Chein Lee Wang

Incorporating the effects of topographic amplification and sliding areas in the modeling of earthquake-induced landslide hazards, using the cumulative displacement method

A procedure that considers topographic effects and runout behavior is proposed for analyzing seismic landslide hazards. The theoretical topographic amplification factors and corresponding amplified ground motion are calculated. By using the amplified motion, a cumulative displacement map is generated through the Newmarks displacement method. The high displacement areas are defined as the source areas of landslides. A runout simulation that identifies sliding routes and the final deposition areas of the sliding material from these source areas is performed. Finally, the complete set of landslide zones, including source, and sliding and deposition areas, is predicted. The landslide hazard maps of the Mt. Baishiya region, Nantou, Taiwan are evaluated, and the maps of actual landslides triggered by the September 21st, 1999, Chi-Chi earthquake are compared with the prediction. The results show that the proposed procedure, which combines topographic effects and runout simulation, can generate more accurate predictions for seismic landslide hazard analysis. However, this slight improvement over the procedure that only considers topographic effects is within the uncertainty levels of the input parameters. This slight improvement is obtained by a relatively complex and time-consuming procedure, and further research is required towards evaluating the viability of the proposed model when topographic effects cannot be neglected.

Estimating poromechanical properties using a nonlinear poroelastic model

AbstractA physics-based method is proposed for simultaneously obtaining the hydraulic conductivity, Young’s modulus, and Poisson’s ratio of soil materials using the uniaxial consolidation test. A nonlinear poroelastic model is presented, and the settlement data from consolidation tests are fitted to the model at each load step with the least-squares error method to inverse the parameters. The model results perfectly fit the experimental data in the initial load steps but slightly deviate from the data in later load steps as a result of secondary settlement and a largely increased Young’s modulus. The inversed parameters are compared with those calculated from the uniaxial consolidation test and those found in the literature. The comparison results demonstrate that the inversed parameters are reasonable. The proposed method provides both an estimation of parameters and the parameter-change information during a consolidation test. The method is simple, efficient, and versatile for obtaining poromechanical p...

Interfacial stress intensity factors for edge-cracked bonded semicircles and strips under out-of-plane shear

Analytical expressions of the mode III interfacial stress intensity factor are derived for the edge-cracked problems in bonded semicircles and strips. The results are extracted from the solutions of the bonded finite sector by the conformal mapping method. Based on the method, the stress intensity factors for the problems with various crack lengths are achieved, and two corresponding cases are presented and discussed. The obtained solutions can serve as a reference for related crack problems.

Evaluation of Hydraulic Properties of Aquitards Using Earthquake-Triggered Groundwater Variation

The hydraulic properties of aquitards are not easily obtained because monitoring wells are usually installed in aquifers for groundwater resources management. Earthquake-induced crust stress (strain) triggers groundwater level variations over a short period of time in a large area. These groundwater anomalies can be used to investigate aquifer systems. This study uses a poroelastic model to fit the postseismic variations of groundwater level triggered by the Chi-Chi earthquake to evaluate the hydraulic properties of aquitards in the Jhoushuei River alluvial fan (JRAF), Taiwan. Six of the adopted eight wells with depths of 70 to 130u2009m showed good agreement with the recovery theory. The mean hydraulic conductivities (K) of the aquifers for the eight wells are 1.62u2009×u200910-4 to 9.06u2009×u200910-4 m/s, and the thicknesses are 18.8 to 46.1u2009m. The thicknesses of the aquitards are 11.3 to 42.0u2009m. Under the isotropic assumption for K, the estimated values of K for the aquitards are 3.0u2009×u200910-8 to 2.1u2009×u200910-6 m/s, corresponding to a silty medium. The results match the values obtained for the geological material of the drilling core and those reported in previous studies. The estimated values were combined with those given in previous studies to determine the distribution of K in the first two aquitards in the JRAF. The distribution patterns of the aquitards reflect the sedimentary environments and fit the geological material. The proposed technique can be used to evaluate the K value of aquitards using inverse methods. The inversion results can be used in hydrogeological analyses, contaminant modeling, and subsidence evaluation.

Development and preliminary testing of a crack detection sensor for crack velocity measurement of an edge-notched disk

In the present study, a crack velocity measuring system is developed based on the electrical method. The proposed crack velocity measuring system and an available crack gage system were attached on opposite sides of an edge-notched granite disk specimen to measure the velocity of crack propagation on each side of the surface crack. Three sensing materials were assessed for their applicability in crack detection. It was found that the sensing materials have a strong effect on the measurement of the crack velocity. Several observations on crack propagation and some aspects of the proposed measuring technique are discussed in this study.