Soil liquefaction in Kathmandu valley due to 25 April 2015 Gorkha, Nepal earthquake

The April 25, 2015 Gorkha earthquake (MW 7.8) affected central Nepal and neighboring areas. Kathmandu valley witnessed severe damage in terms of structural collapse and casualties. Apart from this, soil liquefaction in the form of sand blows and lateral spreading were observed in 12 locations. Soil liquefaction in Kathmandu valley during 1934 (MW 8.1) earthquake was believed to be one of the major cause of damage in structures and lifelines but detail records are not available. To fulfill the gap of documentation in case of strong earthquake events like the Gorkha earthquake, field reconnaissance and collection of samples from each sand blow location have been carried out. In addition to this, numerical analyses based on geotechnical investigation records for seven locations that manifested sand blows have been performed. Common approach of liquefaction susceptibility analysis based on standard penetration resistance is found to be consistent with the surface manifestations. Our comparison between existing susceptibility maps and results of numerical analyses as well as field evidence concludes that the existing susceptibility maps are unrepresentative.