Shield Tunnel Construction Research Articles

Risk Factor Recognition of Shield Tunnel Crossing Underneath the Existing Subway Tunnel

Studying and controlling the risk factors of shield tunnel crossing underneath the adjacent existing subway tunnel will be of great significance for guaranteeing the safety of tunnel structure. Under the background of subway undercrossing engineering in Shenzhen, 3D finite element models under different working conditions were established using the theory of orthogonal experimental design. The disturbing impacts generated by newly built tunnel shield crossing beneath the existing tunnel to the existing tunnel were explored in consideration of different factors. Based on the impact degrees of different experimental indexes, the priority and weight of each index were determined via the analyses of range and variance in the orthogonal experiment. The results show that the clear distance and spatial angle between new and old tunnels, and soil chamber pressure exert highly significant impacts on the settlement of the existing tunnel structure; the maximum tensile stress of the existing tunnel structure is significantly impacted by the clear distance, spacing, thickness of overburden layer, and angle; the settlement value of the existing tunnel is extremely sensitive to the soil chamber pressure, with the impact weight reaching 24.9%, and the maximum tensile stress of the existing tunnel is sensitive to the change in the thickness of overburden layer: With the increase in the thickness of overburden layer, the maximum tensile stress presents a significant trend of progressive increase, and the impact weight reaches 19.25%. The study results will be of reference significance to the safety construction of shield tunnel crossing beneath the adjacent existing subway tunnel.

Research on influence of excavation parameters of shield tunnel based on ABAQUS

At present, the mainstream method of urban subway construction is shield construction. What cannot be avoided in shield construction is the settlement and displacement of the ground surface, and the tunneling pressure is closely related to the grouting pressure and the settlement of the soil. For the overlapping tunnel shield construction, this paper takes the shield construction of the overlapped tunnel section of Kunming Rail transit Line 6 as the research object. Using ABAQUS finite element software to simulate overlap shield tunnel construction, the research of shield tunneling parameters and the relationship between the surface displacement of soil. The results show that reasonable selection of excavation parameters can well control ground settlement.

Soil Conditioning Tests on Sandy and Cobbly Soil for Shield Tunneling

Soil conditioning is an important stage in shield tunnel construction that can effectively improve muck flow plasticity, reduce cutter head wear and improve tunneling efficiency, especially in sandy and cobbly soils. The aim of this paper is to obtain the optimal ratio of residue modifiers in sandy and cobbly soil and to improve the equipment used in residue-related shield machines. Residual soil in a sandy pebble layer was selected, and particles with sizes over 50 mm were removed to form soil samples. Through laboratory tests, the optimal ratio of the modifier was obtained, and the shield tunneling machine equipment was optimized. The research results for the laboratory tests and equipment optimization were verified and adjusted appropriately through field tunneling tests. The following results were obtained. 1) A 3% foaming agent C was selected for the soil conditioning tests. The final mass ratio of the bentonite mixed solution of water, bentonite, soda ash (Na2CO3), and carboxymethyl cellulose (CMC) was 6:1:0.028:0.035. 2) Improving earth pressure balance (EPB) shield machine equipment can improve the effects of soil conditioning. 3) Compared with the volume of residual soil, the optimal ratio of soil conditioning in sandy and cobbly layer was 13% water, 4–5% bentonite mixed solution and 12–15% foam. In addition, the maximum ratio shall be taken for the strata with poor grain composition. These results can be used to provide excavation guidelines for using an EPB machine under these soil conditions.

Computer vision‐based monitoring of the 3‐D structural deformation of an ancient structure induced by shield tunneling construction

Computer vision‐based monitoring of the 3‐D structural deformation of an ancient structure induced by shield tunneling construction

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.

