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Aiguo Xing - One of the best experts on this subject based on the ideXlab platform.
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characteristics and runout behaviour of the disastrous 28 august 2017 Rock Avalanche in nayong guizhou china
Engineering Geology, 2019Co-Authors: Yaoqiang Zhu, Yu Zhuang, Xingjian Dai, Aiguo XingAbstract:Abstract On 28th August 2017, a disastrous Rock Avalanche occurred in Nayong, Guizhou, China. This catastrophic event killed 35 people and destroyed 23 houses. In this study, the failure process of the Avalanche was analyzed using UAV video footage and seismic signal recordings obtained for the pre- and post-failure stages of the landslide. To better understand the possible mechanism of the Avalanche and its dynamic characteristics, a numerical simulation was conducted using a dynamic model (DAN3D) to simulate the runout behaviour of the displaced materials. Simulated results indicate that the failure process of the Nayong Rock Avalanche lasted approximately 30 s; the duration of the failure process is close to that from the UAV video footage and seismic signal recordings (35 s). The duration of movement during the landslide process is estimated to be approximately 90 s with a maximum velocity of 40 m/s. The combined frictional-Voellmy model delivered the most accurate results when simulating this event. The selected models and parameters are expected to aid in clarifying the propagation processes of similar Rock Avalanches and thus improve the accuracy of hazard prediction in mountainous karst areas.
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Numerical investigation of the air blast generated by the Wenjia valley Rock Avalanche in Mianzhu, Sichuan, China
Landslides, 2019Co-Authors: Yu Zhuang, Qiang Xu, Aiguo XingAbstract:On 12 May 2008, a catastrophic Rock Avalanche was triggered by an earthquake in Mianyang, Sichuan, China. This catastrophic event killed 48 people and destroyed some houses at the mouth of Wenjia valley. The sliding mass caused a powerful air blast that blew down the trees on both sides and front margin. To better understand the possible mechanism of the air blast generated by the Wenjia valley Rock Avalanche and provide information for the assessment of this type of disasters in southwestern China, a numerical simulation was performed through a computational fluid dynamics software (Fluent) to simulate the runout behavior of the sliding mass and dynamic characteristics of the air blast. The frictional rheology is used for the source area and the Voellmy model is selected for the erosion and deposition areas. Simulated results indicate that the movement process of Wenjia valley Rock Avalanche lasted approximately 210 s with a maximum velocity of 65 m/s. The maximum velocity and relative pressure of the air blast are 35 m/s and 2.25 kPa, respectively. Furthermore, the variation of topography has a significant effect on the distribution of relative pressure for the air blast. The work conducted in this study is expected to make people deeply realize the disaster caused by the air blast and establish a risk assessment system in the southwestern China.
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simulation of a long runout Rock Avalanche triggered by the lushan earthquake in the tangjia valley tianquan sichuan china
Engineering Geology, 2017Co-Authors: Aiguo XingAbstract:Abstract Only one long-runout Rock Avalanche was triggered by the 2013 Lushan earthquake in the Tangjia Valley, Tianquan, Sichuan, China. The Rock Avalanche involved the failure of ~ 530,000 m3 of sandstone from the source area. The displaced material travelled a horizontal distance of ~ 1600 m with an elevation descent of ~ 480 m, equivalent to a fahrboschung of 16.7°. Based on a detailed field investigation, we introduce basic characteristics of the Rock Avalanche and find that the Rock Avalanche resulted in one run-up in the Chunwojian Valley, a superelevation in the Gangoutou Valley, and increase in volume due to the entrainment of path materials. A numerical model (DAN3D) was used to simulate the post-failure behavior of the Rock Avalanche. By means of trial and error, a combination of the frictional model and Voellmy model is found to provide the best performance in simulating this Rock Avalanche. The simulation results reveal that of the Rock Avalanche lasted approximately 160 s and an average velocity of 10 m/s.
