Earth Pressure Balance Tunnel Boring Machine Research Articles

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.

Investigation of parameters affecting vibration patterns generated during excavation by EPB TBMs

Tunnel Boring Machines (TBMs) are widely utilized for infrastructure projects and they should be operated in accordance with the geological conditions for reaching favorable excavation rates. Therefore, recognizing any type of variance in the excavation conditions and responding properly and quickly have great importance. In that aspect, vibrations generated during mechanized excavation by Earth Pressure Balance (EPB) TBMs are analyzed and correlated with some parameters along the alignment in the present study. A special vibration data recording system is developed and installed onto four EPB TBMs, excavating in three different project sites. Vibration data on a total of 6 km tunnel excavation is recorded in three orthogonal directions and the effects of geological conditions including soils and hard rocks, EPB TBM operating parameters (thrust, torque, face pressure, cutterhead rotational speed, penetration rate), cutter damages/breakages, positions and types of accelerometers, and TBM diameters on vibration are investigated. Geotechnical characteristics of the investigated alignment are obtained from the geotechnical reports of the related sites. Following the detailed analysis of vibration characteristics (time domain parameters) and geotechnical data, it is seen that the vibration patterns generated during the excavation are greatly influenced by geological and lithological changes. The vibrations are also influenced by the TBM operational parameters and cutter conditions. It is realized that the broken disc cutters create specific high-amplitude signals. Generally, as the rock strength increases, TBM vibrations increase and the vibrations reduce greatly in weathered rocks and soils. These results indicate that TBM vibrations may be used for the identification of geological conditions and worn / broken cutters. The study can be further improved with additional data.

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.

Assessment of reliability and maintainability of earth pressure balance tunnel boring machine (EPBTBM) – An approach

Earth pressure balance tunnel boring machines (EPBTBM) are used in soft or mixed ground conditions often encountered in tunneling operations. The performance of EPBTBM could be enhanced to a great extent by appropriate time management, proper maintenance and reduced unproductive times such as idle hours and breakdown hours using reliability analysis. The reliability of a system primarily depends on time between failure (TBF) and maintainability is based on time to repair (TTR). Investigations on EPBTBM system performance were carried out for an irrigation tunnel through mixed strata conditions and the failure/repair data were collected. TBF and TTR data are found independent and identically distributed (IID). This implies that data are not following any particular trend or correlation. Therefore, these data are fitted in different types of probability distributions such as Gamma, Lognormal, Weibull with Easyfit and MATLAB tools. All the distributions are subjected to a Kolmogorov-Smirnov (k-s) test. Data analysis carried out on EPBTBM deployed in tunnels showed that TBF data and TTR data are found to best fit in General Gamma (4p) and General Gamma distribution respectively. Analysis indicated that ninety percent level of reliability of the system is at 2.64 h of operation whereas the mean time to repair is 5.78 h. The overall availability of the system was 67% which is comparatively less. Failure mode effects and criticality analysis (FMECA) was also carried out to find the critical part of the EPBTBM system. Disc cutter got the highest risk priority number indicating that it is the most vulnerable part of the EPBTBM. This paper reports that the availability of such systems can be increased to 80 percent by appropriate scheduling, preventive maintenance, and effective use of skilled manpower.

Soil conditioning tests of clay for EPB tunnelling

Tunnelling with earth pressure balance – tunnel boring machine (EPB-TBM) in clayey soil requires a careful conditioning to reduce the effect of clogging and stickiness. In the last decade, many researches have been carried out to understand how to reduce these negative behaviors using conditioning agents, and different laboratory test procedures have been proposed using both powdered clay and clay chips to quantify and assess the effect of conditioning in terms of reduction of clogging and stickiness. In this paper a review of the various proposed tests is presented. Unfortunately, it can be seen that no unified assessment method on the soil conditioning is available and therefore the designers do not have consistent data on which their choices are based. The present research proposes a laboratory test methodology to study clay conditioning taking both the behavior of chips and powdered clay into account. The proposed procedure has been applied on two different clays, and the test results are presented and discussed to show how the proposed methodology could be applied.

Bioaugmentation With a Consortium of Bacterial Sodium Lauryl Ether Sulfate-Degraders for Remediation of Contaminated Soils.