Influence of Subway Shield Tunnel Construction on Ground Settlement

Shield construction has the advantages of stable driving speed, saving manpower, and being able to carry out construction in complex strata, which has been more and more widely used. In the process of shield construction, there is a gap between shield body and segment, which is easy to cause ground settlement when the grouting speed cannot keep up. This paper summarizes the common methods to predict the surface settlement, analyzes the causes of the settlement, and lists an engineering case to illustrate the factors affecting the surface settlement. Finally, it comes to the conclusion that the main causes of the surface settlement caused by shield tunnel construction are formation loss and consolidation settlement, and the use of small cutterhead and composite cutterhead can reduce the surface settlement, It provides a reference for the development of shield construction.

Technologies on Safe Construction Ventilation of Long-large Shield Tunnel with Low Gas in Metro

Taking the project of long-large shield tunnel with low gas in Xingtian section of Chengdu Metro Line 18 as an example, A new construction ventilation method is established, which includes: the main tunnel ventilation with axial fans installed at the entrance of the tunnel and the local ventilation with jet fans installed in the shield and at the upper part of the bridge and the top of the 4# trailer for the rear supporting system; the connecting passage ventilation with a jet fan installed on the wall; the crossing ventilation with a jet fan installed in the middle of tunnel. The ventilation technology for safe construction of Metro long-large shield tunnel with low gas is established after detailed calculation of the fan selection, which is applied to finish safely and quickly construction task, and which provides reference for similar projects in the future.

Comparative Study on Grouting Protection Schemes for Shield Tunneling to Adjacent Viaduct Piles

Shield tunnels will inevitably pass through viaduct piles at a close distance due to the extensive construction of subways and viaducts in the city. In order to understand the influence of shield tunneling on the deformation of existing pile foundation and grouting protection measures, based on an engineering case, Changsha Metro Line 5 (from South Gaoqiao station to Guitang station), a three‐dimensional finite element model was established to analyze the deformation of bridge pile using grouting protection wall with different depths and shapes when the shield tunnel is under construction. The analytical results indicate that the grouting protection wall can effectively reduce the pile displacement; especially the grouting depth is 3 m below the bottom of the tunnel. Moreover, the L‐shaped grouting protection wall can effectively reduce the longitudinal displacement of the piles. The present findings may provide a reference for the design and construction of shield tunnels passing through viaduct piles.

A Novel Method for Analyzing the Factors Influencing Ground Settlement during Shield Tunnel Construction in Upper-Soft and Lower-Hard Fissured Rock Strata considering the Coupled Hydromechanical Properties

Focusing on the special stratum conditions of upper-soft and lower-hard fissured rock strata, this paper conducts quantitative research and analysis on the factors influencing the ground settlement caused by shield tunnel construction considering the coupled hydromechanical properties and presents a corresponding numerical simulation-artificial neural network-Bayesian network- (NS-ANN-BN-) based method. In this method, with a subway shield tunnel as the engineering context, three numerical models are established, in which the shield tunnel is located in soft strata, the shield tunnel is located in semisoft and semihard strata, or the shield tunnel is located in hard strata. According to the numerical simulation (NS) calculations, the ground settlement values under the three types of strata are 38.96 mm, 10.42 mm, and 3.13 mm, respectively. A radial basis function artificial neural network (RBF-ANN) is used to establish the nonlinear mapping relationship between the stratum parameters and the ground settlement, and the training samples and test samples are generated through NS to train the RBF-ANN. After the training is completed, the accuracy of the neural network meets the requirements. The elastic moduli of coarse sand~gravel sand k3 and moderately weathered rhyolite k4 and the cohesion of moderately weathered rhyolite c4 are selected as the key parameters. A large number of training cases are generated through the RBF-ANN, and the Bayesian network (BN) prior probability is calculated by self-learning. A BN model of ground settlement for shield tunnel construction in the upper-soft and lower-hard fissured rock strata is established. The BN back analysis method is used to quantitatively analyze the influencing factors of the ground settlement. The results show that when the tunnel is located in soft strata, the surface settlement is mainly affected by parameter k3. When the ground settlement increases considerably, the three parameters all have a strong influence. When the tunnel is located in semisoft and semihard strata, the influence of the three parameters on the ground settlement is weak. When the tunnel is located in hard strata, the ground settlement is mainly affected by parameter k4. When the ground settlement greatly increases, parameters k3 and c4 have less influence. When the tunnel is located in strata with different soft-hard ratios, the ground settlement is mainly affected by the elastic moduli of coarse sand~gravel sand and moderately weathered rhyolite. This method can provide a reference for the ground settlement analysis of shield tunnel construction in areas with similar fissured rock strata.

