Dam Section Research Articles

Temperature-stress coupling mechanism analysis of one-time pouring mass concrete

Thermal damage control of mass concrete is the key to guarantee the quality of mass projects. Based on several engineering experiences and finite element software ANSYS, the temperature field and stress field of the typical dam section of the Tengzigou hydropower station in Sichuan province were simulated. Considering the actual materials used, cooling measures, etc., maximum tensile stress and compressive stress at different time points derived from the temperature stress field during the time of concrete maintenance were calculated, and the numerical results showed that strength increment under the given conditions was much less than the actual condition. After the concrete of the dam body of the hydro power station were poured, there was no significant temperature stress crack appeared through a long-term observation, and the project condition was in tune with the calculated expectation. The above research results are valuable to further prediction of concrete temperature in different periods, the pre-study of the effect of temperature control measures, and these could offer guidance of the adjustment of temperature control measures in the case of abnormal conditions.

A deformation separation method for gravity dam body and foundation based on the observed displacements

The displacement at arbitrary point in the dam is composed of two parts: One is the elastic deformation of dam body and the other that is due to the constrained deformation of foundation. The two parts should be separated to obtain reliable information reflecting the different characteristics of dam body and foundation. A simplified simulation method for gravity dam foundations is proposed that reflects the constrained deformation of foundation in a rational manner while taking into account the complex and diverse mechanical properties. Only the effects of the foundation on dam is investigated in the proposed model, and they are considered either centralized constraints or distributed constraints. The solution of the global foundation deformation is based on the monitoring displacements at measuring points in the gravity dam section using the hybrid partition finite element–interface boundary element approach. The reaction of the foundation on dam can be reflected by the global foundation deformation and the constrained force at dam bottom. On the basis, the whole dam response under a given load combination can be estimated using finite element theory. Three analyses have been performed on a typical gravity dam section to verify the feasibility of simplified simulations for different foundations as well as to allow for discussions regarding the differences among the simulations. An example analysis based on the proposed method is performed on a prototype gravity dam, and the results, which compared with actual measurements for discussions, show that the proposed method is reasonable and practical.

Probabilistic stability evaluation for wildlife-damaged earth dams: a Bayesian approach

ABSTRACTThere is a growing body of evidence confirming the detrimental effects of invasive wildlife activities on the performance and – ultimately – the safety of earth dams and levee systems. Modelling cavities and burrows dug by animals in earth structures is rather cumbersome due to their geometrical complexity and randomness. This study proposes the use of the probabilistic approach to estimate the risk associated with the presence of wildlife chambers in an arbitrary dam section. Two dimensional limit equilibrium slope stability analyses were conducted for a homogeneous silty sand dam. The animal chambers were modelled as idealised highly permeable circles with a near-zero strength. Uncertainty in the dam material was introduced using the Monte-Carlo technique to randomise the input parameters. The conditional probability of failure, P(F|C), was spatially evaluated by manual perturbations of chamber locations within the dam section. Using the Bayesian approach, the section was accordingly mapped into three stability zones: “safe”, “marginally safe” and “likely to fail” based on P(F|C) values associated with the chamber location. For this very complex problem, the probabilistic handling seems to provide a mathematically normalised basis for risk assessment in lieu of the classical belief-based single-value factor of safety (FoS).

An Advanced Genetic Algorithm Applied to a Rare Uplifting Earth and Rockfill Dam

A rare uplifting earth and rockfill dam case is introduced. The preliminary analysis on the formation mechanism indicates the uplift of dam body is very likely influenced by water swelling minerals in bedrock. In order to verify the swelling feature of the bedrock, a back analysis on dam surface displacement through Genetic Algorithm (GA) is carried out. Considering the discovered distribution characteristics of the bedrock expansibility, an advanced Sorting Genetic Algorithm (SGA) is proposed by adding a bubble sort procedure to maintain the relations between back analyzed parameters. The Finite Element Method (FEM) is embedded in SGA process as a single displacement calculating module. And two back analysis methods, fixed expansion distribution simulation and free GA simulation, are applied to simulate the uplift displacement of the dam body. The displacement prediction in verification dam section by adopting back analyzed parameters is later carried out to verify this method. The results demonstrate that the back analyzed vertical displacement (uplift) through both methods are in good agreement with the observed ones which verifies the reliability of the proposed method and the existence of swelling bedrock.

