Browsing by Author "Li, Kuo-Wei"

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A comprehensive mechanics-based model to describe bedrock river erosion by plucking in a jointed rock mass
(2016-03)
Li, Kuo-Wei
;
Pan, Yii-Wen
;
Liao, Jyh-Jong
;
土木工程學系
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Department of Civil Engineering
Plucking is an erosion mechanism usually occurring to sub-meter rock blocks in a bedrock channel subjected to intense water current. The removal of a rock block because of plucking can be either a result of impulsive plucking or accumulative plucking. A plate-like block is more likely to escape owing to impulsive plucking, while a pillar-like block is more likely escape because of accumulative plucking. The potential of impulsive plucking can be evaluated by examining the maximum uplift displacement within the period of the maximum upward impulse load acting on a typical rock block in a rock mass. The size of the rock block, various sources of uplift forces and the frictional resistance of lateral joints play major roles in determining whether accumulative plucking will occur. The present work proposes a mechanics-based model that simulates the kinematics of a rock block subjected to an inclined jet flow. A non-dimensional index APP is derived to assess the potential of accumulative plucking. In addition, a comprehensive approach is proposed to evaluate both the potential depths of the scour hole in a plunge pool and the incision in a downstream channel subjected to a prescribed jet flow passing a spillway or an overflowing weir. Finally, a case study adopting the proposed method is presented to demonstrate and to verify the applicability of the comprehensive approach.
Landslide monitoring with interferometric SAR in Liugui, a vegetated area
(2019-08-01)
Shih, Peter Tian-Yuan
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Wang, Huijung
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Li, Kuo-Wei
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Liao, Jyh-Jong
;
Pan, Yii-Wen
Interferometric SAR analysis with a time series of images obtained from satellite has been proven to be a useful monitoring scheme for geomorphological changes, particularly related to the vertical dimension. The success of this technique relies on the coherence between the images. This imposes severe challenges for applications in vegetated areas. In this study, the landslide process of a site located in Liugui, southern Taiwan, is investigated by a time series of SAR images collected from ALOS PALSAR and Sentinel 1A. This landslide monitoring site is heavily vegetated. From the Persistent Scattering (PS) analysis, ALOS PALSAR presented more extracted points. The wavelength of the band may be a decisive factor. The time series of ALOS images spans across the deadliest typhoon impacted Taiwan in recorded history, Typhoon Morakot on 8 August 2009. It is clear that there are more PS points extracted from the time series after the event as compared to before Typhoon Morakot. This is largely explained by the increase in the amount of bare earth after the disaster. From the interferometric SAR analysis, the development of headward erosion could be observed. Although the number of PS points is limited, the understanding of erosion and landslide progress in the area could still be improved while integrating with the digital elevation model collected with airborne lidar, historic aerial photos, and images collected with UAS (Unmanned Aviation Systems). Together with the in situ measurements, the colluvium depth ranges from 2 - 40 m in the area. The surface instability is expected to persist.
Large paleo-rockslide induced by buckling failure at Jiasian in Southern Taiwan
(1970-01-01)
Yang, Che-Ming
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Kang, Keng-Hao
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Yang, Shun-Hsing
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Li, Kuo-Wei
;
Wang, Hui-Jung
The major regions of Taiwan consist of high-relief terrain exposed to frequent typhoons and earthquakes. Recently, thousands of potential large-scale landslides have been delineated via remote sensing analysis and field surveys. However, little attention has been paid to the stability of colluvium, which is a potential hazard. This study investigated a paleo-rockslide site in detail and proposes a geological model to explain the failure mechanism. The studied area is in Jiasian, Southern Taiwan, and the site is a dip slope consisting of Miocene sedimentary rocks. Detailed topographic features, including residual slip surfaces, platforms, scarps, and colluviums, are identified using the slope map of a 1- m airborne remotely sensed digital elevation model. Platforms beneath the residual slip surfaces represent the topographic features of the paleo-rockslide, an interpretation validated by field works and core analysis. The platforms consist of a displaced rock mass (DRM) with a gentle bedding dip angle and interbedded structure that has been preserved. A geological model is established according to the data compiled; outcrops of DRM and colluviums on bedrock were delineated in the geological map and profiles. Outcrops of shear off, buckling, and compressive ridges within the alternating sandstone and shale are distributed at the toe of the residual slip surfaces. A geological model with identified topographic features is adopted to establish the geomorphological evolution of the site. A buckling-induced rockslide model in the dip slope of the interbedded layers is proposed, and potential future slope failure scenarios can be evaluated using the geomorphological evolution model.
Mechanics and response of a surface rock block subjected to pressure fluctuations: A plucking model and its application
(2014-03-13)
Pan, Yii-Wen
;
Li, Kuo-Wei
;
Liao, Jyh-Jong
;
土木工程學系
;
Department of Civil Engineering
Plucking (removal of rock blocks) is often the dominant mechanism for producing a scour hole on riverbeds comprised of heavily jointed rocic masses being subjected to pressure fluctuations from a jet flow. This paper explores the mechanics and response of a surface block subjected to pressure fluctuations. First a particle-flow simulation was conducted to demonstrate how repeated pressure fluctuations are able to gradually remove rock bridges in discontinuities surrounding a rock block, if a pressure fluctuation's intensity is substantial. As a consequence, these weak planes may become fully persistent. The block's uplift speed then depends on the pressure differences on the opposite (horizontal) faces, and the frictional resistance of the lateral discontinuities. This paper proposes a theoretical framework to model the mechanics and response of a rock block subjected to a sinusoidal pressure fluctuation. This model can be applied to estimate the development of a scour hole, through plucking, during a specific flood event. An example demonstrates the applicability of the proposed approach in predicting the potential depth of the scour hole. (C) 2013 Elsevier B.V. All rights reserved.