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characteristics and numerical runout modelling of a catastrophic Rock Avalanche triggered by the wenchuan earthquake in the wenjia valley mianzhu sichuan china
Landslides, 2017Co-Authors: Aiguo Xing, Xiaoyi Yuan, Qihua Zhao, Heqing Huang, Qiangong ChengAbstract:The 2008 Wenchuan earthquake triggered more than 100 Rock Avalanches with volumes greater than 10 million cubic metres. The Rock Avalanche with the longest runout amongst these destructive landslides occurred in the Wenjia valley, Mianzhu, Sichuan, China. The landslide involved the failure of about 27.5 million cubic metres of sandstone from the source area. The displaced material travelled about 4,170 m with an elevation descent of about 1,360 m, equivalent to a fahrboschung of 16.9° and covered an area of 1.5 million square metres, with the final deposited volume of approximately 49 million cubic metres. The catastrophic event destroyed the village of Yanjing, killed 48 people and buried some houses at the mouth of the Wenjia valley. On the basis of a detailed field investigation, we introduce basic characteristics of the Rock Avalanche and find that the Rock Avalanche resulted in two run-ups and a superelevation along the runout path, and downslope enlargement due to the entrainment of path materials. A numerical model (DAN3D) is used to simulate the post-failure behaviour of the Rock Avalanche. By means of trial and error, a combination of the frictional model and Voellmy model is found to provide the best performance in simulating this Rock Avalanche. The simulation results reveal that the Rock Avalanche had a duration of about 240 s and an average velocity of 17.4 m/s.
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investigation and dynamic analysis of a catastrophic Rock Avalanche on september 23 1991 zhaotong china
Landslides, 2016Co-Authors: Aiguo Xing, Yueping Yin, Gonghui Wang, Chuan TangAbstract:At 6:10 p.m. on September 23, 1991, a catastrophic Rock Avalanche occurred in Zhaotong, Yunnan, southwestern China. Over 216 people were killed when the Touzhai village was overwhelmed directly in the path of the landslide. The landslide involved the failure of about 12 Mm3 of jointed basaltic Rock mass from the source area. The displaced materials ran out a horizontal distance of 3650 m over a vertical distance of 960 m, equivalent to a Fahrboschung of 14.7°, and covered an area of 1.38 km2. To provide information for hazard zonation of similar type of potential landslides in the same area, we used a dynamic model (DAN-W) with three alternative rheological models to simulate the runout behaviour of the displaced landslide materials and found that a combination of the frictional model and Voellmy model could provide the best performance in simulating this landslide. The simulated results indicated that the duration of the movement is estimated at about 175 s for a mean velocity 21 m/s.
Qiangong Cheng - One of the best experts on this subject based on the ideXlab platform.
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insights into the kinematics and dynamics of the luanshibao Rock Avalanche tibetan plateau china based on its complex surface landforms
Geomorphology, 2018Co-Authors: Qiangong Cheng, Yufeng Wang, Qiwen Lin, Hufeng YangAbstract:Abstract Complex topographic features on the surfaces of Rock Avalanche deposits have been regarded as important indicators for understanding Avalanche kinematics and dynamics. Based on a combination of remote sensing data and in-situ observations of surface landforms, including toreva blocks, transverse and longitudinal ridges, ridges separated by conjugate troughs, and hummocks, a giant Holocene Rock Avalanche on the Tibetan Plateau is recognized. This work aims to understand the kinematics of this event. In planview, the tongue-shaped Rock Avalanche exhibits a clear sequential distribution of various landforms. The translation zone (II) is characterised by toreva blocks originating from extension. In subzone III-1 of the accumulation zone (III), compression-related transverse ridges are well developed. Longitudinal ridges resulting from lateral velocity differences due to radial spreading are present in the front part of subzone III-1. Farther down, ridges separated by conjugate troughs (generated by a combination of compression and radial spreading) are common in subzone III-2. Subzone III-3 is characterised by abundant scattered hummocks with circular to oval shapes. Based on the distributions of these landforms, this Rock Avalanche is proposed to have mainly experienced a motion featuring laminar flow with radial spreading in its distal and marginal parts. During transport, three distinct processes appear to have occurred in the Avalanche mass from the proximal to the distal zones: extension-dominated sliding in zone II, compression-dominated sliding in subzones III-1 and III-2, and rapid radial spreading in subzone III-3.
