Concrete Face Rockfill Dam Research Articles

Effects of Fly Ash Dosage on Shrinkage, Crack Resistance and Fractal Characteristics of Face Slab Concrete

The crack resistance of face slab concretes to various shrinkages is crucial for the structural integrity and the normal operation of concrete-faced rockfill dams (CFRDs). In this work, the effects of fly ash with four dosages (i.e., 10%, 20%, 30% and 40%) on the drying shrinkage, autogenous shrinkage and the cracking resistance of face slab concrete were studied. Besides, the difference in shrinkage behavior due to fly ash addition was revealed from the viewpoint of the pore structure and fractal dimension of the pore surface (Ds). The findings demonstrate that (1) the incorporation of 10–40% fly ash could slightly reduce the drying shrinkage by about 2.2–13.5% before 14 days of hydration, and it could reduce the drying shrinkage at 180 days by about 5.1–23.2%. By contrast, the fly ash addition could markedly reduce the autogenous shrinkage at early, middle and long-term ages. (2) Increasing fly ash dosage from 0 to 40% considerably improves the crack resistance of concrete to plastic shrinkage. Nevertheless, the increase in fly ash dosage increases the drying-induced cracking risk under restrained conditions. (3) The pore structures of face slab concrete at 3 and 28 days become coarser with the increase in fly ash dosage up to 40%. At 180 days, the pore structures become more refined as the fly ash dosage increases to 30%; however, this refinement effect is not as appreciable as the fly ash dosage increases from 30% to 40%. (4) The Ds of face slab concrete is closely related with the concrete pore structures. The Ds of face slab concrete at a. late age increases from 2.902 to 2.946 with increasing of the fly ash dosage. The pore structure and Ds are closely correlated with the shrinkage of face slab concrete. (5) The fly ash dosage around 30% is optimal for face slab concretes in terms of lowering shrinkage and refining the pore structures, without compromising much mechanical property. However, the face slab concretes with a large fly ash dosage should be well cured under restrained and evaporation conditions at an initial hydration age.

Predicting the Crest Settlement of Concrete Face Rockfill Dams by Combining Threshold Regression and Support Vector Machine

Predicting the Crest Settlement of Concrete Face Rockfill Dams by Combining Threshold Regression and Support Vector Machine

Seismic response analysis of concrete-faced rockfill dams with dual mortar contact method

Many high concrete-faced rockfill dams (CFRD) are constructed or planned with high seismic intensity. It is challenging to evaluate the resultant seismic response involving multi-body interactions. In this paper, a dual mortar contact method for multi-process sequential analysis accounting for staged construction, water storage, creep effects and seismic loading is presented. A complete derivation of the strong and weak forms, spatial and temporal discretizations, material and contact non-linearity treatments is provided as a solid basis to incorporate the rockfill constitutive behavior and stable algorithm for thin-walled inter-slab interfaces. The present method based on using nonconforming meshes is validated by the comparisons with conforming meshes and then applied to an ideal CFRD. The issues of post-earthquake extrusion damage, slab–slab separation and slab–cushion separation, which are major concerns in CFRDs, are discussed in detail. The additional extrusion stress of the concrete face during an earthquake can be up to 20 MPa and therefore calls for considerations in the design and safety assessment.

Effect of engineering geological properties on dam type selection of the Qadis Khordak Dam, Afghanistan

This paper deals with engineering geological properties of Qadis Khordak dam site in Northwest Afghanistan. This study is based on on-site and laboratory tests, surface discontinuity surveying, drilled borehole and permeability test of dam foundation. The engineering geological properties at the dam site were studied in order to evaluate geotechnical characteristics of rock masses at dam foundation, geotechnical properties of alluvium at dam axis, reservoir and borrow materials. The structural geological studies also carried out due to stability and safety of dam on their abutments reservoir and seismicity. Existence of a fault, high permeable zone at dam foundation and the thickness of alluvium at dam axis, are the most engineering geological issues that cause change on dam type selection. In the feasibility phase, the dam type was chosen as the concrete face rock-fill dam, because of state of engineering geological properties of dam site. However, in the design phase dam type has been changed as a rock-fill with a clay core.

