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16 pages, 4305 KiB

Open AccessArticle

Study of Energy Evolution Law and Damage Characteristics during Uniaxial Cyclic Loading and Unloading of Sandstone

by Peng Zhong, Jiachun Li, Xiuwu Zhou, Heng Xiao, Shuaishuai Yue, Pengyu Zhang and Yikai Wang

Appl. Sci. 2022, 12(19), 9985; https://doi.org/10.3390/app12199985 - 4 Oct 2022

Cited by 4 | Viewed by 1533

Abstract

Using the rock mechanics test (RMT) and acoustic emission acquisition system (DS9), based on the energy principle, uniaxial compression, uniaxial cyclic loading, and unloading tests are used to study the energy transformation characteristics of the process of sandstone absorbing axial strain energy, accumulating [...] Read more.

Using the rock mechanics test (RMT) and acoustic emission acquisition system (DS9), based on the energy principle, uniaxial compression, uniaxial cyclic loading, and unloading tests are used to study the energy transformation characteristics of the process of sandstone absorbing axial strain energy, accumulating and releasing elastic strain energy, plastic deformation, and crack extension dissipation energy. The study results show the increase of loading rate, rock fracture surface increases, number of fragments increases, and size of fragments decreases; the sandstone damage process causes: shear damage to tensile shear damage and then splitting damage for change; the input energy and elastic energy increase nonlinearly with an increase of stress, and the dissipative energy is larger at the beginning of loading. After a small decrease, it enters the nonlinear growth stage, and the input energy density grows the fastest. The elastic energy density is the second fastest, and the dissipative energy density grows the slowest; with an increase of loading rate, in any deformation stage, the elastic energy density and dissipation energy density are increased, proportion of elastic energy density is decreased, and proportion of dissipation energy density is increased. Near the peak stress stage, the proportion of elastic energy decreases, and the proportion of dissipative energy increases; the damage variable stress curve of sandstone is “weakly concave”, which is consistent with the logistic function, and the damage evolution process has chaotic dynamics properties; the acoustic emission energy of sandstone in cyclic loading and unloading test has a similar variation with the theoretical calculation of dissipated energy. The cumulative energy curve shows a step-up law, and the stress corresponding to the step point is near the historical maximum stress. Full article

(This article belongs to the Special Issue Structural Mechanics of Rocks and Rock Masses)

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23 pages, 4821 KiB

Open AccessArticle

Calculating Bias-Free Volumetric Fracture Counts (VFCs) in Underground Works and Their Use in Estimating Rock Mass Strength and Deformability Parameters

by Paul Schlotfeldt, Jacob Nikl and Jonathon Sutton

Appl. Sci. 2022, 12(18), 9025; https://doi.org/10.3390/app12189025 - 8 Sep 2022

Viewed by 1962

Abstract

This paper initially provides a practical example on how to estimate a bias-free volumetric fracture count (VFC—fractures/m³) in a tunnel and incorporate it into a new and unified volumetric-based Geological Strength Index (V-GSI) chart. The quantified V-GSI chart and [...] Read more.

This paper initially provides a practical example on how to estimate a bias-free volumetric fracture count (VFC—fractures/m³) in a tunnel and incorporate it into a new and unified volumetric-based Geological Strength Index (V-GSI) chart. The quantified V-GSI chart and the methods shown in the practical example were used extensively as tools to assess rock mass conditions and assist in support determinations on the WestConnex M8 Motorway tunnel project in Sydney, Australia. The reliability of the strength and deformability estimates obtained using the V-GSI ratings while tunneling within the Hawkesbury Sandstone is demonstrated here by providing an example of deformation results obtained through 3-D finite element analysis in a single location in the tunnel. The modelling results are compared to measure convergence in the tunnel in this location, which demonstrated good correlation between predicted and observed deformation. This provides validation that the V-GSI chart and associated Hoek–Brown strength and deformability equations can be used with some confidence to determine potential deformation in underground works. Full article

(This article belongs to the Special Issue Structural Mechanics of Rocks and Rock Masses)

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24 pages, 57341 KiB

Open AccessArticle

On the Influence of Direction-Dependent Behavior of Rock Mass in Simulations of Deep Tunneling Using a Novel Gradient-Enhanced Transversely Isotropic Damage–Plasticity Model

by Thomas Mader, Magdalena Schreter and Günter Hofstetter

Appl. Sci. 2022, 12(17), 8532; https://doi.org/10.3390/app12178532 - 26 Aug 2022

Cited by 7 | Viewed by 1991

Abstract

In engineering practice, numerical simulations of deep tunneling are commonly based on isotropic linear–elastic perfectly plastic rock models. Rock, however, commonly exhibits highly nonlinear and distinct direction-dependent mechanical behavior. The former is characterized by irreversible deformation, associated with strain hardening and strain softening, [...] Read more.

