Evaluation of methods for determining rock brittleness under compression
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Brittleness
Brittleness is one of the important properties of rock, which is of great significance in rock engineering. The evaluation of brittleness index is a useful way for the estimation of rock brittle. However, there is still much uncertainty about the relation between rock brittleness and rock failures such as hydraulic fracturing, rock bursts in coal mines and tunnels. This fact can be attributed to the lack of the universally accepted brittleness concept and brittleness index. In this paper, the relationship of the rock brittleness and mechanical properties such as the post-peak stress drop coefficient in the stress–strain curve as well as the influencing factors to brittle failure are reviewed. Furthermore, the existing estimation methods for rock brittleness index are summarised and their applicability is briefly discussed. Moreover, the representative applications of rock brittleness index on the hydraulic fracturing, rock burst predictions in coal mines and tunnels were reviewed. Finally, the primary problems in the estimating rock brittleness are pointed out, which are expected to provide some guidance for relevant applications in rock mechanics and engineering.
Brittleness
Rock burst
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Brittleness
Rock mass rating
Geological Strength Index
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The complete stress-strain curve of rock is divided into pre-failure and post-failure regions according to the peak stress.Because the post-failure mechanical characteristics of rock are corresponding to a good many rock engineering items,such as underground excavation,pillar,rock burst and so on,the research on the post-failure characteristics of rock is of important significance both in theory and practice.In general,the post-failure regions of rock shows instability in the mechanical response,which is difficult to be described by the strength soften model,but can be described by the brittle-plastic model.To keep the strain rate of axial as a constant,a series of triaxial conventional compress failure tests about marble of Ya'an,red sandstone of Guixi and granite of Dawu were performed by RMT-150B rock mechanics test system,and the complete stress-strain curves of rock specimens under different confining stresses were obtained.Utilizing the stress-strain curves,the relation function between brittle stress drop and confining stress of marble was obtained,and the beneficial reference was provided when applied brittle-plastic model to numerical analysis about marble and its structures as well.
Brittleness
Overburden pressure
Lateral strain
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Brittleness
Geomechanics
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In this paper, we introduce a new type of two-layer porous energy dissipation plate breakwater, consisting of one upper porous plate and a lower plate. The system is used to control energy dissipation in breakwaters. The structure performance of dissipating waves has been investigated in detail in the regular wave tests. The factors identified with the characteristics of the energy dissipation plate are discussed, such as the relative width (B/L), the relative hole-size (A/A0) and the wave steepness (H/L). The comparison and analysis of the energy dissipation coefficients with respect to different factors are presented. Model test results indicate that the two-layer porous energy dissipation system is effective in dissipating a significant amount of wave energy.
Breakwater
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Brittleness
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Two methods are proposed to derive seismic energy dissipation formulas for a new type of energy dissipation shear walls in this paper. Combined with time history analysis, the seismic energy dissipated is calculated for an energy dissipation shear wall structure model. Then, based on the dual damage criterion of foe first exceeding the maximum response and the plastic accumulative damage, the optimal analysis is done for the design parameter of the energy dissipation devices. At last, an calculating example is provided, which indicates that the stiffness and the strength of the energy dissipation devices must be moderate in other to get the optimal seismic control for this type of shear walls.
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Energy dissipation ratio of stepped spillways could not reflect the energy dissipation status in detail.In order to reflect the energy dissipation function of steps,the total energy dissipation is divided into two parts: energy dissipation of traditional spillways and energy dissipation purely created by steps.The unit height energy dissipation ratio of steps and the proportion of energy dissipation created by steps are calculated.Results demonstrate that the unit height energy dissipation ratio of step is about 0.80%/m-0.83%/m,uncorrelated with unit discharge and step amount,and has a slight increase of 4.5% with the increment of step height; the proportion of energy dissipation created by steps increases with unit discharge and decreases with the increase of step amount.The decrease in energy dissipation ratio with the increase of unit discharge is because that the energy dissipation of smooth spillway reduces while the energy dissipation of stepped spillway remains unchanged.
Spillway
Energy Flow
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Abstract We carried out uniaxial compression tests on brittle red sandstone with different heights. The test results show that the uniaxial compressive strength of rock sample increases first and then tends to be stable with the increase of the size, which is approximately stable between 75 and 81 MPa. Both elastic energy and dissipated energy increase with the increase of rock sample size. In order to further analyze the mechanism behind these phenomena, we combined advanced numerical simulation and theoretical analysis to explain these phenomena, and systematically analyzed the end face effect as one of the key factors affecting the uniaxial compression characteristics of brittle red sandstone for the first time. Small sized rock samples are very sensitive to end effect. The middle of the large sized rock samples is in a uniform compression state, and the effect of end effect is weakend. When there are rigid pads at both ends of the rock sample, there is an obvious elastic vertebral body during the loading process of the rock sample. The bearing capacity of rock samples with rigid pads is greater than that of rock samples without rigid pads, and the energy released during instantaneous failure of rock samples without rigid pads is greater than that of rock samples with rigid pads. The findings of this paper make a valuable contribution to establishing optimal study sample sizes and advancing the utilization of laboratory test mechanics parameters in engineering applications.
Brittleness
Sample (material)
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Brittleness is an important parameter controlling the mechanical behavior and failure characteristics of rocks under loading and unloading conditions, such as fracability, cutability, drillability and rockburst proneness. As such, it is of high practical value to correctly evaluate rock brittleness. However, the definition and measurement method of rock brittleness have been very diverse and not yet been standardized. In this paper, the definitions of rock brittleness are firstly reviewed, and several representative definitions of rock brittleness are identified and briefly discussed. The development and role of rock brittleness in different fields of rock engineering are also studied. Eighty brittleness indices publicly available in rock mechanics literature are compiled, and the measurement method, applicability and limitations of some indices are discussed. The results show that (1) the large number of brittleness indices and brittleness definitions is attributed to the different foci on the rock behavior when it breaks; (2) indices developed in one field usually are not directly applicable to other fields; and (3) the term "brittleness" is sometimes misused, and many empirically-obtained brittleness indices, which lack theoretical basis, fail to truly reflect rock brittleness. On the basis of this review, three measurement methods are identified, i.e. (1) elastic deformation before fracture, (2) shape of post-peak stress–strain curves, and (3) methods based on fracture mechanics theory, which have the potential to be further refined and unified to become the standard measurement methods of rock brittleness. It is highly beneficial for the rock mechanics community to develop a robust definition of rock brittleness. This study will undoubtedly provide a comprehensive timely reference for selecting an appropriate brittleness index for their applications, and will also pave the way for the development of a standard definition and measurement method of rock brittleness in the long term.
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