11. Assessment of Liquefaction Potential of Bridge Site Located at Koyalajan Kamla River in Rasalpur and Koyalajan Road, Bihar

In seismically active zones like bridge project sites located at Koyalajan Kamla River in Rasalpur and Koyalajan Road at Block Biraul, Bihar, India structural safety necessitates assessing liquefaction potential. An analysis for a bridge project in these areas, located in seismic zone V, revealed vulnerability due to a previous magnitude 7.5 earthquake with peak ground acceleration (PGA) of 0.36. With groundwater near the surface, two 50-m boreholes were drilled to evaluate site-specific conditions and assess the likelihood of liquefaction. The soil's liquefaction susceptibility was assessed using the Standard Penetration Test (SPT), measuring N-value and fines percentage in line with IS 1893-2016 Annexure-F guidelines for liquefaction potential analysis. The soil investigation report indicated that the site mainly consists of poorly graded silty sand with medium to very dense characteristics (SM). Given the significant foundation load, a well foundation was deemed necessary, and the gross allowable load-bearing pressure at the well tip for bridge abutments and piers was recommended in a range from 85 to 90 T/m². The study's methodology highlighted the importance of being cautious and attentive as the analysis indicated that liquefaction is likely to occur up to 11 m depth below the ground level.