EPB TBM Research Articles

Arroyo Vega flood relief tunnel design

AbstractThis article aims to present structural and geotechnical design challenges of the flood relief project ”Segundo Emisario del Arroyo Vega“, part of Buenos Aires city hydraulic master plan. Works comprised the execution of an 8.4 km‐long tunnel for relief of the existing sewer network. Tunnel alignment develops in a highly populated area, with important interferences such as two metro lines, three railway lines and a main potable water tunnel. All tunnel sections extend mostly within firm, silty soils. Overburden varies between 15 and 25 m. The downstream section was executed with a 6.1 m‐diameter Earth pressure Balance Tunnel Boring Machine (EPB TBM) launched from a 35 m‐diameter shaft with water table pressures up to 200 kPa. Break‐in was performed across a watertight, plastic diaphragm wall cell, which allowed safe shaft wall manual demolition, resulting in a very safe TBM launch. The tunnel upstream section, 2.85 m in diameter, was executed using pipe jacking technology, with the peculiarity of using bidirectional launch shafts along its alignment. To allow water entrance from existing system – through flow diversion chambers – into the new relief tunnel, openings were made in the TBM tunnel, with connection areas of 4 to 7 m2. Its design was particularly challenging, given that unbolted segmental lining was used.

The effect of rock weathering and transition zones on the performance of an EPB-TBM in complex geology near Istanbul, Turkey

The new Istanbul Airport is being constructed over an old coal field area, 35 km away from the city center. The construction of a rail link between the city and the airport entails the excavation of tunnels in the areas of complex geology, creating several problems for tunnel construction. This paper summarizes the effect of different grades of weathering of an interbedded sandstone-mudstone-siltstone sequence and transition zones on the performance of an earth pressure balance tunnel boring machine (EPB-TBM) during this work. The variation of EPB pressure, TBM thrust, torque, penetration, and specific energy values were analyzed in different lithologies and weathering zones and with respect to the attitude of transition zones between different materials. Normalized thrust and torque values considered in respect of penetration rate and EPB pressure showed that the attitude of transition zone on TBM performance is strictly dependent on the position of each geologic formation in the respect to the other, inclined or horizontal. To be specific, in an inclined transition zone, the thrust and torque values were almost double compared to the values obtained in a horizontal transition zone in the same lithology. This was probably due to increased over-break in inclined transition zones, which created loose material that accumulated in front of the cutter head. However, further case studies would be required definitely to confirm this. Mean normalized thrust and torque values were almost half in moderately/highly weathered sandstone compared to fresh/slightly weathered sandstone. The highest mean penetration of 28 mm/rev and mean lowest specific energy of 2.4 kWh/m3 were obtained in transition zone between claystone with silty sand and highly weathered interbedded sandstone-mudstone-siltstone. Due to impact effects, increased disc consumption was experienced where passage was made from low strength due to high strength formations, with up to one disc per 115 m3 of excavated material in the transition zones included in the study. The relatively high production rates were achieved, which attributed to a combination of logging daily the face conditions accompanied by appropriate adjustments of soil conditioning agents (FIR-foam injection ratio and FER foam expansion ratio values) and anti-clogging agents to control the sticking behavior of the spoil. The impact of different ground conditions on EPB-TBM performance in different projects is also discussed in relation to the results obtained in this study. It is believed that this research will help to manage better mechanized tunneling activities in similar conditions.

Analysis of the mathematical modelling results of displacements and deformations induced by the construction of the escalator tunnel of "Mining Institute” station in Saint Petersburg

The article presents the results of mathematical modelling of geomechanical processes that occur during the construction of an escalator tunnel using EPB TBM at the «Mining Institute» station in Saint Petersburg. A numerical model was built using the finite element method implemented in «Plaxis 3D» software. Hardening soil model was used for modelling of soil massif. The analysis of the distribution of displacements and deformations in the main cross-sections of the displacement trough is performed. Issues of assessing the harmful effects of underground construction on undermined buildings and structures are considered. Based on the research, we can conclude that the construction of a tunnel is safe for undermined buildings with strict tunnelling technologies compliance.

