Mechanized tunneling in hard rock is associated with various challenges and risks, one of which is the penetration rate of Tunnel Boring Machine and the occurrence of grinding and chipping in various conditions. When the strength of the rock is high and the amount of jointing is low, the penetration rate of the machine is reduced and instead of forming rock chips in the tunnel face. In these conditions, which is called grinding, tunneling is associated with wear and high consumption of cutting tools as well as a severe reduction in the efficiency of excavation operations. In this paper, the boundary between grinding and chipping processes is investigated and a criterion for determining the minimum normal force in different geomechanical con

The chipping and grinding processes are the basis for understanding rock cutting during TBM excavation in hard rock conditions. The chips are produced when tensile fractures created by adjacent cutters propagate parallel to the tunnel face and coalesce whereas grinding occurs when fractures do not fully propagate through the rock and only fines are generated. Chipping is the normal and efficient boring process using machines equipped with disc cutters. Consequently, almost all of the models proposed for predicting the TBM penetration have been developed by the assumption that chipping is the dominant mode. It is obvious that these models are unable to predict correctly TBM performance when grinding is dominated in the rock cutting process.

Mechanized tunneling in rocks is based on fracture propagation and rock fragmentation under disc cutters. Rock chipping is an efficient kind of fragmentation process, while the grinding process may occur under special conditions. The cutter-head penetration is an appropriate parameter involved in order to distinguish between the chipping and grinding processes in rock cutting. In this work, the grinding and chipping processes are investigated in the Uma-Oya water conveyance tunnel in Sri Lanka. The Uma-Oya project is a water transfer, hydropower, and irrigation system in the SE part of the central highland region of Sri-Lanka. From a geological viewpoint, most parts of the tunnel route in the studied section consist of very strong and abras

Mechanized tunneling in rocks is based on fracture propagation and rock fragmentation under disc cutters. Rock chipping is an efficient kind of fragmentation process, while the grinding process may occur under special conditions. The cutter-head penetration is an appropriate parameter involved in order to distinguish between the chipping and grinding processes in rock cutting. In this work, the grinding and chipping processes are investigated in the Uma-Oya water conveyance tunnel in Sri Lanka. The Uma-Oya project is a water transfer, hydropower, and irrigation system in the SE part of the central highland region of Sri-Lanka. From a geological viewpoint, most parts of the tunnel route in the studied section consist of very strong and abras

When TBMs are applied for tunnel excavation in very strong and massive rocks, the cutting mechanism happening under the disc cutters is converted from chipping to grinding. On the other hand, the most common TBM performance prediction models that have been developed assuming the occurrence of the chipping phenomenon would not be sufficiently accurate in grinding conditions. Therefore, this study aimed to develop a new empirical equation for estimation of the TBM performance in grinding conditions. In this regard, the database composed of actual measured TBM parameters (i.e. penetration rate and cutter load) and engineering rock properties (i.e. UCS, RQD in rock mass) was established using the data collected from a mechanised tunnelling proj

In this paper, the effect of replacing disc cutters with ripper tools on the performance of a TBM in Tehran Metro Line 6 is investigated by comparing the value of operating parameters of TBM before and after the replacement. The results show that this replacement has a positive impact on the TBM performance. ? ? ? Introduction Improvement of the performance of the TBM machine in tunneling has always been in the spotlight of research and development. The type of cutting tool, which is selected based on the mechanical properties of the formations along the tunnel route, could affect the efficiency and production rate in tunneling. In Tehran Metro Line 6, the consumption of disc cutters increased with decreasing the efficiency of disc cutters,

In this paper, a novel method based on a semi-ring support has been developed and proposed to facilitate TBM passing the station and restarting the excavation. The results show that the proposed method can be safely used. Introduction Crossing of station is one of the most challenging problems in construction of metro lines. Given the difficulties and problems of using the push frame in the TBM passing station and restarting excavation, this study presents a method based on the use of segmental rings that has been developed for use in underground stations. Methodology and Approaches In this method, in order to create a support for applying the force of TBM thrust, a different pattern of the installation of the incomplete rings has been

The crack initiation angle and propagation path for two different disc shaped test specimens (ie, SCB and CBD specimen) are investigated experimentally and theoretically. The Maximum Tangential Stress (MTS) criterion does not calculate the crack initiation angle in SCB and CBD specimens correctly. Moreover, at the angles after occurrence of pure mode II, where the stress intensity factor of mode I becomes negative, this criterion is not applicable. Therefore, in this research work, Improved MTS (IMTS) criterion which has been implemented in the extended finite element method and is applicable under tensile and compressive loading conditions to examine the crack propagation path in the aforementioned disc shaped specimens. Furthermore, an ex

