Metodología para el análisis de los efectos de la rotura de un depósito en entorno urbano y clasificación de su riesgo potencial

El riesgo asociado a la rotura de un depósito de agua en entorno urbano (como la ocurrida, por ejemplo, en la Ciudad Autónoma de Melilla en Noviembre de 1997) y los potenciales daños que puede causar, pone en duda la seguridad de este tipo de infraestructuras que, por necesidades del servicio de abastecimiento de agua, se construyen habitualmente en puntos altos y cercanos a los núcleos de población a los que sirven. Sin embargo, la baja probabilidad de que se produzca una rotura suele rebajar los niveles de alerta asociados a los depósitos, haciéndose hincapié en la mejora de los métodos constructivos sin elaborar metodologías que, como en el caso de las presas y las balsas de riego, establezcan la necesidad de clasificar el riesgo potencial de estas infraestructuras en función de su emplazamiento y de estudiar la posible construcción de medidas mitigadoras de una posible rotura. Por otro lado, para establecer los daños que pueden derivarse de una rotura de este tipo, se hace imprescindible la modelización bidimensional de la ola de rotura por cuanto la malla urbana a la que afectaran no es susceptible de simulaciones unidimensionales, dado que no hay un cauce que ofrezca un camino preferente al agua. Este tipo de simulación requiere de una inversión económica que no siempre está disponible en la construcción de depósitos de pequeño y mediano tamaño. Esta tesis doctoral tiene como objetivo el diseño de una metodología simplificada que, por medio de graficas y atendiendo a las variables principales del fenómeno, pueda estimar un valor para el riesgo asociado a una posible rotura y sirva como guía para establecer si un deposito (existente o de nueva implantación) requiere de un modelo de detalle para estimar el riesgo y si es conveniente implantar alguna medida mitigadora de la energía producida en una rotura de este tipo. Con carácter previo se ha establecido que las variables que intervienen en la definición de riesgo asociado a la rotura, son el calado y la velocidad máxima en cada punto sensible de sufrir daños (daños asociados al vuelco y arrastre de personas principalmente), por lo que se ha procedido a estudiar las ecuaciones que rigen el problema de la rotura del depósito y de la transmisión de la onda de rotura por la malla urbana adyacente al mismo, así como los posibles métodos de resolución de las mismas y el desarrollo informático necesario para una primera aproximación a los resultados. Para poder analizar las condiciones de contorno que influyen en los valores resultantes de velocidad y calado, se ha diseñado una batería de escenarios simplificados que, tras una modelización en detalle y un análisis adimensional, han dado como resultado que las variables que influyen en los valores de calado y velocidad máximos en cada punto son: la altura de la lamina de agua del depósito, la pendiente del terreno, la rugosidad, la forma del terreno (en términos de concavidad) y la distancia del punto de estudio al deposito. Una vez definidas las variables que influyen en los resultados, se ha llevado a cabo una segunda batería de simulaciones de escenarios simplificados que ha servido para la discusión y desarrollo de las curvas que se presentan como producto principal de la metodología simplificada. Con esta metodología, que solamente necesita de unos cálculos simples para su empleo, se obtiene un primer valor de calado y velocidad introduciendo la altura de la lámina de agua máxima de servicio del depósito cuyo riesgo se quiere evaluar. Posteriormente, y utilizando el ábaco propuesto, se obtienen coeficientes correctores de los valores obtenidos para la rugosidad y pendiente media del terreno que se esta evaluando, así como para el grado de concavidad del mismo (a través de la pendiente transversal). Con los valores obtenidos con las curvas anteriores se obtienen los valores de calado y velocidad en el punto de estudio y, aplicando la formulación propuesta, se obtiene una estimación del riesgo asociado a la rotura de la infraestructura. Como corolario a la metodología mencionada, se propone una segunda serie de gráficos para evaluar, también de forma simplificada, la reducción del riesgo que se obtendría con la construcción de alguna medida mitigadora como puede ser un dique o murete perimetral al depósito. Este método de evaluación de posible medidas mitigadoras, aporta una guía para analizar la posibilidad de disminuir el riesgo con la construcción de estos elementos, o la necesidad de buscar otro emplazamiento que, si bien pueda ser no tan favorable desde el punto de vista de la explotación del depósito, presente un menor riesgo asociado a su rotura. Como complemento a la metodología simplificada propuesta, y además de llevar a cabo la calibración de la misma con los datos obtenidos tras la rotura del depósito de agua de Melilla, se ha realizado una serie de ejemplos de utilización de la metodología para, además de servir de guía de uso de la misma, poder analizar la diferencia entre los resultados que se obtendrían con una simulación bidimensional detallada de cada uno de los casos y el método simplificado aplicado a los mismos. The potential risk of a catastrophic collapse of a water supply reservoir in an urban area (such as the one occurred in Melilla in November 1997) and the damages that can cause, make question the security in this kind of infrastructures, which, by operational needs, are frequently built in high elevations and close to the urban areas they serve to. Since the likelihood of breakage is quite low, the alert levels associated to those infrastructures have also been downgraded focussing on the improvement of the constructive methods without developing methodologies (like the ones used in the case of dams or irrigation ponds) where there is a need of classifying the potential risk of those tanks and also of installing mitigating measures. Furthermore, to establish the damages related to a breakage of this kind, a twodimensional modelling of the breakage wave becomes imperative given that the urban layout does not provide a preferential way to the water. This kind of simulation requires financial investment that is not always available in the construction of small and medium sized water tanks. The purpose of this doctoral thesis is to design a simplified methodology, by means of charts and attending to the main variables of the phenomenon, that could estimate a value to the risk associated to a possible breakage. It can also be used as a guidance to establish if a reservoir (existing or a new one) requires a detailed model to estimate the risk of a breakage and the benefits of installing measures to mitigate the breakage wave effects. Previously, it has been established that the variables involved in the risk associated to a breakage are the draft and the maximum speed in every point susceptible to damages (mainly damages related to people). Bellow, the equations ruling the problem of the reservoir breakage have been studied as well as the transmission of the breakage wave through the urban network of the city and the possible methods to solve the equations and the computer development needed to a first approach to the results. In order to be able to analyse the boundary conditions affecting the values resulting (speed and draft), a set of scenarios have been designed. After a detailed modelling and a dimensionless analysis it has been proved that the variables that influence the operational draughts and the maximum speed in every point are the water level in the tank, the slope, the roughness and form (in terms of concavity) of the terrain and the distance between the tank and the control point. Having defined the involving variables, a second set of simulations of the simplified scenarios has been carried out and has helped to discuss and develop the curves that are here presented as the final product of the simplified methodology. This methodology only needs some simple calculations and gives a first value of draft and speed by introducing the maximum water level of the tank being evaluated. Subsequently, using the suggested charts, the method gives correction coefficients of the measured values for roughness and average slope of the assessed terrain as well as the degree of concavity (through transverse gradient).With the values from the previous curves (operational draughts and speed at the point of survey) and applying the proposed formulation, an estimation of the risk associated to the breakage of the infrastructure is finally obtained. As a corollary of the mentioned methodology, another set of diagrams is proposed in order to evaluate, in a simplified manner also, the risk reduction that could be gained with the construction of some mitigating measures such as dikes or retaining walls around the reservoir. This evaluating method provides a guide to analyse the possibility to reduce the risk, constructing those elements or even looking for a different site that could be worse in terms of exploitation of the tank but much safer. As a complement to the simplified methodology here proposed, and apart from completing its calibration with the obtained data after the reservoir breakage in Melilla, a number of examples of the use of the methodology have been made to be used as a user guide of the methodology itself, as well as giving the possibility of analysing the different results that can be obtained from a thorough two-dimensional simulation or from the simplified method applied to the examples.

