Shield Tunneling Method Research Articles

Continuous Slag Discharge Construction Technology for Shield Tunneling in Narrow Space Environment

The shield tunneling method is the main construction method in subway tunnel construction, which has the characteristics of safety, efficiency, mechanization, and high degree of automation. However, the shield tunneling equipment is huge, the supporting facilities are numerous, and the site requirements are high. In response to the problems of slow slag removal speed and low construction efficiency in shield tunneling under the construction conditions of small wellhead shield tunneling sections in urban subways, taking the shield tunneling section of Guangzhou Metro Line 13 Phase II as the background,This article introduces the main components, working principles, installation and transportation processes, fault handling, and benefit analysis of the continuous belt conveyor slag removal system,This article elaborates on the method of using a continuous belt conveyor in the tunnel combined with a vertical lifting system at the wellhead to achieve continuous slag removal during underground shield tunneling construction in a narrow wellhead construction site. This not only improves excavation efficiency but also reduces construction costs, solves construction problems, and provides reference for similar projects in the future.

Mechanical characterization of lining under three-dimensional complex load during shield posture adjustment

The shield tunneling method is widely used in urban underpass construction. However, research on the mechanical characteristics of segments during construction is insufficient. Throughout the shield tunneling construction process, segments undergo a diverse range of loads, and their modes become complex. During the adjustment of the posture of the shield machine along a curved path, segments must withstand three-dimensional uneven loads from the shield tail brush and extrusion of the shield shell, in addition to conventional loads. Thus, this study delves into the mechanical characterization of the lining during shield posture adjustment. First, three-dimensional refined models of the longitudinal and circumferential joints were established to investigate their bending and shear mechanical properties. Using the joint and shield tail brush stiffness models, a nonlinear spring-connector-shell model was developed for the mechanical analysis of segments during posture adjustment. Subsequently, a three-dimensional segment load model was formulated for the construction period. The segment response under the influence of different posture adjustments was examined using a numerical model of a tunnel subjected to a complex three-dimensional load. Furthermore, a multistage model of the segment response under various posture adjustments was established. This model serves as a valuable reference for engineering applications.

Experimental investigation of tail void grouting pressure evolution for super-large diameter shield tunnels

The shield tunneling method is widely used in underground construction. Factors such as the variations in grouting pressure and stiffness/strength evolution over space and time directly affect ground deformation and system stability. To investigate the effect of grouting pressure variation, grouting influence zone, and hydromechanical properties on the model responses (e.g., surface settlement and lining forces), an innovative model test setup was developed to simulate the tunneling process wherein the lining could settle or float during grout injection. This setup included tunnel shrinking, loading-unloading, grout injection, and sample preparation systems. The experimental results show that the grouting pressure evolution law may be significantly affected by the tunnel translation. When the tunnel centerline was fixed in the traditional model tests, the resulting grouting pressure in the tail void was lower than that when the tunnel was free to move. This is because the tunnel translation changed the shape of the annular gap and contributed to the measured grouting pressure. The proposed setup is capable of revealing a more realistic law of grouting pressure evolution, and the subsequent spatio-temporal grouting-induced soil/lining behavior is currently being investigated.

Numerical study on the influence of excavation slope on the structural behavior of ground penetrating shield tunnels

The ground penetrating shield technology (GPST) is a fast shield tunnelling method, wherein the shield is launched and received at the ground surface without constructing deep and large working shafts. With regard to the notable sloping excavation characteristics of the GPST, this study established a three-dimensional numerical model to analyze the impact of the excavation slope on the structural response of the tunnel lining based on the South Longshui Road Cross-river Tunnel project in Shanghai. The results indicate that the circumferential earth pressure acting on the lining is determined by both the buried depth and decomposition angle induced by the change in the excavation slope. The distribution of the earth pressure along the longitudinal direction may be affected by the excavation slope, and this subsequently affects convergence deformation of the tunnel. An increase in the excavation slope equalized the distributed force acting on the lining. In addition, the existence of circumferential joints exaggerates the impact of the excavation slope on the differential convergence between adjacent rings. A larger excavation slope resulted in a decrease in the proportion of convergence deformation caused by the longitudinal joints. These findings can provide important guidance for controlling the ovalization and dislocation behaviors of GPST.

