scholarly journals Parametric Evaluation of Simultaneous Effects of Damaged Zone Parameters and Rock Strength Properties on GRC

2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Ali Ghorbani ◽  
Hadi Hasanzadehshooiili ◽  
Amin Eslami
Keyword(s):  
Polynomial Regression ◽  
Accurate Determination ◽  
Strength Criterion ◽  
Geological Strength Index ◽  
Support Pressure ◽  
Material Strength ◽  
Tunnel Section ◽  
Disturbance Factor ◽  
Damaged Zone ◽  
Tunnel Design

The convergence-confinement method via the ground reaction curve (GRC) is used as the common practice of tunnel design which demands accurate determination of the stress state and material strength behavior in different zones around the tunnel section. Besides, formation of the excavation/blast-induced damaged zone (EDZ/BDZ) adds more complexity to the problem due to variation of elasticity modulus of the rock mass in this zone. As a result, advanced numerical methods via finite element/difference commercial packages or user-coded, semi-numerical techniques are required to develop the GRC, which demands a high degree of proficiency and knowledge of computational plasticity and geomechanics. In this study, a new, simple, and accurate method is proposed for prediction of GRC of circular tunnels constructed in the damaged, elastoplastic rock masses obeying softening in the plastic zone. The effects of deterioration caused by the drilling/blast in the EDZ were taken into account by assuming a reduced and varying Young’s modulus using the disturbance factor, in the form of Hoek–Brown failure criterion and the Geological Strength Index (GSI). Besides, effects of intermediate principal stress and the exponential decaying dilation parameter are taken into account thanks to adoption of the unified strength criterion (USC) as the material strength criteria. To do so, genetic algorithm (GA) via the method of evolutionary polynomial regression (EPR) is used to find a relationship between a number of 19 affecting parameters on the GRC as the input, and the internal support pressure as the target of prediction. Verification analysis was performed to verify the validity of the results using field measurements data as well as other advanced numerical studies found in the literature. Lastly, variation of the support pressure with simultaneous changes in the affecting input parameters was investigated using multivariable parametric study.

scholarly journals Evaluation of Excavation-Damaged Zone around Underground Tunnels by Theoretical Calculation and Field Test Methods

Energies ◽  
2019 ◽  
Vol 12 (9) ◽  
pp. 1682 ◽  
Author(s):  
Ming Tao ◽  
Zhixian Hong ◽  
Kang Peng ◽  
Pengwei Sun ◽  
Mingyu Cao ◽  
...  
Keyword(s):  
Seismic Waves ◽  
Seismic Velocity ◽  
Underground Mining ◽  
Hydrostatic Stress ◽  
Friction Angle ◽  
Geological Strength Index ◽  
Excavation Damaged Zone ◽  
Disturbance Factor ◽  
Damaged Zone

Excavation-damaged zones (EDZs) induced in underground mining and civil engineering potentially threaten tunnel safety and stability, and increase construction and support costs. In this paper, an investigation of the excavation damaged zone (EDZ) around roadways in Fankou lead-zinc mine in Guangzhou, China is performed by applying a seismic velocity method accompanied by SET-PLT-01 nonmetallic ultrasonic detector. Meanwhile, the in situ stress in the mining area was measured based on the stress relief method with the Swedish high-precision LUT system. The results indicate that the stress field is dominated by the maximum horizontal tectonic stress, and the extents of the EDZ on the roof-floor region are greater than that on the sidewall. In addition, both of the in situ stresses and EDZs show an increasing trend with an increase of depth. Analytical solutions of EDZ around circular openings in the brittle rock mass subjected to non-hydrostatic stress fields are presented in terms of the Mohr–Coulomb and generalized Hoek–Brown criteria, and validated by several cases mentioned above. The extents of EDZ solved by closed-form solutions were found to be in a great agreement with those obtained in the field. Finally, a series of parametric studies are conducted to investigate the effects of cohesion (c), friction angle (φ), geological strength index (GSI), mi, uniaxial compressive strength (σc), and disturbance factor (D) on EDZ. It is shown that the effects of c, φ, GSI, and σc are significant; however, more attention should be paid to consider the dynamic disturbances induced by mechanical drilling, blasting, and seismic waves in tunnel excavations or operations.

