Landslides (2019) 16:2017–2032 DOI 10.1007/s10346-019-01216-5 Received: 7 February 2019 Accepted: 29 May 2019 Published online: 22 June 2019 © Springer-Verlag GmbH Germany part of Springer Nature 2019 Saima Riaz I Gonghui Wang I Muhammad Basharat I Kaoru Takara Experimental investigation of a catastrophic landslide in northern Pakistan Abstract The territory of Azad Jammu and Kashmir (AJK) is vul- nerable to different natural hazards because of its proximity to a geo- dynamically active zone and its tropical and monsoonal climatic pattern. Both factors operate in various combinations and result in the occurrence of disasters generated by natural hazards like floods, earthquakes, and landslides at different intervals. There are numer- ous landslides in the study area, out of which the Donga Kass landslide has been selected for study due to its ongoing activity which poses a significant risk to the nearby community and infra- structure. Therefore, assessment of two possible triggering factors (i.e., earthquake and rainfall) for this landslide was conducted through the laboratory testing using the DPRI-5 Ring shear simula- tor. Undrained cyclic loading tests were performed to simulate the dynamic loading and earthquake-induced landslides, while pore pressure control tests simulated the rise of groundwater level during rainfall for rainfall-induced landslides. Based on the laboratory test results, a critical seismic acceleration and a critical pore pressure ratio are suggested for Donga Kass landslide. Using these values and combining with rainfall data and monitored pore water pressure in bore holes, early warning system can be activated to reduce any potential landslide risk in the future. Keywords Donga Kass landslide . 2005 Kashmir earthquake . Cyclic ring shear test . Pore pressure control test Introduction Landslides can be considered a symptom of fragility, either natural or human-induced. A small seismic shock in a sensitive moun- tainous system can cause a landslide (Hufschmidt et al. 2005). The 2005 Kashmir earthquake (M = 7.6) was among the worst ever event to hit the region of AJK, Pakistan. The geographical location of Pakistan and Muzaffarabad is shown in Fig. 1a, b, respectively. In the case of AJK, a highly seismotectonic system received a great shock resulting in massive landslide damage. According to Earth- quake Reconstruction and Rehabilitation Authority (EERA 2005), official death toll as of November 2005 stood at 87,350 out of which 26,500 fatalities were directly or indirectly related to landslides. Over time, a steady state will be reached once all active landslides reached to equilibrium stage through a reduction of slope angle or by exhausting all susceptible material (Hufschmidt et al. 2005; Petley et al. 2006). In the meantime, areas with cracks and active landslides will continue to pose a significant risk to communities. Khattak et al. (2010) have surveyed the entire AJK and reported that all landslides are located near rivers and roads. It is estimated that almost all landmass of AJK is vulnerable to rainfall and earth- quakes of different magnitudes which among other factors like deforestation, road construction etc. cause landslides on slopes. According to a study conducted by the Forestry Resource Depart- ment in AJK on existing damage, about 85% of landslides, upon failure, will have a direct impact on the infrastructure such as roads, electricity supply lines, houses, and rural pathways leading to vil- lages. There are numerous landslides in the study area such as Panjgran, Ghori, Dhanni, Sandok, and Shahkot Landslides that are some of the major landslides in terms of size and susceptibility. These landslides are frequently triggered by rainfall especially in the monsoon season which not only result in road closure and damage to private and public property but also loss of invaluable human lives. Muzaffarabad receives heavy rainfall during the monsoon season each year. The average rainfall for the Muzaffarabad is 1395 mm/year (average value from 2000 to 2017), with 30–60% in the form of snowfall during December– February, usually in the areas with an elevation more than 2000 m (AJK Planning and Development Department Report 2015). Figure 2a shows the annual rainfall patterns at Muzaffarabad station and cumulative number of landslides in District Muzaffarabad AJK, Pakistan from 2000 to 2017. Precipitation data was obtained from the Pakistan metrological department, Lahore office, and landslide data was taken from the planning and development department, AJK. Figure 2b depicts the monthly rainfall patterns at Muzaffarabad station and number of land- slides during monsoon season and dry season in District Muzaffarabad AJK, Pakistan from 2004 to 2008. It is shown that the monsoon season starts from July and ends at the end of August (heavy rainfall occurs with monthly extremes of up to 620 mm). In September, rainfall declines, and by November conditions are dry, with minimal rainfall of 30 mm/month. January to May is also dry months in the region. The data shown in the Fig. 2a, b depicts that even before the 2005 Kashmir earthquake, there were many landslides during the monsoon season of the year 2004. During Kashmir earthquake in October 2005 (Fig. 2a), a number of landslides were triggered during the earthquake despite the fact that earthquake was hit the region in the dry season and subsequently drastically increased during the upcoming monsoon seasons of years 2006, 2007, and 2008 which is also described by Saba et al. (2010) and Konagai and Sattar (2011) in their studies. Out of those landslides, Donga Kass landslide was selected for study due to its ongoing activity and impact on the infrastructures (i.e., the Neelum road and the Donga Kass bridge which is the only link to a nearby village and it had been adversely affected by the event of landslide activation, see Fig. 4e, f and also often blocked the pathway to the adjacent village). The risk of landslide in the study area had been recognized by landslide susceptibility maps by the government of AJK and also by some researchers after the 2005 earthquake; however, detailed study to fully understand the possible initiation and move- ment mechanisms of the landslides in this area has not been under- taken; hence, there was a need to assess the landslide risk in this area based on the detailed field and laboratory investigation. To elevate our precision in the risk assessment, this experimental study for the catastrophic landslide in Northern Pakistan is unique and provides basic information from the geotechnical point of view. Study area The Donga Kass landslide is located approximately 6 km to the north of Muzaffarabad city along the main Neelum Valley road. The loca- tion of the landslide is shown in Fig. 1b. It is bounded by longitude Landslides 16 & (2019) 2017 Technical Note Author's personal copy