Full Reservoir Conditions Research Articles

Dynamic response of Akcakoca RCC Dam including galleries

Dams are structures that demand a significant amount of concrete, making them costly constructions. Hence, various alternative methods are employed for dam construction, one of which is the use of Roller Compacted Concrete (RCC). This is a case study, which focuses on examining the behavior of RCC dams with and without galleries under seismic excitations, considering the Akçakoca RCC dam in Düzce Province. The seismic ground motion data from the 1999 Düzce earthquake were utilized. The impact of galleries inside the concrete dams was investigated through stress and displacement, considering both empty and full reservoir conditions. The Eulerian-Lagrangian coupled (CEL) approach was employed for two-dimensional fluid finite elements. This study revealed that reservoir water and galleries have a notable influence on the behavior of dams under seismic forces. In cases with reservoirs and galleries, stress and displacement values increased, and critical changes in stresses were observed around gallery areas. Therefore, careful design considerations are essential for dams with galleries under significant seismic forces.

Assessing Seismic Crack Performance of Diyarbakır Çüngüş Masonry Stone Bridge Considering 2023 Kahramanmaraş, Hatay, Malatya, Gaziantep Earthquakes

Examination of the creep behavior of historical buildings and interpretation of seismic failures in historical buildings are of great importance for the safety and future of these important structures. In this study, time-dependent settlement and three-dimensional (3D) seismic analyzes of a historical stone bridge are investigated using the 3D discrete element modeling technique. For the settlement and seismic analyses, the historical single-span Çüngüş bridge which was built in the 18th century in Diyarbakır-Turkey by Ottoman Empire is used. Since Diyarbakır is in a dangerous zone according to the Turkey seismic map, the examination of this structure is very critical for the history of Turkey. The 3D model of the bridge is created using the FLAC3D program based on the finite difference method and all the stone elements in the historical bridge are modeled separately as blocks. Special interaction elements are defined between the discretely modeled stones. For settlement creep analyses, the Burger-creep material model, which was not used for the creep behavior of historical buildings in the past, is utilized. Firstly, the 500-year long-term creep behavior of the bridge is examined by considering the fix boundary condition and full reservoir condition. According to the creep analyses, it is seen that the most deformation and failure section of the bridge is the arch section. Then, for the seismic analyses of the bridge, free-field and quiet non-reflecting boundary conditions are defined in the model. Furthermore, hysteresis damping coefficients are taken into account in seismic analyzes with the help of special fish functions. 10 various earthquakes are considered for seismic analyses. According to the earthquake analyses, the earthquake behavior of the Çüngüş historical bridge is assessed by considering the full reservoir condition and it is understood that 2023 Kahramanmaraş, Hatay, Malatya, Gaziantep earthquakes significantly changed the seismic safety behavior of Çüngüş single-span historical bridge.

Seismic Response of Concrete Gravity Dams Considering Hydrodynamic Effects

Abstract This paper presents a dynamic analytical study to assess the effect of dam height as well as fluid compressibility on the gravity response of a concrete dam, considering the effects of hydrodynamic interaction. The analysis is carried out using the ADINA Finite Element software for empty and full reservoir conditions by considering several models. In the first model, the mass of fluid is taken into account by the concept of Westergaard added mass, in the second model; an acoustic fluid element is used to simulate the effect of water on the reservoir. The height of the dam is one of the main factors affecting the seismic response of gravity dams; because the change in height provides different responses depending on the natural periods, displacements and stresses obtained from static and dynamic analyses. The numerical results showed that the effect of interaction between the dam and the reservoir plays an important role in the precise estimation of the dynamic response of gravity dams. The hydrodynamic water pressure from the reservoir increases stresses in the dam body and horizontal displacements at the crest. The seismic response obtained by the incompressible water model (Westergaard) is compared with that of the compressible water model.

