Shield Tunnel Project Research Articles

Deformation Regularity and Control of Segment Joints in the Project of Shield Tunneling Prior to the Shafts Excavation

Shield tunneling prior to the shafts excavation is an efficient and economical method in the construction of the heat-supplying shield tunnel. Combining the first large cross-section heat-supplying shield tunnel project in China, the characteristics of the construction method are analyzed, and the control measures of segment joints deformation are put forward. Based on the site conditions, the numerical analysis model including interface element is established, and the control effect of the measures is analyzed and evaluated. Through on-site monitoring, the change law of longitudinal stress and joints deformation in different construction stages are measured. Based on the numerical analysis model, the effects of tunnel depth, stratum and grouting reinforcement area on joints deformation are analyzed. The results show that: the deformation of segment joints can be divided into two stages in the project of shield tunneling prior to the shafts excavation: shaft excavation and segments removal, and the segments removal is the main factor. According to the results of numerical calculation and on-site monitoring, the control measures of longitudinal tension lining and retightening bolt, priority to pouring concrete in the bottom of tunnel and secondary grouting behind lining can control the loss of longitudinal stress, and reduce the joints deformation. The maximum deformation of segment joints is 3.51 mm, which meets the waterproofing requirements of shield tunnels. In the project of shield tunneling prior to the shafts excavation, the deformation control of the top segment joints should be strengthened in the shallow tunnel, while for the deep tunnel, which should be strengthened of the bottom segment joints. When the tunnel passes through the stratum with larger resilience modulus, the deformation of the bottom joints will be larger. Grouting reinforcement of surrounding soil can reduce the loss of longitudinal stress and the joints deformation effectively.

Near real-time circular tunnel shield segment assembly quality inspection using point cloud data: A case study

This paper introduces a near real-time digital method of circular tunnel shield segment assembly quality inspection using point cloud data (PCD) since the conventional manual inspection is untimely and incomplete for a segment assembly process. A three-dimensional (3D) laser scanner is used to capture the geometry information of newly assembled segment-rings via segment-ring PCD (srPCD). With a focus on dislocation and deformation, customized algorithms for segment-rings are proposed, including srPCD pre-processing, segment seam PCD extraction and dislocation and deformation calculation. The dislocation between adjacent segments within one ring and that between adjacent rings as well as the single ring ovality are inspected forthwith. A particular srPCD calculation software is developed based on the proposed algorithms and is implemented in a case study of a practical shield tunnel project. The inspection results validate the effectiveness of the proposed digital method and its advantages over the traditional way, signifying that the dislocation between adjacent rings is most likely to overrun during the assembly process. The error status and variation tendency of the segment-ring dislocation and deformation can also be observed on the srPCDs from progressive measurements when the segment-rings are supported by the shield shell. These show the benefits of the proposed method for shield tunnel construction quality management.

Dynamic prediction for attitude and position in shield tunneling: A deep learning method

Abstract Quality management in shield tunneling projects is a challenging problem. To improve the quality of segment erection, the shield driver must constantly adjust the shield's attitude and position to reduce a snakelike motion for fitting the design tunnel axis based on the driver's experience, which is untimely and less reliable during excavation. Considering the disadvantage of this control method, this paper presents a predictive framework for the attitude and position in shield tunneling by applying a hybrid deep learning model. This framework contains a wavelet transform noise filter, convolutional neural network feature extractor, and long short-term memory predictor for determining the attitude and position of the shield machine in the future. The prediction framework is tested with the collected data of Mixshield operated in the river-crossing tunnel project of Yangtze Sanyang Road, Wuhan, China. Six variables characterizing the shield attitude and position are selected to validate the feasibility and performance of our method. Results reveal that the proposed model outperforms the other three similar models in predictive accuracy and provides decision support for adjusting the attitude and position in shield tunneling.

Influence of Shield Attitude Change on Shield–Soil Interaction

The mechanism of shield–soil interaction and multi-phase equilibrium control theory in shield tunneling process still lack sufficient understanding. Aiming at this problem, with the improved calculation method of loose earth pressure, the initial boundary problem of shield attitude calculation was solved. Based on the ground reaction curve, the shield–soil interaction was simulated by the equivalent springs, and the displacement of surrounding soil was calculated during the change of the shield attitude. Then, the theoretical method of surrounding soil load acting on the shield were obtained. In summary, the calculation method of shield attitude was obtained. This method has three main applications in engineering, namely the inversion of shield–soil interaction force, the prediction of pitch angle and the prediction of yawing angle. Finally, combined with Jinan Metro Line R2 shield tunnel project, the shield attitude was monitored in real time and compared with the theoretical value. The results show that the trend of the theoretical values of pitch angle and yawing angle were basically the same as the measured value, but the theoretical value was generally larger than the measured value. The research results can provide a useful reference for the shield attitude adjustment.

