High Core Rockfill Dam Research Articles

A novel finite element limit equilibrium method and its application in instability analysis for 3-D high core rockfill dams

The safe operation of high rockfill dams is an important issue related to human life and property safety. However, the stability analysis of high core rockfill dams with complex spatial morphology is mostly confined to two-dimensional, and appropriate stability analysis methods are scarce. Therefore, it is necessary to develop the three-dimensional stability analysis method for high core rockfill dams and study the spatial stability mechanism after impoundment. Firstly, a finite element limit equilibrium framework suitable for stability analysis of high rockfill dams is introduced, and the horn-shaped three-dimensional failure mechanism is presented for optimization. Then, according to the statistical results of the actual core rockfill dam above 100 m, 15 high dam models with actual Duncan-Chang parameters between 100 m and 300 m are established to study the three-dimensional instability mechanism. Meanwhile, grey relation analysis (GRA) is used for quantitative analysis of stability sensitive factors. Finally, the stability analysis of the Quxue core rockfill dam (173.2 m) was completed within the established stability framework. The results show that the combined failure mechanism with the horn-shaped is suitable for dam stability analysis, and with the increase of height and slope ratio of dam, the most dangerous sliding surface evolves to shallow layer. In addition, GRA results show that slope ratio is the most sensitive parameter compared to dam height and material parameters. The practical engineering stability results of Quxue show that the research results can provide a reliable reference for the stability of the high core rockfill dam.

Analysis of seepage failure probability for high core rockfill dams during rapid drawdown of reservoir water level

Rapid drawdown (RDD) is an abnormal reservoir flood control operation that may cause seepage failure of high core rockfill dams. In this paper, a novel framework combining Bayesian inference and transient unsaturated seepage simulation is proposed to evaluate the seepage failure probability of the core during RDD. The dynamic hydraulic boundaries utilized in the simulation are first determined by the performance of water release structures. The extreme learning machine (ELM) is then employed as the surrogate model to establish the mapping relationship between material parameters with simulated seepage pressure and hydraulic gradient. The Bayesian inference method is applied to characterize the uncertainty of material parameters based on seepage monitoring data. Finally, the posterior distribution samples of random parameters are utilized to calculate the seepage failure probability of the core. The seepage safety of the core under different drawdown rates is studied with a real 186 m high core rockfill dam. The results reveal that a faster RDD rate can lead to an increased probability of seepage failure. The maximum failure probability is 35.56 % for the four release structures working together (about 0.316 m/h), higher than 23.16 % for the three release structures (about 0.165 m/h). It is also found that the peak of seepage failure probability often occurs in the middle stage of RDD. Therefore, to ensure the safety of the project, it is important to control the RDD rate and carefully monitor the seepage pressure. From the point of view of seepage failure, the proposed method for evaluating the safety of core rockfill dams under RDD is of high guiding significance to the risk assessment of similar projects under extreme conditions.

Study on Impoundment Deformation Characteristics and Crack of High Core Rockfill Dam Based on Inversion Parameters

In the numerical simulation of earth-rock dam, accurate and reliable mechanical parameters of the dam material are the important basis for dam deformation predictions and dam safety evaluations. Based on the deformation monitoring data of Luding core wall rockfill dam, the rheological parameters of rockfill and core wall materials are inverted in this paper. Combined with the actual filling and impoundment process of the dam, the numerical simulation is carried out, and the stress deformation and differential settlement of the dam after completion and impoundment are analyzed. The results showed that the stress deformation results of the dam based on the inversion parameters were in good agreement with the actual deformation. The horizontal displacement, settlement, and principal stress of the dam during the completion period were symmetrically distributed along the core wall. The maximum horizontal displacement occurred at the main dam on both sides of the core wall and the upstream and downstream dam slopes, and the maximum settlement occurred in the middle of the core wall. During the impoundment period, under the action of reservoir water pressure and upstream rockfill wetting deformation, the deformation and stress of the dam body no longer met the symmetrical distribution law, and the maximum horizontal displacement of the dam body during the impoundment period was located at 2/3 of the upstream dam slope. The maximum settlement of the dam body was located at 1/2 of the dam height. The maximum principal stress on the upstream side of the core wall was located on the left side of the bottom of the core wall, and the minimum principal stress was also located on the left side of the bottom of the core wall. The simulation results of the deformation and stress met the general law of earth-rock dam engineering. During the completion period, the deformation inclination of the dam crest was less than 1%. During the impoundment period, the deformation inclination of the dam crest area increased due to the wetting deformation of the upstream rockfill material. At the same time, the deformation inclination of the dam crest axis was larger than that of the upstream and downstream sides, and the deformation inclination of the dam crest at the middle of the valley was the largest, but it did not exceed 3%, that is, there would be no longitudinal cracks, which is consistent with the actual situation. The research results can better predict the stress deformation and crack of the dam body, and provide important support for dam safety evaluations.

