High Concrete-faced Rockfill Dam Research Articles

High modulus partition deformation control of high concrete face rockfill dam

Concrete face rockfill dams, preferred for their adaptability in unloading and soft rock foundations, encounter significant deformation control challenges at increased heights. This study analyses the stress and strain of five Chinese dams, ranging from 179.5 m to 233.5 m, demonstrating improved structural responses by implementing high-modulus zones in the rockfill and concrete embedment. The findings reveal a direct relationship between rockfill settlement, concrete face slab deflection, and dam height. Incorporating a high-modulus zone and concrete embedment resulted in reduced rockfill settlement by 15% and 5.8%, concrete face slab deflection by 17% and 41.9%, and joint deformation by 10%–20% and 21.2%, respectively. This study is expected to support the deformation control of high-concrete-face rockfill dams.

A novel constitutive model for the concrete face slab of a CFRD and the numerical simulation of its seismic behavior

AbstractWith the rising demand for hydropower energy, China has built numerous concrete‐faced rockfill dams (CFRDs) with considerable heights. The potential failure pattern of the concrete face slab is the key to the safety of the anti‐seepage system. However, engineers commonly employ an elastic relationship to model the concrete face slab for simplicity, which induces inaccurate estimation of the face slab's stresses, especially under seismic conditions. On the other hand, the existing elastoplastic models for concrete often require complex derivation of the necessary formula and thus are difficult to apply to finite element (FE) analysis. Under the comprehensive action of the upstream water, supporting rockfill, and surrounding mountains, the damage mode of the quasibrittle concrete slab is not a tensile mode but a compressive shearing mode. Therefore, it is urgent to establish an elastoplastic model that is adapted to the actual working environment of the slab and easy to apply. To this end, a generalized plasticity model is developed within the phenomenology modeling concept, which is validated at both the experimental level and application level. The results indicate that three‐dimensional stress‒strain behaviors, such as the strength nonlinearity, prepeak dilatancy, and postpeak softening, can be effectively captured. In addition, the seismic characteristics of a 200‐m high CFRD are numerically investigated. The findings show that the slab's stress accumulation can be reflected during the earthquake and that the final stress distribution conforms to the field observations. The conclusions of this paper provide a reliable reference for the seismic resistance design of CFRDs.

Simulation of non-stationary ground motions and its applications in high concrete faced rockfill dams via direct probability integral method

Many high concrete face rockfill dams (CFRDs) have been constructed in earthquake-prone areas in recent years, and it is essential to evaluate the seismic safety performance of these dams considering the randomness of seismic excitation. In this paper, the relationship between the stochastic ground motion generation method and the direct probability integral method (DPIM) is established by using the number theory point selection method as the bridge. The DPIM is introduced into the field of stochastic dynamic analysis and multi-index reliability evaluation of high CFRD for the first time. First, a non-stationary stochastic excitation model at five sites is established based on the latest standard for the seismic design of hydraulic structures. Then, taking a practical project as an example, stochastic dynamic response analysis and reliability assessment based on dam crest settlement deformation and dam slope cumulative slippage are conducted by using DIPM. Finally, the influence of these two indexes on reliability is explored by drawing the equal failure probability curve. The results show that the stochastic dynamic analysis and reliability assessment framework established in this paper can provide probabilistic seismic safety assessments for high CFRDs. Sliding damage of the dam slope is more likely than the deformation damage of the rockfill from the perspective of probability.

Stochastic dynamic response and seismic fragility analysis for high concrete face rockfill dams considering earthquake and parameter uncertainties

The multiple uncertainties of soil properties and ground motions significantly affect the seismic response of high concrete face rockfill dams (CFRDs). Three types of randomness (the material parameter randomness, stochastic seismic excitation, and their coupling) are generated by stochastic ground motion model and generalized F-discrepancy (GF-discrepancy) method. The generalized probability density evolution method (GPDEM) is used to analyze the influence of randomness on the stochastic dynamic response and system reliability of high CFRDs. The limit state of CFRD is defined according to the crest subsidence and the stress of face-slab, and a performance-based reliability evaluation framework is established. The results show that the randomness of ground motions dominates stochastic dynamic response of the CFRD and the dynamic reliability at different safety thresholds can be obtained by the above methods. Moreover, the proposed seismic safety evaluation framework provides a significant guidance for designing and analyzing practical engineering projects.

