Roller Compacted Concrete Gravity Dams Reliability Analysis Based on Response Surface Approach

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 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 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.

The roller compacted concrete gravity dam is poured by thin layers and there are many horizontal layer surfaces and joint surfaces in the dam. The shear strength of these surfaces is obviously lower than that of the RCC concrete. These horizontal layer surfaces and joint surface are the key positions affecting the strength, stability and seepage of the dam. The height of the most RCC gravity dams is about 100m. The height is relatively low and the horizontal thrust is relatively small. So anti-sliding stability issue along the layer surfaces has not attracted enough attention. But for the dams 200m high, this problem is very prominent. In this study, using an isotropic damage model, based on the effective stress principle of porous media, taking the stress-seepage-damage coupling effect into account, the failure mechanism of Huangdeng RCC gravity dam is discussed. The results show that the failure mechanism of RCC gravity dam is the shear slipping along the layer surfaces and the foundation surface.

Implementation of BIM + WebGIS Based on Extended IFC and Batched 3D Tiles Data: An Application in RCC Gravity Dam for Republication of Design Change Model

Studies on the theory of structural system reliability includes identifi- cation of main the failure modes and calculation of inclusive failure probabilities for the structural system. The efficient and accurate identification of failure modes in structural systems is difficult and represents a key focus for research in sys- tem reliability. The fundamental theory of the branch and bound algorithm for stage critical strength is reviewed in this paper. Some deficiencies in this method are highlighted. Corresponding approaches to overcome these deficiencies are pro- posed. Calculated system reliability solutions to the classical model, a truss with 10 elements, indicate that the improvement measures proposed in this paper increase the efficiency of recognising the main failure modes of the structural system, and are readily validated. The outcomes of this type of benchmark analysis suggest that the proposed methodology may be capable of representing a suitable basis for the structural system reliability analysis of complex truss-like structures, includ- ing transmission towers. Using the proposed approach, the principal failure modes and system reliability of a transmission tower are calculated. Based on practical engineering considerations, effective methods to improve this structural system re- liability are proposed.

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.

This paper presents a mathematical model about the temperature regime and thermal stress state of Ban Lai roller-compacted concrete gravity dam, built in the climatic conditions of northern Vietnam. The model is made on the basis of the finite element method using the software complex Midas Civil. The three cases of dam construction were considered: The first was construction progress with 0.3 m/day, the second was construction process with 0.4 m/day and the last was actual construction progress. The results obtained from the mathematical model compared to the field measurements are reliable. This allows us to recommend the use of the proposed methodology with similar objects. The obtained values of maximum temperatures and thermal stresses indicate a low probability of temperature cracks.

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.

The Grand Ethiopian Renaissance Dam is the first major dam in the Blue Nile (Abay) River of Ethiopia. GERD is a combination of 175 m high roller compacted concrete gravity dam and a 50 m high concrete faced rock fill saddle dam under construction by Ethiopia. The gravity dam is built across the natural course of the Blue Nile River and the saddle dam provides the design storage and water level due to the relatively low relief of the dam site. The dam is being built at the most downstream site of one of the four potential dam sites proposed by a 1964 feasibility study of the Blue Nile basin development conducted by United States Bureau of Reclamation. The dam has been under construction since 2011 with 70% completed at the beginning of 2018. The installed power generation capacity of 6,000 MW is expected to be generated by 16 Francis Turbines each with 375 MW capacity located at the foot of the main dam. The design flow rate of 4305 m3 s−1 is about 3 times the average flow. At the average flow rate, the expected average annual energy production is 15,700 GWH. The suitability of the dam site, dam design, major components and operations are discussed.

Study of failure mechanism of roller compacted concrete gravity dam (in Chinese) : Duan Yahui & Lai Guowei, Shuili Xuebao/Journal of Hydraulic Engineering, 5, 1995, pp 55–59

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

The saddlepoint approximation (SA) can directly estimate the probability distribution of linear performance function in non-normal variables space. Based on the property of SA, three SA based methods are developed for the structural system reliability analysis. The first method is SA based reliability bounds theory (RBT), in which SA is employed to estimate failure probability and equivalent normal reliability index for each failure mode firstly, and then RBT is employed to obtain the upper and the lower bounds of system failure probability. The second method is SA based Nataf approximation, in which SA is used to estimate the probability density function (PDF) and cumulative distribution function (CDF) for the approximately linearized performance function of each failure mode. After the PDF of each failure mode and the correlation coefficients among approximately linearized performance functions are estimated, Nataf distribution is employed to approximate the joint PDF of multiple structural system performance functions, and then the system failure probability can be estimated directly by numerical simulation using the joint PDF. The third method is SA based line sampling (LS). The standardization transformation is needed to eliminate the dimensions of variables firstly in this case. Then LS method can express the system failure probability as an arithmetic average of a set of failure probabilities of the linear performance functions, and the probabilities of the linear performance functions can be estimated by the SA in the non-normal variables space. By comparing basic concepts, implementations and results of illustrations, the following conclusions can be drawn: (1) The first method can only obtain the bounds of system failure probability and it is only acceptable for the linear limit state function; (2) the second method can give the estimation of system failure probability, and its error mostly results from the approximation of Nataf distribution for the joint PDF of the structural system performance functions and the linearization of the performance functions; (3) the SA based LS method can obtain the estimator of system failure probability, which converges to the actual value along with the increase of sample size. The SA based LS method considers the influence of nonlinearity of limit state function on the failure probability, and it is acceptable for the structural system both with a single failure mode and with multiple failure modes, therefore it has the widest applicability.

Modified subset simulation method for reliability analysis of structural systems

Probabilistic analysis of laterally loaded piles using response surface and neural network approaches