Earth Pressure Balance Tunnel Research Articles

Surface settlement induced by frictional force of epb shield tunneling in sandy gravels.

The excavation of Earth Pressure Balance (EPB) shield can be divided into two distinct stages, i.e. advancing and lining installation. The frictional force applied on surrounding soils reverses at these two stages, which is harmful to the settlement control. Based on Mindlin's method, a new model of surface settlement is derived to involve the reversed friction. A closed form formula is then obtained for the major type of metro tunnels. Main operational parameters are also used as input of the formula. Numerous operational data and measured settlements are collected from EPB tunnels of Chengdu Metro, Line 7. The proposed formula is validated against these field data in sandy gravels. It is shown that the new formula gives reasonable prediction of surface settlement along the tunnel sections. The accuracy of new formula is significantly higher than that of Peck's formula. This study provides a new vision in settlement control of EPB shield tunneling. The increase of chamber pressure will induce higher negative friction during the lining installation. Therefore, surface settlement of EPB tunneling cannot be controlled by just increasing chamber pressure. A balanced relationship between the chamber pressure and the thrust should be maintained instead.

Estimation of foam (surfactant) consumption in earth pressure balance tunnel boring machine using statistical and soft-computing methods

The use of foam, as the most economical soil conditioning technique, in earth pressure balance tunnel boring machine (EPB-TBM) tunneling projects has significant effects on operation efficiency, excavation cost, and operation time. This study mainly focuses on developing models to predict the foam (surfactant) consumption. For this purpose, five empirical models are developed based on a database containing 11048 datasets of real-time foam consumption from three EPB-TBM tunneling projects in Iran. This database includes the most effective machine operational parameters and soil geomechanical properties on the foam consumption. Multiple linear regression analysis, multiple non-linear regression analysis, M5Prime decision tree, artificial neural network, and least squares support vector machine techniques are used to construct the models. To evaluate the performance of developed models, three performance evaluation criteria (including normalized root mean square error, variance account for, and coefficient of determination) are used based on the training and testing datasets. The results show that the developed models have high performance and their validity is guaranteed according to the testing dataset. Furthermore, the M5Prime model, which demonstrates the best performance compared to other models, is applied to predict the foam consumption in 19 excavation rings of Kohandezh station in Isfahan metro, Iran. After conducting an excavation operation in this station and comparing the results, it was found that the M5Prime model accurately predicts foam consumption with an average error of less than 13%. Therefore, the developed models, particularly M5Prime model, can be confidently applied in EPB-TBM tunneling projects for predicting foam consumption with a low error rate.

Development of Thrust, Torque, and Power Estimation Model, and Prediction Performance of Earth Pressure Balance Tunnel Boring Machine in Mixed-Face Strata

Development of Thrust, Torque, and Power Estimation Model, and Prediction Performance of Earth Pressure Balance Tunnel Boring Machine in Mixed-Face Strata

Discussion: Twin earth pressure balance tunnelling – monitoring and numerical study of an urban case

Discussion: Twin earth pressure balance tunnelling – monitoring and numerical study of an urban case

In-Situ Dehydration Test of Shield Spoil in Mudstone and Pebble Soil Composite Stratum

When earth pressure balance (EPB) shield machine is driving in mudstone sand pebble composite stratum, it will produce a large amount of spoil with high water content. The high moisture content of spoil not only increases the difficulty and cost of transportation, but also easily leads to environmental pollution problems. In this paper, based on the shield tunnel project of Chengdu Metro Line 30, the hydraulic characteristic of shield spoil was tested, and on this basis, laboratory tests of shield spoil dehydration were carried out according to the designed precipitation scheme. The results show that: 1) The moisture content of the EPB shield spoil in the mudstone sand pebble composite stratum is as high as 55.2%, and its permeability coefficient is basically the same as that of silt, and the shield residue has the condition of in-situ dehydration. 2) The dehydration amount and residue moisture content of spoil in slope-type spoil pit showed a linear relationship with time, and the dehydration rate is slow and the total precipitation is less. In other schemes, the dehydration amount and water content of spoil increase rapidly in the first 24 hours and slowly in the later period. 3) Considering the total amount and speed of dehydration within 24 hours, the dehydration effect of spoil pit is ranked from high to low: 3D gravel cage wall spoil pit > 3D spoil pit with vacuum pumping > 3D permeable stone spoil pit > 3D spoil pit > Slope-type spoil pit. 4) 3D gravel cage wall spoil pit has high dewatering efficiency, and vacuum pumping can assist the discharge of water. It is recommended to use 3D gravel cage wall spoil pit and vacuum pumping scheme for on-site EPB tunnel spoil dewatering.