Influence of filling sequence of concrete faced rockfill dam on deformation of squeezed sidewall and dam

During construction of concrete faced rockfill dam (CFRD), the extrusion-sidewall will be protruding or deficiency under normal. Before panel construction, local slope cutting should be taken for the squeezed side wall or supplementary filling measures should be taken after excavating the squeezed side wall, which will affect the mechanical deformation of the panel. According to the monitoring data of concrete-faced rockfill dams of some hydro-electric station in Hubei Province, the three-dimensional finite element analysis method is used to simulate the original filling sequence process of the concrete face rockfill dam. By comparing the difference between the monitoring data and the calculation results, the deformation law of the extrusion side wall and the dam is obtained, which verifies the rationality of the three-dimensional simulation analysis of the dam. The characteristic values of settlement and horizontal displacement obtained from dam monitoring and numerical calculation are compared with those of other high concrete faced rockfill dams. The characteristic values of this dam are close to those of general concrete faced rockfill dams. The deformation law of extrusion side wall and dam under two optimization schemes with different filling sequence is studied. It is found that if conditions permit, the upstream should be filled first and then the downstream to reduce the deformation of extrusion side wall to the upstream.

Semi-quantitative risk analysis of high concrete face rockfill dams under seismic action

A dam failures cause immeasurable losses, but more concrete face rockfill dams (CFRDs) are being built in areas where earthquakes occur frequently. If the risk level of CFRDs under seismic action can be identified promptly and corresponding measures taken in advance, dam failure risks can be mitigated to protect life and property. However, no study has been conducted on the seismic risk analysis of CFRDs. This study aimed to meet public security needs; hence, the risk matrix approach was used for analyzing the semi-quantitative risk of CFRDs under seismic action. Considering the seismic failure modes of dam deformation and dam slope instability, we also proposed a calculation technique of seismic failure possibility for high CFRDs. According to the worst-case scenario, the linear weighted sum method was used to assess the comprehensive seismic risk loss of CFRDs in terms of life loss,and economic loss, and socio-environmental impact. The risk levels of CFRDs under seismic action were accurately evaluated, and corresponding risk management measures were proposed according to the “As Low As Reasonably Practicable” principle. The results of this work fill the gap in the risk analysis of CFRDs under seismic action. Additionally, the results provide a theoretical basis and technical support for future seismic designs, seismic risk assessments, and risk decision-making for high CFRDs and similar projects in strong seismic areas.

Effect of Multi-Components Strong Motion Duration on Seismic Performance of High CFRDs Based on Fragility Analysis

ABSTRACT This paper investigates the influence of multi-components strong motion duration on seismic performance of high concrete-faced rockfill dams (CFRDs) by fragility analysis based on the method of incremental dynamic analysis (IDA). The contributions of all compositions of earthquake excitations are considered by the definition of integrated duration based on the concept of significant duration. The nonlinear finite element model of a 2D 200-m-high CFRD is established as a case study and the vertical and horizontal displacements are selected as damage measures. Fragility curves and probabilities of two sets of 23 and 25 spectrally equivalent as-recorded bi-directional long-duration and short-duration motions are determined under different failure grades and intensities. The results show that the duration of vertical component has a certain effect on correction between strong motion duration and deformation of the dam and fragility analysis indicates that the ground motions with long duration can make more risk of failure of high CFRDs than short duration motions. Therefore, the seismic performance of high CFRDs will be reformed by taking the effect of ground motion duration into seismic design and risk assessment consideration.

Criteria for ultimate aseismic capacity of high rockfill dam

<p indent="0mm">The ultimate aseismic capacity is important to evaluate the seismic safety of a rockfill dam. However, no specification in China explicitly stipulates the criteria for the ultimate aseismic capacity of a rockfill dam. Existing evaluation factors and their indices to represent earthquake-induced damage to rockfill dams are not unified, and there is a problem with the safety degrees obtained by the indexes of different evaluation factors not being coordinated. In this study, a large number of systematic analyses of overall elastic-plastic deformation and slip deformation of high rockfill dams (height &gt; <sc>200 m)</sc> under earthquake are performed in addition to a comparative study of measured engineering analysis. Based on the above studies, four basic principles for determining the criteria for the ultimate aseismic capacity of a high rockfill dam are proposed: strictly following the mapping relationship between the relative settlement ratio of dam crest and the damage degree of dams under earthquake, ensuring that the dam can not be a collapse in extreme earthquakes, taking the relative settlement ratio of dam crest as the key control evaluation factor, and ensuring the coordination of different evaluation factors such as the relative settlement ratio of dam crest and the slip deformation of dam slope. Finally, the criteria for the ultimate aseismic capacity of a high concrete face rockfill dam and a core-wall rockfill dam under earthquake conditions are proposed. The findings of the study could provide an important standard basis for determining the ultimate aseismic capacity of a high rockfill dam.

