Predicted and recorded ground-borne vibrations induced by the operation of two shaking tables at the new SOFSI research facility

This work explores the ground vibrations induced by the 31 tonne, 6 m × 4 m, 3-degree-of-freedom (DOF) large shaking table and the 1 tonne, 1 m × 1 m, 6-DOF, high-acceleration “Hexapod” shaking table of the Soil-Foundation-Structure Interaction (SoFSI) Laboratory, Langford Campus University of Bristol, UK. A monitoring scheme was deployed during the operation and the triaxial acceleration responses are recorded at several locations within the university campus. The instrumentation is installed at both free-field conditions and at selected locations on the upper floors of nearby buildings. Acceleration time histories are also recorded on the shaking tables to back up table motions recorded internally by the control system. The latter are used as an input for a refined three-dimensional numerical model of a multi-layered soil volume of 400 m × 400 m × 30 m around the SoFSI building, including the exact geometry of the reinforced concrete reaction mass. The numerical model confirms the attenuation patterns of ground vibration within the area of Langford Campus as observed during field measurements. Epistemic uncertainties are further reduced by validating the measured and simulated data against analytical calculations; the kinematic response of a rigid SoFSI reaction mass is approximated utilising direct steady-state dynamics while vibration attenuation with distance is assessed using the Borntiz exponential decay model. The outcome of this monitoring campaign establishes confidence on the wave propagation attenuation with distance and frequency, and forms the basis for a digital twin for predicting vibrations on the buildings around the SoFSI Facility during operations at maximum performance. Using predictions of probable ground/structure vibration levels at sensitive locations within the campus, operational envelopes of the SoFSI shaking tables are determined so that disruptions in surrounding facilities are avoided.