Shield Tail Research Articles

Research on Deformation Treatment and Control Technology of Tail Shield of Underwater Large Diameter Slurry Shield

The Karnaphuli River underwater tunnel in Bangladesh is located at the estuary of the Karnaphuli River and is constructed with a Φ12.12m air-cushioned slurry pressure balance shield machine. The bottom section of the river mainly passes through a dense silty fine sand stratum, of which the standard penetration value and strength are high. When the shield tunneling got into to the sea area, the tail shield was significantly and unevenly deformed, which caused the shield machine to be trapped in the river bottom. Therefore, the characteristics and causes of the deformation of the shield tail during the tunneling boring process were analyzed on this basis. Studies have shown that the deformation of the tail shield was a gradual development process. If there is a slight lack of rigidity of the outer shell and tail shield on the outside of the shield, it tells that the large resistance of the ground caused by the deviation of shield tunneling is the main reason for the deformation. Besides, given the construction characteristics of the underwater shield and the limited working space in the shield machine, a linear rectification tool was designed. By summing up the rectification methods of the hole making in the tail shield, decompression with sand discharge, and incremental launching with loaded, local deformation of the tail shield was realized, so the trapped shield machine was successfully released. Finally, through the excavation experience after the shield restart, it is concluded that within 5cm of the tail shield steel plate deformation, the experience of deformation rebound can be achieved through measures such as sand discharge through radial holes and bentonite injection, which provides a reference for similar engineering projects in the future.

Influence of Shield Tail Clearance on Surface Settlement during Shield Construction in Soft Soil Area

The shield construction process of shield tail gap caused by formation damage, the formation damage caused by the settlement is as long as the part of tunnel subsidence analysis, therefore in the finite element software analysis of shield construction settlement value, the shield tail clearance simulation is an important link in the entire model, this article analyzes three common finite element simulation method, shield tail clearance displacement convergence method based on non-uniform distribution and actual matches are higher than layer such as generation method and stiffness discount subtraction. Finally, the displacement convergence method is used to simulate the grouting effect of shield tail on the surface settlement.

Spatial distribution model of the filling and diffusion pressure of synchronous grouting in a quasi-rectangular shield and its experimental verification

Considering that the particular geometric shape of a quasi-rectangular shield, the grout flowing law and its motion process are more complicated than those of a conventional circular shield. To interpret the grouting mechanical ehaviour in the special-shape shield tail void, the filling and diffusion mechanism of synchronous grouting was analysed. The grout flowing is separated into two independent motion processes, which contains a circumferential filling and a longitudinal diffusion. The theoretical model of the grout pressure spatial distribution was derived based on the principle of fluid mechanics. Then, the pressure distributions in the two directions were obtained using a case study and compared with the field measured data to verify the validation of the model. Although the overall spatial pattern of grout pressure distribution on the tunnel profile show a change trend dominated by the self-weight effect mostly, its local fluctuation characteristics is very abnormal relative to that of a circular shield tunnel. Moreover, the important factors in the model were analysed, including the grout material parameters, the grouting construction parameters, and some geometry parameters. The results show that the pressure loss along this way is positively correlated with the grout flow velocity and is sensitive to the shear yield stress of the grout. The pressure loss along the circumferential direction is the most sensitive to the thickness of the ring cake, and the value range suitable for the model should be 0.02–0.03 m. The pressure loss along the longitudinal diffusion direction is the most sensitive to the size of the tail void. The research results can provide a theoretical basis for the control of special-shape shield construction.

