Prediction of Disc Cutter Life During Shield Tunneling with AI via the Incorporation of a Genetic Algorithm into a GMDH-Type Neural Network

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.

Parameter identification and pressure control of dynamic system in shield tunneling using least squares method

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.

On the critical particle size of soil with clogging potential in shield tunneling

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.

Pressure Regulation for Earth Pressure Balance Control on Shield Tunneling Machine by Using Adaptive Robust Control

Most current studies about shield tunneling machine focus on the construction safety and tunnel structure stability during the excavation. Behaviors of the machine itself are also studied, like some tracking control of the machine. Yet, few works concern about the hydraulic components, especially the pressure and flow rate regulation components. This research focuses on pressure control strategies by using proportional pressure relief valve, which is widely applied on typical shield tunneling machines. Modeling of a commercial pressure relief valve is done. The modeling centers on the main valve, because the dynamic performance is determined by the main valve. To validate such modeling, a frequency-experiment result of the pressure relief valve, whose bandwidth is about 3 Hz, is presented as comparison. The modeling and the frequency experimental result show that it is reasonable to regard the pressure relief valve as a second-order system with two low corner frequencies. PID control, dead band compensation control and adaptive robust control（ARC） are proposed and simulation results are presented. For the ARC, implements by using first order approximation and second order approximation are presented. The simulation results show that the second order approximation implement with ARC can track 4 Hz sine signal very well, and the two ARC simulation errors are within 0.2 MPa. Finally, experiment results of dead band compensation control and adaptive robust control are given. The results show that dead band compensation had about 30° phase lag and about 20% off of the amplitude attenuation. ARC is tracking with little phase lag and almost no amplitude attenuation. In this research, ARC has been tested on a pressure relief valve. It is able to improve the valve＇s dynamic performances greatly, and it is capable of the pressure control of shield machine excavation.

Energy saving analysis of segment positioning in shield tunneling machine considering assembling path optimization

A motion parameter optimization method based on the objective of minimizing the total energy consumption in segment positioning was proposed for segment erector of shield tunneling machine. The segment positioning process was decomposed into rotation, lifting and sliding actions in deriving the energy calculation model of segment erection. The work of gravity was taken into account in the mathematical modeling of energy consumed by each actuator. In order to investigate the relationship between the work done by the actuator and the path moved along by the segment, the upward and downward directions as well as the operating quadrant of the segment erector were defined. Piecewise nonlinear function of energy was presented, of which the result is determined by closely coupled components as working parameters and some intermediate variables. Finally, the effectiveness of the optimization method was proved by conducting a case study with a segment erector for the tunnel with a diameter of 3 m and drawing comparisons between different assembling paths. The results show that the energy required by assembling a ring of segments along the optimized moving path can be reduced up to 5%. The method proposed in this work definitely provides an effective energy saving solution for shield tunneling machine.

Experimental study on the pressure control of soil chamber in shield tunneling

A mathematical model of the soil pressure system in shield tunneling was proposed to optimize soil pressure control in the soil chamber, based on the constitutive relationship between strain and stress. The desired pressure is determined by using the finite element method. A linear quadratic constant state tracking problem was considered over an infinite time interval. The optimal control law was derived by differentiating the Hamilton function with respect to system input. In order to verify the effectiveness of the proposed mathematical model and optimal control law, an experimental study on the pressure control of the soil chamber in shield tunneling was conducted in a laboratory. The experiment results show that soil pressure in the soil chamber in shield tunneling can be accurately controlled.

Three-dimensional displacement characteristics of adjacent pile induced by shield tunneling under influence of multiple factors

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.

Influence of water-rich tunnel by shield tunneling on existing bridge pile foundation in layered soils

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.

Impact of shield tunneling on adjacent spread foundation on sandy cobble strata

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.

Prediction of surface settlement caused by synchronous grouting during shield tunneling in coarse-grained soils:A combined FEM and machine learning approach

This paper presents a surrogate modeling approach for predicting ground surface settlement caused by synchronous grouting during shield tunneling process.The proposed method combines finite element simulations with machine learning algorithms and introduces an intelligent optimization algorithm to invert geological parameters and synchronous grouting variables,thereby predicting ground surface settlement without conducting numerous finite element analyses.Two surrogate models based on the random forest algorithm are established.The first is a parameter inversion surrogate model that combines an artificial fish swarm algorithm with random forest,taking into account the actual number and distribution of complex soil layers.The second model predicts surface settlement during synchronous grouting by employing actual cover-diameter ratio,inverted soil parameters,and grouting variables.To avoid changes to input parameters caused by the number of overlying soil layers,the dataset of this model is generated by the finite element model of the homogeneous soil layer.The surrogate modeling approach is validated by the case history of a large-diameter shield tunnel in Beijing,providing an alternative to numerical computation that can efficiently predict surface settlement with acceptable accuracy.

