Earth Pressure Balance Machines Research Articles

EPB-TBM cutterhead torque and thrust modelling in rock tunnels through an analytical method and TSFS model

The analysis of cutterhead torque and thrust force is of utmost importance in the selection of a proper tunnel boring machine (TBM) and in achieving optimal operation of the earth pressure balance (EPB) machine for a specific project. This study focuses on the analysis of cutterhead torque and thrust force using data collected from the recent metro project of Tehran, specifically the southern extension of Tehran metro line 6, (TML6-SE). To assess the impact of geotechnical and operational parameters on the measured torque and thrust, a database consisting of 457 data points was established. The excavation of a significant portion of the project took place in a dense and robust limestone using a refurbished EPB machine with a diameter of 9.19 m, initially designed for soft ground excavation. To complete this section of the tunnel, the cutterhead was equipped with disc cutters instead of rippers. Consequently, existing theoretical models for estimating torque and thrust of an EPB machine were modified to accommodate the hard rock boring process. Additionally, the Takagi-Sugeno fuzzy system (TSFS) was utilized in this study. The results of the models yielded quantitative conclusions, and the comparison between the measured and predicted target parameters demonstrated high accuracy. This study contributes to the understanding of the influence of various parameters on the performance of EPB machines in hard rock boring conditions, as well as providing insight into the potential adjustments needed in theoretical models for predicting cutterhead torque and thrust force. The proposed models showed satisfactory and reliable accuracy, with all models having an R2 value above 0.7 and loss function values nearing zero.

Enhancing ground classification models for TBM tunneling: Detecting label errors in datasets

Tunnel Boring Machine (TBM) construction, particularly with closed-face TBMs, faces uncertainties due to the inability of the operator to directly observe the ground ahead. These uncertainties can lead to time delays, cost overruns, and accidents. While supervised machine learning techniques have been used to predict geology from TBM sensor data, their performance drops significantly when applied to other projects, indicating poor generalization. To ensure accurate results and improved generalization to future data, supervised learning models require high-quality, well-labeled data which is not usually the case for TBM datasets. This paper addresses the issue of “noisy” labels in TBM datasets, which human operators and engineers often label with varying interpretations. A data-centric framework was adapted and applied to an Earth Pressure Balance Machines (EPBM) tunnel dataset to detect and identify these mislabeled datapoints. The framework's outputs were validated using two techniques and apply several methods to clean the dataset. The best-performing method was selected for the test set. The paper concludes by discussing the limitations of the proposed method, the challenges encountered, and future research directions in this area.

Prediction of earth pressure balance for EPB-TBM using machine learning algorithms

Face stability control of excavation with earth pressure balance machine (EPB) approach is the best available method to reduce the ground deformation and settlement of surface structures in a tunneling project in urban areas. In the present paper, several models have proposed through a statistical method, including feed-forward stepwise regression (FSR) and machine learning techniques such as support vector machine (SVM), Takagi–Sugeno fuzzy model (TS), and multilayer perceptron neural network (ANN-MLP), to provide a predictive strategy for EPB machine during the tunnel excavation. For this purpose, a monitoring dataset of machine performance parameters including advance speed, screw conveyor speed, screw conveyor torque, thrust force, and cutterhead rotation speed from Tehran Metro Line 6 Southern Extension Sector (TML6-SE) has been compiled. Then, the relation between the performance parameters and target values were investigated to analyze the available inputs and offer a new equation using the FSR. Moreover, evaluation metrics and loss functions were utilized for the evaluation of the developed models’ efficiency. The results proved the significance of the presented methods in this paper that could be used to predict the earth pressure balance operation with high efficiency.

Investigation of the Feasibility of Increasing the Tail-grouting Zone during Mechanized Tunneling in Sandy Soils

