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The paper studies strike-slip fault rupture propagation through dense sand and its interaction with surface foundations, combining physical and numerical modelling. A series of centrifuge tests is conducted using a three-section split-box, which allows the modelling of two strike-slip faults per test. A free-field test is initially conducted, followed by four interaction tests. Eight different foundation configurations are studied, varying the foundation location, surcharge load, aspect ratio and rigidity. The experiments are numerically simulated employing three-dimensional finite-element modelling, combining periodic boundaries and a relatively simple yet efficient constitutive model, developed as part of this study. Based on a Mohr–Coulomb yield criterion, the model incorporates post-yield isotropic frictional hardening and softening (MC–HS). Carefully calibrated on the basis of triaxial tests, the model is validated against the centrifuge model tests, and exploited to derive further insights. The MC–HS model covers the entire range from elastic to fully softened response, capturing the deviatoric and volumetric behaviour of dense sand, and especially its pre-softening volumetric response, which is proven to be crucial for the simulation of the complex mechanisms of strike-slip faulting. Both physical and numerical modelling reveal the formation of diagonal shear ruptures at the ground surface (Riedel shears). These are complex helicoidal structures, formed due to the spatial variation of shear stresses. Foundation response is mainly governed by the kinematic constraint offered by its presence. Fault rupture locations close to its sides typically lead to a translational mechanism, whereas locations close to its centreline lead to a rotational one. Foundation rigidity is proven to be a prerequisite for the development of both mechanisms, which rely on the ability of the foundation to resist the developing normal and shear stresses.

All of us will never forget the year 2020. Those of us in higher education will perhaps reflect on the Spring 2020 semester as a turning point in our approach to education. To prepare higher education for future crises and to create a more buoyant, elastic, and resilient educational paradigm, it is imperative that we learn, right now, from the COVID-19 crisis. This is of particular importance for engineering education, which relies on experiential pedagogical practices that are incongruent with online learning environments. Since 2014, a multi-institutional interdisciplinary team has been addressing improvements to engineering education through mixed reality gaming, an educational model that integrates traditional classroom experiences (e.g., lectures, laboratory work) with virtual activities (e.g., game-based learning). We posit that a mixed reality gaming educational model may help mitigate the impact COVID-19-like crises. Herein, we reflect on implementations of a mixed-reality gaming activity in an introductory geotechnical engineering course on five campuses during the pivot to remote learning, which will be remembered as the hallmark of the Spring 2020 semester. Ultimately, the data gathered from these implementations will be used to study the effectiveness of mixed reality gaming on student learning outcomes (specifically, the ways in which student and instructor motivation shape and are shaped by this educational model) to understand (1) the role of mixed reality gaming;and (2) instructors' and students' motivational shifts during such crises. © ASCE.

This paper combines data from laboratory, centrifuge testing, and numerical tools to highlight the predictive capabilities of the Bayesian method for uncertainty quantification and propagation. The Bayesian approach is employed to estimate uncertain parameters of a multi-yield constitutive model using data from cyclic-triaxial testing. Then, predictive capabilities of a finite element model in reproducing the dynamic response of a saturated sand deposit are investigated by drawing samples from the estimated posterior probability distributions of the constitutive model parameters. Variability of the predicted responses due to estimation uncertainty is evaluated. The response of centrifuge tests is used to assess the simulated responses.

Preshaking by previous seismic activity can significantly affect the liquefaction resistance of saturated sands. Field evidence, cyclic laboratory testing and centrifuge modeling show that: (i) earthquake events that build up excess pore pressures short of liquefaction strengthen the soil; and (ii) liquefying earthquakes may weaken the soil. The paper presents the results of a centrifuge test (Experiment 2), where a 6 m saturated loose silty sand deposit was subjected to 52 successive base shakings. Three types of shakings were used: preshaking Events A, with a shaking duration of 5 cycles, and stronger Events B and C having a duration of 15 cycles, with Events C having the largest input accelerations. A total of 35 Events A, 9 Events B, and 8 Events C were applied at the base of the model in an alternating sequence. All Events C liquefied the deposit, with the Events B inducing liquefaction at the beginning but not at the end of Experiment 2. Events A generally induced excess pore pressures but not liquefaction. In addition to the pore pressures, horizontal accelerations, settlement and densification, and the soil shear wave velocity, Vs, were also monitored during the test. The results were compared with those of Experiment 1, reported in a previous publication, where a similar 6 m deposit of the same silty sand was subjected to a different sequence of shakings A and B which did not include any Event C. Conclusions are drawn on the effect of the strong Events C on the deposit's response. Events A, B and C of Experiment 2 are plotted on existing Vs –based liquefaction charts. The charts predict well the liquefaction response of the deposit at the beginning of Experiment 2. On the other hand, for shakings near the end of the test, the charts predict liquefaction for the Events B, which by this time have stopped liquefying the deposit due to the previous history of shakings. This result is consistent with the field evidence including the presence of a number of “false positives” in the charts for silty sand sites in the Imperial Valley of California, an area of intense seismic activity.