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velocity dependent frictional weakening of large Rock Avalanche basal facies implications for Rock Avalanche hypermobility
Journal of Geophysical Research, 2017Co-Authors: Qiangong Cheng, Y F Wang, Jiajyun DongAbstract:To characterize the hypermobility mechanism of Rock Avalanches, a series of rotary shear tests at different shearing velocities (Veq) ranging from 0.07 m/s to 1.31 m/s and at a normal stress of 1.47 MPa were carried out on soil sampled from the basal facies of the Yigong Rock Avalanche that occurred in the Tibetan plateau in China. Through conducting these tests, the macroscale and microscale features of the deformed samples were analyzed in detail with the following valuable conclusions being reached: (1) soil subjected to rotary shear exhibits a clear velocity-dependent weakening characteristic with an apparent steady state friction of 0.13 being reached at Veq ≥ 0.61 m/s, (2) high-temperature rises and layers with high porosity were observed in the samples sheared at Veq ≥ 0.61 m/s, and (3) the cooperation of thermal pressurization and moisture fluidization induced by friction heating plays an important role in explaining the marked frictional weakening of the soil. In addition, the appearance of nanoparticles due to particle fragmentation should facilitate the weakening of the soil but is not the key reason for the marked frictional weakening.
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characteristics and numerical runout modelling of a catastrophic Rock Avalanche triggered by the wenchuan earthquake in the wenjia valley mianzhu sichuan china
Landslides, 2017Co-Authors: Aiguo Xing, Xiaoyi Yuan, Qihua Zhao, Heqing Huang, Qiangong ChengAbstract:The 2008 Wenchuan earthquake triggered more than 100 Rock Avalanches with volumes greater than 10 million cubic metres. The Rock Avalanche with the longest runout amongst these destructive landslides occurred in the Wenjia valley, Mianzhu, Sichuan, China. The landslide involved the failure of about 27.5 million cubic metres of sandstone from the source area. The displaced material travelled about 4,170 m with an elevation descent of about 1,360 m, equivalent to a fahrboschung of 16.9° and covered an area of 1.5 million square metres, with the final deposited volume of approximately 49 million cubic metres. The catastrophic event destroyed the village of Yanjing, killed 48 people and buried some houses at the mouth of the Wenjia valley. On the basis of a detailed field investigation, we introduce basic characteristics of the Rock Avalanche and find that the Rock Avalanche resulted in two run-ups and a superelevation along the runout path, and downslope enlargement due to the entrainment of path materials. A numerical model (DAN3D) is used to simulate the post-failure behaviour of the Rock Avalanche. By means of trial and error, a combination of the frictional model and Voellmy model is found to provide the best performance in simulating this Rock Avalanche. The simulation results reveal that the Rock Avalanche had a duration of about 240 s and an average velocity of 17.4 m/s.
N Fusi - One of the best experts on this subject based on the ideXlab platform.
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Rock Avalanche geomorphological and hydrological impact on an alpine watershed
Geomorphology, 2016Co-Authors: Paolo Frattini, Giovanni B Crosta, Federico Riva, R Scotti, Luca Greggio, Francesco Brardinoni, N FusiAbstract:Abstract Rock Avalanches are large flow-like movements of fragmented Rock that can cause extensive and rapid topographic changes, for which very few quantitative data are available. This paper analyses the geomorphological and hydrological impact of the 3 million m 3 Thurwieser Rock Avalanche (2004, Italian Central Alps) by using Terrestrial Laser Scanner, airborne Lidar and GNSS data collected from 2005 to 2014. Sediment yield with respect to the normal valley regime, the dynamic and mass balance of affected glaciers, and the reorganization of superficial and groundwater flow networks are quantified. In the middle portion of the Avalanche deposit, a natural sediment trap collected sediments from a new stream channel developed along the upper portion of the deposit and from a lateral drainage basin. This made possible to assess the 10-year impact of the Rock Avalanche on the sediment yield, which increased from about 120 to about 400 t km − 2 ·a − 1 . The Rock Avalanche partially covered a glacier with a shallow debris layer that acted as a thermal insulator, limiting ice ablation and producing a 10-m high scarp between the free surface of the glacier and the debris-covered portion. A reduction of 75% of ice ablation was observed due to thermal insulation. The Rock Avalanche filled a tributary valley, splitting the original drainage basin in two. Under ordinary flows, seepage occurs within the Avalanche deposit along the old valley axis. During high flow conditions, a new stream channel is activated along the middle and lower margin of the deposit, which has produced a new alluvial fan on the main valley floor. The fan evolution is described up to the present volume of about 2000 m 3 .