Dynamic analysis of arch dams considering fluid-structure interaction

The social, economic, and environmental consequences of the failure of an arch dam make it essential to evaluate its dynamic response to mitigate the risk of a disaster. Since the slenderness and flexibility of these dams tend to increase the fluid-structure interaction during an earthquake, this work compares the dynamic response of a hypothetical arch dam in the Marañón river, in northern Perú, for both full and empty-reservoir conditions. Three formulations were used to estimate the hydrodynamic pressures: Westergaard’s added mass, Eulerian and Lagrangian. The comparisons were performed for earthquakes of distinct seismogenic sources, previously matched to a uniform hazard spectrum with a return period of 10000 years. The finite element method was used to derive the seismic demands of the dam-reservoir-foundation system in COMSOL Multiphysics software, carrying out time-history analyses assuming linear elastic behavior of the dam and foundation domains and a massless foundation approach, ignoring the effect of waves propagation in the foundation but considering its stiffness. The results show that the Lagrangian and Eulerian formulations produce similar seismic demands, while Westergaard’s added mass formulation is conservative. The full-reservoir condition generally increases the seismic demands, but the results will depend on the boundary conditions assumed for the fluid and the characteristics of the earthquake, among other factors. Earthquakes matched to the same uniform hazard spectrum do not necessarily produce equal dynamic responses.

Stability correction calculation of new debris flow grille dam considering permeation

When calculating the stability of a permeable dam under half-full or full reservoir conditions, the seepage force has not been considered in the studies reported in the literature. Based on the equation for the stability of a new debris flow grille dam structure, combined with an accumulation seepage model and the Bernoulli principle, a simplified expression for the seepage force was derived and its effect on the dam body was found to be equivalent to the overturning moment; the original equation was thus corrected. The effect of changing the internal friction angle on stability was analysed, making the corrected equation universal and applicable. Verification results showed that the overturning stability coefficient of the blocking dam was positively correlated with the internal friction angle. Compared with the original equation, after considering the seepage force, the anti-overturning stability coefficient of the blocking dam was reduced by about 44.5% on average. The attenuation amplitude increased with an increase of the friction angle in the accumulation, which was closer to the actual stress situation.

Modeling the effect of central impervious core and downstream filter geometry on seepage through earth dams

This investigation aims to identify the seepage discharge in the earth dam resting on an impervious foundation. Twenty-one models of a homogenous earth dam with and without horizontal filter and a central impervious core of different width were constructed in a hydraulic flume. In the present study, fluid and geometrical parameters of the dam, horizontal filter’s and the central impervious core were varied to find their effect on seepage. It was observed that with increasing the dam’s height, filter’s length, downstream slope, and longitudinal slope, there was an increase in seepage discharge and vice versa with upstream slope, clay core’s thickness, the viscosity of the fluid, and the earth dam’s length. Several studies have neglected the variation in fluid's viscosity for the seepage study in earth dam modeling, which is included in this study. Using Slope/w, the stability of the upstream and downstream faces was checked under full reservoir conditions.

An Investigation on performance of the cut off wall and numerical analysis of seepage and pore water pressure of Eyvashan earth dam

One of the most important issues in earth dams is the control rate of seepage from the foundation and dam bodies. Due to the site of the dams, to increase the creep length and reduce the seepage, there are several methods for sealing the reservoir of dams that construction of the cut-off wall under the clay core of the dams is one of the most effective methods. In this study, the seepage rate and pore water pressure of the Eyvashan earth dam, comparison of instrument results with the results of numerical analysis and, finally, the performance of the cut-off wall are investigated. According to the results of instrumental and numerical analysis, the maximum seepage rate in full reservoir conditions is equal to 831,604 m3/year. To fit the data of instrumentation and numerical analysis, multivariate regression was used and the coefficient of determination was used which R2 = 0.9892 and R2 = 0.9834, respectively, were obtained for seepage and pore water pressure. Very good agreement between the results of the observed data and the predicted data indicates the proper behavior of the dam in terms of pore water pressure. Also, due to the results of numerical simulation and instrumentation, the pore water pressure in the downstream part of the cut-off wall is suddenly dropped, which indicates the correct operation of the cut-off wall.