Cracking risk analysis of face slabs in concrete face rockfill dams during the operation period

Due to changes in the environmental load and deformation of rockfill bodies, cracks likely form and develop in the face slab of concrete face rockfill dams (CFRDs), affecting the working behaviour of face slabs and the safe operation of dams. At present, the cracking risk in face slabs has not been studied. Based on field test data and the finite element method, this paper developed a new method of analysing the cracking risk of face slabs. Considering that the uncertainty of construction quality leads to the randomization of rockfill material parameters, the probability function and coefficient of variation in the parameters of rockfill materials were determined based on field test data, and then, parameter samples were obtained by Latin hypercube sampling (LHS). The stress of the face slab was calculated by the Duncan-Chang E-B model and Burgers model with the parameter samples. To reduce the calculation workload of the finite element method based on traditional Monte Carlo samples, LHS and the long- and short-term memory (LSTM) algorithm were applied to obtain the response surface function. The LSTM algorithm was used to train the mapping relationship between the material parameters of the samples and the stress of the face slab. Combining the threshold value of the concrete allowable strength with the response surface method, the implicit cracking limit state function of the face slab was approximated, the cracking risk of the face slab was calculated, and the cracking risk curve of the typical area of the concrete face slab with time was given. In this case, mean absolute error (MAE) is 0.006 and the root mean square error (RMSE) is 0.004. The error of this method is very small, meeting the accuracy requirement. The case showed that the results were consistent with the inspection of the face slab and that the method was feasible and effective.

Creep parameter inversion for high CFRDs based on improved BP neural network response surface method

The creep parameters of rockfill materials obtained from engineering analogy method or indoor tests often cannot accurately reflect the long-term deformation of high Concrete-Faced Rockfill Dams (CFRDs). This paper introduces an optimized inversion method based on multi-population genetic algorithm-improved BP neural network and response surface method (MPGA-BPNN RSM). The parameters used for inversion are determined by parameter sensitivity analysis based on the statistical orthogonal test method. MPGA-BPNN RSM, validated by root-mean-square error, mean absolute percentage error, squared correlation coefficient (R2), etc., completely reflects the response between the creep parameters and the settlement calculation values obtained by finite element method (FEM). MPGA optimized the objective function to obtain the optimal creep parameters. The results show that the settlement values of Xujixia CFRD calculated by FEM using the inversion parameters has great consistency with the monitored values both in size and in distribution, suggesting that the model parameters obtained by the introduced creep parameter inversion method are feasible and effective. The introduced method can improve the inversion efficiency and the prediction accuracy in FEM applications.

As-Built Inventory and Deformation Analysis of a High Rockfill Dam under Construction with Terrestrial Laser Scanning.

The construction of large earth/rock fill dams, albeit its remarkable progress, still relies largely on past experiences. Therefore, a comprehensive yet dependable monitoring program is particularly beneficial for guiding the practice. However, conventional measurements can only produce limited discrete data. This paper exploits the potential of the terrestrial laser scanning (TLS) for an accurate inventory of as-built states of a concrete-faced rockfill dam under construction and for a full-field analysis of the 3D deformation pattern over its upstream face. For the former, a well-designed 3D geodetic system, with a particular consideration of the topography, promises a regulated acquisition of high-quality and blind-zone-free point cloud at field and also eases the cumbersome data registration process while maintaining its precision in house. For the latter, a problem-tailored processing pipeline is proposed for deformation extraction. Its core idea is to achieve a highly precise alignment of the point clouds with Iterative Closed Point algorithms from different epochs in datum areas that displays a featured, undeformed geometry at stable positions across epochs. Then, the alignment transformation matrix is applied to the point clouds of respective upstream face for each epoch, followed by pairwise comparisons of multiple adjusted point clouds for deformation evaluation. A processing pipeline is used to exploit the peal scene data redundancy of the GLQ dam acquired at six different epochs. Statistical analysis shows that satisfactory accuracy for deformation detection can be repeatably achieved, regardless of the scanner’s positioning uncertainties. The obtained 3D deformation patterns are characterised by three different zones: practically undeformed, outward and inward deformed zones. Their evolutions comply well with real construction stages and unique 3D valley topography. Abundant deformation results highlight the potential of TLS combined with the proposed data processing pipeline for cost-efficient monitoring of huge infrastructures compared to conventional labor-intense measurements.

