Classification of fault zones in mechanized tunneling projects (original) (raw)
Related papers
2011
There are many factors such as equipments, management, personnel skills and ground condition that affected the TBM performance and mechanized excavation. The adverse geological condition that encountered in the tunnel is one of the most important parameters that affect the excavation process. Nature of the adverse geological conditions and fuzziness of them cause to decrease the accuracy of their prediction. It seems there are some evidences that can lead us to detect the problematic zones more exactly. To research the role of the geologic evidences in the collapse zones detection, the data gathered from a water conveyance tunnel excavated in central Iran were considered and analyzed. The rock formations along the tunnel path consist of metamorphic and sedimentary rocks aged from Jurassic to cretaceous. During the tunnel excavation the adverse geological conditions several times cause to collapse of tunnel and subsequently sticking of TBM. The parameters such as quartz content, fragment size and maximum fragment size of cuttings and amount of injected pea gravel behind the lining were monitored during the excavation, especially in collapse zones. The mentioned parameters have a variable rate along the tunnel path and these variations depend on the geologic condition. Quartz content of cutting materials in the collapse zones are higher than surrounding ground of these zones and the fragment size and maximum size of fragments in the collapse zones show an increasing trend relative to the normal condition of ground. Also, the injected pea gravel in collapses decreases in respect of other parts of tunnel. The results of this study show that the monitoring of variation in some geological parameters such as the amount of secondary minerals in cutting materials and the size of cutting fragments, also the amount of injected pea behind the lining of tunnel can help us to better prediction of collapse zones in the metamorphic rocks.
Influences of Crushed Fault Zone in the Stability of Zaker-Sorkhedizaj tunnel, NW Iran
2012
This paper presents the results of engineering geological studies of rock masses in the crushed fault zone along a road tunnel in NW Iran. The tunnel is to cross the Western Alborz Mountain Range through 530 m in length with 11.2 m span and 8 m height. Eocene tuffs and andesites crop out in whole of the tunnel route. The final segment of tunnel is composed of porphyry andesites and a strike-slip fault with reverse component has caused the crushed zone with 20-25 m extent and 20 m cover. Empirical and numerical methods were combined for safe tunnel design in the crushed rock masses. The results of the evaluations show that the crushed rock masses is completely instable in the tunnel and need to an especially support system. The performances of the proposed support systems were analyzed by means of numerical analysis. After applying the suggested support system to the crushed rock masses, tunnel deformation and the yielded elements around the tunnel decreased significantly thus it was...
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.
Arabian Journal of Geosciences, 2014
In this paper, the correlations between the different measurements of rock brittleness (i.e., B 1 , B 2 , B 3 , and BI) and the penetration rate (PR) of tunnel boring machine (TBM) through Zagros long tunnel were evaluated. According to the results of simple regression analyses, there was no correlation between the penetration rate of TBM and the brittleness of B 1 , but stronger log-linear correlations have been observed between the penetration rate of TBM and the B 2 , B 3 , and BI brittleness indices. As part of the present study, correlations between some of rock mass classification systems (RQD, RMR, GSI, Q, and Q TBM) and penetration rate of TBM have been investigated. The results of simple regression analyses showed that the first four rock mass classification systems did not exhibit a good correlation with the TBM penetration rate, but the Q TBM had strong correlation with that. Multiple linear regression (MLR) analyses were applied for estimating the TBM penetration rate based on three properties of the rocks (porosity (n), brittleness of B 3 , and elastic modulus (E) of intact rock) and rock mass quality system (Q). Also, in this study, artificial neural network (ANN) analyses were applied on the data to develop predictive models for the penetration rate of TBM from porosity, brittleness of B 3 , elastic modulus, and Q values. The comparison of the models produced from ANN and MLR analyses using the coefficients of determination showed that the ANN models for predicting the TBM penetration rate were more reliable than the MLR models.
Geotechnical considerations on TBM tunneling in rock mass
The industry deals with underground excavation has always shown a major interest in the use of Tunnel Boring Machine (TBM) that is full-face tool to excavate rock, because of their demonstrated capabilities in attaining high rates of advance in tunnel construction. TBM tunneling may differ from other tunneling methods such as; drill and blast, due to the high level of machinerock interaction. Accurate estimates of machine performance are a crucial part of any mechanical tunneling. It is almost impossible for owners or contractors to make realistic evaluations of time and cost required for completing a project, without estimating the machine advancement. Intact rock properties, including uniaxial compressive strength, Brazilian tensile strength and brittleness of rock, and also rock mass properties such as orientation of discontinuities, with machine specifications could be used for investigating TBM performance in rock mass. This paper presents the results of some case histories in TBM tunneling, field and laboratory data processing together with recent improvement for estimating TBM performance in rock mass.
