بررسي زمين شناسي مهندسي و مهندسي ژيوتكنيكي علل رويداد زمين لغزش در ارتفاعات البرز، مازندران

An investigation of the engineering geology and geotechnical engineering reasons of landslides phenomenon in Alborz mountains, Mazandaran

Geologically, northern slope of Alborz Mountain is divided into Khazar plain and northern border regions based on structural and stratigraphic characteristics. In order to study the pushing movement of natural slopes, side slopes in cross sections and geological and geotechnical reasons of landslides in northern slopes of Alborz Mountains, three road axes of Ghaemshahr-Firozkoh, Sari- Kiasar and Rigcheshmeh- Dodangeh have been selected. These regions are formed mostly of eluvia] deposit like silty clay or clayed silt along with fine sand, which has a weak firmness. Flowage of water in the superficial layers, causes surface landslides along the slopes, so that thickness of slipped materials is about 6 to 7m . By analyzing the results of the soil mechanics tests, the causes of failure of landslide are explained. In general, layering of the soil stratum with respect to land slope and dip of soil layers, which are the effective causes of the trenches and embankment stability, are investigated. Limestone layers which are usually perpendicular to land slope, is the reason of increasing safety factor against landslide. In some regions, existence of water in superficial soil layers causes gradual failure or mud flowing. In this research, disturbance of draining water, caused by soil practices of road construction, leads to unstability and side slope sliding is also considered. Finally, shear stress to vertical stress ratio in drained and non-drained conditions are defined as [t/o-a]>=0.4and [t/o-a]>= 0.25 which can be used as quantitative criteria to forecast the occurrence of landslide.