Earth Pressure Balance Tunnel Boring Machine Research Articles

An Experimental Study of the Performance of Two-Component Backfilling Grout Used behind the Segmental Lining of a Tunnel-Boring Machine

Abstract How to fill the empty annular space behind the segmental lining of tunnels is considered one of the most important questions in mechanized excavation, of which the main aim is to minimize settlement on the earth surface. In addition, the grout is the agent that creates a suitable bed for the segment lining of the tunnel and helps with its tightening. There are different methods of filling the empty space. One of them, using excavation by Earth Pressure Balance-Tunnel Boring Machine (EPB-TBM), is the injection of two-component grout at suitable pressure to the back of the segment as the shield of the excavator moves ahead. The grout utilized has suitable mechanical characteristics and efficiency. The main properties of grout refer to bleeding, fluidity and the results of the Marsh funnel test (ability to pump grout), setting time, gelling time (to avoid grout washing out) and compressive strength of grout (to minimize settlement on the earth level). The present study attempts to review the effect of any constituent materials of two-component grout on the parameters. Consequently, different tests with various constituent materials on the properties of grout were conducted.

Three-dimensional numerical simulation of the Shiraz subway second line – influence of the segmental joints geometry and of the lagging distance between twin tunnels’ faces

Due to the widespread need for the urban transportation network, construction of underground railway lines by mechanised shield-tunnelling increases in metropolises. The case of the Shiraz (Iran) subway twin tunnel construction is an example of transport network extension. In the present paper, a three-dimensionalnumerical model was developed to investigate the tunnel’s lining behaviour and the ground displacement surrounding the second line of the Shiraz subway tunnels. All the excavation phases of EPB-TBM (Earth pressure balance, Tunnel boring machine) were simulated using the finite difference method. In most numerical simulations, the segmental joints were assumed parallel to the tunnel axis, despite the fact that the longitudinal joints make an oblique angle with the tunnel. Three kinds of lining pattern were then considered: continuous, straight and oblique joints. The numerical results indicated the necessity of using segmental lining with oblique joints pattern to obtain an accurate evaluation of the structural forces applied in segmental lining. The excavation of a new tunnel near to an existing tunnel with high lagging distance between twin tunnels leads to increase in the normal and the longitudinal displacements, in the internal lining forces and to a decrease in the ground surface settlement above the tunnels.

Estimation of the cutterhead torque for earth pressure balance TBM under mixed-face conditions

In this paper, the cutterhead torque of the modified earth pressure balance (EPB) tunnel-boring machine (TBM) in mixed-face ground is analyzed. The theoretical model of the cutterhead torque of EPB TBM in single soft ground is generalized to the mixed-face ground. To determine cutting torque, a theoretical model for drag bits and disc cutters, which are suitable for mixed-face ground and nonhomogeneous distribution of drag bits on cutterhead, is established and the force formulas are derived. The components of cutterhead torque are investigated in detail. It is found from the results that the friction torques acting on the frontal surface, circumference and back surface of cutterhead, cutting torque, shearing torque acting on opening and agitating torque are important torque components and occupy a fairly large proportion. Moreover, in mixed-face ground, cutting torque induced by disc cutters is an important part, especially when hard rock has a greater proportion.

Physics of adhesion of soils to solid surfaces

Tunnel driving in cohesive soil using slurry- or earth pressure balance-tunnel boring machine often encounters serious problems of clogging of parts of the cutting wheel, the excavation chamber or along the cutting handling and discharge systems. This limits mechanised tunnel driving. Clogging is induced by the adhesion of cohesive soils to solid surfaces. In some cases, clogging brings tunnel excavation to a stand-still. The adhesion of soils to solid surfaces depends on capillary forces of the fluid film in the interface between the soil and the solid surface, and can be understood as a boundary layer effect. This fluid film is mostly present due to the water content of the soil itself, or due to the fluid in slurries or earth mud for face supporting. The capillarity forces increase reciprocally with decreasing thickness of the fluid film. The thickness of the fluid film is not static, but is controlled by the soil that adheres to the solid surface. The thickness of the fluid film depends on two soil properties. The first element is the pore water tension (suction) of the soil, which stimulates fluid flow from the interface into the soil matrix. This reduces the fluid volume in the interface, thus the thickness of the fluid film. Pore water tension depends on the mineralogical properties of the clays as well as on saturation. It is a one-dimensional, transient fluid flow in unsaturated conditions. The second element is the permeability of the soil. This paper provides a physical soil model explaining this process. Results of adhesion tests and pore water tension measurements during adhesion tests on adhesive soils supporting the theoretical approach are presented. Permeability test results on unsaturated clays using a permeameter are given.