Reliability analysis of high core rockfill dam against seepage failure considering spatial variability of hydraulic parameters

Reliability analysis of high core rockfill dam against seepage failure considering spatial variability of hydraulic parameters

The effect of near-fault earthquakes and wavelet-generated artificial near-fault earthquakes on the seismic behavior of rockfill dams

Strong earth vibrations may destroy high asphalt concrete core rockfill dams (ACCRDs) and cause unanticipated economic and social losses. Due to favorable geographical, geological, and environmental characteristics, ACCRDs are always near ruptured fault zones. Compared to far-field and non-pulse earthquakes, near-fault (NF) earthquakes with pulse effect may put high dams under stress. However, seismic design and dynamic assessments of high ACCRDs under pulse-type earthquake stimulation are less popular than NF earthquake recordings. The fundamental explanation is that most earthquake data pertain to non-pulse-type seismic occurrences, whereas pulse-type earthquakes have more sophisticated seismology. This work uses the finite element approach to illustrate the seismic behavior of the ACCRD under pulse-type NF, non-pulse-type NF, and far-fault (FF) earthquake excitations. The pulse-type artificial NF earthquakes are generated using wavelet multi-scale decomposition incorporation (WMSDI), a simplified wavelet theory-based approach. Next, the WMSDI approach of artificial NF earthquake synthesis is tested and compared to earthquake data and structure responses. Forward-directivity pulse-type and fling-step pulse-type earthquakes may induce higher horizontal accelerations and stresses of the high ACCRD than FF earthquakes. FS and FD earthquake excitations with high PGV/PGA ratios cause severe residual deformation and relative settlement ratio to the high ACCRD. The dynamic response of the high ACCRD under pulse-type artificial NF earthquakes also depends on the pulse parameters of the artificial equivalent pulse mathematical models. Thus, pulse-type NF earthquake seismology should be included in rockfill dam seismic design assessments.

The Use of Shape Accel Array for Deformation Monitoring and Parameter Inversion of a 300 m Ultrahigh Rockfill Dam

The global construction of rockfill dams has now surpassed the 300 m height level. Despite great achievements in dam design and construction, monitoring techniques have lagged behind the development of high rockfill dams. Existing deformation monitoring techniques are ill-suited to the high earth and water pressures, and extended monitoring periods are required for ultrahigh rockfill dams. This study introduces, for the first time, the use of a shape accel array (SAA) to monitor internal displacement in a 300 m high earth core rockfill dam. The SAA employs a rope-like array of capacitive MEMS accelerometers for deformation measurement. Compared to conventional monitoring techniques, SAA is a data-intensive monitoring technique. Based on the intensive data obtained from SAA, we employed a parameter inversion method, utilizing multiobjective optimization algorithm, the nondominated sorting genetic algorithm-III (NSGA-III), to inverse the constitutive model parameters of the rockfill dam. The multiobjective parameter inversion method maximizes the use of multisource monitoring data for predicting rockfill dam deformation.

An improved generalized plasticity model for rockfill materials and its experimental and numerical verification

PurposeThe stress–strain behaviors of rockfill materials in dams are significantly affected by the anisotropy and grain crushing. However, these factors are rarely considered in numerical simulations of high rockfill dams. This study intends to develop a reasonable and practical constitutive model for rockfill materials to overcome the above problems.Design/methodology/approachThe effects of anisotropy and grain crushing are comprehensively considered by the spatial position of the reference state line. After the improved generalized plasticity model for rockfill materials (referred to as the PZR model) is developed and verified by laboratory tests, it is used with the finite element method to simulate the stress–strain behaviors of the Nuozhadu high core rockfill dam.FindingsThe simulated results agree well with the laboratory tests data and the situ monitoring data, verifying the reliability and practicability of the developed PZR model.Originality/valueA new anisotropic state parameter is proposed to reflect the nonmonotonic variation in the strength as the major principal stress direction angle varies. This advantage is verified by the simulation of a set of conventional triaxial tests with different inclination angles of the compaction plane. 2) This is the first time that the elastoplastic model is verified by the situ monitoring data of high core rockfill dams. The numerical simulation results show that the PZR model can well reflect the stress–strain characteristics of rockfill materials in high core rockfill dams and is better than the traditional EB model.

