The construction of the new tunnel under the existing railway will break the original stress balance in the engineering area, resulting in the secondary redistribution of surrounding rock stress. The large amount of e...The construction of the new tunnel under the existing railway will break the original stress balance in the engineering area, resulting in the secondary redistribution of surrounding rock stress. The large amount of excavation unloading of the soil below is also easy to induce the uneven settlement deformation of the existing structure above, affecting the safety of driving. Based on the shield tunnel project between Caoqiao Station and Lize Business District Station of Beijing Metro, this paper restores the construction site by constructing the finite element numerical model of the project area, calculates and analyzes the deformation and stress of the existing railway structure before and after the construction of the tunnel, and determines the safety impact of the new structure on the existing railway. The results show that the shield tunnel undercrossing construction will cause the “concave” settlement of the railway subgrade above. Under the condition of grouting reinforcement, the “concave” settlement curve is slower and the distribution range is wider. With the advancement of the construction step, the settlement deformation of the subgrade gradually increases. When the tunnel approaches and passes directly below the subgrade, the settlement deformation curve of the subgrade changes from slow to steep. After the tunnel passes away, the curve changes from steep to slow, and the deformation of the subgrade reaches the maximum after the tunnel is connected. Under the grouting condition, the maximum settlement deformation of the subgrade is 2.08 mm, which is about 45% of the settlement deformation of the subgrade under the non-grouting condition. The ground grouting reinforcement can effectively control the subgrade settlement, and the field monitoring verifies the rationality of the calculation results. After the tunnel passes underneath, the most unfavorable section of the existing railway frame bridge is located at the top plate of the structure, and the maximum crack width is 0.178 mm. After grouting reinforcement, the stress environment of the structure is improved, the crack width generated by the structure is smaller, the reinforcement area required for calculation is less, and the structural safety meets the requirements.展开更多
The recent upsurge in metro construction emphasizes the necessity of understanding the mechanical performance of metro shield tunnel subjected to the influence of ground fissures.In this study,a largescale experiment,...The recent upsurge in metro construction emphasizes the necessity of understanding the mechanical performance of metro shield tunnel subjected to the influence of ground fissures.In this study,a largescale experiment,in combination with numerical simulation,was conducted to investigate the influence of ground fissures on a metro shield tunnel.The results indicate that the lining contact pressure at the vault increases in the hanging wall while decreases in the footwall,resulting in a two-dimensional stress state of vertical shear and axial tension-compression,and simultaneous vertical dislocation and axial tilt for the segments around the ground fissure.In addition,the damage to curved bolts includes tensile yield,flexural yield,and shear twist,leading to obvious concrete lining damage,particularly at the vault,arch bottom,and hance,indicating that the joints in these positions are weak areas.The shield tunnel orthogonal to the ground fissure ultimately experiences shear failure,suggesting that the maximum actual dislocation of ground fissure that the structure can withstand is approximately 20 cm,and five segment rings in the hanging wall and six segment rings in the footwall also need to be reinforced.This study could provide a reference for metro design in ground fissure sites.展开更多
The deformation caused by tunnel excavation is quite important for safety,especially when it is adjacent to the existing tunnel.Nevertheless,the investigation of deformation characteristics in overlapped curved shield...The deformation caused by tunnel excavation is quite important for safety,especially when it is adjacent to the existing tunnel.Nevertheless,the investigation of deformation characteristics in overlapped curved shield tunneling remains inadequate.The analytical solution for calculating the deformation of the ground and existing tunnel induced by overlapped curved shield tunneling is derived by the Mirror theory,Mindlin solution and Euler-Bernoulli-Pasternak model,subsequently validated through both finite element simulation and field monitoring.It is determined that the overcutting plays a crucial role in the ground settlement resulting from curved shield tunneling compared to straight shield tunneling.The longitudinal settlement distribution can be categorized into five areas,with the area near the tunnel surface experiencing the most dramatic settlement changes.The deformation of the existing tunnel varies most significantly with turning radius compared to tunnel clearance and grouting pressure,especially when the turning radius is less than 30 times the tunnel diameter.The tunnel crown exhibits larger displacement than the tunnel bottom,resulting in a distinctive‘vertical egg'shape.Furthermore,an optimized overcutting mode is proposed,involving precise control of the extension speed and angular velocity of the overcutting cutter,which effectively mitigates ground deformation,ensuring the protection of the existing tunnel during the construction.展开更多
Twin curved tunnels are often encountered in shield tunnelling,where significant complexities in densely exploited underground space are observed.In this study,the ground settlement and tunnel deformation due to twin-...Twin curved tunnels are often encountered in shield tunnelling,where significant complexities in densely exploited underground space are observed.In this study,the ground settlement and tunnel deformation due to twin-curved shield tunnelling in soft ground were investigated using numerical simulation and field monitoring.Different curvature radii of twin curved tunnels and subsequent effects of tunnel construction were considered to reveal the tunnelling effect on ground surface settlement and tunnel deformation.The results show that the settlement trough yields one offset towards inside of curved shield tunnelling.The location of settlement trough and maximum settlement were affected by curvature radius but except for the shape and width of settlement trough.Adjacent parallel twin-curved shield tunnelling could increase the offset of existing settlement trough and maximum settlement.Then,an empirical prediction of surface settlement trough due to twin-curved shield tunnelling with same tunnel diameters in soft clay was proposed,which was applicable to curvature radius less than 800 m.Finally,a minimum radius of 600 m of curvature tunnel was proposed in terms of allowable convergence deformation of tunnel.The result could provide guidance on safety evaluation for twin curved shield tunnelling construction.展开更多
This study focuses on the analytical prediction of subsurface settlement induced by shield tunnelling in sandy cobble stratum considering the volumetric deformation modes of the soil above the tunnel crown.A series of...This study focuses on the analytical prediction of subsurface settlement induced by shield tunnelling in sandy cobble stratum considering the volumetric deformation modes of the soil above the tunnel crown.A series of numerical analyses is performed to examine the effects of cover depth ratio(C/D),tunnel volume loss rate(h t)and volumetric block proportion(VBP)on the characteristics of subsurface settle-ment trough and soil volume loss.Considering the ground loss variation with depth,three modes are deduced from the volumetric deformation responses of the soil above the tunnel crown.Then,analytical solutions to predict subsurface settlement for each mode are presented using stochastic medium theory.The influences of C/D,h t and VBP on the key parameters(i.e.B and N)in the analytical expressions are discussed to determine the fitting formulae of B and N.Finally,the proposed analytical solutions are validated by the comparisons with the results of model test and numerical simulation.Results show that the fitting formulae provide a convenient and reliable way to evaluate the key parameters.Besides,the analytical solutions are reasonable and available in predicting the subsurface settlement induced by shield tunnelling in sandy cobble stratum.展开更多
