Creep, once considered an inherent characteristic of granular materials, is primarily governed by time and the current stress state. However, recent studies indicate that creep development is also influenced by the loading history. To better reveal the creep revolution law of the rockfill under the influence of loading history such as historical stress rates, creep tests were conducted under oedometric loading. Alternative loading-creep steps, different stress increment sizes, and various precreep stress rates were considered. Independent of other factors, the development of the creep rate was governed by the recent precreep stress rate (the prior stress rate defined in this study). When the prior stress rate was higher than a threshold value, the relationship between the creep rate and time was double logarithmic linear; thus the creep strain-time relationship tended to converge on a power law (referred to as the creep baseline herein). However, when the prior stress rate was lower than the threshold value, the initial creep rate was lower than that of the creep baseline and did not decrease until several minutes after the start of the creep. The development of the creep rate with time in the initial stage can be generalized as a straight horizontal line, suggesting that the rate remains almost unchanged for a certain time, until the straight horizontal line approached the creep baseline. The inheritance and hysteresis of different strain rates in the initial stage of subsequent creep resulted in differences in the creep magnitude and time development process of the creep rate. The above findings are constructive for predicting the deformation of deep layers of rockfill, such as embankments, with more accuracy, especially for that with some large-sized rigid-structure buildings on its surface.

Rockfill, a coarse granular material commonly used in dam construction, exhibits complex mechanical behavior under generalized stress conditions. This paper investigates the mechanical properties of rockfill through a series of stress-path tests conducted on a self-developed, large-scale true triaxial apparatus with cubical specimens of 60 x 30 x 30cm. Three test series are carried out by varying the mean effective stress, the deviator stress and the Lode's angle, respectively. An elastoplastic constitutive model is presented to describe the behavior of rockfill. An improved dilatancy equation is introduced by considering the phase transformation stress ratio instead of the critical stress ratio.

The variability in particle morphology significantly impacts the mechanical properties of rockfill materials. To enhance the understanding of this influence, this study collected basalt rockfill particles from 6 different site sources, with their morphology captured by 3D scanning technology, and then the morphological characteristics categorized through cluster analysis. True triaxial tests for these 6 particle groups were simulated using discrete element method (DEM), and the effects of elongation, flatness, convexity, and intermediate principal stress coefficient on the stress-strain relationship and peak strength were qualitatively assessed through principal component analysis (PCA). Further, by controlling the elongation, flatness, and convexity, 3D reconstructed particle models were created by spherical harmonics (SH) analysis, and the true triaxial tests on these models were simulated to quantitatively clarify the influence of morphological parameters on the macroscopic stress- strain relationship, peak strength, microscopic contact, anisotropic evolution, and other characteristics. Considering the size effect in rockfill materials, multi-scale models incorporating particle morphology were further evaluated across four sample scales. The results indicate that, on the macro scale, the three morphological parameters and the middle principal stress coefficient each have substantial effects on peak strength independently, while the interaction among these parameters does not have a notable influence on the strength. With increasing convexity, the peak strength of samples gradually decreases, while an increase in elongation and flatness leads to a trend of initially increasing and then decreasing strength. On the micro scale, the increase in both elongation and flatness results in a more uniform fabric in the main and lateral directions, while the coordination number shows a trend of initially increasing and then decreasing before stabilizing gradually. The influence of elongation on the main direction fabric is slightly smaller than that of flatness, while convexity has minimal effect on these microscopic features. Additionally, the morphological parameters not only impact the deformation capacity of samples but also demonstrate heightened sensitivity to the strength-size relationship of the sample due to interlocking and boundary constraints between particles. This underscores the pivotal role of morphological parameters in governing the mechanical motion of particles during the sample size scaling process, consequently influencing the strength of the material.

Due to the time-dependent effect of rockfill dams, the conventional time-invariant finite element method (FEM) can hardly meet practical engineering requirements. This paper proposes an updating Bayesian FEM method for accurate long-term deformation analysis. A combined FEM model is introduced accounting for both instantaneous and creep behaviors. The FEM model is then updated using a Bayesian algorithm, unscented Kalman filter (UKF). The UKF calibrates the prior FEM predictions by incorporating real-time measurement data, thus iteratively reducing discrepancies between model predictions and actual observations. To further enhance the algorithm accuracy, a power-law-based fading memory factor is proposed to mitigate measurement noise in standard UKF. For parameter identification, a slice approach of the high-dimensional covariance confidence ellipsoid is developed. The methodology is validated in Qingyuan rockfill dam, in Guangdong province, China. Results show that the updated FEM is more consistent with the actual monitoring data. The fading memory improves standard UKF performance with a lower relative root-mean-square error (RRMSE). Additionally, the slice method reveals that a specific three-parameter configuration behaves better than the others. The proposed approach can also be extended to other fields including slope and tunneling.

The long initial and coda waves with small amplitude are often observed in an actual earthquake record. Truncating those wavebands that contribute little to structural responses is helpful to focus on the strong shaking phase and reduce computational cost. In the paper, 157 actual earthquake records and the acceleration time windows constrained by truncation thresholds of Arias intensity serve as input ground motions. A large number of elastoplastic dynamic analyses on a 295 m-high core-wall rockfill dam (CRFD) are conducted using the generalized plasticity model and seismic wave input method. Inspired by fragility equation, the probability curves for the accuracy loss of dam response less than different limits under different truncation thresholds are established, quantifying the destructiveness of the truncated seismic acceleration time windows. Results show that the probabilities are minimally affected by peak ground acceleration (PGA); the allowable tail truncation of earthquake records is much more than the leading due to the asymmetry of seismic waveforms and the cyclic hardening characteristic of rockfill materials; the truncation metric of 0.01-98 % Arias intensity is proved to be effective and robust in accelerating dynamic analyses of rockfill dams with an accuracy loss within 5 % and an average reduction in computational workload of approximately 50 %.

