Ciclo Conferencias 2021

Excavation operations produce several tons of soil generally contaminated by the presence of pollutants. In France, excavated soil is considered as waste and it can be either sent to landfill or destined for reuse depending on the level of pollution. In any case, soil should be properly treated in order to: (i) decrease the release of pollutants into the environment, and (ii) minimize the problems involved in civil engineering applications due to the reactions between cementitious phases and pollutants. In the context of this project, we focused on sulfates and molybdenum (Mo). Concerning sulfates, we considered two main issues: (i) external sulfate attack of concrete structures, which are in direct contact with sulfate-rich soil (e.g., dams, foundations), and (ii) the release of sulfates into solution in addition to the swelling and mechanical strength loss in sulfate-rich soil intended for valorization (e.g., reuse in road construction). In the case of Mo, its release into solution is also a serious concern as it can lead to significant risks for the environment. Therefore, in this project, we investigated the reaction of concrete in contact with sulfates, and the stabilization of sulfates by using alternative binders for pollution reduction and for reuse of soil. Additionally, we studied the interaction of Mo with alternative binders and their capacity to stabilize Mo. In this conference, we will first talk about the capacity of several different concretes to resist external sulfate attack. Second, we will discuss about the capacity of four different binders to stabilize sulfates in a sulfate-spiked soil. In this part, we will focus on two main phenomena: (i) soil volume expansions caused by the formation of ettringite, and (ii) the release of heavy metals from treated soils into solution. Finally, we will talk about the interaction of Mo with three different binders and their capacity to stabilize Mo.

Se hará una breve descripción del proceso erosivo, aguas arriba, del río Coca, entre la excascada San Rafael y la captación del Proyecto Coca Codo Sinclair. En especial se describirá un megadeslizamiento en el sector de la población de San Luis y los daños que ha ocasionado a la estructura vial y petrolera, del sector; así como la destrucción del puente sobre el río Coca que accede a un túnel secundario (Ventana 2) que comunica con el túnel principal del proyecto CCS.

Cross-laminated timber (CLT) is a relatively new construction building system based on structural panels made of several layers of boards stacked crosswise and glued together on their faces [1]. As CLT panels are light-weight structural elements with high stiffness and strength to bending, compression and shear, they are an economically competitive building system when compared to traditional options and therefore, are a suitable candidate for some applications which currently use concrete, masonry and steel. Given the numerous advantages of building with timber, an increasing number of multi-story CLT buildings is sprouting around the world.
In this presentation we focus on recent developments achieved in the context of computational modelling of the structural response of timber and CLT structures. In order to determine the mechanical properties of CLT, a computational homogenisation scheme based on the volume averaging of the stress and strain fields over a representative volume element (RVE) of material is adopted. CLT floors and walls are modelled with mechanical properties obtained by the present approach. Metallic connectors are modelled with their hysteretic behaviour, including stiffness and strength degradation, dependency on the loading/unloading cycles, softening and contact effects, among others. The behaviour of each connector is defined along three orthogonal axes. Moreover, we investigate the seismic response of a single-storey CLT building constructed with angle brackets, hold-downs and screw connections. Some of the numerical predictions are compared with experimental results and are validated successfully. This is part of an ongoing researchs.

For many geotechnical problems, a good knowledge of the dynamic soil behavior is important. Simulations of geotechnical problems with cyclic or dynamic loads such as those caused by earthquakes are still the subject of research worldwide. There is often a lack of reliable measurement data for validating the simulations. Model tests in the earth's gravity field (1g) and in centrifuges can provide important insights and measurement data for the derivation and validation of theoretical approaches and simulations. However, physical measurements can be very difficult. In the contribution, the Digital Image Correlation (DIC) method was used to evaluate different types of experiments:
The first part of the contribution deals with static and dynamic compaction processes in model tests. In addition, numerical models have been validated with the experiments using a hypoplastic material law. The experimental results confirm well-known theories of the fundamental deformation behavior of sand. The DIC method allows a detailed and coherent evaluation in a transparent section plane.
The other part of the contribution deals with methods and preliminary results of a currently finished research project at the National Polytechnic University (EPN): PIE-DICA-DAAD-2020 ("CONTRIBUTION TO ASSES THE SEISMIC SAFETY IN QUITO"). One part of the project aims to contribute to the stability assessment of slope systems under the effects of earthquakes. Therefore, small-scaled model tests with a one-dimensional shaking table were developed. It was to be shown to what extent the central measurement method of digital image correlation from recordings of a digital camera can measure the movement behavior of the model and the emergence and progression of the failure mechanisms.