The problem of shield tunnel uplift is a common issue in tunnel construction.Due to the decrease in shear stiffness at the joints between the rings,uplift is typically observed as bending and dislocation deformation a...The problem of shield tunnel uplift is a common issue in tunnel construction.Due to the decrease in shear stiffness at the joints between the rings,uplift is typically observed as bending and dislocation deformation at these joints.Existing modeling methods typically rely on the Euler-Bernoulli beam theory,only considering the bending effect while disregarding shear deformation.Furthermore,the constraints on the shield tail are often neglected in existing models.In this study,an improved theoretical model of tunnel floating is proposed.The constraint effect of the shield machine shell on the tunnel structure is considered using the structural forms of two finite long beams and one semi-infinite long beam.Furthermore,the Timoshenko beam theory is adopted,providing a more accurate description of tunnel deformation,including both the bending effect and shear deformation,than existing models.Meanwhile,the buoyancy force and stratum resistance are calculated in a nonlinear manner.A reliable method for calculating the shear stiffness correction factor is proposed to better determination of the calculation parameters.The proposed theoretical model is validated through five cases using sitemonitored data.Its applicability and effectiveness are demonstrated.Furthermore,the influences of soil type,buried depth,and buoyancy force on the three key indicators of tunnel floating(i.e.the maximum uplift magnitude,the ring position with the fastest uplift race,and the ring position with the maximum uplift magnitude)are analyzed.The results indicate that the proposed model can provide a better understanding of the floating characteristics of the tunnel structure during construction.展开更多
To address the seismic face stability challenges encountered in urban and subsea tunnel construction,an efficient probabilistic analysis framework for shield tunnel faces under seismic conditions is proposed.Based on ...To address the seismic face stability challenges encountered in urban and subsea tunnel construction,an efficient probabilistic analysis framework for shield tunnel faces under seismic conditions is proposed.Based on the upper-bound theory of limit analysis,an improved three-dimensional discrete deterministic mechanism,accounting for the heterogeneous nature of soil media,is formulated to evaluate seismic face stability.The metamodel of failure probabilistic assessments for seismic tunnel faces is constructed by integrating the sparse polynomial chaos expansion method(SPCE)with the modified pseudo-dynamic approach(MPD).The improved deterministic model is validated by comparing with published literature and numerical simulations results,and the SPCE-MPD metamodel is examined with the traditional MCS method.Based on the SPCE-MPD metamodels,the seismic effects on face failure probability and reliability index are presented and the global sensitivity analysis(GSA)is involved to reflect the influence order of seismic action parameters.Finally,the proposed approach is tested to be effective by a engineering case of the Chengdu outer ring tunnel.The results show that higher uncertainty of seismic response on face stability should be noticed in areas with intense earthquakes and variation of seismic wave velocity has the most profound influence on tunnel face stability.展开更多
Severe shield jamming events have been reported during excavation of Uluabat tunnel through adverse geological conditions, which resulted in several stoppages at advancing a single shielded tunnel boring machine(TBM)....Severe shield jamming events have been reported during excavation of Uluabat tunnel through adverse geological conditions, which resulted in several stoppages at advancing a single shielded tunnel boring machine(TBM). To study the jamming mechanism, three-dimensional(3D) simulation of the machine and surrounding ground was implemented using the finite difference code FLAC3D. Numerical analyses were performed for three sections along the tunnel with a higher risk for entrapment due to the combination of overburden and geological conditions. The computational results including longitudinal displacement contours and ground pressure profiles around the shield allow a better understanding of ground behavior within the excavation. Furthermore, they allow realistically assessing the impact of adverse geological conditions on shield jamming. The calculated thrust forces, which are required to move the machine forward, are in good agreement with field observations and measurements. It also proves that the numerical analysis can effectively be used for evaluating the effect of adverse geological environment on TBM entrapments and can be applied to prediction of loads on the shield and preestimating of the required thrust force during excavation through adverse ground conditions.展开更多
For a tunnel driven by a shield machine,the posture of the driving machine is essential to the construction quality and environmental impact.However,the machine posture is controlled by the experienced driver of shiel...For a tunnel driven by a shield machine,the posture of the driving machine is essential to the construction quality and environmental impact.However,the machine posture is controlled by the experienced driver of shield machine by setting hundreds of tunneling parameters empirically.Machine learning(ML)algorithm is an alternative method that can let the computer to learn from the driver’s operation and try to model the relationship between parameters automatically.Thus,in this paper,three ML algorithms,i.e.multi-layer perception(MLP),support vector machine(SVM)and gradient boosting regression(GBR),are improved by genetic algorithm(GA)and principal component analysis(PCA)to predict the tunneling posture of the shield machine.A set of the parameters for shield tunneling is extracted from the construction site of a Shanghai metro.In total,53,785 pairwise data points are collected for about 373 d and the ratio between training set,validation set and test set is 3:1:1.Each pairwise data point includes 83 types of parameters covering the shield posture,construction parameters,and soil stratum properties at the same time.The test results show that the averaged R2 of MLP,SVM and GBR based models are 0.942,0.935 and 0.6,respectively.Then the automatic control for the posture of shield tunnel is illustrated with an application example of the proposed models.The proposed method is proved to be helpful in controlling the construction quality with optimized construction parameters.展开更多
Disc cutter consumption is a critical problem that influences work performance during shield tunneling processes and directly affects the cutter change decision.This study proposes a new model to estimate the disc cut...Disc cutter consumption is a critical problem that influences work performance during shield tunneling processes and directly affects the cutter change decision.This study proposes a new model to estimate the disc cutter life(Hf)by integrating a group method of data handling(GMDH)-type neural network(NN)with a genetic algorithm(GA).The efficiency and effectiveness of the GMDH network structure are optimized by the GA,which enables each neuron to search for its optimum connections set from the previous layer.With the proposed model,monitoring data including the shield performance database,disc cutter consumption,geological conditions,and operational parameters can be analyzed.To verify the performance of the proposed model,a case study in China is presented and a database is adopted to illustrate the excellence of the hybrid model.The results indicate that the hybrid model predicts disc cutter life with high accuracy.The sensitivity analysis reveals that the penetration rate(PR)has a significant influence on disc cutter life.The results of this study can be beneficial in both the planning and construction stages of shield tunneling.展开更多
