GEOSYNTHETICS FOR RISK MITIGATION AND PREVENTION

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GEOSYNTHETICS FOR RISK MITIGATION AND PREVENTION

Patrick Kabir Fuentes Andrade 1 Omar Leonardo Torres Parada 2

1 1Civil Engineer National University of Colombia. Water Resources Specialist with Catholic University of Colombia, Design Engineer and specifications in Hydraulic and Environmental Geomatrix S.A. S. Address: Calle 15 72-72 Bogota Colombia, phone +57-1 424 9999, email [email protected] . 2 2Civil Engineer National University of Colombia. Specialist geotechnical and pavements Universidad Nacional de Colombia - Arizona State University. Technical Director Geomatrix S.A. S. Address: Calle 15 72-72 Bogota Colombia, phone +57-1 424 9999, email [email protected].

ABSTRACT Abstract: The development of engineering works under the concept of risk is focused towards the combination of threat and vulnerability. This can be understood in the probability that an adverse event can occur and what degree of damage this event can cause on a specific system [1]. In this scope, the use of geosynthetics in civil projects has evolved; from being a technical solution in pavement and subdrainage construction. Today, geosynthetics are being used as primordial elements in construction of retaining walls, slope protection, shore protection and enhancement of banks in rivers and coasts. This paper is intended to support the importance of these materials in infrastructure works. Its performance, advantages in construction processes and other required materials make it possible to design and develop structures and engineering solutions that aim to reduce the susceptibility of a system to a specific natural threat. Keywords: Risk, vulnerability, threat, susceptibility, geosynthetics, mechanically stabilized earth walls, erosion control mats, geogrid, fabric form, geotextile tubes.

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mailto:[email protected]

mailto:[email protected]

Revista Guarracuco 1. INTRODUCTIÓN According to [ 1] The risk is the combination of the probability that an event occurs of a certain magnitude, and the probability that the event cause negative effects on a given system, which can be a work of infrastructure or a human settlement. Under this definition, the risk to the system is thus based on two factors, the threat and vulnerability, and can be expressed through the equation (1). Risk=threat ×Vulnerability (1) Where the threat is the phenomenon or dangerous condition that can cause damage on the system, and vulnerability are the characteristics of the system that makes it more or less weak before the negative effects of the threat. The vulnerability in turn is a function of three factors [ 2], as expressed in equation (2) Vulnerability = (Exposure × Susceptibility) / Resilience (2) Donde la exposición es la desventaja del sistema o comunidad por su ubicación o localización; la susceptibilidad es el grado de fragilidad ante la amenaza, y la resiliencia es la capacidad del sistema de resistir, absorber, adaptarse y recuperarse de los efectos negativos causados por una amenaza. Geosintéticos Los geosintéticos son materiales flexibles en forma de láminas [3], fabricados a partir de distintos polímeros (poliéster, polipropileno, polietileno de alta densidad, entre otros) diseñados para complementar y mejorar el desempeño de los materiales térreos en la construcción de obras civiles, optimizando el uso de los recursos en los proyectos. Los geosintéticos cumplen varios propósitos importantes, entre los cuales se destacan mejorar el desempeño de las estructuras (mayor durabilidad y mayor vida útil) y reducir los costos en comparación con soluciones tradicionales (utilización de elementos de menor especificación y mayor rendimiento de construcción). Los primeros geosintéticos utilizados en ingeniería fueron los geotextiles para separación en estructuras de pavimentos y filtro en sistemas de subdrenaje [4]. Hoy en día existen diversos tipos de geosintéticos, cuya aplicación se ha extendido hacia la construcción de estructuras de contención en suelo mecánicamente estabilizado, y control de erosión y manejo hidráulico en ríos y costas. La Tabla 1 relaciona varios tipos de geosintéticos y las funciones que cumplen dentro de las obras de ingeniería. Tabla 1. Relación de tipos de geosintético y sus funciones

Geosynthetic Function Non-woven Geotextiles

Filtration, Separation

Geotextiles fabrics Filtration, Separation, stabilizing, strengthening, erosion control, containment

Geonets Reinforcement,

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confinement Textile Frameworks Confinement Mantles for erosion control