The role of TBM asymmetric tail-grouting on surface settlement in coarse-grained soils of urban area: Field tests and FEA modelling

This paper examines the role of TBM tail-grouting on surface settlement of coarse-grained soils in urban area. The influence of tail grouting on the ground surface settlement is firstly demonstrated through a challenging shield-driven tunnel project in Beijing City, China. FEA modelling incorporating the excavation sequence and tail grouting details is then set up to support the field observations, based on which the influences of different TBM tail-grouting parameters on ground settlement are investigated, especially the asymmetric tail-grouting in which one of the two grouting openings at the upper part of the shield tail is malfunctioned. It is shown that the grouting volume variation is inconsistent with the development of the grouting pressure, and the ground deformation in coarse-grained soils is directly related to the tail-grouting pressure rather than the grouting volume ratio. Asymmetric tail-grouting will result in notable offset of the maximum surface settlement point in settlement trough from tunnel centerline which correlates exponentially with the parameter ξ defined to represent the asymmetry ratio of the grouting pressure.

An Artificial Freezing Technique to Facilitate Shield Tail Brush Replacement under High Pore-Water Pressure Using Liquid Nitrogen

During tunnelling, with the progression of the shield tunnelling machine, the shield tail brush, which is an important accessory required to seal the shield tail and prevent the tunnel from ground water or grouting fluid discharging, will gradually be worn-out/damaged and inevitably lead to safety problems. As a result, problematic tail brush needs to be replaced to prevent more serious problems from happening before any further tunnelling. The replacement of this shield tail brush can be very risky, especially when the shield tunnelling machine is located at a soil layer under high pore-water pressure. This study introduces an engineering practice to facilitate the shield tail brush replacement under high pore-water pressure through the development of a frozen soil wall with the help of an artificial freezing technique using liquid nitrogen. A case study is adopted to demonstrate the implementation of this technique. For the specific site condition, a numerical simulation is usually performed first to determine the design parameters (e.g., liquid nitrogen temperature, length and spacing of the freezing pipes) required for artificial freezing process. Several holes along the radial direction of the tunnel were then made to monitor the temperature of the soil around the tunnel. Subsequently, the artificial freezing process was performed according to the design. The replacement of the tail brush was initiated when the frozen soil wall developed during freezing met the requirements for tail brush replacement. The artificial freezing technique using liquid nitrogen proved to be a reliable and time-effective option to facilitate the tail brush replacement under high pore-water pressure.

Surface Settlement Analysis Induced by Shield Tunneling Construction in the Loess Region

The influence and prediction of shield tunneling construction on surface settlement (SS) and adjacent buildings is a hot topic in underground space engineering. In this work, several analytical methods are utilized to estimate the maximum surface settlement (MSS) and conduct a parametric sensitivity analysis based on Xi’an Metro line 2. The results show that there are mainly nine factors influencing the SS induced by shield tunneling construction in loess strata. The disturbance degree of the surrounding soil during the shield advancing stage has the largest influence on the SS, followed by the seepage of the shield lining segments or falling water levels, which lead to the overlying soil consolidation. After this is the grouting filling effect at the shield tail, followed by the reinforcement effect of the tunnel foundation and the track. The smallest influencing factors on the SS are the shield overexcavation and improper shield attitudes during the construction period. The sensitivity analysis results of the above influencing factors may offer a scientific guidance for the control of shield tunneling construction.

Experimental Study on the Mechanical Properties and Performance of Shield's Tail Sealing Grease

Experimental Study on the Mechanical Properties and Performance of Shield's Tail Sealing Grease

Selection of the Key Segment Position for Trapezoidal Tapered Rings and Calculation of the Range of Jack Stroke Differences with a Predetermined Key Segment Position