Health state of shield tunnels is one of the most important parameters for structure maintenance.Usually,the shield tunnel is extremely long in longitude direction and composed by many segments.It is difficult to quan...Health state of shield tunnels is one of the most important parameters for structure maintenance.Usually,the shield tunnel is extremely long in longitude direction and composed by many segments.It is difficult to quantify the relationship between the structure damage state and shield tunnel structure deformation by the model test because of unpredictable effects of different scales between model test and prototype tunnel structure.Here,an in-situ monitoring project was conducted to study the excavation induced shield tunnel structure damage,which could be considered a prototype test on the tunnel deformation.The disaster performance of tunnel leakage,segment crack,segment dislocation and segment block drop-off during longitude deformation and cross-section ovality developments was analyzed.The results indicate that instead of the longitude deformation,the ovality value has the strongest correlation to the rest disease performance,which could be used as the assessment index of the tunnel health.For this tunnel,it is in health state when the ovality is less than 0.5%,and the serious damage could be found when the ovality value is higher than 0.77%.The research results provide valuable reference to shield tunnel health assessment and help complete the standard of shield tunnel construction.展开更多
Shield tunneling inevitably passes through a large number of pile foundations in urban areas.Thus,an accurate assessment of tunneling-induced pile displacement and potential damage becomes a critical part of shield co...Shield tunneling inevitably passes through a large number of pile foundations in urban areas.Thus,an accurate assessment of tunneling-induced pile displacement and potential damage becomes a critical part of shield construction.This study presents a mechanism research of pile-soil-tunnel interaction through Pasternak-based two-stage analysis method.In the first stage,based on Mindlin’s solution,the soil displacement fields induced by shield thrust force,cutterhead frictions,shield shell frictions and grouting pressure are derived.The analytical solution of threedimensional soil displacement field is established by introducing Pinto’s three-dimensional volume loss formula,which solves the problems that shield construction factors are not taken into account in Loganathan’s formula and only twodimensional soil displacement field can be obtained.In the second stage,based on Pasternak’s two-parameter foundation model,the analytical solution of pile displacement induced by shield tunneling in layered soil is derived.A case was found in the project of interval tunnels from Wanjiali Square to Furong District Government of Changsha Metro Line 5,where the shield tunnels were constructed near viaduct piles.The reliability of the analytical solution proposed in this study is verified by comparing with the field measured data and the results of finite element method(FEM).In addition,the comparisons of longitudinal,horizontal and vertical displacements of soil and pile foundation analyzed by the analytical solution and FEM provide corresponding theoretical basis,which has significant engineering guidance for similar projects.展开更多
In this paper, a 3D finite element （FE） program ADINA was applied to analyzing a tunnel with 9 segment tings. The loads acting on these segment tings included the squeezing action of tail brush of shield machine und...In this paper, a 3D finite element （FE） program ADINA was applied to analyzing a tunnel with 9 segment tings. The loads acting on these segment tings included the squeezing action of tail brush of shield machine under attitude deflection, the jacking forces, the grouting pressure and the soil pressure. The analyses focused on the rebar stress in two statuses： （1） normal construction status without shield machine squeezing; （2） squeezing action induced by shield machine under attitude deflection. The analyses indicated that the rebar stress was evidently affected by the construction loads. In different construction status, the rebar stress ranges from -80 MPa to 50 MPa, and the rebar is in elastic status. Even some cracks appear on segments, the stress of segment rebar is still at a low level. It is helpful to incorporate a certain quantity of steel fiber to improve the anti-crack and shock resistance performance.展开更多
At present,shield tunneling often needs to pass through a large number of bridge pile foundations.However,there are few studies on the influence of shield tunneling on adjacent pile foundations by combining with groun...At present,shield tunneling often needs to pass through a large number of bridge pile foundations.However,there are few studies on the influence of shield tunneling on adjacent pile foundations by combining with groundwater seepage.Based on Winkler model,the calculation equations of shield tunneling on vertical and horizontal displacement of adjacent bridge pile are derived.Meanwhile,full and part three-dimensional finite element models are established to analyze the trend of bridge pier settlement,ground surface settlement trough,vertical and horizontal displacement of the pile and pile stress under three calculation conditions,i.e.,not considering groundwater effect,considering stable groundwater effect and fluid-soil interaction.The results show that the calculated value is small when the effect of groundwater is not considered;the seepage velocity of the soil above the excavation face is faster than that of the surrounding soil under fluid-soil interaction,and after the shield passing,the groundwater on both sides shows a flow trend of“U”shape on the ground surface supplying to the upper part of the tunnel;the vertical displacement of the pile body is bounded by the horizontal position of the top of the tunnel,the upper pile body settles,and the lower pile body deforms upward.The horizontal displacement of pile body presents a continuous“S”shape distribution,causing stress concentration near the tunnel.The calculated results of fluid-soil interaction are in good agreement with the field measured data and accord with the actual situation.展开更多
The section of shield tunnel of the Chengdu Metro line passes primarily through sandy cobble strata. There are many buildings with spread foundations along the lines. Shield tunnel construction will disturb the ground...The section of shield tunnel of the Chengdu Metro line passes primarily through sandy cobble strata. There are many buildings with spread foundations along the lines. Shield tunnel construction will disturb the ground, causing displacement or stress to adjacent spread foundations. Based on the similarity theory, a laboratory model test of shield tunnel driving was carried out to study the influence of shield tunnel excavation on the displace ment of adjacent spread foundation. The results show that foundation closer to the tunnel has greater displacement or settlement than that further away. The horizontal dis placement is small and is influenced greatly by the cutting face. The displacement along the machine driving direction is bigger and is significantly affected by the thrust force. Settlement occurs primarily when shield machine passes close to the foundation and is the greatest at that time. Uneven settlement at the bottom of the spread foundation reaches a maximum after the excavation ends. In a numerical simulation, a particle flow model was con structed to study the impact of shield tunnel excavation on the stresses in the ground. The model showed stress con centration at the bottom of the spread foundation. With the increasing ground loss ratio, a loose area appears in the tunnel dome where the contact force dropped. Above the loose area, the contact force increases, forming an arch shaped soil area which prevents the loose area from expanding to the ground surface. The excavation also changed the pressure distribution around spread foundation.展开更多
Shield tunneling is easily obstructed by clogging in clayey strata with small soil particles.However,soil clogging rarely occurs in strata with coarse-grained soils.Theoretically,a critical particle size of soils shou...Shield tunneling is easily obstructed by clogging in clayey strata with small soil particles.However,soil clogging rarely occurs in strata with coarse-grained soils.Theoretically,a critical particle size of soils should exist,below which there is a high risk of soil clogging in shield tunneling.To determine the critical particle size,a series of laboratory tests was carried out with a large-scale rotary shear apparatus to measure the tangential adhesion strength of soils with different particle sizes and water contents.It was found that the tangential adhesion strength at the soilesteel interface gradually increased linearly with applied normal pressure.When the particle size of the soil specimen was less than 0.15 mm,the interfacial adhesion force first increased and then decreased as the water content gradually increased;otherwise,the soil specimens did not manifest any interfacial adhesion force.The amount of soil mass adhering to the steel disc was positively correlated with the interfacial adhesion force,thus the interfacial adhesion force was adopted to characterize the soil clogging risk in shield tunneling.The critical particle size of soils causing clogging was determined to be 0.15 mm.Finally,the generation mechanism of interfacial adhesion force was explored for soils with different particle sizes to explain the critical particle size of soil with clogging risk in shield tunneling.展开更多
