Influences of Crushed Fault Zone in the Stability of Zaker-Sorkhedizaj tunnel, NW Iran (original) (raw)
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Scientific Research and Essays, 2011
In this paper, a detailed geomechanical investigation of rock masses of North Water Convey Tunnel (NWCT) and its stability analysis has been carried out. The NWCT is located in the north of Iran and is to be constructed in-order to convey water for agriculture purposes. The main instability in the tunnel is joints and faults. The rocks mass encountered in the tunnel route are made of argillaceous, sandstone and shale. The tunnel has been divided into two parts, lot1 and lot2 having a length of 14 km and 26 km respectively. It is proposed to be constructed by telescopic shield method using a tunnel boring machine (TBM). In this study, the most suitable methods are utilized for the stability analysis and design of support of the tunnel. For the empirical investigation, the rock mass were classified based on RMR, Q, RSR, GSI and Rmi systems. The geomechanical properties of the rock mass were determined from the laboratory and field investigations. The results obtained from the analysis show that the tunnel is highly unstable due to the presence of a fault and hence strong supports are need in these regions. The support system used is concrete lining, as the tunnel in used for water conveyance. The tunnel alignment in lot1 is divided into 12 lithology types as; LI-SH1, LI-SH2, LI-SH3, LI-SH4, LI1, LI2, LI3, LI4, LI5, SI, CZ and FZ regions. Similarly, the tunnel alignment in lot2 is divided into 21 lithology types as; SH-ML1, SH-ML2, SH-ML3, MLI-SH1, ML-SH2, ML-SH3, ML-SH4, ML-SH5, SH-LS1, SH-LS2, SH-LS3, SH-LS4, LI2, LI3, LI4, LI5, LI6, LI-MA, LI-SH, CZ, FZ regions. A stability analysis is a necessity as during the tunneling instabilities, such as the presence of a shear zones, may cause an obstruction and delaying of TBM progressing rate. Key words: Tunnel boring, stability analysis, rock mass classification system, empirical and numerical methods, support pressure. w r n a J J RQD Q J J SRF = × × (1) This classification system includes six parameters of rock quality as following: 1. Rock quality designation (RQD) 2. The number of joint sets ( n J ) 3. The joint surface roughness ( r J ) 4. The degree of joint weathering and alteration ( a J ) 5. Joint water reduction factor ( w J )
Bulletin of Engineering Geology and the Environment, 2018
A methodology for designing a tunnel support system according to the actual ground conditions and the critical behaviour types is analysed in this paper. The methodology is justified with the principles of the New Austrian Tunnelling Method that incorporates the top heading and bench method. The role of the geological material and its implication in tunnel design, reinforced with advances in site investigation methods, cannot be based solely on the development of the geotechnical classification systems and the consequent quantification of the rock masses. Support requirements for rock masses with equal classification ratings can be different. The procedure presented in this study cannot bypass the geological and/or in situ characteristics dictating or influencing the tunnel behaviour compared with a standardised classification that could miss the specifics and particularities of and around a tunnel section. The step-by-step procedure is applied in a tunnel excavated in tectonically disturbed heterogeneous flysch sediments in Serbia. The complex structure of these materials, resulting from their depositional and tectonic history that includes severe faulting and folding, presents a challenge to geologists and engineers. The possible ground types are evaluated, and then, combined with the factors of the tunnel geometry, the primary stress condition, and the water conditions, several behaviour types are considered. These classified behaviour types, followed by the suitable mechanical properties that are required for effective tunnel engineering design, are the basis for the numerical design of the appropriate primary support measures to achieve stable tunnel conditions. The twin-tube, two-lane highway tunnel was successfully constructed without significant problems.
Geotechnical and geological studies of NWCT tunnel in Iran focusing on the stabilization analysis an
2011
In this paper, a detailed geomechanical investigation of rock masses of North Water Convey Tunnel (NWCT) and its stability analysis has been carried out. The NWCT is located in the north of Iran and is to be constructed in-order to convey water for agriculture purposes. The main instability in the tunnel is joints and faults. The rocks mass encountered in the tunnel route are made of argillaceous, sandstone and shale. The tunnel has been divided into two parts, lot1 and lot2 having a length of 14 km and 26 km respectively. It is proposed to be constructed by telescopic shield method using a tunnel boring machine (TBM). In this study, the most suitable methods are utilized for the stability analysis and design of support of the tunnel. For the empirical investigation, the rock mass were classified based on RMR, Q, RSR, GSI and Rmi systems. The geomechanical properties of the rock mass were determined from the laboratory and field investigations. The results obtained from the analysis...
Influence of the fault zone in shallow tunneling: A case study of Izmir Metro Tunnel
2013
Today, there is a great need for larger underground spaces for various purposes and hence, construction of new metro tunnels has become a necessity to meet the demand in urban life in spite of certain ground related difficulties such as fault zones, altered and fractured rock mass and ground water. This study has aimed at investigating the risky areas around a shallow metro tunnel in weak, faulted rocks and determining the effects of tunnel behavior on the structures on ground surface. Therefore, an attempt has been made to determine the risky areas on the line of the tunnel by field observations, laboratory work and computer modeling. Later, the data obtained from computer models have been compared to which obtained from in situ measurements. The results from modeling and in situ measurements were interpreted considering the current status of superstructure and the differences between pre-and post-excavation states in the ground. Finally the data obtained from the modeling analysis and measurements provided the necessity of strengthening the already used support system for the safety of the buildings on surface. Shortening the application ranges of the rock bolts, use of face nails with application of umbrella arc and jetgrout methods are among the precautions to be taken.
Design and construction issues of a motorway tunnel close to an active fault.