Durability/corrosion of soil reinforced structures /

"December 1990."

Drawdown tests on earth cover material placed over an asphalt membrane, East Bench Canal, Missouri River Basin Project, Montana /

Mode of access: Internet.

An evaluation of streambank stabilization work on Richland Creek : final report /

"Printed: June 1992."

Poussée des terres ...

Mode of access: Internet.

Modelagem numérica de uma estrutura de contenção de estacas espaçadas atirantadas em areia

Retaining walls design involves factors such as plastification, loading and unloading, pre-stressing, excessive displacements and earth and water thrust. Furthermore, the interaction between the retained soil and the structure is rather complex and hard to predict. Despite the advances in numerical simulation techniques and monitoring of forces and displacements with field instrumentation, design projects are still based on classical methods, whose simplifying assumptions may overestimate structural elements of the retaining wall. This dissertation involves a three-dimensional numerical study on the behavior of a retaining wall using the finite element method (FEM). The retaining wall structure is a contiguous bored pile wall with tie-back anchors. The numerical results were compared to data obtained from field instrumentation. The influence of the position of one or two layers of anchors and the effects of the construction of a slab bounded at the top of the retaining wall was evaluated. Furthermore, this study aimed at investigating the phenomenon of arching in the soil behind the wall. Arching was evaluated by analyzing the effects of pile spacing on horizontal stresses and displacements. Parametric analysis with one layers of anchors showed that the smallest horizontal displacements of the structure were achieved for between 0.3 and 0.5 times the excavation depth. Parametric analyses with two anchor layers showed that the smallest horizontal displacements were achieve for anchors positioned in depths of 0.4H and 0.7H. The construction of a slab at the top of the retaining wall decreased the horizontal displacements by 0.14% times the excavation depth as compared to analyses without the slab. With regard to the arching , analyzes showed an optimal range of spacing between the faces of the piles between 0.4 and 0.6 times the diameter of the pile

