RCC Dams Research Articles

Thermal analysis of RCC dams during construction considering different ambient boundary conditions at the upstream and downstream faces

Thermal analysis of RCC dams during construction considering different ambient boundary conditions at the upstream and downstream faces

Experimental and Analytical Investigation on the Interlayer of Roller Compacted Concrete

AbstractRoller compacted concrete (RCC) is a dry concrete with zero slump and is constructed in layers. RCC dams are generally weak in interlayers. The bond strength and the permeability of the int...

Comparison and Selection of Thermal Insulation Materials for RCC Dam Construction in Dry and Cold Valleys at High Altitudes in Tibet

Effective temperature preservation and moisture retention measures are key techniques in ensuring concrete quality and preventing cracks formation in RCC dams and the concrete surface in the middle reaches of the Yarlung Tsangpo River in dry and cold river valleys. Insulation and moisture retention effect, construction technology, and cost of pasting polystyrene board, spraying foam polyurethane, and rubber plastic sponge insulation membrane on the dam concrete surface were compared and analyzed to determine the thermal insulation material with the best temperature preservation, best moisture retention effect, and high applicability. Finally, the rubber plastic sponge, which matched the trim strip process, was determined as the best insulation material. It features temperature preservation, moisture preservation, no secondary cleaning after removal, good appearance, and high secondary utilization rate. The results of dam overwintering monitoring and uncovering inspection in 2019 showed that the internal and external temperature differences and surface humidity indexes of concrete were within the design index value, and cracks were absent. The purpose of temperature control and crack prevention of dam concrete was achieved, and the material has high application value.

Small temperature difference in the middle and later water cooling stages of RCC dam

Water cooling is the main measure to reduce temperature cracks in RCC dams. But later cooling usually means reducing water temperature rapidly after 120 days of the concrete age, which may cause larger self stress and tensile stress inside the concrete. The small temperature difference cooling can advance the starting time of middle and late cooling stages, and reduce the temperature stress effectively. However, the difference of temperature stress produced by different middle and late stages water cooling methods is large. It is necessary to analyse precisely how to use the small temperature difference methods in the middle and late cooling stages of dams properly. The cooling methods of RCC dam in the middle and late stages are studied by using the self-developed 3-D FEM floating mesh method temperature controlling simulation program. Result shows that when the small temperature difference is used to cool the dam in the middle and late stages, the temperature and temperature stress of the dam reduces obviously. When the age of the concrete is over, the dam should be cooled immediately, several levels of water temperature should be set in the middle and late cooling stages, the temperature of the water should be reduced slowly, which can reduce the temperature and temperature stress of the dam effectively. Study result will provide a favourable reference for practical projects.

Coupled Seepage–Stress Analysis of Selected Roller-Compacted Concrete Gravity Dam with Upstream Impervious Layer Considering the Seepage Behavior of Interface Thickness

The characteristic of seepage through the roller-compacted concrete gravity dams (RCCDs) is inhomogeneous, anisotropic and significantly different from the seepage through conventional gravity dams. This is due to the internal interfaces formed by thin rolling of layers which are weak links and the main channels for seepage. The provision of an upstream impervious layer (UIL) or less pervious upstream layer may efficiently reduce the excessive seepage in RCCDs. Several works such as those of Li et al. (Water Sci Eng 8(4):326–334, 2015) considered the upstream less pervious layer constructed with different concrete materials; however, the properties of interface thickness have not been included in their analysis. The present study attempts to carry out a seepage analysis of RCCDs with an upstream less pervious layer of different types of concrete materials including three-graded RCC, two-graded RCC, conventional vibrate concrete and grout-enriched vibrated RCC with a thickness of 2–3 m considering the significant properties of interface layers, viz. thickness and permeability. The results of the analysis emphasize the effect of less pervious upstream layer or UIL thickness on controlling seepage and also facilitate in understanding its effect on stresses. The property of RCC considered as inhomogeneous multi-laminated medium can be described by tangential and normal major coefficients of the permeability of the layer which depend on the coefficient of permeability and the thickness of the layer following cubic law. These properties are expected to simulate the seepage behavior of RCCD, and also the changes in the mechanical properties such as the elastic modulus with time and temperature are considered to predict the stress behavior of the structure. RCC dams are more pervious than conventional concrete dams and seepage through the dam exerts pore pressure throughout the body of the dam. From the point of its significance, considering the effect of seepage as body force is more realistic than considering it as an external force, viz. uplift pressure at the base of the dam. This method of analysis also facilitates in carrying out stress analysis of dam and foundation together. Hence, a coupled seepage–stress interaction is carried out while analyzing the selected section of RCCD with and without UIL using ABAQUS software. The results provide essential parameters such as pore pressure, stresses required to select the thickness and material of anti-seepage structure.

Probabilistic Risk Assessment of RCC Dam Considering Grey-Stochastic-Fuzzy Uncertainty

Greyness, randomness and fuzziness are three inseparable uncertainty factors influencing the safety of a roller compacted concrete dam (RCC dam), which can be regarded as a system reliability problem associated with multiple failure modes. Aiming at the current probabilistic risk analysis of RCC dams, most of the studies limited to single failure mode and single uncertainty. A probabilistic risk assessment method for dam under Grey-Stochastic-Fuzzy (GSF) uncertainty is proposed to consider the randomness and greyness of parameters and the fuzziness of the failure criteria. First, the fault tree model of an RCC dam is established based on Fault Tree Analysis (FTA). Then, bootstrap repeated sampling is embedded into grey system theory to quantify the grey properties of stochastic variables. The Latin Hypercube Sampling (LHS) function is improved to compensate for the inability of describing the fuzzy failure criteria. Finally, considering the correlated multiple failure modes, the proposed method is applied to analyze the parameter sensitivity and failure probability of the LDL dam in China. The results show that the proposed method is a high-efficiency, fast-convergence and more scientific method with reasonable outputs compared to common uncertainty probability analysis methods. The proposed method also provides an effective basis for the structural design and safety analysis of a concrete dam.