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formation characterisation and modeling of the val pola Rock Avalanche dam italy
Lecture Notes in Earth Sciences; 133, 2011Co-Authors: Giovanni B Crosta, Paolo Frattini, N Fusi, Rosanna SosioAbstract:Landslide dams can be originated by very different phenomena, each characterized by specific types of movement, which control the final characteristics of the material. We present the case study of the Val Pola landslide dam (Central Italian Alps, Lombardy), formed in 1987 by al large Rock Avalanche. We describe the main landslide features as well as those of its accumulation. Data from laboratory and in situ tests performed on the landslide deposits are reported and discussed. The collected data are used to describe the internal structure of the accumulation, the behaviour of the landslide dam during the lake infilling and the overtopping phase. These data are fundamental to interpret the mechanisms of put in place of the accumulation and the theories proposed to explain long runout of Rock Avalanches. We compare the grain size distributions of the deposits and the physical-mechanical properties from different landslide sectors. We stress the relevance of a detailed characterization of the internal structure of landslide dams to perform correct seepage modelling and to perform reliable predictions of landslide dam stability and breaching (geometry, water and sediment discharge, duration). Point-like characterization, often controlled by local conditions and presence of small outcrops, can be misleading both in terms of the evaluation of the stability of the dam and in the understanding of the processes. We used several published relationships and approaches for the assessment of the peak discharge, breaching time and geometry. We confirm the large variability of the results and the difficulties in using collected data for reliable predictions.
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fragmentation in the val pola Rock Avalanche italian alps
Journal of Geophysical Research, 2007Co-Authors: Giovanni B Crosta, Paolo Frattini, N FusiAbstract:[1] Grain size data from the deposit of the 1987 Val Pola Rock Avalanche (central Italian Alps) are compared with data concerning Rock avalanching, Rock fragmentation, and comminution. The Weibull distribution fits a small part of the entire particle-size distribution of debris samples, with a mean value of the curve shape factor of 0.54 ± 0.28. This is typical of multiple comminution, or fragmentation with much shearing. A fractal distribution fits over a greater size range. Computed fractal dimensions range between 1.3 and 3.2 within the deposit, with average values of about 2.6–2.7. These values cover the range between the theoretical values of the plane-of-weakness model (1.97) and the pillar-of-strength model (2.84) and are close to the theoretical value for the constrained comminution model (2.58). These suggest that both texturally mature and immature deposits are present and that more than a single comminution process acted during the Rock Avalanche motion. Variation of the grain size distribution within the deposit and grain size segregation show as trends in the fractal dimension and arise from variation in the fragmentation process. A variety of different physical and empirical laws suggest that 1–30% of the energy expended in the Rock Avalanche was consumed in fragmentation.
Giovanni B Crosta - One of the best experts on this subject based on the ideXlab platform.
