Hard Rock Tunnel Boring Machines Research Articles

Multi-step real-time prediction of hard-rock TBM penetration rate combining temporal convolutional network and squeeze-and-excitation block

Accurate penetration rate prediction enhances rock-breaking efficiency and reduces disc cutter damage in tunnel boring machine (TBM) construction. However, this process faces significant challenges such as the high uncertainty of ground conditions and the complexity of maintaining optimal TBM operation in long and large tunnels. To address these challenges, we propose TCN-SENet++, a novel hybrid multistep real-time penetration rate prediction model that combines a temporal convolutional network (TCN) and a squeeze-and-excitation (SENet) block for aided tunneling. This study aims to demonstrate the application of TCN-SENet++, as well as other models such as RNN, LSTM, GRU, and TCN, for TBM penetration rate prediction. The model was developed using actual datasets collected from the Yin-Song diversion project. We employ a 30-s time step to predict the future time steps of the penetration rate (1st, 3rd, 5th, 7th, and 9th). The features that influence the penetration rate, such as the cutterhead torque, thrust, and cutterhead power, were considered. A comparative analysis using the mean absolute error and mean squared error revealed that the TCN-SENet++ model outperformed the other models, including RNN, LSTM, GRU, TCN, and TCN-SENet+. In comparison, TCN-SENet++ achieved average MSE reductions of 18%, 6%, 3%, 1%, and 2%, respectively. The TCN-SENet++ model demonstrated fewer errors in the new project, validating its effectiveness and suitability for real-time penetration rate prediction in TBM construction.

Evaluation of the effect of TBM disc cutter wear on rock cutting efficiency

AbstractThe geometry of the disc cutter is one of the most important factors in the rock cutting process of mechanized tunnel boring machines (TBMs). However, during excavation, the optimal conditions of the disc cutter are not constant due to disc cutter wear. One of the most significant consequences of cutter wear is the increase in the contact area of the disc cutter with the rock so when the wear of the cutter exceeds its maximum limits, it should be replaced. Therefore, this study will examine the effect of disc cutter wear on TBM operational parameters such as thrust force, net penetration rate, and specific energy. In order to achieve this, six types of worn 17“ disc cutters have been studied graphically, and a method for calculating the surface of contact between the disc cutter and rock as a function of the cutter tip width has been developed. Moreover, a new equation has been proposed to predict normal and rolling cutting forces whose results are in good agreement with the reported laboratory values. As a final step, the hard rock TBM parameters of the Kani Sib water conveyance tunnel have been studied after replacement of worn disc cutters. The results show that replacing the worn disc cutters leads to an increase in penetration rate and a decrease in thrust force, resulting in an increase in specific penetration. On average, specific penetration increases by ≈35 %.

A study of rotary cutting machine (RCM) performance on Korean granite

PurposeDespite the many advantages this type of equipment offers, there are still some major drawbacks. Linear cutting machine (LCM) cannot accurately simulate the true rock-cutting process as 1. it does not account for the circular path along which tunnel boring machine (TBM) disk cutters cut the tunnel face, 2. it does not accurately model the position of a disk cutter on the cutterhead, 3. it cannot perfectly replicate the rotational speed of a TBM. To enhance the knowledge of these issues and in order to mimic the real rock-cutting process, a new lab testing equipment was developed by Hyundai Engineering and Construction.Design/methodology/approachA new testing machine called rotary cutting machine (RCM) is designed to simulate the excavation process of hard-rock TBMs and includes features such as TBM cutterhead, RPM simulation, constant normal force mode and constant penetration rate mode. Two sets of tests were conducted on Hwandeung granite using different disk cutter sizes to analyze the cutting forces in various excavation modes. The results are analyzed using statistical analysis and dimensional analysis. A new model is generated using dimensional analysis, and its results are compared against the results of actual cases.FindingsThe effectiveness of the new RCM test was demonstrated in its ability to apply various modes of excavation. Initial analysis of chip size revealed that the thickness of the chips is largely dependent on the cutter spacing. Tests with varying RPM showed that an increase in RPM results in an increase in the normal force and rolling force. The cutting coefficient (CC) demonstrated a linear correlation with penetration. The optimal specific energy is achieved at an S/p ratio of around 15. However, a slightly lower S/p ratio can also be used in the design if the cutter specifications permit. A dimensional analysis was utilized to develop a new RCM model based on the results from approximately 1200 tests. The model's applicability was demonstrated through a comparison of TBM penetration data from 26 tunnel projects globally. Results indicated that the predicted penetration rates by the RCM test model were in good agreement with actual rates for the majority of cases. However, further investigation is necessary for softer rock types, which will be conducted in the future using concrete blocks.Originality/valueThe originality of the research lies in the development of Hyundai Engineering and Construction’s advanced full-scale laboratory rotary cutting machine (RCM), which accurately replicates the excavation process of hard-rock tunnel boring machines (TBMs). The study provides valuable insights into cutting forces, chip size, specific energy, RPM and excavation modes, enhancing understanding and decision-making in hard-rock excavation processes. The research also presents a new RCM model validated against TBM penetration data, demonstrating its practical applicability and predictive accuracy.