Three dimensional seismic deformation-shear strain-swelling performance of America-California Oroville Earth-Fill Dam

Structural design of the vertical displacements and shear strains in the earth fill (EF) dams has great importance in the structural engineering problems. Moreover, far fault earthquakes have significant seismic effects on seismic damage performance of EF dams like the near fault earthquakes. For this reason, three dimensional (3D) earthquake damage performance of Oroville dam is assessed considering different far-fault ground motions in this study. Oroville Dam was built in United States of America-California and its height is 234.7 m (770 ft.). 3D model of Oroville dam is modelled using FLAC3D software based on finite difference approach. In order to represent interaction condition between discrete surfaces, special interface elements are used between dam body and foundation. Non-reflecting seismic boundary conditions (free field and quiet) are defined to the main surfaces of the dam for the nonlinear seismic analyses. 6 different far-fault ground motions are taken into account for the full reservoir condition of Oroville dam. According to nonlinear seismic analysis results, the effects of far-fault ground motions on the nonlinear seismic settlement and shear strain behaviour of Oroville EF dam are determined and evaluated in detail. It is clearly seen that far-fault earthquakes have very significant seismic effects on the settlement-shear strain behaviour of EF dams and these earthquakes create vital important seismic damages on the swelling behaviour of dam body surface. Moreover, it is proposed that far-fault ground motions should not be ignored while modelling EF dams.

Numerical investigation on seismic behaviour of aged concrete gravity dams to near source and far source ground motions

This study presents a numerical investigation on the seismic behaviour of aged concrete gravity dams under near source and far source ground motions. Two-dimensional formulation of a concrete gravity dam is carried out implementing the finite element technique, considering full reservoir and rigid base condition. Degradation of concrete properties due to hydro-chemo-mechanical effects and the influence of sediment layers are taken into account to calculate the response of the dam-reservoir coupled system at different ages. Two near source and far source ground motions from real earthquake events are selected for time-history analysis. Seismic performance evaluation is also carried out to assess the probable damage level of the dam. The outcomes of this study show the variation of seismic response of the dam over the ages and the necessity of considering the aging effect, e.g. degradation of concrete and influence of sediment layers, in the inspection of seismic safety issues of concrete gravity dam. This study also reveals the critical effect of near source ground motions on concrete gravity dams at later ages.

Influence of Joint Orientation on the Behavior of Dam Resting on Jointed Rock Mass Under Static Condition

In this paper, elasto-plastic analyses of concrete gravity dam are performed to investigate the influences of intact rock, rock foundations with single set of joints (0°, 30°, 60°, 90°, 120° and 150°) and orthogonal set of joints (0°/90°, 30°/120°, 60°/150°) on the stress-deformation behavior of such dam. Discrete element analyses are carried out using UDEC (1993) for two specific static load combinations (LC) i.e. considering dead weight of the dam having empty reservoir (LC-A) and considering dead weight of the dam along with full reservoir condition (LC-B) as per IS: 6512 (Criteria for solid gravity dams, Bureau of Indian Standard, New Delhi, 1984). The orientations and spacing of the single and orthogonal joints in the rock masses are found to play vital roles in stress generation and deformation characteristics within the dam body. For all the dam foundations, the compressive stresses are found greater in magnitude at the heel of the dam than the toe for load combination A whereas, under load combination B, the stresses are higher at the toe of the dam than the heel. The rock foundations having 30°/120° and 0°/90° orthogonal set of joints are found to be critical in terms of possessing maximum compressive stresses in the dam body for load combinations A and B respectively. The magnitude of principal stresses is observed to follow an increasing pattern as the spacing between the joints decreases for all the rock foundations.

Effect of Normal and Shear Interaction Stiffnesses on Three‐Dimensional Viscoplastic Creep Behaviour of a CFR Dam

Rockfill materials and foundation continuously interact with each other during lifetime of the rockfill dams. This interaction condition alters the viscoplastic behaviour of these dams in time. For this reason, examination of the time‐dependent viscoplastic interaction analyses is vital important for monitoring and evaluating of the future and safety of the rockfill dams. In this study, it is observed how the time‐dependent displacement and stress behaviour of a concrete‐faced rockfill (CFR) dam change by the effect of the normal and shear interaction spring stiffness parameters. Ilısu Dam that is the longest concrete‐faced rockfill dam in the world now and has been completed in the year 2017 is selected for the three‐dimensional (3D) creep analyses. The 3D finite difference model of this dam is modelled using FLAC3D software that is based on the finite difference method. The concrete slab, rockfill materials, foundation, and reservoir water are separately created for the 3D interaction analyses. A WIPP‐creep viscoplastic material model and a burger‐creep viscoplastic material model that are special material models for the creep analyses of rockfill dams are used for concrete slab and for rockfill materials and foundation, respectively. Totally 20 different interaction parameters (normal and shear stiffnesses) are separately defined between the rockfill materials and the foundation to represent the interaction condition. According to numerical analyses, the effect of these various interaction parameters on the viscoplastic behaviour of the Ilısu Dam is evaluated for the empty and full reservoir conditions. As a consequence, the most critical normal and shear stiffnesses’ range for creep analyses of the rockfill dams is determined. Afterwards, the long‐term viscoplastic interaction behaviour of Ilısu Dam is examined during 35 years considering this important stiffness values. Settlements, horizontal displacements, and principal stresses are evaluated for both reservoir conditions, and these results are compared with each other in detail.

