António A.S. Correia

Effect of Organic Matter Content and Curing Conditions on the Creep Behavior of an Artificially Stabilized Soil

This paper examines the effect of organic matter content and the curing conditions on the one-dimensional compressibility of Portuguese soft soil stabilized with binders, with a special emphasis on creep behavior. Consolidation and creep oedometer tests were carried out on remolded and stabilized soil samples to study the effects of these factors. The increase of the organic matter content induces the increment of compressibility characteristics, including creep. Curing conditions also affect the one-dimensional compression behavior of the stabilized soil because the underwater curing, the increase of the vertical stress applied on the sample, and the increase of the curing time improve the compressibility characteristics, inducing the reduction of creep deformations.

Effect of Stress Level and Binder Composition on Secondary Compression of an Artificially Stabilized Soil

This paper examines the effect on the compressibility of a Portuguese soft soil stabilized with binders, with a special emphasis on creep characteristics. The effects of vertical stress during curing time and binder composition (type and content) on the creep behavior of a sta- bilized material are analyzed with oedometer tests. The results show the decrease of the secondary compression index with the decrease of the vertical stress applied during creep phase and with the increment of the binder content. The best binder type for this soil, in terms of creep be- havior, iscomposedof portland cement and flyash witha dryweight proportionof 75/25, becausethis promotes thedevelopment of secondary pozzolanicreactions.Theresultsalsorevealthatthebindercompositionshouldhaveaminimumquantityofcementtoimprovethecompression characteristicsofthestabilizedsoiladequately.DOI:10.1061/(ASCE)GT.1943-5606.0000762.

The Force at the Tip - Modelling Tension and Proliferation in Sprouting Angiogenesis

Sprouting angiogenesis, where new blood vessels grow from pre-existing ones, is a complex process where biochemical and mechanical signals regulate endothelial cell proliferation and movement. Therefore, a mathematical description of sprouting angiogenesis has to take into consideration biological signals as well as relevant physical processes, in particular the mechanical interplay between adjacent endothelial cells and the extracellular microenvironment. In this work, we introduce the first phase-field continuous model of sprouting angiogenesis capable of predicting sprout morphology as a function of the elastic properties of the tissues and the traction forces exerted by the cells. The model is very compact, only consisting of three coupled partial differential equations, and has the clear advantage of a reduced number of parameters. This model allows us to describe sprout growth as a function of the cell-cell adhesion forces and the traction force exerted by the sprout tip cell. In the absence of proliferation, we observe that the sprout either achieves a maximum length or, when the traction and adhesion are very large, it breaks. Endothelial cell proliferation alters significantly sprout morphology, and we explore how different types of endothelial cell proliferation regulation are able to determine the shape of the growing sprout. The largest region in parameter space with well formed long and straight sprouts is obtained always when the proliferation is triggered by endothelial cell strain and its rate grows with angiogenic factor concentration. We conclude that in this scenario the tip cell has the role of creating a tension in the cells that follow its lead. On those first stalk cells, this tension produces strain and/or empty spaces, inevitably triggering cell proliferation. The new cells occupy the space behind the tip, the tension decreases, and the process restarts. Our results highlight the ability of mathematical models to suggest relevant hypotheses with respect to the role of forces in sprouting, hence underlining the necessary collaboration between modelling and molecular biology techniques to improve the current state-of-the-art.

Reset-Driven Fault Tolerance

A common approach in embedded systems to achieve fault-tolerance is to reboot the computer whenever some non-permanent error is detected. All the system code and data are recreated from scratch, and a previously established checkpoint, hopefully not corrupted, is used to restart the application data. The confidence is thus restored on the activity of the computer. The idea explored in this paper is that of unconditionally resetting the computer in each control frame (the classic read sensors → calculate control action → update actuators cycle). A stable-storage based in RAM is used to preserve the systems state between consecutive cleanups and a standard watchdog timer guarantees that a reset is forced whenever an error crashes the system. We have evaluated this approach by using fault-injection in the controller of a standard temperature control system. The experimental observations show that the Reset-Driven Fault Tolerance is a very simple yet effective technique to improve reliability at an extremely low cost since it is a conceptually simple, software only solution with the advantage of being application independent.

Effect of Organic Matter Content and Binder Quantity on the Uniaxial Creep Behavior of an Artificially Stabilized Soil

AbstractThe objective of this work is to analyze, based on the results of uniaxial creep tests, the effect of organic matter content and binder quantity on the creep behavior of a Portuguese soft soil chemically stabilized with binders. In general, the results show that the application of a creep load induces a slight degradation of the mechanical properties of the composite material of the same age, as a consequence of the breakage of some cementation bonds owing to the creep deformation. This degradation grows with the increases in binder quantity and the decreases in organic matter content. The uniaxial creep tests indicate an increase in the creep strain rate with log time, allowing the definition of two creep compression indices, Cα1∗ and Cα2∗. Whereas the initial creep compression index (Cα1∗) is independent of the strength and shows a low scatter of values (0.00013–0.0003), the final creep compression index (Cα2∗) decreases with the increment of the strength, i.e., for higher binder quantities and ...

Application of carbon nanotubes to immobilize heavy metals in contaminated soils

The contamination of soils with heavy metals is a growing concern in modern societies. To avoid the spread of contamination, soil stabilization techniques can be applied mixing materials with the soil in order to partially immobilize heavy metals. Carbon nanotubes (CNTs) are nanomaterials known for its exceptional properties, like high surface area and adsorption capacity. Due to these unique properties, the potential use of CNTs in heavy metal contaminated water has been studied, with very satisfactory results; however, their application in contaminated soils is practically unexplored. This experimental work is focused on studying the potential of using CNTs in soil remediation, especially to immobilize the heavy metals ions: lead (Pb2+), copper (Cu2+), nickel (Ni2+), and zinc (Zn2+), commonly present in contaminated soils. In order to avoid CNT agglomeration, which originates the loss of their beneficial properties, an aqueous suspension of CNTs was prepared using a non-ionic surfactant combined with ultrasonic energy to promote CNTs dispersion. Then, the soil, with and without the addition of CNTs, was subjected to adsorption tests to evaluate the CNT capacity to improve heavy metal immobilization. To validate the adsorption test results, permeability tests were executed, simulating the conditions of a real-case scenario. The results obtained led to the conclusion that the addition of a small amount of dispersed CNTs can successfully increase the adsorption capacity of the soil and consequently improve the immobilization of heavy metals in the soil matrix. The immobilization percentage varies with the different heavy metals under study.

Parametric Study of an Embankment Built on Soft Soil Reinforced with Deep Mixing Columns

Department of Civil Engineering, Faculty of Sciences and Technology – University of Coimbra, R.Luis Reis Santos, 3030-788 Coimbra, Portugal; pjvo @dec.uc.pt 2 Martifer, Zona Industrial, Apartado 17, 3684-001 Oliveira de Frades, Portugal;jpolido@hotmail.com Department of Civil Engineering, Faculty of Sciences and Technology – University of Coimbra, R.Luis Reis Santos, 3030-788 Coimbra, Portugal; aalberto@dec.uc.pt