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Theme B of the current 17-th ICOLD Benchmark Workshop is aimed at analysing the structural behaviour of an existing asphalt-concrete core rockfill dam during its first impoundment and operation period. This article presents an overview of the approaches adopted and the results obtained by the contributors to the Theme, as well as a comparison of the numerical results with the corresponding data obtained during the monitoring of the dam.

This article addresses Theme C of the 17th International Benchmark Workshop on Numerical Analysis of Dams. The study investigates the behavior of large concrete-faced rockfill dams (CFRDs) through 2D and 3D numerical simulations using Hardening Soil Model (HSM) and Mohr-Coulomb (MC) constitutive models, focusing on key aspects such as narrow valley effects and scale effects. The results indicate that 2D analyses overestimate settlements and bank-to-bank stresses by approximately 45% due to the narrow valley geometry. Regarding scale effects, the ratio between laboratory and on-site rockfill elastic moduli is assessed by means of a back-analysis of the monitored settlement. For MC and HSM in 2D models its values are 1.40 and 1.14, respectively, while when considering the 3D foundation shape, the HSM factor increases to 1.67. This value remains lower than the one obtained with Frossard equation under similar conditions (2.4), likely due to the high compaction efforts applied to Nam Ngum 3 rockfill. The overall settlement predictions align well with measured values when scale effects are considered, though horizontal displacement precision is lower. Additionally, a stress-dependent creep model is proposed to represent time-dependent deformations after construction, allowing to obtain a precise fit for the different elevations. The developed numerical models provide valuable insights into the behavior of large CFRDs in narrow valleys, contributing to improve prediction methods for future similar structures.

Parameter selection is always a critical issue for the numerical modeling of many geotechnical problems. In this work, an idea of non-parameterized numerical analysis is demonstrated by incorporating tri-axial data as the input into the distinct lattice spring model (DLSM). An automatic parameter acquisition procedure is developed to determine the parameters of a modified Duncan–Chang (DC) model which is implemented in the DLSM through the further development of an incremental DLSM and a fabric stress calculation scheme. These newly developed algorithms are verified against available numerical results and experimental counterparts. Then, the discrete feature of the DC-DLSM is explored and discussed through the numerical modeling of large-scale tri-axial tests and a fracturing test. Finally, a real rockfill dam project is analyzed by using the DC-DLSM with the available tri-axial data as the input, and a reasonable fitting is obtained, which shows the possibility for the numerical modeling of the DLSM with no parameter selection burden.

Although gabion has been utilized in geotechnical engineering fields, research on its failure mechanics lags behind its practical applications due to the discrete nature of its mechanical behavior and the multiple factors. Leveraging uniaxial compression testing, this study compares and analyzes the disparities in failure patterns and mechanical characteristics of gabion elements. The deterioration of gabion elements predominantly exhibits in the form of crushing of the rockfill and the fracturing of the gabion mesh. The undulating nature of the load-ACR curve throughout the loading procedure stems from the continual reconfiguration of the contact force chain among the rockfills. Notably, gabion elements possess exceptional ductility, retaining a substantial load-bearing capacity even under significant deformation conditions. The intricate relationships between experimental mechanics, the external gabion mesh, and the internal rockfill are elucidated. It was found that gabion elements exhibit the highest deformation modulus and peak strength when they feature smaller gabion mesh side lengths, larger rib diameters, higher rockfill strengths, and natural rockfill gradation. Furthermore, the crushing of the rockfill and the failure patterns of the gabion mesh are intricately linked to the strength of the rockfill and the rib diameter. In scenarios where the rockfill strength is substantial, the peak strength of the gabion elements is primarily governed by the rockfill itself. In contrast, under other test conditions, the gabion mesh plays a pivotal role. The order of deformation modulus of gabion elements with different rockfill types is sand pebble > shale > red sandstone. The ultimate failure mechanism of the gabion elements often manifests as the enlargement of mesh openings due to the breakage of mesh ribs, leading to the expulsion of internal rockfill. Notably, gabion elements filled with larger rockfill gradations exhibit the most severe hoop distortions and inferior mechanical properties. Conversely, gabion elements containing sand pebble and natural rockfill size demonstrate superior mechanical characteristics. The methodologies, analytical approaches, and insights presented in this study provide valuable references for selecting gabion structure in practical engineering applications.

This paper presents the synthesis of Theme C of the 17th ICOLD International Benchmark Workshop on Numerical Analysis of Dams, focused on the calibration and prediction of the behaviour of a 210 m-high Concrete Face Rockfill Dam (CFRD), a major component of the Nam Ngum 3 hydroelectric project in Laos. With increasing dam heights, empirical methods traditionally used in CFRD design are proving insufficient to address complex deformation mechanisms, particularly long-term settlements and concrete face cracking risks. Participants performed predictive simulations using laboratory data, then recalibrated their models based on field measurements of vertical and horizontal displacements. The narrow valley geometry causes stress redistribution, highlighting the necessity of using 3D models to accurately simulate the dam’s behaviour. Results show that lab-derived stiffness parameters systematically overestimate in situ rockfill stiffness, with a scale factor of approximately 1.7 required to match settlement measurements in 3D models using advanced constitutive models (especially Hardening Soil Model). In 2D models, the scale effect is smaller - around 1.4 for the Mohr-Coulomb and LADE models, and 1.1 for HSM - due to a compensation effect linked to the absence of vertical stress reduction in the 2D representation. Creep models enable a better match of long-term settlements, although the modelling approaches varied and may lack predictive accuracy. This benchmark highlights the importance of accounting for both scale effects and creep behaviour in 3D numerical models during the design phase of high rockfill dams and more specifically CFRDs and intends to provide a reference dataset and methodology for future predictive and back-analysis studies.