Cavity behind Special Segment Structures in Upward Shield Tunneling: A Numerical Approach

Proper design of special segments under cavity conditions is essential for successfully implementing the upward shield tunneling method. When constructing upward tunnels, the segment structure in the corresponding construction area of the horizontal tunnel is special. To study the internal force distribution on the structure under the worst possible conditions given by the upward shield tunneling method, MIDAS GTS NX software is used to numerically simulate the structure based on the condition of the cavity behind it to determine the most unfavorable radius of the cavity. Moreover, an analysis of the cavity location is conducted. The results demonstrate that when the cavity is located at the bottom of the arch with a radius of 1 m and near the top of the arch with a radius of 0.5 m, the special segment structure is under the most unfavorable combination of stresses. The most dangerous working condition occurs when there is a 0.5 m radius cavity on one side of the arch in the cross‐section of the special segment.

SCA-MADRL: Multiagent deep reinforcement learning framework based on state classification and assignment for intelligent shield attitude control

With the wide application of the shield tunneling method in tunnel engineering, the untimely and incorrect attitude control of shield systems has become an essential factor affecting the quality of shield tunneling. The use of multi-agent deep reinforcement learning (MADRL) algorithm to learn correct and timely shield attitude correction policies is beneficial for handling shield attitude control tasks which are complex and separable. However, the sensing data of the shield systems are complicated and widely distributed, which affects the learning efficiency of the agents. To resolve this problem, this paper proposes a MADRL framework based on state classification and assignment (SCA) for adaptive shield attitude control. SCA-MADRL uses a clustering algorithm to classify states and uses a planning model to make the agent's learning space a consistent state space so that each agent can learn efficiently in its own learning space. The state classification algorithm in the framework can improve the learning efficiency of the agent, and the proposed assignment algorithm can further enhance the learning effect when reusing the agent. This paper verifies the necessity and effectiveness of using task decomposition to implement MADRL for equipment control and provides a practical framework for automated and intelligent shield systems.

Study on Assembly and Tensile Performance of Circumferential Anchor Joint for Shield Tunnel Considering Roughness and Size of Structure

Anchor joint is conducive to improving the automation level of the shield tunneling method, whose mechanical behavior is still not fully clear due to the complicated interaction among various structural components. In this paper, a refined FEM model is established and adopted to investigate the anchor joints' assembly and tensile performance. The operation principles of the anchor joint are first introduced for better understanding. Then, a detailed description is presented for the developed refined FEM, including the material properties, structural features, and verification. After that, 76 working conditions in total are set, and an in-depth study is conducted to examine the influence of surface roughness, gap sizes, and strength grades on the assembly and tensile behavior of anchor joints both quantitatively and qualitatively. The results show that the surface roughness mainly influences the maximum assembly load and tensile capacity of anchor joints. The gap size obviously impacts both quantitative and qualitative assembly characteristics and tensile behavior for anchor joints, whose effect is more significant than the surface roughness. The strength grade has a different influence on the distinct mechanical behavior of anchor joints. There is a positive correlation between anchor joints' assembly and tensile behavior. To satisfy the requirement of enough tensile capacity and reasonable assembly difficulty, a good solution should be to reach an appropriate balance between the assembly and tensile behavior of anchor joints.

Safety level assessment of shield tunneling in water rich sandy pebble strata with large particle size

Shield tunneling method is widely used in urban metro construction. The construction stability is closely related to the engineering geological conditions. Sandy pebble strata have a loose structure and low cohesion, resulting in great engineering-induced stratigraphic disturbance. Meanwhile, the high water-abundance and strong permeability are extremely detrimental to construction safety. It is of great significance to evaluate the dangerousness of shield tunneling in water-rich pebble strata with large particle size. In this paper, risk assessment of engineering practice is carried through with Chengdu metro project in China as a case study. Referring to the special engineering situations and assessment workload, seven evaluation indices, including compressive strength of pebble layer, boulder volume content, permeability coefficient, groundwater depth, grouting pressure, tunneling speed and tunnel buried depth are selected to establish an evaluation system. A complete risk assessment framework is established based on the cloud model, AHP and entropy weight method. Further, the measured surface settlement is taken as the risk degree characterization to verify the results. This study can provide reference for method selection and evaluation system establishment in the risk assessment of shield tunnel construction in water-rich sandy pebble strata, and contribute to proposing safety management in similar engineering projects.