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

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

Machine learning-based automatic control of tunneling posture of shield machine

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.

Compliance of hydraulic system and its applications in thrust system design of shield tunneling machine

As the most significant performance, compliance of hydraulic system is defined as the capacity to accommodate the sudden change of the external load. Due to the different requirements of the compliant tasks, the existing method for mechanical systems cannot be used in the analysis and design of the hydraulic system. In this paper, the definition and expression of compliance of hydraulic system are proposed to evaluate the compliance of the hydraulic system operating under sudden change load. Because the unexpected geological conditions during excavation may exert sudden change load to the shield tunneling machine, the compliance theory has found a right application in the thrust hydraulic system. By analyzing the basic operating principle and the commonly used architectures of the thrust hydraulic system, a compliance based thrust hydraulic system design method is presented. Moreover, a tunneling case is investigated in the paper as an example to expound the validation of design procedure. In conclusion, the compliance of the hydraulic system can be served as an evaluation of the capability in conforming to the load impact, giving supports for the design of the thrust hydraulic system of shield tunneling machines.

A stiffness-matching based evaluation approach for compliance of mechanical systems in shield tunneling machines

As the most important performance,compliance of shield tunneling machines(STM) is defined as the capability to accommodate the sudden change of the load induced by the variable geological conditions during excavation.Owing to the different requirements of the compliant tasks,the existing methods in the robotic field cannot be utilized in the analysis and design of the mechanical system of shield tunneling machines.In this paper,based on the stiffness of the mechanical system and the equivalent contact stiffness of the tunnel face,the tunneling interface-matching index(IMI) is proposed to evaluate the compliance of the machine.The IMI is defined as a metric to describe the coincidence of the stiffness curves of the mechanical system and the tunnel face.Moreover,a tunneling case is investigated in the paper as an example to expound the validation of IMI and the analytical process.In conclusion,the IMI presented here can be served as an appraisement of the capability in conforming to the load fluctuation,and give instructions for the design of the thrust system of shield tunneling machines.

Driving force planning in shield tunneling based on Markov decision processes

In shield tunneling, the control system needs very reliable capability of deviation rectifying in order to ensure that the tunnel trajectory meets the permissible criterion. To this goal, we present an approach that adopts Markov decision process (MDP) theory to plan the driving force with explicit representation of the uncertainty during excavation. The shield attitudes of possi- ble world and driving forces during excavation are scattered as a state set and an action set, respectively. In particular, an evaluation function is proposed with consideration of the stability of driving force and the deviation of shield attitude. Unlike the deterministic approach, the driving forces based on MDP model lead to an uncertain effect and the attitude is known only with an imprecise probability. We consider the case that the transition probability varies in a given domain estimated by field data, and discuss the optimal policy based on the interval arithmetic. The validity of the approach is discussed by comparing the driving force planning with the actual operating data from the field records of Line 9 in Tianjin. It is proved that the MDP model is reasonable enough to predict the driving force for automatic deviation rectifying.

Model test and discrete element method simulation of shield tunneling face stability in transparent clay

The stability of the shield tunneling face is an extremely important factor affecting the safety of tunnel construction.In this study,a transparent clay with properties similar to those of Tianjin clay is prepared and a new transparent clay model test apparatus is developed to overcome the“black box”problem in the traditional model test.The stability of the shield tunneling face(failure mode,influence range,support force,and surface settlement)is investigated in transparent clay under active failure.A series of transparent clay model tests is performed to investigate the active failure mode,influence range,and support force of the shield tunneling face under different burial depth conditions,whereas particle flow code three-dimensional numerical simulations are conducted to verify the failure mode of the shield tunneling face and surface settlement along the transverse section under different burial depth conditions.The results show that the engineering characteristics of transparent clay are similar to those of soft clay in Binhai,Tianjin and satisfy visibility requirements.Two types of failure modes are obtained:the overall failure mode(cover/diameter:C/D£1.0)and local failure mode(C/D≥2.0).The influence range of the transverse section is wider than that of the longitudinal section when C/D≥2.0.Additionally,the normalized thresholds of the relative displacement and support force ratio are 3%-6%and 0.2-0.4,respectively.Owing to the cushioning effect of the clay layer,the surface settlement is significantly reduced as the tunnel burial depth increases.

