Concrete Face Rockfill Dam Research Articles

Denoising method for Fiber Optic Gyro measurement signal of face slab deflection of concrete face rockfill dam based on sparrow search algorithm and variational modal decomposition

In order to suppress the noise in the measurement signal of face slab deflection of concrete face rockfill dam (CFRD) by fiber optic gyro (FOG), a denoising method based on sparrow search algorithm (SSA) and variational mode decomposition (VMD) method is proposed in this paper. Firstly, the SSA algorithm was used to optimize parameters k and α of VMD, the fitness function of the algorithm was established based on the value of the kth intrinsic mode function (IMF) and the center frequency of the k-1th IMF obtained by the VMD decomposition. Then, this paper proposed a method to extract useful IMFs by calculating the mean Mahalanobis distance (MMD) of the Fast Fourier transform (FFT) functions between each IMF and the residual component. Finally, through the noise reduction analysis of FOG dynamic rotation experimental signal and the measured signal in practical engineering application, and compared with the results of traditional empirical mode decomposition (EMD) and VMD methods, the superiority of the proposed method was verified.

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.

Study on Ultimate Seismic Capacity of Concrete Gravity Dam-Superhigh Face Rockfill Dam Compound Structure

Based on a very high for the project of the concrete face rockfill dam, by three-dimensional finite element analysis method, from the seismic permanent deformation, stress, deformation and stability of dam slope angle of joint panel, this paper demonstrates the ultimate seismic capacity of concrete gravity dam - superhigh face rockfill dam compound structure, the research results show that the dam seismic permanent deformation limit aseismic capacity from 0.65 g to 0.72 g, panel stress seismic limit of 0.7 g, joint dislocation of aseismic capacity limit is 0.8 g, dam slope stability of aseismic capacity limit is 0.43 g. The seismic ability of concrete gravity dam - superhigh face rockfill dam compound structure is strong and can meet the local fortification intensity requirements.

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.

Large leakage incident in a Norwegian concrete faced rockfill dam due to ice build up

Aursjø dam is a concrete faced rockfill dam (CFRD) in central Norway built between 1950 and 1958 and owned by Statkraft. The dam was originally constructed with an upstream face consisting of wooden planks, which acted as the impermeable element of the dam. The dam underwent a large rehabilitation between 2005 and 2006, when the wooden planks were replaced with a reinforced-concrete slab. In 2017 a large leakage event occurred at the dam and at its peak was estimated to be up to 600 l/s. This paper covers the incident itself including the emergency response, the investigation into the cause of the high leakage, the potential effect on dam safety, and finally the recommended measures implemented at the dam. During the detailed investigation the cause of the leakage was identified as the release of water after an ice dam within the dam body burst. Ice build-up and subsequent rapid release of water is not an unusual occurrence at rockfill dams in Norway and there are examples where the same phenomena has occurred at other dams.

Subsurface Topographic Modeling Using Geospatial and Data Driven Algorithm

Infrastructures play an important role in urbanization and economic activities but are vulnerable. Due to unavailability of accurate subsurface infrastructure maps, ensuring the sustainability and resilience often are poorly recognized. In the current paper a 3D topographical predictive model using distributed geospatial data incorporated with evolutionary gene expression programming (GEP) was developed and applied on a concrete-face rockfill dam (CFRD) in Guilan province- northern to generate spatial variation of the subsurface bedrock topography. The compared proficiency of the GEP model with geostatistical ordinary kriging (OK) using different analytical indexes showed 82.53% accuracy performance and 9.61% improvement in precisely labeled data. The achievements imply that the retrieved GEP model efficiently can provide accurate enough prediction and consequently meliorate the visualization insights linking the natural and engineering concerns. Accordingly, the generated subsurface bedrock model dedicates great information on stability of structures and hydrogeological properties, thus adopting appropriate foundations.

An approach for simulating the interaction between soil and discontinuous structure with mixed interpolation interface

Structural discontinuities are common (e.g. cracks, segmented structures) especially in large-scale geotechnical structures, which can lead to the discontinuous soil-structure interaction (SSI) problems. Thus, in this paper a mixed interpolation interface with non-matching nodes is introduced for effectively simulating discontinuous SSI problems. This paper provides a conveniently executed numerical implementation of the introduced approach within a finite element method (FEM) analysis platform. The high flexibility and precision of the developed method are demonstrated through fine analyses of 2D and 3D concrete faced rockfill dams (CFRDs). Furthermore, a cracking evolution analysis for a high pedestal of the Quxue asphalt concrete core dam is conducted by coupling the method with a cohesive zone model (CZM). The mixed interpolation interface is verified as an effective tool for solving discontinuous SSI problems. The modeling also sheds light on the process of cracking evolution and the primary failure mechanism for high pedestal.

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.