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Rock Avalanche geomorphological and hydrological impact on an alpine watershed
Geomorphology, 2016Co-Authors: Paolo Frattini, Giovanni B Crosta, Federico Riva, R Scotti, Luca Greggio, Francesco Brardinoni, N FusiAbstract:Abstract Rock Avalanches are large flow-like movements of fragmented Rock that can cause extensive and rapid topographic changes, for which very few quantitative data are available. This paper analyses the geomorphological and hydrological impact of the 3 million m 3 Thurwieser Rock Avalanche (2004, Italian Central Alps) by using Terrestrial Laser Scanner, airborne Lidar and GNSS data collected from 2005 to 2014. Sediment yield with respect to the normal valley regime, the dynamic and mass balance of affected glaciers, and the reorganization of superficial and groundwater flow networks are quantified. In the middle portion of the Avalanche deposit, a natural sediment trap collected sediments from a new stream channel developed along the upper portion of the deposit and from a lateral drainage basin. This made possible to assess the 10-year impact of the Rock Avalanche on the sediment yield, which increased from about 120 to about 400 t km − 2 ·a − 1 . The Rock Avalanche partially covered a glacier with a shallow debris layer that acted as a thermal insulator, limiting ice ablation and producing a 10-m high scarp between the free surface of the glacier and the debris-covered portion. A reduction of 75% of ice ablation was observed due to thermal insulation. The Rock Avalanche filled a tributary valley, splitting the original drainage basin in two. Under ordinary flows, seepage occurs within the Avalanche deposit along the old valley axis. During high flow conditions, a new stream channel is activated along the middle and lower margin of the deposit, which has produced a new alluvial fan on the main valley floor. The fan evolution is described up to the present volume of about 2000 m 3 .
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modelling Rock Avalanche propagation onto glaciers
Quaternary Science Reviews, 2012Co-Authors: Rosanna Sosio, Giovanni B Crosta, Joanna H Chen, Oldrich HungrAbstract:Abstract Ice-Rock Avalanches which occur in glacial environments are controlled by the presence of snow and ice in the moving material and by possible propagation onto icy basal surfaces. All these factors contribute to enhancing the flow mobility. Mixing with ice and snow hampers block collisions and favours dense flow behaviour. Ice melting reduces granular friction by saturation of the basal material and fluidization effects. Propagating onto glaciers offers a smooth surface with low shear resistance. This work is a review of the best documented ice-Rock Avalanches and focuses on evaluating their mobility for hazard analysis purposes by providing a set of calibrated cases. The Rock Avalanches have volumes ranging from 5*10 6 m 3 to 25*10 6 m 3 . We replicate these events by using SPH and FEM numerical methods, assuming frictional and Voellmy basal rheologies. The Voellmy rheology best performs at replicating the landslide propagation. Among the back analyzed cases, the frictional coefficient ranges in the interval 0.03–0.1, the turbulent coefficient within 1000 m s −2 –2000 m s −2 . The bulk basal friction angle ranges within 2.75° and 14° with values inversely related to event volumes. Forward selection of the basal friction angle based on event volume, allows the replication of the Mount Cook ice-Rock Avalanche predicting a maximum runout which is less than 4% larger than observed. In the perspective of forward modelling, large uncertainty is related to the reconstruction of the post-event topographies, particularly for the sliding surface. Mixing with ice and snow reduces basal friction proportionally to ice and snow content. Pure ice has a basal friction which is reduced by about 75% than basal friction of pure Rock. Melting of ice during Rock Avalanche propagation has been evaluated for the Sherman event. The frictional heat generated at the glacier surface results in the melting of 86.2 ± 5.9 kg m −2 , which could have contributed to a minimum 20–35% (±10%) reduction of the material friction angle through the sole pore pressure generation within a 40 and 20 cm thick shear layer, respectively. The largest uncertainty is related to the area of contact between Rock and ice.
