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A new loading-unloading experimental method for simulating the change of mining-induced stress.

ABSTRACT: Based on a self-developed triaxial seepage device, a new loading and unloading experimental method is proposed in this paper to eliminate sample variations. The results show that the strength of sandstone sample and the axial strain at failure increased with the increasing initial hydrostatic stress, but decreased with the increasing loading-unloading rate. Following the alternating loading-unloading test, the stress-strain curves of specimens advanced in wave form, the waves' volatility decreased and then increased. It is found that near the ultimate strength, volatility is the biggest, and the stability of waves' volatility increased along with the increasing initial hydrostatic stress. The similarity of stress-strain curves between the conventional loading-unloading tests and the alternating loading-unloading tests increased along with the increasing initial hydrostatic stress and the increasing initial velocity for the alternating loading-unloading method. Along with the increasing initial hydrostatic stress, the failure behaviour of the sandstone samples tested under loading-unloading methods changed from a tensile state to a tensile-shear coexisting state, and finally to a fully shear failure state. The degree of failure modes increased with the increasing loading-unloading rate.

SUBMITTER: Jiang C

PROVIDER: S-EPMC6599788 | biostudies-literature | 2019 Jun

REPOSITORIES: biostudies-literature

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A new loading-unloading experimental method for simulating the change of mining-induced stress.

Jiang Changbao C Liu Xiaodong X Li Minghui M Yu Huan H Duan Minke M

Royal Society open science 20190619 6

Based on a self-developed triaxial seepage device, a new loading and unloading experimental method is proposed in this paper to eliminate sample variations. The results show that the strength of sandstone sample and the axial strain at failure increased with the increasing initial hydrostatic stress, but decreased with the increasing loading-unloading rate. Following the alternating loading-unloading test, the stress-strain curves of specimens advanced in wave form, the waves' volatility decreas ...[more]

PMID: 31312477

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Project description:A multi-functional true triaxial fluid-structure coupling system was used to conduct water retention and seepage tests of shale under true triaxial loading and unloading stress paths. The stress-strain evolution of shale specimens under different experimental conditions was obtained, and the corresponding deformation and strength were analysed. The evolution and failure characteristics of cracks in shale were obtained by CT scanning images before and after the experiment. The results show that the volumetric strain of shale specimen increases first, then decreases and finally continues to increase with an increase in deviatoric stress under water retention, indicating that the volumetric change has experienced a compaction-expansion-compacting. The σ-ε 1 curve of the sample increases first and then decreases, while the deformation in the σ 2 direction shows the repeated compression and expansion. In the seepage test, the permeability-strain curve can be divided into two parts before and after fracture according to the σ-ε 1 curve. Before fracture, the compression velocity of the specimen in the loading direction exceeds the expansion velocity in the unloading direction, resulting in a decrease in volume and a decrease in permeability. With an increase in deviatoric stress, fractures occur inside the particles and continue to spread from the tip until the fractures break through the shale specimen. The pore fissure area increases and the permeability of the sample increases rapidly. In terms of fracture evolution, for the water retention test, dense tensile and shear cracks appear on the failure plane perpendicular to the σ 1 and σ 3 directions, and complex shear fracture network appears on the failure plane perpendicular to the σ 2 direction. For the seepage test, heavy shear failure occurs throughout the original fracture of the sample. With an increase in the penetration depth, the fracture shape on the failure surface perpendicular to the σ 2 direction gradually changes from single to complex.

Dataset Information

A new loading-unloading experimental method for simulating the change of mining-induced stress.

Publications

A new loading-unloading experimental method for simulating the change of mining-induced stress.

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