Seepage and Stability Analysis of Durgawati Earthen Dam: A Case Study

Analysis of dam slopes is of much importance because its failure may prompt loss of lives and properties. In this paper, both seepage and slope stability analyses of the earthen embankment dam of Durgawati reservoir project in the region of Kaimur–Bihar is presented. The analyses are performed using geotechnical software GEOSTUDIO 2007 (SEEP/W in Seepage analyses, Software permitted for limited period of use by GeoSlope Office, Canada, 2007; SLOPE/W in Stability Analysis, Users guide version 5, GeoSlope Office, Canada, 2002). Two sections of the Durgawati reservoir project have been considered for detailed stability analysis namely one from RD 640.09 m CH 21.00 and another from RD 670.57 m CH 22.00. Both upstream and downstream slopes, located at the dam site have been investigated for long-term stability for full reservoir condition (i.e. steady-state seepage) and drawdown condition (i.e. transient-state). It has been observed that the Factor of safety against slope failure at the upstream face is substantially greater than that of the downstream slope because of resisting effect of the reservoir water on the upstream slope. The stability of the upstream slope of the dam decreased considerably during drawdown condition. The structure lies in the earthquake prone area Zone III as per IS 1893-2002. Therefore, a pseudo-static analysis has been performed using different horizontal earthquake coefficient in combination with both steady-state as well as transient-state seepage condition.

Frequency Domain Analysis of Submerged Tower-Dam Dynamic Interaction

The dynamic response of a coupled gravity dam-reservoir water-intake tower-footing-rock foundation systems is investigated using frequency response functions of the concrete dam and the intake tower structures under horizontal and vertical ground motions. The effects of reservoir water level, reservoir bottom absorption, and presence of the dam on the tower response are studied for two tower and dam types: a squat tower adjacent to a low-height dam; a slender tower adjacent to a high dam. Using three-dimensional finite element method, it is shown that the presence of the low-height dam partially influences the response of the squat tower just for the full reservoir condition. But the high dam causes significant resonances in the response functions of the slender tower even for half reservoir. The reservoir bottom absorption strongly affects these resonances generated by the dam-water-tower interaction. It also drastically reduces the fundamental resonance amplitudes under vertical excitations. The degree of interaction between the dam and the tower is dependent on the flexibility of the foundation rock, the reservoir water level, the reservoir bottom absorption, and the slenderness ratio of the tower.

FLOW AND DEFORMATION ANALYSIS OF ZONED EARTH DAM BY THE FINITE ELEMENT METHOD

A finite element method is practical and applicable for many fields including for geotechnical engineering structures. Seepage through earth dam is difficult to analyze especially dams with multiple zones. The problem becomes complex if it requires deformation analysis taking into account seismic conditions. Therefore, finite element is the best tool for analyzing seepage flow in an earth fill dam. The main objective of the paper is to simulate the seepage flow through an earth fill dam. Hassan Kanosh Dam which is located in the north eastern part of Iraq is chosen as a case study. There are three periods in the life of a dam which may be critical from the standpoint of shear failure and which must be analyzed; during construction condition, full reservoir condition, and rapid drawdown condition. The program SIGMA/W which is a finite element software coupled with SEEP/W, (another GEO-SLOPE software product) to analyze the dam. The stability analysis performed showed that all parts of the dam are safe within the prescribed rang of factors of safety for the possible loading and operation cases. It is recommended, however, that close control of the quality of the works during construction must be maintained to realize the shearing strengths necessary to fulfill the assumed strength and even more. It is recommended to check routinely the foundation conditions during excavation to realize the same end results.