The anionic surfactant sodium lauryl ether sulfate (SLES) is the main component of most commercial foaming agents (FAs) used in the excavation of highway and railway tunnels with Earth pressure balance-tunnel boring machines (EPB-TBMs). Several hundreds of millions of tons of spoil material, consisting of soil mixed with FAs, are produced worldwide, raising the issue of their handling and safe disposal. Reducing waste production and reusing by-products are the primary objectives of the “circular economy,” and in this context, the biodegradation of SLES becomes a key question in reclaiming excavated soils, especially at construction sites where SLES degradation on the spot is not possible because of lack of space for temporary spoil material storage. The aim of the present work was to apply a bacterial consortium (BC) of SLES degraders to spoil material excavated with an EPB-TBM and coming from a real construction site. For this purpose, the BC capability to accelerate SLES degradation was tested. Preliminary BC growth, degradation tests, and ecotoxicological evaluations were performed on a selected FA. Subsequently, a bioaugmentation experiment was conducted; and the microbial abundance, viability, and SLES concentrations in spoil material were evaluated over the experimental time (0.5, 3, 6, 24, 48, and 144 h). Moreover, the corresponding aqueous elutriates were extracted from all the soil samples and analyzed for SLES concentration and ecotoxicological evaluations with the bacterium Aliivibrio fischeri. The preliminary experiments showed the BC capability to grow under 14 different concentrations of the FA. The maximum BC growth rates and degradation efficiency (100%) were achieved with initial SLES concentrations of 125, 250, and 500 mg/L. The subsequent bioaugmentation of the spoil material with BC significantly (sixfold) improved the degradation time of SLES (DT50 1 day) compared with natural attenuation (DT50 6 days). In line with this result, neither SLES residues nor toxicity was recorded in the soil extracts showing the spoil material as a by-product promptly usable. The bioaugmentation with BC can be a very useful for cleaning spoil material produced in underground construction where its temporary storage (for SLES natural biodegradation) is not possible.

Evaluation of the Adaptability of an EPB TBM to Tunnelling through Highly Variable Composite Strata

The adaptability of an earth pressure balance (EPB) tunnel boring machine (TBM) to complex geological strata needs to be evaluated when a tunnel project is set up. It is helpful for better design and more suitable technical parameters of the machine. Because the factors that influence adaptability are numerous and interrelated, their effects also differ; hence, a quantitative assessment of adaptability is generally difficult. In the present study, a method for quantitatively evaluating the excavation adaptability of an EPB TBM was developed using an analytic hierarchy process (AHP) and fuzzy comprehensive evaluation. The method first involves an initial selection of factors that may influence tunnelling. Based on the expert questionnaire and their influence weights determined by AHP, the 10 evaluation indexes from 25 primary indexes were selected to establish the evaluation index system (EIS) including a target, criteria, and index level. Fuzzy membership functions are then derived one after another based on the effect of each evaluation index on the EBP TBM tunnelling process. A fuzzy mathematical method was finally presented to determine the adaptability of an EPB TBM excavation performance. The proposed method was applied to two special sections of diameter 6.98 m excavated by two EPB TBMs in the Shenzhen Metro Line 11 project. The geological exploration shows that these two tunnel sections pass through typical composite strata in Shenzhen. The determined adaptability grades of the EPB TBMs used for composite strata were confirmed by the actual tunnel excavation. It indicates that the developed method is reasonable and useful to evaluate tunnelling adaptability of EPB TBM.

Dispersant for Reducing Mud Cakes of Slurry Shield Tunnel Boring Machine in Sticky Ground

When a slurry shield tunnel boring machine (TBM) encounters sticky ground during tunneling, mud cakes often occur on the cutter head due to the high stickiness of soil. The mud cakes caused several negative issues, such as high torque demand, advancement rate reduction, and additional costs. Existing studies have largely focused on Earth pressure balance TBMs; research on formation and mitigation measures of mud cakes in slurry shield TBMs is limited. Therefore, this study proposes the addition of dispersant to the slurry to prevent mud cakes during the tunneling of slurry shield TBMs by reducing stickiness of excavated clay. The basic properties of slurry were measured experimentally, and the effectiveness of dispersant in reducing the potential for mud cakes was investigated through mixing tests and viscosity experiments. A statistical analysis of the data was performed to determine relationships between slurry properties and material behaviors. The results showed that the slurry with dispersant had a lower viscosity and formed filter cakes more quickly, thereby meeting the performance requirements of a supporting fluid for slurry shield TBMs. Further, dispersant effectively reduced the empirical stickiness ratio and suspension viscosity. Therefore, a slurry with an appropriate dispersant content could effectively reduce the potential for mud cake formation.

