The 9-m and 1-m radius geotechnical centrifuges at the Natural Hazards Engineering Research Infrastructure (NHERI) facility at the University of California at Davis provide the national research community with open access to unique and versatile modeling capabilities for advancing methods to predict and improve the performance of soil and soil-structure systems affected by earthquake, wave, wind, and storm surge loadings. Large-scale centrifuge models are particularly effective for the building of basic science knowledge, the validation of advanced computational models from the component to the holistic system level, and the validation of innovative soil remediation strategies. The capabilities and unique role of large-scale centrifuge modeling are illustrated using three example research projects from the shared-use NHERI facility. Education impacts stemming from operations activities and coordination of activities by the center’s user base are discussed. Future directions and opportunities for research using the NHERI facilities are discussed.

Liquefiable soil-structure interaction material models are developed and implemented in the open-source finite-element modeling platform OpenSees. Inputs to the free end of the p-y materials include the ground motion and mean effective stress time series from a free-field soil column. Example simulations using a single p-y element attached to a soil element demonstrate key features. The models are then used to analyze centrifuge experiments of a single pile in a level liquefiable profile and a six-pile group in a sloping liquefiable profile that resulted in lateral spreading. Measured displacements and mean effective stress time series are used as inputs to isolate the response of the material models from predictive uncertainties in free-field ground motion and excess pore pressure. The predicted pile response agrees reasonably well with measurements. The cyclic mobility behavior of sand in undrained loading is shown to be an important mechanism affecting bending moments in the piles; neglecting the dilatancy component of the sand's response (i.e., ignoring the cyclic mobility behavior) can result in underprediction of the demands imposed on the piles. © 2013 American Society of Civil Engineers.

Equivalent-static pushover analyses with a three-dimensional (3D), nonlinear, finite-difference model are used to investigate the static and seismic stresses imposed on soil-cement grid reinforcements in soft clay profiles by overlying structures supported by shallow footings. The goal is to evaluate the potential stress concentrations in the soil-cement grid during foundation rocking and the potential for large foundation settlements associated with the local crushing of the soil-cement. The numerical analyses are first validated using data from dynamic centrifuge experiments that included cases with and without large foundation settlements and localized crushing of the soil-cement grids. The experimental and numerical results indicate that the stresses imposed on the soil-cement grid by the overlying structures must account for foundation rocking during strong shaking and stress concentrations at the soil-cement grid intersections. The numerical analyses provide reasonable predictions of the structural rocking loads and the zone of the expected crushing or lack of crushing, but underestimate the accumulation of foundation settlements when the seismic demands repeatedly exceed the soil-cement strength. The simulated moment-rotation and uplift behavior of the footings under monotonic lateral loading are reasonably consistent with the dynamic centrifuge test results. Parametric analyses using the validated numerical model illustrate how the stress transfer varies with the area replacement ratio, the thickness of the top sand layer, the properties of the bearing sand layer, and the relative stiffness of the soil-cement and the surrounding soil. A design model for estimating the stresses imposed on a soil-cement grid by rocking foundations was developed and shown to provide a reasonable basis for assessing whether or not local damage to the soil-cement grid is expected.

A set of saturated Ottawa sand models was treated with microbially induced calcite precipitation (MICP) and subjected to repeated shaking events using the 1-m radius centrifuge at the UC Davis Center for Geotechnical Modeling. Centrifuge models were constructed to initial relative densities (DR0) of approximately 38% and treated to light, moderate, and heavy levels of cementation (calcium carbonate contents by mass of approximately 0.8%, 1.4%, and 2.2%, respectively) as indicated by shear wave velocities (light≈200 m/s, moderate≈325 m/s, and heavy≈600 m/s). The cemented centrifuge models were compared to a pair of uncemented saturated Ottawa sand models with initial DR0≈38 and 53% and subjected to similar levels of shaking. Cone penetration resistances and shear wave velocities were monitored throughout shaking to investigate (1) the effect of cementation on cone penetration resistance, shear wave velocity, and cyclic resistance to liquefaction triggering; and (2) the effect of shaking on cementation degradation. Accelerometers, pore pressure transducers, and a linear potentiometer were used to monitor the effect of cementation on liquefaction triggering and consequences. Cone penetration resistances and shear wave velocities were sensitive to light, moderate, and heavy levels of cementation (increases in penetration resistance from 2 to 5 MPa, from 2 to 10 MPa, and from 2 to 18 MPa and increases in shear wave velocity from 140 to 200 m/s, from 140 to 325 m/s, and from 140 to 660 m/s, respectively), and were able to capture the effects of cementation degradation.