It is generally accepted that selecting the key segment position for trapezoidal tapered rings and controlling the shield machine advancement are challenging tasks for shield tunneling projects. In this work, we propose a method for calculating the key segment position based on the shield tail gap, jack stroke difference, and lining trend. To calculate all possible key segment positions other than that corresponding to the straight joint configuration, the shield tail gap that remains after segment assembly and the jack stroke difference corresponding to the advancement of the segmental lining and lining trend were computed; then, values and importance coefficients were assigned to these factors according to current operating conditions. To ensure that the segmental lining can be assembled successfully with the calculated key position, we established a model to calculate the change in the shield tail gap before and after shield machine advancement based on the spatial relationships of the shield machine, the currently installed segmental rings, and the segment to be installed. Further, we propose a method for calculating the range of jack stroke differences when the predetermined “permitted shield tail gap” and key position are provided. The method is based on the change in the shield tail gap calculated with the above model and the positional relationship between the shield machine’s actual axis and the designed tunnel axis after the current segmental ring has been assembled. The calculated range of jack stroke differences may then be used to control the advancement of the shield machine. We validated the viability of our methods by using the data of Phase 1 works on Line 2 of the Ningbo Rail Transit system.

The life-cycle development and cause analysis of large diameter shield tunnel convergence in soft soil area

The tunnel convergence is an important index of the construction quality and operation safety. In the past, most of researches were focused on the shield tunnel lateral convergence and its effect on the safety at operation period. In this paper, by employing the 3D laser scanning test method and convergence ellipse fitting identification technology, the shield tunnel full space convergence can be tested and divided into three typical modes: transverse ellipse, oblique ellipse and vertical ellipse. Based on series of field tests in three large-diameter tunnels under construction and operation, the spatial distribution and life-cycle development laws of above three typical convergence modes were firstly seriously studied, the changes of the long axis, short axis and deflection angle of above convergence modes are given. Meanwhile, the generation mechanism and main cause is studied by analysis of machine-structure interaction, soil pressure and back-fill grouting action during shield construction. It is found, in the soft soil areas, the formation of different convergence modes mainly depends on the initial load condition at the stage of segments leaving the shield tail, and the following action of back-fill grouting will have little effect on the structure convergence, but most on the surrounding soil deformation. Subsequently, the convergence will continue growth with the short axis deformation greater than the long axis, and gradually develop towards symmetry with soil consolidation. Besides that, the obvious coupling relationship between the convergence and the longitudinal settlement can also be found after long-term operation from the tests. The above findings are very helpful to fully understanding the stress and deformation interaction during the large diameter shield tunnel construction and operation.

Hydroschildvortrieb über dem Grundwasserspiegel in hoch durchlässigen Schottern am Eppenbergtunnel – Unerwartete Probleme und ihre Lösung

AbstractAs part of the four‐track improvement of the Zurich‐Berne line near Aarau, the 3.1 km long Eppenberg Tunnel was bored using a multi‐mode TBM. This involved driving more than 700 m in highly permeable soils, mostly above the groundwater table. The hydroshield drive was confronted with considerable problems. The static yield point of the bentonite slurry repeatedly fell below the critical limit of 10 N/m2, despite its frequent replacement. As a result, large quantities of slurry penetrated into the ground and large quantities had to be replaced. In addition, significant additional grout quantities were repeatedly observed for the filling of the annular gap. A systematic and analytical approach in cooperation with all parties involved made it possible to determine the behaviour of the system. Problems started with highly permeable open‐framework gravel layers, which permitted the slurry to penetrate far into the ground. This resulted in overbreak in the crown and local underpressure of the slurry with respect to the grout around the shield. Consequently, the annular gap grout flowed past the shield tail seal and destroyed the thixotropic properties of the slurry by adding free Ca cations. The slurry became unusable and had to be replaced. An extensive set of measures finally made it possible to solve the problems and safely bring the excavation to breakthrough.

Thermal and Mechanical Response of Soil and Tunnel during Replacement of Shield Tail Brush by Freezing Method

In the long-distance shield tunneling process, the shield tail brush needs to be replaced after wear failure, especially in cross-river and cross-sea tunnel projects. Taking the shield tail brush replacement project of Qingchun Road tunnel in Hangzhou, China as the research background, a three-dimensional sequential thermo-mechanical coupled numerical simulation was carried out to study the shield tail brush replacement with liquid nitrogen freezing by ABAQUS software. The development of temperature fields and displacement fields of soil, and the deformations of the tunnel sections along the longitudinal direction induced by freezing were obtained. The numerical model was further validated by site measurement. In addition, the effects of the frozen wall thickness, buried depth, excavation radius, and coefficients of linear thermal expansion of soils on the frost heave were studied.