Study on the Tensile Properties and Application of Gravelly Soil Reinforced by Polypropylene Fiber

Incorporating fibers into gravelly soil is an effective method to prevent the core wall of high earth core rockfill dams (ECRDS) from cracking. In this study, a new type of soil tensile device was used to carry out tensile tests on gravelly soil with different gravel contents and fiber contents. The test results show that as the gravel content increases from 0% to 50%, the improvement in tensile strength decreases from 48.9% to 6.4%, which means the increase in gravel content reduces the improvement in tensile strength significantly. The ultimate tensile strain, tensile strength, and post-peak tensile strength of fiber-reinforced gravelly soil are positively correlated with the fiber content. Combined with the Scanning electron microscopy (SEM) results, the reinforcement effect of the three types of fiber interfaces on the gravel soil is qualitatively analyzed, and the microscopic mechanism of the improvement of the tensile strength of fiber-reinforced gravelly soil is revealed. The energy absorption capacity (EAC) results showed that the lower the gravel content in the soil, the higher the degree of improvement in the EAC value. In practical application, it is recommended to use gravel soil with low gravel content and high fiber content. Finally, a regression model considering the gravel content and fiber content was proposed for fast predicting the tensile strength of the soil. The related results can provide references for the anti-cracking design of the core wall of high ECRDS.

Seismic performance assessment of high asphalt concrete core rockfill dam considering shorter duration and longer duration

The particular interest produced by the seismological characteristics impacting structural response has given a new challenge in the performance-based design of high dams. Recent research has shown that the seismological characteristics of frequency and amplitude inherent in ground motion (GM) records govern the dynamic response of high dams. Therefore, these seismological characteristics have been accepted and incorporated into the seismic design codes of high dams in most countries. However, the duration of strong GMs, as one of the critical seismological characteristics of earthquakes, also needs to be fully understood to carry out a more effective performance-based design of high dams. Based on this observation, the effect of the duration of strong GMs has been explored, investing in the seismic performance of high asphalt concrete core rockfill dams (ACCRDs) by employing an integrated duration (ID) concept that can reflect the duration of all components of GMs. A high ACCRD was firstly built in the commercial software ABAQUS considering the dam-reservoir-foundation interaction systems. Subsequently, the coupled multiple stripe analysis and maximum likelihood estimate method generate seismic fragility curves for a dam according to two damage indicators. Comparison of the results for the seismic performance of the high ACCRD revealed that the longer-duration GMs could give rise to the higher relative settlement ratio, stress demand-capacity ratios, and probability of exceedance (POE) of the dam than shorter-duration GMs. It is recommended that in the current seismic design and seismic performance evaluation, the effects of GM duration, frequency, and amplitude should be considered.

Characteristics and causes of crest cracking on a high core-wall rockfill dam: A case study

Avoiding and controlling dam crest cracking is one of the most difficult problems facing high core rockfill dams of more than 100 m. However, few studies have been conducted on the characteristics and causes of dam crest cracking based on long-term measurement data. In this study, a real case of a dam suffering cracking at the crest was studied. The dam has a maximum height of 186 m and has been in service for 10 years. The spatiotemporal characteristics of the dam crest cracking were determined based on monitoring data obtained using crack monitoring instruments, radar detection, seismic refraction tomography, and pit exploration. The causes of dam cracking were analyzed based on the deformation inclination and strain index. The factors controlling the cracking (such as the dam structure, geological structure, and materials' properties) were investigated. The results show the following. 1) The cracks mainly occurred at the interface between the core wall and the downstream dam shell. 2) The cracks mainly developed during the impoundment and operation periods with high water levels, and there was no convergence trend within the 10 years of operation. 3) Uneven settlement and uneven horizontal displacement were the main reasons for the crack formation. 4) The factors influencing the cracking include dam zoning, the geological structure, wetting, and the rheological properties of the rockfill materials, and the reservoir level. The results of this study provide an important engineering reference for the prevention and control of dam crest cracking in high rockfill dams.

Study on compaction control standard of different contact clay areas for 300m high core rockfill dam

Based on several 300m high core rockfill dam in Southwest China, through studying the stress distribution, shear deformation and stress level of different gravel soil core walls, combined with the mechanical test results of contact clay under different compactness and moisture content, the compactness control standards for different contact clay areas of high core rockfill dam are proposed. The results show that for the contact clay area of dam slope on both banks, for the area where the stress level exceeds 0.9, the compaction degree should be increased, so as to improve the shear strength of the soil in the area; for the area with large shear deformation, the compaction degree should be reduced, so as to adapt to the larger shear deformation with larger allowable shear strain. During the filling of contact clay, the water content should not be too low or too high, and should be controlled in an interval near the optimal water content. Taking the test soil materials of the project as an example, it is suggested that the lower limit of filling water content should be controlled at 1% of the optimal water content, and the upper limit should be controlled at 3.5% of the optimal water content.

