Prediction and interpretation of the performance of a deep excavation in Berlin sand

This paper describes the application of a generalized effective stress soil model, MIT‐S1, within a commercial finite element program, for simulating the performance of the support system for the 20m deep excavation of the M1 pit adjacent to the main station “Hauptbahnhof” in Berlin. The M1 pit was excavated underwater and supported by a perimeter diaphragm wall with a single row of prestressed anchors. Parameters for the soil model were based on an extensive program of laboratory tests on the local Berlin Sands. This calibration process highlights the practical difficulties in both measurements of critical state soil properties and in model parameter selection. The predictions of excavation performance are strongly affected by vertical profiles of two key state parameters, the initial earth pressure ratio, K0, and the in‐situ void ratio, e0. These are estimated from field dynamic penetration test data and geological history. The results show good agreement between computed and measured wall deflections and tie‐back forces for three instrumented sections. Much larger wall deflections were measured at a fourth section and may be due to spatial variability in sand properties that has not been considered in the current analyses. The results of this study highlight the importance of basic state parameter information for successful application of advanced soil models.National Science Foundation (U.S.) (Wester Europe program grant INT-0089508)German Academic Exchange Service (DAAD

Application of the geostatistical program NOMAD-KRIBS to geoenvironmental problems

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2001.Includes bibliographical references (p. 117-120).by Maria-Aikaterini Nikolinakou.S.M

A constitutive model for the compression behavior of Old Alluvium

Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2008.Includes bibliographical references.Old Alluvium is classified as a transported, in-situ weathered tropical soil, and represents a class of geomaterials that have a complex microstructure, including cemented aggregates at the meso-scale and groups of clay stacks at the micro-scale. Despite the presence of significant fractions of nontronite (smectite species), the activity of charged clay particles is initially masked by the aggregation of iron oxides. Compression loading breaks the cementation at the meso-scale and causes physico-chemical changes at the micro-scale, which reveal the expansive characteristics of the clay minerals. It is difficult to achieve a fully disaggregated condition (through mechanical mixing or selective chemical dissolution) and hence, there is little practical value in referencing properties of the intact soil to a hypothetical disaggregated or intrinsic state as proposed for other bonded soils. The proposed formulation describes the variation of compressibility according to a measure of the microstructural changes using the Cation Exchange Capacity as a state variable. Upon load reversal, a model based on double layer theory is integrated to predict macroscopic volumetric expansion due to the swelling of the nontronitic clay fraction. This behavior is also linked to the Cation Exchange Capacity through the preconsolidation stress level, and hence, can accommodate changes in the clay swelling potential caused by mechanical or physicochemical loading. The model parameters depend on the compression characteristics of the intact soil, on measurements of the Cation Exchange Capacity in the intact and partially disaggregated states, on the amount of expandable minerals in the microstructure and on the initial hydration of the clay stacks.(cont.) Overall, the proposed formulation introduces a new way of modeling the compression of bonded materials with evolving microstructural characteristics, which does not require a unique reference state. It builds the swelling response directly on the physicochemical characteristics of the soil. The thesis also includes an experimental program on block samples obtained from a tunneling project in San Juan, Puerto Rico. The laboratory data was used for the calibration and detailed validation of model predictions. The proposed formulation enables predictions of expected engineering properties through the vertical weathering profile of the Old Alluvium.by Maria-Aikaterini Nikolinakou.Sc.D

Vibro-Injection Pile Installation in Sand: Part I—Interpretation as Multi-material Flow

The installation of vibro-injection piles into saturated sand has a significant impact on the surrounding soil and neighboring buildings. It is generally characterized by a multi-material flow with large material deformations, non-stationary and new material interfaces, and by the interaction of the grain skeleton and the pore water. Part 1 in this series of papers is concerned with the mathematical and physical modeling of the multi-material flow associated with vibro-injection pile installation. This model is the backbone of a new multi-material arbitrary Lagrangian-Eulerian (MMALE) numerical method presented in Part 2.DFG, 76838227, Numerische Modellierung der Herstellung von Rüttelinjektionspfähle

Comparison of stresses in 3D v. 2D geomechanical modelling of salt structures in the Tarfaya Basin, West African coast

We predict stresses and strains in the Tarfaya salt basin on the West African coast using a 3D static geomechanical model and compare the results against a simplified 2D plane-strain model. Both models are based on present-day basin geometries, are drained, and use a poroelastic description for the sediments and visco-plastic description for salt. We focus on a salt diapir, where an exploratory well has been drilled crossing a major fault. The 3D model shows a significant horizontal stress reduction in sediments at the top of the diapir, validated with measured data later obtained from the well. The 2D model predicts comparable stress reduction in sediments at the crest of the diapir. However, it shows a broader area affected by the stress reduction, overestimating its magnitude by as much as 1.5 MPa. Both models predict a similar pattern of differential displacement in sediments along both sides of the major fault, above the diapir. These displacements are the main cause of horizontal stress reduction detected at the crest of the diapir. Sensitivity analysis in both models shows that the elastic parameters of the sediments have a minimal effect on the stress-strain behaviour. In addition, the 2D sensitivity analysis concludes that the main factors controlling stress and strain changes are the geometry of the salt and the difference in rock properties between encasing sediments and salt. Overall, our study demonstrates that carefully built 2D models at the exploration stage can provide stress information and useful insights comparable to those from more complex 3D geometrie

How, where, and when do radial faults grow near salt diapirs?