Experimental study of the precursor information of the water inrush in shield tunnels due to the proximity of a water-filled cave

A water-filled cave can easily result in the deterioration of the surrounding rock when a shield tunnel passes through the urban karst area, resulting in engineering disasters such as water inrush, ground collapse, and shield machine malfunction. To study the surrounding rock stability due to the proximity of a cave with confined water, we carried out a large-scale three-dimensional geo-mechanical model test on a tunnel that was excavated by a compound EPB (Earth Pressure Balance) shield machine based on the metro tunnel in the “spring city” of Jinan. We developed a new 3D printing technology for a water-filled cave and a new method for the 3D laser reconstruction of surface settlement monitoring. The multi-physics evolution information, including the soil moisture content of the muck, the displacement, the stress, and the seepage pressure, were obtained and proven consistent with each other. The results showed that the water inrush mainly resulted from a shield tunneling disturbance in conjunction with the confined water in the cave. The process of water inrush in the surrounding rock could be divided into three stages, which included the initial stable period, the variation period with the shield tail passing through, and the final stable period. The rock ahead of the excavation face was characterized by two stages, which included the initial stable period and the sudden collapse of the water-resistant slab. Compared with the tunnel excavated by drilling and with the blasting method, the water inrush triggered by the EPB shield machine tunneling was observed to be more hidden and catastrophic. The displacement and the seepage pressure comprised the most intuitive precursor information. These test results can provide a theoretical basis and guidance for the water inrush prediction for being triggered by a single confined cave with no inter-connections.

3D response analysis of a shield tunnel segmental lining during construction and a parametric study using the ground-spring model

In this research, an analysis method aiming as a tool to investigate the behavior of a tunnel lining during construction is developed based on a nonlinear ground-spring model in conjunction with a finite element method. A nonlinear ground-spring model that considers yield pressures is proposed and implemented into the numerical analysis. All relevant components of the shield tunnel construction process including the TBM, jack thrust force, shield tail wire brush, segmental lining, key-segment and ring and segment joints and proper interactions are considered in the analysis model. The reliability of the developed method is verified by comparing the analysis results with the full-scale test and field measurements of a previous study. The developed analysis method could reasonably reproduce the responses of a segmental lining at various stages with special attention during construction. A series of parametric analyses are conducted to highlight the robustness of the developed method to capture the effect of the key factors on the structural behavior of the segmental lining during construction. The effects of the tunnel depth, forces from eccentric jack thrust together with shield tail wire brush and position of key segment on the induced lining stresses can be well captured.

Analysis of a tunnel failure caused by leakage of the shield tail seal system

This paper presents an analysis of a tunnel failure accident during shield tunnel construction on Foshan Metro Line 2 in China. The failure is caused by the leakage of the multilayer seal system, which consists of several brush seals at the tail of the shield. Four different failure modes for the multilayer seal system are discussed. A simple structural analysis of the brush seals is then conducted, and failure mode 4 (failure due to brush seal deformation) is identified as a major reason for the Foshan tunnel accident. A finite element method (FEM) analysis is employed to validate the conclusions drawn from the simple structural analysis of the brush seals.

