More Like this

1. 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. 

   more » « less
2. In-situ and Laboratory Cyclic Response of an Alluvial Plastic Silt Deposit

   Dadashiserej, A. ; Jana, A. ; Stuedlein, A.W. ; Evans, T.M. ; Zhang, B. ; Xu, Z. ; Stokoe II, K.H. ; Cox, B.R. ( May 2022 , Proceedings of the 20th International Conference on Soil Mechanics and Geotechnical Engineering, Sydney 2021)

   Current best practices for the assessment of the cyclic response of plastic silts are centered on the careful sampling and cyclic testing of natural, intact specimens. Side-by-side evaluation of in-situ and laboratory element test responses are severely limited, despite the need to establish similarities and differences in their characteristics. In this paper, a coordinated laboratory and field-testing campaign that was undertaken to compare the strain-controlled cyclic response of a plastic silt deposit at the Port of Longview, Longview, WA is described. Following a discussion of the subsurface conditions at one of several test panels, the responses of laboratory test specimens to resonant column and cyclic torsional shear testing, and constant-volume, strain-controlled cyclic direct simple shear testing are described in terms of shear modulus nonlinearity and degradation, and excess pore pressure generation with shear strain. Several months earlier, the in-situ cyclic response of the same deposit was investigated by applying a range of shear strain amplitudes using a large mobile shaker. The in-situ response is presented and compared to the laboratory test results, highlighting similarities and differences arising from differences in mechanical (e.g., constant-volume shearing; strain rate-effects) and hydraulic (e.g., local drainage) boundary conditions and the spatial variability of natural soil deposits. 

   more » « less
3. Monotonic, Cyclic, and Post-Cyclic Response of Willamette River Silt at the Van Buren Bridge

   https://doi.org/10.1061/9780784484043.042  

   Dadashiserej, Ali ; Jana, Amalesh ; Ortiz, Susan C. ; Walters, James J. ; Stuedlein, Armin W. ; Evans, T. Matthew ( March 2022 , Geo-Congress 2022)

   Lemnitzer, A. ; Stuedlein, A.W. (Ed.)

   This study presents a laboratory investigation of the monotonic, cyclic, and post-cyclic responses of a lightly overconsolidated, low plasticity silt deposit conducted to support the geotechnical design of a proposed bridge replacement crossing the Willamette River in Corvallis, OR. The design seismic hazard corresponded to the 975-year return period with the Cascadia Subduction Zone contributing the greatest portion of the hazard. The response of the intact, natural specimens was compared to that of specimens reconstituted from the same material for comparison of the effect of soil fabric. Constant-volume cyclic stress controlled direct simple shear tests (CDSS) conducted on the low plasticity silt deposit showed cyclic mobility type behavior and increases in cyclic resistance with OCR. The exponent of the power relationship between cyclic resistance ratio (CRR) and the number of cycles, N, was shown to be smaller than that commonly assumed within the simplified method for cyclic softening of fine-grained plastic soil. Despite higher density, the reconstituted specimens exhibited approximately 16% lower cyclic resistance than their undisturbed counterparts, indicating the importance of soil fabric on the cyclic resistance of natural silt soils. The post-cyclic volumetric strain of the silt deposit was found to be independent of OCR and increased with the maximum excess pore pressure ratio generated during the cyclic tests. 

   more » « less
4. Constitutive modeling of the cyclic loading response of low plasticity fine-grained soils

   https://doi.org/https://doi.org/10.1007/978-981-13-0125-4_1  

   Boulanger, R. W. ; Price, A. B. ; Ziotopoulou, K. ( May 2018 , GSIC 2018, Proceedings of GeoShanghai 2018 International Conference: Fundamentals of Soil Behaviours, A. Zhou et al. (Eds.), Springer Nature Singapore Pte Ltd.)

   Calibrations of the PM4Silt constitutive model are presented for two low-plasticity fine-grained soils that exhibit significantly different cyclic loading be-haviors. The PM4Silt model is a stress-ratio controlled, critical state compatible, bounding surface plasticity model that was recently developed for representing low-plasticity silts and clays in geotechnical earthquake engineering applications. The low-plasticity clayey silt and silty clay examined herein were reconstituted mixtures of silica silt and kaolin with plasticity indices (PIs) of 6 and 20. Un-drained monotonic and undrained cyclic direct simple shear (DSS) tests were per-formed on normally consolidated, slurry deposited specimens. Calibration of the PM4Silt model was based on the monotonic and cyclic DSS test data, plus em-pirical relationships for strain-dependent secant shear moduli and equivalent damping ratios. The calibration process and performance of the PM4Silt constitu-tive model are described for each soil. The results illustrate that PM4Silt is capa-ble of reasonably approximating a range of monotonic and cyclic loading behav-iors important to many earthquake engineering applications and is relatively easy to calibrate. 

   more » « less
5. Gradation and state effects on the strength and dilatancy of coarse-grained soils

   Ahmed, S. Sharif ( January 2023 , Proceedings of the 8th International Symposium on DEFORMATION CHARACTERISTICS OF GEOMATERIALS Porto, 3rd - 6th September 2023)

   Well-graded soils can be found in nature and in engineered structures, such as dams and embankments. Prediction of their behavior is still an engineering challenge in part due to the lack of data in the literature, arguably due to difficulties associated in testing these soils in the laboratory and in situ. Particularly, there is still debate over the effect of the increased range of particle sizes (i.e., widening gradation) on the shear strength and dilatancy of coarse-grained soils. This paper presents the results of drained and undrained isotropically-consolidated triaxial compression tests on six soil mixes of varying gradation. These soils were sourced from a single natural deposit and selectively sieved and mixed to isolate the effects of gradation from those of particle shape and mineralogy. The results indicate that the critical state lines in void ratio – mean effective stress space move downward as the gradation becomes wider. For the same state parameter, the soils with a wider gradation exhibit greater dilatancy and generate negative excess pore pressures with greater magnitudes than the poorly-graded soils. In drained conditions, the greater dilatancy of the well-graded soils leads to greater peak friction angles, while in undrained conditions it leads to greater undrained shear strengths. The results show that these differences in behavior can only be captured when interpreting the results in terms of the state parameter and normalized state parameter, while comparing the results in terms of the void ratio or relative density obscures the effect of differences in gradation. 

   more » « less