Heat Treatment Properties of 42CrMo Steel for Bearing Ring of Varisized Shield Tunneling Machine

The heat treatment properties of 42CrMo steel for bearing ring of varisized shield tunneling machine were investigated by optical microscope （OM）, scanning electron microscope （SEM）, transmission electron microscope （TEM）, and impact tests. The addition of 0.03 wt% C into 42CrMo steel can increase the hardness. But it reduces the impact energy by 46 J because of the appearance of coarser carbides in the matrix and the carbides along the austenite grain boundary. The addition of 0.40 wt% Mn into 42CrMo steel can improve hardenability. However, the toughness of steel is also reduced by 26 J mainly because of the coarsening of carbides and the strengthening of matrix. Both hardenability and toughness of 42CrMo steel can be improved by adding 1.49 wt% Ni and reducing 0.32 wt% Cr. The depth of hardening layer can be raised to 45 mm, and the impact energy at -20 ℃ is 120 J. Thus, it is concluded that a good combination of hardness, hardenability, and toughness of 42CrMo steel can be achieved by alloying with adding some content of C and Ni. Detailed content of C and Ni should be on the requirements of heat treatment properties of steel for bearing ring of varisized shield tunneling machine.

Experimental study on slurry-induced fracturing during shield tunneling

Facial support in slurry shield tunneling is provided by slurry pressure to balance the external earth and water pressure.Hydraulic fracturing may occur and cause a significant decrease in the support pressure if the slurry pressure exceeds the threshold of the soil or rock material,resulting in a serious face collapse accident.Preventing the occurrence of hydraulic fracturing in a slurry shield requires investigating the effects of related influencing factors on the hydraulic fracturing pressure and fracture pattern.In this study,a hydraulic fracturing apparatus was developed to test the slurry-induced fracturing of cohesive soil.The effects of different sample parameters and loading conditions,including types of holes,unconfined compressive strength,slurry viscosity,and axial and circumferential loads,on the fracturing pressure and fracture dip were examined.The results indicate that the fracture dip is mainly affected by the deviator stress.The fracturing pressure increases linearly with the increase in the circumferential pressure,but it is almost independent of the axial pressure.The unconfined compressive strength of soil can reflect its ability to resist fracturing failure.The fracturing pressure increases with an increase in the unconfined compressive strength as well as the slurry viscosity.Based on the test results,an empirical approach was proposed to estimate the fracturing pressure of the soil.

Numerical study on 3D effect and practical design in shield tunneling

In practice,different design methods are used in solving geotechnical problems depending on the type of issue such as the tunneling,braced excavation,or bearing capacity of a foundation,that is,the basic mechanism of the design method differs depending on the problems even for the same ground.A numerical analysis using the finite element method has recently become familiar owing to an improved computing performance;however,it is not widely used in the design of geotechnical problems including tunnel excavation owing to the reliability of the constitutive model of the ground material.If a constitutive model of soils can properly express the properties of the ground material,a numerical analysis will play a vital role in solving the geotechnical problems.In this paper,the current state of a numerical analysis and its applicability in tunnel design are discussed.Herein,the simulation of the ground behavior during tunnel excavation is carried out using sandy and clay ground parameters for shallow and deep tunnel excavations.This paper is mainly focused on the effects of tunnel excavation under three-dimensional(3D)conditions,as well as the current design method.Non-linear 2D and 3D finite element analyses have been conducted,in which the elastoplastic sub-loading tij model has been used as a constitutive model of the soil.The performance and acceptability of the constitutive model have already been proven to reproduce the results of various model tests on different geotechnical problems such as the tunneling,braced excavation,and bearing capacity of a foundation,as well as the measured field data.It was found that a 2D finite element analysis where the rate of stress release is considered,can be used for the prediction of the ground deformation and surface settlement;however,it does not provide rational information in the prediction of tunnel lining forces such as the stress,bending moment,and axial force,which emphasize the necessity of a 3D analysis with a proper construction process in a tunnel design.

Method to avoid the structural interference of the thrust system of a shield tunneling machine

Several malfunctions of the shield tunneling machine （STM） caused by structural interference have been encountered in actual tunnel excavation. This paper is focusing on providing an effective method to avoid the structural interference based on making the reachable and the required workspaces of the thrust system match each other. The main structure of the thrust mechanism is analyzed, and coordinate systems are built up to describe the pose and workspace of the thrust mechanism. Constraint conditions are derived and the formulation of each constraint condition is carried out to facilitate the analysis of the reachable workspace of the thrust mechanism. Meanwhile, a reachable workspace determination algorithm is introduced based on interval analysis method. The mathematical model for determining the required workspace of the thrust mechanism is presented based on the analysis of the process when the STM excavates along a specific tunnel axis. Two applications are included to show how to avoid these problems by choosing reasonable parameters of the designed tunnel axis and the key structural parameters of the thrust mechanism based on workspace matching.