Study on seismic vulnerability of concrete dams based on improved IDA

In existing study of seismic vulnerability of concrete dams, the classification of seismic damage degrees was based on single index and the incremental step length in IDA analysis failed to consider the structural responses. In this study, a seismic vulnerability analysis method of concrete dams based on improved IDA method is proposed. To begin with, the comprehensive damage index of the dam is calculated using the efficiency coefficient method, considering the indexes of crest displacement, stress and damage area, and the variable weight model is adopted to consider the influence of index value on the index weight. In addition, the IDA method is improved by modulating incremental step length based on obtained comprehensive damage indexes and damage degree classification, so that the structural response process of a dam from elastic state to complete failure can be calculated and analyzed more comprehensively. Finally, taking one block section of a concrete dam as an example, the finite element model is established, and the seismic fragility curve is plotted utilizing the improved IDA method. The results prove that this method can be used to analyze the failure probability of concrete dams under different earthquake intensity, and can provide theoretical basis for the seismic safety design of concrete dams.

An Investigation of PSO Algorithm-Based Back Analysis on the Three-Dimensional Seepage Characteristics of an Earth Dam

In view of the problem of seepage safety and the character of dangerous reservoir earth dam, the 3D seepage of FEM back analysis was studied. Based on a reservoir project, the rationality of prototype observation data in recent years is analyzed, and the effective monitoring point and its observation data are selected for back analysis. The simulation calculation model is built, and the permeability coefficient of key materials and seepage characteristics of calculation area of earth dam are obtained after using particle swarm optimization (PSO) algorithm as the inversion algorithm and using FEM as the seepage field algorithm method of improved nodal virtual flux. The results shows that the PSO, which has high efficiency with back analyzing the permeability coefficient of materials in the dam and satisfactory accuracy, can meet the requirements of engineering, and a large seepage gradient in overflow point and boundary of earth dam, which is unfavorable for dam seepage stability, is produced when the problem of contact erosion is also existed in connection part of earth dam section and masonry dam section.

Temperature control and thermal-induced stress field analysis of GongGuoQiao RCC dam

Temperature control is vital to avoid thermal stress cracking in large volume concrete structures. This paper presents numerical modeling results of the temperature field and the thermal-induced stress in the Gongguoqiao roller-compacted-concrete (RCC) dam. The overflow dam section of the Gongguoqiao RCC gravity dam was numerically simulated by the finite element method, in which the boundary conditions and computing assumptions were described according to the in situ conditions. The control criteria of temperature and induced stable stress were determined for the RCC dam in discussion based on the design code for concrete gravity dam. Numerical simulation of the temperature filed and thermal-induced stress field was then carried out during the full-life stages including the construction and the service period of the RCC dam. The numerical results were used as reference to guide the construction and engineering measures to fulfill the requirements of the dam temperature control criteria. Two working conditions, i.e., without and with water-cooling, were analyzed and compared in detail to demonstrate the simulation of the temperature field and the thermal-induced stress field of the Gongguoqiao RCC dam. Temperature control measurements were finally proposed for the discussed RCC dam to assure its safety.

Changjiang nutrient distribution and transportation and their impacts on the estuary

Two investigations of the Changjiang River mainstream and forty-two cruise surveys of the estuary were conducted to determine the distribution of the dissolved inorganic nitrogen (DIN), phosphorus (DIP), and silicon (DSi) contents in the Changjiang, as well as the long-term nutrient transportation trends and impacts on the estuary. The N and P contents in the Changjiang were low in the Jinshajiang section, and then dramatically increased because of intensive anthropogenic activities and convergence of high nutrients tributaries. The DSi was distributed evenly along the Changjiang River, except that low values were observed in the Three Gorges Dam (TGD) section. Since the 1980s, the transportation of nitrate (NO3-N) and DIP nutrients by the Changjiang has exhibited increasing trends. However, DSi transportation did not change significantly, although a decreasing trend in DSi was observed from 2004 to 2010. The nutrients transported by the Changjiang were significantly correlated with the nutrients observed in the estuary, and increased amounts of NO3-N and DIP and ratios of NO3-N:DIP and NO3-N:DSi have been observed in the estuary since the 1980s. The nutrients enrichment and altered ratios have had important impacts on the estuary ecosystem.

