حسین سالاری راد

The purpose of this paper is to investigate analytically the fully grouted rock bolt interaction with grout and rock in pullout test and to determine the load-displacement curve of the bolt head (beginning of the bonded section). Usually, the pullout test output is only the load-displacement curve. This paper discusses how to use this curve to determine the bolt-grout-rock interaction. For modeling bolt-grout interface behavior, coupling (compete for bonding), partial decoupling, decoupling with the residual shear strength, and complete decoupling have been considered. With increasing the applied load, two possible cases including complete pullout and bolt shank yielding are considered. Based on experimental results, a model for the shear stress along a fully grouted bolt is assumed. According to this model, the distribution of axial stress in the bolt and displacement of the bolt head is determined. It is also assumed that the bolt is sufficiently long, which is usually used in underground excavations. Based on the presented analytical method, the bolt head load-displacement curve is determined by assuming input parameters. This curve is compared with a pullout test result.

Displacements around a tunnel, occurring as a result of excavation, consist of the elastic and plastic parts. In this paper, we discuss the elastic part of displacements as a result of excavation, called net displacement. In general, the previous analytical solutions presented for determining the displacements around a circular tunnel in an elastic medium do not give the net displacements directly. The well-known Kirsch solution is the most widely used method for determining the induced stresses and net displacements around a circular opening in a biaxially-loaded plate of homogeneous, isotropic, continuous, linearly elastic material. However, the complete solution for obtaining the net displacements has not been presented or highlighted in the available literature. Using the linear elasticity, this paper reviews and presents three different analytical methods for determining the net displacements directly as well as induced stresses around a circular tunnel. The three solution methods are the Lame' method, airy stress function method, and complex variable method. The tunnel is assumed to be situated in an elastic, continuum, and isotropic medium in the plane strain condition. The solutions are presented for both the hydrostatic and non-hydrostatic in situ stresses in the 2D biaxial loading condition along with an internal pressure. Loading and unloading in tunneling occurring as a result of excavation and stress differences between the induced and initial ones are considered to evaluate the net displacements directly. Finally, some examples are given to demonstrate the complete solution and show the difference between the net elastic displacements as a result of excavation and total elastic displacements that are not real.

This work is aimed to investigate the effects of joints configuration in a rock mass on validity of the deformation values obtained using equivalent continuum approach. For this purpose, discrete element method is utilized to numerically model complicated joint configuration comparing to in-built assumptions of equivalent continuum equations. Then, deformation components obtained by equivalent continuum solutions were compared with the results of discrete element numerical analyses and in-situ tests to demonstrate the effect of geometric parameters. Finally, these results are provided to evaluate validity of equivalent continuum relations in deformation analysis of non-orthotropic rock masses, unlike their assumptions.
 

There are two different techniques to determine deformation behavior of jointed rock masses: direct and indirect methods. Direct methods include laboratory tests on rock specimens and in situ tests on field rock masses. The overall characteristics of large-scale rocks are often not available through direct measurements due to lack of time and financial resources. Indirect methods consist of empirical correlations, analytical solutions and numerical modelling. Empirical methods are based on correlation between rock mass deformability and its classification indices such as rock quality designation (RQD), rock mass rating (RMR) and geological strength index (GSI). In spite of their simplicity, it is not possible to capture anisotropic and scale-dependent behavior of rock mass using empirical techniques. Analytical or closed-form methods consider rock mass as an equivalent continuum in which the deformation is the sum of deformation of the intact rock and deformation of the joint sets. These solutions are digest and simple, and only can be used to analyze deformation of regularly jointed rocks. Most of them are inapplicable when dealing with irregular joint systems which are more common in nature. On the other hand, numerical modelling is advantageous to study the effect of joint sets configuration on deformation behavior of a jointed rock mass, and can be used to determine the accuracy of closed-form deformation analysis of irregularly jointed rock masses.
 

For analysis purposes, the applicability of equivalent continuum approaches in estimating deformation behavior of rock masses with three intersecting joint sets was studied. Two different cases were considered, namely, deviation of the intersection angle and dip direction of the second joint set. 3DEC software contains several different behavior models for intact rock in which one or more of them can be used depending on governing assumptions. According to analytical approaches, isotropic elastic and Coulomb slip models were assigned to intact rock and joints, respectively. Note that joints were prevented to deform plastically because the purpose was to study the elastic deformation of jointed rock masses using both analytical and numerical analysis.
 