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formation characterisation and modeling of the val pola Rock Avalanche dam italy
Lecture Notes in Earth Sciences; 133, 2011Co-Authors: Giovanni B Crosta, Paolo Frattini, N Fusi, Rosanna SosioAbstract:Landslide dams can be originated by very different phenomena, each characterized by specific types of movement, which control the final characteristics of the material. We present the case study of the Val Pola landslide dam (Central Italian Alps, Lombardy), formed in 1987 by al large Rock Avalanche. We describe the main landslide features as well as those of its accumulation. Data from laboratory and in situ tests performed on the landslide deposits are reported and discussed. The collected data are used to describe the internal structure of the accumulation, the behaviour of the landslide dam during the lake infilling and the overtopping phase. These data are fundamental to interpret the mechanisms of put in place of the accumulation and the theories proposed to explain long runout of Rock Avalanches. We compare the grain size distributions of the deposits and the physical-mechanical properties from different landslide sectors. We stress the relevance of a detailed characterization of the internal structure of landslide dams to perform correct seepage modelling and to perform reliable predictions of landslide dam stability and breaching (geometry, water and sediment discharge, duration). Point-like characterization, often controlled by local conditions and presence of small outcrops, can be misleading both in terms of the evaluation of the stability of the dam and in the understanding of the processes. We used several published relationships and approaches for the assessment of the peak discharge, breaching time and geometry. We confirm the large variability of the results and the difficulties in using collected data for reliable predictions.
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complete dynamic modeling calibration for the thurwieser Rock Avalanche italian central alps
Engineering Geology, 2008Co-Authors: Rosanna Sosio, Giovanni B Crosta, Oldrich HungrAbstract:Abstract Few Rock Avalanches have been witnessed and no exact real time description is available. The 2.5 M m 3 Punta Thurwieser Rock Avalanche (September 2004, Italian Central Alps) is a unique event for which many quantitative observations have been gathered. This is the first case ever of a natural Rock Avalanche being recorded on video, and for which an almost exact value of the total time duration, from initial detachment to final deposition, is available. The landslide travelled over 2.9 km from its source partially in a glacial environment. The initial failure and the time for the complete evacuation of the source area were studied and assessed by a series of photos. The mean front velocities along the path have been estimated from the video. The final geometry and the characteristics of the deposit have been obtained by GPS measurements, aerial photos, field surveys and laboratory tests. A quasi-3D continuum dynamic analysis of the landslide motion has been performed assuming both a Voellmy and a frictional rheology in the model DAN 3D. For the first time the landslide front velocities have been used for back analyses and calibration of the rheological parameters, together with the final shape and thickness of the deposit, and its developing extension. The dynamic flow resistance parameters, initially calibrated with DAN, were adopted and validated in DAN 3D, showing good consistency. They are consistent with the existing database for calibrated landslides of similar type and scale. Flow velocities on the path segment underlain by glacial deposits (up to 55–65 m s − 1 ) are more accurately predicted by adopting a frictional rheology (up to 50–55 m s − 1 ) with zero pore pressure and a 26° friction angle than by a Voellmy rheology (up to 40–45 m s − 1 ). Both observations and modelling show that glacial ice plays a substantial role in increasing the Rock Avalanche mobility.
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fragmentation in the val pola Rock Avalanche italian alps
Journal of Geophysical Research, 2007Co-Authors: Giovanni B Crosta, Paolo Frattini, N FusiAbstract:[1] Grain size data from the deposit of the 1987 Val Pola Rock Avalanche (central Italian Alps) are compared with data concerning Rock avalanching, Rock fragmentation, and comminution. The Weibull distribution fits a small part of the entire particle-size distribution of debris samples, with a mean value of the curve shape factor of 0.54 ± 0.28. This is typical of multiple comminution, or fragmentation with much shearing. A fractal distribution fits over a greater size range. Computed fractal dimensions range between 1.3 and 3.2 within the deposit, with average values of about 2.6–2.7. These values cover the range between the theoretical values of the plane-of-weakness model (1.97) and the pillar-of-strength model (2.84) and are close to the theoretical value for the constrained comminution model (2.58). These suggest that both texturally mature and immature deposits are present and that more than a single comminution process acted during the Rock Avalanche motion. Variation of the grain size distribution within the deposit and grain size segregation show as trends in the fractal dimension and arise from variation in the fragmentation process. A variety of different physical and empirical laws suggest that 1–30% of the energy expended in the Rock Avalanche was consumed in fragmentation.
Mauri Mcsaveney - One of the best experts on this subject based on the ideXlab platform.
