Browsing by Author "Weng, Meng-Chia"

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Deformation behaviors of dip slopes considering the scale effect and their geological properties
(1970-01-01)
Huang, Wen-Chao
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Li, Kun-Che
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Hsieh, Jheng-Yu
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Weng, Meng-Chia
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Hung, Wen-Yi
To clarify the scale effect of slope deformation, this study investigates the behaviors of dip slopes with various heights and geological properties using centrifuge and numerical modeling. Three types of physical and numerical models with different rock layer thicknesses and weak plane angles were constructed for analysis and validation. The models were subject to toe submersion to simulate the wetting deterioration condition. Based on the analysis results, the deformation, sliding, and debris accumulation of small slopes (a few meters high) may be insignificant. However, the deformation behaviors of higher slopes with the same angle (with a height of tens to a hundred meters) can be more severe and affect the whole slope, especially if the slope has a high weak plane angle with alternating thin rock layers. Some early warning signs, such as bulging-induced tension cracks close to the toe or the relative sliding of layers at the slope surface or crest, can produce more massive landslides or debris accumulation of the dip slopes, especially for high slopes.
DEM simulation of planar sliding using a particulate interface model considering velocity-dependent friction
(2019-08-01)
Chiu, Chia-Chi
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Weng, Meng-Chia
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土木工程學系
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Department of Civil Engineering
Planar sliding is a typical failure mode of landslides, in which an unstable rock block slides along a weak plane, resulting in a rapid movement. This study proposes a particulate interface model (PIM) that considers velocity dependent friction behavior to simulate the planar sliding behavior of the particulate DEM. To validate the performance of the proposed model, the results of a DEM simulation of the planar sliding of a rigid block are compared with the analytical dynamic solution. The results reveal that the PIM simulation is consistent with the analytical dynamic solution with or without consideration of the velocity-dependent friction law. The ordinary contact model does not accurately reflect the theoretical dynamics owing to the high resistance. The smooth joint model underestimated the shear resisting force of the interface and yielded excessively high velocity and displacement of the block. With respect to the deposition distribution, the different interface models yielded the various velocities before impact, and therefore various failure patterns of the block and appearances of the deposition. The block velocity significantly influences the number of cracks. The results of the analysis reveal that the PIM can capture the planar sliding and deposition behavior of particulate DEM.
Discrete element simulation of the dynamic response of a dip slope under shaking table tests
(2018-09-04)
Lin, Cheng-Han
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Li, Hung-Hui
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Weng, Meng-Chia
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土木工程學系
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Department of Civil Engineering
A dip slope contains weak planes in the same dip direction along the slope face. In this study, a discrete element simulation was implemented to investigate the behavior of a dip slope under shaking table tests. The simulated dip slope model was first verified by testing under different horizontal excitations. Then, the influence of the slope angle and dynamic force on the deformation characteristics of the dip slopes was explored. The simulations provide detailed descriptions of the deformation processes and potential sliding mechanisms associated with the dip slopes. The results of this study are summarized as follows: (1) Two types of slope sliding, namely differential and complete, were recognized. The model with a dip angle lower than 20 degrees was more stable, and differential sliding developed gradually during external excitation. In the model with a dip angle higher than 20 degrees, the external excitation easily triggered complete sliding. (2) For threshold slope angles higher than 20 degrees, the behavior of the dip slope model changed from deformation to sliding, and the displacement within the models increased with increasing slope angle. (3) An increase in frequency led to a decrease in the trigger time for slope sliding. In addition, the slope angle was negatively correlated with the triggering time for sliding. (4) The amplification factor of peak ground displacement (PGD) increased as the slope angle increased. The amplification factors corresponding to low excitation frequencies were considerably lower than those for high excitation frequencies. In contrast to the trends for PGD, the amplification factor of peak ground acceleration (PGA) decreased as the slope angle increased.
Dynamic response of a dip slope with multi-slip planes revealed by shaking table tests
(2018-09-01)
Li, Hung-Hui
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Lin, Cheng-Han
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Zu, Wei
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Chen, Chi-Chieh
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Weng, Meng-Chia
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.
