A Pre-peak Elastoplastic Damage Model of Gosford Sandstone Based on Acoustic Emission and Ultrasonic Wave Measurement

Abstract

The determination of internal material damage is always an arduous challenge. Non-destructive monitoring methods show great potential in quantitatively determining the internal material properties, whereas most of the studies relying on external observations remain in a qualitative stage. They either violate the basic thermodynamic assumptions or are difficult to guide engineering practice. In this paper, following the theory of continuum mechanics, an elastoplastic damage model based on non-destructive monitoring methods (i.e., acoustic emission and ultrasonic wave velocity measurement) has been developed. To capture the continuous and precise damage evolution inside rock mass, P wave velocity obtained by ultrasonic wave measurement was utilised and then considered as an input for the proposed elastoplastic damage model. Triaxial loading test results on six Gosford sandstone samples were analysed first to characterise critical stresses along the stress–strain loading curves, such as crack closure stress, stable crack propagation stress and unstable crack propagation stress. The drop of ultrasonic wave velocity can be seen as an indicator to represent the damage evolution inside rock material. Damage initiation is also closely related to the confining stress and dilation induced volumetric expansion. The test results also suggested that the Drucker–Prager criterion is sufficient to describe the plastic yielding surface and the following material hardening. A non-associated plastic flow assumption was adopted, considering the essence of microcrack shearing in rock failure and the effect of hydrostatic pressure on plastic deformation. A modified Drucker–Prager plastic potential was also introduced to track the orientation of plastic increment with material hardening. A scalar damage variable was derived from ultrasonic wave measurement results to indirectly represent the deterioration of rock properties (modulus). The proposed model was used to match lab test results with high consistency, and the main features of rock behaviour in triaxial loading tests were successfully captured by the model. Finally, the damage evolution of rock samples was analysed, which indicates that damage is dependent on its conjugate force, namely damage energy release rate Y. This study proves that P wave velocity can be an effective approach to measure and forecast the internal damage evolution inside rock mass, which has broad prospects for engineering applications.

Evolution of Crack Source Mechanisms in Laboratory Hydraulic Fracturing on Harcourt Granite

“…It typically faces numerous challenges, such as the elevated expenses associated with equipment set-up and test coordination, inadequately designed sensor networks, suboptimal signal acquisition, unexpected interference from human or natural activities, and limitations in data processing and interpretation (Grigoli et al 2017;Wang et al 2021). Alternatively, lab experiments also play a critical role in testing natural rocks and examining the associated seismic effect both in isotropic and layered specimens (Lockner 1993;Goodfellow et al 2013;Li et al 2022Li et al , 2023. It can facilitate a better understanding of the initiation and propagation of hydraulic fractures and provide design improvements to field operations.…”

A Meso/Macroscale Theoretical Model for Investigating the Large Deformation of Soft Rock Tunnels Considering Creep and Anisotropic Effects

“…The ultimate large deformation of soft rock is a creep-damage coupled problem (Li and Tang 2015;Wang and Cai 2020;Xia et al 2021a, b). Inspired by the fundamental understanding of rock creep and damage mechanics, previous studies have mainly focused on the macroscale level using creep-damage constitutive models to reveal the rheological process of soft rock tunnels (Ping et al 2016;Liu et al 2017;Huang et al 2020a, b;Li et al 2022aLi et al , b, 2023. In addition, the different stages of long-term deformation of soft rocks were also studied from clay mineral slippage and disintegration (Fahimifar et al 2010;Jiang et al 2016;Liu et al 2020a, b;Kovacevic et al 2021;Maheshwari 2021;Cui et al 2022).…”