Tunnel Boring Machine Excavation Research Articles

Reliability analysis of TBM disc cutters under different conditions

The reliability of disc cutters has a significant influence on the safety and working efficiency of tunnel boring machines (TBMs). To investigate the reliability of disc cutters under different geological and operational conditions, we conducted a series of novel rolling cutting tests on intact and jointed sandstone blocks using different dip angles and interlayers. Different normal forces and rotational speeds of the cutterhead were also applied during the experiment. A novel reliability estimation method, based on a logistic regression model, was then proposed, and the influence of dip angle, strata, normal force, and rotational speed on the reliability of the disc cutter were analyzed. The reliability estimation method consisted of data acquisition regarding the normal force and cutter wear, feature extraction using wavelet packet transform and correlation analysis, and the estimation of the logistic regression model. To obtain the spectrum and normalized wavelet energy for each frequency band, we decomposed the time domain of the normal force by the wavelet packet transform. A correlation analysis was employed to determine the feature frequency bands that were sensitive to wear loss. On the basis of salient feature parameters and wear loss, the logistic regression model was established to evaluate the reliability of disc cutters. The analytical results indicated that the optimal dip angle for rock cutting was 30°. In the presence of mixed-face and single ground, the reliability of disc cutters was primarily affected by the difficulty of TBM excavation and wear loss, respectively. An increase in normal force and rotational speed aggravated wear on the cutter, thus reducing reliability. Furthermore, compared with Rabinowicz’s formula, the proposed method considers various geological and operational conditions, making the proposed method more applicable to estimate the reliability of disc cutters.

Supporting Design Optimization of Tunnel Boring Machines-Excavated Coal Mine Roadways: A Case Study in Zhangji, China

Tunnel Boring Machines (TBMs) are a cutting-edge excavating equipment, but are barely applied in underground coal mines. For TBM excavation projects involving the Zhangji coal mine, the surrounding rock properties, stress field, cross section geometry, as well as the excavation-induced stress path of TBM-excavated coal mine roadways are different from those of traditional tunnels or roadways. Consequently, traditional roadway supporting technologies and experiences cannot be relied on for this project. In order to research an appropriate supporting pattern for a TBM-excavated coal mine roadway, first of all, the constitutive model of roadway surrounding rocks was derived, and a rock failure criterion was proposed based on rock mechanical tests. Secondly, a three-dimension finite element model was established and computer simulations under three different supporting patterns were conducted. Stress redistribution, roadway convergence, and excavation damage zone ranges of surrounding rocks under three different support patterns were analyzed and an optimal support design of the TBM-excavated roadway was made based on simulation results. During roadway excavation, convergence gauge and rock bolt dynamometers were installed for monitoring roadway convergence and the axial forces of rock bolts. The in-situ monitoring results verified the validity of roadway supporting designs.

Comparative Study of the Excavation Damage and Rockburst of the Deeply Buried Jinping II Diversion Tunnels Using a TBM and the Drilling‐Blasting Method

The rock mass failure induced by high in‐situ stresses during the excavation of deep diversion tunnels is one of the key problems in the construction of the Jinping II Hydropower Station. Based on the results of acoustic wave tests and rockburst statistical analysis conducted, this study focuses on the excavation damaged zone (EDZ) and rockburst events in the Jinping II diversion tunnels excavated using the tunnel boring machine (TBM) method and the drilling‐blasting method. The unloading failure mechanism and the rockburst induced by the two different excavation methods were compared and analyzed. The results indicate that, due to the different stress adjustment processes, the degree of damage to the surrounding rock mass excavated using the drilling‐blasting method was more serious than that using the TBM method. The EDZ induced by the TBM was usually distributed evenly along the edge of the excavation surface. While, the drilling‐blasting method was more likely to cause stress concentration, resulting in a deeper EDZ in local areas. However, the TBM excavation method can cause other problems in high in‐situ stress areas, such as strong rockbursts. The drilling‐blasting method is more prone to structural controlled failure of the surrounding rock mass, while the TBM method would induce high stress concentration near the edge of excavation and more widely distributed of stress adjustment induced failure. As a result, the scale and frequency of the rockburst events generated by the TBM were significantly greater than those caused by the drilling‐blasting method during the excavation of Jinping II diversion tunnels. The TBM method should be used carefully for tunnel excavation in high in‐situ stress areas with burial depths of greater than 2000 m. If it is necessary to use the TBM method after a comprehensive selection, it is suggested that equipment adaptability improvement, advanced prediction, and prediction technology be used.