The influence of fiber type and length on the cracking resistance, durability and pore structure of face slab concrete

• The drying and autogenous shrinkage reduction effect is greatest for PVA fiber. • The efficiency in improving the cracking resistance follows the order of PVA > PAN > PP. • PAN fibers produce a low porosity, a low hardened air content and a high impermeability. • Durability differences caused by fiber can be interpreted by the pore structure and air void. The crack resistance and durability of face slab concrete are two important factors determining the normal operation and safety of concrete face rockfill dams (CFRDs). This paper investigates the influence of polypropylene (PP), polyvinyl alcohol (PVA) and polyacrylonitrile (PAN) fiber with two lengths (10 mm and 20 mm) on workability, strength, shrinkage behavior, cracking resistance and durability performance of face slab concrete. Besides, the parameters of the pores at multi-scales were investigated by a linear traverse method and the mercury intrusion porosimetry (MIP), respectively. The results in this study demonstrate that: (1) the efficiency in reducing the shrinkage and in enhancing the cracking resistance of face slab concrete follows the order of PVA > PAN > PP. In addition, both the impermeability and frost resistance of concrete can be improved by adding fibers, the efficiency is in the sequence: PAN > PVA > PP and PVA > PAN > PP, respectively. (2) increasing fiber length from 10 mm to 20 mm reduces the shrinkage by about 5.1%−7.0%, enhances the tensile strength ( σ ) by about 7.9%−9.2% and declines the cracking temperature ( T c ) by about 5.6–6.5℃, all of which could significantly improve the cracking resistance. Moreover, the increase in fiber length improves the frost resistance, but increases the relative permeability coefficient ( K r) by about 28%−47%. (3) The correlation analyses reveal that, the addition of PAN fibers produces a lower porosity, a lower fraction of large capillary pores as well as a lower hardened air content than the PVA and PP fibers at 28 days, thereby resulting in better impermeability of concrete. PVA fiber enhanced concrete gives the smallest spacing factor and the largest total number of air voids among all the fiber enhanced concretes, thus exhibiting the best frost resistance.

COMPARISON OF FLY ASH, PVA FIBER, MGO AND SHRINKAGE-REDUCING ADMIXTURE ON THE FROST RESISTANCE OF FACE SLAB CONCRETE VIA PORE STRUCTURAL AND FRACTAL ANALYSIS

Face slab concrete suffers from serious frost damage in the cold regions in China. How to improve the frost resistance of face slab concrete in cold regions is one of the important issues in concrete-faced rockfill dam (CFRD) design and construction. The results in this paper indicate that the frost resistance of concrete can be improved by adding fly ash, fiber, MgO and shrinkage-reducing admixtures (SRAs), and their efficiencies are in the following sequence: (fly ash [Formula: see text] fiber) [Formula: see text] fiber [Formula: see text] fly ash [Formula: see text] MgO [Formula: see text] SRA. The incorporation of 0.8[Formula: see text]kg/m3 polyvinyl alcohol (PVA) fiber and 20[Formula: see text]wt.% fly ash together enhances the compressive strength and tensile capacity of concrete by 6–7% at the late age, whereas the addition of 6[Formula: see text]wt.% MgO or 1[Formula: see text]wt.% SRA reduces the compressive strength and tensile capacity by about 4–10% at various ages. The [Formula: see text] of concrete added with fly ash, fiber, MgO and SRA is within the range of 2.619–2.796. The frost resistance of concrete correlates linearly with the air void parameters, pore structures and [Formula: see text]. The utilization of fly ash and/or PVA fiber refines and optimizes the pore structure, thus increasing [Formula: see text] and improving the frost resistance. On the contrary, MgO and SRA in this study are less effective in refining the pores than PVA fiber and fly ash, thereby producing smaller [Formula: see text] and relatively weaker frost resistance.

Numerical Analysis of Seepage for Concrete Face Rockfill Dam with Cracks Based on Block Equivalent Continuum Method

There are many practical problems in the rapid development of the concrete face rockfill dam, which mainly focus on a large number of cracks and extrusion breakages in the face slab caused by temperature-induced stress, shrinkage stress, deformation of dam and other reasons, which eventually lead to leakage, threatening the safety of the dam. To solve this problem, the three-dimensional finite element analysis method is combined with the block equivalent continuum method to calculate the three-dimensional seepage field of the dam area, in order to study the seepage characteristics of numerous and unevenly distributed cracks in the concrete face rockfill dam; then, the corresponding head distribution and seepage characteristics, including the phreatic line, the hydraulic gradient and the seepage discharge, were obtained. The findings of this paper validate the accuracy and reliability of the block equivalent continuum method. It not only meets the requirements of simulation accuracy, but also can obtain the characteristics of the local seepage field near the crack. At the same time, it greatly simplifies the finite element model and significantly improves the efficiency of seepage calculation. This method provides a reference for the seepage analysis of similar projects.