Seepage and Stability Analyses of Earth Dam Using Finite Element Method

Dams are mainly constructed of earth and rock-fill materials and hence they are generally referred to as embankment dams or fill-type dams. Earth-fill dams are simple structures which are able to prevent the sliding and overturning because of their self weight. Due to lack of suitable clay materials, sometimes the dams are designed as zoned core that is composed of three vertical zones including central impermeable core and two permeable shells on either sides of the core. A failure of earth dam is attributed to the following: hydraulic failure, seepage failure, piping through dam body and structural failure due to earthquake. The design and construction of an earth-fill dam is one of the key challenges in the field of geotechnical engineering, because of the unavoidable variation in foundation condition and the properties of the available construction materials. A homogeneous earth-fill dam should be designed with relatively flat slopes to reduce the risk of failure. The practical seepage problems are not easily convertible into an equivalent numerical counterpart because of the heterogeneity of the natural soils and the varying boundary conditions. The role of drainage system is also vital as it shifts the phreatic surface ensuring the safety of downstream toe. This paper presents the results of seepage and stability analyses of the considered earth dam using finite element method. The seepage analysis is divided into two categories viz. Steady state and Transient analyses. Based on the parametric sensitivity analysis, both the seepage and stability studies have brought out the importance of considering the coupled effects on the overall stability of the earth dam. It is concluded that the coupled analysis is a prerequisite for the design and performance evaluation of the earth dam under all conditions of seepage and stability. The study shows that increase in the Young's modulus of core and shell resulted in the decrease of the maximum crest displacement and the variation in angle of internal friction plays a vital role in the fulfilment of the overall stability criteria. The slope of 1V:2.5H was adopted for both the downstream and the upstream sides. The factor of safety (FS) was greater than 1.6 for both the full (high) reservoir condition and low reservoir condition whereas, the FS values were found to be less than the stipulated values for the other stability considerations.

Time dependent changing of dynamic characteristics of laboratory arch dam model

This paper investigates the time dependent changing of dynamic characteristics of laboratory arch dam models using ambient vibration test. For this aim, a prototype arch dam-reservoir-foundation model is constructed in laboratory conditions. The first experimental measurement tests are performed after the poured concrete aged for 10 months for some damage scenarios such as undamaged, minor-damaged and severely damaged of dam body in November 2009. To extract the experimental dynamic characteristics such as natural frequencies, mode shapes and damping ratios, a small impact effect is used as a source of ambient vibrations. Experimental measurements tests are repeated using same excitations considering severely damaged conditions with and without reservoir water in February 2014, and the dynamic characteristics are obtained, experimentally. Enhanced Frequency Domain Decomposition Method in the frequency domain is used to extract the experimental dynamic characteristics. At the end of the study, experimentally identified dynamic characteristics are compared with each other and time effects are investigated in detail. Maximum differences between the natural frequencies obtained as 15.36% and 14.38% in the third mode for empty and full reservoir conditions, respectively. It is thought that the increase of the natural frequencies is resulted from gaining of rigidity of the concrete, ageing, temperature and different environmental effects.

Variations in Bounding and Scanning Relative Permeability Curves With Different Carbonate Rock Types