El páramo ecuatoriano es un ecosistema neotropical de altura que actúa como una fuente constante de agua de alta calidad, adicionalmente los suelos del páramo almacenan significantes cantidades de carbono a escala regional. Gran parte de sus propiedades viene dada por la sinergia entre la naturaleza de sus suelos; los cuáles en gran medida se han desarrollado a partir de depósitos volcánicos; y las condiciones ambientales, que favorecen la acumulación de carbono. A pesar de la gran importancia que estos ecosistemas poseen, enfrentan crecientes presiones, principalmente actividades agrícolas y de pastoreo intensivo, las cuales podrían tener efectos adversos. En este estudio, comparamos el contenido y los stocks de carbono orgánico en dos tipos de vegetación del páramo: pajonal (Pa) y almohadilla (Al). El estudio se desarrolló en el volcán Antisana. Suelos de dos áreas con diferente vegetación dominante (Pa y Al) fueron muestreados, a dos profundidades diferentes (Horizonte superficial (A) y horizonte enterrado (2Ab)) Los suelos corresponden a Andosoles vítricos los cuáles se desarrollaron a partir de las cenizas depositadas por el volcán Quilotoa (800 yr. BP). Diferencias significativas en el contenido de C del suelo fueron detectadas entre los dos tipos de vegetación estudiadas. Los suelos bajo almohadilla contienen mas carbono que bajo Pajonal (9.4±0.5% vs. 8.0±0.4 respectivamente) en horizontes superficiales. Esta diferencia no es significativa en los suelos enterrados, lo que indica que la vegetación tiene un efecto limitado a la superficie de los suelos estudiados. En términos de stock de carbono, a pesar de tener un mayor contenido de C, los suelos superficiales bajo almohadilla, almacenan menos carbono orgánico que bajo pajonales (18.23±1.0 vs 20.04±1.1 kg/m2). Esto es causado por una disminución considerable de la densidad aparente causado por la vegetación de almohadillas. La cantidad de C almacenada en los páramos del Antisana, es mas del doble que el promedio mundial para Andosoles vítricos (8.2 kg/m2), resaltando la importancia regional de los suelos de los páramos para el almacenamiento de carbono. Estudios adicionales son necesarios para establecer los factores relacionados con la vegetación que gobiernan la dinámica del carbono y su estabilidad en suelos de páramo

En Ecuador, los incendios forestales devastan miles de hectáreas cada año, a ciencia cierta no se conocen sus efectos, cómo es la sucesión (reemplazo o no) de la vegetación luego del incendio, ni su impacto en las propiedades de los suelos, tampoco su repercusión en la disponibilidad de recursos hídricos. El objetivo principal del proyecto es identificar el impacto de los incendios en la vegetación, en las propiedades hidrofísicas del suelo y en la alteración del ciclo hidrológico en el área del incendio. Para esto primero se planteó un mapeo de las coberturas vegetales pre y post incendio a través de imágenes satelitales del área estudiada. Se cuantificó los cambios en las propiedades físicas de los suelos, nutrientes, capacidad de retención de agua, entre otros, bajo diferentes coberturas vegetales en un perfil que ha sido afectado recientemente por un incendio comparándolo con otro que no. Posteriormente se realizó una réplica de incendio en laboratorio con una muestra inalterada del suelo, replicando inclusive las intensidades de precipitación con ayuda de un simulador de lluvia y analizando la propiedades del suelo pre y post incendio para conocer su efecto en el balance hídrico de las dos zonas comparativas.