Facies associations and chemostratigraphy of the Lower Cretaceous Kurnub Group and their boundaries, King Talal Dam section, northwestern Jordan

Integrated petrographic and chemostratigraphic studies have enabled the identification of sequence boundaries, sequence stratigraphy, and their system tracts for the Lower Cretaceous strata of the Kurnub Group (Jordan); the latter is underlain by the Jurassic (Callovian) strata and overlain by the Cretaceous (Cenomanian). Based on physical characteristics (sharp vertical facies changes) and geochemical parameters (SiO2/Al2O3, K2O/Al2O3, TiO2/Al2O3, Sr/Ca millimoles per mole, Mn parts per million, and the minor elements), 4 sequence boundaries are identified, associated with 11 facies types (from alluvial plain to the intertidal environment) and 9 system tracts, thus enabling the identification of record Lower Cretaceous sea-level fluctuations. The identified sequences mirror the Arabian plate sequences and suggest a eustatic origin. The siliciclastic Kurnub Group was derived mainly from felsic granite–gneiss and metasedimentary rocks (Arabian shield) and was deposited in a passive continental margin setting under semiarid-to-humid climatic conditions.

Study of stability against deep sliding of gravity dam based on JC method

In this study, stability against deep sliding of gravity dam is analysed in order to provide guidance for ensuring stability against sliding of gravity dam during the construction and operation periods. Based on checking-point method (JC method), the study proposes an analysis model for stability against deep sliding of gravity dams. In addition, the rigid body limit equilibrium method is utilized to construct the limit state function of deep anti-sliding stability. With sliding plane anti-shear friction coefficient and anti-shear cohesion calculated as random variables, safety degree of stability against deep sliding is analysed. With JC method employed, the calculation program is compiled to calculate the stability against deep sliding of gravity dam and analyse the non-overflow section of gravity dam under normal storage level. According to calculation program, the reliability index β of stability against deep sliding of gravity dam is 4.36, and the failure risk Pf is approximately zero. Additionally, based on the traditional rigid body limit equilibrium method, the safety factor K is 3.23, which meets the requirements of the design specification. According to the above methods, stability against deep sliding of the dam section meets the requirement. In conclusion, JC method provides a calculation and analysis model for gravity dam’s stability against deep sliding, serving as references in the design of gravity dams based on reliability theory.

Temperature control and crack prevention during construction in steep slope dams and stilling basins in high-altitude areas

Temperature cracks commonly occur during mass concrete construction. Research shows that changes in temperature and peripheral constraints mainly cause crack formation in concrete. Engineers who lack experience often build structures prone to concrete cracks. Dams built in the high-altitude areas of Tibet are examples of such structure. Climatic conditions, such as large temperature variation and strong solar radiation, disrupt temperature control and crack prevention in concrete. In this study, we explored the measures for temperature control and crack prevention that are suitable for concrete structures, especially those built in high-altitude areas with large temperature variation and strong constraint zones. The study was performed in a steep slope dam section and stilling basin in Tibet. The finite element method was used to guide the engineering construction in the area. These methods could be applied to the construction of similar projects in other high-altitude areas.

Nonlinear performance of a concrete gravity dam under a moderate seismic shock

In the paper, the dynamic analysis of a concrete gravity dam was presented. The paper concerns the nonlinear dynamic analysis of an existing concrete dam subjected to a real moderate seismic shock calculated by time history analysis. The linear, elastic, response spectrum analysis was also performed. The dynamic analysis was carried out for 2D and 3D numerical models of the dam. The 2D model represented the middle section of dam’s segment, whereas the 3D model reflected the whole segment. The concrete damage plasticity model (CDP) as a constitutive model of concrete was taking into account. Principal stresses, plastic deformations and degradation of the dam under the shock were evaluated. The results obtained for both models (2D and 3D) were compared. The 3D analysis led to the results revealing material degradation (tensile/compression cracks, stiffness degradation). Such behavior was not obtained for the 2D model.

