Roller Compacted Concrete Gravity Dam Research Articles

Assessing the stability of the reservoir rim in moraine deposits for a mega RCC dam

<abstract> <p>Diamer Basha Dam is an under-construction, 272-meter-high, roller compacted concrete (RCC) dam on the Indus River in Pakistan. Once constructed, it will be the world's highest RCC gravity dam with a 105-kilometer-long reservoir. Most of the reservoir lies in unstable moraine deposits with steep slopes. Events like saturation during reservoir filling, alternate wetting, drawdown during reservoir operation, or a seismic event could trigger a large mass movement of these slopes into the reservoir to disrupt the dam functionality. This work identified the 15 most vulnerable slide areas using digital slope maps, elevation maps, and satellite imagery. Deterministic slope stability analysis was carried out on the identified sections under various stages of reservoir operation for static and seismic loading, using pseudo-static and dynamic analysis approaches. Probabilistic analysis was then performed using Monte Carlo simulation. The findings showed that most moraine deposits would collapse under reservoir filling, rapid drawdown, or seismic activity. Following the assessments, landslide susceptibility maps were generated, and an assessment of potential impacts, including the generation of dynamic waves, reservoir blockage, increased sediment loads, and reduced reservoir storage capacity, was also performed.</p> </abstract>

Determination of Safety Monitoring Indices for Roller-Compacted Concrete Dams Considering Seepage–Stress Coupling Effects

Analyzing the working conditions of a dam using safety monitoring indices (SMIs) is a relatively intuitive and effective method for dam safety evaluation. Therefore, a reasonable and accurate method for determining the SMIs of a dam is of vital importance for dam safety assessment. However, the current methods for determining the SMIs of dams, especially roller-compacted concrete (RCC) dams, have many shortcomings, such as ignoring the construction process of the dam, the coupling effect among multiple physical fields, etc. In this paper, a novel SMI determination method considering the seepage–stress coupling effects was proposed for RCC dams with the assistance of a constructed seepage and stress coupling model so as to address the deficiency of existing RCC dams in determining SMIs. The coupled mathematical model was developed in COMSOL Multiphysics to establish a finite element analysis model of an RCC gravity dam in Henan Province, China. Moreover, the seepage anisotropy of the RCC construction layers was also considered in the model. Finally, the seepage, stress, and deformation characteristics of the RCC dam were analyzed based on the model, and the seepage and deformation SMIs of the dam were determined and compared with traditional methods. The results show that seepage, stress, and displacement fields are distributed similarly for both coupled and uncoupled models. However, in contrast to the uncoupled model, the hydraulic head contour distribution is more dispersed in the coupled model. Additionally, the stress and displacement simulated by the coupled model increase at different rates, with a more pronounced stress concentration near the dam heel. Comparing the seepage and stress SMIs of RCC dam obtained from different methods, it was found that the indices of dam seepage discharge and crest displacement that are calculated by considering the seepage–stress coupling effect and anisotropic characteristics of RCC construction layers are 34.78% and 31.98% lower than results obtained by ignoring these two effects, respectively. Therefore, it is crucial to consider the seepage–stress coupling effect and the anisotropic characteristics of RCC when determining the SMIs for RCC dams.

Failure modes and dynamic responses of roller compacted concrete gravity dams subjected to underwater contact explosion based on the cohesive model

Considering the construction technology of roller compacted concrete (RCC) gravity dams, there are layers in dams inevitably, which may affect the blast responses of dams. This paper is aimed to investigate the effects of RCC layers on the failure modes and dynamic responses of RCC gravity dams bearing underwater contact explosion loading. Initially, the zero-thickness cohesive element model is presented to simulate the crack behavior of the RCC layers. An impact test of a concrete beam is selected to verify its reliability. The concrete damage plasticity model considering strain rate effects is utilized to simulate the various responses of concrete under blast load. The dam–reservoir–foundation interactions are described using the coupled Eulerian-Lagrangian method. The numerical methods are validated by a field blast test of a concrete structure. Subsequently, numerical models were established for gravity dam-reservoir-foundation systems, with and without considering RCC layers respectively. Based on validated algorithms, these models were utilized to explore the effects of RCC layers on the blast performance of the dam. Finally, the influence of the parameters of RCC layers on the nonlinear responses and failure modes of the dam is further investigated, including the maximum traction, the fracture energy, and the layer thickness. The results reveal that the layers significantly change the failure modes. The RCC layers are the weak link of the dam and they will lower the anti-explosion performance of the dam. Therefore, it is crucial to take the layers into account when conducting anti-explosion research, and RCC dams cannot be simply simplified as normal concrete dams. To guarantee the safety of the dam, it is important to ensure the layers with sufficient strength and fracture energy, as well as an appropriate thickness.