Landslide dams pose enormous risks to the public because of the potentially catastrophic floods generated by breaching of such dams. The need to better understand the threats of landslide dams raises questions about the proper estimation of breaching parameters (breach size, breaching duration, and peak outflow rate) of landslide dams and the feasibility of applying models for estimating the breaching parameters of man-made earthen dams to landslide dams. This paper aims to answer these two questions. In this study, a database of 1,239 landslide dams, including 257 cases formed during the 12 May 2008 Wenchuan earthquake, has been compiled. Based on records of 52 landslide dam cases with breaching information in the database, empirical models for estimating the breaching parameters of landslide dams are developed. A comparison study between landslide dams and man-made earth and rockfill dams is conducted, which shows that the models for man-made earth and rockfill dams are not suitable for estimating the breaching parameters of landslide dams. Two case studies are presented to show the application of the set of empirical models developed in this paper.

Slope Reliability analyses are widely used in geotechnical engineering. A reliability analysis of the slope stability of rockfill dams is based on the strength of the granular materials used. However, the characteristics of the shear strengths of granular materials are non-linear, so that calculating the reliability index requires significantly more iterations and partial derivatives. To optimise this iterative method, an algorithm is proposed to linearise Duncan’s non-linear strength parameters. This study expands Duncan’s non-linear model using a Taylor series, and derives a relation between the strength parameters used for Duncan’s non-linear criterion and those for the Mohr–Coulomb linear criterion. In the present study, the accuracy of the linearisation algorithm was verified for a simplified slope and the proposed linearisation algorithm is coded into a computer program, STAB. The linearisation algorithm was applied to a reliability analysis of the slope stability of the rockfill used for Shuang Jiang Kou Dam in China. Results indicate that the linearized parameters yield similar reliability indices to the nonlinear parameters, demonstrating the feasibility of the approach for reliability analysis of rockfill dams.

To address the uncertainty problem in the assessment of the overall safety trend of dams and in the selection of safety trend warning indicators, an Extended Cloud Model (ECM) combined with the Extended Analytic Hierarchy Process (EAHP) method is proposed in this study. In this new approach, different factors reflecting dam safety monitoring have been considered as a fuzzy system. Considering the characteristics of the forward cloud model and the backward cloud model, the original data have been extended to classify the division interval and determine the respective indicators. The weight distribution for each indicator level has been determined using the EAHP method. The model developed was applied to evaluate the safety trend of the Jilintai concrete panel rockfill dam. Simulation results showed that the proposed model can generate reliable results, in addition to being used to assess the uncertainty problem and the safety warning indicator. The proposed model is also more flexible and easier to use than other methods.

Fully-developed turbulent flow-through coarse-grained porous media cannot be treated with the Dupuit approach based on Darcy’s law unless Forchheimer’s resistance equation is considered to account for non-linear effects arising from drag forces. By combining this equation with the Reynolds-averaged Navier-Stokes equations, a higher-order, depth-averaged model applicable to the flow of curvilinear seepage in a non-linear turbulent regime was developed. The governing equations were numerically solved with a hybrid scheme that adopts the finite-difference and finite-volume methods. The model’s validity was then examined by carrying out numerical tests involving unconfined non-Darcy flows. The numerical results for such flows through rockfill structures with various geometric shapes were compared with the experimental data and produced a satisfactory agreement. The results of the study demonstrated that a depth-averaged model of this type is mostly preferred for accurately predicting the phreatic surface curvature and the exit height of the seepage line. Furthermore, the overall results confirmed the model’s capability for adequately capturing the dynamic behavior of the turbulent seepage flow. The present model is therefore a useful tool for practicing engineers to evaluate the conceptual design of rockfill dams.

The post-construction settlement of rockfill dams and high filled ground of airport, which is a phenomenon of much significance, is mainly caused by the time-dependent breakage of the rockfill material. In this paper, a random virtual crack DEM model is proposed for creep behavior of rockfill in PFC2D according to the theory of subcritical crack propagation induced by stress corrosion mechanisms. The bonded clusters are adopted to represent the rockfill particles so as to simulate their irregular shapes. Virtual cracks are set at the bonds of the clusters, and the length of the crack is considered as a random value, which leads the crushing strength of a single particle to follow the Weibull’s statistical model and the corresponding size rules. Oedometric creep tests for rockfill are simulated by using this proposed model. The results show that the model, validated preliminarily by some test data, can reflect qualitatively the creep mechanism as well as the size effects reasonably. Particles can develop various breakage patterns during creep, including global breakage, local breakage and even complex mixed breakage. The increase in stress levels and particle size will lead to an obvious growth of the creep strain and creep rate of the rockfill. The scale effects on the creep behavior of rockfill are analyzed through 35 specimens, and formulas including the effects of scales and stress levels are tentatively proposed.