A Prediction Model for Deformation Behavior of Concrete Face Rockfill Dams Based on the Threshold Regression Method

Rapid prediction of deformation behaviors of concrete face rockfill dams (CFRDs) is of great significance in guiding their design and construction. The purpose of this study is to develop robust empirical prediction models with physical significance, which can rapidly predict typical deformation behaviors of CFRDs. Based on 87 case histories of in-service CFRDs, the threshold regression theory is used to develop empirical relationships between three typical deformation indices (maximum crest settlement, maximum internal settlement, and maximum face slab deflection) and six dam-construction-related influencing factors (dam height, intact rockfill strength, foundation behavior, valley shape factor, void ratio, and operation time). The internal correlations between the deformation behavior and influencing factors are discussed. The importances of the influencing factors for each deformation behavior are quantitatively evaluated. The threshold regression models are developed to predict typical deformation behaviors of CFRDs. The developed models are compared with the existing methods to discuss their rationality and accuracy.

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 Comprehensive Evaluation Method of Safety Behavior of Concrete Face Rockfill Dam Based on Regression Relationship Method and Fuzzy Recognition Model

The concrete face rockfill dam (CFRD) generally encounters structural health problems during long-term operation. Therefore, it is necessary to study the safety evaluation of CFRDs. This paper proposes a comprehensive evaluation method for the safety behavior of CFRDs on the basis of regression relationship method and fuzzy recognition model. The method of sub-index safety evaluation is established by using regression relationship method. The multiplication scale method was adopted to determine the sub-indexes weight. In combineing of sub-index safety evaluation value and sub-indexes comprehensive weight, the fuzzy recognition model is used to determine the comprehensive evaluation grade of dam safety. Safety evaluation of several CFRDs were evaluated by the method proposed in this paper and exisiting safety evaluated method to verify reasonable and rationality of the method.

Predicting Maximum Crest Settlement of Concrete Face Rockfill Dams Using a New Ensemble Learning Model

Deformation assessment and control are essential issues in the construction of concrete face rockfill dams (CFRDs). The design and construction of CFRDs require deformation behavior that can be estimated rapidly to support engineering optimization and safety assessment. Based on 87 case histories of in-service CFRDs, a new ensemble learning model has been developed to predict maximum crest settlement (CS) of CFRDs. The model is based on the support vector machine regression algorithm (SVR) combined with multiple variables, and then the foundation model is integrated by the weighted average integration method. It is demonstrated here that the new ensemble learning model weakens the nonlinear characteristics of case data, makes up for the instability of single regression algorithm, improves the generalization ability, and provides a new idea for predicting the CS of CFRDs.

Rheology Test and Finite Element Analysis: A Case Study of a Rockfill Dam in China

Rheology often occurs in the dam rockfill deformation. In this paper, we carried out a large-scale triaxial rheological test for the tuff rockfill materials of a concrete faced rockfill dam in China, and then obtained the parameters of the seven parameter rheology model. Finally, we analyzed the dam rheology using the three-dimensional finite element model. The results show that the dam settlement, horizontal displacement, face deflection and the displacement of the joints around the face slab are all obviously increased when considering the rheological behavior of the rockfill. We find that the calculated settlement of the dam body is in good agreement with the filed measured value when the dam is completed, and the maximum settlement during the impoundment period is within the normal range.

Prediction and numerical simulation of the face‐slab extrusion damage of Dashixia concrete faced rock‐fill dam

AbstractOne of the core issues affecting the safety of high concrete faced rock‐fill dams (CFRDs) is the extrusion damage of the concrete face slabs. In this paper, the causes of the face‐slab extrusion damage under long‐term operational conditions are studied. It is found that not only the creep behavior of the dam materials but also the circulating water load in the reservoir is responsible for the uneven deformation of the dam that induces the extrusion damage of the face slabs. The possibility of the potential extrusion damage of the face slab of the Dashixia dam, which is now under construction in Xinjiang, China, is further predicted by means of a three‐dimensional finite element analysis (FEA). In the FEA, a unified generalized plasticity model that can reflect the volumetric contraction property during the unloading phase of coarse‐grained materials is adopted to overcome the shortcomings of previous studies where the effects of the circulating water load are neglected because of model limitations. Then, combined with an incremental creep model, the long‐term operational characteristics of the Dashixia dam are predicted and thoroughly discussed. Moreover, a submodel of the face slab is developed and introduced in the analysis to simulate the compressive stress along the thickness of the face slab. According to the results, it can be concluded that extrusion damage of the face slab of the Dashixia dam may occur under the current design conditions, and it is recommended to take some engineering measures to strengthen the slab.

Multiple Nonlinear Regression Models for Predicting Deformation Behavior of Concrete-Face Rockfill Dams

Abstract Deformation assessment and control are important issues in the construction of concrete face rockfill dams (CFRDs). The design and construction of CFRDs require deformation behavior that c...