Recently natural hazards like earthquakes, landslides, subsidence, glacier bursts and flash floods have severely impacted Himalayan cities, including Joshimath, Uttarakhand. In January 2023, significant ground cracks were observed, leading to the evacuation of nearly 800 buildings. This study investigates the underlying causes of ground failure and building damage through various geotechnical and geophysical tests at 12 sites in Joshimath, including plate load test, dynamic cone penetration test, field direct shear test, multi-channel analysis of surface waves and horizontal-to-vertical spectral ratio. Soil samples are analyzed for natural moisture content and grain size distribution. There is large heterogeneity in the test results which are highly variable. The field tests indicate the soil fabric of Joshimath is a complex mixture of boulders, gravels and soil. Internal erosion in such soils causes the instability of the whole fabric and results in the readjustment of the boulders resulting in subsidence. Internal erosion, driven by subsurface drainage from rainwater, ice melting and wastewater discharge, destabilizes the soil matrix and causes subsidence. It has also been observed that even at greater depths, no clear uniform strata is present and similar heterogeneous strata extend. Lower shear strength and bearing capacity are observed at several sites, potentially contributing to building damage. The study emphasizes that individual test results alone may not adequately capture site conditions. Instead, a combination of multiple test results is essential for a comprehensive assessment. Based on the test results, a vulnerability map of the area is presented.

来源平台：INDIAN GEOTECHNICAL JOURNAL