Effect of water head on the permeability of foam-conditioned sands: Experimental and analytical investigation

The water permeability of conditioned soils is one of the most essential properties for Earth Pressure Balance (EPB) tunnelling in coarse-grained soils. Permeability tests are conducted to study the influence of water heads on the permeability of foam-conditioned sands. The initial permeability coefficient of foam-conditioned sands increases with the water head, while the stable permeability coefficient and the initial stable period duration decrease. Meanwhile, a novel analytical model is proposed to estimate the initial permeability coefficient. In this model, the effect of the water head on the initial permeability coefficient is incorporated by calculating void ratios of the foam and effective diameters of foam bubbles under different water pressures. Experimental results are in close agreement with analytical solutions, indicating the excellent performance of the proposed calculation method. In addition, the physical mechanisms of how the water head affects the permeability of foam-conditioned sands are discussed from the contraction and evolution of foam bubbles.

Discharge behavior of spherical and rock chip mucks by screw conveyors in TBM: Physical model experiments and DEM simulations

The discharge of muck through a screw conveyor system plays a crucial role in ensuring safe and cost-effective tunneling with earth pressure balance tunnel boring machines (EPB-TBM). However, the discharge mechanism of chip-type rocky mucks through a screw conveyor has not been well examined. Therefore, this study investigates the discharge behavior of rock chips through a screw conveyor by using a 3D discrete element model (DEM). Numerical simulations are conducted with rock chip particles of various sizes, as well as spherical particles, while varying the inclination angle, screw pitch length, and rotational speed of the screw conveyor. The simulation results show that the relative size between the muck particles and pitch has a significant effect on the discharge rate, and an optimal ratio of pitch to flight diameter is suggested. The particle-level analysis reveals distinctive particle discharge paths and a velocity distribution of muck particles along the screw axis. The study proposes the ratio of the screw pitch to the maximum particle size as the primary design parameter to predict the discharge rate. This is because large particles play a critical role in determining the discharge rate. The study highlights the usefulness of 3D DEM-based simulation as a tool to investigate discharge behavior of particulate materials through a screw conveyor. Moreover, it advances our understanding of rock chip-type muck discharge behavior during TBM excavation, providing guidance for screw conveyor design and feedback during TBM operation.

The Benefits of Uncertainty and Risk Assessment Studies on the M5 Metro Line (Istanbul - Turkey)

Uncertainty is often the most significant source of risk associated with a project in tunnel and underground construction. Unforeseen uncertainties can lead to significant construction problems leading to reduced tunnel advances and delays, cost increases, damage to existing infrastructure and/or damage to building equipment. The M5 metro line, which is the subject of the study, is located in Uskudar – Umraniye - Cekmekoy - Sancaktepe district on the Asian side of Istanbul. The line is approximately 17.5 km long and has 16 cut and cover stations. M5 metro line was used the four earth pressure balance (EPB) tunnel boring machines. The effect of uncertainty on risk assessment and decision-making is increasingly given priority, particularly for large infrastructure projects such as tunnels where uncertainty is often the primary source of risk. This article is intended to explain the tangible benefits of underground uncertainty and risk assessment of the M5 metro construction for underground project stakeholders, local authorities, designers, practitioners and researchers.

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.

EPB tunnelling in long, highly sensitive sections – The experience of Grand Paris Line 14 underpassing the Orly Airport

AbstractThe correct definition and application of face confinement pressure is one of the main challenges for urban tunnels, where soil perturbation can affect the surrounding structures with undesirable or even severe consequences. The choice of this parameter needs to comply not only with minimal geotechnical performances, such as volume loss control, water pressure balance, and front stability, but also with optimization criteria (impact on production rate and Tunnel Boring Machine (TBM) components wear). The Grand Paris Line 14 South tunnel has emphasized this concept especially on the 1.5 km section below the Orly International Airport, with two constraints: the limitation of deformations on sensitive airport structures and the tight schedule due to the Olympic Games of 2024. The 8.83 m‐diameter Earth Pressure Balance (EPB) TBM ‘Koumba’ successfully performed the excavation at 20 m depth. The design face pressure profile, varying between 0.8 and 2.6 bar, was studied. A complex monitoring system was also provided to validate design expectations and to update the TBM‐soil interaction prediction model. This article focuses on the experience acquired on the EPB face confinement pressure management along this long, highly sensitive section. The first part presents the comparison between reference values and thresholds given by the designer and the real TBM drive oscillation. The second part is dedicated to the observed influence of the face pressure on the geotechnical aspect, machine mechanical parameters, and production rates.