Effect of Heat-Treatment Remediation on the Mechanical Behavior of Oil-Contaminated Soil
(2020-05-01)
Weng, Meng-Chia
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Lin, Chiou-Liang
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Lee, Cheng-Hsi
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土木工程學系
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Department of Civil Engineering
Featured Application The physical properties of heat-treated soil are clarified in this study before the soil is reused as a construction material in civil engineering. Abstract The heat treatment of oil-contaminated sites is widely carried out for the purposes of remediation. However, heat treatment changes the physical and chemical properties of soil. Before the soil can be reused as a construction material in civil engineering, such as in backfill or road base materials, the changes to its physical properties must be understood. Therefore, this study investigates the changes in the physical and chemical properties of oil-contaminated soil after heat treatment. In this investigation, experimental samples of soil with added oil from a refinery plant are used to investigate the removal rate of total petroleum hydrocarbons (TPHs) by thermal desorption and incineration. The physical properties of the soil, including water permeability and mechanical properties, are compared before and after heat treatment. The results of this study are as follows. (1) Particle size analysis reveals that heat treatment makes soil particles finer. (2) In the burning reduction test, heat treatment at 900 degrees C removes more than 90% of THP. (3) In the direct shear test, the friction angle (phi) increases with the removal rate. (4) In the hydraulic test, as the removal rate increases, the permeability coefficient increases after heat treatment.
Evaluating failure mechanisms of dip slope using a multiscale investigation and discrete element modelling
(2019-12-20)
Weng, Meng-Chia
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Lin, Ming-Lang
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Lo, Chia-Ming
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Lin, Hsi-Hung
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Lin, Cheng-Han
This study proposed an in-depth multiscale analysis procedure to identify the dip slope area and assess dip slope stability and influencing area. The proposed analysis procedure comprised five stages: (1) identifying the potential area of a dip slope, (2) analyzing the possible failure types of the dip slope, (3) evaluating slope activity, (4) analyzing dip slope stability under the influence of possible triggering factors, and (5) assessment of the deformation and deposition area. To validate the proposed procedure, the Chaochouhu region of Taiwan was analyzed as a dip slope case. In stages (1) to (3), the scale of the utilized map and the precision of associated data were evaluated to identify the potential area of a dip slope, the possible failure types, and the activity of each slope unit. In stages (4) and (5), the processes of deformation and sliding in a high-activity slope unit were simulated using the discrete element method. The numerical model was first verified using in-situ monitoring data obtained from inclinometers. Subsequently, the model was used to predict the slope behavior under conditions of wetting deterioration of geomaterial. The multiscale analysis revealed comprehensive information regarding the dip slope. The application of the proposed approach would be useful to civil engineers for evaluating dip slope stability as well as to relevant authorities for planning hazard mitigation strategies.
Evaluating the stability of anti-dip slate slope using an innovative failure criterion for foliation
(2020-09-20)
Weng, Meng-Chia
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Chang, Chien-Yu
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Jeng, Fu-Shu
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Li, Hung-Hui
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土木工程學系
Toppling failure is one main failure types of anti-dip slate slopes, and is strongly affected by the mechanical properties of foliation. This study conducted a series of pull-off tests and direct shear tests on slate foliation to obtain its failure envelope, and an innovative failure criterion was accordingly proposed. The proposed failure criterion exhibits a nonlinear trend in the low normal stress range; considers both tensile and shear strengths, and has three material parameters - tensile strength T-0, alpha, and beta. Parameters alpha and beta are related to the slope variation of the failure criterion. To investigate the effectiveness of the proposed failure criterion on the evaluation of slope stability, it is implemented in a discrete element code UDEC and a simulation was carried out to evaluate the deformation and failure pattern of an anti-dip slate slope. The results of the UDEC analysis demonstrate that the simulated failure pattern and deformation characteristics agree with that of an actual anti-dip slate slope. The proposed failure criterion of foliation and the Mohr-Coulomb criterion are further compared in slope stability analysis. The proposed failure envelope accurately reflects the tensile strength and shear strength under low normal stress, but the Mohr-Coulomb criterion apparently overestimates the strength in this stress range. Therefore, the proposed criterion is more effective than the existing criteria in predicting the toppling failure of slate slopes.
