An Integrated Geomechanical Investigation, Multi-Parameter Monitoring and Analyses of Babadağ-Gündoğdu Creep-like Landslide

A creep-like landslide in the Gündoğdu district of Babadağ town in Denizli (Turkey), where about 2000 people lived within the damaged houses, has been moving with a velocity of 4–14 cm/year since 1940s. Field observations and monitoring together with geomechanical laboratory tests were carried out to investigate the causative factors of the landslide. These studies were conducted as a part of an international research project performed by Turkish and Japanese scientists since 2000. Long-term monitoring stations established involved measurements of meteorological parameters, displacements, acoustic emission counts, variations in groundwater table, borehole strain measurement, in situ permeability and infiltration characteristics of the slope forming materials, and vibrations induced by weaving machines during their operation. Geomechanical properties of the sandstone and marl, which form the unstable slope, were determined from laboratory tests. In addition to the use of conventional 2-D equilibrium method of analyses, a new approach for modelling the long-term creep-like behaviour of the landslide body, based on discrete finite element method, was also proposed and used to analyse the landslide. It was found that the sliding mass has been involving several zones of weakness (interface) between the sandstone and marl layers through in situ monitoring. The monitoring data of pipe strain, groundwater level fluctuation and rainfall, and AE data showed that slope movement accelerated during and after rainy seasons. It was obtained that the proposed numerical method based on discrete finite element method (DFEM), which considers the softening and hardening of stiffness of the weakness zone as a function of rainfall and, is capable of simulating creep-like behaviour of the landslide. Disaster and Emergency Management Authority of Turkey also considered the results of this research and the landslide area was designated as a Natural Disaster Area and the people living in the unstable part of the town were re-settled at a new area.