An advanced method for evaluating the cracking risks of gravity dams during the construction period considering the uncertainty of thermodynamic parameters

The thermal stress field of the gravity dam is often simulated in a deterministic way at present, ignoring the effect of spatial variability of parameters, resulting in unreasonable results of the thermal stress field simulation and cracking risk analysis of the dam body. Therefore, based on the random field theory and autocorrelation function, a simulation method for the spatial variability of thermodynamic parameters is proposed in this paper. The agent risk analysis model for the cracking of a gravity dam during the construction period is constructed with the consideration of spatial variability of material parameters, and then an advanced system cracking risk evaluation method for gravity dams during the construction period considering the spatial variability of thermodynamic parameters is formed. The application of the TJ dam illustrates that the temperature control measures proposed according to the analysis results of the deterministic thermal stress field are dangerous, and considering the spatial variability of material parameters has a significant effect on the cracking risk of the dam body. This study gives a more reasonable and realistic cracking risk assessment of the dam, which can provide technical support for the formulation of temperature control measures and cracking risk control of the roller compacted concrete (RCC) gravity dam.

Type Selection between Arch Dam and Gravity Dam Based on Construction Simulation: A Case Study

The issue of dam type selection is a prevalent challenge in water resource allocation engineering. The site of the Y2 dam in China is suitable for building concrete arch dams and roller-compacted concrete (RCC) gravity dams. To determine which dam type is better in terms of construction progress, this paper proposes a multiattribute decision-making method based on construction simulation. First, the construction characteristics of concrete dams are analyzed, and the construction simulation systems for arch dams and gravity dams are developed based on construction simulation theory. Then, for each dam type, the initial construction schemes are used as the input of the simulation systems, and attribute values of construction progress are output. Secondly, a multiattribute decision-making method is used to select the typical scheme of each dam type from these initial schemes. Finally, the simulation results of the typical schemes for the arch dam and the RCC gravity dam are compared, to determine the optimal dam type for the Y2 dam. The results show that for the Y2 dam, the construction period of the arch dam is 34 months, and that of the RCC gravity dam is 28 months. From the perspective of construction progress, the Y2 dam type should select the RCC gravity dam. Compared with similar dams that have been built, it is concluded that the simulated progress result conforms to the current actual construction level, which also verifies the correctness of the calculation results and the reliability of the construction simulation.

Seismic Response and Damage Characteristics of RCC Gravity Dams Considering Weak Layers Based on the Cohesive Model

Due to the construction technology of roller compacted concrete (RCC) gravity dams, there are many weak layers that have the potential to affect the seismic performance of dams. However, research on the seismic response and failure characteristics of RCC dams considering their layered characteristic is still lacking. In this paper, the zero-thickness cohesive element is presented to model the mechanical behavior of the RCC layers. An impacted concrete beam is selected to verify its effects on simulating crack propagation. Subsequently, the concrete damaged plasticity model is utilized to model concrete under seismic loading. The dynamic interaction in the gravity dam-reservoir-foundation system is considered by coupled acoustic-structural method, whose rationality is validated by seismic failure mode analysis of the Koyna dam under the 1967 Koyna earthquake. The validated algorithms are applied to investigate the influence of the weak layer at different elevations on the seismic response and the failure process of the Guandi RCC gravity dam. On this basis, the effects of well-bonded RCC layers set at intervals along the dam on the nonlinear response and failure modes under strong earthquakes are further investigated. The results reveal that the weak layer will influence the anti-seismic capacity of RCC gravity dams, and the damage characteristics of the dam are significantly changed. In addition, well-bonded RCC layers still affect the seismic response of RCC gravity dams. Increasing displacement response and energy dissipation can be observed. Meanwhile, RCC layers lead to more severe damage to the dam under the same seismic input.

