A comprehensive solution for the calculation of ground reaction curve in the crown and sidewalls of circular tunnels in the elastic-plastic-EDZ rock mass considering strain softening

Zonal disintegration, a phenomenon of fractured zones and intact zones distributed alternately in deep rock mass, is different from the excavation-damaged zone of shallow rock mass. In this study, bonded block model of 3DEC was employed to study the fracture mode and origination condition of zonal disintegration. Initiation, propagation, and coalescence progress of fracture around the roadway boundary under different triaxial stress conditions are elaborated. Numerical simulation demonstrated that zonal disintegration may occur when the direction of maximum principal stress is parallel to the roadway axis. It is interesting to find that the fracture around the roadway boundary traced the line of a spiral line, while slip-line fractures distributed apart from the roadway boundary. The extent of the alternate fracture zone decreased as the confining pressure increased, and alternate fracture zone was no longer in existence when the confining pressure reaches a certain value. Effects of roadway shape on zonal disintegration were also studied, and the results indicated that the curvature of the fracture track line tends to be equal to the roadway boundary in shallow surrounding rock of the roadway, while the fractures in deep surrounding rock seems unaffected by the roadway shape. Those findings are of great significance to support design of deep underground openings.

Section: Introductionmentioning

confidence: 92%

Numerical Study on Zonal Disintegration of Deep Rock Mass Using Three‐Dimensional Bonded Block Model

Tang

Xie

et al. 2019

“…Unlu and Gercek presented a continuous function for the prediction of the longitudinal settlement in the elastic condition as shown in Equation (6). In Equation ( 6), X * � 0 represents the position of the tunnel face; also, negative and positive X values, respectively, stand for the points in front and behind the tunnel face [32].…”

Section: Ree-dimensional Validation Of the Model With Analytical Relationshipsmentioning

confidence: 99%

“…In this regard, proper and accurate design of tunneling projects needs an in-depth understanding of this interaction nature. In recent years, such an investigation has been carried out based on empirical [1,2], analytical [3], and numerical [4][5][6][7][8][9][10] methods. Among these methods, numerical techniques with the ability to model the more complicated problems (in forms of geometry, stress field, material property, etc.)…”

Section: Introductionmentioning

confidence: 99%

Three‐Dimensional Finite Difference Analysis on the Ground‐Sequential Tunneling‐Superstructure Interaction

Lakirouhani

Jafari

Hasanzadehshooiili

2021

Self Cite

In this paper, a three-dimensional finite difference analysis is presented to investigate the interactive effects of sequential tunneling and the superstructure on the settlement profile of the ground. To simulate the practical sequential tunneling procedure, tunnel excavation is conducted in a step-by-step framework; tunnel excavation starts from the beginning of the model and is updated in a continuous manner, and the installation of the tunnel support system is done with a delay step compared to tunnel excavation. The numerical modeling accuracy is validated using the available analytical and numerical solutions for both two-dimensional and three-dimensional simplified cases. The well-validated modeling procedure is adopted to investigate effects of tunnel diameter, depth of tunneling, and number of superstructure stories on the profile of occurring settlements. Two cases of free-field and three-dimensional superstructural modeling are compared with regard to the effect of tunneling. In addition, the effect of tunneling advancement on the generation of excess structural forces and moments are studied as another important factor in the soil-tunneling-superstructure interaction problem. It is observed that, in the free-field case, with advancing the tunnel face, the longitudinal settlement profiles approach the steady-state condition and the maximum ground settlement tends to converge to a specific value, whereas as the tunnel passes under a structure, the settlement increases steadily as the tunnel progresses. There is a direct relationship between the depth and diameter of the tunnel and the settlement. In addition, the effect of the number of superstructure stories on the maximum settlement is more considerable compared to the free-field condition. According to the results, when the tunnel passes under 8-story and 12-story structures, the maximum settlement increases by 40% and 70%, respectively, compared to the free-field condition. It is also shown that tunneling-induced settlements result in the regeneration of structural forces.

“…True characterization of this blast/ excavated induced damage zone (BIDZ/EIDZ) is carried out based on the deterioration of material strength parameters, consideration of the variation of Young's modulus, and the weight of this zone into the problem. e effect of EDZ has been studied numerously [24][25][26][27][28][29][30][31][32][33][34][35][36]. However, there is limited, available solutions, which consider the effects of both softening material behavior in the plastic zone and the existence of BIDZ/EIDZ around the tunnel [26,[37][38][39][40].…”

Section: Introductionmentioning

confidence: 99%

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

Ghorbani

Hasanzadehshooiili

Eslami

2021

Self Cite

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.