Meng-Chia Weng

Mechanical properties of incineration bottom ash: the influence of composite species.

The mechanical properties, including strength, deformational behavior, and wetting softening phenomena of municipal solid waste incinerator (MSWI) bottom ash are one of the major concerns for reuse applications. However, owing to the complex constituents of municipal solid waste, the properties of MSWI bottom ash are often highly variable. A series of artificial specimens with controlled chemical components were tested in this study. The test results show that the artificial bottom ash possesses the following mechanical characteristics: (1) for the strength, the frictional angles of the bottom ash under dry and saturated conditions vary from 34.8 degrees to 51.1 degrees and 26.0 degrees to 37.2 degrees, respectively; (2) for the deformation, the shear stiffness increases with the normal stress arises and degrades upon increased shearing; (3) significant wetting degradation of the strength and stiffness were observed. The multi-variable regression analysis was conducted to evaluate the associated influence of the chemical components on the strength. Among the evaluated components, Fe(2)O(3) and Al(2)O(3) are key factors; an increase in either results in higher strength at both dry and saturated conditions. The results were used to propose empirical relationships for phi(dry) and phi(sat), expressed in terms of Fe(2)O(3) and Al(2)O(3). Accordingly, a strength classification chart is proposed for engineering purposes.

A Generalized Plasticity-Based Model for Sandstone Considering Time-Dependent Behavior and Wetting Deterioration

Based on the concept of generalized plasticity, this study proposes a constitutive model to describe the time-dependent behavior and wetting deterioration of sandstone. The proposed model (1) exhibits nonlinear elasticity under hydrostatic and shear loading, (2) follows the associated flow rule for viscoplastic deformation, (3) adopts a creep modulus that varies with the stress ratio, (4) considers the primary and secondary creep behaviors of rock, and (5) considers the effect of wetting deterioration. This model requires 13 material parameters, comprising 3 for elasticity, 7 for plasticity, and 3 for creep. All parameters can be determined easily by following the suggested procedures. The proposed model is first validated by comparison with triaxial tests of sandstone under different hydrostatic stress and cyclic loading conditions. In addition, the model is versatile in simulating time-dependent behavior through a series of multistage creep tests. Finally, to consider the effects of wetting deterioration, triaxial and creep tests under dry and water-saturated conditions are simulated. Comparison of the simulated and experimental data shows that the proposed model can predict the behavior of sandstone in dry and saturated conditions.

Identification of deformation and failure characteristics in cataclinal slopes using physical modeling

This study investigates the deformation characteristics of cataclinal slopes in central Taiwan prior to landslide failure. Field surveys and physical model tests were performed to explain the gravitational deformation characteristics of cataclinal slopes under various conditions and to derive the deformation process and failure characteristics. The results show that the distribution of erosion gullies (different length of the slope mass), the extent of erosion (different thickness of the slope mass), the foliation dip angle, and the geological material critically affect the deformation of cataclinal slope masses in the study area. The results of physical model tests indicate that increasing the foliation dip angle, the thickness and the length of sliding mass, particle size (spacing between foliations) increases the depth of slope deformation. Foliation dip angle is the most critical factor that controls the deformation of slate slopes. When the cataclinal slopes reached maximum deformation, a shear failure and translational slide occurred within a short period. The deformation zone exhibited significant cracking at the scarp and the bulging of the slope toe, which facilitated the infiltration of surface water and groundwater, accelerating the deformation to failure.

Modeling Particle Rolling Behavior by the Modified Eccentric Circle Model of DEM

This study proposes a modified eccentric circle model to simulate the rolling resistance of circle particles through the distinct element method (DEM) simulation. The proposed model contains two major concepts: eccentric circle and local rotational damping. The mass center of a circular particle is first adjusted slightly for eccentricity to provide rotational stiffness. Local rotational damping is adopted to dissipate energy in the rotational direction. These associated material parameters can be obtained easily from the rolling behavior of one rod. This study verifies the proposed model with the repose angle tests of chalk rod assemblies, and the simulated results were satisfactory. Simulations using other existing models were also conducted for comparison, showing that the proposed model achieved better results. A landslide model test was further simulated, and this simulation agreed with both the failure pattern and the sliding process. In conclusion, particle rolling simulation using the proposed model appears to approach the actual particle trajectory, making it useful for various applications.