Possibility of using torvane shear testing device for soil conditioning optimization

Determining the optimum amount of soil conditioning agents and the behavior of excavated soil + foaming agent mixture during excavation process play an important role in the design and management of EPB TBM tunneling. Although there are some means of defining optimum soil conditioning parameters, there is still a requirement for new and effective methods. This study aims to analyze the possibility of using a torvane shear testing device as a means of soil conditioning optimization. The soil samples used in the experimental studies were obtained from shaft excavations of Zeytinburnu Ayvali 2 Wastewater Tunnel and Mahmutbey-Mecidiyeköy Metro Tunnel located in Istanbul and industrial kaolinite was also used for soil conditioning experiments. The natural water content, specific gravity, size distribution and consistency limits of the soil samples were determined. An anticlay foaming agent was used in the tests. Classical soil conditioning tests including mixing (with power consumption and sticking amount measurements), cone penetrometer, and vane shear (torvane type) tests suggested in this study were performed on the mixture of soil and foaming agent at natural water contents. Foam concentration of 3% and foam expansion ratio of 16 were kept constant and foam injection ratio was varied.The laboratory studies indicated that optimum conditioning parameters and consistency of conditioned soils could be determined by torvane shear testing. There were strong relationships between the results of classical testing methods and the torvane shear device. Using torvane shear testing for soil conditioning purpose would provide an inexpensive and easy method to measure the shear strength of conditioned soils. Additional studies would increase reliability of this method by testing different fine-grained soils at different soil conditioning parameters.

Torque fluctuation analysis and penetration prediction of EPB TBM in rock–soil interface mixed ground

Tunnelling in rock–soil interface (RSI) mixed ground often results in high cutterhead torque and torque fluctuation. Therefore, choosing a reasonable penetration rate to reduce the torque and improve tunnelling efficiency is paramount. In this study, considering the interaction between the cutterhead and RSI, an excavation torque model was first established based on the CSM model for a disc cutter and a new three-dimensional limit analysis model for a scraper. Further, considering the friction at the cutterhead in RSI, a total torque model was developed. Based on the study of excavation torque change characteristics when the cutterhead located in RSI, a simplified relationship among torque, face composition, penetration and rock strength was established. Subsequently, a new prediction index, Mixed-face Torque Penetration Index (MTPI), which includes the torque exerted by the TBM in the calculated penetration rate, was proposed to evaluate rock-soil mixed face cutability. This index allows for the inclusion of a TBM–rock mass and TBM–soil interaction factor. The methodology based on MTPI and TBM torque capacity to predict the penetration rate of the machine in different geological conditions and TBM specifications was proposed. Finally, the predictive capability of the proposed torque model and penetration prediction model were validated by the good agreement between the predictions and field measurement data from the Guangzhou Metro Line 21 tunnel in China. This study can match the tunneling parameters with the geological conditions within the limitation of TBM and provide guidance for TBM operation or evaluate whether the TBM satisfies the project schedule.

Effect of Clogging on EPB TBM Performance: A Case Study in Akfirat Waste Water Tunnel, Turkey

Earth pressure balance tunnel boring machines (EPB TBMs) may sometimes face, during excavation of soft soils, with some challenges of which one of them occurs when mixture of the excavated soil and water generates a sticky muck that adheres to the metal sections of the TBM such as cutterhead, cutting tools and transportation system. This phenomenon commonly referred as clogging leading to blockages and stoppages that decrease the advance rate and increase the project costs, since the excavation process could only be continued after cleaning operation of the blocked parts. This study was conducted in Istanbul Akfirat Waste Water Tunnel to determine the effects of clogging and foam injection ratio (FIR) on the EPB TBM excavation performance (torque, EPB TBM thrust, specific energy, unit penetration rate and/or net cutting rate). The studied tunnel section was divided in three zones with respect to clogging behavior of soils such as high, medium and low clogging zones. Soil sample could only be collected from the tunnel face belonging to high clogging zone during excavation of the tail tunnel. Particle size distribution was analyzed and Atterberg limit tests were conducted on the soil sample. In order to investigate the consistency behavior of the soil sample, slump and flow table tests were performed with changing water contents. Flow table test was performed with two different anticlay foams to investigate the effect of soil conditioning on consistency behavior of the soil sample. Field observations indicated that increasing clogging potential decreased the overall performance (daily advance rates) due to muck transportation problems and frequent stoppages to clean up the clogged cutterhead. Increased FIR reduced the transportation problems and stoppages. However, data analysis indicated that increasing FIR did not improve the penetration rate for open mode (without face pressure) working conditions since the soil on the face was quite firm for the anticlay foam to penetrate into. The mean FIR values were measured three times higher for the high clogging zone than for the low clogging zone. The mean specific energy values for the low and medium clogging zones were almost the same and half of the value obtained during excavation of high clogging zone. The EPB TBM thrust and cutterhead torque values did not exhibit any correlation with adhesion potential.

