the Yangtze River such as Xiluodu and Xiangjiaba Reservoir by using one-dimensional flow and sediment mathematical model. The results suggest that the deposition development in TGR will be postponed with the reservoirs built upstream. Under the condition of the upstream reservoir built, the sediment deposition would not appear at the fluctuating backwater area in the early operation 40 years. Chongqing reach shows scour tendency, deposition basically not occurring in 100 years. [ABSTRACT FROM AUTHOR]