400 g-ton centrifuge
The 400 g-ton centrifuge is the flagship of the CIEST geotechnical facility and is among the most powerful and second-largest geotechnical centrifuges in the United States. It was designed by Wyle Laboratories and fabricated by Alabama Dynamics and has been in operation since 1988. The machine features an asymmetrical rotor arm with a swinging payload platform on one end and a fixed counterweight on the other; with the platform fully extended, it operates at an 18-ft (5.49 m) radius and can accommodate payloads up to 4 × 4 × 3 ft (1.22 × 1.22 × 0.91 m) and 4,000 lb (17.8 kN). A 900 hp (671 kW) DC drive with a 6.4:1 right-angle gearbox accelerates payloads to 200 g in roughly 14 minutes, with pneumatically actuated disk brakes for emergency stopping, active in-flight balancing, chamber cooling, and dedicated real-time control and monitoring.
Dynamic testing on the 400 g-ton centrifuge is enabled by a servo-hydraulic earthquake actuator mounted on the platform and controlled with modern vibration-control software. This system is designed to reproduce high-frequency, high-amplitude base motions consistent with centrifuge scaling laws, allowing realistic seismic loading of soil and soil–structure models at high g levels and accurate replication of target acceleration time histories.
A modular NI PXI / SCXI data acquisition system with 30 channels provides high-rate, synchronized measurements from a wide range of sensors, including LVDTs, strain-gauge–type sensors, accelerometers, capacitance-type differential pressure transducers, and high-speed cameras, with motor-control channels available for servomotors, solenoids, and flow valves. In-flight digital imaging and image-based deformation tracking, originally developed on the instructional centrifuge, are routinely integrated with the 400 g-ton tests to capture detailed soil and structural deformations for subsequent inverse analysis and model calibration.
The 400 g-ton centrifuge works in concert with the suite of CIEST containers—laminar and flexible shear beam boxes for 1D shear response under shaking, rigid and reinforced boxes for 3D problems, cylindrical containers to minimize boundary effects, and tall or windowed containers for embankments, retaining systems, and structures requiring internal or side-view instrumentation. This combination of large radius, high payload capacity, versatile containers, and dense instrumentation allows system-level models of geotechnical and soil–structure systems to be constructed and monitored with the spatial and temporal resolution needed to study complex mechanisms such as liquefaction, ground improvement, embankment deformation, and soil–structure interaction under realistic loading histories.