A review of road structure data in six European countries

The European Union has expanded significantly in recent years. Sustainable trade within the Union, leading to economic growth to the benefit of the ‘old’ and ‘new’ member states is thus extremely important. The road infrastructure is strategic and vital to such development since an uneven transport infrastructure, in terms of capacity and condition, has the potential to reinforce uneven development trends and hinder economic convergence of old and new member states. In the decades since their design and construction, loading conditions have significantly changed for many major highway infrastructure elements/networks owing primarily to increased freight volumes and vehicle sizes. This, coupled with the gradual deterioration of a significant number of highway structures due to their age, and the absence of a pan-European assessment framework, can be expected to affect the smooth functioning of the infrastructure in its as-built condition. Increased periods of reduced flow can be expected owing to planned and unplanned interventions for repair/rehabilitation. This paper reports the findings of a survey regarding the current status of the highway infrastructure elements in six countries within the European Union as reported by the owners/operators. The countries surveyed include a cross-section of ‘existing’ older countries and ‘new’ member states. The current situations for bridges, culverts, tunnels and retaining walls are reported, along with their potential replacement costs. The findings act as a departure point for further studies in support of a centralised and/or synchronised EU approach to infrastructure maintenance management. Information in the form presented in this paper is central to any future decision-making frameworks in terms of trade route choice and operations, monetary investment, optimised maintenance, management and rehabilitation of the built infrastructure and the economic integration of the newly joined member states.

Reliability-based load and resistance factors for soil-nail walls

Existing soil nailing design methodologies are essentially based on limit equilibrium principles that together with a lumped factor of safety or a set of partial factors on the material parameters and loads account for uncertainties in design input parameter values. Recent trends in the development of design procedures for earth retaining structures are towards load and resistance factor design (LRFD). In the present study, a methodology for the use of LRFD in the context of soil-nail walls is proposed and a procedure to determine reliability-based load and resistance factors is illustrated for important strength limit states with reference to a 10 m high soil-nail wall. The need for separate partial factors for each limit state is highlighted, and the proposed factors are compared with those existing in the literature.

Extensional rheology and stability of gas cell walls in bread doughs at elevated temperatures in relation to breadmaking performance

The rheological properties of gas cell walls in bread doughs are considered to be important in relation to their stability and gas retention during proof and baking. Large deformation rheological properties of gas cell walls were measured using biaxial extension for a number of doughs of varying breadmaking quality at constant strain rate and elevated temperatures of 25-60degreesC. Strain hardening and failure strain of cell walls both decreased with temperature, with cell walls in good breadmaking doughs remaining stable and retaining their strain hardening properties at higher temperatures (60degreesC), while the cell walls of poor breadmaking doughs became unstable at lower temperatures (45-50degreesC) and had lower strain hardening. Strain hardening measured at 50degreesC gave good correlations with baking volume, with the best correlations achieved between rheological measurements and baking tests that used similar mixing conditions. As predicted by the considered failure criterion, a strain hardening value of I defines a region below which gas cell walls become unstable, and discriminates well between the baking quality of a range of commercial flour blends of varying quality. This indicates that the stability of gas cell walls during baking is strongly related to strain hardening properties, and that extensional rheological measurements can be used as indicators of baking quality.

Seismic soil-interaction on earth retaining structures. Performance-based seismic design of a Retaining Wall

The design of containment walls suffering seismic loads traditionally has been realized with methods based on pseudoanalitic procedures such as Mononobe- Okabe's method, which it has led in certain occasions to insecure designs, that they have produced the ruin of many containment walls suffering the action of an earthquake. A method is proposed in this papers for the design of containment walls in different soils, suffering to the action of an earthquake, based on the Performance-Based Seismic Design.

Performance-based seismic design of a retaining wall

The design of containment walls suffering seismic loads traditionally has been realized with methods based on pseudoanalitic procedures such as Mononobe-Okabe's method, which it has led in certain occasions to insecure designs, that they have produced the ruin of many containment walls suffering the action of an earthquake. The recommendations gathered in Mononobe-Okabe's theory have been included in numerous Codes of Seismic Design. It is clear that a revision of these recommendations must be done. At present there is taking place an important review of the design methods of anti-seismic structures such as containment walls placed in an area of numerous earthquakes, by means of the introduction at the beginning of the decade of 1990 the Displacement Response Spectrum (DRS) and the Capacity Demand Diagram (CDD) that suppose an important change in the way of presenting the Elastic Response Spectrum (ERS). On the other hand in case of action of an earthquake, the dynamic characteristics of a soil have been referred traditionally to the speed of the shear waves that can be generated in a site, together with the characteristics of plasticity and damping of the soil. The Principle of the energy conservation explains why a shear upward propagating seismic wave can be amplified when travelling from a medium with high shear wave velocity (rock) to other medium with lower velocity (soil deposit), as it happened in the earthquake of Mexico of 1985. This amplification is a function of the speed gradient or of the contrast of impedances in the border of both types of mediums. A method is proposed in this paper for the design of containment walls in different soils, suffering to the action of an earthquake, based on the Performance-Based Seismic Design.