Large-scale model experiment and numerical simulation on convergence deformation of tunnel excavating in composite strata

In this research, a large-scale model experiment was carried out to investigate the convergence deformation and failure characteristics of TBM (tunnel boring machine) excavation surrounding rock in deep buried composite strata. Based on the similar theory, the model test results show that the deformation of tunnel surrounding rock after excavation consists of two parts, instantaneous deformation and continuous creep deformation. When a circular tunnel is excavated in deep buried composite strata, the tunnel surrounding rock is firstly subjected to tensile failure on the soft rock side in the horizontal direction, and shear failure occurs at the top and bottom soft rock areas. With further increase of the external boundary load, the hard rock area of the tunnel in the horizontal direction suffers tensile damage due to stress concentration. Convergence deformation of the tunnel surrounding rock reaches the maximum value in the soft surrounding rock area. And then, based on the proposed damage-softening constitutive model of rock, numerical simulations were conducted out by using the finite difference method in order to analyze the convergence deformation mechanism of tunnel excavating in composite strata. The numerical simulation analysis results show that the damage rule of tunnel surrounding rock is controlled simultaneously by stress and lithological characteristics, which agrees very well with the experimental results.

Analysis of stress evolution characteristics during TBM excavation in deep buried tunnels

Full-face tunnel boring machines (TBMs) are widely used in tunnel engineering projects as an efficient, safe and economical tunneling method. However, TBM excavation causes stress near the tunnel boundary that is disturbed and redistributed under high in situ stress. The changing stress of the surrounding rock can lead to rock failure and cause machinery damage, owing to large rock mass deformations. Research on the impact of TBM excavation on the surrounding rock has mostly focused on the stress magnitude, while the influence of the variation of stress orientation has not been considered. In this study, the practical simulation of a double-shield TBM (DSTBM) construction process was conducted using a three-dimensional (3D) numerical simulation. The rock mass stress changed intensely with the rotations of the principal stress axes as the tunnel face passed through the rock monitoring section during the tunnel excavation. Additionally, the significant influence of stress variation is discussed in qualitative terms, and the analysis results of the stress path are presented. Moreover, using a new self-developed laboratory apparatus, the actual stress path of the surrounding rock is proposed under conditions of a changing principal stress magnitude and changing rotation of the principal axis during the process of TBM excavation.

Full-scale linear cutting test in Chongqing Sandstone and the comparison with field TBM excavation performance

In this study, determination of some machine parameters and performance prediction for tunnel boring machine (TBM) are conducted based on laboratory rock cutting test. Firstly, laboratory full-scale linear cutting test is carried out using 432-mm CCS (constant cross section) disc cutter in Chongqing Sandstone. Then, the input parameters for TBM cutterhead design are extracted; some TBM specifications are determined and then compared to the manufactured values. Finally, laboratory full-scale linear cutting test results are compared with the field TBM excavation performance data collected in Chongqing Yangtze River Tunnel. Results show that laboratory full-scale linear cutting test results, combined with some engineering considerations, can be used for the preliminary and rough design of TBM machine capacity. Meanwhile, combined with some modification factors, it can also well predict the field TBM excavation performance.

Physical model tests of the surrounding rock deformation and fracture mechanism of mixed-face ground under TBM tunneling

To investigate the surrounding rock deformation and fracture mechanism of mixed-face ground under tunnel boring machine (TBM) tunnelling, tests of a mixed-face ground model with TBM tunnelling were conducted by using a self-developed 3D large-scale simulation test machine and TBM excavation equipment. A fibre Bragg grating sensor and a distributed optical fibre sensor have been installed along the micro-pressure cell and are used to monitor the variation of stress, strain and displacement in the surrounding rocks while ‘uncoordinated deformation is observed at the interface’ during the excavation process. By comparing the experimental observation obtained in the soft and hard rocks located near the interface, a significant difference is observed in the deformation and stress measurement. The fractures observed in the shallow layer of the surrounding rock mass were mainly tensile fractures and tensile shear fractures, and pressure shear fractures were observed at a certain depth of the surrounding rock during TBM tunnelling. The results not only provide reference data on the mechanical behaviour of mixed surrounding rocks during tunnelling by TBM but also can guide construction units to prevent and control the disaster of TBM in tunnelling through mixed-face ground.