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from surface morphologies to inner structures insights into hypermobility of the nixu Rock Avalanche southern tibet china
Landslides, 2021Co-Authors: Qingli Zeng, Mauri Mcsaveney, Rongqiang Wei, Guangxiang Yuan, Liye LiaoAbstract:Large Rock Avalanches often result in many deaths and catastrophic damage to infrastructure far from source. No consensus has yet been reached on mechanisms causing their extraordinarily long runout since the first study at the Elm Slide, Switzerland. Much current understanding of Rock Avalanche kinematics and dynamics has been gained from observations of their surface morphologies and inner structures. Based on field surveys, high-resolution satellite image interpretation, and laboratory sieving, we analyzed the ancient, earthquake-induced Nixu Rock Avalanche in southern Tibet, China, which has unique exposures of both morphological features and inner structures of the deposits. The study revealed that (1) the Nixu Rock Avalanche probably could be disintegrated into three emplacement stages, transforming from an initial deep-seated Rockslide into a large secondary debris Avalanche, plus a relatively small third debris Avalanche. The spreading of the secondary debris Avalanche contributed to the subsequent long-runout propagation. (2) The morphological features observed in successive proximal to distal exposures (such as scarps, flowbands, transverse ridges, grid grooves, hummocks, and splash zones) reflect the change in stress-strain state of debris in motion from tension, to compression, to shear and tension. (3) The complicated inner structures exposed along river banks (such as jigsaw structures, fragmented clasts, inner shear zones, conjunction faults, convoluted lamination, decollements, sand injections, and intrusions) indicate the existence of a thin basal shear zone and a pressurized entrained substrate between the substrate and Rock Avalanche debris. (4) This suggests turbulent flow with bulldozing in the front, but a laminar flow under a simple shear model for the main body. (5) The analysis suggests that the Rock Avalanche’s extraordinary mobility involves a combination of momentum transfer, substrate entrainment, liquefied basal shearing, internal shearing, and Rock fragmentation.
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timing and seismic origin of nixu Rock Avalanche in southern tibet and its implications on nimu active fault
Engineering Geology, 2020Co-Authors: Qingli Zeng, Mauri Mcsaveney, Rongqiang Wei, Guangxiang Yuan, Liye LiaoAbstract:Abstract In tectonically active mountain areas, the identification, dating and determination of origin of large landslides are of special importance in recognizing the seismicity and earthquake magnitude of regional faults, reconstructing the prehistoric landscape evolution and estimating the seismic hazards. Based on field survey, high-resolution satellite image interpretation and 14C dating of substrate, this paper studied the large, long-runout Nixu Rock Avalanche (the NXRA) in the Angang graben of the southern Tibetan Plateau. The study revealed that: (1) the deep-seated Nixu Rock Avalanche straddles the Nimu active normal fault and spreads onto the Angang basin with a deposit volume of 47 Mm3 and a travelling distance of 4960 m. (2) Humus samples immediately under the deposit of Rock Avalanche along the natural river-erosion section suggest a 14C age of 820 ± 30 BP (1220 ± 30 CalAD) for the NXRA event. The age well matches the 1264 CE Chubushi earthquake recorded in Tibetan documents. (3) 23 adjacent landslides have been recognized with co-seismic distribution features, such as clustering and distance effect, ridge-end amplification effect and slope aspect effect. Sand liquefaction and peat deformation were discovered in the substrate beneath and at a distance of ~300 m away from the Avalanche deposit. (4) This information indicate that the NXRA was triggered most likely by the 1264 Chubushi earthquake with a magnitude of Mw 7.0–7.2 estimated by empirical equations of Keefer (1994) and Wells & Coppersmith (1994). It is suggested that the Nimu fault of the Yadong-Gulu rift may be more hazardous than the northern and southern part due to its high susceptibility of large co-seismic landslides.
