POST-DISASTER ASSESSMENT OF GEOTECHNICAL FAILURES IN BIHAR: LESSONS FROM FLOODS, EARTHQUAKES AND INFRASTRUCTURE FAILURES

Abstract

Bihar’s complex geotechnical landscape, underlain by alluvial plains, fragile embankments, and active seismicity, has repeatedly succumbed to mega-disasters that underscore persistent deficiencies in disaster preparedness and infrastructure resilience. This paper presents three prominent case studies- the 2008 Kosi Flood, triggered by a catastrophic embankment breach; the seismic events of the 1934 and 1988 earthquakes; and a spate of recent bridge collapses, exemplified by the alarming instance of 15 bridges failing within just two months. The 2008 Kosi Flood is scrutinized with reference to maps delineating the Kosi river course, embankment layouts, and soil profiles highlighting loose silt and expansive clays. The embankment breach is attributed to overtopping, inadequate maintenance, and fundamentally unstable foundation soils. Consequential inundation displaced over two million people across multiple districts, destroyed homes, agricultural lands, and hindered access to essential services. Earthquakes of 1934 and 1988 are examined through tectonic maps, soil liquefaction zones, and ground-shaking intensity distributions. Amplification of seismic waves through soft alluvial soils intensified structural damage, causing widespread building collapse, loss of life, and long-term infrastructural disruption. Sensitivity and historical consistency analyses confirm that the DSVS framework given in the study is robust and capable of capturing district-level spatial patterns of seismic vulnerability. This paper identifies underlying factors across these disasters: heterogeneous and weak soil strata, dynamic river morphology and systemic maintenance lapses. It further highlights future high-risk zones in Bihar, such as the lower Kosi, Gandak, and Bagmati basins, where similar soil types, river behaviour and infrastructure exposure suggest potential for recurrence. The research concludes by advocating for reinforced geotechnical monitoring, embankment rehabilitation, seismic resistant design standards, real time riverbed and scour surveillance, and prioritized investments in vulnerable corridors. These measures are posited as critical components of an integrated, future ready post disaster management framework for Bihar.