Analysis of the Shaft Resistance of Nondisplacement Piles in Sand

The paper examines, using numerical modelling, the problem of the limit shaft resistance of non-displacement piles installed in sands. The modelling makes use of an advanced, two-surface-plasticity constitutive model. The constitutive model predicts the soil response in both the small- and the large-strain range, while taking into account the effects of the intermediate principal effective stress and of the inherent anisotropy of the sand. Finite element analyses of shearing along the pile shaft are performed in order to examine the development of limit unit shaft resistance and the changes in stress state around the shaft upon axial loading of the pile. Special focus is placed on the operative value of the lateral earth pressure coefficient when limit shaft resistance is reached. The analyses offer useful insights regarding the factors controlling the value of unit shaft resistance in sands. The simulations predict a significant build-up of horizontal effective stress for dense sands. Based on these simulations, we propose a relationship between the lateral earth pressure coefficient for use in the calculation of the limit shaft resistance of the pile and the initial density and stress state of the sand

Effect of Relative Density and Stress Level on the Bearing Capacity of Footings on Sand

The design of shallow foundations relies on bearing capacity values calculated using empirical procedures that are based in part on solutions obtained using the method of characteristics, which assumes a soil that is perfectly plastic following an associated flow rule. In this paper the problem of strip and circular footings resting on the surface of a sand layer is analysed using the finite-element method. Analyses are performed using a two-surface plasticity constitutive model that realistically captures the aspects of the mechanical response of sands that are relevant to the bearing capacity problem. In particular, the model accounts for non-associated flow, strain-softening, and both stress-induced and inherent anisotropy. Based on the results of the analyses, the paper examines the validity of the bearing capacity factors N γ and shape factors s γ used in practice. A relationship for determining appropriate values of friction angle for use in bearing capacity calculations is also proposed

Nonlinear analysis of earthquake fault rupture interaction with historic masonry buildings

The response of historic masonry buildings to tectonic ground displacements is studied through analysis of a simple yet representative soil-foundation-masonry wall system. A nonlinear 3D finite element method is developed and employed to reproduce the strong nonlinear response of the rupturing soil, as well as the masonry structure. Following a sensitivity analysis of the effect of the exact location of the structure with respect to the emerging fault, the paper discusses several characteristic mechanisms of soil-structure interaction and evaluates the associated structural distress. The observed failure pattern and the consequent structural damage are shown to depend strongly, varying from minimal to dramatic, on the exact position of the structure relative to the fault. Alleviation of tectonic risk through foundation enhancement/improvement is investigated by considering alternative foundation systems. Results highlight the advantageous performance of rigid embedded and continuous foundations as opposed to more flexible and isolated supports indicating that foundation strengthening may provide important shielding against settlement and structural drift

Bridge-Pier Caisson foundations subjected to normal and thrust faulting:physical experiments versus numerical analysis

Surface fault ruptures can inflict serious damage to engineering structures built on or near them. In the earthquakes of Kocaeli, Chi-chi, and Wenchuan a number of bridges were crossed by the emerging normal or thrust faults suffering various degrees of damage. While piles have proved incapable of tolerating large displacements, massive embedded caisson foundations can be advantageous thanks to their rigidity. The paper explores the key mechanisms affecting the response of such bridge foundations subjected to dip-slip (normal or thrust) faulting. A series of physical model experiments are conducted in the National Technical University of Athens, to gain a deeper insight in the mechanics of the problem. The position of the caisson relative to the fault rupture is parametrically investigated. High-resolution images of the deformed physical model is PIV-processed to compute caisson displacements and soil deformation. A novel laser scanning technique, applied after each dislocation increment, reveals the surface topography (the relief) of the deformed ground. 3D finite element analyses accounting for soil strain-softening give results in accord with the physical model tests. It is shown that the caisson offers a kinematic constraint, diverting the fault rupture towards one or both of its sides. Depending on the caisson's exact location relative to the rupture, various interesting interaction mechanisms develop, including bifurcation of the rupture path and diffusion of plastic deformation.</p

Is diet partly responsible for differences in COVID-19 death rates between and within countries?