Failure mechanism of a mudstone slope embedded with steep anti-dip layered sandstones: case of the 2016 Yanchao catastrophic landslide in Taiwan
(2019-11-01)
Lin, Cheng-Han
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Hung, Ching
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Weng, Meng-Chia
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Lin, Ming-Lang
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Uzuoka, Ryosuke
On September 28, 2016, the torrential rainfall carried by Typhoon Megi induced a catastrophic mudstone landslide in the Yanchao District of Kaohsiung City, Taiwan. The total volume of the sliding mass was approximately 8700 m(3), which blocked an industrial road and displaced a duplex house in the downslope, leading to three deaths. Unprecedentedly, the 2016 Yanchao land-slide was large and quickly raised public awareness regarding the possibility of large landslides that could occur in the nearby mudstone areas. Based on field surveys, topographic and geological maps, unmanned aerial vehicle (UAV) photography, and remote-sensing imagery, the failure mechanism of the 2016 Yanchao landslide is described in this study. The results revealed that steep anti-dip layered sandstones embedded with the mud-stones play a critical role in large, rainfall-induced landslides. In the case of Yanchao landslide, the bedding joint between two formations was associated with the runoff infiltrating the low permeability mudstone. The kinematic process of the landslide consisted of two phases: a circular failure in the lower formation (alternation of mudstone and sandstone) and the subsequent regressive failure in upper formation (thick sandstone interbedded with mudstone). This study discloses the role of steep anti-dip layered sandstone influencing mudstone slope failure behaviors and presents a preliminary guide for assessing large, rainfall-induced landslides in mudstones. The results could also provide useful information for calibrating the numerical modeling of large landslides that may occur in the mudstone area in the future.
Generic transformation models for some intact rock properties
(2018-12-01)
Ching, Jianye
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Li, Kuang-Hao
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Phoon, Kok-Kwang
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Weng, Meng-Chia
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土木工程學系
A global intact rock database of nine parameters, including uniaxial compressive strength and Young's modulus, is compiled from 184 studies. This database, labeled as "ROCK/9/4069", consists of 27.5% igneous rock, 59.4% sedimentary rock, and 13.1% metamorphic rock. The vast majority (>95%) of intact rocks in the database are in their natural moisture contents. About 14% of the data points are for weathered rocks and about 4% are foliated metamorphic rock. It is found that most existing transformation models are data-specific or site-specific in the sense that they fit well to their own calibration databases, but do not necessarily fit well to ROCK/9/4069. One can infer that transformation models for intact rocks are more data-site dependent than those for soils. It is evident that ROCK/9/4069 has coverage wider than most existing transformation models. The ROCK/9/4069 database is then adopted to calibrate the bias and variability of existing transformation models. Transformation models with relatively large application ranges and relatively small transformation uncertainties are selected as generic transformation models. These generic models can be valuable for scenarios where site-specific models are not available, e.g., construction projects with insufficient budget or the preliminary design stage of a project.
Landscape evolution characteristics of large-scale erosion and landslides at the Putanpunas Stream, Taiwan
(2018-01-01)
Lo, Chia-Ming
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Weng, Meng-Chia
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Lin, Ming-Lang
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Lee, Shun-Min
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Lee, Kuo-Chen
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 8.4x 10(7) m(3)) 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.
Measuring Foliation Tensile Strength of Metamorphic Rock by Using Pull-Off Test
(2018-01-01)
Weng, Meng-Chia
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Li, Jin-Hong
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Lin, Cheng-Han
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Liao, Chu-Tsen
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土木工程學系
The tensile strength of rock is an important property of rock engineering. However, the measurement of the tensile strength of rock is often overlooked due to difficulties of specimen preparation and the accuracy of testing results. This study adopted the pull-off test to measure the foliation tensile strength of metamorphic rock such as slate, green schist, and black schist. Compared with contemporary tensile tests, this method is relatively simple and effective, with easy specimen preparation. Additionally, this approach can be conducted not only in the laboratory but also in the field, which is quite useful for evaluating the rock slope stability. This study recommends procedures for sample preparation and testing as well. The test results indicate that the black schist exhibited the greatest tensile strength and that the slate had the lowest strength. Besides this, the slate exhibited significant wetting deterioration. Examination of the failure patterns revealed that the failure planes of all specimens occurred on the foliation planes, indicating reasonable failure patterns. Finally, this study investigated the factors potentially affecting the validity of tensile strength measurement, including the failures occurring at (1) the preexisting joint during sample preparation and (2) the interface of rock and epoxy resin. Procedures for mitigating this effect were also suggested.