External Deformation Monitoring and Improved Partial Least Squares Data Analysis Methods of High Core Rock-Fill Dam (HCRFD).

External deformation monitoring of high core rock-fill dams (HCRFDs) is an important and difficult part of safety monitoring. The traditional method of external deformation monitoring and data analysis for HCRFDs is to use a total station for small angle observations and establish a regression model to analyze the results. However, the small angle method has low accuracy and a low automation degree, and there is multicollinearity between the independent variables, which affects the parameter estimation and leads to the failure of model establishment. The angle forward intersection method is adopted in this paper for observation, and an improved partial least squares method (IPLS) is proposed to eliminate the multicollinearity of the independent variables. Compared to the traditional method, the improved observation method exhibits high accuracy and a high automation degree. The new data analysis method can not only eliminate multicollinearity but also improve the interpretation ability of the model. The data from the initial stage of water storage shows that the displacement increases with the increase in the upstream water level and time, and the speed of water storage is proportional to the displacement. The water level and time are the main influencing factors. This conclusion provides a theoretical basis for reservoir management departments to control water levels and gate opening and closing. The method in this paper can be applied to arch dams, gravity dams, and other types of waterpower engineering systems.

Research on a Seepage Monitoring Model of a High Core Rockfill Dam Based on Machine Learning.

The seepage of a rockfill dam with a high core wall is an important and difficult issue in the safety monitoring of a core rockfill dam, something about which managers are immensely concerned. Seepage of a high core rockfill dam is mainly affected by factors such as water level, rainfall, temperature, filling height, and aging. The traditional research method is to establish a multiple linear regression model to analyze the influence factors of seepage. However, the multicollinearity between these factors affects parameter estimation, and random errors in the data cause the regression model to fail to be established. This paper starts with data collected by an osmometer, uses the 3δ criterion to process the outliers in the sample data, uses the R language to perform principal component analysis on the processed data to eliminate the multicollinearity of the factors, and finally uses multiple linear regression to model and analyze the data. Taking the Nuozhadu high core rockfill dam as an example, the influencing factors of seepage in the construction period and the impoundment period were studied and the seepage was then forecasted. This method provides guidance for further studies of the same type of dam seepage monitoring model.

Research on the Seepage Safety Monitoring Indexes of the High Core Rockfill Dam

The study on developing the reasonable safety monitoring indexes plays a most importantly role in the health monitoring of high core rockfill dams. However, researches on this topic are relatively scarce both at home and abroad. In this paper, the characteristics and failure modes of seepage in high core rockfill dam are analyzed firstly. Then, a safety monitoring index based on seepage quantity, which reflects the overall seepage behavior, is developed, using the real-time monitoring data and its safety monitoring model. Moreover, another safety monitoring index based on seepage gradient, reflecting the local seepage behavior, is proposed, combining the spatial layout of osmo- meters and local failure mechanisms of core wall. Additionally, one more safety monitoring index based on permeability coefficient, which considers the overall and local seepage behaviors, is developed, on the basis of establishing the finite element analysis model and real-time seepage coefficient inversion analysis model of high core rockfill dam. A case study on these indexes of Nuozhadu high core rockfill dam is developed, which improves the reliability of seepage safety evaluation of the dam.

Parameters inversion of high central core rockfill dams based on a novel genetic algorithm

Parameters identification of rockfill materials is a crucial issue for high rockfill dams. Because of the scale effect, random sampling and sample disturbance, it is difficult to obtain the actual mechanical properties of rockfill from laboratory tests. Parameters inversion based on in situ monitoring data has been proven to be an efficient method for identifying the exact parameters of the rockfill. In this paper, we propose a modified genetic algorithm to solve the high-dimension multimodal and nonlinear optimal parameters inversion problem. A novel crossover operator based on the sum of differences in gene fragments (SoDX) is proposed, inspired by the cloning of superior genes in genetic engineering. The crossover points are selected according to the difference in the gene fragments, defining the adaptive length. The crossover operator increases the speed and accuracy of algorithm convergence by reducing the inbreeding and enhancing the global search capability of the genetic algorithm. This algorithm is compared with two existing crossover operators. The modified genetic algorithm is then used in combination with radial basis function neural networks (RBFNN) to perform the parameters back analysis of a high central earth core rockfill dam. The settlements simulated using the identified parameters show good agreement with the monitoring data, illustrating that the back analysis is reasonable and accurate. The proposed genetic algorithm has considerable superiority for nonlinear multimodal parameter identification problems.

