Alternative Approaches for the Determination of Unconfined Rock Deformation and Strength Properties

Abstract

The usage of numerical simulation tools in rock engineering has been the undisputed state of the art for decades. Not only for rock engineering applications in the field of underground and surface stability analysis, but also for the simulation of the rock-cutting process. With increasing computing capacity and as a consequence thereof, increased capabilities of available constitutive laws, the determination of reliable input parameters is critical. The detailed characterization and implementation of stress-strain relations, including the hardening and softening regime, is a major task. While efficient guidelines and established procedures exist for compressive loading, the current state of the art for tensile loading in the majority of the cases is inadequate. Samples often fail invalidly, either due to poor preparation or due to the impact of undesired bending and torsional loading. For that reason, an innovative purely mechanical test setup is proposed in this article, which eliminates the identified confounding effects. Furthermore, an alternative procedure for the investigation of rock dilatancy under unconfined conditions is presented. Although dilatancy is normally associated with multiaxial stress states and determined by triaxial compression tests, the behaviour of unconfined rock under far field compression represents an essential load case in rock cutting, but also in the surroundings of underground openings. The proposed procedure is based on torsion tests because of their capability to generate stress states of pure shear without exhibiting axial splitting and related negative effects. With the help of numerical simulations, a reasonable range for the dilatancy can be estimated and compared to common methods of determination via unconfined compression tests.

Study on the Nanopore Deformation Mechanisms in Shale Oil Reservoir: Insights from the Molecular Simulation

“…Shale oil is widely distributed in the world, and the statistics of resource potential evaluation results from 116 basins worldwide reveal that the total technically recoverable resources of shale oil are about 251.2 billion tons, with huge development potential. − The development process of such tight reservoir is subject to the coupling effect of multiple factors, resulting in the deformation of nanopores. − Shale oil reservoir nanoscale pore deformation is mainly under the coupling effect of stress motivation and adsorption motivation deformation. − The indoor experimental analysis, numerical simulation methods, and micromechanical analytical equation analysis are the stress motivation pore deformation research field. − The experimental analysis method is mainly based on the results of experiments. Moreover, the empirical mathematical model of porosity and permeability variation with pore pressure at the macroscopic scale is obtained by fitting the data. − However, such models still contain certain empirical parameters and have a relatively poor applicability for microscopic scales.…”

Numerical simulation of mechanical behavior of rock samples under uniaxial and triaxial compression testsy

“…One of the most well-known tools for determining the mechanical properties of intact rocks is experimental tes-ting [1]- [3]. These tests shed light on the rock failure mechanism under mechanical loading [4], [5]. Yet, the formation of microcracks, as well as their propagation and coalescence in rock samples, is not completely understood [6], [7].…”

Study on Two-phase Flow Mechanisms in Nanopore Considering Microcosmic Deformation and Dynamic Capillary Force

“…To be specific, the laboratory experimental method employed by Wijaya and Sheng [10], Crawford et al [6], and Kim et al [11] aims to build the empirical model of the variation of porosity with pore pressure macroscopically by fitting the experimental data, whereas such a type of model still covers certain empirical parameters and exhibits relatively poor applicability to the microscopic scale. e numerical simulation method adopted by Stoxreiter et al [12,13] largely complies with the use of finite element techniques to analyze the pore deformation characteristics during triaxial compression. However, the conventional numerical simulation methods applied in the above methods still have some limitations in the application scale and the pore variation is obtained based on the statistical results, which is difficult to accurately describe the deformation of an individual nanopore.…”