A new slurry-based method of preparation of specimens of sand containing fines

A new method of specimen reconstitution is presented that is appropriate for element testing of sands containing either plastic or nonplastic fines. The method allows reconstitution of homogeneous, saturated specimens of sands containing fines whose stress-strain response closely resembles the stress-strain response of natural soil deposits formed underwater (e.g., alluvial and offshore submarine deposits, hydraulic fills, and tailings dams). A procedure is described to evaluate the maximum void ratio (emax) of sands containing fines under conditions that more appropriately represent soil deposition at its loosest state in aquatic environments. For soils deposited in water, the data obtained with the procedure proposed in this paper suggest that ASTM D 4254 overestimates the emax of sands containing plastic fines and underestimates the emax of sands containing nonplastic fines. Copyright © 2008 by ASTM International

Epoxy–silica hybrids for coating applications

When the size of the inorganic domains in a polymer composite are reduced to nano-scale dimensions, the term nano-composites or organic-inorganic hybrids is used to differentiate them from conventional (micro-)composites. Organic–inorganic hybrids are characterised by a morphology in which the two phases are co-continuously dispersed. The inclusion of a nano-sized inorganic phase in an organic matrix, can be brought about by either the addition of pre-formed nanoparticles or by the sol–gel method. The second method is used for the production of hybrids (also known as ceramers). In this study the nano-composites were obtained by casting solutions of epoxy resin and silica precursors both from in-situ generated silica by sol–gel using TEOS in appropriate conditions and as pre-formed dispersions of 7nm diameter silica particles. [Continues.

Ab initio Simulation of Optical Limiting: The Case of Metal-Free Phthalocyanine

We present a fully ab initio, non-perturbative description of the optical limiting properties of a metal-free phthalocyanine, by simulating the effects of a broadband electric field of increasing intensity. The results confirm reverse saturable absorption as leading mechanism for optical limiting phenomena in this system and reveal that a number of dipole-forbidden excitations are populated by excited-state absorption, at more intense external fields. The excellent agreement with the experimental data supports our approach as a powerful tool to predict optical limiting, in view of applications

Use of Micropiles for Foundations of Transportation Structures Final Report

In pile design, piles must be able to sustain axial loads from the superstructure without bearing capacity failure or structural damage. In addition, piles must not settle or deflect excessively in order for the serviceability of the superstructures to be maintained. In general, settlement controls the design of piles in most cases because, by the time a pile has failed in terms of bearing capacity, it is very likely that serviceability will have already been compromised. Therefore, realistic estimation of settlement for a given load is very important in design of axially loaded piles. This notwithstanding, pile design has relied on calculations of ultimate resistances reduced by factors of safety that would indirectly prevent settlement-based limit states. This is in part due to the lack of accessible realistic analysis tools for estimation of settlement, especially for piles installed in layered soil. Micropiles have been increasingly used, not only as underpinning foundation elements but also as foundations of new structures. Prevalent design methods for micropiles are adaptations of methods originally developed for drilled shafts. However, the installation of micropiles differs considerably from that of drilled shafts, and micropiles have higher pile length to diameter ratios than those of drilled shafts. Improved understanding of the load-transfer characteristics of micropiles and the development of pile settlement estimation tools consistent with the load-transfer response of these foundation elements are the main goals of the proposed research. A rigorous analysis tool for assessment of the load-settlement response of an axially loaded pile was developed in this study. We obtained explicit analytical solutions for an axially loaded pile in a multilayered soil or rock. The soil was assumed to behave as a linear elastic material. The governing differential equations were derived based on energy principles and calculus of variations. In addition, solutions for a pile embedded in a multilayered soil with the base resting on a rigid material were obtained by changing the boundary conditions of the problem. We also obtained solutions for a pile embedded in a multilayered soil subjected to tensile loading. We then compared our solutions with the results from FEA and also with other solutions available in the literature. Finally, we compared the results of a pile load test from the literature with the results obtained using the solutions proposed in this study. Using the obtained elastic solutions, we also performed extensive parametric studies on the load-transfer and load-settlement response of rock-socketed piles. The effects of geometry of rock socket, rock mass deformation modulus, and in situ rock mass quality were investigated. To facilitate the use of our analysis, a user-friendly spreadsheet program ALPAXL was developed. This program is based on the elastic solution obtained in this study and uses built-in functions of Microsoft Excel. ALPAXL provides the results of the analysis, the deformed configuration of the pile-soil system and the load-settlement curve in seconds. It can be downloaded at http://cobweb.ecn.purdue.edu/~mprezzi. In the context of an INDOT project, a fully instrumented load test was performed on a rock-socketed micropile. The results of this micropile load test, on a pile with high slenderness ratio and high stiffness of surrounding rock, confirmed that most of the applied load was carried by the pile shaft. The shaft capacity of hard limestone obtained from the load test at the final loading step was 1.4 times larger than the shaft capacity that is obtained using the highest value of limit unit shaft resistance suggested by FHWA (the limit unit shaft resistance qsL from the load test was 2950 kPa, while the suggested values from FHWA were 1035 – 2070 kPa). Using pile and soil properties, predictions were also made using ALPAXL. The results from ALPAXL were in good agreement with the measured data at the design load level

El estado termo-mecánico de los Andes en la región del Altiplano-Puna a partir del cálculo de la profundidad de Curie y el espesor elástico

