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It is necessary to study the propagation path of cracks in concrete materials and its influence on the loading capacity of specimens. The phase-field method for fracture offers a distinct benefit in simulating the crack propagation behavior of brittle materials, which is achieved by implementing a phase field that continuously fluctuates to approximate the crack configuration, abolishing the need for mesh reconstruction and tracking the cracks. In this paper, we have implemented a phase field model using ABAQUS, whose reliability is verified through a tensile test. Then, the splitting test of Brazilian disc is simulated and the results are similar to those of the laboratory experiment. Furthermore, the crack configuration of the prefabricated cracked discs with different tilt angles and different initial lengths is explored. The two important parameters of the phase field method, Gc and l0, are discussed in the Discussion section. A larger Gc value means a larger material toughness and a larger failure load, and a larger l0 value means a larger crack smear range as well as a smaller failure load. [ABSTRACT FROM AUTHOR]

To figure out the influence of soft-hard layer thickness ratio on specimens' mechanical properties evolution and microcracking mechanism, combined with digital image correlation technology and acoustic emission facility, uniaxial compression tests were conducted on soft-hard interbedded rock-like materials considering seven bedding dip angles and two soft-hard layer thickness ratios. The results are as follows: 1) The failure mode and failure pattern of layered rock masses are mainly determined by the bedding dip angle α and are less related to the soft-hard thickness ratio. With the increase of dip angle, the failure strength curve of the specimen is approximately U-shaped, and the soft-hard layer thickness ratio affects the U-shaped. The decrease in soft-hard layer thickness ratio will reduce the uniaxial compressive strength of specimens with low dip angles (α≦30°), cause differences in the evolution path of local strain fields of layered rock masses and reduce the horizontal displacement of the main crack. 2) The increase of the proportion of soft layer in the soft-hard layer thickness ratio will reduce the proportion of tensile cracks in the tensile failure specimens and shear cracks in the shear failure specimens, complicating the process of cracks of the layer rock mass. 3) Increasing the proportion of soft layers in the soft-hard layers thickness ratio promotes the generation of secondary cracks in layered rock masses and further reduces the integrity of specimens. Finally, through the findings in this paper, it can provide a reference for analyzing the crack propagation behavior of layered rock. [ABSTRACT FROM AUTHOR]

To investigate the effects of joint number on dynamic compressive strength, crushing effect, stress wave propagation, stress wave conversion, and energy evolution of rock masses, SHPB and LS-DYNA were used to conduct impact experiments and numerical simulations, respectively. The results demonstrate that the dynamic strength of a multi-jointed (two- and three-jointed) rock are 11.1 and 25.1% lower, respectively, compared with that of a single-jointed rock. The weak surface near the joint causes the rock mass to crack first. The rock cracking time advances significantly as the joints number increases. The reflection coefficient falls as the number of joints increases, because the wave impedance of the joint differs from that of the rock. The transmission coefficient, however, is exactly the reverse. When the P wave strikes the specimen, the vibration direction of the particles is deflected at the joint, resulting in a shear wave. P waves are reflected and superimposed between joints, increasing the strength of shear waves and resulting in more transverse cracks in multi-jointed rock masses under dynamic loading. Meanwhile, the total energy consumed by a bedrock under dynamic loading is obviously larger than that of joints. However, the total energy absorbed by joints exceeds that of the bedrock when the joints number increases. The results further enrich the dynamic basis of jointed rock masses. [ABSTRACT FROM AUTHOR]

Quantitative characterization of the surface roughness plays a vital role in the field of rock mechanics. The objectives of this study were to propose a new index that can describe the various morphological characteristics with different scale fluctuation. The power spectral density (PSD) parameters and conventional statistical parameters were used to analyze the roughness of meso-scale grind surfaces, intermediate-scale synthesis surfaces, and macro-scale shear surfaces. The results showed that the PSD parameters (slope k, intercept b, spectral moment λ0, and spectral shape parameters ω1 and ω2) and conventional statistical parameters (RMS and Z2) have evident uniqueness and uniformity in characterizing the roughness with different scale fluctuation. It is necessary to appropriately use the correct parameters for classifying and quantifying the roughness. For this purpose, a new characterization index SLA was proposed based on the spectral shape parameter ω1, spectral moment λ0, slope k, and angle fractal index C. [ABSTRACT FROM AUTHOR]

This paper investigates the seismic properties of a cross transfer subway station under a horizontal earthquake wave in soft soil stratum. A 3-D simulation analysis model is established considering the dimensions and soil layers of a real structure. The HS-small model is employed to simulate the non-linear stiffness of soft soil. The dynamic responses of a single station case and a cross transfer station case are explored, followed by the direction of the input earthquake wave, the type of soil reinforcement in the overlapping area, had on the dynamic response were also analyzed. The simulation results show that the subway station has better seismic response than the single station, and soil reinforcement can increase the dynamic response of the different components in the overlapping area. As soil reinforcement stiffness increases, the dynamic response increases in both the upper and bottom stations at varying degrees. The findings from this paper provide a reference to the seismic design of cross transfer stations in similar ground. [ABSTRACT FROM AUTHOR]