This paper describes a centrifuge study undertaken to investigate how sand gradation affects the system-level performance of embankments subjected to strong shaking. Current analysis and design practices are primarily based on knowledge from case history records of liquefaction, with the majority of those from sites consisting of clean, poorly graded sands. The narrow range of gradation characteristics represented in the case history database poses a challenge during the analysis of embankment structures traditionally constructed with, or founded on, more broadly graded soils. The tests herein were designed to elucidate how embankments uniformly constructed with a well graded and poorly graded sand perform differently during earthquake shaking. A centrifuge experiment test program was developed and conducted using the 9-m-radius centrifuge at the UC Davis Center for Geotechnical Modeling. The experiment design consisted of two submerged 10-degree embankments positioned side-by-side in the same rigid model container, with one embankment constructed with poorly graded sand and the other with well graded sand. The embankments were dry pluviated to the same relative density, but the absolute densities of the sands were different. The embankments were identically instrumented with dense arrays of in-situ sensors beneath the level ground above the slope and in the mid-slope to measure the dynamic response during liquefaction. Results showed that embankments constructed at equal relative densities would both liquefy (i.e., ru reach 1.0), but deformations were less severe for the embankments constructed with the well graded sand. Greater resistance to the generation and faster dissipation of excess porewater pressures, coupled with stronger dilatancy of the well graded sand increased embankment stability, curtailing liquefaction-induced deformations.

We present a system that visualizes displacement, acceleration, and strain that were measured during an earthquake simulation experiment in a geotechnical centrifuge. Our visualization tool starts by reading the data describing experiment set-up and displaying this data along with icons for the sensors used during data acquisition. Different sensor types (measuring acceleration, displacement and strain) are indicated by different icons. One general experiment set-up is used in a sequence of simulated earthquake events. Once a user has selected a particular event, measured data can be displayed as a two-dimensional (2D) graph/plot by clicking the corresponding sensors. Multiple sensors can be animated to obtain a three-dimensional (3D) visualization of measured data.

The Center for Geotechnical Modeling at UC Davis operates a 9.1-m radius geotechnical centrifuge equipped with a 2 m x 1 m servo-hydraulic shaking table. This equipment has been used in geotechnical earthquake engineering research since 1994. In October 2000, UC Davis was selected as a host equipment site on the National Science Foundation's George E. Brown, Jr., Network for Earthquake Engineering Simulation. This four-year upgrade project represents a $5M investment in the UC Davis centrifuge facilities by NSF with an additional $1M from UC Davis. NEES at UC Davis capitalized on the size of the centrifuge and innovations in instrumentation and information technology to enable generation of higher resolution information (control, sensors, and images) and to create more realistic physical models. With NEES the Center for Geotechnical Modeling is working to implement advanced instrumentation, digital video, robotics, and geophysical testing to increase the quality and quantity of data that can be collected; to increase the capacity of the centrifuge; and to develop a biaxial shaking capability. These improvements will allow us to extract more detailed and more accurate information from experiments and simulations, maximizing the information and knowledge that can be gained from these experiments. The Center for Geotechnical Modeling facilities are intended for use by researchers from academia and industry, from both the US and abroad. The centrifuge at UC Davis will be a shared-use facility under NEES, with experiments being performed by teams of researchers. New hardware and software developments are currently being implemented as part of the NEESgrid System Integration project. These new resources will allow teams to collaborate regardless of their physical location. Remote researchers will be able to control their experiments at UC Davis as easily as local researchers. Further information about the UC Davis NEES site can be obtained at http://nees.ucdavis.edu, or by email to cgm@ucdavis.edu.