Risk-Informed Design of RCC Dams under Extreme Seismic Loading

The knowledge of the behavior of any roller compacted concrete (RCC) dam and its foundation is gained by studying the service action of the dam and its foundation using measurements of an external and internal nature. The information by which a continuing assurance of structural safety of the RCC dam can be gauged is of primary importance. Similarly, the fact that the information on structural and thermal behavior and the properties of concrete that may be used to give added criteria for use in the design of future RCC dams is of secondary importance. Wide spread attention is now being given to the installation of more expensive instrumentation for studying the behavior of concrete dams and reservoirs and forecasting of any adverse trends. In view of this, the paper traces installation and need of the comprehensive instrumentation scheme implemented to monitor the structural and thermal behavior of 102.4 m high RCC dam constructed near Mumbai in India. An attempt is made in the present paper to emphasize the need to undertake an instrumentation program and evaluate their performance during construction and post construction stage of RCC structures. Few typical results, regarding the thermal and structural behavior of the dam, obtained through instrumentation installed at the dam site are presented and compared with the design considerations. The fair agreement is seen in the response observed through instrumentation with that governing the design criteria.

The freezing and thawing durability of Norway's first Roller Compacted Concrete (RCC) dam was studied using the Scandinavian slab test (European/CEN test method for freezing and thawing durability) and ASTM C671 freezing dilation test. RCC with W/(C+FA) = 0.53 and FA/(C+FA) = 0.67 had some scaling and severe internal cracking in the wet freezing and thawing exposure of the slab test. The period of freezing and thawing immunity of RCC in the separated absorption and sealed freezing procedure of the dilation test was shorter than that of the conventional facing concrete (FC). Air entraining improved the RCC's freezing and thawing resistance, although not to be as good as that of FC with W/(C+FA) = 0.50 and FA/(C+FA) = 0 and 0.40. The FC had low scaling and no sign of internal cracking in the slab test, and the RCC's period of freezing and thawing immunity was longer than the 120 days of absorption used in the dilation test. The air voids of the RCC were coarser and the protective share of voids (= voids that are not filled by capillary suction but filled by 10 MPa pressure head) was lower than in the FC. Critical degrees of saturation were determined for service life prediction by combining dilation- and degree of saturation measurements.

Seismic analysis of Roller Compacted Concrete (RCC) dams considering effect of sizes and shapes of galleries

Study on real-time construction quality monitoring of storehouse surfaces for RCC dams

Comision Federal de Electricidad has coal fired power plants in the states of Coahuila and Guerrero, in Mexico. They have production capacities of 2600 and 2100 megawatts respectively, and together they can consume more than 12 million tons of coal every year. During the electricity production process, 12% of the coal remains as ashes and its disposal is expensive. From those residues it is possible to use the fly ash, which represents about 80% of these ashes. Fly ashes have been used for several construction purposes, including the improving of concrete (as an addition). The construction of Roller Compacted Concrete (RCC) dams has been increasing around the world, and Mexico is evaluating these kinds of projects. The use of fly ash (from the Guerrero power plant) on the RCC mixtures is an option that can reduce the amount of cement, decreasing the heat of hydration and improving other characteristics as well.

Roller-compacted concrete (RCC) is widely used for industrial and heavy-duty pavements. An economical and durable material for paving and other applications, RCC has a high strength and a high density. Although the strength of RCC has been thoroughly investigated, the freeze–thaw durability of RCC remains a topic of contention. RCC has often performed well in harsh field environments, but it frequently fails laboratory freeze–thaw durability testing. In this study, 24 specimens were fabricated for freeze–thaw durability testing with a gyratory compactor. The study variables were the degree of compaction, the amount of water, and the water-to-cement (w/c) ratio (and, hence, the amount of cement). The specimens replicated the concrete found in typical RCC pavement and dam construction. The RCC specimens were subjected to up to 300 cycles of rapid freezing and thawing and were tested for fundamental transverse frequency and mass loss. Because of the low aspect ratios of the specimens, fundamental transverse frequency testing was not reliable. Several specimens completed the 300 cycles with a mass loss of less than 10%. The freeze–thaw durability of RCC was found to be dependent primarily on the amount of cement paste and the w/c ratio and to a lesser extent on the degree of compaction.

The strain softening characteristics of the roller-compacted concrete (RCC) level is a key condition in studying the bearing capacity of RCC dam. Assuming that the RCC dam unit is in the adiabatic condition, horizontal and vertical linear expansion coefficients of the RCC level are calculated. These methods were applied in practical engineering, and equivalent thermodynamic parameters can be obtained by taking the weighted squared residuals between numerical values and monitoring data as the optimization objective function in parameter inverse analysis. And the difference of the Poisson ratio and the elastic modulus, the hampering of the ontology on the layer could be reflected accurately.

A coupled thermal-structural analysis is carried out using both a two- and a three-dimensional finite-element method. The computer program ANSYS is used and simulates the construction process of a roller compacted concrete (RCC) dam. Thermally induced stresses are computed for the 60 m high RCC Tannur Dam in Jordan. The actual temperature distribution in the body of the dam measured by thermocouples is compared with that obtained by ANSYS; generally, a good agreement is obtained. The study demonstrates that detailed thermal stress analysis should be performed for large RCC dams to provide a basis to minimize and control the occurrence of thermal cracking.