Tunnelling and Underground Space Technology, 2019
Mechanized tunneling, like other tunneling methods, is not an exception to dealing with complex geological structures in its direction. Therefore, the accurate perception of the geological structures and anomalous through the tunnel path and the challenges ahead of TBM can minimize the operational risk. The faults are complicated, loose, seismic, and saturated structures that present a great deal of danger when passing the tunnel from them, and each of these events, in turn, has the potential to stop the project and exert high economic costs. The instability of the tunnel environments and tunnel face due to the higher amount of stress concentration than the resistance of the host rock, pulpy material flowing from inside of the faults and water inrush are the most important events that TBM faced them through the fault zones. Hence, using the appropriate tool for realizing the operational model can be a considerable help in predicting problems. In this research, using precision numerical methods, accurate simulation of TBM motion was carried out to the excavation of Water Transmission Tunnel, Iran. The Safaroud water transmission tunnel is one of the longest Iranian water transmission tunnels that passes through numerous fault zones along its path. One of the main faults in this area is the Lalehzar fault with 40 m width which motivates us to utilize predicting procedure. The main purpose of this research is numerical modeling of mechanized tunneling in fault zone using FLAC3D and Phase2 software and selection of suitable reinforcement strategies for passing TBM from the fault zone. The results of numerical modeling illustrate the instability of the tunnel in the Lalehzar fault zone. Due to tunnel instability in this zone, reinforcement operations must be taken into account to stabilize the tunnel environment. The numerical modeling of the several reinforcement operations in the fault zone were simulated and we conclude that the combination of umbrella arch and radial grouting method are the most suitable strategies for passing TBM from the Lalehzar fault zone.
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 controls on the breakthrough of tunnel boring machines in hard rock crystalline terrains
Geological factors including the orientation, condition and frequency of discontinuities in rock mass, and also intact rock properties such as strength and brittleness are crucial parameters for performance analysis of hard rock TBMs. These data along with machine specifications such as thrust and power allow the appraisal and prediction of machine penetration rates. Recently completed projects include the Queens freshwater, Manapouri Second tailrace hydropower and the Milyang hydropower tunnels are assessed to investigate the effect of geological and rock mass conditions on the penetrability of utilized full face tunneling machines. Compilation of the experiences and datasets obtained from these projects indicates that even though intact rock properties including mineralogy, texture, metamorphic grade, hardness, strength and brittleness have an effect on the breakthrough of the machines, the most significant and controlling geological parameters are the orientation, condition and frequency of discontinuities in rock mass encountered along the tunnel. Thus, the geological conditions of the site should be investigated in early stage of the constructed tunnel and continuously updated until projects are completed.
TBM Tunneling Problems through Subterranean Rivers: An Evaluation of Nowsud Tunnel in the Iran
Research Square (Research Square), 2022
Fault induced subterranean rivers create a major challenge of tunnel construction. They arises serious problems such as TBM performance, structural stability of segmental rings, destruction of TBM components, large water in ow and regional drawdown. Since, the faulted cavity is one of the infrequent adverse geological conditions, not much executive experience has been provided. The TBM of Nowsud tunnel encountered the fault cavities in three places wherein groundwater inrushes from 4.0 to 0.36 m3/s and delayed for 8 months. In each cavity, the main items such as prospecting methods, water inrush and drawdown, type of TBM damages, TBM performance, managing of TBM advance in relation to water discharge, estimation of rockfall impact force and method of segments strengthening were considered. It is found that the fault cavities create in extension part of strike slip faults. In large faults, the TBM could encounter with accessory cavities which hydraulically interconnected to main cavity. Based on gained experiences, TBM excavation along with probe drillings, TSP and appraisal of water discharge, eliminates the hazard of adverse condition. The TBM submerging and damage of other equipment occurs in short term transient part of ow regime while the need to run and capacity of the pumping system are controlled by steady state part. Since, the most of active and passive forces, acting on the TBM, were absent, the re-advancement carried out by quasi-single mode. In this case, the excessive pressures cause the damage stepping of segmental rings. The rockfall impact load was calculated by analytical and numerical methods.