Deformation and dislocations of segments of shield tunnel in construction stage have apparent effect on tunnel structure stress and even cause local cracks and breakage in tunnel. 3D finite element method was used to ...Deformation and dislocations of segments of shield tunnel in construction stage have apparent effect on tunnel structure stress and even cause local cracks and breakage in tunnel. 3D finite element method was used to analyze two segment ring models under uniform injected pressure: (1) segment ring without wedge-shaped segment, which has 16 types of preinstall erection tolerance; (2) segment ring with wedge-shaped segment, which has no preinstall erection tolerance. The analysis results indicate that different erection tolerances can cause irregular deformation in segment ring under uniform injected pressure, and that the tolerance values are enlarged further. Wedge-shaped segment apparently affects the overall deformation of segment ring without erection tolerances. The uniform injected pressure can cause deformation of ring with wedge-shaped segment irregular, and dislocations also appear in this situation. The stress of segment with erection tolerances is much larger than that of segment without erection tolerances. Enlarging the central angle of wedge-shaped segment can make the irregular deformation and dis- locations of segments smaller. The analysis results also provide basis for erection tolerance control and improvement of segment constitution.展开更多
An estimation approach using least squares method was presented for identificationof model parameters of pressure control in shield tunneling.The state equation ofthe pressure control system for shield tunneling was a...An estimation approach using least squares method was presented for identificationof model parameters of pressure control in shield tunneling.The state equation ofthe pressure control system for shield tunneling was analytically derived based on themass equilibrium principle that the entry mass of the pressure chamber from cutting headwas equal to excluding mass from the screw conveyor.The randomly observed noise wasnumerically simulated and mixed to simulated observation values of system responses.The numerical simulation shows that the state equation of the pressure control system forshield tunneling is reasonable and the proposed estimation approach is effective even ifthe random observation noise exists.The robustness of the controlling procedure is validatedby numerical simulation results.展开更多
This paper concerns the impact of an operating metro train on the structure of a shield tunnel lining and its soft foundation. An elastoplastic 3D dynamic finite difference model was established by using the FLAC3D nu...This paper concerns the impact of an operating metro train on the structure of a shield tunnel lining and its soft foundation. An elastoplastic 3D dynamic finite difference model was established by using the FLAC3D numerical soft- ware. By fully considering the joints, the A-B-K segments and the soft stratum, the dynamic response of the shield tunnel buried in thick, soft soil under the vibrating load induced by a metro train was numerically simulated. The simulation result, for which the joint was considered, was compared with the result when the joint was not considered. The results show that an operating metro train induces a significant dynamic response in the structure of the lining of the shield tunnel and its soft foundation. The severe dynamic response zones of the lining structure are largely distributed in the range of the lower half of the segment-ring and the nearer to the bottom of the segment-ring, the more severe the response. Of two horizontally symmetric, corresponding places on the segment lining, the one near the joint is more severe in its dynamic response than that of the one far from the joint; the nearer the zone of the foundation soil to the lower half of the seg- ment-ring, the more severe the dynamic response. The maximum shear strain of the foundation soil takes place near the joint between two normal segments at the bottom. The dynamic response influenced by joints is more severe than the response not influenced by joints, showing that the non-joint assumption is somewhat impractical.展开更多
The control of slurry pressure aiming to be consistent with the external water and earth pressure during shield tunnelling has great significance for face stability,especially in urban areas or underwater where the su...The control of slurry pressure aiming to be consistent with the external water and earth pressure during shield tunnelling has great significance for face stability,especially in urban areas or underwater where the surrounding environment is very sensitive to the fluctuation of slurry pressure.In this study,an optimal control method for slurry pressure during shield tunnelling is developed,which is composed of an identifier and a controller.The established identifier based on the random forest(RF)can describe the complex non-linear relationship between slurry pressure and its influencing factors.The proposed controller based on particle swarm optimization(PSO)can optimize the key factor to precisely control the slurry pressure at the normal state of advancement.A data set from Tsinghua Yuan Tunnel in China was used to train the RF model and several performance measures like R2,RMSE,etc.,were employed to evaluate.Then,the hybrid RF-PSO control method is adopted to optimize the control of slurry pressure.The good agreement between optimized slurry pressure and expected values demonstrates a high identifying and control precision.展开更多
文摘The construction of the new tunnel under the existing railway will break the original stress balance in the engineering area, resulting in the secondary redistribution of surrounding rock stress. The large amount of excavation unloading of the soil below is also easy to induce the uneven settlement deformation of the existing structure above, affecting the safety of driving. Based on the shield tunnel project between Caoqiao Station and Lize Business District Station of Beijing Metro, this paper restores the construction site by constructing the finite element numerical model of the project area, calculates and analyzes the deformation and stress of the existing railway structure before and after the construction of the tunnel, and determines the safety impact of the new structure on the existing railway. The results show that the shield tunnel undercrossing construction will cause the “concave” settlement of the railway subgrade above. Under the condition of grouting reinforcement, the “concave” settlement curve is slower and the distribution range is wider. With the advancement of the construction step, the settlement deformation of the subgrade gradually increases. When the tunnel approaches and passes directly below the subgrade, the settlement deformation curve of the subgrade changes from slow to steep. After the tunnel passes away, the curve changes from steep to slow, and the deformation of the subgrade reaches the maximum after the tunnel is connected. Under the grouting condition, the maximum settlement deformation of the subgrade is 2.08 mm, which is about 45% of the settlement deformation of the subgrade under the non-grouting condition. The ground grouting reinforcement can effectively control the subgrade settlement, and the field monitoring verifies the rationality of the calculation results. After the tunnel passes underneath, the most unfavorable section of the existing railway frame bridge is located at the top plate of the structure, and the maximum crack width is 0.178 mm. After grouting reinforcement, the stress environment of the structure is improved, the crack width generated by the structure is smaller, the reinforcement area required for calculation is less, and the structural safety meets the requirements.