Effects of Strain Energy Adjustment: A Case Study of Rock Failure Modes during Deep Tunnel Excavation with Different Methods

The strain energy adjustment processes and rock failure modes corresponding to different excavation methods, such as Tunnel Boring Machine (TBM) or blasting, are quite different during construction of deep tunnel. Based on the diversion tunnel excavation of Jin-Ping II hydropower station (JPII) in southwestern China, the distribution characteristics of damage zones and adjustment process of rock strain energy under different excavation methods are analyzed and discussed, and the occurrences of rock bursts in the diversion tunnels are also monitored and analyzed. Research reveals that, the adjustment process of rock strain energy and the distribution of damage zones are obviously different under different excavation methods, and the depth and distribution of damage zone are positively correlated with the accumulation depth of rock strain energy. For blasting excavation, due to the combined effects of blast loading and in situ stress transient unloading, the surrounding rock is damaged seriously. The accumulation depth of rock strain energy is significantly larger than that by TBM excavation, while the accumulation peak of rock strain energy is smaller. For TBM excavation, the strain energy releases smoothly and slowly, and much more strain energy is accumulated in the vicinity of excavation face. Under similar geological conditions in the JPII, the rock bursts of intensive and mediate grades can be more frequently observed after blasting for the impact of severe excavation disturbance, and the strain energy transient adjustment may be the main disturbance contributor. While during TBM excavation, due to the smooth adjustment process of rock strain energy, the disturbance to surrounding rock is limited, and the accumulation peak of rock strain energy is higher and closer to the excavation face, which may result in more spalling events or minor rock bursts.

Rock Joint Rate (RJR); a new method for performance prediction of tunnel boring machines (TBMs) in hard rocks

Rock Joint Rate (RJR) is a novel method for predicting the penetration rate (PR) of tunnel boring machines (TBMs) in hard rock environments. This model is devised based on a combination of geological and operational data obtained from a number of tunnels excavated in igneous and sedimentary rocks. The Geological condition, TBM excavation parameters and the tunnel diameter are regarded as the main input parameters in the RJR method. The rock mass uniaxial compressive strength (UCS) and the discontinuities' characteristics along the tunnel excavation axis including the number, frequency, orientation, spacing and aperture of the joints are the principle geological parameters. In addition, the machine thrust force and the cutterhead rotation speed (RPM) have been introduced as the main involved operational parameters of the machine. Easy to use input parameters, the simple investigation procedure, not requiring complicated laboratory tests and the capability to control the overall costs of a project as well as precise estimations of the operation time by dint of accurate determination of penetration rate (PR) are the main advantages of the proposed RJR model. In this method, a number of indices including the machine stress index (MS), strength ratio (SR), raw penetration rate (PRw) and basic penetration rate (PRb), which are derived from the integration of the main input parameters in RJR model are defined for evaluating the penetration rate of the machine. Overall, in this research, around 140,000 performance databases corresponding to 22,300 boring strokes of three different tunnels with a total excavated length of about 19 km were utilized to validate the proposed RJR model. According to the acquired results in this study, the estimated value of PR by the suggested method of RJR (PRRJR) shows a good agreement with the field penetration rates (PRField). Therefore, this model can be employed as a new method for predicting the penetration rate of TBMs in hard rocks.

Lake Mead Intake No. 3

Abstract As a result of a sustained drought in the Southwestern United States, and in order to maintain existing water capacity in the Las Vegas Valley, the Southern Nevada Water Authority constructed a new deep-water intake (Intake No. 3) located in Lake Mead. The project included a 185 m deep shaft, 4.7 km tunnel under very difficult geological conditions, and marine works for a submerged intake. This paper presents the experience that was gained during the design and construction and the innovative solutions that were developed to handle the difficult conditions that were encountered during tunneling with a dual-mode slurry tunnel-boring machine (TBM) in up to 15 bar (1 bar = 105 Pa) pressure. Specific attention is given to the main challenges that were overcome during the TBM excavation, which included the mode of operation, face support pressures, pre-excavation grouting, and maintenance; to the construction of the intake, which involved deep underwater shaft excavation with blasting using shaped charges; to the construction of the innovative over 1200 t concrete-and-steel intake structure; to the placement of the intake structure in the underwater shaft; and to the docking and connection to an intake tunnel excavated by hybrid TBM.