A study on large volume losses induced by EBPM tunnelling in sandy soils

Tunnelling-induced ground surface settlements can be described by a Gaussian distribution curve with two key factors; the displacement trough width and the volume loss. In most cases the volume losses are well-controlled with maximum settlements less than the allowable limits. However, there have been reports showing abnormally large ground surface settlement, in sandy soil, induced by Earth Pressure Balance Tunnel Boring Machines (EPB TBMs). This research reports field data obtained during the construction of the Metro Line 1 Ben Thanh – Suoi Tien Tunnels in Ho Chi Minh city, Vietnam. Data include ground settlement measurements, the geotechnical conditions and TBM operation parameters. The results show that in locations where large settlements had occurred there were common characteristics of high liquefaction index, large excess pore pressure and abnormally large tail void grouting. A novel equation is suggested to describe the relationship between the volume loss and the liquefaction potential index. This has been calculated using simple and commonly available geotechnical parameters for use in practice as an indicator for potentially large settlements caused by EBP TBM tunnelling in sandy soils.

A new index for cutter life evaluation and ensemble model for prediction of cutter wear

This paper proposed a new index for evaluation of disc cutter life during earth pressure balance (EPB) tunnelling. This new index was defined as the ratio of accumulated cutter radial wear to working time of the shield machine. With this new index, the measured disc cutter wear can be transformed into a time series data. To predict cutter wear with construction process, an ensemble intelligent model integrating one-dimensional convolutional neural network (1D-CNN) and gated recurrent unit (GRU) was developed via incorporating the proposed cutter wear index. A multi-step-forward prediction mode was adopted to train the ensemble model to predict cutter wear in advance. Field data collected from an EPB tunnelling section in Guangzhou-Foshan intercity railway, Guangzhou, China, was used for validation. Results showed that the proposed index and ensemble model can predict wear of a certain cutter with high accuracy. Three other sequential deep networks were employed for comparison to verify the applicability of the proposed index and ensemble model. The proposed index and ensemble model is convenient to be used on site and can predict wear of a certain cutter on cutterhead to help determine which cutter to be replaced during real-time construction.

Probabilistic Life Prediction of Tunnel Boring Machine under Wearing Conditions with Incomplete Information

This paper developed a data analysis approach to estimate the probabilistic life of an earth pressure balance (EPB) tunnel boring machine (TBM) under wearing conditions with incomplete information. The marginal reliability function of each system component of TBM is derived based on data collected from the site. The structure of the failure framework was determined based on the evaluation of influencing factors, including the wearing of the cutter head panel and screw conveyor. The joint distribution model was built by utilizing the best-fit copula function and the remaining reliable mining distance can be predicted from this model. Real data of the remaining thickness of the wearing resistance structure of the cutter head panel and screw conveyor from an earth pressure balance (EPB) TBM were captured. A realistic metro tunneling project in China was utilized to examine the applicability and effectiveness of the developed approach. The results indicate that: (1) With the selection of normal distribution and Gumbel copula as the best-fit marginal distribution function and copula function, the reliable mining distance was predicted as 4.0834 km when the reliability equaled 0.2. (2) The copula function was necessary to be considered to assess the joint distribution of the reliability function, as the predicted mining distance reduces significantly to 3.9970 km if assumed independent. (3) It enables the user to identify the weak component in the machinery and significantly improve the reliable mining distance to 4.5075 km by increasing the initial thickness of the screw conveyor by 0.5 mm. This approach can be implemented to minimize the risk of unintended TBM breakdown and improve the tunneling efficiency by reducing unnecessary cutter head intervention during the mining process.

