Print Email Facebook Twitter Dam Safety Concepts Title Dam Safety Concepts Author Duricic, J. Contributor Vrijling, J.K. (promotor) Van Gelder, P.H.A.J.M. (promotor) Faculty Civil Engineering and Geosciences Department Hydraulic Engineering Date 2014-12-11 Abstract The majority of dams constructed in the world are dams that can be categorized as embankment dams. Throughout history we can point to many failures of dams, and embankment dams in particular. Nowadays it is clear that the goal to construct stable dams has not been achieved, even with advanced technologies and construction techniques available. There are always unexpected factors which can produce unforeseen problems, and also most of the suitable sites are already utilized. This might increase the probability of failure in the future, therefore constructors will have to face more complicated geological conditions. The main reasons for failures are inconsistency between design (design hypothesis) and reality (unpredictability encountered on the site or during construction), natural processes like flash floods, rock and landslides, earthquakes and deliberate human actions. Research on failure case histories and lessons learned from them provide important answers and leads to improvement in dam safety approach. The concerns of dam safety are related to dam procedures that will avoid a dam break or diminish the probability of a dam break or any other abnormal event. Most of dam safety decisions are based on the predictions of the probability of dam failure and of resulting loss-of life. In this thesis the intention is to highlight the methodologies for dam safety decisions. Previously, risk and uncertainty methods have been applied for safety assessments of hydraulic structures but they were restricted to some extent. In this thesis an improvement of the methodology proposed by Hsu et al. (2011) is suggested in three aspects. The first is the development of multivariate flood frequency analyses in which the annual maximum peak discharges and the surface runoff are modeled as a bivariate distribution function. The second is the treatment of the initial reservoir level as a random variable, and the third is the overtopping assessment sample zone which is divided jointly by multivariate flood frequency, wind frequency and initial stage frequency, generating eight sub domains. Damage of property due to dam break discharge is certain, but loss of life depends on the flooded area and population. Therefore, analysis of dam breaching and the resulting floods are crucial for reduction of potential for loss of life and damage of property. Further in this thesis the breach itself and methodologies applied to quantify the peak discharge due to breaching are highlighted. Many computer models are capable of simulating dam-break hydrographs and routing these hydrographs downstream. However, dam break analysis models normally require certain geometric and temporal characteristics of the dam breach as inputs for the model. An alternative approach to estimating these parameters has been the use of case study data to develop empirical-regression relationships relating the peak discharge of the breach to the dam height and/or reservoir-storage volume. An efficient model based on Kriging methodology is proposed to forecast peak discharge at certain height and volume of water respectively, behind the dam at failure. The time of occurrence and magnitude of floods is very difficult to predict while it is possible to predict fairly accurately the propagation of the flood wave along the river, once that a flood wave is generated at some upstream location in the river (in the case of this thesis due to dam break). The dam-break induced loads and their effects on buildings are of vital importance for assessing the vulnerability of buildings in flood-prone areas. A comprehensive methodology, for risk assessment of buildings subject to flooding, is nevertheless still missing. The intention of this thesis is to take a step forward by following previous research. A new and efficient variable that can take into account both the shape of the structure and flow conditions is proposed and new and practical formula for predicting the mean normalized force is suggested for different types of obstacles, which is missing in previous research. As a part of a dam safety assessment, an empirical breaching model is coupled with a numerical model in order to achieve a more accurate prediction. However, empirical models provide only peak discharge calculation, neglecting breach development in time. In this thesis a numerical model is constructed and a hydrograph is calculated based on dam breach development and failure time whereas breach parameters are calculated based on empirical model. Outcomes of this thesis can contribute to a growing tendency to assess the safety levels of existing dams based on risk and uncertainty analysis using mathematical and statistical models with multivariate flood frequency analysis. Previously designed dams should be checked with at least a bivariate analysis especially in the determination of spillway discharge coefficient and dam crest level. Breaching development is a complex process; therefore many assumptions have to be made in order to describe the process as close as possible, in the same time the structural uncertainties related to failure increase. In this thesis an efficient formula for better understanding and application of dam-break flow induced forces on structures of different cross sections is suggested with a new parameter that describes the shape of the obstacle which is named “shape of influence”. The importance of distinguishing the breach initiation time and breach development time is also highlighted in this thesis. So far, breach initiation time has not been considered as a distinct parameter in the majority of dam case studies, and it is not input in most of the numerical models. We could see that distinguishing between these two phases is still a difficult task because the guidance available for determination of the breach initiation time is very limited. In reality we can only predict breach development time. Subject damsafety To reference this document use: https://doi.org/10.4233/uuid:9568dc21-9c84-441f-88a5-c132a6f2a437 ISBN 9789461864079 Part of collection Institutional Repository Document type doctoral thesis Rights (c) 2014 Duricic, J. Files PDF Thesis_final.pdf 4.66 MB Close viewer /islandora/object/uuid:9568dc21-9c84-441f-88a5-c132a6f2a437/datastream/OBJ/view