Evaluation of foam application in providing required conditioning for EPB hard rock TBMs

AbstractUtilizing the earth pressure balancing technique on hard rock tunnel boring machines (TBMs) is an efficient way to overcome engineering geological hazards that disrupt the application of these machines. Considering that geomechanical and engineering geological conditions of soil and rock are dramatically different, proposing a suitable conditioning design for earth pressure balance (EPB) hard rock TBMs requires particular attention to the characteristics of the excavated material and ground conditions. In this paper, foam application providing a favourable support medium for EPB hard rock TBMs is evaluated based on the experience of the Tehran metro line 6 southern expansion sector project, using laboratory and actual data. TBM muck, with different water contents, was used as the test specimen after granulometry correction. The trend of changes in the workability of foam conditioned mix was obtained by performing 350 slump tests. The pressurized permeability cell test (PPCT), a testing device capable of applying high water pressures to the conditioned material, was used to evaluate the impermeability of workable mixes. Results indicate that although foam can efficiently increase the workability of dry and moistened specimens, the presence of a separated liquid phase in the test specimen disrupts its application; moreover, foam conditioned mix is permeable even against low water pressures.

A Numerical Investigation of the Effect of Disc Cutter Wear on Rock-Cutting Forces in Mechanized Tunnel Boring Machines

The wear of the disc cutter results in an increase in contact area with the rock, so when the wearing of the cutter exceeds its maximum limits, it should be replaced. However, this is not done on time because of cost concerns. Therefore, this study will investigate the effects of disc cutter wear on tunnel boring machine (TBM) operational parameters such as thrust force, torque, penetration rate, and specific energy as well as how it impacts advance rate and project time in hard rock TBMs. Finite-element modeling has been performed on 17″ disc cutters, calibrated with the results of linear cutting machine test (LCM). The wear values varied within the range of 0–20 mm and different penetration depths. Numerical results of normal cutting forces are compared with the previously suggested theoretical model, which shows good agreement. According to numerical models, normal and rolling forces are significantly increased as disc cutter wear increases. Increases in vertical and rolling forces are 130% and 75%, respectively. Changes in the side force on the disc cutters indicate that with the wear of the cutters, the result of the side forces is asymmetric and from the inside of the cutter. It causes the bearing system of the disc cutter to fail. The intensity of these asymmetric forces decreases as the installation radius of the disc cutter increases. Further, the wear of disc cutters significantly increases the specific excavation energy, resulting in a significant reduction in excavation efficiency. Finally, disc cutter consumption information for the Kani Sib water conveyance tunnel is also provided, which confirms the findings.

On the Effect of Shield Friction in Hard Rock TBM Excavation

During hard rock tunnel boring machine (TBM) excavation, shields behind the cutterhead are usually in direct contact with the tunnel wall and therefore subjected to friction forces that occur within this interface. The effect of shield friction in hard rock TBM tunneling has received little attention so far and literature on this topic is scarce and conflicting. To investigate the friction coefficient for the planning of TBM excavations, specialized shear tests were conducted where steel specimens were sheared against lithologically different rock specimens under representative normal forces and shearing speeds. The tests were executed with and without the use of bentonite lubrication. The results show that there is a significant difference between different lithologies and also that using bentonite does not lower the friction coefficient as expected. To elaborate on the effect of shield friction during construction, a framework for interpretation of TBM operational data based on experience from construction sites is provided. Whereas thorough interpretation of the data enables one to draw conclusions about the shield friction, it still remains difficult to assess the real effect of shield friction due to the limited possibilities to observe the ongoing phenomena. This study therefore provides the basis for theoretical and practical assessments of the effect of shield friction for the planning and construction phase of a tunnel. This becomes increasingly important in the light of new contractual developments that aim at differentiating “standard” from “special” advance in an objective and reproducible way.

