Master's Thesis Final Presentation (original) (raw)
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NUMERICAL SIMULATION OF TUNNEL SUPPORT SYSTEM BY USING FEM – A PARAMETRIC STUDY
In the majority of the modern rock tunnels, the deformation/stability of the tunnel is controlled by a combination of reinforcement and support system. In this study an attempt has been made to assess the tunnel support system in highly jointed rock mass by using Finite Element method (FEM), a continuum approach. A Tunnel of 5.0m diameter has been studied which passes through weak rock mass of Phyllite and Schistose Quartzite lithology by NATM technique to reduce of environment impact and land slide hazards. Geological strength Index Rock mass classification has been done based on the surface geological mapping of Phyllite and Schistose Quartzite. To support the excavated rock mass, primary and secondary support system based on the RMR & Q system has been developed by means of rock bolt, shotcrete with wire mesh and lattice girders. The initial support for underground excavation is followed by secondary lining of RCC concrete. NATM is characterized by the fact that tunnel excavated in different parts (Heading, Benching, Invert and multi stages). This paper briefly describes the associated ground uncertainty and it's effective contribution over the design of tunnel support system by using continuum modelling. Now a day, it is a cost and time effective tool to optimize the support system based on the observational method. Numerical modelling has also been used to prediction of rock mass stress regime and deformational behavior. It is also important to choose an appropriate tool to analyses the data, otherwise it may mislead the output and planning.
Reducing deformation effect of tunnel with Non-Deformable Support System by Jointed Rock Mass Model
Numerical modeling has been used widely in mining and construction industries in recent years. The most important issue in engineering projects designed with numerical modeling is accurate modeling of rock mass behavior. If the rock mass behavior is modeled accurately, fewer problems will be faced during field application of projects. Selection of the true material model is a very important issue in numerical modeling for the tunnel projects. Non-Deformable Support System (NDSS), which will be mentioned in the scope of this research, does not mean that it does not permit any deformation or is a very stiff system. NDSS is a support system that does not permit deformations exceeding specified deformation amounts which are calculated with determination of the accurate rock mass behavior by the true material model and it must be evaluated with support system and excavation advance specifically. The origin of the paper is that numerical modeling provides more comfortable results in tunneling in case one can determine rock mass deformation and failure behavior appropriately. In (NDSS), however, support system element can only be determined by proper numerical modeling analysis. Moreover, deformation values determined by NDSS analysis are accepted as limit values. Therefore, applied support system should be within deformation tolerance limits determined by NDSS analysis. Briefly, this paper is related to NDSS that should be determined by numerical modeling analysis. In this research, in regard to the excessive deformations in T-35 tunnel which is one of the 33 tunnels of Ankara–Istanbul High-Speed Railway Project, results of the in situ measurements in the tunnel excavated with the new developed NDSS and results of the numerical model made with Jointed Rock Mass Model have been compared. It is determined that the results of the numerical modeling and the in situ measurements are very consistent with each other.
Stress Analysis Around Tunnels During Construction Stages Using Finite Elements Method
ABSTRACT In this study, the stresses around a tunnel during construction stages are discussed. For this purpose, the finite element method (FEM) was adopted as an effective approach to analyze the problem using (SIGMA/W) program. The research includes the study of the behavior of soil due to excavation of tunnel by calculating the displacements and stresses in three positions of tunnel (crown, wall, and invert) during the various stages of construction. The finite element analyses were carried out using (Elastic- plastic) and (linear elastic) models for the soil and the concrete liner respectively. From the results, it can be noticed that increasing the number of excavation stages (using six stages) decreases the displacement comparing with excavation using one stage. Keywords: Tunnels, Construction stages, Stresses, Finite elements.
Applied Mathematical Modelling, 2021
In this article, an alternative numerical procedure to calculate displacements and stresses of supported circular tunnels is proposed, considering the whole process of tunnel advancement, and sequential installation of the primary and secondary support systems. In the derivation, the plastic area of the rock mass is divided into a large number of annulus around the tunnel, and then the Finite Difference Method is employed. First, the strain-softening behaviour model is taken to simulate the post-failure behaviour of the rock mass. Furthermore, the Mohr-Coulomb or the Hoek-Brown failure criteria can be chosen, a nonassociated plastic flow rule is assumed and the dilatancy of the rock mass is considered. After that, the fictitious support forces concept is used to simulate the process of tunnel advancement, and thus, the three-dimensional effect of the tunnel face is considered. Finally, the solutions of displacements and stresses for the rock mass and the supports can be obtained, by using the compatibility conditions of stresses and displacements at both rock-support and support-support interfaces. The results obtained from these solutions agree well with those of the self-similar solutions for circular openings, and the compatibility conditions of supported tunnels were verified. The proposed method has been compared with the convergence-confinement method. Parametric analyses are then carried out to investigate the sensitivity of support forces and displacements to the rock mass behaviour model selection. Then, the application of the proposed solutions in the design of tunnels is presented. The proposed method provides a convenient alternative method for the preliminary design of tunnels.