A Thermal Effects-Based Method for Void Detection in Concrete Face Rockfill Dams

A Thermal Effects-Based Method for Void Detection in Concrete Face Rockfill Dams

Deformasi Bendungan Cirata berdasarkan Analisis Data Instrumen Patok Geser

Concrete-faced rockfill dam (CFRD) has a similar weakness to other types of dams, namely deformation. Surface movement monuments can be used to monitor the deformation that occurs on the surface of the dam. Analysis of the monument's measurement data can show settlement and displacement trends that are closely related to the deformation of the dam itself. In this research, the monuments measurement data are compared to acceptance criteria from ICOLD, Sowers, Clements, Fell, and the Ministry of Public Works and Housing as outlined in the Guidelines for The Design and Construction of Concrete Membrane Stone Backfill Dams. This study aims to analyze data from surface movement monuments to determine the settlement and displacement of the dam based on the criteria of deformation. According to the obtained result, the first segment of surface monuments settlement values ranged from 0.028 to 0.165%, which meet the majority of the criteria. In addition, displacement values at the first segment of surface movement monuments were within 0.022 – 0.071%, which meets the ICOLD and Clements criteria. Meanwhile, for the second to fourth segments of surface movement monuments, settlement values of 0.007 – 0.102% were obtained, which still conform to the ICOLD and Fell criteria.

3D seismic analysis concrete-faced rockfill dam subjected to simulated spatially varying ground motion

3D seismic analysis concrete-faced rockfill dam subjected to simulated spatially varying ground motion

Reliability Analysis of High Concrete-Face Rockfill Dams and Study of Seismic Performance of Earthquake-Resistant Measures Based on Stochastic Dynamic Analysis

The randomness of earthquake excitation has a significant impact on the seismic performance of high earth-rock dams. In this paper, the seismic performance of geosynthetic-reinforced soil structures (GRSS) of high concrete face rockfill dams (CFRDs) is evaluated from the stochastic perspective. Multiple groups of seismic ground motions are generated based on spectral expression-random function non-stationary model. Taking Gushui CFRD as an example, this study calculates the failure probability of each damage level of non-reinforce slopes and reinforce slopes based on generalized probability density evolution method (GPDEM) and reliability analysis is presented though multiple evaluation indicators. The result shows that GRSS can reduce the mild damage of CFRDs during earthquake and restrain the moderate and severe damage. The influence of vertical spacing and length of GRSS on the seismic performance is obtained, which provides a reference for the seismic design and risk analysis of CFRDs.

Reliability-monitoring data coupled model for concrete slab safety evaluation of CFRD and its engineering application

The concrete-faced rockfill dam (CFRD) is one of the widely constructed dam types, the concrete slab is the key anti-seepage structure of CFRD, and its safety directly affects the safety of the dam. In view of the traditional reliability analysis methods are complicated to calculate and cannot assess concrete slab cracking risk in real-time. In this paper, through the analysis of the response mechanism of slab stress and dam deformation, the coupling relationship between the reliability of concrete slab and monitoring data is revealed. Considering the randomness of the material parameters of CFRD, the limit state functions of concrete slab cracking are established by the response surface method (RSM). The accurate numerical simulation of the construction and operation process of CFRD is realized through the back analysis, then the time-variant reliability calculation of the concrete slab is realized. By analyzing the correlation between concrete slab reliability and some key factors such as dam displacement, water level, and time, a coupled evaluation model of reliability and monitoring data is proposed. Houziyan CFRD is selected as an example, the engineering application shows that the simulation relative error by using this coupled evaluation model is less than 5.0%, this model has the advantages of high efficiency, good precision, and strong applicability. The real-time reliability analysis of the concrete slab is realized and a new method for prediction and early warning of concrete slab cracking of CFRDs is provided.

Influence of reactivity and dosage of MgO expansive agent on shrinkage and crack resistance of face slab concrete