基金supported by the National Key Research&Development Program of China(Grant No.2023YFC3008404)the Key Laboratory of Earth Fissures Geological Disaster,Ministry of Natural Resources,China(Grant Nos.EFGD20240609 and EFGD20240610).
文摘The recent upsurge in metro construction emphasizes the necessity of understanding the mechanical performance of metro shield tunnel subjected to the influence of ground fissures.In this study,a largescale experiment,in combination with numerical simulation,was conducted to investigate the influence of ground fissures on a metro shield tunnel.The results indicate that the lining contact pressure at the vault increases in the hanging wall while decreases in the footwall,resulting in a two-dimensional stress state of vertical shear and axial tension-compression,and simultaneous vertical dislocation and axial tilt for the segments around the ground fissure.In addition,the damage to curved bolts includes tensile yield,flexural yield,and shear twist,leading to obvious concrete lining damage,particularly at the vault,arch bottom,and hance,indicating that the joints in these positions are weak areas.The shield tunnel orthogonal to the ground fissure ultimately experiences shear failure,suggesting that the maximum actual dislocation of ground fissure that the structure can withstand is approximately 20 cm,and five segment rings in the hanging wall and six segment rings in the footwall also need to be reinforced.This study could provide a reference for metro design in ground fissure sites.
基金financially supported by the National Natural Science Foundation of China(Grant No.52078334)the National Key Research and Development Program of China(Grant No.2017YFC0805402)the Tianjin Research Innovation Project for Postgraduate Students(Grant No.2021YJSB141).
文摘The deformation caused by tunnel excavation is quite important for safety,especially when it is adjacent to the existing tunnel.Nevertheless,the investigation of deformation characteristics in overlapped curved shield tunneling remains inadequate.The analytical solution for calculating the deformation of the ground and existing tunnel induced by overlapped curved shield tunneling is derived by the Mirror theory,Mindlin solution and Euler-Bernoulli-Pasternak model,subsequently validated through both finite element simulation and field monitoring.It is determined that the overcutting plays a crucial role in the ground settlement resulting from curved shield tunneling compared to straight shield tunneling.The longitudinal settlement distribution can be categorized into five areas,with the area near the tunnel surface experiencing the most dramatic settlement changes.The deformation of the existing tunnel varies most significantly with turning radius compared to tunnel clearance and grouting pressure,especially when the turning radius is less than 30 times the tunnel diameter.The tunnel crown exhibits larger displacement than the tunnel bottom,resulting in a distinctive‘vertical egg'shape.Furthermore,an optimized overcutting mode is proposed,involving precise control of the extension speed and angular velocity of the overcutting cutter,which effectively mitigates ground deformation,ensuring the protection of the existing tunnel during the construction.
基金financially supported by the National Natural Science Foundation of China(Grant No.42307260)the Sichuan Natural Science Foundation(Grant No.2023NSFSC0882)the Open Project of the Research Center of Tunnelling and Underground Engineering of Ministry of Education(Grant No.TUC2022-03).
文摘Twin curved tunnels are often encountered in shield tunnelling,where significant complexities in densely exploited underground space are observed.In this study,the ground settlement and tunnel deformation due to twin-curved shield tunnelling in soft ground were investigated using numerical simulation and field monitoring.Different curvature radii of twin curved tunnels and subsequent effects of tunnel construction were considered to reveal the tunnelling effect on ground surface settlement and tunnel deformation.The results show that the settlement trough yields one offset towards inside of curved shield tunnelling.The location of settlement trough and maximum settlement were affected by curvature radius but except for the shape and width of settlement trough.Adjacent parallel twin-curved shield tunnelling could increase the offset of existing settlement trough and maximum settlement.Then,an empirical prediction of surface settlement trough due to twin-curved shield tunnelling with same tunnel diameters in soft clay was proposed,which was applicable to curvature radius less than 800 m.Finally,a minimum radius of 600 m of curvature tunnel was proposed in terms of allowable convergence deformation of tunnel.The result could provide guidance on safety evaluation for twin curved shield tunnelling construction.
基金This study was supported by the National Natural Science Foundation of China(Grant Nos.51538001 and 51978019).
文摘This study focuses on the analytical prediction of subsurface settlement induced by shield tunnelling in sandy cobble stratum considering the volumetric deformation modes of the soil above the tunnel crown.A series of numerical analyses is performed to examine the effects of cover depth ratio(C/D),tunnel volume loss rate(h t)and volumetric block proportion(VBP)on the characteristics of subsurface settle-ment trough and soil volume loss.Considering the ground loss variation with depth,three modes are deduced from the volumetric deformation responses of the soil above the tunnel crown.Then,analytical solutions to predict subsurface settlement for each mode are presented using stochastic medium theory.The influences of C/D,h t and VBP on the key parameters(i.e.B and N)in the analytical expressions are discussed to determine the fitting formulae of B and N.Finally,the proposed analytical solutions are validated by the comparisons with the results of model test and numerical simulation.Results show that the fitting formulae provide a convenient and reliable way to evaluate the key parameters.Besides,the analytical solutions are reasonable and available in predicting the subsurface settlement induced by shield tunnelling in sandy cobble stratum.