Hard rock tunnel boring machine penetration test as an indicator of chipping process efficiency

The transition from grinding to chipping can be observed in tunnel boring machine (TBM) penetration test data by plotting the penetration rate (distance/revolution) against the net cutter thrust (force per cutter) over the full range of penetration rates in the test. Correlating penetration test data to the geological and geomechanical characteristics of rock masses through which a penetration test is conducted provides the ability to reveal the efficiency of the chipping process in response to changing geological conditions. Penetration test data can also be used to identify stress-induced tunnel face instability. This research shows that the strength of the rock is an important parameter for controlling how much net cutter thrust is required to transition from grinding to chipping. It also shows that the geological characteristics of a rock will determine how efficient chipping occurs once it has begun. In particular, geological characteristics that lead to efficient fracture propagation, such as fabric and mica contents, will lead to efficient chipping. These findings will enable a better correlation between TBM performance and geological conditions for use in TBM design, as a basis for contractual payments where penetration rate dominates the excavation cycle and in further academic investigations into the TBM excavation process.

Acoustic emission monitoring on damage evolution of surrounding rock during headrace tunnel excavation by TBM

The acoustic emission (AE) characteristics of the damage evolution of surrounding rock during tunnel-boring machine (TBM) excavation were studied using AE monitoring and ultrasonic testing. The results indicated that the distribution of the AE signals in the surrounding rock were obtained by the reasonable arrangement of the positions of the probes and the multi-parameter filtering method during TBM excavation. For engineering I, rock damage at different degrees along the direction of the TBM advancement was observed within 5 m ahead of the tunnel face during TBM excavation, while the most severe rock damage appeared 1 m ahead of the tunnel face. The difference in the AE events and energy rates helped distinguish the embedding depths of the loose zone, EDZ and disturbance zone, which were 1, 1–3 and 3–8 m from the tunnel wall, respectively. For engineering II, different degrees of rock damage along the axial tunnel direction were observed within 6 m ahead of the tunnel face, with the most severe rock damage occurring 1 m ahead of the tunnel face. The results can provide significant reference values for the safe and efficient application of TBM excavation in engineering processes.

Multidisciplinary design optimization of tunnel boring machine considering both structure and control parameters under complex geological conditions

A Tunnel Boring Machine (TBM) is an extremely large and complex engineering machine that usually works under a complicated geological environment to excavate tunnel underground. Considering the large number of sub-systems that usually belong to different disciplines, it is a challenging task to define, model, and optimize the whole TBM from the perspective of system engineering. Also, due to the complex mechanism and geological environment, the flexibility and efficiency of existing TBM excavation strategies are generally limited. To address these challenges, a multidisciplinary modeling is presented so that corresponding analytical or empirical models of each sub-system are formulated, and a multidisciplinary design optimization (MDO) method is applied to the TBM system optimization. Four excavation strategies are studied and compared, including: (i) two existing excavation strategies, and (ii) two new proposed excavation strategies by making control and/or structure parameters adaptive to geological conditions. Two case studies with these four excavation strategies are presented to illustrate the effectiveness and benefits of designing TBM using MDO methodologies. Wherein, Case I aims to minimize the construction period taking into account the restriction of sub-systems, and Case II simultaneously minimizes construction period, cost, and energy consumption. Since the resulting MDO formulation is straightforward to be solved as a single problem, the All-At-Once (AAO) method is utilized in this paper. The optimization results obtained by modeling the problem as MDO show that the excavation strategy with adaptive control and structure parameters can significantly reduce the total construction time, with lower cost and energy consumption.