Displacement behavior interpretation and prediction model of concrete gravity dams located in cold area

The measured displacement-driven structural health monitoring (SHM) model is a significant approach to interpreting the influencing mechanism of environmental loads on dam displacement and to predicting the future operating behavior. Considering the large ambient temperature difference in cold area and the insufficient interpretive performance of the hydrostatic-seasonal-time (HST) model on thermal displacement behavior caused by the short-term dynamic fluctuations of ambient temperature, a hydrostatic-thermal-time (HTT) model considering hysteresis effect of boundary temperature is proposed to quantitatively analyze the influencing mechanism of environmental loads on displacement behavior of concrete gravity dams in cold area. Meanwhile, to improve the predictive performance of the proposed HTT model, whale optimization algorithm (WOA)-optimized gated recurrent unit (GRU) network is employed to effectively excavate the complex nonlinear relationship between dam displacement and its explanatory variables. A roller compacted concrete (RCC) gravity dam in cold area is taken as an example, and the cause of the disharmonious horizontal displacement behavior of an overflow dam crest is explained via the proposed HTT model and numerical simulation method. The conclusion is conducive for better understanding the displacement behavior of concrete dams in cold area. Meanwhile, engineering examples show that the proposed HTT model can reasonably interpret the thermal displacement behavior caused by the ambient temperature variations, and the WOA-optimized GRU network-based HTT model exhibits excellent fitting and predicting capabilities. A novel technique is provided for the accurate prediction of dam displacement.

Bubbled roller-compacted concrete dam: an idea of a hollow dam

Roller-compacted concrete (RCC) is widely known for its relatively low cost and short construction time. RCC gravity dams require high foundation (rock) bearing capacity. Research studies have been carried out which propose to rationalise the amount of material in the dam by creating inner voids, in the shape of bubbles. As a key requirement, the introduced bubbles should not affect the dam stability and safety. The bubbles will reduce the self-weight of the dam and minimise the required rock-bearing capacity. A system of pipes connecting the bubbles ensures drainage of the bubbles. The proposed dam would save about 12% of the required concrete volume. Different construction methods were studied and the best alternative is the use of precast hollow boxes. This decreases RCC placement in the dam by 32.5%. The objective is to speed the construction process and minimise the risk of the heat of hydration.

Lower Kaleköy Dam – A tailor made composite dam structure

AbstractWorldwide various type of dams are used to create reservoirs for multiple purposes. Particularly in usual cases, a single dam type is used to form a watertight barrier. Keeping safety and finance in mind, less challenging dam locations, that concerns with aspects like foundation conditions, seismicity at the dam sites, availability of construction materials, etc. are preferred. Ironically, where there is a demand for a reservoir, a suitable dam location is not always available. In those cases, these circumstances make advanced design of dam structures indispensable. An example of such a dam design is the Lower Kaleköy composite dam structure. The same consists of a roller compacted concrete gravity dam at the right bank, which is linked with one of the world's highest deformation joint to the very first asphalt core embankment dam in Turkey, situated on the left bank. The Lower Kaleköy Hydroelectric Power Plant (HEPP) constructed and operated by Kalehan Genç Enerji Üretim A.Ş. with an installed capacity of 500 MW, as part of the Beyhan Kaleköy HEPP cascade is located on the Murat River, a tributary to the Euphrat River in Eastern Turkey. This paper summarizes the design methodology developed by the design consortium (AFRY/Temelsu), headed by AFRY, for the tailored composite dam.

Multi-sensing investigation of crack problems for concrete dams based on detection and monitoring data: A case study

Cracks, a major issue in concrete structures, will reduce structural integrity, stability and impermeability. In this paper, a comprehensive site crack status monitoring system was constructed in a roller compacted concrete (RCC) gravity dam during the construction period, by combining acoustic emission (AE), micro-seismic (MS), cross-hole acoustic wave detection (CAWD), crack gauge and strain gauge techniques; this system was used to investigate crack development problems that may occur under varying construction conditions. Through knocking location tests, the acoustic wave transmission rate of RCC was determined by the AE and MS system, to monitor the real-time status of micro-cracks. Moreover, the crack tip displacement, adjacent concrete strain and concrete ultrasonic velocity were captured, to monitor the propagation of macroscopic cracks. By combining the information obtained at both the micro- and macro- levels, the development trend of a crack was analyzed. Results show that micro-crack signals were captured, but the sensitivity of the AE approach was relatively smaller than that of MS method, and the crack status was in the structural internal stress adjustment stage. On the macro-level, the macroscopic expansion phenomenon of the original crack was not captured by the crack gauge, strain gauge and acoustic penetration. Based on the size, the concentration of micro-cracks and the development trend of the macro-cracks monitored by the multi-sensing system, the crack behavior can be evaluated in huge concrete infrastructures.