Research on Strata Deformation Induced by EPB Tunneling in Round Gravel Stratum and Its Control Technology

Recently, many studies have been conducted on the stratum deformation induced by earth pressure balance (EPB) shield tunneling in soft soil and sand. Movement laws vary largely among different strata. However, at present, relevant research mainly focuses on soft soil and sand, whereas little attention has been paid to the movement law of round gravel stratum with higher instability. In this study, a field monitoring test was carried out on the EPB shield machine when it passes through the round gravel stratum. Based on the analysis of monitoring results under different chamber earth pressures, thrust force, the torque of the cutter, grouting pressure, and grouting volume, the relationships between shield tunneling parameters and their influence on the disturbance of the surrounding soil mass were investigated. It was found that the surface deformation shape of the monitoring section of the south and north lines conforms to the Gaussian curve. The vertical deformation of the stratum at the tunnel axis is the largest. The maximum value is observed when the cutter head reaches the monitoring section. The horizontal deformation reaches a maximum value at the stage of the shield tail pass section. The strata deformation is not only related to the strata properties but also has a strong positive correlation with the shield tunneling parameters. The chamber earth pressure is the main factor affecting the stratum deformation before the arrival of the cutter head, and the grouting volume is the main factor affecting the strata deformation during the stage of the shield tail pass section.

Applications of jet - grouting technology in the Metroline No.1 project at Ho Chi Minh City

The rapid development of economy and the booming urban population in large cities in Vietnam such as Hanoi and Hochiminh city lead to many urban problems of traffic jams and environmental pollutions such as dust and noise contaminations. These issuses effect directly on the health and the living of urban civilians in these cities. In order to solve these urgent transportation and social problems, some metroline projects recently have been carried out in Hanoi and Hochiminh city to meet the high urban transportation demands and to solve congestion problems. Since some Metro line projects in Hanoi and Hochiminh city have been carried out in soft soil conditions, ground improvement methods become a necessary requirement in these projects for ensuring the success of metroline projects and avoiding any potential damage occurred in the tunnelling process. A state - of - the - art soil improvement method with the jet - grouting technology has been applied in Hochiminh Metroline No.1 project with purposes of stabilizing the tunnelling process and protecting nearby existing buildings. This paper presents some applications of the jet - grouting technology when tunnelling by an earth pressure balance tunnel boring machine in the Hochiminh Metroline No. 1 project at the starting and arriving shaft areas for stabilizing the tunnelling process as well as at the Saigon Municipal Opera House area in Hochiminh city with a role of protecting method for the important historical building. By collecting design and site data combining with the analysis of the experimental and observed data obtained from the Hochiminh Metroline No.1 project, the stdy results show the effectiveness of the jet - grouting technology when applying in tunnelling projects with soft soil conditions in Vietnam. The results are also a designing reference for near future metroline project in Hanoi and Hochiminh city.

Laboratory experiments and discrete element modeling on the surface failure induced by EPB tunneling: The effects of cutterhead open ratio and relative tunneling depth

This paper presents laboratory tests and high-fidelity numerical simulations to examine the ground failure induced by Earth Pressure Balance (EPB) Shield Tunneling in granular soils. Specifically, we designed and conducted laboratory tests using a reduced-scale EPB Shield Tunnel machine, and built corresponding three-dimensional (3D) discrete-element method (DEM) models to simulate the dynamic excavation process and to gain further understandings of the mechanisms of the ground movement. The study is particularly focused on the combined influences of the cutterhead open ratio and the relative tunnel depth on the ground motions and stress perturbations during the EPB tunneling, which remain understudied in existing studies. The results show that the open ratio of the cutterhead has significant effects on the ground failure in granular soils, especially in cases of relatively shallow tunnels. The larger the open ratio of the cutterhead, the wider the surface and subsurface settlement trough and the greater the soil pressure in the chamber. The pressure distribution in the soil chamber with a larger cutterhead open ratio is significantly more non-linear than that of the case with a smaller cutterhead open ratio. For a given cover-to-diameter ratio (C/D) of the tunnel, the width parameter (k) is generally constant regardless of the depth for the case with a large cutterhead open ratio, especially in the relatively shallow tunnels, while it increases non-linearly with the depth for the case with a small cutterhead open ratio, especially in relatively deep tunnels. Furthermore, soil arching mechanisms are analyzed qualitatively with respect to different cutterhead open ratios and C/Ds. The study demonstrates quantitatively the response of ground surface to the cutterhead open ratios and C/Ds as well as the associated ground failure mechanisms through a combination of laboratory experiments and 3D DEM simulations, providing further insights into the ground behaviors during the dynamic EPB tunneling process.