Tunnel Lining Segment Deformation and Cracking Mechanisms during Tunneling in Complex Mixed Grounds with the Combined Mining and Shield Tunneling Method

The combined mining and shield tunneling method solves the challenge that shield machine is slow to excavate hard rock formations during tunneling in complex mixed grounds such as soft soils mixed with hard rocks, which, however, causes the deformation and cracking of tunnel segments. Both in-situ field measurements and three-dimensional numerical simulations are conducted in this study to analyze the segment deformation and cracking mechanism of a tunnel excavated in complex mix grounds with the combined mining and shield tunneling method. It is concluded that the segment deformation and cracking are caused by insufficient pea-gravel fillings and uneven grouting pressures. To ensure the tunnel ovality satisfying standards and minimize the segment deformation and cracking, the angle range of the tunnel wrapped in the pea gravel should be greater than 180° and the resistance coefficient provided by the filling layer after grouting should be greater than 20 MPa/m. Moreover, it is found that the difference between the grouting pressures at the top and bottom of the tunnel has a significant impact on the overall deformation and opening amount of the joints between the segments.

Influences of polyanionic celluloses and temperature on the rheological property of seawater slurries

As an increasing number of submarine tunnels are being constructed by the slurry shield tunnelling method, seawater intrusion into slurries and variations in strata temperature are inevitably encountered during construction. They will lead to obvious deterioration in rheological properties of slurries, which can be adverse for the filter cake formation and even cause tunnel face instability. Considering the design of the slurry parameters and the actual slurry support effect, it is essential to select a suitable slurry ingredient and investigate the rheological properties of seawater slurries under different temperature environments. Using polyanionic celluloses (PAC) as the additive to seawater slurries was proposed in this paper. The influence of PAC contents on the rheology and physical stability of seawater slurries was investigated through laboratory experiments, with PAC contents varying from 0 to 0.4%. The rheology enhancement mechanism of PAC was also analyzed. Furthermore, the flow pattern and constitution relationship of seawater slurries with 0.4% PAC were studied at different temperatures from 2℃ to 30℃. The results show the presence of PAC can significantly enhance the viscosity and physical stability of seawater slurries. The seawater slurries incorporating 0.4% PAC and 12% Na-bentonite can maintain an excellent colloidal rate with 97.5% and a high viscosity, which was recommended to be a prospective mixing proportion used in slurry projects. Additionally, the flow characteristic of seawater slurries with different PAC contents can be described by the power law model very well. Moreover, with the increase in temperature, the rheological index showed an increasing trend, but the consistency coefficient gradually decreased. The constitutive equation of seawater slurries considering the effect of temperature was proposed. This research will provide significant guidance for the selection of slurry parameters and the establishment of seawater slurry infiltration theories during the construction of submarine tunnels.

A shield tunneling method for enlarging the diameter of existing tunnels: Experimental investigations

As for the construction of a metro line, excavated stations usually serve as departure and receiving shafts of the shield tunneling machines, used for drilling of station-to-station tunnels. However, the shield tunneling machines may reach the stations before their excavation. In order to avoid stopping of tunneling to wait for the completion of the station, a Shield Twice Tunneling Method (STTM) is developed and applied to a real engineering example. It permits the station-to-station tunneling machines to pass through the stations first. Subsequently, larger-diameter shield tunneling machines are driven from one end of the station to the other one. The resulting tunnels serve as side-platform stations. A model test, simulating the tunneling process of the larger-diameter shield tunneling machines, was carried out. It was designed according to the concept of equivalent specific energy. The experimental results corroborate the rationality of the selected tunneling machine and of its equipment with cutters. In addition, suitable tunneling parameters are provided. The average values of the thrust forces and the torsional moments are predicted, based on the results of the model test. They agree with the monitored results on site. This demonstrates the usefulness of the model test. Application of the STTM to a real engineering project shows that the entire construction period was reduced by 45%.