Nowadays, excavation in urban environments can have many risks; one of these hazards is improper tail-grouting of Earth Pressure Balance Machine (EPBM) and the consequent ground surface settlement. Failure to fill the tail space with suitable grout significantly affects the surface displacements. Injecting more grout to penetrate deeper around the tunnel will play a more effective role in reducing displacements and permeability of the soil. Therefore, experimentally investigation of the feasibility of increasing the tail-grouting zone during excavation around the tunnel space and the effect of this penetration on the amount of ground surface displacements is the main purpose of this paper. Thus, experimental tests were performed with different grout injection pressure and the effect of each of the pressure on the penetration depth of grout into the soil new laboratory model were examined. Then to study the effect of the grout penetration depth on surface settlement to determination of the adequate amount of grout injection pressure a numerical modeling of Tabriz metro line 2 by FLAC3D software were completed. For this purpose, the results of the laboratory tests (the penetration depth of grout) were used in numerical modeling. The results indicated that the amount of penetration in the implemented granulation has increased due to the increase in pressure, so doubling the pressure causes a 30% increase in grout penetration in the surrounding soil. The results of numerical studies showed that increasing the range of injection in the modeling causes a significant reduction (80 percent) in the ground surface settlement.

Measurement and enhancing prediction of EPBM torque using actual Machine data

The cutterhead torque of an Earth Pressure Balance Machine (EPBM) plays a critical role in determining the performance of mechanized tunneling in urban areas. However, as this parameter is not directly set by the operator but is a function of geological conditions, thrust force, screw conveyor revolution speed, and soil conditions, it is closely linked to geotechnical parameters and machine settings. Despite previous attempts to predict EPBM torque using Shi's physical model, accuracy has been lacking. This study aims to improve the accuracy of this prediction by utilizing actual data from an EPBM used in a metro line tunneling project to identify the primary factors influencing torque and to modify related equations accordingly. To evaluate the performance of existing models and the predictions made by the presented method, various metrics are utilized, including the correlation between all torque values, the relationship between torque and thrust values, and the connection between thrust pressure and penetration. The results indicate that in addition to geotechnical parameters, machine settings such as thrust force, cutterhead revolution speed, arching pressure, soil conditions, and chamber pressure significantly impact the torque value. The study found that the thrust force exerted by the EPBM is a key factor influencing torque.

Tunnelling with Full-Face Shielded Machines: A 3D Numerical Analysis of an Earth Pressure Balance (EPB) Excavation Sequence Using the Finite Element Method (FEM)

Urban tunnelling can be highly challenging, especially in areas where limited ground settlements and environmental disturbance is required. Mechanised tunnelling is usually preferred in such ground environments, specifically Slurry or EPBM (Earth Pressure Balance Machine), depending on the ground properties. Being able to predict the anticipated tunnel behaviour at the preliminary stages of the project can be very beneficial in optimising not only the design, but also control the construction activities and completion times. In practice, the short-term excavation response and support performance focus primarily on design, since most site characterisation inputs are focused on material properties gained from short-term testing. Although the analysis of tunnelling is a three-dimensional (3D) problem, conventional approaches and design methods employed during the design and construction of underground openings are often based on the ground’s static response in two dimensions (2D). In this paper, an initial 2D model is generated in PLAXIS2D and RS2 (Rocscience) to test advanced constitutive models and compare transverse settlement profiles; subsequently, a complete 3D FEM numerical model in RS3 (Rocscience) was used to simulate an Earth Pressure Balance (EPB) excavation sequence. The 3D numerical model simulates the relevant EPB components such as face pressure, TBM shield, backfilling of the tail void (time-dependent hardening of the grout) and gradual segmental lining erections in the longitudinal direction. The presented numerical approach can be used by tunnel designers and engineers to predict the soil response in EPBM tunnelling.

Discussion of cutterhead opening design for earth pressure balance machines (EPBMs) in soft grounds

Among the various parts of the earth pressure balance (EPB) cutterheads, the opening distribution on the cutterhead face plays a crucial role in successful of the tunneling projects in soft grounds. However, the amount of published literature on this subject is very limited, as a result, tunnel boring machine (TBM) manufacturers have been developed different soft ground cutterheads with varied opening distributions through their experience. In this paper, at the first step, the field studies results for soft ground cutterheads opening design were expressed. Next, the paper mainly focused on the numerical studies using discrete element method (DEM) to evaluate the adaptability of the EPB system and cohesive and non-cohesive soils fluidity by changing the opening distribution on the cutterhead. Finally, the optimum opening ratio and its distribution for different soils by considering the value of the thrust force, cutterhead torque and soil fluidity condition as important parameters were proposed based on the analysis results from DEM accordingly. Furthermore, the flow characteristics of soil particles inside the EPB chamber was obtained through examination of velocity field, also the practical aspects with further application in TBM industry by considering field studies and a real example were discussed.

