Applicability of UH model to coarse-grained soil

Large-scale triaxial, K0 compression and constant stress ratio path tests were carried out on two kinds of coarse-grained soils. Stress-strain relationships of these tests were simulated by using UH model for sands to study the applicability of the model to different stress paths of coarse-grained soil, and the results were compared with those of Duncan’s E-B model. It is shown that the mechanical behaviors of coarse-grained soil can be well described by the UH model, and overall its capacity to reflect stress-strain relationship under different stress paths is better than that of Duncan’s E-B model. Finally, the UH model and Duncan’s E-B model were used for stress-deformation analysis of a core rockfill dam. The applicability of UH model for sands to coarse-grained soil was verified

Stabilizing role of coarse grains in cohesionless overfilled binary mixtures: A DEM investigation

International audienceCohesionless binary mixtures are commonly encountered in nature and frequently used as filling materials in geotechnical engineering. It is known that coarse grains have a reinforcement effect on overfilled binary mixtures in which coarse grains are embedded in the matrix of fine-grains. However, the micromechanical origin of this reinforcement effect remains unknown. Using 2D discrete element method (DEM) simulations, this study aims at highlighting the impact of coarse grains on the geometrical fabric and mechanical state of cohesionless overfilled binary mixtures. We show that coarse grains contribute to the stability of cohesionless overfilled binary mixtures by limiting macroscopic plastic deformation. Coarse grains play the role of attractors of force chains, as they promote more connected contact force networks in overfilled binary mixtures. The results of micromechanical analyses further show that embedded coarse grains in overfilled binary mixtures have a long-range influence in the surrounding fine-grain matrix in the form of a "fine bridge," which enables better stress transmission and improves the bearing capacity of the mixture

Experimental Studies of Scale Effect on the Shear Strength of Coarse-Grained Soil

Shear strength is an essential index for the evaluation of soil stability. Test results of the shear strength of scaled coarse-grained soil (CGS for short) are usually not able to accurately reflect the actual properties and behaviors of in situ CGS due to the scale effect. Therefore, this study focuses on the influence of the scale effect on the shear strength of scaled CGS, which has an important theoretical significance and application for the strength estimation of CGS in high earth-rock dam engineering. According to previous studies, the main cause of the scale effect for scaled CGS is the variation of the gradation structure as well as the maximum particle size (dmax), in which the gradation structure as a characteristic parameter can be expressed by the gradation area (S). A total of 24 groups of test soil samples with different gradations were designed by changing the maximum particle size dmax and gradation area S. Direct shear tests were conducted in this study to quantitatively explore the effect of the gradation structure and the maximum particle size on the shear strength of CGS. Test results suggest that the shear strength indexes (i.e., the cohesion and internal friction angle) of CGS present an increasing trend with the improvement of the maximum particle size dmax, and thus a logarithmic function relationship among c, φ, and dmax is presented. Both cohesion (c) and internal friction angle (φ) are negatively related to the gradation area (S) in most cases. As a result, an empirical relationship between c, φ, and S is established based on the test results. Furthermore, a new prediction model of shear strength of CGS considering the scale effect is proposed, and the accuracy of this model is verified through the test results provided by relevant literature. Finally, the applicability of this model to different types of CGS is discussed

Numerical Simulation of Hydraulic Fracturing in Earth and Rockfill Dam Using Extended Finite Element Method

Hydraulic fracturing is one of the most important factors affecting the safety of earth and rockfill dam. In this paper, the extended finite element method (XFEM) is used to simulate the hydraulic fracturing behavior in an actual high earth and rockfill dam. The possibility of hydraulic fracturing occurrence is analyzed, and the critical crack length is obtained when hydraulic fracturing occurs. Then, the crack propagation path and length is obtained by inserting initial crack of different lengths at different elevation. The results indicate that hydraulic fracturing will not occur without the permeable weak surface (initial crack). The critical initial crack length required for hydraulic fracturing is 5.3 m of the calculation model in this paper. The propagation length decreases with the increase of elevation, and the average propagation length decreases from 9.4 m to 3.4 m. Furthermore, it is proved that the direction of crack propagation has a certain angle with the horizontal plane toward the downstream. Considering the up-narrow and down-wide type of the core wall, the possibility of hydraulic fracturing to penetrate the core is extremely high when the upper part of the core wall reaches the critical crack length

A Numerical Study on the Influence of Coordination Number on the Crushing of Rockfill Materials

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Experimental and numerical study of size effects on the crushing strength of rockfill particles

International audienceTo better understand the microstructure parameters controlling grain crushing and how the microstructure evolution influences the crushing characteristics of rockfill particles, the emphasis of the present study focuses on the size effects on the crushing strength of rockfill particles, with special attention to internal flaws. Single-particle crushing tests are performed on rockfill particles with four different size fractions. By combining these results with the experimental results from the literature, the suitability of the Weibull model to describe the size effects on the breakage strength of rock grains is discussed. To understand why larger grains possess lower strength, a bonded particle model (BPM) is established in YADE to simulate the particle crushing tests. Model parameters are calibrated against the obtained force–displacement curve. The failure and deformation behaviors of studied rockfill particles are satisfactorily reproduced by the numerical simulation. The size effects are then studied using the agglomerates with different flaw characteristics (e.g., sizes, numbers, volume ratios, distributions, and locations). Numerical results exhibit that for the studied rockfill particles, when the ratio of flaw size to agglomerate size is less than 0.186, the flaw volume ratio is the key factor for size effects, and the breakage strength of particles is slightly related to the flaw size. In contrast, the breakage strength of particles depends not only on the flaw volume ratio but also on the flaw distribution/location when the flaw size is large. Microscopic analysis and DEM modeling can improve the understanding of crushing and deformation behaviors of rockfill particles