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1. Comparison of Seismic Compression Procedure Predictions: Case History from Japan

   Green, R.A. and ( September 2020 , Proc. 17th World Conference on Earthquake Engineering)

   null (Ed.)

   Seismic compression is the accrual of contractive volumetric strain in unsaturated or partially saturated sandy soils during earthquake shaking and has caused significant distress to overlying and nearby structures, to include the 2007, Mw6.6 Niigata-ken Chuetsu-oki, Japan earthquake. Of specific interest to this study is the seismic compression that occurred during this event at the Kashiwazaki-Kariwa Nuclear Power Plant (KKNPP) site. What makes this case history of particular value is that the motions at the site were recorded by a free-field downhole array (Service Hall Array, SHA) and the magnitude of the seismic compression was accurately determined from the settlement of soil around a vertical pipe housing one of the array seismographs. The seismic compression at the site was ~10-20 cm. The profile at the site was well characterized by in-situ tests and laboratory tests performed on samples from the site, which allows seismic compression models to be calibrated. The study presented herein compares the predictions of the simplified and non-simplified forms of the expanded Byrne model. The predictions are in good accord with field observations, but the slight under-prediction by the non-simplified model may relate to estimated soil properties, assumed orientation of the ground motions and accounting for multidirectional shaking, and/or the numerical site response analyses used to compute the variation of the shear strains during shaking at depth in the soil profile. 

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2. Influence of Ground Motion Orientation on Predicted Seismic Compression

   Green, R.A. and ( April 2020 , Proc. New Zealand Society of Earthquake Engineering Annual Conference 2020 (NZSEE 2020))

   null (Ed.)

   Seismic compression is the accrual of contractive volumetric strain in unsaturated or partially saturated sandy soils during earthquake shaking and has caused significant distress to overlying and nearby structures. The phenomenon can be well-characterized by load-dependent, interaction macro-level fatigue theories, which means that the nature of the accumulation of volumetric strain is a function of the absolute amplitude and sequencing of pulses in the loading function. One model that captures this behavior and that can be used to predict seismic compression is the expanded Byrne cyclic shear-volumetric strain coupling model. However, one potential implication of the load-dependent, interaction macro-level fatigue behaviour is that ground motion orientation will influence predicted settlements. To examine the significance of this, the seismic compression that occurred at the Kashiwazaki-Kariwa Nuclear Power Plant (KKNPP) site during the 2007, Mw6.6 Niigata-ken Chuetsu-oki, Japan, earthquake is analyzed using the expanded Byrne model. The horizontal motions recorded at the site by a down-hole array during this event are rotated in 5° increments and the predicted settlements due to seismic compression are computed. The predicted settlements range from 12.3 to 16.1 cm, with a geometric mean of the values for various orientations being 13.8 cm. These results are in general accord with the post-earthquake field observations and highlight the sensitivity of predicted magnitude of the seismic compression to ground motion orientation. 

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3. In-Situ Liquefaction Testing of a Medium Dense Sand Deposit and Comparison to Case History- and Laboratory-Based Cyclic Stress and Strain Evaluations

   Stuedlein, A.W. ; Jana, A. ( September 2022 , 4th International Conference on Performance Based Design in Earthquake Geotechnical Engineering)

   Wang, L. ; Zhang, J.-M. ; Wang, R. (Ed.)

   Observations of the dynamic loading and liquefaction response of a deep medium dense sand deposit to controlled blasting have allowed quantification of its large-volume dynamic behavior from the linear-elastic to nonlinear-inelastic regimes under in-situ conditions unaffected by the influence of sample disturbance or imposed laboratory boundary conditions. The dynamic response of the sand was shown to be governed by the S-waves resulting from blast-induced ground motions, the frequencies of which lie within the range of earthquake ground motions. The experimentally derived dataset allowed ready interpretation of the in-situ γ-ue responses under the cyclic strain approach. However, practitioners have more commonly interpreted cyclic behavior using the cyclic stress-based approach; thus this paper also presents the methodology implemented to interpret the equivalent number of stress cycles, Neq, and deduce the cyclic stress ratios, CSRs, generated during blast-induced shearing to provide a comprehensive comparison of the cyclic resistance of the in-situ and constant-volume, stress- and strain-controlled cyclic direct simple shear (DSS) behavior of reconstituted sand specimens consolidated to the in-situ vertical effective stress, relative density, and Vs. The multi-directional cyclic resistance of the in-situ deposit was observed to be larger than that derived from the results of the cyclic strain and stress interpretations of the uniaxial DSS test data, indicating the substantial contributions of natural soil fabric and partial drainage to liquefaction resistance during shaking. The cyclic resistance ratios, CRRs, computed using case history-based liquefaction triggering procedures based on the SPT, CPT, and Vs are compared to that determined from in-situ CRR-Neq relationships considering justified, assumed slopes of the CRR-N curve, indicating variable degrees of accuracy relative to the in-situ CRR, all of which were smaller than that associated with the in-situ cyclic resistance. 