Modelling of the EPB TBM shield tunnelling advance as a tool for geological characterization

One of the main causes of problems during the construction of tunnels with tunnel boring machines (TBMs) is a lack of characterization of the soil. Both geological and hydrogeological characterizations are essential to avoid unexpected events. The advance of TBMs produces groundwater oscillations due to hydraulic and mechanical effects. The magnitude of these oscillations depends on the characteristics of the soil and on the “parameters” of the TBM (e.g., earth pressures, penetration). Given that the impact caused in the groundwater could be estimated numerically, this paper proposes to use hydrogeological models based on the parameters of the TBM to validate or improve the previous geological characterization. This procedure was tested by modelling the advance of a TBM-type earth pressure balance (EPB) at a real site. This study arose during the construction of the tunnel for the high speed train in Barcelona. The previous geological characterization revealed a vertical fault whose exact position was unknown. The advance of the EPB was modelled to validate the previous characterization and to locate the fault. The numerical model included a detailed geology and hydrogeology of the study site and the parameters of the EPB. Note that the parameters of the EPB used in the model were more related to the groundwater response. These were determined statistically from all of the measures taken by the machine. Given the results obtained, hydrogeological modelling of EPBs was revealed to be a useful tool to validate previous characterizations, both the geological and the hydrogeological, and to determine the position of some geological structures, such as faults.

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.

RAM analysis of earth pressure balance tunnel boring machines: A case study

Earth pressure balance tunnel boring machines (EPB-TBMs) are favorably applied in urban tunneling projects. Despite their numerous advantages, considerable delays and high maintenance cost are the main disadvantages these machines suffer from. Reliability, availability, and maintainability (RAM) analysis is a practical technique that uses failure and repair dataset obtained over a reasonable time for dealing with proper machine operation, maintenance scheduling, cost control, and improving the availability and performance of such machines. In the present study, a database of failures and repairs of an EBP-TBM was collected in line 1 of Tabriz subway project over a 26-month interval of machine operation. In order to model the reliability of the TBM, this machine was divided into five distinct subsystems including mechanical, electrical, hydraulic, pneumatic, and water systems in a series configuration. According to trend and serial correlation tests, the renewal processes were applied, for analysis of all subsystems. After calculating the reliability and maintainability functions for all subsystems, it was revealed that the mechanical subsystem with the highest failure frequency has the lowest reliability and maintainability. Similarly, estimating the availability of all subsystems indicated that the mechanical subsystem has a relatively low availability level of 52.6%, while other subsystems have acceptable availability level of 97%. Finally, the overall availability of studied machine was calculated as 48.3%.

Low-volume-loss tunnelling for London ring main extension

The Thames Water ring main extension is a 4·5 km long tunnel from Stoke Newington, in the London borough of Hackney, to New River Head in Finsbury, in the London borough of Islington. The 2·85 m i.d. tunnel was excavated by an earth pressure balance tunnel-boring machine (TBM) at depths between 40 and 60 m below the surface. Surface settlements along the route were measured by precise levelling, and were found to be small. It was therefore even more important to measure these settlements as accurately as possible, in order to provide informed estimates of subsurface movements induced in third-party underground structures much closer to the tunnel horizon. Because of the relatively large magnitude of the background movements measured, when compared with the small tunnel-induced settlements, it was necessary to adopt a rigorous statistical method to fit a Gaussian curve to the data. This exploited the analogy of the ‘error function' to define the Gaussian curve parameters i and Vl. In all, 13 tunnels were underpassed successfully by the TBM, all within the ‘conservative expected value' predictions, and without incident. The predictions and structural monitoring schemes undertaken for the High Speed 1 tunnels near Corsica Street and the Northern line tunnels near Angel station are described in the paper. It was found that the surface and subsurface trough width parameter K did not vary with depth as predicted: therefore a new relationship is proposed.

Environmental effects of tunnel excavation in soft and shallow ground with EPBM: the case of Istanbul

In metro tunnel excavations, it is important to control surface settlements observed before and after excavation, which may cause damage to surface structures. Otherwise, the metro tunnel cannot perform the task expected, and the advantages of the tunnel are lost. In this study, short-term surface settlements and their effect on buildings are examined in three zones for twin tunnels, which have been excavated between the Otogar and Kirazli 1 stations of the Istanbul Metro line, and are 5.8 km in length. Geology in the study area is composed of fill, stiff clay, dense sand, very dense sand, and hard clay, respectively, starting from the surface. Tunnels are excavated by using two Earth Pressure Balance Tunnel Boring Machines (EPBMs) with a 6.5 m diameter as twin tubes with 14 m distance from center to center. The EPBM in the right tube is followed about 100 m behind the other tube. Segmental lining with 1.4 m of length is currently employed as final support. The results of this study indicate that, with EPBM excavation method in shallow depths and soft grounds, the damage done to the environment prolonged project costs up to 15.8% more. In addition, tunnel conditions prolonged the project schedule to 29.3%.