Theoretical model of the equivalent elastic modulus of a cobblestone–soil matrix for TBM tunneling

Cobblestone–soil mixed ground is a composite comprising cobblestones surrounded by soil. It is typical mixed-face ground encountered during tunnel boring machine (TBM) tunneling, and it may result in cutter wear, jamming of the roller cutterhead, poor TBM performance and cost overruns. The present paper investigates the deformation problem of cobblestone–soil mixed-face ground during TBM excavation. The ground under study is composed of two components (soil matrix and cobblestones) usually firmly bonded together at the interface, and can be regarded as a continuum. Previous studies have proposed many theoretical models for a composite material with two components. Representative models include the parallel model, series model, and effective medium theory model. Nonetheless, these models are limited by their assumptions and preconditions. In the present study, under an assumption of uniform strain, analytical solutions were derived for the equivalent elastic modulus while the cobblestone is assumed to be perfectly spherical or ellipsoidal. Triaxial compression tests were carried out to validate the analytical solutions. The equivalent elastic modulus derived from the triaxial experiments and theoretical models matched rather closely. The analytical solutions are helpful in clarifying the deformation of such ground and enhancing TBM performance.

TBM–Block Interaction during TBM Tunneling in Rock Masses: Block Classification and Identification

A new block-classification method for tunnel construction using a tunnel-boring machine (TBM) to capture the geometrical and mechanical transformation of rock blocks in the course of TBM excavation is proposed in this paper. The machine–block interaction is interpreted by dividing the joint blocks into blocks influenced by TBM excavation and blocks uninfluenced by TBM excavation. The influenced blocks are categorized further as contacting or noncontacting blocks according to whether they are in contact with the TBM. The contacting blocks include the front block, the corner block, and the rear block, based on the spatial location of blocks with respect to the cutterhead. Different types of blocks have distinct kinematic and mechanical characteristics. The sizes and shapes evolve, and the categories may be changed for rock blocks during excavation. The identification algorithms for influenced blocks and three types of contacting blocks are presented. Finally, a simple example considering a double-shield TBM tunnel excavation is used to illustrate the effectiveness of the new block-classification approach to guide TBM tunneling. The new classification approach will be helpful in evaluating the block removability and the possibility of cutterhead clogging and to shield blockage during tunneling with a TBM.

막장전방 예측기법에 근거한 TBM 터널의 리스크 관리 시스템 개발 및 현장적용

ABSTRACT: When utilizing a Tunnel Boring Machine (TBM) for tunnelling work, unexpected ground conditions can be encountered that are not predicted in the design stage. These include fractured zones or mixed ground conditions that are likely to reduce the stability of TBM excavation, and result in considerable economic losses such as construction delays or increases in costs. Minimizing these potential risks during tunnel construction is therefore a crucial issue in any mechanized tunneling project. This paper proposed the potential risk events that may occur due to risky ground cond itions. A resistivity survey is utilized to predict the risky ground conditions ahead of the tunnel face during construction. The potential risk even ts are then evaluated based on their occurrence probability and impact. A TBM risk management system that can suggest proper solution methods (measures) for potential risk events is also developed. Multi-Criterion Decision Making (MCDM) is utilized to determine the optimal solution method (optimal measure) to handle risk events. Lastly, an actual construction site, at which there was a risk event during Earth Pressure-Balance (EPB) Shield TBM construction, is analyzed to verify the efficacy of the proposed system.Keywords: TBM, Risk management, Ahead of tunnel face, Risky ground prediction, MCDM

Study on rock mass boreability by TBM penetration test under different in situ stress conditions

Rock mass boreability is a comprehensive parameter reflecting the interaction between rock mass and a tunnel boring machine (TBM). Many factors including rock mass conditions, TBM specifications and operation parameters influence rock mass boreability. In situ stress, as one of the important properties of rock mass conditions, has not been studied specifically for rock mass boreability in TBM tunneling. In this study, three sets of TBM penetration tests are conducted with different in situ stress conditions in three TBM tunnels of the Jinping II Hydropower Station. The correlation between TBM operation parameters collected during the tests and the rock mass boreability index is analyzed to reveal the influence of in situ stress on rock mass boreability and TBM excavation process. The muck produced by each test step is collected and analyzed by the muck sieve test. The results show that in situ stress not only influences the rock mass boreability but also the rock fragmentation process under TBM cutters. If the in situ stress is high enough to cause the stress-induced failure at the tunnel face, it facilitates rock fragmentation by TBM cutters and the corresponding rock boreability index decreases. Otherwise, the in situ stress restrains rock fragmentation by TBM cutters and the rock mass boreablity index increases. Through comparison of the boreability index predicted by the Rock Mass Characteristics (RMC) prediction model with the boreability index calculated from the penetration test results, the influence degree of different in situ stresses for rock mass boreability is obtained.