scholarly journals A novel solution for ground reaction curve of tunnels in elastoplastic strain softening rock masses

2017 ◽  
Vol 23 (6) ◽  
pp. 773-786 ◽  
Author(s):  
Ali GHORBANI ◽  
Hadi HASANZADEHSHOOIILI
Keyword(s):  
Rock Mass ◽  
Strain Softening ◽  
Numerical Solutions ◽  
Polynomial Regression ◽  
Parameter Determination ◽  
Geological Strength Index ◽  
Support Pressure ◽  
Rock Masses ◽  
Reaction Curve ◽  
Ground Reaction Curve

Ground Reaction Curve (GRC) is one of the most important elements of convergence-confinement method generally used to design tunnels. Realistic presentation of GRC is usually assessed based on the advanced rock strength criteria, also, rock mass behavior (including plasticity and softening treatments). Since taking these parameters into ac­count is not simply possible for practitioners and needs complicated coupled theoretical-numerical solutions, this paper presents a simple novel approach based on Evolutionary Polynomial Regression to determine GRC of rock masses obeying both Mohr-Coulomb and Hoek-Brown criteria and strain softening behaviors. The proposed models accurately present support pressures based on radial displacement, rock mass strength and softening parameter (determination coefficient of 97.98% and 94.2% respectively for Mohr-Coulomb and Hoek-Brown strain softening materials). The ac­curacy of the proposed equations are approved through comparing the EPR developed GRCs with the ground reaction curves available in the literature. Besides, the sensitivity analysis is carried out and in-situ stress, residual Hoek-Brown’s m constant and residual dilation angle are introduced as parameters with the most influence on the support pressure in Hoek-Brown and peak and residual geological strength index are the most affective parameters on the support pressure of tunnels in the strain softening Mohr-Coulomb rock mass.

scholarly journals Investigations of a Weathered and Closely Jointed Rock Slope Failure Using Back Analyses

2021 ◽  
Vol 13 (23) ◽  
pp. 13452
Author(s):  
Kuo-Shih Shao ◽  
An-Jui Li ◽  
Chee-Nan Chen ◽  
Chen-Hsien Chung ◽  
Ching-Fang Lee ◽  
...  
Keyword(s):  
Failure Criterion ◽  
Slope Failure ◽  
Back Analysis ◽  
Jointed Rock ◽  
Geological Strength Index ◽  
Northeastern Region ◽  
In Situ Investigation ◽  
Disturbance Factor ◽  
Value Range ◽  
Jointed Rock Slope

This study presents the case of a landslide triggered by a high groundwater level caused by several days of continuous rainfall in the northeastern region of Taiwan. The slope where this landslide occurred consists of closely jointed and weathered bedrock. By means of finite element limit analysis and the Hoek–Brown failure criterion, this study performed a slope failure simulation similar to the actual landslide and deduced the reasonable value range for the combination of key Hoek–Brown failure criterion parameters through back analyses. The results indicate that the key parameters affecting the bedrock’s slope stability were the geological strength index (GSI) and the disturbance factor (D), whereas the effects of the unconfined compressive strength (σci) were less significant. The results of the back analysis reveal that the suitable D-value range and GSI of closely jointed and weathered sandstone in the northeastern region of Taiwan are 0.8 to 0.9 and 20 to 30, respectively. These back-analyzed value ranges can serve as a reference for broader applications in the preliminary stability analysis of similar rock slopes where it is difficult to perform in situ investigation.

scholarly journals Semianalytical Solution for Large Deformation of Salt Cavern with Strain-Softening Behavior

2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Lina Ran ◽  
Huabin Zhang ◽  
Qingqing Zhang
Keyword(s):  
Plastic Zone ◽  
Large Deformation ◽  
Strain Softening ◽  
Structural Characteristics ◽  
Strength Criterion ◽  
Geological Strength Index ◽  
Salt Rock ◽  
Salt Cavern ◽  
Softening Behavior ◽  
The Impact