Calculation of Optimum Soil Conditioning in EPB Tunneling (Case Study: Ahwaz Metro Project, Line 1)

Determination of the optimum soil conditioning parameters in the earth pressure balance-tunnel boring machines (EPB-TBMs) plays an important role in reaching an optimum thrust force and advance speed. Silty-clay (CL-ML) in line 1 of the Ahwaz metro project is used in order to find the conditioning parameters of slumps with different water contents and foam agents. The results obtained are a quantitative comparison between the parameters with different soil conditioning and water contents. Hence, the test results can be used to determine the most economical and technical conditioning parameters for a special condition of soil. The optimum quantity of foam expansion ratio (FER), foam injection ratio (FIR), percent ratio between the surfactant agent and the water volume (Cf), and cost for foam in this soil (based on the soil conditioning production cost) are 10, 157%, 2.07, 248 units, respectively. Soil conditioning with the optimum parameters obtained are tested in a TBM in two stages during excavation of 140 rings. This results in a lower soil conditioning cost and almost 40% higher advance speed.

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.

Mesocosm Experiments at a Tunnelling Construction Site for Assessing Re-Use of Spoil Material as a By-Product

Mechanized excavation of tunnels with Earth Pressure Balance-Tunnel Boring Machines requires the use of foaming agents. The latter contain the anionic surfactant sodium lauryl ether sulphate (SLES) as the main compound. The re-use as a by-product of excavated soil containing foaming agents (spoil material) can pose a risk for soil and particularly for aquatic ecosystems if they are close to the spoil material final destination site. This work reports the chemical results (SLES residual concentrations) and ecotoxicological effects (battery of five tests) of 28 day-mesocosm studies performed at a tunnelling construction site. The soil mesocosms were set up with two different lithologies, which contained four different foaming agent products at the highest amounts used for excavation. The decrease in SLES concentrations and the ecotoxicological tests were performed in soil and its water extract (elutriate) at different times (0, 7, 14, 28 d). Elutriates were prepared in order to simulate a possible SLES leaching from soil to water. The results showed a decrease in SLES over time and different ecotoxicological responses depending not only on the initial amount of each product, but also on the soil lithology and organism tested (aquatic or terrestrial). This study showed how only site-specific ecotoxicological evaluations can ensure a safe management of the spoil material, making possible the re-use of soil and avoiding production of waste.

Geological Type Recognition by Machine Learning on In-Situ Data of EPB Tunnel Boring Machines

At present, many large-scale engineering equipment can obtain massive in-situ data at runtime. In-depth data mining is conducive to the real-time understanding of equipment operation status or recognition of service environment. This paper proposes a geological type recognition system by the analysis of in-situ data recorded during TBM tunneling to address geological information acquisition during TBM construction. Owing to high dimensionality and nonlinear coupling between parameters of TBM in-situ data, the dimensionality reduction feature engineering and machine learning methods are introduced into TBM in-situ data analysis. The chi-square test is used to screen for sensitive features due to the disobedience to common distributions of TBM parameters. Considering complex relationships, ANN, SVM, KNN, and CART algorithms are used to construct a geology recognition classifier. A case study of a subway tunnel project constructed using an earth pressure balance tunnel boring machine (EPB-TBM) in China is used to verify the effectiveness of the proposed geological recognition method. The result shows that the recognition accuracy gradually increases to a stable level with the increase of input features, and the accuracy of all algorithms is higher than 97%. Seven features are considered as the best selection strategy among SVM, KNN, and ANN, while feature selection is an inherent part of the CART method which shows a good recognition performance. This work provides an intelligent path for obtaining geological information for underground excavation TBM projects and a possibility for solving the problem of engineering recognition of more complex geological conditions.

Toxic response of the bacterium Vibrio fischeri to sodium lauryl ether sulphate residues in excavated soils.