Modeling method for predicting seepage of RCC dams considering time-varying and lag effect

This paper deduces the expressions for equivalent water level and equivalent rainfall. Different factors and methods were considered, such as the lag characteristics of the reservoir water level and rainfall on the seepage of roller-compacted concrete dams, combining the characteristics of layered pouring of the dam body, the time-varying effects of the factors affecting dam seepage, statistical regression, multilevel recursive method, and the numerical analysis method of the model with its corresponding implementation procedures. The safety monitoring model of spatial seepage, which can comprehensively reflect the seepage characteristics of roller-compacted concrete dams is set up. The engineering example shows that this model is obviously better than the statistical model in terms of fitting accuracy and searching ability. The forecast results of this model closely approach the actual monitoring state of the dam and can also be applied to the analysis of the foundation and bypass seepage of dams.

Influence of Casting Temperature and Solar Radiation on the Thermal Field in Roller Compacted Concrete during Construction

Since RCC dams huge volume and poor heat dissipation, thermal analysis plays an important role in the design and construction of RCC dams. This paper focuses on the application and verification of a two-dimensional finite element code developed for the thermal analysis of RCC dams. The effects of solar radiation and casting temperature were also evaluated in the analysis. The result has shown that, solar radiation has an evident influence on temperature history of both central and surface nodes in late ages, but contributes less to the temperature difference of them on the contrary. On the other hand, casting temperatures effect on temperature difference is obvious.

Study on Crack Prevention Measures of Mass RCC Dams

Actually, both simple construction and fast construction are advantages of RCC dams. In view of taking strict temperature control measures, those are turned to be disadvantages instead. The way of fast pouring and the measure of controlling the placing temperature are introduced to RCC dams and 6 cases are analyzed separately to explain the effect of their crack prevention. It is concluded that controlling only the last layer placing temperature of concrete lifts can remarkably decrease the stress of working plane concrete during off period. Furthermore, the pouring way of thick lifts and short off period do not deteriorate the temperature and stress but rather has an impressive effect on crack prevention and construction period contraction.

Computation of Thermal-Stresses and Contraction Joint Distance of RCC Dams

A new approach in 3D numerical modeling for unsteady phased thermal-stress analysis of a massive concrete hydraulic structure is presented. The temperature field is computed first, providing a drive for the unsteady, nonlinear, viscoelastic, stress-strain analysis. This model is devised with actual initial and boundary conditions, appropriate material properties, and the observed concrete placement schedule. The verification is based on the field investigations of the Platanovryssi dam. The results of a long-term analysis have shown close agreement with the observed dam conditions. The proposed model presents a reliable tool for thermal-stress computation and transverse contraction joint distance evaluation.

Appliance of 3-D Composite Layered Element in RCC Dam

A numerical calculation method and a new type element of EFM for the simulation of the RCC dams is presented. It takes into account the more relevant features of RCC, such as the transversely isotropic, the layered character, the strength unequal to tension and compress and the discontinuities. A 3D model of RCC Dam, built in South-West of China, is used to perform the corresponding analyses. The result shows the location of third height to dam heel in upstream dam will be crack between layers. So it is very dangerous for arch dam. In the the locations of third height to dam toe and dam crest of the downstream of the dam will occur the stresses concentration, so some of engineer measures must be adopted to avoid the damage.

Long-term thermal two- and three-dimensional analysis of roller compacted concrete dams supported by monitoring verification

This paper presents two-dimensional (2D) and three-dimensional (3D) numerical models for unsteady phased thermal analysis of RCC dams. The time evolution of a thermal field has been modeled using the actual dam shape, RCC technology and the adequate description of material properties. Model calibration and verification has been done based on the field investigations of the Platanovryssi dam, the highest RCC dam in Europe. The results of a long-term thermal analysis, with actual initial and boundary conditions, have shown a good agreement with the observed temperatures. The influence of relevant parameters on the thermal field of RCC dams has been analyzed. It is concluded that the 2D model is appropriate for the thermal phased analysis, and that the boundary conditions and the mixture properties are the most influential on the RCC dam thermal behavior.

Thermal and stress analysis of Kinta RCC dam

The thermal analysis of roller compacted concrete dams (RCC) plays an important role in their design and construction. This paper focuses on the application and verification of a two-dimensional finite element code developed for the thermal and structural analysis of RCC dams. The Kinta RCC gravity dam, which is the first RCC dam in Malaysia, has been taken for the purpose of verification of the finite element code. The dam is 78 m in height and still under construction. The actual climatic conditions and thermal properties of the materials were considered in the analysis. The predicted temperatures obtained from the finite element code that was developed are found to be in good agreement with actual temperatures measured in the field using thermocouples installed within the dam body.

Experimental study of transition and skimming flows on stepped spillways in RCC dams: qualitative analysis and pressure measurements

This paper is a presentation of an experimental facility used for analyzing the flow over the stepped spillway of an RCC dam. The technique of digitizing video sequences is applied in order to obtain a qualitative analysis of the hydraulic behavior of these chutes. The onset of skimming flow is studied using two different criteria: a visual criterion and another that makes use of the pressure pattern on the horizontal faces of the steps. The evolution along the length of the spillway of pressures measured on the centers of symmetry of the horizontal faces of the steps is also analyzed to obtain further conclusions regarding hydraulic behavior during a skimming flow regime.