| Wenchuan Earthquake is the most great earthquake disaster affecting the widest range and caused the most serious casualties,since the founding of new China.The result of this great disaster is more than 87150 people were killed and a large number of houses and infrastructure damaged, industrial and agricultural production suffered heavy losses, the ecological environment has been severely damaged, with direct economic losses of 845.1 billion RMB Yuan.Strong earthquake triggered a lots of secondary geological disasters such as avalanches, landslides, mudslides and dammed lake, etc, the number and size are immense.Wenchuan Earthquake-induced geological disasters demonstrated a completely different dynamic characteristics with the gravity of geological disasters.Affected by strong ground motion, some giant landslides hazard had the emergence of characteristics with varying degrees of high-speed, strong momentum and a strong fluidization.Wenjiagou Rockslide-Sturzstrom is one of them.Earthquake often happened with very complex dynamic environment, especially in the vicinity of earthquake faults. Therefore, the earthquake-induced landslide generally have the complex movement, just like high-speed and long-range movement, and have the rare dynamic characteristics under the non-seismic conditions.This paper take the earthquake-induced landslide event called Wenjiagou high-speed remote - debris flow as a case. Based on the field survey, the paper analyzed the structure characteristics of deposits in different parts of landslide-sturstrom body, and the formation mechanism and the movement characteristic of stages, just like excitation, startup, acceleration, fragmentation, and stop, and proposed the mechanism theories of excitation and startup with the two-dimensional shaking table physical simulations.Finally, the paper counted and analyzed the 66 landslide events across the world, including Wenjiagou Landslide-Sturzstrom, and obtained results of the relationship and differences on kinematic of earthquake-induced and non-earthquake-induced landslides.1. Wenjiagou Rockslide-Sturzstrom event are high, long-range, ultra-high-speed in deep seated rockslide-sturzstrom process induced by the huge earthquake.The entire incident lasted for about 1min, thickness is 20 ~ 30m, the initial volume of about 2.750×10 7 m 3, and eventually left in the text Ravine valley the total volume of up to 5×10 7 m 3 of deposits, the largest accumulation of thickness nearly 150m.2. The deposits at different positions of Wenjiagou rockslide - sturzstrom content in the particle diameter corresponding to its movement, as follows: levels of large diameter particles reduced with the elevation decline, and secondary particles content increased in diameter.3. Calculation shows that rockslide - sturzstrom can be divided into five stroke based on kinematic characteristics of the whole process of movement, and has undergone a process of acceleration, deceleration, then stop.The first stroke included the startup and acceleration of rockslide.The earthquake-induced rockslide initial speed was 8.32m/s.When the flight phase ended, sliding body was accelerated to 143.80m / s by the seismic force and gravity, then disintegrated and fragmented by the collision.According to the traces at the scene, the change of deposits characteristics, and the spatial relationship between the impact zones and the accumulation zones, this paper rebuilted the whole process and the path of the rockslide - sturzstrom.4. The movement eigenvalue of rockslide-sturzstrom is 0.326,which is a little bigger than normal high-speed long-range slides, it is the result of rockslide/sturzstrom had many collision, which caused kinetic energy lost, with Wenjiagou Valley.5. In the Wenjiagou Valley, the two boundaries of the rockslide and sturzstrom are relatively clear.In the semi-trap valley, the rockslide debris formed after the disintegration mixed with the air quickly, and constituted a two-phase aerosol systems with solid and gas (G-S system).And in that moment, because of debris material still had the high-speed, the mixed material could keep moving fast, to become the high-speed "dry sturzstrom."The gaseous components and four impacts reduced the motor capacity and speed of the sturzstrom, and stop at the entrance of the Wangjiagou Valley.6. The surrounding topography of Wenjiagou Valley made the strong seismic waves generated by Wenchuan Earthquake appeared "Stress Concentration Effect" in the mountain turnning parts and "Cutting-edge Amplification Effect" in the top of tall ridges, and this two effctes superimposed to produce "the topographical clustering effect on seismic energy " which controled the boundary of the source area of rock slide.7. The rockslide source area was a dip slope, which lithology is thick/middle-thick layer of limestone, dolomite rock.The rockmass of the slope was cutted into various sizes of the plate block by long-time cycly seismic force, and extraversion structural surface (including bedding plane) occurred "passivation" then lost cohesion rapid.The blocks of varying sizes of a part of broken rockmass jumped out under the coupling effect of seismic wave in the vertical and horizontal direction and thus have a "domino" effect, then caused the collapse of the whole rockmass.8. The statistical analysis of 66 landslide events shows that there is a higher connection between the volume and movement eigenvalue,and the former one dominated the maximum movement distance. The rockslide movement distance and the destruction area (rockslide area) have a high correlation.To the cases happened on the surface, the landslides with similar causes often have similar movement characteristics, but with similar movement characteristics of the landslides are unlikely to have a similar genetic mechanism.
|
PDF Full Text Request