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.

Slurry Infiltration Column Tests on Saturated Sand

Slurry infiltration process contributes to the stability of tunnel face significantly during slurry shield tunneling construction. The support pressure cannot be transmitted efficiently to the face unless a compact filter cake forms. This paper aims at investigating the formation of filter cake in saturated sand by slurry infiltration column tests. A series of tests were performed under different filtration pressures using three concentrations of slurry in four types of saturated sand stratums. In order to obtain the characters of the infiltration process and filter cake, pore pressure evolution was measured. Three types of filter cakes were observed in the tests, including external filter cake, external filter cake plus internal filter cake and deep infiltration. External filter cake transmits support pressure efficiently, while the other two types of filter cakes cannot provide sufficiently support pressure for the tunnel face. Especially, deep infiltration behaves no capacity of retaining pressure and should be avoided in engineering practice.

A static risk assessment model for underwater shield tunnel construction

The shield method is widely used in underwater tunnel construction. However, the shield construction process faces many uncertain risk factors that increase the level of safety risk during shield tunnel construction. Therefore, risk assessment has become a necessary task in the early stages of tunnel construction. In this study, a new risk assessment model for underwater shield tunnel construction is proposed that combines a normal cloud model with an entropy weight method. The model contains 20 assessment indexes and gives the range of each index corresponding to different risk levels, which comprehensively reflects the influencing factors of risk. By using a normal cloud model, the fuzziness and randomness of risk assessment data are taken into account effectively, and the reliability of assessment results is increased. Based on an entropy weight method, the rules and characteristics of the evaluation data in the model are considered, and the weight coefficient of the evaluation index is determined to avoid the subjectivity of the expert weight method. The risk assessment model is applied using the Xiangjiang shield tunnel as an example. The results show that the overall construction risk level of the Xiangjiang tunnel is level II, which is consistent with the site risk situation and shows that the model can objectively and accurately evaluate the construction risk level of an underwater shield tunnel.

Influence of shield tunnel construction on ground surface settlement under the condition of upper-soft and lower-hard composite strata

Taking the shield tunnel project of Guangzhou Metro Line 8 from Tongdewei Station to Shangbu Station as the research background, using the research method of finite element simulation and site monitoring, this paper analyses the influence rules of shield tunneling on ground subsidence under the condition of different hard rock height ratios. The research results show that in the process of crossing different hard rock height ratio composite stratum, as the hard rock height ratio decreases, the value of ground settlement decreases and settlement tank becomes shallow. The surface subsidence in different hard rock height ratio strata is obviously different, and the maximum difference is about 8.6 mm; The influence of the hard rock height ratio on the surface longitudinal settlement is mainly reflected in the position change of the beginning and the end of the settlement. With the increase of the hard rock height ratio, the shield construction reduces the amount of the surface longitudinal settlement and its influence range; Through the research, it is found that the hard rock height ratio in the 0-0.2 and 0.5-1 is the sensitive interval, and the settlement value in these two hard rock height ratio interval varies greatly. It is necessary to pay attention to the uneven settlement of the ground surface caused by shield construction in the sensitive hard rock height ratio interval. The research results of this paper can provide reference value for similar shield construction in upper soft and lower hard composite stratum.

Numerical Simulation of Site Deformation Induced by Shield Tunneling in Typical Upper-Soft-Lower-Hard Soil-Rock Composite Stratum Site of Changchun

In China, with the rapid development of subway construction, the site deformation induced by subway construction is an interesting and hot issue in civil engineering. Focusing on the mechanism and characteristics of site deformation induced by parallel shield tunnel construction in typical soil-rock composite strata of Changchun region, and relying on the subway tunnel between Northeast Normal University Station and Gongnong Square Station, which belongs to the Changchun Metro Line 1, the tunnel construction process is simulated using FLAC3D software. In this paper, the numerical modeling and parameters for shield tunneling are described in detail, and the mechanism and characteristics of site deformation induced by shield tunneling are discussed systematically. Furthermore, the influence of construction parameters on site deformation, including construction sequence, tunnel spacing and earth chamber pressure, are studied. The results can provide reference for similar projects in the future.

