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Effects of a flexible net barrier on the dynamic behaviours and interception of debris flows in mountainous areas

Journal of Mountain Science 2017年第10期14卷 1903-1918页

作者： HUO Miao zhou jia-wen YANG Xing-guo zhou Hong-wei State Key Laboratory of Hydraulics and Mountain River Engineering Siehuan University Chengdu 610065 China College of Water Resource and Hydropower Sichuan University Chengdu 610055 China

Flexible net barriers are a new type of effective mitigation measure against debris flows in valleys and can affect the kinematic energy and mass of debris flows. Here, ten flume tests were performed to study the dynamic behaviours of debris flows with differences in volumes, concentrations(solid volume fraction), and travel distances after interception by a uniform flexible net barrier. A high-speed camera was used to monitor the whole test process, and their dynamic behaviours were recorded. A preliminary computational framework on energy conversion is proposed according to the deposition mechanisms and outflow of debris flow under the effects of the flexible net barrier. The experimental results show that the dynamic interaction process between a debris flow and the flexible net barrier can be divided into two stages:(a) the two-phase impact of the leading edge of the debris flow with the net and(b) collision and friction between the body of the debris flow and intercepted debris material. The approach velocity of a debris flow decreases sharply(a maximum of 63%) after the interception by the net barrier, and the mass ratio of the debris material being intercepted and the kinetic energy ratio of the debris material being absorbed by the net barrier are close due to the limited interception efficiency of the flexible net barrier, which is believed to be related to the flexibility. The energy ratio of outflow is relative small despite the large permeability of the flexible net barrier.

关键词： Debris flow Flexible net barrier Dynamic behaviours Interception efficiency Kinetic energy absorption High speed photography

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A theoretical model for the estimation of maximum impact force from a rockfall based on contact theory

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Journal of Mountain Science 2018年第2期15卷 430-443页

作者： ZHANG Shi-lin YANG Xing-guo zhou jia-wen State Key Laboratory of Hydraulics and Mountain River Engineering Sichuan University College of Water Resource and Hydropower Sichuan University

Rockfall poses a great threat to buildings and personal security. To understand the dynamic characteristics of rockfalls is a prerequisite for disaster prevention and assessment. Models for rockfalls in different forms are established based on the theory of rigid body motion. The equivalent velocity considering the rotational effect is determined by the energy ratio. Besides, considering plastic deformation and nonlinear hardening, the maximum impact force is estimated based on the Hertz contact theory. Then, a case study is carried out to illustrate the applicability of the model and sensitive analyses on some affecting parameters are also made. Calculation results show that the maximum impact force increases with the increasing of incident velocity, angle and slope gradient reflected by the changing of energy ratio. Moreover, the model for the estimation of maximum impact force is validated by two different scales of experiments and compared with other theoretical models. Simulated maximum impact forces agree well with the experiments.

关键词： RockfaU Motion characteristics Contacttheory Maximum impact force

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Determination Method for Shear Strength Parameters of Rock-Soil Mixtures Using Close-Range Photogrammetry and 3-D Limit Equilibrium Theory

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Journal of Mountain Science 2015年第5期12卷 1068-1083页

作者： zhou jia-wen YANG Xing-guo YANG Zhao-hui State Key Laboratory of Hydraulics and Mountain River Engineering Sichuan University College of Water Resource and Hydropower Sichuan University School of Engineering University of Alaska Anchorage

Using a combination of close-range photogrammetry and three-dimensional(3-D) limit equilibrium theory, a determination method for the shear strength parameters of rock-soil mixture is presented. A close-range photogrammetry method is used for measurement of the 3-D terrain of the experimental target. Auto CAD Lisp and EXCEL VBA are used to perform 3-D limit equilibrium analysis of the stability of sliding mass and perform backanalysis of shear strength parameters. The presented method was used to determine the shear strength parameters of rock-soil mixtures at the Liyuan Hydropower Station. The 3-D terrain of sliding surface could be measured notably well using of closerange photogrammetry. The computed results reveal that the cohesion and friction angle of rock-soil mixtures were 3.15 k Pa and 29.88o for test A, respectively, and 4.43 k Pa and 28.30o for test B, respectively, within the range of shear strength parameters, as determined by field and laboratory tests. The computation of shear strength parameters is influenced by the mesh grid number, especially the cohesion of the rock-soil mixture. The application of close-range photogrammetry can reduce the siteworks and improve the computational efficiency and accuracy.