There is a general consensus in the engineering community that underground structures are not particularly vulnerable to earthquake effects and frequently, seismic effects are neglected in routine tunnel design. However, the possibility of a rock tunnel to suffer direct fault induced shearing during an earthquake, may question the safety or even the feasibility of a project. The Knimis tunnel, a twin tube motorway tunnel 2500 m long, has been constructed in central Greece during 2003-2006 in close proximity to an active fault, whose presence affected to a large extent design procedures, and decisions. The ability to avoid crossing the fault and coping with the earthquake shaking induced deformations, allowed a safe tunnel construction. In the present paper, the geologic and tectonic environment of the project is outlined, the earthquake hazard and relevant risk assessment is presented and the design constrains and objectives of the tunnel project are described. Experiences from the construction are also summarized.
Geohazards analysis of Pisa tunnel in a fractured incompetent rocks in Zagros Mountains, Iran
2011
The Pisa 2 tunnel with 740 m in length and 20°N trend is located along the Kazerun fault zone in Simply Folded Belt of Zagros, Iran. This tunnel has been excavated in the fractured incompetent marl layers with high expansive pressure of up to 2 kg/cm 2 . In this study, the geological hazards along the tunnel have been recognized and categorized. This study revealed that, in the long-term usage of the tunnel, the lining did not endure against the loading and the secondary leakages. It is mainly attributed due to the nonefficiencies of drainage and isolation systems in the tunnel site. Therefore, it caused asphalt damage, drainage damage, and wall distortion. FLAC 3D software has been used in this research. We conducted various analyses for pre-excavation stress states, syn-excavation, and post-excavation strain states. The results showed no indication of instability and critical deformations during the excavation time. It also revealed that due to the non-efficiencies of drainage and isolation systems against secondary leakages and conse-quently marl expansion, the volumetric and shear strains (i.e., expansions and displacements) have exceeded from the critical states of strain along the tunnel. For various remedy purpose, this paper attempted several measures that can be taken in order to modify the drainage and isolation systems along the tunnel area. The reconstruction of drainage systems with suitable reinforced concrete and adequate slope has been proposed. The width of channel and isolation of backside of lining and implementation of multi-order outlets (i.e., backside of lining) for draining of groundwater into where the main drainage systems are located in the tunnel gallery were suggested.
Geological structures and performance of the geodynamic processes can affect engineering projects on their own. Hence, the stability analysis and designing methods for foreseeing the retaining and support system for tunnels are diverse and came from different points of view. So this study seeks to present stability analysis of Imam Reza tunnel in Ardabil Sarcham Road with a special focus on the impact of future earthquakes on its stability using numerical methods. In this study, first designing and operating the initial structure with the height of 5.5 m and a semi-circular cross section. Secondly, drilling with the height of 3m and the width of 7.34 m and with a rectangle cross section. For stabilization, Rock Mass Rating (RMR) geomechanical classification systems and methods used. At the stabilization level, the materials were examined in laboratory, regarding the properties of sides and roof of the tunnel and pressure on them. The results of physical and mechanical experiments shown that the compressive strength ranged from 400 kg/cm 2 to 500 kg/cm 2 on average. The elastic modulus is between 12 and 13 GPa for the rocks. The Cohesion (C) ranged from 4-5MPa to 5 MPa and the Angle of Internal Friction (φ) is between 60ᵒ and 50ᵒ.
Geotechnical and Geological Engineering, 2021
The response of a massif to stresses generated by tunnel excavation depends essentially on the geological conditions, the geometry of the tunnel and its underground position. The major problem related to the construction of these structures is to ensure the stability of the whole tunnel-ground, by controlling the various deformation generated during the construction In this context, the present paper examines the effect of these conditions on the behavior of tunnels and the surrounding soil. The study is applied to a real tunnel, in this case the tunnel of Djebel El Ouahch, Algeria was taken as a reference model. The research includes a parametric study to evaluate the effect of several parameters on the behavior of the tunnel and surrounding soil such as the tunnel anchoring depth, the tunnel-soil interface rate, and the shape of the tunnel cross section. The analysis is performed using the PLAXIS 3D TUNNEL calculation code with an elastoplastic Mohr-coulomb model for the soil behavior. The results show that the strongest and most stable position is the mid-deep tunnel with a circular section, with a non-slip interface between the tunnel and the ground. These outcomes can help to understand the effects of various influences parameters which control the stability of the tunnel in a soil with bad characteristics.
This paper presents engineering geological investigations and the tunnel support design for the Boztepe tunnel of the Ordu Peripheral Highway located in northeast Turkey. In order to characterize the rock masses in Boztepe Tunnel which mainly consist of flysch (mostly alternation of sandstone, marl and siltstone) and pyroclastics (agglomerate and tuff), engineering geological investigations have been carried out in three stages as surface, subsurface and laboratory investigations. Rock mass classification systems (Geomechanics Classification System, RMR; Norwegian Geotechnical Institution Q-system and Geological Strength Index, GSI) have been utilized through information obtained from engineering geological investigations. Sixteen boreholes with a total length of 1497 m have been drilled to assist and verify rock mass classifications. Approximately seventy five rock samples have been obtained for rock mechanics tests. The information provided from all the engineering geological investigation stages has been handled in the characterization of the rock masses at the tunnel elevation. In an attempt to check the validity of empirical tunnel supports of the various rock mass classification systems, stress analysis around the tunnel opening has been executed by the 2D finite element analysis program, Phase 2 where rock mass data obtained through the rock mass classification systems have been utilized as input data. In these analyses, the empirically proposed support systems have been found to be successful to prevent further deformations around the tunnel openings.