Introducing Tree-Based-Regression Models for Prediction of Hard Rock TBM Performance with Consideration of Rock Type

Prediction of machine performance is a fundamental step for planning, cost estimation/control and selection of the machine type when using a tunnel boring machine (TBM). Penetration rate (PR) and machine utilization (U) are the two principal measures of TBM performance for evaluating the feasibility of using a machine in a given ground condition. However, despite the widespread use of TBMs and established track records, accurate estimation of machine performance could still be a challenge, particularly in complex geological conditions. Since different types of rocks have varied texture (cementation and grain size), and respond differently to cutting forces in the TBM tunnelling, incorporating the effects of rock type in performance prediction models can improve the accuracy of the estimates. The aim of this study was to develop models for predicting penetration rate of hard rock TBMs in different types of rock based on field penetration index (FPI), using multivariable regression analysis and machine learning algorithm, including classification and regression tree (CART). The proposed models offer estimated FPIs in different rock types, rock strength, and rock mass properties in the form of graphs (diagrams), which can be used to estimate TBM penetration rate. The proposed models have been developed based on the analysis of a comprehensive database of TBM performance in various rock types and offers more accurate estimates of machine performance by incorporating many of the key parameters available in typical geotechnical reports and contract documents. The models also exhibit sensitivity to rock mass parameters for predicting the penetration rate.

Dynamic analysis and experimental study of a Tunnel boring Machine testbed under multiple conditions

The main drive system is the core of a Tunnel Boring Machine (TBM). The force transmission law of this system is extremely complicated, which leads to severe vibration, structural failure, and safety hazards. Therefore, the dynamic analysis and the study of the vibration transmission law of a TBM main system under different working conditions are very important. In this study, a novel testbed for a hard rock TBM main system and a multi-DOF coupling dynamics model were built by considering the external excitations of the cutters, the time-varying meshing stiffness of the gear teeth, the meshing error, the clearance, and the stiffness of the main bearing. A wireless vibration monitoring system was built on the testbed. Experiments under typical working conditions were done to verify the dynamic model. Finally, the dynamic response of the system was analyzed. The results showed that the maximum error of the theoretical and actual dynamic response was 18.1%, and the dynamic model could be used to analyze the vibration of an actual TBM. The vibration law of the testbed was close to the actual TBM, so the testbed could be used for the vibration law analysis of the actual TBM under other working conditions. The study of the vibration law under different working conditions and different digging parameters could be used to guide the intelligent tunneling of the TBM.

Analysis of Grinding and Chipping Processes beneath Disc Cutters of Hard Rock Tunnel Boring Machines (Case study: Uma-Oya water Conveyance Tunnel, SriLanka)

Analysis of Grinding and Chipping Processes beneath Disc Cutters of Hard Rock Tunnel Boring Machines (Case study: Uma-Oya water Conveyance Tunnel, SriLanka)

Hard-rock TBM jamming subject to adverse geological conditions: Influencing factor, hazard mode and a case study of Gaoligongshan Tunnel