Integrated Metaheuristic Differential Evolution Optimization Algorithm and Pseudo Static Analysis of Concrete Gravity Dam

A differential evolution-algorithm-based optimum design method is presented for concrete gravity dams under stability, principal stress, and sliding constraints. A gravity dam is a large scale hydraulic structure providing its stability based on weight of concrete volume. Hence, optimization of dam cross-section leads to an economic and low cost structure. For this aim, a general dam section is reconstructed with seven proper horizontal and vertical geometric parameters which take into account all possible cross section shapes. Weight of dam is considered as goal function and the optimization problem of geometric parameters is solved using DE algorithm. The DE algorithm written as a MATLAB code are applied to Four benchmark gravity dams including Middle Fork, Richard, Pine Flat, and Friant. The comparison of DE optimum solutions with real dimension of dams and another optimization method in literature shows the performance of the DE algorithm. In mentioned benchmark dams, there are 26.82%, 30.11%, 25.31%, and 20.93% of weight reduction Compared to real values, respectively. Also, optimization results of DE algorithm are compared with literatures. The comparison shows 3.55%, 5.1%, 19.13% and 12.14% reduction of weight compared to GA and PSOD algorithms, respectively.

Experimental Study on Constitutive Property of Cementitious Rockfill Material

With a new round of hydropower development in China, a large number of water conservancy and hydropower projects have been started, and many of them are rockfill dam. Rockfill dam and cofferdam used granular rockfill roller compaction construction, which has low cost, convenient construction, however, with the dam height increase, dam body (cofferdam) section will constantly increase, not only human, material and financial will be spent large, but also construction time will be extend, because of small friction angle and lower or none cohesion of rockfill. If we can improve the cohesion and friction angle of the rockfill, it will greatly reduce the dam section size and project cost. Although the roller compaction construction has the characteristics of convenient construction and high material strength, but as a kind of concrete materials with low water cement ratio, the colloid material proportion is still relatively large, high cost. Obviously, added only trace amounts of colloidal material without the change of construction process, that can improve the mechanical indexes of rockfill is the ideal choice. However, there is a lack of research results in effects of the rockfill filling trace amounts of colloidal material. In this paper, Study on the mechanical properties of the rockfill filling trace amounts of colloidal material has been done through large-scale triaxial shear test, to obtained forced deformation laws and constitutive model of the new material.

Influence of core thickness on stability of downstream slope of earth and rockfill dams under end-of-construction and steady-state-seepage: a comparison

The steepness of the slopes of earth and rockfill dam is governed by stability considerations which in turn are influenced by the strength of the core and shell materials as well as their geometry. An analytical study has been undertaken to evaluate and compare the variation in the factor of safety of the downstream slope of a dam on account of variation in the thickness of vertical core for the two conditions, namely, steady-state seepage condition and end-of-construction condition. A 180-m high earth and rockfill dam section, founded on strong base, having section and slopes similar to a high dam in the northern India was used as a base section for analysis. The study shows that as core thickness increases beyond a critical value, it causes a progressive decrease in the stability of downstream slope. This critical core thickness is observed to lie in the range of 50–150% of dam height for both conditions and a core within this zone does not influence stability of downstream slope. The rate of decrease in factor of safety is also observed to be similar in both conditions. The influence of relative strength of shell to core, height of dam and pore water parameter on critical core thickness is highlighted.

Reliability Analysis of Gravity Dam Based on JC Method

The gravity dam is widely disseminated in our country, and its structure is one of the most important factors. So the theory of reliability is more and more widely used in structural design. In this paper, the reliability theory and its calculation method are introduced, and the iterative process of JC method and the truncated JC method are introduced. And the reliability of anti-slippery and compressive strength of the concrete gravity dam section is analyzed based on the JC method in Matlab. The results demonstrate that using the mathematical software MTALAB to calculate JC method can save a lot of computing time, Get effective and reasonable results.