In engineering practice, numerical simulations of deep tunneling are commonly based on isotropic linear–elastic perfectly plastic rock models. Rock, however, commonly exhibits highly nonlinear and distinct direction-dependent mechanical behavior. The former is characterized by irreversible deformation, associated with strain hardening and strain softening, and the degradation of stiffness; the latter is due to the inherent rock structure. Nevertheless, the majority of the existing rock models focuses on the prediction of either the highly nonlinear material behavior or the inherent anisotropic response of rock. The combined effects of nonlinear and direction-dependent rock behavior, particularly in the context of the numerical simulations of tunnel excavation, have rarely been taken into account so far. Thus, it is the aim of the present contribution to demonstrate the influence of both effects on the evolution of the deformation and stress distribution in the rock mass due to deep tunnel excavation on the example of a well-monitored stretch of the Brenner Base Tunnel (BBT). To this end, the recently proposed gradient-enhanced transversely isotropic rock damage–plasticity (TI-RDP) model, is employed for modeling the surrounding rock mass consisting of Innsbruck quartz-phyllite. The material parameters for the nonlinear transversely isotropic rock model are identified by means of three-dimensional finite element simulations of triaxial tests on specimens of Innsbruck quartz-phyllite, conducted for varying loading angles with respect to the foliation planes and different confining pressures. Subsequently, the results of the nonlinear 2D finite element simulations of tunnel excavation are presented for different anisotropy parameters and different orientations of the principal material directions with respect to the tunnel axis. The capabilities of the TI-RDP model are assessed by comparing the numerically predicted results with those obtained by the isotropic version of the RDP model. Full article

(This article belongs to the Special Issue Structural Mechanics of Rocks and Rock Masses)

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26 pages, 18383 KiB

Open AccessArticle

Geotechnical Study of Raspadalica Cliff Rockfall, Croatia

by Dalibor Udovič, Branko Kordić and Željko Arbanas

Appl. Sci. 2022, 12(13), 6532; https://doi.org/10.3390/app12136532 - 28 Jun 2022

Viewed by 1682

Abstract

The Raspadalica Cliff is an almost vertical 100 m high limestone cliff with a railway line at its foot and is known for numerous rockfall occurrences in the past. This article presents the results of the geotechnical study of the cliff based on [...] Read more.

The Raspadalica Cliff is an almost vertical 100 m high limestone cliff with a railway line at its foot and is known for numerous rockfall occurrences in the past. This article presents the results of the geotechnical study of the cliff based on a traditional geological and geotechnical field survey and remote sensing analysis. Both the traditional geological and geotechnical field survey and remote sensing surveys and analyses enabled the establishment of the structural model of the Raspadalica Cliff and the determination of the discontinuity sets and discontinuity features, such as orientation, spacing, persistence, roughness, discontinuity wall strength, aperture, degree of weathering of discontinuity wall, seepage conditions, and the presence and hardness of discontinuity filling. Kinematic analyses were performed on five cliff zones with slightly different structural features, indicating a relatively low probability of typical failures in the cliff rock mass that precede the rockfall occurrences. Although rockfall phenomena from the cliff face are relatively frequent, the kinematic analyses did not indicate a high probability of their occurrence. The aim of this manuscript is to make scientists and practitioners aware that investigation of rock mass cliffs and possible rockfall failures must not be based on usual methods without critical review of the obtained results and consequences. The combined use of traditional geological and geotechnical methods and more commonly used advanced remote sensing methods leads to better modelling, while the analysis of more associated failure modes can explain the triggering of rockfall. Full article

(This article belongs to the Special Issue Structural Mechanics of Rocks and Rock Masses)

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15 pages, 2020 KiB

Open AccessArticle

Development of a FBG Stress Sensor for Geostress Measurement Using RSR Method in Deep Soft Fractured Rock Mass

by Yuanguang Zhu, Bin Liu, Sheng Wang and Zhanbiao Yang

Appl. Sci. 2022, 12(4), 1781; https://doi.org/10.3390/app12041781 - 9 Feb 2022

Cited by 3 | Viewed by 1577

Abstract

The rheological stress recovery (RSR) method was proposed to obtain measurements of in-situ stress. Rock stress can be evaluated by monitoring the recovery process of stress sensors embedded in rock mass. In order to achieve this application, a novel stress sensor employing the [...] Read more.

The rheological stress recovery (RSR) method was proposed to obtain measurements of in-situ stress. Rock stress can be evaluated by monitoring the recovery process of stress sensors embedded in rock mass. In order to achieve this application, a novel stress sensor employing the fiber Bragg grating (FBG) technique was designed and manufactured. This stress sensor consisted of three parts: A sensing spherical head, connecting rod, and coupler box. In the sensing spherical head, six independent pressure sensing units were assembled together with a temperature compensation unit. In addition, wavelength division multiplexing (WDM) technology was adopted to ensure that only one fiber splice for each stress sensor is output. The fiber splicing of the sensing units was assembled in the coupler box. The transformation equations from the six pressure sensing units to the stress sensor were established. Furthermore, a calibrating device for the stress sensor was designed, and the general calibration and long-term stability tests were carried out to investigate the characteristic indexes (maximum range, full-range output, and sensitivity) and measurement error (zero drift index, hysteresis index, and repeatability index). Measurement errors showed that the degrees of linearity, zero drift, hysteresis, and repeatability were all below 1.5%. The stability test indicated that the creep of the stress sensor can gradually stabilize in 24 days, and the errors were less than 1.5%. As a result, the stress sensor developed here satisfies the requirements for the RSR method and can be used in field. Full article