A Critical Investigation on the Reliability, Availability, and Maintainability of EPB Machines: A Case Study

Tunnelling is a vital geotechnical engineering feature of underground transportation systems that is potentially hazardous if not properly investigated, studied, planned, and executed. A reliability, availability, and maintainability (RAM) analysis is one of the main practical techniques in machinery-based projects to recognize the failure and repair rates of machines during or after their operations. RAM analysis of mechanized tunneling can help to manage the project safety and cost, and improve the availability and performance of the machine. There are several methods to obtain and predict the RAM of a system, including the Markov chain simulation and other statistical methods; however, the result of the analysis can be affected by the selected method. This paper presents the results of a critical investigation on the RAM of the Earth pressure balance machines (EPBMs) used in developing an urban metro project in Isfahan, Iran. The five kilometer length of the first line of the Isfahan metro project was excavated using EPBMs over four years. After overhauling the EPBMs and making some minor changes, excavation of the second line started, and to date, about 1.2 km has been excavated by the refurbished machines. In the present study, a RAM analysis has been applied to electrical, mechanical, and cutter head subsystems of the EPBMs in Lines 1 and 2 of the Isfahan metro project over an 18- and 7-month period of machine operation, respectively. The results show that the estimated availability, A(t), determined by the Markov method, is closer to reality but cannot be propagated to reliability R(t) and maintainability M(t) analysis. It was also revealed that by predicting the required maintenance and proper planning, the overall availability of the EPBM was improved from 45% in Line 1 to 61% in Line 2. The outcomes of this study can be used in the future planning of urban tunneling projects to estimate machine, staff, and logistic performance with the least possible error, and appropriately arrange the factors involved in the system.

A More Comprehensive Way to Analyze Foam Stability for EPB Tunnelling—Introduction of a Mathematical Characterization

In the tunnelling industry, a large share of the market is occupied by EPB (Earth Pressure Balance) machines. To operate this kind of machine, a radical change in the rheological behaviour of the excavated soil must be performed, and this is achieved by adding water, foam, and, eventually, polymers. The stability of the foam is assessed through a half-life test. The main limitation of this test is that only one value is used in the characterization of the foam degradation process, which is insufficient to describe the whole evolution of the phenomenon. The results of more than 270 tests were modelled through a five-parameter mathematical formulation that suited the experimental data. The results show that the influence of concentration on the stability of the foam is not always present and that the flow rate used during production bears an influence on the characteristics of the foam.

Auxiliary air pressure balance mode for EPB shield tunneling in water-rich gravelly sand strata: Feasibility and soil conditioning

Machine loads are always high, or soil conditioning is required to be rigorous when the pressure chamber is full of excavated soil during earth pressure balance (EPB) shield tunneling. This study investigates the feasibility and soil conditioning of the auxiliary air pressure balance mode for EPB shield tunneling in water-rich gravelly sand strata to decrease the machine load based on a project in China. It is indicated that the suitable slump value for the mode to avoid muck spewing should be lower than that for the tunneling mode with the pressure chamber fully of excavated soil. The water pressure monitored in the ground around the tunnel experienced rising, falling and stable stages during the EPB shield tunneling of each lining ring. The peak value of water pressure occurred immediately after the EPB machine stopped and decreased quickly during the first 30 min thereafter, followed by a gradual decrease. The time required for the water pressure to again reach its initial value was 70–90 min and did not influence the tunneling behavior of the following lining ring. The monitored ground displacement was much lower than its allowable value. The monitoring results indicated the success of the application of the auxiliary air pressure balance mode with the discharged muck with a slump value of 2–10 cm in the strata, satisfying the controls of ground displacement and advancing speed. However, the higher soil workability induced a lower thrust force and cutterhead torque, more stable cutterhead torque and chamber pressure, and a higher shield advancing speed. Hence, the ideal slump value was determined to be 8–10 cm for the studied project constructed by the EPB shield with the auxiliary air pressure balance mode in the water-rich gravelly sand strata. Finally, future research is recommended for the application of the tunneling mode.