Adverse geological conditions, the major challenge of tunnel construction, affect the excavation rate and even cause the hard-rock tunnel boring machine (TBM) jamming. Firstly, 121 cases of TBM jamming are analyzed in this study (detailed information can be found in Appendix A). The influencing factors of TBM jamming are studied and the hazard modes are classified into six categories. The selection of shield TBM takes up 77.69% of the 121 cases, occurring in 94 cases. In terms of adverse geological conditions, the fractured zone is one of the most commonly met adverse geological conditions for TBM jamming cases. In addition, groundwater often plays an indirect catalytic role in jamming hazards. It is found that collapse of surrounding rocks is the most common hazard mode for TBM jamming, appearing in 52 cases. Secondly, Gaoligongshan Tunnel, one of the longest railway tunnels in China, is presented as a representative case. The possibility, geological conditions and locations of TBM jamming occurring in the Gaoligongshan Tunnel are studied in site, which verifies the results of case statistics and the geological laws proposed above. The specific steps to predict and control TBM jamming in Gaoligongshan Tunnel are proposed. Finally, the lessons learned are summarized, and the countermeasures for TBM jamming are developed regarding three stages of TBM tunnel construction. The results of this study provide a reference for the mechanism of TBM jamming and share certain practical countermeasures to ensure a safe and efficient TBM excavation in adverse geological conditions.

Excavation of underground research laboratory ramp in granite using tunnel boring machine: Feasibility study

Underground research laboratory (URL) plays an important role in safe disposal of high-level radioactive waste (HLW). At present, the Xinchang site, located in Gansu Province of China, has been selected as the final site for China’s first URL, named Beishan URL. For this, a preliminary design of the Beishan URL has been proposed, including one spiral ramp, three shafts and two experimental levels. With advantages of fast advancing and limited disturbance to surrounding rock mass, the tunnel boring machine (TBM) method could be one of the excavation methods considered for the URL ramp. This paper introduces the feasibility study on using TBM to excavation of the Beishan URL ramp. The technical challenges for using TBM in Beishan URL are identified on the base of geological condition and specific layout of the spiral ramp. Then, the technical feasibility study on the specific issues, i.e. extremely hard rock mass, high abrasiveness, TBM operation, muck transportation, water drainage and material transportation, is investigated. This study demonstrates that TBM technology is a feasible method for the Beishan URL excavation. The results can also provide a reference for the design and construction of HLW disposal engineering in similar geological conditions. © 2020 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Study of common wear prediction models for hard rock TBM disc cutters and comparison with field observation in Kerman water conveyance tunnel

Disc cutters are the most commonly used cutting tools in the hard rock tunneling by tunnel boring machines (TBMs). During operation of a TBM in any project, disc cutters wear out and should be replaced to maintain high machine performance. This is especially true in very strong and abrasive rocks. In the process of planning and estimation of completion time and cost for a given tunneling project, the lifetime of the disc cutter is often predicted using the empirical models due to their simplicity and availability. But understanding the background of the models and the relative difference between both predicted and actual lifetimes is critical for improving the accuracy of estimated cutter life. In this study, the basis and input parameters of the most frequently used empirical models for prediction of disc wear life are examined. The result of estimating cutter life by using these models is compared in similar working conditions, including TBM specifications, operating conditions, and rock abrasivity. The results show that in slightly abrasive rocks, the empirical models should be carefully chosen, because the estimated disc life may spread over a wide range. Furthermore, some models are very conservative, while others offer more compatible estimates with the rock abrasivity. Also, in the Kerman water conveyance tunnel, the predicted and actual cutter lives show good correlation with the ratio of the rock mass and intact rock strengths, in addition to laboratory measures of rock abrasivity.

From Exploratory Tunnel to Base Tunnel: Hard Rock TBM Performance Prediction by Means of a Stochastic Approach

Tunnel boring machine (TBM) performance prediction is often a critical issue in the early stage of a tunnelling project, mainly due to the unpredictable nature of some important factors affecting the machine performance. In this regard, deterministic approaches are normally employed, providing results in terms of average values expected for the TBM performance. Stochastic approaches would offer improvement over deterministic methods, taking into account the parameter variability; however, their use is limited, since the level of information required is often not available. In this study, the data provided by the excavation of the Maddalena exploratory tunnel were used to predict the net and overall TBM performance for a 2.96 km section of the Mont Cenis base tunnel by using a stochastic approach. The preliminary design of the TBM cutterhead was carried out. A prediction model based on field penetration index, machine operating level and utilization factor was adopted. The variability of the parameters involved was analysed. A procedure to take into account the correlation between the input variables was described. The probability of occurrence of the outcomes was evaluated, and the total excavation time expected for the tunnel section analysed was calculated.

