Study On The Formation Mechanism And Stability Of The Suwalong Landslide In The Upper Jinsha River

The Suwalong landslide is located in the Batang-Zhongza reach of the upper Jinsha River, at the southeast margin of the Tibetan Plateau where tectonic activity is very strong and geological environmental is very intricate and has formed a great deal of large paleolandslides or their relicts in the river valley. Studying the formation mechanism, stability and its possible development trend of paleolandslides can provide scientific basis for the layout of major projects in the region.Based on the results of field geological investigation, field measurements and indoor experiment and predecessors’ research findings, this paper has carried on the preliminary research on the spatial distribution of landslides, lacustrine sediments, formation mechanism and destruction characteristics of the Suwalong landslide. Then using FLAC3D software of numerical simulation analysis method studies the stability of the landslide under the condition of natural condition, heavy rain condition and earthquake condition. The conclusions are as followings.(1) The Suwalong landslide is a large rock landslide, and has formed dammed lake after it reached the other side of the Jinsha River. The forming times of the landslide and its surrounding relict lake deposits were studied by using 14C dating and OSL dating. The minimum age of the Suwalong landslide blocking the Jinsha River was shown to be about 1355 yr BP, and those of its surrounding two platforms of lacustrine sediments were shown as 1.8 and 1.3 ka BP.(2) The recordings of two kinds of the soft-sediment deformations (namely the Liquefied convolution bedding and ball-and-pillow structure) are found in the surrounding dammed lake deposits, thus providing substantial evidence for the existence of the paleoseismic events no less than MS 5 in the region under the formation process of lake deposits. It can be inferred that the Suwalong landslide may have been triggered by a paleoearthquake or combination of paleoearthquake and rainfall events.(3) The characteristics and forming times of the landslide-dammed lake deposits around the relict Suwalong landslide dam reveals that the large-scale landslides in the Batang-Zhongza reach of the upper Jinsha River were formed during numerous periods, namely the large-scale landslides may have been triggered by several paleoearthquake events (occurring at around 1900,1355, and 1115 yr BP), indicating that the Jinsha River faults in the area may have been quite active since the late Holocene.(4) The strong geological dynamic action and favorable structural planes are the important condition for the formation of the Suwalong landslide. We can infer that the deformation and failure process are as follows: the formation of stretched fractures on the trailing edge, the fractures are deepened and lengthened, the leading edge of the slope are shear failure, the mountain shatters, the formation of sliding surface, quick sliding, dammed the Jinsha River.(5) Using the FLAC3D software of numerical simulation analysis method studies the stability of the landslide, the results shows that the Suwalong landslide is stable under the natural condition and heavy rain condition, however it will be destroyed under the given earthquake condition in the paper.