Prototype monitoring data-based analysis of time-varying material parameters of dams and their foundation with structural reinforcement

Considering structural reinforcement, a method is studied to implement the back-analysis for the evolution process of dam material property. From a material point of view, the long-term effect of dam reinforcement can be diagnosed using the proposed method. Firstly, the partial least squares algorithm is introduced to obtain the water level component in the prototype observations of dam safety. Secondly, according to all observations and numerical simulation results on dam behavior before and after dam reinforcement, the time-varying characteristics of dam material parameter are back-analyzed. Based on the subsection back-analysis thought, the improved support vector machine is used to implement the back-analysis of dam material parameter and its evolution process. The procedure and algorithm realizing the above goal are proposed. The material parameter evolution model is built. Lastly, the proposed method and model are applied to evaluate the reinforcement validity and long-term effect of one actual concrete gravity dam which has undergone several dangerous treatments. The numerical simulation is implemented to analyze the structural behavior of the typical dam section. The whole sequences of prototype observations and numerically calculated results are divided into several subsequences and then used to back-analyze the elastic modulus and the evolution process of dam body and its foundation. The evolution model of elastic modulus is established to assess the long-term effect improving the dam material performance by dam reinforcement.

Hydrologic Modelling Calibration for Operational Flood Forecasting

Runoff prediction in flood forecasting depends on the use of hydrological simulation models and on the input of accurate precipitation forecasts. Reliability of predictions thus obtained hinges on proper calibration of the model. Moreover, when the model is intended to be used systematically in operational forecasting of streamflows, the calibration process must take into account the variation of the model parameters over time, namely in response to changing weather and hydrological conditions in the basin. The goal of the study was to build a process to adjust, on a daily basis, the simulation model parameters to the current hydrological conditions of the river basin, in order for the model to be run operationally for prediction of the streamflow for the next 10-days period, and, thereby, to forecast the occurrence of flood events. Towards this end, hydrological simulations using the HEC-HMS model were performed, using a 3 h period time step. The present communication focuses on the hydrological model calibration and verification processes and on the evaluation of forecasts’ accuracy. The procedure was applied to a part of the largest (full) Portuguese river basin, the Mondego river basin, corresponding to the Aguieira dam section watershed, which comprises an area of 3070 km2. Four wet periods, associated with the occurrence of flooding, were selected for the calibration and verification of the model, by adjustment of the model parameters. The results of the study aim to define the optimal calibration parameters values to model the observed streamflow for various hydro-meteorological states, thus enabling adequate prediction of flow in flooding situations and proper application of the model in operational flood forecasting.

Identification of Natural Oscillation Modes for Purposes of Seismic Assessment and Monitoring of HPP Dams

The paper puts forward a method for processing data from detailed seismic assessments of HPP dams (dynamic tests). A detailed assessment (hundreds of observation points in dam galleries) is performed with consideration of operating dam equipment and the microseismic noise. It is shown that dynamic oscillation characteristics (natural oscillation frequencies and modes in the main dam axes, the velocities of propagation of elastic waves with given polarization, and so on.) can be determined with sufficient accuracy by using complex transfer functions and pulse characteristics. Monitoring data is processed using data from a detailed assessment, taking account of identified natural oscillation modes and determined ranges of natural frequencies. The spectra of characteristic frequencies thus obtained are used to choose substitution models and estimate the elastic characteristics of the “dam – rock bed” construction system, viz., the modulus of elasticity (the Young modulus), the Poisson ratio, the dam section stiffness with respect to shear, tension and compression and the elastic characteristics of the rock foundation.

Risk analysis of gravity dam instability using credibility theory Monte Carlo simulation model.

Risk analysis of gravity dam stability involves complicated uncertainty in many design parameters and measured data. Stability failure risk ratio described jointly by probability and possibility has deficiency in characterization of influence of fuzzy factors and representation of the likelihood of risk occurrence in practical engineering. In this article, credibility theory is applied into stability failure risk analysis of gravity dam. Stability of gravity dam is viewed as a hybrid event considering both fuzziness and randomness of failure criterion, design parameters and measured data. Credibility distribution function is conducted as a novel way to represent uncertainty of influence factors of gravity dam stability. And combining with Monte Carlo simulation, corresponding calculation method and procedure are proposed. Based on a dam section, a detailed application of the modeling approach on risk calculation of both dam foundation and double sliding surfaces is provided. The results show that, the present method is feasible to be applied on analysis of stability failure risk for gravity dams. The risk assessment obtained can reflect influence of both sorts of uncertainty, and is suitable as an index value.