Experimental Study on Mechanical Properties of Structured Clay under Different Unloading Rates and Unloading Stress Paths

Li, Lu; Zang, Meng; Zhang, Rongtang; Lu, Haijun

doi:10.3390/buildings13061544

Cited by 3 publications

(1 citation statement)

References 19 publications

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“…During the unloading process, the rock was dominated by lateral expansion deformation and brittle failure, resulting in the strong expansion becoming the root cause of the sudden and severe deformation and failure [12,13]. A low unloading rate is beneficial to the degree of rock fragmentation, while a high unloading rate contributes to the brittleness of the rock mass and damage [14][15][16]. Guo, Ji, and Cao [17] also indicated that a high unloading rate may increase the rock burst possibility.…”

Section: Introductionmentioning

confidence: 99%

An Investigation on the Impact of Unloading Rate on Coal Mechanical Properties and Energy Evolution Law

Guo

Sun

et al. 2022

IJERPH

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In order to further explore the relationship between the excavation speed and the damage of surrounding rocks and dynamic manifestation, the stress paths of unloading confining pressure and loading axial pressure were designed based on the changes in the roadway surrounding rock stress in this study. Additionally, the mechanical properties and energy evolution law of the coal body were investigated under various unloading rates. As the unloading rate increased, the mechanical properties of the coal body including the failure strength, the confining pressure, the axial strain, and horizontal strain tended to decrease at the rupture stage, while the volume strain and the elastic modulus increased, indicating that the rupture form evolved from the ductile failure to brittle failure. Regarding the energy, the axial pressure did positive work while the confining pressure did negative work, with the total work and the stored elastic strain energy decreasing. In addition, with the increase of the dissipation energy, the elastic strain energy conversion rate decreased linearly, indicating that the high unloading rate increased the possibility of dynamic disasters induced by the instantaneous brittle rupture of the coal body. On the other hand, due to the low releasable elastic strain energy stored in the coal body, the strength and probability of subsequent dynamic manifestation of coal body destruction were reduced. Therefore, increasing the excavation speed in a controllable way can benefit the safety of mining.

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Section: Introductionmentioning

confidence: 99%

An Investigation on the Impact of Unloading Rate on Coal Mechanical Properties and Energy Evolution Law

Guo

Sun

et al. 2022

IJERPH

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Mechanical and permeability characteristics of Q2 soft-plastic loess under coupled hydro-mechanical conditions

Hong,

Lai,

Liu

2024

Environ Earth Sci

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For the soft-plastic loess tunnel engineering, collapse and damage of the surrounding rock during excavation are often driven by the combined action of the seepage water and the unloading effect. Under water pressure and unloading, the soil suffers complex stress-seepage coupling action causing the inevitable change of permeability and mechanical properties. In this paper, seepage control devices were added to the GDS test device, and a new triaxial permeability measurement system was developed. Triaxial unloading-seepage tests were conducted on soft-plastic loess under the effect of hydraulic coupling. The variation of permeability characteristics of Q 2 soft-plastic loess under lateral unloading and the soil mechanical characteristics under different seepage pressure were analyzed. Meanwhile, microstructure characteristics of soft-plastic loess during the triaxial test were obtained by scanning electron microscope to clarify the deformation and seepage mechanism. The results show that the strength of soft-plastic loess decreases signi cantly with the increase of osmotic pressure. Under the condition of 50 kPa and 100 kPa osmotic pressure, the cohesive force of soft-plastic loess decreases by 15.5% and 39.0% and the friction angle decreases by 9.4% and 22.6%, respectively. The permeability coe cient of loess increases slowly at rst and then increases rapidly during the unloading process. The main reason for the signi cant increase of permeability coe cient is the penetration of soil ssures and the formation of shear bands after entering the plastic deformation stage.

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Mechanical Response Characteristics and Tangent Modulus Calculation Model of Expansive-Clay Unloading Stress Path

Peng,

Li,

Cheng

et al. 2024

Buildings

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As a special type of clay, expansive clay is widely distributed in China. Its characteristics of swelling and softening when meeting water and shrinking and cracking when losing water bring many hidden dangers to engineering construction. Expansive clay is known as “engineering cancer”, and in-depth research on the unloading mechanical response characteristics and the unloading constitutive relationships of expansive clay is a prerequisite for conducting geotechnical engineering design and safety analysis in expansive-soil areas. In order to obtain the unloading mechanical response characteristics and the expression of the unloading tangent modulus of expansive clay, typical expansive clay in the Hefei area was taken as the research object, and triaxial unloading stress path tests were conducted. The stress–strain properties, microstructures, macro failure modes, and strength indexes of the expansive clay were analyzed under unloading stress paths. Through an applicability analysis of several classical soil strength criteria, an unloading constitutive model and the unloading tangent modulus expression of the expansive clay were constructed based on the Mohr–Coulomb (hereinafter referred to as “M-C”) criterion, the Drucker–Prager (hereinafter referred to as “D-P”) criterion, and the extended Spatial Mobilized Plane (hereinafter referred to as “SMP”) criterion theoretical frameworks. The following research results were obtained: (1) The stress–strain curves of the three stress paths of the expansive clay were hyperbolic. The expansive clay showed typical strain-hardening characteristics and belonged to work-hardening soil. (2) Under the unloading stress paths, the soil particles were involved in the unloading process of stress release, and the failure samples showed obvious stretching, curling, and slipping phenomena in their soil sheet elements. (3) Under both unloading stress paths, the strength of the expansive clay was significantly weakened and reduced. Under the lateral unloading paths, the cohesive force (c) of the expansive clay was reduced by 32.7% and the internal friction angle (φ) was increased by 19% compared with those under conventional loading, while under the axial unloading path, c was reduced by 63.5% and φ was reduced by 28.7%. (4) For typical expansive clay in Hefei, the conventional triaxial compression (hereinafter referred to as “CTC”) test, the reduced triaxial compression (hereinafter referred to as “RTC”) test, and the reduced triaxial extension (hereinafter referred to as “RTE”) test stress paths were suitable for characterization and deformation prediction using the M-C strength criterion, D-P strength criterion, and extended SMP strength criterion, respectively. (5) The derived unloading constitutive model and the unified tangent modulus formula of the expansive clay could accurately predict the deformation characteristics of the unloading stress path of the expansive clay. These research results will provide an important reference for future engineering construction in expansive-clay areas.

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Experimental Study on Mechanical Properties of Structured Clay under Different Unloading Rates and Unloading Stress Paths

Cited by 3 publications

References 19 publications

An Investigation on the Impact of Unloading Rate on Coal Mechanical Properties and Energy Evolution Law

An Investigation on the Impact of Unloading Rate on Coal Mechanical Properties and Energy Evolution Law

Mechanical and permeability characteristics of Q2 soft-plastic loess under coupled hydro-mechanical conditions

Mechanical Response Characteristics and Tangent Modulus Calculation Model of Expansive-Clay Unloading Stress Path

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