Control of EPB TBM tunneling parameters to mitigate the effects on Dambovita river structures

This paper presents an assessment of the impact of tunnelling of the M5 Metro line in Bucharest, and its associated risks on Dambovita river development located in the influence zone of tunnelling operation. During the metro performance the undercrossing of the hydraulic works related to the Dambovita River was required. The Dambovita River hydraulic development is made of 2 main components – the upper clean water channel and the sewage/drainage system cassette, placed below (the base slab of the channel representing the roof of the cassette). On the left river bank, the B0 collector is an old structure with uncertain technical condition Tunnelling in proximity of existing development introduces deformations in both structures and in turn induces additional axial and bending forces. In modern mechanized tunnelling, ground convergence is controlled through balancing the earth pressure at the tunnel face. Reducing ground deformation can consequently lower the additional deformations and forces and lessen the associated construction risk. In this paper, a detailed finite element modelling was performed to simulate the sequence of construction works. The model was calibrated based on the measured settlements behind the face. Based on model results the undercrossing area of influence is revealed. Recommendations regarding the tunnelling works are made in order to avoid any damages to the existing facilities.

A study of displacements of structures in the vicinity of deep excavation

In the article the aspects concerning the excavation impact and values of displacements of the ground and existing structures in the vicinity of deep excavations are presented. Four cases of excavations in typical Quaternary soils of Warsaw executed in the close proximity to the existing metro tunnels (and station) are described with special emphasis put on the description and analysis of experimental data including in-situ measurements of vertical displacements of existing metro structures. The discussion and conclusions on the displacements of structures (EPB TBM tunnels with segmental lining and cubature metro stations) in the vicinity of excavations depending on their location relative to excavation are presented. Typical ranges of displacements in relation to the depth, distance and type of structures influenced by deep excavations are given. Equation for the prediction of vertical displacements of TBM tunnels in the vicinity of deep excavation is formulated. In addition, the 2D finite element modelling of one of the described example cases is made and presented in detail. The results of FE analysis are compared to the actual experimental monitoring data.

Design Aspects of Under-Passing a City’s Heritage Landmark with EPB Machines Under Low Overburden; The Case of Chandpole Gate in Jaipur Metro, India

UG1B is the first underground Metro Line under construction in Jaipur which is the capital of Rajastan (India). The twin bore tunnel route pass through the historical centre of the old city of Jaipur called “Pink City”. Significant historical monuments of world’s heritage, such as Hawa Mahal, Jantar Mantar, Isarlat tower, Tripolia Gate (main entrance to the city palace) and Chandpole Gate, are within the greater influence zone of the project. Specifically, the twin bore TBM tunnel passed 4.5 m under the foundation of Chandpole Gate which is one of the main significant historical entrances to the old city, almost 300 years old. The paper addresses the main design aspects of the under-passing of Chandpole Gate in Jaipur by two EPB TBM machines, and introduces the new method which is used for designing these shallow tunnels, by combining the usage of the analytical solution of Massinas and Sakellariou (Geotechnique 59:691–701, 2009) with detailed numerical analysis; the innovative closed form solution has been applied to assess the required support pressure, whereas its results have been used as input to 3-D numerical analyses of tunnel excavation below the Gate to predict induced settlements. The route from the evaluation of the geotechnical model, to the study of the structural and foundation system of the monument, the approach to the necessary tunnel face retaining pressure to be maintained by the EPB machines during under passing and the prediction of the surface and Gate settlement due to tunneling operations is introduced and analyzed. Monitoring of TBM operation parameters and settlement measurements during construction are presented in the form of comparative diagrams and graphs, to illustrate the application of the main design recommendations and verify the design predictions, in terms of applied face pressure and resulting settlements of the Chandpole Gate. Comparison has shown that main recommendations, as derived from the new proposed method of design and followed during the tunnelling operations, resulted to a successful under-passing of Chandpole Gate, with induced settlements within the predicted, permissible limits.