A study of various models used in the estimation of advance rates for hard rock TBMs

A realistic assessment of the time and cost to complete a tunnel using tunnel boring machine (TBM) is directly related to the ability to accurately predict machine advance rate. Advance rate depends on various parameters including rock and rock mass properties, machine characteristics, and working conditions. Review of available literature shows that advance rate and utilization are much less studied than penetration rate, perhaps due to the difficulties in evaluating the interaction between input parameters, which make the advance rate hard to predict. The TBM advance rate can be estimated from either knowledge of penetration rate and utilization or directly from an evaluation of machine, ground, and operational factors by applying empirical formulas. This paper reviews different methodologies used in the prediction of advance rate and highlights potential pitfalls in the process. For this purpose, the capabilities of some commonly applied prediction models are discussed and their validity is examined using a comprehensive database of recently completed tunnels. The results of a comparing the estimated and field/observed advance rates indicate that most predictive models overestimate the performance. The results underline the current shortcomings of TBM advance rate estimation. A new model that is developed based on statistical analysis of a database of more than 300 TBM projects records is introduced for direct prediction of advance rate. The results show, the proposed new model’ estimated advance rate values are in good agreement with the actual values with a high coefficient of determination (79%). This clearly indicates a step forward in improving hard rock TBMs’ performance and project planning evaluation.

Application of block theory for evaluating face stability under disc cutters loading of TBM, case study of a water-conveyance tunnel project

Block theory has been widely used in analyzing the stability of rock blocks during engineering activities in jointed rock masses due to its simplicity and computational efficiency. This paper extended the traditional block theory to tunnels constructed using tunnel boring machine (TBM) by incorporating the disc cutter-block interaction mechanism. The rock blocks were divided into front, corner and rear blocks according to their spatial positions with respect to the cutterhead. The interaction between different blocks and the disc cutters mounted on the cutterhead were examined by estimating the forces exerted by disc cutters on the blocks relative to the location of the blocks in the face, direction of movement of the discs, and the depth of penetration. The estimated forces were then used in a subsequent analysis to calculate factor of safety for individual blocks and probability of blocks dislodging from its location. Two new evaluation parameters, eA and eη, were proposed to account for the probability of block instability. eA is the ratio of exposed area of unstable blocks to the face area and quantifies the size of unstable blocks relative to the face, and eη is the ratio of cutterhead rotation angles making a block unstable to the total rotation angles in a revolution which reflects the possibility of encountering an unstable block during a single round of revolution. This paper discussed the implementation of the idea of using fundamental concepts of block theory to determine block stability at the face and related analysis for assessment of face stability. The proposed method was used in evaluation of the stability conditions for a water-conveyance tunnel in western China that is currently under construction using a hard rock TBM.

Indirect Adaptive Robust Trajectory Tracking Control of Hard Rock TBM with Load Variation of Tunneling Face

Posture adjustment of open-type hard rock tunnel boring machine (TBM) can be achieved by properly adjusting the hydraulic pressure of gripper cylinder and torque cylinders. However, the time-varying inhomogeneous load acting on tunneling face of TBM and complex stratum working condition can cause the trajectory deviation. In this paper, the position and posture rectification kinematics and dynamics models of TBM have been established in order to track the trajectory. Moreover, there are uncertain parameters and uncertain loads from complex working conditions in the dynamic model. An indirect adaptive robust control strategy is applied to achieve precise position and posture trajectory tracking control. Simulation results show when the position deviation only occurs in Y-axis and the current orientation is parallel with the designed axis, the deviation can be corrected by controlling the pressure of gripper cylinder and the actual trajectory meets the designed axis when TBM is pushed forward 0.14 m in X-axis. If the deviation only occurs in Z-axis, then the deviation can be corrected by controlling torque cylinders. If the position deviation occurs both in Y-axis and Z-axis at the same time, the pressure of gripper cylinder and torque cylinders should be controlled at the same time to rectify the deviation. Simulation results are shown to illustrate the effectiveness and robustness of the proposed controller. This research proposes an indirect adaptive robust controller that can track the planned tracking trajectory smoothly and rapidly.

