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        Experimental Investigation on Tensile Strength of Jurassic Red-Bed Sandstone under the Conditions of Water Pressures and Wet-Dry Cycles

        Zhenhua Zhang,Xiaochuan Chen,Huayan Yao,Xiang Huang,Luwang Chen 대한토목학회 2021 KSCE JOURNAL OF CIVIL ENGINEERING Vol.25 No.7

        Jurassic Red-Bed sandstone is one of the main types of rock composing unstable slopes on both banks of the Three Gorges Reservoir (TGR) in China. It is vulnerable to tensile strength degradation when exposed to cyclic wet-dry conditions under reservoir operation. Therefore, the law behind this needs to be clarified in order to accurately evaluate the stability of a sandstone slope located in the drawdown area of the TGR. In this paper, Jurassic Red-Bed sandstone specimens from the Majiagou landslide in the TGR area were collected for experiments with cyclic wet-dry procedures. After each wet-dry cycle, efforts were made to implement splitting tests, measure clay mineral contents and ion contents in the soak solution, and observe changes in microstructures. The tensile strength is experimentally demonstrated to be a process of damage accumulation under the integrated actions of water pressure, calcite dissolution, and clay mineral hydration, among which hydration of illite contributes the most to the damage. The loss of the cement material and the cyclic expansion and shrinkage of clay minerals weaken the cementation between grains, leading to the tensile strength degradation.

      • KCI등재

        Two-Dimensional SPH Analysis of Seepage with Water Injection Process for Different Crack Morphologies

        Haichun Ma,Jingping Wang,Jiazhong Qian,Xiaohui Tan,Luwang Chen,Yaping Deng,Zhitang Lu,Lei Ma 대한토목학회 2021 KSCE JOURNAL OF CIVIL ENGINEERING Vol.25 No.5

        Crack seepage in nature involves natural and water injection flow, causing crack morphology in nature to be varied. Using the numerical simulation method of smoothed particle hydrodynamics (SPH), the natural free flow process in a crack was analyzed. With the interference of the initial velocity of the x = 0 particles, the other terminal particles were shifted, and the particles with initial velocities were reversed. For water injection simulations, ghost particles were set to block particles from overflowing, as particles subjected to injection water were mobilized more quickly than under free flow conditions. For rough cracks, particle magnitude was affected by the boundary shape, but overall particle velocity was influenced little, and the distribution of particles was sparse and densely spaced. For the branch crack simulation, overall particle seepage velocity decreased, but particles moved faster through the wider branch than through the narrower branch. SPH can simulate the seepage through crack networks and be used to analyze the effects of different crack geometries and physical properties.

      • On Objective Functions for Fixed-Outline Floorplanning

        Lu Wang,Xiaolin Zhang,Song Chen,Takeshi Yoshimura 대한전자공학회 2008 ITC-CSCC :International Technical Conference on Ci Vol.2008 No.7

        Fixed-outline floorplanning enables multilevel hierarchical design, where aspect ratios and area of floorplans are usually imposed by higher level floorplanning and must be satisfied. Simulated Annealing is widely used in the floorplanning problem. It is well-known that the solution space, solution perturbation, and objective function are very important for Simulated Annealing. In this paper, we focus on the objective functions used in FOFP problem. Up to now, many kinds of objective functions were proposed in the existing researches, but those objective functions had many limitations, and the applicable situation is not clearly. We summarize and analyze the existing objective functions used in Fixed-Outline floorplanning methods, and then suggest some new objective functions respectively used in the fixed-oultine floorplanning with and without wire-length optimization, respectively.

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