Characterizing the influence of stress on foam conditioned sand for EPB tunneling

To guarantee effective EPB TBM face support and performance, it is necessary to understand the mechanical behavior of foam-conditioned soil under realistic pressure conditions. This paper investigates the behavior of foam-conditioned soil under applied total pressures of up to 5bar. The study examines the effect of total stress, effective stress, and key soil parameter void ratio on the behavior of foam-conditioned soil. Shear strength and compression tests were carried out in a field-portable pressurized test chamber on two granular soils with a variety of foam parameters. The results demonstrate that void ratio and effective stress are the main factors that influence the performance of foam-conditioned soil. It was determined that a certain ratio of void ratio to maximum void ratio was required to prevent the development of appreciable effective stress and, thus, high shear strength and low compressibility.

Empirical modeling for predicting excavation performance of EPB TBM based on soil properties

This study was conducted in order to determine the effects of soil properties on the excavation performance of an earth pressure balance tunnel boring machine (EPB TBM) used in the Istanbul Ayvali Waste Water Tunnel Project in the development of empirical performance prediction models. The tunnel alignment was divided into three general sections in terms of geological and geotechnical conditions. Soil samples were collected from 14 different locations along these sections of approximately 60 segment rings, and subjected to laboratory tests in order to determine the particle size distribution, natural water content, consistency limits (liquid limit, plastic limit, plasticity index, and consistency index), vane shear strength, fall cone penetration depth, unified soil classification, and clogging potential. The field performance data were obtained from the EPB TBM data logger, which operated in open mode without any face pressure being applied. Data analysis was carried out by statistically linking the net cutterhead torque, TBM thrust force, instantaneous cutting rate, and field-specific energy with the geotechnical properties of the excavated clayey soil by using single and linear multi-variable regression methods. The results indicate that, while the performance parameters are similar for the silty sand and lean (low plasticity) clay, the cutterhead torque and field-specific energy are higher, and the thrust and instantaneous cutting rate are lower, for high plasticity clays. The vane shear strength and consistency index may be used for predicting the cutterhead torque, fall cone penetration depth for the thrust force, plastic limit for the instantaneous cutting rate, and plastic limit and plasticity index, as well as the consistency index, for field-specific energy predictions. Additional studies are required to provide more reliable and generalized prediction models, by increasing the number of laboratory and field tests for different soil types and performance data for different EPB TBMs.

Apparent density evaluation methods to assess the effectiveness of soil conditioning

A study was performed on the University Link and Northgate Link projects in Seattle, WA, to investigate the use of apparent density evaluation methods for the identification of air pockets and plugging issues in the chamber of EPB TBMs. Both air pockets and plugging issues can result from improper soil conditioning and the TBM’s inability to mix the soil properly with the conditioning agents. An apparent density below unity indicates the formation of an air pocket in the top part of the chamber and an apparent density above the virgin soil density points to developing plugging issues in the cutterhead bays and pressurized chamber. From the conducted study it can be concluded that the presented apparent density evaluation methods are an effective way to identify issues in the excavation chamber of an EPB TBM and can be used as a mean to improve the soil conditioning process.

An assessment method for fine‐grained sedimentary materials excavated by EPB TBM

AbstractThe aims of this study are to find a solution for the problems (lumping, adhesion, and clogging) encountered with fine‐grained sedimentary materials, minimize the time and cost of excavation, and decrease the potential environmental effects due to soil conditioning chemicals used in the process of excavating a waste water tunnel. Therefore, this study will contribute important technical knowledge regarding design and implementation of excavation with TBM to the mining and construction industries as well as for optimization in mechanical engineering.In this research, real‐time machine operational parameters recorded by EPB TBM and actual geotechnical parameters in an Istanbul‐Büyükcekmece Wastewater Tunnel at seven selected tunnel sections were used as input data for the back analysis and assessment method. The method covers excavated materials with: (1) water and (2) soil conditioning chemicals. The influence of water and soil‐conditioning chemicals of different proportions on torque, thrust, advance rate of the TBM, and plasticity and consistency indices of the material were investigated. Finally, integrated data were evaluated by multiple linear regression models.