The United States Department of Agriculture (USDA), Natural Resources Conservation Service (NRCS) estimates that nearly half of the small watershed dams constructed with their assistance will reach the end of their planned service life within the next 10 years. While many of these structures were originally built in rural environments, urban communities have encroached upon these structures over the years, making it difficult to address issues such as the maintenance of adequate spillway capacity to meet current dam safety standards. The urban infrastructure surrounding these structures limits the options available for dam rehabilitation. For instance, raising the dam or widening the existing auxiliary spillway to increase spillway capacity is often not a viable option due to land right constraints or changes in topography. Therefore, one of the more popular choices for increasing spillway capacity is the use of roller compacted concrete (RCC) stepped spillways. Two advantages of RCC stepped spillways are that they can be placed over the top of the dam and that they can provide considerable energy dissipation within the spillway chute. When placing an RCC spillway over an existing embankment dam, it is often desirable for the width of hydraulic control section to be greater than the width available to outlet the flow into the downstream channel. A generalized study utilizing a three-dimensional, 1:22 scale physical model was conducted to evaluate the influence converging training walls have on the flow characteristics on a stepped spillway. Vertical walls having convergence angles ranging from 0 degrees to 70 degrees were tested in conjunction with a spillway having a chute slope of 3(H):1(V) and a prototype step height of 0.3 m (1 ft). Water surface profiles in the central area of the chute and along the walls were collected and analyzed for each spillway configuration. Results of the study are presented in a format that will assist engineers in determining the required wall height for this type of a converging chute spillway.

Construction simulation has been widely applied in schedule analysis. However, traditional simulation is based on static models built in the planning or design phase, which focuses on overall project-level schedule analysis. To provide activity-level simulation for on-site schedule management, a construction phase oriented dynamic simulation method is proposed, which takes roller compacted concrete (RCC) dam placement process as an example. Considering various innerlayer and inter-layer activities and different construction organization modes, a detailed placement process simulation model is built. Based on construction data collected by real-time monitoring, a construction activity modeling method is given. Additionally, Dirichlet process mixture (DPM) models are applied for simulation parameter updates, which endows density estimation with considerable flexibility and robustness. A fast inference algorithm is also proposed to realize the fast posterior computation of DPM models. The proposed method is tested by an RCC dam project in southwest China. The results show that the proposed method can reflect the dynamic features of the actual placement process in the construction phase and provide accurate schedule predictions for on-site construction management.

Roller compacted concrete (RCC) dams are vulnerable to cracking as a result of high tensile stresses due to material properties, thermal and mechanical loads. Making reliable prediction of stress fields, and thereby temperature cracking risk form an important part of the material modelling. The present study figures out the changes in thermal stresses and crack fields of the Kinta RCC dam at the end of the construction and its service life. Water temperature at various levels of the reservoir and its fluctuations were considered in the present study. The developed finite element program has been used in the analysis. Based on the obtained results, it is revealed that there is an increase in the thermal stresses after some years of dam completion. However, their location and distribution are mostly similar.

There is no doubt that concrete is one of the most consumed materials all over the world. It is a composite mix widely used for constructing structures and infrastructures to sustain environmentally induced stresses such as thermal and seismic. As the mainstream of construction industry is tended to find out feasible solutions, Roller Compacted Concrete (RCC) was introduced to play an essential role in the development of dams and pavements, where over 550 RCC dams were created by the end of 2012. In fact, this material has the same basic constituents of conventional concrete with a zero-slump and a significant difference in the placing process. The majority of available studies in the literature are composed of numerical investigations to assess the thermal and seismic behavior of RCC dams and to provide a clear view on how to improve its performance under various loading conditions. This paper summarizes and compares the general conclusions of recent works on evaluating the structural performance of RCC dams.

Shapai Roller Compacted Concrete (RCC) Arch Dam is the highest RCC arch dam of the 20th century in the world with a maximum height of 132 m, and it is the only concrete arch dam near the epicentre of Wenchuan earthquake on May 12th, 2008. The seismic damage to the dam and the resistance of the dam has drawn great attention. This paper analyzed the response and resistance of the dam to the seismic wave using numerical simulations with comparison to the monitored data. The field investigation after the earthquake and analysis of insitu data record showed that there was only little variation in the opening size at the dam and foundation interface, transverse joints and inducing joints before and after the earthquake. The overall stability of the dam abutment resistance body was quite good except a little relaxation was observed. The results of the dynamic finite element method (FEM) showed that the sizes of the openings obtained from the numerical modeling are comparable with the monitored values, and the change of the opening size is in millimeter range. This study revealed that Shapai arch dam exhibited high seismic resistance and overload capacity in the Wenchuan earthquake event. The comparison of the monitored and simulated results showed that the numerical method applied in this paper well simulated the seismic response of the dam. The method could be useful in the future application on the safety evaluation of RCC dams.

Effects of double expansion agents on the properties of interlayer in roller-compacted concrete

The main objective of this study is to present a method of determining viscoelastic deformation monitoring index of a Roller-compacted concrete (RCC) gravity dam in an alpine region. By focusing on a modified deformation monitoring model considering frost heave and back analyzed mechanical parameters of the dam, the working state of viscoelasticity for the dam is illustrated followed by an investigation and designation of adverse load cases using orthogonal test method. Water pressure component is then calculated by finite element method, while temperature, time effect, and frost heave components are obtained through deformation statistical model considering frost heave. The viscoelastic deformation monitoring index is eventually determined by small probability and maximum entropy methods. The results show that (a) with the abnormal probability 1% the dam deformation monitoring index for small probability and maximum entropy methods is 23.703 mm and 22.981 mm, respectively; thus the maximum measured displacement of the dam is less than deformation monitoring index, which indicates that the dam is currently in a state of safety operation and (b) the obtained deformation monitoring index using orthogonal test method is more accurate due to the full consideration of more random factors; the method gained from this study will likely be of use to diagnose the working state for those RCC dams in alpine regions.