Erosion Control

For drain geocompounds

Drain

Geoceldas Stabilization, erosion control, containment

2. MATERIALES Y MÉTODOS 2. THE GEOSINTÉTICOS AND RISK Frequently used in the design of engineering projects to reduce the risk of the infrastructure and the communities to natural hazards, whose success depends on the susceptibility of each element before the aggressive conditions that may occur during the occurrence of a particular phenomenon. In some cases, these projects must be run on sites that are difficult to access, which increases the requirement of the proposed solutions In this picture is conducive, in different cases, the implementation of geosynthetics due to their contribution to the performance of the structures are reflected in: • Increase in the resistance: Use of geosynthetic materials of high tensile designed for reinforcement of structures. • Deformations tolerant: geosynthetics are flexible elements able to tolerate deformations without losing the integrity. • Durability: polymers are highly durable thanks to its chemical stability. With this contribution of the geosynthetics reduces the susceptibility and increases the resilience of the structures, which entails reducing vulnerability, and therefore to reduce the risk of systems to protect (Equation (1), equation (2)). The following describes some applications and the manner in which its appropriate use reduces the risk of various types of natural hazards. 3. RESULTADOS 3. PREVENTION OF THE RISK WITH GEOSINTÉTICOS BEFORE EVENTS SÍSMICOS 3.1 Containment Structures in soil mechanically stabilized EMS A structure in soil mechanically stabilized (picture 1) is a mass of soil to which you will include reinforcement elements such as sheets, strips or layers with the purpose to increase their resistance to the court [ 5]. This increase in resistance is governed by the resistance of the material forming Térreo (geomechanical parameters), the resistance of the geosynthetics in reinforcement (resistance to voltage per

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Revista Guarracuco unit of bandwidth) and finally the resistance associated with the interaction between the two elements (which depends on the type and shape of the reinforcement element) Photo 1. In soil structure reinforced with geonets

Source: Own. There are two mechanisms for interaction or transfer of efforts between the soil mass and the reinforcing element: • The transfer by passive resistance, which is generated when elements are used with type mesh openings, and is basically the effect of bite of the soil particles in these openings (Figure 1). Figure 1. Transfer of efforts by passive resistance

Source: Own. • The transfer by friction that occurs between the upper and lower layers of soil and the reinforcing element (Figure 2). Figure 2. Transfer of efforts by friction

Geosintético derefuerzo

Fuerza dearrancamiento

Fuerzafriccionante

Presión normal

Partículas desuelo

Source: Own.

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One of the advantages of the structures in reinforced soil is its flexibility and its ability to absorb the deformations; this condition makes them more resistant to the seismic loads compared to rigid structures, such as reported in the FHWA publication FHWA-NHI-00-043, while maintaining the condition of service of a better way in comparison with high-rigidity structures such as concrete. By this condition, to build structures of containment or shaping of fillers in geosynthetic reinforced soil, reduces the susceptibility and increase the resilience of the works before seismic events. As reinforcing elements, geonets are used mainly for high uniaxial tensile, whose interaction with the ground is da by passive resistance and friction. The resistance of the geomalla to use, the separation between reinforcement strips and the length of the reinforcement strips are due to a stability analysis of internal, external and global, for the specific condition of the project. Picture 2 illustrates the construction of a reinforced structure in soil. Photo 2. Construction of structure in soil reinforced with geonets

Source: Own. 4. PREVENTION OF THE RISK WITH GEOSYNTHETICS BEFORE FALLING MATERIAL ON SIDE SLOPES AND HILLSIDES It is often the existence of nearby structures to slopes with potential detachment of materials, such as in the case of tracks with section in court formed by rocky massifs highly fractured or conglomerates with blocks or detritus, as well as urbanized areas on slopes with fall of detritus. A measure to reduce the risk of this type of threat is the lining of the slopes with elements that are able to contain the material to be detached, to which can be used geosynthetics high resistance and durability before the exposure to ultraviolet rays. For this application are used two types of geosynthetics, the mantles for permanent erosion control and geonets biaxial high resistance. 4.1 CLOAKS for permanent erosion control of high resistance Shutters for the products of erosion control are designed to protect the soil surface from erosion and facilitate the establishment of vegetation, however, there are permanent cloaks that in addition to the coverage and dimensionality, offer resistance to the higher voltage to 40 kN/m, so they are able to retain elements of detritus detachment or small blocks of material (Photo 3). These cloaks, moreover, can be supplemented by

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Revista Guarracuco other elements, such as metallic mesh, to increase the capacity of resistance under conditions of increased demand. Photo 3. Drop Control of detritus with cloaks for permanent erosion control.