Sodium lauryl ether sulphate (SLES) is the main chemical component in several lubricant products used for soil conditioning in the mechanized excavation industry using Earth Pressure Balance-Tunnel Boring Machines. During the tunnelling process, huge amounts of excavated soil are produced and the SLES presence can affect the subsequent re-use of this material as a by-product. Currently, there is still no regulatory indication of reliable and sensitive bioassays for monitoring soil quality during the excavation process. The main objective of this work was to verify if the Vibrio fischeri screening test was suitable as a consistent and precautionary tool for this specific purpose. Firstly, the ecotoxicity (EC20 and EC50) of the SLES standard solution and three commercial products (SLES content from 10 to 50%) were evaluated to select the most environmental friendly product. Subsequently, soil samples from about 2 years of tunnelling in a real construction site, conditioned with the selected product, were evaluated for their environmental compatibility with the prescriptions of an Italian site-specific protocol. The latter established 2 mg/L as a threshold value for SLES concentration in soil water extracts and a no toxic response (≤20%) for the Vibrio fischeri test. The comparison of the bacterium bioluminescence inhibition values (%) with analytical determinations showed an ecotoxicity when SLES was >2 mg/L. The toxicity was directly related to SLES concentration, indicating that the V. fischeri test and the SLES analyses are suitable tools for assessing excavated soil as a by-product, ensuring its safe reuse in accordance with a green production process (circular economy).

New technical combination of seawater and ultrasound wave energy for excavation of highly plastic sticky clays in urban EPB tunneling

In urban tunneling with an earth pressure balance-tunnel boring machine (EPB-TBM), highly plastic clays or sticky clay containing fine-grained sediments makes tunneling conditions more difficult. The proper amount and consistency of the ground conditioning chemicals to be used for the excavation of these difficult or complex geological units are also controversial. Due to the lack of proper management and optimization of such chemical foaming agents in accordance with the excavation material and tunneling method, some environmental impacts may occur. However, environmental pollution and its effects, in other words, the ecological costs emerged as a result of exposure to these chemicals, can sometimes be ignored. In this study, the use of seawater is proposed as a ground conditioning agent in EPB-TBM operations and the use in addition of ultrasound wave energy application on fine-grained and highly plastic sedimentary clays conditioned with seawater. Preliminary analyses and evaluations of the new eco-technical combination indicate that the seawater can easily compete with existing sodium-based foaming agent (SLES) on a laboratory scale by providing the required dispersive effect, which can be enhanced with ultrasonic applications.

Investigations into reliability, maintainability and availability of tunnel boring machine operating in mixed ground condition using Markov chains

Drilling and blasting have been the important methods of making underground tunnels for irrigation, subways, metro-lines, drainage and defense. Of late TBM (tunnel boring machine) is considered as the best positive alternative, in view of several advantages offered such as smooth profile, automated faster tunneling rates, easy to implement controls, safe and economic tunneling under favorable conditions. It is a gigantic high performing machine, with minimum hassles of operation if selected and operated judiciously. Thus, this equipment is the best possible choice to obtain a high penetration rate at minimum cost. TBM performs various operations such as rock cutting, discharge of muck, ring building and shifting of rail track (TBM movement). These operations are connected serially having a provision to function in parallel. Considering the high initial cost and import dependence, development of methodologies to establish the reliability of the system is mandatory. The reliability analysis using markov modelling was carried out for an EPBTBM (earth pressure balance tunnel boring machine), being used in an irrigation tunnel, considering its suitability to analyze a continuous production system. Accordingly, the failure and repair rates of the different subsystems were critically analyzed and variability was fixed. Maximum availability can be obtained by increasing reliability and maintainability of the equipment. This paper reports the study on the reliability, maintainability and availability of an EPBTBM deployed for excavating an irrigation tunnel located in Central India and the impacts of these parameters on the progress of tunnel. Availability of EPBTBM was found to be 61% which increased to 70% by proper maintenance and proper planning.