Analysis of the Compressibility Effect of Overburden in a Deep Shield Tunnel Based on the Effect of the Pressure Arch

With the continuous improvement of the planning system for urban subway construction, shield tunnels are being more frequently constructed, and thus, the floating problem of shield tunnels in construction has been paid increasingly more attention. In view of this, in this paper, with the combination of numerical simulation and theoretical analysis, the problem of floating segments compressing the overburden in the deep shield tunnel is discussed. The influential factors of the pressure arch effect are analysed using numerical simulation, the compressive displacement of soil in the plastic zone is investigated in a focused manner based on the pressure arch effect, and the problem of floating segments that the Mindlin solution is applied to under the actions of distributed force and concentrated force is solved. The results show the following: (1) the displacement of the segment is composed of the shield tail gap, the compressive displacement of the soil, and the translational displacement of the soil; (2) the intensity of the pressure arch effect is interactively influenced by the thickness‐diameter ratio and the soil properties; (3) the compressive displacement of the soil mass accounts for a larger proportion of floating segment‐induced displacements; and (4) the perturbation influence calculation formula of the surrounding strata and the building structure is obtained based on the Mindlin solution.

Research on the Distribution Model of the Slurry Pressure in the Shield Tunnel

This paper focuses on the distribution model of the slurry pressure in the shield tunnel when grouting simultaneously. The theoretical derivation of the slurry pressure distribution model is carried out respectively according with Bingham flow model. The theoretical formula of the slurry pressure in the cross section of the shield tail is established. The relationship between slurry viscosity coefficient and the time and the relationship between the slurry pressure and slurry viscosity coefficient are analyzed. On this basis, the law that the slurry pressure changes with time and the distribution of the slurry pressure along the longitudinal direction of the tunnel are summarized. Furthermore, monitoring on the spot proved the rationality of the above theoretical derivation. The results of this paper can provide great reference and guiding significance for the simultaneous grouting of the shield tunnel.

Bedding improvement of lining segments using geotextile tubes

AbstractDuring a shield TBM excavation in hard rock, the immediate backfill of the crown immediately behind the shield is technically difficult to realize. With the advance of the cutter head a relocation process of pea gravel within the annular gap is triggered, leading to an insufficient bedding distribution of the first segments behind the shield tail and to an ovalization of the segmental lining at a certain load level. During a test application as part of an ”TBM research initiative“ of the Austrian Federal Railways geotextile tubes were integrated into the exterior surface of the segments. Immediately after leaving the shield tail, the geotextile tube, which is placed all around one ring of segments, is expanded by injection with grout. As a result, an immediate bedding between the rock mass and segmental lining is established, also preventing the rearrangement of pea gravel within the annular gap when the shield is moved forward. The displacement measurements have shown that the ring of segments equipped with geotextile tubes experiences a more rigid body motion like behaviour after leaving the shield tail with a minimal ovalization only. Numerical simulations show the influence of bedding improvement on the ovalization of the ring of segments after leaving the shield tail.

Performance Assessment of Shield Tunnel Damaged by Shield Shell Extrusion During Construction

A shield tunnel can be damaged by shield shell extrusions, such as shield tunnel floating, which may cause contact (even a squeezing action) between the shield tunnel and shield shell. To fully analyze this problem, a detailed 3D-finite element model (FEM) of a shield tunnel under the effect of a squeezing action in the shield tail, soil pressure, jacking force, and grouting pressure, was established by applying a plastic-damage constitutive model of concrete. A full-scale test of three segment rings was conducted, and the test results verified the feasibility of the constructed FEM. In this study, different squeezing positions and deflection angles of the shield shell were analyzed. The results indicated that the area squeezed by the shield shell experienced the most damage, and the tensile damage to a segment reduced gradually as the squeezing position approached the circumferential seam. The damage range gradually increased with the increase in deflection angle. The effect of the squeezing position of the shield shell on the bending moment was larger than the effect of the deflection angle on the bending moment. However, the effect of the squeezing position and that of the deflection angle on the shear force were the same.

高水压富含水地层盾构盾尾密封装置改进研究——以金陵石化南京长江盾构工程为例

高水压富含水地层盾构盾尾密封装置改进研究——以金陵石化南京长江盾构工程为例

0.65 MPa高水压盾构机新型盾尾密封系统设计与研究

0.65 MPa高水压盾构机新型盾尾密封系统设计与研究