Post-construction safety assessment of a high concrete face rockfill dam

The most important issue regarding the safety and performance of concrete face rockfill dams (CFRDs) is to determine stresses and deformations. However, predictions of crest settlements of CFRDs are usually performed using empirical relationships. In recent years, CFRDs have been constructed much higher and at more complicated topographical and geological dam sites, so numerical analysis is required to evaluate the stress and deformations in the entire dam body. Also, assessing long-term rockfill behaviour and the concrete face membrane crack potential are important for post-construction dam safety. This study evaluates post-construction deformations and crest settlements of a high CFRD under two different loading cases, considering the non-linear elasto-plastic behaviour of the rockfill structure. As a constitutive model, the Duncan–Chang hyperbolic stress–strain model was applied in finite-element simulations considering the failure criterion is isotropic and hardening. Calibration of the rockfill's hyperbolic parameters was performed by comparing the calculated displacements with actual settlement measurements. Computed crest settlements were also compared with those of some CFRDs given in the literature. Calculated crest settlement and other deformations are in good agreement with the rockfill settlement measurements and in acceptable ranges, and do not threaten the dam's safety.

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.

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.

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.

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.

Study on presettlement control measures for high concrete-faced rockfill dams

A finite element (FE) numerical simulation of instantaneous and creep deformation of rockfill bodies during the filling and water storage process of a concrete-faced rockfill dam (CFRD) is carried out based on practical experience in Shuibuya. The results show that the existing presettlement control measures are empirically based on 200-m-high CFRDs. To study the presettlement control measures for higher CFRDs, an FE simulation of slab detachment at the top of different stages during the construction of the 300-m-high CFRDs is carried out based on the inflow during the flood season and the optimised construction process. The results show that under the existing presettlement standards, the presettlement time of the rockfill body and filling height difference between the rockfill body and face slab do not meet the deformation control requirements for 300-m-high CFRDs. Furthermore, new presettlement control measures for 300-m superhigh CFRDs are presented based on numerical analysis.

The simulation of high compressive stress and extrusion phenomenon for concrete face slabs in CFRDs under strong seismic loads

The evaluation of high compression zones for anti-seepage face slabs is an increasingly important task in the safety evaluation of high concrete faced rock-fill dams (CFRDs). This manuscript uses the scaled boundary finite element method (SBFEM) to construct a cross-scale model of the rockfill and bedrock in a high CFRD. Nonconforming elements are applied to independently refine the mesh locally in the concrete face slab, which allows an accurate modeling of the rotating and bending phenomenon experienced by the face slab zone. Meanwhile, the non-matching node interface is introduced to connect the locally refined face slab mesh to the rockfill zone and obtain the final cross-scale model for refined analysis. The generalized plastic constitutive model and a state-dependent elasto-plastic interface constitutive model are employed to capture the complex behaviors of rockfill and soil-structure interaction (SSI). Leveraging the above approaches, static and dynamic analyses of a high CFRD are conducted to identify high compressive stress zones and simulate the extrusion damage. The results indicate that self-weight, water pressure, friction force and seismic loads contribute to rotating and bending between face slabs, and can lead to significant local stress concentration within the surface of face slab near the longitudinal joints and may potentially extrusion damage.

Numerical evaluation of transient solar radiation effect on concrete-faced rockfill dam with dual mortar contact method

Extrusion damage in the concrete face was widely observed in high concrete-faced rockfill dams in the last two decades. However, the accurate estimation of the concrete stress remains a great challenge. In this paper, a thermo-mechanical coupling method is presented to numerically evaluate the solar radiation effect on the concrete stress within the dual mortar finite element framework. The heat conduction is modelled as a transient time-dependent equation and hence the heat flow can be determined by meteorological data. The thermo-mechanical coupling is conducted in a weak way such that the linear system can be split into two subsystems friendly to the linear solver. The present method based on using nonconforming meshes is validated by the comparisons with node-to-segment method, conforming mesh and analytical solution. The application to a concrete-faced rockfill dam indicates that the phase lag and amplitude damping effects are apparent in the thermal analysis, confirming the importance of using transient heat conduction theory. The observed slab-slab separations emphasis the importance of using dual mortar contact method. The thermal stress is found to be larger than 10 MPa and therefore needs to be considered in the design and safety assessment.