Acidizing and chemical solutions may change mechanical properties of rocks and facilitate rock fracturing in different mining operation and enhanced oil recovery projects in oil fields. Characterization of rock properties shows an inhomogeneous and completely anisotropic behavior while some rocks exhibit orthotropic behavior. Chemo-mechanical processes result in the development and intensification of inhomogeneity and orthotropy in rock properties which should be characterized for numerical modeling of fracture initiation and propagation in engineering rock works. An extended finite element code which is a powerful numerical tool, compared to the other numerical methods, is developed to model fracturing graded brittle rocks by chemical corr

Understanding of mechanisms of initiation and propagation of rock fracture is a key factor in many engineering problems in rock. Since most failures in rock occur under compression condition, in this study, the crack propagation in rock specimen with inclined crack under uniaxial compression has been investigated. In order to simulate the crack propagation under compressive loading, the maximum tangential stress (MTS) criterion was firstly improved and incorporated in developed extended finite element method (XFEM) code. The XFEM allows crack growing through the finite element mesh without re-meshing process. The developed code is validated in different bench mark tests under tension by MTS criterion which can precisely predi

The hollow centre cracked disc (HCCD) specimen is one of the suggested alternative methods for determining the fracture toughness of rock. This work aims to investigate the fracture mechanism in HCCD in macro- and micro-scales using numerical methods, extended finite element method (X-FEM) and particle flow code (PFC) modeling, respectively. In the X-FEM, heaviside and near-tip enrichment functions are employed to consider the presence of the crack in the model. In PFC modeling the movement and interaction of stressed assemblies of rigid spherical particles are modeled using the distinct element method (DEM). A numerical code called MEX-FEM based on XFEM has been developed to simulate the problems involving crack. The models

The cracked Brazilian disc (CBD) specimen is widely used in order to determine mode-I/II and mixed-mode fracture toughness of a rock medium. In this study, the stress intensity factor (SIF) on the crack-tip in this specimen is calculated for various geometrical crack conditions using the extended-finite element method (X-FEM). This method is based upon the finite element method (FEM). In this method, the crack is modeled independently from the mesh. The results obtained show that the dimensionless SIFs for the pure modes I and II increase with increase in the crack length but the angle in which pure mode-II occurs decreases. For the mixed-mode loading, with increase in the crack angle, NI value decreases, while NII value increases to a maxi

The semicircular specimen under three-point bending (SCB) has been widely used to investigate mode I, mode II, and mixed mode I/II fracture behavior in brittle rocks. Compared to the other numerical methods, the extended finite element method (X-FEM) models a crack independently of the finite element mesh without any remeshing step in fracture propagation. In this regard, a numerical code called MEX-FEM, based on X-FEM, has been developed for modeling crack propagation in rock material. Since dimensionless stress intensity factors (i.e., Y I and Y II) in crack modeling of SCB specimen depend on crack length, crack angle, and span ratio, these factors and crack propagation trajec

Existence of discontinuity features has a great influence on mechanical properties and cuttability of a rock mass. In the literature, the influence of geometrical properties of joint sets such as joint spacing and orientation on penetration rate (PR) of a tunnel boring machine (TBM) were investigated and reported. However, the actual fracture pattern in a rock mass is more likely a discrete fracture network. The numerical probabilistic distinct element method (DEM) modeling of PR of a TBM is a very useful method that simulates very complex geometrical models of fracture systems, such as stochastic discrete fracture network (DFN) models with different possible fracture patterns close to the tunnel face. The formed chipping are

Performance analysis and accurate prediction of Penetration Rate (PR) of a TBM have been the ultimate goals of many research works. A reliable prediction of a TBM performance is necessary in budget control and also time schedule planning in underground excavation projects. This research aims to investigate the application of Principal Component Analysis (PCA) in prediction of penetration rate of TBM using Artificial Neural Networks (ANN), which has not been used and reported in previous studies in this field of study. PCA is a statistical procedure that uses an orthogonal transformation to convert a set of observations of possibly correlated variables into a set of values of linearly uncorrelated variables called principal components. In th

The ANNs are a form of artificial intelligence which attempt to mimic the function of the human brain and nervous system. ANNs could take into account the impact of all important parameters for predicting a phenomenon. In this study, the obtained data from an excavated tunnel with a length of 10 km in Zagros region in Iran were analyzed, and the penetration rate of a TBM was predicted by taking the ANNs approach in a MATLAB program used for this purpose.