Research on Stress Characteristics of Segment Structure during the Construction of the Large-Diameter Shield Tunnel and Cross-Passage

With the intensive development of China’s high-speed railway network and intercity railway network, the construction of the large-diameter shield tunnels and cross-passages is gradually increasing. The construction of large diameter shield tunnels and the excavation of cross-passages puts forward higher requirements for the stability and safety of segment structure. Based on the Wangjing tunnel project, this paper studies the segment displacement and mechanical response of the shield tunnel with a diameter of 10.5 m in the process of shield construction and cross-passage construction. The results show that during the construction of large diameter shield tunnels, the vault and invert produce inward displacement, the invert uplift usually is more severe than the vault settlement, and the arch waist on both sides produces outward displacement. Near the segment K (capping block), the mechanical performance of the segment is close to that of the hinge or chain rod, which can only effectively transmit the axial force but cannot resist the bending moment and shear force. During construction of the cross-passage, the maximum deformation and stress of shield tunnel segment are symmetrically located at the interface of the main tunnel and cross-passage. The upper and lower edges of the segment at the interface tend to change from compression to tension. At the same time, the steel bars on the inside and outside of the segment vault and the arch waist change from compressive stress to tensile stress, which can easily lead to segment damage, so these positions can be reinforced by erecting section steel frames before construction.

Numerical simulation and analysis of the pile underpinning technology used in shield tunnel crossings on bridge pile foundations

Currently, the pile foundation underpinning technology is widely used when underground transportation infrastructure passes through existing buildings or structures in urban areas. This study aims to investigate stress transfer mechanisms in pile foundations during an underpinning process as well as the influence of shield tunnel construction on pile stability. To this end, the pile foundation underpinning technology used in China’s Shenzhen Metro Line 10 crossing through the bridge pile foundation group of the Guangzhou–Shenzhen highway was analyzed in detailed. The refined numerical simulation of the pile foundation underpinning and shield tunnel construction processes were conducted using the fast Lagrangian analysis of continua in 3 dimensions (FLAC3D) software. The results demonstrate that after the pile foundation underpinned, the previous bridge load system of bridge panel → pile foundation → bearing soil would transform into a bridge panel → existing pile foundation → new underpinning pile → deep bearing soil stratum structure. The overlying load on the underpinned pile could be effectively transferred to a new underpinning pile. In the process of underpinning and tunnel excavation, the settlement and deformation of the foundation can improve the tip resistance and shaft friction of piles, which in turn, can reduce the maximum principal stress in the pile foundation group. The deformation of the bridge pile foundation is mainly caused by ground loss and excavation disturbance generated during shield tunneling as the settlement induced by pile foundation underpinning accounts for approximately 20%–30% of the total settlement. The reduction effects of settlement deformation, lateral displacement, and principal stress are mainly manifested in underpinning piles, while the non-underpinning pile exhibits minimal variation. Meanwhile, the deformation of the segment lining structure of the shield tunnel primarily occurs near the underpinning area of the pile foundation, and it is mainly settlement deformation with a small horizontal displacement.

Human Error Identification and Analysis for Shield Machine Operation Using an Adapted TRACEr Method

AbstractThis paper investigated shield machine operation (SMO) errors involved in shield tunneling construction accidents based on the Technique for the Retrospective and Predictive Analysis of Cog...

