Author: Farshad AminiPublisher:
ISBN:
Category : Sands
Languages : en
Pages : 46
Book Description
Behavior of Stratified Undrained Contractive Silty Sands Under Seismic Liquefaction Conditions
Author: Farshad AminiBehavior of Stratified Undrained Contractive Silty Sands Under Seismic Liquefaction Conditions
Author: Farshad AminiCyclic behaviour and liquefaction potential of silty sand: Experimental and numerical investigations
Author: Abdulaziz Osman AbdelkadrPublisher: BoD – Books on Demand
ISBN: 3737610185
Category : Science
Languages : en
Pages : 274
Book Description
In this study experimental and numerical investigations have been carried out with the emphasis on studying the behaviour and liquefaction state of typical silty sand sampled from the Mekelle area in Ethiopia under monotonic and cyclic undrained loadings. Experiments have been carried out to measure the pore pressure accumulation, deformation characteristics and related effective stress paths. A numerical model was then used to simulate the behaviour and liquefaction state associated with the changes in the stress-strain-pore pressure levels by means of the finite element method (FEM) using the FE code Tochnog (Tochnog Professional Company 2021).
The Behavior of Undrained Contractive Sand and Its Effect on Seismic Liquefaction Flow Failures of Earth Structures
Author: Andres R. Vasquez-HerreraPublisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
Soil Behavior Under Earthquake Loading Conditions
Author: Robert PykePublisher:
ISBN:
Category : Soil liquefaction
Languages : en
Pages : 90
Book Description
Liquefaction of Sands Due to Non-seismic Loading
Author: Steven Lawrence KramerPublisher:
ISBN:
Category :
Languages : en
Pages : 762
Book Description
The Behavior of Sands Under Seismic Loading Conditions
Author: Marshall L. SilverPublisher:
ISBN:
Category : Materials
Languages : en
Pages : 298
Book Description
The volume change characteristics and the dynamic stress-strain properties of dry sand subjected to cyclic shear strains have been investigated and used to check the applicability of a simple method for predicting the vertical settlements due to compaction in layers of dry cohesionless soils subjected to seismic loading conditions. Dynamic testing of a medium quartz sand, performed by repeated load simple shear equipment, indicated that the shear modulus increased slightly with increasing numbers of cycles and with increasing relative density and decreases significantly with increasing values of shear strain amplitude. Modulus values determined near the upper limit of shear strain amplitude that might be expected to be induced by seismic shaking (0.1 percent) were as much as 40 percent lower than modulus values obtained at the lowest values of shear strain that were investigated (0.01 percent). (Author).
Influence of Silt Size and Content on Static Liquefaction Potential of Sand
Author: M. Murat MonkulPublisher:
ISBN:
Category : Silt
Languages : en
Pages : 282
Book Description
Different specimen preparation methods such as moist tamping, dry funnel deposition, slurry deposition, dry air pluviation have been reported in the literature to investigate the undrained behavior of silty sands. Similarly, different means have been used to densify the soils prepared with such methods. However, the influence of the densification technique, utilized within a particular deposition method, on undrained behavior (e.g. change in initial peak deviator stress and instability angle) was not known. Therefore, a new densification technique is developed for the dry funnel deposition method, which avoids tamping, vibrating or mold tapping. This new method of densification is thought to create a much consistent soil fabric for different amounts of densification than other specimen densification techniques. The experimental results show that the change in undrained behavior with increasing density produced by densification is much less pronounced when compared to the other densification methods reported in the literature. Prior research efforts regarding the effect of non plastic silts on the liquefaction behavior of sands mainly focused on the influence of fines content, confining stress, and depositional techniques. However, there is no consensus in the literature regarding the influence of fines content on the undrained behavior of silty sands. Strain-controlled monotonic undrained triaxial compression tests were performed on a single base sand mixed with three different essentially nonplastic silts. First, silt size effects are investigated while other factors like fines content (20%), confining stress (30kPa) and deposition method (dry funnel deposition) were kept the same. The results show that silt size is indeed an important factor which influences the liquefaction potential of silty sands. Different comparison bases for undrained behavior such as the loosest possible density after deposition, intergranular void ratio, void ratio and relative density were also evaluated. It was observed that as the mean grain diameter ratio (D50/d50) of the sand grains (D50) to silt grains (d50) decreases, liquefaction potential for a silty sand increases. This tendency is attributed to more metastable contacts with increasing silt size. Finally, the influence of fines content on the static liquefaction potential of silty sand is investigated for different silt types. It was found that if the mean grain diameter ratio (D[subscript 50-sand]/d[subscript 50-silt]) is sufficiently small, the liquefaction potential of the sand increases steadily with increasing fines content for the studied range (0-20%). As mean grain diameter ratio (D[subscript 50-sand]/d[subscript 50-silt]) increases, the liquefaction potential of the sand first decreases then increases with fines content. For such cases, liquefaction potential of the silty sand might be less than the liquefaction potential of the clean sand. Differences in undrained behavior are explained based on the influence of mean grain diameter ratio (D[subscript 50-sand]/d[subscript 50-silt]) on the initial soil fabric.
