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Dynamic mechanical properties and wave propagation of composite rock-mortar specimens based on SHPB tests

International Journal of Mining Science and Technology 2022年第4期32卷 793-806页

作者： Zhenyu Han Diyuan Li Xibing Li School of Resources and Safety Engineering Central South UniversityChangsha 410083China School of Civil Engineering Southeast UniversityNanjing 210096China Department of Civil Engineering Monash UniversityMelbourneVictoria 3800Australia

Filled inclusions in rock discontinuities play a key role in the mechanical characteristics of the rock and thereby influence the stability of rock engineering. In this study, a series of impact tests were performed using a split Hopkinson pressure bar system with high-speed photography to investigate the effect of interlayer strength on the wave propagation and fracturing process in composite rock-mortar specimens.The results indicate that the transmission coefficient, nominal dynamic strength, interlayer closure, and specific normal stiffness generally increase linearly with increasing interlayer stiffness. The cement mortar layer can serve as a buffer during the deformation of composite specimens. The digital images show that tensile cracks are typically initiated at the rock-mortar interface, propagate along the loading direction, and eventually result in a tensile failure regardless of the interlayer properties. However, when a relatively weaker layer is sandwiched between the rock matrix, an increasing amount of cement mortar is violently ejected and slight slabbing occurs near the rock-mortar interface.

关键词： rock dynamics Wave propagation rock-mortar Stiffness Energy Fracturing

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Application of machine learning in predicting the rate-dependent compressive strength of rocks

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Journal of rock Mechanics and Geotechnical Engineering 2022年第5期14卷 1356-1365页

作者： Mingdong Wei Wenzhao Meng Feng Dai Wei Wu School of Civil and Environmental Engineering Nanyang Technological UniversitySingapore State Key Laboratory of Hydraulics and Mountain River Engineering College of Water Resource and HydropowerSichuan UniversityChengdu610065China

Accurate prediction of compressive strength of rocks relies on the rate-dependent behaviors of rocks, and correlation among the geometrical, physical, and mechanical properties of rocks. However, these properties may not be easy to control in laboratory experiments, particularly in dynamic compression experiments. By training three machine learning models based on the support vector machine(SVM), backpropagation neural network(BPNN), and random forest(RF) algorithms, we isolated different input parameters, such as static compressive strength, P-wave velocity, specimen dimension, grain size, bulk density, and strain rate, to identify their importance in the strength prediction. Our results demonstrated that the RF algorithm shows a better performance than the other two algorithms. The strain rate is a key input parameter influencing the performance of these models, while the others(e.g. static compressive strength and P-wave velocity) are less important as their roles can be compensated by alternative parameters. The results also revealed that the effect of specimen dimension on the rock strength can be overshadowed at high strain rates, while the effect on the dynamic increase factor(i.e. the ratio of dynamic to static compressive strength) becomes significant. The dynamic increase factors for different specimen dimensions bifurcate when the strain rate reaches a relatively high value, a clue to improve our understanding of the transitional behaviors of rocks from low to high strain rates.

关键词： Machine learning rock dynamics Compressive strength Strain rate

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Dynamic strength of rocks and physical nature of rock strength

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Journal of rock Mechanics and Geotechnical Engineering 2009年第1期1卷 1-10页

作者： Qihu Qian Chengzhi Qi Mingyang Wang Engineering Institute of Engtneerlng Crops PLA University of Science and Technology Nanjing 210007 China School of Civil and Communication Engineering Beijing Institute of Civil Engineering andArchitecture Beijing 100044 China

Time-dependence of rock deformation and fracturing is often ignored.However,the consideration of the time-dependence is essential to the study of the deformation and fracturing processes of materials,especially for those subject to strong dynamic loadings.In this paper,we investigate the deformation and fracturing of rocks,its physical origin at the microscopic scale,as well as the mechanisms of the time-dependence of rock strength.Using the thermo-activated and macro-viscous mechanisms,we explained the sensitivity of rock strength to strain rate.These mechanisms dominate the rock strength in different ranges of strain rates.It is also shown that a strain-rate dependent Mohr-Coulomb-type constitutive relationship can be used to describe the influence of strain rate on dynamic rock fragmentation.A relationship between the particle sizes of fractured rocks and the strain rate is also proposed.Several time-dependent fracture criteria are discussed,and their intrinsic relations are discussed.Finally,the application of dynamic strength theories is discussed.

关键词： rock dynamics deformation and fracturing time-dependence dynamic strength criteria of fracturing

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