Prediction of thermal stress in a concrete gravity dam

Temperature is one of the main factors affecting gravity concrete dams. The effects of many temperature factors on the gravity concrete dam cause additional deformations and tensile stress, as a result, thermal cracks appear. In order to determine the predictive model of temperature regime and thermal stress states in gravity concrete dams is a difficult problem. Because there are a large number of factors that influence temperature regime and thermal stress in the dam during construction and operation. This paper presents the results of numerical modeling of the temperature regime and thermal stress state of the Ban Lai roller-compacted concrete gravity dam (Lang Son province, Vietnam) 56 m high. The model was created using the Midas software package and can evaluate the work of the structure under the influence of temperature during construction and operation phases. The results obtained were taken into account when designing the structure and can make appropriate recommendations.

Evaluation Method for Cohesive Crack Propagation in Fragile Locations of RCC Dam Using XFEM

Roller compacted concrete (RCC) dams own a large number of horizontal construction layers, which can easily lead to weak joints among layers and generate interlayer joints with different scales to reduce the dam bearing capacity. In this study, extended finite element method (XFEM) is used to simulate crack propagation, the finite element description is first taken on the strong discontinuity. Subsequently, the displacement function of the crack-tip in the quadrilateral element and the geometric determination method of the crack-tip strengthening region are established. Afterwards, the discrete form of the governing equation is derived and the XFEM increment discretization method of the cohesive crack with the crack-tip reinforcement is proposed using the virtual node method to represent the discontinuity of the fracture element. These methods are validated through simulating mixed-mode cracking of one-sided notched asymmetric four-point bending beam. Eventually, the proposed methods are applied to RCC gravity dam to study the development rule and propagation path of the interlayer joints, so as to evaluate the effect of different lengths of the interlayer joints on the dam structural performance. The estimated critical values of dam deformation are helpful to prevent the dam failure during long term operation.

WebGIS-Based Collaborative Construction Quality Control of RCC Gravity Dam Using Sensing Devices

In recent years, information technology has been widely used in the construction quality control of hydropower stations, and a series of construction management systems based on the internet of things (IOT) have been produced. However, the existing systems are usually aimed at specific construction quality control factors, leading to the independence of all kinds of monitoring information, which also makes it impossible to directly evaluate the causes of quality problems after they occur. Manual multifactor analysis and evaluation are still needed. Based on a roller compacted concrete (RCC) gravity dam as an example, the construction quality control method is achieved by using WebGIS technology, image recognition technology, voxelization technology, and data mining analysis, which can quickly evaluate the causes of quality problems and integrate all kinds of monitoring information of different orders of magnitude into a presentation scene. This method makes the project quality management process more effective and cooperative. This study contributes to the existing body of knowledge of the quality control method based on informatization in construction.

Technique and Practice on Temperature Control and Crack Prevention for RCC Dam at High Altitude in Tibet

The dam in the DG Hydropower Station is currently the world’s highest roller compacted concrete gravity dam. The temperature control and crack prevention of concrete under special climatic conditions have become a key technical problem in dam construction. To avoid temperature cracks in the dam, the proportion of raw materials is determined in accordance with casting time, climatic conditions, and raw material performance parameters. Furthermore, the concrete mix ratio is optimized, and concrete with high cracking resistance, relatively low hydration heat, optimal VC value, and good rolling and bleeding properties is prepared. It effectively prevents the occurrence of temperature cracks in dams and solves the technical problem of temperature control and crack prevention for RCC dam construction in high-altitude areas.