A case study on the stability of the shield excavation face in full-section coarse sand

The estimation of the shield face support pressure is essential for the stability of the shield excavation face. The face support pressure of the earth pressure balance (EPB) shield tunneling machine is mainly composed of the support pressure of the cutterhead and the earth chamber pressure. To ensure the requirements of safe construction, the theoretical face support pressure is one of the most significant references for the earth chamber pressure setting. This paper analyzed the in situ monitoring data of the shield earth chamber pressure from a shield tunneling project of the Xi’an Metro Line 4 in full-section coarse sand. A nonlinear stepwise increase in the earth chamber pressure from the top to the bottom of the tunnel face was obtained. The fluctuation range of the earth chamber pressure gradually increased with an increase in the cover depth. Meanwhile, several types of silo-wedge models were established according to different assumptions proposed by previous studies and this paper. The rationality of their calculations and the applicability of related assumptions were discussed based on practical engineering and new working conditions.

Improved hilbert spectral representation method and its application to seismic analysis of shield tunnel subjected to spatially correlated ground motions

A novel and efficient method for simulation of spatially correlated earthquake ground motions (SCEGMs), named as improved Hilbert spectral representation method, was presented. By using Hilbert–Huang transform (HHT), the known record can be decomposed into a series of intrinsic mode functions (IMFs) and a residual function. Targeting on each IMF, simulated IMFs for every field point were derived through a spatial correlation model. The frequency dependence of the spatial correlation structure was simplified such that only the correlation at the predominant frequency of each target IMF was considered. SCEGMs can then be obtained by superposition of simulated IMFs and the original residual function. Taking the Suai shield tunnel project in China as reference, the intersegment opening width response of shield tunnel under multiple support excitation (MSE) and identical support excitation (ISE) were investigated and compared. First, numerous accelerograms, including horizontal and vertical components, were generated based on selected real records and artificial acceleration time histories on bedrock to realize MSE. The generalized response displacement method (GRDM) in combination with a large-scale FEM model was then utilized to proceed with the study. Results showed that the MSE can lead to a higher opening width of tunnel in general. The distribution of longitudinal opening width under MSE is also different from that under ISE. The sharp variation of soil layer stiffness along the longitudinal direction of tunnel may lead to extremely large intersegment opening width or severe damage.

Experimental analysis of mechanical behavior of segmental joint for gas pipeline shield tunnel under unfavorable compression-bending loads

Shield tunnels are usually affected by the larger water pressure when crossing a river. In this paper, the mechanical behavior of a shield tunnel ring seam under unfavorable compression-bending loads is analyzed by means of experiments. The segmental joint specimens were made of prototype segments which were adopted in a gas pipeline shield tunnel project with an inner diameter of 4.25 m and a 1:1 prototype test is applied for this experiment as well. In the experiment, the surface strain, the joint opening and the deflection were measured. The relationship between the joint opening and the internal force at the longitudinal seam have been verified by the prototype loading tests. The experimental results clearly show that the deformation of the segmental joint under different water pressure is restrained by the bolt. Under the influence of the bolt constraint, the maximum joint opening width and the maximum joint opening height show a different growth trend with the increase of bending moment. The axial force has an important influence on the joint deformation and an appropriate increase in axial force under high water pressure conditions is conducive to the suppression of joint deformation. When the axial force is large, with the increase of bending moment, steel bars that bears tension stress may change to sustain compression stress. The bolt stress changes obviously with the changes of axial force and bending moment of the joint. Both tension and compression cracks occur during the joint failure, and are easily occurred in weak position such as waterproof grooves, hand holes etc.

Technical innovation for super-large-diameter shield tunnel project of combined highway and railway construction in Sanyang Road, Wuhan

Technical innovation for super-large-diameter shield tunnel project of combined highway and railway construction in Sanyang Road, Wuhan

Filter cake formation for slurry shield tunneling in highly permeable sand

For slurry shield tunneling projects excavated in the highly permeable soils, the slurry usually passes through the ground without forming a filter cake. As a result it may be impossible (depending on the yield strength of slurry) to built up the required support pressure which would lead to a face instability. This kind of face instability is influenced by the factors, such as the permeability of ground, the slurry pressure and the properties of slurry. How to form a thin and lowly permeable filter cake efficiently and quickly on the tunnel face becomes a crucial engineering problem for the slurry shield tunneling in the coarse-grained and highly permeable grounds. In this paper, a new apparatus was developed to study the filter cake formation on the surface of coarse-grained sands under elevated pressure. A series of pressure filtration tests were carried out on nine different slurries and five different soils. By measuring the quantities of discharged water during the test and observing the state of filter cakes formed on the soil surface, the criteria of filter cake formation was identified. The test results indicated three different types of slurry infiltration. Correspondingly, the following three different types of filter cakes were observed: a filter cake, a filter cake with an infiltrated zone, and infiltrated zone without filter cake. It was found that the ratio between the average pore size of soil (D0¯) and the particle size for which 85% by weight of particles in the slurry (d85) may be used to classify the types of filter cake formation.