We examine three-dimensional seismic data from the Santos Basin, offshore Brazil, to determine how, where, and when radial faults grow near a salt diapir. We show roof stretching alone cannot account for the large heights and lengths of the kilometer-scale radial faults, suggesting stock widening ('stem push'), a mechanism implied in numerical models but not yet recognized in natural examples, played a pivotal role in fault formation. We suggest that, when a diapir is covered by a roof, radial faults form due to roof stretching, extending no further than the limit of the drape folding. The roof may then be shouldered aside and the faults buried along the stock flanks, exposing these strata to stem push–related stresses that may then re-activate preexisting, or form new, radial faults. We suggest the causal mechanism for radial fault formation will likely change as roof thickness varies during diapirism, with this reflecting the ratio between sedimentation rate and salt volumetric flux

Supplementary data for manuscript "The evolution of pore pressure, stress, and physical properties during sediment accretion at subduction zones"

Elfen Finite Element project files for all analyses discussed in the manuscript: "The evolution of pore pressure, stress, and physical properties during sediment accretion at subduction zones

Do Human Values Matter For Promoting Brands On Social Media? How Social Media Users\u27 Values Influence Valuable Brand-Related Activities Such As Sharing, Content Creation, and Reviews

Companies consider social media‐based consumer engagement behaviors such as sharing, content creation, and reviews for brands as more valuable than “liking” or consuming brand content. Studies show that branded content shared or created by consumers on social media may drive more brand awareness and loyalty than “likes” (Adweek, 2013). Global companies are increasingly focusing their efforts on motivating consumer‐driven content creation (e.g., Coca‐Cola #shareacoke and Apple #ShotoniPhone; Sprout Index, 2018). However, marketing practitioners are only recently beginning to understand social media audiences who engage in such activities (Adweek, 2018). This study posits that human values can be used to identify and segment audiences for social media‐based valuable brand activities. Three online surveys were conducted with Facebook, Twitter, and Instagram users (ages 18–34) on Amazon Mechanical Turk (N = 491). The relationship between social media users\u27 values and their reported social media activities was examined. Findings indicate that the human values examined (conservation, self‐enhancement, openness to change and self‐transcendence) are significant drivers of valuable brand‐related social media activities. Companies should address conservation‐driven users in order to elicit brand sharing and creation activities. Companies should target conservation‐driven users for sharing promotions, self‐enhancement‐driven users for sharing informational content and writing of product reviews, and openness to change‐driven users for user‐generated content. Bussinesses should further highlight their corporate social responsibility efforts as a negative relationship is found between users\u27 self‐transcendence values and brand activities. Recommendations are provided on how brandscan address users\u27 values in their social media marketing to motivate sharing of branded content and content creation

Do human values find genuine expression on social media platforms? The influence of human values on millennials' social media activities

PurposeSocial media has the potential to enable exchange of diverse opinions, foster dialogue on important social issues and exert positive influence on stakeholders and society. However, evidence is contradictory as to whether this is the case; it is possible that millennials' behaviors on social media are mainly driven by conservation (conformity and safety) or self-enhancement (power and achievement). In this research, the authors examine the extent to which different human values (self-transcendence, conservation, self-enhancement and openness to change) influence millennials' activities and behaviors on social media.Design/methodology/approachThe authors conduct three separate surveys on Facebook, Twitter and Instagram with 491 millennials (18–34 years of age) in the USA, examining the influence of four higher-order values of the Schwartz human values model (open self-transcendence, conservation, self-enhancement and openness to change) on specific social media activities (consumption, self-focused and sharing nonpersonal content activities).FindingsFirst, the authors find that for millennial users, human values significantly influence social media activities. Second, conservation values, followed by self-enhancement values, overshadow the expression of open self-transcendence values on social media. Thus, social media platforms may function more as agents of conservation and self-enhancement than agents of personal growth.Originality/valueThis is among the first studies to examine the influence of human values on social media and to find that human values such as conservation and self-enhancement have a strong influence on users' social media activities, while open self-transcendence values, which lead to expansion and growth, do not find genuine expression on social media.</jats:sec