Evaluation of One-Dimensional Site Response Techniques Using Borehole Arrays: Fid-Bau Portal

Evaluation of One-Dimensional Site Response Techniques Using Borehole Arrays

Zalachoris, Georgios / Rathje, Ellen M.

Numerical techniques commonly used to compute the dynamic response of soil deposits under earthquake shaking are investigated by analyzing data from instrumented borehole arrays. Eleven instrumented vertical arrays are investigated using over 650 recorded ground motions that span a range of shaking intensities. Based on data from the selected borehole arrays, site response predictions using one-dimensional equivalent linear (EQL) analysis, equivalent linear analysis with frequency-dependent soil properties (EQL-FD), and fully nonlinear (NL) analysis are compared with the borehole observations. The results across all sites indicate that at peak shear strains less than about 0.1%, all three site response techniques predict, on average, site amplification within $\pm 20 %$ of observed. At peak shear strains larger than 0.1% and at periods less than about 0.4 s, EQL and NL analyses underpredict site amplification and EQL-FD analyses overpredict site amplification. The underprediction for the EQL and NL techniques may be as large as 70–75% when the shear strength is not considered in the assignment of the shear modulus reduction curve, and the underprediction may still be as large as 55–65% when the shear strength is considered. Over the same period range, EQL-FD analysis overpredicts site amplification by as much as 75% at shear strains larger than 0.1%. These results indicate that one-dimensional site response techniques do not accurately predict site amplification at shorter periods and large strains.