ASCE 7-22 Section 11.8 and the International Building Code require a specific assessment of liquefaction potential in regions underlain by saturated, loose granular soils. In Nashville, this isn't just a bureaucratic exercise. The city sits within the New Madrid seismic zone's extended influence, and while Davidson County rests atop Ordovician limestone, the alluvial terraces along the Cumberland River and its tributaries—particularly in areas like the Nations or parts of East Nashville—contain loose sands and silts deposited by historic floods. The average depth to groundwater in these low-lying Nashville neighborhoods is often less than 15 feet, a condition that immediately triggers the need for a site-specific analysis. We run the evaluation using field data from CPT testing to capture continuous tip resistance and friction sleeve readings, which is far superior to relying on blow counts alone when you have to distinguish thin silt seams from truly liquefiable sand layers. For projects near the river, a seismic microzonation study becomes a logical complement, helping define the design acceleration for the specific Nashville site rather than defaulting to the USGS 2,475-year map value. The analysis follows the simplified procedure by Seed and Idriss, but updated with Robertson's CPT-based charts to fit the silty nature of our local deposits.
A fine-grained soil with more than 35% fines and a plasticity index above 12% is generally not considered liquefiable—a critical distinction in Nashville's silty river terraces.