基金the National Natural Science Foundation of China (Grant Nos.52379111,51979270 and 52208380).
文摘The problem of shield tunnel uplift is a common issue in tunnel construction.Due to the decrease in shear stiffness at the joints between the rings,uplift is typically observed as bending and dislocation deformation at these joints.Existing modeling methods typically rely on the Euler-Bernoulli beam theory,only considering the bending effect while disregarding shear deformation.Furthermore,the constraints on the shield tail are often neglected in existing models.In this study,an improved theoretical model of tunnel floating is proposed.The constraint effect of the shield machine shell on the tunnel structure is considered using the structural forms of two finite long beams and one semi-infinite long beam.Furthermore,the Timoshenko beam theory is adopted,providing a more accurate description of tunnel deformation,including both the bending effect and shear deformation,than existing models.Meanwhile,the buoyancy force and stratum resistance are calculated in a nonlinear manner.A reliable method for calculating the shear stiffness correction factor is proposed to better determination of the calculation parameters.The proposed theoretical model is validated through five cases using sitemonitored data.Its applicability and effectiveness are demonstrated.Furthermore,the influences of soil type,buried depth,and buoyancy force on the three key indicators of tunnel floating(i.e.the maximum uplift magnitude,the ring position with the fastest uplift race,and the ring position with the maximum uplift magnitude)are analyzed.The results indicate that the proposed model can provide a better understanding of the floating characteristics of the tunnel structure during construction.
基金Project([2018]3010)supported by the Guizhou Provincial Science and Technology Major Project,China。
文摘To address the seismic face stability challenges encountered in urban and subsea tunnel construction,an efficient probabilistic analysis framework for shield tunnel faces under seismic conditions is proposed.Based on the upper-bound theory of limit analysis,an improved three-dimensional discrete deterministic mechanism,accounting for the heterogeneous nature of soil media,is formulated to evaluate seismic face stability.The metamodel of failure probabilistic assessments for seismic tunnel faces is constructed by integrating the sparse polynomial chaos expansion method(SPCE)with the modified pseudo-dynamic approach(MPD).The improved deterministic model is validated by comparing with published literature and numerical simulations results,and the SPCE-MPD metamodel is examined with the traditional MCS method.Based on the SPCE-MPD metamodels,the seismic effects on face failure probability and reliability index are presented and the global sensitivity analysis(GSA)is involved to reflect the influence order of seismic action parameters.Finally,the proposed approach is tested to be effective by a engineering case of the Chengdu outer ring tunnel.The results show that higher uncertainty of seismic response on face stability should be noticed in areas with intense earthquakes and variation of seismic wave velocity has the most profound influence on tunnel face stability.
基金Alexander von Humboldt-Foundation (AvH) for the financial support as a research fellowthe financial support of the Scientific and Technological Research Council of Turkey (TüB_ITAK) under Project No. MAG-114M568
文摘Severe shield jamming events have been reported during excavation of Uluabat tunnel through adverse geological conditions, which resulted in several stoppages at advancing a single shielded tunnel boring machine(TBM). To study the jamming mechanism, three-dimensional(3D) simulation of the machine and surrounding ground was implemented using the finite difference code FLAC3D. Numerical analyses were performed for three sections along the tunnel with a higher risk for entrapment due to the combination of overburden and geological conditions. The computational results including longitudinal displacement contours and ground pressure profiles around the shield allow a better understanding of ground behavior within the excavation. Furthermore, they allow realistically assessing the impact of adverse geological conditions on shield jamming. The calculated thrust forces, which are required to move the machine forward, are in good agreement with field observations and measurements. It also proves that the numerical analysis can effectively be used for evaluating the effect of adverse geological environment on TBM entrapments and can be applied to prediction of loads on the shield and preestimating of the required thrust force during excavation through adverse ground conditions.
基金supported by the National Natural Science Foundation of China(Grant Nos.52130805 and 51978516)Scientific Program of Shanghai Science and Technology Committee(Grant No.20dz1202200).
文摘For a tunnel driven by a shield machine,the posture of the driving machine is essential to the construction quality and environmental impact.However,the machine posture is controlled by the experienced driver of shield machine by setting hundreds of tunneling parameters empirically.Machine learning(ML)algorithm is an alternative method that can let the computer to learn from the driver’s operation and try to model the relationship between parameters automatically.Thus,in this paper,three ML algorithms,i.e.multi-layer perception(MLP),support vector machine(SVM)and gradient boosting regression(GBR),are improved by genetic algorithm(GA)and principal component analysis(PCA)to predict the tunneling posture of the shield machine.A set of the parameters for shield tunneling is extracted from the construction site of a Shanghai metro.In total,53,785 pairwise data points are collected for about 373 d and the ratio between training set,validation set and test set is 3:1:1.Each pairwise data point includes 83 types of parameters covering the shield posture,construction parameters,and soil stratum properties at the same time.The test results show that the averaged R2 of MLP,SVM and GBR based models are 0.942,0.935 and 0.6,respectively.Then the automatic control for the posture of shield tunnel is illustrated with an application example of the proposed models.The proposed method is proved to be helpful in controlling the construction quality with optimized construction parameters.
基金The research work was funded by“The Pearl River Talent Recruitment Program”in 2019(2019CX01G338)Guangdong Province and the Research Funding of Shantou University for New Faculty Member(NTF19024-2019),China.
文摘Disc cutter consumption is a critical problem that influences work performance during shield tunneling processes and directly affects the cutter change decision.This study proposes a new model to estimate the disc cutter life(Hf)by integrating a group method of data handling(GMDH)-type neural network(NN)with a genetic algorithm(GA).The efficiency and effectiveness of the GMDH network structure are optimized by the GA,which enables each neuron to search for its optimum connections set from the previous layer.With the proposed model,monitoring data including the shield performance database,disc cutter consumption,geological conditions,and operational parameters can be analyzed.To verify the performance of the proposed model,a case study in China is presented and a database is adopted to illustrate the excellence of the hybrid model.The results indicate that the hybrid model predicts disc cutter life with high accuracy.The sensitivity analysis reveals that the penetration rate(PR)has a significant influence on disc cutter life.The results of this study can be beneficial in both the planning and construction stages of shield tunneling.