Enhancing cracking resistance of face slab concrete is essential for the structural integrity and normal operation of concrete-faced rockfill dams (CFRDs). In this study, the effects of MgO with three reactivities and three dosages on the shrinkage and crack resistance of face slab concrete were systematically investigated by slab test, restrained drying shrinkage test and temperature stress test machine (TSTM). The results indicate that: (1) 7 %–25% of the total drying shrinkage and all (or most of) the autogenous shrinkage can be compensated by adding 5 %–10% MgO. The reactive MgO (M60) starts to compensate the drying and autogenous shrinkage at 1 day and compensates more shrinkage at early age than the moderate reactive MgO (M150) and the weak reactive MgO (M300), while M300 begins to compensate the shrinkage at about 50 days and produces larger compensation than M60 and M150 at late age. (2) M60 performs better than M150 in improving the crack resistance of face slab concrete to constraint and thermal stress. The increase in dosage of M60 and M150 from 0 to 10% prolongs the initial cracking time of face slab concrete by 10.0–27.5 h, increases the cracking strain by 9.2 %–25.7%, enhances the cracking tensile stress (σ) by 4.7 %–18.8% and lowers the cracking temperature (Tc) by 2.6–7.4 °C. Conversely, M300 weakens the cracking resistance. (3) The reactive MgO with relatively high dosage is suggested to eliminate the early shrinkage and to improve the cracking resistance of face slab concrete.

Innovation structures of very lean roller compacted concrete dams

Over the past 20 years, rolled compacted concrete (RCC) dams have continued to be built in many countries because of their technical and economic advantages over conventional dams of vibrating concrete and embankment dams. The aim of this study is the development of new structural and technological solutions in RCC dams in order to reduce the consumption of cement and expand their use on non-rock foundations, which will allow them to successfully compete with concrete face rockfill dams. The numerical analyses of static and seismic stress-strain state (SST) of gravitational dams in roller compacted very lean concrete dams have been made, as well as their stability, strength and cost have been assessed. For rock and dense sandy-gravel foundations the most economical is the concrete face rockfill dam and symmetrical RCC dam of very lean concrete with bases (0.5-0.7) of both slopes and outer zones of conventional concrete and central zone of rockfill strengthened by cement-ash mortar. Taking into account that the cost of diversion and spillway tunnels for very lean RCC dam will be less and the construction period - shorter than for the concrete face rockfill dam, it can be concluded that variant of symmetrical RCC dam of very lean concrete is the technically and economically effective. Symmetrical RCC dams of very lean concrete with 1V/(0.5-0.7)H slopes have more seismic resistance and technical and economic efficiency as compared with conventional gravitational RCC dams and other types of dams. These dams up to 200 m high can be built on rock foundations and up to 100 m high - on dense sandy gravel foundations.

Dynamic response of concrete face rockfill dam affected by polarity reversal of near-fault earthquake

Dynamic response of concrete face rockfill dam affected by polarity reversal of near-fault earthquake

Experimental Centrifuge Study of the Effects of Valley Topography on the Behavior of a Concrete Face Rockfill Dam

The recent focus on water conservancy projects globally has resulted in the construction of increased numbers of concrete face rockfill dams in narrow valleys. However, valley topography impacts the deformation of a dam and further influences the distribution of stress and position of cracks on the face slab. This study conducted two centrifuge experiments to study the influence of the valley topography on the behavior of a concrete face rockfill dam from construction to impoundment. Experimental models of concrete face slab sand-gravel dams with “U”-type and “V”-type valley topographies were established. The settlement of the dam crest, the displacement of the upstream slope of the dam, and the stress on both sides of the face slab were observed. The experiment also represented the cracking of the face slab during impoundment. The results showed that the “V”-type valley topography effectively reduced the progression of dam crest settlement and influenced stress on the slab resulting from impounded water pressure. Furthermore, the flexural form of the face slab in the “U”-type valley topography took on a “D” shape and cracks progressively developed on the face slab with increased water load. The flexural form of the face slab in the “V”-type valley topography showed a “B” shape, and cracks occurred under a particular water impoundment pressure.

Numerical simulation of concrete face rockfill dam seepage: case study of Miaojiaba dam, China

Concrete face rockfill dams are widely used in hydropower engineering because of their many advantages. As important structures, if the performance of the concrete face slab and the impervious curtain is weakened, leakages and even serious dam failures can occur. Based on an equivalent quasi-continuum medium model, three-dimensional finite-element numerical simulations of the seepage behaviour of Miaojiaba dam, China, are performed. The seepage field and seepage characteristics, including the phreatic line, maximum hydraulic gradient and seepage discharge, are analysed quantitatively and systematically under various abnormal conditions. The results show that cracks in different areas of the face slab and different degrees of degradation in the impervious curtain influence the seepage field in different ways, with cracks in the lower face slab being the most serious. Ensuring that the face slab and impervious curtain are working as intended is very important for the integrity of the dam. Therefore, the design and construction quality of impervious structures should be strictly controlled. Under abnormal conditions, seepage control should be realised to ensure the safety and stability of concrete face rockfill dams.