Behavior of Saturated Silty Sands Subjected to Undrained Cyclic Loads
Author: Syed Ali AshrafPublisher:
ISBN:
Category : Earthquake engineering
Languages : en
Pages : 176
Book Description
A Sand Plasticity Model for Earthquake Engineering Applications
Author: Aikaterini ZiotopoulouPublisher:
ISBN:
Category : Earthquake engineering
Languages : en
Pages : 0
Book Description
The development of the sand plasticity model PM4Sand (Versions 2 and 3) for geotechnical earthquake engineering applications is presented. The motivation behind this work is twofold. The first goal is to have a constitutive model that is applicable to the wide range of conditions encountered in geotechnical engineering practice, is easy to calibrate utilizing the limited data that are usually available and can reasonably approximate the behaviors of interest. The second goal is to provide an extensive documentation of the capabilities and limitations of the model. The PM4Sand plasticity model is built upon the basic framework of the stress-ratio controlled, critical state compatible, bounding surface plasticity model for sand presented by Dafalias and Manzari (2004). A series of modifications and additions to the model were incorporated by Boulanger (2010; Version 1) and further herein (Version 2 and Version 3) to improve its ability to approximate the stress-strain responses important to geotechnical earthquake engineering practice; in essence, the model is calibrated at the equation level to provide for better approximation of the trends observed in empirical correlations commonly used in practice. Each stage of its development has been guided by consecutive cycles of formulation, validation and calibration against the whole body of available data (case histories, lab, centrifuge and shake table tests) on the cyclic behavior of sands both at the element and at the system level. The formulation of PM4Sand Version 2 for geotechnical earthquake engineering applications is presented followed by its calibration and implementation. A generalized calibration of the constitutive model is presented which attempts to produce drained and undrained, monotonic and cyclic responses under a broad range of stress conditions that are reasonably consistent with the behaviors expected based on engineering correlations to commonly available in-situ test data (i.e., SPT, CPT and Vs data). Simulated single element responses are compared to design correlations to illustrate the efficacy of the model modifications and evaluate the model’s performance. The constitutive model is shown to be relatively easy to calibrate and provide reasonable responses for key liquefaction behaviors. The numerical implementation as a user defined material for use in a two-dimensional explicit finite difference program is described. The formulation of PM4Sand Version 3 for improved modeling of post-liquefaction reconsolidation strains is presented. Modifications are introduced that provide a means for improved modeling of post-liquefaction reconsolidation strains after the end of strong shaking in a nonlinear deformation analysis. The methodology of the approach along with the calibration is presented, followed by a comparison of the response computed for a field case history. A review is presented on the performance of a number of constitutive models in reasonably predicting liquefaction effects under sloping ground conditions. Example results from undrained cyclic DSS tests on clean sands under zero and nonzero static shear stress ratio conditions are presented and findings from past experimental studies for these types of loading conditions are reviewed. Examples are presented of the performance of selected constitutive models in modeling the observed experimental results. It is shown that they all have certain limitations and that the effect of sloping ground conditions is particularly difficult to simulate. Finally, the formulation of PM4Sand Version 3 is further updated to better account for the effects of sloping ground conditions and irregular cyclic loading on liquefaction behaviors and thus improve simulations of liquefaction-induced deformations of sloping ground. Existing laboratory test data are reviewed and new experimental data from undrained cyclic Direct Simple Shear (DSS) lab tests of liquefiable sand under sloping ground conditions subjected to irregular cyclic loading are introduced. Evidence from the tests shows that it is the effect of loading history on the dilatancy and stiffness characteristics of the response that is not properly captured by the model. The modifications made in Version 3 include a revised dependency of dilatancy and plastic modulus on the fabric tensor and its history. These modifications are introduced using the irregular cyclic DSS testing to illustrate the motivations for the changes in the constitutive equations. Finally, two examples of calibration are presented: one against a specific lab test result for a single sand and one against an engineering correlation describing trends observed for many sands across a broader range of relative densities, confining stresses, and loading conditions. The updated formulation in Version 3 of the model is shown to better approximate liquefaction behaviors for sloping ground conditions.