基金Projects(BK20150337,BK20140845,BK20140844)supported by the Natural Science Foundation of Jiangsu Province,ChinaProject(2015Y04)supported by the Transportation Science and Technology Project of Jiangsu Province,China+1 种基金Project(41504081)supported by the National Natural Science Foundation of ChinaProjects(2014M561567,2016T90416)supported by the China Postdoctoral Science Foundation
文摘Health state of shield tunnels is one of the most important parameters for structure maintenance.Usually,the shield tunnel is extremely long in longitude direction and composed by many segments.It is difficult to quantify the relationship between the structure damage state and shield tunnel structure deformation by the model test because of unpredictable effects of different scales between model test and prototype tunnel structure.Here,an in-situ monitoring project was conducted to study the excavation induced shield tunnel structure damage,which could be considered a prototype test on the tunnel deformation.The disaster performance of tunnel leakage,segment crack,segment dislocation and segment block drop-off during longitude deformation and cross-section ovality developments was analyzed.The results indicate that instead of the longitude deformation,the ovality value has the strongest correlation to the rest disease performance,which could be used as the assessment index of the tunnel health.For this tunnel,it is in health state when the ovality is less than 0.5%,and the serious damage could be found when the ovality value is higher than 0.77%.The research results provide valuable reference to shield tunnel health assessment and help complete the standard of shield tunnel construction.
基金Project(52078060) supported by the National Natural Science Foundation of ChinaProject(2020JJ4606)supported by the Natural Science Foundation of Hunan Province,China+1 种基金Project(2018IC19) supported by the International Cooperation and Development Project of Double-First-Class Scientific Research in Changsha University of Science&Technology,ChinaProject(18ZDXK05) supported by Innovative Program of Key Disciplines with Advantages and Characteristics of Civil Engineering of Changsha University of Science&Technology,China。
文摘Shield tunneling inevitably passes through a large number of pile foundations in urban areas.Thus,an accurate assessment of tunneling-induced pile displacement and potential damage becomes a critical part of shield construction.This study presents a mechanism research of pile-soil-tunnel interaction through Pasternak-based two-stage analysis method.In the first stage,based on Mindlin’s solution,the soil displacement fields induced by shield thrust force,cutterhead frictions,shield shell frictions and grouting pressure are derived.The analytical solution of threedimensional soil displacement field is established by introducing Pinto’s three-dimensional volume loss formula,which solves the problems that shield construction factors are not taken into account in Loganathan’s formula and only twodimensional soil displacement field can be obtained.In the second stage,based on Pasternak’s two-parameter foundation model,the analytical solution of pile displacement induced by shield tunneling in layered soil is derived.A case was found in the project of interval tunnels from Wanjiali Square to Furong District Government of Changsha Metro Line 5,where the shield tunnels were constructed near viaduct piles.The reliability of the analytical solution proposed in this study is verified by comparing with the field measured data and the results of finite element method(FEM).In addition,the comparisons of longitudinal,horizontal and vertical displacements of soil and pile foundation analyzed by the analytical solution and FEM provide corresponding theoretical basis,which has significant engineering guidance for similar projects.
文摘In this paper, a 3D finite element （FE） program ADINA was applied to analyzing a tunnel with 9 segment tings. The loads acting on these segment tings included the squeezing action of tail brush of shield machine under attitude deflection, the jacking forces, the grouting pressure and the soil pressure. The analyses focused on the rebar stress in two statuses： （1） normal construction status without shield machine squeezing; （2） squeezing action induced by shield machine under attitude deflection. The analyses indicated that the rebar stress was evidently affected by the construction loads. In different construction status, the rebar stress ranges from -80 MPa to 50 MPa, and the rebar is in elastic status. Even some cracks appear on segments, the stress of segment rebar is still at a low level. It is helpful to incorporate a certain quantity of steel fiber to improve the anti-crack and shock resistance performance.
基金Project(52078060)supported by the National Natural Science Foundation of ChinaProject(2020JJ4606)supported by the National Science Foundation of Hunan Province,China+1 种基金Project(18A127)supported by the Key Foundation of Education Department of Hunan Province,ChinaProject(2018IC19)supported by the International Cooperation and Development Project of Double-First-Class Scientific Research in Changsha University of Science&Technology,China。
文摘At present,shield tunneling often needs to pass through a large number of bridge pile foundations.However,there are few studies on the influence of shield tunneling on adjacent pile foundations by combining with groundwater seepage.Based on Winkler model,the calculation equations of shield tunneling on vertical and horizontal displacement of adjacent bridge pile are derived.Meanwhile,full and part three-dimensional finite element models are established to analyze the trend of bridge pier settlement,ground surface settlement trough,vertical and horizontal displacement of the pile and pile stress under three calculation conditions,i.e.,not considering groundwater effect,considering stable groundwater effect and fluid-soil interaction.The results show that the calculated value is small when the effect of groundwater is not considered;the seepage velocity of the soil above the excavation face is faster than that of the surrounding soil under fluid-soil interaction,and after the shield passing,the groundwater on both sides shows a flow trend of“U”shape on the ground surface supplying to the upper part of the tunnel;the vertical displacement of the pile body is bounded by the horizontal position of the top of the tunnel,the upper pile body settles,and the lower pile body deforms upward.The horizontal displacement of pile body presents a continuous“S”shape distribution,causing stress concentration near the tunnel.The calculated results of fluid-soil interaction are in good agreement with the field measured data and accord with the actual situation.