Face failure in cobble-rich soil: Numerical and experimental approaches on 1 g EPB reduced scale model

Recent years have witnessed several accidents associated with tunnel face failure in cobble-rich soil in the city of Chengdu, China. Due to its lack of cohesion, cobble-rich soil can be easily disturbed by shield tunneling. Based on the general conditions of the Chengdu Metro Line 1 project, the mechanisms of face failure of tunnels in cobble-rich soil driven with earth pressure balance (EPB) machines are studied. Specifically, we present results of tests carried out using a laboratory reduced-scale model of EPB tunneling operations in cobble-rich soil. The failure kinematics and limit face pressures are presented and analyzed. Then a three-dimensional (3D) discrete-element method (DEM) model, which is able to simulate the main EPB excavation processes is employed to gain further insight into the mechanisms of face failure in cobble-rich soil. Comparisons of these results with the observations based on previous studies are discussed. The results reveal a fundamentally different tunnel-face failure mechanism in cobble-rich soil in contrast with that in clayey or sandy soils. It shows that the ground movement during face failure is sudden in cobble-rich soil, which is different from the progressive mechanism in frictional–cohesive materials. The observed sinkhole at surface takes the shape of an oval, and the failure zone behind tunnel face extends almost as far as that ahead of the face, which is different from the observations in previous studies. The failure zone is found to be wider than that of sandy soils in both the transverse and longitudinal directions.

Interaction of Excavated Tunnels by Earth Pressure Balance Machines and Sub-surface Obstacles; Case Study: Tehran Metro Line 7

Tunneling in urban areas has always encountered many uncertainties, which if not considered in both analysis and design of the tunnels, will cause unexpected events during tunnel construction. Obstacles are among the most remarkable uncertainties in tunneling that affect the tunnel construction process. The obstacles in urban tunneling include municipal utilities, surface and sub-surface structures, channels, wells, storages, and unknown cavities. Tehran Metro Line 7 in Iran is no exception to the rule, and has been grappling with the obstacles. In this work, we investigate the effect of the existence of wells and unknown cavities in the zone of influence of excavated tunnels by EPBM. The innovation of this research work is in the EPB tunnel design encountering wells and cavities that are as risky as the adjacent underground structure. In this work, we use a numerical simulation of the 3D finite difference method (FDM) so a series of parametric studies based on the numerical model are examined using the well and unknown cavity geometry and their location relative to the tunnel in alluvium. According to the results obtained, a major disturbance occurs in the near field of the well–tunnel, and the interaction problem happens in front of the tunnel face. The numerical outcome indicates that the most critical state of the ground settlement by EPBM happens when the well and unknown cavity are located in the face of the tunnel. It is also proved that the ground behavior is different for each part of EPBM such as ahead of the face, cutter head, shield, and segmental lining parts.

Evaluating rheology of conditioned soil using commercially available surfactants (foam) for simulation of material flow through EPB machine

The number of soft-ground Tunnel Boring Machine (TBM) with an active support pressure has increased significantly around the globe in the past few decades due to the advances in their capabilities and remarkable achievements. Over 90% of these machines are Earth Pressure Balance (EPB) TBMs. The muck in the excavation chamber and the screw conveyor of an EPB machine is often conditioned to modify its properties for improving the operation of the machine, i.e., reduction of the cutterhead and screw conveyor torque, regulation of the face pressure, and efficient mucking. To achieve these goals, the common targeted properties of the conditioned muck include low permeability, high compressibility, low abrasiveness, low stickiness, and proper balance between flow capability and viscosity. Among the various critical properties, soil rheology offers a comprehensive perspective on the desired features of the conditioned muck. This paper reviews the existing soil rheology measurement systems ranging from small-scale rheometers to large-scale screw conveyor models, including review of a macro-scale rheology measurement system recently developed at Colorado School of Mines (CSM). The new optimal propeller geometry suggested by Computational Fluid Dynamics (CFD) simulation was incorporated into the measurement system. Rheological parameters of soil with different soil conditioning and machine operational settings were investigated with the optimized measurement system. The study shows the interdependency between soil conditioning settings and rheological parameters in the modified soil. The measured rheological parameters of conditioned soil can be used in the simulation of muck flow within the excavation chamber and the screw conveyor of an EPB machine by CFD simulation.