Twin earth pressure balance tunnelling – monitoring and numerical study of an urban case

In recent decades, numerical calculations have often been used to optimise, from a technical and economical perspective, the design of underground works. Using these tools allows efficient and affordable designs to be obtained. Simulation of the tunnelling procedure when using a tunnel-boring machine and in urban areas is a complex soil–structure interaction problem. Here, a three-dimensional (3D) code using finite differences is used. The reference case of this study is Lyon metro line D project in France, where a non-symmetric load is present at the surface due to the presence of a retaining wall. An accurate on-site monitoring system was set up to assess ground movements during the mechanised excavation of twin tunnels. The collected data are used as a reference to show the validity and accuracy of the developed 3D model. Two constitutive models were used to simulate the soil behaviour: plastic hardening (PH) and linear elasticity with perfect plasticity (Mohr–Coulomb shear failure criterion). The Mohr–Coulomb constitutive model shows some drawbacks, which can be eliminated by using PH. The existence of a retaining wall induces a non-symmetric load condition; however, the settlement trough predicted by advanced numerical models shows good agreement with that obtained by monitoring data.

Stability analysis when tunnelling in soft soil condition in Hochiminh city

The rapid development in the economy and the urban population in cities in Vietnam in recent years leads to dramatic growth in traffic congestion, noise and air pollution, and environmental degradation. Urban underground infrastructure thus becomes an inevitable solution since the surface space becomes too expensive and restricted in spite of the high cost of tunnel construction. However, tunnelling in deltaic urban areas, in particular in the cases of Mekong Delta and Red River Delta areas, often faces to difficulties of soft soil conditions and the existence of important historical buildings on the surface. The first metro line constructed in Vietnam from Ben Thanh to Suoi Tien, which is located under crowded areas of Hochiminh city, was tunnelled in such conditions. This paper presents a back analysis for the stability of the tunnelling process in the project. The minimum support pressures is estimated by using the wedge model proposed by Jancsecz, S., & Steiner, W. (1994). Meanwhile, the maximum support pressure is estimated by the blow-out model proposed by Vu et al. (2016). Based on these results, the range of support pressures recommended for the Earth Pressure Balance Tunnel Boring Machine in the Hochiminh Metro Line No.1 project soft soil conditions is derived and compared to in situ support pressures obtained from the monitoring data in this tunnelling project. The study result shows a good agreement between the support pressures obtained from stability analysis models and the monitoring data from the construction site. Based on this back analysis, some recommendations are proposed with the purpose of successful construction in the next tunnelling projects in Hochiminh city.

Effects of changing geology on the performance of a tunnel boring machine for the Thames Tideway Tunnel, London, UK

An earth pressure balance tunnel boring machine (TBM), 8.8 m in diameter, was used to construct a 7.6 km long section of the Thames Tideway Tunnel through central London, UK, between Battersea and Bermondsey. Two major geological structures – the Lambeth Anticline and the London Bridge fault zone – have imposed significant changes in the tunnel face geology. The TBM was continually monitored for operating parameters such as cutterhead torque, thrust and injection of spoil-conditioning additives. This led to recognition of the structures, in addition to a high frequency of sand channels within the Upper Lambeth Group strata. The monitoring led to validation of the pre-construction geological model and, in conjunction with inspection of the tunnel face during scheduled interventions and geological logging of several interception shafts, provided valuable assurances for the predicted ground ahead of tunnelling operations.

Enhancing earth pressure balance tunnel boring machine performance with support vector regression and particle swarm optimization

This paper combined data-driven modeling and optimal control for performance enhancement of earth pressure balance tunnel boring machine (EPBM). Two coupled processes, EPBM advance rate (AR) and cutterhead rotation torque, are modeled using support vector regression (SVR). An optimal control framework was formulated to maximize the AR, solved with particle swarm algorithm. Using the Seattle N125 project as case study, it is found the SVR model can predict EPBM AR with R2 = 0.90, normalized root mean square error (nRMSE) = 0.30 and mean absolute percentage error (MAPE) = 31.2%, and R2 = 0.65, nRMSE = 0.59 and MAPE = 6.7% for torque prediction. Compared to human operator, EPBM with optimal control can increase AR by 0.6–23.3 mm∕min on average, accompanied by an average torque reduction of 83.1 kN - m. It is found higher cutterhead rotation and lower chamber pressure always contribute to faster tunneling, but the optimal total thrust force to apply depends on the chamber pressure.