Slope dynamic Geomorphology of the Mailuu-Suu area, aspects of long-term prediction

Abstract

Long-term monitoring and the analysis of stability of the slopes subject to landslides on the territory of southwest Tien Shan where loessial soils are common, show almost a constant speed of deformation (secondary creep) and accelerating/decelerating movement of unstable masses due to hydrological changes. Landslides can occur without any previous noticeable warning signs. Slow movement of slope cover in Paleogene-Neogene clays over 10 or more years creates the effect of accustoming local residents to the hazard. Under such circumstances, it is important and critical to rank slopes according to a hazard rating; the estimation of the remaining time to slope failure may serve as a criterion of the hazard. We have applied the Saito model coupled with a viscous model for ranking and classifying slopes of the large landslide-prone area of Mailuu-Suu. More than 200 landslides occurred in this mountain territory (~50 km2 in area) over the last 60 years. The reactivation of most paleolandslides is connected with intensive mining activity and urbanization. The proposed model is useful for short, mid and long-term predictions of secondary creep. The main factors in the prediction are slope steepness, steady-state moisture content of clay soils along its contact with the bedrock, a possibility of sudden and fast water table rise, and type of hydrogeological recharge. Thus local site maps were formed as a basis for detailed and systematic study of slopes, starting with the most dangerous ones with the shortest lifetime. It does not matter that long-term predictions remain uncertain due to change of hydrogeological conditions with time and soil degradation. Detailed study of such slopes is carried out for the latter. It is recommended to install automatic extensometers with telemetric transmission of landslide movement data on slopes with predicted life spans of 1-3 years.