A semianalytical solution of stress and displacement in the strain-softening and plastic flow zones of a salt cavern is presented. The solution is derived by adopting the large deformation theory, considering the nonlinear Hoek–Brown (H-B) strength criterion. The Romberg method is used to carry out numerical calculation, and then, the large deformation law of displacement is analyzed. The results are compared with those obtained by former numerical methods, and the solutions are validated. The results indicate that the displacement of the plastic zone decreases with the increase in distance away from the salt cavern. Similarly, it decreases with an increase in the geological strength index or running pressure, with the running pressure having a more significant effect on the displacement. It increases with the dilation angle, and the impact degree gradually increases. Compared with the softening parameter, h, of the plastic zone, the flow parameter, f, has little impact on the displacement. The displacement of the plastic zone obviously increased when considering the strain-softening of salt rock. When considering the shear dilation and softening behaviors of salt rock, the analytical solution obtained by employing the experiential regression Hoek–Brown (H-B) criterion, which considers many factors such as the structural characteristics of the salt formation and the rock mass quality, is safer and closer to the actual situation. This study can provide reference for many applications, including but not confined to analyzing the deformation of the surrounding rock of an underground salt cavern storage facility during construction.

scholarly journals Sensitivity Analysis in the Estimation of Mechanical Parameters of Engineering Rock Mass Based on the Hoek–Brown Criterion

2020 ◽  
Vol 2020 ◽  
pp. 1-18
Author(s):  
Zhiqiang Li ◽  
Guofeng Liu ◽  
Shuqian Duan ◽  
Shufeng Pei ◽  
Changgen Yan
Keyword(s):  
Rock Mass ◽  
Triaxial Compression ◽  
Damage Zone ◽  
Surrounding Rock ◽  
Geological Strength Index ◽  
Sensitivity Factor ◽  
Mechanical Parameters ◽  
Compression Tests ◽  
Disturbance Factor

Geological strength index GSI, disturbance factor (D), material constant mi, and uniaxial compressive strength σci of the intact rock are essential input parameters IPs of the Hoek–Brown H−B criterion. Mechanical parameters MPs of the engineering rock mass, including elastic modulus E, cohesion c, and internal friction angle φ estimated by the H–B criterion, and the predicted excavation response of surrounding rock, including the displacement and excavation damage zone EDZ based on the MPs, are of high relevance with the four IPs of the H–B criterion. In this paper, the deep and huge underground cavern excavated in basalt from a hydropower station under construction in the southwest of China is used to analyse the sensitivity of the IPs on the MPs, the displacement, and EDZ of the surrounding rock mass. Firstly, the H–B criterion is applied to estimate the MPs, among which the IPs are obtained from a series of in situ and laboratory tests, including borehole camera observation, wave velocity test, uniaxial and triaxial compression tests, and so on. Secondly, the sensitivity relationships between IPs, MPs, and prediction results of displacement and EDZ are established and described quantitatively by the sensitivity factor (si). Results show that the MPs of the rock mass are more sensitive to GSI and D⋅GSI and σci are high-sensitivity parameters affecting the displacement and EDZ. Finally, the variations in the estimated MPs and associated prediction results concerning excavation response, which are caused by the uncertainties in the determination of the IPs, are further quantified. This study provides a straightforward assessment for the variability of the rock mass parameters estimated by the H–B criterion. It also gives a valuable reference to similar geotechnical engineering for the determination of rock mass parameters in the preliminary design.

On New Modifications of Some Strength Criteria for Anisotropic Materials

2016 ◽  
Vol 724 ◽  
pp. 53-57 ◽  
Author(s):  
S.L. Shambina ◽  
F.V. Rekach ◽  
Y.V. Belousov
Keyword(s):  
Limit State ◽  
Strength Criterion ◽  
Material Strength ◽  
Small Element ◽  
Exact Results ◽  
Strength Condition ◽  
Stress Space ◽  
Strength Criteria ◽  
State Of Stress ◽  
The Moment

The strength criterion is the strength condition for a small element of the construction’s material. Strength criterion is analytical interpretation in stress space the allowable boundaries of stress state, within these boundaries the material can work under these conditions without breaking. Since analytical interpretation of the experimental data may be performed in different ways, therefore many different strength criteria exist. Properly chosen strength criterion allows determining the moment when the material is destroyed while it is working under various tense conditions. Also it gives an opportunity to assess the limit state of stress in the most loaded points of the structure. This paper suggests new modifications of some well-known strength criteria which are more comfortable for practical use and can help to achieve more exact results.