Summary Relative permeability curves generally exhibit hysteresis between different saturation cycles. This hysteresis is mainly caused by wettability changes and fluid trapping. Different rock types may experience different hysteresis trends because of variations in pore geometry. Relative permeability curves may also be a function of the saturation height in the reservoir. A detailed laboratory study was performed to investigate relative permeability behavior for a major carbonate hydrocarbon reservoir in the Middle East. Representative core samples covering five reservoir rock types (RRTs) were identified on the basis of whole core and plug X-ray computed tomography (CT), nuclear magnetic resonance (NMR) T2, mercury injection capillary pressure (MICP), porosity, permeability, and thin-section analyses. Primary-drainage (PD) and imbibition water/oil relative permeability (bounding) curves were measured on all the five rock types by the steady-state (SS) technique by use of live fluids at full reservoir conditions with in-situ saturation monitoring (ISSM). Imbibition relative permeability experiments were also conducted on the main RRT samples to assess the relative permeability (scanning) curves in the transition zone (TZ) by varying connate-water saturations. Hysteresis effects were observed between PD and imbibition cycles, and appeared to be influenced by the sample rock type involved (i.e., wettability and pore geometry). Variations in relative permeability within similar and different rock types were described and understood from local heterogeneities present in each individual sample. This was possible from dual-energy (DE) CT scanning and high-resolution imaging. Different imbibition trends from both oil and water phases were detected from the scanning curves that were explained by different pore-level fluid-flow scenarios. Relative permeability scanning curves to both oil and water phases increased with higher connate-water saturation. Relative permeability to oil was explained on the basis of the occupancy of the oil phase at varying connate-water saturations. The change in the water relative permeability trend was addressed on the basis of the connectivity of water at the varying connate-water saturations. These results and interpretations introduced an improved understanding of the hysteresis phenomena and fluid-flow behavior in the TZ of a Cretaceous carbonate reservoir that can assist in the overall reservoir modeling and well planning.

Measurement of Archie Parameters of Some Carbonate Cores at Full Reservoir Conditions (Short Communication)

Application of Archie equation in carbonate reservoirs is not easy due to high dependence of its parameters on carbonate characteristics. Carbonates are very heterogeneous in nature and hydrocarbon reserve estimation in these reservoirs of mostly oil-wet and intermediate-wet is highly influenced by the input values of saturation exponent.To our knowledge, non representative oils have been used in most saturation exponent measurements and not many cases have used live oil for carbonate cores at full reservoir conditions. Performing these experiments at laboratory conditions which differs from reservoir ones would not yield reliable results.The main effort of this study was to properly measure saturation exponent on some carbonate core plugs of an Iranian reservoir at reservoir conditions using live oil by porous plate technique. Resistivity index and capillary pressure by drainage process on some plugs from pay-zone and resistivity index by imbibition process on some plugs from near and within transition zone of studied reservoir were measured.Regression fits by using Archie equation were not satisfying. Hence, the regressions were also obtained without taking into account the origin point which insisted the use of a “b” (saturation distribution) factor in the Archie equation.

Probabilistic nonlinear analysis of CFR dams by MCS using Response Surface Method

This paper presents the probabilistic analysis of concrete-faced rockfill (CFR) dams according to the Monte Carlo Simulation (MCS) results which are obtained through the Response Surface Method (RSM). ANSYS finite element program is used to get displacement and principal stress components. First of all, some parametric studies are performed according to the simple and representative finite element model of dam body to obtain the optimum approximate model. Secondly, a sensitivity analysis is performed to get the most effective parameters on dam response. Then, RSM is used to obtain the approximate function through the selected parameters. After the performed analyses, star experimental design with quadratic function without mixed terms according to the k = 1 is determined as the most appropriate model. Finally, dam-foundation-reservoir interaction finite element model is constituted and probabilistic analyses are performed with MCS using the selected parameters, sampling method, function and arbitrary factor under gravity load for empty and full reservoir conditions. Geometrically and materially nonlinearity are considered in the analysis of dam-foundation-reservoir interaction system. Reservoir water is modeled by fluid finite elements based on the Lagrangian approach. Structural connections are modeled as welded contact and friction contact based on Coulomb’s friction law. Probabilistic displacements and stresses are presented and compared with deterministic results.

A variably saturated numerical model for seepage and stability analyses of an embankment dam with a central core

Seepage and slope stability analyses are prerequisites for the safe design of embankment dams. In the present study, a variably saturated numerical flow models is developed for seepage and stability analyses of an embankment dam with a central core. The numerical model solves the variably saturated unsteady state seepage through a vertical section of the dam by fully implicit finite difference scheme. The pore water pressure obtained from the seepage analysis is employed to compute the downstream slope factor of safety under full reservoir condition and upstream slope factor of safety under sudden drawdown using modified Bishop's method. The seismic effects on the stability of both upstream and downstream slopes is carried out using Pseudo Static approach. It is observed that the saturated hydraulic conductivity has significant effect on the factors of safety of both upstream and downstream slopes. Further, it is found that the seismic effects reduce the factors of safety of both upstream and downstream slopes significantly at higher values of saturated hydraulic conductivity of the core material.