Role of strong motion duration on seismic responses of high concrete faced rockfill dams

This study investigates the role of strong seismic motions on the dynamic responses of high CFRDs through elastoplastic analysis. Damage measures (DMs) including vertical and horizontal displacements, plastic shear strain, as well as a face-slab damage index are selected to gauge the deformation, stability of the dam slope and the anti-seepage ability of the face slab, respectively. The selected DMs are key to the safety of high CFRDs. A group of 35 as-recorded ground motions with a wide range of durations are modified to conform to a 5% damped target spectrum are used as input motions for dynamic analysis. A comprehensive understanding of the effects of ground motion duration is obtained through a tri-fold analysis of the ground motion records, the nonlinear dynamic response of CFRDs and the statistics of the results. The definitions of significant duration, bracketed duration and uniform duration, each with consideration to two different thresholds, are selected to characterize strong motion durations. The results suggests that significant duration is the most useful indicator for seismic assessment of high CFRDs and for evaluating the effects of the duration of an earthquake on the integrity of high CFRDs.

Seismic fragility analysis of high concrete faced rockfill dams based on plastic failure with support vector machine

With the rapid growth of economic, a growing number of earth and rockfill dams, especially high concrete faced rockfill dams (CFRDs), are being constructed in the intensity earthquake region in southwest of China. Their proximity to earthquake prone areas sets an imperative to evaluate the seismic performance of these dams. It can partially be evaluated based on fragility analysis and then fragility curves of the dams will be obtained. However, the establishment of fragility curves requires numerous numerical simulations with the finite element method (FEM). In this study, a support vector machine (SVM) is introduced to improve the computational efficiency of estimating structural response. Firstly, one hundred ground motion records are synthesized based on information given in the design scenario, and the corresponding intensity measures (IMs) can be obtained from each record. Secondly, numerical simulations are conducted by FEM and the corresponding damage measures (DMs) can be obtained. Three DMs are considered in this study, including vertical displacement, plastic shear strain, as well as the damage index (DI) of the face slab. Then, SVM models corresponding to the three DMs are trained according to the IMs and DMs, respectively. Finally, the fragility curves of different limit states based on the three DMs are calculated. This method of combining FEM and SVM is used for analyzing the seismic fragility of a 200 m CFRD. The results indicate that this method is effective for fragility analysis of CFRDs.

Stress and Deformation Analysis of High Concrete Face Rockfill Dam Based on COMSOL Multiphysics

In order to study the stress and deformation characteristics of the high concrete face rockfill dam over 100 meters, in this paper, Duncan-Zhang E-B nonlinear elastic hyperbolic model is adopted, the finite element software COMSOL Multiphysics is used to establish the model and the MATLAB function is used for secondary development to analyze the stress and deformation of the concrete face rockfill dam of the Panshitou reservoir. The stress and deformation characteristics of the concrete face rockfill dam at the completion period, normal water storage condition, designed flood level condition and checked flood level condition are obtained through analysis, which provide theoretical guidance for the construction and operation of the high concrete face rockfill dam of more than 100 meters.

A parabolic model and an iterative algorithm for the slab-cushion interface and the application in simulating the dynamic separation between the face slabs and cushion layer

The new damage phenomenon of the Zipingpu concrete-faced rock-fill dam (CFRD) in the 5.12 Wenchuan earthquake has introduced new topics to the study of seismic failure mechanisms and numerical simulation methods of high CFRDs. With respect to the large-scale contact separation between the face slabs and the cushion layer after the earthquake, the conventional method of directly assigning constant values ​​to the normal stiffness of the interface element can only qualitatively reflect the separated or closed state of the interface. In this article, a parabolic model for the normal stiffness of the interface is proposed, and an iterative algorithm for its optimal value is established based on the contact states. Combined with a generalised plasticity constitutive model, the 3 D finite element (FE) coupling analysis of the Zipingpu Dam is performed. The results show good agreements between the numerical calculations and field measurement conclusions. In addition, the opening and closing processes of the interface during the earthquake reproduce the dynamic face-slabs separation situation. It is indicated that the proposed constitutive model and the iterative algorithm can basically realise the quantitative estimation for the range and depth of the separation, providing a reliable method for the seismic analysis of high CFRDs.