Explicit reinforcement models for fully-grouted rebar rock bolts

This paper investigates the explicit use of rock reinforcement in a discontinuous stress analysis model.A series of numerical experiments was undertaken to evaluate the performance of local and global reinforcement models implemented in universal distinct element code(UDEC).This was made possible by calibrating the reinforcement models to the laboratory behavior of a fully-grouted rebar bolt tested under pure pull and pure shear loading conditions.The model calibration focuses on matching different loading stages of the force-displacement curve including the initial elastic response,the hardening behavior and the bolt rupture.The paper concludes with a discussion on the suitability of the different reinforcement models in UDEC including their advantages and limitations.Finally,it addresses the choice of input parameters required for a realistic simulation of fully-grouted rebar bolts.

Responses of jointed rock masses subjected to impact loading

Impact-induced damage to jointed rock masses has important consequences in various mining and civil engineering applications. This paper reports a numerical investigation to address the responses of jointed rock masses subjected to impact loading. It also focuses on the static and dynamic properties of an intact rock derived from a series of laboratory tests on meta-sandstone samples from a quarry in Nova Scotia, Canada. A distinct element code(PFC2D) was used to generate a bonded particle model(BPM) to simulate both the static and dynamic properties of the intact rock. The calibrated BPM was then used to construct large-scale jointed rock mass samples by incorporating discrete joint networks of multiple joint intensities into the intact rock matrix represented by the BPM. Finally, the impact-induced damage inflicted by a rigid projectile particle on the jointed rock mass samples was determined through the use of the numerical model. The simulation results show that joints play an important role in the impactinduced rock mass damage where higher joint intensity results in more damage to the rock mass. This is mainly attributed to variations of stress wave propagation in jointed rock masses as compared to intact rock devoid of joints.

Calculating changes in fractal dimension of surface cracks to quantify how the dynamic loading rate affects rock failure in deep mining

The split-Hopkinson pressure bar(SHPB)and digital image correlation(DIC)techniques are combined to analyze the dynamic compressive failure process of coal samples,and the box fractal dimension is used to quantitatively analyze the dynamic changes in the coal sample cracks under impact load conditions with different loading rates.The experimental results show that the fractal dimension can quantitatively describe the evolution process of coal fractures under dynamic load.During the dynamic compression process,the evolution of the coal sample cracks presents distinct stages.In the crack propagation stage,the fractal dimension increases rapidly with the progress of loading,and in the crack widening stage,the fractal dimension increases slowly with the progress of loading.The initiation of the crack propagation phase of the coal samples gradually occurs more quickly with increasing loading rate;the initial cracks appear earlier.At the same loading time point,when the loading rate is greater,the fractal dimension of the cracks observed in the coal sample is greater.

Degradation of a discrete infilled joint shear strength subjected to repeated blast-induced vibrations

This paper presents the results of a series of numerical modeling experiments aimed at quantifying blast- induced degradation of shear strength of discontinuities. Near-field vibration history of a single-row pro- duction blast in a. limestone quarry was used as input to the nu .merical model. For this. purpose, two rock blocks, representing a stiff massive sulfide rock and a weaker limestone rock, were simulated using the 2D Particle Flow Code （PFC2D）. Rock mass conta!ning a single inclined joint was modeled as Mohr- Coulomb. The results show that the crack generation rate is increased in both samples after repetitive vibration loading. Joint shear strength degradation rate in !he stiffer massive sulfide rock sample is higher than the softer limestone rock, which is attributed to the higher seismic impedance mismatch. The results show that even low-amplitude blasting vibrations （〈80 mm/s）, when repeated as in multi-hole blasts, can significantly degrade joint shear strength in the nearby pit walls.

火山地震活动的实验室模拟

火山体内产生地震活动的物理过程非常复杂,目前仍然没有被完全理解。我们在实验室内用来自埃特纳火山(意大利)的玄武岩做了变形和破碎实验并报道了实验结果。该实验用一组围绕样品的传感器监测,以完成全波形记录及微震事件定位和分析。充满液体的孔隙和损伤区快速破裂后减压激发了许多低频事件,类似于长周期火山地震活动。低频事件与孔隙流体的减压有关,位于破裂样本的损伤区;这些事件都具有一个弱剪切滑动分量(双力偶),与发生在活火山下的流体驱动事件相一致。