Browsing by Author "Li, Hung-Hui"

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Discrete element simulation of the dynamic response of a dip slope under shaking table tests
(2018-09-04)
Lin, Cheng-Han
;
Li, Hung-Hui
;
Weng, Meng-Chia
;
土木工程學系
;
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
;
Lin, Cheng-Han
;
Zu, Wei
;
Chen, Chi-Chieh
;
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.
Evaluating the stability of anti-dip slate slope using an innovative failure criterion for foliation
(2020-09-20)
Weng, Meng-Chia
;
Chang, Chien-Yu
;
Jeng, Fu-Shu
;
Li, Hung-Hui
;
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.