Influence of the Cutterhead Configuration and Operation Parameters on the Face Stability of EPB Shield Tunnels in Dry Granular Soils

This paper presents a study on the face stability of earth pressure balance (EPB) shield tunnels in dry granular soils using the discrete element model (DEM) method to replicate realistic excavation processes of the EPB machine. Analyses were conducted at different buried depths to determine the limit face pressures and the face failure model induced by the EPB shield machine with varying open ratios and rotation speeds of the cutterhead. The failure kinematics of the soil and the soil arching effect were also determined. The results showed that both the open ratio and the rotation speed of the cutterhead have significant effects on the stability of the face in terms of the failure kinematics, limit face pressures, and the soil arching effect. The failure zone was highly dependent on the open ratio, but it depended less on the rotation speed of the cutterhead. The stability of the face is overestimated when the excavation is conducted with a cutterhead that has a large open ratio, but it is underestimated when the excavation is conducted with a cutterhead that has a smaller open ratio. Ignoring the effect of the configuration of the cutterhead and the rotation speed results in unexpected and unrealistic results.

Soil Conditioning Tests on Sandy and Cobbly Soil for Shield Tunneling

Soil conditioning is an important stage in shield tunnel construction that can effectively improve muck flow plasticity, reduce cutter head wear and improve tunneling efficiency, especially in sandy and cobbly soils. The aim of this paper is to obtain the optimal ratio of residue modifiers in sandy and cobbly soil and to improve the equipment used in residue-related shield machines. Residual soil in a sandy pebble layer was selected, and particles with sizes over 50 mm were removed to form soil samples. Through laboratory tests, the optimal ratio of the modifier was obtained, and the shield tunneling machine equipment was optimized. The research results for the laboratory tests and equipment optimization were verified and adjusted appropriately through field tunneling tests. The following results were obtained. 1) A 3% foaming agent C was selected for the soil conditioning tests. The final mass ratio of the bentonite mixed solution of water, bentonite, soda ash (Na2CO3), and carboxymethyl cellulose (CMC) was 6:1:0.028:0.035. 2) Improving earth pressure balance (EPB) shield machine equipment can improve the effects of soil conditioning. 3) Compared with the volume of residual soil, the optimal ratio of soil conditioning in sandy and cobbly layer was 13% water, 4–5% bentonite mixed solution and 12–15% foam. In addition, the maximum ratio shall be taken for the strata with poor grain composition. These results can be used to provide excavation guidelines for using an EPB machine under these soil conditions.

Evaluating the effect of EPBM operational parameters on surface settlement in soft ground

Abstract The present study investigates the effects of some essential earth pressure balance machine (EPBM) operational parameters, including face, annulus and grout pressures, on ground surface settlement during tunnel excavation. A numerical soil-tunnel-fluid coupled model was developed using the finite difference method (FDM) in FLAC3D for the basis of this research. Hence, the effects of geostatic stress in the tunnel face and annulus and the grout pressure behind the segment on ground settlement were investigated by parametric analyses. The results indicated that a reduction in the boundary pressure (from 508 to 335 kPa) on the face and annulus space did not change the settlement significantly, altering the settlement from 1.18 to 1.48 mm. The results of parametric grout pressure analysis showed that applying a grout pressure equal to the vertical geostatic stress (i.e. 335 kPa) had a larger effect than applying horizontal geostatic stress (i.e. 357 kPa) to the tunnel face on controlling the ground settlement—i.e. 1.45 and 1.20 mm, respectively. A lateral earth pressure of below 1 (K0 < 1) led to the estimation of horizontal geostatic stress value that was lower than the vertical geostatic stress value, thereby applying a lower effect to controlling the ground settlement. Grout pressure increment relative to the vertical geostatic stress considerably reduced the ground settlement. However, an excessive rise in the grout pressure could lead to deformation and upward displacements in the form of ground heaving at a transverse distance of above 20 m from the tunnel axis.

Random forest method-based prediction and control of bridge pier displacements during construction of two overlapped EPBM tunnels

In this article, a novel artificial intelligence method, i.e. random forest (RF), was adopted as a computer-aided tool to predict the vertical displacement of several pile-supported bridge piers above two overlapped earth-pressure-balanced machine (EPBM) tunnels. Naive Bayes theory was introduced for the statistical analysis of the results predicted by the RF method to address the operational variables of the EPBMs required to safely pass beneath the bridge piers. The in situ observations indicated that the EPBM variables were reasonably determined based on the fact that the vertical displacements of the concerned piers were successfully controlled within the allowable range.

