Abstract

The Seymareh rock avalanche is in South of Pol-Dokhtar Township between Lorestan and Ilam provinces in SW of Iran. It is known as the largest rock avalanche in the world, and has created a lot of changes in morphology, hydrology and hydrogeology conditions in the N and NE Kabir Kuh Mountain. The creation of 3 landslide dams and its relative lakes include Jaydar in the North, Seymareh in the West and Gori Balmak in the East. The Jaydar dam is the largest of these dams. The Jaydar dam with the width, length and the height 2000, 11000 and 80 m, respectively was created on the Kashkan River and creates a lake with a length of 36 Km which is called Jaydar Lake. A sedimentary zone with an area of 65 Km2 with over consolidated and freshwater soils shows the extent of the lake. After an unknown time, Jaydar lake is drained by a natural spillway in this study based on field observation, the use of GPR, field and laboratory tests will be determined characteristics of engineering geology of dam and lake sediments of Jaydar, as well as the morphology of the area before the landslide. GPR results show that material deposited in the region have a thickness of more than 70 m that reaching to even 100 m. The results showed that the sediments in the region are often over consolidated fine grained includes low plasticity Clay (LL<30) and Clayey Sand (LL<25). The main part of the coarse grain is a GW-SW lens with cu=35, cc=1.6 and k=0.19 m/s with a thickness of less than 30 meters and depth of more than 20 m, which created a confined leakage aquifer. The results of the Crumb, double hydrometer and chemical tests showed that in study area CL and SC Soils has high potential dispersion. Studies show that the bedrock of lake  sediments is evaporates rocks (Gachsaran Formation) with joint set that filled by high dispersion soils. So, expect fresh water lake sediment of landslide dams will have the potential geotechnical problems such as dispersion, piping, collapse and land subsidence

Keywords: Seymareh rock avalanche; Landslide dam; Jaydar lake; Dispersion; Piping; Pol-Dokhtar; Gully erosion