Experimental and Numerical Investigation on the Dynamic Failure Envelope and Cracking Mechanism of Precompressed Rock under Compression-Shear Loads

Yuan Xu,Antonio Pellegrino,Hongbo Du,Feng Dai

doi:10.1061/(asce)gm.1943-5622.0002196

Yuan Xu, Antonio Pellegrino + Show 2 more

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https://doi.org/10.1061/(asce)gm.1943-5622.0002196

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Abstract

The complex response of underground geomaterials subjected to dynamic disturbance arises from the microstructure redistribution under high in- situ stress and the resulting fracture behaviors at multiaxial stress states. Inclined specimens were employed in an axially constrained split Hopkinson pressure bar (SHPB) system to achieve a combination of compression-shear stress states and static-dynamic loads. The loading rate under investigation ranged from 500 to 4,000 GPa/s, along with the axial prestress of 7, 21, 35, 49, and 63 MPa on specimens with an inclination of 0°, 3°, 5°, and 7°. The modified SHPB experimentation and discrete-element method modeling were implemented to unravel the combined effects of the loading rate, preload, and stress path on the failure mechanism of sandstone specimens involving the failure strength and envelope, fracturing pattern, fragmentation, and microcracking process. The positive rate dependence of the failure strength and Drucker–Prager envelope was observed. The preload showed double effects on the failure strength, indicated by an upper bound of the failure envelope as it expanded with the increasing preload. The microdamage accumulated during preloading and the global stress field collectively influenced the failure pattern of the inclined specimen, altering from a shear fracturing mode under dynamic loading or high-preload static-dynamic loading to an axial splitting mode near the specimen surface under low-preload static-dynamic loading.

Highlights

With the development of deep underground engineering involving resource exploitation, transportation, and safety defense, an increasing number of phenomena that are barely observed in shallow rock engineering have been largely reported (Ranjith et al 2017; Khosravi and Simon 2018; Jiang et al.2021)
The preload showed double effects on the failure strength, indicated by an upper bound of the failure envelope as it expanded with the increasing preload
This study examines three more inclinations so as to generalize the data reduction method for inclined specimens to accommodate a wide range of inclinations and to assess the stress path dependence of the failure strength and fracturing process under combined static-dynamic loading

Summary

Introduction

With the development of deep underground engineering involving resource exploitation, transportation, and safety defense, an increasing number of phenomena (e.g., rockbursts) that are barely observed in shallow rock engineering have been largely reported (Ranjith et al 2017; Khosravi and Simon 2018; Jiang et al.2021). A variety of experimental approaches based on SHPB techniques have been developed to address the multiaxial static-dynamic loading events, but they mainly focus on the confining techniques by means of hydraulic pressure chamber (Li et al 2008; Frew et al.2010; Hokka et al 2016; Gong et al 2019; Du et al 2020), metallic ring (Chen and Ravichandran 1997; Forquin et al 2008), or screwdriven platens (Paliwal et al 2008; Farbaniec et al 2017) Such studies simplified the dynamic load to coincide with one principal stress of the static confinement and failed to reflect the realistic complexity of the stress state of rock mass at depth. The interior microcracking process of the specimen under complex loading conditions is captured and contributes to revealing the intrinsic microdamage mechanism

Experimental Methodology

Experimental Results

Findings

Conclusions