Several factors have led to the extended need for investigation of the static and dynamic behaviour of mine tailings and include the rising generation and surface storage of mine waste, its frequent use as a construction material for the retaining structures and the relatively high rate of associated failures, with seismic liquefaction being a rather common cause. In this experimental study, dynamic response and surface slope stability of a layered mine tailings deposit were examined by means of four centrifuge tests performed at the Center for Earthquake Engineering Simulation (Rensselaer Polytechnic Institute). The material under study was fine copper–gold tailings and the varying parameters were average degree of consolidation prior to dynamic loading and base acceleration amplitude. The material was found to be liquefiable and its performance in terms of acceleration, shear strain, slope stability, residual lateral deformation, pore-pressure build-up and liquefied depth was somewhat dependent on the aforementioned parameters. The response of the deposits changed with increasing depth and effective stress, which made centrifuge testing highly advantageous.

This paper explores the generation of harmonics of a monochromatic excitation frequency in the stress response of an excited soil deposit. The relationship between the level of nonlinearity in the soil and the generation of harmonics is investigated in terms of a simple hysteretic stress-strain model. Centrifuge tests of soil deposits subjected to base excitation are used to confirm numerical inferences. Effects of harmonics generation were also analyzed in nonlinear and equivalent-linear numerical simulations of an excited soil deposit. It is shown that the harmonics are present in both physical experiments and nonlinear numerical simulations, but cannot be captured by equivalent-linear analyses.

The paper presents the implementation of an identification technique to characterize the pore pressure behavior of a silty sand centrifuge deposit subjected to more than 70 seismic shakings with full pore pressure dissipation between shakings. The seismic shakings were meant to crudely simulate the seismic history of field deposits in some very seismically active zones in California. The technique estimates shear stresses and strains based on acceleration and pore pressure recorded using a vertical array of sensors in the deposit. A constitutive model was implemented to identify optimal material parameters controlling the contractive behavior of the soil based on the recorded response of all shakings. It was found that the seismic history of soil deposits plays an important role in determining the contractive tendency of the material, significantly influencing the pore pressure response of the deposit. That is, the seismic history can reduce or increase the resistance of a deposit to contraction and liquefaction.

This study investigated the dynamic response and liquefaction of level saturated-sand deposits subjected to biaxial shaking using a number of centrifuge tests. Dense and loose sandy soil deposits were built in a 2D laminar container and subjected to a series of biaxial base excitations that approximate in somewhat realistic fashion the conditions of a site subjected to earthquake shaking. A dense array of accelerometers and pore pressure sensors was used to monitor the deposit response. The recorded accelerations and pore pressures were employed along with a non-parametric identification procedure to estimate the corresponding dynamic shear stress-strain histories. In turn, these histories were employed to assess the effects of non-proportional loading on soil contraction and dilation mechanisms. Pore water pressure buildup was found to be affected by load non-proportionality and a direct function of the phase angle of the induced shear stresses. The loose and dense soil deposits had contrasting as well as similar response patterns.

This article presents numerical simulations investigating pore pressure buildup of a sand layer with a free drainage boundary at the top under both low and high overburden pressures and sub...

Game-based learning has long been heralded as a promise to transform education into a more engaging and experiential paradigm. Its implementation in engineering education has thus far shown that promise, yet more evidence is needed for widespread adoption. Our work focuses on issues of equity, inclusivity, and diversity, thus surfacing the question of whether game-based learning benefits each and every student. To date, these issues have not received much attention in game-based learning educational research landscape, despite its poignancy, given today’s global social climate and the systematic lack of equity and diversity in engineering education. With a focus on gender and race/ethnicity we reflect on the outcomes of implementing game-based learning environment in undergraduate geotechnical engineering courses (n = 362). We find evidence that game-based learning supports positive outcomes and provides an equitable learning environment. However, we also note several challenges that are further discussed.