Ground Surface Displacements and Failure Mechanisms induced by EPB Shield Tunneling Method and Groundwater Levels Changes

Ground Surface Displacements and Failure Mechanisms induced by EPB Shield Tunneling Method and Groundwater Levels Changes

Shield Cutting Pile‐Group Implementation Effects on the Superstructure

The shield tunneling method is widely used in urban subway construction. However, as the layer stress state changes during shield tunnel construction, layer displacement and surface deformation occur accordingly. This study tries to investigate the settlement and deformation of the masonry structure in shield cutting the composite foundation of group piles in a shield tunnel project at Zhengzhou Metro Line 5. To understand the distribution characteristics and changing rules of building settlement during the process of shield cutting group piles composite foundation passing through the masonry structure, a thorough analysis of the ground surface settlement and building settlement, including on‐site measured, was conducted. The results show that piles go down through a composite foundation during shield cutting. The cumulative maximum settlement and maximum differential settlement of the masonry structure were concentrated at the intersection of the tunnel axis and the building. The longitudinal distribution of the cumulative settlement of the south and north wall of the masonry structure changes continuously with the change of the position of the shield excavation surface. That behavior may cause the building to be tilted and deformed and cause the structure to undergo rigid rotation and twisting deformation. Based on the composite pile foundation project of the Shield Tunnel Cutting Group in a specific section of Zhengzhou Metro Line 5, this paper analyzes the surface settlement and foundation settlement data of the building caused by the construction of the shield. It obtains the changes of the surface settlement and the settlement of the foundation of the building. No other changes have been made to the existing cracks in the external walls of the building. At the same time, because of the low angle between the longitudinal axis of the masonry structure and the tunnel axis (22°) and the positive effect of the ring beam and column of the structure in the building, it is clear that the construction of this project has little effect on the upper building, thus showing improved control.

Numerical simulation study of overlapping tunnels in soft soil

In the process of urban subway shield construction, how to ensure the safety of the newly built tunnel and surrounding buildings is the key issue in the construction. Aiming at the overlapping shield tunneling in soft soil layer, this paper takes overlapped shield tunneling using the overlapping shield tunneling method in a subway section of Kunming Line 6 as the research object, and uses the finite element software ABAQUS to simulate the overlapping shield tunneling. The results are compared with the monitoring data of site construction. The results show that the construction sequence of constructing the lower tunnel first and then the upper tunnel and the condition of grouting and strengthening the soil around the overlapping tunnels can control the settlement of the ground to a large extent.

Effects of cement addition on arsenic leaching from soils excavated from projects employing shield-tunneling method

Tunnel construction in soft alluvial deposits is generally done using the shield-tunneling method, a technique that requires the mixing of cementitious materials with excavated soils to reinforce and stabilize the excavated tunnel walls. Although the mechanical properties of soft soils and sediments are improved after introduction of cementitious materials, this process could increase the pH of these geological materials and mobilize naturally occurring arsenic (As). In the present study, the effects of cement addition on As leaching from tunnel-excavated soils naturally contaminated with As were investigated. Sequential extraction experiments were also carried out to determine the chemical forms, solid-phase partitioning and leachability of As in the soils. The results of attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) showed slight changes in the chemical properties of soils due to cement addition but the chemical phases of As remained unchanged. In the absence of cement, sequential extraction showed higher As leaching from the soils when the exchangeable As fraction and total As content increased. In contrast, As leaching increased up to pH 10.3 and then decreased at higher pH values when cement was added. This trend was observed irrespective of the soil samples, which indicates that pH adjustment is an important countermeasure in restricting As leaching from excavated soils.

Design of the metro tunnel project tunnel linings for fire testing

AbstractWith a growing pipeline of major transport infrastructure projects transforming Victoria's road and rail networks, there is an increase in demand for the construction of underground tunnels using the shield tunneling method. Such tunnels need to be designed for fire resistance in order to preserve both structural integrity and serviceability in the event of a fire event. This paper describes the approach taken to design the concrete tunnel lining segments for Melbourne's Metro Tunnel Project for structural stability during a severe fire incident. Two types of fire testing programs were implemented, both of which used the RABT ZTV (rail) fire curve. The first involved the fire testing of 12 unloaded flat panels in order to determine whether a particular concrete mix design would be susceptible to spalling. Second, six prototype full scale tunnel lining segments were subjected to full scale structural fire testing, for the first time in Australia. The results indicated that full scale structurally loaded fire tests are essential as unloaded flat panels underestimate the degree of spalling. Addition of PP fibers are successful in mitigating spalling in addition to using pozzolans cements such as flyash and slag.

