Study On The Failure Mechanismof Granular Mixtures Slopebywind Tunnel Experiments

Granular mixtures slope as a special planar geological disasters, widely distributed in the alpine mountains and earthquake-stricken areas, and its structure is loose, no fine particles and other cements to connec each other, like a plate of "sand".When the external conditions changed, it would damage easily, and cause great harm to human and traffic safety. The formation of granular mixtures slope mainly divided into three classes: ① sliding sand slope formed frost weathering; ② river erosion terraces cut loose accumulation③inverted cone stone formed by dynamic effects of earthquakes. Compared with other geological disasters, its instabilityandfailure also showed a great difference, more frequently.The main failure mode is small-scale progressive destruction.The main predisposing factors are earthquakes, precipitation, freeze-thaw cycles, river erosion, wind load and human engineering activities.Because of the wind loads, slope surface debris are easily destroyed and hit the road, block the traffic. This phenomenon is very common.In this paper, based on fieldwork to study granular mixtures slope in high-altitude alpine mountain, and research development and distribution characteristics of granular slope.Combining with 3D laser scanning technology to study its motion characteristics, thus to analysis its predisposing factors, unstable modes, recharge rates, unstable modes and sand production rate. And focus on the effects of wind load studies, through wind tunnel testing to resrarch wind loads induced instability mechanism of granular slope. The main contents are as follows:(1) Subject to intense cold mountain frost weathering effects granular slope abnormal development. In this paper, based on field surveys, starting from the topography, lithology, slope and other information, to analysis and development distribution of granular mixtures slope. Slope to maintain its stability by natural angle of repose, concentrated in 30° ~ 37°, and to study its predisposing factors.(2) According the causes of granular mixtures slope to divide into 3 categories: the native type, secondary type and growth pattern. Focus on the start of the inducing factors, combined with previous studiesto proposed four basic modes: progressive supply type, traction type, the impact of wind and rolling stones, erosion type. And focusing on wind load effects, proposed instability modes of granular slope under wind loads: the type combined impact of Rolling Stones and wind load; flow-induced vortex-induced type.(3) By means of 3D laser scanning technology, to acquireslope point cloud features, many times. Throughthe comparison analysisof point cloud, to grasp the motion feature of slopes; and to explore the rock erosion cause by ratefrost weathering and slope instability and failure rate cause by the change of external condition.(4) Based on the typical granular slope, and follow the similar guidelines to design wind tunnel experiments to research the instability mechanism of granular mixtures slope caused by the wind.①Through elease stones from chute to imitate rolling stones. By the means of wind tunnel testto research the regular pattern of slope failure; explore the relationship between wind size, rolling impact energy, impact frequency and slope instability scale(Falling sand quality), and to evaluate the impact of gravel by the rolling stones.Lastly, propose the speed recovery coefficient(Rv) and energy recovery coefficient(Re).②Combine pitot tube flow measurement device and numerical simulation software(FLUENT) to study the structural features of the flow field inside and outside of the groove.③In the test, by rebuildinggranular slopewhich has the layer structure to research the starting process and the movement characteristics of particle on the surface of slope in the wind loads, and to explore the groove hole formation and evolution process of erosion. And to study the groove shape, influence of the diffent aspect ratio and other factors on the strength of wind erosion.(5) Combined with wind-driven testing and the sand threshold theory to establish granular mixtures slope of critical starting conditions, the maximum particle size and the sediment discharge model, and borrow the results of wind test to verify the model.