Experimental Study on the Soil Conditioning Materials for EPB Shield Tunneling in Silty Sand

Earth pressure balance (EPB) shield tunneling in a silty sand stratum is frequently faced with the wear of rotary cutter disc, clogging, or even collapse of workface due to its noncohesive and discrete properties of silty sand material. Soil conditioning is an effective way to reduce the discrete and friction properties of silty sand and to increase its rheology and fluidity, thus improving the cutting performance of EPB machines. However, soil conditioning materials were generally prepared and injected based on past limited field experiences or lab tests which were far from reality. In this article, a ground suitability test system for simulating shield tunneling in a conditioned ground was specially developed and used in a series of tests to investigate the influences of key factors of soil conditioning on the shield cutting performance. In addition, a field experiment of shield tunneling in silty sand of Wuhan Metro was conducted for verification. The major findings were obtained as follows. (1) The proposed test system performed well in simulating and assessing the cutting performance of EPB shield in conditioned soils, and the test results agreed well with the field test. (2) The soil conditioning materials can significantly reduce the cutting torque of shield tunneling in silty sand by up to 60%–70%. (3) The optimal foam and slurry parameters are suggested in the paper for shield tunneling in silty sand, respectively. (4) The test results reveal that the slurry conditioning is better than the foam in decreasing the cutter torque in silty sand. To achieve the same effect of soil conditioning, the injection ratios of foam and slurry should be 45% and 10%, respectively, to achieve the torque reduction ratio of 60%. These findings can provide a practical reference for engineers to determine the best‐fit conditioning materials and construction parameters in the silty sand stratum.

A new method to quantify rheology of conditioned soil for application in EPB TBM tunneling

The muck in the excavation chamber and the screw conveyor of Earth Pressure Balance (EPB) TBM, which comprises soil and rock fragments, is often conditioned to adjust its properties for more efficient operation of the machine. The target properties of the conditioned soil include low permeability, high compressibility, proper yield stress and viscosity, and low abrasivity, which are controlled to allow for maintaining face pressure, and facilitate reduced torque and wear of machine components. Among the critical properties, soil rheology plays a major role in offering desired characteristics in the conditioned soil. Measurement and characterization of the rheology of conditioned soil allows for optimizing the conditioning parameters and modeling of the muck flow through the machine. This paper offers a brief review of available testing methods to characterize muck property, with focus on comparison of various soil rheology measurement systems. The main emphasis will be on muck behavior and its impact on operation of soft ground EPB machines. A new device for evaluation of soil rheology under specific settings of the conditioned soil in soft ground tunneling is introduced and the preliminary results of the proposed testing method are discussed. The initial process of optimizing the configuration of the device for higher accuracy and sensitivity to rheological properties of conditioned soil through computational models are explained. The results of numerical modeling using CFD simulation software to identify the preferred configuration of the new soil rheology measurement device will be discussed and the feasibility of using the proposed system for quantification of the soil rheology for tunneling applications is examined.

Clogging and flow assessment of cohesive soils for EPB tunnelling: Proposed laboratory tests for soil characterisation

For earth pressure balance (EPB) machines, it is fundamental to characterise the excavated ground in its natural and conditioned states. The characteristics of the excavated material have a direct influence on machine operation, impacting the functions as a support medium maintaining the support pressure ahead of the tunnel face, besides its transportation and disposal. The current available methods to assess the clogging potential focus mainly on sedimentary pure clayey soils, not including mixed soils. Mixed soils exist widely in nature, including a wide variety of residual soils, which are by-products of intense tropical weathering. This paper presents a combined laboratory routine to characterise and evaluate the clogging and fluidity of soils, including mixed soils by considering different clay fractions. This routine still requires tests conducted directly on-site, where the results should be compared with machine operation parameters, such as torque of cutterhead and screw conveyor, temperature, pressure, as well as occurrence of clogging. This testing procedure provides on-site assessment that can also be conducted prior the excavation using borehole material. The intention of this routine is to provide a geological-geotechnical qualitative characterisation of the material to be excavated, and of the effectiveness of the additives that could be added, as a general guidance for EPB soil conditioning, especially of cohesive soils. The advantage of this routine is its simplicity and low cost to be reproducible in different laboratories and jobsites, making feasible the comparison between different soils by different operators, before and during excavation.