The article presents simulations of the seismic liquefaction response of dense and loose clean Ottawa sand under low and high overburden in the centrifuge, using Program FLAC3D and the P2Psand constitutive model. P2Psand was initially calibrated in the paper with cyclic stress-controlled triaxial tests and then modified with information from two centrifuge experiments. The calibrated model was used to simulate four centrifuge tests covering relative densities from 45% to 80% and overburden pressures from about 100 kPa (∼1 atm) to 600 kPa (∼6 atm). The four numerical computations were fully coupled effective stress simulations that allowed for pore water pressure buildup and dissipation at every time step. The calibration yielded very good matches between numerical and experimental results in all four centrifuge experiments, and calibrated P2Psand input parameters are suggested for practitioners in similar clean sands. The simulations confirmed the increased diffusivity of the sand layer under high overburden obtained before from the centrifuge results. The reason is that P2Psand assumes that the sand bulk modulus is proportional to the square root of the mean effective stress, consistent with the similar conclusion derived from the centrifuge data by the authors. The calibrated P2Psand model was also used to perform “no flow” simulations of the same four centrifuge experiments, in which fluid flow was not allowed during or after shaking. No flow simulations are used sometimes in practice to reduce numerical effort, on the assumption that liquefaction in the field is mostly undrained. It was found that this assumption may produce useful engineering results for a low overburden of 1 atm, but it may become increasingly incorrect and too conservative at higher overburden. The reason is that for certain field conditions, fluid flow becomes more significant during shaking under high overburden due to increased sand diffusivity.

Liquefaction induced ground failures during seismic events have been of major concern to the engineering community. Laboratory, full-scale, and centrifuge experimentation has provided valuable insights on the mechanics and propagation of liquefaction. Concurrently, advances in the computational field have led to refined numerical tools to simulate the liquefaction phenomenon. In an effort to better evaluate the modeling capabilities, the Liquefaction Experiments and Analysis Project (LEAP) aims at providing numerical modelers with high quality experimental data that can be used in a series of prediction exercises. For this purpose, in early 2015 several centrifuge tests were conducted at different facilities all over the world and were followed by numerical simulations. This paper presents the centrifuge test that was conducted at the Center for Earthquake Engineering Simulation at Rensselaer Polytechnic Institute and discusses the modeling techniques that were employed in order to gain a variety of information on the soil response.

The Liquefaction Experiments and Analysis Projects (LEAP) is an international effort to produce a set of high quality test data and to then use it in a validation exercise of existing computational models and simulation procedures for soil liquefaction analysis. A validation effort (LEAP-GWU 2015) was undertaken using a benchmark centrifuge model of a sloping deposit tested in a rigid-wall container. This article presents and discusses the shear stress-strain responses and effective stress paths of the LEAP-GW 2015 centrifuge tests and numerical predictions (including an assessment of the effects of the rigid boundaries).

LEAP (Liquefaction Experiments and Analysis Projects) is an effort to formalize the process and provide data needed for validation of numerical models designed to predict liquefaction phenomena. For LEAP-GWU-2015, one project within LEAP, an experiment was repeated at 6 centrifuge facilities (Cambridge University, Kyoto University, University of California Davis, National Central University, Rensselaer Polytechnic Institute, and Zhejiang University) and the results were shared and archived for the purposes of validation of numerical models. This paper describes the specifications for the LEAP-GWU-2015 experiment and compares the experimental results from the six facilities. The specified experiment was for uniform medium dense sand with a 5 degree slope in a rigid container subject to a ramped, 1 Hz sine wave base motion. The experiment was meant to be relatively simple to enable different facilities to produce comparable experiments. Although it cannot be claimed that identical experiments were precisely replicated on different centrifuges, it is argued that the results are similar enough that each experiment lends veracity to the set of results. A benefit of variability between experiments is that the variety enables a more general validation. Important lessons with regard to specification of future experiments for validation of numerical models are summarized. LEAP-GWU-2015 has demonstrated an approach that is a useful reference for future validation studies.