(This article belongs to the Special Issue Structural Mechanics of Rocks and Rock Masses)

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15 pages, 19782 KiB

Open AccessArticle

A Rough Discrete Fracture Network Model for Geometrical Modeling of Jointed Rock Masses and the Anisotropic Behaviour

by Peitao Wang, Cao Liu, Zhenwu Qi, Zhichao Liu and Meifeng Cai

Appl. Sci. 2022, 12(3), 1720; https://doi.org/10.3390/app12031720 - 7 Feb 2022

Cited by 12 | Viewed by 2126

Abstract

The geometry of the joint determines the mechanical properties of the rock mass and is one of the key factors affecting the failure mode of surrounding rock masses. In this paper, a new rough discrete fractures network (RDFN) characterization method based on the [...] Read more.

The geometry of the joint determines the mechanical properties of the rock mass and is one of the key factors affecting the failure mode of surrounding rock masses. In this paper, a new rough discrete fractures network (RDFN) characterization method based on the Fourier transform method was proposed. The unified characterization of the complex geometric fracture network was achieved by changing the different Fourier series values, which further improved the characterization method of the RDFN model. A discrete element numerical calculation model of the complex RDFN model was established by combining MATLAB with PFC code. Numerical simulation of the anisotropic mechanical properties was performed for the RDFN model with a complex joint network. Based on the results, the geometry of the joint network has a significant influence on the strength and failure patterns of jointed rock masses. The failure modes of the opening are highly affected by the orientation of the fracture sets. The existence of the rough fracture sets could influence the failure area of different excavation situations. The study findings provide a new characterization method for the RDFN model and a new characterization approach for stability analysis of complex jointed rock masses. Full article

(This article belongs to the Special Issue Structural Mechanics of Rocks and Rock Masses)

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15 pages, 3318 KiB

Open AccessArticle

Numerical Analysis for Elucidating the Effect of Tunnel Excavation in Gravel-Mixed Ground

by Hisashi Hayashi, Yasuyuki Okazaki, Daisuke Sakai, Shingo Morimoto and Masato Shinji

Appl. Sci. 2022, 12(3), 1667; https://doi.org/10.3390/app12031667 - 5 Feb 2022

Cited by 3 | Viewed by 1537

Abstract

In tunnel construction in gravel-mixed ground, it is extremely important to predict the risk of gravel dropout and the accompanying large deformation of the substrate ground. The distribution and shape of gravel vary, and it is difficult to reproduce the situation depending on [...] Read more.

In tunnel construction in gravel-mixed ground, it is extremely important to predict the risk of gravel dropout and the accompanying large deformation of the substrate ground. The distribution and shape of gravel vary, and it is difficult to reproduce the situation depending on the individual site. Therefore, in this study, we created a model of the gravel-mixed ground using the Voronoi partition model. Then, by mathematical analysis, the gravel shape that appears in the actual phenomenon could be reproduced in consideration of randomness and inhomogeneity. In addition, it was clarified that the gravel extrusion phenomenon and the large deformation of the ground can be expressed. Full article

(This article belongs to the Special Issue Structural Mechanics of Rocks and Rock Masses)

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19 pages, 12752 KiB

Open AccessArticle

Mechanical Properties of Roof Rocks under Superimposed Static and Dynamic Loads with Medium Strain Rates in Coal Mines

by Kun Zhong, Wusheng Zhao, Changkun Qin, Hou Gao and Weizhong Chen

Appl. Sci. 2021, 11(19), 8973; https://doi.org/10.3390/app11198973 - 26 Sep 2021

Cited by 8 | Viewed by 1867

Abstract

Roof rocks in coal mines are subjected to the combination of in situ stresses and dynamic stresses induced by mining activities. Understanding the mechanical properties of roof rocks under static and dynamic loads at medium strain rates is of great significance to revealing [...] Read more.

Roof rocks in coal mines are subjected to the combination of in situ stresses and dynamic stresses induced by mining activities. Understanding the mechanical properties of roof rocks under static and dynamic loads at medium strain rates is of great significance to revealing the mechanism of rock bursts. In this study, we employ the digital image correlation (DIC) technique to investigate the energy concentration and dissipation behaviors, failure mode, and deformation characteristics of roof rocks under combined static and dynamic loads. Our results show that both the static pre-stress and dynamic loading rate have significant effects on the uniaxial compressive strength of rock specimens. From the energy principle, when the static pre-stress is the same, both elastic strain energy density and dissipated energy density increase with increasing dynamic loading rate. The hazard of rock bursts increases with decreasing static pre-stress and increasing dynamic loading rate. At higher dynamic loading rates, more cracks are generated, and the failure becomes more violent. The crack initiation, propagation and coalescence processes are identified, and the failure mode is closely related to the evolution of the global principal strain field of the rock specimens. Full article

(This article belongs to the Special Issue Structural Mechanics of Rocks and Rock Masses)

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