Roller compacted concrete (RCC) dams own a large number of horizontal construction layers, which can easily lead to weak joints among layers and generate interlayer joints with different scales to ...reduce the dam bearing capacity. In this study, extended finite element method (XFEM) is used to simulate crack propagation, the finite element description is first taken on the strong discontinuity. Subsequently, the displacement function of the crack-tip in the quadrilateral element and the geometric determination method of the crack-tip strengthening region are established. Afterwards, the discrete form of the governing equation is derived and the XFEM increment discretization method of the cohesive crack with the crack-tip reinforcement is proposed using the virtual node method to represent the discontinuity of the fracture element. These methods are validated through simulating mixed-mode cracking of one-sided notched asymmetric four-point bending beam. Eventually, the proposed methods are applied to RCC gravity dam to study the development rule and propagation path of the interlayer joints, so as to evaluate the effect of different lengths of the interlayer joints on the dam structural performance. The estimated critical values of dam deformation are helpful to prevent the dam failure during long term operation.
The Foziling multi-arch dam, one of the few multi-arch dams in the world, was built on the bedrock with complicated geological conditions. It has undergone several reinforcements since it was put ...into service in the 1950s. In this study, the dam safety is evaluated by analyzing the measured displacements and simulating stresses in the concrete. Firstly, the multiple linear stepwise regression (MLSR) is used to train and test the relationships between the loads and displacement based on the hydrostatic-temperature-time (HTT) model. Subsequently, the contributions of water level, temperature, and time to displacements are determined, and the influence characteristics of water level and temperature on displacements are interpreted. Finally, the dam stress state is evaluated by establishing a dam finite element model and simulating the stress distribution in various operating conditions. The results indicate that (1) the dam is currently in an elastic state after the last reinforcement; (2) temperature contributes the most to the displacement, and the drastic fluctuation of temperature is the disadvantage factor for multi-arch dam safety; (3) the stresses generally can meet the requirements of code; and (4) the ideas and methods of the study can provide references for the safety evaluation of other concrete dams.
The seepage of the fractured rock mass in dam foundations involves complex fluid-structure coupling behavior, due to practical hydrogeological conditions. In this work, the seepage characteristics of ...the fractured rock mass and their correlations with the structural permeable mediums are experimentally explored to reveal the cracking effect on the hydromechanical properties firstly. Subsequently, the tangential and the compression creep damage constitutive models are, respectively, established by introducing a nonlinear viscoplastic body to improve the Nishihara model. Afterwards, an innovative evolution equation of the permeability coefficient considering the creep damage is proposed. It can indicate the time effect of the porosity, the permeability, and damage variables of the fractured rock mass under the long-term infiltration action of the hydraulic pressures. Ultimately, the proposed methods are applied to the seepage simulation on the dam foundation of the Longyangxia hydropower station and the significantly increased leakage is in good agreement with the measured values during the storage period. It was further confirmed that the crack expansion and penetration in the rock masses can be constantly intensified by the seepage pressures. The research results can provide a reference for engineering repair and supervision through controlling the permeability performance for long-term operations.
Monitoring indexes are significant for real-time monitoring of dam performance in ensuring safe and normal operation. Traditional methods for establishing monitoring indexes are mostly focused on ...single point displacements, and rational monitoring indexes based on multi-point displacements are rare. This study establishes monitoring indexes based on correlation and discreteness of multi-point displacements. The proposed method is applicable when several monitoring points show strong correlation. In this study, principal component analysis (PCA) was introduced for preprocessing the observations of multi-point displacements. Correlation and discreteness of multi-point displacements were extracted and constructed. The correlation and discreteness parts described the integral and local variance of the displacement field. On this basis, the annual maximum values of the correlation and discreteness parts were selected and their probability density functions (PDF) could be generated by employing the principle of maximum entropy. PDF was constructed using maximum entropy method and was least subjective because it barely provided the moment information of the observations. The multi-point monitoring indexes were then determined by the typical low probability method based on the obtained PDFs. Finally, the proposed method was analyzed using a practical engineering and was verified in terms of its feasibility.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
•The geometry centroid is defined for arch dam performance evaluation.•The space-time monitoring model for the centroid deformation is established.•The nonlinear PCA-LSSVM prediction model is ...developed.•Accurate prediction is achieved on the world’s highest arch dam.
The purpose of this study is evaluating the arch dam performance through modelling on the defined centroid deformation with the measured data. The space-time distribution characteristics of the arch dam deformation are firstly identified through the comparative analysis of typical arch dams with height of 200–300 m in China. Subsequently, the geometry centroid of the deflection curve of an arch or a cantilever, composed of multiple monitoring points, is defined to indicate the global structural behavior of the arch dams. In order to evaluate the future performance of the arch dams, the space–time monitoring model for the centroid is established by introducing its initial coordinates based on the traditional statistical models. Afterwards, a novel centroid prediction model is developed based on the least squares support vector machine to balance the empirical risk and generalization ability of the statistical regression models. The input factors of the prediction model are determined in advance by principal component analysis to eliminate the multi-collinearity and reduce the computational complexity. The model construction and validation of the centroid deformation method are implemented on the world’s highest arch dam through evaluating its structural behavior and predicting the development trend. The results can provide strong technical support to better grasp its performance during long-term operation.