The Liquefaction Experiments and Analysis Projects (LEAP) is an international effort to use experimental data from physical modeling at different (international) centrifuge facilities to validate soil liquefaction numerical models and analysis tools. The goals of LEAP-2017 experimental efforts are to assess the repeatability potential at each facility, the reproducibility of centrifuge tests among different facilities, and the sensitivity of the experimental results to variation of testing parameters and conditions. A number of tests of the same (sloping deposit) centrifuge model were repeated at Rensselaer Polytechnic Institute in 2015 and 2017. This paper focuses on two specific tests to assess and demonstrate repeatability at this facility.

This paper compares experimental results from every facility for LEAP-UCD-2017. The specified experiment consisted of a submerged medium-dense clean sand with a 5-degree slope subjected to 1 Hz ramped sine wave base motion in a rigid container. The ground motions and soil density were intentionally varied from experiment to experiment in hopes of defining the slope of the relational trend between response (e.g., displacement, pore pressure), intensity of shaking, and density or relative density. This paper is also intended to serve as a useful starting point for overview of the experimental results and to help others find specific experiments if they want to select a subset for further analysis. The results of the experiments show significant differences between each other, but the responses show a significant correlation, R2 ~ 0.7–0.8, to the known variation of the input parameters.

The experimental results of LEAP (Liquefaction Experiments and Analysis Projects) centrifuge test replicas of a saturated sloping deposit are used to assess the sensitivity of soil accelerations to variability in input motion and soil deposition. A difference metric is used to quantify the dissimilarities between recorded acceleration time histories. This metric is uniquely decomposed in terms of four difference component measures associated with phase, frequency shift, amplitude at 1 Hz, and amplitude of frequency components higher than 2 Hz (2 + Hz). The sensitivity of the deposit response accelerations to differences in input motion amplitude at 1 Hz and 2 + Hz and cone penetration resistance (used as a measure reflecting soil deposition and initial grain packing condition) was obtained using a Gaussian process-based kriging. These accelerations were found to be more sensitive to variations in cone penetration resistance values than to the amplitude of the input motion 1 Hz and 2 + Hz (frequency) components. The sensitivity functions associated with this resistance parameter were found to be substantially nonlinear.

The paper presents numerical predictions of excess pore pressure, liquefaction and settlement response of four centrifuge model tests of 6 m uniform deposits of saturated clean Ottawa sand, placed by dry pluviation and having a relative density ranging from 38% to 66%. The deposits were subjected to 1D uniform base shaking consisting of 10–15 cycles of peak acceleration ranging from 0.04 to 0.12 g. All predictions were conducted with the nonlinear effective stress numerical code Dmod2000. Significant effort was spent in calibrating Dmod2000 by matching the pore pressure and settlement measurements of the first shaking (S1) of a series of shakings conducted in centrifuge Experiment 3. This resulted in very good predictions of both pore pressures and settlement measured in this shaking S1. The exercise showed the importance for realistic simulations of having the correct soil compressibility and permeability. This calibrated version of Dmod2000 was used for a good pore pressure prediction of the preshaken deposit in the same Experiment 3 (S36), by modifying only one parameter in the undrained pore pressure model; and also well predicted pore pressure responses in Tests FFV3 and PFV1, without any change in the parameters of Dmod2000 except for use of the new input motions (Type B predictions). The experimental and numerical results showed that both cyclic shear stress/strains and upward water flow determine together the pore pressure buildup and liquefaction phenomena. The soil response is partially drained rather than undrained, and pore pressure dissipation does take place during shaking both before and after liquefaction occurs.

T-walls are pile-supported floodwalls commonly built in New Orleans. They are founded on long concrete or steel battered piles and include a sheet pile cut off for seepage and gradient control. Since soils in southern Louisiana contain soft and compressible silt and clay, these floodwalls need to be designed to resist flood loads and loads produced by consolidation of soft soil under the weight of new fill. In an attempt to develop a comprehensive T-wall design procedure that appropriately considers field conditions, the United States Army Corps of Engineers New Orleans District partnered with Rensselaer Polytechnic Institute and Virginia Polytechnic Institute and State University. A testing programme was developed to perform centrifuge tests that would provide insight into the mechanisms and magnitudes of settlement-induced bending moments and reliable datasets for validation of numerical models. This paper describes the experimental approach and presents two centrifuge tests with T-walls resting directly on clay. The bending moments on the battered piles significantly increased under the weight of the new fill. With settlement around the piles reaching values of 1·5 m, the bending moments at least doubled over the testing course, with maximum values observed at the top third of the pile length.