关键词： Rock-soil mixtures In-situ horizontalpush-shear test Photogrammetry Limit equilibrium Shear strength parameters

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Comprehensive analyses of initiation and failure mechanisms of the 2017 Xinmo catastrophic rockslide

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Journal of Mountain Science 2022年第6期19卷 1525-1540页

作者： zhou jia-wen FAN Gang CHEN Qin YANG Xing-guo State Key Laboratory of Hydraulics and Mountain River Engineering Sichuan UniversityChengdu 610065China State Key Laboratory of Geohazard Prevention and Geoenvironment Chengdu University of TechnologyChengdu 610059China College of Water Resource and Hydropower Sichuan UniversityChengdu 610065China

The failure of the 2017 Xinmo catastrophic rockslide in Maoxian County, Sichuan, Southwest China was a combined effect of long-term and shortterm triggering factors. Field investigation, historical data collection, laboratory tests, chemical and microstructure analysis and numerical simulations were adopted herein to reveal the initiation and failure mechanism of the Xinmo rockslide. The analytical results showed that this failure involved the coupling of several triggering factors. The initial cracks in the rock mass were induced by historical earthquakes due to the convex topography and the direction effect. Rock masses from the source area of the Xinmo rockslide contain water-sensitive minerals, i.e., albite and chamosite, and the easily oxidized chemical element Fe, resulting in obvious strength deterioration under the action of water. The scanning electron microscopy(SEM) experimental results indicated that the internal structure of the rock mass is conducive to weathering. The compressive and shear strengths of the rock mass were reduced due to freeze-thaw cycles and weathering. The antecedent rainfall further deteriorated the stability of the slope, and stress and deformation accumulated continually in the locked section. Finally, the locked section sheared out, and the slope failed. An entrainment effect was observed in the Xinmo rockslide due to the presence of old landslide deposits and the antecedent rainfall, resulting in an amplification of the catastrophic rockslide. A simplified three dimensional analysis model was established in this study to reveal the influence of the triggering factors on the failure mechanism of the Xinmo rockslide.

关键词： Xinmo Rockslide Landslide Failure mechanism Long-term evolution Rainfall Entrainment effect

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An estimation model for the fragmentation properties of brittle rock block due to the impacts against an obstruction

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Journal of Mountain Science 2017年第6期14卷 1161-1173页

作者： HOU Tian-xing XU Qiang XIE Hong-qiang XU Nu-wen zhou jia-wen State Key Laboratory of Hydraulics and Mountain River Engineering Siehuan University Chengdu 610065 China State Key Laboratory of Geohazard Prevention and Geoenvironment Protection Chengdu University of Technology Chengdu 610059 China College of Water Resource and Hydropower Sichuan University Chengdu 610065 China

Mountain hazards with large masses of rock blocks in motion – such as rock falls, avalanches and landslides – threaten human lives and structures. Dynamic fragmentation is a common phenomenon during the movement process of rock blocks in rock avalanche, due to the high velocity and impacts against obstructions. In view of the energy consumption theory for brittle rock fragmentation proposed by Bond, which relates energy to size reduction, a theoretical model is proposed to estimate the average fragment size for a moving rock block when it impacts against an obstruction. Then, different forms of motion are studied, with various drop heights and slope angles for the moving rock block. The calculated results reveal that the average fragment size decreases as the drop height increases, whether for free-fall or for a sliding or rolling rock block, and the decline in size is rapid for low heights and slow for increasing heights in the corresponding curves. Moreover, the average fragment size also decreases as the slope angle increases for a slidingrock block. In addition, a rolling rock block has a higher degree of fragmentation than a sliding rock block, even for the same slope angle and block volume. Finally, to compare with others' results, the approximate number of fragments is estimated for each calculated example, and the results show that the proposed model is applicable to a relatively isotropic moving rock block.