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the 2009 jiweishan Rock Avalanche wulong china precursor conditions and factors leading to failure
Engineering Geology, 2018Co-Authors: Ming Zhang, Mauri Mcsaveney, Hai Shao, Chenyang ZhangAbstract:Abstract This study investigates the predisposing geological and anthropogenic factors and indicative precursors preceding the fatal 5 June 2009 Jiweishan Rock Avalanche. It began as a Rockslide and transformed into a Rock Avalanche that killed 74 people and caused major property loss due to misdiagnosis of the failure mode, and underestimation of volume and travel distance. Besides topography, structure and stratigraphy that favoured failure, mining below the failed Rock mass had changed the state of stress and altered groundwater flow. The anthropogenic factors caused deformation and accelerated failure of the slope, and therefore were important contributions. Cracks and a karstic zone had developed along regional joints and defined several boundaries of the failed Rock mass. Furthermore, a 2-m-wide crack developed since 1958 revealed a potential basal failure surface at the contact between karstic limestone and an underlying pre-sheared thin shale aquiclude. Increasing magnitude and frequency of Rockfalls and tension cracks at the front end of the sliding block appeared three days before the event and implied the likely movement direction of the sliding Rock mass. These could have warned of a developing giant failure. Topography included a large elevation difference between the toe of the failure surface and the cliff base, a narrow valley to channel debris, and the steep gradient of the downstream Tiekuang Creek, could have suggested that failure might lead to a rapid and long-runout Rock Avalanche. However, access to the densely vegetated source area before the failure was difficult, and local investigators did not have all of the evidence that might have led them to recognize that potential danger was more than continuing Rockfalls.
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Rock Avalanche deposits store quantitative evidence on internal shear during runout
Geophysical Research Letters, 2017Co-Authors: Ming Zhang, Mauri McsaveneyAbstract:We investigated the quantitative effect of internal shear on grain breakage during Rock-Avalanche runout, by means of 38 ring-shear experiments on identical sand samples at different normal stresses, shear strains and shear-strain rates. We compared sample grain-size characteristics before and after shearing. We found that grain size decreased with increase in normal stress and shear strain. Reduction in grain size was inferred to occur through grain breakage associated with grain interactions in strong force chains during strain. The results were consistent with observations of both inverse-grading structure in deep Rock-Avalanche exposures, and fining and grading of particles with increasing Rock-Avalanche travel distance. Our study suggested that with appropriate calibration, variations in grain-size distributions within a Rock-Avalanche deposit would provide quantitative information on the distribution of internal shear during its runout.
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dynamics of the 2008 earthquake triggered wenjiagou creek Rock Avalanche qingping sichuan china
Engineering Geology, 2016Co-Authors: Ming Zhang, Yueping Yin, Mauri McsaveneyAbstract:Abstract The Wenjiagou Creek Rock Avalanche was triggered by the 2008 Wenchuan earthquake. It traveled 4.6 km and left a granular deposit of 1.5 × 108 m3 in Wenjiagou Creek valley. The dynamics of the Rock Avalanche were studied through field and laboratory investigations and remote sensing. The dynamic course was divided into three segments: (1) Failing — the original slope failed due to the huge earthquake ground accelerations acting on a Rock mass weakened by severe karstification; (2) Falling — the Rock mass experienced several drops due to abrupt changes in slope, and broke into granular debris during collisions with the ground and mountain flanks; and (3) Flow — the broken granular mass flowed approximately 3 km down the valley of Wenjiagou Creek. The transport mechanism of the granular mass of debris was studied by analyzing the structure of the deposit and through ring-shear tests. A gully incised into the deposit by rainfall runoff and debris flows enabled the internal structure of the deposit to be examined and sampled. In cross-section, the exposed deposit was finest near the base, and gradually became coarser towards the surface (inverse grading); in longitudinal section, deposits near the base and on the surface both became finer with increasing travel distance. Near the base, the granular debris experienced the maximum normal and shear stresses, and fragmented into the finest grains. Both normal and shear stresses between the grains gradually decreased from near the base to the surface. Samples were sheared in a ring-shear apparatus to simulate the shearing within the granular debris. Shear resistance between grains was found to decrease as grains became finer due to pervasive fragmentation, which is one of the possible mechanisms by which the granular debris was able to travel a long distance at a high speed.
