Engineering geological assessments of the repeated plane shear slope instability threatening Babadag (Turkey) and its environmental impacts

Abstract

Babadag, in the Denizli province of Turkey, is one of the oldest textile industry settlements. The town has suffered from a very slow slope movement for about 60 years. One-third of the population lives in the unstable area. The slope movement resulted in significant ground deformations and damage to buildings, roads and buried utilities, and negatively affects socioeconomic life in the town. This paper contributes to the understanding of the long-term plane shear slope movement at the town, analyzes the main causes of the movement, and describes the slope instability and its effects. Movement occurs at an annual rate of between 3.8 cm and 15 cm along weak bedding planes in the alternating marl and sandstone beds forming the slope. Engineering geological assessments based on movement, groundwater and rainfall monitoring data, laboratory testing, and stability analyses indicate the following main factors contributing to the movement: (a) the unfavorable orientations and low shear strength of the bedding planes, (b) variations in the groundwater table related to precipitation and waste water seeping from the damaged sewage system, and (c) undercutting at the toe of the slope by a creek. Particularly due to fluctuations in the groundwater table or variations in pore pressures, the slope movement exhibits increasing and decreasing rates of movement without catastrophic failure.