During the operational period, unexpected upstream deformation has been observed in several super-high arch dams located in the alpine and gorge regions. In addition, the phenomenon of the downstream ...dam deformation monitoring values being apparently smaller than the numerical simulation results appears in some super-high arch dams. This paper focuses on the genetic mechanism of a super-high arch dam’s special deformation characteristics. The finite element method (FEM) was used to analyze the effects of solar radiation, valley contraction, and overhanging on super-high arch dam’s deformation behavior. First, the influences of solar radiation on the temperature field and deformation characteristics of the super-high arch dam under the shading effects of the mountain and the dam body were investigated. Second, the impacts of valley contraction on the deformation characteristics of the super-high arch dam during the storage period were studied. Subsequently, the impact of the overhanging effect on the super-high arch dam’s deformation was explored. Finally, a case study was conducted on the basis of the Jinping I super-high arch dam to evaluate the effectiveness of the proposed analytical method. It is indicated that the dam’s special deformation can be explained reasonably. Above all, in order to accurately analyze and predict the deformation characteristics of super high-arch dams in the alpine and gorge regions of Southwest China, solar radiation, valley contraction, and the dam-overhanging effect need to be considered as influencing factors of dam deformation.
The physical and mechanical parameters of hydraulic structures in complicated operating conditions often change over time. Updating these parameters in a timely manner is important to comprehend the ...operating behaviors and monitor the safety of hydraulic structures. Conventional inverse analysis methods can only generate inversions on the comprehensive deformation modulus of concrete dam structures, which contradict practical conditions. Based on the researches on conventional reversion methods of the deformation modulus of the dam body, foundation, and reservoir basin, the objective fitness function is established in this paper according to engineering-measured data and finite element simulation results. The quantum genetic algorithm has high global search efficiency and population diversity. A mechanical parameter inversion of high-arch dams is built from the intelligent optimization of an established algorithm by applying the quantum genetic algorithm. The proposed algorithm is tested to be feasible and valid for practical engineering projects and therefore shows scientific and practical application values.
•The deformation variation law is a direct indicator of dam overall stability.•A geometric center of an irregular deformation plane is proposed.•The unified egg-shaped ellipse equations are developed ...for ultrahigh arch dams.•The critical indexes are estimated considering the abnormal probabilities.
This paper presents an innovative critical threshold estimation approach using unified egg-shaped ellipsoid modelling to study the deformation behavior of ultrahigh arch dams. First, the deformation variation law is regarded as a direct indicator of the overall stability and potential damage of ultrahigh arch dams based on comprehensively comparison with the results of theoretical calculations, experimental tests, numerical simulations and monitoring data. Subsequently, a novel geometric center of an irregular deformation plane constituted by all the deflection curves is proposed according to the measured distribution characteristics of the deformation spatial fields of the Xiaowan and Jinping I arch dams. Furthermore, unified egg-shaped ellipse equations are proposed to systematically identify the deformation critical attributes of Jinping I dam. Eventually, based on the peaks over threshold model, critical indexes are estimated considering the abnormal probabilities. The proposed methods are applied to Xiaowan dam as well. Results demonstrate that unified ellipsoid modelling can uniformly describe the abnormal features of the deformation behaviors of different ultrahigh arch dams, thereby the universal structural evolution characteristics to be understood in a wider range during their long-term operations.
Existing component separation methods fail to consider the complex nonlinear relationship between dam effect quantities and environmental variables. In this study, a novel nonlinear component ...separation method for the effect quantities is proposed by combining kernel partial least squares (KPLS) and pseudosamples. By this method, a nonlinear monitoring model is established based on KPLS, and the complicated nonlinear relationship between the effect quantities and environmental variables can be determined accurately through the model. Furthermore, special pseudosamples are constructed to separate independent components and coupling influence components of environmental factors from the KPLS model. These methods have been applied into a super-high arch dam, and the separated displacement components conform to the general deformation law. The presented results indicate that it is more reliable than traditional multiple linear regression models.
Summary
The deformations of ultrahigh arch dams can comprehensively indicate the dynamic variations of their structural behavior to judge the normal or not for timely discovering anomalies. First, ...the panel data features on the deformation behavior are extracted to effectively indicate the overall structural evolution of the Jinping I arch dam combing with the time series and the cross‐section series. Afterwards, a regression panel model (RPM) on the multi‐dimensional variables is proposed to model the deformation panel data consisted of multi‐monitoring points synchronously. Subsequently, an innovative functional relationship between the measured values and the real‐time risk probabilistic function is established due to the RPM estimation accuracy. In order to estimate the risk probability of the whole arch dam, the Copula function is used to build a multivariate joint probability distribution function to indicate the correlation among the random variables. The proposed methods are validated by an application on the Jinping I arch dam to evaluate its risk probability, which explores a novel approach for the arch dam safety assessment.
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