Source: Own 4.2 Geonets for control of fall of detritus An alternative to contain or dissipate the energy of the falling of stones on rocky slopes fractured is the use of geonets biaxial high resistance. When simply requires dissipate energy during the fall of stones, anchored geonets are used only in the crown of the slope, surfacing the slope due to way to curtains, in such a way that cushion the decline of blocks that are given off. This solution does not imply the use of anchors because the objective is not to avoid the detachment of the detritus or blocks, but also to ensure a safe drop (picture 4). This solution requires a proper management of the material loosened in the leg of the slope, that is to say, their implementation is feasible always and when you have enough space in the lower area to receive the material loosened. Picture 4. Geonets biaxial for dissipation of falling blocks.

Source: Own When it is required to avoid the falling blocks, the geomalla must be securely anchored to the slope with anchors properly distributed on the surface. In this case, the geomalla is the element that operates as a flexible display of high resistance, capable of transmitting the force exerted by the blocks toward the anchors (Photo

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5). The complete solution must be designed entirely from the geotechnical point of view, defining the length and spacing of the anchorages and the resistance to minimum voltage required in the geomalla. Photo 5. Geonets biaxial for control of fall of blocks.

Source: Own PREVENTION OF THE RISK WITH GEOSYNTHETICS FLOOD AND WINTER SEASONS PROTRACTED Coatings The effect of excessive increases in the levels of the water bodies during long winter seasons generates deterioration and erosion of the shores, which is why it is important the implementation of coatings or protections. In this field the geosynthetics they offer practical solutions for this type of need, with significant advantages over other systems, mainly by the flexibility and durability of these elements (polymers are inert to chemical and biological agents in the soil and bodies of water), and the ease to interact with different materials, and may take advantage of the resources available on the web sites of implementation of the projects. Textile Frameworks One of the solutions of coatings with geosynthetics are the Frameworks textiles, which were components manufactured with two layers of geotextile intertejidos symmetrically distributed in points, forming a bag that is filled with fluid concrete coatings, to get adjusted to the ways of the land, whose advantage in this case is the ease and speed of installation, without requiring additional elements for the leveling of concrete. These systems allow the construction of the coatings in particular thicknesses of homogeneous, in addition, its configuration generates surfaces with roughness similar to rocks of boulders, which favors the power dissipation of the flow (Photo 6). Another important advantage of the Frameworks textiles are the points of intertejido that control the thickness of the element during filling and during the service allow the relief of the hydrostatic pressure within the field (the geotextiles allow the passage of water through their openings)

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Revista Guarracuco Photo 6. Protection of shores with concrete using Frameworks textiles.

Source: Own The coatings specifically built with Frameworks textiles are a versatile solution for surface protection of dams, by reducing the susceptibility of the structures before events that could cause erosion and before the sudden fall of water level known as flooding fast. 5.1.2 Geomats or mattresses of surrounded Another coating system that employs geosynthetics is the formation of mattresses are surrounded of content within mats or baskets made with polymeric mesh designed for that purpose. These coatings are hard shells that protect the ground before the erosion, and in addition are conducive to coat and protect structures submerged in the scour, since its main virtue is to be highly flexible, able to tolerate deformations and absorb processes of scour. These coating systems to be porous media must be accompanied by the use of geotextiles for erosion control, in such a way that there is no loss of particles through the surrounded. These structures are highly cost-effective in places where you can take advantage of the site material for filling, such as in banks where there are nearby aluvales deposits; its filling is artisanal, allowing you to leverage local labor, without requiring the use of sophisticated equipment, and may be carried out the activity in areas of difficult access (Photo 7). Photo 7. Protection of shores are surrounded with mattresses of trusting with polymeric mesh.

Source: Own

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The durability of the polymeric mesh is vital for the life of the structure, important advantage offered by the geosynthetic materials before another type of systems because it didn't suffer deterioration by corrosion, as is the case of polyester that is resistant to aggressive natural environments, allowing the implementation of these solutions in shorelines (Photo 8). Photo 8. Protection of shorelines with mattresses of geonets are surrounded with trusting of polyester.