Response surface and genetic method of deformation back analysis for high core rockfill dams

High core rockfill dams exhibit complex deformation mechanisms because of complicated geological conditions, many material partitions and severe weather conditions. When realistic parameters cannot be obtained through laboratory tests or engineering analogies because of effects of size or time, back analysis is necessary to predict deformation characteristics. This paper proposes a method of deformation back analysis based on the response surface method and genetic optimization theory. The parameters of the creep and Duncan–Chang models for the Pubugou gravelly soil core rockfill dam are sequentially calculated. Back analysis performed using this method efficiently yields more precise results than those obtained from laboratory-determined parameters.

STRUCTURAL DESIGN OF NEW LINING FOR DIVERSION TUNNELS: ROGUN DAM AND HPP PROJECT

Rogun dam is a 335m high clay core rockfill dam which will be constructed on Vakhsh River in Tajikistan. Originally, two diversion tunnels with similar geometry were designed for discharging the seasonal floods, up to 3290m3/s. River diversion was carried out in November 1987 and a 45m high rockfill cofferdam was constructed. However, because of two collapses in the diversion tunnels, the cofferdam was overtopped in May 1993. Reconstruction of these tunnels started in 2009 and the collapsed areas were repaired. Nowadays, the design of complementary rehabilitation including new concrete lining for those parts of the tunnels will be used as tailrace tunnels are underway. The present paper describes the present conditions of diversion tunnels No. 1 and 2, explains the procedure used for the structural design of these tunnels, and presents the results of such design.

Back Analysis of the Permeability Coefficient of a High Core Rockfill Dam Based on a RBF Neural Network Optimized Using the PSO Algorithm

It is important to determine the seepage field parameters of a high core rockfill dam using the seepage data obtained during operation. For the Nuozhadu high core rockfill dam, a back analysis model is proposed using the radial basis function neural network optimized using a particle swarm optimization algorithm (PSO-RBFNN) and the technology of finite element analysis for solving the saturated-unsaturated seepage field. The recorded osmotic pressure curves of osmometers, which are distributed in the maximum cross section, are applied to this back analysis. The permeability coefficients of the dam materials are retrieved using the measured seepage pressure values while the steady state seepage condition exists; that is, the water lever remains unchanged. Meanwhile, the parameters are tested using the unstable saturated-unsaturated seepage field while the water level rises. The results show that the permeability coefficients are reasonable and can be used to study the real behavior of a seepage field of a high core rockfill dam during its operation period.

Coupled Elastoplastic Analysis of Dam Seismic Stability

A nonlinear procedure for coupled elastoplastic analysis of the dam seismic stability was presented in this paper. The soil nonlinear dynamic behavior was modeled using by a multiple yield surface model based on the numerical framework of u-p formulation. The strength reduction method was used to determine the factor of safety of dam slope and the location of failure surface. A case study of a 293.5 m high clay core rockfill dam was used to demonstrate the application of the method. Based on the computed results, it is founded that the maximum acceleration amplification coefficient is 1.72, which is almost 20% less than that obtained from the equivalent linear analysis. The most dangerous slip surface was at the shallow zone of the lower part of the upstream slope, which was different from the predicted location from the equivalent linear analysis. The earthquake induced pore water pressure and permanent deformation were also studied in detail.

Characteristics of Earthquake Damage for High Core and Concrete-Faced Rock-Fill Dams by Shaking Table Tests

The pattern and characteristics of seismic damage for Shuangjiangkou ECRD and Houziyan CFRD models were studied through large-scale earthquake simulation shaking table tests in this work. The test results showed that the main earthquake damage pattern of rock-fill dam is permanent residual deformation and shallow slide on the downstream slope. Seismic residual deformation of rock-fill dam, which is filled and compacted well, is very small. Regardless of ECRD or CFRD, the horizontal displacement and settlement on downstream slope are significantly larger than upstream slope under empty reservoir. The analysis of residual deformation and vibration frequency before and after failure indicated that aseismic performance of CFRD is superior to ECRD. Because of the remarkable whipping effect in the high rock-fill dam, the key parts of aseismic design is downstream slope near the dam top, where appropriate aseismic measures should be taken.