Theoretical model for loads prediction on shield tunneling machine with consideration of soil-rock interbedded ground

The loads acting on shield tunneling machines are basic parameters for the equipment design as well as key control parameters throughout the entire operation of the equipment. In the study, a mechanical analysis for the coupled interactive system between the cutterhead and the ground at the excavation face is conducted. The normal and tangential loads acting on the cutterhead are decoupled and solved, with consideration of the influence of three key factors on loads: geological condition, operating status and equipment structure. Then analytical expressions for the thrust and the torque acting on the equipment under uniform geological condition are established. On this basis, the impact of soil-rock interbedded ground on acting loads is further considered. A theoretical model for loads prediction of earth pressure balance (EPB) shield machines working under soil-rock interbedded ground is proposed. This model is subsequently applied to loads prediction for a shield tunneling project under soil-rock interbedded ground. The computational value of the thrust and the torque, the measured loads and the load ranges from Krause empirical formula are compared. Thus, this model for loads prediction acting on shield tunneling machines under soil-rock interbedded ground has been proved to be effective.

Technology of Pile Foundation Underpinning in Shield Tunnel of Xi’an Subway

The technology of shield has been widely used in city subway design, when the shield tunnel encounters a bridge across the river; the key issue is to complete the pile foundation underpinning according to the diverse geological conditions. With an example of subway Shield tunnel project from Xi’an, The paper presents the working procedure and emphases of pile foundation underpinning.Based on the configuration design, both the load beared by one single stake and the distortion of the joists are calculated, the carrying capacity computations indicate that pile foundation underpinning is feasible.

A Loading Test Method of Prototype Structure for Nanjing Changjiang Tunnel

Considering the features of underwater shield tunnel with large cross-section, a prototype test of segmental lining structure for Nanjing Changjiang Tunnel (Φ14.5m) is carried out by using a new loading test method. And with “Multi-function Shield Tunnel Structure Test System” developed according to this test method, the effect of high hydraulic pressure can be equivalently imposed upon the structure by hoop, and then the earth pressure can be equivalently applied to the structure by radial concentrated force. The structures were loaded by the device according to a certain hydraulic and earth pressure. Meanwhile, the mechanical characteristics can be further studied. In a word, it can provide reliable test means for research, design and construction of underwater shield tunnel project.

Development and practical applications of twin-screw shield method

As Japan's population becomes more concentrated in large cities, the demand for urban facilities and diverse urban functions is resulting in greater congestion underground. Meeting this demand requires the development of a low-cost technology for constructing large-scale facilities at great depths below the surface. The current dominant technology for constructing tunnels in urban areas is the shield method, which includes both the slurry and mud-pressure methods. The latter method is seldom used at depths of 30 m or more below the surface because at such depths, the face of the tunnel is subject to high water pressures, which cause the muck and groundwater to spurt out from the screw conveyor of the shield-tunneling machine. The soil pressures at the tunnel face then become uncontrollable, causing the ground around the tunnels to deform. To solve this problem, Taisei Corp. and Ishikawajima-Harima Heavy Industries Co. Ltd. began researching screw conveyors in 1996 and recently developed the twin-screw (TS) shield method. In the twin-screw shield method, the muck is continuously and stably discharged by automatically controlling the rotational speed of the twin-screw conveyor. This maintains the desired soil pressure at the tunnel face at all depths, no matter how fast or slow the machine is advanced. The two screws are engaged and rotated in opposite directions, creating a mechanical seal zone in the conveyor that prevents muck and groundwater from spurting out from the conveyor. The benefits of this method include the ability: (1) to control the soil pressures at the tunnel face so that the surrounding ground does not deform, (2) to control the muck discharge volume by controlling the rotational speed of the twin-screw conveyor, and (3) to transport the muck from the discharge nozzle to the back of the machine. This method has been applied in two shield-tunneling projects, first for a utility conduit with the overburden of 22 m in cohesive soil, and then for a subway tunnel with the overburden of 8 m in sand and gravel. The success of projects proved the excellence of the method. For both projects, soil pressures at the tunnel face could be kept at a set value by the automatic control of the win-screw conveyor's rotational speed even when the advance speed of the shield tunneling machine was changed. As a result, deformation of the ground around the tunnels could be controlled. Further studies are under way for the measures against the wear of flights and casing of the twin-screw conveyor that is expected in the ground containing much gravel. The authors aim to make the twin-screw shield method into a standard mud pressure shield method by providing the twin-screw conveyor with greater durability through the studies. (A) Reprinted with permission from Elsevier. For the covering abstract see ITRD E124500.