Tunnelling through a frequently changing and mixed ground: A case history in Singapore

The Kranji tunnel is part of the Deep Tunnel Sewerage System in Singapore. It is approximately 12.6 km in length. Along the tunnel alignment, all the ground is composed of granite with different weathering grades (from fresh rock to residual soil). The changing ground from hard rock to mixed face and soft ground (and vice versa) at the tunnel level was anticipated. The tunnel depth along the route is between 15 m and 50 m. Two EPB TBMs were deployed at this tunnel with a bored diameter 4.90 m. These machines were designed so that both hard rock and soft ground could be excavated. The cutter head was equipped with a combination of both rippers and disc cutters. During the excavation, it was found that the frequency of the ground change between hard rock and residual soil is much higher than that expected. Due to the frequently changing ground, correspondingly the tunnel boring machine (TBM) operation mode had to be transferred frequently from hard rock tunnelling to transition mode and to earth pressure balance (EPB) close mode. It resulted in great difficulties for the TBM in an optimized operation condition. These difficulties included high cutter wear and flat cutters, tunnel face instability, water inflow at weathering interface, and time delays. In order to overcome these problems and speed up the tunnelling progress, the TBM used in the north drive was modified to attempt the frequently changing ground. The performance of the modified TBM was highly improved. However, the highly abrasive and frequently changing mixed face ground still caused high cutter wear, especially flat cutter wear. These posed many challenges to the equipment and the tunnel crew.

Torino metro line 1: Use of three TBM-EPBs in very coarse grained soil conditions

Earth Pressure Balance type Tunnel Boring Machines (TBM - EPB) were introduced in the tunneling industry about 30 years ago with the aim of facilitating mechanized excavation in ground containing a significant proportion of fine grained soils, which were problematic for the existing slurry shield machines (TBM - SS). Until recently, TBM-EPB applications have continued to be limited to ground containing fine grained soil and low water permeability because of the difficulty, in coarse grained soil, of controlling the earth pressure transferred to the tunnel face. However, the addition of fines in the excavation chamber has permitted efficient and economical TBM - EPB employment in coarse grained soils of mainly sand and gravel. Therefore, these machines are gradually increasing their market. One example of successful TBM - EPB exacavation in highly permeable coarse grained soils is Turin's first subway line, which includes 9 km of tunnels, 15 stations, a train depot and control centre, building protection measures and other secondary structures. Construction began in November 2000 and the metro line shall be operational at the end of 2005. Tunneling was completed between October 2002 and March 2005 with three earth pressure balance tunnel boring machines (EPB-TBMs) in Turin's fluvial and glacial deposits of gravel, sand and cobbles in a silty matrix, with a grain-size curve falling outside the typical normally recognised limits of application of EPB shields. Soil improvement by grouting was undertaken to limit risk of damage to pre-existing structures potentially influenced by tunnel excavation. Ground conditioning in the excavation chamber took place with injection of a mix of a calcium carbonate filler in water, to compensate the natural grain-size curve and integrate use of traditional ground conditioning foams. A monitoring system with over three thousand instruments, based on a Web-GIS architecture, was installed to control safety during construction. The Turin experience is a clear demonstration that, taking correct measures, it is possible, even in an urban context which requires careful control of ground settlements, to economically employ EPB shields in very coarse and highly permeable soils, traditionally considered unsuitable for these machines. (A) This paper was presented at Safety in the underground space - Proceedings of the ITA-AITES 2006 World Tunnel Congress and the 32nd ITA General Assembly, Seoul, Korea, 22-27 April 2006. For the covering abstract see ITRD E129148. Reprinted with permission from Elsevier.

Denmark’s First Metro System

A new mass transit system, the Copenhagen Metro, has been planned to connect the central part of Copenhagen and ∅restad. The contract for the detailed design and construction of the first phase of the Copenhagen Metro was signed in October 1996. The construction of the tunnels and underground stations could affect the stability of buildings and lead to formations of cracks resulting in structural damage unless adequate precautions are taken during the design and execution of the works. The key element in the control of risk of settlement damage is to adopt construction methods that minimise the likelihood of significant ground movement. The requirements led to a design based on tunnelling with earth pressure balance tunnel-boring machines and underground station excavations within retaining walls of secant piles, protected by grout curtains and grout blankets.