Multivariate probability distribution for some intact rock properties
(2019-08-01)
Ching, Jianye
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Phoon, Kok-Kwang
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Li, Kuang-Hao
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Weng, Meng-Chia
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土木工程學系
A multivariate probability distribution model for nine parameters of intact rocks, including unit weight (gamma), porosity (n), L-type Schmidt hammer hardness (R-L), Shore scleroscope hardness (S-h), Brazilian tensile strength (sigma(bt)), point load strength index (Is(50)), uniaxial compressive strength (sigma(c)), Young's modulus (E), and P-wave velocity (V-p), is constructed based on the ROCK/9/4069 database that was compiled by the authors. It is shown that the multivariate probability distribution captures the correlation behaviors in the database among the nine parameters. This multivariate distribution model serves as a prior distribution model in the Bayesian analysis and can be updated into the posterior distribution of the design intact rock parameter when multivariate site-specific information is available. In this paper, the parameters for the posterior distribution of the design intact rock parameter are summarized into user-friendly tables so that engineers do not need to conduct the actual Bayesian analysis. Caution should be taken in extrapolating the results of this paper to cases that are not covered by ROCK/9/4069, because the resulting posterior distribution can be misleading.
Simulating interface characteristics by using a particulate interface model of a discrete element method
(2019-05-01)
Chiu, Chia-Chi
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Weng, Meng-Chia
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土木工程學系
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Department of Civil Engineering
This paper proposes a particulate interface model to simulate the interface by using a particulate discrete element method. Six modifications are adopted in the numerical calculations to improve the stability and accuracy. The interface model provides two failure criteria: one is the Mohr Coulomb failure criterion and the other is the Barton-Bandis shear strength criterion. To verify the proposed model, the failure envelope, the shear-displacement curve, the closure curve, and the dilation curve were analyzed and simulated. The simulations demonstrated good agreement with the theoretical curves. The influence of the particle size was also investigated; the results proved that the quantity or size of the particle did not affect the performance of the proposed model. Finally, a rock bolt pull-out problem was simulated. The results proved that the proposed interface model can reasonably predict the shear stress acting on the interface between the rock bolt and rock.
Spatial characteristics of rock joint profile roughness and mechanical behavior of a randomly generated rock joint
(2018-11-01)
Le, Hoang Khanh
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Huang, Wen-Chao
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Liao, Ming-Che
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Weng, Meng-Chia
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土木工程學系
Barton's formula is one of the most widely used equations for estimating the shear strength of rock joints. The Joint Roughness Coefficient (JRC) in the equation is a crucial parameter of the shear strength because it controls the roughness of the profile. To explore the spatial characteristics of the roughness of a rock joint profile, a total of 86 actual rock joint profiles were collected from published researches and digitalized. The Profile Height Variation (PHV) for each profile group was analyzed statistically. The standard deviation of the PHV was found to depend strongly on the JRC value. This correlation of the standard deviation of the PHV with the JRC can be used easily to estimate the JRC of a given joint profile. Owing to the above statistical features of the PHV, any random profile with a given JRC can be generated for further analysis. Therefore, Direct Shear (DS) tests were simulated for two joint profiles (a randomly generated profile with JRC = 19.6 and Barton's standard profile with JRC 18-20) using the Discrete Element Method (DEM). The simulation results revealed that both of the joint profiles have similar joint shear strengths, indicating that the randomly generated JRC profile can function as a good artificial profile in an engineering simulation. Finally, DEM simulation also indicated that the shear strength of rock joints originates from the roughness of the joints, and shearing-off of the joints occurs at a normal stress larger than 4 MPa.