Pressurised TBM tunnelling in mixed face conditions resulting from tropical weathering of igneous rock

Weathering is a process that turns rock into soil. Deep weathering is prevalent in tropical and sub-tropical areas. The resulting sub-surface conditions can be very onerous for tunnelling, with tunnel drives commonly encountering a significant proportion of mixed face conditions, comprising partly rock and partly soil. Problems that have been encountered have included: inability to maintain the face pressure, ground loss, sinkholes, slow rates of tunnelling, rapid tool wear, damage to tools, mixing arms and other parts of the TBM, very frequent and long interventions, clogging and blow-outs. The nature and extent of the problems on any particular tunnel have depended on the type and design of the TBM, the nature of the rock and the proportion of the tunnel in mixed ground. In Singapore this has resulted in a change from mainly EPB to mainly slurry tunnelling in weathered igneous rock; however, predominantly EPB TBMs have been used in weathered sedimentary rock. Information from EPB and slurry TBM drives is used to illustrate the issues involved.

New Method of Surface Settlement Prediction for Saint-petersburg Metro Escalator Tunnels Excavated by EPB TBM

The article describes a new technology of escalator tunnel construction using earth pressure balance tunnel-boring machines (EPB TBM) in complex geological conditions of St. Petersburg soils. The results of field surveying observations of settlements and strain calculations arisen from the construction of the escalator tunnels of the St. Petersburg metro “Obvodny kanal”, “Admiralteyskaya”, “Spasskaya” stations are presented. It is established that the evolving strain can be dangerous for undermining buildings and structures. The method of escalator tunnel construction numerical modeling based on the finite element method is used to evaluate the qualitative relations of the geomechanical processes. A new method of surface settlement prediction is based on the results of complex processing of field data and results of construction numerical modeling. This method involves determination of the following characteristics of the displacement process: the position of the point of the maximum settlement in a subsidence trough, the size of a subsidence trough, the value of the maximum settlement, distribution of displacements and strains in the trough. The developed method for calculation of the settlements was tested on Saint-Petersburg metro escalator tunnels. Comparison of results for predicted and observed data indicate the reliability of the developed settlement and deformation prediction method in the construction of the escalator tunnels using the TBM in St. Petersburg.

An evaluation of fine grained sedimentary materials in terms of geotechnical parameters which define and control excavation performance of EPB TBM’s

Studies have been conducted on Istanbul-Büyükcekmece Waste Water Tunnel route in order to determine the influence of plastic behavior and adhesion potential of fine grained clayey sedimentary soils as well as the lump form effect on the EPB-TBM’s excavation performance. This research was designed to develop data modelling methodology for a risk assessment of excavating in form of lumps, the adhesion problem on the metal surfaces, and clogging.Back analysis was carried out by linking advance rate (mm/min) data with geotechnical properties of the excavation material. The influence of water and other conditioning chemicals in different proportions on the plasticity index and consistency index of the material was also investigated. In this research, material samples from 14 different points between 1285 and 2186m of Büyükcekmece Waste Water Tunnel (6.09km in total length and 20–40m in depth) that was being excavated in sedimentary clayey materials of Gürpınar formation with an EPB-TBM (Ø=3.45m excavation diameter) were evaluated.

TBM and spoil treatment selection process – case history Crossrail C310 Thames Tunnel

AbstractSlurry TBM versus EPB TBM The contract C310 comprises the construction of the Plumstead and North Woolwich Portals and the twin tube Thames Tunnel, which has a length of approximately 2.6 km between the two portals. The two TBMs used for the construction of the Thames Tunnel will drive through varying ground conditions (Thanet Sand, River Terrace Deposit (gravel), and chalk) below the water table. During the drive under the River Thames, the tunnels will only have an overburden of approximately 12 m. The effect of pressure variation due to the tidal River Thames has to be accounted for in the control of the tunnelling. The tunnel will pass underneath several grade II listed buildings, utilities, adjacent to operational railway tracks and close to existing subway tunnels. Previous experience of the handling and disposal of excavated chalk has been gained on several tunnelling projects in chalk, most notably the Dartford Road Tunnels, the Channel Tunnel, the Brighton Stormwater Tunnel, the Lille Metro Tunnel, the Socatop Road Tunnel near Paris and Channel Tunnel Rail Link CTRL 320. The Contract allowed for both Mixshield and EPB TBM Technology. The advantages and disadvantages of a TBM‐S with Earth Pressure Balanced face support (EPB‐TBM) and a TBM‐S with Slurry Face support (Mix‐Shield TBM) for the C310 Thames Tunnels were discussed after contract award and a comparative risk assessment was developed. A Mixshield TBM is more expensive but outperformed the EPB TBM in the overall scoring of risk assessment and therefore it has been decided to use this type at C310.