May a Standard VOF Numerical Simulation Adequately Complete Spillway Laboratory Measurements in an Operational Context? The Case of Sa Stria Dam

The present work aims to assess whether a standard numerical simulation (RANS-VOF model with k − ϵ closure) can adequately model experimental measurements obtained in a dam physical model. The investigation is carried out on the Sa Stria Dam, a roller compacted concrete gravity dam currently under construction in Southern Sardinia (Italy). The original project, for which a physical model was simulated, included a downstream secondary dam. However, due to both economic and technical reasons, the secondary dam may not be built. Hence, it is important to assess the flood discharge routing and energy dissipation in the modified plan. Numerical validation is performed adopting the same laboratory configuration, in presence of the downstream dam, and results show a good agreement with mean experimental variables (i.e., pressure, water level). An alternative configuration without the downstream dam is here numerically tested to understand the conditions of flood discharge and assess whether its results can give relevant information for the design of mitigation measures. The topic is of interest also from a more general perspective. Indeed, the feasibility to integrate numerical models with existing laboratory measurements can be very useful not only for new constructions but also for existing dams, which may need either maintenance or upgrading works, such as in case of flood discharge increment.

Nonlinear Dynamic Response of a CC-RCC Combined Dam Structure under Oblique Incidence of Near-Fault Ground Motions

The velocity pulse contained in near-fault ground motions have a tremendous impact on dam safety. Previous studies have mainly focused on the response of dams under near-fault seismic records without considering the obliquely incident seismic waves. In this study, the structure–soil interaction (SSI) is taken into consideration, and the nonlinear behavior of a conventional concrete roller-compacted concrete (CC-RCC) gravity dam under near-fault pulse records and non-pulse records is investigated with consideration of the obliquely incident P waves. On the basis of the dam site conditions, three groups of near-fault pulse records are chosen, and three corresponding non-pulse records are fitted by their acceleration response spectra. Combining with the viscous-spring artificial boundary, the wave input method is proposed to transform the near-fault seismic records into the equivalent nodal forces at the boundary of the foundation. The concrete damaged plasticity model is used for the nonlinear analysis. The results show that the pulse ground motions are more destructive than the non-pulse motions. The nonlinear behavior of the dam varies with the incidence angle of P waves and generally reaches a maximum at 60° and 75°, the worst damage occurs at the interface between different materials of the dam, and the spatial variation of its damage is very obvious under near-fault seismic records with various incidence angles. Therefore, the effect of the angle of obliquely incident seismic waves and near-fault pulse effect should be considered comprehensively in the seismic analysis of dams.

Deformation monitoring analysis of an RCC gravity dam considering frost heaving in an alpine region: a case study

This study investigates the use of a modified statistical model to quantitatively analyze and assess the current operation status of an RCC (Roller Compacted Concrete) gravity dam in an alpine region. Initially, combined with the measured temperature analysis and temperature field simulation results of a typical dam block, it is demonstrated that frost heaving data are essential to monitor dam crest deformation. The frost heaving factor is introduced using an engineering analogy method, and a modified statistical model considering frost heaving based on the Heaviside step function adaptive model is established. The analysis shows that (a) in the low-temperature season, the deformation near the dam crest is affected due to a wide range of negative-temperature zones; (b) the frost heaving component identified using the novel statistical model shows that the dam crest frost heaving deformation presents a variation law of periodic pulsed fluctuation and a ten-day cycle of hysteresis. The safety assessment of concrete dams crest without any insulation measures in alpine regions should thoroughly consider the displacement caused by frost heaving, which is highly relevant to improving the accuracy of dam safety evaluations over long-term service periods.

Mathematical model of temperature regime and thermal stress state of roller-compacted concrete gravity dam

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.

Seismic behaviour of roller compacted concrete dams under different base treatments

The effect of base roughness on the seismic behaviour of roller compacted concrete gravity dams were investigated by pseudo-dynamically testing two 1/75 scaled specimens with smooth and rough base treatments. Both specimens were tested under the effect of three different hazard level earthquakes and also a pushover experiment was conducted to obtain the capacity curve of each specimen. The smooth base specimen exhibited significant sliding under the effect of the maximum credible earthquake motion. In contrast, the rough base specimen had no base sliding response even during the pushover experiment, whereas large body cracks reaching almost the downstream toe of the specimen was the main reason for the loss of lateral strength. The numerical simulation of these two experiments were also conducted by using the sliding response analysis and the finite element method. The base sliding response of the smooth-base specimen was simulated successfully by considering a variable friction coefficient. The finite element results for the rough-base specimen was also promising as far as the base shear and tip displacement estimations were considered. However, the crack propagation estimates were inconclusive due to the severe diffusion of the cracks.

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.