According to the obtained results, following conclusions can be reported for the conducted study:
Axial analytical and numerical deformation values have a high sensitivity to intersection angle but there is no evidence to know how they change with this parameter.
Further deviation of intersection angle results in increasing difference of numerical and analytical lateral deformation in the direction perpendicular to intersecting joint sets.
Low discrepancies were recorded for lateral strains parallel to intersecting joint sets strike while changing intersection angle. Therefore, it can be concluded that the application of equivalent continuum method to estimate this component would be somehow accurate.
The effect of dip angle of intersecting joint sets is not considered in the non-orthotropic equivalent continuum approach. However, results generally show a considerable effect of this parameter on the discrepancy of analytical and numerical values.
Differences between analytical and numerical deformation results show that changing the dip direction does not significantly affect the results, but applicability of the corresponding equivalent continuum solution is questionable in some cases.
Application of analytical equation for axial strain estimation is not recommended when dip angle of intersecting joint sets has a dominant contribution to deformation.
In the case of dip direction deviation, lateral strain estimation parallel to joints strike through the corresponding analytical solution has an acceptable accuracy.

The injection or extraction of gas can change the pore pressure within the reservoir, which in turn results in redistribution of the stress field. Consequently, the induced deformations within the reservoir and the sealing caprock can potentially prompt a damage zone in the caprock.The main objective of this paper is to develop a model to estimate the growth and extension of cracks in the caprock. In order to achieve this aim, the smeared crack approach is used to model the process of cracking in the caprock. To do this, we will employ smeared crack approach to study the initiation and propagation of cracks in caprock of subsurface reservoir. There are generally three approaches in solid mechanics when modelling cracks: discrete crack, interface elements and smeared crack. Although, discrete crack approach reflects the fracture development phenomenon most closely, it does not fit the nature of numerical methods and it can computationally expensive with development of cracks, each node is replaced by more nodes, which entails re-definition of finite element mesh and hence more computational resources are needed. On the other hand, smeared crack approach assumes that the cracked solid is a continuum and permits the description of the medium in terms of conventional stress-strain equations. Within the smeared crack framework, small cracks are formed in the band are gradually connected to each other and one or more cracks may be defined for each gauss point of each element. As one of the important innovations of this paper, the study of the effect of fluid pressure on the smeared crack propagation, has been done, which is based on coding in FORTRAN programming environment. Due to the results obtained by the flow of fluid into the crack, the crack opening increased significantly.

Today, precast concrete lining (segmental) are used as system maintenance in the majority of tunnels excavated by TBM. On the other hand, the mechanism of the joint between two segments is not known under seismic loads. In this paper a numerical study about the effect of the earthquake on the segmental supporting system and the resultant vertical and shear forces on the contact surface between two segments is investigated. The Tehran -Karaj water conveyance tunnel (Amirkabir) was used as a case study. In this study, the UDEC software was used. At the first step, the segmental lining were simulated under no slip and full slip conditions and the normal and shear forces were studied. Finally, the effect of joint stiffness between two segments were investigated. Results showed that with increasing the interface properties, the normal and shear forces in the segmental joints increased. Also with increasing the joints stiffness, the normal and shear forces on the joints increased and the normal and shear displacement decreased. In other words, the rigidity increament of supporting system is associated with flexibility decrement of lining with respect to rock medium. So, the stresses increased and displacement decreased.

The rock materials surrounding the underground excavations typically demonstrate nonlinear mechanical response under high stress states. The dominant causes of irreversible behavior are plastic flow and damage process. The plastic flow is controlled by the presence of local shear stresses which cause dislocation to some preferential elements due to existing defects. During this process, the net number of bonds remains practically unchanged. The main cause of irreversible changes in quasi-brittle materials such as rock is the damage process occurring within the material.
In this paper, a coupled logarithmic damage and plastic model was used to simulate irreversible deformations and stiffness degradation of rock materials under loading. In this model, damage evolution and plastic flow rules were formulated in the framework of irreversible thermodynamics principles. To take into account the stiffness degradation and softening in post-peak region, logarithmic damage variable was implemented. Also, a plastic model with Drucker-Pruger yield function was used to model plastic strains. Then, an algorithm was proposed to calculate the numerical steps based on the proposed coupled plastic and damage constitutive model. The developed model was programmed in VC environment. Then, it was used as a separate and new constitutive model in DEM environment code (UDEC). Finally, the experimental oolitic limestone rock behavior was simulated based on the developed model. The irreversible strains, softening and stiffness degradation were reproduced in the numerical results. Furthermore, the confinement pressure dependency of rock behavior was simulated in according to experimental observations.