Presentamos nuevos resultados de la distribución de temperatura en la corteza en la región del Atiplano-Puna y un nuevo modelo de espesor elástico para los Andes Centrales. El objetivo de este trabajo es determinar el estado térmico del plateau y alrededores, y analizar su influencia en el espesor elástico y la resistencia a la deformación de la litósfera. Realizamos un análisis estadístico de la anomalía magnética en dominio de frecuencias para obtener la profundidad a la base de la capa magnética, interpretada como la isoterma de Curie. El espesor elástico fue calculado a partir del análisis flexural de la deflexión de la corteza y la pseudo-topografía (construcción artificial que permite incluir las cargas internas) en el dominio de frecuencias. Hallamos que las profundidades más someras de la isoterma de Curie y los valores más altos de flujo térmico se encuentran debajo de la Puna y el arco volcánico, en coincidencia con anomalías de conductividad, velocidad y atenuación sísmica que sugieren la presencia de fundidos en la corteza. Además, observamos que el Altiplano exhibe una isoterma de Curie más profunda coincidente con otras observaciones que apuntan a una litósfera más resistente que la de la Puna. Nuestros resultados muestran que el espesor elástico se correlaciona solo parcialmente con el estado térmico y que en consecuencia, otros procesos tales como herencia del espesor elástico deben ser considerados a la hora de explicar los resultados para así evitar interpretaciones erróneas acerca de la variabilidad del campo termal.We present new constraints on the temperature distribution beneath the Altiplano-Puna plateau region and a new model of effective elastic thickness for the Central Andes. The aim of this study is to better assess the thermal state of the plateau and surrounding regions and analyze its influence on the elastic thickness and strength of the lithosphere. We performed a statistical analysis of the magnetic anomaly in frequency domain in order to obtain the depth to the bottom of the magnetic layer, interpreted as the Curie isotherm. The effective elastic thickness was calculated from the flexure analysis in frequency domain of the deflection of the crust and the pseudo-topography (an artificial construction that allows accounting for the internal loads). We find that the Puna and the volcanic arc present the shallowest Curie isotherm and highest heat-flow in agreement with conductivity, velocity and attenuation anomalies suggesting the presence of partial melts within the crust. In addition, the Altiplano exhibits a deeper Curie isotherm in coincidence with other observations pointing to a stronger lithosphere than in the Puna. Our results show that the effective elastic thickness correlates only partially with the thermal state and that, consequently, other processes, such as inheritance of the elastic thickness, need to be considered to explain the observations and avoid misinterpretations in the variability of the thermal field.Fil: Ibarra, Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; ArgentinaFil: Prezzi, Claudia Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentin

Settlement Analysis of Axially Loaded Piles

In pile design, settlement controls the design in most cases because, by the time a pile has failed in terms of bearing capacity, it is very likely that serviceability will have already been compromised. This notwithstanding, pile foundations are often designed based on the calculations of ultimate resistances reduced by factors of safety. This is in part due to the lack of accessible realistic analyses for estimation of settlement, especially for piles installed in layered soil. This paper presents a new settlement analysis method for axially loaded piles in multilayered soil and analyzes two case histories for which load tests were performed on nondisplacement piles. The analysis follows from the solution of the differential equations governing the displacements of the pile-soil system obtained using variational principles. The input parameters needed for the analysis are only the pile geometry and the elastic constants of the soil and pile. A user-friendly spreadsheet program (ALPAXL) was developed to facilitate the use of the analysis

Biexciton stability in carbon nanotubes

We have applied the quantum Monte Carlo method and tight-binding modelling to calculate the binding energy of biexcitons in semiconductor carbon nanotubes for a wide range of diameters and chiralities. For typical nanotube diameters we find that biexciton binding energies are much larger than previously predicted from variational methods, which easily brings the biexciton binding energy above the room temperature threshold.Comment: revtex4, final, twocolumn. to be published in Phys.Rev.Let. 5 pages 3 figure

Pile Driving Analysis for Pile Design and Quality Assurance

Driven piles are commonly used in foundation engineering. The most accurate measurement of pile capacity is achieved from measurements made during static load tests. Static load tests, however, may be too expensive for certain projects. In these cases, indirect estimates of the pile capacity can be made through dynamic measurements. These estimates can be performed either through pile driving formulae or through analytical methods, such as the Case method. Pile driving formulae, which relate the pile set per blow to the capacity of the pile, are frequently used to determine whether the pile has achieved its design capacity. However, existing formulae have numerous shortcomings. These formulae are based on empirical observations and lack scientific validation. This report details the development of more accurate and reliable pile driving formulae developed from advanced one-dimensional FE simulations. These formulae are derived for piles installed in five typical soil profiles: a floating pile in sand, an end‐bearing pile in sand, a floating pile in clay, an end‐bearing pile in clay and a pile crossing a normally consolidated clay layer and resting on a dense sand layer. The proposed driving formulae are validated through well-documented case histories of full-scale instrumented driven piles. The proposed formulae are more accurate and reliable on average than other existing methods for the case histories considered in this study. This report also discusses the development of a pile driving control system, a fully integrated system developed by Purdue that can be used to collect, process, and analyze data to estimate the capacities of piles using the Case method and the pile driving formulae developed at Purdue

A Continuum-Based Model for Analysis of Laterally Loaded Piles in Layered Soils

An analysis is developed to calculate the response of laterally loaded piles in multilayered elastic media. The displacement fields in the analysis are taken to be the products of independent functions that vary in the vertical, radial and circumferential directions. The governing differential equations for the pile deflections in different soil layers are obtained using the principle of minimum potential energy. Solutions for pile deflection are obtained analytically, whereas those for soil displacements are obtained using the one-dimensional finite difference method. The input parameters needed for the analysis are the pile geometry, the soil profile, and the elastic constants of the soil and pile. The method produces results with accuracy comparable with that of a three-dimensional finite element analysis but requires much less computation time. The analysis can be extended to account for soil non-linearity