GEOTECHNICAL INVESTIGATION AND CHARACTERISTICS OF SEISMICALLY INDUCED BOTHA LANDSLIDE, MUZAFFARABAD, AZAD KASHMIR

Abstract

The Muzaffarabad city is in the north of Pakistan and is the part of Sub-Himalaya of Himalayan region with an area of about 1324 Km2 which host the total population about 0.65 million inhabitants (Planning and Development Department, 2015). There was a historic destruction in 2005, caused by a seismic activity with a recorded magnitude of 7.2. This earthquake was disastrous to human life and infrastructure as well as to the geology of the region, it produced hundreds of large scale and small scale landslides in the region. After the Earthquake many researchers did case studies on different areas of Kashmir and many large scale landslides were investigated. Botha landslide is a seismically induced landslide of the 2005 Earthquake, lies in the northeast of the city. Botha landslide was lacking a detailed geotechnical investigation. In this research work, a detailed geotechnical investigation is carried out in order to find out its failure mechanism and geotechnical characteristics. This study includes field surveys, soil sampling, geotechnical mapping and laboratory evaluation of soil samples. Stratigraphically, the landslide is highly disturbed and contains mixed transported material Paleocene- Eocene sequence. Tectonic condition was also observed in the field and a parallel splay fault was marked on the left flank that is produced as an effect of Muzaffarabad fault activity. Landslide was marked in three zones for better understanding (Depletion zone, Transition zone and Accumulation zone). Laboratory evaluation includes grain size distribution (Sieve analysis), Atterberg limits (Liquid Limit, Plastic Limit) and Standard compaction test (Proctor Test). The laboratory test procedures are performed carefully as per ASTM standards. Grain sizevii distribution of the samples shows that the soil of Botha landslide ranges from mediumcoarse sand to fine-medium gravel. The plasticity index of soil came out to be 5%. The moisture content from standard compaction test gave the values ranging from 8.9% to 12.8% whereas, the dry density value ranges from 1.71 g/cm3 to 1.82 g/cm3.The plasticity index shows the low plasticity of the soil. Botha landslide is hazardous to its surrounding inhabitants and needs a proper attention of the authorities. Slope terraces and major vegetation should be applied to avoid any land loss or road blockage.