Ming-Lang Lin

Mechanism of initiation of debris flow

Publisher Summary The initiation condition and failure mode of debris flow have been studied by many researchers, and several possible mechanisms of initiation of debris flow have been proposed. However, due to the difficulty of observing the initiation condition of debris flow in the field before and while it occurred, a model study was performed in this research. Material used in the model test was reconstituted with scaled-down particles and laws of similitude were taken into account while forming the model. The chapter also studies and stimulates mobilization of debris flows by inducing pore water pressure in samples during triaxial tests. The rate of the increase in pore water pressure was based on rainfall intensity and the coefficient of storage of the soil. The results show that the strength parameters of soils and the factors of safety obtained in slope stability analysis from conventional tests are higher than those obtained from this proposed method.

Characteristics of seismic energy release of subduction zones—examples from Taiwan

Abstract The characteristics of seismic energy releasing for oceanic subduction and continental collision or subduction zones were explored by a proposed observational approach based on contour maps of seismic energy release on both horizontal and vertical planes, magnitude–energy curve and magnitude–energy–time relationship. It was found that distinct features of energy-releasing behavior exist for the two types of subduction. The oceanic subduction tends to have a more active background noise by continuously emitting small magnitude earthquakes and to release energy from a wider range of depth owing to the existence of subducted plate. On the other hand, surficial strata of a continental subduction tend to release almost all of the seismic energy through a major earthquake with relatively much less long-term noise. Meanwhile, several seismic gaps have been found based on the proposed release energy contour. Together with the tectonic framework and the regional geologic setting, these gaps potentially may involve aseismic zones (e.g., accretionary deposit) or zones awaiting to release its accumulated energy (e.g., the upper crust). The quite zones prone to yielding major earthquakes are accordingly highlighted for a further study.

A Study on the Damage Degree of Shield Tunnels Submerged in Overburden Soil During the Thrust Fault Offset

When an under-lain thrust fault slips, especially triggered by earthquakes, the overburden soil may deform and fail so that a fault zone also develops inwardly. The research about the deformation and the failure of the overburden soil is an essential issue to evaluating the safety of ground or underground structures near the potential faulted zone. In this study, a MRT tunnel, closed to a thrust fault and fault dip 60 degree, is considered, both of the sandbox experiment and the numerical analyses are adopted to discuss the damage degree of a tunnel submerged in an overburden soil under the thrust faulting. In the numerical analyses, a small-scale model, simulation of the sandbox, is justified according to the experimental results and used to discuss the base behavior of the overburden soil. In addition, a full-scale model is used to evaluate the damage degree of tunnel segments by defining a dangerous factor. Moreover, considering the real behaviors of sand particles, the distinct element method is adopted as well. In the sandbox experiment, the results indicate that the development of the shear zone was apparently hindered by the existence of a model tunnel near the fault tip, and induced significant deformation of the tunnel. In addition, the results from numerical analyses, the finite element method and the distinct element method, are similar to the experimental results. The numerical analysis results of the full-scale model indicate that the damage degree is increased while the tunnel is close to the fault tip, and the footing wall is more dangerous than the hanging wall. The defined dangerous factor is able to reflect the damage degree of the tunnel. In the distinct element analysis, the full-scale model, it can be observed that a fault zone extends from the fault tip to the ground surface, but discussions on the distribution of stress and moment in the tunnel are not included and will be considered in the future study.Copyright

Consideration of the Maximum Impact Force Design for the Rock-Shed Slab

This study aims at the estimation of the maximum impact force for a rock-shed slab under collision by a rock fall. A DEM program calibrated from small-scale physical experiments is used to model the movement of rock fall clusters and to measure the resultant impact forces. The results obtained from the small-scale experiments show that the maximum impact forces are significantly affected by the mass of the rock fall, the height from which they fall as well as the falling process. Full-scale numerical modeling based upon a field case not only confirms the experimental results but also sheds light upon the influence of the rock fall mode and the contact stiffness between the rock and the rock-shed. This study provides guidelines for the design of rock-shed structures countering large rock fall problems.