Effect of Shield-Tunnel Excavation on Adjacent-Pile Foundation Based on Modified Cam-Clay Model

To ensure the safety of shield tunneling near pile foundation and reduce the disturbance of this phenomenon in an urban metro in the loess area of China, a three-dimensional finite-element analysis model of shield-tunneling construction is established based on ABAQUS numerical simulation software and modified Cam-clay model. The deformation and ground settlement of adjacent-pile foundation during shield tunneling are analyzed. The law of descent is calculated and analyzed. Results show that the influence of tunnel shield on adjacent-pile foundation is primarily manifested in the X-direction displacement of the buried depth of the tunnel. During the shield-excavation process, the X-direction displacement of the pile increases gradually with decreased distance between the excavation face and the pile. When the distance between the pile axis and the excavation face of the tunnel is approximately[-0.5D, +0.5D], the displacement is the largest; when D continues to increase, the X-direction displacement is the largest. The displacement also continues to increase and eventually stabilizes. By obtaining the deformation curve of ground settlement, we find that the ground deformation is the largest above the tunnel axis and gradually decreases to both sides, whereas the pile cap is affected by uneven settlement. In the actual excavation of the tunnel project, strengthening the monitoring of the uneven settlement of the cap is necessary to take timely control measures.

Recycling of discharged soil from EPB shield tunnels as a sustainable raw material for synchronous grouting

EPB shield tunnel construction will discharge a large amount of soil. Directly transporting this discharged soil to dumping grounds not only increases the machinery and labor costs but also raises environmental concerns. In this paper, we presented and explored a guiding framework for recycling the discharged soil from EPB shield tunnel construction as the raw materials for synchronous grouting. The proposed method was proved to be feasible by a detailed experimental study based on samples taking from the Zhengzhou metro line 3 project. The preparation and formulation process of those raw materials was designed to meet the requirements not only for engineering application but also for green environmental protection and sustainable development. The properties and performance of the synchronous grouting material, including its specific gravity, fluidity, gel time, bleeding rate, bulk shrinkage rate and unconfined compression strength, were investigated by the U15∗ (154) uniform design experimentation. The effects of ratios of water/binder (cement + fly flash), the binder/coarse-grains (the discharged soil from the west bound tunnel + river sand), fine-grains (the discharged soil from the east bound tunnel)/water and the fly flash/cement on the response value of the synchronous grouting material performances have been investigated with stepwise nonlinear regression analysis model and 3D response surface diagrams. Moreover, the optimal mass ratio for the synchronous grout is also proposed with a new Goal Programming model to obtain an optimum performance. The results indicate that the discharged soil from the east bound tunnel in this project can be directly reused as bentonite, while the discharged soil from the west bound tunnel should be mixed with river sand at a mass ratio of 1:1 before reusing it as the raw material of synchronous grout. Furthermore, the performance of the synchronous grouting was demonstrated highly depending on the proper selection and optimization of mass ratios for water/binder, binder/coarse-grains, fine-grains/water and fly-ash/cement. The presented experimental investigation and the proposed strategy for determining the optimal formulation for synchronous grouting materials demonstrated a feasible way of recycling discharged soil from EPB shield tunnel construction.

A Risk Assessment Method for Metro Shield Tunnel Construction Based on Interval Number

In recent years, metro construction is flourishing in China. In the construction process of the metro shield tunnel, there are various complex potential risk factors fraught with many uncertainties. Therefore, it is crucial to conduct a risk assessment on urban metro shield construction. To improve the accuracy of the risk assessment results of metro construction projects, a risk assessment model based on interval numbers is proposed from the perspective of uncertainty. The experts’ evaluation information is represented by the interval number, and then the operation rule and membership function of the interval number is used to calculate the risk level of each potential risk factor. Afterward, the weight of each evaluation index is calculated based on the interval number and the C-OWA operator. From the bottom of the evaluation system, the layer-by-layer operation is carried out to determine the risk level of the assessment index of each layer, and the risk grade is divided according to the risk matrix. Taking a section of the shield tunnel of Shenzhen Metro Line 12 as an example, the proposed method is used to evaluate the construction risk, and the potential risk factors that require the implementation of risk prevention measures in the project are obtained. The calculation results show that the assessment model is reasonable and reliable, and has high stability.