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Yanqui C.,National University of San Agustin
Computer Methods and Recent Advances in Geomechanics - Proceedings of the 14th Int. Conference of International Association for Computer Methods and Recent Advances in Geomechanics, IACMAG 2014 | Year: 2015

Among others, lateral earth pressure on a rigid retaining wall is one of the soil mechanics problems which can be successfully solved using the granular mechanics, provided that the contact force network is caused by the soil own weight. Assessment of the backfill stress state is reduced to the geometric problem of determining the intersections between the force network lines and the backfill sloping surface, having account of the constraints imposing by the wall back side. The backfill pressure on the wall may be calculated by finding the stress tensor at every point of the backfill, or by applying the law of sines to the unit forces polygon. In this paper, the coefficient of lateral earth pressure is derived for two cases: A backfill with uniform stress state, and a backfill with wall friction; both of them at rest and plastic states. For yielding soils, the first case is compared with the generalized Rankine's theory, revealing the total conformity of both theories; and the second, with the rigorous Boussinesq's plastic theory, showing to be the best fit. From the results, it is concluded that granular mechanics compresses in a unique theory the at rest and plastic states of granular soils, furnishes generalized formulas for calculating the lateral pressure exerted by a straight-boundary soil, and provides a rigorous but very simple method for a broken-boundary soil. © 2015 Taylor & Francis Group, London.

Jimenez M.A.,University of Santiago de Chile | Jimenez M.A.,Institute Ecologia y Biodiversidad IEB | Jimenez M.A.,National University of San Agustin | Jaksic F.M.,University of Santiago de Chile | And 10 more authors.
Ecology Letters | Year: 2011

Extreme climatic events represent disturbances that change the availability of resources. We studied their effects on annual plant assemblages in a semi-arid ecosystem in north-central Chile. We analysed 130years of precipitation data using generalised extreme-value distribution to determine extreme events, and multivariate techniques to analyse 20years of plant cover data of 34 native and 11 exotic species. Extreme drought resets the dynamics of the system and renders it susceptible to invasion. On the other hand, by favouring native annuals, moderately wet events change species composition and allow the community to be resilient to extreme drought. The probability of extreme drought has doubled over the last 50years. Therefore, investigations on the interaction of climate change and biological invasions are relevant to determine the potential for future effects on the dynamics of semi-arid annual plant communities. © 2011 Blackwell Publishing Ltd/CNRS.

Yanqui C.,National University of San Agustin
Computer Methods for Geomechanics: Frontiers and New Applications | Year: 2011

The careful experiments run by several scientists have shown that the stress transmission in granular matter is a complex problem that embodies mainly the development of strong inhomogeneities and the polarization of the grain contacts. So that some theories based on the statistical mechanics have been proposed to solve some simple problems. In this paper, the principle of the biased mean value is used to determine each separable variable of the stress function. This simplifi es the Burmister's problem, to the point that only second-order transfer matrices are needed to describe the continuity conditions of the vertical displacement and stress at the interface between two consecutive layers. The imposition of the boundary conditions to the overall system not only completes the required number of equations needed to fi nd all the constants of integration but also provides a differential equation for the horizontal plane, much simpler than the Lagrange's equation for plates. Stresses, displacements and strains at any point are determined by means of hyperbolic functions of each layer thickness; for a load uniformly distributed over a circular area and over an arbitrary area as well. The values so calculated fi t well the Boussinesq's solution and the Burmister's rigorous results for small values of the coeffi cients of layer interaction, as befi ts a granular material.

Meza-Lovon G.L.,National University of San Agustin | Meza-Lovon G.L.,San Pablo Catholic University
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2012

Over the last years, the interest in preserving digitally ancient documents has increased resulting in databases with a huge amount of image data. Most of these documents are not transcribed and thus querying operations are limited to basic searching. We propose a novel approach for transcribing historical documents and present results of our initial experiments. Our method divides a text-line image into frames and constructs a graph using the framed image. Then Dijkstra algorithm is applied to find the line transcription. Experiments show a character accuracy of 79.3%. © Springer-Verlag Berlin Heidelberg 2012.

Harpel C.J.,Oregon State University | Harpel C.J.,Nanyang Technological University | De Silva S.,Oregon State University | Salas G.,National University of San Agustin
Special Paper of the Geological Society of America | Year: 2011

Misti volcano in southern Peru has a record of explosive eruptions and a nearby population of over 810,000, making it a hazardous volcano. The city center of Arequipa, Peru's second most populous city, is 15 km from the summit of Misti, and many neighborhoods are closer. As the population increases yearly, the urban boundary continues to move up the south side of the volcano. Many parts of the city are built upon the deposits from Misti's most recent Plinian eruption at ca. 2 ka. The 2 ka Plinian eruption (Volcanic Explosivity Index [VEI] 5) produced a 1.4 km 3 tephra-fall deposit and 0.01 km 3 of pyroclastic-fl ow deposits in ̃2-5 h. Column height varied during the eruption but ascended up to 29 km. Pyroclastic fl ows descended only the south side of the volcano. The tephra fall spread southwest, resulting in ̃20 cm of tephra accumulation in the area now occupied by the city center. The fl owage deposits were previously identifi ed as pyroclastic-fl ow deposits, but new sedimentologic and textural evidence suggests that ̃80% (by volume) of the deposits were emplaced wet and relatively cold. As such, they are lahar deposits. A Neoglacial advance concurrent with the eruption supports evidence for voluminous snow and ice on the edifi ce. Pyroclastic fl ows melted between 0.01 km 3 and 0.04 km 3 of ice and snow on the volcano, triggering lahars that descended the volcano and inundated channels and some interfl uves on the south fl ank. The lahars evolved downstream from proximal debris fl ows to distal hyperconcentrated fl ows, emplacing ̃0.04 km 3 of deposits. Four facies of lahar deposits are present in the channels and another facies occurs on the interfl uves. Such a comprehensive understanding of the 2 ka eruption will help to inform future volcanic hazards assessments. Pyroclastic-fl ow and tephra-fall deposits of the same magnitude could occur again and are useful in hazards assessment. The 2 ka lahars required voluminous water, which is no longer available on the volcano, and, within modern climate conditions, these deposits are not representative of possible future events. Estimations of water available from modern rain and snow suggest that lahars with volumes between 1 × 10 5 m 3 and 3 × 10 6 m 3 are possible. Lahars are more likely if an eruption occurs during a period of high snow accumulation or during subsequent heavy rainfall. Lahars up to 1 × 10 7 m 3 are possible if the Río Chili is dammed during an eruption. Lahar hazard zones generated using these volumes suggest the largest lahars could enter Arequipa. © 2011 The Geological Society of America.

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