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4. Volumetric strains from inverse analysis of pore pressure transducer arrays in centrifuge models

   https://doi.org/10.1061/9780784481455.058  

   Darby, Kathleen M. ; Boulanger, Ross W. ; DeJong, Jason T. ( June 2018 , Proc., Geotechnical Earthquake Engineering and Soil Dynamics V, Geotechnical Special Publication 290, S. J. Brandenberg and M. T. Manzari, eds., ASCE)

   Inverse analyses were used to evaluate the degree of partial drainage occurring during dynamic shaking of liquefying soil profiles in a set of centrifuge model tests. Three tests were performed using the 9-m radius centrifuge at the UC Davis Center for Geotechnical Modeling on saturated Ottawa sand models with initial relative densities of 25, 43, and 80%. Models were subjected to multiple sinusoidal shaking events with acceleration amplitudes ranging from 0.03 to 0.55g. Densely spaced pore pressure transducer arrays provided profiles of pore pressure generation and dissipation; inverse analyses of the pore pressure data were used to obtain volumetric strain profiles during shaking and dissipation. Surface settlements computed by integrating the volumetric strain profiles are compared to surface settlements measured from linear potentiometers. The magnitude of the volumetric strains due to partial drainage and their potential effects on liquefaction responses are discussed. 

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5. Enhanced Rainfall‐Induced Shallow Landslide Activity Following Seismic Disturbance—From Triggering to Healing

   https://doi.org/10.1029/2020JF005669  

   Leshchinsky, Ben ; Lehmann, Peter ; Or, Dani ( January 2021 , Journal of Geophysical Research: Earth Surface)

   Evidence suggests that following earthquakes, landslide activity, and susceptibility remain elevated for months to years after cessation of shaking. In landslides constrained within the soil mantle, enhanced post‐seismic activity may be attributed to persistence of progressive failure surface development that results in delayed triggering. With subsequent post‐seismic hydrologic disturbance, a commensurate decay in activity over time reflects evacuation of damaged hillslope materials and mechanical healing of colluvial media and vegetation recovery. In this study, we propose a hydromechanical model for representing the interplay of these processes including trends in timing and magnitude of post‐seismic shallow landslide activity. The hydromechanical model considers seismic or hydrologic disturbances as drivers for failure surface development in the soil mantle over a hillslope with commensurate weakening through accumulation of internal compression, shear softening, and loss of root strength. In the absence of well‐instrumented post‐seismic landslide measurement of evolving stress conditions and deformation, predictions were made against a unique field case study where hydrologically induced hillslope failure kinematics and internal compression were measured. The model accounts for seismic disturbances, demonstrating that certain peak ground accelerations directly reduce subsequent rainfall‐induced landslide‐triggering thresholds relative to undisturbed hillslopes. The model framework can be used to describe progressive, post‐seismic landslide activity, demonstrating that consideration of root or soil healing may suppress subsequent landslide triggering and contribute toward recovery to pre‐seismic disturbance levels of strength. Factors such as shear softening, vegetation, and healing are explored in the context of the temporal evolution of landslide rates after a seismic event. The results of this paper show mechanistically how (1) progressive development or cessation of a failure surface in active, post‐seismic landslides may describe elevated post‐seismic landslide rates and (2) that hillslope healing plays a modest role in the magnitude and timescale of attenuated landslide activity.

    

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