| We found Huilongqiao landslide group that are made of four large or giant landslides of millions or tens of millions in volume distributing in the lower reaches of Mengtunhe River. Huilongqiao landslide group caused a barrier lake. Due to pushing of Huilongqiao landslide group, this section of the valley is extremely narrow, but the upper and lower reaches of the valley is relatively wide. The upper reaches of the landslide group distribute an important plant and residential area in Xiamengxiang township, where the economy is relatively developed and the population is dense, so once the landslide group lose stability, the consequences will be unbearable to contemplate. In addition, landslides distribute both sides of the bank, producing relative sliping landslide group on the both banks of river, and the left bank, the right bank respectively is phyllite consequent slope and phyllite toppling rock slope. Therefore, genetic mechanism of Huilongqiao landslide group is worth studying. Based on the investigation and research of Huilongqiao landslide group's characteristics, discussing genetic mechanism and motion process of the landslide group has important theoretical and practical significance.Through field geological investigation, engineering geological survey, exploration on landslide Huilongqiao landslide group, we respectively clarify geological environment conditions and basic features of Huilongqiao landslide group, combined with drilling data, there is a main and detailed study on Huilongqiao landslide. Based on summarizing the common features of Huilongqiao landslide group, comparing with seismic landslides, we found the landslide group are seismic landslides. Combined with the main control factors, we analyzed genetic mechanism and motion process of the landslide group. Finally, take Huilongqiao landslide and Daping landslide for example, using UDEC, 3DEC to simulate the genetic mechanism and the movement process. Draw the following conclusion:(1) On the spatial distribution characteristics. The landslide group distribute on the both banks of Mengtunhe river, and concentrate in the area of about 2 km upstream and downstream of the river. Slip source areas of landslides on the right bank are higher than the river 300~700m, slip source area of Daping landslide on the left bank is higher than the river 112~310m, the river develeps a planation surface where is higher than the river 600~750m, landslides on the right bank distribute slope break,landslide on the left bank distributes gorge area; As slope is at the same time cut by Mengtunhe River, Zagunao River and Xiaogou, four landslides all develope in both sides of the thin ridge airpor.(2) On formation age of the landslide group. In the barrier lake, there is the first stage terrace, according to drilling data, slip surfaces of them are bedrock-cover discontinuity, it can be concluded that the the first stage terrace formed later than the barrier lake did, Huilongqiao landslide group formed earlier than the first stage terrace formed.(3) In terms of shape and scale.Huilogqiao landslide and Daping landslide are large landslides, Mozibao landslide and Kualiusha landslide are giant landslides. The minimum volume for Daping landslide, which is 216×104m3, the maximum volume for Kualiusha landslide, which is 1664×104m3; On landslide profile, mainly showing steep front convex, the middle and back part of landslides are relatively gently, the front part of landslides are cliffy because of Mengtunhe River.(4) In terms of boundary and structure characteristics. Huilongqiao landslide group have steep and rough landslide wall, the slope is 45 degrees to 50 degrees, lateral margins are also steep cliff, like Huilongqiao landslide; Anterior borders of Huilongqiao landslide group are in the river, slip surfaces are below the water surface. The accumulation body is mainly composed of crushed stone soil, block and detritus have large particle size, high content, littery structure, high density, gray to dark gray color; There are a lot of huge rock blocks in the front of landslides, that is, "false bedrock", showing of some the original rock structure. There are a large number of large grain size boulder in the front of landslides; Deposit along the sliding direction, and particle size was significantly increasing feature, the back is given priority to with gravel soil, central stone quantity increase gradually, the front has a large boulder piling up.(5) In kinematics and stability. Landslides' movement distance are about 1 km, the maximum movement distance is 1.2km, the minimum for Daping landslide, up 0.5km. landslide group formed for a long time, compaction better, through field investigation and quantitative calculation found good integral stability of landslide group.(6) High and steep topographic features of slope break or gorge area, soft phyllite lithology, anti-dumping, along the dip slope structure, in Longmenshan mountain fault zone seismic zone are the main control factors.(7) Huilongqiao landslide group centralized distribution, development groups, phylogenetic position of the high and steep topographic features of slope break or gorge area, large scale, boulder ejection, steep and rough slip wall, transport distance, and high stability are same as seismic landslides, this paper argues that the landslides are triggered by a earthquake.(8) Genetic mechanism of landslides on the right bank is different from the left one. Genetic mechanism of landslides on the right bank: rock phyllite produces toppling deformation and break to generate outside slope crack, slip in the earthquake under the action of cracking, speed down, the evolution process can be summarized as:the incised valley, slope unloading?the bending deformation of rock slope?rock slope toppling fracture damage?earthquake triggered slip crack, landslide damming four stages. Genetic mechanism of Dapinglandslide on the left bank :strong seismic force firstiy produced tension crack along the weak bedding plane(rock stratum), and then at the foot of the slope produced the shear layer as the sliding surface, generating tension-cracking and bedding sliding landslide.(9) UDEC, 3DEC were respectively used to simulate genetic mechanism and motion process of Huilongqiao landslide and Daping landslide', and study slope seismic dynamic response. And the results of the simulation is consistent with the field investigation. |
PDF Full Text Request