GEOLOGICAL ENGINEERING EVALUATION OF LANDSLIDES IN THE SOUTHEASTERN BANGLADESH

Bangladesh is prone to numerous natural disasters, including floods, cyclones, storm surges and earthquakes. In recent years, landslides have become a prominent geological hazard in the southeastern region due to modification of natural slopes, deforestation, urban expansion and prolonged torrential rainfall. During the last 2–3 decades the frequency of devastating landslides has sharply increased, which has resulted in deaths of hundreds of people and significant loss of property. In South-Asia, Bangladesh ranks first in terms of landslide-related deaths. Understanding of landslide processes has become essential for disaster management and sustainable development. Geo-engineering evaluation of landslides in the region has recently been completed for Chittagong, Cox’s Bazar, Rangamati, Bandarban, Teknaf and Moheshkhali Island. The landscapes of these urban clusters are formed by dissected hills and valleys in a tectonically active region. Hills and slopes are underlain by young folded and faulted sedimentary rocks. Folds trend NNW-SSE and rock units are highly fractured, jointed and commonly distorted. Stratigraphic formations most susceptible to mass movements are the Dihing, Dupi Tila, Tipam and Boka Bil Formations. Slope movements in the region are classified as: lateral spreading failures, rotational and translational slides, and planer slides. Man-made slides are classified as rock fall and debris avalanches and are considered to be the most devastating types of mass movement.

For this investigation, rock masses were characterized by following ISRM suggested method and Slope Stability Probability Classification System and divided into eight geotechnical units. The present study reveals that contributing factors to landslides in this region include attitudes of bedrock units, faults and other discontinuities in rock formations, shear strength properties of constituent materials, and unusual hydrological conditions. Increase in the human interference has become a major factor in the slope failures. Landslides in the southeastern Bangladesh can be reduced when proper slope design and management are applied, and a monitoring system for geotechnical control is developed.