Numerical analysis of groundwater flow behaviour at a dam site in Karst area during its reservoir impoundment

The Jiangpinghe concrete-faced rockfill dam, with a maximum height of 219 m, is located in the karst area in western Hubei Province, China. The bedrocks at the dam site are highly dissolved, in which karst conduits, faults, fractures and weak interlayers are developed. Given the complex geological conditions, a large-scale grouting curtain covering an area of 376,000 m2 was built to control the seepage in the dam foundation. However, the piezometers in the middle section of the lowest grouting tunnel at the right bank manifest an abnormal rise of hydraulic head after reservoir impounding. The hydraulic head varies with a good correlation with the reservoir water level. This abnormal rise of hydraulic head can be attributed to higher permeability of strata where small-scale karst pipes and conduits are developed. In this study, an inverse modelling procedure combined orthogonal design, finite element forward modelling of transient groundwater flow, artificial neural network, and genetic algorithm was adopted to evaluate the permeability of the strata. The inverse results show that the permeability of shallow-buried rocks is one order of magnitude larger than that of deep-buried rocks in the right bank. The numerical simulations show good agreement with field measurements. Based on the inversed results, the groundwater flow behaviour at the dam site was analysed and the performance of the seepage control system was evaluated. It is demonstrated that the abnormal rise of hydraulic head is induced by the permeable structures developed along karst strata, and the seepage control system performs well in lowering the hydraulic head and limiting the amount of leakage through the dam foundation.

GPDEM-based stochastic seismic response analysis of high concrete-faced rockfill dam with spatial variability of rockfill properties based on plastic deformation

The spatial variability of rockfill properties is the key factor affecting stochastic seismic responses. Herein, an efficient probabilistic analysis method for stochastic seismic analysis named the generalized probability density evolution method (GPDEM) is proposed and combined with the random field generated by K-L decomposition to evaluate the stochastic seismic responses of concrete-faced rockfill dams (CFRDs) during earthquakes. The vertical plastic deformation is selected as a significant index to quantify the effect of rockfill spatial variability. First, a series of 2D random fields and a finite element model of the CFRD profile are established. Each realization of random fields is assigned to each grid depending on the coordinates. Then, four working conditions (different constitutive model parameters, cross-correlation coefficients, concrete-faced slab contact positions and earthquake intensities) are investigated and compared in CFRD dynamic calculations. Finally, the GPDEM-based vertical plastic deformation results are obtained, and probabilistic analyses are carried out to evaluate the influence of rockfill property uncertainty on the stochastic seismic responses. Multiple figures of the probability density function (PDF) and cumulative distribution function (CDF) of dynamic calculations are shown as examples to analyze the marked effect of rockfill spatial variability. The results demonstrate that the control parameter (Mf) is the most influential parameter of stochastic seismic responses in the GPDEM. The cross-correlation coefficient increases the probability of large vertical plastic deformation compared to zero. Moreover, the nonfaced-slab side is more sensitive to the effect of rockfill uncertainties. Increasing the seismic motion intensity causes a larger probability beyond the limit.

Three-dimensional refined analysis of seismic cracking and anti-seismic measures performance of concrete face slab in CFRDs

The concrete face slab is the primary anti-seepage component of concrete faced rockfill dams (CFRDs). Therefore, the seismic safety of the slab is an important issue. In this paper, the cohesive zone model and the explicit solution are expanded to conduct 3D seismic failure analysis of a CFRD. A combination of the generalized plasticity model of rockfill, state-dependent elasto-plastic model of soil-structure interfaces, a non-uniform wave input method and the scaled boundary finite element method is used to perform an elasto-plastic, cross-scale analysis of the seismic cracking evolution of concrete face slabs. The above combined method is used to investigate the cracking mechanism, cracking characteristics and potential anti-seismic measures. The results indicate that the cyclic deformation caused by the earthquake results in the formation of horizontal, connected cracks in the middle of the slab at 70–75% of the dam height. In addition, the plastic deformation of the rockfill leads to the formation of horizontal, unconnected cracks on both sides of the slab at 85% of the dam height. A comprehensive anti-seismic measure is proposed based on material property improvement and structural optimization, decreasing the maximum crack width and the total crack length by 21% and 89.9%, respectively.