Theme Lecture – Seismic downhole arrays as a validation tool for computational analysis
S. Kontoe, Reader in Soil Dynamics, Imperial College London, UK
Dynamic Finite Element Analysis (DFEA) is a powerful tool for the design of geotechnical infrastructure under seismic loading, but any new computational developments require careful validation through experimental or field data to improve their reliability. Seismic downhole arrays are offering the opportunity to assess the performance of several aspects of DFEA under realistic conditions without some of the limitations often faced in experimental settings where simplified ground profiles are normally adopted.
The presentation will focus on carefully selected downhole data from KiK-net in Japan to assess the performance of a newly introduced cyclic nonlinear constitutive model for a deep deposit consisting of several materials, under multi-directional loading and for a wide of ground motion intensities. Starting with a comparison of nonlinear DFEA with conventional equivalent linear site response analysis tools, emphasis will be given on the correct application of the input motion accounting for the impedance contrast at the base downhole instrument. Then focusing on bi-directional analysis and making use of advanced post processing tools, the developed nonlinearity and associated energy dissipation as the waves propagate towards the ground surface through the different soil materials are captured in time domain. This allows to decouple the energy dissipated through shearing and through compression, as well as to identify the relative contribution of each material to the overall energy dissipation. The impact of the ground water modelling on the accuracy of bi-directional predictions is also emphasised through comparison with the field data. Overall, the findings provide guidance for the use of cyclic nonlinear models in DFEA under multidirectional loading and a steppingstone for more accurate three-dimensional predictions.