There is substantial evidence that crushable soils (e.g., sands, gravels, rockfills, etc.) undergo particle crushing upon shearing or over creeping. To investigate the evolution of grading and particle crushing of coarse-grained materials, a series of consolidated and drained triaxial shearing and creep tests were conducted on rockfills using a large-scale triaxial apparatus. The test data from the sieve analysis test, both before and after the triaxial tests, were subjected to a comprehensive qualitative and quantitative analysis of the variation of grading or breakage index. Research findings indicate a decrease in the percentage of coarser particles in the particle components of rockfills, accompanied by an increase in the amount of particle crushing upon shearing or over creeping. Furthermore, a series of empirical expressions were proposed through nonlinear fitting of test data to characterize the relationship between the breakage index and two variables (i.e., the normalized plastic work and mean effective stress) under various confining pressures and stress levels upon shearing or over creeping. These findings can provide a scientific basis for the design, construction, and maintenance of rockfill dams or high rockfill embankments in the practical engineering application.

With the frequent occurrence of natural disasters, the problem of dam failure with low probability and high risk has gradually attracted people's attention. This paper uses flume model tests to systematically analyze the overtopping failure mechanisms of concrete face rockfill dam (CFRD) and identify its failure modes. The tests reveal that the longitudinal erosion of the CFRD breach progress through stages of soil erosion, panel failures, and water flow stabilization. Meanwhile, the cross- breach process involves the evolution of breach size in rockfill materials, including traceable erosion, lateral broadening, and breach morphology stabilization. The fracture characteristics of the water-blocking panel are primarily evident in the flow-time curve. By analyzing the breach morphology evolution processes in longitudinal and cross sections, the flowtime curve can be subdivided into stages of burst flow formation, breach expansion with flow increase, rapid increase of breach flow discharge due to panel failures, and stabilization of breach flow and size. The primary damage process of the CFRD occurs in a cyclical stage of breach expansion, flow increase, panel failure, and rapid discharge. The rigid face plate and granular body structure contribute to partial dam failure, showing a tendency for gradual expansion of the breach. The longitudinal illustrates dam failure resulting from panel fracture and rockfill erosion interaction, while downstream slopes exhibit failure due to lateral intrusion of rockfill and cyclic instability. These research results can serve as a reference for constructing a concrete CFRD failure prediction model and conducting disaster risk assessments.

Deformation predictions in high Concrete Face Rockfill Dams tend to underestimate observed settlements due to scale effect and breakage phenomena that cannot be adequately captured by laboratory tests. This paper presents a Visco-Elasto-Perfectly Plastic (VEPP) model for predicting deformations in high Concrete Face Rockfill Dams (CFRDs) that addresses these challenges incorporating explicitly key rockfill parameters like grain size and post-compaction porosity, which influence both the non-linear elastic and plastic behaviors of rockfill. The VEPP model enables deformation prediction while using standard laboratory test results. The model's effectiveness was demonstrated through its application to the 233 m high Shuibuya Dam, the tallest CFRD in the world. The VEPP model predictions closely align with observed deformations throughout the dam's construction, impoundment, and early operational stages. By using physically meaningful parameters, the model reduces the uncertainty associated with the empirical assessment of model parameters using back-analysis from similar projects. While the VEPP model offers improved predictive accuracy, particularly during early design phases, further advancements could be achieved by refining the creep formulation and accounting for grain size evolution during construction. This approach has the potential to optimize the design and construction of future high CFRD.

During the operational phase of pumped storage hydropower stations, rockfill materials within the dam experience cyclic loading and unloading due to water level fluctuations. This cyclic behavior can result in the accumulation of irreversible deformation, posing a substantial threat to dam safety. However, there is an absence of a constitutive model capable of accurately capturing the low-frequency multi-cycle hysteresis behavior of rockfill materials due to the constraints of conventional laboratory test methods. In this study, we employed the combined finite and discrete element method (FDEM) to investigate the mechanical characteristics of rockfill materials and develop an improved constitutive model capable of effectively capturing their hysteretic behavior. The results demonstrate the FDEM accurately reproduces the mechanical behavior of rockfill material under shear and cyclic loading and unloading conditions. The hysteresis loop exhibits a discernible densification trend with increasing cycles. And the variations in elastic modulus and strain primarily occur within the initial five cycles. The plastic strain increment exhibits a strong positive correlation with stress level, while its relationship with confining pressure is comparatively less pronounced. The proposed constitutive model successfully captures the complex low-frequency multi-cycle hysteresis characteristics of rockfill material with few parameters, showing substantial potential for practical applications.

During the construction of earth-rock dams in cold regions, the freezing-thawing of impervious soil causes significant changes in its physical and mechanical properties, which affects the quality and operation safety of the project. To enhance the impervious soil anti-freezing capacity, the hollow polycarbonate panel heating method (HPPHM) was innovatively proposed. Based on the mechanism and in-situ tests, the heating mechanism and effect of HPPHM on impervious soil were investigated. The test results indicated that HPPHM can primarily heat the soil through solar radiation, raising the soil temperature. Furthermore, the air layer inside the panel serves as thermal insulation, effectively preventing the soil internal heat from dissipating. The in-situ test results showed that soil freezing was not observed under HPPHM, and the soil surface temperature was approximately 6 degrees C higher compared to the control site. The heating influence depth of HPPHM on the impervious soil was approximately 175 cm. Additionally, the soil heat under HPPHM experienced a significant increase of 12537.1 kJ. This study provides a scientific method for improving construction efficiency and quality in cold regions.