Influence of Corrosion on the Abrasion of Cutter Steels Used in TBM Tunnelling

Abrasion on tunnel boring machine (TBM) cutters may be critical in terms of project duration and costs. Several researchers are currently studying the degradation of TBM cutter tools used for excavating hard rock, soft ground and loose soil. So far, the primary focus of this research has been directed towards abrasive wear. Abrasive wear is a very common process in TBM excavation, but with a view to the environment in which the tools are working, corrosion may also exert an influence. This paper presents a selection of techniques that can be used to evaluate the influence of corrosion on abrasion on TBM excavation tools. It also presents the influence of corrosion on abrasive wear for some initial tests, with constant steel and geomaterial and varying properties of the excavation fluids (soil conditioners, anti-abrasion additives and water). The results indicate that the chloride content in the water media greatly influences the amount of wear, providing evidence of the influence of corrosion on the abrasion of the cutting tools. The presence of conditioning additives tailored to specific rock or soil conditions reduces wear. However, when chloride is present in the water, the additives minimise wear rates but fail to suppress corrosion of the cutting tools.

Use of TBM excavated materials as rock filling material in an abandoned quarry pit designed for water storage

Material from tunnel excavations (muck) for Istanbul's metro rail transport system must be rapidly removed from the construction site and stored in a suitable area. This time restriction necessitates categorization of the excavation materials according to technical specifications and usability. The excavated material (muck) could be used as aggregate in concrete, filling and paving material in road construction, and as a soil replacement for covering or foresting stony/rocky areas, etc. This study examines the use of the tunnel boring machine (TBM) excavation material (muck) as rock filling in water storages, and as rock embankments in abandoned quarry pits designed for water storage. The study was designed in two phases. In the post excavation phase, physical and mechanical properties of materials [sandstone, shale, and diabase] excavated from the Kadıköy–Kartal metro tunnels were tested under laboratory conditions for their suitability as rock and crushed stone (aggregate) material. In the pre-excavation phase, a total of 227 samples representing eight different rock types were analyzed in this geotechnical study of the tunnel route. This phase contains core-drilling data during the tunnel opening survey.Analyses indicate that the various TBM excavation materials from the Kadıköy–Kartal metro tunnel are suitable for use as filling material in abandoned quarry pits for water storage in a forested hillslope. The establishment of a storing area based on water inflow from precipitation and infiltration of water from naturally-sloping forested land could provide the needed water and perhaps generate revenue.

Mechanical response of surrounding rock of tunnels constructed with the TBM and drill-blasting method

There are two kinds of excavation methods in underground engineering: the tunnel boring machine (TBM) and the drill-blasting method. A large number of studies have shown that the deformation and failure, the degree of disturbance, the stability and the reinforcement measures of surrounding rock using the TBM and drill-blasting method vary from each other. To accurately master these macroscopic damages, it is necessary to focus on the investigation of the micro-mechanical responses of the surrounding rock. Scanning electron microscopy tests, acoustic emission tests and tunnel acoustic detection tests were carried out to analyze the mechanical response of surrounding rock of tunnels, which were excavated in marble by, respectively, the TBM and the drill-blasting method. The tests results showed that most of the rock fractures cut by TBM is wipe along the crystal, and the failure mechanism is mainly cutting, while most of the rock fractures induced by the TBM coincide with crystal planes, its mechanism is mainly tensile. The stress–strain curves of rocks cut by the TBM method are rather flat around the peak strength, which means a strong resistance to deformation around the peak load. The response of AE for the rock cut by the TBM method appears after larger strains than the response of the rock constructed by the drill-blasting method. This suggests that the resistance to damage is higher under TBM excavation conditions. The relaxation depths of the tunnel excavated by the drill-blasting method are larger than the tunnel excavated by the TBM method. The research can provide more insight into tunnel failure mechanisms and provide a framework for reinforcement measures.