关键词： Rock block Rock fragmentation Rock movement process Crushing work ratio Average fragment size

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Entrainment effects and the dynamical evolution of debris avalanche/flow on substrate materials

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Journal of Mountain Science 2019年第8期16卷 1760-1773页

作者： HUO Miao YANG Xing-guo zhou Hong-wei LIANG yu-feng zhou jia-wen State Key Laboratory of Hydraulics and Mountain River Engineering Sichuan UniversityChengdu 610065China College of Water Resource and Hydropower Sichuan UniversityChengdu 610065China

A pair of flumes with variable inclinations were employed to investigate the entrainment mechanics and dynamical evolution of a debris avalanche/flow. A fixed quantity of solid and water mixture was released from a constant elevation and accelerated along a higher chute to impact substrate materials with different water contents and particle size distributions in the lower chute. Two high-speed cameras, pore and earth pressure detecting devices, were placed in the substrate materials where severe scouring occurs in order to collect multiple measurements of dynamical and mechanical parameters. The entrainment dynamics were verified by geometrical analysis and quasi-static simulation. The results show that wet and fine materials that are placed in the lower chute with steeper slopes are easily entrained during debris flow initiation, the pattern of which can be described by Coulomb friction and the Mohr-Coulomb law. Elaborate measurements of dynamical parameters enable the results of an elementary computational framework to predict the time-dependent scouring depth ht, which provides insight into rapidly determining debris flow propagation. Finally, the post-entrainment dynamics were studied. The results indicate that the propagation and the amplification of debris flows along erodible beds are dominated by the velocity and the solid volume fraction of the mixed substrate, and the coarse particle group of the substrate is a key feature affected by momentum changes.

关键词： Debris avalanche Debris flow initiation Entrainment mechanism Flume experiment Dynamical evolution

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Failure mechanism and stability analysis of the Zhenggang landslide in Yunnan Province of China using 3D particle flow code simulation

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Journal of Mountain Science 2016年第5期13卷 891-905页

作者： SHI Chong LI De-jie CHEN Kal-hua zhou jia-wen Key Laboratory of Ministry of Education for Geomechanics and Embankment Engineering Hohai UniversityNanjing 210098China Institute ofC eotechnical ResearchHohai UniversityNanjing 210098China State Key Laboratory of Hydraulics and Mountain River Engineering $iehuan UniversityChengdu 610065China

Based on the principle of 3D particle flow code,a numerical landslide run-out model is presented to simulate the failure process of the Zhenggang landslide(in southwestern China) under the effect of water after a *** relationship between the micro-mechanical parameters and the macro-shear strength of the grain material is determined through numerical *** the rainfall effect is considered in numerical simulations and rain-induced sliding processes are performed,which help us to discuss the mechanism of deformation and failure of this landslide together with field *** shows the Zhenggang landslide would most likely be activated in Zone I and would gain momentum in Zone *** order to prevent the potential disaster,a tailing dam is advised to be designed about 175 m downstream from the current landslide boundary of Zone *** by field observations,the presented landslide model can reflect the failure mechanism after *** can also provide a method to predict the potential disaster and draft disaster prevention measures.

关键词： Back analysis Deposit avalanche Dynamic process Landslide Particle flow code

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Effect of Freeze-Thaw Cycles on Mechanical Properties and Permeability of Red Sandstone under Triaxial Compression

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Journal of Mountain Science 2015年第1期12卷 218-231页

作者： YU Jin CHEN Xu LI Hong zhou jia-wen CAI Yan-yan Institute of Geotechnical Engineering Huaqiao University School of Civil and Hydraulic Engineering Dalian University of Technology State Key Laboratory of Hydraulics and Mountain River Engineering Sichuan University

Geological disasters will happen in cold regions because of the effects of freeze-thaw cycles on rocks or soils, so studying the effects of these cycles on the mechanical characteristics and permeability properties of rocks is very important. In this study, red sandstone samples were frozen and thawed with o, 4, 8 and 12 cycles, each cycle including 12 h of freezing and 12 h of thawing. The P-wave velocities of these samples were measured, and the mechanical properties and evolution of the steady-state permeabilities were investigated in a series of uniaxial and triaxial compression tests. Experimental results show that, with the increasing of cyclic freeze-thaw times, the P-wave velocity of the red sandstone decreases. The number of freeze-thaw cycles has a significant influence on the uniaxial compressive strength, elastic modulus, cohesion, and angle of internal friction. The evolution of permeability of the rock samples after cycles of freeze-thaw in a complete stress-strain process under triaxial compression is closely related to the variation of the microstructure in the rock. There is a highly corresponding relationship between volumetric strain and permeability with axial strain in all stages of the stress-strain behaviour.