Non-linear vibration analysis of hard rock TBMs with regenerative and stick–slip effects

The significant vibration caused by hard rock tunnel boring machines (TBMs) increases structural damage and reduces excavation efficiency and therefore has become a subject of major study within the tunnelling process. A two degrees-of-freedom model that accounts for axial and torsional vibrations that are coupled through the disc cutter–rock interaction is established in order to qualitatively analyse the complicated dynamic behaviours of the TBM system. Introducing a regenerative cutting effect into the cutter–rock interaction laws results in three interaction modes which are formulated based on the Colorado School of Mines (CSM) model. The regenerative effects and the friction caused by axial stick–slip motion are the sources responsible for the TBM self-excited vibration, of which the dynamics are described by state-dependent delay differential equations (DDEs). The DDEs are linearised and discretised into piecewise ordinary differential equations (ODEs) by using the semi-discretization method. Based on the Floquet theory, the stability limits of a TBM system are obtained, showing that the stable lobes are intermittently distributed in the operational parameter space. The parameter regime corresponding to the practical tunnelling is unstable, indicating that the vibrations of TBMs are easily excited by disturbances and never vanish in practical tunnelling. The axial vibration of TBMs with regenerative and stick–slip effects experiences a subcritical Hopf bifurcation, when the TBM goes from unstable to stable parameter regimes. The stick–slip effect suppresses the vibrations, which would otherwise increase without limit until cutter bounce appears if only the regenerative effect is considered. It is found that both the amplitude and the frequency of the axial stick–slip vibration increase with the increase in the steady advance velocity. The predicted axial stick–slip vibration and its amplitude in this investigation are both in good agreement with the observations obtained from a practical tunnelling project. This study provides reasonable insight into the vibration mechanism of TBMs and serves as a basis for choosing proper operational parameters in a practical project to achieve smooth and efficient tunnelling.

Influence of Subjectivity in Geological Mapping on the Net Penetration Rate Prediction for a Hard Rock TBM

The net penetration rate of hard rock tunnel boring machines (TBM) is influenced by rock mass degree of fracturing. This influence is taken into account in the NTNU prediction model by the rock mass fracturing factor (ks). ks is evaluated by geological mapping, the measurement of the orientation of fractures and the spacing of fractures and fracture type. Geological mapping is a subjective procedure. Mapping results can therefore contain considerable uncertainty. The mapping data of a tunnel mapped by three researchers were compared, and the influence of the variation in geological mapping was estimated to assess the influence of subjectivity in geological mapping. This study compares predicted net penetration rates and actual net penetration rates for TBM tunneling (from field data) and suggests mapping methods that can reduce the error related to subjectivity. The main findings of this paper are as follows: (1) variation of mapping data between individuals; (2) effect of observed variation on uncertainty in predicted net penetration rates; (3) influence of mapping methods on the difference between predicted and actual net penetration rate.

Coordinated Control for Overactuated Hard Rock Tunnel Boring Machine Cutterhead Driving System

Coordinated Control for Overactuated Hard Rock Tunnel Boring Machine Cutterhead Driving System

Performance Evaluation of Hard Rock TBMs considering Operational and Rock Conditions

This paper focuses on studying the correlations of the performance of hard rock tunnel boring machines (TBMs) with operational and rock conditions. Firstly, a rigid‐flexible coupled multibody dynamic model of an opening hard rock TBM is established for the analysis of its vibration. Then four performance indexes including mean vibration energy dissipation rate, dynamic specific energy (DSE), disc cutter wear rate, and load sharing coefficient are introduced and formulated, respectively, for evaluating the vibration level, excavation energy efficiency, cutter’s vulnerability to wear, and load transmission performance of cutterhead driving system of the TBM. Finally, numerical simulation results of the TBM tunneling performance evaluation are obtained and validated by on‐site vibration measurement and tunneling data collection. It is found that operational and rock conditions exert important impact on TBM vibration level, excavation energy efficiency, and structure damage. When the type of rock to be cut changes from soft to hard with operational parameters held constant, TBM performance evaluated by these three indexes deteriorates significantly, and both the decrease of excavation energy efficiency and the increase of cutter wear rate caused by TBM vibration are obvious. This study provides the foundation for a more comprehensive evaluation of TBM performance in actual tunneling process.