Modeling scale effects on consequent slope deformation by centrifuge model tests and the discrete elementmethod

A consequent slope comprises weak planes in the same dip direction along a slope face. This study investigated scale effects on the gravitational deformation of consequent slopes. A series of centrifuge model tests under simplified environmental conditions were performed. Particle image velocimetry (PIV) was then adopted to evaluate the displacement distribution from the centrifuge model test results. On the basis of the PIV results, the relationship between slope deformation and surface settlement was investigated. Subsequently, the discrete element method (DEM) was used to execute simulations to provide detailed descriptions of the crack development and failure mechanisms associated with consequent slopes at different scales. The results of this study are summarized as follows. (1) The slopes exhibited similar deformation patterns in the centrifuge model tests. As the gravitational force increased, the magnitude of slope deformation increased significantly. (2) A modified dimensional relationship of material parameters was proposed for DEM simulation. According to this relationship, the simulated deformation patterns were in strong agreement with the actual deformations at various slope scales. (3) According to the DEM simulations, for the slopes with the same slope and weak plane angles, more cracks and displacements were generated in the higher slopes, leading to a greater sliding volume.

Dynamic response of a dip slope with multi-slip planes revealed by shaking table tests

This study investigated the effect of internal discontinuity on the dynamic response of a dip slope and evaluated the performance of Newmark’s theory on the sliding of a dip slope with multi-slip planes. A series of shaking table tests were performed under various geometric conditions to explore the dynamic behavior of a dip slope under different external excitations. The test results, including for deformation processes and critical accelerations, under various slope angles, slope sizes, and seismic intensities were examined and further compared with Newmark’s theory. The results of this study are summarized as follows: (1) two types of slope sliding (differential and complete) were determined. (2) Increasing the slope angle and the height of sliding mass tended to shorten the duration of slope deformation. (3) Critical acceleration of the slope increased gradually with increasing peak ground accelerations of input excitations; when the slope height and dip angle increased, the critical acceleration decreased. (4) The triggering time became earlier as the frequency of input excitation increased; the magnitude of sliding mass greatly depended on the amplitude of the input excitation. (5) By comparing critical acceleration between the experimental and theoretical results, Newmark’s theory was determined to overestimate critical acceleration during seismic-induced dip slope failure. This may cause unsafe evaluations, and sliding along existing discontinuities develops more easily in reality.

Deformation analysis of tunnel excavation in gravelly formation using the anisotropic degradation model

This study adopts a shear-induced anisotropic degradation model to analyze the deformation of excavation in gravelly formations. The adopted model is a variable moduli model with the following characteristics: the stress–strain relationship originates from degradation of the bulk modulus and shear modulus subjected to different loadings. Under hydrostatic loading, gravelly soil may behave as an isotropic material. However, when gravelly soil is subjected to shear loading, the material becomes anisotropic and degrades before ultimate strength is attained. Therefore, this study introduces an anisotropic factor to reflect the tendency to shear-induced volumetric deformation. To analyze the deformation of the Pakuashan tunnel, which passes through a gravelly formation in Taiwan, the model was first validated by comparing the drained triaxial test results of gravelly materials sampled from the tunnel. The proposed model is implemented with a finite element code to predict the tunnel deformation under construction. A comparison between the monitoring data and numerical analysis shows that the proposed model can reasonably simulate the behavior of a gravelly formation under excavation. Numerical analysis shows that the main deformation of the tunnel is the result of significant degradation of the moduli around the whole section, especially at the crown and invert of the tunnel.

Landscape evolution characteristics of large-scale erosion and landslides at the Putanpunas Stream, Taiwan

ABSTRACT This study used multi-temporal terrain and remote sensing images to investigate the geomorphological evolution of the Putanpunas stream caused by large-scale erosion and landslides over the last decade. Discrete element method was then performed to gain the physical insight of the slope failure mechanisms and landslide movement. Our results show topographical changes in the alluvial fan downstream and the deposits in the midstream and downstream segments of the Putanpunas Stream between 2005 and 2009. In 2009, torrential rainfall induced large-scale landslides (the volume was about 8.4 × 107 m3) that greatly altered the terrain of the Putanpunas Stream valley and the alluvial fan. A thick, unstable layer of colluvium (the thick of colluvium more than 150 m) was also deposited in the valley. In 2012, further large-scale landslides turned the colluvial layer into debris flows that cut across the Ryukyu Terraces downstream to the downstream segment of the Laonong Stream to the south-west. The change of debris flow direction from southeast to south-west eventually posed a considerable threat to the safety of protected targets and the access road downstream.

Modeling Roughness Effect of Joint Using Rough-Joint Model

This study proposed a rough-joint model to simulate the strength and deformability of rock joint under various loadings. The proposed model adopted the Barton model to consider the roughness effect of joint. To implement the rough-joint model in DEM software, three calculation modifications are performed. Afterward, the proposed model was verified by comparing to theoretical model. The comparisons showed that the proposed model is versatile in simulating the shear displacement and shear dilation of joint. Moreover, this study investigated the influence of particle size on the applicability of rough-joint model, and the results indicate that particle sizes have no significant influence on shear behavior, which indicates the rough-joint model is suitable for different scale simulations.