关键词： Freeze-thaw cycles Red sandstone Triaxial compression Permeability Mechanicalproperties

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Risk assessment and landslide prevention design using numerical modelling——A case study in Qingliu,China

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Journal of Mountain Science 2023年第4期20卷 943-961页

作者： LI Cong-jiang HU Yu-xiang jiaNG Nan LI Hai-bo zhou jia-wen State Key Laboratory of Hydraulics and Mountain River Engineering Sichuan UniversityChengdu610065China College of Water Resource and Hydropower Sichuan UniversityChengdu610065China

Numerous Quaternary deposits are existed in the mountainous areas of Southwest China,especially in the transition zone between the QinghaiTibet Plateau and the Sichuan Basin,where strong tectonic movements and frequent climatic changes increase the potential *** possible deformation and failure process of potential landslides and their impacts on the surrounding environment are important research *** investigation and monitoring indicate that the Qingliu landslide in Xiameng town,Li County,Sichuan Province,China has been continuously deforming since August *** deformation zone has a maximum deformation depth of approximately 18.9m,a total area of 54,628 m2,and a volume of 34.0×104 m3,which seriously threatens infrastructure projects and *** a result,understanding the Qingliu landslide evolution process,assessing the hazard risk,and planning disaster prevention measures are of great significance for reducing disaster *** this study,the mass movement process and hazard risk of the Qingliu landslide are evaluated,and the effects of different prevention measures are compared and *** using the depth-integrated method,the mass movement of the Qingliu landslide is *** numerical simulation results indicate that the maximum velocity of the Qingliu landslide is approximately 37.5 m/s,and the duration of the landslide is approximately *** simulated landslide can eventually form a deposited mass with a maximum deposit thickness of 19.4 m and an area of approximately 60,168.3 m2,thereby blocking the river and burying ***,a risk assessment of the Qingliu landslide under different forms of protection measures is also produced and discussed by considering the hazard level and economic vulnerability level of the affected *** three layers of anti-slide piles on the deformation zone to reduce the hazard risk of the Qingliu landslide is a better *** results may be useful for planning preventio

关键词： Qingliu landslide Numerical simulation Mass movement Risk assessment Prevention measures

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Large deformation and failure mechanism analyses of Tangba high slope with a high-intensity and complex excavation process

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Journal of Mountain Science 2019年第2期16卷 453-469页

作者： HOU Qi-dong WU Gao-jian LI Hai-bo FAN Gang zhou jia-wen State Key Laboratory of Hydraulics and Mountain River Engineering Sichuan University Sinohydro Bureau 5 CO.LTD Power Construction Corporation of China College of Water Resource and Hydropower Sichuan University

The Tangba high slope is mainly composed of coarse soils and supplies core wall materials for the construction of the Changheba dam. Since the filling intensity of the Changheba dam is high, the Tangba high slope suffers from a high-intensity excavation process, and reinforcement measures are usually not implemented immediately. Moreover, the distribution of useful materials is uneven and insufficient, and the mixing of different soil materials is necessary; thus, multiple simultaneous excavations and secondary excavation are inevitable. In the construction period from 2012 to 2016, large deformations occurred in this area, and one of the largest monitored horizontal deformations whose direction points to the opposite side of the valley even reached more than 8000 mm. According to field investigation, site monitoring and theoretical analysis, the large deformation in the Tangba high slope can be divided into two phases. In the first phase, the excavation construction breaks the original stress equilibrium state; in the second phase, the precipitation infiltration accelerates the deformation. Thus, the excavation construction and precipitation infiltration are the two major factors promoting the deformation, and the high-intensity and complex excavation process is the fundamental cause. Notably, rate of slope deformation significantly accelerated in rainy seasons due to precipitation infiltration; the rate also accelerated in early 2016 due to the high-intensity, complex excavation process. Comprehensively considering the above factors, timely and effective reinforcement measures are essential.

关键词： Coarse soil slope Large deformation High-intensity and complex excavation Failure mechanism Reinforcement measures

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