Source: Own The mattresses are surrounded of confined with mesh polimericoas coatings that are best suited to the condition of the dynamic and meandricos developed rivers, because of its flexibility, maintain the integrity of the protection while they support processes of scour. Its porous nature allows for rapid integration into the environment as they normally sediments, rich in nutrients are embedded in the matrix are surrounded, allowing the establishment of vegetation 5.2 Protection and management hydraulic The geosynthetics also participate in a major way in the construction of hydraulic works for handling, as invasive structures into bodies of water and marginal structures of enhancement, which is commonly built to guide the riverbed, check the erosional events. 5.2.1 Geotextile Tubes The geotextile tubes are assembled elements with high strength geotextiles [ 6], that make up a large container (perimeters of up to 13.0 m) that are filled with sand hydraulically to form nuclei of structures. The geotextile tubes are designed according to the height to reach, normally the height of a single element varies between 1.0 m and 2.0 m, but combined in pyramid type structures to achieve the heights required (Photo 9). The design of the element is in the verification of the required strength in the geotextile for heights.

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Revista Guarracuco Photo 9. Geotextile Tubes for protection of shores.

Source: Own The geotextile tubes are highly stable structures given the geometry that is obtained in the filling, its aspect ratio is always less than 0.7 . This type of item it is highly efficient for the formation of core of the management of hydraulic structures (such as barriers for protection of shores, jetties and dykes to relace of shores, as shown in the photograph 10) in places where you can take advantage of the bed material of the body of water (rivers or developed in coastal areas). Photography 10. Breakwaters to channelling formed with geotextile tubes.

Source: Own Given that a geotextile tube is basically sand-like material encapsulated in geotextile high-resistance, this encapsulation is vulnerable to mechanical damage that can be generated by the impacts of material transported by the currents or by human activities, so it should be supplemented with coating systems that generate a hard shell that can withstand these conditions. This coating system can be built with geosynthetics, such as the usage of Frameworks textiles (Photo 11) or mattresses confined with hidromallas surrounded, or simply loose surrounded.

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Photography 11. Coating with Frameworks geotextile tubes filled with concrete textile.

Source: Own 5.2.2 Dykes in reinforced soil Geosynthetics are also an alternative for the construction of structures of enhancement and flood control such as dykes, and can reduce the slope of the slopes, optimizing the space available for the structures, and increasing the resistance of the body of the structure before erosion or scour. Foto 12. Photo dike in reinforced soil

Source: Own These structures can be constructed with geonets or geotextiles as reinforcing elements. During the design must be carefully defined the system to close the layers for both a wet face and Dryside, in accordance with the conditions to which the structure will be subjected during his period of service. When geonets are used as reinforcing elements, in the wet face must be included in each layer a strip of geotextile filter to control the erosion of the particles that make up the structure. When the structure is constructed using geotextiles as reinforcement, each layer of geotextile serves as closure type. "Wrap around". To reduce the susceptibility of the structure, can be projected an additional coating in a wet face, that can serve as protection against mechanical shock or before human activities, such as docking of small boats.

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Revista Guarracuco The face can be lined with dry cloaks for erosion control to promote the growth of grasses on the facade. 6. CONCLUSIONS In summary, the contribution of resistance, the increase in durability, the tolerance to on stresses and deformations, make use of the geosynthetics materials widely used in fundamental structures in which the concept of risk is a crucial element in the design and functionality. 6. REFERENCES 6.2 Books: [3] D. Holtz,Robert Christopher, R Barry. Berg,Ryan R. Geosynthetics Engineering, First Printing, 1997. [4] M . Koerner, Robert, Designin with Geosynthetics, Fifth Edition, 2005. [5] US Department of Transportation Federal Highway Administration FHWA, Publication No.FHWA-NHI-00-043 Mechanically Stabilized Earth Walls and Reinforced Soil Slopes Design & Construction Guidelines, March 2001. 6.4 Technical Reports: [1] Estrategia Internacional para la Reducción de Desastres de las Naciones Unidas UNISDR, Terminología sobre Reducción de Riesgo de Desastres para los conceptos de Amenaza, vulnerabilidad y riesgo, 2009. 6.5 Papers: [6] Espinosa, Carlos E. Torres, Omar L., Tubos Geotextil, características, conceptos, materiales y aspectos de análisis. XV Jornadas Geotécnicas de la Ingeniería Colombiana, Sociedad Colombiana de Ingenieros, Bogotá. 6.6 Works Available Online: [2] Centro Internacional para la Investigación del Fenómeno de El Niño CIIFEN, Definición de Riesgo, http://www.ciifen.org/index.php?option=com_content&view=category&id=84&layout=blog&Itemid=111&lang=es

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GEOSYNTHETICS FOR RISK MITIGATION AND PREVENTION

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