Correction: Volume: 10 Issue: 1 Article Number: 44 DOI: 10.1186/s13601-020-00351-w Published: OCT 26 2020Reported COVID-19 deaths in Germany are relatively low as compared to many European countries. Among the several explanations proposed, an early and large testing of the population was put forward. Most current debates on COVID-19 focus on the differences among countries, but little attention has been given to regional differences and diet. The low-death rate European countries (e.g. Austria, Baltic States, Czech Republic, Finland, Norway, Poland, Slovakia) have used different quarantine and/or confinement times and methods and none have performed as many early tests as Germany. Among other factors that may be significant are the dietary habits. It seems that some foods largely used in these countries may reduce angiotensin-converting enzyme activity or are anti-oxidants. Among the many possible areas of research, it might be important to understand diet and angiotensin-converting enzyme-2 (ACE2) levels in populations with different COVID-19 death rates since dietary interventions may be of great benefit.Peer reviewe

Nrf2-interacting nutrients and COVID-19 : time for research to develop adaptation strategies

There are large between- and within-country variations in COVID-19 death rates. Some very low death rate settings such as Eastern Asia, Central Europe, the Balkans and Africa have a common feature of eating large quantities of fermented foods whose intake is associated with the activation of the Nrf2 (Nuclear factor (erythroid-derived 2)-like 2) anti-oxidant transcription factor. There are many Nrf2-interacting nutrients (berberine, curcumin, epigallocatechin gallate, genistein, quercetin, resveratrol, sulforaphane) that all act similarly to reduce insulin resistance, endothelial damage, lung injury and cytokine storm. They also act on the same mechanisms (mTOR: Mammalian target of rapamycin, PPAR gamma:Peroxisome proliferator-activated receptor, NF kappa B: Nuclear factor kappa B, ERK: Extracellular signal-regulated kinases and eIF2 alpha:Elongation initiation factor 2 alpha). They may as a result be important in mitigating the severity of COVID-19, acting through the endoplasmic reticulum stress or ACE-Angiotensin-II-AT(1)R axis (AT(1)R) pathway. Many Nrf2-interacting nutrients are also interacting with TRPA1 and/or TRPV1. Interestingly, geographical areas with very low COVID-19 mortality are those with the lowest prevalence of obesity (Sub-Saharan Africa and Asia). It is tempting to propose that Nrf2-interacting foods and nutrients can re-balance insulin resistance and have a significant effect on COVID-19 severity. It is therefore possible that the intake of these foods may restore an optimal natural balance for the Nrf2 pathway and may be of interest in the mitigation of COVID-19 severity

Cabbage and fermented vegetables : From death rate heterogeneity in countries to candidates for mitigation strategies of severe COVID-19

Large differences in COVID-19 death rates exist between countries and between regions of the same country. Some very low death rate countries such as Eastern Asia, Central Europe, or the Balkans have a common feature of eating large quantities of fermented foods. Although biases exist when examining ecological studies, fermented vegetables or cabbage have been associated with low death rates in European countries. SARS-CoV-2 binds to its receptor, the angiotensin-converting enzyme 2 (ACE2). As a result of SARS-CoV-2 binding, ACE2 downregulation enhances the angiotensin II receptor type 1 (AT(1)R) axis associated with oxidative stress. This leads to insulin resistance as well as lung and endothelial damage, two severe outcomes of COVID-19. The nuclear factor (erythroid-derived 2)-like 2 (Nrf2) is the most potent antioxidant in humans and can block in particular the AT(1)R axis. Cabbage contains precursors of sulforaphane, the most active natural activator of Nrf2. Fermented vegetables contain many lactobacilli, which are also potent Nrf2 activators. Three examples are: kimchi in Korea, westernized foods, and the slum paradox. It is proposed that fermented cabbage is a proof-of-concept of dietary manipulations that may enhance Nrf2-associated antioxidant effects, helpful in mitigating COVID-19 severity.Peer reviewe

Active pressure on gravity walls supporting purely frictional soils

The active earth pressure used in the design of gravity walls is calculated based on the internal friction angle of the retained soil or backfill. However, the friction angle of a soil changes during the deformation process. For drained loading, the mobilized friction angle varies between the peak and critical-state friction angles, depending on the level of shear strain in the retained soil. Consequently, there is not a single value of friction angle for the retained soil mass, and the active earth pressure coefficient changes as the wall moves away from the backfill and plastic shear strains in the backfill increase. In this paper, the finite element method is used to study the evolution of the active earth pressure behind a gravity retaining wall, as well as the shear patterns developing in the backfill and foundation soil. The analyses relied on use of a two-surface plasticity constitutive model for sands, which is based on critical-state soil mechanics. </jats:p

Effect of relative density and stress level on the bearing capacity of footings on sand

The design of shallow foundations relies on bearing capacity values calculated using empirical procedures that are based in part on solutions obtained using the method of characteristics, which assumes a soil that is perfectly plastic following an associated flow rule. In this paper the problem of strip and circular footings resting on the surface of a sand layer is analysed using the finite-element method. Analyses are performed using a two-surface plasticity constitutive model that realistically captures the aspects of the mechanical response of sands that are relevant to the bearing capacity problem. In particular, the model accounts for non-associated flow, strain-softening, and both stress-induced and inherent anisotropy. Based on the results of the analyses, the paper examines the validity of the bearing capacity factors Nγ and shape factors sγ used in practice. A relationship for determining appropriate values of friction angle for use in bearing capacity calculations is also proposed. </jats:p