Periodic inspection of gauge cutter wear on EPB TBMs using cone penetration testing

Cutterhead maintenance is usually required when the gauge cutters (over-cutters) wear down to the shield diameter. In soft ground pressurized shielded TBMs, inspection of gauge cutters usually involves complete stoppage of the operation. This can be a dangerous, costly, and time consuming process. In this study, a novel approach has been developed to monitor gauge cutter wear by considering the relationship between the overcut length and the length of the gauge cutters. By using the proposed testing system, frequent monitoring of gauge cutter length is possible at appropriate intervals during ring builds or maintenance without the need to enter the harsh environment of the excavation chamber. This monitoring system was used within an EPB TBM during the excavation of the University Link Light Rail Tunnel (U230) in Seattle, WA.

Torino Metro Line 1 south extension – modelling and settlement monitoring / Süderweiterung der Turiner Metro Linie 1 – Modellierung und Monitoring der Setzungen

AbstractThe excavation of a 3.6 km long tunnel for the Torino Metro Line 1 South Extension was recently completed by a 7.8 m diameter EPB TBM. A critical section of the tunnel was near Corso Spezia, in the Lingotto area, where the main difficulties were the presence of the water table and the poor ground conditions encountered. Another concern was the effect of the excavation on two five‐storey masonry buildings adjacent to the tunnel alignment, which were constructed in 1930 and suffered severe damage during World War II. Continuous monitoring was undertaken during excavation as time dependent settlements occurred. 2D Finite Element modelling was used to simulate the excavation and its effects on the buildings. This paper describes the most significant performance monitoring data, which is compared with the results of modelling.Kürzlich wurde der Vortrieb eines 3,6 km langen Tunnels für die Süderweiterung der Turiner Metro Linie 1 mittels einer EPB‐Tunnelbohrmaschine mit einem Durchmesser von 7,8 m abgeschlossen. Ein kritischer Abschnitt des Tunnels lag nahe dem Corso Spezia, im Lingotto Bereich. Die Hauptschwierigkeiten dort waren die Lage des Grundwasserspiegels und die schlechten angetroffenen Bodenverhältnissen. Eine weitere Sorge galt den Auswirkungen des Tunnelvortriebs auf zwei nahe der Tunneltrasse gelegene, fünfstöckige Mauerwerksgebäude, die in den 1930er Jahren erbaut wurden und bereits im zweiten Weltkrieg erhebliche Schäden erlitten hatten. Während des Vortriebs wurde daher eine kontinuierliche Überwachung der auftretenden zeitabhängigen Setzungen durchgeführt. Eine 2D Finite‐Elemente Modellierung diente der Simulation des Vortriebsvorgangs und dessen Auswirkungen auf die Gebäude. Im vorliegenden Beitrag werden die wichtigsten Daten des Monitorings dargestellt und mit den Modellierungsergebnissen verglichen.

The use of analytic hierarchy process in the selection of suitable excavation machine for Dez - Qomroud water conveyance tunnel (lot 1&2), Iran

Qomroud water conveyance tunnel (lot 1&2) with the length of 16 kilometers is considered as one of the greatest development and national projects in Iran. Since about 2 kilometers of tunnel pass through alluvium and the rest of the tunnel pass through various types of geological units, and due to the complexity of geological condition and variety of effective criteria, suitable selection of excavation machine is crucial. In this respect, application of a suitable method which can select the best, according to the consideration of these entire criteria would be so important. One of the best decision making methods is Analytic Hierarchy Process (AHP) which has a strong theoretical basis. Using this method, this paper selects the most suitable excavation machine for Qomroud water conveyance tunnel. The results show that the EPB TBM Single Shield is the best alternative.