Reliability, availability and maintainability analysis of the conveyor system in mechanized tunneling

Evaluation of reliability, maintainability and availability (RAM) plays an important role in performance estimation of tunneling systems. Reliability predictions, maintenance planning, reliability assessment, failure detection and risk evaluation are necessary for tunneling machines. The RAM analyses of tunneling equipments have been widely investigated in recent years. The aim of this study is to RAM analysis of the material hauling system in an earth pressure balance tunnel boring machine (EPB-TBM). For this purpose, failures and repairs data from main conveyor system of Tabriz Metro Line 2 in Iran were collected. Performing trend and serial correlation tests showed that the data are independent and identically distributed (iid) and therefore the statistical techniques can be used for modeling. To carry out the analysis, the main conveyor system was divided into three sub-systems including conveyors 1, 2 and 3, which are located on the TBM machine, inside the tunnel and station. Analysis resultsindicated that reliability of conveyor subsystems 1, 2 and 3 after 267, 58 and 300 h reaches to zero, respectively. Moreover, availability results showed that all subsystems are available for more than 89 percent of the time. To improve system reliability, preventive maintenance is required for each subsystem. Based on the obtained results, reliability-based preventive maintenance time intervals for 80 percent of reliability level for subsystem 1, 2 and 3 are 43, 3 and 6 h, respectively.

Three-dimensional numerical simulation of pile-twin tunnels interaction – Case of the Shiraz subway line

The use of an underground transportation network to solve urban traffic problems is a practical solution. Shiraz, one of the most famous touristic cities of Iran, is developing its own urban railway network using mechanized twin tunnels. It is almost inevitable for tunnels to pass nearby an existing pile foundations. In this study, a three-dimensional numerical model was developed to investigate the pile-tunnel interaction. All the mechanized excavation phases of an EPB-TBM (Earth pressure balance, Tunnel boring machine) and the segmental lining were modeled using a finite difference code. The role of the Constitutive soil’s model is also investigated by using both a linear elastic-perfectly plastic one (failure criteria of Mohr-Coulomb type) named as MC and a nonlinear perfectly plastic one the Cap-Yield (CYsoil) constitutive model. Two different scenarios were considered: the influence of tunneling on existing piles and the impact of installing bridge piles nearby existing twin tunnels. The influence of the soil/structure interaction is presented in terms of surface settlements, forces induced in the tunnel lining and forces along the piles. It should be noted that on the base of the obtained results, the MC model cannot accurately estimate the ground settlements and the forces in tunnel and piles, therefore it is necessary to use advanced constitutive models like CYsoil for design purposes.

ECOTOXICITY OF FOAMING AGENT CONDITIONED SOILS TESTED ON TWO TERRESTRIAL ORGANISMS

Huge amounts of soil debris are produced during the underground excavation with Earth Pressure Balance-Tunnel Boring Machines (EPB-TBM). Soil debris may contain residual concentrations of the anionic surfactant sodium lauryl ether sulphate (SLES), the main component in some foaming agents used as excavation additives. The reuse of this debris or its discharge as waste is a critical environmental question in construction engineering. There are only few studies on ecotoxicological effects on soil debris coming from a real excavation site. The aim of this study was to evaluate the ecotoxicity of two deep soils, with different lithological compositions, conditioned with three foaming agents. In some cases, lime was added to the soil. The soils were placed in mesocosms (1 m3) to simulate the temporary storage of the soil debris at a construction site. At fixed times, soil sub-samples were collected and ecotoxicological tests on terrestrial organisms (Lepidium sativum, Eisenia foetida) and an assessment of SLES concentration were performed with soils and aqueous elutriates produced from them. Results showed that at day 28, a SLES reduction was observed in both the soil and aqueous elutriates, with various rates of decrease. The differences were due to different soil lithological compositions and foaming agent products composition. In general, the two soils were not suitable for both plant growth and earthworm reproduction, but in Soil 1 the earthworm mortality was very low, except when lime was added. Tests with soil elutriates showed that 7 days after conditioning no toxic effect was found for the organisms tested.

Performance analysis of tunnel-boring machine by probabilistic systems approach

In this paper, the performance of an earth pressure balance tunnel-boring machine (EPB-TBM) during tunnel construction is analysed. A case study with data from the east–west part of the Tehran metro line 7 is employed to develop a methodology. Several parameters of different types that influence TBM operations in soft ground are identified and analysed, and the probabilistic systems approach is utilised to interpret the interactions between pairs of parameters. For this purpose, the probabilistic expert semi-quantitative and Monte Carlo simulation techniques have been employed. An index is developed to calculate the utilisation along the studied tunnel path. The results have been compared with real utilisation factor values from the project, showing an excellent agreement between estimations and observations.

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.