A Research on Strength Criteria Based on Material Structure

2014 ◽  
Vol 518 ◽  
pp. 236-243
Author(s):  
Zhen Hai Wei ◽  
Meng Shu Wang ◽  
Ding Li Zhang
Keyword(s):  
Random Distribution ◽  
Strength Criterion ◽  
Tensile Failure ◽  
Material Strength ◽  
Material Structure ◽  
Friction Materials ◽  
Strength Criteria ◽  
Complex Material ◽  
Material Theory ◽  
Strength Models

Strength criteria for materials in the classical elastoplastic theory are formed mostly based on experiments and some assumptions [1, . However, no concensus has been achieved though many strength models were put forward to explore the applicable material strength criteria previously. Even the influence of material structures on strength has not been realized. In this article, the tensile failure strength criterion, shear strength criterion and strength criterion of friction materials are explored on the basis of the model of material with a structure of uniformly random distribution. Through analysis, it can be discovered that the strength criteria in the classical elastoplastic theory can be derived from the complex material theory based on the concept of material structure. However, as the theoretical basis, conditions of derivation and assumptions of concepts are totally different, it is proved that the complex material theory used for studying the material structures can fully cover the contents and conclusions obtained in classical elastoplastic theory.

Material Strength: A Rational Nonequilibrium Energy Model for Complex Loadings

2020 ◽  
Vol 88 (2) ◽  
Author(s):  
Biao Wang
Keyword(s):  
Failure Process ◽  
Strength Criterion ◽  
Energy Model ◽  
Natural Phenomenon ◽  
Material Strength ◽  
Strength Theory ◽  
Reliable Prediction ◽  
Strength Criteria ◽  
Safety Considerations ◽  
Nonequilibrium Energy

Abstract The failure of materials with some sort of loading is a well-known natural phenomenon, and the reliable prediction of the failure of materials is the most important issue for many different kinds of engineering materials based on safety considerations. Classical strength theories with complex loadings are based on some sort of postulations or assumptions, and they are intrinsically empirical criteria. Due to their simplicity, classical strength theories are still widely used in engineering, and they are very easy to incorporate into any finite element code. Recently, a new methodology was proposed by the author. Instead of establishing empirical models, the material failure process was modeled as a nonequilibrium process. Then, the strength criterion was established with the rational stability analysis for the failure process. In this study, the author tried to use this idea to develop a rational thermodynamic strength theory and to make the theory easy to use in engineering, similar to the classical strength criteria. It was found that the predictions of the rational energy strength theory were very reasonable compared to the experimental data even if no postulation was taken. Through the analysis, it seemed that the strength problem could be efficiently tackled using the rational nonequilibrium energy model instead of using some sort of empirical assumptions or models.

scholarly journals Simulation of fracture propagation in fibre-reinforced concrete using FDEM: an application to tunnel linings

2019 ◽  
Vol 7 (5) ◽  
pp. 961-974 ◽  
Author(s):  
A. Farsi ◽  
A. Bedi ◽  
J. P. Latham ◽  
K. Bowers
Keyword(s):  
Reinforced Concrete ◽  
Fracture Propagation ◽  
Fibre Reinforced Concrete ◽  
Finite Element Code ◽  
Bending Tests ◽  
Three Point Bending ◽  
Tunnel Section ◽  
Tunnel Design ◽  
Joint Element ◽  
Design Case

AbstractThe application of the combined finite-discrete element method (FDEM) to simulate fracture propagation in fibre-reinforced-concrete (FRC)-lined tunnels has been investigated. This constitutes the first attempt of using FDEM for the simulation of fracture in FRC structures. The mathematical implementations of the new FDEM joint-element constitutive model are first introduced, and the numerical model is then validated comparing the results for plain and FRC beams with three-point bending experimental data. The code has also been applied to two practical tunnel design case studies, showing different behaviours depending on the type of concrete and shape of tunnel section. The FDEM simulations of the linings are also compared with results from a finite element code that is commonly used in the engineering design practise. These results show the capabilities of FDEM for better understanding of the fracture mechanics and crack propagation in FRC tunnels. A methodology for directly inferring the numerical parameters from three-point bending tests is also illustrated. The results of this research can be applied to any FRC structure.

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