Stability analysis of embankment dams Hana shehu ZEKIRIJA IDRIZI

Introduction – Dams and their purpose The importance of Dams as structures water supply, flood control, irrigation, navigation, sedimentation control, and hydropower. The Design and Construction “trial and error” vs. “computations” THE SINGLE PURPOSE DAMS

The history of building dams “Sadd-el-Kafara” Dam – Egypt Dams of the mining industries – Harz Mountains - Germany 11m high rockfill dam – earth core 2600 BC (flood control) Destroyed during construction - overtopping Old method of Construction New method of Construction

Water resources and dams in Kosova Kosova has 5 artificial lakes which are the main form of water supply: BATLLAVA BADOVCI RADONIQI UJMANI (Gazivoda) PËRLEPNICA “UJMAN” lake and embankment dam Height:107.5 meters

Embankment dams – types and characteristics Embankment dams – Earth fill and Earth - Rockfill materials 75% of all world dams The prevailing of embankments in the modern dam construction is mainly because of: The climate, topography, and geology conditions Construction materials are principally supplied near the dam site Economical advantage The development of rock and soil mechanics The advanced construction equipments (heavy vibrating roller, hydraulic vibrating plate, laser- oriented gradall, etc.)

STABILITY ANALYSIS OF EMBANKMENT DAMS LOADS ON EMBANKMENT DAMS The stability of dams and their foundation – different conditions and load cases and combinations Construction Exploitation period. Loads can be: Static loads (dead load and impounding) Dynamic loads (seismic forces) hydrostatic forces, dead load, filtration counter pressure and filtration forces appearing in the body of the dam Primary loads wave pressure, ice pressure Secondary loads inertial seismic forces on horizontal and vertical directions and inertial water mass forces) Special loads

STATIC LOADS DEAD LOAD Deformation of the dam body – dam zoning and material properties Dead load – during construction Dam construction (individual layers) - settlements of the previous dumped layers and of the foundation. Pore water pressure - all fine grained materials, construction materials, the foundation. Kinda Dam – settlements after construction Measured – 130cm and Computed – 180 cm

Static loads IMPOUNDING The stress and strain conditions - change under the effect of the water load. Change is in principle different for dams with an internal sealing and dams with a face sealing. This follows from the different locations of the resultant of the hydrostatic pressure. Kinda Dam - Computed lines of equal horizontal displacements after impounding to 0.7H

Failure of embankment dams Failures of embankment dams can generally be grouped into three classifications: HYDRAULIC from the uncontrolled flow of water due to the erosive action of water on the embankment slopes 1)Overtopping 2)Wave and Top Erosion 3)Gullying SEEPAGE Seepage failures account for approximately 40 percent of all embankments or dike failures. Seepage can also cause slope failures by saturating the slope material STRUCTURAL separation (rupture) of the embankment material and/or its foundation. It is more prominent in large embankment dams.

Slope stability analysis Slope stability analysis – practical importance Stability is determined by the balance of shear stress and shear strength. “If the forces available to resist movement are greater than the forces driving movement, the slope is considered stable.” Factor of safety Different slope sliding surfaces “To determine the surface of sliding, with the smallest factor of safety - we need to examine quite a number of surfaces of sliding in different positions”

METHODS OF STABILITY ANALYSIS Development of methods for determination of the static stability - make possible the design of a safe and economical dam structure. The methods for calculating the stability of embankment dams are divided into: Classical Infinite Slope Analysis Limit Equilibrium methods Modern Finite Element Method

Limit Equilibrium methods METHODS OF SLICES Swedish Slip Circle Method of Analysis Oldest method - This method gives lower values for the safety factor, as compared to the more accurate methods by 5–20%. Ordinary Method of Slices Modified Bishop’s Method of Analysis suitable for programming, more accurate than the Swedish one, while the disregard of the safety factor does not exceed 7%. Lorimar’s Method of Analysis Spencer’s Method of Analysis 𝐹𝑠= 𝑐 ′ + σ ′ tan 𝜑′ 𝐺 · sin α = 𝑐 ′ 𝐿ₐ+ tan 𝜑′ 𝑁 𝐺 · sin α

Limit Equilibrium Methods Finite Element Method Simplicity and accuracy. Must search for critical surface by using geometry. The method of slices is based purely on the principles of statics; the summation of moments, vertical and horizontal forces It requires only a simple Mohr - Coulomb soil model. It cannot compute displacement. It cannot model progressive failure. Computer performance has improved application of FE in geotechnical analysis. The critical surface is automatically fond out by various software’s. Better visualizes the deformation of soil in place. It must have complete stress- strain model for soil. It can compute displacement. It can model progressive failure.

Conclusions Dams - high economic and political importance, critical role in agriculture, development of urban and rural areas, water supply, generation of hydroelectric energy, control and regulation of water current velocity. Slope stability analysis is very important to ascertain the stability of the structure. It depends on its geometry, its components, materials, properties of each component and the forces to which it is subjected. A failure of earth dam is attributed to the following: hydraulic failure, seepage failure, piping through dam body and structural failure due to earthquake.

conclusions There are several applicable methodologies that have been put forward for analyzing the overall stability of a dam, from classical methods to modern ones; The infinite slope model is more suitable and convenient for the surficial slope stability analysis The limit equilibrium models are professional for the circular slip surface analysis in the deep slope and could provide a much higher accuracy but with much more complicated calculation process.

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