Today, with advances in technology, enable the design and construction of accurate underground structures are provided. Nevertheless, the analysis of underground structures due to interaction between the soil or rock surrounding infinite medium and tunnel supporting system, is very complex and then lower research is done.
The response of tunnel supporting system under seismic loads is a function of the ratio flexibility of the lining and rock or soil medium. This ratio represents the stiffness difference between the ground and tunnel lining. And in fact, the interaction of the tunnel lining and medium is indicated.
Methodology and Approaches :In this paper, two analytical methods for investigating the underground spaces behavior under seismic loading is presented. Then, the response of tunnel monolithic lining in no-slip and full-slip conditions with using analytical and numerical methods with considering of interaction between tunnel lining and medium is investigated.
Results and The results showed that the stress induced by seismic loads in tunnel lining in no slip condition is 2.7 times higher than in full slip condition. Also, monolithic lining strain value in full slip condition is further than no slip condition. Results of numerical method shows good agreement with analytical methods.

In general، mine faces are separated from the mine ventilation network. In mine face workers are exposed to contaminants such as dust and gas. Mine faces are ventilated by auxiliary ventilation optimal design of this system is very complicated. Accumulation of methane gas in mine faces have high potential of disaster. In order to solve this problem، we must have Comprehensive view of methane behavior and distribution in mine faces. In this paper، in order to reach this goal، three-dimensional model of auxiliary ventilation system of Mike mine ​​ was constructed by CFD code fluent. model geometry was meshed by hybrid cell: Quadrilateral cell with 5 cm in model face، fan and out let and Hexagonal cell with 20 cm in model ceiling، floor. Fluid turbulence flow and methane concentration are modeled with and methane air mixture. According to simulation result there is direct relation between high concentration of methane and return flow so high concentration of gases occurs under ventilation ducts and face corners. Finally، there is a good agreement between numerical result and mike mine Measurements.

Smoke and toxic gases created by fire accidents in tunnel are very harmful for tunnel users health and safety .So fresh air supply for fire smoke control in the fire upstream, is important .Thus, the critical velocity is a most important factor for this .In order to determine the critical velocity during fire in the Alborz tunnel 3dimensional model of the tunnel and fire was created by FDS software .Fire with 100 mw size for 960second in model with 500m length was simulated. Fire and Smoke was modeled by HRR and heptanes’ combustions. Unsteady flow and combustions was simulated by LES and Eddy break up model. Model was meshed by 50 cm cell. Finally, simulation result was validated by experimental equation .simulation predicted value for critical velocity is 3.5 m/s which have good agreement with Oka and Atkinson experimental equation so we propose 3.5 m/s as critical velocity for fire with 100 mw in Alborz Tunnel .

Air curtains are ventilation control devices for temporary or permanent use in underground mining. They can be used to deflect air into the unventilated areas such as dead end regions. Their design and installation are fundamental issues for maintaining a sufficient supply of fresh air and achieving effective air circulation and contaminant removal. At the same time, they should have little impact on the mine ventilation system. This paper presents the results of a two-dimensional CFD model, which examines the effects of air curtain dimension on fluid flow behavior in the mine dead end regions. By using CFD code Fluent, which uses model for fluid flow turbulence modeling, a 2D model of dead end was constructed. The result showed that with no brattice that streamlines proved weak compared to when a brattice was used. Depending on air curtain dimension, the use of an air curtain increases the airflow into the dead end region. Higher air curtain length and width showed a higher velocity near the right wall of the dead end, a minimum air re-circulation and, therefore, a better ventilation mechanism

Nowadays statistic approaches are widely used for rock slope stability, because they are simple and quick. The most famous of these methods for stability analysis of fractured rock masses is the key-block method (KBM). An extension to KBM, called key-group method (KGM) considers not only individual key-blocks but also groups of collapsible blocks into an iterative and progressive analysis. In iterations some of the groups can be extended and included a great part on the rock slope. One of the most important problems in this approach is to define the critical surface (critical key-group). In this paper we present an approach for finding the critical group which can be called directional key-group method, Because grouping of blocks progresses in the direction of slide surfaces of groups. This was carried out using the Mathematica high-level programming language. Finally it was shown that the proposed method yields more realistic results than the basic key-block method and a comparison with results obtained using a distinct element method (UDEC), demonstrated the ability of this method.