This paper presents an integrated experimental and numerical study of high-density polyethylene pipeline behavior under earthquake faulting that induces both bending and compression. The experiment...

The paper presents a series of centrifuge tests simulating a level site consisting of granular soil deposits subjected to various biaxial and uniaxial base excitations. The tests were conducted at RPI NEES centrifuge facility to assess the dynamic response characteristics of level deposits under multidirectional shaking. Synthetic sinusoidal waves were used as base excitations to test loose models under biaxial and uniaxial shaking. Dense arrays of accelerometers were used to monitor the deposit response along with pore water pressure transducers. Two uniaxial tests and one biaxial shaking test were conducted on three similar soil models to study the impact of multidirectional shaking on the generation of soil liquefaction. The two uniaxial shaking tests consisted of: (a) a test with input energy content using an Arias intensity similar to that of the biaxial input shaking and (b) a test with 10% increase in one of the components of the biaxial shake amplitude, as commonly done in practice for uniaxial simulation of multidirectional field shaking. The observed acceleration and pore pressure are used along with non-parametric identification procedures to estimate the corresponding dynamic shear stress–strain histories. The measured results along with the stress and strain histories obtained are used for two purposes: first, to shed light on the properties of liquefaction occurring through the stratum under uniaxial shaking; second, to show the difference in soil behaviour when it is subjected to biaxial shaking. The latter purpose is evident in the strain energy generated in the biaxial test compared to that of equivalent and traditional uniaxial tests.

This paper presents an identification technique to characterize the contractive and pore pressure behavior of loose sandy soils under seismic excitation. The technique relies on acceleration and pore pressure records provided during excitation by vertical arrays of accelerometers and pore pressure sensors. The technique employs non-parametric estimates of shear stresses and strains. A multi-surface plasticity approach is used to model the soil response. A reduced scale centrifuge model and a large scale experiment are used to demonstrate the capabilities of the developed technique. The technique allows for a more complete interpretation of the coupled shear–volume behavior of a soil deposit.

After catastrophic levee failures triggered by the 2005 Hurricane Katrina, concrete T-walls with batter piles are extensively used to enhance the integrity of levees in the New Orleans area. Since the foundation soils in this region typically include soft and compressible clays, T-walls with batter piles should be designed to account for bending moments and stresses induced by settlement. However, the current T-wall design procedure for estimating these settlement-induced bending moments (SIBMs) only takes a limited range of conditions into consideration. This paper presents results from a series of finite-difference numerical simulations to investigate the effects of various parameters on SIBM in pile-supported T-walls. The numerical model was first used to simulate a centrifuge test and upon comparison, a reasonable agreement was observed between the numerical simulation and experimental results. The numerical model was then used to investigate the effects of different parameters including pile connecti...

Accurate evaluation of soil dynamic properties is essential for seismic response analyses of sites. In a number of studies, site properties have been identified using one-dimensional analyses. Such analyses uncouple the two-dimensional (horizontal) response of soil deposits, which is inherently coupled. This paper presents a system identification technique that takes into account the coupled two-directional response of soil deposits. The technique employs non-parametric estimates of the shear stresses derived from acceleration records provided by a vertical (downhole) array. A multi-yield surface plasticity approach is used to model the multi-dimensional stress-strain relation. The identification technique is first verified using finite elements computational simulations. This technique was then used to assess the coupled response of the Wildlife liquefaction research site (Imperial Valley, California). The identified shear moduli and shear wave velocities were found to be in a very good agreement with those measured in the field using crosshole seismic testing.

The effect of preshaking and repeated liquefaction on liquefaction resistance was studied in a large-scale shaking table experiment, in which a sequence of 51 shakings was applied to the ba...

Two centrifuge experiments were conducted at Rensselaer Polytechnic Institute (RPI) to evaluate and assess the validity of the generalized scaling laws. The experiments were performed within the framework of the Liquefaction Experiments and Analysis Project (LEAP) and consisted of testing a saturated sloping deposit subjected to a tapered base input acceleration. The two tested models reflected consistent soil conditions but were built based on different scaling principles. The first model observed the conventional scaling laws for centrifuge physical modeling. The second model reflected the generalized scaling laws. The two tested models exhibited consistent response before liquefaction. The generalized scaling model showed a higher susceptibility to liquefaction and had a higher rate of pore pressure buildup.