Research On Development Characteristics And The Formation And Evolution Process Of Mahu Landslide Group

Mahu landslide lies in the town of Huanglang of Leibo county of Liangshan prefecture of Sichuan province, formed many giant landslides in many times under the action of strong earthquake motions, formed weir dam and barrier lake by the recent active was kept intact, was the best place of resolving of historical earthquake landslide.Mahu landslide group were formed from Duimen mountain, their accumulation body covered the entire town of Huang-lang. from south of Mahu Lake Haikou, north to Chejiawan(Sanjiawan), west of Kuanghaiba, east to Xiaheba. The average thickness of the landslide accumulation body was about 100 m. Inferred by exposed body, the total volume of the landslide accumulation body were nearly 20 billion m3. Landslide showed trough and ridge topography after stack, river erosion, human transformation and other factors.In this paper, Mahu landslide group as the research object, on the basis of geological investigation, data collection and analysis, expounds in detail the engineering geological condition of landslide, which generalized the landslide formation geological conceptual model. This article will fall Mahu landslide group of deposit according to its development stage, and detailed description and analysis. According to the characteristics of the deposit of each period of time and development mechanism of origin of Mahu landslide group, and the inversion of landslide group and landslide area landform development and evolution process. Finally, use discrete element software to simulate landslide movement process numerical simulation. Main conclusion and cognition as follows:1) There was five times of landslide happened with five seismic events, the landslide formation modes of the all of the landslide group was the vibration crack planar block slip. Mahu landslide group was caused by the action of earthquake and the following factors:(1) was located in the multiphase tectonic superposition parts;(2) as the result of the incision of Guhuanglang River was because of the rapid incision of Jinshajiang River since the pleistocene epoch of Quaternary period;(3) the existence of weak intercalations weaken the bonding force between the layers of rock mass;(4) the transverse crack and the longitudinal crack produced by the Chengqiangyan anticline and Bajiaoyan anticline weaken the integrity of rock mass;(5) the superposition effect of action of seismic wave of the terrain amplification.2) The formation of Mahu landslide group had a series of laws, and their slide source area was like that peeling off the skin of the onion, happened slide failure one layer by one layer. Because of ancient times dammed Guhuanglang River by Mahu landslide group, prompting the change direction of the river many times, and forming the nowadays Mahu Lake of and the landscape of trough valley and low hills and shallow hill. Drainage ways of Mahu Lake was mainly for the "dam seepage", the basic balance of supply and drainage of Mahu Lake, making the Horse Lake extant today. Because the seepage of the lake, the north of the dam formed depressions trough topography. The component of the pile of the fourth landslide was limestone gravel and soils, formed the Dianziping depression and Ganchitang depression by dissolution obvious, which also developed erosion funnel.3) The numerical simulation of landslide movement with UDEC, can draw landslide motion feature.(1) Start-up Stage, when the 2-6s, the landslide suddenly started, the starting speed of 1m/s.(2) Start-Acceleration –Departure Stage, After the starting of the landslide, landslide accelerated to maximum speed of 67m/s in the 6-30 s, this time completely out of the slip source of landslide, this speed could be approximated as the upper limit of the speed of departure landslide, landslide the whole process is accelerated to slide the maximum speed 72 m / s in the 30-40 s.(3) Deceleration Climbing Stage, the hampered landslide started climbing when 40 s, the velocity of the landslide gradually became smaller, and stabilized at the time of 70 s.(4) Stable Stage, landslide halt when 70-100 s, the migration of the overall landslide is 2.4km, the sliding distances of the leading edge of landslide was about 2~2.4km,the sliding distances of the central of landslide was about 1.5~1.7km, the sliding distances of the top of landslide was about 1.2~1.6km.