Failure Assessment of Embankment Dam Elements: Case Study of the Pirot Reservoir System

The paper presents a functionality investigation of the key dam elements based on finite element analysis. A detailed analysis of filtration processes, dam strength, and the surrounding rock mass was conducted. Dam elements whose potential damage could jeopardize the normal functioning of the embankment dam have been identified. A particular emphasis was placed on the analysis of dam elements that have been identified as weak points. A numerical analysis of the impact of individual grout curtain zone failure on leakage under the dam body, a strength analysis of the overflow section, as well as the analysis of the slope stability that can compromise the functioning of the spillway have been performed. To analyze the partial stability of individual structural elements, a new measure of local stability was introduced as the remaining load-bearing capacity. As a case study, the Zavoj dam, which is a part of the Pirot reservoir system in the Republic of Serbia, was used. Investigation revealed that local damage to the grout curtain will not significantly increase leakage under the dam body, the overflow section is one of the most robust elements of the dam, but the slope above the spillway can compromise the functioning of the overflow and thus the safety of the entire dam. Based on the analysis of the results of the remaining load-bearing capacity, the dependence of the spillway capacity on earthquake intensity has been defined. The established relationship represents a surrogate model for further assessment of dynamic resilience of the complex multipurpose reservoir system, within the scope of the advanced reservoir system management.

Design Methodology for Grout Curtains Under Dams Founded on Rock

Grout curtains are commonly constructed under dams to reduce the seepage through the rock foundation. In the design of grout curtains, empirical methods have mainly been used since the introduction of dam foundation grouting. Although empirical methods have been used with success in several projects, they have their limitations, such as poor control of the grout spread, only an indirect consideration of the threat of internal erosion of fracture infillings in the grouted zones, and the risk of hydraulic jacking. This paper presents a theory-based design methodology for grout curtains under dams founded on rock. In the design methodology, the grout curtain is designed as a structural component of the dam. The risk of erosion of fracture infilling material is explicitly accounted for along with the reduction of the hydraulic conductivity of the rock mass, and an optimization of the total uplift force. By applying the proposed design methodology, engineers can create a design better adapted to the prevailing geological and hydrogeological conditions in the rock mass, resulting in more durable grout curtains. The proposed methodology also enables cost and time estimates to be calculated for the grout curtain’s construction. Applying the principles of the observational method during the grouting execution also allows the design to be modified via predefined measures if the initial design is found to be unsuitable.

Potential leakage paths at the dams constructed on karst terrains in Iran

Water leakage has been reported from several dams constructed on karst terrains in Iran. In this study the main reasons for dam leakage were identified by studying ten examples, the Lar, Kowsar, Seymareh, Tangab, and Shah-Ghasem dams with considerable leakage, and the Karun I, Karun III, Karun IV, Salman-Farsi, and Marun dams with negligible leakage. The “Potential Leakage Passage (PLP)” is defined as those parts of a karst aquifer which transfer reservoir water to downstream. The most important control on leakage is in the narrowest part of the PLP, the “bottleneck” that depends mainly on the geological settings. At the dams with negligible leakage, sealing of the PLPs was found to be technologically and economically feasible by connecting all the edges of grout curtain to the natural impermeable barriers. In the cases of dams with considerable leakage, wider PLPs were not completely sealed and the installed grout curtain did not fully connect to the impermeable rock. To reduce the risk of leakage and inform effective design of grout curtains, the characteristics of the PLP should be determined during the initial stage of dam studies, and incorporate geological and hydrogeological information in the ground model. This study highlights the significant risk of engineering project failures that can occur if hydrogeological conditions are not properly assessed, understood and managed early in development of dam location, design and construction.

Karstification Problems in the Haditha Dam, West Iraq

Haditha Dam is constructed on the Euphrates River in the western part of Iraq completed in 1988 and located 14 km west of Haditha town. Haditha Dam is a combined earthfill and concrete dam with a total length of 9064 m. The maximum height of the dam is 57 m from the deepest point at the river channel and dam crest level is 154.00 m (a.s.l.). The storage capacity is 6×109 m3 at normal operation water level of 143 m (a.s.l.). The exposed formations in the dam site and reservoir area are the Euphrates (Lower Miocene) and Fatha (Middle Miocene) formations. Both formations are well known in Iraq to be karstified at different intensities. The right bank of the Euphrates River is severely karstified with tens of sinkholes of different shapes, dimensions and activities. The presence of the karstified rocks is the main reason the dam has a very long grout curtain which extends along its entire length and includes the concrete powerhouse and spillway structure in the river channel, and the right and left bank extensions. The right bank extension of the grout curtain is exceptionally long due to the extent of the sinkhole area. Grouting was performed here in boreholes drilled at one-meter spacing to reduce water penetration and movement through the flank of the dam. The grout curtain under the embankment in the river section was done in two rows, while under the concrete structure it is comprised of three rows of holes. The left bank extension has two rows. The depths of all parts of the curtain varied following the karstification zones and intensities. The main aim of the current study is to elucidate and discuss the influence of the karstified rocks at the dam site and reservoir on the design and especially the length of the dam and the need for side extensions.

Determining the Appropriate Sealing Conditions through a Permeability and Groutability Evaluation: A Case Study of Sivaki Dam, Iran

The Sivaki Dam is an earth dam that is located near Yasuj city, 5.3 km northwest of Sepidar village. During excavations at the dam construction site, the high potential of water seepage from the foundation and its abutments has been proven. Some cavities and dissolution have been observed on both sides of the dam, suggesting the possibility of Karstification at greater depths. Most of the outcropping rocks in the study area comprise Asmari Limestone. These rock masses, despite their medium to high strength, have provided unfavorable conditions in terms of permeability and weathering. In this study, the foundation and both abutments of the dam were evaluated and analyzed to determine the permeability and groutability characteristics. To achieve this goal, the engineering characteristics of the rock mass of the construction site were examined by performing rock mass rating (RMR) and geological strength index (GSI) classifications. Moreover, the Lugeon test, secondary permeability index (SPI), rock quality designation (RQD), and monitoring hydraulic flows were used for this purpose. According to the results of this study, for abutments of the dam and in the case of alluvial substrates, grout curtain and the cutoff wall are respectively the best and most compatible methods available.

Dam Foundation Treatment: High Stress Watetightness

By its dual function of consolidation and sealing, injection treatment is the most appropriate process to solve the majority of problems in the most diverse soils. Concerning a foundation, the use of this treatment makes it possible to reduce or eliminate karst risks by taking into account the geological implications of each region. However, its effectiveness is difficult to measure, especially when it comes to the treatment of a dam site where the waterthigtness of the foundation is essential for overall stability. A control of the parameters that regulate the injectability of the karst as well as a good knowledge of the karst environment allows the correct evaluation of the nature of the products and the methods of implementation of the grout curtain guaranteeing the safety of the structure. It is from this perspective that a statistical study of karst anomalies was carried out on the foundation of El Ghrass dam in order to define an adequate distribution of these karsts, which is essential for the determination of the pattern of injection (drilling spacing, alignments) necessary for the preparation of the quantities of the injection market.