Rock mechanics or rock engineering was developed since the 1960s, but the underground excavation in rocks is still at its infant stages. The construction and maintenance of underground rock tunnel or caverns require prudent and detailed designs in the excavation process. To be able to predict the effects of the excavation process and estimate the effectiveness of the support designs, one has to understand the properties of the rock materials and their likely behaviour with the physical elements. This places great importance on the study of the deformation of the rock tunnel during excavation, particularly because deformations such as inward displacement can influence its stability. In this project, using stress analysis, investigations on the extent of deformation of rock tunnels during excavation will be conducted. Also uncover out the factors that contribute to the instability and displacement of underground excavations.
A Review study on the Analysis and Design of Underground Tunnel Support by FEM
IRJET, 2022
Underground structures have recently gained importance all over the world. Successfully completed these projects are based on careful and realistic design, one that is neither optimistic, conservative, and considerate. It is the need of the moment. This article presents a comparative study of media design, such as Terzhagi's load theory. Quantitative methods for rock mass quality (Q), and rock mass assessment on Bieniawski and RS2 Numerical modeling. The results showed that the final support measures such as casting, thickness, rocky dome, length, the frequency, and requirements of steel support are better. Based on engineering reasoning and analytical methods, PSAs for tunnels have been obtained.
The effect of disturbance factor on the stability of tunnels (Case study: Tunnel No.2 of Kurdistan)
Disturbance factor (D) is related to excavation method and cause damage and stress relief in the rock masses. The convergence and plastic zone around tunnels depends on the disturbance factor of rocks.This study has been in the tunnel No.2 of Kurdistan in NW of Iran which is composed of shale rocks. In tunnel modeling, different disturbance factors(0 to 1) areanalyzed using phase2 software and the amount of displacement and extent of plastic zone in around the tunnelis determined. The obtain results show that by increasing of disturbance factor, the displacement and plastic zone around the tunnel has increased and the most increase has occurred in disturbance factors 0.8 to 1. Therefore, for excavation of this tunnel, the blasting method should not be used and instead of it, the mechanical methods must be used.
TO STUDY(CASE) THE PRODUCTIVITY OF ROCK SUPPORTS IN TUNNELING PROJECTS
For underground projects and works throughout the world tunnels are very significant. Diverse geological conditions are observed during tunneling works. During tunneling rock mass alongside the tunnel becomes unstable due to blasting, benching and other methods of tunneling. This unstable rock mass is to be stabilized for effective working and long life of tunnel. Controlling and recording of such process is very important during the excavation in underground works. Tunneling works also consume the major cost of underground projects as well as immense time is consumed during tunneling and rock mass stabilization including reworks.Rock supports being a vital part underground projects and also foremost contributor to expenditure and time, is one of the region where effort desired to be done. The installation of tunnel rock support systems is usually not planned because of strange conditions of rock can be observed
Studia Geotechnica et Mechanica, 2016
The paper analyses the geological conditions of study area, rock mass strength parameters with suitable support structure propositions for the under construction Nahakki tunnel in Mohmand Agency. Geology of study area varies from mica schist to graphitic marble/phyllite to schist. The tunnel ground is classified and divided by the empisical classification systems like Rock mass rating (RMR), Q system (Q), and Geological strength index (GSI). Tunnel support measures are selected based on RMR and Q classification systems. Computer based finite element analysis (FEM) has given yet another dimension to design approach. FEM software Phase2 version 7.017 is used to calculate and compare deformations and stress concentrations around the tunnel, analyze interaction of support systems with excavated rock masses and verify and check the validity of empirically determined excavation and support systems.
Elastoplastic numerical calculation model for three dimensional finite element for tunnel is set up based on PLAXIS 3D and displacement prediction model for tunnel surrounding rock is established based on improved grey prediction theory; with stress distribution, strain pattern and displacement variation pattern in excavation process of tunnel analyzed, relation between parameter and deformation studied, calculation procedure and method for improved grey prediction theory presented so as to obtain settlement and displacement of arch crown in front of tunnel face within certain extent in tunnel excavation process by prediction. Suitong Tunnel is taken as test subject to carry out contrastive analysis relation among three displacement-time curves namely value of simulating calculation, predicted value and measured value and perform cross validation of the above mentioned three values. The validation result shows that the model is able to properly embody deformation pattern of surrounding rock, with prediction precision of displacement value satisfying requirement of specification and having larger scope of application in prediction of surrounding rock stability than that of other methods. The abstract section is mandatory, with a word limit of 200 words. The scope, aims, results and conclusions may be summarized here. Avoid inserting any reference in this section.