基金funded by the National Natural Science Foundation of China (Nos. 51278422 and 50925830)the National 973 Plan Topics of China (No. 2010CB732105)+1 种基金the National Science and Technology Pillar Program of China (No. 2012BAG05B03)the Sichuan Youth Science and Technology Foundation, China (No. 2012JQ0021)
文摘The section of shield tunnel of the Chengdu Metro line passes primarily through sandy cobble strata. There are many buildings with spread foundations along the lines. Shield tunnel construction will disturb the ground, causing displacement or stress to adjacent spread foundations. Based on the similarity theory, a laboratory model test of shield tunnel driving was carried out to study the influence of shield tunnel excavation on the displace ment of adjacent spread foundation. The results show that foundation closer to the tunnel has greater displacement or settlement than that further away. The horizontal dis placement is small and is influenced greatly by the cutting face. The displacement along the machine driving direction is bigger and is significantly affected by the thrust force. Settlement occurs primarily when shield machine passes close to the foundation and is the greatest at that time. Uneven settlement at the bottom of the spread foundation reaches a maximum after the excavation ends. In a numerical simulation, a particle flow model was con structed to study the impact of shield tunnel excavation on the stresses in the ground. The model showed stress con centration at the bottom of the spread foundation. With the increasing ground loss ratio, a loose area appears in the tunnel dome where the contact force dropped. Above the loose area, the contact force increases, forming an arch shaped soil area which prevents the loose area from expanding to the ground surface. The excavation also changed the pressure distribution around spread foundation.
基金The financial support from the National Natural Science Foun-dation of China(Grant Nos.52022112 and 51778637)the Sci-ence and Technology Innovation Program of Hunan Province(Grant No.2021RC3015)are acknowledged and appreciated.
文摘Shield tunneling is easily obstructed by clogging in clayey strata with small soil particles.However,soil clogging rarely occurs in strata with coarse-grained soils.Theoretically,a critical particle size of soils should exist,below which there is a high risk of soil clogging in shield tunneling.To determine the critical particle size,a series of laboratory tests was carried out with a large-scale rotary shear apparatus to measure the tangential adhesion strength of soils with different particle sizes and water contents.It was found that the tangential adhesion strength at the soilesteel interface gradually increased linearly with applied normal pressure.When the particle size of the soil specimen was less than 0.15 mm,the interfacial adhesion force first increased and then decreased as the water content gradually increased;otherwise,the soil specimens did not manifest any interfacial adhesion force.The amount of soil mass adhering to the steel disc was positively correlated with the interfacial adhesion force,thus the interfacial adhesion force was adopted to characterize the soil clogging risk in shield tunneling.The critical particle size of soils causing clogging was determined to be 0.15 mm.Finally,the generation mechanism of interfacial adhesion force was explored for soils with different particle sizes to explain the critical particle size of soil with clogging risk in shield tunneling.
文摘Deformation and dislocations of segments of shield tunnel in construction stage have apparent effect on tunnel structure stress and even cause local cracks and breakage in tunnel. 3D finite element method was used to analyze two segment ring models under uniform injected pressure: (1) segment ring without wedge-shaped segment, which has 16 types of preinstall erection tolerance; (2) segment ring with wedge-shaped segment, which has no preinstall erection tolerance. The analysis results indicate that different erection tolerances can cause irregular deformation in segment ring under uniform injected pressure, and that the tolerance values are enlarged further. Wedge-shaped segment apparently affects the overall deformation of segment ring without erection tolerances. The uniform injected pressure can cause deformation of ring with wedge-shaped segment irregular, and dislocations also appear in this situation. The stress of segment with erection tolerances is much larger than that of segment without erection tolerances. Enlarging the central angle of wedge-shaped segment can make the irregular deformation and dis- locations of segments smaller. The analysis results also provide basis for erection tolerance control and improvement of segment constitution.
基金Supported by the National Basic Research Program of China(2007CB714006)the National Natural Science Foundation of China(90815023)
文摘An estimation approach using least squares method was presented for identificationof model parameters of pressure control in shield tunneling.The state equation ofthe pressure control system for shield tunneling was analytically derived based on themass equilibrium principle that the entry mass of the pressure chamber from cutting headwas equal to excluding mass from the screw conveyor.The randomly observed noise wasnumerically simulated and mixed to simulated observation values of system responses.The numerical simulation shows that the state equation of the pressure control system forshield tunneling is reasonable and the proposed estimation approach is effective even ifthe random observation noise exists.The robustness of the controlling procedure is validatedby numerical simulation results.
文摘This paper concerns the impact of an operating metro train on the structure of a shield tunnel lining and its soft foundation. An elastoplastic 3D dynamic finite difference model was established by using the FLAC3D numerical soft- ware. By fully considering the joints, the A-B-K segments and the soft stratum, the dynamic response of the shield tunnel buried in thick, soft soil under the vibrating load induced by a metro train was numerically simulated. The simulation result, for which the joint was considered, was compared with the result when the joint was not considered. The results show that an operating metro train induces a significant dynamic response in the structure of the lining of the shield tunnel and its soft foundation. The severe dynamic response zones of the lining structure are largely distributed in the range of the lower half of the segment-ring and the nearer to the bottom of the segment-ring, the more severe the response. Of two horizontally symmetric, corresponding places on the segment lining, the one near the joint is more severe in its dynamic response than that of the one far from the joint; the nearer the zone of the foundation soil to the lower half of the seg- ment-ring, the more severe the dynamic response. The maximum shear strain of the foundation soil takes place near the joint between two normal segments at the bottom. The dynamic response influenced by joints is more severe than the response not influenced by joints, showing that the non-joint assumption is somewhat impractical.
基金This work was supported by the Fundamental Research Funds for the Central Universities(2020YJS141)the Key Project of High-speed Rail Joint Fund of National Natural Science Foundation of China under Grant No.U1834208.
文摘The control of slurry pressure aiming to be consistent with the external water and earth pressure during shield tunnelling has great significance for face stability,especially in urban areas or underwater where the surrounding environment is very sensitive to the fluctuation of slurry pressure.In this study,an optimal control method for slurry pressure during shield tunnelling is developed,which is composed of an identifier and a controller.The established identifier based on the random forest(RF)can describe the complex non-linear relationship between slurry pressure and its influencing factors.The proposed controller based on particle swarm optimization(PSO)can optimize the key factor to precisely control the slurry pressure at the normal state of advancement.A data set from Tsinghua Yuan Tunnel in China was used to train the RF model and several performance measures like R2,RMSE,etc.,were employed to evaluate.Then,the hybrid RF-PSO control method is adopted to optimize the control of slurry pressure.The good agreement between optimized slurry pressure and expected values demonstrates a high identifying and control precision.
