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This study used the 2D boundary element method in time domain to examine the screening effectiveness of open trenches on reducing vibration generated by a high-speed train. The parameters included configurations of the trench, train speed, the distance between the source and the trench, and the Poisson’s ratio of the soil. A reducing displacement level (in dB scale) was defined and used to evaluate the screening effectiveness of a wave barrier. The maximal reducing displacement level reached 25 dB when an open trench was used as a wave barrier. The depth of an open trench is a main influential parameter of screening effectiveness. The cutoff frequency of the displacement spectrum increases with decreasing trench depth. The maximal screening effectiveness occurs when the depth is 0.3-0.4 Rayleigh wavelength. Using an open trench as a wave barrier can reduce 10–25 dB of vibration amplitude at frequencies between 30 and 70 Hz. A considerable increase in screening effectiveness of the open trench was observed from 30 to 70 Hz, which matches the main frequencies of vibration induced by Taiwan High Speed Rail. The influence of trench width on screening effectiveness is nonsignificant except for frequencies from 30 to 40 Hz. Poisson’s ratio has various effects on the reduction of vibration at frequencies higher than 30 Hz.

Abstract. The dynamic response of the Liyutan earth dam to the 1999 Chi-Chi earthquake (M L =7.3) in Taiwan was numerically analyzed. First, the staged construction of the dam was simulated. Then, seepage analysis, considering a 60-m water level, was performed. After seepage analysis, the initial static stress (prior to dynamic loading) was established in the dam. Both the horizontal and vertical acceleration time histories recorded at the base of the dam were used in the numerical simulations. The dynamic responses of the dam were analyzed for 50 s in the time domain. The simulated results were in agreement with the monitored data. The transfer function analysis and Hilbert-Huang Transform (HHT) were used to compare the results and to perceive the response characteristics of the dam. In particular, the time-frequencyenergy plots of the HHT can reveal the timing and time frame of the dominant frequencies of the dynamic response. The influences of the initial shear modulus and uni-axial earthquake loading were also investigated.

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This paper investigates the dynamic response of the Pao-Shan II Dam subjected to the Chi-Chi earthquake (M L =7.3) in Taiwan by using FLAC 3D. The elastic modulus of the dam is considered to vary with mean stress in this study. Staged construction, seepage, static equilibrium and dynamic response are sequentially analyzed. Fourier power spectra are analyzed as the earth dams subjected to a sweep frequency dynamic loading. Influences of core dimensions on the dynamic responses of the earth dam are investigated. The influence of the core width-height ratio and length-height ratio of the dam on the first natural frequency is studied in this study. The results show that 3D effect could be neglected for 4   cases. The first natural frequency decreases with the increase of core width-height ratio or length-height ratio of an earth dam. The first natural frequency increases slightly after the seepage phase. The stiffness of the dam decreases at the end of an earthquake which causes the first natural frequency to decrease.

Failure of a landslide dam might occur by river discharge or rainfall. A rise of the upstream water level of a landslide dam and rain infiltration into the dam body increase pore water pressure and the weight of the dam. In this study, transient seepage analysis of rainfall infiltration and dam stability analysis are performed. A two-phase flow simulation using the FLAC finite difference code is adopted to analyze unsaturated seepage flow in transient fluid-mechanical calculations. The safety factor of dam stability is evaluated using the shear strength reduction technique. The parameters discussed in this study include the rising speed of the water level, rain infiltration, and the hydraulic conductivity of soil. The results show that the time to slope failure of the dam is approximately 247 min when only the effect of the rising upstream water level of the dam is considered. The failure time decreases to 189 min when the rain infiltration and rising upstream water level of the dam are considered. The results also indicate that the hydraulic conductivity of the dam affects dam failure time.

Geosynthetics such as geogrid or geotextile are often used for the reinforcement of weak soils. A lot of research has been performed to investigate the bearing capacity of reinforced shallow foundations using limit equilibrium method with Mohr-Coulomb failure criterion. In this paper, the loading behavior of reinforced strip footings was studied numerically using a commercial Finite Difference program with a Double-Yield soil model. First, the load-settlement curve of an unreinforced strip footing was simulated using both Mohr-Coulomb failure criterion and the Double-Yield model. The simulated bearing capacities were then compared with Terzaghi's solution. The effects of various parameters, such as burial depth and length of the reinforcement, as well as arrangement of two reinforcement layers were also studied. Results of this study indicate that the loading behavior of strip footings simulated with the Double-Yield model is more realistic and the Manuscript Click here to download Manuscript: ASCE-IJG manuscript_revision 3.docx 2 optimum burial depth and length of reinforcement obtained from this study also agree with values reported by previous investigators.