Analysis of Influences of Shield Tunneling Method on the Existing Upper Road Structures

Analysis of Influences of Shield Tunneling Method on the Existing Upper Road Structures

Analysis of Ground Settlement in Metro Tunnel Construction with Shield Tunneling Method

With the continuous development of underground space, subway tunnel construction methods are constantly updated and developed. And shield tunnel method has become one the most common methods of subway tunnel construction. However, shield construction is often accompanied with the occurrence of surface subsidence. There may be a collapse of the surface when the surface settlement reaches a certain amount and the up buildings on the surface may be seriously influenced. The construction model was established based on FLAC3D software by using the engineering geological characteristic parameters of the study area and the observation data of ground subsidence during construction, which was compared and verified with the field vmonitoring value, and the subsidence was simulated and predicted. Using FLAC3D to establish a settlement prediction model for tunnel excavation and record the space-time changes of surface subsidence, it can better reflect the land subsidence situation and law in the horizontal and vertical directions of the axis of the subway tunnel.

The Effects of Tangential Ground–Lining Interaction on Segmental Lining Behavior Using the Beam-Spring Model

The shield tunneling method is widely used, especially in urban areas, since it is efficient for minimizing disturbances to surroundings. Although segmental lining is commonly used in this method, in both the research and practice of tunnel lining design, the interaction between the ground and lining in the tangential direction remains unclear; that is, the mobilizing shear stress due to load models and the degree of the bond in the tangential direction. Therefore, to clarify the effects and mechanism of the tangential ground–lining interaction on segmental lining behavior, a parameter study was carried out, taking tangential spring stiffness, load models, soil stiffness, and shallow and deep tunnels as parameters. The interaction conditions were based on the existing literature. It was found that (1) the tangential spring has small effects on lining behavior, (2) the load model significantly affects the sectional forces, (3) the initial tangential earth pressure and slip ground–lining boundary provide more safety from a design viewpoint, and (4) in the case of shallow tunnels in soft ground, tensile stress appears in the lining. Therefore, it is important to take the tangential ground–lining interaction conditions into consideration during tunnel lining analysis.

Study of the Construction Sequence of Overlapping Tunnels by the Shield Tunneling Method: A Case Study of the Longest Overlapping Tunnel in China

In this study, the reasonable construction sequence of an overlapping tunnel shield is investigated. Taking the overlapping tunnel of Tianjin Metro Line 5 as the background, a three‐dimensional numerical model was established using Flac3D software to study the influence of the “first up and then down” and “first down and then up” construction sequences of the overlapping tunnel on the surface settlement, stratum displacement, lining radial stress, and displacement. The research results show that the shape and width of the final settlement tank on the ground under the two conditions are basically the same, and the difference between the maximum cumulative settlements is small. The accumulated ground settlement caused by the first up and then down construction sequence is 1.8 mm larger than that caused by the first down and then up sequence. The difference between the two working conditions on the vertical displacement of the stratum mainly occurs in the middle stratum of the upper and lower tunnels, and the proportion of the strata in the uplifted state and subsidence state is different. The construction sequence has little effect on the radial stress on the lining of the upper and lower tunnels. Under these two conditions, the excavation of the second tunnel causes a small change in the radial stress of the preceding tunnel lining, both within 4.2%. Under the working condition of first down and then up, the construction of the second tunnel causes the lining of the preceding tunnel to rise by 7.2∼9.2 mm. Under the condition of first up and then down, the construction of the second tunnel causes the lining of the preceding tunnel to sink again by 9.1∼10.4 mm. By comparing the effects of the two working conditions on the stratum and the tunnel lining, it is recommended that the construction be carried out in the order of first down and then up.